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. H

    Combining thermal conductivity

    If thermal resistance is additive, then how can the thermal conductivity of two (or more) materials be combined? Can it? Eg. a wall filled with straw and air, a hollow brick, a mixture of polystyrene and fibreglass wool (just some random ideas off the top of my head).
  2. W

    Why is the Fermi level a constant in thermal equilibrium?

    Why is the Fermi level a constant in thermal equilibrium? just like PN diode (P=material 1 ; N=material 2) the fermi levels are the same (Ef1=Ef2) in thermal equilibrium i confused that why there is no energy transfer so that can judge each energy E will obey rate from 1 to 2 ~...
  3. S

    Engine thermal efficiency and Volume ratios

    The question: A perfect gas undergoes the following cyclic processes: State 1 to 2 cooling at constant pressure. State 2 to 3 heating at constant volume. State 3 to 1 adiabatic expansion. Deduce an expression for the thermal efficiency of the cycle in terms of r the...
  4. V

    Thermal annealing to induce nanoparticle formation

    Good day, I was recently asked to look into the process of thermal annealing of thin metal films in order to induce nanoparticle formation. However, I have been terribly unsuccessful in finding any sources that describe exactly how this works. I understand the basic idea of thermal annealing...
  5. F

    Thermal physics - entropy change (latent heat, specific heat etc)

    Hi all, could somebody have a look over my answers for this question please? The value I got for the second part seems quite feeble. Homework Statement The Attempt at a Solution Part a) Key m = mass cs = specific heat bronze cm = specific heat molten bronze Tfus = melting...
  6. M

    How to Calculate Final Temperature in a Water and Aluminum System?

    Homework Statement 160 grams of boiling water (temperature 100° C, heat capacity 4.2 J/gram/K) are poured into an aluminum pan whose mass is 950 grams and initial temperature 26° C (the heat capacity of aluminum is 0.9 J/gram/K). (a) After a short time, what is the temperature of the water...
  7. B

    Searle's experiment for measuring the thermal conductivity of copper

    Hello, i'm doing my prep for my lab experiment tomorrow and have a few questions about the experiment. The schematic is attached. My lab script says the following; 2 questions. It says the precise rate of flow of water through the heat exchanger is unnecessary to know. Is this...
  8. Kelsi_Jade

    Carnot Cycle Refrigerator - Thermal Battery Problem

    The question is: Consider a thermal battery - a device for storing mechanical energy. Use two large containers as heat reservoirs where one contains ice and water in equilibrium and the other contains steam and water in equilibrium. Both are held at pressure=1atm. Energy is stored by using a...
  9. T

    How Does Temperature Change Affect the Stress in a Bridge's Expansion Joint?

    Hello everybody, Here is a problem I have. QUESTION: The main span of a bridge has a length of 473 m. On each end there are the expansion joints like the one on the photo below. One day the city changed from -4 to +15 degrees between 6 in the morning and 2 in the afternoon. At 6 in...
  10. L

    I interpreting my results for a thermal decomposition lab

    Homework Statement I performed an experiment recently, which required me to heat a flask and an unknown compound to constant weight. The unknown was supposed to be a mixture of calcium sulfate dihydrate and NaCl. My goal for this lab was to determine the % NaCl in the mixture. My percent error...
  11. B

    What is the Temperature at which the Gap Between Two Bars will be Closed?

    Homework Statement A brass bar and an aluminium bar are each attached opposite each other to immovable walls. (There is a diagram, but I think the idea is clear enough). There is a gap between the two bars of 1.3x10-3m at 28°C. At what temperature will the gap be closed? coefficient of...
  12. S

    Analyzing Assumptions for Neutron Flux: Fast & Thermal Groups

    Assumptions 1) a=absorption 2) f=fission 3) ∅=neutron flux 4) time independent 5) group 1, fast neutrons 6) group 2, thermal neutrons 7) All fission neutron are boring in fast group 8) All neutrons created by thermal group, thus vƩf2 exists vƩf2 does not 9) Down scattering occurs but up...
  13. M

