Guest essay by: Thomas E. Shula
Rancho Mirage, CA
The figure below, published by NASA, is one example of many that attempt to visualize the various factors in the “Energy Budget” of the Earth. The yellow arrows on the left depict the incoming solar radiation. It is in part absorbed by the atmosphere, partially reflected into space by clouds and the atmosphere, partially reflected by the surface of the Earth, and a bit less than 50% is absorbed by the surface of the Earth and converted into heat. On the right, the red arrows depict the paths that transport the energy from the Earth’s surface to space, as postulated by the greenhouse effect. This model of the “Energy Budget” is the basis of climate models attempting to predict the effects of hypothesized Anthropogenic Global Warming (AGW) from greenhouse gases.
Diagram Courtesy of NASA
As the inset paragraph in the NASA diagram states, “On average, and over the long term, there is a balance at the top of the atmosphere.”
The values associated with each of the arrows in the diagram are the corresponding energy fluxes in Watts/m2. These values are derived in different ways, some of which are relevant to this exposition and will be described below. These values are used in climate models and may vary as the models evolve, though typically not by much. Some typical values from a NASA document can be found on page 16 HERE.[1] Certain assumptions led to the development of the Greenhouse Gas Theory. One of the conclusions explained at Earth Temperature without GHGs – Energy Education[2] is that without greenhouse gases, the earth would be approximately 33 C cooler, essentially an average temperature near freezing. This is the result of treating both the Earth and its atmosphere as blackbodies following the Stefan-Boltzmann Law, as is discussed in this VIDEO[3] from an online course about climate modeling.
From the energy budget diagram, there are four red arrows corresponding to (average) longwave (Infrared) radiation flux. They are as follows:
- 398.2 Watts/m2 longwave radiation upwelling from the surface
- 18.4 Watts/m2 upward from conduction/convection
- 86.4 Watts/m2 upward from evapotranspiration
- 340.3 Watts/m2 longwave radiation downwelling from the atmosphere as Back Radiation
According to the greenhouse effect, it is the downwelling Back Radiation that “traps” the heat in the atmosphere to keep the Earth warm.
For purposes of this exposition, we will consider only first two components above, as we will be investigating the relationship between upwelling longwave radiation and conduction/convection at the Earth’s surface. According to the model explained above, 398.2 W/m2 represents approximately 95.5% of shared heat transport and conduction/convection approximately 4.5% of shared heat transport.
How might we measure this? We know that there are three mechanisms for transport of heat energy: conduction, convection, and radiation. One needs to design an experiment that can discern the proportion of heat loss due to radiation versus the heat loss due to conduction and convection. It so happens that there is a common instrument that has been in use for over 100 years that does precisely this.
The Pirani Gauge
This image was provided with permission by MKS Instruments, Inc. (Andover, MA)
The modern Pirani Gauge is used to measure vacuum in the range from 760 Torr to 10-4 Torr, though some are designed to measure higher pressures up to 1000 Torr. It was invented in 1906 by Marcello Pirani, a German physicist working for Siemens & Halske, and has been used in a myriad of applications for over 100 years. The operating principle of the gauge is simple. Inside the gauge body there is a filament that is heated and maintained at a constant temperature. The energy going into the filament is controlled via the current flowing through it. Energy can be dissipated from the filament in four ways:
- Gas Conduction
- Gas Convection
- Radiation
- End Losses (i.e., conduction of heat from the filament to its support structure.)
The Radiation and End Losses are constant and can be measured by creating an adequate vacuum inside the gauge so that losses from conduction and convection are negligible. When gas is introduced to the enclosure, heat is removed from the filament via conduction and convection. The input power required to maintain the temperature of the filament will depend on how much energy is being removed via conduction and convection by the gas. In summary, the Pirani gauge tells us the relative contributions to heat transport by radiation versus conduction/convection as a function of gas pressure for an object (the filament in this case) held at a constant temperature. Referring to the paragraph preceding the above image, this is exactly the measurement we are looking for.
