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. 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...
  2. 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
  3. 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 $A=V_0^2/(8RhL)$...
  4. 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.
  5. 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...
  6. 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...
  7. Isolde Wilde

    How Does Heat Affect the Motion of a DIY Stirling Engine's Wheel?

    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...
  8. 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’...
  9. 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...
  10. 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...
  11. 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...
  12. 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...
  13. R

    Biogas or solar heat storage cooker for rural villages?

    Hello everyone, For villages in Africa and Asia that still use wood, dung or other biomass in simple stoves which option do you think will be better? Concentrate solar energy into an insulated unit with a molten salt which can then be used at any time or build a simple biogas generator (large...
  14. hnnhcmmngs

    Minimum heat removed from gas to restore its state

    Homework Statement After a free expansion to quadruple its volume, a mole of ideal diatomic gas is compressed back to its original volume isobarically and then cooled down to its original temperature. What is the minimum heat removed from the gas in the final step to restoring its state...
  15. S

    Most lightweight method for storing heat?

    Hello everyone, I'm aiming to produce a lightweight steam engine, which will essentially have a coil of copper tube inside the walls of a tube made of >your suggestions here<. this tube is the exhaust for a blowtorch. The principle is that this tube gets very hot, then transfers heat to the...
  16. hagopbul

    About the heat carrier in a nuclear reactor

    Hello: I have small question , as I read about the ATF research in the news ,a question present it self , why no one does any research on heat carrier in nuclear reactor that can absorb nuclear radiation and change it to infra red radiation ? Best H
  17. C

    I Trying to better understand what viscosity really is

    I'm trying to get a better handle on the actual physical phenomena underlying viscosity (for Newtonian fluids). Something I could word in the format of "this happens (and this and this), and so the fluid resists flow." What I've found online is that when gasses are at higher temperatures, they...
  18. jybe

    Constant pressure heat of reaction -> constant volume q

    Homework Statement For the reaction below, the constant pressure heat of reaction is qp = −3256 kJ mol−1 at 25 °C. What is the constant volume heat of reaction, qV , at 25 °C? 16 CO(g) + 33 H2(g) ⟶ C16H34(l) + 16 H2O(l) Enter your answer in kJ mol−1, rounded to the nearest kilojoule...
  19. S

    1-D Heat Distribution in Long Cylinder

    Hi there, I've got a Heat Transfer problem that I can't seem to get right. I will list all information in the problem without 'interpreting' it: Givens: 100 cm long cylinder filled with hot water, and constantly heated to maintain the water at 100°C. Heat is transferred via conduction from...
  20. CrosisBH

    Mass of Ice required to achieve a certain final Temperature

    Homework Statement An insulated beaker with negligible mass contains a mass of 0.350 kg of water at a temperature of 76.5 °C. How many kilograms of ice at a temperature of − 23.9 ∘C must be dropped in the water to make the final temperature of the system 40.0 ∘C? Take the specific heat for...
  21. A

    Higher and Lower heat value of combustion of Coal?

    hello my friends , i have two question about calorific value of coal why Lower heating value decrease with increase oxygen content but increase with increasing hydrogen , sulfur and carbon content ? Do this elements influence the higher heating value or not ?
  22. P

    Calculating the mass and price of LPG needed to heat water

    Hello everyone, Homework Statement How many kilograms of lpg will you use if you heat 5 litres of water from 20C to 90C everyday for 30 days and how much will that cost if a 12.5kg cylinder is 1750 Rupees The attempt at a solution To heat 1 liter of water by 1C requires 4.18kJ so you then...
  23. W

    Heat bath and canonical ensembles

    Hi all, I have encountered the idea of a heat bath but am slightly perplexed as to what it is. There was a textbook example that looked to find the number density expression for gas molecules as a function of position (image below). It then said that the probability ##P(z)## of finding the...
  24. S

    Can Using a Mass Heater Improve the Efficiency of a Radiator?

