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. T

    Why is a resistor for convection not included in the thermal circuit solution?

    Homework Statement Here is a picture of the question with the solution: When I attempted this I added a resistor for the convection of the fluid inside. But the solution does not do this, does anyone know why?
  2. G

    Find Thermal Diffusivity from Kelvin Functions

    Homework Statement I performed an experiment where we have to find the thermal diffusivity of rubber. This is done using the phase difference of the axial and external temperatures of the rubber. The teacher's guide says to use the Kelvin functions, plot them against x. Where x = r(√(2pi/TD))...
  3. J

    Varying thermal conductivity with length

    I'm interested in modeling a system where the material varies along its length, thus the conductivity coefficient would be a function of both T, and x. k(T,x). For starters, if I assume negligible change w.r.t T, then he heat diffusion equation would be d/dt(k(x)dT/dx)=0. Correct? What if k just...
  4. K

    Linear thermal expansion problem

    Hey fellas please consider helping me with this.. There is a bar of some material that is heated from state 1 to 2 to 3. If l1 is the length at 1 then we have, l2 - l1 = l1(1 + a(t2-t1)) l3 - l1 = l1(1 + a(t3-t1)) If, t3-t2 = t2-t1, Then l3-l2 = l2-l1 But if it is written l3 - l2 =...
  5. M

    Thermal equilibrium for ice being added to liquid water

    Homework Statement 0.05625 m^3 of H2O(s) is added to a thermally isolated system of 20 L of H2O (l). If the ice was initially at 0 C and the liquid water was initially at 95 C, what is the final state and temperature? The Attempt at a Solution I missed class for this so I'm going by...
  6. W

    Thermal decomposition of calcium carbonate - problem

    Hello, here goes the problem: The mass of calcium carbonate upon thermal decomposition decreased by 1/5. (a) How many molecules of CaCO3 per 100 molecules were decomposed to CaO and CO2. (b) The content of CaO in the final sample express in molar fraction. My solution: I set the starting...
  7. C

    Heat flux as a fraction of energy flux due to thermal re-radiation

    Homework Statement Radioactive decay of elements in the Earth's interior results in a mean heat flux through the Earth's surface of 5x10^-2 W/m^2. What is this flux expressed as a fraction of the energy flux due to thermal re-radiation of absorbed solar energy? If radioactive decay were the...
  8. M

    Thermal decomposition of calcium carbonate ?

    In general, we heat CaCO3 to temperature of approximately 825°C it decomposes into calcium oxide and liberates carbon dioxide gas: CaCO3 →825°C→ CaO + CO2 Is it possible to heat the calcium carbonate at temperatures below 825 degrees Celsius, so the decomposition into calcium oxide.
  9. L

    Thermal transfer improvement from adding fins

    Hi All, I'm designing a heater for some cylindrical tubes. In my original design, I simply had a flat plate contacting the bottom of the tube. Since the tubes are only conducting on the bottom, the temperature of the contents in the tube are somewhat off from the actual base temperature. I...
  10. Mechatron

    Thermal Noise Frequency & Gaussian Plot

    I want to develop a new model for calculating the frequency of thermal radiation. It is generally accepted that thermal radiation emits white noise with all the frequencies within a certain bandwidth. But when white noise interferes with communication systems, it is carried on what is known as a...
  11. G

    What is the Behavior of Particle Distribution Near Maximum in Thermal Physics?

