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).
Homework Statement
I came across this equation ##L / T = \Delta S## and am not too sure about its derivation.
From what I know, ##L = Q/m## and ##Q = TdS ##.
Substitution gives me ##\Delta S = mL / T## which isn't correct.
Could someone assist me in understanding the derivation?
Thanks...
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When mixing a strong acid and water, the temperature increases. There is production of water molecules from H + and OH- ions. If you plunge a glass of pure water into an intense electric field, the ions present in the pure water will migrate. The pH equilibrium will no longer be...
Homework Statement
A standard man climbs 15 m up a vertical rope. How much energy (in cal) is dissipated as heat in a single climb if 23% of the total energy required is used to do the work? (Assume the standard man has a mass of 70 kg.)
Homework Equations
Q = mgΔh
The Attempt at a Solution
I...
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I am reviewing some thermodynamics and heat engines. Heat engines are cyclical machines able to convert a portion (just a portion) of the thermal energy extracted from a hot reservoir into mechanical work. The residual thermal energy must dump into a lower temperature reservoir...
Hello.
I have an 'Earth and Space Science' topic test tomorrow.
Heavily revising, I come across a section that will be in the test: geothermal energy.
It works by cold water being pumped down in pipes, underground and then back up, hot, in form of steam to spin turbines and generate...
Homework Statement
A 2.56g sample of anthracene, C14H10, was burned to heat an aluminum calorimeter (mass=945 g). The calorimeter contained 1.50 L of water with an initial temperature of 20.5 C and a final temperature of 34.3 C.
a) Calculate the molar heat of combustion of anthracene...
I'm involved in a project with central heating. Due to a miscalculation the apartment radiators are about 50% too large. The current system water flow is based on the assumption that the radiators are the correct size (i.e. smaller), even though they are not. Due to this the water takes longer...
Homework Statement
The experiment :
How the elasticity of material might change under heat treatment?
The experiments conducted in two different way, first one the hot bobby pin set to cool down slowly after heated (the professor called annealing treatment), and the second one the pin set to...
I only have a background in mathematics, and I lack knowledge on this matter.
I want to get quantitive value about that problem.
What would be the kind of wave or EM field that could heat human tissu of 1°C in (say a body part like the thigh), say in one hour, at a distance of 2m ?
We could...
Homework Statement
Hi all,
I came across these steps in my notes, relating to a step whereby,
$$\hat{G} (k, t - t') = \int_{-\infty}^{\infty} e^{-ik(x - x')}G(x-x' , t-t')dx$$
and performing the following operation on ##\hat{G}## gives the following expression,
$$[\frac{\partial}{\partial t}...
Homework Statement
Hello Everyone,
We did an experiment using 3 types of heat exchangers this week, double-pipe, shell in tube and plate type. Water was flowing in the HEs, the temperature was set. We had to change the flow-rate only. After the experiment, we were given lots of online...
Homework Statement
Question C(ii)
Homework Equations
dQ/dt =-kA(dθ/dx)
dQ/dt = (θ1-θ2)/ ((lx/kxAx)+ (ly/kyAy))
The Attempt at a Solution
So the first time I tried at this question, I was using the second equation provided above,but when I check the answer, they put the area on the numerator...
Hi, wondered if anyone can give me a pointer on this problem I am working on.
6 Diesel engines each with power 55kW running, given output cooling water temperature of 80°C, and required return temp of 60°C. The coolant is to be fed through a heat exchanger, with the heat exchanger outlet to be...
Homework Statement
Question (b) (iii)
Homework EquationsThe Attempt at a Solution
The energy required to melt the ice is
Q1=mL=3*0.025*3.3*10^5=24750J
The energy released by water is
Q2=mcT=0.33*4200*(22-T)
Shall I calculate the energy that the ice needs after it melts into water?
i.e...
I am trying to write code for analytical solution of 1D heat conduction equation in semi-infinite rod. The analytical solution is given by Carslaw and Jaeger 1959 (p305) as
$$
h(x,t) = \Delta H .erfc( \frac{x}{2 \sqrt[]{vt} } )
$$
where x is distance, v is diffusivity (material property) and t...
Homework Statement
Here is the original question (just read the English version).
Homework Equations
Q = mcθ
Specific heat capacity of water, c = 4200 J/kg °C
The Attempt at a Solution
I did Q_(absorbed) = Q_(released)
mcθ = mcθ
mθ = mθ
And I solved for the final temperature, which is...
The solution of 1D diffusion equation on a half line (semi infinite) can be found with the help of Fourier Cosine Transform. Equation 3 is the https://ibb.co/ctF8Fw figure is the solution of 1D diffusion equation (eq:1). I want to write a code for this equation in MATLAB/Python but I don't...
