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

Abstract

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).

State-of-the-Art Measurement Instrumentation and Most Recent Measurement Techniques for Parabolic Trough Collector Fields

“…Closed thermowells, therefore, protect the sensing element in such aggressive environments. The sensor location can influence the measurement error significantly higher than the error tolerance given by the instrument's manufacturer [5,7]. Besides the permanently installed temperature sensors, clamp-on sensors are often used for temporally limited, special measurement events such as the recalibration of existing sensors, performance and acceptance testing or troubleshooting during operation [7].…”

“…To determine the HTF temperature, a correction function has to be applied. In the case of Nouri et al [7], a polynomial correction function from experimental data with typical solar field parameters was carried out. In addition, a correction via dimensional analysis for more general applications was performed.…”

Non-invasive temperature measurement of turbulent flows of aqueous solutions and gases in pipes

“…The situation is axisymmetric at this stage, and the thermal behavior of the setup in a steady state can be described by a linear chain of thermal resistances (see e. g. [5,8] for previous work on this approach). Details of our specific formulation and use of the model are given in Section 3.1.…”

“…Through dimensional analysis, a considerable number of parameters are organized to give an estimate that demonstrates a range of process conditions where a surface measurement is adequate. Nouri et al [8] propose an elaborated shielded cable sensor setup for achieving reliable accuracy indicating clearly that the performance of the sensors can be improved with careful design.…”

Optimization of parabolic trough power plant operations in variable irradiance conditions using all sky imagers

“…These additional data provide flow and temperature measurements within the test loops with a high temporal resolution. For this purpose the loops were equipped with a FLEXIM FLUXUS ADM 6725 clamp on ultrasonic flow meters with wave injectors for high temperature applications at the loop center (cross over piping) and a clamp-on temperature measuring system based on PT100s at the loop inlet and outlet (Nouri et al 2018a). The validation was conducted over distinct cases including normal operations with predominantly clear conditions, start-up situations in clear mornings and conditions with strong transients due to cloud passages.…”