Modellgestützte Entwicklung von Adsorptionswärmepumpen
- Model-based development of adsorption heat pumps
Lanzerath, Franz; Bardow, André (Thesis advisor)
1. Aufl.. - Aachen : Mainz (2014)
Dissertation / PhD Thesis
In: Aachener Beiträge zur Technischen Thermodynamik : 3
Page(s)/Article-Nr.: 162 S. : Ill., graph. Darst.
Zugl.: Aachen, Techn. Hochsch., Diss., 2014
The worldwide increasing heat and cold demand leads to rising energy consumption and emission of CO2. In contrast, a decrease of CO2 emissions is necessary to limit climate change. Thermally driven adsorption heat pumps and chillers can reduce CO2 emissions by use of waste heat or solar radiation. Thus, adsorption heat pumps can provide heat and cold almost emission free at high primary energy efficiencies. A drawback of the adsorption technology is the size and cost of the devices. Compared to mechanical compression heat pumps and chillers adsorption devices are significantly larger. Furthermore, the heat exchangers of adsorption chillers are bigger and low number of units leads to higher costs. Current research activities focus on the efficiency and the specific heating and cooling capacity of adsorption units to make them economically competitive. System design, new adsorbent materials and heat exchanger design are the main research topics. Much less attention is given to evaporator and condenser design although these components are equally essential for operation of the adsorption device. For targeted development dynamic computer models are usually employed. In general, the models are neither experimentally calibrated nor validated at different operating points of real adsorption systems. Thus, high uncertainty in model-based development of adsorption units remains. The present dissertation refines model-based development of adsorption heat pumps and chillers on two levels: On the system level a dynamic model of an adsorption unit is developed, experimentally calibrated and validated at different operating points of a real adsorption system. The model provides qualified prediction of system behavior since accurate and coherent models are used. Furthermore, the model allows for reliable evaluation of new adsorbent materials as it is validated against the change of material parameters. This renders the possibility of integral optimization of process and material. On the component level the development potential of adsorption units is exemplary demonstrated for the evaporator. The evaporator usually possesses low heat transfers characteristics and limits the capacity of the whole adsorption unit. Heat exchangers employing capillary action lead to significantly higher evaporation performances. In this work porous coatings are investigated to promote capillary-assisted evaporation. The coating is applicable to many heat exchanger designs and may lead to powerful and cost-efficient evaporators in future. In addition, this work studies the general influence of the evaporator on the performance of adsorption units. The developed system model is used to quantify the evaporator influence and to determine the optimal test conditions for experimental evaluations. The results allow sound design of the evaporator and identification of optimal process conditions to exploit the full potential of the adsorption unit. Thus, validated simulation models allow targeted optimization of adsorption heat pumps and chillers. This work provides a tool to increase the efficiency and capacity of adsorption units that is essential for the consumer acceptance and distribution. In future, the adsorption technology may therefore contribute to a larger extent to cover the worldwide heat and cold demand with the economically friendly use of waste heat and solar energy.
- Chair and Institute of Technical Thermodynamics