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. W

    Problem involving thermal radiation and specific heat

    Homework Statement A satellite to reflect radar is a 3.5-m-diameter, 2.0-mm-thick spherical copper shell. While orbiting the earth, the satellite absorbs sunlight and is warmed to 50 °C. When it passes into the Earth's shadow, the satellite radiates energy to deep space. You can assume a...
  2. S

    Calculate Cooling Time: Aluminum Block in Steel Crate at 90°C

    How to calculate cooling time for a aluminum block in a steel crate placed in a room...both at 90°c ...how much time aluminum block will tak take to cool down to 25°c?
  3. A

    Heat Transfer in Electrical Engineering (EE): What to Expect?

    I want to pursue EE, but there are still some subjects in ME that I enjoy. Do heat transfer topics ever come up in EE? I would imagine cooling circuit board requires lots of knowledge of heat transfer/thermodynamics. I studied Haberman's PDEs as part of my chemistry undergrad and all it talked...
  4. Vitani11

    Why is the equation for heat flow negative?

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  5. Z

    I Heat energy: statistical mechanics vs atomic orbitals

    Normally, I prefer to do my own research, but I'm drawing a blank on this one. Any help would be appreciated. My understanding is that statistical mechanics accounts for all of the heat energy in a gas by the kinetic energy of the molecules. I also understand that atomic orbitals have different...
  6. D

    Solving Heat Transfer Problem in Rectangular Vessel

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  7. A

    Temperature on the outer surface of insulation

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  8. F

    How do conduction tobacco vaporizers create heat?

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  9. Z

    Heat question -- Ice cube in a cup of water....

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  10. Chrono_13

    B A Question about tiny tiny stars, and radiating heat

    A brilliant person once said “First get your facts strait, then proceed to distort them at will” or something like that. My question, is what would happen if say… a sun of relative density to our own, but only the size of a golf ball, just appeared in say… downtown LA, and sustained at that...
  11. S

    Why we use enthelpy when we calculate latent heat?

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  12. S

    What does the T-S diagram look like for an ammonia heat pump?

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  13. C

    Research project on heat transfer

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  14. knc

    What is the Work Done by a Gas in a Cycle?

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  15. knc

    Heat transfer in series and parallel

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  16. electr

    Estimate the local heat transfer flux

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  17. P

    Calculating Heat Load: Understanding Formulas and Physical Properties

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  18. C

    Alternate Heat Expansion Media for Nuclear Power Plants

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  19. maistral

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  20. Z

    Calculate reaction heat from quantum mechanics

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  21. S

    Heat capacity at constant volume and density

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  22. BL4CKB0X97

    Heat: Cause or Effect of Vibrating Atoms?

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  23. S

    Heat transfer. Could anyone explain the solution?

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  24. J

    How to calculate heat dispersion through a solid copper rod?

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  25. Kevin Halagan

    Having trouble with a heat sink in ANSYS NLT

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  26. E

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  27. T

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  28. T

    How Long Should My Double Pipe Heat Exchanger Be for a 22kW Capacity?

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  30. grandpa2390

    Calculating the Efficiency of a Heat engine

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  31. E

    Temperature in a Carnot heat engine

    Homework Statement A Carnot heat engine takes 95 cycles to lift a 10 kg. mass a height of 11 m . The engine exhausts 14 J of heat per cycle to a cold reservoir at 0∘C. What is the temperature of the hot reservoir? Homework Equations η=1-(Tc/Th)=W/Qh The Attempt at a Solution I've tried...
  32. E

    Heat required to heat water and ice

    Is the answer in my physics book wrong or did I miss something? Homework Statement A vessel whose walls are thermally insulated contains 2.40 kg of water and 0.450 kg of ice, all at 0.0°C. The outlet of a tube leading from a boiler in which water is boiling at atmospheric pressure is inserted...
  33. C

    Calculating Flow Rates for Cascading Heat Pumps

    Homework Statement I am given that a Chemical Company wants to implement a cascading refrideration cycle to provide 1 MM Btu/hr of cooling. We are given the three compounds we are using. Evaporator Temperature (F) Compresspr Out Pressure(psia) Cycle 1...
  34. asteeves_

    Solve Entropy Gen of Water-Ice Contact, 100J Transferred

    Homework Statement 5 kg of water at 60 degrees are put in contact with 1 kg of ice at 0 degrees and are thermally isolated from everything else. The latent heat of ice is 3.3x105 J/kg. What is the change of entropy of the universe when 100J of energy are transferred from the water to the ice...
  35. N

    Heat Transfer From Resistance Element to Metal Component

    Hello Physics Forums! My problem is as follows. I have a device that produces heat via Nichrome coils. I want to heat another small piece of metal (in this case stainless steel) with those Nichrome coils. I need to reach 175 degrees C, and so far I haven't found a readily available thermal...
  36. G

