Thermal Definition and 1000 Threads

Homework Statement [/B] Explain how the concept of thermal resistance can be used in the analysis of heat transfer problems 2. The attempt at a solution So I'm made a few key points but I am not sure if I have answered the question fully: Thermal resistance is a heat property and a...

suppose there are two bodies A and B with emissive powers e1 and e2 respectively and with absorptive powers a1 and a2 respectively... now both bodies are at the same temperature T. Hence e1/a1 = e2/a2 = const by kirchhoffs law. for the body A, energy emitted is e1 and...

Homework Statement There is an electronic transition between the first energy state and the ground state of a neon atom, emitting a wavelength of 746nm. The question asks for the energy of the transition and an estimate of the fraction of atoms in a sample that is thermally excited at 300K...

Hello Guys, Could someone explain to me the meaning of greater thermal boundary layer over hydrodynamic boundary layer over a flat plate surface? I know how to calculate both streams, but I don't understand the meaning of smaller thermal boundary vs. hydrodynamic boundary and vice-versa. What...

I was watching this video and I have the question, if using a bjt as a diode what is the difference (thermal characteristics) from a regular diode, I ask this because on-semi makes bjt's with diodes in them specifically for class ab amps, is their any benefit besides less thermal lag?

1. My Conceptual Questions (5) is at 3. CONSIDER: Case 1: two dissimilar slabs of material (say slab 1 and slab 2) connected in series (bonded at their interface). There is a temperature difference: T1 @ slab1 and T2 @ slab2. Case 2: two dissimilar slabs of material bonded together, i.e...

I am little confused as to why temperature is a measure of thermal energy. Thermal energy is defined as the total internal kinetic energy of an object. Temperature, on the other hand, is defined as the measure of the average kinetic energy of an object, or the thermal energy per particle. If...

Hi i am performing a multiphysics simulation in which i am importing results of Electric-Thermal domain into Transient Structural domain in Ansys Workbench 14.5. As the simulation time is 5 hrs and given that i have to perform 20 case studies , so i want to know is their a way around in Ansys...

Hi I have a project where I am trying to make a coating or paint that will give off heat when an electrical current is passed through it. I got graphite powder and made it into a paste and allowed it to dry on a substrate. The problem is that it is highly resistive (a small section has a...

Good Day, I am working on a problem in which i am coupling "Thermal-Electric" physics with "Transient Structural" in Ansys workbench V 14.5. I am supplying electric energy(Voltage) to a structure which gets heats up due to Joule Thomson effect, and then i connect it's "Solution" to "Setup" tab...

Homework Statement Interstellar medium is composed of atomic hydrogen at 100 K and number density 2E-7 m-3. Compute the average thermal energy density of the milky way disk. Then find the average magnetic energy density given the magnetic field strength of 3E-10 T. Homework Equations E=3/2 kT...

Homework Statement a) a styrofoam cup contains 200g of water at 20 C.What will be the equilibrium temp of the system after 100g of silver,initially at 300 C,has been added?you may assume that the heat capacity of the cup is negligible and that no heat is lost to the surroundings. (b) a further...

Hi, I am writing program to model the heat flow through different space shuttle tiles. I have got it working using four different methods: Forward differencing, Backward differencing, Crank-Nicolson, DuFort-Frankel and all four methods give me similar results. What are the advantages and...

Hi, I am writing a MATLAB program to model the heat flow through space shuttle tiles. Does anyone know where I can find the thermal conductivity, density and specific heat of the different tiles on a space shuttle?

Why does the thermal decomposition of group 1 metals, except for lithium, yield a nitrite while that of group 2 metals yield oxides?

Hi there, I'm trying to clear up some misconceptions I have about emission spectra from various substances. Most of the discussion about gases focusses on the line emission spectra from a hot, low density gas due to electron shell transitions. But I also know that any charges that are made to...

Homework Statement A block of mass M is pulled at constant speed with force F a distance d across a surface. Using the energy principle, what can you say about the change in thermal energy of the block? a)...