    Hello all, I suffer from having a very cold house - as it is rented, we cannot put insulation in or change the windows (single glazed!), so I am looking for non-permanent options to maximise the warmth we can get from it. We have a log burner, and I have found that it is still kicking heat out...
  25. S

    Heat needed to expand a circular metal plate

    Homework Statement A circular metal plate of diameter D needs Q Joule of heat to expand and the temperature changes from 40oC to 58oC. What is the thermal energy needed to expand identical metal plate having twice the diameter for same increase in temperature? Homework Equations Q = mcΔT The...
  26. C

    Global Ice melt and heat balance

    Can anyone point to a refereed paper exploring the heat absorbed by melting around 500 GT of ie per year (Antarctic - 127 GT pa; Greenland 286 GT pa; sea ice, glaciers estim. 100 GT pa)? As latent heat of fusion is 333.55 KJoules per Kg, I reckon the heat absorbed per year is around 1.67 X 1023...
  27. P

    Thermodynamics Problem: Calculate the heat input for this work output

    Homework Statement An inventor claims to have developed a device with the following properties: net work output per cycle = 20,000 J heat output per cycle = 50,000 J high temperature = 450 C low temperature = 160 C Calculate the heat input per cycle. Homework Equations ΔETH = W + Q efficiency...
  28. K

    Heat diffusion into an infinite rod

    I have recently been curious about heat diffusion. If there is space in one dimension with any kind of temperature dispersed throughout, then the heat equation states that the derivative of the temperature with respect to time at any point equals some constant (k) multiplied by the second...
  29. F

    Does a good heat engine make a bad refrigerator?

    Hi all, the efficiency ##\eta## of a generic heat engine working between two temperatures is bound from above by the efficiency ##\eta_{\rm C}## of a Carnot machine working between the same temperatures. That is, if the temperatures are the same, a (ideal) Carnot machine is better than any...
  30. K

    Latent Heat: An Alternative Explanation

    1. In studies of the heat budget of the global free atmosphere, the concept of “latent heat” (now known as “enthalpy of condensation”) plays an important role[1]. 2. Both observation and experiment confirm that when humid air condenses the temperature of the remaining air increases[2]. 3. This...
  31. F

    Can a defective DRC on a heat pump cause the fan motor to go bad?

    I noticed that the outdoor fan on my residential, split-system heat pump stopped working in mid-October. I don't know for sure exactly when my outdoor fan on my heat pump stopped working. It might be that my outdoor fan did not work for months before I noticed that the outdoor fan did not work...
  32. F

    Why does the outdoor fan on a heat pump need to run on heat mode?

    The outdoor fan on heat pumps always runs when the compressor is pumping refrigerant when the heat pump is in heating mode unless the heat pump has defect(s). I don't understand why the outdoor fan on a split system heat pump needs to run when the heat pump is in heating mode. When a split...
  33. Lukeblackhill

    Heat during the Day: Answers to Your Questions

    Hi! My question is: I understand that at noon-day it’s hotter because of the angle with which sun rays enter our atmosphere. But at the same time, I was wondering that the band of radiation responsible for heating things is infrared, and that at noon basically all bands of lower frequency than...
  34. S

    What exactly produces and regulates body heat?

    I read some Yogi can sleep naked at snow. Is there any scientific studies how they did it? Also what exactly regulate our body temperature? How much is the role of ATP in it?
  35. C

    How to calculate heat from enthelpy of reaction

    1. Homework Statement The chemical reaction is given: 2C2H2 + 5O2 -> 4CO2 + 2 H2O. ΔrH* = -1299 kJ / mol. How much heat is released when 50 grams of C2H2 is burned? Homework EquationsThe Attempt at a Solution First, I convert mass into moles. M(C2H2) = 2*12+2 = 26 g/mol n(C2H2) = m/M = 50 g...
  36. G

    What is the name of this Heat Engine?

    We all know how a thermostat works 2 different type of metal are attach together, when temperature changes 1 metal strap expands more than the other strap causing the straight metal strap to bend. 45 years ago when I was in college the professor brought a desk top heat engine to class. He...
  37. YoungPhysicist

    B Can liquid helium conduct heat infinitely fast?

