Definitive Contract NNG07CA14C

SBIR PHASE II AWARD FOR EFFORT ENTITLED: THERMAL CONTROL FOR INSTRUMENTS - MINIATURE LOOP HEAT PIPE (LHP) WITH MULTIPLE EVAPORATORS AND MULTIPLE CONDENSERS. LHP IS A HIGH-PERFORMANCE HEAT TRANSPORTATION DEVICE USING CAPILLARY FORCES TO CIRCULATE THE WORKING FLUID IN A CLOSED LOOP. CONVENTIONAL LHP'S USUALLY HAVE ONE CAPILLARY PUMP (EVAPORATOR) TO ACQUIRE WASTE HEAT FROM A HEAT SOURCE. RECENT EFFORTS HAVE FOCUSED THE DEVELOPMENT OF LHP'S THAT CONTAIN TWO OR MORE EVAPORATORS. EVEN THOUGH TWO- EVAPORATOR LHP'S PERFORMED VERY WELL, THE VOLUME OF EACH COMPENSATION CHAMBER (CC) BECAME MUCH LARGER THAN THAT OF THE SINGLE-EVAPORATOR COUNTERPART. THE REASON WAS THAT ALL BUT ONE CC WOULD BE LIQUID-FILLED DURING NORMAL OPERATION. THE ONE THAT WAS NOT LIQUID-FILLED HAD TO LARGE ENOUGH TO ACCOMMODATE THE SYSTEM LIQUID EXPANSION AT MAXIMUM TEMPERATURE. AS A RESULT, LHP'S WITH MORE THAN 3 EVAPORATORS WERE NOT FEASIBLE FOR PRACTICAL APPLICATIONS SIMPLY BECAUSE THE CC'S BECAME PROHIBITIVELY LARGE. IN THE CURRENT RESEARCH, THE CC'S OF A MULTIPLE-EVAPORATOR LHP WERE CAPILLARY-LINKED. IN OTHER WORDS, THE CC'S ALWAYS CONTAINED A MIXTURE OF LIQUID AND VAPOR (TWO- PHASE), ALLOWING THE LOOP TO OPERATE WITH A MUCH SMALLER FLUID CHARGE. CONSEQUENTLY, THE REQUIRED CC VOLUME WAS ALSO REDUCED.