| Summary: | 碩士 === 國立清華大學 === 工程與系統科學系 === 97 === Supercritical Water Reactor (SCWR) is one of the Gen IV systems. SCWR has the advantages of high thermal efficiency (45%) and highly simplified plant systems. Due to the large variations of thermal properties of supercritical water when the temperature is close to the critical temperature or pseudo critical temperature , there are two things of concern for the design of supercritical water reactor. These are the heat transfer phenomenon of supercritical water and the prediction of heat transfer coefficient. SCWR operate at very high pressure (25 MPa) , therefore ; it is very expensive to study heat transfer phenomenon of supercritical water experimentally. Commercial Computational Fluid Dynamics (CFD) software FLUENT is used to study the heat transfer of supercritical water.
Usually, Dittus-Boelter correlation is used to predict heat transfer coefficient of forced convection. If the heat transfer coefficient as predicted by the Dittus-Boelter correlation is higher than the experimental data, the situation is termed heat transfer deterioration. If the heat transfer coefficient as predicted by the Dittus-Boelter correlation is lower than the experimental data, the situation is termed heat transfer enhancement. The results of simulation demonstrated that heat transfer enhancement can be accurately predicted using the RNG turbulence model. Maximum heat transfer coefficient is occurred before the bulk temperature reaches the pseudo-critical temperature because the wall temperature reaches the pseudo-critical temperature earlier than the bulk coolant temperature does. The results of the analyses show that the phenomena of heat transfer deterioration can be simulated. Nevertheless, the locations of the heat transfer deterioration as predicted by the FLUENT code are deviated from the experimental data of Shitsman’s. It is also found that the phenomenon of heat transfer deterioration can be avoided by increasing the inlet temperature or operation pressure.
The results of simulation demonstrated that the buoyancy has no effect on heat transfer enhancement. Nevertheless, it is the main reason of the heat transfer deterioration.
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