TAIWAN 2003

Slide1: 

Loop Heat Pipes - Development and Application Yu. F. Maydanik

Slide2: 

Contents Identifications of a Loop Heat Pipe Historical background Theoretical foundations of the LHP operation Materials and working fluids Classification of LHPs Different types of LHPs and the main results of their investigations Application of LHPs Conclusion

Slide3: 

Brief historical background The LHP creation was a response to the challenge to develop a heat-transfer device operating on the principle of a heat pipe and possessing all its advantages, but at the same time capable of transferring heat for distances up to 1 m and more at different orientations in the gravity field. Such a device was first invented in 1972 by Yu. Gerasimov and Yu. Maydanik at the Ural Politechnical Institute. The first name of the device was “a heat pipe”. Later the names “a heat pipe with separate channels” and “an antigravitational heat pipe” were used. In 1989, when these devices came into use in space engineering, there appeared a new name “a Loop Heat Pipe”, which is now generally recognized.

Slide4: 

The first LHP scheme evaporator main wick vapor removal channels secondary wick compensation chamber liquid line vapor line condenser Total length, mm  1000 Evaporator diameter,mm  30 Active zone length, mm  60 Body material ss Wick material nickel Working fluid water Capacity, W  500 Year of development 1972 USSR certification 449 213 1974 Specification

Slide5: 

Identifications of the Loop Heat Pipe (LHP) 1. By the principle of operation A loop heat pipe is a hermetic heat-transfer device operating on a closed evaporation-condensation cycle, in which the circulation of vapor and liquid flows in the transportation section is realized along separate smooth-walled tubing, and the capillary structure (wick), localized in the heat-supply zone, acts simultaneously as a capillary pump, a thermal and a hydraulic gate. 2. By design A loop heat pipe is a hermetic heat-transfer device made in the form of a closed loop filled with a working fluid in the vapor and in the liquid phase containing an evaporator with a capillary structure (wick) combined with a compensation chamber and a condenser connected to the evaporator by means of separate smooth-walled tubing of a relatively small diameter.

Slide6: 

Scheme of a traditional heat pipe Scheme of a LHP liquid vapor wick heat supply heat removal liquid wick vapor heat supply heat removal

Slide7: 

Scheme of classification of heat-transfer devices by the main design features the condenser is located above the evaporator separate smooth-walled tubing for vapor and liquid Loop Thermosyphon Loop Heat Pipe the wick is located in the evaporator separate smooth-walled tubing for vapor and liquid the compensation chamber (reservoir) is combined with the evaporator Conventional Heat Pipe single body the wick is located along the whole length Capillary Pumped Loop the wick is located in the evaporator separate smooth-walled tubing for vapor and liquid separate reservoir with an additional heater Separate Tubing Heat Pipe the wick is located along the whole length separate tubing for vapor and liquid

Slide8: 

saturator line liquid line vapor removal channels TEMPERATURE PRESSURE wick evaporator compensation chamber vapor line condenser 1, vapor state over the evaporating menisci in a wick 1-2, vapor motion in vapor-removal channels with superheating 2-3, adiabatic vapor motion in vapor line 3-4, vapor cooling and condensation in a condenser 4-5, liquid supercooling in a condenser 5-6, adiabatic liquid motion in a liquid line with allowance for the hydrostatic resistance 6-7, liquid motion in a compensation chamber 7-8, liquid motion in a wick P1 P6 P8  PC T6 T7 T4 T1  PEX T3 T7 T6 T1 T2 T4 T5 Scheme and diagram of working cycle of an LHP

Slide9: 

Conditions of an LHP serviceability 1. Condition of balance of the capillary head and the sum of pressure loses in all sections of the working fluid circulation (hydrodynamic condition): PC = P1-8 = D PL+ D PV + D PG 2. Condition of correlation between the temperature and the pressure of saturated vapor above the surface of menisci in the evaporation zone and above the surface of the interface in the compensation chamber (start-up condition): dP/dT (T1 - T7)  P1 - P7 3. Condition of liquid supercooling (thermodynamic condition): dP/dT (T5 - T4)  P5 - P6 4. Condition of relationship between the internal volumes and the volume of a liquid: VCC  VVL + VC VL = VW + VLL + VCC + VCCH {

