Experimental Study of Heat Pump Thermodynamic Cycles Using CO 2 Based Mixtures -Methodology and First Results

The aim of this work is to study heat pump cycles, using CO 2 based mixtures as working fluids. Since adding other chemicals to CO 2 moves the critical point and generally equilibrium lines, it is expected that lower operating pressures as well as higher global efficiencies may be reached. A simple stage pure CO 2 cycle is used as reference, with fixed external conditions. Two scenarios are considered: water is heated from 10 {\textdegree}C to 65 {\textdegree}C for Domestic Hot Water scenario and from 30 {\textdegree}C to 35 {\textdegree}C for Central Heating scenario. In both cases, water at the evaporator inlet is set at 7 {\textdegree}C to account for such outdoor temperature conditions. In order to understand the dynamic behaviour of thermodynamic cycles with mixtures, it is essential to measure the fluid circulating composition. To this end, we have developed a non intrusive method. Online optical flow cells allow the recording of infrared spectra by means of a Fourier Transform Infra Red spectrometer. A careful calibration is performed by measuring a statistically significant number of spectra for samples of known composition. Then, a statistical model is constructed to relate spectra to compositions. After calibration, compositions are obtained by recording the spectrum in few seconds, thus allowing for a dynamic analysis. This article will describe the experimental setup and the composition measurement techniques. Then a first account of results with pure CO 2 , and with the addition of propane or R-1234yf will be given

Ecoulement sonique de vapeurs saturees : application a la determination du debit massique des soupapes de surete

SIGLECNRS T 56399 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Online composition measurements of refrigerant mixtures by optical fibres and infrared spectroscopy

International audienceAs refrigeration and heat pump industries use more and more mixtures as refrigerants it is useful to measure the composition of the fluid at different locations in the machine. For our own research purposes on mixture based cycles, we have implemented an online non-intrusive technique basedon infrared spectroscopy. This paper describes the apparatus used and also the data treatment that allows to extract valuable information from the recorded spectra. The calibration of the method for a given mixture is obtained by recording spectra with known concentrations, pressure and temperature. Partial least squares (PLS) or principal component regression (PCR) statistical methods are used to build a model. Then compositions can be determined for unknown mixtures. Results are presented for CO2+Propane mixtures. The sensitivity of the method to baseline treatment is tested. The best accuracy obtained so far is of the order of 2%The method is well tested and can be applied to other mixtures

Online, Non-Intrusive Composition Measurements Of Circulating Co2 Based Mixtures In An Experimental Heat Pump By Means Of Infra-Red Spectroscopy.

Using CO2 based mixtures as a working fluid in refrigeration and heat pumps is a potential alternative to the use of traditional fluids (HFC, HFO, …) which are environmentally problematic. In order to investigate the efficiency of such systems, we have designed an experimental heat pump equipped with different measurement devices. In the present article, we will focus on the mixture composition measurement technique. In order to fully understand the behaviour of such a heat pump, it is necessary to measure the composition of the mixture at each point of the cycle. In order to do so, we have used a technique based on infra-red spectroscopy and chemometry. At each point in the loop, we have installed optical cells equipped with transparent windows and optical fibres. The spectra are recorded by a Fourier transform infra-red spectrometer. The mixtures composition is then extracted from the spectra by the partial least squares (PLS) method which is a now common method in analytical chemistry. But, beforehand, the PLS method has to be calibrated. This is done by recording a statistically meaningful set of spectra on samples of known composition. Then a model can be derived to relate the compositions to the characteristics of the spectra. The calibration stage can be performed independently on separate well controlled samples. In our case, the calibration has been carried out directly on the experimental loop. To this end, micro sampling devices (ROLSI TM) have been installed in different places next to the optical cells. During this calibration process, the composition of the fluid is measured by gas chromatography at varying conditions and compositions along with the recording of the spectra. Once this calibration is done, the composition can be measured in short times, typically of the order of the second by the spectroscopic technique. This allows for a dynamic analysis of the working conditions. This article will describe in detail the experimental set up and the calibration process for a mixture of CO2 and ethanol on the composition range of interest at temperatures ranging from -20°C to +100°C and pressures from 20 to 120 bars and the expected accuracy will be discussed

Méthodologie et banc d'essais relatifs à l'étude expérimentale de cycles thermodynamiques de pompe à chaleur utilisant des mélanges à base de CO2.

International audienceThe aim of this work is to study heat pump cycles, using CO2 based mixtures as working fluids. Since adding other chemicals to CO2 moves the critical point and generally equilibrium lines, it is expected that lower operating pressures as well as higher global efficiencies may be reached. A simple stage pure CO2 cycle is used as reference, with fixed external conditions. Two scenarios are considered: water is heated from 283 K to 338 K (10 °C to 65 °C) for Domestic Hot Water scenario and from 303 K to 308 K (30 °C to 35 °C) for Central Heating scenario. In both cases, water at the evaporator inlet is set at 280 K (7 °C) to account for such outdoor temperature conditions. In order to understand the dynamic behaviour of thermodynamic cycles with mixtures, it is essential to measure the fluid circulating composition. To this end, we have developed a non intrusive method. Online optical flow cells allow the recording of infrared spectra by means of a Fourier Transform Infra Red spectrometer. A careful calibration is performed by measuring a statistically significant number of spectra for samples of known composition. Then, a statistical model is constructed to relate spectra to compositions. After calibration, compositions are obtained by recording the spectrum in few seconds, thus allowing for a dynamic analysis. This article will describe the experimental setup and the composition measurement techniques. Then a first account of results with pure CO2, and with the addition of propane will be given

