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. Nick Goodson

    Figuring Out Heat Transfer & Entropy of Steam at 10 MPa

    Hello everybody, would somebody please put me on the right track to answering this question? 'Consider water undergoes a heat transfer at constant pressure of 10 MPa and changes from liquid to steam. Find the entropy of the system (sfg) as well as the heat transfer per unit mass in this...
  2. guyvsdcsniper

    Work required to extract heat from a refrigerator

    The answer key says the work done should be +.043cal. I am getting a negative sign. I have posted my work in the attached image. My logic is that since this a reversible engine we can say the integral of dQ/T=0. Looking at the cycle, Qc isi being absorbed (Qc>0) and Qh is being rejected...
  3. guyvsdcsniper

    Finding an expression for the efficiency of a heat engine

    My book states the answer to this problem is . I have gotten very close to the answer. My problem is my Tc/th and tc/tm are flipped compared to the solution. I feel like I am missing something in my algebra but can't see where I am going wrong. Could I get some help identifying where my...
  4. Raihan amin

    Understanding a heat sensor circuit?

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  5. Shreya

    Is Heat Transfer between 2 Walls Independent of Temperature Assumptions?

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  6. H

    MATLAB Modelling a Heat Pump with Linear Compressor using MATLAB Simulink

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  7. guyvsdcsniper

    Evaluation of heat and work for a stirred liquid

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  8. A

    A Calculating the heat loss of an open water tank (aquarium)

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  9. FEAnalyst

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  10. N

    Why Is My Calculation of Heat Energy Incorrect?

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  11. bluesteels

    Quick question about the heat Q transferred between water and skin

    My work Q= 0.025 * 4190 * (34-100) = -6910 but on chegg but did they do Q= 0.025 * 4190 * (100-34) = 6910. I thought the initial is 100C and final is 34 because it goes from 100 to 34
  12. H

    B How does heat conductivity work? Al -> Cu

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  13. bluesteels

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  14. C

    I 64% n.th + COP4 = more heat out of fuel than its calorific value?

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  15. L

    B Heat and Infrared radiated from an object

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  16. Melbourne Guy

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  17. F

    A Can the Solution of a Heat Equation Only Get Smoother as Time Increases?

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  18. M

    I Making a heat shield for my car's exhaust

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  19. cianfa72

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  20. S

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  21. K

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  22. S

    A Casimir heat transfer (Ballistic heat transfer) paper

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  23. fluidistic

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  24. M

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  25. Clemens Khoo

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  26. V

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  27. V

    Energy transformations in an IC engine cylinder

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  28. A

    Heat Transfer Through Cylindrical Nuclear Fuel Pin

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  29. L

    I Understanding relationship between heat equation & Green's function

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  30. Ale_Rodo

    I Why is Entropy defined as a fraction of heat over temperature?

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  31. ikihi

    I Power equation using heat instead of work

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  32. L

    I General solution of heat equation?

    We know $$ K(x,t) = \frac{1}{\sqrt{4\pi t}}\exp(-\frac{x^2}{4t}) $$ is a solution to the heat equation: $$ \frac{\partial u}{\partial t} = \frac{\partial^2 u}{\partial x^2} $$ I would like to ask how to prove: $$ u(x,t) = \int_{-\infty}^{\infty} K(x-y,t)f(y)dy $$ is also the solution to...
  33. warhammer

    Entropy Change & Heat Transferred to a Gas

    By using the given relationship that S=a/T --(1) along with the equation ∫ (delta Q rev)/T=∫dS -- (2) I found out that my answer for the value of Q is mc*ln (T2/T1)*a upon equating (1) & (2). But the solution is instead given as Q=a*ln*(T1/T2). I would be grateful if someone would point out...
  34. rudransh verma

    I How Does Heat Transfer Impact Our Sensation of Temperature?

    We know heat is the motion of molecules of a gas for example. As temperature increases this motion increases and the gas expands. We know this gas would be hot if we touch it. So I want to ask how does the fast motion of molecules somehow translates to the heat that we feel. Why does it feel...
  35. StarChem

    Vaporization Heat and the Heat Capacity of H20 comparison

    According to the Vaporization Heat table, the heat needed for 1 mol of H2O to evaporate at 100°C is 40.7KJ and 44.0KJ/mol is needed to evaporate H2O at 25°C. Thus 44.0-40.7=3.7KJ is the energy needed to heat H2O to 100°C from 25°C. However, according to the heat capacity of H2O, 3.7KJ will only...
  36. organiclatte