    Can liquid helium is superfluidity state conduct heat infinitely fast? I thought I have seen this is a paper somewhere a long time ago, but now I am not sure about that.
  38. D

    Heat flow in and out of a cabaret

    Homework Statement Keeping the cabaret door closed is important, so you install a sophisticated door control system that keeps the air exchange between inside and outside to a minimum. Why will such air exchanges always require the climate control system to work harder and consume extra...
  39. D

    Heating efficiency of a Heat Pump and a Space Heater

    Homework Statement Instead of pumping heat into the cabaret air from the outside air, you could simply put an electric space heater inside the cabaret. A space heater turns electrical energy directly into thermal energy. Why would operating a space heater consume more electric power than...
  40. A

    Design of a Double Pipe Heat Exchanger

    Homework Statement It is desired to heat 5130 kg/hr of cold benzene from 80 to 120℉ using hot toluene using double pipe heat exchanger. Toluene will be cooled from 160 to 100℉. The specific gravities at 68℉ are 0.88 and 0.87 respectively. A fouling factor of 0.001 should be provided for each...
  41. S

    Help with Heat of Neutralization Homework

    Homework Statement Im confused about this and need help We did heat of nuetralization lab where we reacted 25mL of HCL and 25mL of NaOH using calorimeter. The temp difference was an increase of exactly 7degC One question asks me to show q_water (J) and to assume 50g water for the calculation...
  42. P

    Calculating Heat Released During Water Freezing

    Homework Statement Calculate the amount of heat emitted when 12.4 g of water freezes to solid air. Homework Equations heat of fusion = 6.02 KJ 1 mol H2O = 18.02 g H2O The Attempt at a Solution 12.4 g H2O x 1 mol H2O/ 18.02 g H2O x (-6.02 KJ) / 1 mol H2O = - 4.14 kJ I am unsure whether the...
  43. S

    Can I get specific heat without a final temp? (heat of Rxn)

    Homework Statement I have delta H _solution, and also the mass of the solitd and q_water and q_reaction. Im using Dulong Petit to get MM but I need specific heat of the solid obviously. I don't have a final temp of the unknown solid, just the delta T for the water thanks for any help Homework...
  44. H

    Why doesn't Q=0 instead of Q=W if T=constant in first law?

    My understanding of heat is the energy transferred as a result of temperature imbalance between systems. If two systems at different temperatures are in contact with each other, a temperature change for both systems and an energy transfer Q is occurring. It is known that Q=W for a closed...
  45. A

    Specific heat at constt. volume of an ideal gas

    The ans comes out (c) if I take specific heat at constt volume to be independent of temp. Whether the specific heat is always temp. independent for an ideal gas??
  46. D

    Electrical Conductor is in relation to heat transfer

    Homework Statement One of the two glass panes in each window is coated with a transparent electrical conductor. Why does this coating improve the window's insulating ability? Select one: a. The transparent conductor is black in the infrared, with a low-temperature emissivity of almost 1. b...
  47. K

    Polypropylene question: "high heat tolerance"

    The following red highlight is quoted from a website " 5. PP: polypropylene. PP is used to make yogurt containers, deli food containers and winter clothing insulation. PP actually has a high heat tolerance and as such, does not seem to leach many of the chemicals other plastics do." However...
  48. Akash47

    A wet cloth has been hung out to dry....

    Homework Statement Wet clothing at 0°C is hung out to dry when the air temperature is 0°C and there is a dry wind blowing. After some time, it is found that some of the water has evaporated and the remainder has frozen. Estimate the fraction of the water originally present in the clothing which...
  49. N

    What will happen to the heat input of the two-phase system?

    If I have a tank half-filled with low boiling point liquid at ambient temperature, then this tank is placed inside dry oven whose temperature is kept to be around 5℃ above the liquid boiling temperature. A fan is placed inside the dry oven as an effort to make temperature distribution even or at...
  50. M

    Heat Energy and Power -- Heating ice in a copper pan

    Homework Statement Calculate the power needed to heat a 1360 gram chunk of ice in a 600 gram copper pan from 0 ◦C to the system’s final temperature of 35◦C in a time of 10 minutes. Homework Equations Q=mcchange in temp Q=mLf P= energy/time The Attempt at a Solution I thought that adding the...
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