| Summary: | When designing a heat pump evaporator, it is necessary to use correlations that ensure small deviations of the designed and realized process parameters for specific input data. The aim of the work is to propose a suitable mathematical model for the physical process in the tubular evaporator of the heat pump. The applicability of the proposed mathematical model in the design of the heat pump was evaluated by comparing the results obtained from the experimental tests of the tubular evaporator of the heat pump with the numerical results obtained from the application of the proposed mathematical model. For the experimental tests, a tubular evaporator was made and 10 measuring points were set up, where the process parameters were measured (temperature and pressure drop of the working media R134a and water). Theoretical results were obtained by dividing the evaporator into control volumes and solving the corresponding system of equations of the proposed mathematical model using the Runge-Kutta and Adams Moulton predictor-corrector method. As an independent parameter, the water temperature at the inlet to the evaporator was varied in the range of 10 °C to 18 °C. The test results show that the largest deviation of the calculated and measured water temperature is +0.41 °C to −0.58 °C, while the refrigerant temperature is +0.43 °C to + 0.52 °C. The largest deviation of the evaporator thermal capacity based on the calculations and experimental tests is +9.39% to −6.31%. Based on the obtained results, it is possible to recommend the use of the proposed mathematical model for the design of the tubular evaporator of a heat pump.
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