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International audience; As the concern for CO2 emissions and global warming raises, the Stirling machine appears as a candidate alternative technology to vapor compression cycles that use refrigerant fluids. In this paper, we present the design, manufacturing and testing of a Beta Stirling machine for refrigeration applications. The first part of the paper presents the principle of the Stirling cycle, the mechanical configuration of the designed machine, and the key design parameters. The second part describes the experimental test bench and instrumentation of the Stirling machine. The last part of the paper presents experimental results. The prototype typical performance is a 450 W heat lift at 4°C and a COP of 0.9 when Nitrogen is used as the working gas. Cold end temperature variation as a function of heat lifts and charge pressure are presented. Coefficient of Performance is also discussed. Mechanical power, instantaneous torque and velocities curves are reported.

International audience; Abstract

International audience; In this paper, we present a new model design and parametric studies of a miniature Stirling cooler machine for on-site refrigeration. The MEMS (Microelectromechanical systems) technology is investigated to design this machine. The concept could be used to provide cooling at chip scale and mitigate hot spots in electronic devices. Whereas numerous works deal with Stirling engines at a macroscopic scale, only a few works concern miniaturized Stirling engines. Therefore, a model analysis giving insights of the impact of the technological choices and downsizing of the machine is needed. A base design model is presented. The model results lead to a cooling power of 10 mW and a Coefficient Of Performance of 1.45. A parametric study is conducted for operational and design parameters. Compared to macro-scale design, the same trend is observed for the influence of the thermal performance regenerator. Different trends from macroscopic engines were observed for hysteresis losses importance, and the choice of the working gas. The raise in power due to the raise in frequency expected for micro-scale devices is counterbalanced by the degradation of the COP due to the increase in thermofluidic losses. Squeeze film damping and finite speed losses can be neglected at this scale.

A regenerator of a Stirling machine alternately absorbs and releases heat from and to the working fluid which allows to recycle rejected heat during theoretical isochoric processes. This work focuses on a milli-regenerator fabricated with a multiple jet molding process. The regenerator is a porous medium filled with a dense pillar matrix. The pillars have a geometrical lens shape. Two metallic layers (chromium and copper) are deposited on the polymer pillars to increase heat transfer inside the regenerator. We performed experiments on different milli-regenerators corresponding to three porosities (ε = 0.80, 0.85 and 0.90) under nitrogen steady and oscillating compressible flows (oscillating Reynolds number in the range 0 < Reω < 60 and Reynolds number based on the hydraulic diameter ReDh,maxT < 100°C). Temperature, velocity and pressure experimental measurements are performed with microthermocouples (type K with 7,6 µm diameter), hotwires and miniature pressure sensors, respectively. We identified a threeterm composite correlation equation for the friction factor based on a Darcy-Forchheimer flow model that best-fit the experimental data. In steady and oscillating flows permeabilities and inertial coefficients are of the same magnitude order. Inertial coefficients decrease when the porosities increase.

International audience; In this paper, we present a new model and design of a MEMS Stirling machine. The concept could be used to provide electricity to low level power systems. A modified adiabatic model including losses of a Stirling engine such as regenerator thermal efficiency, wall conduction, pressure drop, hysteresis, membrane finite speed and squeeze film damping losses is presented. A base design machine is proposed. A parametric study is conducted and used to derive guidelines for miniature design. Compared to macro-scale design, the same trend was observed for the influence of the thermal performance regenerator. However, different trends from macroscopic engines were observed: conduction losses are of major importance due to the low power of the miniature engines, hysteresis losses in the bounce space are also of high amplitude due to the small size if this volume, the choice of the working gas leads to hydrogen or air and not helium. We computed that membrane finite speed losses and squeeze film damping losses can be neglected in the investigated machine size. The first part of the paper presents the micro-machine specific features, the second part describes the model, the last part presents the base design results and design guidelines.

International audience; In this paper, a parametric investigation of domestic regenerative Stirling refrigeratingmachines is conducted using a modified simple model. The model is adapted from an ideal adiabaticengine model and different losses have been included at different stage based on their effect. Themodel is validated experimentally using the Beta type FEMTO 60 Stirling engine as a case study.The simulation and experimental results show that the coefficient of performance of the Stirling cyclerefrigerator at a charging pressure of 17.5 bar, frequency of 12.1 Hz, cold end temperature of −22oCand using nitrogen as a working fluid are found as 38.2% and 35% respectively. Furthermore, theeffects of phase angle, working fluid type, operating pressure, and operating frequency of a machine onthe performance of a regenerating Stirling cycle refrigerator are investigated.

