SIMULATION OF SOIL TEMPERATURE VARIATION FOR GEOTHERMAL APPLICATIONS

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 8, Issue 2, February 2017, pp. 167–175 Article ID: IJMET_08_02_020
Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=2
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
SIMULATION OF SOIL TEMPERATURE
VARIATION FOR GEOTHERMAL APPLICATIONS
Raviranjan Kumar Singh
Research Scholar, Department of Mechanical Engineering, N.I.T. Jamshedpur, India
R.V. Sharma
Professor, Department of Mechanical Engineering, N.I.T. Jamshedpur, India
ABSTRACT
This paper aims to predict ground temperature variation with depth for time variant
ambient air temperature and solar radiation data for Jamshedpur, India. Fourier series and
CFD techniques have been employed to determine diurnal and annual temperature variation
for the hottest and the coldest day of the year 2015.The diurnal temperature variation is up to
0.2m depth of soil whereas annual temperature variation is up to 3m depth.
Key words: Soil temperature; CFD Simulation; Fourier series.
Cite this Article: Raviranjan Kumar Singh and R.V. Sharma. Simulation of Soil Temperature
Variation for Geothermal Applications. International Journal of Mechanical Engineering and
Technology, 8(2), 2017, pp. 167–175.
http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=8&IType=2
NOMENCLATURE
α Thermal Diffusivity of soil (m2
/s) k Thermal conductivity of soil (W/mK)
α0 Absorptivity of solar radiation at the
surface
T Soil temperature (K)
c Specific heat(J/kgK) Ta Air temperature (K)
ε Emissivity of soil surface Te Effective temperature (K)
h Convective heat transfer coefficient on
the soil surface (W/m2
K)
t Time (s)
ΔR Long-wave radiation (W/m2
) ω 2П/period (rad/s)
ρ Density of ground (kg/m3
) y Vertical axis (m)
S Intensity of solar radiation (W/m2
)
m Number of terms of Fourier series
1. INTRODUCTION
Prediction of soil temperature has important 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 temperature at different depths. The air temperature and solar radiation are the main
meteorological parameters to change the regular periodic variation in thermal regime of the soil. Soni
et al. [1] presented excellent review of research in the area of earth air heat exchangers.

Simulation of Soil Temperature Variation for Geothermal Applications
Khatry et al. [2] presented a technical note for ground temperature variation with depth taking into
account the periodicity of solar radiation and atmospheric temperature for Kuwait. Bharadwaj and
Bansal [3] calculated daily and annual variations of the ground temperature for dry sunlit, wet sunlit,
dry shaded and wet shaded surface conditions at New Delhi. Mihalakakouet.al.[4]and Mihalakakou [5]
estimated ground surface temperature for bare and short-grass covered soil employing Fourier analysis
and validated results by measurements in Athens and Dublin. Ozgeneretal.[6] measured and predicted
temperature of soil at various depths in Izmir, Turkey.
In the present investigation temperature variation of soil for dry sunlit condition has been modeled
employing Fourier as well as CFD techniques for time varying boundary condition for Jamshedpur,
India.
2. MATHEMATICAL FORMULATION
The variation of ground temperature followed one-dimensional, transient heat conduction equation
given by [9].
2
2
( , ) 1 ( , )T y t T y t
y tα
∂ ∂
=
∂ ∂ (1)
Solution of above equation is subjected to the boundary condition at the ground surface given by
[3]:
0 0
0
( )a y
y
T
k h T T R S
y
ε α=
=
∂
− = − − ∆ +
∂
(2)
Left side of above equation shows the conduction through ground surface. First term of right side
equation shows convective heat transfer between ground surface and air. Second term of above
equation is long wave radiation and third term denotes solar radiation absorbed by the ground surface.
The above equation can be written in the form of general convective heat transfer boundary condition
as:
0
0
( )e y
y
T
k h T T
y
=
=
∂
− = −
∂
(3)
The effective temperature Te can be expressed as,
0 / /e aT T S h R hα ε= + − ∆
(4)
2.1. Fourier Analysis
Ambient air temperature Ta and solar radiation intensity Svary periodically which can be expressed as
Fourier series. The effective temperature Te will also be expressed as Fourier series:
0
1
cos( )e m m
m
T a a m tω ψ
∞
=
= + −∑
(5)
The solution of one dimensional heat conduction equation (1) for T to be finite when
y→ ∞ become [9]:
0
1
( , ) exp[ ( ) )m m
m
T y t A A i m t yω α
∞
=
= + +∑
(6)
Where
1/2
(1 )( / 2 )m i cm kα ωρ= − −
(7)

