Heat exchanger shell-side fouling coefficient

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... 

The corrected overall heat transfer coefficient is within the design range (140-260 Btu/ft h °F). The assumed value should match U-value estimated from the heat exchanger design specifications that depends on the film heat transfer coefficient of tube side and shell side, fouling factor, and metal resistance. 

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. 

The range of overall heat transfer coefficients (U) is about 10 - 200 Btu/hr fC°F. Table 8-11 lists the U-values for various types of equipment, and fouling factors of some flowing media are shown in Table 8-12. Table 8-13 illustrates a heat exhanger specification form. Factors governing the selection of process fluids in the tube and shell sides of an exchanger are illustrated in Table 8-14. 

Acetone (s = 0.79) at 250°F is to be sent to storage at 100°F and at a rate of 60,000 Ib/hr. The heat will be received by 185,000 Ib/hr of 100 percent acetic acid (s = 1.07) coming from storage at 90°F and heated to 150°F. Pressure drops of 10.0 psi are available for both fluids. Assuming that the fouling factor on the tube side is 0.001 and that on the shell side is 0.003, calculate the heat transfer coefficients for the tube and shell sides, the overall heat transfer coefficient for the exchanger, outside area of unit, and the heat transferred. 

Standard construction for shell-and-tube exchangers includes nickel tubes and carbon steel in cooling water service on the shell side. Compact heat exchangers also are widely used in caustic service. They have found a growing market in chlor-alkali plants. Their high heat-transfer coefficients and resistance to fouling reduce the surface area required. This is especially valuable when using expensive materials such as nickel, titanium, and the Hastelloys. 

At one Midwest refinery, on a 180,000 BSD crude unit, two parallel, 6000 square ft, titanium twisted tube bundles have been in service for a number of years. Crude tower overhead vapors plus steam are condensing on the shell side. Crude is on the tube side. Fouling on both the shell side and the tube side appears to be quite minimal. However, the heat-transfer coefficient is bad only about 20-25 Btu/hr/ ft /°F, even when the exchanger is clean. 

Another example from oil refineries is in crude preheat service with vacuum resid again on the shell side (with the helical baffles). Once again, similar results are seen as described above, with less fouling, reduced rate of increase in pressure drop, and better maintenance of heat-transfer coefficient as compared to the conventional shell-and-tube exchanger design. Our more direct experience of this comes from current practice in the United States, but we have also seen evidence of similar applications in Australia, as discussed in a recent article on the subject of crude preheat exchanger train redesign. ... 

The thermal performance of the designed heat exchanger can be checked by calculating the overall heat transfer coefficient. This required calculating the tube side and shell side heat transfer coefficients, the tube wall contribution to the resistance, and the appropriate fouling resistance. The overall heat transfer coefficient, based on the outside surface area of the tubes is... 

---