Homework Statement
Calculate q, w, ∆E, and ∆H for the process in which 93.0 g of nitrous oxide gas (N2O) is cooled from 179°C to 55°C at a constant pressure of 4.00 atm.
Cp(N2O) = 38.70 J K-1 mol-1
Homework Equations
q= mCΔT
ΔH=n(Cp)=n(qv)ΔT
ΔE=q+w
w= -pΔV
*Probably something else too but I'm...
Homework Statement
A fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15% butene (C4H8) by volume.It is to be fed to the combustion chamber in 10% excess air at 25oC, where it is completely burnt to carbon dioxide and water. The flue gases produced are to be used to generate 5...
Hello,
After the last post I completely changed the system. I now have a new system. Based on the feedback from last time I increased the time in contact with the block significantly. And I have made it a two stage unit.
Here are the parameters for the first stage. An Aluminum block. (assume...
Homework Statement
Find the expression for c_p - c_v for a van-der-waals gas, with the equation of state
\Bigg{(}p+\dfrac{a}{V^2}\Bigg{)}(V-b)=RT
Homework EquationsThe Attempt at a Solution
Basically I've proved
c_p - c_v = \Bigg{[} p + \Bigg{(}\dfrac{\partial E}{\partial V}\Bigg{)}_T...
Capillary action is a form of work, i.e. an object (water) moved by a force (capillary action) over a distance.
Since all work requires energy, what supplies the energy for capillary action? Is the chemical energy of the water increased by adhering to a surface? Perhaps the heat energy of the...
Homework Statement
There is a picture attached showing the entire problem.
Equation 2.78 is the Clausius Clapeyron equation.
Homework Equations
Clausius Clayperon equation.
L = L'T (since there is a linear dependence on temperature)
The Attempt at a Solution
$$ \frac{de_s}{dT} =...
Homework Statement [/B]
Phospine exist in three forms. known as the \alpha, \beta and \gamma forms. The \alpha and \beta forms are in equilibrium with each other at 49.43 \, K, and the \alpha and \gamma forms are in equilibrium at 30.29 \, K. Obtain the molar heat of transformation for the...
since specific heat c changes with temperature, but its treated as a constant in the heat formula, so that means that heat formula Q=mc(T2-T1) is just an approximation? correct?
I see some texts define heat as Heat, q, is thermal energy transferred from a hotter system to a cooler system that...
Homework Statement
I have the heat equation
$$u_t=u_{xx}$$
$$u(0,t)=0$$
$$u(1,t) = \cos(\omega t)$$
$$u(x,0)=f(x)$$
Find the stable state solution.
The Attempt at a Solution
I used a transformation to complex to solve this problem, and then I can just take the real part to the complex...
Homework Statement
I need to find the time it takes to heat a vessel of water which is closed.
Here is what I have:
Specific heat capacity of water: 4184 J kg^-1 K^-1
Density of water: 1000 kg m^-3
Volume of water added and volume of vessel: 500 L or 0.5 m^3
Heat capacity of the vessel: 91000...
Homework Statement
A great deal of effort has been expended to find “high temperature superconductors”: materials that are superconductors at temperatures higher than the boiling point of liquid nitrogen (77 K). Most of the older superconductors had to be operated with liquid helium (boiling...
I'm a bit confused as to how to imagine a negative sensible heat flux near the Earth's surface. Negative means that sensible heat is moving towards the surface. My book states that that would mainly occur at nighttime.
During day there is a positive sensible heat flux and sensible heat moves...
But not for the reason or application you might think...lol
I live in SE Texas, just south of Houston. It is hot as balls here in the summer. (Which accounts for three of our seasons here) My neighborhood is on a "community well" type water system, and the well is in the back of the...
I would really like a logical explanation for some of the factors that affect convective heat transfer coefficient. I have only found mathematical one.
For example:
1) Properties of the fluid:
1)Velocity: My professor said that the lower the velocity the more time the fluid gets to interact...
Homework Statement
A short metal cylinder 145 mm in diameter and 145 mm high at 1045 K
is suddenly exposed (all sides exposed) to a room air temperature at
300 K with h=25 W/m².K. Assume that for the metal k=40W/m.K, den=7800 kg/m3
and Cp=c=600 J/kg.K. Estimate (a) the time required for the...
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Hello all! This is my first post in this forum. I am struggling with the following question regarding a hair dryer. The hairdryer can be seen as a cilinder with a fan inside blowing air at speeds from the table below and 1 nichrome wire which heats up consuming different...
