The overall heat transfer coefficient is used to calculate heat energy transfer between a fluid and solid. It is proportional to the heat flux divided by the temperature difference driving the heat flow. The coefficient depends on factors like heat transfer mode, fluid type, and flow conditions. It can be estimated from properties like thermal conductivity and characteristic length or calculated from the Nusselt number. Examples of typical overall heat transfer coefficients are provided for combinations of common fluids, materials, and heat transfer environments.
Maximizing Incident Investigation Efficacy in Oil & Gas: Techniques and Tools
heat.ppt
1. Overall heat transfer coefficient
Done by:
Andrew Sung
Lee Men Quan
Khoo Chun Yet
2. Contents
What is overall heat transfer coefficient
The equation for overall heat transfer
coefficient
Types of uses of overall heat transfer
coefficient
3. 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
5. 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
6. 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)
7. 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.
8. 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.
9. The equation for overall heat transfer
coefficient
The overall heat transfer coefficient
can 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).
10. The equation for overall heat transfer
coefficient
The heat transfer coefficient is often
calculated from the Nusselt number (a
dimensionless number).
where:
L = characteristic length
kf = thermal conductivity of the fluid
h = convective heat transfer coefficient
11. The equation for overall heat transfer
coefficient
Thermal resistance
The overall heat transfer coefficient can also
be calculated by the view of thermal
resistance.
12. The equation for 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.
13. Types of uses of overall heat transfer
coefficient
Fluid Transmission Surface Fluid
overall heat transfer
coefficient
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
14. • Air Cast Iron Air 1.0 5.7
• Air Mild Steel Air 1.4 7.9
• Steam Cast Iron Air 2.0 11.3
• Steam Mild Steel Air 2.5 14.2
• Steam Copper Air 3.0 17
• Steam Cast Iron Water 160 910
• Steam Mild Steel Water 185 1050
• Steam Copper Water 205 1160
• Steam Stainless Steel Water 120 680
