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. T

    Heat Transfer and Combustion: Estimating Heat Loss in Insulated Pipes

    Question: A pipe of outside diameter 200 mm is lagged with an insulating material of thermal conductivity 0.06 W m–1 K–1 and thickness 75 mm. The pipe carries a process fluid at a temperature of 300 °C and the average temperature of the outer surface of the lagging is 45 °C. (a) Estimate the...
  2. R

    Calculate Resultant Temperature: 100g Steam at 100°C + 500g Ice at -20°C

    1. The problem What is the resultant temperature when 100g of steam at 100°C is passed through 500g of ice at -20°C.Homework Equations Q=mCDeltaT[/B] The Attempt at a Solution I am not sure whether both the quantities will combine to from water
  3. CHANDRABHAN

    Can black body retain it`s absorbed heat energy?

    Can black body retain it`s absorbed heat energy? If yes, then why we can not convert this energy into a usefull form such as into electric energy as solar do?
  4. G

    What Is Cv for an Ideal Gas with Cp = 35.4 J/mol⋅K?

    Homework Statement If Cp for an ideal gas is 35.4 J/mol⋅K, which of the following is Cv for this gas? a. 12.5 J/mol⋅K b. 20.8 J/mol⋅K c. 29.1 J/mol⋅K d. 27.1 J/mol⋅K e. 43.4 J/mol⋅K Homework Equations ΔH = ΔE + Δ(PV) = Q + W + Δ(PV), and for ideal gas, ΔH = nCvΔT + Δ(nRT) = nCvΔT + nRΔT =...
  5. K

    Is Infrared Light a kind of light or just heat?

    Hi guys I know we feel infrared light as heat but my question is that is infrared a kind of light or just heat ? Thank you
  6. C

    How much heat in joules is needed to raise the temperature

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  7. R

    I Heat death of the universe and the 3rd law of thermodynamics

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  8. J

    Heat Transfer through multiple walls

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  9. B

    Radiant heat transfer and specific heat

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  10. Humbleness

    Heat transfer, how long it takes ice to reach melting point

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  11. M

    Heat transfer from a closed cylinder filled with fluid

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  12. T

    Radial Heat Conduction through a Cylindrical Pipe

    Homework Statement A 1.75m long PVC pipe with a thermal conductivity of 0.19 W/mK has an internal diameter of 3mm and an external diameter of 5.5mm. Inner temperature is 298K and outer temperature is 273K. Calculate the heat transfer rate through the pipe and thus the decrease in the inner...
  13. xavier_Ghz

    (Specific) Heat capacity of brass at milliKelvin temperatures

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  14. tito agiffaz efata

    Steam heating system transfers heat to a room (Thermodynamics)

    Homework Statement A steam heating system is used in winter season, The radiator of a steam heating system has a volume of 25 liters and is filled with superheated water vapor at 200 kPa and 200C. At this moment both the inlet and the exit valves to the radiator are closed. After a while it is...
  15. T

    Determining a heat pump's yearly energy output

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  16. David Dincer

    Cooling for Underwater Monitor Housing

    Hi, I have an underwater monitor housing made out of carbon fiber and an acryllic Glass on the other side. Over time the monitor heats up. I guess carbon fiber is a bad heat conductor :(. the Acryllic glass is almost 1cm thick. Does anybody have an advice on how to cool something like this...
  17. SHANKARALINGAM

    Heat Flux Calculation for Titanium & Aluminum

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  18. P

    Why don't units have match for specific heat and mass

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  19. dRic2

    Entropy and heat bath/reservoir

    If I have and object at a different temperature than the thermal/heat reservoir (whatever it's called) an heat flow will take place. If I write the entropy balance for the thermal reservoir it will be: ##\frac {dS} {dt} = \frac {\dot Q} T + \dot S_{gen}## Now I remember something my professor...
  20. Jason Louison