    Thermal Diffusivity in practice

    I have a system with two gasses separated by a wall as in a heat exchanger. One of the gasses changes temperature by the action of an outside agent and I'm trying to estimate the heat flow between the two gasses over time. I know that thermal diffusivity is a factor in this, but I don't know...
  14. E

    Moderation of Fast moving thermal neutron

    If a fast moving thermal neutron can be slowed down to increase absorption chances, is there a way it can be brought a halt? If yes, what will be the behavior of such neutron?(Apart from a simple fact that reaction comes to a halt)
  15. D

    Lee's Disc experiment for Thermal Conductivities

    Here is the experiment in brief for those uninitiated : http://media.uws.ac.uk/~davison/labpage/leedisk/leedisk.html My question is, when the steady state has been obtained (heat flowing into Brass Disc = heat flowing out of it), why do we remove the upper Brass Base and then heat the disc...
  16. W

    Thermal intake of melting ice as compared to thermal capacity of earth

    Though this topic mentions climate change, I don't think it really is about it that, strongly anyway. I've just joined and noticed a ban on climate change discussions before posing this one, I don't think this is one, but if it is, I suppose the beast must have one of it's many heads chopped...
  17. camipol89

    Are Thermal States Always Mixed States?

    Hey guys, I was reading about thermal states and now I have a doubt: is a thermal state always a mixed state with density matrix ρ=exp(-βH)/Tr(exp(-βH)), or is there also a pure thermal state? Thank you
  18. A

    Thermal diffusivity vs conductivity

    I'm not sure I fully understand the difference between thermal conductivity and thermal diffusivity as thermal properties of a material and would appreciate if anyone could clarify. I understand thermal diffusivity is for a transient case and conductivity is for steady state. This is what...
  19. A

    What liquid has ideal thermal properties for this project?

    I want to circulate cold water through copper tubing curled in a spiral about a fan. I'll cool the water with a large block of ice that I can remove and replace like a battery. To avoid making a mess I can freeze the ice inside of a copper housing, and pump the water in copper tubes around that...
  20. L

    Boundary Value Problem from Laplace's eq (Thermal)

    Homework Statement A rectangular plate extends to infinity along the y-axis and has a width of 20 cm. At all faces except y=0, T= 0°C. Solve the semi-infinite plate problem if the bottom edge is held at T = {0°C when, 0 < x < 10, T = {100°C when, 10 < x < 20. Homework Equations ∇2T=0...
  21. A

    Thermal Stresses on a New Building

    My University just build this amazing library exclusively for the engineering departments and similar fields of study. This is my first time taking advantage of the new complex and I am sitting on the 3nd floor over an all glass-wall window. As the sun was setting I notice tiny popping noises on...
  22. M

    Is thermal equilibrium possible by the Law of Cooling?

    Law of cooling states that the rate of loss of heat by a body is directly proportional to the excess temperature of the body above that of its surroundings. The equation of determining temperature in time T(t)=Ta+(T0-Ta)*e^kt (Ta-ambient temperature, T0-initial temperature, k-heat transfer...
  23. P

    Potential and Thermal Energy

    Homework Statement Starting from rest, a railroad car rolls down a hill 20 m high and hits another identical car at rest. The cars lock together after the collision. What fraction of the first car's change in potential energy is converted into thermal energy in the collision?Homework Equations...
  24. I

    Thermodynamics - thermal energy?

    The thermal energy comes from the translational kinetic energy right? The relationship between the two being E(kin)=1.5kT how would i go about finding the total thermal energy of a system of a given volume and pressure?
  25. I

    Thermodynamics; find the thermal energy

    question:Calculate the total thermal energy in a liter of helium at room temperature and atmospheric pressure. Then repeat the calculation for a liter of air. I'm just confused because i thought thermal energy only depended on the translational kinetic energy of the particles. So why do i...
  26. H

    Thermal excitation of electrons in semiconductors

    Which mechanism in semiconductors is responsible for electron excitation from valence to conduction band in thermal equilibrium at temperature T? Do valence electrons take their excitation energy from the lattice by absorbing phonon? If so, they can be excited at each arbitrary temperature no...
  27. J

    Do Neutrons Emit Infrared Radiation at Room Temperature?

