Heat Definition and 1000 Threads

In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. The various mechanisms of energy transfer that define heat are stated in the next section of this article.
Like thermodynamic work, heat transfer is a process involving more than one system, not a property of any one system. In thermodynamics, energy transferred as heat contributes to change in the system's cardinal energy variable of state, for example its internal energy, or for example its enthalpy. This is to be distinguished from the ordinary language conception of heat as a property of an isolated system.
The quantity of energy transferred as heat in a process is the amount of transferred energy excluding any thermodynamic work that was done and any energy contained in matter transferred. For the precise definition of heat, it is necessary that it occur by a path that does not include transfer of matter.Though not immediately by the definition, but in special kinds of process, quantity of energy transferred as heat can be measured by its effect on the states of interacting bodies. For example, respectively in special circumstances, heat transfer can be measured by the amount of ice melted, or by change in temperature of a body in the surroundings of the system. Such methods are called calorimetry.
The conventional symbol used to represent the amount of heat transferred in a thermodynamic process is Q. As an amount of energy (being transferred), the SI unit of heat is the joule (J).

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  1. Second Law of Thermodynamics and Heat Engines #11

    Second Law of Thermodynamics and Heat Engines #11

    The Second Law of Thermodynamics is not an easy topic. However, if you understand the concept of direction of thermodynamic processes and heat engines, you w...
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  2. S

    Heat Equation with Periodic Boundary Conditions

    I'm solving the heat equation on a ring of radius ##R##. The ring is parameterised by ##s##, the arc-length from the 3 o'clock position. Using separation of variables I have found the general solution to be: $$U(s,t) = S(s)T(t) = (A\cos(\lambda s)+B\sin(\lambda s))*\exp(-\lambda^2 kt)$$...
  3. B

    Heat distribution in a piece of glass receiving protons

    First of all, I didn't know whether to pick this subforum or the engineering/compsci one, I understand this might need to be moved to a more appropriate subforum. The general approach is fairly obvious, use implicit method to construct the tridiagonal matrix for Thomas method and solve. However...
  4. V

    Radiation heat transfer in channel flow

    Hi guys, I am confused about the heat transfer mode of between two contacting material, especially in a channel flow. Obviously, conduction or convection dominate the heat transfer process in the process with low object temperature . But I am not sure if I have a fluid of 500 Kelvin, flowing...
  5. L

    Calculating heat recovery from engine exhaust gases

    Hello, I am doing a study for my final years Uni project, which includes waste heat recovery from gas fuelled engine exhaust. I am using a data sheet for a Jenbacher J620 engine-. In the data sheet it is stated that; exhaust gas mass flow (wet) = 17325 kg hr ( not sure about the wet part?)...
  6. R

    Modelling Heat Transfer for Pulsating Laminar Duct Flow

    Good evening everybody. I am new here I hope it is okay to ask this question here. As part of a project I am trying to examine the effect of a pulsating laminar duct flow on the heat transfer behavior for constant heat flux at the wall for a Newtonian incompressible fluid. As such I am...
  7. A

    The derivative of Heat Capacity with respect of pressure

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  8. M

    I Alternating Direction Implicit method for solving 2D Heat diffusion

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  9. imselva

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  10. imselva

    Radiation heat transfer using 12 heat sources

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  11. Y

    Why use c_p and not c_v as specific heat - Thermodynamics

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  12. imselva

    What is the Equilibrium State in Radiation Heat Transfer?

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  13. V

    Classical Textbook for light, heat, waves

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  14. gaurav_samanta

    Is latent heat only released and absorbed as radiation?

    Can water simply absord the kinetic energy from colliding air molucules to change its phase? And can water transformed into ice simply have the kinetic energy of its molecules increased to balance out the lost latent heat? Would not this again change ice into water?
  15. gaurav_samanta

    Can heat transfer break an equilibrium?

    Here is one scenario: I have placed a metal in my room which is at room temperature. Air has little much heat capacity and metals don't like to store heat. Would heat transfer occur? Whatif I set the temperature of both to a certain degree where it crosses heat capacity of metal but not of air?
  16. Libensek

    How can I make a Heat Flow Meter?

    I tried to created it but i dknt know how to even start
  17. I

    Question about thermal physics -- Ice cubes melting in water

    First, I calculated the heat required for the ice to melt: Q=mLf Q=0.150×330 Q=49.5 J Then, I calculated the final temperature of the water by forming the following equation: Q=mcΔT −49.5=(0.15+0.35)×4200×(Tf −80) Tf=80.0 degrees Celcius But the answer says 32 degrees Celsius.
  18. C

    How can units of heat ever be ft^3/s?

