Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Steam pressure (psig) Steam temperature (o 5 F) 226 Heat of evaporation (BTU/lb) 960 Table IV: Steam Table Nominal Pipe Size (in.) 1 1½ 2 3 Table V: Nominal Pipe Size for Various Steam Requirements where ln = Naperian (natural) logarithms. Steam pressure produces specific temperatures that will be used in the cal- culation of the LMTD. Typical values are given in Table IV. As an example, assume 10 psig steam is to be used to heat a solution from 65O (ambient shop temperature) to 140O F Steam temperature (from Table IV): 240O T1 T2 F (solution operating temperature). F = 240 - 65 = 175O =240 - 140 = 100O F F LMTD = (175 - 200)/[ln(175/100)] = 75/0.55 = 134O F The heater area required to steam heat a process solution equals the design heating requirement, divided by the overall heat transfer coefficient, times the log mean temperature. Design heating requirement (BTUH)/Overall heating require- ment LMTD As with any immersion heater, the heater surface temperature will be higher than the solution tem- perature. Obviously, it cannot exceed the steam temperature. If the solu- tion has a high temperature limit below available steam temperatures, you may require a custom electric immersion heater or a hot water (or thermal fluid) heater with a lower heating temperature. Although the heater tempera- ture is limited to the steam tem- perature, damage to process tanks and accessories can result from overtemperature or low liquid lev- els. It is wise to equip your process tank with overtemperature and low liquid level cutoffs. Once a coil size is selected, pip- ing size should be investigated. The 669 10 240 950 15 250 945 20 260 940 25 266 935 Steam Required (lb/hr) Up to 100 100-300 300-500 300-1,000 30 274 930

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