| Summary: | 碩士 === 國立聯合大學 === 材料科學工程學系碩士班 === 100 === The boiling phenomena of water coolant, within copper cooling wheel in planar flow casting, have been numerical modeled in this study. Firstly, a real experiment was conducted by heating a copper tube, in which water coolant with a constant velocity flow; and, boiling phenomena were observed. Then, the commercial computational fluid dynamics (CFD) package, Flow3D ™ was used. Optimizing model setup has been verified by this real experiment.
The boiling phenomena of water coolant within D-shaped cooling channel in the permanent mold were studied. In the mold, the heating cycles of a high temperature (1573K) for 0.5 ms and a low temperature (473K) for 49.5ms, which is 30 cycles within 1.5 seconds, was designed.
The boiling of water coolant begins as the velocity of flow into the channel is under a critical velocity (or mass flow rate). In the boiling state, the values of heat transfer coefficient (i.e., heating capability to coolant) and heat flux (i.e., heat absorbed capability by coolant) are much greater than those in the un-boiling state. The degree of the subcooling temperature affects the initial time for boiling, which is time for bobble nucleate.
In the diagram of heat flux as function of heat transfer coefficient, the value of the slope represents the capability of the coolant removing the heat from the mold system. If the value is a positive one and large, the heat removed from the system is great. It implies that the coolant has great capability to remove heat. This value could be to classify the states of boiling phenomena, which are boiling nucleate, bubble flow, and plug flow states.
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