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•Reduced dimensions elastocaloric materials (i.e. films, ribbons, wires and foams) are reviewed, which are expected to potential candidates for miniaturized refrigeration.•Based on ...various properties,e.g. ∆σhys, ∆Tad/∆σcr and ∆Tad/∆εtr their elastocaloric performances (∆Tad/∆Siso) are explored.•For their commercialized application, the fatigue life and cooling efficiency (COPmat and COPmat/COPCarnot) are demonstrated.•The challenges/proposed solutions and recent achievements for micro cooling eCE demonstrators/prototypes based on small-sized eCMs are ultimately outlined.
Elastocaloric cooling technology has obtained huge attraction over vapor compression systems because it is more efficient with negligible environmental impact. The elastocaloric effect (eCE) is generally concerned with superelasticity and latent heat of shape memory alloys (SMAs), related to the martensitic transformation (MT) under uniaxial loading/unloading. There are various small-scale applications such as microelectromechanical systems, medical devices and lab-on-chip systems, where active local cooling with precise temperature control is essential for their proper functioning. To explore potential eCE for miniaturized active refrigeration, reduced dimensions SMAs (i.e. thin films, microwires, ribbons and foams) may be attractive for micro cooling devices by providing a large surface to volume ratio and thus high heat transfer capacity, low thermal hysteresis and high working frequency. Therefore, the eCE properties of the state-of-the-art reduced dimensions elastocaloric materials (eCMs) are thoroughly reviewed and comparatively discussed with their bulk counterparts. The most appropriate eCMs for miniaturized eCE refrigeration are revealed on the basis of large adiabatic temperature change (△Tad), low stress hysteresis (△σhys), high cyclic stability and large coefficient of performance of material (COPmat). The challenges and recent achievements for micro cooling eCE devices/prototypes based on small-sized eCMs are summarized.
Miniaturization and utilization of low-dimensional structures of recent electronic devices have witnessed some new micro cooling methods which can fulfil the cooling demand for the electronic ...devices. Microchannel heat sink (MCHS) is one of the micro cooling method which appears as a promising method that can provide high heat transfer rate due to small hydraulic diameter. Furthermore, microchannel heat sink is easy to be fabricated compare to other micro cooling device. Due to fast development in electronic industry, hybrid microchannel heat sink with optimal design has received a great deal of attention in order to provide sustainable cooling solutions. However, most of the studies of hybrid microchannel heat sink only provided the numerical analysis without any validation of the proposed design experimentally. This is very important since it also will determine whether the proposed hybrid microchannel heat sink can be fabricated or not. Therefore, the aim of this article is to validate the numerical model of hybrid microchannel heat sink (TC-RR-SC MCHS) experimentally. The validation result showed that the maximum discrepancy between both simulation and experimental analyses for Nusselt number and friction factor were 15.8% and 17.4%, respectively, which is less than 20%. The different number of microchannels between the simulated TC-RR-SC MCHS and fabricated TC-RR-SC MCHS is one of the factors that contribute to the data discrepancy. Furthermore, the poor finishing during the fabrication process also another factor because the burrs and debris at the top and bottom surface of microchannels affect the convective heat transfer area and the flow area of fluid.
This paper presents a systematic numerical study of the effects of heat transfer and pressure drop produced by vortex promoters of various shapes in a 2D, laminar flow in a micro-channel. The liquid ...is assumed to be water, with temperature dependent viscosity and thermal conductivity. It is intended to obtain useful design criteria of micro-cooling systems, taking into account that practical solutions should be both thermally efficient and not expensive in terms of the pumping power. Three reference cross sections, namely circular/elliptical, rectangular, and triangular, at various aspect ratios are considered. The effect of the blockage ratio, the Reynolds number, and the relative position and orientation of the obstacle are also studied. Some design guidelines based on two figures of merit (related to thermal efficiency and pressure drop, respectively), which could be used in an engineering environment are provided.
•The use of micro-cooling channels to cool a liquid propellant microthruster is suggested.•A liquid propellant microthruster with micro-cooling channels was fabricated with a photosensitive glass ...MEMS process.•The feasibility of using micro-cooling channels was successfully validated through the design, fabrication and testing of a liquid propellant microthruster.