    Calculation of heat created during compression

    Homework Statement Hello, I have a task to make a heat balance of the evaporator. To do this, I was told to carry a few smaller energy balances in different parts of the evaporator. One of the things I had to calculate was the heat generated during steam compression. -steam is entering...
  37. F

    Algorithmic differentiation in unsteady heat equation

    Homework Statement Okey her we go I was given a base code called heat_equation_primer. The goal is to implement a optimizer into the program. The two methods that are going to be used is the Quasi-Newton and Steepest descent with search line. So I need gradients. So I tried to differentiate as...
  38. Sirsh

    Heat Transfer - Conduction/Convection Question - Which area?

    Homework Statement Its been assumed that the surfaces TL and TR of the same constant temperature. Homework Equations Tmax = TL/R + (qdoto*L2)/(8*k) q = ΔT/R Rconvection = 1/hA The Attempt at a Solution The problem I am having with this question is conceptualising which dimensions to use...
  39. G

    Heat injection and work during Rankine cycle

    I have been researching the Rankine cycle. I know that it consists of two adiabatic and two isobaric processes. However, I'm not entirely sure why we ignore the work done during the isobaric processes (this seems to be the case in the analysis I'm looking at). Is that because the work done there...
  40. F

    Heat conduction between 2 objects

    Can someone tell me if my logic is correct here. I am trying to figure out how the cross sectional area to make the heat transfer from one object be the maximum amount of heat transfer with the minimal amount of area... I know the thermal transfer coefficient is watts per (meter*kelvin). I find...
  41. Rizwan Yaseen

    Heat capacity equation units

    How we change the units of Heat capacity equation to British engineering system Cp=2. 657*10^4 +42. 37T - 1. 425*10^-2T^2
  42. V

    Examples of conversion of gravitational PE to heat energy?

    Homework Statement I was looking for some examples where gravitational potential energy is converted to heat energy. Are there many such examples of this conversion? I could only come up with one such example and even that could be an incorrect example. Homework Equations PEg = mgh The...
  43. G

    Stirling cycle: Why neglect isochoric heat transfers?

    Hi. To prove that the Stirling cycle has Carnot efficiency, one needs to neglect the isochoric heat transfers. Sure they have the same absolute value (but different signs), but it's still heat energy lost to the cold reservoir during the isothermic compression.
  44. P

    Method for determining the latent heat of oils

    Just a basic question. It's as the title says, If I'd want to determine the latent of oils (or any material for that matter), is the same methodology used for determining the L.H. of ice applicable? (e.g...
  45. Carlos

    Heat capacity as a function of T under 298 K for metals

    The heat capacity equation Cp for copper as a function of temperature (Shomate equation) for the solid phase is defined for the range of 298-1358 K in the Nist Webbook and in many books. http://webbook.nist.gov/cgi/inchi?ID=C7440508&Mask=2#Thermo-Condensed And I need to calculate the heat...
  46. G

    Definition of efficiency of a thermodynamic cycle

    Hi. Sorting the exchanges of heat and mechanical work in a thermodynamic cycle by the signs and summarizing, I get ##Q_{in}>0##: heat transferred into the system ##Q_{out}<0##: heat transferred to the cold reservoir ##W_{out}<0##: work done by the system ##W_{in}>0##: work done on the system...
  47. Nacho Verdugo

    Diffusion of energy by heat flow

    Homework Statement This problem belongs to the Intermediate Physics for Medicine and Biology, Hobbie Chapter 4. The heat flow equation in one dimension $$ j_H=-\kappa \partial_x T $$ where ## \kappa ## is the termal conductivity in ## Wm^{-1}K^{-1}##. One often finds an equation for the...
  48. rachel6589

    Calculating Heat Exchange for a Water Pump

    Homework Statement A pump, operating at 10 W, is used to raise the pressure of a stream of water at 2.5 mol/s from 1 bar to 2 bar. At steady state, if the water temperature should remain constant at 25oC, how much heat exchange between the pump and its surroundings is required? Note that 1 bar...
  49. B

    How Energy Is Spread In An Electric Kiln

    Heat from the coiled wire is transferred in three possible ways: conduction (through physical contact of the heating element and the material being heated); convection (through the air movement in the kiln); and by radiation (directly from the elements to the material being heated). It seems to...
  50. V

    How to apply the First Law of Thermodynamics to this problem?

    Homework Statement A spring (k = 500 N/m) supports a 400 g mass which is immersed in 900 g of water. The specific heat of the mass is 450 J/kg and of water is 4184 J/kg. The spring is now stretched 15 cm and, after thermal equilibrium is reached, the mass is released so it vibrates up and...
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