SIMULATION OF SOIL TEMPERATURE VARIATION FOR GEOTHERMAL APPLICATIONS

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volue 8, Issue 2, February 2017, pp Article ID: IJMET_08_02_020 Available online at ISSN Print: and ISSN Online: IAEME Publication SIMULATION OF SOIL TEMPERATURE VARIATION FOR GEOTHERMAL APPLICATIONS Raviranjan Kuar Singh Research Scholar, Departent of Mechanical Engineering, N.I.T. Jashedpur, India R.V. Shara Professor, Departent of Mechanical Engineering, N.I.T. Jashedpur, India ABSTRACT This paper ais to predict ground teperature variation with depth for tie variant abient air teperature and solar radiation data for Jashedpur, India. Fourier series and CFD techniques have been eployed to deterine diurnal and annual teperature variation for the hottest and the coldest day of the year 2015.The diurnal teperature variation is up to 0.2 depth of soil whereas annual teperature variation is up to 3 depth. Key words: Soil teperature; CFD Siulation; Fourier series. Cite this Article: Raviranjan Kuar Singh and R.V. Shara. Siulation of Soil Teperature Variation for Geotheral Applications. International Journal of Mechanical Engineering and Technology, 8(2), 2017, pp NOMENCLATURE α Theral Diffusivity of soil ( 2 /s) k Theral conductivity of soil (W/K) α 0 Absorptivity of solar radiation at the T Soil teperature (K) surface c Specific heat(j/kgk) T a Air teperature (K) ε Eissivity of soil surface T e Effective teperature (K) h Convective heat transfer coefficient on t Tie (s) the soil surface (W/ 2 K) ΔR Long-wave radiation (W/ 2 ) ω 2П/period (rad/s) ρ Density of ground (kg/ 3 ) y Vertical axis () S Intensity of solar radiation (W/ 2 ) Nuber of ters of Fourier series 1. INTRODUCTION Prediction of soil teperature has iportant applications such as the passive heating and cooling of buildings and agricultural greenhouses. For design of earth-to-air heat exchangers it is necessary to know the ground teperature at different depths. The air teperature and solar radiation are the ain eteorological paraeters to change the regular periodic variation in theral regie of the soil. Soni et al. [1] presented excellent review of research in the area of earth air heat exchangers editor@iaee.co

2 Siulation of Soil Teperature Variation for Geotheral Applications Khatry et al. [2] presented a technical note for ground teperature variation with depth taking into account the periodicity of solar radiation and atospheric teperature for Kuwait. Bharadwaj and Bansal [3] calculated daily and annual variations of the ground teperature for dry sunlit, wet sunlit, dry shaded and wet shaded surface conditions at New Delhi. Mihalakakouet.al.[4]and Mihalakakou [5] estiated ground surface teperature for bare and short-grass covered soil eploying Fourier analysis and validated results by easureents in Athens and Dublin. Ozgeneretal.[6] easured and predicted teperature of soil at various depths in Izir, Turkey. In the present investigation teperature variation of soil for dry sunlit condition has been odeled eploying Fourier as well as CFD techniques for tie varying boundary condition for Jashedpur, India. 2. MATHEMATICAL FORMULATION The variation of ground teperature followed one-diensional, transient heat conduction equation given by [9]. 2 T ( y, t) 1 T ( y, t) = 2 y α t (1) Solution of above equation is subjected to the boundary condition at the ground surface given by [3]: T k = h( Ta Ty= 0) ε R + α0s y y= 0 (2) Left side of above equation shows the conduction through ground surface. First ter of right side equation shows convective heat transfer between ground surface and air. Second ter of above equation is long wave radiation and third ter denotes solar radiation absorbed by the ground surface. The above equation can be written in the for of general convective heat transfer boundary condition as: T k = h( Te Ty= 0) y y= 0 The effective teperature T e can be expressed as, Te = Ta + α0 S / h ε R / h 2.1. Fourier Analysis Abient air teperature T a and solar radiation intensity Svary periodically which can be expressed as Fourier series. The effective teperature T e will also be expressed as Fourier series: Te = a0 + a cos( ωt ψ ) = 1 (5) The solution of one diensional heat conduction equation (1) for T to be finite when y becoe [9]: Where T ( y, t) = A + A exp[ i( ωt) + α y) 0 = 1 α = (1 i)( ωρc / 2 k) 1/2 (3) (4) (6) (7) editor@iaee.co

