Estimation of Thermal and Hydraulic Characteristics of Compact Brazed Plate Heat Exchangers

Sammanfattning: This thesis work presents various performance estimation methods of compact brazed plate heat exchangers (BPHE) operating in single phase, condenser, evaporator, cascaded and transcritical applications. Such methods play a vital role in development of heat exchanger selection software and during geometry parameter estimation in the new product development process. The suitability of employing commercial computational fluid dynamics (CFD) codes for estimating single phase thermal and hydraulic performance is investigated. Parametric studies are conducted on geometries of single phase fluid sections to isolate and quantify the influence of individual geometric parameters. The influence of mesh characteristics, choice of boundary conditions and turbulent flow modeling on the accuracy of the thermal and hydraulic predictions is presented. Benefits of simulation of fluid flow in entire channels and characteristics of channel flow for different geometric patterns are also presented. A computationally light, general, robust and continuous rating calculation method is developed for implementation in BPHE selection software. The pressure-enthalpy based method provides a generic rating core for various types of applications and provides extensive post processing information of the heat transfer process. General single phase thermal and hydraulic empirical correlations are developed as functions of plate geometric parameters. For facilitating better integration of the developed calculation method with other refrigeration system simulation software, first or higher order continuity is maintained in the sub-routines used for calculating local heat transfer coefficients and refrigerant properties. A new finite grid interpolation method is developed for fast and accurate retrieval of refrigerant properties. The developed method is currently implemented in SSPG7 (BPHE selection software of SWEP International AB) for supporting transcritical CO2 calculations and cascaded heat exchanger calculations. Additionally, the methods developed for single phase and two phase test data evaluation based on meta-heuristic optimization routines is also presented. The application and results of using the developed rating models for various types of calculations is summarized. Other topics such as influence of variable fluid properties on BPHE rating calculations, influence of multi-pass flow arrangement on lumped BPHE rating calculations are briefly presented.