    All bodies with a temperature emit electromagnetic radiation also known as thermal radiation or blackbody radiation. If I understand it correctly, the origin of this is the thermal motion (acceleration) of the atoms and their included positive and negative charges leads to EM radiation...
  28. V

    Thermal Engineering_Heat Transfer

    Hi, I am new to this Forum... So please let me know this is not the correct sub heading under which i am suppose to post the question... I would like to the basic relation between the Air density, Air Mass Flow Rate and heat Transferred to air by Convection... Changing the Air Flow Rate...
  29. J

    Thermal expansion of aluminum disc

    I have an aluminum disc that is 15in in diameter and about 1in thick. I am going to put it in a 400°F oven and I need to know how much the diameter will expand. One of the engineers I work with(i'm an intern) is using what I found to be the linear expansion equation (ΔL/Li=αΔT)...so Length...
  30. 3

    Affleck-Dine and thermal equilibrium

    Hi, I am currently studying Cosmology on my own, and I am learning about the Affleck-Dine mechanism of baryogenesis. I understand that in this case the baryon asymmetry is generated by the decay of a supersymmetric flat direction carrying B, which is excited during inflation. Regarding...
  31. G

    Thermal stress questiontopic strengths of materials

    1.The center rod CD of the assembly shown in the figure is heated from T1 = 30oC to T2 = 180oC using electrical resistance heating. The two end rods AB and EF are heated from T1 = 30oC to T2 = 50oC. At the lower temperature T1, the gap between C and the rigid bar is 0.7 mm. Rods AB and EF are...
  32. W

    How Does Temperature Affect the Fit Between a Brass Ring and an Aluminum Rod?

    1.A brass ring of diameter 10.00 cm at 20.0°C is heated and slipped over an aluminum rod of diameter 10.01 cm at 20.0°C. Assuming the average coefficients of linear expansion are constant, (a) to what temperature must this combination be cooled to separate them? Is this attainable? (b) What if...
  33. R

    How Do Pressure and Temperature Changes Affect Stresses in a Pressure Vessel?

    Homework Statement Problem is described as follows, I have a pressure vessel which basically consists of a hollow cylindrical body with two hemispherical shells attached to both ends. Within the vessel, there is a gas flowing from top to bottom. Over a period of one week, the vessel was...
  34. M

    Question about Thermal Energy Transfer

    Homework Statement A silver block, initially at 58.5* C is submerged into 100.0 g of water at 24.8* C, in an insulated container. The final temperature of the mixture upon reaching thermal equilibrium is 26.2* C. What is the mass of the silver block? Homework Equations q = M x Cs x Δ T 1/M...
  35. E

    How can Solar Thermal Rocket Engines revolutionize space exploration?

    Dear visionary inventors, megalomaniac engineers and audacious explorers, Chemical rocket engines aren't up to our desire to hop in the Solar system: go quickly to Mars, deviate Earth-threatening objects, and so many more missions. We need a higher ejection speed to save propellant mass, but...
  36. H

    Linear thermal expansion of steel

    1. a steel plug has a diameter of 10.0 cm at 30 degrees celsius. at what temperature will the diameter be 9.986 cm? 2. a steel measuring tape is exactly 50,000 m long at 20 degrees celsius . (a) what is the length on hot summer when the temperature is 35 degrees celsius? (b) if such steel tape...
  37. S

    Difference in thermal n cross section for Be-9 and B-10

    I have a question. From this government reference: http://www.ncnr.nist.gov/resources/n-lengths/ the thermal neutron cross section for stable isotope Be-9 = 0.0076 barns. This means Be-9 is not expected to absorb a thermal neutron, the probability of this is very, very low. The Be-9...
  38. H

    Heat gained and lost by aluminium and water in thermal equilibrium

    Homework Statement A physicist pours 100g of water at 100'C into a 20g aluminium cup which already contains 50g of water at 20'C. The final equilibrium temperature of the water is 71.847. C(water)=4186J/kgC C(aluminium)=900J/kgC 1. the amount of heat lost by the hot water 2. the amount...
  39. E

