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. D

    Thermal radiation in transparent objects

    Every objects emit thermal radiation. Now consider this case: Sun emits waves in a certian electromagneic spectrum (UV + thermal radiation + ecc...); glass is transparent to thermal radiation that usually reach Earth's surface. UV and other radiations are mainly absorbed by Ozone and other...
  2. T

    Maxwell Relation, Gibbs Free Energy, Thermal Expansion Coefficient

    Homework Statement By means of a Maxwell relation derived from the Gibbs free energy and making use of the third law of thermodynamics, prove that the thermal expansion coefficient β must be zero at T = 0. I tried but I got something funny. Homework Equations $$G=U-TS+PV$$ $$dG=\mu...
  3. T

    Maxwell Relation, Gibbs Free Energy, Thermal expansion

    By means of a Maxwell relation derived from the Gibbs free energy and making use of the third law of thermodynamics, prove that the thermal expansion coefficient β must be zero at T = 0. I tried but I got something funny. My working:
  4. B

    Thermal equilibrium and isolation

    If two objects are at the same temperature, but thermally isolated from one another, are they still considered to be in thermal equilibrium with one another?
  5. J

    A What is the method for calculating the dampening of thermal oscillations?

    Hello, I am attempting to solve the 1 d heat equation using separation of variables. 1d heat equation: ##\frac{\partial T}{\partial t} = \alpha \frac{\partial^2 T}{\partial x^2}## I used the standard separation of variables to get a solution. Without including boundary conditions right now...
  6. W

    Thermodynamic Identity: Chemical Potential

    Homework Statement Homework Equations Thermodynamic Identity The Attempt at a Solution While I was able to work out the problem with the help of the hint, I couldn't completely understand the implication of said hint. The hint suggests that the equations for Chemical Potential in a process...
  7. W

    Thermal Physics: Thermodynamic Identity

    Homework Statement Homework Equations ##dS = \frac{1}{T} (dU - PdV)## assuming dN = 0 The Attempt at a Solution I have actually managed to solve all 4 parts correctly, except for the fact that I solved Part d) with the Sackur-Tetrode equation rather than the thermodynamic identity. I...
  8. Pushoam

    Mean thermal energy of a system with given potential energy

    Homework Statement Homework EquationsThe Attempt at a Solution ## V(r) = \frac 1{r^3} \left( A - Br^2 \right )## At the bottom of the well, r is verry small. So, ## V(r) = \frac A{r^3}## Assuming the validation of Equipartition of energy theorem, since the degrees of freedom is 1, the...
  9. Biker

    Questions About Stephan's Law of Thermal Radiation

    I took Stephan's law for thermal radiation and I have a couple of questions about it. 1) The law states that the full energy radiated in 1 sec is equal to c T^4 where c is 5.67*10^-8 and T in kelvins and In the book they said if it has surroundings then the net energy emitted would be q = c A...
  10. M

    Estimating density, viscosity and thermal conductivity

    Homework Statement Hi there, I am designing a heat exchanger and I am really struggling to find out how to fairly accurately estimate the density, viscosity and thermal conductivity of a gaseous mixture at ~~20bar. There is 8 components in the mixture: methane, ethane, ethene, ethlyene oxide...
  11. U

    Somewhat Complicated Thermal Problem

    Problem Description: I have a solar panel of some surface area, material, and thickness mounted to an enclosure. The panel is isolated from the enclosure at some distance with a multitude of materials (air, insulation, plastic, metal) between the back surface of the panel and interior volume...
  12. F

    PVC vs Copper Pipe Thermal Conductivity

    Question#1 I would like to compare a 100' length of 4" PVC pipe with air in it surrounded by Earth and/or water. What length of 4" copper pipe would equal a 100' length of PVC? Question#2 If the inside of the pipe had turbulence what length of non-turbulent 100' PVC 4" pipe would it equal? I...
  13. R

