SOLAR FLAT PLATE COLLECTOR HEAT TRANSFER ANALYSIS IN THE RAISER WITH HELICAL FINS Mohammed Mohsin Shkhair* 1, Dr.

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1 ISSN IJESR/May 2015/ Vol-5/Issue-5/ Mohammed Mohsin Shkhair et. al./ International Journal of Engineering & Science Research SOLAR FLAT PLATE COLLECTOR HEAT TRANSFER ANALYSIS IN THE RAISER WITH HELICAL FINS Mohammed Mohsin Shkhair* 1, Dr.Narsimhulu Sanke 2 1 ME Student, Dept. of Mechanical Engineering, Shatra Technical Institute, Ministry of Higher Education & Scientific Research, Republic of Iraq, Iraq. ABSTRACT 2 Director, Centre For Energy Technology, Osmania University, Hyderabad, India. The project focuses on the process of energy transition from the collector to the working fluid to improve the efficiency in a flat plate collector employing helical fins in the risers to induce a gradient of heat capacitance. A solar flat plate collector is analyzed with fins and s in a raiser for improvement the heat transfer rates. Heat transfer analysis is done by using CFD ANSYS 14.5 and compares the heat transfer rates on the two models of the collector and optimum geometry of the fin is determined. Keywords: Solar system, Flat plat collector, Helical fins, Circular tube, Heat transfer. 1. INTRODUCTION Flat Plate Collector is widely used for domestic hot-water, space heating/drying and where the fluid temperature is less than 100 o C. The main components of the collector are absorber plate, top covers and heating pipes. The absorber plate is selective coated to have high absorptivity. It receives heat by solar radiation and by conduction; heat is transferred to the flowing liquid through the heating pipes. The fluid flow through the collector pipes is by natural (thermosyphon effect). Conventionally, risers of all flat plate collectors are circular pipe copper/aluminum sheets however, which limits on the heat collection surface transfer area. Thus, higher heat collection surface area is optimized by changing its geometry with the same space of conventional collector. The objective of present study is to evaluate the performance of flat plate collector with different geometric riser tube configuration. It is expected that with the same collector space higher thermal efficiency or higher water temperature can be obtained. Thus, cost of the solar collector can be further bringing down by enhancing the collector efficiency. 2. METHODOLOGY 2.1 Modeling of flat plat collector The fins pattern has been specifically designed to increase the heat transfer area in applications using a fluid with low thermal conductivity. The both models are created by Pro-Engineering simple and modified. The simple has cross section area is circle (Fig. 1) and the modified has a cross section area is circle with four helical fins in it (Fig. 2).Internally profiled tubes are circular pipes that have been enhanced on the inside surface by the addition of helical fins. Table 1: Riser description Name Parameter Dimension Diameter 10mm Riser tube Thickness 0.8 mm Number 8 Spacing between 130mm Diameter 22mm Header tube Thickness 1mm Spacing between 1734mm Width of fin 2 mm Helical fin Height of fin 2 mm Pitch of helical 100 mm *Corresponding Author 352

2 Fig. 1: Flat plate collector raiser 2.2 Meshing Fig. 2: Flat plate collector raiser with four helical fins The computational domain is mesh as shown in Figure 3 & 4. Creation of an accurate computational mesh for the domain under investigation was of paramount importance in CFD simulations. The shape of control volumes should satisfy certain geometry requirements in order to eliminate irregularities in computational results. The mesh is used ANSYS ICEM CFD tetrahedrons for collector the numbers of elements are and nodes are The number of element for collector with fins and the nods Collector Collector with helical Fig. 3: Meshing system of flat plate collector raiser 3. BOUNDARY CONDITIONS Fig 4: Meshing system of flat plate collector raiser with four helical fins The boundary conditions are inlet temperature to riser 30 o C, heat flux of average day of June approximately was 930 W/m 2, mass flue rate is Kg/s and working fluid is water, the riser tube material is copper. The properties of water and copper are in the table 3. Table 2: Specifications of flat-plate collector Collector parameter Value Gross surface area 2 m 2 Absorber surface area 1.7 m 2 Length of collector 1000 mm Width of collector 2000 mm Thickness of collector 87 mm Weight of collector 45kg Absorbing coating Black chrome Absorbing factor 80% Emission 5% Copyright 2015 Published by IJESR. All rights reserved 353

