This is a comment Tom Shula made on his interview by Tom Nelson, explaining how the Pirani gauge precludes the "climate crisis" :
There have been a number of comments/questions regarding the Pirani gauge. Rather than addressing each individually I will attempt explain in more detail here how the heated element in the Pirani gauge serves as a proxy for the surface of the Earth in my exposition. Most of the concepts involved are in the Appendix section of my paper. Also, for reference I will use the chart of the Pirani gauge response. Finally, the Pirani gauge is designed to measure vacuum in a limited range of pressures. There are other devices that operate outside those ranges in applications that need them. We are not concerned with the precision of the gauge. It's value in this exposition is its principle of operation and ability to directly measure the relative contributions of radiation vs. conduction/convection to heat transport in a gaseous environment.
Let's start with the Pirani gauge in a state with a near perfect vacuum in its enclosure. If calibrated as the device represented in the response graph, the controller will provide a current that heats the filament to a specific temperature, in this case the power dissipation is 0.4 milliwatts. That power represents the radiation loss from the filament as well as other losses from junction heating, etc. and may heat the enclosure slightly. At steady state this does not matter, because irrespective of the size of the enclosure the temperature of the filament will remain constant.
In this state, the filament can be expected to emit radiation according to a modified Stefan Boltzmann Law based on its temperature and (typically low by design) emissivity. In this case there is a spontaneous emission of photons from the filament that balances the power input (0.4 mw) from the power supply.
Now, let's introduce some air into the enclosure. We need to look at what is happening at the boundary layer at the filament/air interface. As soon as the gas molecules are introduced, they begin colliding with the filament. Three things happen: 1. Some of the colliding gas molecules pick up energy from the filament at a higher temperature. 2. Removal of the energy from the filament by 1 lowers the temperature of the filament. 3. As a result of 1 and 2, the frequency and average energy of photon emission by the filament is reduced. It is at this atomic level at the boundary where the heat transport begins, and where nature decides the balance.
The gauge controller responds by increasing the power to the filament until it returns to the original temperature, but now in a gaseous environment rather than a vacuum. The additional power is providing a continuous influx of heat capacity (remember this concept) that exactly balances the heat energy that the gas molecules receive from the filament. We know the power input required to maintain temperature under vacuum, and we know the power input required to maintain temperature at pressure. The difference between those two is the power that is being removed by the gas via conduction/convection.
Note that so far there has been no need to take into account enclosure size, enclosure finish/emissivity, filament emissivity, or specific temperature. These can change sensitivity, precision, range, and other operating characteristics of a specific gauge, but the operating PRINCIPLE remains the same. In determining heat transport between a solid surface and a gas, it's what happens at the boundary layer that counts. There is one requirement: the temperature of the filament must be higher than the temperature of the gas, otherwise there would be no net energy transfer from the filament to the gas.
If we are going to consider a particular pressure regime, we might as well look at atmospheric pressure at sea level since that's the place of interest in this exposition. What is the boundary layer at the surface? At atmospheric pressure the molecular mean free path is about 70 nanometers, and the collision rate with a planar surface is about 3 X 1027 collisions/m2-sec. As in the Pirani gauge, conduction at the surface is what triggers heat transport and creates convection. The rate of conduction is proportional to the difference of temperature between the surface and the gas, and INVERSELY proportional to the thickness of the boundary layer. With a mean free path of 70 nm the boundary layer thickness is extremely small, so even a small temperature difference can produce efficient conduction. It also perturbs the radiation output negatively. In the case of a large temperature difference, for example pavement on a very hot day, we can actually see a "mirage" in the distance due to the large lower density convective layer at the surface refracting the sunlight. For smaller temperature differences, it may not be that striking but convection is still occurring. The surface temperature is almost always higher than the air temperature above it. A layman's explanation of why this occurs in soil can be found at: soil temperature
Relative to air, the surface of the Earth whether land or water has a tremendous heat capacity, which is why this has a small effect on the temperature of the surface. This is all that is necessary to demonstrate that the principle of the Pirani gauge applies to the (land) surface of the Earth.
The heating of the surface is from incoming solar radiation. As the solar radiation wanes, the surface will cool, and so the air will cool as well, typically at a faster rate than the surface. The diurnal cycle is dynamic, and it changes throughout the day.
In the case of a water surface (extremely important so not to neglect it) evaporation is occurring on a more or less continuous basis which results in convective transport as well.
Nature has priorities. Flowing water will follow the most efficient path driven by gravity. If something gets in the way, it will go around it or annihilate it. Heat will follow the most efficient path driven by temperature differences. Radiation is natures last resort, when there is no physical medium to transport the heat. When the options of conduction or convection are available, they will always win.
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