3 Substituting for T e and T( y, t ) fro equation (5) and (6) respectively, into the equation (3), one obtains [3]: Where T a B = 0 + = 1 B [(1 = a + 1 kωρc 2 µ = ( ) / h 2 β 1 = tan Raviranjan Kuar Singh and R.V. Shara exp( α y) cos( ωt α y ψ β ) 1/2 1/2 µ ) + µ ] 1/ /2 1/2 µ 1/2 (1 + µ ) 2.2. CFD Analysis The ground is considered as sei-infinite solid subject to tie variant boundary condition. Two diensional axis-syetry geoetry of soil 10 depth and 1 radius is created in ANSYS workbench. Structured unifor esh size of 0.05 and tie step of 5in have been considered optiu for siulation. The geoetry and esh of the odel are shown in Fig.1. The teperature field in the soil has been obtained by solving energy equation throughh FLUENT 14.5 with convergence criteria set to CFD siulation has been run for one year with tie variant hourly data for abient air teperature and solar radiation eploying user defined function. (8) (9) (10) (11) 3. RESULTS AND DISCUSSION Figure 1 Geoetry and Mesh for CFD analysis For Fourier and CFD analysis of ground teperature variation, the soil is taken as a hoogeneous and its physical properties are assued constant as given in [1]: k = 0.51 W/K, ρ= 2050 Kg/ 3, c p = J/Kg K α 0 =0.9, ε=1, ΔR=63.1 W/ 2 and h=22.7 W/ 2 K (at 3 /s wind speed). The teperature distribution in the soil depends on the air teperature and solar radiation. Data for abient air teperature and solar radiation are continuously easured every inute at National editor@iaee.co

4 Siulation of Soil Teperature Variation for Geotheral Applications Institute of Technology, Jashedpur, India [11]. Diurnal variation of hourly abient air teperature and solar radiation for the hottest day and the coldest day are shown in Fig.2 and Fig.3 respectively. The hottest day for the year 2015 is 10 June whereas coldest day for the sae year is 28 Deceber. Annual variation of daily average abient air teperature and solar radiation are shown in Fig.4 and Fig.5 respectively. These variations can be expressed as Fourier series with six haronics which are sufficient for atching all the given data with R 2 = 99% approxiately. Fourier series coefficients for abient air teperature, solar radiation and effective teperature are given in Table 1, Table 2 and Table 3 respectively. Figure 2 Hourly abient air teperature for the hottest day (10 th June) and the coldest day (28 th Dec) 2015 in Jashedpur, India Figure 3 Hourly solar radiation intensity for the hottest day (10 th June) and the coldest day (28 th Dec), 2015 in Jashedpur, India editor@iaee.co

5 Raviranjan Kuar Singh and R.V. Shara Figure 4 Monthly average abient air teperature in Jashedpur, India for year 2015 Figure 5 Monthly average solar radiation intensity in Jashedpur, India for the year 2015 Table 1 Coefficients of Fourier series for abient air teperature (T a ) in Jashedpur, India Annual A ψ Hottest day A ψ Coldest day A ψ editor@iaee.co