    Homework Statement There is a box of volume V that is divided into two equal parts: Left side = V/2 = right side. The problem is: Assume that there are n = (Na/2) + k particles in the left hand partition where k is a small integer ( k << Na). Show that the behavior near the maximum where n...
  12. F

    Thermodynamics? number crunching thermal conductivity

    I am working on some basic calcs for heat transfer from polyethylene pipe. My numbers are not working out right so I need a little refresher. The PE pipe would have a TC of about .46 W/(m.*C). to get to BTU/(hr.ft.*F), I mult by .5779 to get .266. Assuming 10sf of PE pipe, and let's...
  13. Saladsamurai

    Stress Due to Thermal Gradient

    I am trying to understand stresses that are induced by thermal gradients. Now, I can think of a hundred different questions to ask, but I want to take baby steps to get there. Let's just talk about a simple cantilever beam in the x-y plane where the x-axis is the beam's longitudinal axis and...
  14. Mechatron

    Thermal White Noise - Johnson–Nyquist noise

    I'm trying to measure the thermal white noise generated by chemical batteries. So far I've measured the current noise, the voltage noise (V noise) and the bandwidth (delta v). From the equation below, I'm trying to solve the equation for the frequency. The problem is that there's an...
  15. C

    Thermal conductivity between sheets of two different metals

    Homework Statement A copper sheet of thickness 2.37mm is bonded to a Aluminum sheet of thickness 1.29mm. The outside surface of the copper sheet is held at a temperature of 100.0°C and the Aluminum sheet at 24.5°C. a) Determine the temperature of the copper-aluminum interface. b) How much...
  16. C

    Using thermal conductivity to melt ice

    Homework Statement An ice cube at 0.00 °C measures 14.9 cm on a side. It sits on top of a copper block with a square cross section 14.9 cm on a side and a height of 18.1 cm. The bottom of the copper block is in thermal contact with a large pool of water at 92.5 °C. How long does it take the...
  17. B

    Thermal Physics Expansion Coefficient Problem

    Homework Statement When the temperature of liquid mercury increases by one degree Celsius (or one kelvin), its volume increases by one part in 550,000. The fractional increase in volume per unit change in temperature (when the pressure is held fixed) is called the thermal expansion coefficient...
  18. B

    Simple Method to Measure Thermal Conductivity of Insulation

    Hi, I'm doing a group investigation on external wall insulation for my school building. The walls do not have a cavity and thus it has been proposed to put insulation over the exterior render of the wall. This is a fairly common building procedure. However, my task is to investigate the...
  19. O

    Signal to noise ratio for thermal and shot noise

    Homework Statement The output of a sensor which produces 10000 electrons is connected to parallel RC circuit with Resistance= 50 ohm, and the capacitance=10pF. Calculate the signal to noise ratio at temperature 300K. Homework Equations SNR= 10 log (power of signal/ power of noise) Or...
  20. S

    What are the Issues with Airborne Structures/Circuits in Electronics?

    What are the problems that exists in airborne structure/ circuit ? - Electronics
  21. B

    Thermal Physics Adiabatic Heating Problem

    Greetings all, My first post here on this forum. I'm currently revising for exams and have got stuck on a question where I'm not sure where I'm going wrong...Question: 1g of iron filings at 500 °C are inserted into a sealed 20 litre vessel containing 1 mol of an ideal monatomic gas at a...
  22. F

    Thermal physics - how are Cp and Cv used?

    Afternoon all. I've have the following equations: Cp - Cv = nR = Nkb Cv = nRf / 2 Cp = nR(2+f) / 2 CvlnT = -nRlnV + const where f is degrees of freedom Do the Cp and Cv just stand for pressure and volume (where both are constant), so for example can the first equation only...
  23. U

    How Do You Calculate Thermal Conductivity Using Kinetic Theory?

    Homework Statement Find an expression for thermal conductivity using kinetic theory. Given a vacuum flask of these dimensions, find the heat loss per unit time. Estimate the time taken for the water to cool down to 40 deg. Homework Equations The Attempt at a Solution...
  24. W

    Thermal properties - Experimental Design

    Apologies for the break from format, but I'm not sure how to make this fit! I'm designing an experiment to compare the insulation properties of several materials. I would like to find the Thermal Conductivity (K) or the U (or R) values of these materials. However essentially all I am after...
  25. H

    Deformation due to thermal expansion/contraction

    Dear all, I have a 3D cube with a nonuniform distribution of temperature. In order to calculate the deformation of the cube using the finite element method, we need nodal forces. How we calculate the nodal force from the temperature distribution? I am aware of a the method based on the...
  26. M

    Does Temperature Affect the Time to Reach Thermal Equilibrium?

