Isobutane as a Refrigerator Freezer Refrigerant

Transcription

1 Purdue Uniersity Purdue e-pubs nternational Refrigeration and Air Conditioning Conference School of Mechanical Engineering 1994 sobutane as a Refrigerator Freezer Refrigerant D. R. Riffe Americold Follow this and additional works at: Riffe, D. R., "sobutane as a Refrigerator Freezer Refrigerant" (1994). nternational Refrigeration and Air Conditioning Conference. Paper This document has been made aailable through Purdue e-pubs, a serice of the Purdue Uniersity Libraries. Please contact epubs@purdue.edu for additional information. Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at HerrickEentsorderlit.html

2 SOBUTANE AS A REFRGERATOR FREEZER REFRGERANT Delmar Ray Riffe Americold Abstract sobutane is considered as a possible candidate for the refrigerant to be used in the consumer refrigerator freezer. Results of an analytical analysis that predicts the perfonnance of isobutane in the consumer refrigerator freezer and results of calorimetric measurements of compressors operating with isobutane are presented. Both the analytical analysis and the experiment suggest that the use of isobutane as a refrigerant, compared to the presently used dichlorodifluoromethane, R-12, (or tetrafluorothene, R- 134a) will result in a reduction in power. ntroduction The refrigerant, dichlorodifluoromethane, R-12 or CFC 12, that has been used in the consumer refrigerator freezer for the past half a century almost certainly will not be used much longer. Because of its alleged contribution to both atmospheric ozone depletion and global warming it is being phased out. Tetrafluoroethane, R-134a or HFC 134a, is the present leading candidate to replace R-12 but neertheless there is some drawbacks to the use ofr-134a. t is generally assumed, with some dissension, that R-134a does not work well with the presently used low cost mineral oil that is used with R-12. Soine ester oil is likely to be used with R- 134a but the use ofthis ester oil with R-134a does lead to some potential chemical incompatibility problems and some solubility problems that do not exist with R-12 and mineral oil and possibly would not exist or would be less seere with isobutane and mineral oil. 245

3 lsobutane As a Refrigerant Seeral different hydrocarbons hae been proposed for use as refrigerants for the consumer refrigerator freezer. Results of an ealuation of one of these, isobutane (R-6a), is presented herein. Some desirable features and the only known significant undesirable feature of isobutane is listed in Table 1. Table 1 Features of!so butane As a Refrigerant Desirable Features Undesirable Features High Efficiency Nontoxic Miscible and Compatible with Mineral Oil Relatiely nert Chemically Almost no Global Warming Potential Flammable Zero Ozone Depletion Potential Low Cost The fact that isobutane is flammable is undesirable eerywhere but this undesirable feature is weighted differently at different places, and probably differently at different times. t is presently used in many refrigerator freezers in Germany. Other parts of Europe and Asia presently hae some reserations about using isobutane. The United States presently has een greater reserations. The currently used R-12 is not flammable. The mineral oil that is used with R-12 is flammable but not so easily ignited. Howeer if it is ignited the total amount ofheat that would be liberated by burning this mineral oil normally used in an R-12 compressor is much greater than the heat that would be liberated by burning the isobutane that would be used in a isobutane refrigerator freezer. Mineral oil has been used for a long time and is generally acceptable. sobutane is used much as a propellant in the home and this is acceptable also but a small amount of the same isobutane used in the sealed system in a refrigerator freezer may not be acceptable. 246