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Substituting for Te and ( , )T y t
obtains [3]:
0
1
m m m
m
T a B m y m t m y
∞
=
= + − − − −∑
Where
[(1 ) ]m mB a m m= + +
1
2
( ) /
2
k cωρ
µ =
1
tan
(1 )
m
m
β −  
=  + 
2.2. CFD Analysis
The ground is considered as semi
dimensional axis-symmetry geometry
workbench. Structured uniform
optimum for simulation. The geometry and mesh of the model are shown in Fig.1. The temperature
field in the soil has been obtaine
convergence criteria set to 10-6
. CFD simulation has been
data for ambient air temperature and solar radiation employing user defined function.
Figure
3. RESULTS AND DISCUSSI
For Fourier and CFD analysis of ground temperature variation, the
its physical properties are assumed
k = 0.51 W/mK, ρ= 2050 Kg/m
α0=0.9, ε=1, ΔR=63.1 W/m2
and h=22.7 W/m
The temperature distribution in the soil
ambient air temperature and solar radiation are continuously
Raviranjan Kumar Singh and R.V. Sharma
IJMET/index.asp 169
( , )T y t from equation (5) and (6) respectively, into the equation (
1/2 1/2
exp( )cos( )m m mT a B m y m t m yα ω α ψ β= + − − − −∑
1/2 2 2 1/2
[(1 ) ]B a m mµ µ −
= + +
( ) / h
1/2
1/2
(1 )
m
m
µ
µ
 
 + 
semi-infinite solid subject to time variant boundary condition.
symmetry geometry of soil 10m depth and 1m radius
uniform mesh size of 0.05m and time step of 5min have been considered
The geometry and mesh of the model are shown in Fig.1. The temperature
field in the soil has been obtained by solving energy equation through
CFD simulation has been run for one year with time variant
temperature and solar radiation employing user defined function.
Figure 1 Geometry and Mesh for CFD analysis
RESULTS AND DISCUSSION
of ground temperature variation, the soil is taken as a homogeneous and
assumed constant as given in [1]:
= 2050 Kg/m3
, cp = 1842.3 J/Kg K
and h=22.7 W/m2
K (at 3 m/s wind speed).
The temperature distribution in the soil depends on the air temperature and solar radiation
ambient air temperature and solar radiation are continuously measured every minute
editor@iaeme.com
into the equation (3), one
exp( )cos( )
(8)
(9)
(10)
(11)
to time variant boundary condition. Two
is created in ANSYS
and time step of 5min have been considered
The geometry and mesh of the model are shown in Fig.1. The temperature
through FLUENT 14.5 with
for one year with time variant hourly
temperature and solar radiation employing user defined function.
soil is taken as a homogeneous and
on the air temperature and solar radiation. Data for
every minute at National

Institute of Technology, Jamshedpur, India [11]. Diurnal variation of hourly ambient air temperature
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 same year is 28 December.
Annual variation of daily average ambient air temperature and solar radiation are shown in Fig.4 and
Fig.5 respectively. These variations can be expressed as Fourier series with six harmonics which are
sufficient for matching all the given data with R2
= 99% approximately. Fourier series coefficients for
ambient air temperature, solar radiation and effective temperature are given in Table 1, Table 2 and
Table 3 respectively.
Figure 2 Hourly ambient air temperature for the hottest day (10th
June) and the coldest day (28th
Dec) 2015 in
Jamshedpur, India
Figure 3 Hourly solar radiation intensity for the hottest day (10th
June) and the coldest day (28th
Dec), 2015 in
Jamshedpur, India

Figure 4 Monthly average ambient air temperature in Jamshedpur, India for year 2015
Figure 5 Monthly average solar radiation intensity in Jamshedpur, India for the year 2015
Table 1 Coefficients of Fourier series for ambient air temperature (Ta) in Jamshedpur, India
0 1 2 3 4 5 6
Annual Am 26.99 4.910976 2.573121 0.916304 0.942657 0.479378 0.517238
ψm -0.08008 0.339793 -0.35989 1.013456 -0.37594 0.104728
Hottest day Am 36.58 5.74124 0.772853 0.73958 0.121835 0.512296 0.138914
ψm 0.949696 -1.27728 -0.02204 -0.7817 -0.7484 0.6251
Coldest day Am 15.11 5.801712 1.907854 1.857241 0.685227 0.234354 0.038269
ψm 1.005455 1.113712 0.398105 1.202187 0.2662 0.039154

