A simple transducer is used to measure low rates of convective and conductive heat transfer from a fluid to a cooled surface under steady-state conditions. Temperature drop is measured by two thermocouples imbedded in a rod of low thermal conductivity

Laumann, E. A.

English

NASA Technical Reports Server

October 1964
	 Brief 64-10122 
NASA TECH BRIEF
-I&  
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint 
industry with the technical content of an innovation derived from the space program. 
Simple Transducer Measures Low Heat-Transfer Rates 
STop View of Rod 
Heat Flow 
U Upper Thermocouple	 • 
Thermal Insulation
Rod of Low 
Thermal Conductivity 
ds from YL.a
pper Thermocouple 
Lower Thermocouple 
Electrical Insulation 
Leads from Lower 
Thermocouple II	 II	 II 
Ii	 II	 II 
II	 II	 II 
Leads to Meter
Aluminum Base 
The problem: Measuring low rates (0.1 to 2.0 
BTU/sq ft/sec) of convective and conductive heat 
transfer from a fluid to a cooled surface under steady-
state conditions. 
The solution: A small device (approx. 1/2" long 
x 1/2" O.D.) employing a rod of low thermal con-
ductivity in which two thermocouples are imbedded to 
measure the temperature drop in the direction of heat 
flow.
of chromel-constantan are mounted in recesses in the 
rod, one near the top of the rod and the other near 
the bottom of the rod. Leads from the upper junction 
are wound in a spiral around the rod and pass out 
through holes in the aluminum base. This method of 
winding is to prevent the leads from conducting excess 
heat from the device and thus give a false tempera-
ture reading at the upper junction. The leads from 
both thermocouples are electrically insulated from the 
aluminum base. The wire-wound rod is surrounded 
by fibrous potassium titanate to minimize the loss of 
heat from the rod in a direction transverse to the 
axis of the rod. 
How it's done: The main element of the trans-

ducer, a rod of polytetrafluoroethylene is mounted on

-9a heavy aluminum base. Two thermocouple junctions
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19640000037 2020-03-11T17:06:20+00:00Z
In operation of the device, it is necessary that heat 
be continuously removed from the aluminum base to 
ensure steady-state conditions. This may be done by 
directing ajet of cold inert gas (e.g., nitrogen) onto the 
base. Temperature readings obtained from the two 
thermocouples together with specific parameters of 
the device are inserted into equations which have been 
derived to yield a measure of the rate of heat transfer. 
Notes: 
1. A device employing a rod of polytetrafluoroethyl-
ene can be operated continuously at temperatures 
of up to only 350'F. For operation at higher tem-
peratures a ceramic rod must be substituted for the 
plastic rod. 
2. In calibrating the device, a correction factor must 
be determined to compensate for changes in the 
heat-transfer rate that would be effected by inser-
tion of the device into the thermal environment.
3. Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Jet Propulsion Laboratory 
4800 Oak Grove Drive 
Pasadena, California, 91103 
Reference: B64-10122 
Patent status: NASA encourages the immediate 
commercial use of this invention. It is owned by 
NASA and inquiries about obtaining royalty-free 
rights for its commercial use may be made to NASA 
Headquarters, Washington, D.C., 20546. 
Source: Eugene A. Laumann 
(J PL-466) 
Brief 64-10122


Simple transducer measures low heat-transfer rates

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