    Please and thank you!
  19. Yeahaight

    Steam = 100C -- how much steam got injected into the water to heat it up?

    I guess, firstly I have to calculate the heat that is needed. Q=c*m(t2-t1) I'm not sure what to do further from here.
  20. Yeahaight

    Amount of heat = 80 kJ -- how much ice can you melt?

    I've been messing with the Q = cm(t2-t1)=cmΔt formula If I change it to m=Q/(c*Δt) everything is fine until I reach the c part, because there has been given the c of ice and the c of water too, do I just subtract c ice from c water?
  21. S

    Calculate the flow of steam to heat wort (in the brewing process)

    I need help solving this please. Its a past exam paper. requires wort to undergo 5% by mass evaporation in one hour does this mean starting vol is 500hl and after one hour vol should be 475hl Wort volume = 500 hl = 50,000 L / hr 1 L = 10^-3 m^3 50,000 L = 50 m^3 /hr = 0.833 m^3 / min = 0.01388...
  22. tanaygupta2000

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  23. R

    I Change of variables for this derivative in a heat transfer equation

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  24. A

    Conceptual thermodynamics question regarding specific heat ratio

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  25. D

    A/C style heat exchanger instead of intercooler

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  26. E

    Thermodynamic sign convention for heat (i.e. in heat engines)

    Just to clarify, I'm aware of the two equivalent expressions of the first law ##\Delta U = Q + W## and ##\Delta U = Q - W## when applied to a certain system, though my question is primarily about ##Q## - for which, as far as I am aware, the convention is almost universally that ##Q > 0## if heat...
  27. B

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    I have one project in my mind bu tI have no eductaion in this topic. please help. question is: if there is container of water. and we have certain number of solar rays getting into this container how does process of water warm up look like comparing: 1. direct sun rays into water vs 2. on...
  28. D

    Physics Homework about using Electricity to Heat Flowing Water

    This is the question: You want to make an electric instantaneous water heater in which 5.0 liters of water flows past a resistance per minute and heats water from 10.0 ° C to 45.0 ° C. Calculate the magnitude of the resistance to use and the amperage. The flow-through is connected to 230V So...
  29. E

    Engineering Efficiency of Heat Engines & Refrigerators: Is Impossible Possible?

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  30. M

    Heat Transfer - Radiation - Net heat transfer between two mirrors

    Hi, So there is already a written solution which I have, but this is more a question about why we omit reflection that come back to the same mirror? Method: Let us consider one of the mirrors, we know it will emit a heat flux given by: q_{1} = \epsilon_{1} \sigma T_{1}^4 . Given that we are...
  31. B

    Ammonia Rankine cycle heat engine calculation

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  32. HighFive5

    Chemistry Does Decarboxylation Occur in Gamma-Keto Acids Under Heat?

    Hello all! I have learned beta-keto acids are able to undergo carboxylation when subjected to heat. Do gamma-keto acids undergo decarboxylation when subjected to heat as well? If not, why? I identified C as a gamma-keto acid. Do you agree? Thank you for your help.
  33. Cammers5

    Specific heat capacity aluminium

    say I used a good insulator?
  34. F

    Can graphene be usefull as armor against HEAT rounds?

    From what I understood from articles like this(https://scitechdaily.com/microbullets-demonstrate-graphenes-energy-absorbing-strength/) graphene is really good at distributing the energy from impacts over larger area and can even turn into diamond-hard material called diamene upon impact when...
  35. cookiemnstr510510

    Chemistry Why does a negative ΔH indicate an exothermic reaction?

    Hello All, I wanted some insight on my answer to this problem. Lets say we have the reaction PCl3(g) + Cl2(g) ↔PCl5(g) ΔH0=-111KJ So for this reaction we know it is exothermic (because my textbook told me). But I want to make sure I understand why it is. If I were to look at this reaction and...
  36. Prabs3257

    Heat dissipated in a Resistor-Capacitor circuit

    I tried to conserve the charge on the left plates of both the capacitors as intially the total charge on both is 48 and at t=t0 the total charge is 36(on c1) +4V(V is the potential across c2) so i got V=3 and then i conserved the energy Initial energy on both capacitor = final energy on both +...
  37. A

