,direct ,conversion of ,energy ,illustration3 uncaptioned ,by ,william ,r4 ,corliss ,u4,s4 ,,atomic ,,energy ,,commission ,division of ,technical ,information ,,one ,,of ,a ,,series ,,on ,,understanding ,,the ,,atom ,,united ,,states ,,atomic ,,energy ,,commission ,dr4 ,glenn ,t4 ,seaborg1 ,chairman ,james ,t4 ,ramey ,dr4 ,gerald ,f4 ,tape ,wilfrid ,e4 ,johnson ,nuclear energy is playing a vital role in the life of every man1 woman1 and child in the ,united ,states today4 ,in the years ahead it will affect increasingly all the peoples of the earth4 ,it is essential that all ,americans gain an understanding of this vital force if they are to discharge thoughtfully their responsibilities as citizens and if they are to realize fully the myriad benefits that nuclear energy offers them4 ,the ,united ,states ,atomic ,energy ,commission provides this booklet to help you achieve such understanding4 ,edward ,j4 ,brunenkant ,edward ,j4 ,brunenkant ,director ,division of ,technical ,information ,,contents ,,introduction #a ,,direct ,,versus ,,dynamic ,,energy ,,conversion #c ,,laws ,,governing ,,energy ,,conversion #h ,,thermoelectricity #ab ,,thermionic ,,conversion #af ,,magnetohydrodynamic ,,conversion #ai ,,chemical ,,batteries #bb ,,the ,,fuel ,,cell3 ,a ,,continuously ,,fueled ,,battery #bd ,,solar ,,cells #bf ,,nuclear ,,batteries #bh ,,advanced ,,concepts #cj ,,suggested ,,references #cc ,,answers ,,to ,,problems #cd ,library of ,congress ,catalog ,card ,number3 #fd-fagid ,,about ,,the ,,author ,illustration3 ,william ,r4 ,corliss ,,william ,r4 ,,corliss is an atomic energy consultant and writer with #ab years of industrial experience including service as ,director of ,advanced ,programs for the ,martin ,company's ,nuclear ,division4 ,mr4 ,corliss has ,b4,s4 and ,m4,s4 ,degrees in ,physics from ,rensselaer ,polytechnic ,institute and the ,university of ,colorado1 respectively4 ,he has taught at those two institutions and at the ,university of ,wisconsin4 ,he is the author of ,propulsion ,systems for ,space ,flight 7,mc,graw-,hill #aifj71 ,space ,probes and ,planetary ,exploration 7,van ,nostrand #aife71 ,mysteries of the ,universe 7,crowell #aifg71 ,scientific ,satellites 7,,gpo #aifg71 and coauthor of ,radioisotopic ,power ,generation 7,prentice-,hall #aifd71 as well as numerous articles and papers for technical journals and conferences4 ,in this series he has written ,neutron ,activation ,analysis1 ,power ,reactors in ,small ,packages1 ,,snap--,nuclear ,reactor ,power in ,space1 ,computers1 ,nuclear ,propulsion for ,space1 ,space ,radiation1 and was coauthor of ,power from ,radioisotopes4 ,,introduction ,a flashlight battery supplies electricity without moving mechanical parts4 ,it converts the chemical energy of its contents directly into electrical energy4 ,early direct conversion devices such as ,volta's battery1 developed in #agie1 gave the scientists ,ampere1 ,oersted1 and ,faraday their first experimental supplies of electricity4 ,the lessons they learned about electrical energy and its intimate relation with magnetism spawned the mighty turboelectric energy converters--steam and hydroelectric turbines--which power modern civilization4 ,we have improved upon ,volta's batteries and have come to rely on them as portable1 usually small1 power sources1 but only recently has the challenge of nuclear power and space exploration focused our attention on new methods of direct conversion4 ,to supply power for use in outer space and also at remote sites on earth1 we need power sources that are reliable1 light in weight1 and capable of unattended ,operation for long periods of time4 ,nuclear power plants using direct conversion techniques hold promise of surpassing conventional power sources in these attributes4 ,in addition1 the inherently silent operation of direct conversion power plants is an important advantage for many military applications4 ,the ,atomic ,energy ,commission1 the ,department of ,defense1 and the ,national ,aeronautics and ,space ,administration collectively sponsor tens of millions of dollars worth of research and development in the area of direct conversion each year4 ,in particular1 the ,atomic ,energy ,commission supports more than a dozen research and development programs in thermoelectric and thermionic energy conversion in industry and at the ,los ,alamos ,scientific ,laboratory1 and other direct conversion research at ,argonne ,national ,laboratory and ,brookhaven ,national ,laboratory4 ,reactor and radioisotopic power plants utilizing direct conversion are being produced under the ,,aec's ,,snap#a program4 ,some of these units are presently in use powering satellites1 ,arctic and ,antarctic weather stations1 and navigational buoys4 ,further applications are now being studied1 but the cost of direct conversion appears too great to permit its general use for electric power in the near future4 ,direct techniques will be used first where their special advantages outweigh higher cost4 ,,direct ,,versus ,,dynamic ,,energy ,,conversion ,dominance of ,dynamic ,conversion ,we live in a world of motion4 ,a main task of the engineer is to find better and more efficient ways of transforming the energy locked in the sun's rays or in fuels1 such as coal and the uranium nucleus1 into energy of motion4 ,almost all the world's energy is now transformed by rotating or reciprocating machines4 ,we couple the energy of exploding gasoline and air to our automobile's wheels by a reciprocating engine4 ,the turbogenerator at a hydroelectric plant extracts energy from falling water and turns it into electricity4 ,such rotating or reciprocating machines are called dynamic converters4 ,a ,new ,level of ,sophistication3 ,direct ,conversion ,a revolution is in the making4 ,we know now that we can force the heat-and-electricity-carrying electrons residing in matter to do our bidding without the use of shafts and pistons4 ,this is a leading accomplishment of modern technology3 energy transformation without moving parts4 ,it is called direct conversion4 ,the thermoelements shown above the turbogenerator in ,figure #a illustrate the contrast between direct and dynamic conversion4 ,the thermoelements convert heat into electricity directly1 without any of the intervening machinery seen in the turbogenerator4 ,illustration3 ,figure #a ,direct conversion devices1 such as the spokelike lead telluride thermoelectric elements inside the ,,snap #c radioisotope generator shown above 7courtesy ,martin ,company71 convert heat into electricity without moving parts4 ,in contrast1 the ,,snap #b dynamic converter shown below ,,snap #c 7courtesy ,thompson ,ramo ,wooldridge1 ,inc47 includes a high-speed turbine1 an electric generator1 and pumps to produce electricity from heat4 7,na,k is a liquid mixture of sodium and potassium47 ,,direct ,,versus ,,dynamic ,,conversion ,,snap #c ,,less ,,than #e ,,watts #e ,,snap #b #cjjj ,,watts #bd ,,alternator ,,rotor ,,alternator ,,stator ,,turbine ,,rotors ,na,k ,,pump ,,diffuser ,na,k ,,pump ,,rotor ,,mercury ,,jet ,,booster ,,pump ,,mercury ,,centrifugal ,,pump ,,mercury ,,thrust ,,bearing ,,mercury ,,bearing ,,mercury ,,bearing ,why is ,direct ,conversion ,desirable8 ,there are places where energy conversion equipment must run for years without maintenance or breakdown4 ,also1 there are situations where the ultimate in reliability is required1 such as on scientific satellites and particularly on manned space flights4 ,direct conversion equipment seems to offer greater reliability than dynamic conversion equipment for these purposes4 ,we should recognize that our belief in the superiority of direct conversion is based more on intuition than proof4 ,it is true that direct converters will never throw piston rods or run out of lubricant4 ,yet1 some satellite power failures have been caused by the degradation of solar cells under the bombardment of solar protons4 ,the other types of direct conversion devices