Abstrakt

The dissertation aims to develop a method for predicting heat transfer during flow condensation, especially at high values of reduced pressure and saturation temperature. The existing laboratory testing rig has been expanded, acceptance tests have been performed and measurement campaign has been conducted. Experimental data were collected on flow condensation of R1233zd(E) in a mini-channel at medium and high values of saturation temperatures. The heat transfer coefficient for flow condensation in a horizontal copper tube with an inner diameter of 3 mm was investigated. The experiment was carried out for saturation temperatures in the range from 78°C to 152°C, corresponding to reduced pressure values from 0.2 to 0.8. The flow structures inside the test measurement section on a section of a glass tube with a diameter of 3 mm was recorded. Experimental flow maps were developed based on experimental data from 4 literature sources. In addition, an extensive database of experimental heat transfer coefficient points from the literature was collected, consisting of 4659 points for 25 fluids. The collected database covers the range of reduced pressure from 0.1 to 0.9 for different values of mass velocities and test section diameters. Two alternative models for determining the heat transfer coefficient during flow condensation were developed. The first is a modification of the semi-empirical model based on the energy dissipation hypothesis, an in-house model which has been under development for years, for predicting the heat transfer coefficient during condensation. The second approach is a model using a unidirectional neural network to predict the heat transfer coefficient. In addition, maps of two-phase flow structures during condensation were developed in terms of the transition from annular flow to the transition region and single bubbles.

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