| Summary: | 碩士 === 國立交通大學 === 機械工程系所 === 101 === Abstract
In the present study, a numerical simulation program is developed to calculate the pressure drop, velocity distribution and temperature of both water and supercritical carbon dioxide in a plate heat exchanger. The critical state of carbon dioxide is at 7.8 MPa and 330 K, respectively. Therefore the heat exchanger is operated above critical point as a gas cooler. Since the physical properties of carbon dioxide vary drastically near the critical point, therefore the conventional numerical simulation methods for plate heat exchanger are not available. The objective of this study is to develop a carbon dioxide based program which includes the pressure drop, velocity distribution, temperature and physical properties such as density, viscosity and heat capacity. By using appropriate correlations of the Nusselt number and the friction coefficient, the flow and the temperature distribution can be correctly calculated. The effect of the pressure drop, velocity distribution and temperature was calculated with different mass flow rate, inlet pressure, inlet velocity, inlet temperature, number of channels and different plates. In a water to carbon-dioxide plate heat changer, the simulation results show that the flow distribution of water did not change significantly with temperature. Due to the physical properties of carbon dioxide vary drastically at supercritical state, the density and viscosity of the impact cannot be ignored. For an example, when temperature variation between the plates
change rapidly, it will cause considerable flow distribution effect ,and may change the flow velocity distribution pattern change from decreasing type into increasing type. In addition, the heat transfer effect will be significantly improved when the carbon dioxide near the critical temperature, when designing of heat transfer, it could be taken into account of the characteristics.
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