A cfd investigation and pressure correlation of solar air heater
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  • 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME401A CFD INVESTIGATION AND PRESSURE CORRELATION OFSOLAR AIR HEATERAnup Kumar*, Anil Kumar Mishra*** Dept. of Mechanical Engineering, Birla Institute of Technology, Mesra, India**Dept. of Mechanical Engineering, Birla Institute of Technology, Mesra, IndiaABSTRACTThe intent of the present work is to study the behavior of solar air heater with andwithout porous media and also to compare their performance under different set ofconditions, obtained by changing various governing parameters like air mass flow rate, inletair temperature, spacing between top cover and absorber plate and intensity of solar radiation.The problems have been solved by the Finite Difference Method. This study presents themathematical model for predicting the heat transfer characteristics and the performance ofsolar air heater with and without porous media. The solar air heater with porous media giveshigher thermal efficiency than without porous media. The thermal conductivity of porousmedia has significant effect on the thermal performance of the solar air heater. The work hasbeen carried out on GAMBIT and FLUENT software as it is standard tool for flow analysisand widely acceptable. A double pass flat plate solar air heater model is prepared subjected tothe relative loads and constraints and results are obtained for the proposed models.Keyword: Solar Air Heater, Porous Media, Pressure Drop, CFD1. INTRODUCTIONEnergy is a vital need in all aspects and increasing demands for energy is notsufficient for basic requirement. Therefore, human being is looking for renewable source ofenergy such as solar energy, geothermal energy, and wind energy. Humans have always usedthe Solar energy is the radiation produced by nuclear fusion reactions in the core of the sun.This radiation travels to earth through space in the form of energy called photons. Solarenergy collectors are special kind of heat exchangers that transform solar radiation energy tointernal energy of the transport medium. The major component of any solar system is theINTERNATIONAL JOURNAL OF MECHANICAL ENGINEERINGAND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online)Volume 4, Issue 2, March - April (2013), pp. 401-417© IAEME: www.iaeme.com/ijmet.aspJournal Impact Factor (2013): 5.7731 (Calculated by GISI)www.jifactor.comIJMET© I A E M E
  • 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME402solar plate collector. This is a device which absorbs the incoming solar radiation converts itinto heat, and transfers this heat to a fluid (usually air, water, or oil) flowing through thecollector. The solar energy thus collected is carried from the circulating fluid either directlyto the hot water or space conditioning equipment or to a thermal energy storage tank fromwhich can be drawn for use at night and/or cloudy days. Solar collector may be classifiedaccording to their collecting characteristics, and the way in which they are mounted anddepends on the type of working fluid which is employed into the collector. A collectorgenerally uses liquid or a gas as working medium to transfer heat. The most common liquidsare water or a water-ethylene glycol solution. The most common gas is air.Figure 1 Exploded view of the Flat plate collectorDepending upon the air passage in the solar air heater the air heaters can be classified in thefollowing ways-Single glass cover air heater- In this type of solar heater there is only one glass surface onthe top and the absorber is below the glass plate. The air flows between the glass plate andthe absorber plate. (Figure 2)Double glass cover air heater- This type of air heater includes two glass cover on the topsurface and the air flows between the glass cover and the absorber plate. (Figure 3)Double pass air heater without porous matrix- In this type of solar air heater, air flowsbetween two glass plate in one direction and then between the glass plate and the absorberplate in the opposite direction. (Figure 4)Double pass air heater with porous matrix- The constructional part of solar air heater withporous media same as solar air with non- porous media but only difference is that the porousmaterial is used in second pass of air flow. Porous materials have become increasinglyattractive for application in high temperature heat exchangers. The high effectiveness of theheat exchange mechanism is mainly due to the intimate contact in the interstices between thegas particles and porous plate. (Figure 5)
