Heat flow visualization during mixed convection within entrapped porous triangular cavities with moving horizontal walls via heatline analysis. (May 2017)

• Record Type: Journal Article
• Authors: Roy, Monisha; Biswal, Pratibha; Roy, S.; Basak, Tanmay
• Is Part Of: International journal of heat and mass transfer. Volume 108:Part A(2017)
• Page Start: 468
• Page End: 489
• Publication Date: 2017-05
• Subjects: Entrapped triangular cavities -- Porous media -- Mixed convection -- Heatline analysis -- Nusselt number -- Thermal management; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2016.10.114
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Mixed convection in porous entrapped triangular cavities is studied. Mixed convection in entrapped triangular cavity has application in heat exchanger. Effect of horizontally moving walls on the thermal field is analyzed using heatlines. Effect of various thermal parameters on the trends of flow fields is examined. Heat flow rates are found to be highly influenced by motion of the horizontal walls. Abstract: This paper analyzes the fluid and heat flow within entrapped porous triangular cavities involving various thermal boundary conditions (case 1: hot horizontal walls and cold inclined walls; case 2: cold horizontal walls and hot inclined walls). Finite element based numerical study has been performed for various values of Prandtl number ( Pr m = 0.026 and 7.2 ), Darcy number ( Da m = 10 - 4 - 10 - 2 ), Reynolds number ( Re = 1 - 1000 ) at a high value of Grashof number ( Gr = 10 5 ). The upper cavity for the case 1 and the lower cavity for the case 2 show almost similar trends and vice versa based on the exact opposite thermal boundary conditions. Heat transfer is conduction dominant at Da m = 10 - 4 involving both Pr m whereas, convection heat transfer dominates at Da m = 10 - 2 especially for Pr m = 7.2 . Although the motion of the horizontal walls significantly influences the fluid flow field within the cavities, due to the decoupling between the fluid and thermal fields at the low Pe m ( Pe m = 0 . 026, 0 . 26 and 2.6 ), conduction dominant heat transfer occurs. At the high Da m and Pr m = 7.2, a pair of symmetric streamline or heatline cells are seen for Re ≤ 1 whereas, a bigger primary streamline or heatline cell is accompanied by a secondary streamline or heatline cell for 1 ⩽ Re ≤ 100 . At 500 ⩽ Re ⩽ 1000, the single larger streamlines or heatline cells are seen especially for Pr m = 7.2 involving Da m = 10 - 2 . At Pr m = 0.026, the average heat transfer rates ( Nu t ‾, Nu b ‾, Nu l ‾ and Nu r ‾ ) are almost constant with Re and Da m . At Pr m = 7.2, the larger magnitudes of Nu t ‾ and Nu l ‾ are observed for Re ≤ 10 compared to those for Re = 100 involving Da m ⩾ 10 - 3 whereas, the magnitudes of Nu r ‾ are almost similar for all Re involving all Da m in the upper cavity (case 1) within Re ⩽ 100 . In the lower cavity (case 1), the magnitudes of Nu b ‾ and Nu r ‾ are larger for Re = 100 whereas, the magnitudes of Nu l ‾ are larger for Re ≤ 1 for almost entire range of Da m within Re ≤ 100 involving Pr m = 7.2 . The average Nusselt numbers are significantly larger at the high Re ( Re = 500 and 1000) involving all Da m (except for the horizontal walls involving Da m ⩽ 8 × 10 - 4 ) in the cases 1 and 2 at Pr m = 7.2 .