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Accurate heat generation data from batteries and ultracapacitors are essential to properly design thermal management systems. We use a customized large conduction calorimeter to measure heat generation at various rates, temperatures, SOCs, and heat capacities from full-size, multiple-cell battery modules and ultracapacitor stacks. State-of-the-art high-power cyclers cycle the modules in the calorimeter.
Description
Large conduction calorimeter.
This heat-conduction-type calorimeter is based in part on a commercially available isothermal calorimeter (CSC Model 4400 Isothermal Microcalorimeter). Heat conduction calorimeters sense heat flux between the sample and a heat sink, an enclosure that is fabricated with aluminum surrounded by an isothermal bath which contains the sample. If the sample is hotter or colder than the heat sink, heat flows between the heat sink and the sample. In practice, the thermal conductivity of the path between the sample and the heat sink is matched to the expected heat flow to minimize the temperature difference. The temperature of the heat sink is kept constant and the entire calorimeter shielded from its surroundings by a constant-temperature bath. The temperature control of the heat sink (together with proper matching of the thermal conductivity of the path between the sample or measurement cavity and the heat sink) renders a passive isothermal measurement condition.
Calorimeter test chamber.
The measuring unit of the calorimeter comprises a 39 cm L x 21 cm W x 20 cm H aluminum enclosure connected to a large aluminum heat sink via heat flow sensors (semiconductor thermoelectric devices) between the heat sink and the sample cavity. The bath temperature, which operates at -30°C to +60°C, is controlled with a stability of 0.001°C. For calibration purposes, the measuring unit also incorporates electrical heaters that allow for heat input at rates of 1-80 W. The measuring unit is designed so large-gauge leads, which must be connected to the sample battery for charging and discharging experiments, achieve thermal equilibrium. The large gauge leads generate a negligible amount of heat even at very large current. Further, they are attached to the isothermal aluminum enclosure, and have an insignificant impact on the accuracy of heat generation data obtained for battery modules. The battery temperature (internal or surface) in the calorimeter is measured with an accurate platinum resistance temperature device (RTD).
The measurement cavity can be either dry or filled with a dielectric, inert heat-transfer fluid. The air in the dry chamber can be stirred with small fans while the liquid-filled chamber is stirred with constant-speed stirrers to speed heat transfer from samples to the measurement chamber walls. The small amount of heat added for mixing is taken into account. The time response of the calorimeter is not affected by the stirring. However, the improved heat transfer between the sample and the calorimeter will significantly shorten the time required to reach a steady-state response for a battery at constant power. Even under the best circumstances, the time constant for a typical large battery module will be much longer than the response time for the calorimeter.
Read the following to learn more about this unique tool. "A Unique Calorimeter-Cycler for Evaluating High-Power Battery Modules" (PDF 188 KB) Download Acrobat Reader.
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