Distributed Temperature Measurements Research Articles

An improved method for upscaling borehole thermal energy storage using inverse finite element modelling

Dimensioning of large-scale borehole thermal energy storage (BTES) is inherently uncertain due to the natural variability of thermal conductivity and heat capacity in the storage volume. We present an improved method for upscaling a pilot BTES to full scale and apply the method to an operational storage in Brædstrup, Denmark. The procedure utilizes inverse 3D finite element method (FEM) modelling of distributed temperature measurements inside the BTES for inferring the thermal properties of the subsurface. We find that individual geological layers can be distinguished in terms of their heat capacities and thermal conductivities using inverse modelling. The depth integrated estimate of thermal conductivity differs significantly from that obtained from a single thermal response test (TRT) at the site. As such, we find significant scaling effects in terms of the subsurface thermal conductivity distribution which are expected to be further amplified in an expansion of the pilot BTES to full scale. The methodology presented in this paper therefore provides an improved basis for upscaling pilot BTES systems. The operational data and BTES temperature measurements are published with the present paper in the supplementary material.

Ultrasonic bent waveguides approach for distributed temperature measurement

This paper describes novel techniques for simultaneous measurement of temperatures at multiple locations using two configurations (a) a single transducer attached to multiple waveguides of different lengths (each with a single bend) and (b) single waveguide with multiple bends connected to single transducer. These techniques improve upon the earlier reported studies using straight waveguides, where the non-consideration of the effect of temperature gradients was found to be a major limitation. The range of temperature measurement is from room temperature to maximum utility temperature of the waveguide material. The time of flight difference of reflected ultrasonic longitudinal guided wave modes (L(0,1)) from the bend, which is the reference signal, and another signal from the end of the waveguide, is utilized to measure the local temperature of the surrounding media. Finite element simulations were employed to obtain the appropriate dimensions and other design features of the multiple bent waveguide. This work is of interest to several industrial applications involving melters and furnaces.

Fluid flow and heat transfer modeling in the event of lost circulation and its application in locating loss zones

Lost circulation is one of the most persistent and costly drilling problems that drilling engineers have been struggling with for decades. The pinpointing of the zones of loss allows the treatments to be applied directly to the points of loss rather than to the entire open hole.This paper presents an approach to predict the location of single loss zone in a vertical well by interpreting the transient mud circulating temperature profiles altered by mud loss. The fluid flow and heat transfer numerical model in estimating the transient mud circulating temperature profiles during a lost circulation event was developed. The temperature profile in both the flow conduits (drillpipe and annulus) were modeled using mass and energy balances. The flow rate of drilling mud decreases in the annulus above the loss zone as part of the fluids lost into the fractures, which in turn alters the heat transmission status between the drillpipe, annulus, and near-wellbore formation. The wellbore is divided into two sections, which accounts for single loss zone. Case studies were performed and numerical solution results were presented and analyzed. According to the results, alterations induced by mud loss include: 1) Declines in both annular mud temperature and drillpipe mud temperature over time, and 2) Discontinuity in the first order derivative of annular mud temperature with respect to depth at the location of loss. By matching the simulated results with the distributed temperature measurements at different time stamps, the depth of the loss zone can be identified.

On-Line Characterization of Gamma Radiation Effects on Single-Ended Raman Based Distributed Fiber Optic Sensor

We report distributed temperature measurements based on Raman scattering performed during steady state $\gamma $ -ray irradiation at a dose rate of 1 kGy( ${\rm SiO}_{2}$ )/h and up to a total ionizing dose (TID) of $\sim 0.1 \hbox{MGy}$ . We characterize on-line the evolution of the performances of a single-ended Raman distributed temperature sensor (RDTS) during the $\gamma $ -ray exposure of different classes of commercial multimode fibers (MMFs) acting as the sensing element. RDTS is influenced by the radiation-induced attenuation (RIA) phenomena leading to both large errors in the temperature measurements and a diminution of the useful sensing length. The amplitude of the radiation-induced temperature error strongly depends on the fiber choice and on the irradiation conditions. For the single-ended RDTS operation in the targeted Cigeo application the selection of a radiation tolerant sensing fiber will be mandatory, but not sufficient, to overcome the expected severe ambient conditions around radioactive wastes. For efficient temperature sensing up to an accumulated dose of 0.1 MGy, pre-irradiation of the selected radiation resistant (RR) fibers appears also necessary to improve the sensor performances.

Real-time optimization of an industrial steam-methane reformer under distributed sensing

Industrial hydrogen production takes place in large-scale steam methane reformer (SMR) units, whose energy efficiency depends on the interior spatial temperature distribution. In this paper, a control-relevant empirical reduced-order SMR model is presented that predicts the furnace temperature distribution based on fuel input to a group of burners. The model is calibrated using distributed temperature measurements from an array of infrared cameras. The model is employed to optimize in real-time the temperature distribution and increase the energy efficiency in an industrial furnace. Experimental results confirm that the proposed framework has excellent performance.