Bulles d’eau à pression sub-atmosphérique : étude expérimentale et analyse dimensionnelle dans un canal vertical confiné

National audienceLa dynamique d’éclatement de bulles d’eau dans un environnement sub-atmosphérique a été peu étudiée dans la littérature. Sa compréhension est pourtant indispensable à l’amélioration de certains échangeurs fonctionnant à l’eau. Par une analyse dimensionnelle, cette étude a pour objectif de mettre en lumière les forces prédominantes au moment de l’éclatement. Un lien a également pu être établi entre ces forces et la hauteur de projection des gouttelettes (paramètre caractérisant l’éclatement)

Water boiling at low pressure: dynamics of growth and bursting of bubbles in a plate-type evaporator

International audienceWater is a good candidate to be used as an eco-friendly refrigerant. However, its behaviour under subatmospheric pressure needs to be better understood to optimize the efficiency and sizing of compact evaporators. Previous studies conducted in a plate-type evaporator highlighted that after the bubbles burst, the formation and evaporation of a thin liquid film on the evaporator wall has a major contribution on heat transfer. This work thus aims to characterize the dynamics of vapour bubbles during nucleate boiling, and more specifically the projection height after the free surface breakup. Using previous high-speed visualizations, the bubbles' characteristics are computed thanks to an ad-hoc Python program. It is shown that the projection height is correlated with the growth velocity and the size of the bubble reached just before it bursts. The influence of relevant dimensionless numbers on the projection height is also studied to determine the underlying predominant forces

Vaporisation de l’eau à pression sub-atmosphérique : dynamique de croissance et d’éclatement de bulles dans un échangeur à plaques

International audienceDans le milieu de la réfrigération, la réglementation des fluides de travail est de plus en plus contraignante. En effet, l’impact environnemental de certains de ces fluides (quantifié notamment par l’ODP et le GWP) les conduit à voir leur utilisation réduite voire interdite dans les prochaines années. Des efforts doivent donc être réalisés afin de proposer des alternatives à ces fluides : l’eau, dont l’ODP et le GWP sont nuls, fait partie de ces possibles alternatives. Cependant, son utilisation en climatisation est généralement liée à des conditions sub-atmosphériques dans l’évaporateur. Ces conditions d’ébullition particulières ont très peu été étudiées dans la littérature. D’après de précédentes études réalisées au laboratoire sur un canal d’évaporateur à plaque lisse, les transferts thermiques sont en majeure partie liés à l’évaporation d’un film liquide sur la paroi de l’évaporateur. Ce film est formé par croissance et éclatement des bulles de vapeur de taille centimétrique. Afin de maitriser la production frigorifique, il est nécessaire de maîtriser le film liquide et par conséquent de caractériser la dynamique des bulles de vapeur pendant l’ébullition nucléée et, plus particulièrement, la hauteur de projection après explosion. C’est l’objectif de cette étude. Des vidéos, capturées précédemment par caméra rapide, sont analysées à l’aide d’un programme Python développé spécifiquement afin de calculer les caractéristiques de la bulle. Il est notamment mis en évidence que la hauteur de projection est corrélée à la vitesse de croissance et la taille de la bulle avant éclatement

Vaporisation de l’eau à pression sub-atmosphérique : dynamique de croissance et d’éclatement de bulles dans un échangeur à plaques

International audienceDans le milieu de la réfrigération, la réglementation des fluides de travail est de plus en plus contraignante. En effet, l’impact environnemental de certains de ces fluides (quantifié notamment par l’ODP et le GWP) les conduit à voir leur utilisation réduite voire interdite dans les prochaines années. Des efforts doivent donc être réalisés afin de proposer des alternatives à ces fluides : l’eau, dont l’ODP et le GWP sont nuls, fait partie de ces possibles alternatives. Cependant, son utilisation en climatisation est généralement liée à des conditions sub-atmosphériques dans l’évaporateur. Ces conditions d’ébullition particulières ont très peu été étudiées dans la littérature. D’après de précédentes études réalisées au laboratoire sur un canal d’évaporateur à plaque lisse, les transferts thermiques sont en majeure partie liés à l’évaporation d’un film liquide sur la paroi de l’évaporateur. Ce film est formé par croissance et éclatement des bulles de vapeur de taille centimétrique. Afin de maitriser la production frigorifique, il est nécessaire de maîtriser le film liquide et par conséquent de caractériser la dynamique des bulles de vapeur pendant l’ébullition nucléée et, plus particulièrement, la hauteur de projection après explosion. C’est l’objectif de cette étude. Des vidéos, capturées précédemment par caméra rapide, sont analysées à l’aide d’un programme Python développé spécifiquement afin de calculer les caractéristiques de la bulle. Il est notamment mis en évidence que la hauteur de projection est corrélée à la vitesse de croissance et la taille de la bulle avant éclatement