I am looking at an Energy Balance equation (see images) for latent and sensible heat. However, I don't understand the terms 'advection of latent heat' Alat and 'advection of sensible heat' Ah. They positively enter the system, but how do they differ from latent and sensible heat itself?
Homework Statement
The second law of thermodynamics says that we cannot have an engine which converts all the heat into the work.This is because an engine has to work in cyclic process and we cannot have cyclic process which converts all the heat into the work. Right?
For example, in Carnot...
Homework Statement
Homework Equations
I'm not sure.
The Attempt at a Solution
I tried to solve this as you would with electric charges. I added up the temperatures and then divided by 2, to get (C) 17.5 degrees Celsius. The answer key gives the answer as (D) 20.0 degrees Celsius. I'm not...
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Assuming that by the word "Work", work on the system is meant.
Both heat and work is energy in transit.
I think heat is work done by constituent particles of a system on another system in contact.
Now the work done by us on a system...
Hello,
I got this problem but I don't know How can Find Heat loss (or gain) - Q3 - from the curved surface of the metal rod to the surrounding.
This is the problem:
A metal rod, of diameter (d) and length (L), runs between two hot walls at temperatures, T1 (Wall
1) and T2 (Wall 2)...
Homework Statement
https://i.imgur.com/f2vSXtq.png
Homework Equations
https://i.imgur.com/Kjy1Tzh.png
The Attempt at a Solution
In this question, the pressure is different at different point, in other words it is not constant throughout the system. Why the solution use c(p) (or "enthalpy" h...
Hello,
I have studied about heat transfer through conduction only in steady state but I wondered about this problem that I created.
Suppose you have a box that is insulated from all sides but Suppose a constant heat flow from that wall. Inside that box you have M kg of water at the same...
Homework Statement
Modify the initial conditions (for the diffusion equation of a circle) to have the initial conditions ## g(\theta)= \sum_{n=-\infty}^{\infty}d_{n}e^{2\pi in\theta} ##
Using the method of Green's functions, and ## S(\theta,t)= \frac{1}{\sqrt{4\pi...
So, if frequency(max) of light emitted from an object proportional to temperature in kelvin, how can sun have max frequency around the yellow region while blue flames are much less hot?
My doubt it is simply if have other reason to don't use this principle for the specific heat of diatomic gases.
Homework Equations
$$U=NkT=nRT$$
$$u_n=\frac{U}{n}=RT\text{ molar energy}$$
$$u_N=\frac{U}{N}=kT\text{ average energy}$$
$$Z=\sum{e^{-\omega_i/kT}}\text{ with $\omega_i$ particular...
Homework Statement
Show that k(x,0)=δ(x).
Where k(x,t) is the heat kernel and δ(x) is the Dirac Delta at x=0.
Homework Equations
k(x,t) = (1/Sqrt[4*π*D*t])*Exp[-x^2/(4*D*t)]
The Attempt at a Solution
I am just clueless from the beginning. I am guessing this is got to do with convolution...
Hi All
I need to do an evaluation of a pilot plant heat exchanger that we have installed and see if it would be better suited than our current bigger installations. I was trying to calculate the effectiveness of the heat exchanger but I keep on getting 1 with the NTU method. Below is the...
Air is flowing through a pipe, through a heater matrix.
Flow, Inlet temperature and heater power vary. Is it possible to calculate the heat capacity of the matrix by using the Inlet & outlet temperatures, power & flow?
I'm assuming no heat loss to the pipe walls to make it easier, but I'm not...
Homework Statement
'A shell and tube exchanger is used to do heating, with single shell and 2 tube passes. There are 70 tubes each with an outside diameter of 25mm and length of each tube pass is 6m. '
I am wondering whether the 70 tubes are in between the 2 tube passes, or is it 1 tube pass...
Hello,
So I am assembling some testing equipment. I have an active circuit, microcontroller, and two battery packs inside a black polypropylene case (which is around 1 ft x 1 ft x 0.5 ft). I was performing a thermal analysis because I want to make sure the electronics do not heat up past around...
##\displaystyle \frac{\partial u(x,t)}{\partial t}-p(x) \frac{\partial^2 u(x)}{\partial x^2}-\frac{\partial p(x)}{\partial x}\frac{\partial u(x)}{\partial x}=f(x,t)##.
With periodic boundary conditions: ##u(x,t)=u(x+2\pi,t)##. The right hand side is also a periodic function of space, and it can...
Hi I am trying to do a transient heat transfer calculation.
The water flowing through the pipe is laminar (1 m/s, id = 0.0127 m, Re_d = 0.01) transferring heat to the pipe via convection, then the pipe (od = 0.015875 m, l = 144 m) transfers heat to the ground again via conduction.
I found this...