What is Heat transfer coefficient: Definition and 54 Discussions
The heat transfer coefficient or film coefficient, or film effectiveness, in thermodynamics and in mechanics is the proportionality constant between the heat flux and the thermodynamic driving force for the flow of heat (i.e., the temperature difference, ΔT):
The overall heat transfer rate for combined modes is usually expressed in terms of an overall conductance or heat transfer coefficient, U. In that case, the heat transfer rate is:
Q
˙
=
h
A
(
T
2
−
T
1
)
{\displaystyle {\dot {Q}}=hA(T_{2}-T_{1})}
where:
A
{\displaystyle A}
: surface area where the heat transfer takes place, m2
T
2
{\displaystyle T_{2}}
: temperature of the surrounding fluid, K
T
1
{\displaystyle T_{1}}
: temperature of the solid surface, K.The general definition of the heat transfer coefficient is:
h
=
q
Δ
T
{\displaystyle h={\frac {q}{\Delta T}}}
where:
q: heat flux, W/m2; i.e., thermal power per unit area, q = d
Q
˙
{\displaystyle {\dot {Q}}}
/dA
h: heat transfer coefficient, W/(m2•K)
ΔT: difference in temperature between the solid surface and surrounding fluid area, KIt is used in calculating the heat transfer, typically by convection or phase transition between a fluid and a solid. The heat transfer coefficient has SI units in watts per squared meter kelvin: W/(m2K).
The heat transfer coefficient is the reciprocal of thermal insulance. This is used for building materials (R-value) and for clothing insulation.
There are numerous methods for calculating the heat transfer coefficient in different heat transfer modes, different fluids, flow regimes, and under different thermohydraulic conditions. Often it can be estimated by dividing the thermal conductivity of the convection fluid by a length scale. The heat transfer coefficient is often calculated from the Nusselt number (a dimensionless number). There are also online calculators available specifically for Heat-transfer fluid applications. Experimental assessment of the heat transfer coefficient poses some challenges especially when small fluxes are to be measured (e.g.
Say I have a real counter flow heat exchanger using air and water. I run a test so I know every parameter; mass flow rate of both fluids, surface area, and in and out temps.
This is great. Now I can calculate the heat transfer rate, my log mean temperature difference, and overall heat...
I have a cube with a volume of 1000m3 at an initial temp of 290K. The bottom side (10m by 10m) is open to the ambient air. I put this cube into a huge fridge and cool the whole volume by 5K. I close the open side by placing a cover on it. This cube has now got a volume of air at a temperature of...
So firstly, I don't understand if the mass flow rate is for steam or for water. If it is for water, I know I can find the heat transfer rate using equation:Q=mcdeltaT.
But then I don't know how to find h (the average heat transfer coefficient) because I don't know the surface area (As). I can...
Hi, I'm looking to find a very very basic model to calculate the heat transfer coefficient in a tube with given heat power exchanged ##Q##. The fluid inside the tube starts sub-cooled (##T_{in}## is known) but exits the tube with a quality of steam around 0.15 (pressure is supposed constant)...
I would like to fully understand two parameters involved in convection heat transfer systems. I have read the document https://fenicsproject.org/pub/tutorial/sphinx1/._ftut1005.html, and I am interested in the parameters ##r## and ##s## in eq. 69.
As far as I understand, when one solves the...
Hello, I have a question with regard to equipment design.
How do I calculate the overall heat transfer coefficient for a large pipe who has smaller pipes in it? Say I have water flowing on the large pipe, and inside it there are three pipes with hot acid in them. Assuming they flow concurrently...
Hi there,
Hopefully this is a very easy question and you all can just confirm this for me.
When calculating heat transfer into a fluid from a heated tube, is it correct to say that the heat transfer coefficient is *not* dependent on the tube diameter?
So, if we solve for T_{out}, we get...
Homework Statement
(I) Explain what is meant by an 'overall heat transfer coefficient'.
(II) Explain what is meant by fouling and what its effect will be on the value of the overall heat transfer coefficient.
Homework Equations
None provided.
The Attempt at a Solution
(I) The overall heat...
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...
I have a cuboid shaped box. It is being used as a chilling tank in my refrigeration system based on Evan Perkins cycle. For heat load calculation I tried to calculate the heat leakage in the sysyem. So I considered conduction and natural convection. I am in preliminary stage, so no use of...
Hi all!
I'm analyzing a fermenter and the water cooling system that cools it down.
In analyzing this I've found kW and kWh required to cool down the fermenter using Q = dt*cp*m
However when I try to find the overall heat transfer coefficient U using the data, I find that it varies with...
