Towards close-to-zero CO2 emission for energy systems: study of a novel heat and mass exchanger for water-based heat-pump
- Bourget, ON
- Temporary
- Full-time
150). Among the possible replacement fluids, natural fluids can offer interesting performance and are a long-term and sustainable solution. If one considers water, water also offers the advantage to be commonly used in sorption systems like in Lithum-bromide absorption systems, which combined storage capability and allow to upgrade the heat provided by the source with a low temperature level at a higher temperature level with a negligible amount of mechanical work input. Thus, these systems present an interesting option to faster the decrease of CO2 emission while increasing the efficiency of energy systems in the broadest sense, by a recovery of the under-exploited waste energy and renewable sources.However, although water is an apparently well-known fluid, its behavior in conditions representative to conditions encounter in thermal energy systems is not yet perfectly apprehended. The particularity of exchangers, used in water-based systems in contact with a low exergetic level energy sink, is the working pressure: at the lowest-pressure stage, the working pressure could be 100 times lower than the atmospheric pressure (around 10 mbar). Phase-change phenomena are different than the ones observed at higher pressure due to the change of thermophysical properties (Fig.1 to 3). The topology of two-phase flows is completely transformed (Fig.2). As a consequence, commercialized water-based systems (based on mechanical and thermal compressions) are at least two times bigger than conventional commercialized systems based on HCFC fluids. But, to allow the deployment of water-based systems, and thus faster the decrease of CO2 emission, the cost and the size of these systems must be reduced, which means to improve the compactness of key components like exchangers.Content of the PhD thesis and main tasks:Experimental and numerical studies will be conducted to understand and quantify observed phenomena occurring inside the novel heat and mass exchanger designed for water-based systems. In this novel heat-exchanger, growth and bursting of bubbles are expected to be observed. These bubbles will allow the deposition of a thin liquid film that will be drained and/or vaporised. The local heat-transfer coefficient are thus expected to be significantly improved compared to conventional falling-film heat-exchanger since the deposited liquid film thicknesses by the burst of bubble could be significantly thinner than falling film thicknesses usually obtained in traditional exchangers (for water, the estimated deposited film thicknesses observed in the two-phase flow heat exchanger studied in [3] range from 66 µm to 155 µm vs. falling film thicknesses higher than 500 µm measured in [4]).To provide experimental information required to conduct these analyses, a new optical measurement technique will be developed at LEMTA (Nancy) to measure the temperature and the concentration of LiBr. The focus will be on laser-induced fluorescence (LIF) using fluorescent dyes that are sensitive to temperature and to the presence of Br-/ Li+ ions.Thus, in addition to the valorisation and dissemination of the obtained results, the main tasks of the PhD student will be:
- To design and develop a simplified experimental setup to adjust the concentration of LiBr and the temperature at atmospheric pressure. This prototype will be used for the validation of the measurement technique develop at LEMTA.
- To develop a novel measurement technique to characterize the volumetric mean of the temperature and the concentration of the working fluid (LEMTA Laboratory);
- To conduct phenomenological and thermal studies of heat and mass transfer occurring in the novel exchanger (already designed) with water and (water + LiBr) solution (LOCIE Laboratory);
- To develop simple physical models for the main heat and mass transfer phenomena.
- Characterization of the novel heat and mass exchanger in term of simple models and performances maps;
- Development of innovative measurement techniques to access the volumetric mean temperature and concentration in LiBr.
- 2 existing lowpressure experimental test benches with their acquisition chains
- 1 highspeed high-resolution camera (Photron FastCam Mini)
- 1 confocal device
- Support of the technical team
- photomultipliers, USB spectrometers, laser diodes
- dyes
- Strong knowledge on thermal and energy systems, heat and mass transfer, fluid mechanics, thermodynamics;
- Aptitude for experimental manipulation;
- Basics skills on Python or other programming language.
- Localisation of the PhD thesis:
- Supervision teams: DR CNRS Guillaume Castanet, MCF. Florine Giraud
- Starting of the PhD position: September 2024
- Founding: National French Agency - Research project NEWS
Savoie Technolac / 73376 Le Bourget du Lac / FRANCEtel: (+33) 4 79 75 85 85 / poste : 7729References :[1] Van Stralen S. J. D., Cole R., Sluyter W. M., Sohal M. S., 1975. Bubble growth rates in nucleateboiling of water at subatmospheric pressures. Int. J. Heat Mass Transfer. Vol. 18, p. 655-669.[2] Giraud, F., Toublanc, C., Rullière, R., Bonjour, J., & Clausse, M. (2016). Experimental study of water vaporization occurring inside a channel of a smooth plate-type heat exchanger at subatmospheric pressure. Applied Thermal Engineering, 106, 180-191.[3] Giraud, F., Rullière, R., Toublanc, C., Clausse, M., & Bonjour, J. (2015, August). Preliminary experimental investigation on water boiling phenomena in a liquid layer at subatmospheric pressure. In 24th International Congress of Refrigeration (ICR 2015).[4] Collignon, R., & Stutz, B. (2022). Numerical simulation and modeling of the heat and mass transfer in a grooved flat falling film evaporator. Int. J. Heat Mass Transf.In France, leaks of refrigerant in closed thermal system for refrigeration and excluding automotive air-cooling is responsible for 3,5 million tons equivalent CO2 release to the atmosphere per year. CODA Stratégies, ADEME (2021), La climatisation dans le bâtiment.Funding category: Contrat doctoral
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PHD title: Énergétique et Génie des Procédés
PHD Country: FranceRequirementsSpecific RequirementsDiploma: Master 2 in physics or energy field
Strong knowledge on thermal and energy systems, heat and mass transfer, fluid mechanics, thermodynamics;
Aptitude for experimental manipulation;
Basics skills on Python or other programming language.Additional InformationWork Location(s)Number of offers available 1 Company/Institute Laboratoire LOCIE, Université Savoie Mont Blanc Country France City Bourget du Lac GeofieldWhere to apply WebsiteContact WebsiteSTATUS: EXPIRED
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