Heat Flow Sensors Research Articles

Determination of the fire hazard of forest plantations depending on surface fuels under laboratory combustion conditions using thermophysical parameters

The work aims to investigate experimentally the assessment of the combustion parameters of forest vegetation based on received ignition and combustion characteristics according to the presence of surface forest fuels (FF). The research was carried out using the laboratory test facility, which allowed simulating various types of combustion. Using the thermocouple method, as well as the heat flow sensor, made it possible to control the thermal characteristics. The maximum heat fluxes that are characteristic of FF fractions, such as oak bark, Salix acutifolia branches, and oak wood reached 49±3.5 kW/m2. Among grass species, the highest heat fluxes were recorded during the combustion of narrow-leaved bluegrass (47.4±3.21 kW/m2). The amount of stored energy directly depends on the material structure, density, and initial moisture content. It should be taken into account that the fire hazard of a forest area depends on pyrological properties, and especially on the moisture content of the dominant type of fuel bed.

Examination of thermophysical characteristics of food products

The development of food, biotechnological, and processing industries, the invention of new ingredients, optimisation and improvement of technological processes require reliable information about the main thermophysical characteristics of raw materials and materials of biological origin. This paper presents the results of the cooperation of specialists from leading universities and scientific institutions of Ukraine, embodied in the developed methods of analysing the parameters of thermodynamic and mass transfer processes and determining the thermophysical characteristics of the latest substances and products using modern metrologically certified devices and information-measurement systems. The main problem in analysing materials of biological origin is the inhomogeneity and heterogeneity of the structure of samples. It is demonstrated that it is advisable to determine the coefficient of effective thermal conductivity of bulk materials and cereals in a stationary thermal mode on a device for determining the thermophysical characteristics of materials and thermal effects, equipped with heat flow and temperature sensors, in which a symmetric scheme of the thermometric measurement method is implemented. The simultaneous use of four measuring cells allows for performing a synchronous comparative analysis of several samples, and the rotary-clamping mechanism helps to minimise contact resistances. The developed method of measuring the coefficient of effective thermal conductivity considers the features of bulk food products and substantially improves the accuracy of the examination by introducing a correction for the contact resistance of the wall layer. Long-term observations allow for analysing thermolabile materials, examining thermal effects in samples, and evaluating volumetric and integral heat generation. It is necessary to use the STA system to conduct calorimetric studies of a wide range of biological materials and substances with the necessary accuracy, which implements methods of step-by-step scanning and synchronous thermal analysis to determine the specific heat capacity, the heat of evaporation, and the ratio of free and bound moisture in nonhomogenous materials. These characteristics are necessary parameters for analysing the kinetics and optimisation of heat and mass transfer processes, in particular, drying, in the calculation and design of technological equipment

Analysis of the characteristics of bimetallic and semiconductor heat flux sensors for in-situ measurements of envelope element thermal resistance

Monitoring of the thermal resistance of building envelopes for assessing their energy efficiency is carried out through in-situ measurements of the heat flux. It is therefore necessary to take into account not only the heat transfer conditions of the studied object but also the characteristics of the measuring instruments, which may depend on these conditions. This paper presents the results of a study of the characteristics of heat flux sensors of two types —bimetallic and semiconductor — which are the most common in the control of building envelopes. The case studies were focused on the characteristics of the sensors, such as the conversion coefficient (inversely proportional to sensitivity to the heat flux), the temperature dependence of the conversion coefficient, the response time of the sensors, and the emissivity of the sensor surface. The conversion coefficient of a bimetallic sensor was determined under the conditions of conduction and radiation supply of heat energy, which revealed the dependence of the conversion coefficient on the heat transfer conditions of the sensor surface. The value of the emissivity of the semiconductor sensor surface is lower than that of bimetallic sensors, and the time constant of bi-metallic sensors is two times less than that of semiconductor sensors. Verification of the obtained results was carried out by studying the metrological characteristics of the multi-channel thermal resistance control system, which included bimetallic heat flux sensors as sensitive elements. Thus, we suppose that the results of our study could be used to improve the accuracy in measuring the thermal resistance of building envelopes by the correct selection of heat flow sensors, or by making corrections to the measurement results that take into account the influence of experimental conditions on the characteristics of the sensors.

