Surface Temperature Measurements Research Articles

Aerodynamic and heat transfer effects of distributed hemispherical roughness elements inducing step changes in a turbulent boundary layer

This work details an experimental investigation aiming at characterizing aerodynamic and heat transfer effects induced by roughness elements on a fully-rough zero-pressure-gradient turbulent boundary layer (TBL). The studied rough surfaces were composed of distributed hemispherical elements in staggered arrangement over part of an otherwise flat plate, inducing step changes in roughness height and wall temperature. While the arrangement and the geometry of the roughness elements were fixed (constant density, constant plan and frontal solidities), the effect of varying the ratio of the boundary layer thickness δ to the roughness height k was investigated with a particular emphasis on low values of δ∕k. In a first part of the study, mean friction coefficients and equivalent sand heights were estimated for four configurations. Quasi-wall-similarity was observed on velocity statistics, two-point correlations and spectra measured by PIV and hot-wire anemometry, suggesting that TBL large-scale structures were not significantly influenced by such large roughness elements. In a second part, heat transfer effects were investigated using mean temperature profiles and transient surface temperature measurements, highlighting discrepancies between the two approaches. Relying on the first one, a parametrization of the non-dimensional wall temperature step function was obtained for this configuration of roughness elements. Based on this result, a semi-empirical relation for the Stanton number associated with such roughness geometries and accounting for a step change in surface temperature was derived.

Boiling flow patterns and dry-out characteristics of R-1234ze(E) in a plate heat exchanger

ABSTRACT In this study, boiling flow patterns and dry-out characteristics of R-1234ze(E) in a plate heat exchanger (PHE) are investigated through visualizations and surface temperature measurements. The boiling flow patterns in the PHE are classified into three regimes by reflecting an evident flow direction and intermittent flooding (IF): rough liquid film flow, pulsating annular flow, and steady annular flow. Boiling mechanisms in the liquid-preferred and vapor-preferred paths are analyzed in a single channel. A boiling flow pattern map of R-1234ze(E) in the PHE is developed in terms of liquid and vapor superficial momentums, and the criteria for the transitions of the flow regimes are proposed to provide a reference for predicting flow characteristics during phase changes. Based on the measured surface temperatures, the partial dry-out is observed at medium to high vapor qualities in the center of the vapor-preferred path owing to the lack of the liquid phase. In addition, the relationships between the IF, partial dry-out, and heat transfer coefficients are comprehensively analyzed with physical interpretations.

Surface Temperature Measurements of Burning Solid Propellants Using Phosphor Thermography

In recent years, phosphor thermography has received increased attention as an alternative to other common temperature measurement techniques (e.g., thermocouples, pyrometry). This technique has been successfully used for surface temperature measurements on coated surfaces (e.g., turbine blades, furnace walls) and, in some cases, mixed with a reacting material. However, this technique has yet to be used for measuring the surface temperature of burning energetic materials (e.g., propellants, explosives). Adapting this technique to the study of energetic materials would enable temporally and spatially resolved surface temperature measurements that also lack some of the shortcomings of conventional methods. This work investigates the feasibility of using phosphor thermography to measure the surface temperature of burning nitrocellulose, an energetic material used extensively in single-, double-, and triple-base propellant formulations. Using phosphor thermography, two-dimensional time-resolved surface temperature measurements were obtained across the surface of a burning nitrocellulose pellet. The average surface temperatures measured with this approach () were in good agreement with previously published measurements for nitrocellulose obtained with embedded thermocouples (). This work demonstrates the viability of using phosphor thermography for measuring the surface temperature of burning solid propellants as well as other types of energetic material compositions.

