Optimal Sizing of Two-Phase Heat Exchangers

Correlations for two-phase heat transfer and pressure drop developed by ACRC Project 01 are presented and discussed. In particular, these correlations are used to assess the impact of the tube diameter on the required length of heat exchanger to perfonn phase-change processes. The correlations are integrated into a spreadsheet for evaporation and condensation that predicts the required length of two-phase heat exchanger when supplied with the operating conditions. The spreadsheets and macro sheets which provide needed thennodynamic and transport properties are included with the report. The spreadsheets were used to study the impact of tube diameter on the required length of condenser and evaporator tube to transfer a flXed amount of heat as mass flow rate and air side resistance were held constant. The results revealed that over a wide range of diameters, the required length was relatively insensitive to the tube diameter. In this region, the required length increased slightly as the diameter was decreased. As the diameter became sufficiently small, pressure drop destroyed much of the driving temperature difference. At diameters below this, the required length of heat exchanger increased greatly with further decreases in diameter.