Thermal evaluation of coaxial deep borehole heat exchangers

This paper presents a performance study of deep borehole heat exchangers. The coaxial borehole heat exchanger (BHE) has been selected because for the present conditions it has a better performance than the conventional U-tube BHE. A numerical model has been developed to study the coaxial BHE. The model predictions are compared to detailed distributed temperature measurements obtained during a thermal response test. The model is found to accurately predict the behavior of a coaxial BHE. The influence of the flow direction of the mass flow is studied for BHEs in the range 200 m–500 m. A parametric performance study is then carried out for the coaxial case with different borehole depths, flow rates and collector properties. The results clearly show a significant increase in the system performance with depth. In addition, it is shown that with increasing borehole depth, the heat load that can be sustained by the BHE is significantly increased. An overall performance chart for coaxial BHEs for the depths of 300–1000 m is presented. The chart can be used as a guide when sizing deep BHE installations.

Hybrid distributed acoustic and temperature sensor using a commercial off-the-shelf DFB laser and direct detection.

We demonstrate a hybrid distributed acoustic and temperature sensor (DATS) using a commercial off-the-shelf (COTS) distributed feedback (DFB) laser, a single-mode optical fiber, and a common receiver block. We show that the spectral and frequency noise characteristics of the laser, combined with a suitable modulation scheme, ensure the inter-pulse incoherence and intra-pulse coherence conditions required for exploiting the fast denoising benefits of cyclic Simplex pulse coding in the hybrid measurement. The proposed technique enables simultaneous, distributed measurement of vibrations and temperature, with key industrial applications in structural health monitoring and industrial process control systems. The sensor is able to clearly identify a 500 Hz vibration at 5 km distance along a standard single-mode fiber and simultaneously measure the temperature profile along the same fiber with a temperature resolution of less than 0.5°C with 5 m spatial resolution.

基于分布式光纤测温的电缆故障监测系统设计与实现

电缆沿线的温度实时监测是保障其安全运行的重要手段。在理论分析光纤后向拉曼散射和光时域反射原理的基础上，设计了分布式光纤测温系统和方案和软件构架，并将设计的系统应用于动力电缆的在线监测，取得了良好的测试结果，为动力电缆的故障预警提供了可靠的科学手段。 Real-time monitoring of temperature along the cable is very important for ensuring the safe oper-ation. Based on the theoretical analysis of Raman back scattering of optical fiber and optical time domain reflection principle, optical fiber distributed temperature measurement system, scheme and software architecture are designed. The system is applied to the online monitoring of power cable, and good results are achieved. It provides a reliable scientific tool for the fault early warning of power cable.

Raman Distributed Temperature Sensing at CERN

A field trial has been performed at the CERN high-energy accelerator-mixed (CHARM) field facility, newly developed for testing devices within accelerator representative radiation environments, to validate the use of Raman-based optical fiber sensors for distributed temperature measurements in highly radiative environments. Experimental results demonstrate that Raman distributed temperature sensors, operating in loop configuration on radiation-tolerant optical fibers, are able to compensate for wavelength-dependent losses and are, therefore, robust to harsh environments, in which a mixed-field radiation, including protons, neutrons, photons, and other particles, is potentially altering the fiber material properties. The temperature profile measured on commercial radiation-tolerant optical fibers shows that a temperature resolution <1 °C, 0.5-m spatial resolution, is highly reliable and sets the first step toward a distributed measurement system able to monitor the temperature at the CERN’s large hadron collider for safety purposes. Such a system will also be helpful in correcting the radiation-induced attenuation temperature dependence in distributed radiation sensing systems based on radiation-sensitive optical fibers.

Heat-based hyporheic flux calculations in heterogeneous salmon spawning gravels

Groundwater-surface water interactions in rivers are a critically important factor for fish spawning, as streamwater downwelling or upwelling of low-oxygen groundwater can affect egg survival. Assessing such dynamics at the reach scale using distributed temperature measurements as a tracer proved reliable in determining flux rates and directions in the hyporheic zone in a number of studies. Here, we report heat-based vertical flux rates from a heterogeneous gravel-bed stream reach used by spawning Atlantic salmon in the Scottish Highlands. Results showed mostly small downwelling fluxes (~0.3 m d−1), which were largely independent of discharge. Contrasting, and at times unusual flux-depth profiles (e.g., increasing flux with depth) were detected, consistent with the heterogeneous streambed material causing diverse hyporheic flow paths. This was tested in a numerical 2-D model setup attempting to reproduce such behavior with variable random hydraulic conductivity (K) fields. The 2-D model clearly demonstrated that strong deviations from the expected decrease of fluxes with depth can be explained by high heterogeneity coupled with relatively low K fields. This showed that using simple 1-D heat-based flux estimates in combination with 2-D models is a useful approach to testing hypotheses about the influence of variable streambed materials on groundwater–surface water exchange in an ecological context.