This paper reports a feasibility study of regenerative micro-cooling channels in a liquid microthruster composed of thermally fragile materials. Glass, which is among the most thermally insulating materials, has been used as microthruster fabrication material to suppress excessive heat loss in micro scale thruster. However, the frangibility of glass has remained a challenge to be solved. To thermally manage the fragile structure, the use of regenerative micro-cooling channels in a microthruster is suggested in this work, and the feasibility was tested through design, fabrication and experimental performance of a glass microthruster with microchannels. Nine photosensitive glass layers were wet etched and integrated to fabricate the microthruster. Before integration of the layers, a fabricated Pt/Al2O3 catalyst was inserted into the chamber of the microthruster for propellant decomposition. Hydrogen peroxide (90wt%) was used as a monopropellant and served as the working fluid for regenerative cooling. A liquid microthruster with micro-cooling channels was successfully fabricated with a photosensitive glass MEMS process. Experimental performance tests were conducted while measuring the microthruster chamber pressure, chamber temperature, and surface temperatures. The test results showed normal operation of the microthruster, which had an estimated thrust of approximately 48 mN and temperature efficiency of approximately 41%. The decreasing surface temperatures of the microthruster during thruster operation successfully validated the cooling effect of the micro-cooling channels and demonstrated their practicality for the regenerative cooling of liquid microthrusters.
With the development in additive manufacturing, the use of surface treatments for gas turbine design applications has greatly expanded. An experimental investigation of the pressure loss and heat ...transfer characteristics within impingement jet arrays with arrays of target surface micro cooling units is presented. The discharge coefficient and Nusselt number are measured and determined for an evaluation of the pressure loss of the flow system and heat transfer level, respectively. Considered are effects of impingement jet Reynolds number ranging from 1000 to 15,000 and micro cooling units (square pin fin) height (h) with associated values of 0.01, 0.02, 0.05, 0.2, and 0.4 D, where D is the impingement hole diameter. Presented are variations of Nusselt number, and Nusselt number ratio, discharge coefficient, discharge coefficient ratio, discharge coefficient correlation. Depending upon the micro cooling unit height, discharge coefficient ratios slightly decrease with height, and the ratio values generally remain unit value (1.0). When Rej = 1000 and 2500 for several cooling units height values, discharge coefficient ratios show the pressure loss decreases about 2–18% and 3–6%, respectively, when compared to the data of a baseline smooth target surface plate. The observed phenomenon is due to the effects of flow blockage of micro cooing units, local flow separation, and near-wall viscous sublayer reattachment. Results also show that heat transfer levels increase 20–300% for some of the tested toughened target surface plates when compared to smooth target surface plates. The heat transfer level enhancement is because of an increase in thermal transport and near-wall mixing, as well as the increased wetted area. In addition, micro cooling units elements break the viscous sublayer and cause greater turbulence intensity when compared to the smooth target surface. Overall, results demonstrate that the target surface micro cooling units do not result in a visible increment in pressure loss and reduce pressure loss of the flow system for some of the tested patterns. Moreover, results show the significant ability of micro cooling units to enhance the surface heat transfer capability of impingement cooling relative to smooth target surfaces.
► One proposes a magnetic refrigerator not requiring the use of fluids. ► Materials whose thermal conductivities depend on an applied magnetic field are used. ► Numerical simulations show that the ...coefficient of performance attained reaches 1.5. ► The device can be triggered from cooler to heat source by varying the frequency.
The viability and operation of a fully solid state magnetic refrigeration system with envisaged applications on chip, sensor and device cooling is here tested using numerical simulations. The proposed system relies on the combined use of materials displaying the magnetocaloric effect and of materials whose thermal conductivities are controlled by an external magnetic field. This allows the switching of the heat flow direction in sync with the temperature variation of the magnetocaloric material, removing the necessity to use fluids which has for long hindered the implementation of magnetic refrigeration. We have found the optimum operating conditions of the proposed refrigerator, for which a cooling power density of ∼2.75Wcm−2 was obtained for an operating temperature of ∼296K, using Gadolinium as the magnetocaloric material and an applied magnetic field of 1T. The coefficient of performance (COP) achieved by this refrigerator was found to be COP ∼1.5, making it a viable alternative to thermoelectric refrigeration.
The Gigatracker detector of the NA62 experiment at CERN SPS Federici, L.; Aglieri Rinella, G.; Alvarez Feito, D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2019, Letnik:
936
Journal Article
Recenzirano
Odprti dostop
The NA62 experiment at the CERN SPS is a fixed target experiment designed to measure the branching ratio of the ultra-rare Kaon decay K+→π+νν̄. The experiment uses an high-momentum K+ decay in-flight ...technique to increase the rejection power of the main background: K+→π+π0.
