Array Of Thermocouples Research Articles

Development of a thermal diagnostic system for the SPARC tokamak.

The SPARC tokamak will have scrape-off layer parallel heat fluxes on the order of GW/m2. Managing power exhaust of this magnitude will be mandatory for a reactor-scale device. To enable this mission, a thermal diagnostic suite will be deployed to measure the in-vessel structural temperatures to ensure they do not exceed their design limits and to determine the spatial distribution and magnitude of energy deposited onto the first wall. Thermocouples and fiber Bragg gratings have been selected for their environmental compatibility and proven useful on other fusion devices. High-density thermocouple arrays in the divertor will have two spring-loaded thermocouples per divertor target tile, which are being used as calorimeters, and will look to resolve the temperature distribution within the tile due to a swept or static strike point. All systems will need to survive the vacuum vessel bake, set at a minimum plasma facing surface temperature of 350 °C, which presents a particularly challenging environment for the fiber-based subsystem. Along with this temperature design requirement, all the materials in the primary vacuum need to be ultra-high vacuum compatible, able to handle the expected neutron and gamma radiation, as well as tritium exposure, all of which restrict material options. Finally, due to the expected activated environment in SPARC, there will be little chance to replace defective sensors, so system resilience is ensured through toroidal redundancy, probe material selection, and mitigating the impact of common-mode failures. Initial testing of sensors show that intershot structural measurements are sufficiently captured with the raw output, but intrashot measurements of the plasma facing material requires model-based interpretive tools.

Design and fabrication of metal spherical conformal thin film multisensor for high-temperature environment

Conformal thin-film sensors enable precise monitoring of the operating conditions of components in extreme environments. However, the development of these sensors encounters major challenges, especially in uniformly applying multiple film layers on complex metallic surfaces and accurately capturing diverse operational parameters. This work reports a multi-sensor design and multi-layer additive manufacturing process targeting spherical metallic substrates. The proposed high-temperature dip-coating and self-leveling fabrication process achieves high-temperature thin-film coatings with excellent uniformity, high-temperature electrical insulation, and adhesion properties. The fabricated Ag/Pt thin film thermocouple arrays and a heat flux sensor exhibit a maximum temperature resistance of up to 960 °C, with thermoelectric potential outputs and high-temperature resistance closely mirroring those of wire-based Ag/Pt thermocouples. Harsh environmental testing was conducted using high-power lasers and a flame gun. The results show that the array of thin-film conformal thermocouples more accurately reflected temperature changes at different points on a spherical surface. The heat flux sensors achieve responses within 95 ms and withstand environments with heat fluxes over 1.2 MW/m2. The proposed multi-sensor design and fabrication method offers promising monitoring applications in harsh environments, including aerospace and nuclear power.

Experimental study of the temperature profile induced by the tunnel wall fire plume at various source-ceiling heights

The smoke temperature profile beneath the ceiling of tunnel is one of the most important parameters to evaluate the tunnel fire risk and guide the early fire detection. This paper investigates experimentally the temperature profile induced by the tunnel wall fire plume at various source-ceiling heights. A series of experiments were carried out in a reduced-scale tunnel and a burner combustion inside. The burner elevation above the tunnel floor was changed at the center of the tunnel, and it attaches the side-wall of the tunnel to simulate the wall fire plume evolution with fire growth inside the tunnel. The temperatures beneath the ceiling were measured by the thermocouple array at the corner between the ceiling and side-wall of the tunnel. The maximum temperature beneath the ceiling could be correlated by the heat release rate and the source-ceiling height. A new characteristic parameter model considering the virtual point source at the side of the tunnel was proposed firstly considering the tunnel fire scenario to describe the tunnel plume temperature profile. The obtained experimental data and proposed temperature profile model in this work provide a basic understanding of the heat/thermal impact on the tunnel wall fire plume.

