Heat transfer coefficients fouling factors

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

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. 

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... 

Heat transfer coefficients are empirical data and derived correlations. They are in the form of overall coefficients U for frequently occurring operations, or as individual film coefficients and fouling factors. 

The practical heat-transfer coefficient is the sum of all the factors that contribute to reduce heat transfer, such as flow rate, cocurrent or countercurrent, type of metal, stagnant fluid film, and any fouling from scale, biofilm, or other deposits. The practical heat-transfer coefficient ((/practical) is, in reality, the thermal conductance of the heat exchanger. The higher the value, the more easily heat is transferred from the process fluid to the cooling water. Thermal conductance is the reciprocal of resistance (/ ), to heat flow ... 

A fouled condenser can be identified by an increase in vapor condensing temperature, whereas a fouled general cooler will not provide the anticipated hot water return temperature. Fouling is the primary factor in heat-transfer coefficient with which we are most concerned, and one which we can directly influence with a good water treatment program. 

Finally, fouling factors typical of the two fluid media are taken from Table 12 in Ref. El (p. 645) and converted into their metric equivalents. All factors are then combined into the final equation for determination of the overall heat-transfer coefficient ... 

Suppose the water in Example 10-2 is seawater above I25°F and a fouling factor of 0.0002 nr °C/W is experienced. What is the percent reduction in the convection heat-transfer coefficient ... 

The fouling factor influences the heat-transfer coefficient on the inside of the pipe. We have... 

Individual heat-transfer coefficients and the fouling resistance or fouling factor, are listed... 

The heat transfer-coefficients and fouling factors are listed in Table 7.2.1. Because of the acetic acid, select SS316 as the material of constraction. The thermal conductivity, k, of SS316 and the wall thickness of the reactor, Xw, are given in Table 7.2.1. 

Heat-transfer coefficient for cross flow over an ideal tube bank Fouling coefficient on outside of tube Heat-transfer coefficient in a plate heat exchanger Shell-side heat-transfer coefficient Heat transfer coefficient to vessel wall or coil Heat transfer factor defined by equation 12.14 Heat-transfer factor defined by equation 12.15 Friction factor... 

These re.si.rtflnces include the inside-the-jacket film heat-transfer coefficient (HTC) and fouling factor, the inside-the-reactor HTC and fouling factor, and the reactor-wall resistance. Assuming U, M, Cp and A are con-... 

A double pipe (shell-and-tube) heat exchanger is constructed of a stainless steel [k = 15.1 W/m O inner lube of inner diameter O/ = 1.5 cm and outer diameter 1.9 cm and an outer shell of inner diameter 3,2 cm. The convection heat transfer coefficient is given to be h,- = 800 W/m °C on the inner surface of the tube and h = 1200 W/m °C on the outer surface. For a fouling factor of f f, - 0.0004 m °C/W on the tube side and Ri =- 0.0001 m °C/W on the shell side, determine (a) the thermal resistance of the heat exchanger per unit iength,and (6) the overall heat transfer coefficients, Ujand U based on the inner and puter surface areas 0) the tube, respectively. 

SOLUTION The heat transfer coefficients and the fouling factors on the tube and shell sides of a heat exchanger are given. The thermal resistance and the overall heat transfer coefficients based on the inner and outer areas are to be determined. 

Since no fouling factors were given, assume the heat transfer occurs when the heat exchange process has just initiated operation. Calculate the effective outside heat transfer coefficient. 

In order to calculate the overall heat transfer coefficient in the equation above, the heat transfer properties of the heating medium and the liquor are described in terms of individual heat transfer coefficients, and the heat transfer properties of the separating solid in terms of its thermal conductivity. Deposits at the interface, which one might expect to be described by a thermal conductivity, are usually described instead in terms of either a fouling (heat transfer) coefficient or a fouling factor (which is usually defined to have a value of 1000/[fouling coefficient]). 

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