Page 414 - Handbook of Energy Engineering Calculations
P. 414

FIGURE  5  Effect  of  heat-exchanger  fouling  on  the  overall
                     coefficient  of  heat  transfer.  (Condenser  Service  and  Engineering  Co.,
                     Inc.)



               Related  Calculations.  Table  2  gives  fouling  factors  for  a  wide  variety  of
               service  conditions  in  applications  of  many  types.  Use  these  factors  as
               described previously, or add the fouling factor to the film resistance for the

               heat exchanger to obtain the total resistance to heat transfer. Then U = the
               reciprocal of the total resistance. Use the actual value U  of the heat-transfer
                                                                                    a
               coefficient when sizing a heat exchanger. The method given here is that used
               by Condenser Service and Engineering Company, Inc.


               BAROMETRIC AND JET CONDENSER HEAT TRANSFER




               A counterflow barometric condenser must maintain an exhaust pressure of 2
                     2
               lb/in  (abs) (13.8 kPa) for an industrial process. What condensing-water flow
               rate is required with a cooling-water inlet temperature of 60°F (15.6°C); of

               80°F  (26.7°C)?  How  much  air  must  be  removed  from  this  barometric
               condenser if the steam flow rate is 25,000 lb/h (11,250 kg/h); 250,000 lb/h
               (112,500 kg/h)?


               Calculation Procedure:


               1. Compute the required unit cooling-water flow rate

               Use  Fig.  6  as  a  quick  guide  to  the  required  cooling-water  flow  rate  for
               counterflow barometric condensers. Thus, entering the bottom of Fig. 6 at 2-
                     2
               lb/in  (abs) (13.8-kPa) exhaust pressure and projecting vertically upward to
               the 60°F (15.6°C) and 80°F (26.7°C) cooling-water inlet temperature curves
               show that the required flow rate is 52 gal/min (3.2 L/s) and 120 gal/min (7.6
               L/s), respectively, per 1000 lb/h (450 kg/h) of steam condensed.
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