Modeling and Experimental Study of a Heat Pump Water Heater Cycle

Heat Pump Water Heaters are becoming more and more interesting technologies for efficient sanitary hot water production. The specificities of hot water production compared to the traditional use of heat pumps for space heating are the relatively constant energy needs for different outdoor temperatures and the more rapid dynamics associated with water temperature elevation. This study focuses on the modeling and performance evaluation of an R134a air to water heat pump water heater with an external mantle heat exchanger. By nature being a thermo-hydraulic kind of system, a heat pump water heater requires both the aspects of fluid mechanics and heat transfer to be covered when modeling the global system composed of the heat pump and the thermal storage tank. Hence, a detailed thermodynamic model of the heat pump cycle is developed using Modelica covering a description of all the components of the thermodynamic cycle from compressor to evaporator and all the possible operating conditions such as heating and defrosting. This model is associated with a zonal model accounting for the convective behaviour patterns of the water observed in the storage tank at different operating conditions and boundary conditions imposed by the heat pump cycle. This dynamic model is compared against experimental data acquired from an instrumented system tested in laboratory conditions for different phases such as draw-off, standby and heating. Good precision ( \u3c 5-10%) is attained for the heat flow rates, temperatures along the thermodynamic cycle and temperature profiles in the water tank for the different phases tested. It is shown that the water tank plays an important role in the performances of the system that is very sensitive to the operating conditions such as draw-off flow rate, heat pump operating capacity or thermal losses, that cause mixing and destruction of the thermal stratification and a reduction in the available energy for the end user

Experimental Investigation of a New High Temperature Heat Pump Using Water as Refrigerant for Industrial Heat Recovery

Currently, improving energy efficiency becomes a main challenge for all industrial energy systems. This challenge involves an improved recovery of wasted heat generated by several industrial processes. Large energy savings and potential environmental benefits are associated with the use of industrial heat pump mainly at high temperature levels. A laboratory flexible industrial scale heat recovery system is able to reproduce the operating conditions of real case simulating energetic losses and requirements in high temperature industrial applications. The integrated heat pump is an electrically-driven vapor compression using a twin screw compressor. Water vapor has been adopted as a working fluid using a modified screw compressor to carry out a dry compression process at high temperature levels. This heat pump generates vapor using flash evaporation. A purging valve is implemented in order to eliminate non-condensable gases present in system. Experimental simulation of the start-up phase has been presented showing the non-condensable purging process and the evolution of some parameters of the heat pump. Several scenarios of industrial processes for high-temperature heat recovery (heat sources between 80°C and 90°C) and heat upgrading are numerically simulated. The presented results show the global energy savings and the environmental benefits of using water as refrigerant at high temperature levels

Modelling Of An Automotive Multi-Evaporator Air-Conditioning System

With the arrival of plug-in hybrid electric vehicles (PHEV) and battery electric vehicles (BEV) with significant autonomy, battery cooling becomes a necessity in driving mode to ensure their durability and ability to charge rapidly.  For these vehicles, the refrigerating system may be composed of two evaporators (for front and rear passengers) in order to afford cooled air in the cabin and a chiller or a built-in battery evaporator to cool down the traction battery. This kind of multi-evaporator air-conditioning system has a number of technological barriers that must be undone. They are related to the components sizing in a context of cost reduction and control of such complex systems. The study therefore focuses on understanding the dynamic coupling of the several loop components such as the three evaporators having different cooling capacities. Understanding the behaviour of their respective expansion devices and the choice of these latter is also essential to control properly the transient phase and ensure an optimal operation of the air-conditioning system. In the literature, the effect of battery cooling by means of a chiller on the automotive air-conditioning loop has been already proved by simulation in the Dymola® [1] environment. The simulation results for several driving cycles, refrigerants and ambient conditions emphasize the thermal discomfort caused by the use of the chiller loop. However, no global control strategy has been established. More recently, a first study of an air conditioning system model with three evaporators was carried out [2]. After the validation of their component models, a cool down test was performed to test the performance of their air conditioning system. From a control point of view, a simple PI control on the temperature of air blown at the front evaporator was used to regulate the speed of the compressor. In the building sector [3], the benefits of a supervisory controller to regulate the multi-evaporator air conditioning system was developed. Although this type of decentralized model seems to be robust and applicable to the car, it requires the use of sensors and components currently too costly and subject to a less restrictive environment than in automotive. The challenge of such a cooling loop lies in the dynamic coupling of components as well as their design. The model of a multi-evaporator automotive air conditioning system (two evaporators and a chiller) is thus produced using the 0D AMESim® software. In order to obtain more representative results in the transient state, the majority of components, including the chiller and regulators, are physical models giving a good representation of their internal geometries. These models were validated using experimental test maps. The first results highlight the importance of the regulators choice on the loop stability. A comparison of several types of expansion valves (orifice, thermostatic and electronic) will be conducted in order to select the most suitable to meet the price-performance compromise. Finally, control strategies are studied in transient state to further improve the stability and speed of convergence to the target instructions

Performances d'une machine frigorifique munie d'un détendeurà éjecteur utilisant du HFO 1234yf

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Simulation of the behaviour of a centrifugal chiller during quick start-up

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Ébullition convective du Dioxyde de Carbone (étude expérimentale en micro-canal)

