Point Temperature Measurements Research Articles

Investigation of measurement methods for soil thermal conductivity based on optical frequency domain reflection technology

Thermal conductivity is an important parameter reflecting the heat transfer capacity of soil. In engineering applications, the thermal conductivity of soil varies with influencing factors such as particle size, porosity, water content, saturation, and seepage velocity of soil. At present, the thermal probe method and the traditional thermal response test method are mainly used to determine the thermal conductivity of soil. However, these methods can only perform point temperature measurements and require an inversion calculation based on a particular heat transfer model to obtain the value of soil thermal conductivity. Compared with this and other temperature monitoring methods, optical frequency domain reflectometry (OFDR) offers the advantages of distributed measurement, high measurement accuracy, high spatial resolution, and fast speed. In this paper, an OFDR-based measurement of soil thermal conductivity is designed. Taking sand as an example, the influence of different influencing factors on the measured value of thermal conductivity of soil was studied through the measurement test of thermal conductivity of soil, and the results are compared with the calculation results of the theoretical model of thermal conductivity and the results measured by the thermal probe method. The test results showed that when there was no seepage in the soil, the thermal conductivity of the soil exhibited an “S"-shaped growth trend with increasing water content; when the soil had seepage, the thermal conductivity of the soil was larger than that without seepage, and the thermal conductivity showed a positive linear increase with the increase in seepage velocity; With the increase of heating power, the measurement results tend to be stable. By comparing with the results obtained by other methods, the measurement results of the thermal conductivity measurement method proposed in this study have high accuracy.

Modeling and compensation of the axial thermal error of electric spindles based on HHO-GRU method

As the core component of precision CNC machine tools, a lot of heat is generated from the internal heat source of electric spindles during operation, resulting in thermal deformation and thermal errors that affect machining accuracy. Thermal error compensation is an economical method for reducing thermal errors, through which the impact of thermal errors on machining accuracy can effectively decrease. Taking a high-speed electric spindle as the research object, the temperature measurement points are selected as its front and rear bearing seat, as well as some positions far from the heat source. The temperature changes at the front and rear bearing as well as in the environment are monitored, then the thermal errors are measured using a Lion spindle rotation accuracy instrument. The optimal training parameters of the gated recurrent unit (GRU) network are optimized utilizing the global optimization ability of a Harris Hawks optimizer (HHO). Finally, the thermal error prediction model of the GRU electric spindle optimized using the Harris Hawks optimizer (HHO-GRU) is established, based on which axial thermal error compensation experiments are conducted. The results show that using the HHO-GRU prediction model for compensation, the axial thermal errors of the electric spindle can be reduced by more than 80%, which can be controlled within 5 μm.

Experimental Study of Deformation Risk and Interpolation Analysis of Temperature for Water Walls under Flexible Low-Load Conditions

With the development of renewable energy in power generation, a large number of thermal power plants operate under flexible working conditions. To study water wall deformation risk under flexible low-load conditions, a lab-scale opposed firing boiler was built to measure and analyze the temperature and thermal stress of the water wall under low-load flexible operating conditions with several nontypical burner arrangements. The results showed that flame radiation and flue gas convection heat transfer induced a high-temperature zone. Thermal stress was mainly caused by thermal expansion of the metal and expansion or extrusion deformation of other areas. Also, local thermal stress fluctuations and excessive values appeared under variable conditions. In addition, the burners’ symmetrical arrangement in the center effectively reduced thermal stress fluctuations and overall thermal stress under flexible working conditions. Finally, based on the limited temperature measurement points in this experiment, the optimal power parameter α for the inverse distance weighted (IDW) method and the shape parameter ε for the radial basis function (RBF) method were found to make a reasonable interpolation prediction of the temperature distribution of the water wall. This study highlights the recommended burner arrangements under flexible low-load conditions and the optimal parameters of the IDW and the RBF methods for estimating temperature in guiding safe operation of the water wall.

