Thermal Definition and 1000 Threads

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. katelr

    When/How does thermal radiation stop (if it stops) and conduction

    Consider two solid objects in the vacuum (of different materials, if you will) at different temperatures approaching each other until they make "perfect contact" through flat surfaces (no gaps or defects, so that thermal contact conductance effects are absent, even though interfacial thermal...
  2. H

    Thermal ballast (or whatever it's called)

    During weather-based heat waves or cold snaps, a completely sealed house with all windows/doors shut (but using no HVAC, heating-ventilation-AC) will take "a while" to cool down or heat up. If the heat wave or cold snap is quick (e.g., 24 hrs), a resident inside the house will experience almost...
  3. M

    Comparison of thermal shock profiles

    Could someone help me in comparing 2 different thermal shock test profiles effect on a component. The 2 profiles are varied in deg C /min change and also the dwell time in low and high tempwratures. Any references are highly appreciated. Thank you
  4. L

    What Happens to Water Temperature and State After Heating for 25 Minutes?

    A heater so P=500Js^-1,heats up a tank of water of 200ml from 25°C for 25 minutes. What is the final form(solid ,liquid or gas)and the final temperature of the water? The answer: Final form : Liquid+vapour Final temperature: 100°C I have no idea how to do this! Plz help!
  5. baldbrain

    Iron Ring Expansion: Solve for Δθ to Find Temp Increase

    Homework Statement An iron ring of radius 2.1 m is to be fitted on the rim of a wheel of radius 2.121 m. The coefficient of volume expansion for iron is 3.6 x 10-5 K-1. By how much should the temperature of the ring be increased? (a) 532 °C (b) 833 °C (c) 278 °C (d) 378 °C Homework Equations...
  6. sweet springs

    Exchanging roles of variable and thermal potential

    In thermal physics entropy S is regarded as a system variable in 1st theorem of thermal dynamics, i.e. dE(S,V)=TdS-pdV=T(S,V)dS-p(S,V)dV Entropy is regarded also as thermal potential,i.e. dS(E,V)=\frac{1}{T(E,V)}dE + \frac{p(E,V)}{T(E,V)}dV S,V,p,T are usually regarded as variables. My...
  7. Cassius1n

    Heat loss in a conductor based on Fourier's law

    Homework Statement Find the admissible current density Jadm for a wire that has no insulation and also for a wire that has two layers of insulation and compare it to Jadm for the case when the wire has only one layer of insulation.2. The attempt at a solution and equations In the image I've...
  8. H

    A Do thermal quantities change in quantum phase transition?

    Such as, Chern insulator, normal insulator, topological insulator, do they have any discontinuous change in thermal quantities? Do they have order parameters?
  9. P

    Thermal equilibrium in open systems

    Is it possible for an open system to reach thermal equilibrium? why/why not?
  10. N

    I "Thermal" neutrino generation?

    Consider the Sun. It radiates energy by generating EM radiation. However, Sun is not transparent to EM, and therefore energy can only escape from the surface using this mechanism. Hot plasma below the surface generates and absorbs gazillions of photons, but they are "trapped" there. But EM is...
  11. S

    Max Heat Transfer w/ Low Conductivity Brick & Copper

    Hello, Just a quick question if I have a let's say a heat source of under a layer of bricks that have a thermal conductivity of 1.6 (W/m/°C.) and on top of the brick a layer of copper with a thermal conductivity of 398 (W/m/°C.). Is my assumption right that since the layer of brick has such a...
  12. Casper Hansen

    Accelerated lifetime / thermal ageing of power cables

    Hi PF Is it possible to perform accelerated lifetime test of thermal ageing on power cables? Let's assume that the cable manufacturer guarantees a service life time of 20 years at max operation temperature 90 [degC]. Is it possible to estimate the expected life time of a cable if I choose to...
  13. Clara Chung

