Analysis and optimization of air coolers using multiple-stage thermoelectric modules arranged in counter-current flow

•Counter-flow arrangement of Peltier modules increases system efficiency.•Optimal number of modules was calculated as a function of thermal load.•Splitting each stream into parallel channels further improves the COP.•COP of counter-flow arrangement is higher than ideal COP of cascade unit. We evaluate the thermal behavior of a thermoelectric cooler composed of Peltier modules connected in series by two air streams in counter-current flow, i.e., in the so-called horizontal stack configuration. An advantage of this configuration over cascade (pyramid-like, or vertical stack) arrangements to achieve large temperature spans is the comparatively higher coefficients of performance of the former at large values of heating load and temperature span. In the counter-flow configuration, the temperature span per Peltier module is relatively small, giving rise to much higher individual (i.e., per module) coefficients of performance. In this paper, we outline a procedure to determine the optimal number of modules in a counter-current flow unit as a function of the applied thermal load (up to approximately 200 W), considering all relevant loss mechanisms (Joule heating and heat conduction in the semiconductors and fluid friction). Pin-fin heat sinks are employed to reduce the fluid-surface temperature differences on the hot and cold sides of the thermoelectric modules. An assessment of the influence of the number of parallel channels on each stream (hot or cold) was also carried out.