described in the following pages may also break down in ways as yet unknown4 ,still1 today's knowledge gives us hope that direct conversion will be more reliable and trustworthy than dynamic conversion4 ,direct conversion equipment is beginning to be adopted for small power plants1 producing less than #ejj watts1 designed to operate for long periods of time in outer space and under the ocean4 ,some day1 large central-station power plants may use direct conversion to improve their efficiencies and reliabilities4 ,how is ,energy ,transformed8 ,what is energy and how do we change it8 ,energy is a fundamental concept of science involving the capacity for doing work4 ,kinetic or mechanical energy is the most obvious form of energy4 ,it is defined as ,e mv where ,e energy 7expressed in joules7 m mass of the moving object 7in kilograms7 v velocity 7in meters per second7 ,energy can also be stored in chemical and nuclear substances or in the water behind a dam4 ,in these quiescent states it is called potential energy4 ,if the potential energy in a substance is abundant and easily released1 the energy-rich substance is called a fuel4 ,,energy ,,conversion ,,matrix ,illustration3 ,figure #b ,to find how one form of energy is converted into another1 start at the proper column and move down until the column intersects with the desired row4 ,the box at the intersection will give typical conversion processes and examples4 ,,from ,,electromagnetic ,,chemical ,,nuclear ,,thermal ,,kinetic ,,electrical ,,gravitational 7,,mechanical7 ,,to ,,electromagnetic ,chemiluminescence ,gamma reactions ,thermal radiation ,accelerating ,electromagnetic ,unknown 7fireflies7 7,co source7 7hot iron7 charge radiation#b ,a-bomb 7cyclotron7 7,,tv transmitter7 ,phosphor#b ,electroluminescence ,,chemical ,photosynthesis ,radiation ,boiling ,dissociation by ,electrolysis ,unknown 7plants7 catalysis 7water_/steam7 radiolysis 7production of ,photochemistry 7hydrazine plant7 ,dissociation aluminum7 7photographic ,ionization ,battery charging film7 7cloud chamber7 ,,nuclear ,gamma-neutron ,unknown ,unknown ,unknown ,unknown ,unknown reactions 7,be ,ben7 ,,thermal ,solar absorber ,combustion ,fission ,friction ,resistance-heating ,unknown 7hot sidewalk7 7fire7 7fuel element7 7brake shoes7 7electric stove7 ,fusion ,,kinetic ,radiometer ,solar ,muscle ,radioactivity ,thermal expansion ,motors ,falling objects cell#b 7alpha particles7 7turbines7 ,electrostriction ,a-bomb ,internal combustion 7sonar transmitter7 7engines7 ,,electrical ,photoelectricity ,fuel cell#b ,nuclear ,thermoelectricity#b ,,mhd#bc ,unknown 7light meter7 ,batteries#b battery#b ,thermionics#b ,conventional ,radio antenna ,thermomagnetism#b generator ,solar cell#b ,ferroelectricity#b ,,gravitational ,unknown ,unknown ,unknown ,unknown ,rising objects ,unknown 7rockets7 ,the ,energy ,conversion ,matrix ,forms of energy are interchangeable4 ,when gasoline is burned in an automobile engine1 potential energy is first turned into heat4 ,a portion of this heat1 say #be1 is then converted into mechanical motion4 ,the remainder of the heat is wasted and must be removed from the engine4 ,a multitude of processes and devices have been found which make these transformations from one form of energy to another4 ,many of these are listed in the blocks in ,figure #b4 ,asterisks refer to direct conversion processes1 the subject matter of this booklet4 ,to demonstrate how this diagram is to be read1 let us use it to trace the energy transformations involved in an automobile engine4 ,we begin with sunlight because all coal and oil deposits 7the fossil fuels7 received their initial charge of energy in the form of sunlight4 ,the first conversion1 therefore1 is from electromagnetic energy to chemical energy via photosynthesis in living things4 ,we trace the transformation by moving down the column marked ,electromagnetic ,energy until it intersects the horizontal row labeled ,chemical ,energy4 ,there we see photosynthesis listed in the block4 ,the next conversion is from chemical energy to thermal energy via combustion4 ,we trace this by moving down the ,chemical ,energy column to the ,thermal ,energy row2 combustion is listed in the appropriate block4 ,the third and final conversion takes place when thermal energy is transformed into mechanical energy via the internal combustion engine4 ,by the repeated use of the ,energy ,conversion ,matrix in this way1 we can chart any energy transformation4 ,problem #a ,continue the automobile example by going through the matrix twice more showing how mechanical energy is converted into stored chemical energy in the car's battery4 ,problem #b ,if #a gram of gasoline 7about a tablespoonful7 yields #dh1jjj joules of thermal energy when burned with air1 how fast can it make a #ajjj kilogram car go8 ,assume the car starts from rest and its engine is #be efficient4 ,answers to problems are on page #cd4 ,,laws ,,governing ,,energy ,,conversion ,the ,big ,picture3 ,thermodynamics ,to the best of our knowledge1 energy and mass are always conserved together in any transformation4 ,this summary of experience has been made into a keystone of science3 the ,law of ,conservation of ,energy and ,mass4 ,it states that the total amount of mass and energy cannot be altered4 ,this law applies to everything we do1 from driving a nail to launching a space probe4 ,while the conscience of the scientist insists that he continually recheck the truth of this law1 it remains a bulwark of science4 ,the ,law of ,conservation of ,energy and ,mass is also called the ,first ,law of ,thermodynamics4 ,it is related to the ,second ,law of ,thermodynamics1 which also governs energy transformations4 ,the ,second ,law says1 in effect1 that some energy will unavoidably be lost in all heat engines4 ,the first two laws of thermodynamics have been paraphrased as 7#a7 ,you can't win2 7#b7 ,you can't even break even4 ,let us look at them further4 ,you ,can't ,win ,we used to think that energy and mass were conserved independently1 and for many practical purposes we still consider them so conserved4 ,but ,einstein united the two with the famous equation ,e mc where ,e energy 7in joules7 m mass 7in kilograms7 c speed of light 7#cjj1jjj1jjj meters per second7 ,notice the resemblance to the kinetic energy equation shown earlier4 ,energy cannot appear without the disappearance of mass4 ,when energy is locked up in a fuel1 it is stored as mass4 ,in the gasoline combustion problem1 #a gram of gasoline was burned with air to give #dh1jjj joules of energy4 ,einstein's equation says that in this case mass disappeared in the amount m ,e_/c 7#d4h #aj7_/7i #aj7 #e4c #aj kilogram 7half a billionth of a gram7 ,but1 when an ,h-bomb is exploded1 grams and even kilograms of mass are converted to energy4 ,in direct conversion processes we do not need to worry about these mass changes1 but at each point we must make sure that all energy is accounted for4 ,for example1 in outer space all energy released from fuels 7even food7 must ultimately be radiated away to empty ,space4 ,otherwise the vehicle temperature will keep rising until the ,spaceship melts4 ,you ,can't ,even ,break ,even ,any engineer is annoyed by having to throw energy away4 ,why is energy ever wasted8 ,the ,second ,law of ,thermodynamics guides us here4 ,experience has shown that heat cannot be transformed into another form of energy with #ajj efficiency4 ,we can't explain ,nature's idiosyncracies1 but we have to live with them4 ,so1 we accept the fact that every engine that starts out with heat must ultimately waste some of that energy 7,figure #c74 ,illustration3 ,figure #c ,a typical heat engine showing heat input1 useful power output1 and the unavoidable waste heat that must be rejected to the environment4 ,a pressure-volume diagram is shown underneath for a closed gas-turbine cycle4 ,circled numbers correspond4 ,the energy produced is represented by the shaded area4 ,similar