Document 7RLJxB1XBr1aDgkvB6Q5YZZqB

'20 CHAPTER 1 . 1965 Guide And Data ?Book * T. L. Hill: Statistical Thermodynamics (Addison-Wesley:; Refrigeration and Air.Conditioning Engineering, (John Wiley and Publishing Co., Inc., Reading, Mass., 1960). Sons, Inc., New York, 1945). ' M. W. Zemansky: Heat and Thermodynamics (McGraw-Hill. A. A. Berestneff: Absorption refrigeration (Mechanical Engi Co., New York, 4th ed., 1957). neering, VoL 72, 1950, p. 216). -' / * H. B. Callen: Thermodynamic* (John Wiley A Sons, New *R M. Buffington: Qualitative requirements for absorbent- York, 1960). refrigerant combinations (Refrigerating Engineering, April * A. H. Wilson: Thermodynamics and Statistical Mechanics '. , 1949, p 343) -- (Cambridge Press, 1957). " L. Pauling: The Nature of the Chemical Bond (Cornell Uni u G. N. Lewis and M. Randall (revised by K. S. Pitser and L., versity Press, Ithaca, New York, 1939). Brewer): Thermodynamics (McGraw-Hill Book Co., New York, 17 G. F. Zellhoefer: Commercial refrigeration bv low-pressure 2nd ed., 1961). steam (Refrigerating Enqineerino, Vol. 33, 1937, p. 317). u Swigert and Beardsley:. Empirical Specific'Heat Equations M B. J. ISaumMi, Jr.: Why Refrigerant 22 should be favored for Based Upon Spectroscopic Data (Georgia Institute of Technology^' absorption refrigeration, (ASHRAE Journal, December 1959, 1938). : P- 45)- : " M. Benedict, G. B. Webb, and L. C. Rubin: An empirical ** George Scatchard etal: Thermodynamic properties-aaturated equation for thermodynamic properties of light hydrocarbons and ' ;, liquid ana vapor of ammonia-water mixtures (Refrigerating their mixtures (Journal of Chemistry and Physics, April 1940, p.. Engineering, May 1947, p. 413)' '. J 334). ` * F. H. Kohloss and G. L. Scott: Equilibrium properties of u J. J. Martin and Y. Hou: Development of an equation of aqua-ammonia in chart form (Refrigerating Enqineerino, state for gases (AlChE Journal, Vol. 1,1955, p, 142). October 1950, p. 970). M T. R. Strobridge: The Thermodynamic Properties of Nitrogen Thermodynamic properties of ammonia-water solutions ex from 64 to 300 K, Between 0.1 ana tOO Atmospheres (National tended to higher temperatures .and pressures (ASHRAE Trans Bureau of Standards Technical Note 129,1962): actions, ' Vol/70, 1964). ' : ' ' * " -J: 0; Hirschfelder ei al: Generalised equation of state for gases W. Pennington: How to .find, accurate vapor pressures of and liquids (Industrial and Engineering Chemistry: Vol. 50,-1958, lithium bromide water solutions (Refrigerating Engineering, p. 375). i<r:. ... , May 1955, p. 57).' ^ ' ' ' H W. F. Stoecker: Chanter 4, Refrigeration arid Air Condition R. T. Islington ct ed: The Absorption Cooling Process (Insti ing (McGraw-Hill Book Co., Inc., New York, 1958). . tute .of .Gas Technology, Research Bulletin No. 14,, Chicago, IT N. R. Sparks and C. C. Dillio: Chapters 6 and 9, Mechanical Illinois,-1957).' . , Refrigeration (McGraw-Hill Book Co., Inc.,.New York, 1959). H.-J. Madntire and F. W. Hutchinson: Chapters IV and V, Refrigeration Engineering (John Wiley and Sons, Inc.,. New York, 1950). ; 11 J. L. Threlkeld: Chapter 3, Thermal Environmental Engineer ing (Prentice-Hall, Inc., Englewood Clifisj N. J.' 1962)1' "W. H. Sevems'and J:`R. Fellows: Chapter 17, Air Con ditioning and Refrigeration (John Wiley ana' Son. Inc.. New York, 1958). . .** Norman Sharpe: Chapter 3, Refrigeration Principles and Pjactices,(McGraw-Hill Book Co., Inc., New York,.1949). - B International Critical. Tables' (McGraw-Hill Book Co., Inc., New York, VoL in, 1928, p.,77). E. Lange'and E. Schwarts: .The heats of .solution and dilu tion of salts from extreme dilution to saturation. IV lithium bromide (Z. Physik. Chem., Vol. 133,.1928, p. 129).: , i-: * Private communication from Dow Chemical Company. 'n G. G. Brown: Unit Operations (John Wiley and Sons, Inc., New York, 1950).- *! " E. P. Whitlow and J. 8. Swearingen: An improved absorp tion refrigeration cycle (Gas Age, VoL 122,-No. 9, 1958, p. `19). . B. R. C. Jordan and G. B. Priester: Chapter. 13, Refrigeration 'V." J. H. Keenan arid G. K.