Heat exchanger control scheme

Claim 1

A HEAT EXCHANGER UNIT OF THE TYPE DESIGNED FOR A LOW PRESSUR DROP THERETHROUGH COMPRISING: A SHELL; A TUBE BUNDLE SUPPORTED AND DISPOSED THEREIN; INLET AND OUTLET HEADERS AT OPPOSITE ENDS OF THE HEAT EXCHANGER AND IN FLUID COMMUNICATION WITH THE TUBES OF SAID TUBE BUNDLE; MEANS DEFINING A COLLECTION CHAMBER IN FLOW COMMUNICATION WITH SAID TUBES ADJACENT THE OUTLET HEADER AND ARRANGED TO COLLECT THE FLUID PASSING THROUGH SAID TUBE BUNDLE, SAID MEANS HABING AN OPENING THEREIN IN FLUID COMMUNICATION WITH SAID OUTLET HEADER; A FIRST BUTTERFLY-TYPE VALVE DISPOSED IN SAID OPENING; A BY-PASS LINE DISPOSED WITHIN SAID SHELL EXTENDING BETWEEN SAID INLET AND OUTLET HEADERS AND BY-PASSING SAID COLLECTION CHAMBER, SAID BY-PASS LINE BEING OF LARGER DIAMETER THAN THE TUBES OF SAID TUBE BUNDLE AND HAVING A LOWER HEAT FLOW RATE FROM THE FLUID PER UNIT OF FLOW; A SECOND BUTTERFLY-TYPE VALVE DISPOSED IN SAID BY-PASS LINE; FIRST ADJUSTING MEANS FOR OPENING AND CLOSING SAID FIRST BUTTERFLY-TYPE VALVE; AND SECOND ADJUSTING MEANS FOR OPENING AND CLOSING SAID SECOND BUTTERFLY-TYPE VALVE.