In a conventional shell-and-tube heat exchanger, fluid contacts with tubes flowing up and down in a shell, therefore there is a defect in the heat transfer with tubes due to the stagnation portions. Fins are attached to the tubes in order to increase heat transfer efficiency, but there exists a limit. Therefore, it is necessary to improve heat exchanger performance by changing the fluid flow in the shell. In this study, a highly efficient shell-and-tube heat exchanger with spiral baffie plates is simulated three-dimensionally using a commercial thermal-fluid analysis code, CFX4.2. In this type of heat exchanger, fluid contacts with tubes flowing rotationally in the shell. It could improve heat exchanger performance considerably because stagnation portions in the shell could be removed. It is proved that the shell-and-tube heat exchanger with spiral baffie plates is superior to the conventional heat exchanger in terms of heat transfer.
The thermal response of electronic assemblies during forced convection-infrared reflow soldering is studied numerically. Soldering for attaching electronic components to printed circuit boards is performed in a process oven that is equipped with porous panel heaters, through which air is injected in order to dampen temperature fluctuations in the oven. Forced convection-infrared reflow soldering process with air injection is simulated using a twodimensional numerical model. The multimode heat transfer within the reflow oven as well as within the electronic assembly is simulated. Parametric study is also performed to study the effects of various conditions such as conveyor speed, air injection velocity, and electronic assembly emissivity on the thermal response of electronic assemblies. The results of this study can be used in the process oven design and selecting the oven operating conditions to ensure proper solder melting and solidification.
Reflow soldering with nitrogen injection is simulated. Soldering is performed in a process oven that is equipped with porous panel heaters through which air or nitrogen is introduced to the reflow environment. The injected gas is introduced selectively through top or bottom infrared heaters in order to dampen temperature fluctuations which can be established by thermal buoyancy forces in the oven gas. The heat transfer processes are simulated using an existing, general numerical model that accounts for multimode effects, and is capable of predicting large and small scale thermal and species concentration phenomena. With selective injection, it is shown that high frequency convective heating and/or cooling of the card assembly can be eliminated, and oxygen concentrations in the reflow section can be controlled to low levels.
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