  • 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME403A porous medium is a material containing pores (voids). The skeletal portion of the materialis often called the "matrix" or "frame". The pores are typically filled with a fluid (liquid orgas). The skeletal material is usually a solid, but structures like foams are often also usefullyanalyzed using concept of porous media. A porous medium is most often characterized by itsporosity. It is also observed that thermal efficiency of solar air heater can be increased byminimizing heat loss from collector to maximize heat transfer from absorber [8]. To providea counter flow passage an extra top cover can be provided to increase volumetric heat transferco-efficient.2. MATHEMATICAL FORMULATIONIn the present study, at first mathematical model is obtained by the application of thegoverning conservation laws. The heat balance is accomplished across each component ofgiven solar air heater i.e., the glass covers, the air stream and the absorber plate. The heatbalance for the air stream yields the governing differential equations and the associatedboundary conditions. The main idea is to minimize heat losses from the front cover of thecollector and to maximize heat extraction from the absorber. Porous media forms anextensive area for heat transfer, where the volumetric heat transfer coefficient is very high; itwill enhance heat transfer from the absorber to the airstream. In the design of this type ofcollector, this combines double air passage and porous media pressure drop should beminimized[11]. The basic physical equations used to describe the heat transfer characteristicsFigure 2 Single glass cover air heater Figure 3 Double glass cover air heaterFigure 4 Double pass air heaters withoutporous matrixFigure 5 Double pass air heaterswith porous matrix
  • 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME404are developed from the conservation equations of energy. The heat and fluid flow areassumed steady and one dimensional. It is because of the radiation heat exchange terms thatrender the problem non-linear hence making the exact solution cumbersome. So a numericalapproach is applied which would give a solution with a fairly good accuracy.The model is based on the assumption made by Naphon and Kongtragool[2] -Flow of air is steady.Outside convective heat transfer coefficient is constant along the length of solar airheater.Inside convective heat transfer coefficient is constant along the length of solar airheater.Thermal conductivity of the porous media is constant along the length of solar airheater.The temperatures of the cover and plates vary only in the direction of fluid flow (x-direction);The side losses are negligible and leakage of air to/or from the collectors is negligible.Ideal gas with constant specific heat.The air flow is forced, steady and one-dimensional and the thermo-physical propertiesof air and packed bed are independent of temperature.The plug flow condition exists throughout the length of heater, i.e., the air velocity inthe channel at any section is constant.The porous absorber and the air stream are in thermal equilibrium because the valueof volumetric heat transfer coefficient in the pores of the porous matrix is very high.2.1 Factors Affecting Efficiency of flat Plate Solar Air Heater2.1.1 Porous Medium - The solar air heater with the porous media gives 25.9%higherthermal efficiency than that without porous media. The thermal conductivity of porousmedia has significant effect on the thermal performance of the solar air heater [2].Asporous mediumis characterized by its porosity or measure of voids and the skeletal portionof the material is often called the "matrix" or "frame". The measure of void isa fraction of thevolume of voids over the total volume, between 0–1, or as a percentage between 0–100percent. There is also a concept of closed porosity andeffective porosity, i.e., the pore spaceaccessible to flow.