Particle–Substrate Transient Thermal Evolution During Cold Spray Deposition Process: A Hybrid Heat Conduction Analysis

A hybrid analytical heat conduction model was developed to predict the transient thermal evolution at the particle–substrate interface during the deposition of cold spray process. First, three-dimensional heat conduction model based on classical diffusion approach was developed to predict the transient surface temperature of the substrate. To that end, the traveling wave solution technique was utilized in order to take into account the effect of the movement of the cold spray nozzle. The results of the analytical model were validated with the experimentally measured surface temperature which was obtained by employing a low-pressure cold spray unit to generate the impingement of a compressed air jet on a flat substrate. The analytical model was further utilized to investigate the effect of the non-dimensional characteristic velocity of the traveling heat source on the surface temperature profile of the substrate. It was found that both the maximum surface temperature and the spatial variation of surface temperature profile of the substrate decreased as the non-dimensional characteristic velocity increased. The mathematical model was further extended by developing a one-dimensional hyperbolic (non-Fourier) heat conduction model to predict the temperature rise at the particle–substrate interface during the cold spray deposition process. In order to validate the results of the hybrid model, a three-dimensional finite element model was developed in ABAQUS to simulate the thermal and dynamic behavior of a single particle upon impact. The results of the hybrid analytical model for the temperature at the particle–substrate interface were compared to the results of the numerical model, and good agreement was found. It was concluded that by coupling the classical diffusion theory and hyperbolic heat conduction approach, the proposed hybrid analytical model can be utilized to predict the transient temperature of the particle–substrate interface during the cold spray deposition process a priori before experimentation.

Exploration into the potential for a low-enthalpy geothermal power plant in Cape fold belt

South Africa has long been dependent on coal and other fossil fuels for cheap electricity generation. While there has been an increase in utilising renewable energy over the last two decades, the main focus has been on solar and wind, which are intermittent, with geothermal energy not even considered. With advances in technology that harness geothermal energy, geothermal resources as low as 85 °C have been reported attainable when using low-enthalpy technologies as such binary systems. This makes geothermal energy a reality for regions in South Africa where moderately high geothermal gradients exist.The initial high level assessment of the geothermal potential of the Cape Fold Belt region was done through accessing eight hot springs found to have the highest temperature from previous studies. Temperature measurements were taken as close to the source as possible as well as collection of water samples for ICP-AES analysis for major cations. The cation concentrations from the ICP-AES analysis (completed with the Thermo ICap 6200 ICP-AES) allowed for geothermometry calculations to be conducted which gave the minimum temperature estimates of the reservoirs of each hot spring. Both the surface temperature measurements and the estimates of the reservoir temperature resulted in two locations that were in the top three for both measurements. These two locations were Calitzdorp and Caledon, having water temperatures of 47 °C and 45 °C at surface and estimates of the reservoir temperatures of 117 °C ± 13 °C and 108 °C ± 21 °C respectively.The hydro-geological analysis of the Oudtshoorn region, where the Calitzdorp hot spring is located, was conducted using published geophysical data in the form of magneto-telluric (MT) survey that was carried out in 2005 by the Agulhas-Karoo Geoscience Transect project. The MT data was presented in a paper by Weckmann et al. (2012) as a cross sectional profile from Mossel Bay to Prince Albert to a depth of 30 km, where a large region of low resistivity was found below the Oudtshoorn basin. The Calitzdorp hot spring is positioned at the surface above this region. The geological cross sections and regional interpretation presented in this study infers that a major syncline of the Cape Supergroup exists below the basin, potentially as deep as 10 km, and covers the low resistivity area shown in the MT profile. This led to the inference that the large region of low resistivity is most probably due to a large water reservoir. This potential reservoir is about 40 km in length with a depth of 2.5 km–7 km at its thickest, tapering out towards the edges.The depth to the top of the potential reservoir and the estimated reservoir temperature from the geothermometry results in a geothermal gradient of 39 °C/km ±4.3 °C/km. Thus Calitzdorp was identified as a promising location for further exploration, ideally deep boreholes or more geophysical surveys, to validate the existence of a reservoir and take down-hole temperature measurements. The depth and size of this potential reservoir would make it a favourable candidate for a pilot low-enthalpy geothermal power plant within the Cape Fold Belt and South Africa.

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

Abstract Accurate and responsive non-invasive temperature measurements are enablers for process monitoring and plant optimization use cases in the context of Industry 4.0. If their performance is proven for large classes of applications, such measurement principles can replace traditional invasive measurements. In this paper we describe a two-step model to estimate the process temperature from a pipe surface temperature measurement. This static case model is compared to and enhanced by computational fluid dynamic (CFD) calculations to predict transient situations. The predictions of the approach are validated by means of controlled experiments in a laboratory environment. The experimental results demonstrate the efficacy of the model, the responsiveness of the pipe surface temperature, and that state of the art industrial non-invasive sensors can achieve the performance of invasive thermowells. The non-invasive sensors are then used to demonstrate the performance of the model in industrial applications for cooling fluids and steam.

