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. Q

    Thermal insulation and positive pressure

    I was having a discussion about thermal insulation (high temperature) and I thought that positive pressure (meaning the heat is being blown onto the insulation) would reduce how effective the insulation was. Say a 1/2" of insulation reduced temperature from 1000 degrees F to 500 degrees F...
  2. S

    Experiment for thermal properties of glazing

    Hi all, i'm trying to devise an experiment for measuring the thermal conductivity and other properties of a layer of glaze (~5mm thick, glaze is similar to that used in pottery and tiling). At this stage, the only samples of the glaze I have access to are fixed to a small clay tile (roughly...
  3. F

    2D heat diffusion simulation with thermal insulators

    Hi. I don't know if this is the correct place to ask this, but prefer you to suggest me where I should ask. I'm starting with numerical simulation and I've been playing with the finite differences method to solve the heat equation on 1D, 2D and 3D uniform grids. This was really simple. Now I...
  4. L

    Thermal Radiation: What is Nonthermal Radiation?

    I read somewhere on the net that almost 100 percent of radiation in the universe is thermal. What then is nonthermal radiation? Can it be said that blackbody radiation is purely thermal? What about all the radiation that is reflected, diffracted or partly transmitted by bodies, is that...
  5. C

    Calculation of thermal stress.

    Hi. I am trying to calculate thermal stress in a simple structure (cube) exposed to two different mediums at different temperatures. I have come across 4 formulaes, can anyone please advice on which one would be most appropriate. Please see the attached file as the fourth formulae is too big...
  6. A

    Thermal sunyaev-zeldovich effect

    i am having problem in solving equation VI given in attachment, the solution of which is also provided just below the equation. the attachment is a research paper related to sunyaev-zeldovich effect.
  7. L

    Coupling neutronic and thermal hidraulics

    I am on the last year of my study in nuclear ( engineering bachelor degree ). I will make a software that can coupling neutronic and thermal hidraulics in my thesis But i still confuse in case of choose the basic of software to make it because to handle Coupling neutronic and thermal...
  8. phinds

    Fundamental question about thermal radiation

    I've always thought that the following was true but posts in another thread lead me to believe I might have a fundamental misunderstanding. The other thread was a different topic and I didn't want to hijack it, so here's my question. What I THOUGHT was true but am not now sure about: an...
  9. 1

    Why Does Heated Wire Remain Elongated After Cooling?

    thermal expansion of wire?? hi I've got this 3mm iron-chromium-aluminium wire fixed at both ends, heated to approx 1000k (max 1200K) and suspended horizontally approx 1metre long. the wire it would appear has been extended by about 8mm, similar to what would be expected when its hot, only it...
  10. E

    How fast would a body reach thermal equilibrium ?

    For example, I place a simple steel cube weighting 1 kg in a room [filled with air] at 20C [room temperature]. - how fast would the cube heat up to 20C (yes, actually equilibrium would be a bit lower than 20C, but lets.. imagine that is is a infinitely large room and .. yes, you get it ) ? Yes...
  11. R

    Emissivity & Thermal Transmission

    Stainless steel has emissivity of 0.12. It means it only absorbs 12% of radiation and reflect the rest of the 88% as well as tranmitting the 12%. Now if you heat the stainless steel to say 300 Celsius. It won't transmit the 300 Celsius but only a little of it. This is why thermal imagers can see...
  12. G

    Time to reach thermal equilibrium and/or a steady state

    I want to calculate the time it takes for a spherical sample (radius, r) to reach thermal equilibrium in an oven where the temperature is held constant. I don’t need a super accurate answer, within 5-10 seconds is sufficient. Is it reasonable to simply say that when the Fourier Number (Fo) is...
  13. O