Les préoccupations relatives à la destruction de la couche d ozone et au réchauffement climatique ont suscitées un regain d intérêt pour l usage du dioxyde de carbone comme fluide frigorigène. La présente étude a pour objectif de synthétiser l état des connaissances sur l ébullition convective du CO2 mais aussi d élargir l investigation à des conditions nouvelles. Les données d échanges thermiques disponibles dans la littérature sont analysées en fonction du diamètre du canal et de la température de saturation. Une réflexion est proposée sur les mécanismes physiques, y compris les configurations d écoulement, qui influencent les échanges thermiques et qui leur donnent des caractéristiques particulières. La validité des méthodes de prédiction du coefficient d échange thermique et des pertes de pression est discutée pour le cas du CO2. Du point de vue expérimental, une section d essai a été mise au point pour étudier l évaporation du CO2 dans un micro-canal de 0,529 mm de diamètre. Des mesures de pertes de pression et du coefficient d échange thermique local ont été obtenues principalement pour trois températures de saturation, - 10 ; -5 et 0 C, trois densités de flux thermique, 10 ; 20 et 30 kW/m2, et pour des vitesses massiques comprises entre 200 et 1200 kg/m2.s. Les résultats des principales méthodes de prédiction sont comparés à nos mesures et de nouvelles approches corrélatives sont proposées. L évaporation convective (en opposition à l ébullition nucléée) semble jouer un rôle important dans les échanges thermiques. Par ailleurs, une augmentation inattendue du titre de début d assèchement avec la vitesse massique a été observée pour une température de - 10 CEnvironmental concerns regarding ozone depletion and global warming induced a renewed interest in the use of carbon dioxide as a refrigerant. The aim of the present study is to do a synthesis of the current knowledge on CO2 flow boiling. The purpose is also to extend the experimental investigation to new conditions. Heat transfer data from the open literature have been analysed depending on the channel diameter and the saturation temperature. A reflection is presented on the physical phenomena, including flow patterns, playing a part in the heat transfer and leading to specific behaviours. Regarding the available methods to predict the heat transfer coefficient and the pressure drop, their adequacy is also discussed for the case of CO2. Concerning the experimental work, a test section was set up so as to study the CO2 vaporisation in a single 0.529 mm tube. Local heat transfer coefficient and pressure drop data were obtained mainly for three saturation temperatures, i.e. -10; -5 and 0 C, three heat fluxes, i.e. 10; 20 and 30 kW/m2, and for mass velocities ranging from 200 to 1200 kg/m2.s. Results from well know prediction methods are compared to our measurements, and new correlative approaches are also suggested. It seems that convective vaporisation (as opposed to nucleate boiling) represents an important contribution to the heat transfer. Moreover, an unexpected increase of the dryout inception quality when the mass flux rises is observed for a temperature of - 10 C.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Performances d'une machine frigorifique munie d'un détendeur à éjecteur utilisant les fluides R134a et HFO 1234 yf

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Performances énergétiques des coulis d'hydrates dans une boucle pilote de réfrigération secondaire

Pour être utilisé en réfrigération secondaire comme matériau à changement de phase dans un fluide frigoporteur, un hydrate doit posséder une enthalpie de dissociation élevée, à une température adaptée à l application (positive pour de la climatisation) et à une pression acceptable pour une installation industrielle. De plus, le mélange diphasique doit présenter de bonnes conditions d écoulement et d échanges thermiques. Un dispositif dynamique constitué d'un réacteur agité et d'une boucle de circulation, placé dans une chambre climatique, a été développé pour l étude de coulis d hydrates de dioxyde de carbone. Pour ce dispositif, un protocole a été mis en œuvre pour le refroidissement d une solution chargée en CO2, générant des coulis d'hydrate à taux d hydrate allant jusqu'à 25% véhiculant une chaleur latente importante (374 kJ.kg-1). Une étude cinétique sur la formation des hydrates de CO2 dans le réacteur agité à été réalisé et montre que la cinétique de formation de ces hydrates est de 2 %.h-1 dans le réacteur pour une pression, une température, et une vitesse d'agitation de départ de 3 MPa, 12 C et 1042 tr/min et pour une température de consigne du groupe froid de -1 C. L étude rhéologique du coulis a permis de mettre en place une corrélation empirique de type Herschel-Bulkley en fonction du taux d hydrates qui permet une caractérisation satisfaisante du comportement rhéologique du fluide. Les résultats de l étude thermique ont permis d établir des corrélations entre les nombres de Nusselt et de Reynolds qui caractérisent les régimes de fonctionnement thermique du système.To be used as phase change material in a secondary refrigerant, a hydrate must enclose a high dissociation enthalpy, at a temperature adapted to the application (positive for air-conditioning) and a pressure suitable for an industrial facility. Moreover, the two-phase mixture must present good conditions of flowing and heat exchange. A dynamical set-up with a stirred tank reactor with a loop of circulation, placed in a thermostated room, was developed for the study of carbon-dioxide-hydrate slurries. In this set-up, one protocol was carried out: by cooling of a water-CO2 solution, generating slurries hydrate rates 25 %, conveying a high latent heat (374 kJ.kg-1). A study of CO2 hydrate formation kinetics was lead in the tank reactor and the results showed the CO2 hydrate formation kinetics is 2 %.h-1 for a pressure, temperature and a stirring rate at the begin of 3 MPa, 12C and 1042rpm and a temperature of the chiller about -1C. A study rheological allows the development of an empirical Herschel-Bulkley-type correlation as a function of the hydrate rate was achieved for rheological characterization of the fluid behavior. The thermal results obtained allow establishing correlation as a function of Nusselt and Reynolds number which characterize operational regimes of the system thermal.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocVILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Performances d'une machine frigorifique munie d'un détendeur à éjecteur utilisant les fluides R134a et HFO1234 yf

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