Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.
Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described in the second law of thermodynamics.
Heat convection occurs when bulk flow of a fluid (gas or liquid) carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by use of a pump, fan or other mechanical means.
Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid or gas). It is the transfer of energy by means of photons in electromagnetic waves governed by the same laws.
Assume that a closed system of cylindar filled with ideal gas consists of a movable piston.We know from the 1st law dQ=dU +dW.
According to the 2nd law mechanical energy can be totally converted into heat energy but heat energy cannot be converted completely into mechanical energy.The question...
Hello,
My house has some heat loss. As an example I know the outside door temperature. How can I calculate the heat loss delta if I reduce the door temperature by 1 degree?
I know that there is a formula to calculate a heat loss based on the U-value of a fabric. But I can't get those values...
During the procedure, 30% of heat is lost. So that means that 70% of water+container is contributing to melting the ice, right? And the other 30% contributing melting the ice is down to, well, the "heat being lost to the surroundings" (not sure what this really means).
We compute the sum and...
Hi,
I have been calculating a series of hypothesis for some aquariums/tanks situations, using heat transfer equations (conduction, convection, radiation, evaporation)
Typically we have aquariums that run at higher temperatures than the surroundings in winter and lower temperature than the...
My goal is to determine the ideal amount of air flow, in order to keep CO2 below 1000ppm and to minimize heat loss.
I calculated the following based off a similar post in this forum, and I am hoping this can be verified so I know that i am in the right ballpark and going in the right direction...
Hi all,
I have a copper pipe which has 15mm of insulation on it. The outside radius of the pipe is 17.2mm and the inside radius is 14.8mm. The insulation will have a conductivity of 0.025.
I found an question which is meant to show an equation for the heat loss in an Insulated Cylinder or...
This is a past exam paper Q.
I think i might be missing info though.
For i) i use q=UAdT
A= 35m2
dT= (80-20)
They haven't given U but if i know answer should be 1,050W
So if i set U to 0.5
(0.5)(35)(60)
= 1050W
Am i missing something or could I calculate U with the info given?
Also ii)
Use...
I do not know where I am doing wrong. I asked a tutor, he said I was doing it correctly.
Below is my work. Please help!
Net loss by radiation in 10.0 mins is 74.8 kJ
Hi,
If it is assumed the temperature of a shower is to be 43°C and the electric shower consumes 50 litres of water at that temperature, then the Energy required for an electric shower would be:
QElectric Shower = mcΔT
QElectric Shower = 50 * 4.181 * (43-10)
QElectric Shower = 6.89945 kJ or...
Hi,
I wanted to do some rough "back of the envelope"-calculations of heat losses from pipes, with water circulating in them, to compare to the results of various programs' simulations.
I was not very successful as I was perhaps hoping to get rough estimates in the range 20-200% off, but right...
Hi everyone
I'm new around here and I wonder if anyone can help please. I'm taking hot air off the chimney stack inside a factory at a temperature ranging between 700 and 400 degrees going through a 4 inch stainless steel pipe with 3mm wall thickness. This pipe line will be about 35 meters long...
Homework Statement
Find the admissible current density Jadm for a wire that has no insulation and also for a wire that has two layers of insulation and compare it to Jadm for the case when the wire has only one layer of insulation.2. The attempt at a solution and equations
In the image I've...
Homework Statement
A careless farmer sends this sheep out to graze on a very cold winter day when the temperature is -10oC. The sheep's coat has a thickness of 4.7 cm and a surface area 1.3 m2.
Calculate the rate of heat loss from the sheep on this cold day. Assume that heat is lost only...
<< Mentor Note -- poster reminded to use the standard Template >>
Question Three
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...
Question - Four
A pipe carrying superheated steam at 300 °C has an outside diameter of 120 mm and is lagged with two layers of insulating material. The first layer (adjacent to the outer pipe wall) is 25 mm thick and has a thermal conductivity of 0.072 W m-1 K-1. The second layer (covering the...
