Experimental Study of a natural ventilation strategy in a Full-Scale Enclosure Under Meteorological Conditions: A Buoyancy-Driven Approach

The performance of a natural ventilation strategy, in a full-scale enclosure under meteorological conditions is studied through an experimental study, a buoyancy-driven approach, by means of the estimation of the air exchange rate per hour and ventilation power. A theoretical and an empirical model are proposed based on the airflow theory in buildings and blower-door tests. A preliminary validation, by comparing our results with standards in air leakage rate determination, is made. The experimental study conducted here has shown that the natural ventilation strategy implemented reach promising air exchange rate levels, as they are rather high compared to other experimental studies found in the literature.  The proposed models have shown good potential and further analysis should take place. Also, other methods for validating these models should be implemented (for instants: CFD simulation or tracer gas methods), as the one in the standards is rather rough estimations.Keywords: Buoyancy-driven, natural ventilation, ventilation power, blower-door test, airflow in buildings

Estimation de la cartographie du coefficient d'échange convectif par thermographie infrarouge

Le coefficient d'échange convectif est un paramètre pertinent lorsqu'il s'agit de modéliser le comportement thermique d'un système physique. Dans ce texte, à partir de deux modèles thermiques écrits et discrétisés à l'échelle du pixel nous avons construit deux fonctionnelles qui relient variables observables en occurrence les champs de températures mesurés par une caméra infrarouge et les variables à estimer (coefficient d'échange convectif et/ou diffusivité thermique). Les cartographies du coefficient d'échange convectif sont obtenus en minimisant ces deux fonctionnelles. Ici, les résultats que donnent ces deux modèles sont présentés et confrontés. Nous montrons que lorsque les effets de refroidissement sont prépondérants, la diffusion de la chaleur dans le système physique peut être négligée dans l'estimation du coefficient d'échange convectif. Les valeurs de corrélations linéaires entre le champ de température et sa dérivée temporelle montrent que ces deux grandeurs sont relativement bien corrélées

Fast sizing of the width of infinite vertical cracks using constant velocity Flying-Spot thermography

Constant Velocity Flying-Spot thermography consists in scanning the sample surface by a focused CW-laser spot moving at constant speed. This technique was designed to study large surfaces in short times. In this work, we propose a method, based on a Flying-Spot thermography setup, to size the width of vertical cracks by fitting the temperature profile along the line that contains the center of the laser spot and is perpendicular to the crack to its analytical expression. This method is also valid in the opposite configuration, where the laser spot remains at rest and the sample is moving at constant velocity. This configuration is useful for in-line inspection in factories, for detecting and sizing cracks in real time, without stopping the production chain. Experimental measurements on stainless steel samples containing calibrated vertical cracks confirm the validity of the method to measure the crack width with high accuracy, even for submicronic wide cracks.This work has been supported by Ministerio de Economía y Competitividad (DPI2016-77719-R, AEI/FEDER, UE), by Gobierno Vasco (PIBA 2018–15), by Universidad del País Vasco UPV/EHU (GIU16/33) and by Conacyt (Beca Mixta 2017 Movilidad en el extranjero)

Experimental Study of an Air-PCM Heat Exchanger: Melting in a Cylindrical Container

This paper presents experimental results of an air-PCM heat exchanger, with an in-line arrangement of cylindrical containers. The objective is to highlight the physical phenomena occurring in a single container during the phase change. Temperature and airflow measures were carried out. These values were used to find the heat exchanges on the container. The experimental heat values were compared and validated with the theoretical heat stored obtained from the material properties. An only conduction 1D radial model is proposed to describe the melting front in the container.Keywords: phase change materials, thermal storage unit, cylinder, latent heat, radial conduction

Modélisation unidimensionnelle multi-physique du comportement d'un joint à faces radiales pour la maintenance d'un circuit carburant

La présente étude porte sur la modélisation unidimensionnelle multi-physique d'un joint d’étanchéité à faces radiales appelés « garnitures mécaniques » pour des arbres tournants. Ces garnitures fonctionnent à des pressions très élevées générées par le film de lubrification entre les faces des joints dont les performances sont directement affectées par la géométrie de l'interface qui dépend des effets thermiques, mécaniques et de la cinématique appliqués. La modélisation unidimensionnelle proposée prend en compte le transfert thermique et la déformation des faces du joint, couplés au modèle de Reynolds décrivant le champ de pression dans le film lubrifiant. Le choix de ce type de modélisation résulte dans le compromis entre le nombre de paramètres du modèle et la complexité du code de calcul associé. Ce modèle permet ainsi de déterminer de façon simple et rapide les performances caractéristiques d’une garniture mécanique. Cette démarche de modélisation est appliquée au cas d’une garniture mécanique à stator flottant pour un circuit carburant de turboréacteur de faibles dimensions (rayons intérieur et extérieur respectivement de 6 et 7,4 mm) et fonctionnant à des vitesses de rotation relativement élevées (4000 à 5000 tr/min) pour des pressurisations extérieures relativement faibles (0,3 à 0,6 MPa). La détermination des paramètres du modèle est explicitée et les résultats de simulation sont comparés avec les résultats expérimentaux issus de bancs machines et de banc laboratoire afin de caractériser la qualité du modèle obtenu