Table 2 Coefficients of Fourier series for solar radiation intensity (S) in Jamshedpur, India
0 1 2 3 4 5 6
Annual Am 191.7 34.99706 25.98472 14.50651 5.384759 16.90552 9.964501
ψm -0.93507 0.094001 -1.40186 0.14912 0.428086 -1.35907
Hottest day Am 232.6 376.6289 195.0089 6.141652 21.08999 38.40026 33.88953
ψm 0.012397 0.009574 -1.26192 -0.86124 -0.39115 0.093973
Coldest day Am 153.2 261.5779 155.2413 19.99031 15.2605 24.03611 9.634712
ψm 0.07201 0.126848 -0.18749 0.868574 0.596888 0.578877
Table 3 Coefficients of Fourier series for effective temperature (Te) in Jamshedpur, India
m 0 1 2 3 4 5 6
Annual Am 31.8107 5.915448 3.581173 1.304678 0.905214 1.06062 0.68356
ψm -0.25852 0.269736 -0.75036 0.66965 0.096553 -0.50745
Hottest
day
Am 43.02229 18.88938 7.551657 0.813822 0.957667 2.010426 1.518494
ψm 0.256314 0.107977 -0.29612 -0.85115 -0.48037 0.160371
Coldest
day
Am 18.40427 14.58854 7.380677 2.555577 1.27243 1.119579 0.349717
ψm 0.397331 0.344217 0.225846 1.045844 0.437155 0.635142
Figure. 6 and 7 show variation of soil temperature for the hottest and coldest day respectively.
Results obtained by Fourier series and CFD methods are close. As the depth of soil increases,
amplitude of temperature decreases. After a depth of 0.2m, there is no diurnal variation of soil
temperature.
Figure 6 Variation of soil temperature for the hottest day at various depths

Figure 7 Variation of soil temperature for the coldest day at various depths
Fig. 8 shows annual variation of soil temperature with depth. After a depth of 3m, the soil
temperature becomes constant. Results obtained by both Fourier series and CFD methods are close.
The minor variation is due to input methods. In Fourier series, data for six harmonics are input
whereas CFD simulation is run for monthly data points.
Fig. 9 shows variation of soil temperature depth wise for the hottest day and the coldest day.
Diurnal variation of soil temperature is up to 0.2m whereas annual variation is up to a depth of 3m.
Fig.10 shows variation of heat flux on the ground surface for the hottest day and coldest day of the
year 2015 in Jamshedpur, India. The heat flux is positive during sunny hour and negative for other
time. Net heat transfer during whole day is negligibly small.
Figure 8 Annual variation of soil temperature with depth

Figure 9 Variation soil temperatures 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 temperature variation with depth in Jamshedpur, India
employing Fourier series and CFD methods. Both Fourier series and CFD simulation have been used
for the hottest day (10th
June), the coldest day (28th
December) and whole year 2015. Results obtained
by both methods are close. Diurnal variation of soil temperature is found up to depth of 0.2m whereas
annual variation is up to 3m of depth.

REFERENCES
[1] K.S. Soni, M. Pandey,V. N. Bartaria, Ground coupled heat exchangers: A review and applications,
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(Technical note), Solar Energy20,1978, 425-427.
[3] S.S. Bhardwaj, N.K. Bansal,T emperature distribution inside ground for various surface conditions,
Building and environment 3,1981, 183-192.
[4] G. Mihalakakou, M. Santamouris, J.O. Lewis, F.N. Asimalopolous, On application of the energy
balance equation to predict ground temperature profile, Solar energy 60,1997,181-190.
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[6] O. Ozgenner, L. Ozgener, W.J. Tester, A practical approach to predict soil temperature variation for
geothermal (ground) heat exchanger application, International journal of heat and mass transfer
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[7] R.N. Bracewll, The Fourier Transform and its applications, McGraw-Hill, New York, 1978.
[8] D. Hillel, Introduction to environmental soil physics, Elsevier academic press, 2004.
[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, http://www.cwetsolar.com.
[12] Khayyat, H. A. and Sohail Md. CFD Simulation of Flow Behaviour in Evaporating Unit of a
Window Air-Conditioning System. International Journal of Mechanical Engineering and
Technology, 6 (10), 2015, pp. 243-2 51.
[13] Chandrashekhar R. Suryawanshi, Geothermal Energy; the Eco-Friendly Alternative Source of
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SIMULATION OF SOIL TEMPERATURE VARIATION FOR GEOTHERMAL APPLICATIONS

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