2.2.1. Cooling Plate Technology

A typical cooling plate is made of a metal plate on which flow paths are machined. The cooling liquid flows along the flow paths absorbing the cells' heat waste and dissipating it through the plate (by means of conduction and convection heat transfer). The factors that influence the efficiency of this technology are the shape and the size of the flow paths, the available contact surface between the coolant and the flow path walls, the type of coolant, the flow rate, and the material of the plates. Cooling plates can be divided into two categories: the ice plates, which show the best performances and are placed between the battery cells, and the cold plates, which have lower performances but are easier to install because they are placed as a floor under the cells. Ice plates are often preferred in BEVs for their high efficiency, but the tight spaces represent a hard challenge. Darcovich et al. [50] compare the two technologies showing what happens to the maximum cell temperature if we change the cell case material and the coolant. They also take into account two different drive cycles: the US06, an urban-like driving-cycle, and the HWY, for cars which drive along the highways. They also obtain the maximum cell temperature and the battery lifetime as a function of a range of values of SOH. They obtain better temperature uniformity with ice plates than with cold plates. The higher the value of the heat transfer coefficient is, the lower the maximum temperature of the battery is for any kind of cell case materials and driving cycles. This means a longer battery lifetime of about 2 years if we consider US06 driving-cycles, 1 year for HWY driving-cycles. Studies about new technologies suitable to improve cold plates' cooling systems have been done on new kinds of channels such as

leaf-like channels [51]. The design project provides four collection channels arranged along diagonal lines where the decrease in the temperature gradient is required. After many simulations on the channels analyzing the influence of width and length ratio, as well as channel thickness, and also investigating the optimum inlet mass-flow rate, optimal values of heat dissipation and power consumption have been found. Leaf-like channels can be helpful in the study of fractal networks for cold plates [51].
