Performance improvement of thermosyphon heat exchangers by using two kinds of working fluids

In this study, the concept of introducing two-fluid thermosyphons is examined. Calculations were performed for both low and high temperature ranges with parallel and counter-flow arrangements. For lower-temperature application, 125°C > T_hi > 75°C, use of ammonia in some rows and water in the rest of the thermosyphon can slightly improve the associated heat transfer performance for balanced counter-flow arrangement. However, for balanced parallel-flow arrangement in both low- and high-temperature applications, the concept of using two-fluid thermosyphons may not be feasible. The use of two-fluid thermosyphons is especially advantageous for high-temperature applications. For instance, in the range of 375°C > T_hi > 350°C, the two-fluid thermosyphons (Dowtherm A-water) shows a 15-99% increase of heat transfer performance relative to Dowtherm A alone.