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).

View More On Wikipedia.org
Recent contents Top users
  1. shivamchouhan5077

    Heat flux through a material with variable heat conductance

    My first thought was that as the heat current ##I_H## is going to be constant at any cross section of the rod, by the equation of continuity, as the area of cross section is constant throughout the rod. So using: (where ##R_{total}## is the total thermal resistance of the rod) $$I_H =...
  2. jmex

    HVAC Converting a Heat Source to Energy

    Hello All, I have some space outside my room which have sunlight all day. The room heats up to very high temperature. Is there any way I could use that heat to cool down my room without using solar panels? Just a thought.
  3. jmex

    Solenoid valve thermal part

    Hello folks, I have a new different design of solenoid valve and would like to evaluate heat generation in the system. I am a mechanical engineer and might have less understanding of electrical components. Just trying to understand, the solenoid valve will have heat generation due to current...
  4. joejoe121

    A household fridge removes heat, determine power the fridge draws

    I'm confused about the wording "runs one-fourth of the time". My professor said we multiply the Q_L by four, but I don't get it conceptually.
  5. L

    I First law of thermodynamics -- two different expressions for dQ

    Okay, so the first law ##dU=dQ+dW##. We all know that ##dU=C_VdT##. So that means that we have: $$dQ=C_VdT+PdV$$ Now I have a problem. We also have that $$dU=\left(\frac{\partial U}{\partial V}\right)_TdV+\left(\frac{\partial U}{\partial T}\right)_VdT$$ and substituting that in to ##dQ=dU+dW##...
  6. L

    Thermodynamics: Violating Clausius => Violating Kelvin

    I am not convinced that the heat entering ##T_l## from ##T_h## is equal to ##Q_l## in the Carnot engine. Why should it be? thanks
  7. Feynstein100

    B Would isolating the Solar System prevent its heat death?

    I have a thought experiment in mind. Crudely speaking, the second law of thermodynamics implies that there is only a finite amount of change possible in the universe. Once this limit is reached, no more change can occur. The key thing here though is reversibility. If changes were reversible...
  8. Nabir14

    Mouth heating up after eating biscuits

    I recently noticed that my mouth is heating up after eating some biscuits named as Energy Biscuit. It's not the taste because I can feel it by touching. It's very weird as I have never experienced it before when eating biscuits. So why is this biscuit heating my mouth so much? The product...
  9. P

    Why Isn't My Endothermic Crystallization Working?

    I'm using a process that uses heat to catalyze crystallization. I don't have to equipment to really understand what's going on, it could just be incomplete nucleation from a super saturated solution, but when I cool it, it doesn't crystallize. Now, I am in an acid solution (pH between 4-5) so if...
  10. L

    B Calculating Heat from Drag force on a Rocket Airframe

    Ok, so i have a question, and an approach to my question. Am i going in the correct direction? Here si the question: I have a high powered rocket i made. It sometimes hits mach 1.9. I would like to calculate the heat generated from going that fast so i can test other materials. Here is what...
  11. SimoneSk

    I Estimate thickness of an object based on radiative heat flux decay curve

    Dear all, I have a slab of unknow thickness, with a starting temperature of 1400 K, emplaced over cold ground at a temperature of 285 K (air temperature assumed to be the same and held constant). I do have measures of its cooling curve in terms of radiative heat flux (in Watt) loss at the...
  12. M

    Behavior of heat addition in a compressible flow

    Rayleigh flow refers to frictionless, non-adiabatic flow through a constant area duct where the effect of heat addition or rejection is considered. Consider the case of air traveling through a heat exchanger: The air travels through the duct and picks up heat from the surface of the heat...
  13. S

    How much will my seaweed tanks heat up in the hot Indian summer?