    Finding coefficient of thermal expansion and isothermal compressibility

    Homework Statement To a very good approximation, ammonia obeys the Bertholet equation of state, which readsPV=nRT+\frac{9}{128}(\frac{nRTc}{Pc})(1-6\frac{Tc^2}{T^2})Pa)Suppose we have 500 grams of ammonia under a pressure of P=3.04 atm and at T=323K. Calculate the volume of ammonia according...
  14. J

    Thermal conductivity and resistance

    Homework Statement i need to find the thickness of the insulating material that is needed to block out the heat that is coming into the room. the area of the affected wall is 3.3m2 the temp in first room is 18 degree celsius while the 2nd room is 45 degree celsius. the thermal...
  15. O

    Why can't thermal energy be converted completely to motion

    In my thermo class I'm currently taking, the professor constantly says thermal energy cannot be completely converted into energy of motion. Just to be clear, I'm not arguing this point. I'm just wondering why we say that, when earlier in the course it said that thermal energy at the...
  16. S

    How Does a Thin Plate Between Infinite Plates Affect Heat Transfer?

    Homework Statement Two infinite plates are kept at different temperatures T_{cold}<T_{hot}, with vacuum between them. A very thin plate, isolated from the environment, is inserted between the two plates. How will the net rate of heat emission from the hot plate to the cold plate change...
  17. K

    Difference between thermal and non-thermal Bremsstrahlung

    Can anyone give me a nice explanation of the difference between thermal and non-thermal Bremsstrahlung? Thank you!
  18. U

    Reversible reaction activated only by thermal energy

    Dear all, I am not an expert of Chemistry and I would like to know if there is a reversible reaction that can be activated only by thermal energy. The result of the reaction should be something which can be brough again to the initial state, releasing again the thermal energy stored. I was...
  19. D

    Thermal Properties of Sulphuric Acid Anodic Coatings

    Hi, Can anyone tell me at what temperature a 25micron sulphuric acid anodic coating will start to breakdown. I have noticed that after exposure to 135°C the electrical properties of the coating have dropped drastically. Regards Dan
  20. J

    Neutron Capture Cross Section Dependence on Target Material Temperature

    So I have been reading about the cross section of neutron capture and have been reading about how the cross section for neutrons in a given material depends on neutron energy, the most important factor obviously. But I have not seen as much information on how, for a neutron of a given thermal...
  21. C

    Calculation of Thermal stress in a steel cube put inside another bigger steel cube

    Hi. I am trying to calculate the thermal stresses in a steel cube which is placed inside another steel cube of bigger dimensions, supported by steel bars at the base and sides. Both the cubes are in contact with fluids at different temperatures. Can someone please suggest the methodology as i...
  22. K

    How Do Pressure and Impurities Affect Water's Melting and Boiling Points?

    Not homework, just need some help with explaining the effect of the following 2 things on the melting point/freezing point and boiling point of water; 1. Pressure is increased 2. Impurities are added If possible, can the explanations be as explicit as possible?? I have really no idea how to...
  23. M

    Thermal Radiation v Absorption of Light

    A layman with an interest in quantum mechanics here. Just want to check I understand something... Is the phenomenon of electromagnetic waves being emitted by an atom due to it being hot (black body radiation) different to that of such waves being emitted as a result of absorbing light...
  24. G

    Transient Thermal Analysis in Ansys (APDL)

    Hi, I have to model a transient thermal problem in Ansys. I just need an outline of how I should proceed. The Problem: I am trying to model the cooling of a solar collector reciever tube from 150 degree celsius to ambient. My attempts have involved the following: 1. Initial condition...
  25. T

    Thermal expansion of metals question.

