Model maintains a preselected temperature in the near vicinity of a variable source of thermal energy. Heat input is controlled by a variable transformer and a voltage drop across the heater is used to calculate power dissipated

Fitz, F. A.

English

NASA Technical Reports Server

July 1970	 Brief 70-10111 
•	 NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued toencourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Passive Heat Transfer Control 
n
F
The problem of maintaining a preselected tempera-
ture in the near vicinity of a variable source of thermal 
energy has been recently investigated. One typical 
situation is a solid state power circuit that generates 
heat, dependent on power requirements, and the sta-
bility of which is temperature dependent. 
_______ Adjustable Head & Heater 
Heater Power -
Main Cylinder 
amework
I
	
I
I. 
/	 Heat Sink 
Coolant
Conical Washer 
* Thermocouple Locations 
A useful concept has been reduced to an operating 
prototype stage that exhibits the desired characteris-
tics of passive thermal control. The model used consists 
of a rigid framework mounting active elements as 
shown in the figure. The adjustable head contains a 
resistance wire heat source operated by 60-cycle ac 
and has a maximum output of approximately 2000
Btu/hr. A solid cylinder of 6061 T6 aluminum exerts 
vertical motion and force, as a result of thermal ex-
pansion on a conical washer which rests on a water-
cooled heat sink. 
Heat input to the main cylinder is controlled by a 
variable transformer, and a voltage drop across the 
heater is used to calculate power dissipated in con-
junction with the known resistance of the heater. Heat 
sink temperature is held essentially constant by a large 
flow of tap water and is monitored by periodic sam-
pling of water inlet and outlet temperature and tem-
perature at a selected point on the heat sink shell. 
This model control is used as the basis for predic-
tions of control temperature as a function of the pre-
load, or initial gap at the outer edge of the conical 
washer with all elements of the control at known 
temperatures. Heat "leakage" through the two rings 
of contact at the washer, prior to full compression, 
controls heat flow before the control point is reached. 
Contact conductance between the annular area of the 
washer and the hot cylinder and heat sink governs 
temperature of the cylinder after full compression of 
the washer is accomplished. 
Notes: 
I. Results of two control runs designed to control at 
average cylinder temperatures of 150 0 and 185°F, 
show positive control especially at the higher tem-
perature run in which control was achieved well 
within 5°F of predicted average cylinder tempera-
ture. 
2. The thermal conductance behavior of the conical 
washer appears ideal for this application with the 
exception of the relatively high initial "leakage" 
through the circular contact points. 
-	
(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=19700000107 2020-03-17T00:26:43+00:00Z
3. Requests for further information may be directed 
to:
Technology Utilization Officer 
Headquarters 
National Aeronautics 
and Space Administration 
Washington, D.C. 20546 
Reference: B70-10111
Patent status: 
No patent action is contemplated by NASA. 
Source: Frank A. Fitz of 
Southern Methodist University 
under contract to 
NASA Headquarters 
(HQN- 1004 1) 
Brief 70-10111	 Category 03
.-


Passive heat transfer control

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server