6 Siulation of Soil Teperature Variation for Geotheral Applications Table 2 Coefficients of Fourier series for solar radiation intensity (S) in Jashedpur, India Annual A ψ Hottest day A ψ Coldest day A ψ Table 3 Coefficients of Fourier series for effective teperature (Te) in Jashedpur, India Annual A Hottest day Coldest day ψ A ψ A ψ Figure. 6 and 7 show variation of soil teperature for the hottest and coldest day respectively. Results obtained by Fourier series and CFD ethods are close. As the depth of soil increases, aplitude of teperature decreases. After a depth of 0.2, there is no diurnal variation of soil teperature. Figure 6 Variation of soil teperature for the hottest day at various depths editor@iaee.co

7 Raviranjan Kuar Singh and R.V. Shara Figure 7 Variation of soil teperature for the coldest day at various depths Fig. 8 shows annual variation of soil teperature with depth. After a depth of 3, the soil teperature becoes constant. Results obtained by both Fourier series and CFD ethods are close. The inor variation is due to input ethods. In Fourier series, data for six haronics are input whereas CFD siulation is run for onthly data points. Fig. 9 shows variation of soil teperature depth wise for the hottest day and the coldest day. Diurnal variation of soil teperature is up to 0.2 whereas annual variation is up to a depth of 3. Fig.10 shows variation of heat flux on the ground surface for the hottest day and coldest day of the year 2015 in Jashedpur, India. The heat flux is positive during sunny hour and negative for other tie. Net heat transfer during whole day is negligibly sall. Figure 8 Annual variation of soil teperature with depth editor@iaee.co

8 Siulation of Soil Teperature Variation for Geotheral Applications Figure 9 Variation soil teperatures with depth for the hottest and the coldest day Figure 10 Variation of heat flux over ground surface for the hottest and the coldest day 4. CONCLUSIONS The present investigation reports results of soil teperature variation with depth in Jashedpur, India eploying Fourier series and CFD ethods. Both Fourier series and CFD siulation have been used for the hottest day (10 th June), the coldest day (28 th Deceber) and whole year Results obtained by both ethods are close. Diurnal variation of soil teperature is found up to depth of 0.2 whereas annual variation is up to 3 of depth editor@iaee.co

9 REFERENCES Raviranjan Kuar Singh and R.V. Shara [1] K.S. Soni, M. Pandey,V. N. Bartaria, Ground coupled heat exchangers: A review and applications, Renewable and Sustainable Energy Reviews 47,2015, [2] A.K.Khatry, M.S. Sodha, M.A.S. Malik, Periodic variation of ground teperature with depth (Technical note), Solar Energy20,1978, [3] S.S. Bhardwaj, N.K. Bansal,T eperature distribution inside ground for various surface conditions, Building and environent 3,1981, [4] G. Mihalakakou, M. Santaouris, J.O. Lewis, F.N. Asialopolous, On application of the energy balance equation to predict ground teperature profile, Solar energy 60,1997, [5] G. Mihalakakou,On estiation soil teperature profile, Energy and building 34,2002, [6] O. Ozgenner, L. Ozgener, W.J. Tester, A practical approach to predict soil teperature variation for geotheral (ground) heat exchanger application, International journal of heat and ass transfer 62,2013, [7] R.N. Bracewll, The Fourier Transfor and its applications, McGraw-Hill, New York, [8] D. Hillel, Introduction to environental soil physics, Elsevier acadeic press, [9] H.S. Carslaw, J.C. Jaeger, Conduction of Heat in Solid, Oxford Science Publication,1980. [10] ANSYS, ANSYS Fluent User s Guide Release 14.5, 2012 [11] National Institute of Wind Energy India, [12] Khayyat, H. A. and Sohail Md. CFD Siulation of Flow Behaviour in Evaporating Unit of a Window Air-Conditioning Syste. International Journal of Mechanical Engineering and Technology, 6 (10), 2015, pp [13] Chandrashekhar R. Suryawanshi, Geotheral Energy; the Eco-Friendly Alternative Source of Energy. International Journal of Advanced Research in Engineering and Technology, 4 (2), 2013, pp editor@iaee.co