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).
I am not a mechanical engineer; but I have physics background.
I want to lift about 250 watts of heat from a metal block.
At the same time I have to maintain its temperature at 30 deg Cel.
For this I want to use water-air heat exchanger (HE).
Heat exchanger will have inlet & outlet pipes. Hot...
Homework Statement
Im working on the following problem and could need some help in answering them:
Work is being produced from a cycle. In order to produce this work, energy is being taking from a high temperature sources at a ratio of 1000 kJ/kg and the extra energy is being deliver to a...
In running my vacuum cleaner, I have noticed that the plug end of the cord gets warmer than the rest of the cord. Since the wire gauge and current must be the same through the entire length, why would this happen? I have noticed this regardless of the wall socket that I use and it doesn't seem...
Homework Statement
A 75.0g ice cube at 0 C is placed in 825g of water at 25 C. Find final temp.
Homework Equations
Well none really, this should be simple plugging into to heat equations.
The Attempt at a Solution
Heat required to melt ice = (0.075kg)(3.33*10^5) = 24975 J
Heat required to...
First of all, even I did mentioned Solar Cooker, the main goal is to reach most temperature of 500ml of water in 30 minutes.
Basic information that I have is some material with different thermal conductivity. I seek for simple english language and a bit complex physics language. The idea of...
Homework Statement
The mass of liquid nitrogen in an open beaker is found to have decreased by 46.3 g in 10 minutes. If the s.l.h of vaporisation of nitrogen at its boiling point is 1.99 x 105, at what rate were the surroundings heating the beaker? Why is the heat capacity of the beaker...
I have a heat source in the form of a waste oil heater for a small workshop, i get around 200 degrees C from it and it warms the workshop up nicely.
What i am wondering is is there a way i could produce enough electricty to run a small water pump from the excess heat? Something like a 12v pump...
Homework Statement
Kindly refer to part (c). The woking should be power/0.35 (what I think according to the graph). But the answer is power (that is the answer of part b) divided by 0.02
Homework Equations
I have used the ratio method simply
The Attempt at a Solution
According to part (b)...
I was wondering how a boundary layer would be dissipative of momentum if it was under the influence of a positive heat gradient.
I understand that the reason that we don't see the boundary pressure equal the stagnation pressure is that the boundary is dissipative (so excess pressure above...
I’m working on an experiment and would appreciate some guidance to characterize the performance of it. I have a small homemade copper coil submerged in a 3 gallon water tank. I’m delivering hot water to the coil that in turn heats the water in the tank. I sense I’m looking for a rate of heat...
So i did a lab were we melt an ice cube in water. So i have to find the heat of fusion for the ice cube. But i am not sure how to do that.
What i was thinking of doing is finding the energy released by temperature of the ice cube increasing, then make that value of q, equal to m*hf, when it is...
Homework Statement
A metal block of heat capacity 60 J K -1 loses 1MJ of heat energy to its surroundings. Find the decrease in its temperature.
Homework Equations
Q = m c Δ θ
Heat energy added = mass x specific heat capacity x rise in temperature
heat energy lost = blah blah blah x drop in...
Homework Statement
A 1x106 kg piece of ice is placed into a lake. How much heat is taken from the lake to raise the temperature of the ice from 0 °C to 1x10-20 °C? How much volume does the lake increase by?
Latent heat for water is 334x103 J/kg
Homework Equations
Found in my textbook,
cice =...
Homework Statement
I do not need to solve this problem, see below.
EXAMPLE 7.1
Air at a pressure of 6kN/m2 and a temperature of 300C flows with a velocity of 10m/s over a flat plate 0.5m long. Estimate the cooling rate per unit width of the plate needed to maintain it at a surface temperature of...
I was doing a science experiment involving enzymes and hydrogen peroxide, and by adding heat to the catalase, it should have sped up the reaction, but instead it slowed it down. Is there a reason why this happened?? Isn't heat supposed to speed up the reaction, instead of slowing it?
