What is the thermal resistance of the cast aluminum heating tube?
For the high-temperature liquid metal working medium cast aluminum heater, because the working medium and the metal tube core have the same magnitude of thermal conductivity, the equivalent thermal conductivity of the working medium filled with the working medium is equivalent to the metal thermal conductivity. The radial thermal resistance has a certain influence, but it is not very large, and its radial thermal conductivity is low. For medium and low temperature cast aluminum heaters, many experimental data show that due to the low thermal conductivity of the working fluid itself, the temperature difference mainly depends on the tube core structure and whether the liquid is boiling. Of course, for the same die structure. The larger the thermal conductivity of the liquid, the smaller the corresponding thermal resistance, but there is no linear relationship between the two.
In the cast aluminum heater, whether the working fluid boils or not has a great influence on the thermal resistance. -Generally speaking, when the heat flux is high, the liquid in the core of the Yanfa section will boil. For different tube cores, the effect of boiling is different. For the axial channel tube core, the vapor bubbles generated by boiling can easily escape to the vapor space, so the boiling will not affect the liquid flow in the tube core, but strengthen the heat exchange.
However, for tube cores with nets on the axial channel or tube cores with annular flow channels, the steam generated by boiling in the tuck body channel is not easy to escape because of the obstruction of the liquid film on the fine mesh net, thus increasing the size of the liquid The flow resistance even causes local dry bundling in the evaporation section. All of these will cause unpredictable degradation of cast aluminum heater performance. Therefore, for this type of tube core, a working fluid that is not prone to boiling should be selected.