    I'm growing seaweed in outdoor concrete tanks and trying to figure out how much the tanks would heat up during the day. The water is already at 30 C and we don't want them to heat up much more. Our tanks are rectangular and made of concrete, with internal dimensions of 1.8m (L) x 0.8m (W) x...
  14. PaulMuadDib

    Signal processing engineer wondering if a seasonal heat storage is feasible

    Hello there, My background is about signal processing, and after having installed a complete photovoltaic generator (7.2 kWp in 3 directions, Victron system) & storage (21 kWh of Pylontech batteries), heat pumps to heat the house (combined a small Jötul stove) and the domestic hot water, I am...
  15. D

    Classical Looking for a thermodynamics book that 'ties it all together'

    I am currently a highschool student, and while I've learnt a bit about thermodynamics such as the first and second laws, their implications, I'd like to know how that stuff relates to gases and (without going too deep into it) phase change. Due to the structure of our curriculum, I've learnt...
  16. SimoneSk

    I Generate heat conduction curves at different time steps

    Dear all, I am having some difficulties in generating some heat conduction curves. My problem is: I have an object at a temperature (Th) of 900 K placed on top of a surface with a temperature (Ta) of 300 K (see Figure). The thermal conductivity (K; W M-1 K-1) is 1.5 whilst the thermal...
  17. D

    How does the rise in temperature of fuse wire depend upon its radius?

    I tried the following: We know, Q = mc (delta t) but by Joule's law of heating, we also know that H = I^2 R t Assuming that no heat is lost in the surroundings, we get Q = H => mc (delta t) = I^2 R t => (delta t) = (I^2 R t)/(mc) But m = V d = AL d and R = (rho L) / A => (delta t) =...
  18. G

    I How does BTU convert to heat in degrees in a greenhouse?

    Information online claims sun is 200 btu per sq ft in winter only when sun is perpendicular to plastic or glass of a green house. When sun hits glass or plastic at an angle there are losses. The steeper the angle the more losses will be. Is it possible to calculate how warm a green house will...
  19. MatinSAR

    Question about the thermodynamic temperature scale

    My first problem is to find the absored and rejected heat. Can I say that it is equal to the work done in an isothermal proccess (##dQ=Pdv##)? My reasoning : We have ##dQ=C_V d\theta + Pdv##. For constant temperature it becomes :$$dQ=Pdv$$
  20. MatinSAR

    I Work done in cycle of a refrigerator (in Heat and Thermodynamics by Zemansky)

    I guess the first one is wrong. Because in this cycle we have ##|Q_H| > |Q_L|## then ## |Q_L| - |Q_H| ## is negative and caanot be equal with ##|W|##. Am I right?
  21. J

    I Measurement of heat as an interval measurement or a ratio measurement

    Hello! I am new to this forum and I'm not even sure if this is the right place to ask but here goes: I am studying Research Methods. I got to the part where the teacher is teaching us about levels of measurement. They said that there are a few levels but the two that are significant to my...
  22. A

    B How much heat energy can give out put by ionization gas?

    I mean by accelerating electrons and ions for energy levels in atom
  23. L

    Why does this question make this simplifying assumption?

    The question says to "neglect the change of volume of the water". This confuses me. Why do we neglect the change of the water's volume? Let's say we didn't. A = Q/It, where A is area, Q is heat, I is intensity, t is time. Q = mc(deltatheta), mass is constant, specific heat is constant (as mass...
  24. bushmonk

    I Measurement and Thermal Effects Similar?

    A weak (one photon at a time) beam of laser light strikes a double slit. In case 1 the barrier forming the double slit is a mirror. In case 2 the barrier is flat black. An array of detectors surround the experiment and can detect the photon whether it goes through the slit or is reflected. In...
  25. R

    I Is low entropy found in something very hot?

    If we have a kg of something that is 100miljon Celsius degrees, and can controlably use this heat somehow, we can sustain life, grow crops, drive steam engines and with these we could build a whole city like New York, we can create a lot of mass with very low entropy, things that are very...
  26. E

    I Why is ##dQ = dH## still valid for chemical reaction (Callen)?