A hybrid fiber-optic sensing system for down-hole pressure and distributed temperature measurements

Abstract A hybrid fiber-optic sensing technique, combining the extrinsic Fabry–Perot interferometer (EFPI) based pressure sensor with the incoherent optical frequency domain reflectometry (IOFDR) based distributed temperature sensor (DTS), is presented for down-hole measurements. By using a laser diode as the common light source, a highly integrated hybrid EFPI/DTS sensing system has been developed with a single fiber. With the injection current of the laser diode below lasing threshold, the broadband spontaneous emission light is used for EFPI based pressure sensing; while with the injection current above the threshold, the stimulated emission light is used for Raman based distributed temperature sensing. There is no overlap between the spectral range of the reflected light from the EFPI sensor and the spectral range of the Raman scattered light. Pressure and distributed temperature can thus be measured by using wavelength-division multiplexing (WDM) technology. Experimental results show that both the pressure and the distributed temperature are measured with little interference. Furthermore, the pressure measurement can be compensated by the measured temperature values.

Simplified Brillouin Optical Correlation-Domain Reflectometry Using Polymer Optical Fiber

To perform distributed strain and temperature measurement, we have recently developed simplified Brillouin optical correlation-domain reflectometry (S-BOCDR), in which the light that is Fresnel reflected at the ends of the fiber under test (FUT) is used as a reference light. Here, we implement S-BOCDR using a polymer optical fiber (POF) as an FUT, which provides the following advantages over S-BOCDR using a standard silica single-mode fiber (SMF): 1) The beat signal of the Stokes light and the Fresnel-reflected light that is obtained at the interface between the POF and the SMF (the pigtail of an optical circulator) can be stabilized, and 2) the effect of the zeroth correlation peak can be easily and effectively suppressed by exploiting a so-called Brillouin frequency shift-hopping phenomenon. We then experimentally demonstrate a distributed measurement and detect a 0.46-m-long heated POF section.

Robust Ultrasonic Waveguide Based Distributed Temperature Sensing

This is a novel technique for distributed temperature measurements, using single robust ultrasonic wire or strip-like waveguides, special embodiments in the form of Helical or Spiral configurations that can cover large area/volume in enclosed regions. Such distributed temperature sensing has low cost applications in the long term monitoring critical enclosures such as containment vessels, flue gas stacks, furnaces, underground storage tanks, buildings for fire, etc. The range of temperatures that can be measured are from very low to elevated temperatures. The transduction is performed using Piezo-electric crystals that are bonded to one end of the waveguide which acts as both transmitter and receivers. The wires will have periodic reflector embodiments (bends, gratings, etc.) that allow reflections of an input ultrasonic wave, in a pulse echo mode, back to the crystal. Using the time of fight (TOF) variations at the multiple predefined reflector locations, the measured temperatures are mapped with multiple thermocouples. Using either the L(0,1) or the T(0,1)modes, or simultaneously, measurements other than temperature may also be included. This paper will describe the demonstration of this technology using a 0.5MHz longitudinal piezo-crystal for transmitting and receiving the L (0, 1) mode through the special form of waveguide at various temperatures zones.

Methodological challenges with marijuana research in the U.S

In this paper a simplified and not fully discretized numerical model is used to simulate the performance of a non-grouted (water filled) borehole heat exchanger (BHE). The model enables simulation of the initial transient behavior of a BHE and gives transparent insight into the heat transfer mechanism acting during the startup and operation of the BHE installation. To account for the thermal effect of natural convection that arises in non-grouted BHEs, the model is complemented with a Nusselt-correlation. The model is presented in detail in Holmberg et al. (2014) and in the present paper it is evaluated based on distributed temperature measurements from Acuña (2010). The measurements were obtained during a distributed thermal response test (DTRT) and during heat pump operation, both on a 261 m deep borehole equipped with a U-tube collector and a distributed temperature sensing system. Despite the simplifications involved with the model, it agrees well with the measured data even on a time scale on the order of minutes. The Nusselt number related to natural convection in the borehole was found to be 6.4 during the DTRT and 3.68 during heat pump operation. This indicates the large differences in the borehole thermal resistance during heat injection and heat extraction.