    Question about Maxwell equation in thermal physics

    Homework Statement Homework EquationsThe Attempt at a Solution How to do part ii)? I differentiate part i with respect to p (∂H/∂P)T = T (∂S/∂P)T + V ...(1) Then I used the equation given in the question, Applying maxwell equation I got (∂T/∂V)S = -(∂P/∂S)V ...(2) I planned to substitute...
  14. E

    Internal energy and thermal energy

    I'm watching a lecture introduction internal energy and in it, the lecturer states the following for some system: E_{internal} = E_{translational} + E_{vibrational} + E_{rotational} + E_{other} where ## E_{other} ## could be chemical energy, magnetic energy, electrostatic energy etc. Then...
  15. S

    Need help to explain the peak of thermal conductivity

    Progress This is the experimental data of thermal conductivity of stainless steel 304L at low temperature. The data is calculated with the Fourier's law of thermal conduction. I checked many times in the excel file and I confirmed that there is no mistake in the calculation. The parameters are...
  16. isukatphysics69

    Where Does Thermal Energy Come From in an Inelastic Collision?

    Homework Statement Homework Equations n/a The Attempt at a Solution I am going through the final exam problem sets right now and just looked at the answer key and wondering where in this system there could be thermal energy? while i was working through the problem i assumed no thermal energy...
  17. T

    Negative Heat Sink thermal resistance

    I'm currently developing a heat sink for a product that produces up to 150 W max power dissipation. I'm currently getting a negative thermal resistance for the heat sink. I don't think that is possible.. I'm not sure how to move on at this point to properly design a heat sink to meet the heat...
  18. T

    Thermal Resistance between Chip to Gold Tin Solder

    I'm currently doing a heat sink calculation design and having a little confused moment with the area of the chip with a AuSn (Gold Tin Solder) pre-cut that's attached to the bottom of the chip. I've tried looking around online for AuSn's thermal resistance value, but there is none besides a...
  19. jdawg

    Engineering Heat and Mass Transfer: Thermal Radiation Circuit

    Homework Statement 1.) A piece of bread (ε = 0.85) is being toasted in a toaster, as shown below. The heating element of the toaster consists of a wire 2 mm in diameter that is wound to approximate cylinders spaced 2 cm apart. This element acts as a blackbody. The housing for the toaster is...
  20. mjda

    I Stellar Thermal Energy with no Nuclear source

    Can anyone enlighten me as to why the total thermal energy of a star will increase with time if the star has no nuclear energy source?
  21. physea

    Fabric with high thermal robustness

    Hello! Is there any material that is like fabric and can withstand high temperatures maybe 1k, 2k C etc? I also need it to be waterproof, ie to be able to hold liquid. Thanks!
  22. Ryan Doucette

    Nuclear Fusion: Electron Thermal Transport Terminology

    I am an undergrad physics major in my final semester currently taking Intro to Thermodynamics. As a final project, each student must choose a topic related to thermodynamics that is more advanced than what is covered in the curriculum and write a paper and present our findings to the class on...
  23. J

    How to quantify the thermal advantages of a white thermos?

    My understanding is that you could expect a white thermos to hold heat better than a black one as it doesn't lose heat through radiation as much. Is there a way to calculate the difference in heat retention?
  24. T

    B Does Thermal Radiation from Ordinary Materials Span All Wavelengths?

    Hi. I want to know does thermal radiation contain all the wavelengths (from very near zero to almost infinity) or not? I want the thermal radiation of normal things like hot Tungsten (wolfram) or hot Iron. I don't want the black body radiation of a star. I think, theoretically it must contain...
  25. J

    I Thermal field theory of an isolated electroweak plasma

    The theory of electroweak temperature says that when you have a plasma of particles at energy above the electroweak phase transition (100 GeV). The Higgs field would turn from nonzero vev to zero and the electroweak forces would unite and the electroweak bosons would become massless. What...
  26. lookez

    Thermal dilation formula discrepancy?

