Abstract

In this study, the free convection with volumetric radiation in a water–alumina nanofluid flowing between two inclined concentric cylinders was simulated. The enclosure, or the cavity between the two circular quadrants in which the inner and outer pipes were respectively at high and low temperatures, was exposed to a magnetic field, and the remaining walls were insulated. Simulations were performed using control volume and the SIMPLE algorithm. The effects of the Rayleigh and Hartmann numbers, cavity or enclosure angle, magnetic field angle, nanopowder volume fraction, radiation intensity, and aspect ratio were investigated on the Nusselt number, irreversibilities and the Bejan number. According to the results, the Rayleigh number, hot pipe diameter, and adding more nanopowder have increasing and the Hartmann number has decreasing effect on the thermal performance and irreversibilities. Adding more nanopowder and increasing the enclosure angle also improved heat transfer. Increasing the magnetic field angle first increased and then decreased irreversibilities. In fact, increasing the magnetic field angle increased up to 15°, the heat transfer rate increased, and further increase of the magnetic field angle from 15° to 90° decreased the heat transfer rate.

摘要

在这项研究中，模拟了在两个倾斜的同心圆柱体之间流动的水-氧化铝纳米流体中具有体积辐射的自由对流。内管和外管分别处于高温和低温的两个圆形象限之间的外壳或空腔暴露在磁场中，其余的壁被绝缘。使用控制体积和 SIMPLE 算法进行模拟。研究了瑞利和哈特曼数、腔或外壳角、磁场角、纳米粉末体积分数、辐射强度和纵横比对努塞尔数、不可逆性和 Bejan 数的影响。根据结果​​，瑞利数，热管直径，并且添加更多的纳米粉末对热性能和不可逆性有增加和降低哈特曼数的影响。添加更多的纳米粉末并增加外壳角度也改善了热传递。增加磁场角首先增加然后减少不可逆性。事实上，将磁场角增加到 15°，传热率增加，磁场角从 15° 进一步增加到 90°，传热率降低。