Experimental study on the thermal performance of a novel two-phase loop thermosyphon under low-heat-flux conditions

Two-phase loop thermosyphons are efficient heat transfer components that do not require extra power and can effectively transfer heat over long distances. In this study, two kinds of novel ethanol loop thermosyphons with and without wicks inside their evaporators were fabricated to experimentally investigate the start-up characteristics and thermal performance of the systems under low-heat-flux conditions and with different filling ratios; in addition, there was no height difference between the evaporator outlet and condenser inlet. As a result, temperature overshoot and geyser boiling were evidenced as start-up phenomena specific situations. Both systems failed to transfer heat when the filling ratio was below 30 % because some temperature measurement points were higher than 100 °C, at which point the limits of the experiment were reached. When the heat input was higher than 10 W, the loop thermosyphon with a wick structure could run and stay stable, while the regular loop thermosyphon system stabilized when the heat input was higher than 25 W. The increase in the filling ratio worsened the uniformity of the temperature distribution in the evaporator. The thermal resistance of the system was at its minimum when the filling ratio was 70 %. Both systems had good heat transfer performance when the heat input was high enough.

Experimental investigation of the combustion characteristics in oxy-fuel combustion of hydrogen-enriched natural gas on a semi-industrial scale

The present paper deals with the influence of different hydrogen enrichment on oxy-fuel combustion of natural gas, enabling important insights regarding decarbonization of high-temperature processes. Experiments were conducted using a high-impulse multifuel burner for industrial applications for hydrogen contents between 0 and 100%. The fuel input varied between 100 and 140 kW, while water-cooled lances were used to simulatethermal loads. The analysis included temperature measurement points, atomic and energy balances and the cooling capacity of the thermal load for steady-state operation. The obtained results show that the flue gas temperature decreases by up to 126 K for pure hydrogen, while the cooling capacities of the thermal load increased by up to 16.3% at constant calorific energy input. The flames for different hydrogen enrichments were also compared visually. Overall, all investigated fuel blends were highly interchangeable with the investigated burner and showed high potential for a timely decarbonization of industrial heating.

Design of Temperature Monitoring System for Air Cooled Radiators Based on LoRa

Air cooling technology is widely used in the north. When the winter temperature in the north is too low, the cooling radiator is prone to freezing, leading to the inability of air cooling units to operate normally and causing huge economic losses. In response to the above issues, this article designs a monitoring system for air cooled radiators based on LORA communication, based on Internet of Things technology. Analyze the A-type tower structure and heat dissipation principle of the air-cooled condenser, reasonably select the temperature measurement point position, and achieve temperature data transmission through LoRa communication and Ethernet communication technology. The monitoring software is programmed in C # language, which can visually display the temperature distribution information of the air-cooled condenser and store data in real time. The experimental results indicate that the system has certain guiding significance for preventing the freezing phenomenon of air cooled condensers and optimizing operation.

Infrared thermography monitoring of rock faces – Potential and pitfalls

Rock surface temperatures are of fundamental importance for studies on weathering, rockfall and permafrost. Point temperature measurements may not reflect the small-scale variability of temperature as a function of micro-topography. To close this gap, infrared thermography (IRT) seems to be a simple and promising approach. However, there are several pitfalls in terms of interpretation, as radiation temperatures depend on emissivity and reflectivity of the rock, which in turn are influenced by rock type, surface roughness, wetness, surrounding weather conditions, and angle to the camera axis.We performed laboratory and exemplary field experiments in order to estimate the magnitude of possible errors. We used rough and smooth (sawn) specimen of six different stone types in wet and dry condition and took IRT images at different tilt angles between camera axis and rock surface. Furthermore, we applied the approach to a small rock outcrop (approx. 3 × 3 m) and to a rockwall (approx. 100 × 100 m).The results of the laboratory measurements show that the temperature error increases with increasing tilt angle of the rock surface. Depending on the nature of the reflected surroundings, radiation temperatures can be warmer or cooler than sensor temperatures. In typical settings, the error is low (<0.5 K) up to a tilt of 40° but it may increase to >1 K at tilt angles of 50° and more. Smooth and wet surfaces tend to be more prone to deviations.The field examples confirm the results of the laboratory tests. But they show that spatial differences in temperature can still be detected as the “true” differences are usually larger than the magnitude of error. We suggest to reduce the error of the IRT image by correcting temperatures using a high-resolution surface model.