Numerical model for non-grouted borehole heat exchangers, Part 2—Evaluation

In this paper a simplified and not fully discretized numerical model is used to simulate the performance of a non-grouted (water filled) borehole heat exchanger (BHE). The model enables simulation of the initial transient behavior of a BHE and gives transparent insight into the heat transfer mechanism acting during the startup and operation of the BHE installation. To account for the thermal effect of natural convection that arises in non-grouted BHEs, the model is complemented with a Nusselt-correlation. The model is presented in detail in Holmberg et al. (2014) and in the present paper it is evaluated based on distributed temperature measurements from Acuña (2010). The measurements were obtained during a distributed thermal response test (DTRT) and during heat pump operation, both on a 261m deep borehole equipped with a U-tube collector and a distributed temperature sensing system. Despite the simplifications involved with the model, it agrees well with the measured data even on a time scale on the order of minutes. The Nusselt number related to natural convection in the borehole was found to be 6.4 during the DTRT and 3.68 during heat pump operation. This indicates the large differences in the borehole thermal resistance during heat injection and heat extraction.

Long-Range High Spatial Resolution Distributed Temperature and Strain Sensing Based on Optical Frequency-Domain Reflectometry

A novel approach to realize long-range distributed temperature and strain measurement with high spatial resolution, as well as high temperature and strain resolution, is proposed based on optical frequency-domain reflectometry (OFDR). To maintain the high measurement resolution and accuracy while increasing the sensing length, an optimized nonlinearity compensation algorithm is implemented to ensure a large wavelength tuning range. The compensated OFDR trace exhibits improved sensing resolution at a short distance, and the spatial resolution gradually deteriorates at the far end due to accumulated phase noise induced by fast tuning of the laser wavelength. We demonstrated the spatial resolution of 0.3 mm over a single-mode fiber sensing length of over 300 m, and temperature and strain resolution of 0.7 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex></formula> and 2.3 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\varepsilon$</tex></formula> with spatial resolution of up to 7 cm, respectively.

Evaluation of thermal imaging system and thermal radiation detector for real-time condition monitoring of high power frequency converters

We have carried out at laboratory test to study the feasibility of using thermal radiation detectors for online thermal monitoring of electrical systems in wind turbines. A 25 kW frequency converter is instrumented with a thermal camera, operating in the 8–14 μm wavelength range, and a single-pixel thermopile sensor, operating in the 4–8 μm wavelength range, to monitor the temperature development of the power electronics under various load sequences. Both systems performed satisfactorily with insignificant temperature deviations when compared to data from calibrated point contact sensor. With spatial averaging over a 7 mm × 7 mm for the camera and temporal averaging over 60 s for the thermopile sensor, we reduce the root mean square noise to 45 mK and 68 mK respectively. The low cost and simple operation of the thermopile sensor make it very attractive for condition monitoring applications, whereas the attractive feature of the camera is the possibility of multi-point or distributed temperature measurements.

Distributed Temperature Sensing in Polymer Optical Fiber by BOFDA

Distributed temperature measurements in a perfluorinated graded-index polymer optical fiber (POF) with 50- μm core diameter are reported for the first time, to the best of our knowledge. Brillouin optical frequency-domain analysis is shown to be able to resolve spatially the temperature-dependent Brillouin frequency shift profile along a 20-m POF fiber sample, at a nominal spatial resolution of 4 m. The results indicate that POFs are potentially useful for distributed temperature measurements based on stimulated Brillouin scattering.

Evaluation of the Performance of Distributed Temperature Measurements With Single-Mode Fiber Using Rayleigh Backscatter up to 1000$^{\circ}{\rm C}$

In this paper, inexpensive single-mode silica optical fibers were interrogated with Luna Innovations' optical backscatter reflectometer to perform distributed temperature measurements at temperatures up to 1000 °C. Measurements of the Rayleigh backscattered signal were taken continuously to determine the amount of light that is backscattered as a function of temperature and position along the length of the fiber. These data were post-processed to determine the spectral shift in the Rayleigh backscatter signature. The spectral shift data were then calibrated to a change in temperature. This paper determines an upper operational temperature limit of 650 °C for the distributed measurement technique based on Rayleigh backscatter using Corning's SMF-28e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> commercially available single-mode fiber.

Adaptive data acquisition algorithm in Raman distributed temperature measurement system

The sampling rate of data acquisition card (DAQ) employed in Raman distributed temperature sensor (RDTS) system is set to be constant, which exceeds 100MHz for a higher spatial resolution of 1m. The acquired data need to be averaged tens of thousands times to improve the signal-to-noise ratio (SNR). High-speed DAQ and cumulative average algorithm put forward higher request to the hardware device and the stability of data transmission between DAQ and computer. In this paper we propose a new adaptive data acquisition algorithm to regulate the sampling rate automatically according to the changes of data. The theoretical simulation of this algorithm in RDTS is analyzed in detail. The results indicate that the amount of computation is reduced efficiently and the measurement time is decreased correspondingly.