Preliminary analysis of the influence of environmental boundary conditions on convective heat transfer coefficients

In this contribution, a hot box apparatus was used to investigate convective heat transfers through an experimental setup composed of a heat-flow sensor, air and surface temperature probes installed on the wall tested in the hot box and a hot-wire anemometer. The air near the wall was indirectly moved by means of a forced convection system through which the air velocity can be modified to simulate different environmental conditions. The hot box apparatus was used in order to investigate the influence of the air velocity on internal convective heat transfer coefficients (hc), under natural/mixed convection conditions. The Standard ISO 6946 suggests a typical internal convective heat transfer coefficient equal to 2.5 W/m2K when horizontal heat fluxes occur. No detailed information about this value are reported in the Standard. So, the final aim of this study is to assess the applicability of the internal convective heat transfer coefficient value proposed by ISO 6946 under different air velocity values, quantifying how hc varies as air velocity changes.

Calibration methodology for contact heat flux sensors with enhanced accuracy

This paper presents a method for the calibration of contact heat flow sensors and the measures taken to improve the overall standard uncertainty of the measurements. This may be particularly relevant for applications such as the thermal characterization of Li-ion battery cells, where small amounts of transferred heat must be measured. The designed calibration set-up is based on the measurement of temperature gradients within a reference object, which is a common and well known approach. However, certain aspects must be considered in order to obtain accurate results. In this paper all steps taken to improve the overall measurement uncertainty are described. One of the most important characteristics of the presented methodology is the experimental determination of an equivalent thermal conductivity of the used reference object. To do so, a single-sided guarded hot plate apparatus is integrated into the calibration set-up to generate a precisely known heat flow. This approach is comparable to the determination of the ‘energy equivalent’ in calorimeters. The measured equivalent thermal conductivity agrees well to literature values, but the achieved standard uncertainty is significantly lower. By way of example, the calibration method is applied on a thermoelectric generator, where the temperature dependent sensitivity and the Seebeck coefficient are determined and compared to literature values. The average standard uncertainty of the sensor sensitivity is ±1.86%, which is lower than most results published in the literature. At 20 °C the absolute value of the determined Seebeck coefficient of the examined thermoelectric element is only 2.7% higher than the value expected for the used material ().

Fully Printed Flexible Heat Flow Sensors and their Utilization toward Heat Generation Monitoring for People and Machineries

AbstractA flexible and highly sensitive heat flow sensor, which can be attached to the human body and to various types of machinery for measuring their heat generation, is an ideal device for monitoring human health and the operational conditions of machinery. These sensors may be of great value for the implementation of sophisticated cyber physical systems. However, the fabrication of flexible and highly sensitive heat flow sensors is challenging because it is difficult to fabricate efficient heat–voltage conversion materials on flexible film substrates. In this study, a fully printed flexible heat flow sensor with high sensitivity is examined, which allows the detection of minute quantities of heat flow with the magnitude of several tens of milliwatts. The sensor features a device structure, wherein thermoelectric layers comprising carbon nanotube and polymethyl methacrylate coating are placed on the top and bottom surfaces of the flexible substrate and are connected by through‐holes. Due to the resultant flexibility and high sensitivity, the sensor can be attached to a human arm and detect the heat emanating from it. Additionally, it is demonstrated that changes in the load of a machine under operation can be monitored by attaching the flexible heat flow sensor to the machine.

High-speed amplifier development for the heat flow sensor

This article describes characteristics of preamplifiers for Atomic Layer Thermopile (ALTP) sensor based on precision operational amplifiers AD8597, ADA4004, ADA4075, ADA4896 and ADA4528. Transfer functions and total output noise values of these preamplifiers were obtained experimentally using an Agilent InfiniiVision 3000 series X oscilloscope. Results of experimental verification of preamplifier characteristics using a high-speed heat source are presented and discussed; the best operational amplifier for the application is determined.