Homework Statement
Homework Equations
Heat equation
The Attempt at a Solution
I can derive E(t) to get integral of du/dt over 0 to L, which is the same as integrating the right hand side of the original equation (d2u/dx2+sin(5t); while this allows me to take care of the d2u/dx2, I don't know...
Homework Statement
n = 3.8-mol of diatomic gas is allowed to expand isothermally from Vini = 1.9-m3 to Vfin = 10.5-m3. The initial pressure is Pini = 1.38-atm. After this the gas is raised at a constant volume by a temperature ΔT = 35-K. Calculate the total heat flow into the gas.
Homework...
I have not much experience in solving pde before except using the separation of variables. I am trying to solve the following equation where omega is a box. Is there a close form of the solution? How should I approach the problem? Much thanks!
Homework Statement
A spherical shell has inner and outer radii r_a and r_b, respectively, and the temperatures at the inner and outer surfaces are T_a and T_b. The thermal conductivity of he shell material is k. Derive an equation for the total heat current thought the shell in the steady...
Hi everybody!
I was wondering, what substances do form when plastic is heated? I found on the internet that if plastic is heated in the oven (not microwave) at 325°C, it shrinks and become more thick, and it can be used for art work. I tried to search about it, but I found different opinions...
Homework Statement
a copper pot's radius is 12 cm, the thickness is 5 mm. It is placed on the stove for boiling, if the temperature of the stove is 115 oC while the water is 100 oC. How much of water that evaporates per minute
Homework Equations
ΔQ/Δt = (A)(k)(ΔT) / (L)
Q=mcΔT
The Attempt...
HOMEWORK POSTED IN WRONG FORUM, SO NO TEMPLATE
I have encountered a problem at the university in which there is a thermally isolated container of constant volume in which the number of particles and temperature change with time(the temperature increases). The change in particle number ensures...
I am building a Rapid Pulse Carbonation prototype Reactor unit, I am capturing the Steam form the process and passing it though a Plate and Tube condenser to produce water, also I will capture the CO2 gas from the heating system. How would I reduce the exhaust gas heat before I pass the exhaust...
There's one equation that I've seen being used already, which by itself is quite simple, but I can't understand where it comes from.
The context is as follows: suppose we have one heat engine operating between systems A and B whose temperatures are T_A>T_B. Let's suppose further that the...
I was watching a video in which they said that HSP is produced to help proteins fold correctly and to prevent them from tangling up and misfolding. But, if the cell is producing another protein, wouldn't the chances of tangling up and misfolding increase (because now you have one extra protein...
I need to cool a slow moving small flow of hydroponic plant water, at most 1000 ppm nutrients, with a pH of typically around 6.
I'd like to use aluminum or copper heat sink directly in that fluid stream to drop temp 10 or 20 degrees F down to 50-60F neighborhood.
My concern is I don't want...
A gas in a cylinder with constant pressure, the gas cooled down and its internal energy decreased as well as its volume. The heat Q will be flowing into the gas or out of the gas?
My try for the solution: As the volume decrease the work done by the gas will be negative.
The gas cooled down, so...
Technically, this isn't a question concerning supercritical fluids. It's more about converting thermal energy into velocity by playing "keep-away" with molecules that want to go supercritical.
The idea is simple. In an fully contained system, we can more or less say volume is static...
Hi, layman here.
As I understand, the theoretical Heat Death of the universe would imply that the accelerating space expansion reaches an expansion rate so big that it takes bodies and eventually even fundamental particles apart, leaving them alone up to an ultimate point in which no particle...
Hi,
I am looking for the reasons for the generation of heat developed in a material due to electron bombardment. Searching in the internet gives me only the estimations of the heat developed, but not the physical reasons for the heat development. Appreciate if I am provided any insight into the...
Homework Statement
Homework EquationsHEAT PRODUCED=WORK DONE BY BATTERIES - ENERGY ABSORBED BY CAPACITORS
The Attempt at a Solution
INITIALLY BEFORE SWITCH CLOSED :Initially a current flows only in the left most loop involving 4 microfarad capacitor.The charged on the capacitor during...
My longtime friend moved recently and his new place has an in-ground pool. He's a bit* of an Engineering nerd he has decided to build a solar heater from scratch. Him being a neophyte at the art of pool science though, I felt it my duty - despite being someone who never got his own custom...