Slide10: 

Correlation of volumes in an LHP 1. The volume of the compensation chamber VCC must be equal to or exceed the sum of the volumes of the vapor line VVL and the condenser VC VCC  VVL + VC 2. The volume of the liquid VL in an LHP must be equal to the sum of the volumes of the liquid in the wick VW, the liquid line VLL, the compensation chamber VCC and the central channel VCCH VL = VW + VLL+ VCC + VCCH VCC VW VCCH VVL VC liquid level liquid level VLL before start up after start up liquid level

Slide11: 

Classification of LHPs LHP design LHP dimensions Evaporator shape Evaporator design conventional (diode) reversible flexible ramified Condenser design pipe-in-pipe flat coil collector miniature all the rest Number of evaporators and condensers one two and more cylindrical flat disk-shaped flat rectangular Temperature range cryogenic low-temperature high-temperature one butt-end compensation chamber two butt-end compensation chambers coaxial Operating- temperature control without active control with active control

Slide12: 

Metal-theramic wicks for LHPs Material Nickel Titanium Effective pore radius, m 0.5 - 2 3 - 10 Porosity, % 65 - 75 55 - 70 Permeability, m2 10-14 10-13 Year of development 1972 1978 Specification

Slide13: 

Tested LHPs material- working fluid combinations stainless steel Body Wick Working fluid nickel water, ammonia, acetone, pentane, freon-152A, freon 11, propylene stainless steel titanium water, ammonia, acetone, pentane, freon-152A, toluene stainless steel stainless steel ammonia nickel titanium ammonia nickel ammonia nickel copper water copper

Slide14: 

LHPs with a high heat-transfer capacity evaporator condenser vapor line liquid line condenser evaporator

Slide15: 

Ammonia two-meter LHP with two butt-end compensation chambers HEAT LOAD, W EVAPORATOR TEMPERATURE, 0C 0 200 400 600 800 1000 1200 1400 1600 10 20 30 40 50 60 vertical position, evaporator above condenser horizontal position evaporator horizontal, above vertical condenser vertical position, condenser above evaporator ambient temperature 19±10C condenser cooling temperature 17±10C CC1 CC2 Evaporator scheme CC1 CC2

Slide16: 

Effective length, mm 450 Evaporator diameter, mm 20 Vapor line diameter, mm 6/4 Liquid line diameter, mm 4/3 Heating zone area, cm2 4.25 Max heat flux, W/cm2 130 Max heat transfer coef., W/m2 K 30 000 Year of development 1997 Ammonia High-Heat Flux LHP Specification

Slide17: 

Flexible LHPs

Slide18: 

Total length, mm 2000 Evaporator diameter, mm 24 Active zone length, mm 100 Vapor line diameter, mm 6 Liquid line diameter, mm 4 Max capacity, W 900 Min thermal resistance, 0C/W 0.02 Year of development 2000 Specification Reversible LHP scheme General view of ammonia RLHP evaporator condenser

Slide19: 

Specification Total length, mm 865 Evaporator diameter, mm 30 Evaporator thickness, mm 13 Vapor/Liquid line diameter, mm 2/1.2 Condenser length, mm 720 Body material ss Wick material nickel/titanium Working fluid ammonia Total mass, g 167 Max capacity, W 110/90 Min thermal resistance,0C/W 0.30/0.41 Year of development 1999 - 2001 LHPs with flat evaporators

Slide20: 

LHP with temperature active control T, 0C 42,1 42,0 41,9 41,8 -10 0 10 20 TCOOL, 0C set point 420C Q = 6…10 W +0,1 0C -0,1 0C regulating heater control unit thermocouple vapor line  2 mm liquid line  2 mm evaporator  8 x 120 mm condenser radiator controlled temperature T

Slide21: 

