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 Factors 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

4. The equation for overall heat transfer coefficient

5. 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 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).

10. Factors of overall heat transfer coefficient 1. Thermal resistance The overall heat transfer coefficient can also be calculated by the view of thermal resistance.

11. 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.

12. Factors of overall heat transfer coefficient 2. Materials of transmission surfaces and the 2 fluids

13. Factors of overall heat transfer coefficient FluidTransmission SurfaceFluid overall heat transfer coefficient Thermal conductivity (Btu/ft2 hr oF) (W/m2 K) WaterCast IronAir or Gas1.47.9 WaterMild SteelAir or Gas2.011.3 WaterCopperAir or Gas2.313.1 WaterCast IronWater40 - 50230 - 280 WaterMild SteelWater60 - 70340 - 400 WaterCopperWater60 - 80340 - 455

14. Factors of overall heat transfer coefficient AirCast IronAir1.05.7 AirMild SteelAir1.47.9 SteamCast IronAir2.011.3 SteamMild SteelAir2.514.2 SteamCopperAir3.017 SteamCast IronWater160910 SteamMild SteelWater1851050 SteamCopperWater2051160 SteamStainless SteelWater120680

15. Bibliography www.engineeringtoolbox.com/overall-heat- transfer-coefficient-d_434.html - 29k www.engineeringtoolbox.com/overall-heat- transfer-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

16. Bibliography www.newmars.com/wiki/index.php/Overall_h eat_transfer_coefficient - 15k www.afcl.com/overall-heat-transfer- coefficient.html - 42k en.wikipedia.org/wiki/Heat_transfer_coeffici ent - 38k http://www.jhu.edu/virtlab/heat/nusselt/nusselt.htm

17. Thank you!