Hi i am working on a research paper for which i need very good citation for the analytic analysis coupling Electric - Thermal-Structural physics(via Joule Thomson effect & Thermal stress/strain). Please provide any good source of mathematical relations describing the above complete or in part...

hallo to all, i use a Radiation Pyrometer to measure temperature and Radiation Trough a datalogger i get those measurements in Volt i am able to convert the Volt back in the temperature but in Radiation it is more difficult i found the Plancksche function, but i do not really understand that...

Hello I am trying to learn about the change of state between solids, liquids and gases but I don't understand exactly how it works. I've been reading material given by my school, but I got these two questions to ask because I can't answer them. These are not questions on the sheet they just...

Homework Statement A hair dryer consists of a coil that warms air and a fan that blows the warm air out. The coil generates thermal energy at a rate of 600 W. Take the density of the air to be 1.25 Kg/m^3 and its specific heat capacity to be 990J/Kgk. The dryer takes air from a room at 20C and...

Homework Statement A possible ideal-gas cycle operates as follows: (i) from an initial state (p1,V1), the gas is cooled at constant pressure to (p1,V2) (ii) the gas is heated at constant volume to (p2,V2) (iii) the gas expands adiabatically back to (p1,V1). Assuming constant heat capacities...

Hi I am trying to characterize a microscale resistive heater. In my Bode plot there is decay that is less than -20dB/decade indicating that there is a zero in the system. Anyone having an idea of what physical meaning a zero in a resistive heater has? Thanks.

Hello, I have heard many times that red lighting is good for imaging applications where the effect of ambient light needs to be reduced to a minimum. What is the theory behind this? Why does red light (vs. other colors) reduce the effect of ambient light? Thank you.

MODERATOR NOTE: MISPLACED HOMEWORK, SO NO TEMPLATE When filling up the tub for a bath, only the hot water tap was turned on. After realizing the mistake after a minute with half the tub at 60 C, how much cold water (as fraction of the whole tub) at 9 C must be added such that the final...

I am looking to improve the thermal insulation on one of my favorite glass mugs. I am choosing between a silicone glove or a neoprene wrap. What is the difference between a silicone baking mat and silicone rubber? Does silicone or neoprene have better thermal insulation?

Hi, I'm doing a 1D thermal conduction simulation on Comsol Multiphysics 4.4 and my first component is vacuum. I did'nt found the vacuum in the material list. Should I create a new component with a null thermal conductivity ? Thanks

Homework Statement In thermal equilibrium, the particle in a gas are distributed in velocity space according to the Maxwell distribution f(v) = A*exp(-mv^2/(2KT)) What is the average velocity ? What is the most probable velocity ? Homework Equations <v> = ∫∫∫vf(v)d3v = (0 to infinty)...

Homework Statement a) Assume that a substance in a closed container is at thermal equilibrium with about half of its molecules in the gas phase and half of its molecules in the liquid phase. How could you use the Particle Model of Thermal Energy to explain which molecules are moving faster, on...

Hi, I am trying to design a tubular probe that's made of stainless steel (304), from what I've read it has a Thermal expansion coefficient of around 9.6 x10^-6 in/in/F give or take on the quality. I want to fill this tube halfway with an Epoxy, however from what I've read this epoxy has a...

Hi, my name is John and I am working on a textbook called Physics Syllabus Stage Six (PSSSix). I have done a draft of chapter 2, Thermal Physics. Although I have requested if this consultation is suitable for this forum, but yet been replied. This textbook is free (online definitely) or...

Homework Statement Hello, I have the following problem (an ABCD question): Two objects near each other are at the same temperature. Which of the following statements has to be true? A. The objects have the same internal energy. B. The objects have the same thermal capacity. C. No...

Recently there was an interesting thread on physics forum about possible uses of spent nuclear fuel. It seems to me that one of the problems with using decay heath from spent nuclear fuel is the low power density. This got me thinking that maybe with enough insulation the low quality heat...