    Engine Finite Heat Release Model (With Heat Transfer) Help

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  21. Lukeblackhill

    Mechanical Collision: Measuring Sound & Heat

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  22. jdawg

    Heat and Mass Transfer: Heat Out

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  23. T

    Interpreting Molar Specific Heat number

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  24. J

    Final Temperature of Copper and Water in Insulated Vessel

    Homework Statement A 529 g piece of copper tubing is heated to 89.5°C and placed in an insulated vessel containing 159 g of water at 22.8°C. Assuming no loss of water and a heat capacity for the vessel of 10.0 J/°C, what is the final temperature of the system [c of copper = 0.387 J/g · K]...
  25. dRic2

    Calculating Heat Exchange Surface for Fluid Flow

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  26. P

    Building a solar cooker which can store heat

    Hi everyone, I'm currently trying to build a solar cooker which can also be used during the night / the next day so I was wondering if I can get some advice about how it can be done, especially the material that I can use to store the heat. I saw an article that said a professor from MIT had...
  27. A

    Heating a small greenhouse - heat loss

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  28. S

    A Heat equation on infinite domain

    Hi everyone, I'm reading this paper about the solution of the heat equation inside an infinite domain: https://ocw.mit.edu/courses/mathematics/18-303-linear-partial-differential-equations-fall-2006/lecture-notes/fourtran.pdf 1) Please let me know if the following discussion is correct. The...
  29. Richie Smash

    Rate of conversion of P.E. to heat for a waterfall

    Homework Statement There is a waterfall 230m high, take acceleration due to gravity to be 10 m s-2 and the specific heat Capacity off water to be 4200 J Kg-1K-1 First find the speed of the water hitting before htitting the ground using the Principle of Conservation of energy Second assume all...
  30. E

    How long to heat a given volume of air?

    Homework Statement I am working on a problem where I need to determine the time taken for an air heater with an 8kW output to heat a volume of air of 9m^3 by 25C. I am neglecting all losses at the moment. It almost seems too simple in my mind that I'm concerned I'm overlooking...
  31. B

    Transient heat transfer in a cylinder with internal heating

    hi, I met a problem about heat transfer in cylinder, if you can help, I will appreciate it. The question is simple. I want to know the transient heat distribution in a cylinder with internal heating(constant temperature not constant flux). The boundary conditions comprises two constant...
  32. Ali Durrani

    Optimum boiler pressure for Waste heat recovery system

    Hello Guys, I am a mechanical Engineer working on a semester project, to design a waste heat recovery system for a cement plant Air quenching cooler (AQC). For WHR i have to first design a AQC Boiler. According to the Data provided by the plant incharge, Air at the exit of cooler has a volume...
  33. A

    I have a material that conducts heat very rapidly

    I tested it by heating it up for 2 min on a electric stove and pour about 200 to 300 ml water in bowl and did a very quick dip in and out like that and when i touch it, it was cold same temperature as the water. I also test with aluminium but when I touch it, it was will hot I burnt my finger...
  34. J

    How to generate 100 watts of heat from a car battery

    I have lots of batteries 12 volt charged by the sun what I need is something that would draw 100 watts and give heat when connected to a car battery? I have ac heating pads, 2000 watt hot water elements lots of copper wire, light bulbs any other ideas?
  35. lavendly

    Final temperature of the water after adding heat?

    Homework Statement You add 1500 cal of heat to a cup of water at 22.5ºC. The water has a mass of 500.0g. What is the final temperature of the water? Homework Equations Q=mcΔT The Attempt at a Solution so i tried solving it by finding the energy of the water Q=(500g)(1.0cal/g)(22.5ºC) Q=11250...
  36. Y

    How to calculate heat transfer?

    I have a practical engineering problem for which I really have no background on how to solve. I am looking for help, but don't even know what field of engineering would be likely to know the answer, so not quite sure where to ask. Any formulas that I might use to calculate the answer would...
  37. N

    Would an object heat up or cool down more quickly?