I have to build a small green house and to calculate if one heating wire is enough (or even too much...)
Just for my curiosity I would like to understand the physics implied in this.
The starting point is the desired dimensions: two modules of greenhouse with the following dimensions:
60 cm...
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...
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...
halo every one... i have question . if i have pipe inside building with 9 floor's length ,and i have calorie meter between the incoming and outgoing pipe's. how i can calculate the losses of pipe if i now that temperature inside building is 22. i want to be sure that the system working normal. i...
Homework Statement
Determine the heat loss in the circuit that is connected in series with two batteries (12 V and 6V) and two resistors (6ohms and 4 ohms).
Homework EquationsThe Attempt at a Solution
I used the difference in P = V^2/R, the power dissipated in the circuit, to calculate the...
I am new and have a math and finance background. Because of my work I am starting to get into engineering related questions, specifically in piping. I flyfish a lot and can give pointers to anyone that helps me with my questions.
Say I have a 5-10' length of pvc, metal or copper pipe that is 4...
Hi i was thinking about how to calculate the temperature lost by Degree Celsius per minute and was wondering if you had the surface area of the object, its initial temperature, a constant flow rate of air around the object and probably also need some coefficient of heat loss based on the...
I got an original side door from 1922. Needless to say it's all warped and dented around the sides. My best attempts to weatherize have failed. It's extremely drafty. Various weather strips have not worked and the storm door helps very marginally. I was about to give up and just plastic wrap it...
Homework Statement
I have a bloc sitting on a horizontal table, and we shoot a ball through it. The speed right before entering the block is v and the speed when it exits the block is v/2. I need to prove that the fraction of the initial energy that is lost due to heat is 3/4 - γ/4, where γ is...
Hello people of PhysicsForum
Apologies in advance if my prefix selection is inaccurate and for my absolute physics noobness. I know no physics jargon so I'm sure my question will be phrased in the same way a 10 year old might.
So here is my silly, trivial question:
First of all, remove all...
I'm designing an oven and want to ensure that the insulation I specify has a low enough Thermal Conductivity (k) to resist excessive heat loss. I determine heat loss (Hout)with the following equation: Hout=A*U*(T1-T0). U is dependent on k (U=k/L). I omitted the heat transfer coefficient in...
Homework Statement
Hello everyone, I hope that you guys could lend me a hand.
I need to calculate the heat loss at any point over a long pipe while considering lambda of the pipe. I am trying to use octave to find a reasonable flow-rate to keep the temperature loss to a minimum at a reasonable...
Hi,
I'm trying to calculate energy loss between two areas. One area is -25C and another is +15. The contact area(door) is 20m^2. Is convective heat transfer formula the right way to calculate it, or what should I use? I want to find out the how many kW I need to keep cold area at -25 when the...
Usually it is said that loss of heat through a chunk of material because of conduction is proportional to difference in temperature and inversely proportional to thickness of material.
E.g. if I got a wall to ΔQ = K*S*ΔT/D.
where ΔQ - is energy flow through material. K - constant characteristic...
Homework Statement
We recently did an experiment in class and we were asked to get some ideas together to try and explain our results. We measured the time it took water to fall from 70 degrees to 65 degrees C. The water was placed in a shiny steel container (which had a volume of about 400ml)...
I was reading an article about how Heineken has replaced its short stubby bottles with the standard American longnecks, with reason:
In 2013 the company replaced its old stubby bottles with a fashionably long-necked version that supposedly keeps the beer cold longer...
Hi all,
I'm sorry if this is an inappropriate question. I have built a basement swimming pool for my wife. Unfortunately I neglected to insulate outside the concrete and insulating inside the concrete has caused some construction issues so I am trying to work out the heat loss if I go ahead...
Homework Statement
A box-shaped house has a square floor. Three times as much heat per square foot is lost through the roof as through the walls, but no heat is lost through the floor. If the house encloses 1500 cubic feet, then find the area of the floor that minimizes heat loss.
