# What is Heat and thermodynamics: Definition and 60 Discussions

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering and mechanical engineering, but also in other complex fields such as meteorology.
Historically, thermodynamics developed out of a desire to increase the efficiency of early steam engines, particularly through the work of French physicist Nicolas Léonard Sadi Carnot (1824) who believed that engine efficiency was the key that could help France win the Napoleonic Wars. Scots-Irish physicist Lord Kelvin was the first to formulate a concise definition of thermodynamics in 1854 which stated, "Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency."
The initial application of thermodynamics to mechanical heat engines was quickly extended to the study of chemical compounds and chemical reactions. Chemical thermodynamics studies the nature of the role of entropy in the process of chemical reactions and has provided the bulk of expansion and knowledge of the field. Other formulations of thermodynamics emerged. Statistical thermodynamics, or statistical mechanics, concerns itself with statistical predictions of the collective motion of particles from their microscopic behavior. In 1909, Constantin Carathéodory presented a purely mathematical approach in an axiomatic formulation, a description often referred to as geometrical thermodynamics.

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1. ### B Efficient way to warm a concave body such as Pita bread

What is the optimal and efficient way to warm a concave body on a plain source of heat (such as heating concave pita bread) on its peak top or opposite (on the larger surface with gap)? Imagine you have a body in U shape. Is the best way to warm it with the U position or opposite?
2. ### Thermodynamics - Hot copper block dropped in ice water

1) Q=m*L -.10*333 2)Q=mc deltat -.10*381*180-0 im unsure about the rest
3. ### B Temperature of container, temperature of contents

someone claims that the metal of a beer can can be colder than the beer itself when the ambient temperature of the room was warmer than the beer originally was. Can someone with a physics background back me up on this or am I completely wrong? The beer came out of the fridge at fridge...
4. ### A Can the Magnetocaloric effect be used for heating liquids?

There's a recent article about cooling hydrogen in an industrial scale with the magnetocaloric effect. Read the article here But where does the heat go there? Can it be used for heating liquids? Could it be used for an ecologically and economically viable source of energy like a heat pump...
5. ### A Discretization of diffusion equation of a fluid in movement

Hello, I want to model the thermal behaviour of a moving heat transfer fluid in 1D, with convective exchanges with the walls. I have obtained the following equation (1 on the figure). I have performed a second order spatial discretization with decentred schemes at the extremities (y = 0 and H)...
6. ### 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...
7. ### Splitting Rock with Superficial Heat

Hi. I'm an amateur mason - I currently use drills and plugs to split granite boulders. I've used sledge hammers, chisels and levers. I've dropped rocks, used hydraulic presses and tended fires to crumble and split rock. It's hard work. It's long hour work. I'm wondering if there's not a better...
8. ### I Difference between the thermal and mechanical efficiency

Hello, I'm confused between the difference between the thermal and mechanical efficiency of a Sterling heat engines or heat engines in general. I hope you could be able to guide and help me. Thank you
9. ### Heat transfer problem for a long rectangular bar

Summary:: Determine the temperature distribution in a bar (very long– 2D) with rectangular cross section, in steady state, with imposed flux at one face, convection at the opposing face (Tinf, h), and imposed temperature (T1) at the two remaining walls. I am trying to find the analytical...
10. ### 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
11. ### Heat conduction in a solid

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...
12. ### 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...
13. ### White Roof Vs. Black Roof on a house

Homework Statement Your house will have a white roof, rather than the traditional black roof. A white roof reflects 90% of sunlight (its high-temperature emissivity is almost 0) but emits its own thermal radiation with almost perfect efficiency (its low-temperature emissivity is almost 1). How...
14. ### Ceiling fans and room cooling Physics question

Homework Statement Why will operating ceiling fans during the winter improve the house's heating efficiency and reduce the heat flow between the ceiling just below the attic and the cold attic itself? a. Stirring air always makes it feel warm and helps prevent thermal conductivity. b...
15. ### Is this question regarding insulation in a house correct?

Homework Statement 2. The attic of your house will be vented to the outside and neither heated nor cooled. It will become relatively hot in summer and cold in winter. You will therefore need to put thick insulation in the attic floor to reduce heat flow between the air below that floor and air...
16. ### Variation of energy but constant entropy

Hello; If a system receives a thermal energy Q, can it keep its entropy constant (that is, with equal value before it receives the energy) without wasting the energy received?
17. ### Heat in Crowded Places: Origin and Explanation

So, I have noticed that when people are crowded in small rooms, it feels hot. In fact, everyone in the crowd feels hot and starts sweating. I am wondering about the origin of all this heat. I do know that by first law of thermodynamics, if two people touch each other and if one of them feels...
18. ### How many energy requires to increase 1℃ of 1 liter of water using MICROWAVE?

we planning to heat water directly using microwave for industrial purpose. we need only 33deg Celsius for that I need this.
19. ### Telescope dew heater band

I want to make my own scope dew heaters, I have 8 meters of nichrome band, with 1,82 ohm/meter resistance. How do I calculate the length for a specific temperature (around 8 Celsius over ambient) and how to wrap it i.e. in a coil or in a series of parallel 320° circles? The circumference of the...
20. ### How to design canal to reduce stream temperature?

