Combined effects of the filling ratio and the vapour space thickness on the performance of a flat plate heat pipe

International audienceAn experimental study of a flat plate heat pipe (FPHP) is presented. Temperature fields in the FPHP are measured for different filling ratios, heat fluxes and vapour space thicknesses. The system is hermetically sealed with a transparent plate for meniscus curvature radius observations by confocal microscopy. Experimental results show that the liquid distribution in the FPHP - and thus its thermal performance - depends strongly on both the filling ratio and the vapour space thickness. A small vapour space thickness induces liquid retention and thus reduces the thermal resistance of the system. Nevertheless, the vapour space thickness influences the level of the meniscus curvature radii in the grooves and hence reduces the maximum capillary pressure. As a result, it has to be carefully optimised to improve the performance of the FPHP. In all the cases, the optimum filling is in the range one to two times the total volume of the grooves. A theoretical approach, in non working conditions, has been developed to model the distribution of the liquid inside the FPHP in function of the filling ratio and the vapour space thickness

Nucleate boiling in a flat grooved heat pipe

International audienceThe present paper is devoted to an experimental study aiming at determining the thermal behavior of a flat plate heat pipe (FPHP) with micro grooves and at focusing especially on the effect of boiling in the grooves. The FPHP is hermetically sealed on its upper face with a transparent plate for observations. Experimental results obtained with methanol are presented. Nucleate boiling in the grooves is observed for relatively small heat fluxes (3 Wcm−2). The presence of nucleate boiling in the grooves improves the thermal performance of the flat heat pipe, and it must be emphasized that it does not constitute an operation limit as it is generally stated. The dry out of the evaporator is observed for heat fluxes much higher than the heat flux of onset of nucleate boiling. The results obtained for different filling ratios show the influence of this parameter that has to be optimized to improve the performance of the device

Investigation of evaporation and condensation processes specific to grooved flat heat pipes

International audienceTemperature and liquid-vapor interface measurements obtained with a flat plate heat pipe (FPHP) in various experimental conditions are presented. The grooved FPHP is made of copper. The results are compared to a thermal model, developed in a previous work, in which heat conduction in the FPHP wall as well as evaporation and condensation heat transfer phenomena are taken into account. The model depends on the shape of the liquid-vapor interface in the grooves and on the fins at the condenser. A good agreement is found between the evaporation model and the experimental data. However the results of the condensation model overestimate the heat transfer coefficient, due to a bad estimation of the condensate film on the fins. Experimental measurements obtained with a second FPHP made of silicon are used to analyze the shape of this film. For both evaporation and condensation models, the results show a strong influence of the accommodation coefficient

Ébullition

Les différents régimes de l’ébullition en vase et de l’ébullition convective. Modèles pour la prédiction des coefficients d’échange

Numerical Simulation of the Heat Transfer in a Refrigerated Trailer Equipped with Eutectic Plates for Frozen Food Delivery

The present work reports the Computational Fluid Dynamics simulation and analysis of the heat transfer inside a refrigerated truck trailer equipped with three eutectic plates and fans. The numerical model solves the conjugated heat transfer inside the trailer in 2D using the �� −�� Shear Stress Transport (SST) turbulence model. It has been already favorably validated against the numerical and experimental data of Lafaye de Micheaux el al. (2015) by Croquer et al. (2019). These simulations are used to improve the configuration of the refrigeration system with the eutectic plates as well as to investigate the feasibility of the eutectic plates for the transport of frozen food products under different operating loads and transport temperature requirements. Three eutectic plates having an optimal inter-plate distance of 6 cm to maximize the air flow between the plates (Croquer et al., 2019) are either placed in series on the roof of the trailer or vertically at its back. For both configurations, fans are blowing the air from the eutectic plates to the inside of the trailer and modeled by adding a source term into the momentum equations. During the door opening period, the configuration with the plates placed on the roof of the trailer without the cargo has noticeably lower area-averaged temperature inside the trailer than the configuration with the plates placed on the back of the trailer due to the presence of the circulation zones and the cold plates located near the doorway. However, introduction of the cargo into the simulations eliminates the formation of the circulation zones that prevents the infiltration of the atmospheric air. Also, the configuration with the plates placed on the roof of the trailer allows the atmospheric air to infiltrate earlier, therefore resulting in an overall higher temperature observed in the cargo

