What is Heat: Definition and 1000 Discussions

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. JD_PM

    Heat engine undergoing an elliptical cycle

    An ideal diatomic gas undergoes an elliptic cyclic process characterized by the following points in a ##PV## diagram: $$(3/2P_1, V1)$$ $$(2P_1, (V1+V2)/2)$$ $$(3/2P_1, V2)$$ $$(P_1, (V1+V2)/2)$$This system is used as a heat engine (converting the added heat into mechanical work). Evaluate the...
  2. HumanistEngineer

    A Solving the Convection-Diffusion Equation for this Pipe with a Heat Sink

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  3. T

    Heat capacity vs Thermal conductivity in a LN2 bath

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  4. D

    Can someone please debunk this claim that CO2 does not trap heat?

    Hi everybody I follow climate denier pages and every now and then come across a claim that doesn't seem to have been debunked yet. One such claim is made here: <link to uacceptable source deleted> The gist of the article is that scientists experimented with using different gases in double...
  5. heatupgrade

    Can we make electricity from heat?

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  6. santimirandarp

    Isothermal expansion of a gas: heat of surroundings

    In an isothermal process, for an expanding gas ##\Delta U_{sys}=0## and ##Q=-W## but then, How can we evaluate ##Q_{surr} ##? It should be ##Q_{surr}=-Q_{sys}##, but I don't know how to show it in equations. If I try to get the result through the principles: ##\Delta U_{sys}=-\Delta U...
  7. santimirandarp

    Understanding q: Why does dqsurr = -dqsys?

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  8. didaw

    The efficiency of a furnace’s heat transfer process

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  9. saratavares

    Heat exchangers and energy balances

    I have to do a project using Aspen and need to do some math before hand. Can you please help me? Here's the problem: A heat exchanger with 10 m2 of heat transfer area is provided to supply 58 kW to a water stream available at 15 ° C and 1 bar. The available hot fluid is freon-12 at 32 ° C and 7...
  10. A

    I Is there a limit to how hot something can get, and if so why?

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  11. R

    Heat transfer to solution per litre

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  12. W

    Calorimetry Lab Analysis (predict specific heat of unknown metal)

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  13. S

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  14. D

    Heat Energy Intercepted by the Earth

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  15. E

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  16. D

    Thermodynamic possiblity for outlet temperatures of heat exchanger

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  17. sww_world

    Heat Capacity energy exchange problem

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  18. C

    Could somebody please explain the vapor compression cycle?

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  19. J

    Definition of Heat and the First Law of Thermodynamics (discrepancy?)

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  20. I

    How does radiation become heat?

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  21. callie123

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  22. Zeynaz

    Help with a heat transfer question

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  23. seb7

    Two or three types of heat transfer?

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  24. Zeynaz

    Could you help me with this thermodynamics question?

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  25. C

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  26. Clara Chung

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  27. PCal

    Effectiveness to calculate the outlet temperatures of a heat exchanger

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  28. J

    Finding heat capacity for liquids

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  29. thaiqi

    Why doesn't the atom absorb heat energy when it is low?

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  30. H

    A Irreversible processes. Heat equation, diffusion equation

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  31. C

    What is the intuitive meaning behind the polytropic process.

    What does it actually mean from an intuitive standpoint? I don’t want to simply memorize the equation. What is it really and when can it be used? What is the usefulness of it? Thanks.
  32. C

    What is the difference between flow energy and boundary work?

    What is the difference between the two? Also, as another question, for enthalpy, is it correct to define it to be the sum of internal energy and flow energy or is there another understanding for it? Thanks in advance
  33. C

    Why is air in atmospheric pressure and room temperature a gas?

    This seems like a simple thermodynamics question but I would like clarification. So the absolute critical temperature is 132.5 K (-221.17 F) and the absolute critical pressure is 3.77Mpa (546.7 psi). I understand that for temperatures above the critical point, a pure substance undergoes an...
  34. C

    How does specific volume play its role in the phase diagram?

    So, I am casually sifting through a chapter in a thermodynamics textbook talking about the multiphase process that pure substances go through. I understand how the P-v and T-v diagram works and that out of the three properties (specific volume, temperature and pressure), two of them are...
  35. T

    Efficiency of a Heat Engine: How to Calculate Heat Transfer in a Monotonic Gas

    Homework Statement I am having an issue trying to decipher this question, as I am not sure if it a lack of knowledge on my half or there is an assumption I have to make. Homework Equations ##\epsilon=\frac{W_{total}}{Q_{in}}## The Attempt at a Solution My issue is calculating the heat...
  36. C

    Does temperature increase when water is boiling at 100C......

