Search

Abstract: This paper examines the steady natural convection in a partially opened enclosure filled with porous media using the Brinkman–Forchheimer model. Whilst the part of the left vertical wall of the cavity is heated, the other walls are adiabatic or thermally insulated Based upon numerical predictions, the effects of pertinent parameters such as Grashof number, Darcy number, porosity, length of the heated wall and the location center of the opened cavity are examined. It is found that as the Grashof number increases, due to strengthening buoyancy driven flows, the local Nusselt number from partially heated vertical wall, at a given position on this wall increases. This, in turn, increases the temperature of the heated wall. The results of this study can be used in the design of an effective cooling system for electronic components to help ensure effective and safe operational conditions. [Copyright &y& Elsevier]

Abstract: This paper conveys a numerical simulation of an active enhancement device for natural convection in the interfin spaces of a fin array. A baseline solution for the non-enhanced situation revealed that the confinement created by the walls of adjacent fins and the base surface gave rise to a drastic reduction of the heat transfer coefficient values compared with those for the standard vertical plate. This outcome demonstrated the necessity for enhancement. The enhancement device investigated here communicated with the interfin space via an opening in the base surface. Enhancement was achieved by alternately introducing and extracting air into and from the space. The frequency of the introduction/extraction cycle was varied over values of 0, 10, 50, and 100Hz. For each of these cases, spatially local, cycle-averaged heat transfer coefficients were determined on the bounding surfaces of the interfin space and on the outboard surface of a fin that faced a large ambient space. Results were also obtained for the cycle- and spatially averaged coefficients. Even at a low oscillation frequency of 10Hz, the interfin heat transfer coefficients were significantly enhanced but not sufficiently to overcome the confinement effect. At 100Hz, the enhancement gave rise to coefficient values that are about 64 times greater than the unenhanced values. [Copyright &y& Elsevier]

Abstract: In the present study, a 3D numerical simulation of a whole heat exchanger with middle-overlapped helical baffles is carried out by using commercial codes of GAMBIT 2.3 and FLEUNT 6.3. At first, the computational model and numerical method of the whole heat exchanger with middle-overlapped helical baffles is presented in detail, and parallel computation mode is adopted for the simulation of a whole heat exchanger with six cycles of the middle-overlapped helical baffles of 40° helical angle on a grid system of 13.5-million cells; second, the validation of the computational model is performed by comparing the total pressure drop and average Nusselt number of the whole heat exchanger with experimental data. Reasonably good agreement is obtained, and the reasons causing to the discrepancy are analyzed. The shell-side fluid pressure and temperature fields of the whole area are then presented. Finally the cycle average Nusselt number of different cycle in the heat exchanger are compared and it is found that within the accuracy allowed in engineering computation, periodic model for one cycle can be used to investigate the heat transfer and pressure drop characteristics for different heat exchanger to save computational source. The companion paper will provide details of simulation results using the periodic model for different helical angles and different structures of helical baffles. [Copyright &y& Elsevier]