Analysis of transient mixed convection in a horizontal channel partially heated from below

Mahmoud A Mashkour

doi:10.15587/1729-4061.2021.238649

Abstract

The heat convection phenomenon has been investigated numerically (mathematically) for a channel located horizontally and partially heated at a uniform heat flux with forced and free heat convection. The investigated horizontal channel with a fluid inlet and the enclosure was exposed to the heat source from the bottom while the channel upper side was kept with a constant temperature equal to fluid outlet temperature. Transient, laminar, incompressible and mixed convective flow is assumed within the channel. Therefore, the flow field is estimated using Navier Stokes equations, which involves the Boussinesq approximation. While the temperature field is calculated using the standard energy model, where, Re, Pr, Ri are Reynolds number, Prandtl number, and Richardson number, respectively. Reynolds number (Re) was changed during the test from 1 to 50 (1, 10, 25, and 50) for each case study, Richardson (Ri) number was changed during the test from 1 to 25 (1, 5, 10, 15, 20, and, 25). The average Nusselt number (Nuav) increases exponentially with the Reynold number for each Richardson number and the local Nusselt number (NuI) rises in the heating point. Then gradually stabilized until reaching the endpoint of the channel while the local Nusselt number increases with a decrease in the Reynolds number over there. In addition, the streamlines and isotherms patterns in case of the very low value of the Reynolds number indicate very low convective heat transfer with all values of Richardson number. Furthermore, near the heat source, the fluid flow rate rise increases the convection heat transfer that clarified the Nusselt number behavior with Reynolds number indicating that maximum Nu No. are 6, 12, 27 and 31 for Re No. 1, 10, 25 and 50, respectively

Highlights

The study of convection heat transfer is an important topic, which is due to its great importance in many sectors
The results showed that the agreement relation between the Reynolds number and Nusselt number, as well as the Richardson number value, rises at the same value of Reynolds number leading to the Nusselt number rise within the cavity
It is shown that at a low Reynolds number, there is no effect of the Richardson number on the Nusselt number; at a high Reynolds number, the Nusselt number increases as the Richardson number increases

Summary

Introduction

The study of convection heat transfer is an important topic, which is due to its great importance in many sectors. Big efforts are being made in studying convection heat transfer in order to save energy and money depending on many factors such as the physical geometry taken into account. The kind of geometry affects significantly the hydrodynamic and thermal distributions, as well as the heat transfer enhancements. An example of this is the heat transfer enhancement techniques corresponding to “double pipe, square duct, rhombus duct, wavy channel, flow around a hexagonal cylinder, center-trimmed twisted tape, diamond shape cylinder, corrugated tube with spring tape, inclined tabulator, and twisted tape insertion” [7,8,9]

Objectives

Methods

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Conclusion