    Does temperature increase when water is boiling at 100C in a closed system? I am picturing a scenario where I am boiling water in a pot to make pasta. However, I decide to close the pot as the water is still boiling. By doing this I am sealing away the system of study from the environment. Thus...
  37. M

    Calculate the amount of heat supplied to a gas

    Homework Statement 1kmol of multatomy(I hope you understand - gas with many atoms) gas is heated for 100K (conditions of free expansion). I have to calculate the amount of heat supplied to gas. I have no idea how to do it. The right answer is 3320kJ Homework EquationsThe Attempt at a Solution
  38. EastWindBreaks

    Heat exchanger - efficiency of the cycle

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  39. davidhe96

    Heat transfer problem for cooling a solar panel

    I am currently trying to solve a problem for my dissertation. Help would be greatly appreciated. :) A silicon solar panel of area 1m^2 is being warmed by the sun. It achieves a constant temperature of 80 degrees celcius. I am trying to cool this panel which is constantly being provided solar...
  40. W

    Capture and re-use the heat generated from Air Compression

    I am trying to fill pipes with a volume of 556 cuft to 15,000 psi. I want to capture and re-use the heat generated from the compression process and re-use it. Is this amount of compression and heat exchanging possible with current technology
  41. B

    I Solution of the 1D heat equation

    $$\frac{\partial T}{\partial t}=\alpha\frac{\partial^2 T}{\partial^2 t}$$ with an initial condition and boundary conditions $$T(x,0)=T_0$$ $$T(L,t)=T_0$$ $$-k\left.\frac{\partial T}{\partial x}\right|_{x=0}=2A\cos^2\left(\frac{\omega t}{2}\right)=A(\cos\omega t+1)$$ where $A=V_0^2/(8RhL)$...
  42. F

    I Heat Equation Problem: Solving c + 3d = 0

    I’ve attached an image of a solved problem related to the heat equation. Can somebody explain the -c + 3d = 0 comes from? I’m having trouble following the work shown.
  43. M

    Heat transfer - will my lipstick formula melt in the storage package?

    Hi, I am a makeup formulator and need to make a lipstick that would be stable at 50ºC. The stability is tested in a chamber with an inner temperature of 50ºC. The lipstick is in a plastic packaging - a regular one that can be seen in any store. The question is: Will the temperature of the...
  44. rumborak

    Fluid going through pipe: what is the influence of speed on exchanging heat?

    I'm doing a fun home project, and it involves water flowing through a metal pipe, where the surrounding is significantly lower temperature than the water in the pipe. The point of the exercise is to cool the water in the pipe as it flows through it. The question is, what influence does flow...
  45. Isolde Wilde

    DIY Stirling engine project

    hello, I had made an DIY alpha type Stirling engine for my physics project and now I have to write an report about the relationship between the heat given to the engine and the motion of the wheel. I had searched a lot about Stirling engines and I learned about work, energy, efficiency...
  46. F

    Understanding Specific Heat: A Derivation of the Correct Equation

    Homework Statement 1.2.6. Supose that the specific heat is a function of position and temperature, c(x,u). (a)Show that the heat energy per unit mass necesary to raise the temperature of a thin slice of thickness deltax from 0°to u(x,t) is not c(x)u(x,t), but instead int((0->u)c(x,u’))du’...
  47. W

    Work Check: Heat transfer between reservoir and small system

    Homework Statement Could someone look through my work? The parts where I wrote (??) are steps I am especially unsure about. Many thanks in advance. A large reservoir at temperature ##T_r## is placed in thermal contact with a small system at temperature ##T##. They end up at temperature...
  48. IshaanM8

    Question about Phase Change & Latent Heat

    Homework Statement When running, some (heat) energy is lost by the evaporation of sweat. If a runner loses 1.0 MJ( Mega Joules) of energy via sweating, calculate an approximate mass of sweat evaporated from the runner. Homework Equations Q = McΔT Q (Joules) = M (Mass) c (Maximum Heat...
  49. S

    Help with some sort of formula to determine resistance to heat

    I am not that smart when it comes to math. But I was wondering if there is a formula calculator or something online that would help me with the example of a problem. For instance if the attic is 130 degrees and I have a 14 inch round metal duct to my air conditioner in the Attic is there a way...
  50. A

    What is the role of vibrational energy in heat conduction in solids?

    It is easy to understand heat conduction in a gas as the nucleus of atoms may collide with transfer of kinetic energy. But the space within a solid is vastly empty space and the nucleus of the atoms cannot collide. So if the surface of a solid is in contact with a hot gas, how is kinetic energy...
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