4 Analytical Analysis No recommendations either pro or con is made herein for the use ofisobutane as a refrigerant but some results of a thermodynamic ealuation of isobutane as a refrigerant is presented. Results of an analytical analysis that predicts the performance of the refrigerant and results of calorimeter testing of compressors operating with isobutane is presented. Tables 2 and 3 presents some results of an analytical analysis that predicts the performance of R-12, R-134a and R-6a. Figures 1, 2, 3 and 4 presents graphically some ofthese results. For purpose of comparison the capacity of each compressor is assumed to be 75 Btuhr at the AR rating point and the required displaced olume is determined accordingly. Some things are significant. First, based on this analytical analysis it is obsered that isobutane will result in a reduction in power consumption of about 6% compared to R-12 (or R-134a). For purpose of this comparison the isentropic compression efficiency is assumed to be 59% for each refrigerant but the relatie comparison is alid regardless of what the isentropic compression efficiency is proided it is the same for each refrigerant. The second significant obseration is that for equal capacities the cylinder olume of a R- 6a compressor is about 2 times as great as it is for an R-12 compressor. f the bore to stroke ratio is equal in each case (assumed to be to 1 for purpose of calculating bearing loads) then the piston diameter for a R-6a compressor is about 126% that of an R-12 compressor piston. For equal pressure differentials this would result in higher bearing loads and higher bearing friction power loss in the R-6a compressor but the pressure differential is not equal. The pressure differential is lower in the case of the R-6a compressor. The net effect is that the bearing loads and bearing friction power loss is slightly less in the R-6a compressor than it is in the R-12 compressor. The larger piston in the R-6a compressor results in more space for better placement and sizing of the ales. Eerything considered the larger piston in the R-6a compressor is an asset not a liability. Experimental Ealuation Calorimeter testing of seeral R-6a compressors tends to confirm, within the limits of experimental error, that the theoretical prediction of a 6% efficiency improement is an actual reality. Actual test results indicate only about 2% improement but it is belieed that with a little more compressor optimization the 6% will be realized. Table 4 presents results of the actual calorimeter measurements of the compressor performance. A precise one to one comparison is not possible because for equal capacity compressors the cylinder displacement olume is about 2 times greater in a R-6a compressor than it is in an R-12 compressor. The R-6a compressors are compared to a similar capacity but different displaced olume, R-12 compressors. 247

5 Refrigerant TEap R-12-2f -1f R-134a -2 F -1 F - R6a -2f -loof Table 2 Calculated Performance TCond Power Watts 9 F f , F F f F F F Capacity EER Btulhr Btu!W*Hr liquid temp= 9 F; return gas temp= 9 F 248

6 Table 3 Calculated Performance Refrig Ps Pn psi a R R-134a R6a Note 1 Rc psta Ref Work Btullb Btullb Note2 COP EER BtuW-hr Note 3 Note4 Refrig Flow Flow lblhr ftjhr R R-134a R6a Note 5 Cyl Vol Bore Stroke in.j m. in Area in.l Piston max force lb Note 1: Rating Point: -1 F eap; 13 F cond; 9F liquid; 9F return gas Note 2: Assumes 59% isentopic compressor efficiency Note 3: Assumes 75 Btu!hr at rating point; displaced olume determined accordingly Note 4: Assumes 7% olumetric efficiency Note 5: Assumes bore to stroke ratio of

7 TABLE4 CALORMETER TEST RESULTS REFRGERANT: R-6a (sobutane) Lab Number Capacity Power EER Y Y Y Y Y Y REFRGERANT R-12 * Capacity Power EER *Aerage of many compressors Aerage Bore: Stroke: Displacement: 1.75 inch.75 inch.64 cu.in. Bore: Stoke: Displacement:.8125 inch.62 inch.312 cu.in. Conclusion t can be concluded that from a thermodynamic performance point of iew isobutane is superior to R-12 (or any other commonly proposed refrigerant) for use in the consumer refrigerator freezer compressor. t is belieed that isobutane will result in a 6% power saings compared to the presently used R-12 or the leading candidate R-134a. 25

8 R12... N... Xm c... ::::J... :JeD 4-J OJ >- 4-J rl u... ro.. ro u D EER l == CAPA TY. 15, F Con WA rs 9 F Cond cu. in disp. 9 F Return Bas 9 F Liquid to m mm ::.1:1- H N:J o"c oc rt' QJ -rr orr () Eaporating Temperature Fig r

9 R134a... ru F Cond EER rn mrn : Xm t..,:j :r:... :JCD 4-.J co ;:>. rl u" ro a. ro u.. ' CAPA TY & 3 F Cond WA ""TS J=o. H ru::j o"'o oc c+ OJ...c+ Or+ ocn.37 cu. in diap. 9 F Return Gas 9 F LiQUid Eaporating Temperature Fig

10 R6a -1\J '" Xm ' :J :c... :;:,m ""-' en >...,_, rl u... co a. 1' u EER ,... L CAPA bity. 15, F Con. WA TS T --,- - 9 F Cond cu. in d1ep. so F Return Bes 9 F Liquid Eaporating Temperature Fig lo m mrn A JJ w oo orr -, H ru o"'o oc rt :E Q)... rt on ocn

11 ... 9 F Return Gas 9 F Liquid & 13 F Cond Disp. from 75 Btuhr at AR rating pt. N r '" EER xm '- :::J :r: ' m CD > +' X u ro o u, T r on WA TS, gm 1-1 ru:::j oc X Q) Eaporating Temperature mr cu in R13 a-.37 cu in ARSOOa-.67 cu in Fig