    Problem concerning about thermal physics

    Homework Statement A metal rod of length length L, linear coefficient of expansion a, is fixed at both ends to the walls. When the temperature is increased byΔT, the rod bends into a circular arc due to thermal expansion. 2 Relevant equations a)Find the radius of curvature R of the rod by...
  14. P

    Thermal radiation inside a cooler

    I am trying to calculate how much a foil liner helps keep the inside of a package cool. I have calculated the rate of conduction but am now concerned with radiation. Above is the equation I am using. The emissivity for the material is 0.05, the area is 1 m^2, the outside air temp is 295...
  15. R

    Magnetic conductive material but thermally non conductive

    HI, I have application where i need to lift metal plate, 3kg weight, ( 3mmX 15mm), 250degree.C hot, for the period of 1min and put it back. For lifting purpose i am using actuators. As i have no opportunity to make hole in plate i have to use magnet for lifting purpose. I got Electromagnet...
  16. W

    Thermal Physics: Freezing Lake

    Homework Statement Homework Equations dQ/dt = -kA(dT/dx) The Attempt at a Solution I tried to use Fourier's law of Conduction on this one. I subbed dT for (Θ0 - Θ1), and l(t) (function for thickness of ice against time) for dx, reason being that the sheet of ice should get thicker. I then...
  17. W

    What is the Thermal Conductivity of a Diatomic Gas?

    Homework Statement Homework EquationsThe Attempt at a Solution Part 1.1) I managed to find the energy needed to melt the ice, before using ΔU = Nf½KΔT to solve for the new temperature, which was correct Part 1.2) Initially tried using ΔQ = mcΔT before realising that I didn't have the mass...
  18. M

    Thermal Tumbler and unusual noise....

    Back in... man... probably 1996 I went to work with a thermal tumbler filled with some hot beverage or another. I settled in and took a swig; the liquid was good and hot and I kind of marveled at how well the tumbler worked and how it was nice to have a warm drink in my cool environment and...
  19. S

    Solar Thermal Optics - Concentrated Light

    Hi, Can someone start me out with creating predictable temperatures and inputs for calculations. Here is a miniature example of the type of parabolic circulated water heating devices I have been building. My first questions would be what is the potential heating energy of the sun per cm2? And...
  20. L

    Can a 2500 Gallon Water Tank Sufficiently Cool a Condenser Without a Chiller?

    Hello! Hopefully someone here can help with this problem: I have a condenser that holds 35 gallons of water to cool the copper coil on my still. I need to know if I can create a closed loop system of cooling water that allows me to avoid running a chiller. I know that there is probably an...
  21. S

    What differentiates thermal and sound energy?

    Since thermal energy is the vibration of molecules and sound is too, what is the difference? And why exactly do atoms radiate different energies as a result of vibrations?
  22. R

    IR spectra (in thermal scope vs IR spectroscopy)

    In thermal imager vs IR spectroscopy, they both look at the IR radiation of an object. What is the difference between the two.. I know IR spectroscopy look at the dipole moments of molecules. But in thermal imager.. do they also image the dipole moments of molecules? Also why you see images in...
  23. Const@ntine

    Cylinder & Mineral: Thermal Dilation

    Homework Statement A hollow aluminum cylinder with a depth of 20.0 cm has an internal capacity of 2.000 L at 20.0 C. It's full with mineral turpentine, at 20.0 C. The two of them are heated slowly, until the temperature reaches 80.0 C. a) How much of the mineral is spilled outside the...
  24. G

    Is a fast reactor more cost-effective than a thermal one?

    Is a "fast" reactor more economical in terms of capital investment than a thermal one? I am asking this because I assume a fast reactor only needs a smaller startup U235 source of on average 20% enrichment but can later run on its own produced fissile material and would normally for the rest of...
  25. J

    Question about thermal conductivity in thermoelectrics

    Does the phonon thermal conductivity account for a large part of the total thermal conductivity in thermoelectric materials like Bismuth Telluride? As far as I know, the phonon conductivity is the largest contributor to the total thermal conductivity in semiconductors. Is this still true for...
  26. H

    How to find added thermal heat in monoatomic gas?