`Keyes: Thermodynamic Properties of and Air Conditioning (Prentice-Hall, Inc., Englewood. Cliffs, Steam (John Wileyand Sons, New York, 1936). ' N. J., 1956). . * R.'' Plank: ' Bandbuc/s dcr "Kaltetechnik (Springer Verlag, ** B. F. Raber-and F. W. Hutchinson: Chapters II and III, Berlin,'VoL VII,.1959). ` ac-rl otr',;3 tV CHAPTER 2 THERMOELECTRIC COOLING Discovery, Performance of Thermoe/ecfnc Couples, Refrigerating System Analogies, Advantages, Applications, Design N 1821 Seebeck observed that, if a closed circuit wa3 made I of two dissimilar metals, an electrical current flowed in the circuit when the'two junctions were maintained at-different temperatures.. His investigations were very extensive, cover ing a .wide range of elements and- compounds. This re sulted in publication of a series in which the materials he had investigated<were arranged in a logical sequence, in the order of the magnitude of-their effect. However, he failed'to realise the significance of his discovery. In 1834 Peltier.observed the inverse effect, namely,, that if an electrical current flowed across the junction between two dissimilar materials, heat was either absorbed or evolved. Peltier did not realise the signifi cance of bis discovery either, and moreover failed to recog nise the connection between his discovery and that of See beck. It is alleged that Lens ended all conjecture surrounding these discoveries by freezing a small quantity of water placed in the vicinity of the junction between a bismuth and anti mony rod through which a direct current was passed. These were two of the materials in which Seebeck had observed his effect to be most pronounced. A third effect was'pointed out-by Thomson (Lord Kelvin) in 1851.' It related the heat absorbed or evolved in a single conductor to the temperature gradient along it and the current flowing through it. This is ah effect which takes place in addition to the Joule (PR) heating. However,- in thermoelectric cooling materials, Kelvin's is a second order effect, compared with those of Peltier and See beck, and will not be further considered. For many years, the practical application of these, thermo electric effects was almost exclusively restricted.to thermo couples for the measurement of temperature, became metals exhibit a comparatively small Seebeck effect. However, the Seebeck effect in semiconductors can be considerably greater. The advent of the transistor and other semiconductor devices has stimulated research pertaining to the properties of semi conductors in general, and from this has come materials-in which the thermoelectric effects are of sufficient magnitude so that the fabrication of useful devices has become a reality. ' In practice; the'absolute Seebeck"coefficient, a, of a material is determined frith respect to a material such as lead, in which the Seebeck coefficient is negligible. rIh metals, a does not exceed 0.00005 volt per C deg; in semiconductors'currently (1964) available for thermoelectric applications,' a is typically 0.0002 to 0.00025 volt per C deg. Peltier Effect (Fig. 2). The same circuit can be considered as bring made up of materials A and B, into which a battery is introduced to provide a direct current, l. At the junction between the two dissimilar materials, the heat evolved or absorbed-in unit time is proportional to the current flowing and is given by: where (2) Q * heat evolved or absorbed in unit time, watts. tab B relative'Peltier coefficient for materials A and B. I -- direct current flowing, amperes. THERMOELECTRIC EFFECTS S&beck Effect (Fig. I). For a small temperature difference between the two junctions of materials A and B, the open circuit voltage developed is proportional to the temperature difference and is given by: COLO where AB " OabAT (l) AB -- open circuit voltage developed. *n " relative Seebeck coefficient (the difference between the absolute Seebeck coefficients for materials A and B). AT ~ temperature difference between junctions of materials A and B. ceacrml Jgnwiwfbility Ux this chapter is amScood to TC 1.13, Tbermo- Rg. 2____Peltier Effect The Absorption ood Evolution ot Hoof of the Junctions Sefwan Two Df- dmSar Mutetkds Prodvcscf by An Passage of an Qncfrfc Curmtf Tfcrocyb (bn Junction*;!r: -' ' 1 21