Design and simulation of finned-tube heat exchangers using pure and mixed refrigerants

A computational model for the detailed design of finned-tube heat exchangers is presented. Coils are discretised into tube elements for which the governing equations are solved using local values of temperature, pressure, physical properties and heat transfer coefficients. Single phase, condenser and evaporator cases can be treated using water, R22, R134a, and various refrigerant mixtures based on R32, R125, and R134a. The software can handle non-conventional coil circuits with different numbers of inlets and outlets, non-uniform air distribution at coil inlet face, using smooth and internally finned tubes. All data is supplied through a user-friendly PC-Windows based graphical interface, allowing very flexible design and selection of various circuit configurations. User-defined heat transfer and pressure drop correlations can also used for both the internal fluid and air. This paper also presents new validation results from experiments using water and R22, with and without moisture condensation on the fins. Comparisons with tests show errors of less than 5% on the coil duty. A performance simulation of a coil using R22 and a ternary mixture is presented to validate the programme algorithms developed for mixtures.