Performance analysis of overlapped solar air heater using CFD

Transcription

1 Performance analysis of overlapped solar air heater using CFD Ponnusamy S 1 1 Associate Professor, Department of Mechanical Engineering, K.S.R Institute for Engineering and Technology, Tiruchengodu yesponnu@yahoo.co.in Dr. K. Visagavel 2 2 Professor and Head, Department of Mechanical Engineering, Knowledge Institute of Technology, Kakapalyam vp@kiot.ac.in Abstract In general air conditioning was used to controlling the room temperature which is very expensive. In this project the temperature of the collector to be maintained by vacuum pressure and exhaust air movement has been created by solar heater. The air movements inside the collector have two factors i.e., wind driven and buoyancy driven. For the first case, more ventilation has to be provided. In addition, climatic condition has to be assisted. But in the second case, irrespective of the climatic condition air movement could be created by adding some heating devices. Here solar air heater is used to make buoyancy effect inside the collector. Now the flat plate air heater is replaced with overlapped glass plate air heater. This problem is analysed using CFD for flat plate air heater and over lapped solar air heater.the objective of this work is to analyze the effect of the pressure, temperature and velocity of air flowing through the overlapped glass plate collector with respect to the time and to compare overlapped glass plate results and flat plate work results by using computational fluid dynamics (CFD) tool with respect to flow and temperature distribution inside the solar collector. Keywords - Solar Air Heater; Natural Ventilation; AC; SSVR; Computational Fluid Dynamics I. INTRODUCTION The thought of exhaustible nature of the resources and the environment damage from the use of these resources never occur either to the inventor of the subsequent generations. In the quest to sustain galloping economical activities, the dependence on coal and oil products has soar at a phenomenal rate over the years. Our primary source of clean, abundant energy is the sun. The sun deposits 1, 20,000 TW of radiation on the surface of the Earth, far exceeding human needs even in the most energies demand their scenarios. Solar energy can be used by man in a planned direct either indirect way. In the case of indirect utilization of available solar energy we consider the use of renewable energies which are secondary effects of solar energy i.e., wind energy, hydro energy, ocean energy, and secondary energy from photosynthetic process that is mostly connected with the use of biomass and biofuels. Ventilating is the process of "change" or replace air in any space to provide high indoor air quality (i.e. to control temperature, Fresh oxygen, or remove moisture content, odors, smoke, heat, dust, airborne bacteria and carbon dioxide). Ventilation is used to remove smells and excess moisture, introduce outside air, to keep interior building air circulation and to prevent stagnation of the air. The major function of buildings is to provide acceptable indoor environment which allows occupants to carrying various activities. The three main energy building services are space condition (thermal comfort), lighting (visual comfort), and ventilation (indoor air quality). The purpose of this paper is to address issues that relate renewable energy to the last of these. The main sections of this report indicate how renewable technologies will contribute both to energy and indoor pollution and help frame the discussion of the trade-offs. II. REVIEW OF LITERATURE Choiu et al [2] investigated the use of porous matrices as the heat-absorbing media in air-cooled solar collectors. Because heat transfer and fluid friction data s have been obtained on slit-and-expanded aluminum-foil matrices, this type is particularly discuss. Porous matrices absorb solar radiation in depth, and when arranged in a parallel-flow system, their upper area surface is subject to cool air, so that the upper losses are minimized. They also have high heat-transfer area and volume ratios. A 1757

