International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 09 Issue: 05 | May 2022
p-ISSN: 2395-0072
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CFD Simulation of Solar Air Heater having Inclined Discrete Rib Roughness with Staggered Element Mahendra Kumar Ahirwar1, K R Aharwal2 1MTech
2Professor,
student, Thermal Engineering, Maulana Azad National Institute of Technology, Bhopal, India Dept. of Mechanical Engineering, Maulana Azad National Institute of Technology, Bhopal, India
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Abstract - In this study 3-D CFD simulations are done to
essential components of a solar air heater. Because of its basic design, solar air warmers are among the most affordable and extensively used solar energy equipment. Solar air heaters have a variety of applications, including room heating, curing of industrial items, and curing/drying of concrete/clay building components. We know that the convective heat transfer coefficient between the air and the absorber plate in a solar air heater is quite low due to the low thermal conductivity of air [1]. In order to enhance heat transmission in the solar air heater, we must first improve heat transfer in the solar air heater. The study of heat transfer mechanisms and fluid flow is critical for improving performance in terms of improved thermodynamic efficiency and power production for heat exchanging devices such as solar air heaters and heat exchangers. The computational fluid dynamics (CFD) technique is less expensive than experimental research for evaluating the thermal performances of heat exchanging devices. The advantages of CFD are that we can make different complex geometries, different shape and sizes and can produce a large number of results at no added expense and it is very cost effective to perform parametric studies for optimization of the equipment performance. There are several strategies for improving heat transmission in a solar air heater. However, boosting the heating capacity of the solar collector by adding artificial roughness to the absorber plate is the simplest and least expensive method [2]. Various researchers [2-4] investigated the forms and placements of ribs experimentally. A 3D CFD analysis of heat transfer and fluid flow characteristics through an artificially roughened solar air heater with arc-shaped rib roughness was carried out by Kumar and Saini [5]. They offered the artificial roughness in the form of arc-shaped thin circular wire. They covered a wide range of roughness parameters (e/D from 0.0299 to 0.0426 and a/90 from 0.333 to 0.666) as well as operating parameters (Reynolds number, Re from 6000 to 18,000 and solar radiation of 1000 W/m2). Their maximal enhancement ratio value was 1.7. Karmare and Tikekar [6] performed a 3D CFD simulation of fluid flow and heat transfer in an intentionally roughened solar air heater with metal grit rib roughness. They created the roughness with metal ribs with round, square, and triangular crosssections that were angled at 60 degrees to the air flow. They used the parameters: e/Dh = 0.044, p/e = 17.5 and l/s = 1.72, for the Reynolds number range 3600–17,000.
investigate heat transfer and fluid flow characteristics of artificially roughened duct using Ansys-Fluent. We saw how Reynolds number affects the Nusselt number. The air flow has been computed in terms of Reynolds numbers ranging from 6000 to 12000 using the finite volume approach and the SIMPLE algorithm. The roughness pitch to rib height ratio ranged from 6 to 12, the length of staggered element to gap width ratio was 2, the relative staggered position was 0.6, and the width of the gap to roughness height ratio was 1. The Nusselt number, flow friction, and thermal performance of the rectangular channel with inclined rib staggered arrangement were compared to inclined rib with a staggered element. The staggered element increases the turbulence intensity in its vicinity, resulting in increased heat transfer and so strengthening the flow. A commercial bundle with a limited volume software ANSYS FLUENT R1 2021 is used to analyse and visualise the flow over the duct of a solar air heater. The geometry of the model is created in design modeller, then meshed, analysed, and post-processed with Ansys-fluent R1 software. Heat transfer and fluid flow are simulated and compared using a turbulent flow model (RNG k-), using steady-state solvers to determine pressure drop, flow, and temperature fields. The duct's bottom wall is roughened by various geometries of discrete ribs. The heat transfer simulation results for different roughness configurations varies slightly, and the Ansys-Fluent programme was used to simulate the flow fields in a rectangular duct. CFD simulation results were found almost close to the experimental results and with the standard theoretical approaches. We found that the Nusselt number increases with increase in Reynolds number. The maximum increment in Nusselt number and friction factor is 3.445 and 3.5 respectively, at P/e 10. The maximum thermohydraulic performance obtained is 2.3378 at the Reynolds number of 12000. Key Words: CFD Simulation, Heat transfer, Solar air heater, Artificial roughness.
1. INTRODUCTION A solar air heater is a form of solar thermal system in which air is heated in a collector and then transported to either the interior space or a storage medium. Solar collection panels, a duct system, and diffusers are the
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