    Homework Statement You use a steel measuring tape and measure the length of an aluminum bar. You measure a length of 20.700 m when the temperature is 21.2 degrees C. What is the measured length when the temperature is 29.4 degrees C? Homework Equations L = L0(1+\alpha\DeltaT...
  26. K

    Seeking Thermal Insulator & Electrical Insulator for Peltier Device

    Hey all, I'm using a peltier device for a cooling system I'm working on. The metal leads connecting the peltier to a power source keep falling off. I am looking to coat them with epoxy that must be a thermal insulator. It also MUST be an electrical insulator. The problem I've had is that...
  27. R

    Question : Thermal Equilibrium in 3 substances

    Note : My syllabus only go until thermal equilibrium in 2 objects , i am wondering what will happen and how to calculate if there are 3 substances in contact. So i formed a question on my own hoping it can be solved. *my teach refused to show me calculations saying it is unrelevant to exam...
  28. S

    Is Mass Transport the Same as Forced Convection in Thermal Engineering?

    Hi All, I'm looking at the fundamental aspects of heat transfer - as I'm not a mechanical/thermal engineer but soon to undergo a project wherein I need to deal with some aspects of thermal engioneering. In the text, which I've been reading (for finite element analysis), it talks of mass...
  29. E

    How Does Engine Efficiency Affect Cooling System Temperature?

    Homework Statement HELP with physics homework, thermal energy? I cannot figure out how to solve this problem, can someone show me how? A small engine pumps 100 liters of water from a well 300m deep. What would the change in temperature be for the engine 20 liter cooling system (filled...
  30. M

    Calculating Thermal Conductivity & Mean Free Path of Argon

    Homework Statement obtain an expression for the thermal conductivity of a gas at ordinary pressures. The thermal conductivity of Argon (atomic weight 40) at STP (standard temp and pressure) is 1.6e-2 W/mK. Use this to calculate the mean free path in Argon at STP. Express the mean free path...
  31. V

    What type of tape is best for attaching thermocouples to a light?

    Hello all, Sorry if this is under the wrong section. I need to attach some thermocouples to a light to test how it heats up over time, and I was wondering what type of tape I should use to attach them. I was thinking some kind of conductive tape. Has anyone done this before/have a suggestion...
  32. S

    Thermal physics; specific heat capacity

    Homework Statement In an experiment to measure the temperature of the flame of a Bunsen burner, a lump of copper of mass 0.12 kg is heated in the flame for several minutes. The copper is then transferred quickly to a beaker, of negligible heat capacity, containing 0.45 kg of water, and the...
  33. P

    Why Is a Turbine More Efficient in Winter?

    Hello, An electrical power station situated in Northern Canada uses water to cool the steam as it leaves the turbine. Suggest why the efficiency of the turbine would be greater in winter than in summer: I first started to think in terms of the efficiency equation I have for heat engines...
  34. P

    What Is the Difference Between Temperature and Thermal Energy?

    Hi, :smile: While running, a person generates thermal energy but maintain approximately constant temperature: Distinguish between the terms: Temperature and Thermal Energy I know temperature is a measure of the average Kinetic Energy of molecules but I always get confused when it comes...
  35. D

    Thermal expansion across a copper rod

    Homework Statement Determine the actual shape of a copper bar in contact with a furnace at a constant 200 C at one end and a constant ice bank at 0 C at the other end. Diameter of the rod is 2.54 cm. Length is .5 meters. Thermal conductivity of copper is 380 J / (smC) Homework...
  36. V

    Time and Thermal Time constant explaination

    Hi, I have read the defination of a time constant on the internet and yet still don't quite understand it. How do I relate it to the following sentece and what does it mean: " The transient energy will have a duration much shorter than the thermal time constant of a bridge wire." ANY...
  37. B

    Understanding Joule Expansion and Its Implications on (dT/dV) const U = 0

    Homework Statement \"Explain why the joule expansion experiment implies that (dT/dV) const U = 0\" Homework Equations The Attempt at a Solution So I\'m not sure how to do this! Using 1st law we can say that at const U Tds = pdV, but not sure how to get what they want..
  38. P

    Thermal Physics - Gas Problems:

    Hi :smile: 1. A car tyre has a volume of 18 x 10-3 m3 and contains air at an excess pressure of 2.5 x 105 N/m2 above atmospheric pressure (1.0 x 105 N/m2) Calculate the volume which the air inside would occupy at atmospheric pressure assuming that its temperature remains unchanged: My...
  39. B

    Find the joint with the best thermal conductivity ?

