Simulation of a micro heat pump cycle
Van Eldik, Martin
MetadataShow full item record
The purpose of this study was to develop a thermal cycle simulation for a micro heat pump. A feature of the simulation is that it can simulate the four qasic components in detail, based on fundamental principles. The product of this study is a simulation routine which can be used as a design tool for micro heat pumps as well as its individual components. Experimental tests were conducted on an existing R-134a micro heat pump.and the results were successfully used to verify the simulation routines. An extensive literature survey was conducted on heat pump component models as well as heat transfer correlations. In this study models were developed for each of the four basic components used in the micro heat pump, i.e. fluted tube water heating condenser, air-cooled evaporator, reciprocating compressor and capillary tube. The theory on which each model is based, was derived from first principles and the relevant model algorithms were developed and implemented in C++ computer routines. The component models were also integrated to allow a complete cycle simulation at different operating conditions. An advantage of the fluted tube condenser model is that it allows the surface area to be divided into any number of sections over which the change in refrigerant and water properties can be evaluated. The evaporator model calculates the change in refrigerant properties along the length of each tube in the coil. It can also predict in detail the state of the air across the coil face and along the depth of the coil. A model for simulating the compressor was derived which solves for both the mass flow rate and the refrigerant outlet conditions. Two capillary tube models were implemented. The first was based on a theoretical model obtained in the literature. This model did not provide sufficiently accurate results, however the second capillary tube model was based on a dimensional analysis providing a non-dimensional correlation for the mass flow rate. The coefficients of the correlation had to be modified for this application. The individual component models as well as the integrated cycle were both verified by means of the experimental data. The verification study showed that for the integrated cycle the condenser and evaporator heat transfer rates were predicted with average accuracies of 97% and 96% respectively. The refrigerant mass flow rates predicted by the compressor and the capillary tube models resulted in an average accuracy of 95%. The high degree of accuracy obtained with the individual models as well as with the integrated cycle provides confidence in the simulation results. The simulation can therefore be applied as a design tool for micro heat pumps and its individual components.
- Engineering