diagrams can be made for all heat engines as an aid in studying their performance4 ,a ,,typical ,,heat ,,engine ,,heat ,,in ,,heat ,,source ,,reactor1 ,,boiler ,,electricity ,,out ,,energy ,,converter ,,pump ,,fluid ,,pipe ,,radiator ,,waste ,,heat ,,out ,,pressure-,,volume ,,diagram ,,heat ,,in ,,energy ,,out ,,gas ,,pressure ,,waste ,,heat ,,out ,,gas ,,volume ,direct conversion devices are no exception4 ,consequently1 every thermoelectric element or thermionic converter will have to provide for the disposition of waste heat4 ,the designer will try1 however1 to make the engine efficiency high so that the waste heat will be small4 ,figure #d shows the extensive waste heat radiator on a ,,snap #ej power plant planned for deep space missions4 ,illustration3 ,figure #d ,model of ,,snap #ej power plant planned for deep space missions showing extensive waste heat radiator4 ,the system will provide #cjj to #ajjj kilowatts of electrical power4 ,carnot ,efficiency ,in #ahbd ,sadi ,carnot1 a young ,french engineer1 conceived of an idealized heat engine4 ,this ideal engine had an efficiency given by e #a - ,tc_/,th 7,th - ,tc7_/,th where e the so-called ,carnot efficiency 7no units7 ,tc the temperature of the waste heat reservoir 7in degrees ,kelvin1 ,k#d7 ,th the temperature of the heat source 7in ,k7 ,unhappily1 ,tc cannot be made zero 7and e therefore made equal to #a1 which is #ajj efficiency74 ,physicists have shown absolute zero to be unattainable1 although they have approached to within a hundredth of a degree in the laboratory4 ,waste heat1 since it must be rejected to the surrounding atmosphere1 outer space1 or water 7rivers1 the ocean1 etc471 must be rejected at ,tc greater than #cjj,k4 ,the reason for this is that these physical reservoirs have average temperatures around #cjj,k 7about #hj;,f7 themselves4 ,the fact that ,tc must be #cjj,k or more is a basic limitation on the ,carnot efficiency4 ,the loss in efficiency with increased ,tc explains why a jet plane has a harder job taking off on a hot day4 ,one way to improve the ,carnot efficiency1 which is the maximum efficiency for any heat engine1 is to raise ,th as high as possible without melting the engine4 ,for a coal-fired electrical power plant1 ,th #fjj,k and ,tc #cjj,k1 so that e #a - #cjj_/fjj #j4e #ej ,the actual efficiency is somewhat less than this ideal value because some power is diverted to pumps and other equipment and to unavoidable heat losses4 ,later on1 we shall see that magnetohydrodynamic 7,,mhd7 generators hold prospects for increasing ,th by hundreds of degrees4 ,everything that has been said about the ,second ,law of ,thermodynamics 7,you can't even break even7 applies to heat engines1 where we begin with thermal energy4 ,suppose instead that we start with kinetic or chemical energy and convert it into electricity without turning it into heat first4 ,we can then escape the ,carnot efficiency strait jacket4 ,chemical batteries perform this trick4 ,so do fuel cells1 solar cells1 and many other direct conversion devices we shall discuss4 ,thus1 we circumvent the ,carnot efficiency limitation by using processes to which it does not apply4 ,problem #c ,some space power plants contemplate using the space cabin heat 7,th #cjj,k7 to drive a heat engine which rejects its waste heat to the liquid-hydrogen rocket fuel stored at ,tc #bj,k4 ,what would be the ,carnot efficiency of this engine8 ,,thermoelectricity ,after #adj ,years3 ,seebeck ,makes ,good ,the oldest direct conversion heat engine is the thermocouple4 ,take two different materials 7typically1 two dissimilar metal wires71 join them1 and heat the junction4 ,a voltage1 or electromotive force1 can be measured across the unheated terminals4 ,t4 ,j4 ,seebeck first noticed this effect in #ahba in his laboratory in ,berlin1 but1 because of a mistaken interpretation of what was involved1 he did not seek any practical application for it4 ,only recently has any real progress been made in using his discovery for power production4 ,to use the analogy of ,a4 ,f4 ,joffe1 the ,russian pioneer in this field1 thermoelectricity lay undisturbed for over a hundred years like ,sleeping ,beauty4 ,the ,prince that awoke her was the semiconductor4 ,as long as inefficient metal wires were used1 textbook writers were correct in asserting that thermoelectricity could never be used for power production4 ,the secret of practical thermoelectricity is therefore the creation of better thermoelectric materials4 7,creation is the right word since the best materials for the purpose do not exist in nature47 ,to perform this alchemy1 we first have to understand the ,seebeck effect4 ,electrons and ,holes ,let's examine the latticework of atoms that make up any solid material4 ,in electrical insulators all the atoms' outer electrons#e are held tightly by valence bonds to the neighboring atoms4 ,in contrast1 any metal has many relatively loose electrons which can wander freely through its latticework4 ,this is what makes metals good conductors4 ,,thermoelectricity ,illustration3 ,figure #e ,thermoelectric couple made from p- and n-type semiconductors4 ,the impurity atoms 7,i7 are different in each leg and contribute an excess or deficiency of valence electrons4 ,heat drives both holes and electrons toward the cold junction4 ,tc ,,waste ,,heat ,,out ,,electrons ,,load ,,cold ,,junction ,,holes ,,electrons p ,,semiconductor n ,,semiconductor ,,hot ,,junction ,th ,,heat ,,in ,simplified ,sketch of ,atomic ,lattice ,,hole ,,electron ,,valence ,,bonds ,,semiconductor ,,lattices ,i ,impurity atom ,figure #e suggests the latticework of a semiconductor4 ,it is called a semiconductor because its conductivity falls far short of that of the metals4 ,the few electrons available for carrying electricity are supplied by the deliberately introduced impurity atoms1 which have more than enough electrons to satisfy the valence-bond requirements of the neighboring atoms4 ,without the impurities1 we would have an insulator4 ,with them1 we have an n-type semiconductor4 ,the n is for the extra negative electrons4 ,a p- or positive-type semiconductor is also included in ,figure #e4 ,here the impurity atom does not have enough valence electrons to satisfy the valence-bond needs of the surrounding lattice atoms4 ,the lattice has been short-changed and is1 in effect1 full of positive holes4 ,strangely enough1 these holes can wander through the material just like positive charges4 ,the electron-hole model does not have the precision the physicist likes1 but it helps us to visualize semiconductor behavior4 ,the ,seebeck effect is demonstrated when pieces of p- and n-type material are joined as shown in ,figure #e4 ,heat at the hot junction drives the loose electrons and holes toward the cold junction4 ,think of the holes and electrons as gases being driven through the latticework by the temperature difference4 ,a positive and a negative terminal are thus produced1 giving us a source of power4 ,the larger the temperature difference1 the bigger the voltage difference4 ,note that just one thermocouple leg can produce a voltage across its length1 but couples made from p and n legs are superior4 ,practical ,thermoelectric ,power ,generators ,the first nuclear-heated thermoelectric generator was built in #aied by the ,atomic ,energy ,commission's ,mound ,laboratory in ,miamisburg1 ,ohio4 ,it used metal-wire thermocouples4 ,in contrast1 the ,,snap #c series thermocouples shown in ,figure #a are thick lead telluride 7,pb,te7 semiconductor cylinders about two inches long4 ,in contrast to the thermocouple wires' efficiency of less than #a1 ,,snap #c series generators have overall efficiencies exceeding #e4 ,this value is still low compared to the #ce-dj obtained in a modern steam power plant1 but ,,snap #c generators can operate unattended in remote localities where steam plants would be totally unacceptable4 ,look again at the thermoelements in ,figure #a and the schematic1 ,figure #e4 ,underlying the apparent simplicity of the thermoelectric generator are extensive development efforts4 ,the ,figure #a thermoelectric couple1 for example1 shows the fruits of thousands of experimental brazing tests4 ,it turns out to be uncommonly difficult to fasten thermoelectric elements to the so-called hot shoe 7metal plate7 at the bottom4 ,the joint has to be strong1 must withstand high temperatures1 and must have low electrical resistance4 ,we see also that the elements are encased in mica sleeves to prevent chemical disturbance of the delicate balance of impurities in the semiconductor by the surrounding gases4 ,a further complication is the extreme fragility of the elements1 and this has yet to be overcome4 ,nuclear thermoelectric generators that provide small amounts of electrical power have already been launched into space aboard ,department of ,defense satellites 7,figure #ab71 installed on land stations in both polar regions1 and placed under the ocean4#f ,propane-fueled thermoelectric generators1 such as shown in ,figure #f1 are now on the market for use in camping equipment1 in ocean buoys1 and in remote spots where only a few watts of electricity are needed4 ,the ,russians have long manufactured a kerosene lamp with thermoelements placed in its stack for generating power in wilderness areas4 ,illustration3 ,figure #f ,,general ,,purpose ,,generator ,commercially available thermoelectric generators using propane fuel can provide more than enough electrical power to operate a portable ,,tv set4 ,courtesy ,minnesota ,mining ,manufacturing ,company4 ,for the present the role of thermoelectric power appears to be one of special uses such as those just mentioned4 ,when higher efficiencies are attained1 thermoelectric power may1 one day1 supplant dynamic conversion equipment in certain low-power applications regardless of location4 ,,thermionic ,,conversion 8,boiling0 ,electrons ,out of ,metals ,like the thermoelectric element1 the thermionic converter is a heat engine4 ,in its simplest form it consists of two closely spaced metallic plates and resembles the diode radio tube4 ,whereas thermoelectric elements depend on heat to drive electrons and holes through semiconductors to an external electricity-using device or load1 the salient feature of the thermionic diode is thermionic emission1#g or1 simply1 the boiling-off of electrons from a hot metal surface4 ,the thermionic converter shown in ,figure #g powers a small motor when heated by a torch4 ,metals1 as we have already seen1 have an abundance of loosely bound conduction electrons roaming the atomic latticework4 ,these electrons are easily moved by electric fields while within the metal2 but it takes considerably more energy to boil them out of the metal into free space4 ,work has to be done against the electric fields set up by the surface layer of atoms1 which have unattached valence bonds on the side facing empty space4 ,the energy required to completely detach an electron from the surface is called the metal's work function4 ,in the case of tungsten1 for example1 the work function is about #d4e electron volts#h of energy4 ,illustration3 ,figure #g ,vacuum type thermionic converter in operation4 ,courtesy ,general ,electric ,company4 ,as we raise the temperature of a metal1 the conduction electrons in the metal also get hotter and move with greater velocity4 ,we may think of some of the electrons in a metal as forming a kind of electron gas4 ,some electrons will gain such high speeds that they can escape the metal surface4 ,this happens when their kinetic energy exceeds the metal's work function4 ,now that we have found a way to force electrons out of the metal1 we would like to make them do useful electrical work4 ,to do this we have to push the electrons across the gap between the plates as well as create a voltage difference to go with the hoped-for current flow4 ,reducing the ,space ,charge ,the emitted or boiled-off electrons between the converter plates 7,figure #h7 form a cloud of negative charges that will repel subsequently emitted electrons back to the emitter plate unless counteraction is taken4 ,to circumvent these space charge effects1 we fill the space between the plates with a gas containing positively charged particles4 ,these mix with the electrons and neutralize their charge4 ,the mixture of positively and negatively charged particles is called a plasma4 ,the presence of the plasma makes the gas a good conductor4 ,the emitted electrons can now move easily across it to the collector where1 to continue the gas analogy1 they condense on the cooler surface4 ,illustration3 ,figure #h ,,thermionic ,,conversion ,thermionic converters may be flat-plate types or cylindrical types4 ,the cylindrical converter 7a7 is an experimental type for ultimate use in nuclear reactors4 ,courtesy ,los ,alamos ,scientific ,laboratory4 a ,,insulator ,,cooled ,,collector ,,incandescent ,,uranium ,,fuel ,,element ,,cesium ,,plasma ,,circulating ,,coolant ,,vacuum ,,insulator ,,cesium ,,pool b ,,waste ,,heat ,,out ,,load ,,electrons ,,low ,,work ,,function ,,collector ,tc ,,cesium ,,ion ,,plasma ,,filled ,,gap ,,boiled ,,off ,,electrons ,,high ,,work ,,function ,,emitter ,tc ,,heat ,,in ,result3 ,a ,plasma ,thermocouple ,unless a voltage difference exists across the plates1 no external work can be done4 ,in the thermocouple the voltage difference was caused by the different electrical properties of the p and n semiconductors4 ,both the emitter and collector in the thermionic converter are good metallic conductors rather than semiconductors1 so a different tack must be taken4 ,the key is the use of an emitter and a collector with different work functions4 ,if it takes #d4e electron volts to force an electron from a tungsten surface and if it regains only #c4e electron volts when it condenses on a collector with a lower work function1 then a voltage drop of #a volt exists between the emitter and collector4 ,to summarize1 then1 the thermionic emission of electrons creates the potentiality of current flow4 ,the difference in work functions makes the thermionic converter a power producer4 ,there is an interesting comparison that helps describe this phenomenon4 ,consider the emitter to be the ocean surface and the collector a mountain lake4 ,the atmospheric heat engine vaporizes ocean water and carries it to the cooler mountain elevations1 where it condenses as rain which collects in lakes4 ,the lake water as it runs back toward sea level then can be made to drive a hydroelectric plant with the gravitational energy it has gained in the transit4 ,the thermionic converter is similar in behavior3 hot emitter 7corresponding to the sun-heated ocean72 cooler collector 7lake72 electron gas 7water72 different electrical voltages 7gravity74 ,without gravity the river would not flow1 and the production of electricity would be impossible4 ,thermionic ,power in ,outer ,space ,thermionic converters for use in outer space may be heated by the sun1 by decaying radioisotopes1 or by a fission reactor4 ,thermionic converters can also be made into concentric cylindrical shells 7,figure #h;a7 and wrapped around the uranium fuel elements in nuclear reactors4 ,the waste heat in this case would be carried out of the reactor to a separate radiator#i by a stream of liquid metal4 ,since thermionic converters can operate at much higher temperatures than thermoelectric couples or dynamic power plants1 the radiator temperature1 ,tc1 will also be higher4 ,consequently1 space power plants using thermionic converters will have small radiators4 ,once thermionic converters are developed which have high reliability and long life1 they will provide the basis for a new series of lighter1 more efficient space power plants4 ,,magnetohydrodynamic ,,conversion ,big ,word1 ,simple ,concept ,magnetohydrodynamic 7,,mhd7 conversion is very unlike thermoelectric or thermionic conversion4 ,the ,,mhd generators