Rescue blankets hamper thermal imaging in search and rescue missions

Thermal imaging for unmanned aerial vehicles is used to search for victims in poor visibility conditions. We used a gimbal-mounted camera for thermo-radiation measurements of body temperature from persons covered with rescue blankets in the hibernal wilderness setting. Long-wave infrared radiation in the spectral range between 7500 and 13,500 nm was evaluated. Parts of this research have previously been published in a review on electromagnetic radiation reflectivity of rescue blankets (https://www.mdpi.com/2079-6412/10/4/375/htm). Surface temperature measurement was diminished by clothing, namely by 72.6% for fleece, by 82.2% for an additional down jacket and by 92.3% for an additional all-weather jacket, as compared to forehead temperature. Furthermore, we detected that a single-layer rescue blanket is sufficient to render recognition of a body shape impossible. With three layers covering a clothed body infrared transmission was almost completely blocked. However, rescue blankets increase visibility for thermal cameras due to high gradients in temperature. Conspicuously low temperatures from objects of 1 to 2 m length may indicate reflections from rescue blanket surfaces in a cold environment. Ideally, rescue blankets should be removed from the body to increase the chance of being located when using thermal imaging to search for victims in search and rescue missions.

Temporal temperature measurement on burning biomass pellets using phosphor thermometry and two-line atomic fluorescence

We report accurate in-situ optical measurements of surface temperature, volatile gas temperature, and polycyclic aromatic hydrocarbon (PAH) emission over the whole burning history of individual biomass pellets in various combustion atmospheres. Two biomass fuels, wood and straw, were prepared in cylindrical pellets of ∼300 mg. The pellets were burned in a well-controlled combustion atmosphere provided by a laminar flame burner with temperature ranging from 1390 K to 1840 K, and oxygen concentration from zero to 4.5%. The surface temperature of burning biomass pellets was accurately measured, for the first time, using phosphor thermometry, and the volatile gas temperature was measured using two-line atomic fluorescence thermometry. PAH emission was monitored using two-dimensional laser-induced fluorescence. During the devolatilization stage, a relatively low surface temperature, ∼700 K, was observed on the burning pellets. The volatile gas temperature was ∼1100 K and ∼1500 K 5 mm above the top of the pellets in a gas environment of ∼1800 K with 0.5% and 4.5% oxygen, respectively. PAH mainly released when the temperature of the pellet exceeded ∼600 K with the highest concentration close to the surface and being consumed downstream. The weight of the released PAH molecules shifted towards lighter with a reduction of gas environment temperature. The wood and straw pellets had almost the same surface and volatile gas temperature but different compositions in the released volatile gases. The temperature information provided in the present work aids in revealing the reactions in the burning biomass fuels regarding species release, such as various hydrocarbons, nitrogen compounds, and potassium species, and is valuable for further development of biomass thermal conversion models.

Sentinel-3A/B SLSTR Pre-Launch Calibration of the Thermal InfraRed Channels

The first two models of the Sea and Land Surface Temperature Radiometers (SLSTR) for the European Copernicus Sentinel-3 missions were tested prior to launch at the Rutherford Appleton Laboratory space instrument calibration facility. The pre-launch tests provide an essential reference that ensures that the flight data of SLSTR are calibrated to the same standards needed for surface temperature measurements and to those used by shipborne radiometers for Fiducial Reference Measurement (FRM). The radiometric calibrations of the thermal infrared channels were validated against accurate and traceable reference BB sources under flight representative thermal vacuum environment. Measurements were performed in both earth views for source temperatures covering the main operating range, for different instrument configurations and for the full field-of-view of the instruments. The data were used to derive non-linearity curves to be used in the level-1 processing. All results showed that the measured brightness temperatures and radiometric noise agreed within the requirements for the mission. An inconsistency that particularly affected SLSTR-A was observed which has been attributed to an internal stray light error. A correction for the stray light has been proposed to reduce the error. The internal stray light error was reduced for SLSTR-B by replacing the coating on the main aperture stop. We present a description of the test methodology and the key results.