    Thermal Conductivity of Air: Pressure and Insulation

    Hi, I was hoping someone could enlighten me on the thermal conductivity of air. I'm aware the λ for air is 0.024. Meaning its a very good insulating material. Much better than the conventional insulating material we use for conventional buildings such as EPS and XPS which are at λ 0.030...
  40. O

    Heat loss and thermal equilibrium of underground aquifer

    Homework Statement I am working on a project where I have to design and size an aquifer. There are two which either store hot or cold water for 6 months which is then pumped up to be used in either the summer or winter. The aquifer is going to be 80 meters under the ground. The rest is...
  41. C

    Thermal Physics, energy and temperature

    Homework Statement In section 2.5 I quoted a theorum on the multiplicity of any system with only quadratic degrees of freedom: In the high-temperature limit where the number of units of energy is much larger than the degrees of freedom, the multiplicity of any such system is proportional to ##...
  42. S

    ANSYS APDL help for 3D Thermal problem

    Hello, Greetings! How do I get the convective surface matrix from ANSYS for 3D thermal problem. Consider a volume, where some of its surfaces are subjected to convective boundary conditions. What is the way to get those (only convective surface) matrices generated by ANSYS. Any help in...
  43. B

    FEA Thermal Stress Factor of Safety Question

    Hi Guys I'm analysing a heat exchanger based on an existing commercial model in SolidWorks Simulation. The same materials etc have been applied to it in the Static analysis. Deflection on the heat exchanger is very small. The one thing that baffles me though is how, regardless of even...
  44. R

    How Do I Calculate Thermal Efficiency with the Brake Equation?

    Can you please help me? I am trying to calculate this equation but can't get correct answer: Thermal Efficiency, Brake = 1/(bSPC x QHV) bSPC (brake Specific fuel consumption) = 0.396 kg/KWh QHV (Heating Value for fuel) = 44 MJ/Kg The correct answer is meant to be: Thermal Efficiency, Brake...
  45. B

    Why is thermal neutron with energy of 0.0253eV so important?

    I want to know the reason why the thermal neutrons with energy of 0.0253eV is so important. As far as I know, a neutron with an energy of 0.0253 eV is used as reference to measure nuclear cross sections such as absorption, fission, scattering, etc. And I want to know the details and more...
  46. T

    Condensed Matter: Thermal Expansion coeff. using diffraction angles

    Homework Statement At a temperature of 18°C a beam of diffracted monochromatic x-rays is observed at an angle of 150.8° to the incident beam after being diffracted by a crystal with cubic structure. At a temperature of 318°C the corresponding beam makes an angle of 141.6° with the incident...
  47. K

    Thermal radiation and emission spectra

    I have some questions regarding thermal radiation spectra of different objects. Is thermal radiation of objects due to electromagnetic radiation alone? Does my desk which is at room temperature emit as a blackbody with the proper factor for emissivity? Where is the "cavity" that the radiation is...
  48. S

    Cubic and Linear Thermal Expansion.

    Homework Statement 1. a 100m long copper wire of diameter 4mm is heater from 20C to 80C. What is the change in the length of the wire? 2. a 0.2m diameter aluminium sphere is cooled from 250C to 0C. What is the change in the volume of the sphere? The coefficients of linear and cubic expansion...
  49. J

    Thermal Conduction Homework: Find Rod's Conductivity

    Homework Statement A rod, with sides insulated to prevent heat loss, has one end immersed in boiling water at 100C and the other end immersed in a water/ice mixture at 0C. The rod has uniform cross-sectional area of 4.04 cm^2 and length 91cm. Under steady state conditions, heat conducted by...
  50. B

    The thermal activation cross section of H-3,C14

    I am doing a research on activation radionuclides resulting from thermal neutron(2200 m*s-1 or 0.0253eV) capture. The activation cross section of some nuclides(H-3,C-14,54Mn,58Co), still can't be found even many efforts were taken. The related reactions...
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