    Is there a relationship between increasing temperature in one test tube and keeping the other temperature constant and the time it takes to reach thermal equilibrium Homework Statement Is there are relationship between increasing the temperature of water and keeping the other same and the...
  27. E

    Development thermal boundary layer

    Can anyone explain me why the thermal boundary layer develops faster for viscous fluids? I would just say it would develop more slowly because due to high viscosities there are low reynoldsnumbers and thus less turbulence or mixing. This causes a slow homogenization of temperature (assume a...
  28. A

    Thermal conductivity in a heating system

    Homework Statement In a domestic heating system, a room is warmed by a 'radiator' through which water passes at a rate of 0.12kg s-1. The steady-state difference between the inlet and outlet temperatures of the water is 6.0 K. The radiator is made of iron of thermal conductivity 80 W...
  29. T

    Airborne particle focusing in heated chamber using thermal emission?

    Greetings PFers, I'm working on a project where micron size metal or plastic particles are carried inside an argon or nitrogen stream at ~1 atm. The particles travel through at 1/4'' ID nylon tube before they enter a chamber where they then travel through a pyrex tube. I have four 4'', 500W...
  30. B

    Carnot efficiency vs thermal efficiency

    Is Carnot efficiency the same as thermal efficiency?
  31. bhanesh

    Thermal Noise Voltage of 3 Resisors in Series

    What is thermal noise voltage of three resisors connected in series
  32. L

    Magnetism, electrical and thermal conductivity of metals

    1. I would like to test myself on how well I know my information about certain metals, some of them get me a bit puzzled. How would you rate the electrical conductivity of cast iron? Poor, good, excellent or best? Also the thermal conductivity of 304 stainless steel? Poor, good, excellent or...
  33. L

    Magnetism, electrical and thermal conductivity of metals

    I would like to test myself on how well I know my information about certain metals, some of them get me a bit puzzled. How would you rate the electrical conductivity of cast iron? Poor, good, excellent or best? Also the thermal conductivity of 304 stainless steel? Poor, good, excellent...
  34. A

    Heat transfer and time needed to reach thermal equilibrium

    I was hoping someone could lend a hand with a question about thermodynamics. It's been years since I've done work on thermodynamics. Let's say I have a plastic 275 gallon liquid container, filled with a mixture of Propylene Glycol and Water (50/50 by volume). The container is placed inside of...
  35. E

    How Do You Calculate Thermal Efficiency in a Diatomic Gas Heat Engine Cycle?

    Homework Statement You build a heat engine that takes 1.00 mol of an ideal diatomic gas through the cycle abc, where segment bc is isobaric and segment ca is isochoric. calculate the thermal efficiency of the engine. this is a 5 part problem and I already solved for Wo and Wo=Qo I solved...
  36. P

    Statistical and spectral function in thermal state

    Homework Statement The statistical and spectral functions for bosonic operators \phi_a are: G_{ab}(t,\vec{x})=\frac{1}{2}\langle \{\phi_a(t,\vec{x}),\phi_b(0,\vec{0})\}\rangle , \rho_{ab}(t,\vec{x})=\langle [\phi_a(t,\vec{x}),\phi_b(0,\vec{0})]\rangle . The expectation values are in...
  37. E

    What Is the RMS Speed of Deuterons in a Fusion Reactor?

    Homework Statement A deuteron is the nucleus of a hydrogen isotope and consists of one proton and one neutron. The plasma of deuterons in a nuclear fusion reactor must be heated to about 300 million K. (a) What is the RMS speed of the deuterons? Is this a significant fraction of the speed of...
  38. S

    Thermal radiation lab experiment

    Hi, I have to plan and carry out an experiment on thermal radiation as part of my physics lab module. The description of the experiment is as follows: Investigate the radiation from a bulb filament as a function of input power, using a pyrometer to measure the temperature of the filament...
  39. MacLaddy

    Thermal Efficiency in an Ideal Diesel cycle.

