# What is Thermal: Definition and 1000 Discussions

A thermal column (or thermal) is a column of rising air in the lower altitudes of Earth's atmosphere, a form of atmospheric updraft. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example of convection, specifically atmospheric convection. The Sun warms the ground, which in turn warms the air directly above it. A thermal is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically.

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1. ### A Gravity in the Thermal Interpretation

This question is mainly for @A. Neumaier, but I post it in public in case others are interested. The usual reason given for needing to quantize gravity is, heuristically, that, in the presence of quantized stress-energy where there can be a superposition of different stress-energy tensors...
2. ### I Atmospheric escape parametre statistics

What could be most sensible parametre for atmospheric escape excluding higher order (and nonlinear!) effects? Black body radiation is proportional to fourth power of temperature. Therefore temperature of black body is proportional to 4th root of incident radiation. Radiation from a point source...
3. ### I Nuclear power plant vs coal power plant efficiency

Hello, I have been reading that a coal power plant and a nuclear power plant have similar efficiencies, i.e. ~30%. This 30% refers to the conversion of thermal energy into electricity. For example, for 100 Joule of thermal energy, we only get 30 Joule out of electrical energy. How is that...
4. ### Stress in cylinders due to thermal expansion

I have two concentric thick cylinders in close tolerance (currently 50 micron gap), with a thin layer of glue between them. Internal cylinder is made from steel and external cylinder is made from ceramic (so the thermal expansion coefficient is not the same) The assembly is headed form inside...
5. ### I How do emissivity and absorptivity affect thermal imaging results?"

Hi all, I’ve run into a number of paints that are sold as “thermal” paints, or insulation paints. I know it’s mostly bs, but want a clarification on how emissivity and infrared absorption relate. The salesperson says the paint surface has an emissivity of 0.91, and reflects 99.5% of infrared...
6. ### Designing a Thermal Protection System for Spacecraft: Where to Begin?

Hello, I want to learn how to design a spacecraft's thermal protection system. But I don't know where to start. Someone can help me?
7. ### Engineering Thermal expansion of oil overflowing from a tank

Just wanted to know if I was barking up the wrong bush or not with my working out if anyone could help?
8. ### Average thermal power produced

I'm curious as to why the average power is not negative in this scenario, since I thought the friction force is in the opposite direction of velocity. As far as I see friction force is the only acting force in the problem, but I may be wrong. I solved this by simply doing (Friction Force *...
9. ### Thermal neutron detection using MCNP

How can i detect the thermal neutron, E = 0.025 Ev, by MCNP using CUToff Or PHYS:N cards?
10. ### Is Thermal Expansion Fatigue a Concern for Aluminum Alloy Motorcycle Frames?

Hello, assuming to keep an aluminum alloy motorcycle frame not in use, still, will the daily temperature variations cause thermal fatigue due to the continuous expansions and retractions or is the force developed by a few degrees of variations not sufficient to create microstructural dislocations?
11. ### A Measurement uncertainty due to thermal noise

I have a charged particle in a Penning trap. The particle motion is non-relativistic and the energy is high enough such that we can assume it is not in the quantum regime. For the purpose of the question I am interested only in the axial motion of the particle, so basically this is a classical...
12. ### Engineering COMSOL plot of thermal radiation from heated surfaces -- Help please

There is heating of the surface of the material using an electron beam. It is necessary to calculate how much heat will be released and build a graph of dependence. Please tell me how this can be done, which modules in COMSOL can be used?Thank you!
13. ### A Two level system in a thermal noise electric field

Hello! I have a 2 level system with a dipole moment d. I want to simulate numerically the evolution of the system under an external sinusoidal electric field (far off resonant). This is straightforward using SE. However I also have on top of that another electric field, created by a coupling of...
14. ### Thermal lattice Boltzmann model ignoring source term -- python code help please

LBM model for phase change- relevant equations found here. Also here. #Thermal LBM #solves 1D 1 phase phase-change #D2Q5 Lattice nx=100 # the number of nodes in x direction lattice direction ny=5 # the number of nodes in y...
15. ### Measuring thermal conductivity of a metal

What'd be practical method and/or portable, simple tool (like sort of electricians' multimeter) to meter the heat conductive constant of a metal?
16. ### Thermal expansion of square from temperature increase of 50K

For this problem, The solution is, I understand their logic for their equation, but when I was trying to solve this problem, I came up with a different expression: ##\Delta A = \Delta L_x\Delta L_y## ##\Delta L_x =\Delta L_y = \Delta L## since this is a square. ##\Delta A = \Delta L^2##...
17. ### A Heat exchange in a thermal storage based on phase change materials

Hello, I want to model a thermal battery based on phase change materials (PCM). It is a plate heat exchanger immersed in a PCM bath. The diagram is given in the attached file. I want to determine the temperature at each moment and from everywhere in the battery. The hypotheses are the...
18. ### B Heat exchange after thermal equilibrium

