Heat pipe is used in the primary heat exchanger for nuclear power plants, as a heat sink for high-power electronic devices, and in a closed-cycle heat rejection mechanism for cryogenic storage tanks. It serves simultaneously as a heat transfer device and as a structural member

Mc Kinney, B. G.

English

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September 1970	 Brief 70-10106 
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Water-Filled Heat Pipe Useful at Moderate Temperatures 
Containing Envelope
Liquid Flow 
Cross-Sectional View of a Heat Pipe 
A heat pipe is a self-contained device that achieves 
very high thermal conductance by means of two-phase 
fluid flow. As shown in the illustration, the fluid evap-
orates near one end of the pipe and recondenses near 
the other, thus transferring heat from the evaporator 
to the condenser. The vapor flows naturally through 
the central space toward the condenser, while the 
condensate returns to the evaporator by capillary flow 
through a porous material known as the wick. 
The heat pipe has been applied in the primary heat 
exchanger for nuclear power plants, as a heat sink 
for high-power electronic devices, and in a closed-
cycle heat rejection mechanism for cryogenic storage 
tanks. Because of its construction, it may serve simul-
taneously as a heat transfer device and as a structural 
member, frequently resulting in lighter weight designs
than are possible with more conventional heat transfer 
techniques. 
A theoretical and experimental study of the water-
filled heat pipe has verified its usefulness as a heat 
transfer medium in the temperature range from 200° to 
350°F. Some of the conclusions of the study are as 
follows: (I) existing heat pipe equations can be used 
with confidence to predict the heat transfer efficiency 
of water-filled heat pipes within the stated temperature 
range; (2) the absence of gravitational forces does 
not affect the performance of heat pipes; (3) thermal 
conductivity of nonmetal wicks is too low for use in 
heat pipes designed to transfer larger heat loads; (4) 
the wick material should be firmly bonded to the inner 
wall of the heat pipe container to decrease thermal 
resistance; (5) the heat load capacity of a heat pipe 
Adlk	 (continued overleaf) 
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is determined by capillary pumping limitations and by 
the onset of film boiling, but in the pipes studied, the 
capillary-pumping limitation was more crucial; and 
(6) the startup of a frozen heat pipe, even at low power, 
may result in burnout. 
Note: 
The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-TM-X-53849 (N69-38853), An 
Experimental and Analytical Study of 
Water Heat Pipes for Moderate Temper-
ature Ranges
Patent status: 
No patent action is contemplated by NASA. 
Source: B.G. McKinney 
Marshall Space Flight Center 
(M FS-20543) 
Brief 70-10106	 Category 03


Water-filled heat pipe useful at moderate temperatures

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