Theoretical Study of Various Fluids on the Transient Performance of a Two-Phase Closed Thermosyphon (TPCT)

Passive cooling heat exchangers are important for a nuclear reactor. Due to many advantages of passive cooling mechanism it may be used in nuclear reactors by employing two-phase closed thermosyphon (TPCT) during shutdown regime. Many thermosyphons can be penetrated in cooling system so that, the condenser section is exposed to air and the evaporator (evaporator) section immersed into water pool. Our study is proposed to predict the thermal behaviour of TPCT with different fluids, Water, Toluene, Acetone and Heptane. The fluid which realizes better heat transfer characteristics prediction is our study objective. The mathematical model is developed to predict thermal behaviour of these fluids to classify the most appropriate fluid. Water, acetone, heptane, and toluene are selected as working fluids in this study. Engineering Equation solver is used to formulate our model with finite difference numerical method. The results show that, Acetone has the highest heat transfer coefficient and the lowest thermal resistance in evaporator section. Water has the highest critical heat flux and highest evaporator surface temperature. Water as well has higher heat transmission coefficient in the evaporator section after Acetone. It has also low wall temperature and highest heat transfer coefficient in condenser section. Water heat transfer coefficient is three times more than the other fluids and more output cooling capacity. For the same size of TPCT, while the Acetone is the lowest thermal resistance, but water is more preferable working fluid because it is more available with low thermal resistance as well and highest cooling capacity which enables the TPCT to have more cooling capacity Validation of the proposed theoretical model is performed and showed a good evaporator and condenser surface temperature agreement with the empirical results.