The response curve for a typical gauge is shown in next illustration. Both illustrations can be found in the Technical Note “Introduction to Vacuum Pressure Measurement” published by MKS Instruments, and the specific gauge illustrated in the figure is an MKS Instruments convection enhanced Pirani gauge.
This image was provided with permission by MKS Instruments, Inc. (Andover, MA)
The red line in the chart represents the (constant) total radiative and end losses of approximately 0.4 mW. The blue line represents the power loss due to gas only, and the green curve that flattens out on the two ends represents the total loss, i.e., the total energy input required to maintain the temperature of the filament as a function of pressure. At atmospheric pressure, 760 Torr, the power required to maintain the temperature of the filament is 100 mW. Since the radiative and end losses are 0.4 mW, this means that the heat transport by gas is 99.6%, with only 0.4% due to radiative and end losses. This should not be surprising, because all gas molecules can transport heat via conduction and convection, not just the tiny fraction that constitute the so-called “greenhouse gases.”
We can also consider the case of a vacuum pressure of 10 Torr, the equivalent of about 110,000 feet above sea level. In this case, about 60 mW of power is required to maintain the filament temperature, so the gas is still accounting for about 99.3% of heat transport with radiative and end losses only 0.7%. As one goes higher in altitude a larger proportion of the heat transport is attributable to radiation, and that is how all the heat eventually returns to space in the extreme upper atmosphere. The crossover point, where gas losses are equal to radiative and end losses, is at about [20] milliTorr (.02 Torr), equivalent to an altitude beyond 250,000 feet. The response of the Pirani gauge is independent of the enclosure it is in or the lack thereof. If we took a “naked” Pirani gauge to an altitude where the atmospheric pressure is 10 Torr, the response would be the same as if it was attached to a vacuum system at a pressure of 10 Torr. There have been Pirani gauges made in many different sizes and configurations, some with radiative losses on the order of 0.1% at standard atmospheric pressure.[4]
The filament in the Pirani gauge is analogous to the surface of the Earth. The gas molecules collide with the surface and absorb energy raising their effective temperature (conduction). A “bubble” of this warmer gas then rises relative to the cooler gas around it as the cooler gas drops to the surface and repeats the cycle continuously (convection). This cools the surface and is perfectly illustrated by the response of the Pirani gauge. This is well understood by those who have worked with high temperature processes in vacuum systems, and no doubt by many others. The author can only speculate regarding why this has not been given consideration earlier.
Conclusions
The Pirani gauge provides a method to measure the relative contributions of radiation vs. conduction/convection to heat transport in a gaseous environment as a function of pressure. At pressures relevant to the lower atmosphere (troposphere + stratosphere) radiation accounts for less than 1% of the upward heat transport. This does not refute the existence of said radiation in the lower atmosphere, it only demonstrates experimentally that its role in upward heat transport is insignificant.
It has been demonstrated via the Pirani gauge operating principle that upward heat transport via radiation plays an insignificant role in the transport of heat at atmospheric pressures from the surface to the upper stratosphere. The greenhouse effect, if it exists, is based on upward heat transport via radiation in the lower atmosphere. Therefore the greenhouse effect, if it exists, plays an insignificant role in heat transfer and, by extension, the energy balance of the atmosphere.
Contemporary climate models are based on energy balance models of the type depicted in the NASA diagram at the beginning of this paper. It is clear from the NASA diagram as well as similar diagrams from other sources that the fundamental assumption of these models is that radiation is the primary driver of upward heat transport in the lower atmosphere. Because radiation is an insignificant driver of upward heat transport in the lower atmosphere, these models are based on a false assumption and are therefore invalid. Finally, because the models are generally intended to support the theory of Anthropogenic Global Warming because of the greenhouse effect, there is no scientific evidence for the greenhouse effect or Anthropogenic Global Warming.