Characterization and Calibration of a Photodiode Based Pyranometer for Solar Energy Applications

<p>In the domain of solar science, a pyranometer assumes a pivotal position, functioning as an indispensable tool for appraising solar irradiance across the abbreviated wavelengths of the solar spectrum, spanning from 300 to 3000 nanometers. Conventional pyranometers typically employ intricate and labour intensive thermopiles. These devices rely on arrays of thermocouples interconnected either serially or in parallel and necessitate rare earth minerals for efficient operation. In this investigation, we advocate for an innovative methodology employing photodetectors, specifically photodiodes and phototransistors, to surmount the limitations linked with traditional pyranometers. Photodiodes, commonly utilized for this purpose, proffer numerous benefits, including accelerated response times, customizable spectral range selection, and cost-effectiveness. Nonetheless, they cannot entirely supplant thermopiles owing to impediments such as the generation of dark current in the absence of illumination, temperature-dependent functionalities, and saturation at elevated irradiance levels. To counteract these constraints, we have devised a pioneering design of a photodiode-based pyranometer that incorporates a data acquisition system and correction mechanism. This innovative approach furnishes a feasible resolution for autonomous solar radiation measurement, furnishing enhanced precision and dependability.</p>

Temperature distribution and heat transfer mechanism at the upstream surface of a moving burner

Moving fires are challenging because of their aerodynamic effects, which have gained wide attention recently. Concurrent flame spread can occur due to tilted flames, and the backward heating behavior of moving fires has not yet been addressed. To investigate these fundamental problems, a 1:10 scale burning car with an embedded propane-fueled porous burner was designed. Moving model experiments with eight heat release rates (HRRs) ranging from 6.1 to 27.3 kW and seven moving velocities varying from 2 to 10 m/s were conducted. The upstream two-dimensional temperature and the heat flux were measured by a thermocouple array and water-cooled heat flux gauges, respectively. The flame was extinguished when the velocity of the burning car (VBC) reached a threshold value, and this critical extinction VBC generally increases with the HRR. The maximum temperature on the upstream surface generally increased with the increase in VBC, and an exponential increase followed by a power law decay was observed for larger dimensionless HRRs (6.24–7.243). The upstream centerline temperature was correlated as two regimes because the difference between the intermittent and plume regions was small at higher VBCs. The exponents for the intermittent and plume regions were 0 and −7/2, respectively. Finally, the heat transfer mechanism for moving fires was elucidated. The movement effect played a dual role: accumulating and dissipating heat during the combustion process, and the cooling effect of the fuel-rich zone was more obvious for larger fuel supply flows.

An experimental setup for investigating the blowdown of liquid CO2 down to -50°C

In many Carbon Capture and Storage (CCS) technologies, CO2 is transported in a dense phase between 1 and 10 MPa, depending on the temperature. Previous investigations demonstrated that major accidents may occur during transportation or transfer operations in case of vessel or pipe depressurization to the atmosphere. Amongst the scenarios potentially leading to this, tank blowdown is a major concern due to two factors: the risk of brittle rupturing caused by low temperatures and the possibility of dry ice formation in the piping. Current flow models cannot properly model this, and further experimental evidence and detailed data are required.To provide the required information, a specific experimental setup was developed and tested. The tank is a 2 m3 sphere, carefully insulated and connected to a 40 mm diameter, 3 m long release pipe terminated by a discharge orifice to control the depressurization rate. The pipe can be connected either on the side of the vessel to release the gaseous phase or at the bottom to release the liquid phase.Optic ports are provided on the vessel and on the pipe to observe phase transition and monitor the liquid level. The instrumentation is a set of pressure transducers and arrays of thermocouples inside the CO2 and in the shell of the vessel. The tank is continuously weighed during the blowdown and the data are treated so that the mass flowrate can be obtained.The performance of the system is discussed based on a gaseous phase blowdown starting from a half-filled vessel with liquid CO2 at -38 °C and 1 MPa. Detailed data are presented and discussed. All phases - liquid, gas, and solid - appeared during the release, and temperatures dropped to nearly -80 °C in the shell and lasted for hours.

Selection of Exposure Parameters for a HIFU Ablation System Using an Array of Thermocouples and Numerical Simulations

