Heat flow in low pressure, knudsen number

In summary, the conversation discusses the topic of heat transfer in low pressures, specifically in a vacuum chamber where an object is much smaller than the mean free path of air. The question is how to calculate conduction and convection to the surrounding air, which is believed to be low due to the size of the chamber. The use of molecular flow and viscous flow is also mentioned.
  • #1
Flanders3
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0
Hi! Been lurking around here for a while but joined today :)

My question is about heat transfer in low pressures. I have an object in a vacuum chamber that is much smaller than the mean free path of the air in the chamber. However, the general dimensions of the chamber are much larger than the air mean free path. Heat radiation from the object is easy to calculate but how about conduction/convection to the surrounding air? I'm pretty sure it is low, but how low?
 
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  • #2
I thought i couldn't use molecular flow because the air in the chamber is viscous, but I can't use viscous flow either because the air molecules are so likely to 'miss' the heated object.
 

Related to Heat flow in low pressure, knudsen number

1. What is heat flow in low pressure and how does it differ from high pressure?

Heat flow in low pressure refers to the transfer of thermal energy in a system with a lower pressure compared to its surroundings. This can occur in a vacuum or in a low pressure environment, such as outer space. In contrast, heat flow in high pressure occurs in systems with higher pressures, such as inside a sealed container or within a gas or liquid under high pressure.

2. What is the Knudsen number and how does it relate to heat flow in low pressure?

The Knudsen number is a dimensionless parameter that describes the ratio of the molecular mean free path to a characteristic length scale. In the context of heat flow in low pressure, it is used to determine whether the flow is in the continuum or rarefied regime. At high Knudsen numbers, molecular collisions become less frequent, leading to non-continuum behavior and different heat transfer mechanisms.

3. What factors affect heat flow in low pressure and how?

There are several factors that can affect heat flow in low pressure, including the pressure gradient, temperature gradient, gas composition, and the geometry of the system. These factors can influence the density, viscosity, and thermal conductivity of the gas, which in turn affect the rate of heat transfer through the system.

4. How is heat flow in low pressure measured and what units are used?

Heat flow in low pressure can be measured using various techniques such as calorimetry, thermocouples, and infrared thermography. The units used to measure heat flow depend on the specific technique, but commonly used units include watts (W), joules per second (J/s), and calories per second (cal/s).

5. What are the applications of studying heat flow in low pressure?

Understanding heat flow in low pressure has many practical applications. It is essential in designing and optimizing thermal insulation for spacecraft, satellites, and other equipment operating in extreme low pressure environments. It is also important in the development of vacuum technologies, such as vacuum pumps and vacuum chambers. Additionally, studying heat flow in low pressure can provide insights into the behavior of gases at the molecular level and aid in the development of more efficient energy systems and processes.

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