3 Table 3: Properties of copper and water Parameter Density of Copper Specific heat of Copper Thermal conductivity of Copper Density of water Viscosity of water Specific heat of water Thermal conductivity of water Value 8978 Kg/m3 381 J/kg-K W/m-K 997 Kg/m kg-k 4182 J/kg-K 0.6 W/m-K Assumptions Water is a continuous medium and incompressible. The flow is steady and possesses turbulent flow characteristics. The thermo-physical properties of the absorber plate and absorber tube are constant with respect to the operating temperature. The bottom portion of the absorber tube and bottom face of the absorber plate is assumed to be adiabatic. Fig 5: Top views of the risers () 4. ANALYZING Fig 6: Top views of the risers (with helicalfins) Steady state simulations are carried out with a 2 m 2 flat plate solar collector panel. The geometrical dimensions are shown in Table 4.3. Due to the large difference in the dimension of absorber tube length (1734 mm) and tube hydraulic diameter (10 mm), a very fine grid distribution is needed in the cross-section of the riser tube.after doing the mesh by ANSYS fluent 14.5 import the mesh file to fluent solver 14.5 to inter the boundary condition for both the modeling (with helical fins and ) to do analysis for heat transfer and compare between two cases. After open the fluent Solver Manager 14.5 and import to run solver and wait to convergent the solver. 5. RESULTS AND DISCUSSION The results are shown that the maximum temperature occurred after the peak solar radiation. During the simulation of the flat plate collector for both raisers (with and without helical fins) has inlet fluid temperature of 303K.In CFD analysis the average temperature of the fluid flow through in helical fins traced in outlet header is 329.2K, where as in s the outlet temperature is K for same boundary conditions. The maximum temperature in modified shape of the risers is progress up to 8.3 K because of turbulence and velocity decreases in raiser tube. Copyright 2015 Published by IJESR. All rights reserved 354

4 Fig 7: Temperature distributions in the collector () Fig. 8: Temperature distributions in the collector (with fins) The pressure in the riser pipe for the given boundary conditions in both cases was relatively high, s has 24.2 Pa and that for with helical fins42.0 Pa. Due to do modified on the shape of the risers the pressure of fluid were higher than the simple risers at entrance in this case the temperature of working fluid has been increased. The figure 5.1&5.2 has indicated very clearly the different between in two case studies in paper. When the pressure was high at entrance of the both collectors riser then, the pressure drop and the velocity became high at outlet of collectors. Fig 9: Pressure distributions in the collector () Fig 10: pressure distributions in the collector (with fins) PressurePa Fig 6: Temperature comparison between riser tubes with and with and Fig 7: pressure comparison between riser tubes Copyright 2015 Published by IJESR. All rights reserved 355

5 6. CONCLUSION It is traced that, the outlet temperatures of collector is K, and with helical fins K, for same inlet conditions, the outlet temperature is increased about 8.3 K in helical fins as compared to without fins. The efficiency ranges depended on the ambient temperatures and the time of the day, the collector with helical fins is 17.5 % more efficient than collector. The pressure in the raiser (heating pipe) for the given boundary conditions in both cases was relatively high, being about 24.4 Pafor s and 42 Pa for with helical fins. The modified risers achieve better result than the simple, in this analysis. Which the modified has velocity m/s and the collector has m/s. The modified raiser (with helical fins in the raiser) has more turbulence. REFERENCES [1] Mohammed Mohsin, M.E Thesis. Heat transfer analysis in a flat plate collector with helical fins, Osmania University, Hyderabad, India, [2] Kumar P, Ganesan R. A CFD Study of Turbulent Convective Heat Transfer Enhancement in Circular Pipe flow. World Academy of Science, Engineering & Technology 2012; 68: 853. [3] Ehrmann N, Reineke-Koch R. Selectively coated high efficiency glazing for solar-thermal flat-plate collectors. Journal of Thin Solid Films, Paper in press, [4] AlShamaileh E. Testing of a new solar coating for solar water heating applications. Solar Energy 2010; 84: [5] Duffie JA, Beckman WA. Solar Engineering of Thermal Processes, 2 nd Edition, John Wiley & Sons, New York, Copyright 2015 Published by IJESR. All rights reserved 356