• Energy Research

Thermal management in integrated chips is one of the major challenges on micro- and nanoelectronics. The rise of power density raised the need for microchannel liquid cooling solutions. This technology has poor temperature uniformity and requires high pumping powers. In this work, a cooling scheme aiming for high temperature uniformity and low pumping power is numerically studied. The cooling scheme consists in a matrix of microfluidic cells with thermally activated microvalves, which tailor the local coolant flow rates to avoid overcooling and improve the temperature uniformity. This system is assessed with steady state CFD studies combined with temporal integration in a time dependent and non-uniform heat load scenario. The studied cooling scheme improves, with respect to existing devices for similar applications, the chip temperature uniformity while reducing the pumping power by 50%. The research leading to these results has been performed within the STREAMS project and received funding from the European Community's Horizon 2020 program under Grant Agreement No. 688564.

Abstract Current technologies for the cooling of high power integrated circuits (IC) chips employ single-phase liquid flow through microchannel heat sinks. The surface temperature in these devices increases along the flow direction, leading to temperature nonuniformities in the cooled device. Mitigation of this temperature nonuniformity, while enhancing the heat exchange along the flow path, has been demonstrated through the use of variable fin density microchannels. This paper demonstrates experimentally and numerically the potential of micro-pin-fin heat sinks as an effective alternative to microchannel heat sinks for dissipating high heat fluxes from small areas. Results from this experimental and numerical investigation demonstrate the ability of variable pin-fin density with offset configurations to reach low thermal resistance coefficients and reduce the surface temperature nonuniformity while presenting low-pressure drops. For the maximum Reynolds number considered in this study (2200), we demonstrate the capacity of the cooling scheme, when submitted to a heat flux of 50 W/cm2, to reach a pumping to chip power ratio of 0.37%, a thermal resistance coefficient of 0.26 cm2 K/W and a temperature uniformity along the 5 cm long cooling device of 2 °C.

Poor temperature uniformities and high pumping powers due to large pressure drops are the major drawbacks of the conventional microchannel cooling solutions. In this work, a liquid cooling device based on a matrix of microfluidic cells is presented. The coolant flow rate in each microfluidic cell is individually tailored, through thermally activated microvalves, to the local heat extraction needs in order to improve the temperature uniformity and avoid overcooling. A numerical study is implemented to assess the thermo-hydraulic performance of the cooling device. The analysis is performed in a steady state CFD study and integrated along a time dependent and non-uniform heat load scenario. The results show an enhancement of the temperature uniformity along the whole system while reducing the energy needed for the pumping power by 89.2% compared to the conventional microchannel technology.

Abstract The performance of dense array Concentrating PhotoVoltaics (CPV) receivers is reduced by the increase of average temperature and temperature non-uniformities which arise from illumination profiles and the characteristics of the cooling mechanism used. The magnitude of the impact of both illumination and temperature non uniformities depend on the electrical configuration of the CPV cell array. In this study, the impact of a cooling device, formed by a matrix of microfluidic cells with individually variable coolant flow rate, on the performance of a CPV receiver submitted to a non-uniform irradiance scenario is assessed and compared with microchannel cooling for three electrical configurations. The proposed cooling scheme tailors the flow rate distribution, and therefore the local heat extraction capacity, to the illumination profile, allowing the reduction of the temperature difference across the CPV receiver up to one third of the one obtained through microchannel cooling. This characteristic of the microfluidic cells cooling device, combined to its low pumping power, generates an improvement of the Net PV power of 3.83% for one of the configuration, the 6x8 matrix one.

Efficiency losses resulting from electrical mismatching in densely packed photovoltaic arrays present a significant challenge, particularly exacerbated in nonuniformly illuminated receivers and under varying temperatures. Serial configurations are particularly susceptible to radiation nonuniformities, while parallel systems are negatively affected by temperature variations. Various authors have recommended the incorporation of electrical voltage and current sources to mitigate these losses. This study explores different electrical connection configurations utilizing concentrated photovoltaic (CPV) cells and DC-DC electrical current converters. A self-adaptive microfluidic cell matrix cooling system is employed to mitigate thermal dispersion caused by the highly nonuniform illumination profile. The obtained results for each configuration are compared with the total electrical power produced by individual cells, operating under identical radiation and temperature conditions to those of the entire array. The results reveal a noteworthy increase in production across all studied configurations, with the parallel–series arrangement demonstrating the most promising practical utility. This configuration exhibited a remarkable 50.75% increase in power production compared with the standard series connection.