Heat transfer coefficients during evaporation in a horizontal smooth tube for R-22 and R-407C (R-32/125/134a, 23/25/52 wt.) have been measured using thermochromic liquid crystal. Focus has been put on the circumferential variation of heat transfer coefficients at several cross-sections of the test tube with inner diameter of 11.3 mm for several vapor qualities of refrigerant. The inner wall temperatures were calculated by one dimensional heat conduction equation from the measured outer wall temperatures, which were obtained using an image processing technique with thermochromic liquid crystal (TLC). The relation between measured temperature and color information (Red-Green-Blue values) of thermochromic liquid crystal was calibrated by a neural network method. Results show that circumferential variation of heat transfer coefficients for R-22 is quite large with the highest heat transfer coefficient at the top of the tube. For zeotropic mixture of R-407C, similar trend has been observed with less difference between the heat transfer coefficients at the top and bottom than that of R-22.
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