The radiation energy that the Earth absorbs from the Sun arrives at the speed of light. The Earth loses heat at a speed driven by convection in a process we call “weather.” Weather is the chaotic process by which the Earth’s atmosphere continuously tries to reach thermal equilibrium but never succeeds. The convection takes place continuously, but the speed at which heat is transported by convection is MUCH slower than the speed of light. This means that heat energy leaves the Earth more slowly than it arrives, and that is why the Earth is warmer than predicted by the Stefan-Boltzmann Law.
Appendix
(April 11, 2023)
How did “Climate Science” get this so wrong?
The two fundamental assumptions leading to the Greenhouse Effect are that 1) The primary mechanism by which the surface of the Earth loses heat is radiation and, 2) Based on the Stefan-Boltzmann Law the temperature of the Earth’s surface should be 33K cooler than what we observe.
The Stefan-Boltzmann Law (SBL) defines a blackbody (which is an idealized object that does not exist in nature) as having the following characteristics:
- It exists in an environment at 0K, i.e., a perfect vacuum.
- It is in equilibrium with its environment.
- It is a perfect absorber of radiation.
With certain adjustments such as emissivity, the SBL provides a convenient means of measuring the temperature of an object based on its emitted radiation even in non-ideal environments. The estimation of the temperature of stars for example, and the use of infrared cameras to detect “hot spots.” One must be careful, however, to keep in mind that it is only the “idealized” black body that behaves strictly according to the SBL.
The Earth and its atmosphere do not satisfy any of the conditions of SBL. Additionally, it has become common to ignore condition number 1 above. If one looks up the definition of a blackbody, a reference to the 0K (perfect vacuum) condition is often not mentioned. This typically has little effect when it comes to temperature measurements using optical techniques, but it is extremely important in understanding the dynamics of heat transfer in, for example, terrestrial conditions.
This is neglected in climate models. It assumes that with the surface temperature of 288K the power radiated upward from the surface is 398 Watts/m2 and that it is all longwave IR radiation. It then becomes necessary to “balance” that upwelling radiation with “back radiation” to obtain “radiative balance” in the atmosphere.
What is happening is quite different. At 288K temperature the photon flux (generously assuming it is all at 15 micron wavelength to maximize the number of IR active photons) is approximately 3X1022 photons/sec-m2. That is a lot of photons, and if the surface was in a perfect vacuum that radiative flux would be the only way for the surface to release energy.
But we have an atmosphere. At standard temperature and pressure, air has some very interesting properties. It is much denser than we typically imagine.
Average molecular velocity approximately 470 m/sec (1050 mph, supersonic at the macro level)
Molecular collision frequency (each with another) approximately 7,000,000,000 collisions/sec (7 GHz)
Mean free path approximately 70 nm (about 1/10 wavelength of visible light)
Frequency of collisions with an ideal planar surface approximately 3X1027 collisions/sec-m2
To put this in perspective, the last number is quite useful. The average surface area of an adult human is around a square meter. That means that each second about 100 lbs. of air molecules collide with each of us with an average speed of about 1050 mph. More importantly, given the photon flux at 288K this means that approximately 100,000 air molecules collide with the surface for each potential infrared photon emitted. Because the energy transfer from collisions will change the equilibrium at the surface by removing energy through conduction, it is likely that the actual emitted photon flux will be even less. To believe that radiative transfer is the primary mechanism for upward heat transfer at the Earth’s surface would mean that one IR photon would transfer more energy than 100,000 molecular collisions. These numbers are for a perfectly smooth planar surface. The actual surface area at an atomic level can be much greater.
Clearly, the interface between the surface of the Earth and the atmosphere is an extremely chaotic place at the atomic level. This gives perspective to explain what we see in the operation of the Pirani gauge as explained in the body of this paper.
