Skip to main content
European Commission logo print header
Contenuto archiviato il 2019-03-15

HEAT TRANSFER, VAPOUR-LIQUID FLOW INTERACTION AND MATERIALS COMPATIBILITY IN TWO-PHASE THERMOSYPHONS

Obiettivo



GRAVITY ASSISTED HEAT PIPES AND TWO PHASE THERMOSYPHONS HAVE EXCELLENT HEAT TRANSPORT PROPERTIES. TYPICALLY, 1 KW CAN BE TRANSFERRED THROUGH A TUBE WITH A DIAMETER OF 10 MM. HEAT INTRODUCED AT THE "HOT" END OF THE TUBE EVAPORATES A LIQUID AND THE VAPOUR TRANSPORTS THE LATENT HEAT TO THE COLD END OF THE TUBE WHERE IT CONDENSES AND RELEASES THE HEAT; THE CONDENSED LIQUID RETURNS TO THE EVAPORATOR. IN A HEAT PIPE THE LIQUID IS RETURNED BY CAPILLARY FORCES, TYPICALLY IN A WIRED MESH LINING THE INSIDE WALL OF THE TUBE; IN A THERMOSYPHON THE LIQUID RETURNS BY GRAVITY.

THE OBJECTIVE OF THE IKE STUDY IS TO INVESTIGATE THREE MAIN ASPECTS OF TWO-PHASE THERMOSYPHONS IN ORDER TO IMPROVE THEIR PERFORMANCE : HEAT TRANSFER CHARACTERISTICS, VAPOUR-LIQUID FLOW INTERACTION AND MATERIALS COMPATIBILITY.

TESTS WERE CARRIED OUT FOR A VARIETY OF SMALL-DIAMETER, SHORT HEAT PIPES/THERMOSYPHONS (5 TO 13.5 MM I.D. 0.5 M LENGTH) WITH SMOOTH OR CHEMICALLY/MECHANICALLY ROUGHENED INNER SURFACE, SCREEN-WICK OR AXIAL GROOVE. THE EXPERIMENTAL DATA WERE CORRELATED TO PREDICT THE HEAT TRANSFER CAPACITY AND THE RADIAL EVAPORATOR HEAT FLUX. IT WAS FOUND THAT THE BOILING LIMIT WAS IN GENERAL THE PERFORMANCE LIMIT WHEN SHORT EVAPORATOR SECTIONS WERE USED. IN MANY CASES THE VAPOUR-LIQUID FLOW INTERACTION WAS THE MOST IMPORTANT PHENOMENON.

HEAT TRANSFER MEASUREMENTS REVEALED COEFFICIENTS OF 10,000 AND 100,000 W/M2 DEGREE K FOR THE EVAPORATOR AND CONDENSER RESPECTIVELY. THE OVERALL THERMAL CONDUCTANCE OF HEAT PIPES WAS GREATER THAN OF THERMOSYPHONS (THIS WAS DUE TO THE WICK WHICH PROVIDED BETTER WETTING BY THE RETURNING LIQUID FROM THE CONDENSER TO THE EVAPORATOR AND ENHANCED THE HEAT TRANSFER COEFFICIENT). TYPICAL AXIAL HEAT FLUXES ACHIEVABLE IN HEAT PIPES AND THERMOSYPHONS WERE IN EXCESS OF 1 KW/CM2.

VARIOUS FLOW SEPARATORS WERE TESTED WITH COPPER/WATER THERMOSYPHONS (OF 17 MM I.D. AND 2.5 M LENGTH) HAVING CIRCUMFERENTIAL GROOVES (FOR CAPILLARY STRUCTURE). THEIR MAXIMUM PERFORMANCE WAS ABOUT 3.5 KW. TESTS WERE ALSO CARRIED OUT WITH A COPPER/WATER THERMOSYPHON (74 MM I.D. AND 4.7 M LENGTH) WITH AND WITHOUT CIRCUMFERENTIAL GROOVES AS WELL AS WITH AND WITHOUT THE COCENTRIC PERFORATED TUBE SEPARATOR. THE MAXIMUM PERFORANCE OF THE SMOOTH THERMOSYPHON WAS 21 KW AND THAT OF THE GROOVED 18 KW. IT WAS ALSO FOUND THAT THE USE OF A FLOW SEPARATOR, IN GENERAL, LED TO AN INCREASE OF THE THERMAL CONDUCTANCE.

IKE IDENTIFIED SUITABLE WORKING FLUID/MATERIAL COMBINATIONS FOR USE IN HEAT PIPES AND THERMOSYPHONS AT HIGH TEMPERATURES (TYPICALLY 400 DEGREES C VAPOUR TEMPERATURE). WHILE CHEAP CARBON STEELS MAY BE USED AS CONTAINERS FOR FLUIDS SUCH AS NAPHTHALENE AND TOLUENE AT TEMPERATURES UP TO 270 AND 280 DEGREES C RESPECTIVELY, MORE EXPENSIVE MATERIALS ARE LIKELY TO BE NEEDED IF ORGANICS ARE TO BE SUCCESSFULLY USED AT HIGHER (350 - 400 DEGREES C) TEMPERATURES.

TYPICAL PAYBACK PERIODS OF 0.5 - 3 YEARS MAY BE OBTAINED.

Argomento(i)

Data not available

Invito a presentare proposte

Data not available

Meccanismo di finanziamento

Data not available

Coordinatore

INSTITUT FÜR KERNTECHNIK UND ENERGIEWANDLUNG eV
Contributo UE
Nessun dato
Indirizzo
HOLDERBUSCHWEG 52
7000 STUTTGART
Germania

Mostra sulla mappa

Costo totale
Nessun dato