2 matrix collector is also inexpensive and simple. An analysis of heat transfer and fluid friction characteristics of such a collector denotes maximum efficiency than that of flat-plate collectors, and friction losses that are much lower. David et al [3] analyzes the technical performances of seven solar air heaters of conventional design and generalized by means of two coefficients: air mass flow rate/unit collector area (G) and the collector geometric coefficient (K), which make collectors performance invariant, under the same conditions of design, material choice and ambient values. By use of the zero capacitance model and the air heater performances were computed for the most usual range of design and working condition; the graphs presents can be used when dealing with planning problems of air collectors. Gupta et al [5] determine the effect of transverse wire roughness on heat and fluid flow characteristics in transitionally roughness flow region for rectangular solar air heater ducts with an absorbed plate having transverse wire roughness on its underside of the collector. The investigation covered a Reynolds number range for a duct aspect ratio, relative roughness height at a relative roughness pitch of encompassing a range of roughness Reynolds number. Simple correlations for a Nusselt number and friction factor had been developed in terms of geometrical parameters of roughness, duct cross section, and the flow Reynolds number. Mohamed selmi et al [6] analyzed the problem of flat plate solar energy collector with water flow is simulated and analyzed using computational fluid dynamics (CFD) software. The considered case includes the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between tube surface, glass cover, side walls, and insulating base of the collector as well as the mixed convective heat transfer in the circulating water inside the tube and conduction between the base and tube material. The collector performance, after obtaining 3-D temperature distribution over the volume of the body of the collector, was studied with and without circulating water flow. An experimental model was built and experiments were performed to validate the CFD model. The outlet temperature of water is compared with experimental results and there is a good agreement. Chan et al [1] studied the Heating, ventilating, and air-conditioning (HVAC) are parts of the major energy consumption in a building. Conventional heating and cooling systems are having an impact on carbon dioxide emissions, as well as on security of energy supply. In this regard, one of the attempts taken by researchers is the development of solar heating and cooling technologies. The objective of this paper is to review the passive solar technologies for space heating and cooling. The reviews were discussed according to the working mechanisms, i.e. buoyancy and evaporative effects. The advantages, limitations and challenges of the technologies have been highlighted and the future research needs in these areas have also been suggested. From the survey there are lot of work has been done with flat plate collector for various application. But there is no work has been done with over lapped glass plate collector for ventilation purpose. In addition efficiency, outlet temperature and air distribution of the overlapped glass plate collector not compared with flat plate collector. III. PROPOSED METHODOLOGY 3.1 Design of Solar Air Heater Assisted Ventilation System (SAHAVS) The schematic diagram of overlapped glass plate collector with its details is given in fig 1. The setup consists of clear white colored glass for solar penetration, black colored glass plate for absorption and inlet & outlet for flow process. Here the glass plates are overlapped in series for a better absorption and the temperature created inside the collector is too high. Due to effect of high temperature, the pressure created inside the collector is too high. Because of the overlapped setup of the collector, the velocity create inside the collector is too low and it will affects the ventilation process. The heat transfer analysis of the overlapped glass plate solar air heater based on the quasi-steady state performances and was carried out in two sectors. The glass plate is assumed to absorb the solar short wave radiation, but the long wave emission from the glass plates ignored. The approximate glass temperatures obtained from the previous step is used in the exact determination of the long wave radiation between the glass plates. Therefore improved results were obtained for our project work. 1758

3 Fig. 1. Schematic Diagram of Over Lapped Glass Plate Air Heater 3.2 Design of Overlapped Glass Plate Solar Air Heater (OGPSAH) Here the overlapped glass palate solar air heater can be designed by using two software: CAD & Solidworks. In order to achieve a greater finish surface with higher accuracy we need to move solid works as designing software for the final rendering process. The design of the proposed model is shown in the fig 2. (a) 1759

4 (b) Fig 2 (a) & (b). Solidworks model of the proposed OGPSAH After completion of this process we can get the real image of designed object. Here the dimensions of the solar air heater are taken from the literature survey and the concept is a novel idea. In the previous experiment the Galvanized iron sheet is used in the place of the black Colored glass plate. The main advantage of the Black colored glass plate is it will absorbs the short wave radiations and it does not reradiated back to the atmosphere. So with help of this process we can achieve a more heat and due to increase in the temperature there is automatically increase in the efficiency of the solar air heater. Computational domain of solar air heater assisted ventilation system is taken from literature review. IV. ANALYSIS RESULT & DISCUSSION Solar air heater consists of absorber plate and transparent cover, insulation material, and frame and air passage. A photograph of experimental set up, construction detail and main properties of different solar air heaters are shown in the above figure. The air and glass plate temperatures were calculated by taking into account the uneven distribution of the income air stream between the glass plates, obtained from the atmosphere. The model was constructed and tested under clear-sky conditions with respect to the time. The air and glass temperatures were measured on each plate using CFD. The solar air heater has overall dimension of 1.83x0.128x0.069m.The solar air heater is fitted with a glass plate on top surface, a serious of glass plates which is overlapped in serious in the middle of the heater area at a distance of 0.305m from the glass plate. The solar air heater is kept tilted at 11 according to latitude of the position so that the heater experiences solar energy ranging from 30 W/m 2 to 900 W/m 2. The fluid properties and boundary conditions are given in SI units. Single glass cover was used in these types of solar air heaters. The skeleton of solar air heater was manufactured by insulation material of 50 mm thickness and Transparent glass cover was taken which have thickness of 3mm. Thermocol insulation was provided which have thickness of 50 mm. Insulation was provided to reduce heat loss. Two holes were made at both sides of skeleton for inlet and outlet in the dimension of 70mm in diameters. The tilt angle of solar air heater was taken 11 o by adjustable part. Solar air heater was placed in direction of northsouth without any shadow. Air is circulated by means of atmospheric pressure. 1760

