Document V3YKa0ZQEgjLmdmJ3YR9eyzV8

632 CHAPTER 37 EL Anderson: Some factors and.prindpleei involved' in the separation andcoUection ofjdust.-mist, and-fume from.gases (American Instituteof Chemical Engineer* Transaction*. Vol. 16,.1924, p: 69).^ `-'v -u- - -(*y ; B." Rathbuh: Electrical precipitation^of solids from smelter cases'(4mertcoh Institute of Electrical Engineers Trans actions,`Wd. 41,1922, p. 815): =1' .: . - - A,-.C.-.Stem et aL.:^ Characteristics . of unit dust< collectors (ASHVE Transactions, VoL 52,1946, p. 237).- . J..M. Kane: Operation,,application and effectiveness of dust oijllectioriw^upmen^ (R^crcncelSection, Heating 'and Ventilating,'. 1965 Guide And .Data Book' C.-. A--.-tappIe:. Chaptil;9 {Air,Pollution, Abatement, Manual. Manufacturing. Chepiists.Association). , " ... - S.jK. Friedlander rf \al.Handbook,on-Air-Cleaning^ Atomic Energy Commission, Washington, D. C.). M. W. First et aL: Performance of wet-cell washers for various aerosols-jC/nducfrioLorfd <EftgineertngsChetnistry,.VoL .43.4951 t\ 13S31............... . .*, ' 'J. 'Hi' Perry:'Chemical Engineer* Handbook (McGraw-Hill Book Co.',-New York,-1950, .3ra ed.).' ' :R.- J.,;Ruff:''Design factore in-'catalytic fume''elimination {Heating`and .*Ventilating; September:1953) p.* 84): r-*s i .n v., ^LSSSmm !vr >, i;' Is-' " ?-~.b COMPRESSORS HEOPKOCAr/NG: Performance, Features, App/rcafron,- ROTARY: Performance, Features, lubrication, Motor Se/ection, large Rolary Type; CENTRIFUGAL: Cycle, Refrigerants, Compressor Types, System Components, Performance, Controls, Multiple Machine Operations, Selection - HE compressor is one of the five essential parts of the between the refrigerant liquid at a temperature corresponding Tcompression refrigeration system,1 along with the! con to the pressure of the vapor leaving tire compressor and' the denser the expansion valve (or its equivalent), the evaporator refrigerant vapor entering the compressor. It is usually meas sod the interconnecting piping. Since the compressor is the principal moving part, a knowledge of its .construction,and behavior is of fundamental importance. .' , j ured in Btu per hour. The performance factor for a hermetic compressor indicates combined operating efficiency of motor and compressor. This chapter discusses the design features and.performance of refrigeration compressors. Reciprocating compressors are disriiwH in Part I, rotary in Part IT, and1centrifugal in Part III. Theoretical and actual compression cycles are treated in Chapter 1. Capacity, iu Btuh Performance factor (hermetic) " --P-o-w--e--r --inpr--ut,,:-in----w: a t ts The performance factor for an open compressor does' not involve motor efficiency. ' ' . PARTI: RECIPROCATING COMPRESSORS Performance factor (open) Power input, in Bhp 'Capacity, in tons Most reciprocating compressors are single acting; using trunk-type pistons driven directly through a pin and con necting rod from the crankshaft. Double-acting compressors utilising piston rods, crossheads, stuffing boxes, and oil injec tion are considered obsolete and are not covered in this chapter. This section covers two elasaifieatinra that include thema- jority of reciprocating refrigeration compressors, the halo- carbon compressor and the ammonia compressor. The most widely used is the halocarbon compressor, manu factured in three types of design, (1) open, (2) semi- of bolted hermetic, and (3) the welded shell hermetic. : Open-type compressors are those in which the shaft,extends through the crankcase for an external drive. Hermetic compressors are those in which the motor and compressor are contained within the same pressure vessel, with the motor shaft integral with the compressor crankshaft, and with the motor in oontact with the refrigerant. . . -..A semi-, (bolted), (accessible), or. (serviceable):hermetic compressor is of bolted construction capable of field repair..'. A welded shell, (sealed) hermetic compressor in which' the motor-compressor is mounted inside a steel shell which in turn is sealed by welding. Combinations of design features used are shown in Table 1; The Ideal Compressor Thecapacity of a compressor at a given operating condition is determined by the weight oF gas it can compress in unit time. Ideally, the weight of gas compressed per unit time is equal to the density of the gas times the compressor displace ment per unit time as shown in Equation 1: - .r 10 = HMSnArp/1728 - - . (1) tcrtcre ' ' to -- weight of gas compressed per unit of time, pounds of gas per hour. ' A " area of cylinder, square inches. . S stroke, inches, n -- number of cylinders. N -- compressor speed, revolutions per minute. p m density of gas entering compressor, pounds per cubic foot. The ideal refrigeration cycle is discussed in Chapter 1; and the following quantities can be determined from the pressure Enthalpy diagram in Fig. 2 of Chapter 1: Refrigeration effect (Btu/lb) = Qs-*= (hi -- K1)' "* PERFORMANCE '-Work of compresor (Btu/lb)' * Qw = (Ai -- M- The performance of a machine is an evaluation of the ability of tiie machine.to accomplish its *ggneH task. Compressor performance is the result of a design compromise which must conform to certain physical limitations of the' refrigerant,' compressor, and motor, while attempting to provide: :.; - 1. Die most refrigeration effect for the least power input. 2. The greatest trouble-free life expectancy. .a. The lowest cost.. . ' 4. A wide range of operating conditions. ,( - Two useful measures of compressor performance1are the capacity, which;inay be related to compressor displacement,' and the performance'factor. ' Capacity is the refrigeration effect that can be accomplished by a compressor. It is equal to the difference w total enthalpy Tbs (ami raspanaibiGt)' far dtaptcr awigwd to TC KRieipro- Eatery Comprawor Unit*: and TC U, Maefeiiea. Using to, the pounds of gas per hour, determined above:'-. Ideal capacity .(Btuh).-- toQs > Ideal.power input (Btuh) = ioQw , -,,i . > Actual Compressor Performance ,'V;; ',;There are many deviations' from the ideal cycle in'fFreLj fiigeration compressor. These deviations are in, the fprmojf,. Inaswa which are charged to the compressor and tend to reduce; the capacity and raise the power input from those determined) for an ideal compressor. The more important 1osses-are'con-1 sidered here*, . ;' ( t ` ' .'.J, v --l.; Pressure;,drop within-the'compressor, due to the following; restrictions:..-- i-.j<. t:..-. *'i .d cor.q< ^*><- o. Suction and discharge shut-off valves. 633