Thermal Modeling Approaches for a LiCoO2 Lithium-ion Battery—A Comparative Study with Experimental Validation

Temperature prediction of a battery plays a significant role in terms of energy efficiency and safety of electric vehicles, as well as several kinds of electric and electronic devices. In this regard, it is crucial to identify an adequate model to study the thermal behavior of a battery. This article reports a comparative study on thermal modeling approaches by using a LiCoO2 26650 lithium-ion battery, and provides a methodology to characterize electrothermal phenomena. Three approaches have been implemented numerically—a thermal lumped model, a 3D computational fluid dynamics model, and an electrochemical model based on Newman, Tiedemann, Gu and Kim formulation. The last two methods were solved using ANSYS Fluent software. Simulations were validated with experimental measurements of the cell surface temperature at constant current discharge and under a highway driving cycle. Results show that the three models are consistent with actual temperature measurements. The electrochemical method has the lower error at 0.5C. Nevertheless, this model provides the higher error ( 1.3∘C) at 1.5C, where the maximum temperature increase of the cell was 18.1∘C. Under the driving cycle, all the models are in the same order of error. Lumped model is suitable to simulate a wide range of battery operating conditions. Furthermore, this work was expanded to study heat generation, voltage and heat transfer coefficient under natural convection.

Comparison of Thin Film Heat Flux Gauge Technologies Emphasizing Continuous-Duration Operation

Abstract Thin-film heat flux gauges (HFGs) have been used for decades to measure surface temperatures and heat flux in test turbines with the majority being used in facilities that are short-duration. These gauges are typically composed of two resistive temperature devices deposited on opposing sides of a dielectric. However, because these sensors have been traditionally applied for measurements in transient-type facilities, the challenges facing adaptation of this technology for a steady facility warrant investigation. These challenges are highlighted, and the solutions are presented throughout the paper. This paper describes the nanofabrication process for heat flux gauges and a new calibration method to address the potential deterioration of gauges over long runtimes in continuous-duration facilities. Because the primary uncertainty of these sensors arises from the ambiguity of the thermal properties, the emphasis is placed on the property determination. Also, this paper presents a discussion on the use of impulse response theory to process the data showing the feasibility of the method for steady-duration facilities after an initial settling time. The latter portion of the paper focuses on comparing well-established heat flux gauges developed for short-duration turbine test facilities to recently developed gauges fabricated using modern nanofabrication techniques for a continuous turbine test facility. The gauges were compared using the test case of an impinging jet over a range of Reynolds numbers. The comparison between the PSU gauge and the reference device indicated agreement within 14%, and similar results were achieved through comparison with established sensors from partner institutions.

Surface Water CO2 variability in the Gulf of Mexico (1996\u20132017)

Approximately 380,000 underway measurements of sea surface salinity, temperature, and carbon dioxide (CO2) in the Gulf of Mexico (GoM) were compiled from the Surface Ocean CO2 Atlas (SOCAT) to provide a comprehensive observational analysis of spatiotemporal CO2 dynamics from 1996 to 2017. An empirical orthogonal function (EOF) was used to derive the main drivers of spatial and temporal variability in the dataset. In open and coastal waters, drivers were identified as a biological component linked to riverine water, and temperature seasonality. Air-sea flux estimates indicate the GoM open (− 0.06 ± 0.45 mol C m−2 year−1) and coastal (− 0.03 ± 1.83 mol C m−2 year−1) ocean are approximately neutral in terms of an annual source or sink for atmospheric CO2. Surface water pCO2 in the northwest and southeast GoM open ocean is increasing (1.63 ± 0.63 µatm year−1 and 1.70 ± 0.14 µatm year−1, respectively) at rates comparable to those measured at long-term ocean time-series stations. The average annual increase in coastal CO2 was 3.20 ± 1.47 µatm year-1 for the northwestern GoM and 2.35 ± 0.82 µatm year−1 for the west Florida Shelf. However, surface CO2 in the central (coastal and open) GoM, which is influenced by Mississippi and Atchafalaya River outflow, remained fairly stable over this time period.

