Experimental Investigation of Heat Transfer at Downflow Condensation of Refrigerant R-21 in Assemblage of Minichannels

Presented are results of experimental investigation of heat transfer at downflow condensation of refrigerant R-21 in a vertical assemblage of minichannels in a plate-fin heat exchanger with plane fins. Selection of refrigerant was caused by the fact that its physical properties at room temperature are similar to those of cryogenic liquids at low temperatures. A pattern of vapor-liquid downflow in the heat exchanger channels was plotted using the working section with a transparent wall. For the mass velocity in the range of 30 to 50 kg/m2s and the wall subcooling below −2◦C, the dependence of the heat transfer coefficient on the mass vapor content is determined and a method is proposed to calculate the heat transfer coefficient that is in good agreement with the experimental data.