• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.288-301
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• 2002

A vacuum freeze drying experiment of skim milk solution in a cylindrical container is conducted to investigate the multi-dimensional drying characteristics of the process during the primary drying stage. Temperature histories at several positions are measured under the same process condition that is carefully controlled. Then the measured temperature histories at different positions are combined to produce instantaneous temperature distribution fields inside the cylindrical container. Along with the temperature measurement, the mass reduction history of the skim milk solution is also measured. From the measured temperature distribution curved configurations of sublimation interfaces and 2-dimensional heat transfer is inferred. The freeze drying under the present experimental setup is simulated with a calculation program that is based on a finite volume method with a moving grid system. Good agreements between the numerical and experimental results are observed. The present experimental results and the numerical approaches can be useful information in developing the analysis tools for practical vacuum freeze drying processes.

• International Journal of Aeronautical and Space Sciences
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• v.3 no.1
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• pp.74-85
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• 2002

The numerical experiment has been conducted to investigate the unsteady shock wave reflecting phenomena. The cell-vertex finite-volume, Roe's upwind flux difference splitting method with unstructured grid is implemented to solve unsteady Euler equations. The $4^{th}$-order Runge-Kutta method is applied for time integration. A linear reconstruction of the flux vector using the least-square method is applied to obtain the $2^{nd}$-order accuracy for the spatial derivatives. For a better resolution of the shock wave and slipline, the dynamic grid adaptation technique is adopted. The new concept of grid adaptation technique, which is much simpler than that of conventional techniques, is introduced for the current study. Three error indicators (divergence and curl of velocity, and gradient of density) are used for the grid adaptation procedure. Considering the quality of the solution and the numerical efficiency, the grid adaptation procedure was updated up to $2^{nd}$ level at every 20 time steps. For the convenience of comparison with other experimental and analytical results, the case of interaction between the straight incoming shock wave and a sharp wedge is simulated for various flow conditions. The numerical results show good agreement with other experimental and analytical results, in the shock wave reflecting structure, slipline, and the trajectory of the triple points. Some critical cases show disagreement with the analytical results, but these cases also have been proven to show hysteresis phenomena.