Dynamic optimization of heat exchanger using entropy generation minimization - Archive ouverte HAL
Communication Dans Un Congrès Année : 2021

Dynamic optimization of heat exchanger using entropy generation minimization

Résumé

In order to reduce fossil fuel consumption for heat and cold generation, different low temperature heat sources have been considered for heat pump operations such as sewage systems, sea water, ground water and drinking water. Raw water systems can also be used as a heat source for heat pump, heat sink for chiller, or for direct cooling. These systems represents a high thermal potential for some clients, according to their activity. In this study, the thermal potential of a raw water system (made up of 5000 km of piping and carrying 200 million m3 annually in the south of France) is investigated. To this day, this source has not been used. The main problem is the optimisation of the equipment sizing according to the temporal variability of water flow, temperature and heat (or cold) demand. The dynamic behaviour of heat exchanger between network and user is the key parameter to enhance the performance of the system. For the raw water source, temperature, flow, and heat demand are highly time dependent. The method is based on the minimization of entropy generation in the heat exchangers between the water pipes and the users. The optimisation of the sizing and the location indicate where to install direct heat exchange systems. In order to calculate entropy generation in the heat exchanger, a dynamic model of a simple heat exchanger (concentric tube) is developed. It determines the pressure and temperature profile along the heat exchanger according to time. Temperature is calculated for water and for the heat exchanger partition wall. By integrating the terms of entropy generation due to temperature difference and to pressure drop along the heat exchanger, the value of total entropy generation is obtained under transient operation. Total entropy generation is used as an objective function to optimize heat exchanger geometry (length and diameters) and control mechanism. The method has been used to model direct cooling of a datacenter using a raw water network as a heat sink. Optimization is done considering a year of operation; seasonal and daily fluctuations for water flow and temperature are considered. Results show that entropy gain is important when the heat exchanger optimal size is chosen. The use of the raw water network connected to reversible heat pump for building heating and cooling have also been studied and achieves high gain compared to air-source heat pump.
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Dates et versions

hal-03598501 , version 1 (07-03-2022)

Identifiants

  • HAL Id : hal-03598501 , version 1

Citer

J-H Ferrasse, S Sole, J-F Cloarec, Gautier Hypolite. Dynamic optimization of heat exchanger using entropy generation minimization. CHISA 2021 VIRTUALLY - 24th International Congress of Chemical and Process Engineering, Mar 2021, Prague (online), Czech Republic. ⟨hal-03598501⟩
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