[7]2.2.2 Transmissivity-Absorptivity Product-Transmissivity-Absorptivity product is definedas the ratio of the flux absorbed in the absorber plate to the flux incident on the cover system,and is denoted by the symbol (τα). Out of fraction τα transmitted through the cover system, apart is absorbed and a part reflects back diffusively. Out of the reflected part, a portion istransmitted through the cover system and a portion reflected back to the absorber plate. Theprocess of absorption and reflection at the absorber plate surface (figure 6) goes onindefinitely, the quantities involved being successively smaller.Thus, the net fraction absorbed (τα) = ταሾ1 ൅ ሺ1 െ αሻρୢሺ1 െ αሻଶρୢଶ൅ ‫]ڮ‬ൌταଵିሺଵିαሻρౚ(1)
  • 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME405Figure. 6 Process of Absorption and Reflection2.2.3 Overall Loss Coefficient- The heat loss from the collector in terms of overall losscoefficient defined by the equationqଵ ൌ UଵA୮൫T୮୫ െ Tୟ൯ (2)The heat loss from the collector is the sum of heat loss from the top, bottom and the sides.Thusqଵ ൌ q୲ ൅ qୠ ൅ qୱ (3)q୲ ൌ U୲A୮൫T୮୫ െ Tୟ൯ (4)qୠ ൌ UୠA୮ሺT୮୫ െ Tୟሻ (5)qୱ ൌ UୱA୮ሺT୮୫ െ Tୟሻ (6)Uଵ ൌ U୲ ൅ Uୠ ൅ Uୱ (7)2.2.4Top loss coefficient ‫܃‬‫ܜ‬- The top loss coefficient is evaluated by considering convectionand radiation losses from the absorber plate in the upward direction. For the purpose ofcalculation, it is assumed that the transparent covers and the absorber plate constitute asystem of infinite parallel surfaces and that the flow of heat is one-dimensional and steady. Itis further assumed that the temperature drop across the thickness of the covers is negligibleand the interaction between the incoming solar radiation absorbed by the covers and theoutgoing loss may be neglected. The outgoing re-radiation is of larger wavelength. For thesewavelengths, the transparent cover is assumed to be opaque.Sukhatme [3] suggested thatheattransferred by convection and radiation at different layers as follows-(a) The absorber plate and the first cover;୯భ୅౦ൌ h୮ିୡଵ൫T୮୫ െ Tୡଵ൯ ൅ σሺ୘౦ౣర ି୘ౙభర ሻଵ஫౦ൗ ାଵ஫ౙൗ ିଵ(8)(b) The two glass covers;୯భ୅౦ൌ hୡଵିୡଶሺTୡଵ െ Tୡଶሻ ൅ σሺ୘ౙభర ି୘ౙమర ሻଵ஫ౙൗ ାଵ஫ౙൗ ିଵ(9)(c) The second glass cover and the sky;୯భ୅౦ൌ hୟሺTୡଶ െ Tୟሻ ൅ σεୡሺTୡଶସെ Tୱ୩୷ସሻ (10)
  • 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME406Sukhatme [3] also suggested the empirical relation for the top loss coefficient as-U୲ ൌ ሾ୑൬ి౐౦ౣ൰ቀ౐౦ౣష౐౗౉శ౜ቁబ.యయ ൅ଵ୦౗ሿିଵ൅ ሾσሺ୘౦ౣమ ା୘౗మሻሺ୘౦ౣା୘౗ሻభε౦శబ.బబఱ౉ሺభషε౦ሻାమ౉శ౜షభεౙି୑] (11)Where, f ൌ ሺ1 െ 0.04hୟ ൅ 0.0005hୟଶሻሺ1 ൅ 0.091ሻMC ൌ 365.9൫1 െ 0.00883β ൅ .0001298βଶ൯M=number of glass covers2.2.5Heat transfer coefficient at the top cover- The convective heat transfer coefficient(hୟ) at the top cover has been calculated from the following empirical correlation suggestedby McAdams [4],hୟ ൌ 5.7 ൅ 3.8V (12)Where, V is the wind speed in m/s.An another important dimensionless correlation have been suggested by Sparrow andhiscoworkers [5] given as,j ൌ 0.86ሺRe୐‫כ‬ ሻିଵ/ଶ; (13)Where, j=j-factor given by୦౗ρେ౦୚Prଶ/ଷRe୐‫כ‬= Reynolds number based on the characteristics dimensionL ൌ 4Aୡ/CୡAୡ=Collector gross areaCୡ=Circumference associated with the collector gross area.2.2.6Sky Temperature- As suggested by Sukhatme [3] Sky temperature is usuallycalculatedfrom empirical relation in which temperature are expressed in KelvinTୱ୩୷ ൌ Tୟ (14)2.2.7Bottom loss coefficient(Ub)-The bottom loss coefficient is calculated by consideringconduction and convection losses from the absorber plate in the downward direction[6]. Itwill be assumed that the heat flow is one dimensional and steady (Fig.7). In most cases, thethickness of thermal insulation is provided such that the thermal resistance associated withconduction dominates. Thus, neglecting the convective resistance at the bottom surface of thecollector casing.Uୠ ൌ K୧/δୠWhere, k୧=Thermal conductivity of the insulationδୠ= Thickness of the insulation.