    Consider a system which is characterized by the extensive variables ##(U,V,N_1,...,N_m)##. For a quasistatic process which occurs in contact with some pressure reservoir and where the ##N_i## are constant, one has $$dU = TdS -PdV \implies TdS = dQ,$$ where the implication follows from the First...
  27. S

    Correct statement about thermodynamics process

    I know process B absorbs heat but I can't determine the heat of process A. In adiabatic process, Q = 0 but process A is not adiabatic. I only know both W and ΔU will be negative for process A but how to know Q? Thanks
  28. RobbyQ

    I Does heating weaken the strong nuclear/electromagnetic forces

    In this steel forging video, does the heat weaken the strong nuclear and electromagnetic forces allowing compression?
  29. jackkk_gatz

    Electric heat generation from parallel rods carrying current in an oil bath

    I know that ##\dot e_{gen} = \frac {R_{e}i^2} {\pi r^2 L}## the thing is I don't know the value of i. I didn't write it, but another thing that the problem asks is to determine the flow of electric current. The model I came up with using heat generation due to electrical current is $$ \frac...
  30. singularcell

    Efficiency and Temperature in Heat Engine Cycles: Approaching Parts B, C, and D

    I didn't have much trouble with part a but I'm struggling with b,c, and d. I considered the efficiency formula for a heat engine e = work done by engine/ qh but i am unsure of how to approach it. for part c) not sure how i can get to Tc without knowing Th for d) my gut is telling me 5/2 but i...
  31. pinball1970

    Record Heat for the Oceans in 2022

    "Changes in ocean heat content (OHC), salinity, and stratification provide critical indicators for changes in Earth’s energy and water cycles. These cycles have been profoundly altered due to the emission of greenhouse gasses and other anthropogenic substances by human activities, driving...
  32. R

    Problem about a block of ice melting (specific latent heat)

    Energy lost by water = Energy gained by ice Energy lost by water = 0.16 x 4200 x (100-t) Energy gained by ice = 0.205 x L + 0.205 x (t) (where t is the temperature at thermal equilibrium). However, there does not appear to be enough info to continue. The solution, however, considered t to be...
  33. M

    Heat added to system increases mass

    According to this, The heat added to the system is proportional to the mass. Does someone please know how that highlighted statement is so? I think it is because the heat increases the internal energy of a system and internal energy is the sum of the translational, rotational, and vibrational...
  34. S

    Improving heat transfer in domestic hot water tank?

    A typical UK domestic hot water tank holds c. 200 litres of water. Hitherto the common method of heating it to say 60C has been by means of an internal coil of copper pipe through which is pumped hot water from a gas boiler at ~ 70C. Heat transfer on the outside of the coil is by natural...
  35. Scott Chapel

    Enclosure Panel Material and Heat Transfer

    Referring to the attached, the bottom right is an electronics compartment. The external panels are 20GA steel powder coated yellow. There is 1-inch of R-6 foam board insulation on the inside of all external walls. The skid is exposed to ambient heat and direct sunlight when on site. If we...
  36. M

    Deriving general specific heat capacity formula

    For this, Dose anybody please know of a better way to derive the formula without having ##c = \frac{\Delta Q}{m \Delta T}## then taking the limit of both sides at ##\Delta T## approaches zero? I thought ##\Delta Q## like ##\Delta W## was not physically meaningful since by definition ##Q## is...
  37. R

    B Heat transfer -- Several questions

    I am constantly research a wide range of areas and often run into questions I cant seem to find the answer to, no matter how much I ask uncle google. I am looking for open dialog and discussion, so I dont mind getting off topic a bit. I like the inspiration. Tho periodically I may need a...
  38. R

    Can passive heat collection be used to heat water to very high temperatures?

