Facts at Your Fingertips: Heat Transfer System Design  

Pumps Centrifugal pumps with cast or forged steel casings are typically appropriate for systems with large flowrates Positive displacement pumps frequently can handle smaller flowrates of less than 100 gal/min Sealless pumps (canned motor or magnetic drive) avoid the installation of mechanical seals A typical centrifugal pump can be expected to deliver operational head of about: where g is gravitational acceleration in m/s 2, D is the rotor diameter in m and n is the rotor speed in rpm. Pump manufacturers usually specify that above 450°F (230°C), a cooled, jacketed stuffing box or a cooled mechanical seal should be used. Secondary sealing with vent and drain glands is suggested to collect fluid leakage and to provide space for inerting the outside of the seal. Inert blanketing of the seal with steam or nitrogen eliminates oxidation deposit formation, which can lead to seal leakage. This secondary sealing provides additional safety in the case of sudden seal failure. Some fluid leakage at the seal is common in mechanically sealed pumps. For those applications where the small leakage is undesirable, consider the use of a sealless pump. When selecting a sealless pump, the designer must consider the impact of heat generated…