HexTraSim - Optimal Modeling of Heat exchangers for transient simulations

Due to the enormous number of refrigerators worldwide and the associated high total energy demand of the refrigeration sector as well as the resulting emissions, manufacturers of refrigerators are challenged to develop even more efficient appliances which should guarantee an optimal use of energy. Since the climate debate has now also become a major issue in society, the efficiency of refrigerators also plays an important role in terms of purchasing decisions. According to the current state of knowledge at the Institute of Internal Combustion Engines and Thermodynamics about the refrigeration process and especially about its modelling, heat exchangers are the components that still hold the greatest uncertainty and thus the greatest potential in terms of efficiency. The planned research project therefore focuses on deepening the basic knowledge of the heat exchangers used in household refrigeration appliances in order to subsequently optimize their energy utilization and thus the entire refrigeration cycle. This will result in an increase in efficiency and, due to the high number of refrigerators worldwide, in a significant reduction in electricity consumption and of the associated emissions. This basic research on heat exchangers is carried out by means of experimental investigation on a calorimeter test bench and by means of simulated analysis (CFD). In order to be able to model the heat exchangers with high accuracy and thus use them in a 1D refrigeration cycle simulation, the so-called method of influence factors is applied. The influencing factors are to be determined experimentally as well as simulation-based and both methods are to be compared regarding their suitability for application in a development process. The experimental measurement of transient operating conditions of the entire unit will validate the 1D overall simulation model including the heat exchangers. By means of this 1D refrigeration cycle model, it is possible to predict the energy efficiency of household refrigeration appliances, e.g. when using different heat exchanger variants. Furthermore, for the first time meaningful insights into the refrigerant charge, its distribution and displacement under transient operating conditions can be gained. The project idea was born during a joint discussion between the company and the Institute for Internal Combustion Engines and Thermodynamics, during which the findings from the project ECO-Simulation (FFG No. 865103) were analysed. In the course of this discussion, the challenges for the next major innovation step in refrigeration technology were discussed. The method of modelling and integrating heat exchangers for a more precise simulation-supported design of the refrigeration process of household refrigeration appliances, which is planned as a result of this project, will serve as a basis for the optimization of the appliances, which can be fully exploited through further cooperation.