Multiple Points Measurement-Based Junction Temperature Estimation of IGBT Module

The junction temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_j</i> ) estimation of IGBTs is critical for improving their reliability. To obtain <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_j</i> , the existing reference point temperature (RPT) measurement based methods require the power loss information, which is difficult to obtain accurately in the real-time applications. Also, these methods utilise the thermal model of IGBT which changes with ageing, resulting in an error in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_j</i> estimation. In this paper, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_j</i> estimation technique is proposed which utilises the temperature of multiple leads/terminals of an IGBT module. Unlike the existing methods, the proposed technique does not require the information of power losses in the power semiconductor chips (PSCs). Instead, the power losses in the PSCs are additional outcome of the proposed technique. Also, even for a degraded IGBT module, the proposed technique provides an accurate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_j</i> estimation. The proposed technique also has the capability of estimating <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_j</i> of multiple PSCs in an IGBT module simultaneously. A mathematical analysis of leads selection for the proposed technique is presented in this paper. Furthermore, a comparative analysis is presented between the proposed and the conventional method for a degraded IGBT module. The simulation studies of the proposed technique are carried out in ANSYS ICEPAK software. The proposed technique is also validated on an experimental setup developed in the laboratory.

The effect of an emulator inductive power transfer pad on the temperature of an asphalt pavement

This paper utilises experimental and numerical methods of determining the temperature distribution in an asphalt slab containing an energized embedded emulator Inductive Power Transfer (IPT) pad. In the series of experiments, five different ambient temperatures from 15 to 50 °C, four IPT pad power loss values from 5 to 30 W, and three pavement layer configurations were considered. A thermal camera was used to measure the surface temperature distribution of the asphalt slab, while a Fiber Bragg Grating (FBG) sensor and six thermistors were used for point temperature measurements. A numerical simulation, using a combination of experimentally determined, and literature-sourced thermal properties was developed for the experimental set-up, which was validated against the measured temperatures. Results show good agreement between the experimental and the simulation models with a maximum point-wise differential of 12.9%. It was found that increasing the ambient temperature from 15 to 50 °C, at a constant pad power loss of 30 W, increased the simulated asphalt surface temperature (25 mm offset from the pad) from approximately 32 to 65 °C. Moreover, varying the IPT pad power loss from 5 to 30 W, at an ambient temperature of 50 °C, increased the simulated asphalt surface temperature at the same location from approximately 53 to 65 °C. However, changing the asphalt thickness from 43 mm to 86 mm, or adding a compacted aggregate base course layer below the IPT-asphalt slab, only marginally decreased the temperature values. An increase in the thermal conductivity of the asphalt from 1 to 3 Wm−1°K−1, results in the temperatures reducing by a maximum of approximately 21% at the bottom of the pad. However, changing the specific heat has a very small effect on the heating and cooling rates. A numerical study of an in-service New Zealand asphalt pavement, containing an emulator IPT pad and utilising a three-day period of recorded New Zealand summer climatic data is presented. The method can be used to identify IPT-pavement hotspots and aid in the design of thermally robust IPT-pavement systems.

Miniaturized High-Sensitivity Temperature Sensor Based on Cascaded Fiber-Optic FPI

In letter, a cascaded fiber-optic Fabry-Perot interferometers temperature sensor with high-sensitivity and small-dimension is proposed and demonstrated. The sensor is fabricated by filling the polydimethylsiloxane (PDMS) and air between two single-mode fiber end-faces located in a section of silica capillary, thus a PDMS-based glue cavity, an air cavity and combined PDMS-air cavity are constructed. Due to the similar optical length between PDMS glue cavity and PDMS-air cavity, the conditions for Vernier effect can be easily satisfied in the sensor fabrication. The temperature sensitivity of proposed sensor is effectively improved in experiment. The research results show that the sensitivity of sensor is enhanced from 2.62 nm/°C to 23.22 nm/°C, which is about 8.86 times than that of the single PDMS-based glue cavity, and the linearity of temperature-dependent wavelength shifts is superior to 0.99 in temperature range of 32~50 °C. The sensor has advantages of high sensitivity, simplicity and easy to fabrication, and the small-dimension merit make it more suitable for point-temperature measurement.

