246
K. Mekrisuh et al.
the entire system to acquire high total melting time of PCM. This issue is addressed
differently by various researchers. Akgün et al. [2] studied this effect through the
modification of storage geometry by making the outermost surface of the PCM
domain tilt 5° angle to achieve greater area at the top region than the lower region.
They concluded that the 5° inclination leads to a 20% decrease in total melting time of
PCM when compared with 0° inclination. Mahdi et al. [3] addressed this issue while
studying horizontal triplex tube TES system by incorporating longer longitudinal fins
toward the bottom region where the melting rate is slower. Further, the same author
has reported that introducing more number of fins in the bottom region has better
enhancement compared to fins placed in the upper region [4]. Singh et al. [5] reported
a novel fin design of vertical shell and tube TES. The novel fin design introduced in the
PCM domain is of decreasing fin height along the length of the TES system (longer
at the bottom, shorter at the top). It resulted in 16% reduction in total melting time
of PCM. As the HTF leaves the TES system with a decreased temperature during
the charging of PCM, PCMs of different melting temperatures are employed and
contained in the order of their decreasing melting temperature along the flow direction
(Cascade system). One of the early studies on such systems has been reported by Farid
and Kanzawa [6]. They have investigated the performance of a TES system filled
with PCM. Multiple PCMs of different melting temperatures have shown significant
difference in charging/discharging rates of the TES system. Extensive investigations
on this method were performed. Fang and Chen [7] numerically investigated such
system on melt fraction, thermal energy stored and HTF outlet temperature. They
concluded that there exists an optimum proportion of multiple PCMs besides their
melting temperature difference which plays an important role in obtaining the best
charging rate of a thermal storage system. Adine and Qarnia [8] numerically analyzed
the thermal behavior of the storage system filled with two different PCMs of melting
temperatures 50 and 27.7 °C at various HTF inlet temperatures (55–65 °C), HTF
mass flow rate (10
–4 to 10
–2 kg/s) and proportion of PCM mass. They concluded that
with the HTF mass flow rate of 10
–3 kg/s, TES is more efficient at a low HTF inlet
temperature of 55 °C. Li et al. [9] investigated the horizontal shell- and tube-type
TES system using three different PCMs of high melting temperatures. The domain
size for this different PCM within the storage system was suggested based on total
melting time of the PCM.
To address the issue of late melting of PCM situated at the lower portion of
a vertically oriented shell- and tube-type PCM-based TES system, a partition is
introduced in the PCM domain which divides the PCM domain into the upper and
lower (or inner and outer) zones. As natural convection plays a major role during
the melting of PCM, providing partition will achieve two circulation zones and may
result in more uniform melting in the entire PCM domain. The optimum proportion of
PCM mass in each zone is to be analyzed for the same storage capacity and operating
conditions. This is said to achieve when the complete melting of PCM of each zone
takes place at the same time. Considering this, effect of the location of the partition
in the PCM domain is investigated in the present work. This study is important as it
aims to control overcharging of PCM located at the top region due to early melting
than at the bottom region of the TES system as identified from the previous study
K. Mekrisuh et al.
the entire system to acquire high total melting time of PCM. This issue is addressed
differently by various researchers. Akgün et al. [2] studied this effect through the
modification of storage geometry by making the outermost surface of the PCM
domain tilt 5° angle to achieve greater area at the top region than the lower region.
They concluded that the 5° inclination leads to a 20% decrease in total melting time of
PCM when compared with 0° inclination. Mahdi et al. [3] addressed this issue while
studying horizontal triplex tube TES system by incorporating longer longitudinal fins
toward the bottom region where the melting rate is slower. Further, the same author
has reported that introducing more number of fins in the bottom region has better
enhancement compared to fins placed in the upper region [4]. Singh et al. [5] reported
a novel fin design of vertical shell and tube TES. The novel fin design introduced in the
PCM domain is of decreasing fin height along the length of the TES system (longer
at the bottom, shorter at the top). It resulted in 16% reduction in total melting time
of PCM. As the HTF leaves the TES system with a decreased temperature during
the charging of PCM, PCMs of different melting temperatures are employed and
contained in the order of their decreasing melting temperature along the flow direction
(Cascade system). One of the early studies on such systems has been reported by Farid
and Kanzawa [6]. They have investigated the performance of a TES system filled
with PCM. Multiple PCMs of different melting temperatures have shown significant
difference in charging/discharging rates of the TES system. Extensive investigations
on this method were performed. Fang and Chen [7] numerically investigated such
system on melt fraction, thermal energy stored and HTF outlet temperature. They
concluded that there exists an optimum proportion of multiple PCMs besides their
melting temperature difference which plays an important role in obtaining the best
charging rate of a thermal storage system. Adine and Qarnia [8] numerically analyzed
the thermal behavior of the storage system filled with two different PCMs of melting
temperatures 50 and 27.7 °C at various HTF inlet temperatures (55–65 °C), HTF
mass flow rate (10
–4 to 10
–2 kg/s) and proportion of PCM mass. They concluded that
with the HTF mass flow rate of 10
–3 kg/s, TES is more efficient at a low HTF inlet
temperature of 55 °C. Li et al. [9] investigated the horizontal shell- and tube-type
TES system using three different PCMs of high melting temperatures. The domain
size for this different PCM within the storage system was suggested based on total
melting time of the PCM.
To address the issue of late melting of PCM situated at the lower portion of
a vertically oriented shell- and tube-type PCM-based TES system, a partition is
introduced in the PCM domain which divides the PCM domain into the upper and
lower (or inner and outer) zones. As natural convection plays a major role during
the melting of PCM, providing partition will achieve two circulation zones and may
result in more uniform melting in the entire PCM domain. The optimum proportion of
PCM mass in each zone is to be analyzed for the same storage capacity and operating
conditions. This is said to achieve when the complete melting of PCM of each zone
takes place at the same time. Considering this, effect of the location of the partition
in the PCM domain is investigated in the present work. This study is important as it
aims to control overcharging of PCM located at the top region due to early melting
than at the bottom region of the TES system as identified from the previous study