Thermal performance and thermal resistance of fibre cement roof tiles: Experimental study

A better understanding of the thermal performance of construction systems may help engineers and architects to select the most suitable materials for the solutions that meet their objectives. In warm-climate countries like Brazil, the thermal performance of roofs is of particular importance. Thus, this study presents an evaluation of the thermal performance of roofs built in reduced scale on an experimental test rig, in Florianópolis, capital of the state of Santa Catarina, southern Brazil. Four roofs were evaluated, all with fibre cement tiles and a polyvinyl chloride (PCV) ceiling: the first was used as a reference, the second had the tiles painted white, the third had a radiant barrier installed and the fourth had conventional thermal insulation based on expanded polystyrene (EPS). All roofs were instrumented with temperature and heat flow sensors and data was collected over a period of eight months. The results show that all of the test roofs had a lower thermal gain than the reference roof, with reductions of 55% for the roof with white tiles, 67% with a radiant barrier and 70% with conventional thermal insulation. The thermal resistance for downward heat flow of the roof with conventional thermal insulation was 1.29m2K/W and that of the roof with the radiant barrier was 1.20 m2K/W, with a difference between the two of only 7%. When comparing the thermal resistance obtained experimentally with values obtained with the international standard ISO 6946 and with the Brazilian standard NBR 15220-2 it was found that the radiant barrier roof presented the greatest differences, of 41% and 30%, respectively. This demonstrates that it is important to review the calculation procedure, especially when a radiant barrier is used for thermal insulation.

High-temperature heat-flux inverse drop calorimeter

A new high-temperature (up to at least 1273 K) setup for inverse drop calorimetry was designed and assembled. This calorimeter uses a differential thermopile as a heat-flow sensor. The thermopile design features significant number of thermocouple junctions at the bottom of the measurement crucible in addition to those surrounding its side surface. The samples, held at room temperature, can be introduced through an autosampler into the crucible inside the calorimetric cell, heated up by means of a homebuilt three-winding wire furnace with large isothermal zone. The calorimeter performance in drop experiments was verified and compared with that of a commercially available device of the same kind. In addition, a few drop solution experiments were made; obtained, as a result, enthalpies of formation of CsPbX3 (X = Br, I) were found to be in agreement with those reported earlier.

Determination of thermal conductivity of backfill

Shallow foundations with thermal insulation can be used in the construction of low-rise buildings. Thermal insulation prevents freezing of soils under the foundation. The article presents the results of determining the thermal conductivity of sand with the addition of crushed brick and concrete rubble. The research was carried out in a specially designed unit, which consists of two climatic chambers connected to each other. The soil sample is maintained into the special cell. Heat flow and temperature sensors are placed in the soil sample. Before soil testing a numerical simulation of laboratory test was implemented in GeoStudio. Due to numerical modelling optimal dimensions of testing cell was defined. Results of laboratory testing of sand with a known thermal conductivity with using designed parameters of cell has a good agreement with calculated value. The test procedure was extended to soils with construction waste. The addition of 20% crushed brick to the sand reduces its thermal conductivity coefficient by 20.6% in the frozen state and by 10.1% in the thawed state. At the same time sand with concrete rubble showed a decrease in the thermal conductivity coefficient in the frozen state by 6.4% and an increase by 13.4% in thaw. The effect is occurred because of the addition of particles of different mineralogical composition with different thermal conductivity. The results of testing can be used in making forecast of the thermal regime of soil stratum when designing shallow foundations.