    Considering the linear thermal dilation formula ΔL=Li*a*ΔT (length change equals initial length times thermal dilation coefficient times temperature change), I was wondering why does it not work backwards? am I using it wrong or is there something missing? For instance if we assume a=5*10^-5 ...
  27. S

    Stress and Thermal Creep in ANSYS Mechanical

    Just wish to know if there are GOOD EXAMPLES out there on the topics above. I am particularly looking for thermal creep using ANSYS Mechanical Workbench ... Thank you much.
  28. A

    Using an IR Thermal Gun to check for steam passing valves

    Greetings I am asking about the reliability of using a thermal gun to check if there is passing downstream the valve. The fluid is either steam or air. Wouldn’t the pressure and temperature drop sharply downstream the valve if it is closed but passing ? again I am talking about air or steam...
  29. J

    What happens to the angle of a circular ring as temperature increases?

    Homework Statement A part of a circular ring is missing .What happens to the angle when temperature is increased ? 1) θ increases 2) θ decreases 3) θ remains same 4) θ increases initially but becomes constant after a particular temperature . Homework EquationsThe Attempt at a Solution As...
  30. O

    Thermal neutron flux distribution in reflected core

    Hi, The figure given below was taken from "Nuclear Systems" by TODREAS and KAZIMI. it shows the effect of neutron reflector on the thermal neutron flux radial distribution. Is this correct? Because it does not show the extrapolated distance. It seems to me that the reflector, somehow...
  31. J

    Thermal expansion of air inside a bottle -- some questions....

    For thermal expansion in a bottle - is there a theoretical model on the pressure exerted on the inside of the bottle due to the air inside expanding when the bottle heats up. The air will be expanding randomly in all directions so the pressure exerted at any point on the inside of the bottle...
  32. O

    I U-235 thermal neutron capture gamma ray

    Hi, When U-235 captures a neutron, it may end up with a fission reaction or an excited U-236 isotope. This U-236 emits gamma rays as it goes to its ground state. What I want to learn is that how much is the contribution of these gamma rays' energy to overall fission energy. I checked the...
  33. B

    B Thermal Dependence of the Higgs Mechanism

    I'm familiar with the Higgs mechanism.. but what perplexed me so much is the temperature dependence. I know about superconductivity or magnetic-temperature analogy.. or generally I understand what's written in wiki https://en.wikipedia.org/wiki/Higgs_mechanism "Below some extremely high...
  34. B

    Thermal Neutron Absorption Rate in Water?

    Homework Statement "The 2200 m/s flux in an ordinary water reactor is 1.5*10^13 neutrons/cm^2*s. At what rate are the thermal neutrons absorbed by the water?" Homework Equations (unsure) The Attempt at a Solution I know that absorption of a thermal neutron (a neutron in thermal equilibrium)...
  35. dRic2

    Viscosity and thermal diffusivity in liquids and gases

    Hi PF, I was wondering about this for some time and I can get my head around it. Viscosity ##\mu## is a "measure" of the momentum flux Thermal diffusivity ##\alpha## is a "measure" of the heat flux (kinetic energy of molecules) In gases both viscous stresses and heat flux take place due to...
  36. D

    What Is the Formula for Calculating Thermal Stabilization Time?

    Hello all. Been a long time since I took a thermal course. I'm looking for a formula to work with the thermal stabilization of something. Specifically, I want to minimize the time required for thermal stabilization to occur and how to mathematically calculate what that set temperatures should...
  37. PKM

    How to find the thermal compressibility of a gas

    Homework Statement : [/B] A gas obeying the equation of state PV=RT undergoes a hypothetical reversible process PV^\frac{5}{3} e^\frac{-PV}{E_0} = c_1 Can we prove that the thermal compressibility of the gas undergoing this process tends to a constant value at very high temperature? Here, E_0...
  38. X

    Thermal efficiency of a Diesel engine

    Hi, i’m learning about the thermal efficiency of a diesel cycle at university and I'm trying to understand the equation. The first law of thermodynamics states Wnet + Qnet = 0, but one of the attachments below says Qnet - Wnet = 0 and I don't understand how this is the case. Also, for process...
  39. Ricardo Gomes

    ANSYS - Radiation of a satellite - Surface-to-surface or to-ambient

    Hi all, I'm performing a thermal analysis of a satellite subsystem (antenna). However, I'm having some issues relating to the model that I'm implementing on ANSYS. I've already computed the values for the solar flux, albedo and IR that the satellite is subject and I've applied it to different...
  40. Jo MacDonald

    Does the Coefficient of Thermal Expansion Apply to Both Expansion and Contraction?