Image-guided High Intensity Focused Ultrasound (HIFU) technique is dynamically developing technology for treating solid tumors due to its non-invasive nature. Before a HIFU ablation system is ready for use, the exposure parameters of the HIFU beam capable of destroying the treated tissue without damaging the surrounding tissues should be selected to ensure the safety of therapy. The purpose of this work was to select the threshold acoustic power as well as the step and rate of movement of the HIFU beam, generated by a transducer intended to be used in the HIFU ablation system being developed, by using an array of thermocouples and numerical simulations. For experiments a bowl-shaped 64-mm, 1.05 MHz HIFU transducer with a 62.6 mm focal length (f-number 0.98) generated pulsed waves propagating in two-layer media: water/ex vivo pork loin tissue (50 mm/40 mm) was used. To determine a threshold power of the HIFU beam capable of creating the necrotic lesion in a small volume within the tested tissue during less than 3 s each tissue sample was sonicated by multiple parallel HIFU beams of different acoustic power focused at a depth of 12.6 mm below the tissue surface. Location of the maximum heating as well as the relaxation time of the tested tissue were determined from temperature variations recorded during and after sonication by five thermo-couples placed along the acoustic axis of each HIFU beam as well as from numerical simulations. The obtained results enabled to assess the location of each necrotic lesion as well as to determine the step and rate of the HIFU beam movement. The location and extent of the necrotic lesions created was verified using ultrasound images of tissue after sonication and visual inspection after cutting the samples. The threshold acoustic power of the HIFU beam capable of creating the local necrotic lesion in the tested tissue within 3 s without damaging of surrounding tissues was found to be 24 W, and the pause between sonications was found to be more than 40 s. (f-number 0.98) and propagated in two-layer media: water/ex vivo pork loin tissue (50mm/40mm). The thickness of a water layer was determined from a nonlinear propagation model. To determine a threshold power of the HIFU beam capable of creating a necrotic lesion in small volume within a tested tissue during exposure less than 3s the tissue samples were sonicated by parallel HIFU beams with a varied acoustic power (8W - 36W) focused at a depth of 12.6 mm below the tissue surface. The location of the maximum heating spot induced by these beams as well as the tissue relaxation time were determined from temperatures recorded by a thermocouple array placed on the acoustic axis of each HIFU beam. The results obtained enabled to detect the location of necrotic lesions as well as the scanning speed of the tumor by means of the HIFU beam focus. The location of necrotic lesions was verified by ultrasonic images of tissue samples after their sonication and by visual inspection of visible lesions after cutting the samples. Results of the experiments showed that the threshold acoustic power of the HIFU beam capable of creating local necrotic lesion in the ex vivo pork loin tissue within 3s without damaging of surrounding tissue structures amounted to 24 W, and the interval between exposures, resulting from the relaxation time of tissue, was above 40 seconds.

Transverse and lateral temperature profiles of the window-ejected thermal plume along the facade

The window-ejected thermal plume along the building facade is one of the most classical scientific problems of building fire dynamics, which is an important transition of the fire from the inside of the compartment to the building facade. The present study investigates the temperature profiles and evolutions of the window-ejected thermal plume by experimental and theoretical analysis. The experiments were conducted using a reduced-scale cubic compartment and a facade. Three-dimensional (transverse/lateral/vertical) temperature fields are measured and quantified by the thermocouple array considering various heat release rates, window dimensions and its aspect ratios. It is found that: (1) the vertical temperature along the center line of facade first increases then changes a little at the flame region, decreases at the plume region. (2) The transverse or lateral temperature decreases more significantly at the flame region than the plume region. (3) For the flame region, the temperature first changes a little or decreases slightly with increasing transverse distance, however, for the plume region, the temperature first increases, then decreases with increasing transverse distance. A physical model of the window-ejected thermal plume considering the flame and plume regions including characteristic length scales is proposed to describe the transverse and lateral temperature profiles, in which the window characteristic length, effective characteristic width/thickness and the height above the neutral plane are considered in general to reflect temperature profile. The present study provides new observations, experimental data and theoretical analysis of the window-ejected thermal plume temperature profile, which is beneficial for the building facade fire-proof design.

Spray impact onto a hot solid substrate: Film boiling suppression by lubricant addition

Spray cooling of solid substrates is one of the methods used in various industrial processes such as forging, quenching or other metallurgical applications, electronics, pharmaceutical industry, medicine, or for cooling of powerful electrical devices. Spray cooling is governed by various hydrodynamic and thermodynamic processes, like drop impact, heat conduction in the substrate and convection in the spreading drops, and different regimes of boiling. The problem of modeling spray cooling becomes even more challenging if the liquid is multicomponent. The presence of components with various physicochemical properties (surfactants, binders, dispersed particles, etc.) can significantly affect the entire process of spray impact, as well as the outcome of the known cooling regimes and could lead to a formation of a thin deposited layer on the substrate. In this experimental study, spray impact onto a substrate, initially heated to temperatures significantly exceeding the liquid saturation point, is visualized using a high-speed video system. The heat transfer associated with spray impact is characterized using an array of thermocouples installed in a thick metal target. As a working fluid, a mixture of a distilled water and industrial white lubricant was used. It is observed that the presence of very small concentrations of lubricant augments the heat flux dramatically, particularly at high wall temperatures, at which usually film boiling is observed for spray cooling by using distilled water. Three main mechanisms lead to the increase of heat flux and shift of the Leidenfrost point. They are caused by the significant viscosity increase of the evaporating lubricant solutions, by an increase of the substrate wettability and by the emergence of stable liquid sheets between bubbles, preventing their coalescence and percolation of the vapor channels.