Extension of Murray's law using a non-Newtonian model of blood flow

<p>Abstract</p> <p>Background</p> <p>So far, none of the existing methods on Murray's law deal with the non-Newtonian behavior of blood flow although the non-Newtonian approach for blood flow modelling looks more accurate.</p> <p>Modeling</p> <p>In the present paper, Murray's law which is applicable to an arterial bifurcation, is generalized to a non-Newtonian blood flow model (power-law model). When the vessel size reaches the capillary limitation, blood can be modeled using a non-Newtonian constitutive equation. It is assumed two different constraints in addition to the pumping power: the volume constraint or the surface constraint (related to the internal surface of the vessel). For a seek of generality, the relationships are given for an arbitrary number of daughter vessels. It is shown that for a cost function including the volume constraint, classical Murray's law remains valid (i.e. Σ<it>R</it>^{<it>c </it>}= <it>cste </it>with <it>c </it>= 3 is verified and is independent of <it>n</it>, the dimensionless index in the viscosity equation; <it>R </it>being the radius of the vessel). On the contrary, for a cost function including the surface constraint, different values of <it>c </it>may be calculated depending on the value of <it>n</it>.</p> <p>Results</p> <p>We find that <it>c </it>varies for blood from 2.42 to 3 depending on the constraint and the fluid properties. For the Newtonian model, the surface constraint leads to <it>c </it>= 2.5. The cost function (based on the surface constraint) can be related to entropy generation, by dividing it by the temperature.</p> <p>Conclusion</p> <p>It is demonstrated that the entropy generated in all the daughter vessels is greater than the entropy generated in the parent vessel. Furthermore, it is shown that the difference of entropy generation between the parent and daughter vessels is smaller for a non-Newtonian fluid than for a Newtonian fluid.</p

Contributions du Génie Frigorifique et du Génie des Procédés pour un meilleur environnement

In order to reach a better environment, two groups of methods can be considered: substituting polluting by clean (or at least with a lower impact) operations or developing pollution treatment solutions. This document first presents various researches in Refrigeration aiming to limit the environmental impact of some activities in this field. For instance, researches on boiling heat transfer -and specifically on the mechanisms governing this phenomenon- are developed. The motivation of such studies lies in the enhancement of evaporators. The effect of the presence of oil or of the choice of zeotropic mixtures on refrigerating machines performances is then highlighted. Lastly, a new method for the optimization (minimization) of the energy consumption of water-cooled ammonia compressors is proposed.Process Engineering provides solutions for the treatment of some air pollutants (e.g. Volatile Organic Compounds or carbon dioxide), among which some use the phenomenon of adsorption, and allow the pollutant separation, capture, concentration and possibly recovery. A new TSA (Temperature Swing Adsorption) process with indirect heating and cooling is developed for performing these operations.This TSA process can be enhanced if combined with other processes such as condensation. The analysis methods typical of Energy Engineering (mainly Refrigeration and Air Conditioning) are shown to be an appreciable help for the optimization of the overall air treatment system. This is the incentive for suggesting the use of a new tool, namely a psychrometric-like chart for nitrogen-toluene mixtures in the presence of an activated carbon adsorbent.Pour évoluer vers un meilleur environnement, deux types de méthodes peuvent être envisagées : substituer aux opérations "polluantes" des opérations "propres" (ou moins polluantes) ou proposer des solutions curatives de traitement de la pollution. Ce document présente tout d'abord quelques initiatives dans le domaine du Génie Frigorifique visant à limiter l'impact environnemental de certaines de ses activités. Il s'agit par exemple d'actions de recherche sur le transfert de chaleur par ébullition, visant à maîtriser les mécanismes régissant ce phénomène et finalement à améliorer les évaporateurs des machines frigorifiques. L'impact de la présence d'huile de lubrification dans les circuits frigorifiques sur les performances des installations est ensuite évoqué, de même que l'effet du choix de fluides zéotropes. Une démarche d'optimisation (minimisation) de la consommation énergétique des compresseurs de machines à ammoniac refroidis par eau est enfin proposée.Le Génie des Procédés fournit quant à lui des moyens de traitement de polluants de l'air (Composés Organiques Volatils, dioxyde de carbone, ...), entre autres grâce au phénomène d'adsorption, en vue de leur séparation, leur capture, leur concentration et éventuellement leur récupération. On présente ici le développement d'un nouveau procédé TSA (Temperature Swing Adsorption) à chauffage et refroidissement indirects permettant ces opérations.Ce procédé peut être amélioré en le combinant à d'autres procédés comme la condensation. Les modes d'analyse usuels en Génie Energétique (et notamment ceux du Génie Frigorifique et du Génie Climatique) peuvent constituer une aide pour optimiser une telle chaîne de traitement de l'air. En particulier, on suggère l'utilisation d'un outil original pour l'évaluation de procédés couplés : un diagramme de type psychrométrique pour le couple azote-toluène en présence d'un charbon actif adsorbant

Droit de la sécurité de l'approvisionnement énergétique : les contraintes physiques

National audienc

Some fundamental steps for the improvement of various energy conversion technologies: investigating boiling phenomena in an extended range of thermodynamic conditions

International audienc

Some important specificities of the boiling behavior of water used as (the most natural) refrigerant. (Invited keynote lecture)

International audienc