use high-velocity electrically conducting gases to produce power and are generically closer to dynamic conversion concepts4 ,the only concept they carry forward from the preceding conversion ideas is that of the plasma1 the electrically conducting gas4 ,yet they are commonly classified as direct because they replace the rotating turbogenerator of the dynamic systems with a stationary pipe or duct4 ,illustration3 ,figure #i ,in the ,,mhd duct 7a71 the electrons in the hot plasma move to the right under influence of force ,f in the magnetic field ,b4 ,the electrons collected by the right-hand side of the duct are carried to the load4 ,in a wire in the armature of a conventional generator 7b7 the electrons are forced to the right by the magnetic field4 a ,,mhd ,duct ,,hot ,,plasma ,,in ,,cool ,,gas ,,out ,,to ,,radiator ,magnetic ,field ,,load ,,electrons b ,,conventional ,,generator ,,shaft ,,load ,magnetic ,field ,,armature ,,wire ,,electrons ,in the conventional dynamic generator1 an electromotive force is created in a wire that cuts through magnetic lines of force1 as shown in ,figure #i;b4 ,it may be helpful to visualize the conduction electrons as leaving one end of the wire and moving to the other under the influence of the magnetic field4 ,the force on the electrons in the wire is given by ,f qv,b where ,f the force 7in newtons#aj7 q the charge on the electron 7#a4f #aj coulomb7 v the wire's velocity 7in meters per second7 ,b the magnetic field strength 7in webers per square meter#aj7 ,the surge of electrons along the length of the wire sets up a voltage difference across the ends of the wire4 ,a generator uses this difference to convert the kinetic energy of the moving wire or armature into electrical energy4 ,the wire is kept spinning by the shaft which is connected to a turbine driven by steam or water4 ,let us try to eliminate the moving part1 the generator armature4 ,what we need is a moving conductor that has no shaft1 no bearings1 no wearing parts4 ,the substance that meets these requirements is the plasma4 ,examine ,figure #i;a4 ,the ,,mhd generator substitutes a moving1 conducting gas for the wires4 ,under the influence of an external magnetic field1 the conduction electrons move through the plasma to one side of the duct which carries electrical power away to the load4 ,the ,,mhd generator gets its energy from an expanding1 hot gas2 but1 unlike the turbogenerator1 the heat engine and generator are united in the static duct4 ,the gradual widening of the duct shown in ,figure #i;a reflects the lower pressure1 cooler plasma at the duct's end4 ,some of the plasma's thermal energy content has been tapped off by the duct's electrodes as electrical power4 ,the ,fourth ,state of ,matter ,plasma can be created by temperatures over #bjjj,k4 ,at this temperature many high-velocity gas atoms collide with enough energy to knock electrons off each other and thus become ionized4 ,the material thus created1 shown as a glowing gas in ,figure #aj1 does not behave consistently as any of the three familiar states of matter3 solid1 liquid1 or gas4 ,plasma has been called a fourth state of matter4 ,since we have difficulty in containing such high temperatures on earth1 we adopt the strategy of seeding4 ,in this technique gases that are ordinarily difficult to ionize1 like helium1 are made conducting by adding a fraction of a percent of an alkali metal such as potassium4 ,alkali metal atoms have loosely bound outer electrons and quickly become ionized at temperatures well below #bjjj,k4 ,illustration3 ,figure #aj ,glowing plasma in experimental device at ,general ,atomic's ,john ,jay ,hopkins ,laboratory1 ,san ,diego4 ,t-shaped plasma gun provides data for research in thermonuclear fusion4 ,courtesy ,texas ,atomic ,energy ,research ,foundation4 ,a helium-potassium mixture is a good enough conductor for use in an ,,mhd generator4 ,in this plasma the electrons move rapidly under the influence of the applied fields1 though not as well as in metals4 ,the positive ions move in the opposite direction from the electrons1 but the electrons are much lighter and move thousands of times faster thus carrying the bulk of the electrical current4 ,,mhd ,power ,prospects ,the ,,mhd duct is not a complete power plant in itself because1 after leaving the duct1 the stream of gas must be compressed1 heated1 and returned to the duct4 ,very high temperature materials and components must be developed for this kind of service4 ,moreover1 while the duct is simple in concept1 it must operate at very high temperatures in the presence of the corrosive alkali metals4 ,this presents us with difficult materials problems4 ,when the problems are solved1 probably within the next decade1 ,,mhd power plants should be able to provide reliable power with high efficiency4 ,they may then serve in large space power plants1 and1 most important1 they may provide cheaper electricity for general use through their higher temperatures and greater efficiencies4 ,,chemical ,,batteries ,electricity from the ,chemical ,bond ,if you vigorously knead a lemon to free the juices and then stick a strip of zinc in one end and a copper strip in the other1 you can measure a voltage across the strips4 ,electrons will flow through the load without the inconvenience of having to supply heat4 ,you have made yourself a chemical battery4 ,the chemical battery was the first direct conversion device4 ,two hundred years ago it was the scientists' only continuous source of electricity4 ,since the chemical battery does not need heat for its operation1 it is logical to ask what makes the current flow4 ,where does the energy come from8 ,the battery has no semiconductors1 but1 like the thermoelectric couple and the thermionic diode1 it uses dissimilar materials for its electrodes4 ,a conducting fluid or solid is also present to provide for the passage of current between the electrodes4 ,in the example of the lemon1 the copper and zinc are the dissimilar electrodes1 and the lemon juice is the conducting fluid or electrolyte that supplies positive and negative ions4 ,the battery derives its energy from its complement of chemical fuel4 ,the voltage difference arises because of the different strengths of the chemical bonds4 ,the chemical bond is basically an electrostatic one2 some atoms have stronger electrical affinities than others4 ,chemical ,reactions ,used in ,batteries and ,fuel ,cells ,consider the following chemical reactions of common batteries together with some fuel cell reactions which will be discussed further in the next section4 ,battery ,reactions ,pb ,pb,o #b;,h,,so #b,pb,s,o #b;,h,o ,fe ,ni,o ,fe,o ,ni,o ,zn ,ag,o ,h,o ,ag ,zn7,,oh7 ,pb ,ag,o ,pb,o #b;,ag ,fuel ,cell ,reactions #b,li,h #b,li ,h #b;,cu,br #b;,cu,br ,br #b;,h ,o #b;,h,o 7,bacon cell7 ,pb,i ,pb ,i ,in principle all these reactions are the same as those going on inside the lemon1 although each type of cell produces a slightly different voltage because of the varying chemical affinities of the atoms and molecules involved4 ,there are literally hundreds of materials which can be used for electrolytes and electrodes4 ,no heat needs to be added as the electrostatic chemical bonds are broken and remade in a battery to generate electrical power4 ,the chemical reaction energy is transferred to the electrical load with almost #ajj efficiency4 ,the ,carnot cycle is no limitation here2 only 8cold0 electrostatic forces are in action4 ,the reactions cannot go on forever1 however1 because the battery supplies the energy converter with a very limited supply of fuel4 ,eventually the fuel is consumed and the voltage drops to zero4 ,this deficiency is remedied by the fuel cell in which fuel is supplied continuously4 ,an ,old ,standby in ,outer ,space ,almost every satellite and space vehicle has a chemical battery aboard4 ,it is not there so much for continuous power production but as a rechargeable electrical accumulator or reservoir