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C: Heat Transfer ExperimentsTubular heat exchanger: heat transfer coefficient h = f(Re); purpose - heating or cooling; existing in each factory; steam-electricity co-generation system;

Drying: operation; sources of heating: convection (hot air), radiation (lamp (wavelength), solar light, xenon lamp, etc)

Picture taken from wikipedia

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C1: Tubular Heat Exchanger

Very traditional; steam is often used as the heating source; boiler to generate steam (may need licence to operate this equipmentOverall heat transfer efficient (Uo or Ui): outside heat transfer coefficient ho, outside scale resistance Ro, tube heat transfer resistance kw, inside scale resistance Ri, inside heat transfer coefficient hi 1/Uo = 1/ho + Ro + xw/kw (Do/Dm) + Ri (Do/Di) + 1/hi (Do/Di); Dm = log mean dia.

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liquid-side film heat transfer coefficient: ho, hi; usually assume other heat transfer resistance negligible, Q = m Cp (T out – T in) = hi Ai Tlm, with Tlm = (T2 - T1)/log (T2/T1) we may have co-current flow, counter-current flow, etc. In general: Nu = F(Re, Pr, L/D) Nu = Nusselt number = h D/k =convective heat transfer coefficient/conductive heat transfer coefficient Pr = Prandtl number = viscous diffusion rate/thermal diffusion rate = Cp/k

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Many correlations proposed: e.g. Colburn j -factor: Nu = 0.023 Re^0.8 Pr^1/3 (for Pr: 0.7 – 160) L/D < 60: entrance effect may not be neglected A simplified correlation: hi = a V^0.8 (1+ 0.0146 T)steam: saturated, superheating, super-cooling vent: safety purpose Source of heat: natural gas, diesel fuel (C8 – C21; BP: 200 – 320oC), coal, solar, waste heat, etc. heavy oil: very viscous, > C60, high percentage of aromatics, naphthalene, high amounts of NSO; bottom product from distillation

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PsB4B5 B3 B2

TcTc

B1

steam inlet valvesteam pressure

by pass valve

steamtrap

steam outlet

safety valve

cold water

hot water

Steam trap: to discharge condensate, non-condensable gases, with minimum loss of steam; usually automatic valve;

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C2: Drying

Simultaneous heat and mass transfer Free moisture content, meaning some water may be chemically bond to solid material, may need “dehydration” moisture inside pores: may be slow to evaporate from air point view: percentage humidity (relative to saturation humidity) wet bulb temperature (adiabatic saturation temperature) vs dry bulb temperature vs dew point; humidity chart

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Wet bulb globe temperature: originally developed by US marine corps. To determine heat stress of work WBGT = 0.7 Tw (wet bulb temp., humidity effect)+ 0.2 Tg (solar radiation) + 0.1 Td (dry bulb temp)

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pre-heat period, constant rate period, falling rate period (first & second falling rate); constant rate period reach “critical point”, then mass transfer becomes important

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Dryer: with hot air drying + IR heater For industrial operation: usually in continuous mode (on a belt), tunnel kiln, etc.

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Pictures taken from: Vandenbroek International website; drum dryer Spray drying; (others: fluidized drying, etc)