    Homework Statement for number 3,4,5 I'm still tryingHomework Equations PV/T = PV/T q = ΔU + W W = P ΔV The Attempt at a Solution (3) I used PV/T = PV/T to find the ΔT for each process for A→B I find PV/TA = P3V/TB ----- TB = 3TA (T increase) for B→C I find P3V/TB = 4P3V/TC ----- TC =...
  27. C

    Can I use thermal expansion to hold together materials?

    Okay, I will give a quick run down of what I am trying to do here. What I want to do is build a tesla turbine from old hard drive disks. Being that they're already rated for high RPM, it seems like a viable option. Now these disks are probably going to be aluminum and I am probably going to buy...
  28. A

    Negative heat capacity and thermal reservoir

    Say you have an object with a negative heat capacity. This means that the object increases in temperature as it radiates energy and decreases in temperature as it absorbs energy. I don't understand why this object cannot be in thermal equilbrium with a reservoir. Any help would be greatly...
  29. K

    Why Doesn't Decreasing Volume Increase Molecular Speed According to Boyle's Law?

    Hi guys, From Boyles Law, we know that Volume is inversely proportional to Pressure give that the temperature is kept. My question, if we decrease the volume, the pressure will increase due to rate of change of momentum ( we can say those two are proportional), then why can we not claim that...
  30. W

    Problem involving thermal radiation and specific heat

    Homework Statement A satellite to reflect radar is a 3.5-m-diameter, 2.0-mm-thick spherical copper shell. While orbiting the earth, the satellite absorbs sunlight and is warmed to 50 °C. When it passes into the Earth's shadow, the satellite radiates energy to deep space. You can assume a...
  31. A

    Thermal Expansion: Volume vs. Linear - 0.11L Spilled

    Homework Statement A one-liter pot is completely filled with oil. Heat is applied to the pot&oil and the temperature rises from 15°C to 190°C. How much oil is spilled over? The linear coefficient of thermal expansion for oil is 0.68*10-3; the one for the pot is 2.4*10-5 Homework Equations...
  32. S

    Studying Bombed Thermal Midterm, Advice for Final Exam

    Hello all, I am a third year physics and math major at a quarter system public school. This year I've been getting pretty decent grades and achieved a 4.0 last quarter on 4 upper div math and physics classes. This quarter I am taking Topology II, EM Waves, Thermal Physics and a breadth class...
  33. H

    Full thermal decomposition of metal oxides?

    I haven't been able to find much information on the thermal decomposition of metal oxides into their corresponding metals and oxygen. What temperature would Fe3O4 decompose mostly(80%) into its base elements? Additionally, how can this information be determined based upon bond...
  34. H

    Thermal expansion of each dimension of a solid

    Hi, I am trying to work out how much each dimension of a solid (for instance an annular disc) made out of steel changes assuming that the solid is heated uniformly and is not constrained at any of its boundaries. Am I right in saying that, the linear expansion equation L = L_0 (1+ α ΔT) can be...
  35. G

    Thermal Expansion of A-36 Steel Rails: -20F to 90F

    Homework Statement The 40 ft long A-36 steel rails on a train track are laid with a small gap between them to allow for thermal expansion. Determine the required gap in inches so that the rails just touch one another when the temperature is increased from -20 F to 90 F. The cross sectional...
  36. W

    Thermal resistance without area

    I'm (self)studying the physics of heat transfer at the moment. My book gives a relationship between heat transfer rate and thermal resistance as ##\phi=\frac {A \Delta T} {R}##. My book is not in English, so hopefully that is not the cause of this misunderstanding. I double checked that heat...
  37. N

    Has thermal conductivity any relationship with energy?

