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Single-pass SW/DW heat exchanger with double-tube sheets
EXPANSION   TANKS

Fire Controlman Volume 04-Fire Control Maintenance Concepts
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exchanger.  This  type  of  heat  exchanger  is  less  ef- ficient  than  a  single-pass  exchanger  and  is  subject  to internal  undetectable  leakage  across  the  flow  divider in  the  inlet-outlet  water  box. Heat   exchangers   must   periodically   be   cleaned. The  secondary  section  (distilled  water)  is  cleaned  by circulating   chemicals   through   the   secondary   cooling system  to  remove  any  buildup  of  scale  deposits  that may  accumulate  on  the  surface  of  the  tubes. The  procedure  for  routine  cleaning  of  the  primary section  of  the  heat  exchanger  is  to  first  secure  the  sea connections   to   prevent   flooding.   In   some   cases,   an inspection   port   in   the   water   box   can   be   opened   to remove  any  foreign  matter  lodged  inside  and  against the  tubes.  If  you  are  unable  to  get  at  the  ends  of  the heat  exchanger  to  remove  the  water  boxes,  then  you must  remove  the  heat  exchanger  from  its  location  and place  it  on  the  deck  or  on  a  suitable  work  surface. Mark each unit removed so that it can be positioned in its   proper   place   during   reassembly.   With   the   water boxes  removed,  an  air  lance  should  be  passed  through each  tube  and  the  passages  washed  out.  Where  severe fouling  exists,  a  water  lance  should  be  pushed  through each   tube   to   remove   foreign   matter   attached   to   the tube   walls. Where   extreme   fouling   exists,   special   cleaning equipment  operated  by  personnel  skilled  in  its  use  is required.   The   ship’s   engineering   officer   is   normally the   best   person   qualified   to   determine   which   proce- dure   to   use   and   whether   the   job   can   be   performed aboard  ship  or  if  it  must  be  transferred  to  a  repair facility.   You   should   take   precautions   to   ensure   that tools,  such  as  screwdrivers  and  wire  brushes,  are  not used  in  such  a  way  that  they  may  scratch  or  mar  the tube   surfaces. Over  a  period  of  time,  electrolysis,  which  results because   of   dissimilar   metals   in   the   cooling   system, will  slowly  dissolve  the  insides  of  various  compo- nents   in   the   primary   seawater   cooling   system.   Elec- trolysis  is  not  a  problem  in  chilled-water  systems  to the  extent  that  it  is  in  seawater  systems.  The  type  of metal   used   in   the   fabrication   of   the   heat   exchanger tubes   is   the   deciding   factor   as   to   the   use   of   zincs. Zincs   are   disks,   rods,   bars,   or   plates   made   of   zinc metal   that   are   installed   inside   the   heat   exchanger’s water  boxes.  When  they  are  installed,  the  electrolytic action is concentrated on the zinc and not on the metal of  the  heat  exchanger  tubes.  As  electrolysis  dissolves the   zincs   instead   of   the   heat   exchanger   tubes,   they should   be   replaced.   (The   purity   of   distilled   water inhibits   electrolysis   in   the   secondary   system.) In  an  older  cooling  system,  you  should  be  on  the lookout  for  thin  pipes  in  the  seawater  side  of  the cooling  system.  Check  for  bad  pipes  by  gently  tapping the   empty   pipes   with   the   ball   end   of   a   ball-peen hammer.  A  bad  piece  of  pipe  will  make  a  dull  sound and  will  dimple  as  it  is  struck  lightly. The  heat  exchangers  in  the  distilled-watercooling systems   that   cool   electronic   equipment   are   either liquid-to-air  or  coolant-jacket  type  of  heat  exchangers. The  liquid-to-air  heat  exchangers  are  mounted  inside cabinets  containing  the  heat-producing  electronic components. A  cabinet  fan  circulates  the  air  across  the  heat exchanger  and  to  the  heat  source  in  an  airtight  circuit. In   the   coolant-jacket   type   of   heat   exchangers,   the distilled  water  is  circulated  through  an  integral  water jacket  in  a  large  heat-producing  component,  such  as  a power-amplifier  tube,  a  plate  transformer,  or  the  load isolators. Vent  and  drain  connections  are  provided  to  permit venting   trapped   air   and   draining   water.   Temperature gages  may  be  provided  in  the  inlet  and  outlet  piping to  check  performance  of  the  heat  exchanger.  Label plates  indicate  the  water-flow  direction  through  each cabinet. Flow  regulators  (orifice  plates  or  constant-flow devices)  usually  provide  a  constant  flow  of  coolant  to the  individual  component,  cabinet,  or  bay  of  elec- tronic  equipment  to  be  cooled.  On  critical  electronic components   that   would   be   damaged   without   coolant to   remove   the   heat,   coolant-flow   and   temperature switches   monitor   the   coolant. 2-8






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