5 (a) (b) (c) Fig 3 (a), (b) and (c) shows the pressure, temperature and velocity distribution inside the collector Experiments on solar air heaters were performed in clear days of April and May in Knowledge Institute of Technology, Salem. Tests were conducted between 06:00 to 18:00 solar times. The solar radiation, wind speed, air velocity in the heater, ambient air temperatures, heater inlet and outlet air temperatures were taken in every one hour interval periods. The data is plotted in respective graphs. Anemometer was used for measuring wind speed, thermocouples were used for measuring temperatures at different point of solar air heaters and solar power meter was used for measuring solar radiation. 1761

6 The computational analysis of the respective data was done using the Ansys 15.0 and the results obtained are plotted in the fig 3. From fig 4, it can be seen that the temperature distribution of the glass plate collector is slightly higher than that of flat plate collector because of the transitivity of the glass. The pressure distribution of the flat plate collector is exhibiting a linear pattern. There is an increment in the glass plate collector during the high intensity radiation period. The velocity distribution is of the flat plate collector is exhibiting a linear pattern and higher value. There is a small increment in velocity for the glass plate model during the intense radiation period. The minimum deviation of the glass plate collector during the intense radiation period is due to the higher pressure build up inside the glass hood and the solar heater tubes. TEMPERATURE DISTRIBUTION INSIDE THE COLLECOTR TEMPERATURE (KELVIN) 3.25E E E E E E E+02 GLASS PLATE COLLECTOR FLAT PLATE COLLECTOR 2.90E TIME (HOURS) (a) PRESSURE (PASCAL) 5.00E E E E E E E E E E E+00 PRESSURE DISTRIBUTION INSIDE THE COLLECOTR GLASS PLATE COLLECTOR FLAT PLATE COLLECTOR TIME (HOURS) (b) 1762

7 3.90E+00 VELOCITY DISTRIBUTION INSIDE THE COLLECOTR GLASS PLATE COLLECTOR FLAT PLATE COLLECTOR VELOCITY (M/S) 3.80E E E E E E TIME (HOURS) (c) Fig 4 (a), (b) and (c) shows the temperature, pressure and velocity distribution inside the collector 4. CONCLUSION The effects of flow characteristics inside the collector were examined by solving the pressure, temperature and velocity distribution using CFD with the standard k ε turbulence model. The effect of the pressure, temperature and velocity of the over lapped glass plate solar air collector is 15% higher than flat plate solar air collector. This investigation also revealed that high temperature can be created inside the collector, which can be used for clothes drying, bricks dryer, buffage system for food and many more heat applications. References [1] Chan H.Y., Riffat S.B. and Zhu J, Review of passive solar heating and cooling technologies Renewable Sustain Energy, Vol.14, pp , [2] Chiou, J.P., Wakil E.L. and Duke J.A, A slit-and-expanded aluminium-foil matrix solar collectors Solar Energy, Vol.9, pp , [3] David Luna, Yves Jannot and Jean-Pierre Nadeau, An oriented-design simplified model for the efficiency of a flat plate solar air collector, Applied thermal engineering Vol.30, pp , [4] Decho Thueaktphum and Kittitep Fuenkajorn, A rock fills based solar thermal energy storage for housing, Sience Asia, Vol.36, pp , [5] Gupta D., Solanki S.C., and Saini, J.S, Heat and fluid flow in rectangular solar air heater ducts having transverse rib roughness on absorber plates Solar Energy, Vol.51, pp , [6] Mohamed Selmi, Mohammed J. and Abdulhamid Marafia, Validation of CFD simulation for flat plate solar energy collector, Renewable Energy,Vol.33, pp , [7] Norton B, Anatomy of a solar collector: Developments in Materials, Components and Efficiency Improvements in Solar Thermal Collector Systems, Vol.7, pp , [8] Pangavhane R. and R.L.Sawhney R, Review of research & development work on solar dryers forgrape drying, energy conversation and management, Vol.43, pp , [9] Rhushi Prasad P., Byregowda H.V. and Gangavati P.B, Experiment Analysis of Flat Plate Collector and Comparison of Performance with Tracking Collector, European Journal of Scientific Research, Vol.40, pp ,