Test results are presented which describe dryout in type-304 stainless steel heat pipes when ammonia is the working fluid. Graph compares heat transfer capabilities of both ammonia and water. Heat pipe apparatus and performance are described

Schwartz, J.

English

NASA Technical Reports Server

December 1970	 Brief 70-10726 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
Virginia 22151. Requests for individual copies or questions relating to the Tech Brief progarn may be directed to the Tech-
nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Performance Map of a Heat Pipe Charged with Ammonia 
Ammonia and water were compared as working 
fluids in heat pipes of type-304 stainless steel; 
a performance map for ammonia is presented. Each 
pipe measured 15.5 in. (length) by 0.44 in. (outer 
diameter) by 0.020 in. (wall thickness), and had 
a wick of two-layer 100-mesh screen lining the 
interior. Two flow-through calorimeter-type heat ex-
changers, using water, served as a heat source for 
the evaporator and as a heat sink for the condenser 
-. Condensor Section 
Evaporator 
	
Section	 \	 j	 Fill Valve 
Out T / Heat Pipe 
ln	 *In 
To Hot 
	
Water Bath
	 Chiller 
Flow o 	 Flow 
Meter .fl 	 II Meter 
Pump
	
	 Pump 
Figure 1. Apparatur Schematic 
(Fig. I). Heat input to the pipe ranged from 5 to 
60 W; "dryout" began at the higher power. The 
condenser loop was fed from a reservoir chilled to a 
constant temperature. 
The heat pipe is a self-contained engineering struc-
ture with a thermal conductance which exceeds the 
capability of a homogeneous piece of any known 
metal. Conductance proceeds by evaporation of a
liquid within one part of a container (one end of a 
tube), transfer of the vapor to another part of the 
container, condensation of the vapor, and return of the 
condensate to the evaporator through a suitable 
capillary wick. 
A performance map is useful, during preliminary 
design evaluation, for predicting heat pipe capability; 
it is especially useful for comparing pipes of varying 
dimensions and working fluids. 
In the tests with ammonia, two phenomena were 
associated with dryout. First, the quasi-equilibrium 
state occurred at the onset of dryout,\when one part of 
the evaporation section rose much higher in tempera-
ture than the rest of the section. This condition 
prevailed for as long as 1 hi, even though the 
thermal input continually increased. Some time later, 
the entire section rose in temperature, and "burn-
out" resulted. Second, the dryout front advanced 
along the evaporation section, beginning farthest 
from the condenser. At the onset of burnout, this 
front moved in steps toward the adiabatic section. 
The lower the temperature of the condenser sink, 
the greater the heat transfer by the pipe, but the 
lower its operating (vapor) temperature at dryout. 
At operating temperatures below about 90°F, am-
monia transfers up to three times as much heat as 
does water. At higher temperatures, however, water's 
advantage increases to 30% at the onset of dryout 
(Fig. 2). The relative performances of ammonia and 
water indicate that the figure of merit (for vapor as 
well as for liquid) is a fairly accurate basis for pre-
liminary performance evaluation. 
The temperature drop across the container and 
saturated wick was slightly higher for water than for 
ammonia; but the curves differ little in slope be-
low the onset of dryout of the ammonia heat pipe, 
(continued overleaf) 
-.
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19700000695 2020-03-17T01:06:21+00:00Z
C 
x 
U-
a) 
0 0
E 
a) 
I—
which was under a smaller heat load than was the 
water pipe. 
The effective thermal conductance of liquid am-
monia was lower by a factor of 7 than that of 
Vapor Temperature, °F 
Figure 2. Transport of Heat by Two Working Fluids 
the ammonia-saturated wick. The water-saturated 
wick's conductance, however, was only half that of 
the ammonia-saturated wick. This fact reflectsthe rel-
atively higher vapor pressure of ammonia, which
caused the meniscus to recede much further into 
the ammonia-saturated wick than in the water-
saturated wick. Thus, in the former, there was a 
thinner layer of liquid and a shorter thermal path 
than in the latter. 
The vapor mass-flow rates in both pipes were 
linear functions of heat load. The rate in the am-
monia pipe was twice that in the water pipe be- 
cause of ammonia's lower heat of vaporization. 
The difference in density between the two vapors 
made the velocity of the ammonia vapor through 
the vapor core lower by about three orders of mag-
nitude than that of the water vapor. 
Notes: 
1. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: N65- 20720, Theory of Heat Pipes. 
2. Technical questions may be directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP70- 10726 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code I 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Joe Schwartz of

Caltech/JPL
under contract to

NASA Pasadena Office

(N PO- 1 1454)
cii 
-41 
. 
Brief 70-10726	 Category 03


Performance map of a heat pipe charged with ammonia

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server