250
K. Mekrisuh et al.
considered constant at 368 K. All the outer walls of the storage system are considered
adiabatic. PCM is considered to be in the solid state initially with its temperature
well below its solidus temperature (i.e. 298 K). Initial and boundary conditions are
expressed mathematically as below:
T (r, z, 0) = T i
(7)
T (r, Z , t) = T in (0 ≤ r ≤ r i )
(8)
dT (0, z, t)
dr
= 0 (0 ≤ z ≤ Z )
(9)
3.2 Solution Procedure
In the present work, two-dimensional axisymmetric geometry of the TES system as
shown in Fig. 1 is considered. Commercial software, Ansys ICEM, is used for geometry modeling and meshing of the computational domain. The governing equations,
Eqs. (1)–(6), are solved considering the following schemes: SIMPLE algorithm is
utilized for the pressure–velocity coupling, energy and momentum equations are
discretized using the QUICK differencing scheme and PRESTO scheme is used for
the pressure correction. The under-relaxation factors for pressure, momentum, energy
and liquid fraction are taken as 0.3, 0.7, 1.0 and 0.9, respectively. The convergence
criteria for the continuity and momentum equations are taken as 10
–6 , and for energy
equation as 10
–8 .
4 Model Validation and Independence Study
Numerical model used in the study has been validated with the experimental study
of Agyenim et al. [13]. The experiments [13] were performed on the TES system
with Erythritol (PCM) filled in the annular space and silicon oil at 140 °C flowing
in a tube of 0.051 m diameter at a mass flow rate of 30 kg/min. HTF flow was in the
laminar regime. Numerically obtained average temperature of PCM in the present
study was found to be in good agreement with the reported experimental data [13]
with just 1.76% deviation.
The reliability of the numerical result with least possible computational time
is ensured by conducting detailed grid and time step size independence studies.
The results of the base case considered in the present study are discussed as far
as independence study is concerned. For brevity, the results corresponding to other
cases are not discussed here. Grid independence study is performed with the time
K. Mekrisuh et al.
considered constant at 368 K. All the outer walls of the storage system are considered
adiabatic. PCM is considered to be in the solid state initially with its temperature
well below its solidus temperature (i.e. 298 K). Initial and boundary conditions are
expressed mathematically as below:
T (r, z, 0) = T i
(7)
T (r, Z , t) = T in (0 ≤ r ≤ r i )
(8)
dT (0, z, t)
dr
= 0 (0 ≤ z ≤ Z )
(9)
3.2 Solution Procedure
In the present work, two-dimensional axisymmetric geometry of the TES system as
shown in Fig. 1 is considered. Commercial software, Ansys ICEM, is used for geometry modeling and meshing of the computational domain. The governing equations,
Eqs. (1)–(6), are solved considering the following schemes: SIMPLE algorithm is
utilized for the pressure–velocity coupling, energy and momentum equations are
discretized using the QUICK differencing scheme and PRESTO scheme is used for
the pressure correction. The under-relaxation factors for pressure, momentum, energy
and liquid fraction are taken as 0.3, 0.7, 1.0 and 0.9, respectively. The convergence
criteria for the continuity and momentum equations are taken as 10
–6 , and for energy
equation as 10
–8 .
4 Model Validation and Independence Study
Numerical model used in the study has been validated with the experimental study
of Agyenim et al. [13]. The experiments [13] were performed on the TES system
with Erythritol (PCM) filled in the annular space and silicon oil at 140 °C flowing
in a tube of 0.051 m diameter at a mass flow rate of 30 kg/min. HTF flow was in the
laminar regime. Numerically obtained average temperature of PCM in the present
study was found to be in good agreement with the reported experimental data [13]
with just 1.76% deviation.
The reliability of the numerical result with least possible computational time
is ensured by conducting detailed grid and time step size independence studies.
The results of the base case considered in the present study are discussed as far
as independence study is concerned. For brevity, the results corresponding to other
cases are not discussed here. Grid independence study is performed with the time