On the resistance to heat flow across soil-structure interfaces

A number of recent publications have suggested that in order to reproduce thermal testing of energy piles, a finite value for the geo-contact thermal resistance (geo-CTR) at the soil-structure interface needs to be introduced. There is currently no guidance as to what value the geo-CTR should have. The geo-CTR will have two potential impacts in terms of the use of energy geo-structures, (i) reducing heat exchange efficiency, and (ii) increasing temperature changes and associated mechanical impacts within the geo-structure. This article sets out a new experimental method for quantifying the geo-CTR. The proposed method is based on the imposition of a heat flux through the two solid materials that form the contact. Its novelty rests with the acknowledgement that heat loss is inevitable and that the geo-CTR can be more reliably defined based on heat flow measurements at the actual contact. This concept is demonstrated via numerical modelling of a generic test set-up, where the errors induced by not accounting for heat loss, the interpolation of temperatures to the contact and the presence of the heat flow sensor were assessed. Initial test results are then presented that demonstrate how the method works. These results suggest that for a dry medium sand, while the geo-CTR is sensitive to the soil density, it is small and the effect on heat transfer is also likely to be small. Further testing will explore the relative importance of a number of factors and in particular, the soil type, on the geo-CTR.

Heat flow measurements on high-speed aircraft models

The functionality of “Hypersonic aerodynamic shock tube” facility was expanded to obtain more complete validation of developed computer codes for the prospective high-speed aircraft aerothermodynamics description. The method of luminescent temperature converters was applied in the laboratory installation. Measuring of temperature fields on the surface of models installed in the aerodynamic unit when they have ambient air flow at Mach numbers M=5-7, have been implemented. The calorimetric type heat flow sensor was selected among existing heat flow sensors as it based on microsecond inertia, miniaturization, and relative ease of manufacturing. The sensitive elements of the calorimetric sensors were manufactured for the laboratory installation. The ability of the manufactured sensors to work and the dependence of the response time from the thickness of the heat-receiving surface were revealed.

Testing the superblock deck by dynamic loads

Tyumen oil and gas industry province is being developed with the use of complete block construction. Especially increases the importance of building large blocks with installed equipment and superblocks on a floating mobile base. Styrofoam concrete is used to insulate the superblock deck. According to the developed methods, the adhesion strength of Styrofoam concrete to the superblock deck was tested and its characteristics for vibration resistance after the test were studied. The thermal characteristics of Styrofoam concrete used for superblock deck insulation are established, taking into account the vibration effects during transportation and operation. For testing, the deck fragment was installed in a climate chamber, and heat flow and temperature sensors were fixed to the surface of the fragment. As a result, it was found that dynamic loads reduce the resistance to heat transfer by 8-12 % due to the opening of cracks and the appearance of convective heat exchange. It is shown that the actual thermal resistance of the superblock deck with a thickness of 0.25 m and after exposure to dynamic loads remains at a sufficiently high level.

Sensor Technologies for Automobiles and Robots

AbstractThis paper reviews various sensor technologies with application in automobiles and robots. Several automotive sensors have been developed using the micro‐electromechanical systems (MEMS) technology. The technologies related to combustion pressure sensors, yaw rate sensors, acceleration sensors, and optical scanners are described here. The combustion pressure sensors are used for engine control, while the yaw rate sensors of quartz and silicon crystals and the acceleration sensors are applied for vehicle motion control. Optical scanners are developed for autonomous driving. Several automotive sensors have been significantly reduced in size and cost, and their performance has been improved dramatically by MEMS technology. The inertial force‐sensing system with yaw rate and acceleration sensors enabled the assistant and partner robots to stand on two legs, walk, or invert and move on two wheels. Because the robots are required to have a variety of sensors, a nerve‐net sensing system was developed. This sensing system has three layers: the host, relay, and sensor nodes. The sensor node is a special large‐scale integration called a ‘nerve‐net chip.’ A triaxial force tactile sensor integrated with the nerve‐net chip was developed as a 2.8‐mm square surface‐mountable chip. A force and thermal tactile sensor was also developed, which detected heat flows and discriminated the materials of contacted objects. The heat flow sensor was thinned with thin‐film technology. The sensor technologies will be used for eco cars and autonomous vehicles. Next‐generation robots are also supported by several automotive sensor technologies. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Modulating the Spin Seebeck Effect in Co2FeAl Heusler Alloy for Sensor Applications.