If i have atm temperature around 32 deg Celsius, volumetric flow 6000m3/h, fluid temperature inlet 47 deg Celcius. How to get minimum possible dimension for my canal if its maximum possible length is 180 m and fluid temperature outlet at least 40 deg Celcius?
21. ### I A question about dehumidifiers and condensation

Hi guys! My question is about the heat sinks (cold side) used in some dehumidifiers. It appears that thick, well spaced fins are used, as opposed to a larger number of thin fins, which I would expect to provide better heat transfer. Am I right in assuming that this is to allow space for...
22. ### 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...
23. ### Calculating thickness of insulation, rate of T rise and fall

Homework Statement A.[/B] Someone is walking outside when the temperature of the air is -10°C. The metabolic rate of walking is 140 Cal/m2hr, and the usual muscle efficiency (20%) applies. They are completely covered by clothing with a coefficient of thermal conductivity of 0.36 Cal-cm/m2hr...
24. ### Heat Transfer. Ice and steam in a container (easy)

Homework Statement "In a container of negligible mass, equal amounts (in weight) of ice at 0◦C and steam at 100◦C are mixed at the atmospheric pressure. Assuming no heat exchange with the surroundings, what is the temperature when the system reaches equilibrium? What are the fractions of...
25. ### Heat exchange in an isolated system

Homework Statement In a container of negligible mass, equal amounts (in weight) of ice at 0°C and steam at 100°C are mixed at atmospheric pressure. Assuming no heat exchange with the surroundings, what is the temperature when the system reaches equilibrium? What are the fractions of weights of...
26. ### Otto cycle combustion heat question

I have been trying to determine the efficiency of an ideal Otto cycle based on the compression ratio of my car and the heat of combustion of gasoline and I think I'm not entierly wrong but there is something quite off. When trying to calculate the temperature of the combustion stage my result...
27. ### How increase in evaporator increases Refrigeration effect?

It appears very non intuitive to me seeing TS diagram of vapour compression system; Area under the curve increases. But how seriously how higher evaporator temperature will lead to higher refrigeration effect. Refrigeration effect means lower temperature.
28. ### What will be the equilibrium state in the liquid N2 chamber?

Suppose there is a test chamber containing liquid nitrogen. The container is insulated and only a small opening is there so that chamber is exposed to atmospheric condition. As the saturation temperature of liquid nitrogen is -196 degree Celsius at 1 atm pressure. chamber will remain at -196...
29. ### Prove dQ is an inexact differential

Homework Statement ##dz=Mdx+Ndy## is an exact differential if ##(\frac{\partial M}{\partial y})_x=(\frac{\partial N}{\partial x})_y##. By invoking the condition for an exact differential, demonstrate that the reversible heat ##Q_R## is not a thermodynamic property. Homework Equations...
30. ### Constant pressure specific heats when temperature changes

Homework Statement Im trying to understand what would be the correct approach for calculating the constant pressure specific heat for an ideal gas undergoing a process where the temperature is changing. The reason I am asking is because the equation used to calculate Cp0 is dependent on the...
31. ### Fourier's Equations: difficult problem

Homework Statement So I have a problem where I have a series and two other parallel insulators bringing a system from a temperature of Tzero to Ttwo. However, the two aforementioned temperatures have a huge difference thus causing kappa to vary with temperature. I am trying to know how to...
32. ### Which will boil faster: steel ball in container or just water?

Homework Statement Case 1: Which will boiling faster the container having steel ball dipped in it or container having only water? Case 2: Which one will attain thermal equilibrium faster? Consider balls are just in middle of the container. every condition of each the cases have same volume...
33. ### A problem in thermodynamics

Homework Statement Please see the attached image Homework Equations pv=nRTThe Attempt at a Solution i don't know how to calculate the work done by the gas in the question and i calculated the change in internal energy.
34. ### Inverse Square Law, Temperature Change, and Heat Source Temp

I've been trying to wrap my head around the relationship between temperature increase of an object at a distance and temperature of a heat source. From what I've found, the temperature increase of an object from thermal radiation is affected by the inverse square law...
35. ### Heat conduction and phase changes