Precise infrared thermometry with considering background radiation for gas turbine air cooling application

The turbine inlet temperature keeps increasing as high-efficient gas turbines have been developed for the last decades. The increase of turbine inlet temperature makes the turbine blades being exposed in thermally severe conditions, leading to thermal damage. The thermal management with advanced cooling techniques is thus necessary to protect turbine blades from thermal deformations. For properly evaluating the air-cooling effects on turbine blades, the more accurate surface temperature measurement must be preceded. Infrared thermometry has often been employed for high-temperature turbine blades due to its convenience. However, background radiation must be carefully considered if the surrounding environment is at a higher temperature than the surface to be measured, as in the case of a gas turbine blade. In addition, the spectral emittance of an object should also be known a priori. In this study, we propose an accurate measurement scheme of infrared thermometry by properly considering the background radiation from the high-temperature environment as well as the spectral emittance of an object. The accuracy of infrared thermometry was examined for two exemplary surfaces with low and high emittance in a high-temperature wind tunnel. The proposed measurement scheme was found to be in good agreement with the thermocouple measurements within 5% for both surfaces.

Temperature Measurement of Laser-Irradiated Metals Using Hyperspectral Imaging

Accurate noncontact surface-temperature measurements during laser-based materials processing remain challenging due to the difficulty of establishing reliable emissivity values as a function of temperature and wavelength. Direct measurement of emissivity is difficult, as the emissivity may be changing constantly in the laser-material interaction region, where the temperature gradients are extreme and surface displacement can complicate the measurement. Here, we present a hyperspectral imaging method using a multiwavelength camera to capture the spectral radiance in eight different bands and fit the wavelength-dependent radiance to Planck's law. Time-resolved temperature measurements during microsecond pulsed-laser irradiation of a metal plate made of the titanium alloy $\mathrm{Ti}$-6$\mathrm{Al}$-4$\mathrm{V}$ provide temperature information about the irradiated surface with an estimated accuracy of $\ifmmode\pm\else\textpm\fi{}10\mathrm{%}$. The extracted wavelength-dependent emissivity slope compares well with reported results for macroscale titanium melts obtained using IR spectroscopy, which measure temperature without any built-in assumptions about the emissivity. The results are directly applicable to temperature monitoring during welding, additive manufacturing, and semiconductor growth.

An observer for partially obstructed wood particles in industrial drying processes

In order for biomass drying processes to be efficient, it is crucial to achieve the target residual water content within a close margin, since more conservative drying would result in a waste of energy. A method for a reliable estimation of the water content is therefore of obvious importance. Ideally, such a method does not require any expensive sensors. We show reduced order models and extended Kalman filters can be combined to reliably determine the water content and temperature of wood particles based on only surface temperature measurements. The proposed observer works reliably if measurements are only available for parts of a particle face. It can therefore still be applied if particle surfaces are partially obstructed, which is a prerequisite for use in industrial processes and units, such as rotary dryers. The extended Kalman filter uses a reduced order model that is obtained by applying proper orthogonal decomposition and Galerkin projection to coupled PDEs that model heat conduction and water diffusion in anisotropic particles. In contrast to the original PDE simulation model, the reduced model and the filter based on it are suitable for real time computations and monitoring.

Real-time cure monitoring of fiber-reinforced polymer composites using infrared thermography and recursive Bayesian filtering

Despite the desirable characteristics of fiber-reinforced polymer (FRP) composites, their utilization in high volume production industries is limited by a lack of efficient manufacturing techniques. Monitoring the curing process of these composites can help with improving the quality and efficiency of the manufacturing process. This article discusses a method that uses Kalman-filter-based fusion of the information obtained from infrared thermography (surface temperature measurements) and a heat conduction model to estimate degrees of cure and internal temperatures of curing FRP composite parts in real time. The effectiveness of the methodology is demonstrated by successfully monitoring the curing of an FRP composite part in a laboratory experiment. The proposed methodology is a crucial step towards identifying anomalies in the curing process that negatively impact the quality of FRP composite parts.