References:
[1] Kelly, Schmidt, et al, GISS-E2.1: Configurations and Climatology
[2] Earth Temperature without GHGs – Energy Education
[3] (224) Climate Dynamics Lecture 02 Energy and the Earth System – YouTube
[4] Fabrication of thermal‐based vacuum gauge – Jung – 2014 – Micro & Nano Letters – Wiley Online Library
fantasized AGW
as hot molecules go up the pressure they are exposed to drops off which means they “cool” without a drop in specific energy… not understanding actual physics is what causes “global warming” like how mercury thermometers take longer to cool than heat and how thermistors have to be double-adjusted and placed VERY carefully and take humidity into account to produce an actual temp reading
So many different opinions as to how our climate warms, I am totally lost.
Let me ask this.
Whenever there is an El Nino in the Pacific ENSO area, global temperatures always rise.
What is the mechanism for the global temperature increase?
That is outside the the purview of this topic, but in a nutshell El Niño is characterized by an upwelling of warmer water in the Pacific Ocean off the west coast of South America. La Ninã is the opposite when the surface temperatures are colder than average.
This is a good explanation of how a Pirani gauge works. They are very useful and I’ve used them for decades. They are great for telling you if you can spin up your turbo pump. They’re not precision instruments, though, and their readings depend on the gas species in the system. If you want accuracy in this pressure range, you go with something like a capacitive manometer (also made by MKS).
One thing that worries me about the analogy being employed: I’ve never operated a Pirani where one side of it is held at ~288K and the other at just a few degrees K. Just sayin’.
But with a few modifications the device could be used to establish the transition point in the atmosphere where radiation begins to dominate sensible heat transport.
-Paint inside and outside black to Peter represent the emissivity of ice..
-Make temperature difference between filament and body say 250K but over a range – ideally temperatures similar to the atmosphere so the body very cold.
-Produce calibration curves over a range of body temperature for saturated air rather than just N2.
The Pirani gauge offers a simple method to make meaningful experiments of atmospheric heat transport processes representative at different altitudes.
They got it so wrong because it was never about temperatures in the first place. In the 20th century, paleontologists found that life was most abundant and varied with temperatures 2-4 degrees C above present.
It was about power and control–and about causing the extinction of Life on Earth in all its forms from humans, pets, mammals, reptiles, amphibians down to fish, trees, flowers, mosses, grasses fungi, bacteria.
All life on land depends on photosynthesis: CO2 + H2O + sunshine in a green plant —> sugar and O2. Because we need air so urgently, the oxygen is described as the product of photosynthesis. Because our schoolteachers are the dumbest people who can still graduate from college, most Americans and other earthlings are innumerate and cannot reason with one O2 per CO2 in 0.04% CO2 versus about 20-21% oxygen and how much difference photosynthesis really makes. I expect some WUWT readers will now do the math since I have called your attention to it.
From the sugar, plants make all the rest of their bodies, which herbivores and omnivores eat. Food. They are trying to starve us all to death.
Story Tip
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:
https://accessiblegardens.org/soil-temperature-why-its-hotter-than-air-temperature/#:~:text=The%20majority%20of%20soil%20temperatures%20are%20lower%20than,can%20hold%20onto%20it%20for%20a%20long%20time.
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.
I hope this has been helpful.
“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.”
Which is why the Pirani gauge is not a relevant model for the Earth as the earth’s surface has a near black-body emissivity as has been pointed out to you several times in the comments. If you wanted a Pirani gauge to simulate the Earth’s surface you’d need to have the element coated with platinum black, but then the results would be much different.
If we were looking at the Earth from the Moon or Mars, we could look at it as a modified black body because the only energy transport we would detect would be radiation. That’s not what we’re doing here.
It is invalid to treat the SURFACE of the Earth as a black body. It is enveloped in an atmosphere, and that changes the energy transport dynamics completely. That is what is demonstrated here.
It is not invalid to do so, the surface of the Earth radiates depending on its temperature and emissivity and is close to a true blackbody (averages about 0.95). The energy transport dynamics of the Earth’s surface are dominated by radiation. Your comparison with a Pirani gauge is invalid because the wire in the gauge is deliberately chosen to have an emissivity close to zero (0.05) so that conduction and convection dominate. The atmosphere does effect the energy transport dynamics to space, it’s known as the Greenhouse effect due to IR absorbing gases such as CO2, O3 and water vapor.
