ISSN Online: 2377-424X
ISBN Print: 978-1-56700-421-2
International Heat Transfer Conference 15
Heat Transfer in Latent Heat Thermal Energy Storage Device for Automobile Applications
Abstract
Thermal Energy Storage (TES) devices can be utilized to provide heat during engine warm-up in cold weather
which would reduce fuel consumption and greenhouse gas emissions in automobiles. A TES device could be
charged from an engine's waste heat during normal operation. In this work, a latent heat TES device has been
designed, constructed and tested to investigate waste heat recovery and reduction of engine warm-up time by
using phase change materials (PCMs) as a thermal energy storage (TES) medium. Two types of paraffin waxes
with melting points of 70 and 83 °C, and a 50/50 mixture have been examined to characterize their behaviors
under repetitive heating/freezing cycles. The paraffin was placed in a rectangular container and hot or cold water
was circulated through thin cooling plates, which were placed in the container at regular spacing. Thin aluminum
fins were also placed between the cooling plates to increase heat transfer inside the paraffin. In the experiments,
temperature variations in the paraffin and at the water inlet and outlet were recorded for a period of five minutes.
From the experimental results, the fins enhanced heat transfer for both narrow and wide plate spacing, but the
enhancement was more significant for the wider plate spacing. The efficiency of heat recovery was also
positively correlated to the high circulating flow rate of the cold water and the use of a 50/50 mixture of the two
paraffin waxes. An overall heat transfer coefficient was evaluated from the heat transfer rate and the temperature
difference between the average water and paraffin temperatures. The product of the overall heat transfer
coefficient and plate surface area was found to nearly double by inserting the thin aluminum fins. In five
minutes, the total heat recovered from 3.6 kg of paraffin ranged from 600 to 1,000 kJ, depending on the water
flow rate and plate spacing. Finally, experiments were conducted to heat up an aluminum block weighing 30 kg
which simulated a common engine block. The aluminum block was heated up from 0 °C by water circulating
through multiple TES containers containing 3.6 kg of paraffin each. In five minutes, the aluminum block's
temperature could be increased by 30, 34 and 42 °C, using 2, 3 and 4 TES containers, respectively. The results of
these engine block heat-up simulation experiments demonstrated the potential of the latent heat TES device for
use in engine warm-up during a winter season.