In screenshot below, systems A and B are separated by an adiabatic wall initially while each of them exchanges energy with system C via a diathermic wall. Once A and B reach thermal equilibrium with C, then A,B are allowed energy exchange via a diathermic wall, and energy exchange between A and...
19. ### Doubling the Thermal Energy of a Frozen Chocolate Bar

The farthest I got was double thermal energy equals mass times specific heat capacity times change in temperature (115+34) 2Eth=(mc149) To Eth=mc74.5 I'm not sure where to go from here. It seems like I don't have enough information.
20. ### Link between increase in Potential energy and the thermal energy lost

"Heat is the transfer of kinetic energy between molecules. If the velocity is more, the kinetic energy will be more so that the heat is more." "As an object's speed increases, the drag force from the fluid increases exponentially. For example, when you drive at high speeds, the frictional force...
21. ### B The collision of molecules during thermal expansion

Greetings everyone. I learned that the distance between molecules in liquid increases while the temperature increases. Hence, its density is decreased. The process is thermal expansion. At the same time, the collision between molecules would be more frequent when the temperature increases...
22. ### A Electrical & thermal conductivities

What's the mechanism underlying the correlation between electrical & thermal conductivities in metals ?
23. ### Thermal expansion of air bubbles in plastic

I am interested in the potential for air bubbles in a plastic structure to expand with heat, and put pressure on the plastic surrounding the air bubble. In this case the plastic structure is formed by melting a thermoplastic powder. In between the grains of powder are voids with air in them. As...
24. ### Triangular cavity thermal radiation simulation

Hi, I'm trying to solve a problem involving radiation in a triangular cavity: As you can see, lengths and emissivities of all surfaces are given. For two of them, the heat flux is known and the temperature has to be found while for the remaining surface it's the other way around. I have the...
25. ### I The CMB has a thermal black body spectrum

https://en.wikipedia.org/wiki/Wien's_displacement_law "Maxima differ according to parameterization ... Using the value 4 to solve the implicit equation yields the peak in the spectral radiance density function expressed in the parameter radiance per proportional bandwidth. (That is, the density...
26. ### How does energy affect the melting point of water?

Im not really sure how to answer this question. Would you have any ideas?
27. ### Is the Calculation of Thermal Energy in Mixing Water and Steam Accurate?

Q=Qwarm water+Qsteam Q=mct+mLv Q=(8kg)(4200J)(100C-25C)+(2kg)(2.3*10 to the power of 6 J/Kg) Q=7.12*10 to the power of 6 J Is this the correct answer?
28. ### I Concept of Thermal Equilibrium in the Context of Canonical Ensemble

Canonical ensemble can be used to derive probability distribution for the internal energy of the closed system at constant volume ##V## and number of particles ##N## in thermal contact with the reservoir. Also, it is stated that the temperature of both system and reservoir is the same, i.e...
29. ### Thermal energy dissipated from the brakes in a car

My sign doesn't check out and I don't get why that'd be the case. Forces that act --> ##F_{fr} and F_g## derivation: ##\Delta K = W_{NC} + W_C (1)## ##\Delta K + \Delta U = W_{NC}## ##\frac 12 mv_2^2 - \frac 12 mv_1^2 + mgy_2 - mgy_1 = W_{NC}## NOTE: ##y_2## assumed to be datum line so ##y_2 ==...
30. ### Photovoltaic vs. thermal radiator Solar Panel comparison (using a lens)

Hi, Has anyone experience with photovoltaic solar panels and thermal radiator type solar panels? 1/ How do they compare when both have the same collection area? If the thermal radiator was much smaller than the collection area, and a lens the size of the collection area was used, focused on...
31. ### I Simple model of thermal shape fluctuations of liquid interface

Consider a container filled with two essentially incompressible liquids with densities ##\rho > \rho'## and (respective) volumes ##V##, ##V'##, rotated by a centrifuge in some orbit-based space lab to maintain a roughly constant (co-moving) simulated "gravitational field" g. Let's suppose that...
32. ### Thermal Dissipation of High-Power Electronic Subassemblies

High-power electronic subassemblies – housing CPU or power-conversion semiconductors, for instance – require significant thermal dissipation to keep their chip-junction temperatures at or below their maximum operating temperature. (As a rule-of-thumb, every 10oC increase in junction temperature...
33. ### I Does pressure affect the thermal breakdown of water?

As per the title, I'm trying to research how the thermal breakdown (thermolysis) of water works. I gather that you need circa 3000°C to get it to break down, which is a lot, and I'm curious as to how pressure might affect this. I know that pressure affects the boiling point of water, and as...
34. ### I Calculating the thermal coefficient between the insulated interior of a telescope instrument package and the cold ambient air outside

I've built an insulated chamber to protect a sensitive instrument at freeze temperatures in the winter. The instrument is mounted on a telescope, so the heat inside the chamber will slowly dissipate in the ambient. A digital PID thermostat is used to keep the temperature at a safeguard level...
35. ### Question about these thermal expansion coefficient units (m/mK)

so I have never seen this unit before. 10^-6m/mK for the thermal expansion (linear expansion). I believe this unit is micrometers divided by mili kelvins?
36. ### I Is it cooler hanging ice packs from a fishnet bag or in a thermal lunch-bag?

