Research Papers

Characterization and Corrections for Clamp-On Fluid Temperature Measurements in Turbulent Flows

[+] Author and Article Information
Bijan Nouri

German Aerospace Center (DLR),
Institute of Solar Research,
Plataforma Solar de Almería (PSA),
Tabernas 04200, Spain
e-mail: Bijan.nouri@dlr.de

Marc Röger, Christoph Hilgert

German Aerospace Center (DLR),
Institute of Solar Research,
Plataforma Solar de Almería (PSA),
Tabernas 04200, Spain

Nicole Janotte

German Aerospace Center (DLR),
Institute of Solar Research,
Linder Höhe Köln 51147, Germany

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received May 8, 2017; final manuscript received October 11, 2017; published online March 28, 2018. Assoc. Editor: Sandra Boetcher.

J. Thermal Sci. Eng. Appl 10(3), 031011 (Mar 28, 2018) (11 pages) Paper No: TSEA-17-1156; doi: 10.1115/1.4038706 History: Received May 08, 2017; Revised October 11, 2017

A clamp-on measurement system for flexible and accurate fluid temperature measurements for turbulent flows with Reynolds numbers higher than 30,000 is presented in this paper. This noninvasive system can be deployed without interference with the fluid flow while delivering the high accuracies necessary for performance and acceptance testing for power plants in terms of measurement accuracy and position. The system is experimentally validated in the fluid flow of a solar thermal parabolic trough collector test bench, equipped with built-in sensors as reference. Its applicability under industrial conditions is demonstrated at the 50 MWel AndaSol-3 parabolic trough solar power plant in Spain. A function based on large experimental data correcting the temperature gradient between the measured clamp-on sensor and actual fluid temperature is developed, achieving an uncertainty below ±0.7 K (2σ) for fluid temperatures up to 400 °C. In addition, the experimental results are used to validate a numerical model. Based on the results of this model, a general dimensionless correction function for a wider range of application scenarios is derived. The clamp-on system, together with the dimensionless correction function, supports numerous combinations of fluids, pipe materials, insulations, geometries, and operation conditions and should be useful in a variety of industrial applications of the power and chemical industry where temporal noninvasive fluid temperature measurement is needed with good accuracy. The comparison of the general dimensionless correction function with measurement data indicates a measurement uncertainty below 1 K (2σ).

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Fig. 1

Different temperature measurement approaches on pipes: 1—wetted sensor using thermowell with compression fitting, 2—embedded sensor using closed thermowell, and 3—sensor clamped on pipe surface

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Fig. 2

Mounted clamp-on measurement setup without insulation

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Fig. 3

Schematic illustration of clamp on test setup at the KONTAS test facility: 1—pipe, 2—reference PT100 sensors, 3—clamp-on PT100 sensor with sensor holder, 4—copper temperature shield, and 5—insulation

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Fig. 4

Temperature deviation of test sensors to calibrator reference (first cycle, calibration)

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Fig. 5

Temperature deviation of a test sensor to the calibrator reference after corrections with polynomials of Fig. 3. Second and third cycle: with unchanged sensors (no mechanical stress), fourth cycle: after bending (introducing mechanical stress).

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Fig. 6

Influence of thermal insulation on clamp-on measurement method as a function of fluid temperature

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Fig. 7

Influence of temperature shields on clamp-on measurement method

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Fig. 8

Measured and calculated influence of Reynolds number on temperature deviation between fluid and sensor temperature for clamp-on system (exemplarily for Tf = 350 °C)

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Fig. 9

Temperature gradient of clamp-on test setup from fluid to ambient conditions of an exemplary measurement point at the KONTAS test facility (wind speed of 1 m/s and mass flow of 6 kg/s): (a) simplified sketch with the most important temperatures and (b) thermal equivalent circuit describing the heat transfer steps

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Fig. 10

Resulting temperature deviation of the clamp-on measurement system as a function of the absolute HTF temperature for typical conditions of a parabolic trough CSP plant

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Fig. 11

Histogram of the deviation in temperature gradient between values generated by the derived correction function (Eq. (10) and Table 7) and the model equations of Sec. 5.1

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Fig. 12

Comparison of the predictions of the fitted correction function Eq. (10) and the model of Sec. 5, and measurements with the uncorrected clamp-on sensor (Syltherm-800, Tair: 20–30 °C, hair: 6.5–26.3 W/(m2 K); clamp-on geometry and materials as in Sec. 3)



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