Bayesian Inference for 3D Volumetric Heat Sources Reconstruction from Surfacic IR Imaging

The domain of non-destructive testing (NDT) or thermal characterization is currently often done by using contactless methods based on the use of an IR camera to monitor the transient temperature response of a system or sample warmed by using any heat source. Though many techniques use optical excitation (flash lamps, lasers, etc.), some techniques use volumetric sources such as acoustic or induction waves. In this paper, we propose a new inverse processing method, which allows for the estimation of 3D fields of heat sources from surface temperature measurements. This method should be associated with volumetric heat source generation. To validate the method, a volumetric source was generated by the Joule effect in a homogeneous PVC sample using an electrical thin cylindrical wire molded in the material. The inverse processing allows us to retrieve the depth of the wire and its geometrical shape and size. This tool could be a new procedure for retrieving 3D defects on NDT

Mid-infrared spectroscopic thermotransmittance measurements in dielectric materials for thermal imaging

Thermal considerations affect the performance of most microsystems. Although surface techniques can give information on the thermal properties within the material or about buried heat sources and defects, mapping temperature and thermal properties in three dimension (3D) is critical and has not been addressed yet. Infrared thermography, commonly used for opaque materials, is not adapted to semi-transparent samples such as microfluidic chips or semiconductor materials in the infrared range. This work aims at answering these needs by using the variations of transmittance with temperature to obtain information on the temperature within the thickness of the sample. We use a tunable mid-infrared light source combined with an infrared camera to measure these variations of transmittance in a glass wafer. We couple this technique with a thermal model to extract the thermotransmittance coefficient—the coefficient of temperature variation of the transmittance. We then introduce a semiempirical model based on Lorentz oscillators to estimate the temperature-dependent optical properties of our sample in the mid-IR spectral range. Combined with the measurement, this paper reports the spectroscopic behavior of the thermotransmittance coefficient in the mid-IR range and a way to predict it

Measurement of in-plane thermal diffusivity of solids moving at constant velocity using laser spot infrared thermography

In this work, an infrared thermography setup is proposed to measure the in-plane thermal diffusivity of (an)isotropic samples that are moving at constant velocity, as it is the case of in-line production or in-line quality control processes in factories. The experiment consists in heating the moving sample with a focused laser spot, which remains at rest, and recording the surface temperature by an infrared camera. An analytical expression for the surface temperature of the moving sample has been obtained. By analyzing the surface temperature in logarithmic scale, three simple linear relations are obtained, whose slopes give the thermal diffusivity in the direction of the sample movement and in the perpendicular direction. These three linear methods, which are not disturbed by heat losses by convection and radiation, are valid for both opaque and semitransparent samples. Measurements performed on calibrated samples confirm the validity of the methods, which are also valid when the sample is at rest and the laser spot scans its surface at constant velocity, the so-called ‘‘flying spot” technique.This work has been supported by Ministerio de Economía y Competitividad (DPI2016-77719-R, AEI/FEDER, UE), by Universidad del País Vasco UPV/EHU (GIU16/33) and by Conacyt (Beca Mixta 2017 Movilidad en el extranjero)

Investigation into the use of thermoelectric modules as an alternative to conventional fluxmeters: Application to convective and radiative heat flux in building

The present work aims to propose the use of Peltier modules for the superficial heat flux measurement, as an alternative to conventional heat flux sensors. In this study, the function of Peltier modules (TEM) as heat flux sensors is compared to the Captec® heat flux sensors (FGT), based on the premise that conventional heat flux sensors such as Captec® have been proven to have acceptable performance for the heat flux measurement, i.e., conduction, convection and radiation. A simple measurement device and a simple general formulation for decoupling the convective and radiative parts from the heat flux measurement are proposed. The latter are implemented in an experimental case presenting weak convective and radiative heat fluxes, using a black-shiny couple of Peltier modules and a black-shiny couple of Captec. The radiative part was found to be the same when comparing FGT and TEM measurements. However, the convective part when using TEM measurements was found to be around two times larger than when using FGT measurement. It has been encountered that this difference is better explained by the geometrical and thermal properties of both sensors

Interdiffusion measurements in thermally controlled microchannel using infrared spectroscopic imaging

many applications, knowledge of the mass diffusivity coefficient is mandatory to optimize the design and operating conditions of microfluidic devices and chemical reactions. The literature reports few values due to limited techniques, and the impact of the fluid temperature is rarely taken into account when the diffusivity is measured. In this study, we present an imaging method to investigate and quantify the interdiffusion of two fluids in a microchannel under controlled temperatures. The experimental setup combines a thermally controlled microfluidic chip and a microscale infrared (IR) spectroscopy imaging technique. The mass diffusivity of formic acid (HCOOH) in sulfuric acid (H2SO4) was measured from room temperature to 50 ◦C to demonstrate the performance of the setup. This work offers a rapid tool and a methodology for accurate contactless interdiffusion measurements in thermally controlled T-shape reactors applicable a large set of chemicals