Layperson question: If heat transport dynamics are dominated by IR radiation vs air, 95% IR per the NASA energy budget illustration, doesn’t that mean hot water in a vacuum flask, that is limited to IR transport through the vacuum (aside from conduction losses thru the flask materials), would cool down hot water almost as fast as hot water in an un-insulated container? And if the Pirani gauge element had an emissivity 20 times higher than the the one it’s made with to match earth, are you saying the Gauge result would flip from <1% IR/99%gas, to 5% gas/95% IR?
That’s why the vacuum flask is coated with a reflective material, to reduce any radiative losses. Yes the increased emissivity would have the effect you suggest.
Vacuum coffee mugs like those Contigo driving containers Costco sells have no reflective coatings, just a vacuum between two dull stainless steel walls. They work pretty much as well as a glass vacuum flask (surface temp on the side wall is only a degree or two warmer than ambient with boiling water in it), except for higher conduction losses though the large plastic lid. Reflective emergency blankets can block the IR emissions from a human body, but only if there is an air a gap, and so can a canvas tarp https://www.youtube.com/watch?v=97l5xvslmsg. So I’m not buying that. It’s clearly the gap with no gasses in it that makes a vacuum flask work at all.
On the emissivity, my gut tells me the difference between .05 and .95 might change the ratio from <1% IR/99% gas, to maybe, 5%IR/95% gas or even 10%IR/90% gas, but not completely flip to 95% IR and 5% gas, as the models require. This makes no sense whatsoever. The engine on my airplane has a cooling plenum in the cowling and baffles designed to force air *between* the cooling fins on the cylinders at maximum velocity in flight to properly cool the engine. All it takes is a baffle that’s not positioned correctly, allowing air to get around the fins instead of between them, and there will be damaging local hot spots. If the majority of heat rejection from an object was IR, per the climate models, this would be completely unnecessary. People paint cylinders and heat exchangers flat black, emissitivity of .98, hoping to improve engine cooling, and it makes no difference whatsoever. Aircraft engine manufacturers paint them gloss grey b/c the paint is just for corrosion protection. Clearly 99% of cooling IS conduction/convection.
In that vein, this guy demolishes the whole IR vs cond/conv battle as it applies to autmotive heat exchangers. Examples of Tom’s Pirani Gauge comparison are all around us all the time. I’m really thinking this is a King Has No Clothes moment and we’ve been sold a completely false paradigm. It’s Saturated Fat Clogs Arteries all over again.
Unlike the presenter of your video I taught Thermo. at university to both undergrad and grad students and ran a world class combustion engine lab. The engine cylinder walls are heated by radiation and convection from the flame, that heat is then transferred by conduction through the walls. Heat loss to the outside is then by radiation and convection, in order to increase the heat loss forced convection is used which is increased by greatly increasing the surface area by adding fins and increasing the air velocity across them. Since the radiation surface area isn’t increased the radiation loss doesn’t increase, in fact it decreases because the surface temperature decreases and radiation heat loss depends on T^4. There is no resemblance to the Pirani gauge.
Vacuum flasks don’t actually work very well at near boiling water conditions, they’re much more efficient for cold materials. I used to use them in the lab for storing liquid nitrogen, under those conditions the reflective coatings are very useful.
As far as your ‘gut’ is concerned about radiational heat loss, it’s wrong.
This is very unconvincing. If IR was the majority of the heat loss, you wouldn’t need fins. You have to address that.
Even if the radiation is the majority of the unenhanced heat loss it isn’t enough. The easiest component to increase is via forced convection: increasing the area and also the velocity of the cooling gas. For larger engines that doesn’t work too well and then liquid cooling is used.
