Abstract
In the geyser boiling mode, the working fluid state is divided into a boiling process and a quiet process, and the sodium-potassium (Na-K) alloy heat pipe can discontinuously transfer heat at each boiling. The overheating of the liquid working fluid at the bottom causes short-term boiling and forms slug bubble, the strong condensing ability quickly conducts heat from the evaporator section. And geyser boiling can occur before the working fluid forms continuous flow, so it transfers more heat at lower temperatures than natural convection cooling. In this study, the heat transfer process of a Na-K alloy heat pipe with forced convection cooling under different heating power was experimental studied. The geyser boiling mode can make the Na-K alloy heat pipe work below 650 °C and reduce the start-up time. In the process of geyser boiling, the heat transfer quantity was increased by the boiling frequency and the amount of vapor produced in a single boiling. The boiling temperature had no obvious change with the increased of heating power, and the condenser section temperature increased with the heating power.
Highlights
The results showed that the heat transfer performance of the alloy is better than sodium and potassium
Due to geyser boiling can occur before continuous flow is formed in the condenser section under forced convection cooling, the start-up capacity and heat transfer capacity of a Na-K alloy heat pipe under forced convection cooling were experimentally studied at different heating power (800 W, 1000 W, 1200 W and 1400 W)
The Na-K alloy heat pipe can work in geyser boiling mode, and transfer a lot of heat quantity at lower temperature than natural convection cooling
Summary
Potassium and other alkali metals are often used as working fluid for high temperature heat pipe because of their high boiling temperature, low saturation pressure, high latent heat of vaporization and high heat transfer performance. Na-K alloy was the first used as coolant in nuclear industry, Anderson et al [16] proposed to replace pure metals such as sodium and potassium as high temperature heat pipe working fluid. The start-up performance of liquid metal heat pipes is very different from the low temperature heat pipes, the effect of compressibility must be considered at start-up stage because of the low pressure and low density of vapor. The continuous flow can be formed only after the working fluid reaches a certain temperature, the vapor density and pressure increase significantly and the heat pipe can transfer heat effectively. Similar to other alkali metal heat pipes, the heat transfer limits such as sonic limit and viscosity limit appear in the start-up process of
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