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TECHNICAL REPORTS or higher, which was shown to be comparatively small. Regarding inlet quality Xi, the larger Xi was, the more the performance deterioration was reduced. The influ- ence of the header position or the pipe insertion at the distribution section on performance, was confirmed to be limited. The factor of the findings mentioned above can be explained as follows. In Fig. 6, the horizontal axis shows the corrected gas mass velocity, calculated by dividing the mass velocity Gg of the refrigerant gas in the inlet header as expressed by equation (6) by parameter λ(3) in the Baker map, which is used as the flow regime map of the two-phase flow, while the vertical axis shows the ratio of the thermal conductance AK to AK during even distribution without maldistribution. (The value was obtained by dividing the data marked with , , +, and x by the data marked with in Fig. 5.) Gg λ=XiGhd λ (6) AK increases with increasing Gg/λ to gradually approached 1. From this, it can be assumed that the reason why even distribution is advanced with increas- ing flow rate and inlet quality, and performance dete- rioration is consequently reduced, is that the gas veloc- ity increases in the inlet header and the mixing of gas and liquid is increased in the flow. The authors clearly identified the basic characteris- tics of the refrigerant-refrigerant microchannel heat exchanger. The authors are going to expand the range of conditions for evaluating the characteristics and continue the study to improve flow distribution. References (1) F. W. Dittus, L.M.K. Boelter: Univ. Calif. Publ. Eng., 2, 433 (1930). (2) K. Kuwahara et al.: Trans. of JAR, 21(2), 121-128 (2004). (3) O.Baker:J.Oil&Gas,53,185(1954). 1.1 1 0.9 0.8 0.7 Fig. 6 Thermal conductance with varying corrected mass velocity in the header Header in horizontal position and pipe insertion δ=2 [mm] Header in horizontal position and δ=0 [mm] Header in vertical position and δ=2 [mm] Header in vertical position and δ=0 [mm] 0 5000 10000 15000 Corrected gas mass velocity Gg/λ [kg/m2h] Mitsubishi Electric ADVANCE December 2007 23 Thermal conductance AK (ratio against even distribution performance)PDF Image | Heat Pump with Natural Refrigerants 3041
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