    Specific heat of a monotomic gas

    Given this problem I have calculated the partition function as $$z=1+e^{-\beta E_1}$$ And calculated the average internal energy as $$<U>=\frac{E_1 e^{-\beta E_1}}{1+e^{-\beta E_1}}$$ And thereafter taking the partial derivative of <E> with respect to temp. T the specific heat obtained is...
  38. jisbon

    Fourier’s Law Of Heat Conduction (Window Pane)

    In this case with a presence of the airgap, what should I do with the equation that is provided to be? Must the temperature gradient be caculated spearately (glass+air+glass) ? My tutor provided the hint that the heat flux should be constant for the windows, so in this case should I just omit...
  39. patricio ramos

    Question about initial and boundary conditions with the heat equation

    I am seeing the heat conduction differential equation, and I was wondering about a boundary condition when the equation is of transient (unsteady) nature. When analyzing boundary conditions at the surface of say, a sphere, the temperature does not depend on time. For example, if you have...
  40. LordGfcd

    What is the continuity condition for the heat flux through a boundary?

    Assume there is a boundary separates two medium with different heat conductivity [κ][/1] and [κ][/2]. In one medium, the temperature distribution is [T][/1](r,θ,φ) and on the other medium is [T][/2](r,θ,φ). What is the relationship between [T][/1] and [T][/2] ? Is it - [κ][/1]grad [T][/1]=-...
  41. H

    I Does the expansion of the Universe heat stars and bodies?

    The expansion of space is about 68 km/s/Mpc, or 0.00002 km/s/light year. The radius of the sun is about 700000 km. Thus, initially ignoring additional forces, the change in radius of the sun due to the expansion of space is about 1.5*10^-9 m/sec, or 5 cm/year. I assume that this expansion is...
  42. M

    Engineering Thermodynamics - Second Law: 2 Heat Engines Connected Between 3 Metal Blocks

    Hi, I posted a similar question recently and gained some insight on these types of problems. However, I am slightly stumped on how to approach this variation of the problem. So I know that: - there is no net change in enthalpy of the blocks and the engine as the processes are reversible -...
  43. G

    Heat in a const. pressure/volume calculation

    Hi All, In thermodynamics close system there are two const. processes in which we can calculate the heat: const. pressure const. volume I took 2 simple examples for these processes to test the results according the manufacturer data: For const. pressure I choose 1 liter 1.5 KW teapot For const...
  44. M

    Thermodynamics Problem: Heat Engine Between Two Blocks

    Hi, I am quite confused about how to approach this problem. I have seen variations of this problem where there is a heat engine between two blocks, but in this case the surroundings are massless, so I don't believe that approach will work here. Method: I have first started with the case that...
  45. M

    B Why / How do we feel heat from the sun

    Probably a silly question and a simple one for yourselves which I can't figure out myself. Hopefully I can explain it properly. Lets say I am standing on the equator and the sun is directly overhead. I am probably in the middle of a desert and it's around 50 degress centigrade. Assuming I could...
  46. K

    I Ligo Heat Dissipation: How Do They Protect Mirrors?

    Hello! I am not sure I understand how the heat from the lasers get dissipated in LIGO, at the mirrors. Given the high power of the lasers, the mirrors heat up, but the setup is in vacuum, so it is difficult to get rid of that heat. How do they make sure that the mirrors don't get too much damage...
  47. S

    Calculate the number of plates required for a heat exchanger

    Cooling water inlet temp is 4 degrees C Cooling water outlet temp is 80 degrees C Density of water is 1000 kgm-3 Specific heat water is 4.2kJkg-1K-1 Density wort is 1060 kgm-3 Specific heat wort is 4.0Kjkg-1K-1 Overall heat transfer coeff is 3000Wm-2k-1 Area of each plate is 0.75m2 For water...
  48. J

    Heat transfer through a MultiLayer Cylinder (find the Temperature inside)

    Hello, I am a Mechanical Engineer a little out of practice on Heat transfer. I am trying to solve this problem. It must be solvable but i have yet to find right equations online. I have a multi Layer Cylinder made up of C350 marraging Steel,Zinc Alloy-12 , then 6061 Aluminum T6. All that is...
  49. H

    Heat Loss in insulated Pipework

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  50. J

    Australian Open Heat Stress Scale

    Watching the Australian Open and they use a heat stress rating to protect the players. I've searched for the details of how it is calculated without success. Anyone know the formula that they use? Just curious.
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