We measured the heat transfer efficiency of short heat exchangers along the vent tube of a helium cryostat, and measured the temperature profile of the helium vapor along the vent tube. The results of our measurements show that the heat exchangers are in some cases considerably more efficient than indicated by simple model calculations. With a flow rate of 4.4×10−3 g/s, a heat-sink length of 7 cm is just long enough to sink 2.3 W at about 138 K with a few Kelvins temperature drop, while a 5 cm length is more than adequate to sink 0.5 W at 25 K.
This study demonstrated a general correlation to predict the saturated flow boiling heat transfer of R410A in horizontal macro and mini-channels. The experimental data were observed in various tube diameters of 1.5, 3.0, 6.61 and 7.49 mm, mass fluxes of 100 -600 kW m -2 s -1 heat fluxes of 10 -40 kW m -2, saturation temperature of 5 -15 ºC and vapor quality from 0.2 to 1. The database was compared with numerous wellknown correlations. The proposed correlation was based on the superposition model of nucleate boiling and force convective boiling contribution. The new modified-correlation showed a good prediction against our database.
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