Conclusion for modeling study - SUMMARY AND CONCLUSIONS

CHAPTER 5 SUMMARY AND CONCLUSIONS

5.2 Conclusion for modeling study

On the modeling side, a single tube model is first developed using a thermodynamic approach to take account of the thermodynamic and transport properties of refrigerant-oil mixture and their impact on boiling heat transfer and pressure drop characteristics. Then a two tube model which is assembled by two single tube model is used to demonstrate how oil affects the flow resistance of each tube, and thus, affect distribution. After that, a heat exchanger model only considering lubricant effect among parallel microchannel tubes is developed and it have been shown that 1) high viscosity is detrimental for refrigerant distribution; 2) as OCR increases, distribution becomes worse but at very high OCR, distribution becomes better.

In order to improve the model by taking account of lubricant effects in the inlet header, attempts have been made to calculate refrigerant distribution inside of microchannel tubes reversely from the infrared image of the heat exchangers. As a result, a non-intrusive and low cost distribution quantification method has been developed correlating the liquid refrigerant distribution with evaporator air inlet temperature (measured by thermocouple) and evaporator wall temperature (measured by infrared camera). This method has been validated against wide range of experimental datas and it can be applied for different types of heat exchangers and various heat exchange designs.

The newly proposed distribution quantification method can serve the same role as a quality distribution function in a mircochannel heat exchanger model (If used as a distribution function, it cannot perform prediction because it comes from the infrared image taken in the experiment.

So this method is mainly used as a quantification tool for refrigerant distribution), by this means the lubricant effect in the inlet header is taken into account. Combining the distribution function reversely calculated from the infrared image with the parallel tubes model introduced earlier, a complete heat exchanger model is formed fully incorporating lubricant effects. This model is validated against the experimental data (shown in appendix) and better prediction of performance has been confirmed over pure refrigerant models especially at high OCR’s.

APPENDIX

Experimental results

Table A-1 Experimental results of R134a and PAG46 pair in HX1

OCR Qe Qair Qref Wc _isen ^COP^ave ^COP^air^COP^ref ^m^total ^xⁱⁿ

Table A-2 Experimental results of R134a and PAG46 pair in HX2

OCR Qe Qair Qref Wc _isen ^COP^ave ^COP^air ^COP^ref ^m^total ^xⁱⁿ

Table A-3 Experimental results of R134a and PAG100 pair in HX2

OCR Qe Qair Qref Wc _isen ^COP^ave ^COP^air ^COP^ref ^m^total ^xⁱⁿ

Table A-4 Experimental results of R134a and PAG150 pair in HX2

OCR Qe Qair Qref Wc _isen ^COP^ave ^COP^air^COP^ref ^m^total ^xⁱⁿ 0.1% 2.271 2.300 2.241 1.256 0.414 1.807 1.830 1.784 14.28 0.253 0.5% 2.324 2.352 2.295 1.218 0.460 1.908 1.931 1.885 14.83 0.252 2.8% 2.346 2.357 2.335 1.109 0.574 2.116 2.126 2.106 15.83 0.244 6.2% 2.183 2.168 2.197 1.092 0.582 1.999 1.986 2.012 16.09 0.246 7.8% 2.180 2.167 2.194 1.081 0.592 2.017 2.005 2.030 16.27 0.245

REFERENCES

Ahmad, M., Berthoud, G. and Mercier, P., 2009. General characteristics of two-phase ﬂow distribution in a compact heat exchanger. International Journal of Heat and Mass Transfer 52:

442–450.

Bandarra-Filho, E.P., Chen, L., Thome, J.R., 2009. Flow boiling characteristics and ﬂow pattern visualization of refrigerant/lubricant oil mixtures. International Journal of Refrigeration 32, 185–

202.

Baustian, J.J., Pate, M.B. and Bergles, A.E., 1986. Properties of oil refrigerant liquid mixtures with applications to oil concentration measurement: part 1- thermophysical and transport properties. ASHRAE Transaction 92 (1), 55–73.

Bielskus, A.V. and Hrnjak, P. S., 2011.Two phase flow distribution in parallel flow heat exchangers – experimentally verified model. Technical Report TR-286, Air Conditioning and Refrigeration Center, University of Illinois, Urbana-Champaign, IL.

Bowers, C.D., Hrnjak, P.S., 2010. Effects of oil and saturation temperature on developing two phase flow of R134a in an air-conditioning system. ASHRAE Transaction 116(2): 290-299.

Bowers, C.D., Hrnjak, P.S., 2010. Quantification of refrigerant distribution and effectiveness in microchannel heat exchangers using infrared thermography. International Refrigeration and Air Conditioning Conference, Paper 1016.

Burr, J.D., Newell, T.A., Hrnjak, P.S., 2005. Experimental investigation of viscous two-phase flow in microchannels. Technical Report TR-252, Air Conditioning and Refrigeration Center, University of Illinois, Urbana-Champaign, IL.

Chen, J.C., 1966. Correlation for boiling heat transfer to saturated fluids in convective flow.

Industrial & Engineering Chemistry Process Design and Development 5(3): 322-339.

