Combined Material and Process Development for Efficient Adsorption Heat Pumps

• Applicants: Professor Dr.-Ing. Bastian Etzold; Professor Dr.-Ing. Ulrich Nieken
• Subject Area: Chemical and Thermal Process Engineering
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 266154638

Exergetically high-grade electrical energy is used for the operation of conventional heat pumps for heating and cooling purpose. Thermally driven adsorption heat pumps using solar thermal power, geothermal power or industrial waste heat are an interesting alternative. Characteristic for adsorption heat pumps is the cyclic change between loading and regeneration of the solid adsorbent, and the operation between three temperature levels. Conditions for a high thermal efficiency are: 1) The adsorbent used has to have a high adsorption capacity and - relative to the whole process - fast sorption kinetics. The material should have a high inner surface (micro pores) and good accessibility through an adequate number and arrangement of transport pores (macro pores). 2) To ensure fast heating and cooling of the adsorbent the thermal conductivity of the adsorbent should be high for a fast and complete temperature change. 3) The adsorbent (and the sorbate) are heated up and cooled down periodically. One goal of the overall process is to minimize such heat charge losses. This can be achieved - in addition to the issues mentioned in 2) - by minimizing the heat capacity of the adsorbent and reduction of inert masses or a process control with multiple modules in a simulated countercurrent flow of adsorbent and heat carrier which leads to an internal recovery of stored heat. 4) Minimization of transfer resistances of the sorbate flow between adsorbent and phase change zone (condenser/evaporator). It is possible to optimize each of the aforementioned requirements taken in isolation, but not all properties simultaneously. For example, on the one hand a high thermal conductivity of the adsorbent can be achieved through the addition of conductive materials which reduces the adsorption capacity on the other hand. The influence of single material properties also depends on the favored overall process: the efficiency of a process with high internal heat recovery (simulated countercurrent process) is less sensitive against inert masses than a simple two-bed process. Material and process development is carried out independently of each other so far. Goals of material development are mainly at tasks 1) and 2) while the process technology development (3) and 4)) usually acts on the assumption of given and not influenceable materials. As a result of the described dependencies it can be assumed that this approach does not result in a common optimum of material and process. In the submitted project proposal both developments shall be brought in synergy to identify an ideal combination of material and process and exemplarily derive a methodology of combined material and process technology design.

• DFG Programme: Research Grants
• Major Instrumentation: Heißpresse mit Vakuummöglichkeit
• Instrumentation Group: 2130 Pressen und Maschinen zum Biegen, Drücken, Stanzen, Prägen, Ziehen