For heat sinks forced convection set more than 95% of heat losses and 70% for natural convection. IR heaters dont heat the air, even If they emitt more 15um radiation than Earth surface according to Planck Law. Radiation is a nothingburger in relation to surface – air heat transfer. Heat capacity is as oceans dont radiate at 120C aka 1380wm2 in equator at noon like on the Moon. Oceans store a huge heat that they release slowly. Ground surface too. Thats why even during 30 days long Moon night, T surface stay at 100K and never reach 3K. If Moon had same daynight cycle duration than Earth, its Equator mean T would be higher than Earth Equator. GHG emitt less wm2 at higher altitudes cause work is done by air parcel aka kinetic energy is lost. This fact dont show heat trapping but work done.
M, m, and I, Thanks for chiming in. I agree wholeheartedly. I am grateful to those participants in this discussion who both have an open mind and can look at the big picture.
One of the things I have come to understand in this discussion is that most invoked in the mainstream debate have only looked at the process through the lens of radiation. They are ignoring what is happening at the boundary layer at the atomic level where the atmosphere meets the surface. The mean free path of an air molecule at STP is only 70nm, so there’s a lot going on in the first micron or so of air where it meets a terrestrial surface.
Which is why a vacuum bottle works. Can you post a link to the table?
The largest aircraft engines, approaching 4000 hp, were air cooled. You use liquid cooling because it’s easier to manage temperature and if you want to use an inline engine for the lower frontal area, air cooling works very poorly because of air distribution issues.
You’re implying that convection is only needed to achieve a marginal requirement, which you have to do to defend the climate model assertion that 95% of heat is rejected by IR emission in the lower atmosphere. I don’t need to build an elaborate forced air cooling system with fins to cope with a 5% requirement. I do when it’s a 95% requirement. Again, this makes no sense If convection is only 5% of heat transport in the lower atmosphere.
The difference is that at the Earth’s surface the difference in temperature between the surface and the air is small which gives low convection. In the engine case there’s a much higher temperature difference driving convection. Convection is the process which can be significantly enhanced by forcing the coolant at a high velocity and increasing the contact area (fins).
Phil, I’ll agree with your vacuum flask comment. Vacuum flasks are more efficient at keeping cold things cold that hot things hot. But they do slow down heat transfer in both directions. I appreciate that every day as I can enjoy a big thermal mug of hot coffee over a couple of hours while my iced drink in the same container will maintain ice in it all day.
I also agree that the radiator for your ICE has little in common with the Pirani gauge. I have to ask the question, if you think radiative loss is more important, why do you think radiators are designed to increase convection rather than increase radiation?
I don’t “think radiation is more important”, in certain circumstances it can dominate in others not.
Regardless, if IR transport is 95% and convection/conduction only 5% in the lower atmosphere, as the climate models claim, a vacuum flask will transport nearly all the differential heat, in or out, by IR radiation through the vacuum gap,independent of atmospheric pressure, and it will work no better than a pop bottle. There is a giant logical gap here.
That’s why the walls of the vacuum gap are coated with a reflective surface.
Oops forgot the second link https://www.youtube.com/watch?v=z_mmmXTbLP0
Tom, is it fair to say, for a layperson, that if the IR radiation dominance hypothesis underpinning the Greenhouse Effect was true, a vacuum thermos wouldn’t work (because the vacumm in the bottle would serve no purpose and if anything coffee would cool down faster than just in the open air), air cooled engines could be cooled just as well without blowing air on them since almost all the heat rejection off the cooling fins is IR? A whole range of practical effects that are blindingly obvious in everyday life?
Sorry I missed your earlier comment in the previous thread. I see that Phil replied regarding the reflective coating, and that is true. The more important characteristic of the vacuum bottle, however, is that the vacuum between the double walls of the thermos stops convection which is the dominant mode of heat transfer at atmospheric pressure. Your analogy regarding air cooled engines is a good one as well. If radiation was dominant, there would be less need to blow air over the cooling fins.
When you go outside on a cold day in short sleeves, your arms don’t get cold because you are radiating more (your body temperature hasn’t changed), your arms feel cold because the cold air is conducting heat away from your body and it’s carried away by convection. Cover your arms, and you don’t get cold so quickly.
