Fordamping og kondensasjon i varmerør med kalium som arbeidsmedium

Abstract

In order to reduce energy consumption, high temperature heat recovery is of great interest in industry. Liquid metal heat pipes are of special interest due to their superior thermomechanical properties. This master s thesis is a part of a Ph.D., and a rectangular heat pipe design, with potassium as working fuid, is under construction in order to utilize the heat directly from the side walls of the electrolyte cell. The main purpose in this master s thesis is to develop a thermal-hydraulic model in order to simulate operation temperatures under different operational conditions, being heat fluxes in the range of 150 to 300 kW/m2 and temperatures between 400 and 650 . The pressure variation and the heat transfer processes with their corresponding limits are evaluated with the different operation conditions. In order to achieve reliable results, a review had to be performed on available potassium data at saturation. It is found impossible to operate in the whole temperature range by only changing the heat flux. The condenser length has to be reduced to 120 mm in order to obtain operation temperatures from 400 to 650 in the heat flux range present. Nusselt laminar film condensation theory is found to be valid for all operational conditions in the proposed system. The investigated correlations on pressure variation neglects the effect of friction, this is believed to be a righteous assumption if one assumes 40 to 50 percent pressure recovery in the condenser. When decreasing the condenser length, the sonic limit will be reached with a heat flux of 150 kW/m2. Both the boiling and capillary limitation is found to not be of concern. Several correlations are available for the flooding limit, however they give scattering results. In order to avoid flooding according to the correlations used here, the channel gap has to be increased to 50 mm. However, the background for the correlations will be needed in order to justify their validity.