Study of the anode energy in gas metal arc welding

Recent research of gas metal arc welding (GMAW) has proved that the sheath voltage dominates the total voltage fall in the current circuit and provides the most energy to the wire and the weld pool. In this paper, the energy delivered to the wire anode is studied experimentally for a typical pulsed GMAW process in the one drop per pulse mode to provide a more complete picture of the energy balance of the process. Welding of mild steel under Ar with 2.5% CO2 with different peak currents from 350 to 650 A and constant wire feed speed of 4 m min−1 as well as constant arc height are considered. The processes were studied with non-intrusive optical methods, i.e. without strong modifications. The droplet energy was determined by high-speed two-colour pyrometry and an analysis of the droplet surface temperature and geometry. In addition, Joule heating in the wire anode was also estimated from surface temperature measurements. It was found that the averaged droplet energy is almost independent of the peak current and approximately one-third of the total electric energy. A voltage equivalent of the energy delivered to the wire anode from the plasma was defined. Substracting the work function of iron, the value of this voltage is in the range of 3.25± 0.43 V and increases by 0.5 V when the current increases from 350 to 650 A. The sum of the cathode and anode sheath voltages have been estimated to be in the range between 18 and 23 V in preceding works.

Time‐Lapse Seismic Imaging of Oceanic Fronts and Transient Lenses Within South Atlantic Ocean

AbstractOceanic fronts play a pivotal role in controlling water mass transfer, although little is known about deep frontal structure on appropriate temporal and spatial scales. Here, we present a sequence of calibrated time‐lapse images from a three‐dimensional seismic survey that straddles the Brazil‐Malvinas Confluence—a significant feature of the meridional overturning circulation. Eight vertical transects reveal the evolution of a major front. It is manifest as a discrete planar surface that dips at less than 2° and is traceable to 1.5–2 km depth. Its shape and surface expression are consistent with sloping isopycnal surfaces of the calculated potential density field and with coeval sea surface temperature measurements, respectively. Within the top ∼1 km, where cold fresh water subducts beneath warm salty water, a series of tilted lenses are banked up against the sharply defined front. The largest of these structures is centered at 700 m depth and is cored by cold fresh water. Time‐lapse imagery demonstrates that this tilted lens grows and decays over 9 days. It has a maximum diameter of <34±0.13 km and a maximum height of <750±10 m. Beneath 1 km, where horizontal density gradients are negligible, numerous deforming lenses and filaments on length scales of 10–100 km are being swept toward the advecting front.

Role of thermal gradients on the depolarization and conductivity in quenched Na1/2Bi1/2TiO3-BaTiO3

Quenching has been demonstrated to increase the thermal stability of the piezoelectric properties of relaxor (1−x)Na1/2Bi1/2TiO3-xBaTiO3 (NBTxBT) by 40 °C. This work establishes a correlation between the quenching temperature and salient electrical (conductivity, piezoelectric and dielectric) properties of two NBTxBT variants. The impact of quenching on the mechanical properties is quantified in terms of changes in Young's modulus. The perspective for application is interrogated using a variation in the sample thickness and separating the sample interior from the sample surface. An in situ measurement of surface temperature during the quenching treatment is applied to validate the simulation for thickness-dependent thermal transport in the material and ensuing transient thermal stresses. The calculated stress intensity factor is then compared with the fracture toughness of the material. This study asserts that air quenching can be conducted without mechanical degradation. Thus, it can be an important alternative to existing industrial strategies to enhance the thermal stability of the piezoelectric properties of relaxor NBTxBT.

Determining heat intensity of a fatigue crack from measured surface temperature for vibrothermography

We propose a simulation-assisted linear-inversion method to estimate heat intensity generated at a fatigue crack during vibrothermographic nondestructive evaluation. In vibrothermography, mechanical excitation is applied to a test specimen, and the contacting crack faces generate heat which flows to the surface and can be detected by an infrared camera. The heat intensity generated at the crack is not a directly measurable quantity, and instead has to be estimated by inverting the measured crack surface temperature. This inversion is an ill-posed problem because of the inherently diffusive nature of heat flow. The proposed method in this paper attempts to estimate the crack heat intensity by minimizing the squared error between numerically modeled crack heating and the experimentally measured surface temperature of the crack. We demonstrate that with reasonable assumptions, the effect of diffusion on the heat intensity can be overcome, and it is possible to estimate the crack heat intensity. Furthermore, we reconstruct the surface temperature on two different material systems and quantify the reconstruction accuracy of the least-squares inversion algorithm.