The second law of thermodynamics is applied to evaluate the influence of entropy generation on the performances of a cold heat exchanger of an experimental Stirling refrigeration machine by means of three factors: the entropy generation rate N S , the irreversibility distribution ratio ϕ and the Bejan number B e | N S based on a dimensionless entropy ratio that we introduced. These factors are investigated as functions of characteristic dimensions of the heat exchanger (hydraulic diameter and length), coolant mass flow and cold gas temperature. We have demonstrated the role of these factors on the thermal and fluid friction irreversibilities. The conclusions are derived from the behavior of the entropy generation factors concerning the heat transfer and fluid friction characteristics of a double-pipe type heat exchanger crossed by a coolant liquid (55/45 by mass ethylene glycol/water mixture) in the temperature range 240 K &lt, TC &lt, 300 K. The mathematical model of entropy generation includes experimental measurements of pressures, temperatures and coolant mass flow, and the characteristic dimensions of the heat exchanger. A large characteristic length and small hydraulic diameter generate large entropy production, especially at a low mean temperature, because the high value of the coolant liquid viscosity increases the fluid frictions. The model and experiments showed the dominance of heat transfer over viscous friction in the cold heat exchanger and B e | N S &rarr, 1 and ϕ &rarr, 0 for mass flow rates m ˙ &rarr, 0.1 kg.s&minus, 1.

International audience; In this paper, we study the influence of annealing on the performance of Resistive Temperature Detectors made from Nickel thin films. The aimed application is heat flux sensing. The substrate is made of Borofloat glass with a Chromium adhesive layer. Several annealing temperatures between 150°C and 300°C are applied to this assembly. The thin films as deposited and after annealing are analyzed through SEM images. The evolution of the resistance and the temperature coefficient of the sensor are discussed. An annealing temperature is selected that ensures the repeatability of measurements.

International audience; Résumé - Cette étude se situe dans le cadre du développement de fluxmètres thermiques en microtechnologie. Ces fluxmètres consistent en deux résistances de platine déposées sur un substrat en verre. Dans une première partie, nous présentons le principe du fluxmètre et de la mesure de température. Dans une deuxième partie, nous présentons également les étapes de fabrication en salle blanche et les différentes températures de recuits étudiées. Nous présentons des résultats expérimentaux sur la variation de résistance observée selon les différentes températures de recuit et une analyse par Diffraction de Rayons X complétée par des images au microscope à balayage. Nous proposons comme hypothèse que la baisse de résistivité observée pour les faibles températures de recuit est due à l’amélioration du réseau cristallin et que la hausse observée pour les températures les plus élevées est due à la diffusion de la couche d’accroche en chrome dans le platine.

International audience; In this paper, we present an experimental study on the pressure, pressure drop, velocity and friction factor in a regenerator made from an array of pillars in reciprocating flow conditions. The fluid used in the experiment is air. We show that the pressure drop depends on the porosity, frequency and stroke. We observe a phase shift between the crank angle sinusoidal variation of the piston and the pressure variation that increases with frequency. We also observe that the instantaneous friction factor is higher in the discharge phase than in the suction phase, and higher in the acceleration than in the deceleration phase. Friction factor in oscillating flow appears to be higher than friction factor in steady unidirectional flow for the highest porosity. For the lower porosities, we observe that the pressure drop and friction factors are similar for maximum Reynolds numbers lower than 5000. An experimental correlation for the friction factor of the regenerator is derived in order to design a millimetric Stirling engine. The friction factor is compared with friction factors reported for woven screens, metal felts and involute foil regenerators.

International audience; This paper describes a Stirling Engine used as an Auxiliary Power Unit in a Series Hybrid Vehicle. The engine modeling is presented, then its integration in the vehicle power train is described. Fuel consumption, power train efficiency are compared between Stirling Engines and Spark ignition Engines. The results show that Stirling engines present good performances compared to internal combustion engines in the same configuration. Finally, the prototype design and first results are presented.

International audience; Study of dynamic response of silicone elastomer microfabricated hybrid membranes versus temperatures and aging time

International audience; The article presents the design, fabrication and characterization of platinum thin-film Resistance Temperature Detectors (RTDs)for heat flux sensing applications. The microfabrication process is described and the thin films are analysed by several methodsincluding SEM, XRD and profilometry. Estimation of experimental uncertainties is performed. The influence of annealing, selfheating,2-wire and 4-wire connections are studied. The analysis and experimental results show that the RTDs have a goodrepeatability when an annealing process is performed and a maximal injected current are used. A measurement uncertainty of0.14°C is achieved. The observed Temperature Coefficient Ratio is sufficient to ensure variation of the resistance in thetemperature range. The heat flux measurements made with the sensor are validated in a dedicated test bench and present agood repeatability.

International audience; This paper reports the design, fabrication and CFD modeling of a microregenerator in order to be integrated in a multiphase piezoelectric smart membrane Stirling engine. The application aims to recover waste heat at low temperatures and to convert it into electricity via the piezoelectric element. The suggested geometry for the microregenerator is a microchannel integrated with staggered DRIE etched silicon micropillars, the whole is encapsulated between two glass wafers. The porosity ranges from 0.8 to 0.9. A 2D numerical study of the microregenerator thermofluidic performances was investigated. Three gases (air, helium andhydrogen) were investigated. The gas flow is set to be incompressible and viscous under laminar unidirectional steady flow conditions for low Reynolds number (

International audience; Design and microfabrication of a Microscale-Stirling Engine (M-SE) for low temperature heat recovery

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