Conde MR., 1996. Estimation of thermophysical properties of lubricating oils and their solutions with refrigerants: an appraisal of existing methods. Applied Thermal Engineering 16(1):51–61.

Dang, C., Iino, K., Fukuoka, K., Hihara, E., 2007. Effect of lubricating oil on cooling heat transfer of supercritical carbon dioxide. International Journal of Refrigeration 30(4): 724–731.

DeAngelis, J.M. and Hrnjak, P.S. 2005. Experimental study of system performance improvements in transcritical R744 systems with applications to bottle coolers. Contract Report CR-57, Air Conditioning and Refrigeration Center, University of Illinois, Urbana-Champaign, IL.

Dschida, M. and Hrnjak, P.S., 2008. Evaluation of microchannel heat exchangers for a residential mini-split type air-conditioning/heat pump system. Contract Report CR-67, Air Conditioning and Refrigeration Center, University of Illinois, Urbana-Champaign, IL.

Field, B.S. and Hrnjak, P.S., 2007. Two-phase pressure drop and flow regime of refrigerants and refrigerant-oil mixtures in small channel. Technical Report TR-261, Air Conditioning and Refrigeration Center, University of Illinois, Urbana-Champaign, IL.

Filippov, L.P., 1955. Vest. Mosk. Univ., Serv. Fiz. Mat. Estestv. Nauk 8, 67–69.

Jensen, M.K. and Jackman, D.L., 1984. Prediction of nucleate pool boiling heat transfer coefficients of refrigerant-oil mixtures. Journal of Heat Transfer 106: 184-190.

Jin, D., 2006. Investigation on refrigerant distribution in evaporator manifolds. Doctoral Dissertation. University of Maryland, College Park, MD.

Kim, N.H., Kim, D.Y. and Byun, H.W., 2011. Effect of inlet configuration on the refrigerant distribution in a parallel flow minichannel heat exchanger. International Journal of Refrigeration 34: 1209–1221.

Kuang, G., Ohadi, M.M., Zhao, Y., 2003. Experimental study of miscible and immiscible oil effects on heat transfer coefﬁcients and pressure drop in microchannel gas cooling of supercritical CO2, In Proceedings of the HT 2003, ASME Summer Heat Transfer Conference, June 21–23, 2003, Las Vegas, Nevada, USA, pp. 671–675.

Lee, J. K., Lee, S. Y., 2004. Distribution of two-phase annular flow at header-channel junctions.

Experimental Thermal Fluid Science 28: 217-222.

Lee, J.K., 2009. Two-phase flow behavior inside a header connected to multiple parallel channels. Experimental Thermal Fluid Science 33: 195-202.

Li, H.Z., and Hrnjak, P.S., 2013. Effect of lubricant on two-phase refrigerant distribution in microchannel evaporator. SAE International Journal of Materials and Manufacturing 6(3): 231-239.

Liley, P.E. and Gambill, W.R., 1973. Physical and chemical data. Chemical Engineering Handbook. 5th edition. New York: McGraw-Hill, 226-250.

Litch, A. D. and Hrnjak, P. S., 1999. Condensation of ammonia in microchannel heat exchangers.

Contract Report CR-22, Air Conditioning and Refrigeration Center, University of Illinois, Urbana-Champaign, IL.

Lottin, O., Guillemet, P. and Lebreton, J., 2003. Effects of synthetic oil in a compression refrigeration system using R410A. Part I: modeling of the whole system and analysis of its response to an increase in the amount of circulating oil. International Journal of Refrigeration 26:

772-782.

Lottin, O., Guillemet, P. and Lebreton, J., 2003. Effects of synthetic oil in a compression refrigeration system using R410A. Part II: quality of heat transfer and pressure losses within the heat exchangers. International Journal of Refrigeration 26:783-794.

McMullan, J.T. and Murphy, N.E., 1998. The effect of oil on the performance of heat pumps and refrigerators-II. Experimental results. Heat Recovery Systems & CHP 8(2):95-124.

McMullan, J.T., Hewitt, N.J., Masson, A.J. and Murphy, N.E., 1992. The Influence of oil viscosity and refrigerant quality on evaporator performance. International Journal of Energy Research 16:567-581.

Mermond, Y., Feidt, M., Marvillet, C., 1999. Thermodynamic and physical properties of mixtures of refrigerants and oils. International Journal of Refrigeration 22: 569–79.

Milosevic, A. and Hrnjak, P.S., 2010. Effect of using flash gas bypass on evaporator effectiveness and system efficiency when operating with low pressure refrigerants. Technical Report TR-283, Air Conditioning and Refrigeration Center, University of Illinois, Urbana-Champaign, IL.

Mishima, K. and Hibiki, T., 1996. Some characteristics of air-water two-phase flow in small diameter vertical tubes. International Journal of Multiphase Flow 22:703-712.

Moffat, R.J., 1988. Describing the uncertainties in experimental results. Experimental Thermal Fluid Science 1 (1):3-17.

Nebuloni, C., Thome, J.R., 2013. Numerical modeling of the effects of oil on annular laminar film condensation in minichannels. International Journal of Refrigeration 36(5): 1545–1556.