Determination of critical control points of air temperature measurement in cold chambers

Determination of critical control points of air temperature measurement in cold chambers

Effects of Duct Height and Fire Location on Fire Phenomena of Enclosure with Two Horizontal Vents Installed on Ceiling

The effects of duct height (DH) and fire location (FL) in an enclosure on the mass flow rate and flow pattern of horizontal vent (HV) flow and temperature distribution in the enclosure were investigated through numerical simulations under the condition that two HVs were installed on the ceiling of the enclosure. To evaluate the effect of DH, DHs of HV1 were set to 0.19 m (HV1_DH0.19) and 0.05 m (HV1_DH0.05) under the condition that DH of HV2 was 0.05 m (HV2_DH0.05). The effect of FL was evaluated in three cases where the fire sources were located in the center of the floor (F LC), below HV1 (F L1), and below HV2 (F L2). With respect to the DH effect, the total mass flow rate of the vent flow was slightly higher and temperature was slightly lower in the case of HV1_DH0.19 than that in the case of HV1_DH0.05. However, considering the error bars, the effect of DH in this numerical simulation condition was considered to be insignificant. Furthermore, bidirectional flow patterns appeared in HV1 and HV2 in both DH conditions. Meanwhile, with respect to the FL effect, a bidirectional flow dominated by the mass flow rate of outflow occurred in the HV where the fire source was located, and a unidirectional inflow dominated by the mass flow rate of inflow occurred in the HV where the fire source was not located. The total mass flow rates of FL1 and FL2 conditions were similar, which were higher than those of FLC condition. The temperature was higher in FLC than those in FL1 and FL2. This was due to the small mass flow rate through the HV in the FLC. Meanwhile, an increasing trend of the temperature with the rising measurement height from the floor was observed at most of the temperature measurement points. However, when the fire source was located below HV1 and HV2, as the height from the floor increased, the temperature decreased and the overall temperature was low at the temperature measurement points below the vent where the fire source was not located. This trend was attributed to the occurrence of a strong unidirectional inflow wherein a large volume of low-temperature air flowed into the enclosure from the HV where the fire source was not located.

Advanced Representative Rail Temperature Measurement Point Considering Rail Deformation by Meteorological Conditions and Rail Orientation

Advanced Representative Rail Temperature Measurement Point Considering Rail Deformation by Meteorological Conditions and Rail Orientation

Design and parameter optimization of community bins based on evaporative cooling

ABSTRACT Aiming at the challenge of bad odors emanating from rotting perishable kitchen waste in summer within the garbage collection chain, the fan-pad system, which is widely used in agricultural facility systems, was applied to the design of community bins. In this regard, a community bin based on a fan-pad operating mechanism was developed. Computational fluid dynamics (CFD) was then used to numerically analyze the cooling effect of the community bin. Under conditions comprising of an outdoor temperature of 35 °C, an installation height of the wet curtain of the cooling system h 1, an installation height of the fan h 2, and varying distance d between the trash can and the wet curtain, and the average temperature T of 16 temperature measurement points was analyzed. Design-Expert software was used to design the Box-Behnken Design (BBD) experiment, and regression analysis was carried out. Under the optimized parameter combination, the average temperature T of the temperature measurement point was 24.82 °C by simulation. Through field test verification, it was established that the maximum relative error between the temperature of each measuring point and the simulation result was 1.54%, and the average temperature T fluctuated within the range of 0.5 °C of the simulation value. Implications Statement: By creatively integrating the agricultural apparatus with our daily community bin, our research presents great interdisciplinary originality and potential in wide application. Meanwhile, our research also gives a new solution to saving the energy wasted by community dust room based on air conditioner cooling. We hold the believe that our research can arrest great attention of scholars, managers, and people interested in sanitation apparatus. Additionally, our research also provides more theoretical and technical support for the design and application of sanitation collecting apparatus

Design of a wearable multi-point temperature monitoring system – practical application in waist temperature monitoring

