A comparison of parallel and colliding jet arrays in a compact vapour compression heat sink for electronics cooling

Highlights: • Different spray schemes are compared in the same compact vapour compression system. • Spray interaction and liquid film evaporation is evaluated via high-speed imaging. • Comparison is based on heat transfer coefficient (HTC) and critical heat flux (CHF). • The 9.84-mm high, 5-parallel jet scheme presented the highest HTC (29 kW/m²K). • The 23.84-mm high, 3-colliding jet scheme presented the highest CHF (41.6 W/cm²). The present work compares the cooling performances of two different multiple orifice spray cooling strategies driven by a compact R-134a vapour compression loop equipped with a small-scale oil-free linear compressor. The strategies – an array of parallel sprays that impinge at a 90° with the heated surface and an array of oblique jets that collide against each other to form an impinging spray cone – are compared in terms of the number of orifices in the array, nozzle-to-surface distance, inter-nozzle distance, thermal load and temperature of the heat rejection medium. The comparisons are made for equivalent orifice flow restrictions and the same mass flow rate of 1.36 g/s at the lowest thermal load. For a hot end temperature of 25 °C, a maximum average heat transfer coefficient of 29.0 kW/m²K was achieved with a 5-parallel spray configuration with a 9.84-mm nozzle-to-surface distance. The maximum heat flux sustained by the system, 41.6 W/cm², was achieved with a 3-colliding jet scheme with a nozzle-to-surface distance of 23.84 mm. To shed some light on the underlying heat transfer mechanisms, images extracted from high-speed video are used to show the interaction between the droplets, the liquid film and the heated surface. The refrigeration system performance parameters, such as the coefficient of performance and the compressor electrical power consumption are mildly affected by the spray characteristics.