Hi All,
I have a situation were I need to evaluate the heat transfer coefficient of a horizontal surface. The surface has tubes within although I first used "flow across a bank of tubes", this has been untrue due to the air flow coming from above the surface flowing vertically (and...
I'm setting up a thermal resistance network to determine the heat loss through the insulated wall of a heated fuel/crude oil tank but i can't seem to find values for the convective heat transfer coefficient of the fuel oil (kerosene) or the crude oil at elevated temperatures. I have only found...
I am trying to design a heat exchanger for a stratified hot water tank which means that the heat transfer on that side of the exchanger will be totally dependent on free convection. I plan on using a shell and tube set-up but I have no idea on how to calculate the required mass flow rate from...
Hello, PF! Recently, while reading chapter 10 (microscopic energy balances) of the second edition of BSL, I found a minor discrepancy which is confusing me, especially when considering the mathematical analogies of heat and mass transfer.
In section 10.1, the authors introduce Newton's law of...
I am working on a model for predicting cooling in a system that evacuates a vessel and cools by evaporation of water and the water vapor is condensed in a tube and shell heat exchanger. My concern is the prediction of the steam side heat transfer coefficient as the air is removed from the...
I am working on the simulation of a heater in ANSYS. I'll explain the geometry:
- Top plate - Ceramic Porcelain material - 2.65in x 4.8in x 0.06in - carries a small heater (2in x 0.125in x 0.01in) on top of it which generates 18W of heat.
- Bottom heater - 5.8in x 3.65in x 0.03in - Stainless...
Hello,
I have a swimming pool with a waterfall feature.
I need to know how much does the waterfall contributes to cooling the pool.
I tried to use Newton's law of cooling, but I have a problem with the Heat Transfer Coefficient in this case.
Following are the Givens:
Waterfall Width= 5m...
Hi,
I need to measure heat transfer coefficient in the block channel. However, the block is not general block. Inside block, there is trapezoid object. So, water flow rate in the first is low speed because big square.
Then the square size will decrease then the speed is high.
Do you know how...
Hello all.
I need to design a radiator for 43kw heat dissipation. I have used the LMTD method for finding out the contact surface area of the radiator. But I have a small problem. I cannot find the area unless i know the overall heat transfer coefficient. Can somebody please give an estimate of...
Not sure if I'm getting this right, my answer seems very small, can anyone advise?
Question- butanol at a temperature of 28oC is pumped at a velocity of 14ms-1 through a 100mm diameter tube kept at a wall temp of 90oC. The properties of butanol are below. Determine the convective heat...
How do I find the heat transfer coefficient for a meteorite?
The meteorite is made of carboneus chondrite, but approximations with heat transfer coefficients for regular stones or rocky materials would be just as fine.
Furthermore, how would I calculate the energy required to vaporize 1 g of...
Hi, I've recently been given a series of questions on heat transfer to do and have done most of them with general ease, but this one question I've been stuck on for ages and i can't seem to figure out:
"A double pipe heat exchanger is made up from a length of 25mm i.d. steel pipe of 2.5mm...
1) PROBLEM:
Task is to find the thermal conductivity of steel experimentally.
I have conducted relevant experiments and I am trying to solve for the thermal conductivity (k) itself. My final however is ten times too large in size, and I am having trouble identifying where the error is coming...
Homework Statement
The cross section of a wall is shown in the figure below. To reduce the heat flow, an air gap (still air) of 6cm is created between the brick wall layers of 14cm thick, each. The thermal conductivities of the brick wall and the still air are: Kair = 0.032 W/m.K and Kbrick =...
1. Homework Statement and the attempt at the solution
Alright, here is a picture of the problem along with my solution:
My solutions gives the correct answer but the only part I don't understand is why the heat transfer coefficients are the same. If the two rods are made of different...
Hey all,
I'm trying to simulate a simple chip-heatsink situation in SolidWorks using their thermal modeling suite. I have found an ideal set of parametric values for the chip to work at a reasonable temperature, but I need to figure out what the convection coefficient means in terms of air flow...
Hi There
Does anyone out there know a good estimate or any real values for the total heat transfer area for the hot and cold sides of a domestic refrigeration system? i.e. the sum of the areas of the evaporator and the condenser.
For the Evaporator:
QL=UL.AL.(TL-T1)
AL=heat transfer...
let say a cylinder(steel) is 6 cm diameter and length of 3.5 cm length. and is heated to 1000 degree c.
in a room of free air and room temperature of 20.
will convective heat transfer dominate? it radiation is negligible?
what would the convective heat transfer be?
what power(watt)...
whats would be typical value for free air convection heat transfer coefficient at high temperature of 1000 degree c?
let say i have a vertical cylinder of diameter 5 cm and 3 cm high. and i heat it to 1000 degree c. the room temperature is 20c . what would the convection heat transfer...