Homework...
This is mainly just a theoretical question: say you have a rectangular box made of styrofoam (one of those ice cooler things) and it is levitating in air at room temperature conditions. It also has one hole at the top of the container so that heat can get out of it. Inside the box is a lightbulb...
Hey guys
Don't know if this is posted in the right category.
doing an technical report on industrial gas turbines. but i am kind of lost. Does anyone have any input to what we can write about? I'm thinking of any problems with the turbines that we can write about.
What heat loss and how much...
Hi, I'm a mechatronics student and I am currently working on a project on the effectiveness of a vortex tube to cool a cabinet. The cabinet has a thermostat inside and if the temperature exceeds a threshold, an air compressor is turned on, causing the vortex tube to cool the cabinet. The cabinet...
Hello
To calculate the heat loss of a fridge, do I need to take the surface area of the in- or outside of the fridge?
Heat loss formula = k * delta T * A
k = heat transmission coefficient
A = surface area
<< Moderator note: This thread is missing the homework template due to originally being posted in another forum. >>
hello everyone, this is my first post and I am looking for some help.
in my lab we did an experiment to calculate specific heat values for various metals using a calorimeter.
the...
I'm working on a problem involving steel structural members on the exterior of a building. I need to figure out how much insulation (for summer conditions) and possible heat tracing (for winter conditions) would be required to maintain minimum and maximum temperatures. I know I need to use the...
Hi all, I have a (probably very simple) problem that I need some help with. If I have a body of water in which the temperature of the water, ambient air temperature and mass of the water is known; how do I calculate the rate of heat loss from the water?
Using Q=m*cp*(Twater-Tair) I can find out...
Homework Statement
A 60 kg person is exercising in the gym, doing external work at a rate of 200W. If they have an efficiency of 20%, calculate the rate of temperature increase of their body if none of this heat was able to be transferred to their surrounds.
(a) 828 ◦C per hour. (b) 13.8 ◦C...
Homework Statement
Heat is convected away from an object at the rate given by the following formula:
ΔQ / Δt = h*A*ΔT
Calculate the rate of convective heat loss in watts for an unclothed person standing in air at 23°C. Assume that the skin temperature is 34°C and that the body surface...
hi.I would like to know something about the IC engine.I just read an article.It said that 30% efficiency is gone through conduction of heat by the cylinder wall.If it is reason for one of the efficiency loss why can't we build an cylinder coated with a material that is non conduction.So only...
I have a centrifugal water pump that I would like to protect during the winter months. The pipes can be drained, but there are some locations that are at risk for retaining trapped water, which can be problematic whenever we actually need to run the pumps. I am proposing that a heated...
So I'm trying to figure out where a heat tracing program is getting some numbers.
What I'm trying to figure out is how the program calculates the internal temperature of the tracing lines.
What I know is the k value of the insulation 0.0215 watts per metre*degree
I know the temperature...
Hi there, I am dealing with a pipe that is surrounded by air and trying to calculate the temperature drop. The inlet temperature is 1273K and the ambient air is 293K.
In my quest to do so I have calculated the overall heat transfer coefficient to be around 10 W/m2K, which I believe for a gas...
Homework Statement
A vacuum flask of radius r and length l consists of two concentric cylinders separated by a narrow gap containing a gas at pressure 10^-2 Nm^-2. The liquid in the flask is at 60 degrees Celcius and the air outside is at 20 degrees celcius. Estimate the rate of heat loss by...
Homework Statement
I'm struggling to understand question 1.C
How do I incorporate Tw and later eliminate this?
Homework Equations
-k*A*(ΔT/ΔX)
The Attempt at a Solution
For 1.a I used this equation: -k*A*((Tinside-Toutside)/thickness wall) I thought to put T inside first as...
Hi
Qoutation:
"Kinetic theory of matter: All matter is made up of atoms and molecules that are constantly moving.
When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases. The motion and spacing of the particles...