The Gigatracker is a hybrid silicon pixel detector, exposed to a 750 MHz high-energy charged hadron beam, built to give an accurate measurement of K+ momentum and direction together with an high precision measurement of the beam particle arrival time (115 ps RMS resolution per plane). It comprises three stations placed right before the K+ decay region and inserted around two achromats. The detector works in vacuum (∼10−6mbar) at about −10°C.
Each station is made of a 200μm thick silicon sensor readout by 10 TDCPix, custom 100μm thick ASICs, and cooled by an innovative double circuit silicon micro-channel cooling system. All these parts are designed to minimize the total material budget which, in the final detector, amounts to less than 1.5% X0 for the three stations.
In order to sustain the high rate of incoming particles, each TDCPix, operating in a self triggered mode, is equipped with four 3.2 Gb/s serializers sending data to the detector DAQ system based on a read-out card per TDCPix chip sending trigger-matched hits to 6 PC servers. I will describe the whole detector and present some of the results from data collected during the 2016 NA62 runs.
The impact of micro-pin fins on heat transfer performance in this study is analyzed numerically. Navier-Stokes equations are solved by steady-state three dimensions turbulent forced convection. ...Various numbers of micro-pin fins with in-line configuration and different micro-pin fins configurations such as staggered configuration additionally to the in-line configuration are explored. In addition, comparison between micro-pin fins duct and smooth duct is studied. Results illustrate that the thermal performance was enhanced by 7.9 - 9.3% with increasing the number of micro-pin fins from 902 to 1312 and by 10.2 - 11.1% with increasing the number from 902 to 1640. Also, displays that the heat transfer performance in the staggered configuration is slightly better than the in-line configuration by 2.6 - 4.2% with the same micro-pin fins number. Moreover, the micro-pin fins duct gave an increase of 30.24% in heat transfer performance relative to the smooth duct.
In bone fixation, frictional heat effect in orthopedic surgery has a potentially hazardous for soft tissues. Saline water irrigation has frequently been practiced preventing the thermal damage and ...limiting the applied cutting forces in high-speed orthopedic drilling. The application of excessive cutting fluids limits the heat and applied forces; however, it isn’t an environmentally friendly solution. In this work, a novel micro-irrigation system was developed to provide a mixture of air and saline water, having a small quantity of cooling spray (SQCS) at higher pressure into the cutting zone. This SQCS limits the frictional heat and providing lubrication and near to dry clean operative zone through a superior cooling effect compared to conventional irrigation. The carbide drills were used to make a hole in the fresh calf tibia bone. In addition, response surface methodology (RSM) was used to design the experiments. The regression models were developed between the input design parameters and performance measures to explore the relation under proposed micro-irrigation and facilitate the multi-objective optimization. Besides, cost analysis for the process has been performed. Thus, this work offers an integrated analysis to purely study and understand the bone drilling process under employing micro-cooling spray.
We present in this paper a fundamental hydrothermal investigation of the next generation interlayer integrated water cooled three-dimensional (3D) chip stacks, with high volumetric heat generation. ...Such investigation of flow through microcavities with embedded heat transfer structures such as micro pin-fin arrays and microchannels is crucial for the successful realization of 3D chip stacks. We focus mainly on the complex physics of the entrance region of the cooling microcavities in order to assess its importance. The flow and heat transfer in the entrance region is strongly influenced by developing boundary layers and, as we show herein, the development lengths can occupy a significant portion of the microcavity due to the size restrictions of the 3D chip stack. These effects make a fundamental understanding of conjugate heat transfer in microcavities with heat transfer structures a necessity. The flow field and heat transfer in the entrance region are characterized by means of correlations determining the effective coolant permeability as well as the heat transfer coefficient as a function of the streamwise coordinate x, the flow Reynolds number (Re) and the Prandtl number. Based on a thermal non-equilibrium porous medium model relying on these results, a substantially improved estimation of pressure drop and temperature distribution inside the chip stack is realized. The modeling results are validated against measurements on a 3D chip stack simulator. The range of flow rates and thermal loads in the hot spots of the chip stack, over which it is crucial to consider the developing hydrothermal effects, are analyzed and discussed in detail. Moreover, microchannel and micro pin-fin structures are compared, showing more than 20% increased performance of the latter for all operating conditions investigated.
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