Vacuum Tube Thermal Conductivity

It should be a heat pipe, which contains a volatile liquid and uses phase change to dissipate heat

Heat pipes are highly efficient heat transfer elements. The ends of a metal tube sealed up to the tube into the appropriate amount of working fluid, pumped into the vacuum on the formation of a heat pipe

The typical heat pipe by the tube shell, suction core and end caps, the tube will be pumped into the 1.3 × (10 minus 1 - 10 minus 4) Pa negative pressure after filling with the appropriate amount of working fluid, so that the wall of the tube tightly against the volatile liquid, the heat pipe is a highly efficient heat transfer element. The tube is pumped into 1.3 × (10 minus 1 - 10 minus 4) Pa negative pressure and then filled with the appropriate amount of working liquid, so that the liquid-absorbing core capillary porous material immediately adjacent to the inner wall of the tube is filled with liquid and sealed. One end of the tube for the evaporation section (heating section), the other end of the condensation section (cooling section), according to the application needs in the middle of the two sections can be arranged adiabatic section. When one end of the heat pipe is heated when the liquid in the capillary core evaporates and vaporizes, the steam flows to the other end under a slight pressure difference and releases heat to condense into liquid, and the liquid flows back to the evaporation section along the porous material by the action of capillary force. So the cycle is not their own, the heat from one end of the heat pipe to the other - end. Heat pipe in the realization of this heat transfer process, including the following six interrelated major processes:

(1) heat from the heat source through the heat pipe wall and full of working liquid suction core transfer to the (liquid - vapor) interface;

(2) liquid in the evaporation section of the (liquid - vapor) interface;

(2) the liquid in the evaporation section of the (liquid - vapor) interface. section;

(3) the vapor in the vapor chamber flows from the evaporation section to the condensation section;

(4) the vapor condenses on the vapor-liquid dividing surface in the condensation section:

(5) the vapor is transferred to the condensation section through the wall of the heat pipe and the suction core filled with the working liquid. Liquid dividing surface condensation:

(5) heat from the (vapor - liquid) interface through the suction core, the liquid and the wall of the pipe to the cold source:

(6) in the suction core due to the capillary effect of the condensed working liquid back to the evaporation section.

The heat pipe is a heat transfer element that relies on the phase change of the working liquid within itself to realize heat transfer, and has the following basic characteristics.

1, high thermal conductivity

The heat pipe mainly relies on the vapor and liquid phase change of the working liquid inside the heat transfer, the thermal resistance is very small, so it has a very high thermal conductivity. Compared with silver, copper, aluminum and other metals, heat pipes can transfer several orders of magnitude more heat per unit weight. Of course, high thermal conductivity is also relative, the temperature difference always exists, it is impossible to violate the second law of thermodynamics, and the heat transfer capacity of the heat pipe is limited by a variety of factors, there are a number of heat transfer limit; heat pipe axial thermal conductivity is very strong, radial and not much improvement (except for radial heat pipe).

2, excellent isothermal

The steam in the inner cavity of the heat pipe is saturated, saturated steam pressure is determined by the saturation temperature, saturated steam from the evaporation section to the condensing section of the pressure drop is very small, according to the thermodynamics in the equation can be seen, the temperature drop is also very small, and thus the heat pipe has excellent isothermal.

3, heat flow density variability

The heat pipe can independently change the evaporation section or the cooling section of the heating area, that is, a smaller heating area to input heat, and a larger cooling area output heat, or heat pipe can be a larger area of heat transfer to input heat, and a smaller area of the cooling output heat, so that you can change the density of the heat flow, to solve a number of other methods of heat transfer problems are difficult to solve. Heat transfer problems.

4, the direction of heat flow discretionary reversibility

A horizontally placed cored heat pipe, because of its internal circulation power is capillary force, so any end of the heat can be used as an evaporation section, and the other end of the outward heat dissipation becomes the condensation section. This feature can be used for spacecraft and artificial satellites in space temperature leveling, can also be used for exothermic and then heat absorption of chemical reactors and other devices.

5, thermal diode and thermal switch performance

Heat pipe can be made into a thermal diode or thermal switch, the so-called thermal diode is to allow the flow of heat in one direction only, but not allowed to flow in the opposite direction; thermal switch is when the temperature of the heat source is higher than a certain temperature, the heat pipe begins to work, when the temperature of the heat source is lower than the temperature, the heat pipe does not transfer heat.

6, thermostatic characteristics (controllable heat pipe)

Ordinary heat pipe of the parts of the thermal resistance basically does not change with the change in the amount of heat, so when the amount of heat changes, the temperature of the heat pipe part of the preparation also changes. But people developed another kind of heat pipe - variable heat pipe, so that the condensing section of the thermal resistance with the increase in the amount of heat and reduce, with the decrease in the amount of heat and increase, so that the heat pipe in the case of a large change in the amount of heat, the steam temperature change is very small, to achieve temperature control, which is the thermostatic properties of the heat pipe.

7, the adaptability of the environment

The shape of the heat pipe can be changed with the conditions of the heat source and cold source, the heat pipe can be made into the motor's rotor shaft, gas turbine blades, drills, scalpels, etc., the heat pipe can also be made into a separate type to adapt to the heat transfer over long distances or the impulse of hot fluids can not be mixed in the case of heat transfer; heat pipe can be used for both the ground (gravitational field), but also can be used for the space (non-gravity field). .