Development and Validation in Thermal Design Program of Thermosyphon Heat Exchanger

With the rising energy demand, waste heat recovery applications become more important than ever. A thermosyphon heat exchanger is one of the most effective devices for recovering waste heat. Numerical methods can be applicable to design thermosyphon heat exchangers, but it takes huge computation time and cost. For these reasons, several studies tried to calculate the thermal performance of thermosyphon heat exchangers without numerical methods. However, these attempts did not consider phase-change phenomena in thermosyphon and pressure drop through heat exchangers. A design program using an empirical analysis model has been proposed to avoid a complex numerical simulation. The proposed thermal design program includes the thermal resistance model, empirical correlations of tube banks with external flow, and the ε-NTU method for heat exchangers. The overall heat transfer coefficient is obtained through the thermal resistance model to design the heat exchanger based on the ε-NTU method. Empirical correlations are used to obtain phase-change heat transfer coefficients, external convection heat transfer coefficients, and pressure drops of thermosyphon heat exchangers. A heat exchanger including 95 thermosyphons in a staggered array has been manufactured and tested in 9 different conditions to validate the thermal design program. Comparing the design program with the thermal performance test result shows an average error of 0.8% for thermal performance and a maximum error of 5.2% for pressure drop. This result shows that the thermosyphon heat exchanger design program presented in this study can be useful in the design process in its engineering applications.