Fouling factors, heat transfer

F specific energy (= force constant), kj/kg FF fouling factor (heat transfer), J/(m2 s °C)... 

Fouling factors, heat transfer, 180 data, 183, 184, 186 Fourier equation, 169 Fractionation. See Distillation Fractionator conntrol lower ends, 49,50 upper ends, 51,52 Freeze drying, 639 cvcle lengths. 639 products 646 Friction, 93 Friction factor, 92 Colebrook equation, 94 granular beds, 117 non-Newtonian fluids, 109 Rounds equation, 94... 

Ganapathy, V, Nomograph Relates Clean and Dirty Heat Transfer Coefficients, Fouling Factor, Heating/Piping/Air Conditioning, Jan. (1979) p. 127. 

Factors involved in heat transfer, such as surface-to-volume ratio, agitation characteristics, mixing efficiency, fouling of heat transfer surfaces, scale of operations, and the resulting heat exchanged depend on the system under consideration (e.g., liquid-liquid transfer, liquid-gas transfer, free convection, or forced convection). Standard chemical engineering texts and reference books contain detailed discussions on heat transfer in process equipment. Only a brief summary follows ... 

The rate of heat-transfer q through the jacket or cod heat-transfer areaM is estimated from log mean temperature difference AT by = UAAT The overall heat-transfer coefficient U depends on thermal conductivity of metal, fouling factors, and heat-transfer coefficients on service and process sides. The process side heat-transfer coefficient depends on the mixing system design (17) and can be calculated from the correlations for turbines in Figure 35a. 

For overall tubeside plus shellside fouling use experience factors or 0.002 for most services and 0.004 for extremely fouling materials. Neglect metal wall resistance for overall heat transfer coefficient less than 200 or heat flux less than 20,000. These will suffice for ballpark work. 

Experience and judgment as to fouling severity are required to estimate fouling factors (FF , FFj) to determine the overall heat transfer... 

A, = area of inside of. surface for heat transfer, such as coil, flat surface, or other barrier, sq ft/ft h = inside heat transfer fluid side coefficient, in coil, flat plate, or otlier barrier, Btu/hr/sq fl/°F ro = fouling resistance (factor) associated wTth fluid on outside (tank process side) of heat transfer... 

Often, a reasonable and convenient way to understand the heat transfer process in a heat exchanger unit is to break down the types of heat transfer that must occur such as, vapor subcooling to dew point, condensation, and liquid subcooling. Each of these demands heat transfer of a different type, using different AT values, film coefficients, and fouling factors. This is illustrated in Figure 10-36. It is possible to properly determine a weighted overall temperature... 

The percentage effect of the fouling factor on the effective overall heat transfer coefficient is considerably more on units with the normally high value of a clean unfouled coefficient than for one of low value. For example, a unit with a clean overall coefficient of 400 when corrected for 0.003 total fouling ends up with an effective coefficient of 180, but a unit with a clean coefficient of 60, when corrected for a 0.003 fouling allowance, shows an effective coefficient of 50.5 (see Figure 10-39). 

The fouling factors are applied as part of the overall heat transfer coefficient to both the inside and outside of the... 

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