  • 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME407Figure 7. Bottom and side losses from a flat-plate2.2.8 Side loss coefficient (‫܃‬‫ܛ‬)-The assumptions applied for side loss coefficient isconduction resistance dominates and that the flow of heat is one dimensional and steady state.The one-dimensional approximation can be justified on the grounds that Uୱis always muchsmaller than theU୲.If the dimensions of the absorber plate are L1 x L2 and the height of the collector is L3 andassuming that the average temperature drop across the insulation is (T୮୫ െ Tୟሻ/2 andthethickness of this insulation isδୱ.qୱ ൌ2LଷሺLଵ ൅ Lଶሻk୧ሺT୮୫ െ Tୟሻ2δୱUୱ ൌ2LଷሺLଵ ൅ Lଶሻk୧ሺT୮୫ െ TୟሻLଵLଶδୱ2.3 Governing EquationUnder steady state operating conditions, the energy balance for the conventional andcounter flow collectors as suggested by Mohammad [1] and applying the finite differencemethod on the proposed double-pass flat-pate solar air heaters without and with porous mediawhich are as follows:For top glass cover:G.E:Iαୡ ൌ hୟሺTୡଵ െ Tୟሻ ൅ h୤ୡଵሺTୡଵ െ T୤ଵሻ ൅ h୰.ୡୡሺTୡଵ െ Tୡଶሻ...(15)For down flow air stream:G.D.E.: mcୢ୲౜భୢ୶ൌ h୤ୡଵሺTୡଵ െ T୤ଵሻ ൅ h୤ୡଶሺTୡଶ െ T୤ଵሻ…(16)For second glass coverG.E.:Iαୡτୡ ൌ h୰.ୡୡሺTୡଶ െ Tୡଵሻ ൅ h୤ଵୡଶሺTୡଶ െ T୤ଵሻ ൅ h୤ଶୡଶሺTୡଶ െ T୤ଶሻ ൅ h୰.୮ୡሺTୡଶ െ T୮ሻ…(17)For up follow air stream:G.D.E.: mcୢ୘౜మୢ୶ൌ h୤ଵୡଶሺTୡଶ െ T୤ଶሻ ൅ h୤ଶ୮ሺT୮ െ T୤ଶሻ...(18)
  • 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME408For absorber plate:G.E.: Iα୮τୡ ൌ h୤ଶ୮൫T୮ െ T୤ଶ൯ ൅ h୰.୮ୡ൫T୮ െ Tୡଶ൯ ൅ UୠሺT୮ െ Tୟሻ…(19)Double-pass flat-pate collector with porous mediaFor top glass cover:G.E: Iαୡ ൌ hୟሺTୡଵ െ Tୟሻ ൅ h୤ୡଵሺTୡଵ െ T୤ଵሻ ൅ h୰.ୡୡሺTୡଵ െ Tୡଶሻ...(20)For down flow air stream:G.D.E.: mcୢ୲౜భୢ୶ൌ h୤ୡଵሺTୡଵ െ T୤ଵሻ ൅ h୤ୡଶሺTୡଶ െ T୤ଵሻ…(21)For second glass coverG.E.:Iαୡτୡ ൌ h୰.ୡୡሺTୡଶ െ Tୡଵሻ ൅ h୤ଵୡଶሺTୡଶ െ T୤ଵሻ ൅ h୤ଶୡଶሺTୡଶ െ T୤ଶሻ ൅ h୰.୮ୡሺTୡଶ െ T୮ሻ ...(22)For up flow air stream:G.D.E.:mcୢ୘౜మୢ୶ൌ Kୣ୤୤ୢమ୘౜మୢ୶మ ൅ h୤ଶୡଶሺTୡଶ െ T୤ଶሻ ൅ UୠሺTୟ െ T୤ଶሻ ൅ Iα୮τୡτୡ...(23)For the sake of convenience the heat transfer coefficients between the air stream and thecovers and between the air stream and the absorber plate are assumed equal and can becalculated as follows:h୤ଵୡଵ ൌ h୤ଵୡଶ ൌ h୤ଶୡଶ ൌ h୤ଶ୮ ൌ h୤…(24)The air density: ρ ൌ୔౗ୖ୘౗…(25)Kinematic viscosity: ν ൌµρ…(26)Thermal diffusivity: α ൌ୩ρୡ౦…(27)Prandtl number: P୰ ൌνα…(28)Hydraulic diameter: D୦ ൌସ୅౜୔ൌ 2D…(29)Reynolds number: Rୣ ൌρ୙ୈ౞µൌଶ୫µ…(30)Grashof Number =௚ఉ∆்య௩మ …(31)Nusselt number; Nu ൌ 0.0333 Rୣ଴.଼P୰଴.ଷଷ…(32)
  • 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME409Convective heat transfer coefficient between any two surfacesh୰ଵଶ ൌσሺ୘భା୘మሻሺ୘భమା୘మమሻభεభାభεమିଵ…(33)When the air flows through the channel in the air heater, due to friction the air pressure dropalong the of the flow channel. This pressure drop across the duct is given by the:p ൌ f ቀ୫యρቁ ቀ୐యୈయቁ…(34)Where, f ൌ f଴ ൅ yሺୈ୐) …(3.40)The value of f଴ and y are:f଴=24/Re, y=0.9 for Laminar flow (Re<2550) …(34)f଴ = 0.0094, y =2.92Re-0.15for transitional flow (2550<Re<104) …(35)f଴ = 0.059 Re-0.2, y =0.73 for turbulent flow (104<Re<105) …(36)So far as pressure drop (pumping power) is concerned, the counter flow solar air heater has aU-turn section and extra-length for air passages. Hence