    We did an activity today in class where we placed an empty 2L bottle in the Freezer, let it contract, then calculated the coeffcient of volumetric expansion using ΔV = VoβΔT. We got pretty close to the accepted value. The question is... Does the coefficient of thermal expansion only work for...
  41. C

    Thermal Expansion to Retain a Bolt

    I have 1" aluminum rod and I want to dril a hole in a steel structure for the bolt. If I have a 1" drill and take .001" inches off of it at the machine shop, so that it is now 0.998 inches, there will have to be about a 200°C difference in temperature between the two articles (aluminum...
  42. T

    Thermal Resistance to Centerline

    Hello, Given an infinitely long cylinder with a specified surface heat flux, the thermal resistance of an annular region is given by, R_th = ln(r_out / r_in) / (2 pi L k). When I'm calculating the thermal resistance to the centerline, r_in = 0. Does that mean there is infinite thermal...
  43. P

    How Is the Equilibrium Temperature Derived in a Coaxial Cylinder Configuration?

    Homework Statement Gas with thermal conductivity κ fills the space between two coaxial cylinders (inner cylinder radius a, outer cylinder inner radius b). A current I is passed through the inner cylinder, which has resistivity ρ. Derive an expression for the equilibrium temperature of the inner...
  44. F

    What is the Velocity of Thermal Neutrons at 25 Degrees Celcius?

    Homework Statement Estimate the velocity of thermal neutrons at 25 degrees celcius Homework EquationsThe Attempt at a Solution I attempted to use KE=0.5mv^2 but I realized that I didn't know the Kinetic energy
  45. PeppaPig

    Thermal expansion of bimetallic strip

    Homework Statement [/B] A bimetallic strip is made of metal which has coefficient of thermal expansion is equal to α1 and the other's is equal to α2 at the temperature of T0. The temperature is increased to T0 + ΔT (ΔT > 0). The strip curves as shown in the figure. If both strip have the same...
  46. K

    Thermal Energy Equation Term - Chain Rule

    Homework Statement I am going through a derivation of the thermal energy equation for a fluid and am stumped on one of the steps. Specifically, the text I am using converts the term: P/ρ*(Dρ/Dt) to: ρ*D/Dt(P/ρ) - DP/Dt where: ρ = density P = pressure D/Dt = material derivative The text...
  47. G

    Thermal radiation and charged particle acceleration

    A non ionized neutral gas should still emit thermal radiation.,say xenon. Is this solely because of electron transitions ? I ask this because a lot of sources attribute the emission to charge particle acceleration,so neutral atoms should not do this,is this right?
  48. B

    How Does Statistical Mechanics Predict the Expectation Value in Quantum States?

    Homework Statement I am having trouble connecting the expectation value of ##\hat a^\dagger \hat a## to the prediction from statistical mechanics for the state $$\hat \rho = \sum_n \frac{\bar n^n}{(1 + \bar n)^{n+1}} |n\rangle \langle n|$$ Homework EquationsThe Attempt at a Solution [/B]...
  49. W

    Partial Pressures and Vapour Pressure

    Homework Statement Two systems in diffusive equilibrium have equal chemical potentials. We can use this fact to solve the following problem. We begin with a closed system consisting of a liquid such as water in diffusive equilibrium with its vapour. At the start, only the liquid and its vapour...
  50. Lugonja

    Thermal Night Vision: Physics Explained

    I am interested to know how does thermal night vision works. Can anyone explain that to me, I would be thankful. I want to see the physics perspective on this.
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