Hi there,
I am doing a project modelling and simulating a gas engine waste heat recovery system using an organic rankine cycle.
As part of this project I would like to size the surface area of a heat exchanger (if only roughly). I have found the appropriate formula using Q = U.A.LMTD and...
I'm doing a steady-state thermal analysis for a cylinder geometry.
Inside the cylinder is a heat source and this heat is going to water channel
(modelled with FLUID116 elements) and the air.
For air convection I have to define a heat transfer coefficient which is
dependent on the flow of air...
Homework Statement
We are having a fictive, non existing heat exchanger with the following parameters:
Outer tube diameters: 20 & 12 mm
Wall thickness inner tube: 1mm, outer tube; 2 mm
flow area hot side: 0.0226m2, cold side; 0.0272 m2
The heatexchanger is going to cool some hot...
Hi,
I would like to know if somebody has the formulas to find the heat transfer coefficient while the nucleate boiling and the film boiling, for a plate heat exchanger...
I really look forward reading someone.
Thanks
Homework Statement
This is a lab report that I'm working on. I'm almost done, except for the last part which consists of finding the error in the result for our heat transfer coefficient h using Newton's law of cooling. I've tried this in different ways but I can't seem to get it right.
We...
i prepared a setup wherein i heat a nichrome wire with 3 volts battery, measure its power, the temperature of the nichrome and the temperature of air.. by using the formula
ΔT=PRsurf
where
ΔT=Tnichrome - Tair
P=VI
Rsurf=1/hA,
R is, basically, the thermal resistance to heat...
I have a circular cross-section of steel, around which I have air of constant temperature flowing. I want to calculate the heat flux, but I don't have the value of heat transfer coefficient,h (W/m^2.K) between steel and this air at 350C. Please suggest how to get the value for h. I am neglecting...
Hi all :)
I'm trying to figure out how much heat I can save from covering a tank which is open (uncovered). The tank is rectangular made of steel and is filled with water, heated to 50C, and is not insulated with any material. The outside temp and humidity is assumed to be 25C and 60%...
Homework Statement
The application of the Heat Transfer Coefficient in the case where the surface area of heat
flow is decreasing
Homework Equations
h = q/A * delta T
h = cal/sec/M2 ( C )
q= cal/sec
A= M2
delta T (C).The Attempt at a Solution
If the surface area, A, is decreasing, then is...
Homework Statement
One liter of water at 30 C (30000 calories )
A 100 gram sphere of ice at 0 C in center of water volume .
The ice will absorb 80000 calories melting, and final water temperature
= 22000 cal/1100g = 20 C.
Assume mixing and uniform water temp during melting and water vessel...
Homework Statement
One liter of water at 30 C ( 30000 calories )
100 gram (100 cc ) sphere of ice at 0 C is in center of water volume.
The ice will absorb 8000 cal melting and final water temp = 22000 cal/ 1100 g = 20 C
Assuming mixing and uniform water temp during melting ,and vessel is...
Hi,
I am in a Heat Transfer class at school and my professor has set an interesting challenge before me. It is not a homework problem or anything, just a side project he challenged us to look into relating to external flow.
The question is as follows:
In fluid (e.g air, water) flow over a...
I'm working on a project where I have to construct a cubic box, then find the heat transfer coefficient through the box. I will be placing various object in the box to run tests on how they change the eat transfer coefficient. If I want to use the equation: Q=h*A*delta-T, how do I find Q, the...
I'm working on a project where I have to construct a cubic box, then find the heat transfer coefficient through the box. I will be placing various object in the box to run tests on how they change the eat transfer coefficient. If I want to use the equation: Q=h*A*delta-T, how do I find Q, the...
hi,
Is somebody here a casting simulation engineer. I am in the processs of learning, the complete process of modelling it and am stuck with Interface heat transfer coefficient between the mold and the casting. I am using procast inverse method, but am having difficulty finding the solutions...
Hai
I have a problem with heat transfer coefficient estimation. Please help
Here is the problem: Two experimental scenarios are compared.
Case 1: I have a well defined rectangular area in a silicon wafer. Water is completely spread over it. The mass of water is known. Air is blown over...
Hi guys. Without going into too much detail. Basically I have a counter-flow heat exchanger problem where I need to find one of the outlets temps only given the inlet temps of each fluid. I have no idea how to do it though as I'm not given a value for over heat transfer coefficient (U) or...
Ok it's my first time here and I was hoping to get some help on some questions I have been given. I am a first year chem eng and I'm finding the work pretty hard so any help at all will be useful, thanks.
I need to find the convective heat transfer coefficient, h for petrol using this...