the extra pressure drop is introducedby this design. The pressure drop in the u-section can be calculated as:ᇞ p ൌ୏୫మଶρୈమ…(37)K=1forU-sectionThe pumping power can be calculated asW ൌ୫ᇞ୮ρ…(38)3. MODELING AND ANALYSISThe finite difference method (FDM) is used to solve the differential equations andhence to simulate a given solar air heater. In FDM technique, the first step involves thetransformation of the actual physical domain into the computational grid. Second step is totransform the differential equations into difference equations, which along with the equationsobtained by heat balance across the covers and the absorber are the simultaneous nonlinearalgebraic equations. The next step is to solve those numerically using gauss eliminationmethod. The solution is obtained in the form of nodal temperatures for the covers, the airstreams and the absorber. Study has been extended by changing the various governingparameters like the air mass flow rate, the inlet air temperature, the depth of the collector ductand the intensity of solar radiation and finally the performance characteristics have beenobtained. A computer program is developed using Dev C++ programming language based onalgorithm and flow chart.
  • 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME4103.1 Technical SpecificationsInput Parameters and Constants for the proposed model.Sl.No. Input Parameters Values1. Length of solar air heater, L(m) 2.02. Width of solar air heater, w(m) 1.03. Depth of upper channel solar air heater, D1(cm) 4.5,5.5,6.54. Depth of lower channel solar air heater, D2(cm) 4.5,5.5,6.55. Emissivity of glass covers, εୡ 0.926. Emissivity of absorber plate and packed bed,ε୮ 0.927. Transmissivity of glass cover and absorber,߬௖ ‫ݎ݋‬ ߬௣ 0.928. Absorptivity of glass cover,αୡ 0.069. Absorptivity of absorber,α୮ 0.9210. Inlet air temperature, Ti(K) 288,30311. Air mass flow rate per unit width, m (kg/m s) 0.01-.212. Back insulation thickness(m) 0.0513. Side insulation thickness(m) 0.0514. Porosity of Porous medium( Glass wool) 0.815. Plate Type Flat Plate3.2 Proposed ModelThe design of thermal equipment must focus on a combination of numerical andexperimental techniques hence, a three-dimensional numerical model was developed usingthe CFD numerical package FLUENT. The proposed model is modeled by using CATIA V5R19 which is used for analysis by applying boundary conditions. An analysis of proposedmodel is also performed by using CFD package as CFD is concerned with the efficientnumerical solution of the partial differential equations that describe fluid dynamics. A modelfor virtual prototyping of thermal equipment must be detailed enough in order to consider allthe main physical phenomena that are taking place as well as giving results in a reasonablecomputational time. The mesh size is critical for CFD analysis, especially when dealing withnatural convection.3.3 Algorithm for Computer ProgramFollowing steps are involved in the simulation of double pass flat plate solar air heater:Step 1: Enter values of m, L, D, Tୟ, pୟ, R, hୟ, µ, Uୠ, αୡ, α୮, τୡ, σ, c୮, k୤.Step 2: Select the type of heater.Step 3: Calculateν, P୰, Rୣ, N୳, h୤.Step 4: Initialize with T୤ሾ0ሿ ൌ T୧, h୰.ୡୡሾiሿ ൌ 5, h୰.୮ୡሾiሿ ൌ 5 for all i.Step 5: Solving the finite difference equations for a given solar heater to calculate the nodaltemperatures by using the appropriate boundary conditions and gauss elimination method forsolving the simultaneous equations as described above. After that following parameter arecalculated.P ൌ f ቆmଷρቇ ቆLଷDଷቇη ൌmc୮∆TIA
