Comparative analysis and optimization of one- and two-stage cooling systems with thermoelectric cells with respect to supercooling

The paper discusses issues related to the modelling of a cooling system equipped with thermoelectric modules to achieve the lowest possible temperature of the cooled space. Considerations were made for both the steady state and the momentary capability to reach the lowest possible temperatures. The analysis concerns modules arranged as the in-series thermal connection in a sandwich configuration and the parallel connection in a single layer. It was assumed that in each case the modules worked with identical heat exchangers. Optimal sizes were found for the modules in each of the analysed configurations, both considering and omitting in the model the thermal resistance between the system elements. Taking resistance into account results in an almost 50% increase in the module dimensions to 90/250, compared to 60/170, and also in the minimum temperature rise by even up to 20K. Inducing higher currents in the circuits of the modules can cause momentary supercooling of the cold heat reservoir significantly below the temperature achievable in the steady state. The highest values of momentary drops in temperature can be achieved through current pulse in the circuits, and also for higher thermal capacities of the upper and additional internal reservoir in a sandwich system. To determine optimal supply currents for the modules, optimization was carried out. In the considered configurations this made it possible to achieve momentary supercooling temperatures by about 18K lower compared to the steady state. The most essential design variables are the number of thermoelectric legs, the shape of the thermal capacity of the current pulse shape and the internal reservoir.