Experimental study on a channel-embedded sensible thermal energy storage unit with the heat storage body immersed in heat-conducting oil

ABSTRACT

In order to study the feasibility of a liquid working medium working in a solid heat storage body, this paper experimentally studied a novel pilot-scale sensible thermal energy storage unit (STESU) with a channel-embedded solid thermal energy storage body (STESB). The material of the body with fluid channels is corundum castable, and the heat-conducting oil works as a heat-transfer medium. While working, the heat-conducting oil flows through the fluid channels of the solid thermal energy storage body, and the oil submerges the body for convection heat exchange in the unit. The charging experiments under different flow rates were carried out to evaluate the thermal performance of the heat storage unit, including temperature, power, and efficiency. The results indicate that the unit’s thermal energy storage capacity is about 1.054 × 10⁶ kJ. When the flow rate increases from 2.0 kg · s⁻¹ to 2.8 kg · s⁻¹, the heat storage power increases from 71.90 kW to 90.58 kW, the total heat transfer area and heat transfer coefficient increases from 3.29 to 3.60 W/K, and the working efficiency of the charge-discharge cycle is 95.6%, which indicates that the thermal performance of the unit is better than that of heat storage unit which uses air as the heat transfer working medium.

KEYWORDS:

• Sensible heat storage unit
• Channel-embedded solid heat storage body
• Heat-conducting oil
• Contact heat transfer directly
• Energy efficiency

Nomenclature

$c_p$	=	HTF’sspecific heat (kJ/kg.℃)
$\mathit{E}$	=	Total heat input or absorbed by the HTF in the STESB (kJ)
$\mathit{Qcha}.\mathit{oil}$	=	Energy stored by the oil of STESU during charging (kJ)
$\mathit{Qcha}.\mathit{storage}$	=	Energy stored by STESB during charging (kJ)
$\mathit{Qdis}.\mathit{storage}$	=	Energy released by STESB during discharging (kJ)
$\mathit{Qdis}.\mathit{oil}$	=	Energy released by the oil of STESU during discharging (kJ)
$\mathit{Qcha}.\mathit{lose}$	=	Heat loss in the charging (kJ)
$\mathit{Qdis}.\mathit{lose}$	=	Heat loss in the discharging (kJ)
$Q_o\mathit{il}$	=	Heat stored in the HTF (kJ)
$q_m$	=	Mass flowrate (kg/s)
$\mathit{cp}.\mathit{solid}$	=	STESB ’s specific heat (KJ/m3.°C)
$\mathit{V}$	=	Volume (m3)
$\mathit{P}$	=	Average charging power (kW)
$q_v$	=	Volumetric flowrate (m3/s)
T	=	Temperature (°C)
t	=	Time (minute)
UA	=	Total HTC and the HTA
Acronyms	=
STESB	=	Solid thermal energy storage body
STESU	=	Sensible thermal energy storage unit
TESS	=	Thermal energy storage system
HTC	=	Heat transfer coefficient (W/m2 °C)
HTA	=	Heat transfer area (m2)
HTF	=	Heat transfer fluid
Subscripts	=
cha	=	Charging process
dis	=	Discharging process
in	=	Inlet
out	=	Outlet
Greek symbols	=
$\mathit{\gamma }$	=	Working efficiency
$\mathit{\epsilon }$	=	Effectiveness
ρ	=	HTF’s density (kg/m3)
$\mathit{\eta }$	=	Thermal efficiency

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [52036008].

Notes on contributors

Fangzheng Cheng

Fang Zheng Cheng is a postgraduate student at the State Key Laboratory of Clean Energy Utilization at Zhejiang University. He has been working on energy-efficient and clean utilization, including energy conversion, storage, heat, and mass transfer.

Yang Zou

Yang Zou currently works at Shanghai Boiler Co., LTD. He has rich experience in heat and mass transfer and heat storage.

Yifan Zhu

Yifan Zhu works at the State Key Laboratory of Clean Energy Utilization, Zhejiang University. He has rich experience in the field of clean energy utilization.

Xinyi Wang

Xinyi Wang currently works at Shanghai Boiler Co., LTD. He has rich experience in heat and mass transfer and heat storage.

Bida Xie

Bida Xie works at the State Key Laboratory of Clean Energy Utilization of Zhejiang University. He has rich experience in clean energy utilization.

Yan Rong

Yan Rong is a postgraduate student at the State Key Laboratory of Clean Energy Utilization at Zhejiang University, focusing on researching beneficial energy storage.

Xinfeng Yu

Xinfeng Yu is a postgraduate student at the State Key Laboratory of Clean Energy Utilization of Zhejiang University, dedicated to research on clean energy utilization.

Hao Zhou

Hao Zhou is a professor at Zhejiang University and a winner of the National Outstanding Youth Fund of China. He has made fruitful achievements in the fields of energy conservation and emission reduction, energy carbon neutrality, oil and gas combustion vibration, solar power generation, heat storage and energy storage, steel low-carbon technology, micro-flow, complex system parameter measurement simulation and optimization.