Effect of environmental pressure on heat and mass transfer characteristics for fin-and-tube heat exchangers under non-unit Lewis factor

The heat and mass transfer characteristics for fin-and-tube heat exchangers with low environmental pressures have been experimentally investigated. The variation trends of the jh factor, jm factor and Lewis factor were examined in this study when environmental pressure decreases from 101.3 to 40 kPa. The errors caused by non-unit Lewis factor when calculating the total heat transfer rate using the logarithmic mean enthalpy difference (LMED) method were discussed. It was found that the inlet humidity ratio for the incoming air is inversely proportional to environmental pressure under the experimental conditions. Both the heat and mass transfer performances decrease when the environmental pressure is reduced. However, the jm factor shows a transient rise when Re < 1100. Test results show that the heat and mass transfer analogy is roughly applicable, and the Lewis factor is in the range of 0.73-0.96. The maximal relative deviation of the total heat transfer rate calculated by the LMED method is about 18.7%. However, a modified LMED (m-LMED) method can describe the total heat transfer rate within 3.8%.