PurposeHuman skin temperature data can provide reference advice for diagnosing many diseases, but current wearable skin temperature monitoring systems have few points and may miss temperature information in critical areas. This paper aims to develop a wearable system that can be used for local temperature monitoring and restore better the actual state of local human temperature by exploring ways to extend more temperature measurement points. This will provide better assistance in developing medical targeting and intelligent clothing.Design/methodology/approachThe temperature measurement system contains modules for temperature monitoring, digital-to-analog conversion and regulated power supply, enabling fast reading of 12 channels of monitoring data. The microprocessor unit is the STM32F407. The instructions and control modes are written in C. The waist area was chosen as the monitoring area because it is susceptible to temperature, and many diseases are associated with skin temperature. Twelve points, including temperature-related acupuncture points and heat-sensitive points, were selected for testing and the data results agreed well with the infrared imaging results.FindingsThe waist is selected as the monitoring object, and an easy-to-wear waist temperature monitoring belt is designed to verify the application value of the system. The development of the system provides reference suggestions for the exploration of multi-point temperature monitoring systems and the integration capabilities of temperature measurement modules in wearable multifunctional systems.Practical implicationsIn addition to waist temperature monitoring, the wearable temperature measurement system developed in this study can also be applied to other body parts. In addition, the system can be efficiently and effectively combined with various garments, making it a useful tool for researching human skin temperature.Originality/valueThe wearable temperature monitoring system designed in this paper extends the number of temperature test points to 12. The number of test points covers as many localized body areas as possible to indeed reproduce the temperature distribution of the human body. In addition, the selection of test points combines medically relevant body points with physiologically relevant heat-sensitive areas, which makes the temperature measurement data more valuable.

Thermal error modeling of electrical spindle based on optimized ELM with marine predator algorithm

High-speed electric spindle is an important part of computer numerical control (CNC) machining equipment, and the thermal displacement generated by the electric spindle during operation affects the electric spindle machining stability and machining accuracy. Error compensation for the high-speed motorized spindle can well compensate for the influence of thermal displacement on machine tool processing. Therefore, the prediction of thermal displacement of electric spindle is particularly important. In this paper, firstly, the temperature field information is obtained by simulating and analyzing the calculation of the heat generation and heat exchange inside the electric spindle. Set up the experimental platform with reasonable temperature measurement points according to the simulation results; secondly, the temperature sensitive points are screened by fuzzy C-mean clustering algorithm and Pearson correlation coefficient, which can effectively improve the covariance and correlation between temperature variables; finally, based on the screened data for thermal error modeling, an optimized extreme learning machine based on marine predator algorithm (MPA-ELM) is provided to predict the thermal displacement of electric spindles model. And comparing the model accuracy of extreme learning machine (ELM), MPA-ELM and extreme learning machine optimized by genetic algorithm (GA-ELM), the experimental data show that MPA-ELM has better prediction accuracy.

Evaluation of temperature of a full ceramic total knee arthroplasty during MRI examinations.

Background:A diagnosis by magnetic resonance imaging (MRI) is often necessary before surgery of degenerative spine diseases. This can lead to a possible conflict with an inserted implant of the hip or knee. Heat generation or movement could be caused by the magnetic field. The aim of this study is to investigate temperature development in vitro in a 1.5T MRI of a ceramic knee arthroplasty.Methods:A full ceramic, complete metal-free non-constrained primary total knee arthroplasty is investigated. Temperature change was measured between platinum resistors before and after each MRI sequence by change of resistance. The knee implant was placed in a plastic container after the sensors were attached. Then the container was completely filled with ultrasound gel. To document any possible movement of the implant, a grid was placed under the container to document the position of the implant before and after the scans.Results:A total of four standard knee sequences were performed. The temperature at sites 1 to 5 per implant was always documented in the as-is state before MRI and then after each sequence. A total of 5 temperature measurement points were taken per implant. It was found that there were extremely small temperature variations. These were always in the range of less than 1°C. There was no case of movement of the implant triggered by the MRI scan.Conclusions:The experimental investigations carried out here showed homogeneous results with this experimental setup. It is concluded that, at least in vitro, that this ceramic knee implant can be used in MRI examinations without heating or movement.