    Hi Experts I'm joining aluminium fins to an aluminium body as part of a heat exchanger project. There are a number of variables here and I would like to evaluate them to achieve the best results. The best (simplest ?) method I can come up with is to attach several groups of fins to a common...
  40. M

    Converting between units for thermal conductivities (BTUs involved)

    The thermal conductivity of wood is 1 BTU per hour, per square foot, for a temperature gradient of 1 F° per inch. Convert this to units of W/mK, knowing 1 F° = 5/9 C° 1 inch = 0.0254 m 1 foot = 0.3048 m 1 lb = 0.453593 kg 1 kcal = 4184 JI know there are conversions between BTU and...
  41. P

    Why Did My Calculation of the Heat Transfer Rate in Thermal Physics Go Wrong?

    Hi The mass of liquid nitrogen in an open beaker is found to have decreased by 46.3 g in 10 minutes. If the S.L.H of vaporization of nitrogen at is boiling point is 1.99 x 105 J/Kg, at what rate were the surroundings heating the beaker? This is what I did: Q / 600 = 0.0463 / 600 x 1.99...
  42. P

    Specific Latent Heat and Thermal Physics

    Hi :smile: The mass of liquid nitrogen in an open beaker is found to have decreased by 46.3 g in 10 minutes. If the s.l.h of vaporisation of nitrogen at its boiling point is 1.99 x 105, at what rate were the surroundings heating the beaker? Why is the heat capacity of the beaker irrelevant...
  43. F

    Thermal Conductivity vs U Factor

    I understand that thermal conductivity is W/(m.K) and u-factor is W/m² K. Obviously U factor is energy transfer over an area but how does this compare to thermal conductivity?
  44. B

    Solve Thermal Radiation HW: Find Temperature Inside Insulating Case

    Homework Statement An ipod is left running inside a thin insulating case 2.5mm thick with thermal conductivity of 0.02W/K/m. The case is black and at 25 degrees C and exchanges energy with its surroundings, all of which are at 20 degrees C by radiation alone. What is the temperature inside...
  45. L

    Thermal Expansion of brass rod

    Homework Statement A student measures the length of a brass rod with a steel tape at 20.0°C. The reading is 80.00 cm. What will the tape indicate for the length of the rod when the rod and the tape are at each of the following temperatures? a) -18.0°C Homework Equations...
  46. V

    Thermal capacitance/Heat Transfer

    Guys, Maybe someone can help, as I am having a brain fart here trying to think of how this all works. Say for instance I have an electrical part that dissipates 10 W of power and I am removing this power through the use of a thermal strap to a heatsink. I think the...
  47. P

    Thermal Physics: Water vs. Wood at 50°C

    Hi, :smile: I am learning about thermal physics and I have a doubt: Say that water and a box of wood, both with the same mass, are at 50 degrees Celsius. This does not mean that they have the same amount of energy (internal energy in this case?) right? That is because in water for...
  48. C

    Best computational tool that could be used for calculation of thermal stresses

    Hi everyone. I am working to find out temperature distribution and thermal stresses in a structure. Can anyone please advice on which could be the best computational tool (ANSYS or ABAQUS or any other) for such kind of calculations. Thanks in advance.
  49. C

    Confined thermal stress with changing modulus

    Hello, I would like to compare rods made of different materials based on the amount of force or stress they would generate when fixed at both ends. normally, I would just compare the product of the coefficient of thermal expansion ( \Alpha ), change in temperature ( \Delta T ) and modulus (E)...
  50. R

    Youngs Modulus in case of thermal expansion

    We know that youngs modulus(E) is stress/strain. In case of free body thermal expansion, if the material is allowed to expand and contract freely, than there are no stresses in the body. The body has only strains. That means the stresses are zero in case of free expansion. So in this case...
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