  • 11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME411Step 6: Once all these temperature are obtained, the following performance characteristics areobtained:1. ∆P Vs m2. η vs ܶ௣3. η Vs m4.ୢ୘୍Vs m5. ߟ ܸ‫ݏ‬ௗ்ூFigure 8. 3-D Model of Solar Air HeaterFigure 9. Mesh generation of 3-D Model
  • 12. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME4123.4 Flowchart for the simulation of double pass flat plate solar air heaterStartObtain the following characteristics1. ΔP Vs m2. η vs ܶ௣3. η Vs m4.ୢ୘୍Vs m5. ߟ ܸ‫ݏ‬ௗ்ூEndΔT୥ ൌ maxሺTୡଵሾiሿ െ TୟሻΔܶ௣௙ ൌ max ሺܶ௣ሾ݅ሿ െ ܶ௙ሾ݅ሿሻP ൌ f ቆmଷρቇ ቆLଷDଷቇߟ ൌ݉ܿ௣ሺܶ଴ െ ܶ௜ሻ‫ܫ‬ሺ‫ݔܮ‬ሻ;Obtain:Input the Values of݉, ‫,ܮ‬ ‫,ܦ‬ ܶ௔, ‫݌‬௔, ܴ, ݄௔, ߤ, ܷ௕, ߙ௖, ߙ௣, ߬௖, ߪ, ܿ௣, ݇௙Substituting these values in the set of equations obtained byenergy balance for a given solar air heater and solving themsimultaneous by gauss-elimination method to evaluateTୡଵ, Tୡଶ, T୤ଵ, T୤ଶ and T୮n; ρ; ν; ߙ; ܲ௥; ܴ௘; ܰ‫ݑ‬Calculate
  • 13. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME4134. RESULT AND DISCUSSIONThe majority of the heat transfer occurred at the bottom section of the solar airheater,rather than near the level between the inlet fluid temperature and the fluid insidethesolar air heater.The variation of pressure drop with different mass flow andefficiencywithmass flow rate, plate temperature, solar radiation for both solar air heater without porousand with porous media are shown in graph 10, 11, 12, 13 and 14.The pressure drop increasesin both solar air heater without porous and with porous media with increase in mass flow rate.Figure 10. Variation of Pressure with Mass flow rateFigure 11. Variation of efficiency with Mass flow rate
  • 14. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME414Figure 12. Variation of efficiency with plate temperatureFigure 13. Variation of efficiency with dT/IFigure 14. Variation of dT/I with mass flow rate
  • 15. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME415Figure 15. Variation of Pressure Drop across solar Air HeaterFigure 16. Variation of Air Velocity across Solar Air heater5. CONCLUDING REMARKSThe variations of pressure in solar air heater model with different mass flow rate fornon-porous and porous media are shown in figure 10 for different depth, inlet temperatureand solar radiation. It is concluded that outlet temperature is decreasing with increase in massflow rate. It is found that the use of porous media in lower channel increases the outlettemperature. The use of porous media in solar air heater increases the system efficiency andoutlet temperature. This increase, results an increase in the pressure drop for solar collectorwith porous media, which means increasing of the cost of the pumping power expanded inthe collector. But this factor has no significant for low flow rates.
