A new model and solutions for a spiral heat exchanger and its experimental validation

A spiral heat exchanger was applied in a ground source heat pump (GSHP) system that is primarily used for residential indoor heating. Studies that have been performed on the heat transfer of spiral heat exchanger have focused on field measurements and numerical analysis; however, theoretical research on the subject is absent in the literature. In this study, a methodology is proposed to analyze the heat performance of a spiral heat exchanger. A ring source model was established and solved analytically to describe the temperature variation of the ground caused by a spiral heat exchanger. The validity of the model was examined by an experiment on the soil temperature variation with a spiral heater. The virtual ring tube surface temperature response of unit ring circle was calculated by a superposition of the contributions of the ring source itself and adjacent ring sources. Furthermore, a fast algorithm was created to compute the average tube surface temperature resulting from the dimensionless temperature rise at a point far from the ring source that is constant when the non-dimensional distance is less than 0.13. The author confirmed that the calculation time of this proposed algorithm decreased by a factor of 100 compared with the traditional integration method. A system designer will find this algorithm helpful when determining the size of a heat exchanger under a required heating load, particularly for different arrangement of spiral heat exchangers.