Pottker, G., and Hrnjak, P.S., 2012. Designated vs non-designated areas for condenser subcooling. International Refrigeration and Air Conditioning Conference, Paper 1332.

Qi, Z.G., Chen, J.P., and Radermacher, R., 2009. Investigating performance of new mini-channel evaporators. Applied Thermal Engineering 29(17-18): 3561-4567.

Seeton, C.J. and Hrnjak, P.S., 2009. CO₂-lubricant two-phase flow patterns in small horizontal wetted wall channels: the effects of refrigerant/lubricant thermophysical properties. Technical Report TR-269, Air Conditioning and Refrigeration Center, University of Illinois, Urbana-Champaign, IL.

Shen, B. and Groll, E.A., 2005a. Critical review of the influence of lubricants on the heat transfer and pressure drop of refrigerants, part I: lubricant influence on pool and flow boiling. HVAC&R Res. 11 (3): 341–360.

Shen, B. and Groll, E.A., 2005b. Critical review of the inﬂuence of lubricants on the heat transfer and pressure drop of refrigerants, part II: lubricant inﬂuence on condensation and pressure drop.

HVAC&R Res. 11 (4): 511–526.

Shi, J.Y., Qu, X.H., Qi, Z.G., and Chen, J.P., 2011. Investigating performance of microchannel evaporators with different manifold structures. International Journal of Refrigeration 34(1): 292-302.

Song, S., Bullard, C.W., Hrnjak, P.S., 2002. Frost deposition and refrigerant distribution in microchannel heat exchangers. ASHRAE Transaction 108 (2): 944–953.

Thome, J. R., 1999. Flow boiling of refrigerant-oil mixtures in plain and enhanced tubes. Heat Transfer Enhancement of Heat Exchanger 355, 487-513.

Thome, J.R., 1995a. Comprehensive Thermodynamic approach to modeling refrigerant–

lubricating oil mixtures. HVAC&R Res., 110–126.

Thome, J.R. 1995b. Flow boiling of refrigerant-oil mixtures: a current review. In Proceeding of the Convective Flow Boiling Conference, Banff, Canada, Paper VI-6: 285-290.

Tuo, H.F., Bielskus, A.V. and Hrnjak, P.S., 2011. Effect of flash gas bypass on the performance of R134a mobile air-conditioning system with microchannel evaporator. SAE International Journal of Materials and Manufacturing 4(1): 231-239.

Tuo, H.F., Bielskus, A.V. and Hrnjak, P.S., 2012a. Experimentally Validated Model of Refrigerant Distribution in a Parallel Microchannel Evaporator. SAE International Journal of Materials and Manufacturing 5(2): 365-374.

Tuo, H.F., and Hrnjak, P.S., 2012b. Flash gas bypass in mobile air conditioning system with R134a. International Journal of Refrigeration 35(7): 1869-1877.

Tuo, H.F., and Hrnjak, P.S., 2013a. Effect of the header pressure drop induced flow maldistribution on the microchannel evaporator performance. International Journal of Refrigeration, DOI: 10.1016/j.ijrefrig.2013.06.002.

Tuo, H.F., and Hrnjak, P.S., 2013b. New approach to improve performance by venting periodic reverse vapor flow in microchannel evaporator. International Journal of Refrigeration, DOI:

10.1016/j.ijrefrig.2013.05.020.

Vist, S., Pettersen, J., 2004. Two-phase flow distribution in compact heat exchanger manifolds.

Experimental Thermal Fluid Science 28: 209-215.

Youbi-Idrissi, M. and Bonjour, J., 2008. The effect of oil in refrigeration: Current research issues and critical review of thermodynamic aspects. International Journal of Refrigeration 31:165–179.

Youbi-Idrissi, M., Bonjour, J., Marvillet, C. and Meunier. F., 2003. Impact of refrigerant-oil solubility on an evaporator performances working with R-407C. International Journal of Refrigeration 26:284-292.

Youbi-Idrissi, M., Bonjour, J., Terrier, M.-F., Marvillet, C. and Meunier. F., 2004. Oil presence in an evaporator: experimental validation of a refrigerant/oil mixture enthalpy calculation model.

International Journal of Refrigeration 27:215-224.

Yun, R., Hwang, Y. and Radermacher, R., 2007. Convective gas cooling heat transfer and pressure drop characteristics of supercritical CO2/oil mixture in a minichannel tube. International Journal of Heat and Mass Transfer 50: 4796–4804.

Zou, Y. and Hrnjak, P. S., 2013. Refrigerant distribution in the vertical header of the microchannel heat exchanger-measurement and visualization of R410A flow. International Journal of Refrigeration, DOI:10.1016/j.ijrefrig.2013.04.021.

Zou, Y. and Hrnjak, P.S., 2013. Effect of oil on R134a distribution in the microchannel heat exchanger with vertical header, Int. J. Refrig., DOI:10.1016/j.ijrefrig.2013.09.037

Zou, Y., Hrnjak, P. S., 2013. Experiment and visualization on R134a upward flow in the vertical header of microchannel heat exchanger and its effect on distribution. International Journal of Heat and Mass Transfer 62: 124-134.

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