Homework Statement Suppose we have a lake and a layer of ice on top such that the bottom of the lake is maintained at a constant temperature T_{bot} which is above the freezing point of water, and top of the ice is maintained at the air temperature T_{air} which is below the freezing point of...
36. ### Temperature change in ice water interface

A metal block at 500 K is kept on a large ice slab at 273 K.The metal block completely sinks inside the ice slab. I was told that the water in contact with ice would not change its temperature while the block sinks down and hence the "only" heat transfer from the metal block to ice slab will...
37. ### Efficiency of Irreversible Engine

I have a small confusion that can an irreversible engine have greater efficiency than reversible engine if both have different source and sink temperatures?I know that under same conditions reversible engines are more efficient but what can be concluded under different conditions like both...
38. ### Answer: Is My Logic Correct: Reversible Processes & Heat Transfer?

If for two reversible processes we have the same internal energy change, if work done is maximum for one, is heat transfer minimum and vice versa? The logic that I use is that since dU=dQ+dW, for constant dU if dW is more for one, heat transfer dQ is less and vice versa just to keep the sum...
39. ### Compute work in Carnot Refrigerator

Homework Statement The temperature inside the room ##T_I= 25 C ## and the temperature outside the house is ##T_O = 32C##. The temperature difference causes energy to flow into the room (by conduction through the walls and window glass) at the rate 3,000 J/s. To return this energy to the...
40. ### How to calculate amount of vapor given q(t) and p(t)?

Hi everybody, I am trying to build a small model which basically should be able output "mass flow of water vapor as a function of time" given following inputs: - initial mass liquid water m_l_0 [kg] - initial temperature of liquid water T_l_0 [°C] - initial pressure p_0 [Pa] - heat added as...
41. ### Time for a steel die to reach temperature

Hello. I will be doing some experiments with boron steel. The idea is to heat a steel specimen (200x20x1,5 mm dimensions) to 950°C and then quickly transfer it from the oven to the die at room temperature. When the specimen reaches the steel die it will supposedly be at around 800°C. At this...
42. ### Heat Transfer through a cooking pot

Hello, I am working a designing a cooking pot with thermoelectrics integrated into the design. I am trying to find the heat flow through the pan to estimate how much electricity the design will produce. First off some constants - The design has a base area of .0491 m2, or a diameter of 25 cm...
43. ### How can boiling water freeze faster than water at room temp?

Hi guys n girls, I have a real conundrum today. There us a rumor that if you put 2 pots of water, that are absolutely identical except that in one the water is boiling hot in the other it is room temperature, the one with the boiling water freezes faster. How can that be ? Pure logic dictates...
44. ### Calculating the Heat Capacity of Diamond

Homework Statement Heat capacity is the ability of the material to store energy internally. If I completely insulated diamond and I put heat into it, It would have the ability to store 6.57 (Joules/mole) per degree Kelvin. Use this formula q=Cp (ΔT/ Δt) where q is heat in Watts, ΔT is...
45. ### Heat Transfer by Nichrome wire and Steel

Hello all. I want to do some experiment but I thought I would go over this theoretically before trying out and now I have a doubt. Homework Statement I have a driver which produces say 600mA. I connect the driver to one end of Nichrome Wire. And the other end of Nichrome wire is in contact...
46. ### Thermal Resistance due to Convection Heat Transfer

Homework Statement 1) A typical wall construction for a single-family residence might consist of 0.375 inches of outer sheathing (insulating board, hardwood siding, etc.), 3.5 inches of mineral fiber insulation and then a 0.375 inches inner surface (gypsum, etc.). Typical thermal...
47. ### Uniformity of thermal vibrations

Hello, I have a question on the nature of vibrations due to thermal energy. Earlier today I read this article which talked about cooling a glass string to near absolute zero using feedback from a high precision sensor. http://phys.org/news/2015-08-smallest-vibration.html what I understood from...
48. ### Rate of water cooling through copper pipe?

So say I have a tank of water of about 2000mls which is at around 80 degrees celsius and is pumped around a copper system which is 3/8th inch thick pipe. how many meters would the water have to travel through copper pipe to return to ambient room temperature of about 20 degrees celsius. any help...
49. ### Numerical modeling of hot magma

Ok, I've built a numerical model to show the cooling of hot magma sills entered into the crust over time. The results show that the volume of the "hot" zone when the emplacement of a constant volume of hot sills is all done will vary as a matter of two things: the overall rate at which the magma...
50. ### Heat transfer of a hot plastic thread in a cold water bath

Hi, I'll describe my problem more specific. I have a continuous flow of this polymer thread (polystyrene) at 465 °K (190°C sorry I'm metric) that needs cooling down. It passes trough a water bath which is kept at 310°K (35°C). Now i try to calculate the heat exchange into the water, to...