Jérôme Barrau

Uniform temperature profile for a dense array CPV receiver under non uniform illumination profile

Previous experimental and numerical studies of hybrid cooling devices for CPV receivers were developed under uniform illumination profile conditions; but literature review shows that this uniformity assumption is difficult to satisfy in real conditions. This investigation presents the design and the validation of a hybrid cooling device able to tailor its local heat extraction capacity to 2D illumination profiles in order to provide a uniform temperature profile of the PV receiver as well as a low global thermal resistance coefficient. The inputs of the design procedure are the solar concentration, the coolant flow rate and its inlet temperature. As the illumination profile is 2D dependent, a matrix of pin fins is implemented and a hybrid Jet Impingement /Matrix of Pin Fins cooling device is experimentally tested and compared to a hybrid Jet Impingement / Microchannels cooling device developed previously. The results demonstrate similar performances for both designs. Furthermore, in contrast to the cooling scheme using longitudinal fins, the distribution of the pin fins can be tailored, in two dimensions, to the local need of heat extraction capacity.

Experimental demonstration of a tailored-width microchannel heat exchanger configuration for uniform wall temperature

In this work, an experimental study of a novel microfabricated heat sink configuration that tends to uniform the wall temperature, even with increasing flow temperature, is presented. The design consists of a series of microchannel sections with stepwise varying width. This scheme counteracts the flow temperature increase by reducing the local thermal resistance along the flow path. A test apparatus with uniform heat flux and distributed wall temperature measurements was developed for microchannel heat exchanger characterisation. The energy balance is checked and the temperature distribution is analysed for each test. The results show that the wall temperature decreases slightly along the flow path while the fluid temperature increases, highlighting the strong impact of this approach. For a flow rate of 16 ml/s, the mean thermal resistance of the heat sink is 2,35?10?5 m2?K/W which enhances the results compared to the millimeter scale channels nearly three-fold. For the same flow rate and a heat flux of 50 W/cm2, the temperature uniformity, expressed as the standard deviation of the wall temperature, is around 6 ?C.

Distributed and self-adaptive microfluidic cell cooling for CPV dense array receivers

Temperature non uniformities of the CPV receivers lead to mismatch losses. In order to deal with this issue, a cooling device, formed by a matrix of microfluidic cells with individually variable coolant flow rate, has been developed. This device tailors the distribution of the heat extraction capacity over the CPV receiver to the local cooling needs in order to reduce the temperature non uniformities with respect to microchannel devices when submitted to uniform or non-uniform illumination profiles. At equal average temperature of the CPV receiver, power generation applying the matrix of microfluidic cells with individually variable coolant flow rate is 9.7% higher than the one with conventional microchannel technology.

Design Of A Hybrid Jet Impingement / Microchannel Cooling Device For Densely Packed PV Cells Under High Concentration

A hybrid jet impingement / microchannel cooling scheme was designed and applied to densely packed PV cells under high concentration. An experimental study allows validating the principles of the design and confirming its applicability to the cited system. In order to study the characteristics of the device in a wide range of conditions, a numerical model was developed and experimentally validated. The results allow evaluating the contributions of the cooling device to the performances of densely packed PV cells under high concentration. The main advantages of the system are related to its compactness, its good capacity of heat extraction associated to relatively low pressure losses and its capability to improve the temperature uniformity of the PV receiver with respect to other cooling schemes. These features improve the net electric output of the whole system and its reliability.

Self-adaptive microvalve array for energy efficient fluidic cooling in microelectronic systems

In the present work, the performance of temperature-regulated microvalves is investigated analytically for energy efficient fluidic cooling of microelectronic systems. The objectives are to decrease the overall mass flow rate of coolant (hence decreasing the pumping power) as well as to improve the temperature uniformity across the chip surface with hot spots. For this purpose, temperature-regulated microvalves are used to manage the coolant mass flow rate distribution throughout the chip based on the local chip temperature. The aim of this study is to find the optimum temperature response function of the microvalves to have more energy efficient cooling. Linear, quadratic and exponential temperature response behaviors are considered for the microvalves. Results show that for the linear microvalves, the mass flow rate and the temperature non-uniformity across the chip decrease by 50% and 29% respectively by using active self-adaptive microvalves, compared to the reference condition without any microvalve. These enhancement values are respectively 45% and 55% when using exponential instead of linear microvalves. This study shows that the concept of self-adaptive microvalve arrays for distributed chip cooling can have a significant impact on power and performance, opening a new approach for microfluidic cooling compared to traditional fixed microchannels.

Assessment And Comparison Of Concentrator Cell Carrier Efficiencies Under Very High Fluxes

The present work aimed at assessing and comparing the thermal performances of two different types of cell carriers exposed to natural sunlight beams concentrated up to 1,500–4,500 suns. Metallic and hybrid metal‐ceramic carriers of various dimensions, or bonded to cells of different sizes, were considered. Temperature profiles inside the carriers exposed to concentrated beams were measured using temperature sensors placed at two different locations. 3D heat transfer simulations of a carrier bonded either to the real Ge‐based solar cell or to the dummy cell instrumented for our temperature measurements showed that the measured temperatures differed by less than a couple of degrees from the real solar cell surface temperatures within a large range of concentration. Experimental results and thermal simulations confirmed the need to select a high‐conductivity carrier combined with a very efficient active device for cooling the solar cells under very high concentration. In addition, the key role played by ther...