Thermal characteristics of a 90-mm bore cylindrical roller bearings for aerospace applications: All-steel versus hybrid bearings

Modern aircraft engines have to meet rigorous requirements such as thrust to weight ratio, efficiency and new regulations related to environment protection. These requirements affect all engine modules and components, including rolling element bearings. The latter have to withstand severe operating conditions because of the high thermal impact due to elevated rotational speeds and loads. In this study, two test campaigns were carried out under realistic operating conditions of load, speed, and oil flow rate to investigate and compare the thermal characteristics of two distinct cylindrical roller bearings: a hybrid bearing featuring silicon nitride (Si3N4) rollers and an all-steel bearing. Each bearing was instrumented with an array of thermocouples around its circumference to determine temperature profile under various test conditions. In addition, oil supply and drain temperatures were also measured to estimate the power loss. The experiments were conducted on a high-speed rolling-element test rig operating at speeds up to 30,000 rpm and under radial loads of up to 4500N.

Review on temperature monitoring system for welding application – A case study on thermocouple array

Process Monitoring System is implemented in machining process to get the quality products, increase the precision, reduce defects, reduce machining time. The process monitoring system, involves in monitoring many parameters such as temperature, force, pressure, voltage, vibration etc., these parameters are implemented in machining process like lathe operation, milling operation, drilling operation, boring, welding etc. On a traditional way of process monitoring system, there are two techniques namely sensor-based technique and image processing technique. In sensor-based techniques different types of sensors has been used for monitoring such as thermocouple, thermistor, RTD, pressure sensor, accelerometer, vibration sensor, load cell, strain gauge etc., these sensors have been calibrated with a microcontroller for data analysis. Image Processing technique involves in capturing the radiation of the machined/machining product by using Infrared camera, ultraviolet camera, photoelectric thermoscope, optical thermoscope, thermal image camera, continuous circuit television etc., the data captured by using the image sensing devices has been processed and analysed by using machine learning algorithm. In this work monitoring system was developed for monitoring the temperature of the weld region that were welded using MIG/TIG, GTAW, GMAW, Laser, Gas Welding. It can be achieved by using Sensor-based technique. A K-Type thermocouple is fixed with a titanium alloy. This kit is placed under the welded metal and the heat distribution of the metal is studied and analysed.

Liquid Metal‐Carbon Fiber Thermocouple Array for Detection of Human Thermal Parameters

AbstractContinuous and accurate measurement of human thermophysical properties has become a vital research field in non‐invasive physiological diagnosis. However, traditional electronic devices have been greatly restricted due to the disadvantages of large volume, heavy weight, and mechanical rigidity. In this work, a kind of fiber‐structured LMs thermocouples composed of LMs fibers and nickel‐coated carbon fibers to solve the dilemma of good thermoelectric performance and sufficient flexibility is synthesized. With high thermoelectric properties as well as flexibility and knittability, the fiber‐structured LMs thermocouples can be assembled into a thermocouple array for multipoint temperature measurement in living organisms. While the nickel‐coated carbon fiber as the electric heating component further endowed the heating function for the fiber‐structured LMs thermocouples array, thus a linear heat source‐pulse heating method is successfully developed for qualitative/quantitative thermophysical parameters measurement (including thermal conductivity, thermal diffusivity, and blood perfusion rate). Collectively, the fiber‐structured LMs thermocouple array has shown promising prospects in human physiological measurement and thermophysical properties measurement.

Design and application of a thermal characteristic test platform for hydrogen fuel cells

<p indent="0mm">A high-power, full-load domestic hydrogen fuel cell faces the thermal management challenges of temperature consistency and waste heat utilization. To obtain the thermal characteristics of a hydrogen fuel cell, a modular test platform was built, and application research was conducted to verify the functionality of the platform. The test platform included a cooling module, a thermal characteristic test module, a data acquisition module, and a control module. On the basis of monitoring the key temperature of thermal management and real-time analysis of the heat production, thermal imaging and thermocouple arrays were used to test and evaluate the temperature consistency, aiming to provide test methods and a data basis for the research of advanced thermal management technologies, such as waste heat utilization, and the improvement of temperature uniformity. This work is of great significance for promoting the energy saving and high efficiency of fuel cell vehicles.