  • 16. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME416NomenclatureAf-Front AreaCp- Specific heat capacityD-Depth of the ductDh-Hydraulic DiameterL-Length of the ductn1-Refractive indexh-Heat transfer coefficientm- Mass flow ratek- Thermal conductivityI- Intensity of solar radiationU- Overall heat transfer coefficientT- TemperatureV-Ambient Air velocityW-Pumping factorGREEK LETTERS߳-Emissivity߬ -Transmissivityߙ- Absorptivityߚ-Diffusivityߟ- Thermal efficiency߮- Porosityߩ- Extinction coefficient∆Difference of two quantitiesSUBSCRIPTSa- Ambientb- Bottomc- Covere-Effectivef- Fluidp- Packing platet- Top1- First glass cover2- Second glass coverREFERENCE[1]Mohamad.A.A,“High efficiency solar air heater”, solar energy vol.60 No.2, pp.71-76,1997.[2]-Naphonparison,“Effect of porous media on the performance of the double pass flat platesolar air heater”, solar energy, Vol.12 No.1, pp.90-99, 1996[3]Sukhatme S.P., “Solar energy”, 3rd ed., 1984, Tata McGraw Hill, New Delhi.[4] McAdams.W.H, “Heat Transmission”, 3rd ed.., McGraw Hill, New York, 1954.[5] Sparrow, E.M., and Tien, K.K., “Forced convection heat transfer at an inclined and yawedsquare plate application to solar collectors”, Heat transfer, Vol. 99 pp.507-522, 1977
  • 17. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME417[6] Raja shekhar,Y.,Sharma,K.,V.,,Rao,M.,B.,“Evaluation of heat loss coefficients in solarflat plate collectors”,ARPN Journal, Vo. l4,No.5, pp. 15-19,2009.[7] Languri,E.,M.,Taherian, H.,“Enhanced double –pass solar air heater with and withoutporous medium”, International Journal of green Energy, Vol. 8, pp. 643-654,2011.[8] Pradharaj,M.,Velmurugan,V., Moorthy, H., “Review on porous and non-porous flat plateair collector with mirror enclose”, International journal of Engineering and Technology, Vol2pp.4013-4019,2010[9] Yousef.BAA, Adam.NM, “Performance analysis for flat plate collector with and withoutporous media”, Journal of energy in Southern Africa, vol.19 No.4, pp.32-42, 2008.[10] Zhao, Q., Salder, G.W., Leonardo, J.J., “Transient simulation of flat-plate solarcollectors”, Solar Energy, Vol.40, pp.167-174, 1988.[11] Lansing.F.L,Reynold.R, “High performance flat plate solar collector”, solar energyvol.24 No.2, pp.90-99, 1996.[12] Ajay Kumar Kapardar and Dr. R. P. Sharma, “Experimental Investigation of Solar AirHeater using Porous Medium”, International Journal of Mechanical Engineering &Technology (IJMET), Volume 3, Issue 2, 2012, pp. 387 - 396, ISSN Print: 0976 – 6340,ISSN Online: 0976 – 6359.[13] Yogesh C. Dhote and Dr. S.B. Thombre, “Parametric Study on the Thermal Performanceof the Solar Air Heater with Energy Storage”, International Journal of MechanicalEngineering & Technology (IJMET), Volume 3, Issue 1, 2012, pp. 90 - 99, ISSN Print:0976 – 6340, ISSN Online: 0976 – 6359.[14] Ajay Kumar Kapardar and Dr. R. P. Sharma, “Numerical and CFD Based Analysis ofPorous Media Solar Air Heater”, International Journal of Mechanical Engineering &Technology (IJMET), Volume 3, Issue 2, 2012, pp. 374 - 386, ISSN Print: 0976 – 6340,ISSN Online: 0976 – 6359.