1. Heat Transfer Equations

2. Fouling Layers of dirt, particles, biological growth, etc. effect resistance to heat transfer We cannot predict fouling factors well Allow for fouling factors when sizing heat transfer equipment Historical information from similar applications Little fouling in water side, more on product

3. Log Mean Temperature Difference Parallel FlowCounter Flow Length Temperature T1T1 TT T2T2 Length Temperature T1T1 TT T2T2

4. Log Mean Temperature Difference For Round Tubes

5. Heat Losses Total Heat Loss = Convection + Radiation Preventing heat loss, insulation Air – low thermal conductivity Air, good Water – relatively high thermal conductivity Water, bad Vessels/pipes above ambient temperature – open pore structure to allow water vapor out Vessels/pipes below ambient temperature - closed pore structure to avoid condensation

6. Radiation Vibrating atoms within substance give off photons Emissivity of common substances Polished aluminum: 0.04 Stainless steel:0.60 Brick:0.93 Water:0.95 Snow:1.00 Radiation between surface and surroundings:

7. Radiation Sometimes, we’ll make an analogy to convection A 3 cm diameter, 15 m long pipe carries hot wort at 85  C. The pipe has 1.0 cm thick insulation, which has thermal conductivity of 0.08 W/m.K. The insulation exterior surface temperature is 35  C and its emissivity is 0.85. The temperature of the surroundings is 20  C. Determine the rate of heat loss by radiation.

8. Heat Transfer – Continued Hot wort at 95  C is transferred from one tank to another through a 2.5 cm diameter stainless steel pipe (k = 120 W/m.K, wall thickness 0.2 mm). The pipework is 150 m long and the wort has specific heat capacity of 4.0 kJ/kg.K and density of 1020 kg/m 3. The heat transfer coefficients on the inside and outside of the pipe are 4000 W/m 2 K and 125 W/m 2 K and the temperature of the surroundings is 10  C. Assume that the pipe’s wall is “thin.” Approximate the rate of heat loss from the pipe and the exit temperature at the end of the pipe. The velocity in the pipe is 1.0 m/s.

9. Heat Transfer – Continued Previous Problem continued… Our pipe has an external emissivity of 0.7. Calculate the heat loss by radiation and compare it to the heat loss by convection. Steam…