The liquid metal thermal management test device in the field of aerospace technology testing was developed by the Institute of Physics and Chemistry Technology of the Chinese Academy of Sciences and installed in the aerospace basic test cabinet of the Mengtian Experimental Module of the space station. It uses bismuth-based metal with low melting point, high biosafety and stable chemical properties. Carry out characteristic research and experimental verification of flow heat dissipation and phase change temperature control technology in space microgravity environment.
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The location of the liquid metal thermal management test device in the aerospace basic test cabinet
PART.1
What is liquid metal? What principles are involved in testing?
Liquid metal is an amorphous, flowable liquid metal. It is a general term for a series of low melting point metals and alloy materials. It is liquid at room temperature or lower heating temperature and has fluidity. It has strong electrical conductivity and thermal conductivity. It has the characteristics of high efficiency, low viscosity and wide liquid temperature range. This experiment mainly used two heat dissipation principles of liquid metal, namely convection heat transfer and solid-liquid phase change thermal control.
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liquid metal
Convection heat transfer means that liquid metal flows through a heating surface, absorbs surface heat, and maintains the temperature of the heating surface at a certain appropriate value. The liquid metal absorbing heat will heat up, transfer the heat to the environment in a certain heat dissipation device, and then recover. to the initial temperature, thereby flowing through the heating surface again to achieve circular flow;
Solid-liquid phase change thermal control is a phase change heat sink installed on the heating surface that melts after absorbing heat and changes from solid to liquid. The melting process absorbs heat but the temperature does not change, thereby controlling the heating surface at a certain appropriate temperature. When the heating surface no longer works, the liquid metal gradually solidifies into a solid state. During the solidification process, the temperature remains unchanged but heat is released. This heat gradually dissipates into the environment. The completely solidified metal is ready for the next work of the heating surface. The solid state The metal materials used for liquid phase change thermal control have a low melting point, generally below 100°C, and can be adjusted according to needs.
PART.2
What results did the trial achieve?
In this on-orbit test, the convection heat dissipation test module obtained the variation characteristics of heat transfer coefficient with flow rate, which is mainly aimed at low flow rate applications of small fluid circuits. Prior to this, there was no reliable heat transfer coefficient characteristic data for designers to refer to in the low flow rate area that this test project focused on. The results of this test have filled this gap;
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The phase change temperature control module obtains the temperature change curve of the metal material melting process with time. The temperature distribution of the material during the melting process is significantly affected by gravity. When there is gravity, the density difference caused by different fluid temperatures will trigger a natural flow. This flow It will cause the internal temperature of the liquid metal to become uniform more quickly; while the gravity of the space environment is extremely weak, the density difference will not cause natural flow, and the temperature distribution inside the liquid metal will be relatively uneven. This test is equipped with a metal phase change An enhanced heat transfer structure is set up in the cavity of the material, which can quickly transfer heat to the inside of the metal material, making it melt more uniformly, resulting in a more uniform temperature. The test verification results are in line with expectations.
In addition to verifying convection heat transfer and phase change temperature control technology, this test also verified key technologies such as controlled melting, expansion buffering, and interface thermal conduction of bismuth-based metal in space microgravity environment.
Key technical terminology knowledge posts
Controlled melting: refers to the controlled melting of metals in sequence according to preset positions and sequences.
Expansion buffering: refers to buffering the volume change when the metal solid liquid changes. For a closed circuit, if this volume change is not buffered, the pipeline will burst.
Interface thermal conductivity: refers to the tiny gaps that will appear when two solid surfaces are in contact. The remaining air in these gaps will hinder the transfer of heat between the two solid surfaces. Therefore, the gaps need to be filled with thermal interface materials, such as liquid metal. This filling The thermal conductivity of the material is much higher than that of air, allowing heat to be transferred between two solid surfaces with a small temperature difference.
PART.3
What are the research implications of the test?
This project is the first time in the world to use a low-melting-point bismuth-based alloy with high biosafety to carry out on-orbit testing and verification of key technologies for liquid metal space thermal management. The relevant results can be used for future space nuclear power supplies, high power density avionics and civilian high-power Provide key technical support for engineering or industrial applications that require efficient heat transfer and dissipation, such as devices.
PART.4
In what areas do you expect to see applications in the future?
The achievements achieved by this project in liquid metal convection heat dissipation and phase change temperature control are mainly aimed at engineering thermal control needs such as continuous heating or intermittent high-load heating of high heat flux density electronic devices. With the development of artificial intelligence technology, virtual reality technology and high-speed With the continuous development of flux image processing technology and other fields, the power density of electrical equipment with these functions continues to increase. In order to ensure the working performance of electrical components under high load conditions, it is necessary to adopt more efficient, simple and reliable heat dissipation technology. This project The two liquid metal heat dissipation technologies involved are experimental verifications carried out in response to this industrial demand, and are expected to play a major role in many fields.
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Content source: China Manned Spaceflight Author: Liu Guilin, Institute of Physics and Chemistry, Chinese Academy of Sciences