    I ask this question making refference to the Evacuated Tube Solar Water Heaters that have alcohol in their core tube to transfer heat from the Evacuated Tube to the water. Is it possible to make a passive water heater that uses a step system of tubes filled with water in a gradually decreasing...
  39. M

    Finding how much heat released by evaporation of water

    For this, Dose anybody please know where they got the 120W from? Many thanks!
  40. M

    Heat exchanged in Expanding and cooling gas

    For part(b), My solution is, ##\Delta E_{int} = Q - W = \frac{3}{2}(P_fV_f - P_iV_i)## ##Q = W + \frac{3}{2}(P_fV_f - P_iV_i)## ##Q = 4000 + \frac{3}{2}((1 \times 10^6)(6 \times 10^{-3}) - (3 \times 10^6)(2 \times 10^{-3})## ##Q = 4000 J## However, according to the solution b. ##−4000 J## Can...
  41. M

    Finding heat exchanged work done to compress gas

  42. D

    Rate of cooling of aluminum parts after a glycol heat process

    I work for an aerospace supplier across different departments. I was recently shown how the production workers straighten aluminum parts after a glycol heat solutionizing process. The aluminum parts undergo a heat treatment for a few hours and are quenched in glycol. I can't get too in-depth...
  43. M

    A Practical use of an overall heat transfer coefficient?

    Say I have a real counter flow heat exchanger using air and water. I run a test so I know every parameter; mass flow rate of both fluids, surface area, and in and out temps. This is great. Now I can calculate the heat transfer rate, my log mean temperature difference, and overall heat...
  44. Darmstadtium

    B Conversion of Potential Energy: Sound or Heat?

    When a coin is dropped from a certain height and collides with a glass surface, is the majority of the potential energy converted to sound or heat? And how would one determine this as I only hear the sound and cannot measure the significant change in temperature?
  45. D

    A Heat exchange in a thermal storage based on phase change materials

    Hello, I want to model a thermal battery based on phase change materials (PCM). It is a plate heat exchanger immersed in a PCM bath. The diagram is given in the attached file. I want to determine the temperature at each moment and from everywhere in the battery. The hypotheses are the...
  46. Tone L

    Heat Transfer & Cooling Capacity

    Hi, zero education on heat transfer here, need some help. I have an electronics module that generates 15 W of electrical power over a 70mm x 20mm x 15mm heat load volume (aluminum). The ambient temperature is 25° C, the maximum temperature the heat sink can be is 40° C (ΔT = 15° C). Does...
  47. M

    Misc. Looking for help calculating heat transfer for PEX ground loop project

    Looking to build a suitable closed loop water (probably glycol mix) circulation system to prevent livestock water troughs from freezing. I assume that I need to calculate how much heat loss is predicted from the water tank in ambient air (varies, but assume worst case), then what length of heat...
  48. S

    B What causes the drop of latent heat at lower temperatures in liquid helium?

    The dependency of liquid He latent heat of evaporation on temperature shows a conspicuous maximum. https://www.nist.gov/system/files/documents/srd/jpcrd551.pdf for 4He. Section 16, pages 1264-1266 on pages, 48-50 on pdf. From fig. 16.1 and table 16.3, the maximum is around 3,1 K and 94 J/mol. At...
  49. E

    I PDE - Heat Equation - Cylindrical Coordinates.

    Would method of separation of variables lead to a solution to the following PDE? $$ \frac{1}{r} \frac{ \partial}{\partial r} \left( kr \frac{ \partial T}{ \partial r}\right) = \rho c_p \frac{\partial T }{ \partial t }$$ This would be for the transient conduction of a hollow cylinder, of wall...
  50. kartini99

    I 1D Heat Transfer Analytical Wall

    Hello everyone, I'm trying to solve the transient heat transfer problem within the ID wall. The material is steel, and it is isotropic. The properties are given below : L = 5 mm qin = 0 Tinf = 100 deg C Tini = 20 deg C rho = 7850 kg/m3 cp = 460 W/Kg.K k = 45.8 W/m.K h = 20 W/m^2.K alpha = k /...
Back
Top