Technical Briefs

Dynamic Calibration of a Coaxial Thermocouples for Short Duration Transient Measurements

[+] Author and Article Information
Rakesh Kumar

Research Scholar

Niranjan Sahoo

Associate Professor
e-mail: shock@iitg.ernet.in
Department of Mechanical Engineering,
Indian Institute of Technology Guwahati,
Guwahati 781 039, India

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 31, 2012; final manuscript received May 5, 2013; published online September 27, 2013. Assoc. Editor: Oronzio Manca.

J. Heat Transfer 135(12), 124502 (Sep 27, 2013) (7 pages) Paper No: HT-12-1258; doi: 10.1115/1.4024593 History: Received May 31, 2012; Revised May 05, 2013

Coaxial thermocouple sensors are suitable for measuring highly transient surface heat fluxes because the response times of these sensors are very small (∼0.1 ms). These robust sensors have the flexibility of mounting them directly on the surface of any geometry. So, they have been routinely used in ground-based impulse facilities as temperature sensors where rapid changes in heat loads are expected on aerodynamic models. Subsequently, the surface heat fluxes are predicted from the transient temperatures by appropriate one-dimensional heat conduction modeling for semi-infinite body. In this backdrop, the purpose of this work is to design and fabricate K-type coaxial thermocouples in-house and calibrate them under similar nature of heat loads by using simple laboratory instruments. Here, two methods of dynamic calibration of coaxial thermocouples have been discussed, where the known step loads are applied through radiation and conduction modes of heat transfer. Using appropriate one dimensional heat conduction modeling, the surface heat fluxes are predicted from the measured temperature histories and subsequently compared with the input heat loads. The recovery of surface heat flux from laser based calibration experiment under-predicts by 4% from its true input heat load. Similarly, recovery of surface heat flux from the conduction mode calibration experiments under-predicts 6% from its true input value. Further, finite-element based numerical study is performed on the coaxial thermocouple model to obtain surface temperatures with same heat loads as used in the experiments. The recovery of surface temperatures from finite element simulation is achieved within an accuracy of ±0.3% from the experiment.

Copyright © 2013 by ASME
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Fig. 4

Schematic representation calibration technique for coaxial thermocouple: (a) laser based experiment (Method I); (b) conduction based experiment (Method II)

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Fig. 3

Determination of TCR: (a) schematic diagram of oil bath calibration method; (b) variation of voltage during heating and cooling process

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Fig. 5

Comparison of temperature history for various step heat loads: (a) 60 kW/m2; (b) 70 kW/m2; (c) 80 kW/m2; and (d) 90 kW/m2

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Fig. 6

Recovered of surface heat flux by using one-dimensional modeling compared with input heat loads at 60 kW/m2, 70 kW/m2, 80 kW/m2, and 90 kW/m2

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Fig. 7

Finite element modeling of the coaxial thermocouple: (a) and (b) computational model; (c) enlarged view to show the finite element mesh at the interface region

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Fig. 2

Calibration methodology for the co-axial thermocouple

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Fig. 1

A coaxial thermocouple (K-type): (a) schematic diagram; (b) geometric configuration




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