    If we have two identical objects each placed in rooms at 25°C room temperature. In the first room, the object is at 0°C. In the second room, the object is at 50°C. Which object will reach the room temperature of 25°C first?
  38. R

    Wires in an circuit, different materials, heat

    Homework Statement In an electric circuit, consisting of copper wires with cross section area of Sc=5mm2 and a temperature of t=25C, a lead fuse is added melting when the copper wire temperature increases by Δt=25C. Find the cross section area of the lead fuse wire Sl=x. specific heat...
  39. Deepak dabby

    How can I cool down and heat up any liquid with the same element.

    Hlo
  40. Pushoam

    Minimum consumption rate of a heat pump

    Homework Statement Homework EquationsThe Attempt at a Solution Effiency of a heat pump is given as ## \eta = \frac { T_h }{T_h – T_c} = 30 ## W * 30/s = 6000*4.2 cal /s Minimum consumption rate = W/s = 840 watt Is this correct?
  41. P

    Heat equation and stainless-steel wire

    Homework Statement A stainless-steel wire is 0.1 mm in diameter and 1 m long. If the outside of the wire is held fixed at 20◦C, estimate the steady-state current passing through the wire when the stainless steel at the centre of the wire begins to melt.Homework EquationsThe Attempt at a...
  42. maajdl

    Surprise? Entropy changes for systems in a canonical state

    Every year since the 90's I come back to some of my pet topics in physics, like statistical physics. This time it was the reading of a Wikipedia article on entropy that surprised me. The derivation of the second law from the Gibbs entropy was unknown to me. I didn't know how heat, how change of...
  43. Paul Howard A

    Exploring Force, Heat & Rigidity: Answers to Common Questions

    From previous threads I understand that perfectly rigid bodies cannot exist. Two, perhaps, simple questions: 1. Can atoms be stretched or compressed? 2. Does a theoretically rigid/immobile object get warm when a changing forces are applied?
  44. Nikhil Rajagopalan

    Do SI Units Eliminate the Need for Mechanical Equivalent of Heat?

    When computing the rise in temperature on a body due to mechanical work, if we stick to using SI units, do we need the conversion factor called mechanical equivalent of heat. That is, can we readily equate W = Q and hence W = m x C x ΔT . Where 'm' is the mass of the substance on which work is...
  45. Luke Strand

    Finding Initial Temperature Entropy and Heat Exchange

    Homework Statement A 2.45 kg aluminium pan at 155 C is plunged into 3.58 kg of water. If the entropy change of the system is 162 J/k, what is the initial temperature of the water? Homework Equations Q = mcΔT ΔS=mcln(T_2/T_1) Q_water + Q_Aluminium = 0 c water = 4184 J/kg*K c aluminium = 900...
  46. H

    Exam help regarding heat exchanger, forced convection questions

    hello, im in bachelors mechanical engineering programme and my thermodynamics papers are in few days one question is related to heat exchangers or forced convection, but our professor has hinted that in the exam the question regarding heat exchanger, forced convection will be a case study of a...
  47. C

    Difference Between Heat & Agitation - Atomic Scale

    hello. Simple question here for somebody just learning the basics. On the atomic scale what’s the difference between agitation and heat? For example, diluting salt in water. If you increase the heat of the water, more salt dissolves. Stirring it also makes the salt dissolve more too it seems...
  48. C

    Which Type of Geothermal Power System is the Best?

    There are three geothermal systems that are commonly used: sry steam, flash steam, and binary cycle https://www.eia.gov/energyexplained/index.cfm?page=geothermal_power_plants . What are the efficiencies of the plants from best to least effecient on average?
  49. L

    Need Help Understanding Heat of Rxn and Q

    Homework Statement Homework Equations q = mCat The Attempt at a Solution I'm kinda confused the different between Hrxn and q? I know the reaction warms the water with q=mcat = 150*4.18*(59.5-20)=24766.5 J. This is the heat released from 1.25 grams of Ca which is 0.03 moles of Ca. But, the...
  50. Franz Rojas Ayala

    Heat energy input from a hot source in a heat engine

    Greetings! I did the famous "Mass Lifter Heat Engine" experiment in which a mass is put at the top of a piston enclosed within a cylinder. The cylinder is connected to an aluminium canister of air and the air inside this canister expands and contracts the piston with thermal contact. We had 2...
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