    Air-to-Water Heat Exchanger - Car radiator

    I'm looking for a way to keep a liquid under 50°C. This liquid has a thermal conductivity of .1396 and a specific heat of 2.054 both at 40°C. and a constant energy source submerged in it ranging from 16KW to 17.5KW. I'm barely starting to read about this topic, according some forums, a car...
  37. T

    Calculating Transient Heat Transfer in Pipes with Thick Walls

    Hi Everyone, I am looking to find how much heat can be stored in a concrete pipe of roughly 0.3-0.4m diameter, and an internal diameter of 0.05m. Air will travel through the internal diameter at 500°C and 17.5bar which will provide the heat for the pipes. This system will then be reversed so...
  38. E

    How to find the heat energy produced in a resistor?

    i found current to be 2/5 A. then 2/5A multipled by 6s = 2.4C. and since one joule per coulomb is equal to the unit of p.d, i get 2.4J. I don't get 4.8J(supposed answer)
  39. Edwardminett

    Heat Exchanger: +40C rise at 16 liters/minute flow rate

    Summary:: How to calculate the rate of heat transfer between hot external water and cold internal water in a pipe. The image attached is my attempt at the question however, I find myself stuck trying to work out internal and external heat transfer coefficient.
  40. sarahjohn

    Finding Specific Heat of a solid

    I thought it might me a ratio of the atomic masses. 27 / 63.6 = x / 900 x = 382 J/kg-K
  41. D

    B Is Mean Temp in 2 phase Heat Exchangers Higher Than Logarithmic Mean?

    Is Mean Temp in 2 phase Heat Exchangers Higher Than Logarithmic Mean? I am looking at this paper: https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1314&context=iracc Having a bit of trouble understanding all of it, but my basic question is just: If I have a heat pump where the hot...
  42. G

    I Heat capacity for a real gas using the ideal gas (zero pressure) equation

    Summary:: Heat capacity for real gas with ideal gas (zero pressure) equation I'm looking at this problem and I'm stuck. I usually question everything but this problem is confusing me. I don't know how they've made the jump from reduced properties (from generalized Cp charts(?)) to...
  43. Wrichik Basu

    Solving the heat equation numerically using Python

    I want to solve the heat equation numerically. The equation is: $$k \dfrac{\partial^2 T}{\partial x^2} = \dfrac{\partial T}{\partial t}.$$ This is a parabolic PDE. Following this pdf (specifically, equation 7 given on page 3), I wrote the following Python function to implement the explicit...
  44. D

    B Lorenz COP of a heat pump and the temperatures of the hot/cold reservoirs

    @Dale : “The COP of a heat pump and the efficiency of a heat engine both depend strongly on the temperatures of the hot and cold reservoirs. For this calculation you need to go back and check the sources for the temperatures corresponding to each of these numbers. You will find that the Stirling...
  45. D

    B Can a Heat Pump and Stirling Engine Create a Perpetual Energy Cycle?

    I was reading about heat pumps and it made me wonder… would the following process be physically possible…? I attach the hot side of the heat pump to the hot side of the stirling engine. 400% COP (coefficient of performance) means 1 kilowatt hour of electricity consumed by the heat pump delivers...
  46. cwill53

    I Entropy and Heat Capacity Relation

    I have a simple question sort of about exact differentials and deciding which variables matter and when. I know we can write entropy ##S## as ##S(P,T)## and ##S(V,T)## to derive different relations between heat capacities ##C_V## and ##C_P##. I was wondering if it is technically correct to...
  47. Ashshahril

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  48. L

    Engineering Reviewing Efficiency of Otto & Diesel Cycle Heat Engines

    Hi, i have this question and don't understand it. can somebody explain what i have to do. i know a ideal engine is a engine running on carnot cycle i what the cycles are i don't know what relative efficiency is and what there looking for (Q) Review the relative efficiency of ideal heat engines...
  49. M

    Question about Refrigerants used within a Heat Pump

    I've been given the following 2 questions (please see below), and I've been asked to come with answers and arguments for my decision for the proposed answer, since there is just 1 correct answer per question. (so you can see my attempt below) Q1)The refrigerants have to: a)Vapourise at high...
  50. A

    Calculating work and heat transfer in this Carnot process

    Hey guys! This is problem from Callens Thermodynamics textbook and I'm stuck with it. My goal was to get a expression for the entropy ##S## which is dependent on ##T## so I can move into the ##T-S##-plane to do my calculations: I startet by expressing the fundamental equation as a function of...
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