Overall heat transfer coefficient

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. 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 coefficientcan 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

14. Factors of overall heat transfer coefficient • 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

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/overall_heat_transfer_coef.htm • www.engineersedge.com/heat_transfer/overall_heat_transfer_co.htm • www.cheresources.com/uexchangers.shtml - 46k

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

17. Thank you!