Local and average mass transfer rates from a rectangular cylinder having various width to height ratios are measured using naphthalene sublimation technique, and influence of flow characteristics on mass transfer is investigated. The experimental apparatus comprises a wind tunnel, a naphthalene casting facility and a sublimation depth measurement system. Mass transfer data are compared with those of heat transfer which are obtained using thermocouples in the constant heat flux boundary condition, and analogy between heat and mass transfer is examined. The reasons for discrepancy in both transport values are explained in detail.
When heat is released by forced convection from electronic modules in a narrow printed circuit board channel, complex flow phenomena—such as stagnation and acceleration on the front surface, separation and reattachment on the top surface, wake or cavity flow near the rear surface—affect the heat transfer characteristics. The purpose of this study is to investigate how these flow conditions influence the local heat transfer from electronic modules. Experiments are performed on a three-dimensional array of hexahedral elements as well as on a two-dimensional array of rectangular elements. Naphthalene sublimation technique is employed to measure three-dimensional local mass transfer, and the mass transfer data are converted to their counterparts of the heat transfer process using the analogy equation between heat and mass transfer. Module location and streamwise module spacing are varied, and the effect of vortex generators on heat transfer enhancement is also examined. Dramatic change of local heat transfer coefficients is found on each surface of the module, and three-dimensional modules have a little higher heat transfer value than two-dimensional modules because of bypass flow. Longitudinal vortices formed by vortex generator enhance the mixing of fluids and thereby heat transfer, and the rectangular wing type vortex generator is found to be more effective than the delta wing type vortex generator.
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