    More thermal conductivity means there's more energy?...
  38. E

    Relation between Young's modulus and the coefficient of thermal expansion

    Is it true for all material that if young's modulus is high then melting point will be high and coeff of thermal expansion will be lower? Any example that doesn't follow the above statement. Many Thanks
  39. CMJ96

    What happens at the lambda point of superfluid Helium?

    Homework Statement 2. Homework Equations are given in the above picture 3. The attempt at the solution In part a) I simply rearranged the other expressions given and subbed them into the relationship for relative velocity and came out with Vns= Qdot/ρsT(1- ρn/ρs).Then in part b) I started by...
  40. R

    How can thermal fluctuations decrease entropy?

    https://en.wikipedia.org/wiki/Future_of_an_expanding_universe "Over an infinite time there could be a spontaneous entropy decrease, by a Poincaré recurrence or through thermal fluctuations (see also fluctuation theorem)"
  41. P

    Why does 135Xe have a high thermal neutron cross section?

    Title says it all. Made a few google searches and couldn't find any information. Is there a reason why it is so large, or is it just a coincidence of nature?
  42. C

    I Scale invariant thermal fluctuations

    There's something that has been bugging me for over a year now and I seem to be unable to find the answer. I would appreciate it very much if somebody could help me out. The thing is that I don't understand how it is possible that in second order phase transitions the correlation legth becomes...
  43. K

    Thermal expansion of liquid into gas void

    I have a question about thermal expansion of liquid into a gas void. Imagine a closed upright cylinder filled mostly with water – say 99%, and the remaining 1% is gas. Now imagine that you heat the cylinder and its contents. The water will expand by ΔV owing to thermal expansion. The gas...
  44. M

    B Thermal and Non thermal light emission

    I am now working on Thermal and Non-thermal light emission of materials, particular concerning the Planck law and Generalize Planck Law. I really want to understand the fundamental concept of this. So could you please suggest me some material, book on this subject? Thank you so much in advance,
  45. V

    Solve Thermal Rad. Homework: Box Painted Black, 500 W Light

    Homework Statement A wooden box is painted completely with black paint. The interior dimensions are 18”x24”x3.5”. The bottom and sides are made with 9 pieces of 2x4 douglas-fir-larch dimension wood lumber. The top of the box is open and is covered with 0.118” thick clear acrylic. The acrylic is...
  46. G

    References on thermal power stations and supercritical technology

    Hi. This is technically an assignment question, but it's not really a problem that I have to solve. It's more of an investigation so I thought this would be a more appropriate place to discuss it. The question basically asks you to compare the thermodynamic cycle of water in a typical thermal...
  47. P

    Thermal motion of an ionised gas molecule in an electric field

    What I want to discuss here is what happens to the thermal velocity when an ionised gas molecule has been put into an electric field. Due to the charge (e) and potential difference (V), how much velocity has been gained by the ion can be calculated easily.eV = ½mv2 Where e is the charge of the...
  48. Bonapartist

    Thermal energy problem: Gas expansion in cylinder

    Homework Statement A vertical heat-insulated cylinder is divided into two parts by a movable piston of mass m. Initially, the piston is held at rest. The top part is evacuated and the bottom part is filled with 1 mol of monatomic gas at temperature 300 K. After the piston is released and the...
  49. P

    Thermal Expansion: Finding common temperature (Ring/Sphere)

    Homework Statement Find the common temperature at which the inner diameter of the ring is 0.05% larger than the diameter of the sphere. Given: Lead sphere d = 5cm To = 70°C ∝ = 29x10-6/C° Steel ring d = 4.9975cm (the sphere is 0.05% larger than the inner diameter of the ring, hence this value)...
  50. haushofer

    I Inflation, horizon-problem and thermal equilibrium

    Dear all, for the topic https://www.physicsforums.com/threads/problems-with-the-theory-of-inflation.905230/ I came across the following paper: https://arxiv.org/abs/1505.01456. In this paper the following arguments are given why the horizon problem is a fake problem. It raised by me the...
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