98 Fermentation and Biochemical Engineering Handbook Table 3. Maximum Heat Transfer Surface Area Available(ft?)on 80% of the Straight Side H/d F(it) D (ft) Jacket Coils* 27313.79381,2 2.5 31.7 12.71,0101,340 35811.91,0701,400 3.5 1,455 43.4 10.81,1801,150 *Coil area is based on 3. 5 inch o d, 3. 5 inch spacing between helical coils and 12 inches between the tank wall and the center line of the coil It can be seen by comparing Tables I and 2 that if mechanical agitation is used and a jacket is desired, then additional internal coils are required. the intermal coils can be vertical, like baffles, or helical. Agitation experts state that helical coils can be used with radial turbines if the spaces between the coil loops are I to 1.5 pipe diameters. Once helical coils are accepted, Why use a jacket at all? Reasons in favor of coils (in addition to the better heat transfer coefficient)are 1. Should stress corrosion cracking occur(due to chlorides in the cooling water), the replacement of coils is cheaper than the tank wall and jacket 2. The cost of a fermenter with helical coils is cheaper than a jacketed tank with internal coils 3. Structurally, internal coils present no problems with continuous sterilization However ifbatch sterilization is insisted upon, vertical coils are one solution to avoiding the stress between the coil supports and tank wall created when cooling water enters the coils while the broth and tank wall are at 120C. notice that the method of medi sterilization batch or continuous. is related to the fer menter design and the capital cost98 Fermentation and Biochemical Engineering Handbook Table 3. Maximum Heat Transfer Surface Area Available (ft2) on 80% of the Straight Side H/D F (ft) D (ft) Jacket Coils* 2 27.3 13.7 938 1,245 2.5 31.7 12.7 1,010 1,340 3 35.8 11.9 1,070 1,400 3.5 39.7 11.3 1,130 1,455 4 43.4 10.8 1,180 1,150 *Coil area is based on 3.5 inch o.d., 3.5 inch spacing between helical coils and 12 inches between the tank wall and the center line of the coil. It can be seen by comparing Tables 1 and 2 that if mechanical agitation is used and ajacket is desired, then additional internal coils are required. The internal coils can be vertical, like baffles, or helical. Agitation experts state that helical coils can be used with radial turbines if the spaces between the coil loops are 1 to 1.5 pipe diameters. Once helical coils are accepted, Why use ajacket at all? Reasons in favor of coils (in addition to the better heat transfer coefficient) are: 1. Should stress corrosion cracking occur (due to chlorides in the cooling water), the replacement of coils is cheaper than the tank wall and jacket. 2. The cost of a fermenter with helical coils is cheaper than a jacketed tank with internal coils. 3. Structurally, internal coils present no problems with continuous sterilization. However, if batch sterilization is insisted upon, vertical coils are one solution to avoiding the stress between the coil supports and tank wall created when cooling water enters the coils while the broth and tank wall are at 120°C. Notice that the method of media sterilization, batch or continuous, is related to the fer￾menter design and the capital cost