A METHODOLOGY AND BENCH DESIGN FOR EXPERIMENTAL STUDY OF HEAT PUMP THERMODYNAMIC CYCLES USING CO_2 BASED MIXTURES: METHODE ET BANC D'ESSAIS POUR L'ETUDE EXPERIMENTALE DE CYCLES THERMODYNAMIQUES DE POMPE A CHALEUR UTILISANT DES MELANGES A BASE DECO_2

摘要

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 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 CO_2, and with the addition of propane will be given.