What is the relationship between the operating temperature of a heat pipe, its startup temperature, and the amount of fluid filled in it?

The operating temperature of a heat pipe, as well as its startup temperature, are related to the physical properties of the working medium. The amount of fluid filled in the heat pipe is influenced by the properties of the medium, the amount of heat to be transferred, as well as the structure and size of the heat pipe. The calculations involved are complex, with many factors to consider; for more details, refer to specialized books on the subject. The operating temperature exists as a range

The operating temperature of a heat pipe is the temperature at which it can be used properly. The startup temperature of a heat pipe is the lowest temperature at which it begins to transfer heat; below this temperature, the heat pipe will not function (i.e., it will not transfer heat). The amount of fluid filled in the heat pipe is determined based on factors such as its heat transfer capacity, the working fluid used, the geometric dimensions of the heat pipe, and its installation configuration. There is experience value. There are also calculated values. The operating temperature is a range rather than an absolute value; it can increase under certain changing conditions as well.

When a heat pipe is in operation, isn’t its operating temperature the saturation vapor temperature? It should be a constant value, right? For the filling rate of the siphon heat pipe I’m looking at, can it be set between 0.1 and 0.2? Why is the startup temperature a few degrees lower than the operating temperature? When designing a heat pipe, it is such that once a certain pressure is reached inside the heat pipe, and the working fluid reaches its boiling point corresponding to that pressure during heat exchange, the heat pipe can start to function. When operating normally, the inside has the saturated temperature and saturated pressure of steam.

When a heat pipe is in operation, isn’t its operating temperature the saturation vapor temperature? It should be a constant value, right? For the filling rate of the siphon heat pipe I’m looking at, can it be set between 0.1 and 0.2? Why is the startup temperature a few degrees lower than the operating temperature? When designing a heat pipe, it is such that once a certain pressure is reached inside the heat pipe, and the working fluid reaches its boiling point corresponding to that pressure during heat exchange, the heat pipe can start to function. When operating normally, the inside has the saturated temperature and saturated pressure of steam.

When a heat pipe is in operation, isn’t its operating temperature the saturation vapor temperature? It should be a constant value, right? When a heat pipe is in operation, the pressure inside it changes. At different pressures, the saturation temperature varies, as do the heat transfer coefficients and heat flux densities in the hot and cold sections of the pipe. The pressure and temperature within the pipe change, and the operating temperature is also related to the material of the heat pipe. The filling rate for siphon heat pipes, as I’ve seen, can be set at 0.1–0.2; this is an empirical value. Why is the startup temperature a few degrees lower than the operating temperature? The startup temperature is the lower limit of the operating temperature for the heat pipe. When designing a heat pipe, it is such that once a certain pressure is reached inside the heat pipe, and the working fluid reaches its boiling point corresponding to that pressure during heat exchange, the heat pipe can start to function. When operating normally, the inside has the saturated temperature and saturated pressure of steam. Before a heat pipe is ready for operation, there is a negative pressure inside it (a certain level of vacuum). When heat is supplied from the outside, the fluid inside vaporizes at that vacuum level, and the heat pipe then starts to function. Under normal and stable operating conditions, the temperature of the steam inside the heat pipe corresponds to the saturation temperature corresponding to the pressure inside the pipe.

I’ve never been able to understand this concept; the materials I’ve read don’t provide any information on these basic principles. I’d like to ask for some guidance: during design, the operating temperature of the heat pipe is set at 35 degrees. However, the operating temperature of a heat pipe is related to the temperatures of the hot and cold fluids as well as the thermal resistance, so the actual operating temperature range for the heat pipe is between 51 and 19 degrees. Don’t heat pipes have isothermal properties? The temperature of the working fluid is the saturation steam temperature; then why does the temperature of the working fluid inside change so much? ? In that case, should the startup temperature be set below 19 degrees, maybe around 17 degrees? The pressure generated corresponds to the pressure at the boiling point, that is, the tube needs to be evacuated to this level of vacuum, rather than the pressure corresponding to 35 degrees

The operating temperature range of the heat pipe is 51–19 degrees. During design, the working fluid must be selected to have a starting temperature 19 degrees lower; don’t heat pipes possess isothermal properties? . When used to flatten the temperature field, heat pipes take advantage of their isothermal property; whereas when used as heat exchange elements, they rely only on their \"superconducting\" heat transfer properties, and it is not possible for them to achieve isotropy. In that case, should the startup temperature be set below 19 degrees, maybe around 17 degrees? The pressure generated corresponds to the pressure at the boiling point, that is, the tube needs to be evacuated to such a vacuum level; it’s not the pressure corresponding to 35 degrees. This statement is basically correct

In other words, when it is operating normally, the pressure changes, which in turn causes the corresponding saturated steam temperature, that is, the operating temperature of the heat pipe, to change, right? The lower limit of the operating temperature is 19 degrees, so how is the startup temperature determined? Is it three degrees lower than the operating temperature based on empirical values, or is it calculated? Is ethanol the common working fluid at this operating temperature? Does that expert have a table of physical property parameters for ethanol? The information I found online isn’t complete; the boiling point is above 40 degrees in all cases. Or could you tell me where I can find it? Thank you

I am referring to heat pipe exchangers, not individual heat pipes, for recovering the waste heat from flue gas; the operating temperature of the heat pipes at the flue gas inlet is 50, while it is 20 at the outlet

In the case of a heat pipe heat exchanger, starting from the wind-facing side, the operating temperature varies for each row, and the temperatures on the cold and hot sides are also different; one can refer to books on heat pipes for more information. What type of waste heat recovery does your company use? Can it reduce the temperature of flue gas from 50 degrees to 20 degrees for heating purposes?