Analysis of grain tribology and improved grinding temperature model based on discrete heat source

A high grinding temperature will cause thermal damage to a workpiece surface and deterioration of surface integrity, which is the bottleneck of grinding. The present grinding temperature theoretical model is based on grain homogeneity and the continuous heat source distribution in the grinding zone. However, the random change in interference between the effective grains and a workpiece during the machining process causes a change in the grain tribological properties, resulting in varying transient grinding temperatures. Based on the current situation, the grain tribological mechanism and an improved temperature model based on a discrete heat source are proposed to reveal the temperature variation law of a workpiece in an actual grinding process. First, the surface topography model of a grinding wheel is established based on the geometric characteristics of grains, and the determination mechanism of effective grains is revealed. Furthermore, the interference mechanical behavior of the grains and workpiece is analyzed according to the kinematic law of grains in the sliding, plowing, and cutting stages. The mechanical model and specific grinding energy model at different stages are established, and the thermal distribution mechanism of effective grains is revealed. Finally, a temperature field mathematical model of a discrete heat source is established, and numerical simulation is performed to demonstrate the dynamic temperature change process of different grains. A new experimental method for measuring temperature at different positions of the workpiece with a bipolar thermocouple array is designed, and a regional numerical simulation and experimental temperature comparison method is innovatively proposed. Experimental results show that the grinding temperature measured under different cutting depth conditions is in good agreement with the numerical results, and the variation law is consistent. The minimum error in 64 groups of experimental measuring and numerical calculation comparison zones can reach 4.9%, and the proportion of zones with errors less than 10% can approach 86%. This study will provide a theoretical basis for the accurate suppression of workpiece surface thermal damage and the development of precision grinding in engineering discipline and machinery industry.

Weather and Fuel as Modulators of Grassland Fire Behavior in the Northern Great Plains.

Fuel and weather interact to affect wildland fire behavior, but little is known about associations between these variables in the northern Great Plains of North America. Few studies consider rate of spread or statistically test the influence of fuel and weather. We measured overall fuel load and moisture ahead of prescribed fires in North Dakota, USA, and used a thermocouple array to measure two-dimensional rate of spread, soil surface temperature, and aboveground flame temperature, to compare with fire weather data. Flame temperatures averaged 225 °C during spring burns and 250 °C during fall burns, and were generally higher with greater fuel loads and lower overall fuelbed moisture. Surface temperatures averaged ≈100 °C, although 50% of observations were ≤60 °C. Fires spread at an average of 2.5 m min-1, increasing with wind speed. As such, prescribed fire in northern Great Plains working rangeland appear to spread slowly and effect low soil surface temperatures, often limited by high fuelbed moisture. Fire behavior measurements respond differently to variability in fuel and weather. Belowground heating is likely minimal. We suggest ecologists ought to consider which fire behavior measurements best relate to fire effects, and managers consider weather and ignition pattern mitigations when fuels constrain desired fire behavior to ensure effective burns.

Atomic Layer Thermopiles: Comprehensive static calibration, comparison and application in subsonic and supersonic flows

This paper compares the calibration of different heat flux sensors in radiation- and convection-based sub- and supersonic operation. First, four heat flux sensors based on different principles: ALTP (Transverse Seebeck Effect), HFM-8E (differential-layer device), coaxial Thermocouple and a TG-2000 (circular-foil gage) are calibrated in a laser-based radiation setup. In a second step, all heat flux sensors are compared with a slug-calorimeter within a subsonic convection-dominated facility based on stagnation-point measurements of an impinging hot air jet. The obtained results indicate that a sensitivity transfer between a radiative calibrated sensor used in a mainly convective environment is not always possible and can lead to significant, systematic errors. Calibration in a subsonic shear flow with thermocouple readings demonstrate small divergence from the manufacturer provided sensitivity. Finally, supersonic testing with high frequency shock-boundary layer interactions highlight the need for ALTP rather than the conventional use of thermocouple arrays to resolve the high frequency phenomena associated with shock boundary layer interactions.