to provide electricity during peak loads4 ,the battery is also needed to store energy for use during the periods when solar cells are in the earth's shadow and therefore inoperative4 ,in this capacity the dependable old battery serves the most modern science very well indeed4 ,,the ,,fuel ,,cell3 ,a ,,continuously ,,fueled ,,battery ,potential ,fuels ,the battery has a very close relative1 the fuel cell4 ,unlike the battery the fuel cell has a continuous supply of fuel4 ,illustration3 ,figure #aa ,this diagram shows how a hydrogen-oxygen fuel cell works4 ,the chemical battery works in the same way1 except that the chemicals are different and are not continuously supplied from outside the cell4 ,the water produced by the ,h-,o cell shown can be used for drinking on spaceships4 ,,anode ,h ,,in ,,cathode ,o ,,in ,,electrons ,,load ,,koh ,,electrolyte ,k ,,ion ,,oh ,,ion ,,negative ,,ion ,,flow #dj;,h #b;,h #d;,h,o #d;e ,o #b;,h,o #d;e #dj;,h ,the hydrogen-oxygen cell of ,figure #aa is typical of all fuel cells4 ,it essentially burns hydrogen and oxygen to form water4 ,if the hydrogen and oxygen can be supplied continuously and the excess water drained off1 we can greatly extend the life of the battery4 ,the fuel cell accomplishes this4 ,fueled electrical cell would be more descriptive since the physical principles are identical with those of the battery4 ,perhaps the most challenging task contemplated for the fuel cell is to bring about the consumption of raw or slightly processed coal1 gas1 and oil fuels with atmospheric oxygen4 ,if fuel cells can be made to use these abundant fuels1 then the high natural conversion efficiency of the fuel cells will make them economically superior to the lower efficiency steam-electric plants now in commercial service4 ,so far we have dwelt on the fuel cell as a cold energy conversion device that is not limited by the ,carnot efficiency4 ,a variation on this theme is possible4 ,take a hydrogen iodide 7,,hi7 cell1 and heat the ,,hi to #bjjj,k4 ,some of the ,,hi molecules will collide at high velocities and dissociate into hydrogen and iodine3 #b;,,hi ,h ,i2 the higher the temperature1 the more the dissociation4 ,by separating the hydrogen and iodine gases and returning them for recycling to the fuel cell where they are recombined1 we have eliminated the fuel supply problem and created a regenerative fuel cell4 ,we have1 however1 also reintroduced the heat engine and the ,carnot cycle efficiency4 ,the thermally regenerative fuel cell is a true heat engine using a dissociating gas as the working fluid4 ,scheme for ,project ,apollo ,most of the impetus for developing the fuel cell as a practical device comes from the space program4 ,the cell has admirable properties for space missions that are less than a few months in duration4 ,it is a clean1 quiet1 vibrationless source of energy4 ,like the battery it has a high electrical overload capacity for supplying power peaks and is easily controlled4 ,it can even provide potable water for a crew if the ,bacon ,h - ,o cell is used4 ,for short missions where large fuel supplies are not needed1 it is also among the lightest power plants available4 ,these compelling advantages have led the ,national ,aeronautics and ,space ,administration to choose the fuel cell for some of the first manned space ventures4 ,project ,apollo1 the manned lunar landing mission1 is the most notable example4 ,here the fuel cell will be not only an energy source1 but also part of the ecological cycle which keeps the crew alive4 ,problem #d ,a manned space vehicle requires an average of #b electrical kilowatts4 ,a nuclear reactor thermoelectric plant having a mass of #ajjj kilograms1 including shielding1 can supply this power for #aj1jjj hours4 ,the basic fuel cell has a mass of #ej kilograms and consumes kilogram of chemicals per hour4 ,the chemical containers weigh #be kilograms4 ,what is the longest mission where the total weight of the fuel cell will be less than the weight of the nuclear power plant8 ,,solar ,,cells ,photons as ,energy ,carriers ,all our fossil fuels1 such as coal and oil1 owe their existence to the solar energy stream that has engulfed the earth for billions of years4 ,the power in this stream amounts to about #adjj watts per square meter at the earth1 nearly enough to supply an average home if all the energy were converted to electricity4 ,the problem is to get the sun's rays to yield up their energy with high efficiency4 ,the sun's visible surface has a temperature around #fjjj,k4 ,any object heated to this temperature will radiate visible light mostly in the yellow-green portion of the spectrum 7#eejj ,a#aa74 ,our energy conversion device should be tuned to this wavelength4 ,the energy packets arriving from the sun are called photons4 ,they travel1 of course1 at the speed of light1 and each carries an amount of energy given by ,e hf hc_/ where ,e energy 7in joules7 h ,planck's constant 7#f4fb #aj joule-second7 f the light's frequency 7in cycles per second c_/7 c the velocity of light 7#cjj1jjj1jjj meters per second7 the wavelength 7in meters7 ,using the fact that an angstrom unit is #aj meter1 the energy of a #eejj ,a photon could be calculated as ,e hf hc_/ 7#f4fb #aj #c4jj #aj7_/7e4ej #aj7 #c4fa #aj joule #b4b electron volts ,comparing this result1 #b4b electron volts1 with the energies required to cause atomic ionization or molecular dissociation 7an electron volt or so71 we see that it is in the right range to actuate direct conversion devices based on such phenomena4 ,harnessing the ,sun's ,energy ,historically1 the sun's energy has most often been used by concentrating it with a lens or mirror and then converting it to heat4 ,we could do this and run a heat engine1 but a more direct avenue is open4 ,about a decade ago it was found that the junction between p and n semiconductors would generate electricity if illuminated4 ,this discovery led to the development of the solar cell1 a thin1 lopsided sandwich of silicon semiconductors4 ,as shown in ,figure #ab1 the top semiconductor layer exposed to the sun is extremely thin1 only #b4e microns4 ,solar photons can readily penetrate this layer and reach the junction separating it from the thick main body of the solar cell4 ,illustration3 ,figure #ab ,,the ,,solar ,,cell ,the photograph shows the solar cell in use on a satellite4 ,the spherical1 radioisotope1 thermoelectric generator at the bottom of the satellite is used to supplement the solar cells4 ,in the solar cell1 hole-electron pairs are created by solar photons in the vicinity of a p-n junction4 ,courtesy ,u4 ,s4 ,air ,force and ,national ,aeronautics and ,space ,administration4 p ,,silicon n ,,silicon ,,electron-,,mole ,,pairs ,,junction ,,photons ,,from ,,sun ,,or ,,radioisotope ,,electrons ,,energy ,,out ,whenever p- and n-type semiconductors are sandwiched together a voltage difference is created across the junction4 ,the separated holes and electrons in the two semiconductor regions establish this electric field across the junction4 ,unfortunately1 there are usually no current carriers in the immediate vicinity of the junction so that no power is produced4 ,the absorption of solar photons in the vicinity of the junction will create current carriers1 as the photons' energy is transformed into the potential energy of the hole-electron pairs4 ,these pairs would quickly recombine and give up their newly acquired potential energy if the electric field existing across the junction did not whisk them away to an external load4 ,the solar cell produces electricity when hole-electron pairs are formed4 ,any other phenomenon that creates such pairs will also generate electricity4 ,the source of energy is irrelevant so long as the current carriers are formed near the junction4 ,thus1 particles emitted by radioactive atoms can also produce electricity from solar cells1 although too much bombardment by such particles can damage the cell's atomic structure