Thermal and Viscous Performance in Finned Heat Pipes Heat Exchangers Using the Thermal Efficiency Method: IFHPHE versus AFHPHE

Abstract

This work compares two heat exchangers that use finned heat tubes: a crossflow finned tube heat exchanger with individual fins (IFHPHE) and an axially finned tube heat exchanger with parallel flow in the evaporator and counterflow in the condenser (AFHPHE). The IFHPHE heat exchanger was designed and experimentally implemented to operate in small air conditioning systems with air flow rates in the range of 300 to 500 m 3 /h. The AFHPHE heat exchanger is in the theoretical design phase and has the potential to be used in air conditioning systems for operating rooms of 60 m 3 , with an air flow rate of 0.20 kg/s. The method used for theoretical comparisons between heat exchangers is the thermal efficiency method, and the main quantities obtained for comparison are velocities, Nusselt numbers, thermal effectiveness, air outlet temperatures, pressure drops, and Bejan numbers in the evaporator, condenser, and heat exchanger. The working fluid used is refrigerant R404a. The saturation temperature is 17.0˚C, with a fixed number of fins for both heat exchangers, equal to 30 fins, and 49 heat pipes as standard. Comparisons demonstrate superior thermal performance and very similar viscous performance when AFHPHE is compared to IFHPHE with 30 fins. When the simulations consider 70 fins for the IFHPHE, the thermal performances are very close to those of the AFHPHE with 30 fins. However, in this last case, with 70 fins, the viscous performance is very high and should not be implemented in real-world situations.