Air side performance of fin-and-tube heat exchangers with a hydrophilic layer under low-temperature frost-free conditions

In this paper, to provide a reference for the application and thermal design of fin-and-tube heat exchangers (FTHEs) under low-temperature frost-free conditions (LTFFCs) and to improve the dehumidification performance of cooling dehumidifiers in greenhouse environments of low temperature and high humidity, the air side per-formance of FTHEs with a hydrophilic layer under LTFFCs was experimentally investigated. The experimental findings were compared with the results of ordinary temperature conditions (OTCs). The critical environmental conditions for frosting FTHEs were obtained. The applicability of existing performance prediction correlations under the LTFFCs was discussed and corrected. The findings show that at the same inlet temperature difference between air and refrigerant, the LTFFCs have smaller heat transfer rates than the OTCs. Varying inlet conditions showed that in the test conditions range, the test FTHEs are at risk of frosting when the inlet air relative humidity is 95 %, inlet air temperature is 281 K, frontal velocity is 1 m/s, and inlet refrigerant temperature is as low as 270 K. The data analysis revealed that existing correlations could not accurately predict the experimental data under LTFFCs. By adding the correction coefficients for temperature and relative humidity to existing correla-tions, the corrected correlations describe the experimental data for 90.6 % and 87.5 % of the heat transfer factor and mass transfer factor, respectively, within +/- 20 %, and the deviation of all friction factors is within +/- 10 %. The mean deviations of the heat transfer factor, mass transfer factor, and friction factor are 8.2 %, 10.8 %, and 4.8 %, respectively.