Base design variants of ramified LHPs CC1 COND CC2 EV1 EV2 CC1 CC2 EV2 EV1 COND COND CC CC COND1 COND2 CC COND2 COND1 EV EV EV2 EV1

Slide22: 

Two evaporator-condenser LHP condenser 1 evaporator 1 condenser liquid line vapor line evaporator compensation chamber cooling jacket • TV TCh1 TCh2 • • TCOOL1 • • TL • TCOOL2 Specification Total length, mm 1000 Evaporator diameter, mm 24 Vapor line diameter, mm 6/4 Liquid line diameter, mm 4/3 Max capacity, W 1400 Year of development 2002 evaporator 2 condenser 2

Slide23: 

TIME, s TEMPERATURE, 0C Test results of ramified LHP Q1 = 400W, Q2 = 200W G1 = 0.1kg/s, G2 = 0.05kg/s  = 90o 0 200 400 600 800 1000 1200 1400 1600 30 25 20 15 10 5 0 Tv Tlc1 Tlc2 Tl Tcool

Slide24: 

Miniature LHPs

Slide25: 

Effective length, mm 300 230 Evaporator diameter, mm 6 5 Lines diameter, mm 2.5 2 Active - zone length, mm 20 20 Condenser length, mm 60 60 Thermal interface, mm 20 x 20 20 x 20 Heat load, W 130 70 Evaporator temperature 98 70 Own thermal resistance, 0C/W 0.10 0.12 Total thermal resistance - (evaporator-ambient), 0C/W 0.59 0.68 Year of development 2003 2002 Specification Body-working fluid Copper- water SS-ammonia General view of MLHP evaporator condenser vapor line liquid line saddle

Slide26: 

Tests results of miniature LHPs HEAT LOAD, W TEMPERATURE, 0C 0 20 40 60 80 100 120 140 40 20 120 60 80 100 SS-ammonia Condenser cooling by water, 200C HEAT LOAD, W 0 20 40 60 80 100 120 140 0.0 0.4 0.8 1.2 1.6 2.0 THERMAL RESISTANCE, 0C/W 0 20 40 60 80 100 120 140 25 20 10 HEAT LOAD, W HEAT TRANSFER COEF. x 10 -3, W/m2 0C 0 20 40 60 80 100 120 140 20 40 60 80 HEAT LOAD, W air, 200C Copper-water SS-ammonia Copper-water Condenser cooling by water, 200C air, 200C HEAT TRANSFER COEF. x 10 -3, W/m2 0C Condenser cooling by air, 200C Condenser cooling by water, 200C air, 200C SS-ammonia Copper-water 15 30 35

Slide27: 

Comparison of operating characteristics HP (Fujikura) and LHP (ITP) HP Fujikura working fluid - water Leff - 150 mm Le - 50 mm Lc - 250 mm T? - 500C LHP ITP working fluid - ammonia Leff - 230 mm Le - 20 mm Lc - 62 mm Te - 500C Condenser water cooling 200C Condenser air cooling 200C LHP LHP

Slide28: 

The first flight experiment with an LHP aboard the spacecraft «GORISONT» in 1989 The first application of an LHP aboard the spacecraft «OBZOR» in 1994 optical instruments arterial HP LHP OI LHP RSS LHP Rad

Slide29: 

Thermoregulation system with LHPs for the international program «MARS-96» penetrator TRS assembling TRS LHP

Slide30: 

Cooling of the copper bus of an electrolysis-bath electrode liquid line cooling water vapor line current-carruing wire bath electrolyte electrode condenser evaporator saddle

Slide31: 

Cooling of quantum-electronic converters Cooling of powerful transistors

Slide32: 

25 W CPU coolers for a mobile computer evaporator CPU liquid line 5.6 12 fan 60 96 vapor line condenser

Slide33: 

45 W CPU Cooler for a Mobile PC

Slide34: 

Conclusion Loop Heat Pipes are very promising and universal heat-transfer devices, whose potential of development and application has not been used in full measure.