Another good example is double pane windows. They don’t necessarily stop radiation, but they do reduce conduction and convection by a considerable amount.
Suggestion! Can you take a Pirani Gauge and paint the element flat black to raise its emissivity to around earth’s and do some measurements for comparison? You have to find a way to put that counter argument to bed. Or, some engineering guy at the manufacturer should be able to provide data on how much the measurements would change with an element with .95 emissivity.
The Pirani gauge with the wire at 60ºC would radiate ~650W/m^2K with an emissivity of 0.95 only ~35W/m^2K with 0.05 as designed. Such a wire in atmospheric pressure air at 20ºC will lose ~400W/m^2K via natural convection, that will be lower at lower pressures.
Phil, you don’t seem to understand that the emissivity of the sensor is irrelevant, because the radiative loss in the Pirani gauge is a constant, not a variable. A low emissivity sensor is chosen to improve the sensitivity/SNR. That does not change the operating principle.
You only look at the world through the lens of radiation. That is why you cannot see this. If you had experience in applications where you actually see heat transport in action, you would understand that radiation is nature’s last resort. It takes over when conduction/convection is not available or saturated.
The emissivity of the sensor is not important in the operation of the sensor but is chosen to be low to ensure that convection is the dominant process. The only reason I brought it up is your claim that “The filament in the Pirani gauge is analogous to the surface of the Earth”, which is not true because of the major difference in emissivity in the two cases.
I don’t “look at the world through the lens of radiation”. I have considerable experience in applications involving heat transfer, radiation is not the “last resort” it is present all the time, boundary conditions determine the relative importance of different mechanisms.
A person standing in a room maintained at 22°C at all times. The inner surfaces of the walls, floors, and the ceiling of the house are observed to be at an average temperature of 10°C in winter and 25°C in summer. The rate of radiation heat transfer between this person and the surrounding surfaces if the exposed surface area and the average outer surface temperature of the person are 1.4 m2 and 30°C, respectively and the emissivity of a person is 0.95.
Q=154W in winter and 40W in summer.
The experimentally determined convection heat transfer coefficient from a person is ~6 W/m2·°C so the heat loss by convection is ~67W.
You are assuming again that the radiative transfer dominates. How do you calculate the convective heat loss? What was the experimental methodology used to determine the number you present?
No assumption, just calculating using measured quantities. Convective heat loss = hA(T1-T2)
The human body generates roughly 90-110W of total energy, so based on your example, convection is roughly 70% and IR is 30% in the lower atmosphere. But climate models assume roughly 95% IR and 5% convection. So even if I accept those values, how do you go from 30% to 95% IR, and 70% to 5% kinetic gas transfer? The climate models are way off, based on your own example, right?
No, you don’t appear to understand that the losses depend on the boundary conditions. For example in the winter condition calculated the losses are Radiation 154W, convection 67W, increase the wall temperature by 15ºC and it becomes 40W and 67W.
However the Earth surface isn’t at 30ºC surrounded by a wall at 10ºC!
Just to be clear, do you assert that if the Pirani Gauge had an element with an emissivity of .95, the ratio of kinetic transfer would completely flip, from <1% IR/99% convection/conduction with .05 emissivity, to 95% IR and only 5% convection/conduction, as the climate models claim, with a .95 emissivity element?
Back to my coffee vacuum mug. The liner is dull SS, not a mirror and in any case the liner becomes heat soaked with the hot water by conduction, so even if there’s a mirror finish it’s going to emit IR across the vacuum gap from the back of the mirror anyway, to the outer wall, being heat soaked from conduction, and the outher wall has no reflective surface, just dull SS, so it’s going to absorb most of the IR. The outer wall should get warm if IR is so dominant. Yet it stays within a couple degrees from ambient down the barrel away from the lid, with the lid area that is conducting heat to the outside through its plastic, is about 40C.