Flexible miniaturized thin film thermocouples arrays for high temperature applications

Thin film thermocouples (TFTCs) are critical for surface temperature measurements of hot components in high temperature environments. In this paper, miniaturized Pt/Pt-10%Rh thin film thermocouple arrays were fabricated on flexible Hastelloy substrates by magnetron sputtering. The morphology and microstructure of Al2O3/Y2O3 insulating films were investigated by a field-emission scanning electron microscope with an energy dispersive X-ray spectroscopy system. The thermoelectric performance of the TFTCs arrays was investigated by cyclic calibration and bending tests. During the whole calibration process, the average maximum temperature differences (ΔT′ ) of measuring points 2, 3, and 4 are 637 °C, 617 °C, and 574 °C, respectively, which differ from the maximum temperature difference (ΔT max ) of measuring point 1 by -13 °C, -34 °C, and -76 °C, respectively. The calibration results show that each single measuring point has good repeatability and stability during the five calibration processes, and the temperature difference between multiple measuring points is obvious, stable and reliable. The thermoelectric properties of the thin film thermocouple arrays barely change after 10,000 cyclic bending tests.

Acoustic Speed Measurement Platform for Monitoring Highly Concentrated Gas Temperature Distribution

Acoustic thermography reconstructs 2-D gas temperature distributions by using sound speeds from multiple paths across a plane. However, a reliable platform that can provide accurate sound speeds in a highly concentrated temperature distribution environment has not been fully discussed. Most of the existing temperature reconstruction algorithms are developed using simulated data and validated with customized systems. The results from the reported systems are difficult to reproduce due to the lack of critical information, such as the methods for determining the time of flight (TOF). Moreover, previous attempts have not investigated the effect of a sharp temperature gradient, in which the difference of acoustic impedance between high- and low-temperature regions cannot be neglected. In response, this letter demonstrates a reliable acoustic platform designed specifically for measuring the acoustic speeds in an environment with a critical temperature distribution. The main components of the proposed platform are discussed in detail, including the TOF calculation technique, the hardware architecture, and the working principle. The performance of the platform has been evaluated by comparing the captured acoustic velocities and the reconstructed temperature map with results from a thermocouple array. The average acoustic velocity measured by the proposed platform for 100 times is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$341 \pm \ 3$</tex-math></inline-formula> m/s at room temperature (25 °C) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$354 \pm \ 5\ $</tex-math></inline-formula> m/s after heater turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> (38.27 °C). Moreover, the 2-D temperature map reconstructed by acquired acoustic velocities also matches the results from the thermocouple array. Therefore, the proposed platform can be considered as an accurate and reliable acoustic speed measurement system for monitoring the 2-D temperature distribution.

Heat transfer enhancement in fin channels using aeroelastically fluttering reeds

AbstractForced convection heat transfer in rectangular channels is enhanced by aeroelastically fluttering thin reeds extending over the channel span. The resulting small‐scale vortical motions substantially increase local heat transfer at the channel walls and mixing between the wall thermal boundary layers and the channel's core flow. Mechanisms associated with evolution of these small‐scale motions and their thermal effects are experimentally studied in a channel of width W, span , and length . Reed effects on heat transfer are characterized at Reynolds numbers (Re) of 2000, 7000, and 12,000 using embedded thermocouple arrays, and related to small‐scale motions by particle image velocimetry and hot‐wire anemometry. Reed‐induced small‐scale motions increase turbulent kinetic energy, increasing the global Nusselt number (by up to 145% at Re = 7000), with enhancement being sustained even when the base flow becomes fully turbulent (Re = 12,000). Enhancement is also demonstrated for fin arrays. Single‐reed computations show the effect of reed length on enhancement. Computations with two reeds, one downstream of the trailing edge of the other, predict heat transfer enhancement significantly greater than twice the single‐reed result, and point the way to use of a streamwise array of reeds in long channels. A techno‐economic analysis for an air‐cooled condenser suggests that fluttering reeds can be economically justified for a range of operating conditions.

Sensors-on-paper: Fabrication of graphite thermal sensor arrays on cellulose paper for large area temperature mapping

This paper reports on a fabrication method to obtain multiple thermal sensors by employing an array of graphite thermocouple patterns on commonly available Xerox paper. The graphite thermocouples are patterned using two different grade graphite pencils, which show a stable and reproducible thermal sensitivity. The fabricated paper devices with multiple thermocouple arrays are capable of producing temperature mapping of the desired area. Different thermal conditions were applied to test and confirm the working of these devices. The present work shows that simple graphite trace patterns can convert a piece of paper into a thermal mapping device.