    Homework Statement Helium in an ideal Diesel cycle is compressed from 4 L to 0.25 L, and then it expands during the constant pressure heat addition process to 0.50 L. Under air standard conditions, the thermal efficiency of this cycle is: a) 79.5% b) 20.5% c) 61.4% d) 67.4% e) 84.3%...
  40. R

    Units of the Thermal de Broglie wavelength?

    1. Units of the Thermal de Broglie wavelength? 2. λ = h / (2*pi*mkT)^(.5) 3. through dimensional analysis i get S (J / kg)^.5 can you even have .5 of a unit?
  41. M

    Thermal Physics adiabatic and isothermal compressibilty

    Ok so I found something online but I need to understand this problem Prove that the ratio of the adiabatic compressibilty ks to the isothermal compressibility kr is equal to the ratio of the specific heat at constant colume, Cv, to that at constant pressure, Cp Definitions of the...
  42. B

    Archived Finding the thermal energy and Q for an isobaric process.

    Homework Statement How much work is done on the gas in the process shown in figure P12.24. This is from College Physics: A strategic approach, 2nd addition, by Knight, et al. Ch.12, #24 The graph shown is kPa vs V(cm^3). It's a constant temperature process (isobaric) at 200 kpa. I was able to...
  43. M

    Thermal Physics problem: Van der Waals

    [b]1. Find an expression that relates T and V in a process in which the entropy S is constant, by doing the following: a) From thermodynamic identity dS=(1/t)dU + (p/v)dV find the expression for dS as a function of T and V (and dT and dV). b) Integrate the expression found in (a)...
  44. N

    Thermal expansion of water and a bubble

    Homework Statement A scuba diver is 17.4m below the surface of the lake, where the water temperature is 8.25∘C. The density of fresh water is 1000 kg/m3. The diver exhales a 23.6cm3 bubble.What's the bubble's volume as it reaches the surface, where the water temperature is 15.1∘C? Homework...
  45. N

    How much does a steel measuring tape expand on a hot day?

    Homework Statement A 61.00m long steel measuring tape is calibrated for use at 20.0∘C. How long is this tape under the following conditions: a hot day with 38∘C? Express your answer using four decimal places and include the appropriate units. i've been losing my mind over this, i swear...
  46. Gamma

    Why Does a Sealed Water Bottle Crack in the Freezer?

    This is not a homework question, but a conceptual question that I am trying to understand. We all have experienced/heard that if you put a completely full water bottle with the cap on in the freezer, the bottle cracks as the water freezers. The explanation is that the water expand as it...
  47. K

    Two Level System with thermal population

    Hello, the task is the following: Consider a two-level system with thermal population. a) Show that the rate equation for the state N_2 is the following: \frac{dN_2}{dt}=w(N_1-N_2)-\frac{N_2-N_2^e}{\tau} w=B_{12}\rho({\nu}) \,\,\, N_2=N_2^p+N_2^e\,\,\, N_1=N-N_2 N_2^p is the portion of...
  48. A

    Thermal Conductivity: Nonmetal Impact on Change

    For a nonmetal what determines thermal conductivity is the propagation of lattice vibrations. As T increases these lattice vibrations collide with each other more often. Does this mean that the thermal conductivity will de- or increase?
  49. L

    Suggestion on books for Thermal Physics and Statistical Mechanics

    I am planing to study thermal physics on my own as I got an incompetent faculty who doesn't know anything about this subject. I want to have a detailed understanding about the topic. So can somebody suggest me which book I should follow from the following list. 1. Schroeder, Thermal...
  50. A

    Why Doesn't Volume of Crystal Depend on Temperature?

    In the harmonic approximation, why is the volume of a crystal not temperature dependent? Does it have something to do with the fact that the amplitude of a harmonic oscillator is independent of the frequency?
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