Research Papers

Analysis and Testing of a Portable Thermal Battery

[+] Author and Article Information
Robert A. Taylor, Evatt R. Hawkes

School of Mechanical
and Manufacturing Engineering,
University of New South Wales,
Sydney, NSW 2052, Australia;
School of Photovoltaic
and Renewable Energy Engineering,
University of New South Wales,
Sydney, NSW 2052, Australia

Chia-Yang Chung, Karl Morrison

School of Mechanical
and Manufacturing Engineering,
University of New South Wales,
Sydney, NSW 2052, Australia

Manuscript received August 11, 2013; final manuscript received November 21, 2013; published online January 31, 2014. Assoc. Editor: Hongbin Ma.

J. Thermal Sci. Eng. Appl 6(3), 031004 (Jan 31, 2014) (8 pages) Paper No: TSEA-13-1136; doi: 10.1115/1.4026092 History: Received August 11, 2013; Revised November 21, 2013

Portable energy storage will be a key challenge if electric vehicles (EVs) become a large part of our future transportation system. A big barrier to market uptake for EVs is driving range. Range can be further limited if heating and air conditioning systems are powered by the EV's batteries. The use of electricity for HVAC can be minimized if a thermal storage system, a “thermal battery,” can be substituted as the energy source to provide sufficient cabin heating and cooling. The aim of this project was to model, design, and fabricate a low-cost, modular thermal battery for EVs. The constructed thermal battery employs a phase change material erythritol (a sugar alcohol commonly used as artificial sweetener) as the storage medium sealed in an insulated, stainless steel container. At a total prototype cost of ∼$311/kW-h, the system is roughly half the price of lithium ion batteries. Heat exchange to the thermal battery is accomplished via water (or low viscosity engine oil), which is pumped through a helical winding of copper tubing. A computational fluid dynamics (CFD) model was used to determine the geometry (winding radius and number of coils) and flow conditions necessary to create adequate heat transfer. Testing of the fabricated design indicates that the prototype thermal battery module can store enough heat and discharge it fast enough to meet the demand of cruising passenger vehicle for up to 1 h on a cold day. The battery is capable of storing nearly 100 W-h/kg and can provide a specific power density of 30 W/kg. The storage density is competitive with lithium ion batteries, but work is needed to improve the power density.

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Fig. 1

Breakdown of EV energy losses at cruising speed-data from Ref. [2]

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Fig. 2

Battery prototype test—(a) coiled copper tubing, (b) final insulated thermal battery design, and (c) thermocouple locations

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Fig. 3

Mesh of the thermal battery—(a) coiled copper tubing, (b) full mesh geometry (∼0.9 × 106 elements), and (c) zoomed view of mesh reduction around tubes

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Fig. 4

Schematic diagram of the experimental test loop

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Fig. 5

Temperature variation with time at various locations (error is ±1 °C)

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Fig. 6

Temperature variation inside the thermal battery (error is ±1 °C)

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Fig. 7

Thermal battery comparison on a Ragone chart—data from US Defense Logistics Agency [25]




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