This is an experiment I have wanted to do for a few years now but don't have the necessary equipment. GR tells us if you have identical objects with the same weight exactly when they are at the same temperature, then when one object is heated, it will weigh more. This is because the...
Does anyone here have experience with COMSOL?
I want to model a system where i have a fluidic channel containing warm fluid running through a block and I want to analyze the heat transfer from the channel into the block .
To establish the warm fluid I put an initial temperature condition at...
A HUGE topic of conversation on many car forums, I thought I would bring it here.
Many cars have chrome tin in the engine compartments to make them look flashy. However, for decades now, people say the chrome reflects the heat back onto the engine block and to paint the engine compartment black...
Hello, I have a final tomorrow and I am having a difficulty to understand the heat treatment subject. I would be happy if someone can explain this question or suggest a good document shorter than Askeland (i know it is very good but there is no time unfortunately). Thank you.
Two different high...
Homework Statement
I would really appreciate if you could give me some hints regarding what exactly to do at iv)[/B]
iv)
Given formulas:
Homework Equations
f(y)=(ro*R^5/E*t^2)
The Attempt at a Solution
we know that f(y)=0.75
1ton TNT=4.184*10^9 J
ro=1.003kg/m^3
We have the above...
Homework Statement
so, i had this question where i had a sphere and a cylinder with given dimensions and propreties ( roh, C and k) he also gave me initial temperatures, then both of them dipped in a bath of water of given temperature but unknown h ( convective coefficient) then he gave me the...
Homework Statement
Homework Equations
The Attempt at a Solution
I do not know exactly how to start this problem.
I would really appreciate it if you could give me some hints.
I know that e^ - t/tau=T(t)-Twall/Ti-Twall
where tau=m*cp/hA
where h=convective heat tr.coeff
and T(t) is desired temp...
Hi Guys
While studying physics for my masters (doing it in material science engineering), huge amount of questions appeared.
First, let's imagine two experiments
1) One enclosure with perfect reflective walls (R=1 over the entire thermal radiation spectra) at a temperature T1 and a body inside...
Homework Statement
State and use simple assumptions to show that ' Power is proportional to V^5' is the expected relationship for a pure tungsten filament bulb.
Homework Equations
V=IR
I=dq/dt
Q=mcT
The Attempt at a Solution
I tried to use a simple model where the rate of heat loss is...
Hey all, first time posting!
So I'm having trouble with understanding the differences between the constant heat flux and constant temperature condition when not in a textbook. Some research I have begun working on involves a strip of heat tape sandwiched between two aluminum plates which are...
Hello, i am new at the forum and i hope i can help and get helped so we can move forward in our projects/jobs/studies. I also ask please to correct any gramatical or vocabulary mistake, since i am still learning english.
Now to the actual problem.
I am already building some kind of epoxy resin...
Homework Statement
Using equipartition law, find specific heat of gas containing triatomic linear molecules. Will the result be different if the molecule was non- linear? In what way?
Homework Equations
According to equipartion theorem, each degree of freedom gets (1/2)kT kinetic energy and...
I have uploaded a page from my prof's lecture on specific heat.
Its given that average energy for each vibrational mode is $$\frac{h\nu}{e^{\frac{h\nu}{T}}-1}$$
Hence $$U=(\text{number of vibrational modes)}\times\frac{h\nu}{e^{\frac{h\nu}{T}}-1}$$
In the lecture slide, the number of...
Homework Statement
Hello, I am struggling with this heat transfer and fluid flow problem.I would really appreciate if someone could have a look over what I have done on it.
I am not sure if what I have done is correct ,I would really appreciate if you could tell me if it is correct or wrong.And...
I am trying to estimate the amount of electrical power needed to heat up a material from 20C to 1000C in 20 seconds. Assuming it is 18sqin and 3mm thick, I used the specific heat which was given as 0.78 J/gC and weight 11.39g (from the destiny of 3.26).
0.78 J/gC x 11.39g x (1000C - 20C) /...