Optimization of the Cooling Scheme of Artificial Ground Freezing Based on Finite Element Analysis: A Case Study

The present study was envisaged to evaluate the influence of different brine cooling schemes on the freezing process in the formation of sand-cobble strata in an underground connection aisle in Hohhot, China. The brine cooling schemes were set up by modifying the starting and ending brine temperatures in the construction of an underground connection aisle. Using ADINA finite element software, the simulation of the temperature field during the freezing process of the sand and pebble strata under three different schemes was performed. It was found that the freezing process was accelerated by lowering the freezing start temperature during the cooling process when the starting and ending brine temperatures remained unchanged. Furthermore, if the initial freezing temperature was changed, keeping the same freezing time at constant soil thermophysical parameters, the final effective thickness of the frozen wall was almost identical. Considering the same location of the temperature measurement points, the measured temperature of the inner and outer holes of the freezing curtain was found to be consistent with the numerical simulation, demonstrating the rationality of the numerical model. On the basis of this study, a brine cooling plan is proposed, which could serve as a reference for future construction.

Tilted Fiber Bragg Grating Measurements During Laser Ablation of Hepatic Tissues: Quasi-Distributed Temperature Reconstruction and Cladding Mode Resonances Analysis

In this work, we investigate the application of tilted fiber Bragg grating (TFBG) sensors during <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex vivo</i> laser ablation of porcine hepatic tissues. Initially, TFBG’s ability to measure the surrounding refractive index (RI) for different sucrose concentrations and the possibility to measure the RI of the targeted tissue during laser ablation (LA) is analyzed. After, the temperature sensing modality of TFBG is investigated in detail. We have implemented an algorithm for quasi-distributed spatial temperature profile reconstruction along TFBG. The algorithm models the TFBG core mode spectrum as a chain of Bragg gratings (each Bragg grating is modeled <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">via</i> coupled mode theory), where each grating is sensitive to local temperature changes. After, the Gaussian-shape temperature profile along the TFBG is reconstructed using the iterative optimization technique. Temperature measurements have been compared with highly-dense FBG array measurements and with conventional TFBG point temperature measurements based on the core mode tracking techniques (maximum tracking, X-dB Bandwidth, centroid methods). Overall, the proposed reconstruction algorithm is able to provide a quasi-distributed temperature profile along TFBG, which is not possible to obtain using conventional point temperature measurements based on the TFBG’s core mode tracking. The resulted root-mean-square error in comparison to FBG array reference measurements is 7.8±1.7 °C. In general, the results show that the main reliable sensing modality of TFBG during LA is temperature monitoring, which can be significantly improved by the proposed algorithm.

Application of Temperature Fall-Off Interpretation Method in Superheavy Oil or Oil Sand SAGD Process

SAGD technology has been successfully and widely applied in the development of superheavy oil and oil sand projects. Before normal SAGD process, some preheating ways are often needed to realize interwell hydraulic connection, and this means that determining reasonable SAGD conversion timing from the preheating stage is an essential precondition for good performance. Previous numerical simulations or qualitative analysis of temperature fall-off data are often adopted in the industry, but they have deficiencies in terms of dependent on static geological model or insufficient data utilization. Therefore, on the basis of the temperature and pressure monitoring process comparison in China’s superheavy oil and Canada’s oil sand projects, this paper proposed a temperature fall-off interpretation model to obtain thermal diffusivity and preheating radius at different measurement points along the horizontal section by combining an unsteady thermal conduction model under constant heating power of wellbores in the radial coordinate system and approximately unsteady thermal conduction model with constant wellbore temperature and Fourier’s law of thermal conduction. Besides, the duration time, interpretation method, and application flow chart of temperature fall-off test were presented. Then, it was validated to successfully determine the timing of SAGD conversion from the preheating stage by an example combining with tracking numerical simulation, temperature inflection point analysis, and index analysis during the partial-SAGD and initial SAGD stages. The findings of this study can help determine the SAGD conversion timing from the preheating stage simpler and faster especially for the case of long horizontal well section deployed with more temperature measurement points.