Summary: I think I found the solution at the end of the post, posting in case someone has a better idea. I plan on going shopping somewhere a bit distant because my local supermarkets dropped the majority of store brands. I suspect the whole trip will take 90-120 mins. I have a deep freezer...
37. ### I Difference between the thermal and mechanical efficiency

Hello, I'm confused between the difference between the thermal and mechanical efficiency of a Sterling heat engines or heat engines in general. I hope you could be able to guide and help me. Thank you
38. ### Night vision technology vs thermal imaging

Hello Everyone, I have a thermal imager and I am interested in better understanding night vision (NV) technology. Apparently, NV goggles respond to NIR and SW See this article. NV goggles can see from the near infrared (NIR) to the shortwave infrared (SWIR) portions of the light spectrum. Do...
39. ### I Interpreting Thermal Power in Cylinder with Source & Sink

I have a cylinder that is separated with an insulator. In the internal cylinder there is a thermal source, while outside the insulator we have a thermal sink. The power of the internal cylinder is positive, while of the external one in total is negative. How I should interpet the results. Like...
40. ### I What are thermal fluctuations?

I often think thermal fluctuations as random changes in the temperature but when it is said in the context "thermally fluctuate over the energy barrier" does it mean to classically overcome the barrier?
41. ### Lithium hydroxide from Li-7 as used in thermal reactors

So I read that lithium hydroxide made from Li-7 is used as an anti-corrosion additive in light water reactors purely for the "longevity" and "well being" of the vessel and structural auxiliary elements like steam pipes etc. Lithium separation is a rather chemically "nasty" task if using the...
42. ### Thermal physics question: Specific heat capacity

At first, I tried to calculate the heat energy required by doing this: I realized I should calculate heat energy separately instead of grouping glass and water together so I did this: But the answer is supposed to be 6.29 x 10^4. I don't know how to solve this. Can anyone help please? Thank you
43. ### Thermal Physics Problem -- Dropping a hot mass of iron into 20C water

Hi, The solution for this question is thermal energy lost= thermal energy gained 0.200x450x(300-T)=1.0x4200x(T-20) T=26 degrees celcius. However, I am struggling to grasp why (300-T) is used. I have always known a change in something to be final - initial. Therefore change in T= Final-...
44. ### Thermal Printing and Ink fading

Hello, I am not sure if this is the right place but I would appreciate some help. Basically I have been trying to accelerate the fading of the ink on thermally printer paper. “Receipts are typically printed on thermal paper, a chemically coated paper that produces text and image when the...
45. ### Thermal insulating materials suitable for making piston and cylinder?

What materials would be suitable for a cylinder and piston that is thermally insulating, reasonably durable for low speeds and very slow cycle rates, and not be a carbon or silicon based polymer? I've been looking at manual lever operated espresso machines lately. Particularly ones that are...
46. ### I Thermal Expansion of A Square Shaped Object

Suppose a square shaped object has an initial length of L1 and final length (after thermal expansion) of L2. Initial temperature is T1 and final temperature is T2. Suppose it has an area of A. So initial area is A1 and final area is A2 (after thermal expansion). Here A1 = (L1)^2 and A2 = (L2)^2...
47. ### I Estimating a thermal equilibrium on a custom made fridge

Hello, I'm trying to build a custom made fridge made by a cube by 120cm on each side. The material used to isolate the cube will be some polystyrene panels, with thickness s=4cm. Let's imagine to cool the dry air inside in order to reach the internal temperature of 8 degree Celsius, while the...
48. ### A How to calculate the temperature change of a laser-irradiated material

I am looking to approximately calculate the temperature change of a sample that was exposed to a laser pulse. Experimentally, we know the optical absorption, reflection, and transmission, as well as the source parameters for our laser system. I realize that I will have to make approximations...
49. ### Maxwell 3D & Icepak thermal simulation for a air coil

Hi Guys, I am doing a Maxwell 3D&Icepak thermal simulation for a air coil. I want to get its temperature when loading 1.6A current. So I use Eddy Current type in Maxwell 3D and Temperature and Flow type in Icepak. Then I load 1.6A solid current and adaptive frequency of 800 MHz for the coil...
50. ### Steady State Thermal Analysis - Simulation

I am simulating a hot forging process in LS-Dyna. A tool is contacting a hot workpiece for 2 sec every 10 sec (--0 sec--contact--2 sec--no contact---10 sec--) in a factory. Since this is a continuous process, the tool should, at some point, attain steady temperature. I have tried to recreate it...