Homework Statement The peak of the thermal radiation power spectrum (dR/dλ) is at a wacelength of about λm=hc/5kT. Why is the peak of the same power spectrum plotted as dR/df not at fm=c/λm= 5kT/h? Homework Equations dR/dλ= 2πhc2/(λ5(e(hc/λkT)-1)) f=c/λ The Attempt at a Solution

Hello everyone! First time asking a question here, go easy on me! I am a first year Mech-Eng student in Ireland, and I need some guidance from one of the amazing brains here at physicsforums. I am told by my thermofluids lecturer that in thermal expansion, the amount of material expanding is...

Homework Statement A python can detect thermal radiation with intensity greater than .60 W/m2. A typical human body has a surface area of 1.8 m2, a surface temperature of 30°C, and an emissivity e=0.97 at infrared wavelengths. What is the maximum distance from which a python can detect your...

I am trying to get a formula to estimate the heat lose in an airship. Is a mod for KSP, things that have into account: pressure, wind speed, temperature, air viscosity, thermal capacity of the atmosphere, gravity, etc. There are things that can be ignored as shape (or just use constant...

Imagine there is a semi-infinite semi-transparent body--such as a glass--at some temperature T. No surfaces exist. What is the energy intensity of thermally emitted light from any point in the body? If you use an absorption or emission coefficient (as I suspect is correct), can you explain how...

Homework Statement For the example that two spin systems in thermal contact and attain equilibrium, the product of the original multiplicity function will be the new total multiplicity function, Now, we want to find the probability of the system to be slightly deviated from the equilibrium...

This is not a homework problem but rather a passage from my textbook that I don't understand. I don't think I quite understand the concept of reversible processes. Here is the passage from my book: "Consider a system in the quantum state s of energy Es. We assume Es to be a function of the...

Homework Statement This is not a homework problem but rather a passage from my textbook that I don't understand. I don't think I quite understand the concept of reversible processes. Here is the passage from my book: "Consider a system in the quantum state s of energy Es. We assume Es to be a...

Homework Statement Energy can be transmitted via radiation, the rate at which this happens is H=σAT4. A bar of iron is 0.5m long, 0.2m wide and 0.2m high. Iron has a density of 7900 kg/m3, a heat capacity of 400J/kgC, and a coefficent of linear expansion of 1.2x10-5 What is the rate at which...

I am looking Kaowool Thermal insulation for a project. It looks like the values presented are @2000 F, 1.28 BTU, .20 w/m*k I was wondering if someone could help me to figure out what the "output" heat would be at 2000 F. For example: If I have an aluminum rod sitting over a fire burning at...

Looking for some help here. If I have two objects, (1) a heat source that, let's say can get up to 1500 degrees, and (2) a simple metallic object, and let's say the object and heat source are relatively close to each other. Object number (2) has a small metallic probe that goes into the heat...

hello is there a good article or reference to outline the available methods to harvest ambient or solid thermal energy and their efficiency and limitations? thanks!

I am trying to figure out what the total thermal energy emitted by completely transparent matter. It seems Planck's law can't do this because the thickness or geometry of the mass is not given, only it's surface area. The spectral radiance of a black body is given by Planck's law...

I have a heat exchanger with water/air as medium and we test it in a facility where we cycle the water temperature between 25 to 95 degrees Celcius with a cycle time of 5 minutes for thermal fatigue. Our customer require the testing to be between 5 to 95 degrees instead with 3 minute long...

Homework Statement I need to find thermal stresses that will be produced in a tank barrel as a result of firing. First of all, I want to know if theses stresses can be small enough to be neglected? And if not, then how can they be calculated? I basically know the solution but I want to be sure...

So I'm not too sure about the answer to this question: explain why it is advisable to add water to an overheated automobile engine only slowly, and only with the engine running? So if something is overheating, it makes sense to want to cool it. Since the water's temperature is less than that...

Hi, The coefficient of thermal expansion for aluminium is 23ppm/C at 20C = 0.000023m per degree in temperature (C). Is this temperature: (1) the temperature of the air circulating around the material in the sun, (2) the temperature in the shade at that time of the day, or (3) the tactile...