Performance investigation of lab-scale sensible heat storage prototypes

ABSTRACT

This paper presents the performance investigation of three lab-scale solid sensible heat storage (SHS) prototypes. The prototypes analyzed are of shell-and-tube type configuration, in which the SHS material is kept in the shell region and the heat transfer fluid (HTF) is allowed to pass through the tubes. Thermal performances such as complete and effective charging/discharging times, and energy storage/retrieval rate of three different prototypes viz., cast steel prototype (termed as M1), concrete prototype with copper finned tubes (termed as M2) and concrete prototype with mild steel finned tubes (termed as M3) designed for a storage capacity of 15 MJ each are studied. The thermal gradient (∆T) between the heat transfer fluid (HTF) and the storage prototype is fixed as 60 K (for M1) and 80 K (for M2 & M3). The performance of the heat storage prototype is simulated employing a finite element based 3-D mathematical model and solved using COMSOL Multiphysics 4.3a. The developed model is validated with the experimentally measured temperature data extracted from the in-house lab scale experimental prototype. The charging/discharging time of the cast steel (M1) prototype in the temperature range of 353–413 K is 1106/1572 s. The effective charging/discharging time of the concrete prototypes, M2 and M3 in the temperature range of 353–423 K are 4371/5196 s and 6155/6360 s, respectively. The total amount of energy stored/retrieved in M1 and M2/M3 prototypes at the respective charging/discharging times are 15 MJ and 14.06 MJ, respectively.

KEYWORDS:

• Sensible heat storage
• solid storage media
• thermal modeling
• heat transfer enhancement
• performance investigations

Nomenclature

a	=	Center-to-center distance between the adjacent HTF tubes (m)
b	=	Thickness of the fins (m)
$C_{ps}$	=	Specific heat of the solid SHS material (J kg−1 K−1)
$C_{pf}$	=	Specific heat of the HTF (J kg−1 K−1)
d	=	HTF tube’s internal diameter (m)
D	=	Diameter of the storage prototype (m)
h	=	Height of the fins (m)
$k_s$	=	Thermal conductivity of the storage material (W m−1 K−1)
L	=	Length of the SHS prototype (m)
n	=	Number of HTF tubes
$n_{fin}$	=	Number of fins on a HTF tube
Q	=	Thermal storage capacity (J)
t	=	Charging / discharging time (s)
$T_{ch}$	=	Average temperature of the SHS prototype during charging (K)
$T_{ini}$	=	Initial temperature of the storage prototype (K)
$T_{inlet}$	=	Inlet temperature of the HTF (K)
$T_{outlet}$	=	Outlet Temperature of the HTF (K)
$\overrightarrow{v}$	=	Velocity of the HTF (m s−1)
V	=	Volume of the storage material in the SHS prototype (m3)
${\rho }_s$	=	Density of the solid SHS material (kg m−3)
${\rho }_f$	=	Density of the HTF (kg m−3)
µ	=	Dynamic viscosity of the HTF (N s m−2)

Acknowledgments

The authors express their gratitude to the Department of Science and Technology, Government of India, for their financial support (Project No: DST/TMD/SERI/D12(C)).

Highlights

• Performance investigations of the sensible heat storage prototypes are presented.

• Concrete, cast iron and cast steel are considered as storage materials.

• Heat transfer augmentation for concrete SHS prototypes is applied.

• Heat storage prototype performance is simulated using COMSOL Multiphysics 4.3a.

• Numerically predicted results match well with the experimental data.

Additional information

Funding

This work was supported by the Department of Science and Technology (DST), Government of India [DST/TMD/SERI/D12].