László Garbai

Measurement testing of heat transfer coefficients in the evaporator and condenser of heat pumps

In our earlier studies, it has been stated that the validity and limits of correlations developed for the calculation of heat transfer processes in the evaporator and condenser of heat pumps are not published in general. The values yielded for model structures and process characteristics indicate extreme ranges of standard deviation. While the description and physical and mathematical modeling of phenomena occurring in heat pump components have developed really much and the mathematical accuracy of solutions can be increased at one’s own discretion, descriptions of changes in heat transfer and heat transfer coefficients in the course of refrigerant flow are quite uncertain. At the same time, these factors highly influence the accuracy of the solution. Our study presents the measurements and the new proposed heat transfer correlations, developed on the basis of such measurements, which can be used for calculating heat transfer in heat pump evaporators and condensers with higher accuracy than existing correlations in the literature.

Operation of Looped District Heating Networks

The study presents a methodology for the optimal operation of district heating networks with a circular conduit system. The authors discuss this this topic in an absolutely general form. By a special statement and solution of Kirchhoff Laws, node equations and loop equations, the hydraulic end point of the circle is determined, including the supply ratio of the consumer located at the hydraulic end point. Two objective functions are stated by the authors; one of them for the minimum of flow work, and the other for the minimum of power supplied. It is demonstrated that the objective functions yield different results. Theoretically more economical operation is ensured by the flow pattern resulting from the minimization of the power supplied.