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Natural convection heat transfer in a rib-roughened asymmetrically heated channel
| Content Provider | Semantic Scholar |
|---|---|
| Author | Abidi-Saad, Aissa Popa, Catalin Beaumont, Fabien Polidori, Guillaume |
| Copyright Year | 2016 |
| Abstract | A two dimensional numerical simulation is carried out to investigate the effect of two adiabatic square ribs on laminar flow and heat transfer in an asymmetrically heated channel. The two ribs are symmetrically located on each wall, exactly above the heating zone. The adiabatic square ribs could be an effortless and cheap means that can be incorporated in natural ventilation systems (double skin facades, trombe walls.) to control the mass flow rate and heat transfer. The computational procedure is made by solving the unsteady bi-dimensional continuity, momentum and energy equations with the finite volume method. The investigations focused more specifically on the influence of the ribs sizes RS (0, b/18, 2b/18, 3b/18, 4b/18, 5b/18 and 6b/18) on the flow structure and heat transfer enhancement. The numerical study is carried out for a fixed modified Rayleigh number Ra = 2.86× 10 and for a fixed aspect ratio of the heated part Rf= 5.2. The modified Rayleigh number based on the heat flux density (φ) and the thickness of the channel (b) also takes into account the aspect ratio of the heated part Rf. Concerning the value of the heated part aspect ratios Rf, it is within the range of those found for horizontally divided double-skin facades of high-rise buildings. The results showed that the variation of the ribs sizes significantly alters the heat transfer and fluid flow distribution along the channel, especially in the vicinity of protrusions. Also, the results show that streamlines, isotherms, and the number, sizes and formation of vortex structures inside the channel strongly depend on the size of protrusions. The changes in heat transfer parameters have also been presented. The present numerical results are compared with experimental data and a good agreement was found. INTRODUCTION In the literature, a large number of numerical and experimental works have dealt with natural convection phenomenon in vertical channels. The main cause of interest in the study of free convection in channels is not just for the fundamental nature of the problem, but also mainly from the fact that this type of thermally driven flow is cheap, reliable, quiet and free maintenance and it is encountered in numerous applications such as the chimney, the solar panel, the trombe wall and double-skin facade as well. Since the pioneering work of Elenbaas [1] natural convection in open smooth channels have been extensively studied over the last past decades, both experimentally [2] and numerically [3] for vertical or inclined configurations. Several studies have shown that the inclusion of nanoparticles in the coolant fluid or the change of the geometry with various shapes of protrusions or fins considerably increase the heat transfer energy. For the sake of the enhancements of the limited heat transfer performance of a heated vertical channel, numerous numerical and experimental works have modified the geometry of the simple channel configuration. Some of these works have investigated the effects of an adiabatic extension in the entry or exit section, as investigated by Lee [4] and the chimney effect as in [5]. Other works treated the influence of adding internal heated or adiabatic plates as in [6]. Another most important method to enhance the thermal performance of channels is by adding roughness elements (ribs) on one or both surfaces forming the vertical channel. Compared with the plentiful literature on natural convection in channels with smooth surfaces, relatively little works have treated with the effect of roughness elements on natural convection heat transfer in channels as those studied by [7, 8]. At the author knowledge and depending on the literature review the case of free convective heat transfer in an asymmetrically heated vertical channel filled of water and having two ribs symmetrically located on each wall, exactly attached above the heated zone in downstream of the channel seems not to have been investigated in details in the past and this has motivated the present study. Various aspect ratios of the ribs in the range of 0≤Rs≤6b/18 are studied for a fixed Ra* = 2.86×10 and fixed Rf = 5.2. The adiabatic square ribs could be an effortless and cheap means that can be incorporated in natural ventilation systems (double skin facades, Trombewalls.) to control the mass flow rate and heat transfer. 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://repository.up.ac.za/bitstream/handle/2263/61880/AbidiSaad_Natural_2016.pdf?isAllowed=y&sequence=1 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
