Overall heat transfer coefficient
Done by:
 Andrew Sung
 Lee Men Quan
 Khoo Chun Yet
Contents
 What is overall heat transfer coefficient
 The equation for overall heat transfer
coefficient
 Factors of overall heat transfer coefficient
What is overall heat transfer
coefficient
 Found in thermodynamics and in mechanical
and chemical engineering
 It is used in calculating the heat energy
transfer, typically by convection or phase
change between a fluid and a solid
The equation for overall heat transfer
coefficient
The equation for overall heat transfer
coefficient
Whereby
 h = heat transfer coefficient, W/ (m^2K)
 ΔQ = heat input or heat lost, J
 A = heat transfer surface area, m^2
 ΔT = difference in temperature between the
solid surface and surrounding fluid area, K
 Δt = time period, s
The equation for overall heat transfer
coefficient
From the above equation, the heat transfer
coefficient is the:
 Proportionality coefficient between the
heat flux (change in heat), Q/ (A Δt)
 Thermodynamic driving force for the flow
of heat (the temperature difference, ΔT)
The equation for overall heat transfer
coefficient
 The heat transfer coefficient has SI units in
watts per meter squared-Kelvin (W/ (m^2K)).
 Heat transfer coefficient is the inverse of
thermal insulation.
The equation for overall heat transfer
coefficient
 There are numerous methods for calculating
the heat transfer coefficient:
 different heat transfer modes
 different fluids
 flow regimes
 under different thermo hydraulic (driven by
fluid) conditions.
The equation for overall heat transfer
coefficient
 The overall heat transfer coefficient
can also be estimated by dividing the thermal
conductivity of the convection fluid by a length
scale (particular length or distance
determined with the precision of one or a few
orders of magnitude).
Factors of overall heat transfer
coefficient
1. Thermal resistance
 The overall heat transfer coefficient can also
be calculated by the view of thermal
resistance.
Factors of overall heat transfer
coefficient
 The wall is split in areas of thermal resistance where:
 the heat transfer between the fluid and the wall is
one resistance
 the wall itself is one resistance
 the transfer between the wall and the second fluid
is a thermal resistance
 Surface coatings or layers of “burned” product
add extra thermal resistance to the wall decreasing
the overall heat transfer coefficient.
Factors of overall heat transfer
coefficient
2. Materials of transmission surfaces and
the 2 fluids
Factors of overall heat transfer
coefficient
overall heat transfer
coefficient
Fluid
Transmission Surface
Fluid
Thermal
conductivity
(Btu/ft2 hr oF)
(W/m2 K)
Water
Cast Iron
Air or Gas
1.4
7.9
Water
Mild Steel
Air or Gas
2.0
11.3
Water
Copper
Air or Gas
2.3
13.1
Water
Cast Iron
Water
40 - 50
230 - 280
Water
Mild Steel
Water
60 - 70
340 - 400
Water
Copper
Water
60 - 80
340 - 455
Factors of overall heat transfer
coefficient
•
•
•
•
•
•
•
•
•
Air
Air
Steam
Steam
Steam
Steam
Steam
Steam
Steam
Cast Iron
Mild Steel
Cast Iron
Mild Steel
Copper
Cast Iron
Mild Steel
Copper
Stainless Steel
Air
Air
Air
Air
Air
Water
Water
Water
Water
1.0
1.4
2.0
2.5
3.0
160
185
205
120
5.7
7.9
11.3
14.2
17
910
1050
1160
680
Bibliography
 www.engineeringtoolbox.com/overall-heat-
transfer-coefficient-d_434.html - 29k
 www.engineeringtoolbox.com/overall-heattransfer-coefficients-d_284.html - 30k
 www.engineersedge.com/heat_transfer/over
all_heat_transfer_coef.htm
 www.engineersedge.com/heat_transfer/over
all_heat_transfer_co.htm
 www.cheresources.com/uexchangers.shtml 46k
Bibliography
 www.newmars.com/wiki/index.php/Overall_h
eat_transfer_coefficient - 15k
 www.afcl.com/overall-heat-transfercoefficient.html - 42k
 en.wikipedia.org/wiki/Heat_transfer_coeffici
ent - 38k
 http://www.jhu.edu/virtlab/heat/nusselt/nusselt
.htm
Thank you!