adoration bundle which pushes air across the finned tubes. An induced draft unit has a fan above the tube bundle which pulls air across the finned tubes, ai cooled condensers are normally controlled by using controllable-pitch fans Good air distribution is achieved ifat least 40% ofthe face area of the bundle is covered with fans. It is most economical to arrange the bundles and select the fan diameters to minimize the number of fans. Controllable-pitch fans permit only the air flow required for heat transfer to be pumped. An important added advantage is the reduction of the power required for operation when ambient air temperature is lower than that used for design Controllable-pitch fans can result in a 50% reduction in the annual power consumption over fixed-blade fans There are many ways to waste energy in pumping systems. As energy costs have continued to climb, it has often been found that a complete pumping unit 's initial investment can be less than the equivalent investment value of one electrical horsepower. Calandria circulating pumps require a certain available NPSH. This is usually obtained by elevating theevaporator, often with a skirt. Quite often the designer establishes the skirt height before he selects the calandria recirculating pump. In the interest of economy he provides a skirt as short as possible, often without realizing that he will be forever paying an energy penalty for a smaller initial capital savings. More efficient pumps often require greater NPSH. Therefore, it is prudent to check the NPSH requirements of pumping applications before establishing skirt heights of evaporator systems Heat pumps or refrigeration cycles involves the use of external power to "pump"heat from a lower temperature to a higher temperature. The working fluid may be a refrigerant or a process fluid. Heat pumps use energy that often would otherwise be thrown away in the form of waste heat effluents or stack gases. The external energy input can be reduced by a facto of 4 to 5, depending on the temperature difference and temperature level of the heat pump system There are several ways to increase the steam economy, or to get more evaporation with less steam input, for certain types of evaporation applica tions. The use of multiple-effect configurations or compression evaporation can be considered for large flow rates of relatively dilute aqueous solutions Both multiple-effect and compression evaporation systems require a sizable cremental capital investment over single-effect evaporators, and these systems are larger and more complex than the simpler one-stage evaporato Like the multiple-effect evaporators described above, compression evapora tion systems can only be justified by a reduced level of steam consumptionEvaporation 513 bundle which pushes air across the finned tubes. An induced draft unit has a fan above the tube bundle which pulls air across the finned tubes. Air￾cooled condensers are normally controlled by using controllable-pitch fans. Good air distribution is achieved ifat least 40% ofthe face area ofthe bundle is covered with fans. It is most economical to arrange the bundles and select the fan diameters to minimize the number of fans. Controllable-pitch fans permit only the air flow required for heat transfer to be pumped. An important added advantage is the reduction of the power required for operation when ambient air temperature is lower than that used for design. Controllable-pitch fans can result in a 50% reduction in the annual power consumption over fixed-blade fans. There are many ways to waste energy in pumping systems. As energy costs have continued to climb, it has often been found that a complete pumping unit’s initial investment can be less than the equivalent investment value of one electrical horsepower. Calandria circulating pumps require a certain availableNPSH. This is usually obtained by elevating the evaporator, often with a skirt. Quite often the designer establishes the skirt height before he selects the calandria recirculating pump. In the interest of economy he provides a skirt as short as possible, often without realizing that he will be forever paying an energy penalty for a smaller initial capital savings. More efficient pumps often require greater NPSH. Therefore, it is prudent to check the NPSH requirements of pumping applications before establishing skirt heights of evaporator systems. Heat pumps or refrigeration cycles involves the use of external power to “pump” heat from a lower temperature to a higher temperature. The working fluid may be a refrigerant or a process fluid. Heat pumps use energy that often would otherwise be thrown away in the form of waste heat in effluents or stack gases. The external energy input can be reduced by a factor of 4 to 5, depending on the temperature difference and temperature level of the heat pump system. There are several ways to increase the steam economy, or to get more evaporation with less steam input, for certain types of evaporation applica￾tions. The use of multiple-effect configurations or compression evaporation can be considered for large flow rates of relatively dilute aqueous solutions. Both multiple-effect and compression evaporation systems require a sizable incremental capital investment over single-effect evaporators, and these systems are larger and more complex than the simpler one-stage evaporators. Like the multiple-effect evaporators described above, compression evapora￾tion systems can only be justified by a reduced level of steam consumption