and reduce its output4 ,the solar cell is not a heat engine4 ,yet it loses enough energy so that the sun's energy is converted at less than #ae efficiency4 ,losses commonly occur because of the recombination of the hole-electron pairs before they can produce current1 the absorption of photons too far from the junction1 and the reflection of incident photons from the top surface of the cell4 ,despite these losses solar cells are now the mainstay of nonpropulsive space power4 ,,nuclear ,,batteries ,energy from ,nuclear ,particles ,as we have seen1 solar cells are able to convert the kinetic energy of charged nuclear particles directly into electricity1 but a simpler and more straightforward way of doing this exists4 ,this involves direct use of the flow of charged particles as current4 ,the nuclear battery shown in ,figure #ac performs this trick4 ,a central rod is coated with an electron-emitting radioisotope 7a beta-emitter2 say1 strontium-#ij74 ,the high-velocity electrons emitted by the radioisotope cross the gap between the cylinders and are collected by a simple metallic sleeve and sent to the load4 ,simple1 but why don't space charge effects prevent the electrons from crossing the gap as they do in the thermionic converter8 ,the answer lies in the fact that the nuclear electrons have a million times more kinetic energy than those boiled off the thermionic converter's emitter surface4 ,consequently1 they are too powerful to be stopped by any space charge in the narrow gap4 ,nuclear batteries are simple and rugged4 ,they generate only microamperes of current at #aj1jjj to #ajj1jjj volts4 ,illustration3 ,figure #ac ,a ,,nuclear ,,battery ,the nuclear battery depends upon the emission of charged particles from a surface coated with a radioisotope4 ,the particles are collected on another surface4 ,,energy ,,out ,,insulator ,,layer ,,of ,,beta-,,emitting ,,radioisotope ,,vacuum ,double ,conversion ,in the earlier description of the energy conversion matrix1 we saw that we could go through the energy transformation process repeatedly until we obtained the kind of energy we wanted4 ,this is exemplified in a type of nuclear battery which uses the so-called double conversion approach4 ,first1 the high-velocity nuclear particles are absorbed in a phosphor which emits visible light4 ,the photons thus produced are then absorbed in a group of strategically placed solar cells1 which deliver electrical power to the load4 ,although efficiency is lost at each energy transformation1 the double conversion technique still ends up with an overall efficiency of from #a to #e1 an acceptable value for power supplies in the watt and milliwatt ranges4 ,,advanced ,,concepts ,ferroelectric and thermomagnetic conversion are subtle concepts which depend upon the gross alteration of a material's physical properties by the application of heat4 ,devices employing such concepts are true heat engines4 ,instead of the gaseous and electronic working fluids used in the other direct conversion concepts1 the ferroelectric and thermomagnetic concepts employ patterns of atoms and molecules that are actually rearranged periodically by heat4 ,ferroelectric ,conversion ,ferroelectric conversion makes use of the peculiar properties of dielectric#ab materials4 ,barium titanate1 for example1 has good dielectric properties at low temperatures1 but1 when its temperature is raised to more than #abj;,c1 the properties get worse rapidly4 ,we cannot discuss dielectric behavior thoroughly in this booklet2 suffice it to say that in this process heat is absorbed in a realignment of molecules within the barium titanate latticework4 ,if we now place a slab of barium titanate between the two plates of an electrical condenser and charge the condenser1 as shown in ,figure #ad1 we have a unique way of converting heat into electricity directly4 ,when the barium titanate is heated above its ,curie point#ac of #abj;,c1 the condenser's capacitance is radically reduced as the dielectric constant falls4 ,the condenser is forced to discharge and move electrons through an external circuit consisting of the load and the original source of charge4 ,useful electrical energy is delivered during this step4 ,figure #ad shows the process schematically and mathematically4 ,when the dielectric is cooled1 waste heat is given up by the barium titanate1 and the cycle is complete4 ,illustration3 ,figure #ad ,,ferroelectric ,,energy ,,conversion ,the ferroelectric converter is really an electrical capacitor whose capacitance is changed by temperature4 ,when heat is added1 capacitance drops1 voltage rises1 and the capacitor is made to discharge through the load4 ,,cycle3 ,switch #a closed1 #b open4 ,condenser charges from battery to charge ,q at voltage ,v with capacity ,c4 ,all switches open4 ,heat added1 capacity changes from ,c to ,c1 charge remains constant1 so voltage changes from ,v to ,v4 ,switch #b closed1 #a open4 ,condenser discharges through load and battery to charge ,q at voltage ,v with capacity ,c4 ,all switches open4 ,heat rejected1 capacity changes from ,c to ,c1 charge remains constant1 so voltage changes from ,v to ,v4 ,,cycle ,,then ,,repeats4 ,energy supplied from battery each cycle is ,e4 ,energy delivered to load and battery each cycle is ,e4 ,net energy converted is then ,e - ,e1 the difference in the shaded areas4 7a7 ,,circuit ,,heat ,,in ,,barium ,,titanate ,,dielectric ,,waste ,,heat ,,out ,,switch #b ,,load ,,switch #a ,,battery 7b7 ,,cycle ,,diagram charge volts ,q1 ,q1 ,e1 ,e1 ,v ,v ,v ,,general ,,information3 ,c ,c ,v ,q_/,c ,thermomagnetic ,conversion ,the analog#ad of ferroelectricity is ferromagnetism4 ,a converter employing similar principles to those in ferroelectricity can be made using an electrical inductance with a ferromagnetic core4 ,when the temperature of the ferromagnetic material is raised above its ,curie point1 its magnetic permeability drops quickly1 causing the magnetic field to collapse partially4 ,energy may be delivered to an external load during this change4 ,instead of energy being stored in an electrostatic field1 it is stored in a magnetic field4 ,ferroelectric and thermomagnetic conversion both represent a class of energy transformations which involve internal molecular or crystalline rearrangements of solids4 ,there is no change of phase as in a steam engine1 but the energy changes are there nevertheless4 ,in thermodynamics such internal geometrical changes are called second-order transitions1 as opposed to the first-order transitions observed with heat engines using two-phase working fluids like water_/steam4 ,on the ,frontier ,other potential energy conversion schemes are being investigated by scientists and engineers4 ,those listed in the ,energy ,conversion ,matrix 7,figure #b7 only scratch the surface4 ,in particular1 we are just learning how to manipulate photons4 ,there are photochemical1 photoelectric1 and even photomechanical transformations4 ,these have hardly been tapped4 ,consider the reaction when an electron and its antimatter equivalent1 the positron1 meet4 ,they mutually annihilate each other in a burst of energy6 ,this energy will be harnessed someday4 ,what energy conversion device are we going to use to completely convert mass into energy8 ,the energy requirements for interstellar exploration are so great that these voyages will be impossible unless a new device is found that can completely transform mass into energy4 ,then again1 we haven't the faintest idea of how to control gravitational energy1 but we may learn4 ,the panorama is endless4 ,problem #e ,a #a1jjj1jjj-kilogram spaceship takes off for ,alpha ,centauri1 our nearest star1 #d4c light years away4 ,if it accelerates to nine-tenths the velocity of light1 what is its kinetic energy8 ,how much fuel mass will have to be completely converted to energy to acquire this velocity8 ,,suggested ,,references ,articles ,fuel ,cells1 ,leonard ,g4 ,austin1 ,scientific ,american1 #bja3 #gb 7,october #aiei74 ,a survey of the different types4 ,nuclear ,power in ,outer ,space1 ,william ,r4 ,corliss1 ,nucleonics1 #ah3 #eh 7,august #aifj74 ,a review of all nuclear space power plants4 ,fuel ,cells for ,space ,vehicles1 ,m4 ,g4 ,del ,duca1 ,astronautics1 #e3 #cf 7,march #aifj74 ,fuel ,cells1 ,e4 ,gorin and ,h4 ,l4 ,recht1 ,chemical ,engineering ,progress1 #ee3 #ea 7,august #aiei74 ,thermionic ,converters1 ,karl ,g4 ,hernqvist1 ,nucleonics1 #ag3 #di 7,july #aiei74 ,the ,revival of ,thermoelectricity1 ,abram ,f4 ,joffe1 ,scientific ,american1 #aii3 #ca 7,november #aieh74 ,excellent historical and technical review4 ,the ,photovoltaic ,effect and ,its ,utilization1 ,p4 ,rappaport1 ,,rca ,review1 #bj3 #cgc 7,september #aiei74 ,recommended for advanced students4 ,the ,prospects of ,,mhd ,power ,generation1 ,leo ,steg and ,george ,w4 ,sutton1 ,astronautics1 #e3 #bb 7,august #aifj74 ,conversion of ,heat to ,electricity by ,thermionic ,emission1 ,volney ,c4 ,wilson1 ,journal of ,applied ,physics1 #cj3 #dge 7,april #aiei74 ,recommended for advanced students4 ,improved ,solar ,cells ,planned for ,,imp-,d1 ,r4 ,d4 ,hibben1 ,aviation ,week ,space ,technology1 #hc3 #ec 7,july #bf1 #aife74 ,thin-film ,solar ,cells ,boost ,output ,ratio1 ,p4 ,j4 ,klass1 ,aviation ,week ,space ,technology1 #hc3 #fg 7,november #bi1 #aife74 ,books ,direct ,conversion of ,heat to ,electricity1 ,joseph ,kaye and ,john ,a4 ,welsh1 ,john ,wiley ,sons1 ,inc41 ,new ,york #ajjaf1 #aifj1 #chg pp41 #aa4ej4 ,recommended for advanced students4 ,selected ,papers on ,new ,techniques for ,energy ,conversion1 ,sumner ,n4 ,levine1 7,ed471 ,dover ,publications1 ,inc41 ,new ,york #ajjad1 #aifa1 #ddd pp41 #c4jj4 ,a reprinting of many classical papers on direct conversion4 ,energy ,conversion for ,space ,power1 ,nathan ,w4 ,snyder1 7,ed471 ,academic ,press1 ,inc41 ,new ,york #ajjjc1 #aifa1 #ggi pp41 #h4ej4 ,a collection of ,american ,rocket ,society papers4 ,man and ,energy1 ,alfred ,rene ,ubbelohde1 ,george ,braziller1 ,new ,york #ajjaf1 #aiee1 #bdg pp41 #e4jj 7hardback72 #a4be 7paperback71 from ,penguin ,books1 ,inc41 ,baltimore1 ,maryland #babaa4 ,a popular treatment of energy and power4 ,motion ,pictures ,the following films are produced by ,educational ,services1 ,inc41 and are available from ,modern ,learning ,aids1 ,a ,division of ,modern ,talking ,picture ,service1 ,inc41 #c ,east #edth ,st41 ,new ,york #bb1 ,new ,york4 ,energy and ,work1 #jcaa1 #bi minutes1 #aej4 ,mechanical ,energy and ,thermal ,energy1 #jcab1 #bg minutes1 #abj4 ,conservation of ,energy1 #jcac1 #bg minutes1 #aej4 ,photo-,electric ,effect1 #jdag1 #bh minutes1 #bbj4 ,,answers ,,to ,,problems ,first1 mechanical energy drives the car's electric generator4 ,second1 the electrical energy is converted into chemical energy when the battery is recharged4 99 99 99 99 99 99 99 ,from the kinetic energy equation we get v 7#b ,e_/m7 ,since the engine is #be efficient1 the energy available to propel the car is #dh1jjj #j4be or #ab1jjj joules4 ,so v 7#bd1jjj_/a1jjj7 #bf #d4i meters per second 99 99 99 99 99 99 99 e 7#cjj - #bj7_/cjj #ad_/ae #j4ic #ic ,the crossover point1 t1 in hours is found by equating the nuclear power plant mass and that of the fuel cell with its associated fuel4 ,the equation is #ajjj #ej #be t t #ahej hours #gg days 99 99 99 99 99 99 99 ,e mv 7#aj7j4i #c #aj77_/b #c4f #aj joules ,the ship will use the same amount of energy to decelerate at its destination4 ,note that this calculation assumes a perfect efficiency in converting the energy of matter annihilation into the kinetic energy of the space ship4 ,the mass consumed is m ,e_/c 7#c4f #aj7_/7i #aj7 #d4j #aj kg almost half the spaceship mass4 ,footnotes #a,systems for ,nuclear ,auxiliary ,power4 #b;,described in this booklet4 #c,magnetohydrodynamics4 #d,the ,kelvin temperature scale starts with zero at absolute zero instead of at the freezing point of water4 ,therefore1 ,k ,c #bgc2 ,k _/ 7,f #dfj74 #e,termed valence or conduction electrons1 these are responsible for chemical properties1 bonds with other atoms1 and the conduction of electricity4 #f,see the companion ,understanding the ,atom booklet1 ,power from ,radioisotopes4 #g;,discovered by ,thomas ,edison in #ahhc4 #h;,an electron volt is equal to the kinetic energy acquired by an electron accelerated through a potential difference of #a volt4 ,it is equal to #a4f #aj joule4 #i;,in outer space1 waste heat must be radiated away4 ,the rate at which heat is radiated is proportional to the fourth power of ,tc 7,stefan-,boltzmann law74 #aj,the newton and the weber are mks 7meter-kilogram-second7 units4 #aa;,an angstrom unit 7,a7 is a unit of distance measurement equal to #aj meter4 #ab;,dielectric materials are nonconductors such as are those used between the plates of a condenser to increase its electrical capacity4 #ac,the ,curie point is the temperature at which a material's crystalline structure radically changes and becomes less orderly4 #ad;,ferroelectricity and ferromagnetism are very similar4 ,the equations describing these phenomena are almost identical except that capacitance is replaced by its magnetic analog1 inductance1 and so on4 ,this booklet is one of the 8,understanding the ,atom0 ,series4 ,comments are invited on this booklet and others in the series2 please send them to the ,division of ,technical ,information1 ,u4 ,s4 ,atomic ,energy ,commission1 ,washington1 ,d4 ,c4 #bjede4 ,published as part of the ,,aec's educational assistance program1 the series includes these titles3 ,accelerators ,animals in ,atomic ,research ,atomic ,fuel ,atomic ,power ,safety ,atoms at the ,science ,fair ,atoms in ,agriculture ,atoms1 ,nature1 and ,man ,careers in ,atomic ,energy ,computers ,controlled ,nuclear ,fusion ,cryogenics1 ,the ,uncommon ,cold ,direct ,conversion of ,energy ,fallout ,from ,nuclear ,tests ,food ,preservation by ,irradiation ,genetic ,effects of ,radiation ,index to the ,,uas ,series ,lasers ,microstructure of ,matter ,neutron ,activation ,analysis ,nondestructive ,testing ,nuclear ,clocks ,nuclear ,energy for ,desalting ,nuclear ,power and ,merchant ,shipping ,nuclear ,power ,plants ,nuclear ,propulsion for ,space ,nuclear ,reactors ,nuclear ,terms1 ,a ,brief ,glossary ,our ,atomic ,world ,plowshare ,plutonium ,power from ,radioisotopes ,power ,reactors in ,small ,packages ,radioactive ,wastes ,radioisotopes and ,life ,processes ,radioisotopes in ,industry ,radioisotopes in ,medicine ,rare ,earths ,reading ,resources in ,atomic ,energy ,research ,reactors ,,snap1 ,nuclear ,space ,reactors ,sources of ,nuclear ,fuel ,synthetic ,transuranium ,elements ,the ,atom and the ,ocean ,the ,chemistry of the ,noble ,gases ,the ,first ,reactor ,whole ,body ,counters ,your ,body and ,radiation ,a single copy of any one booklet1 or of no more than three different booklets1 may be obtained free by writing to3 ,,usaec1 ,p4 ,o4 ,,box #fb1 ,,oak ,,ridge1 ,,tennessee #cghcj ,complete sets of the series are available to school and public librarians1 and to teachers who can make them available for reference or for use by groups4 ,requests should be made on school or library letterheads and indicate the proposed use4 ,students and teachers who need other material on specific aspects of nuclear science1 or references to other reading material1 may also write to the ,oak ,ridge address4 ,requests should state the topic of interest exactly1 and the use intended4 ,in all requests1 include 8,zip ,code0 in return address4 ,printed in the ,united ,states of ,america ,,usaec ,division of ,technical ,information ,extension1 ,oak ,ridge1 ,tennessee ,may #aifh ,transcriber's ,notes --,silently corrected a few typos4 --,modified some image references to reflect the pageless flowable e,book format4 --,retained publication information from the printed edition3 this e,book is public-domain in the country of publication4 --,in the text versions only1 text in italics is delimited by underscores4