The thermoelectric conversion technique has been explored in a broad range of heat-flow sensors. In this context, the Spin Seebeck Effect emerges as an attractive candidate for biosensor applications, not only for the sensibility improvement but also for the power-saving electronic devices development. Here, we investigate the Longitudinal Spin Seebeck Effect in films with a CoFeAl/W bilayer structure grown onto GaAs (100) substrate, systems having induced uniaxial magnetic anisotropy combined with cubic magnetic anisotropy. From numerical calculations, we address the magnetic behavior and thermoelectric response of the films. By comparing experiment and theory, we explore the possibility of modulating a thermoelectric effect by magnetic anisotropy. We show that the thermoelectric voltage curves may be modulated by the association of magnetic anisotropy induction and experimental parameters employed in the LSSE experiment.

Angstrom configuration for absolute measurement on heat losses of metal sample by active thermography

Obtaining the precise value of the sample averaged heat loss coefficient has been a challenge that yet is not been satisfactorily resolved. This paper proposes an experimental setup and an optimized method to evaluate the averaged heat loss coefficient by the surface of the metal sample without need to know the thermal properties of the sample. A thermal camera along with the heat flow sensors was used to measure the heat loss coefficient in an absolute (non-relative) way. Also, a numerical simulation was done where minimum approximations are applied, and it is not necessary to make any adjustments with a complicated theoretical model. Then, it was experimentally demonstrated that the heat loss coefficient does not depend on the thermal properties of the metal sample. The influence in the difference of the temperature of the sample with the room temperature, on the factor h is monotonously increasing independent from heating or cooling regime. The proposed method has the advantage that the value of the heat loss coefficient is obtained experimentally, and the results are congruent with the COMSOL simulation outcomes.

Perioperative measurement of core body temperature using an unobtrusive passive heat flow sensor.

Clinicians strive to maintain normothermia, which requires measurement of core-body temperature and may necessitate active warming of patients. Monitoring temperature currently requires invasive probes. This work investigates a novel foam-based flexible sensor worn behind the ear for the measurement of core body temperature. This observational study uses the device prototype and clinical data to compare three methods for calculating the temperature from this sensor: a basic heat-flow model, a new dynamic model that addresses changing surrounding temperatures and one that combines the dynamic model with a correction for adhesive quality. Clinical validation was performed with 21 surgical patients (average length of surgery 4.4 h) using an esophageal temperature probe as reference. The operative period was divided into four segments: normal periods (with stable surrounding temperatures), surrounding temperatures increasing due to the use of the Bair Hugger™, stable periods during Bair Hugger™ use and surrounding temperatures decreasing due to its removal. The error bias and limits of agreement over these segments were on average of - 0.05 ± 0.28 °C (95% limits of agreement) overall. The dynamic model outperformed the simple heat-flow model for periods of surrounding temperature changes (12.7% of total time) while it had a similar, high, performance for the temperature-stable periods. The results suggest that our proposed topical sensor can replace invasive core temp sensors and provide a means of consistently measuring core body temperature despite surrounding temperature shifts.

Measurement of the component-by-component flow rate of a gas-liquid medium by thermal method

A thermal method for measuring the component-by-component flow rate of a gas-liquid medium flowing through a channel with evenly distributed thermal energy is considered. Taking some heat energy evenly distributed over the cross-section of the channel, the components, due to their different heat capacity, acquire each its own pulse heat charge. Then, moving along the flow, the components give this information about the charge value to the heat flow sensors, which is used to form the fractions of each component in a numerical block. Each component is able to take a heat charge in proportion to its heat capacity. By the amount of heat absorbed, you can determine the type of component and its quantity. This thermal method does not require the use of complex equipment. To measure the heat capacity with minimal heat flow transmission measurements, the latest gradient-type sensors with a small value of the time constant and high sensitivity are used.

Research and development of surface heat flux sensor for high speed aircraft

A water-cooled high temperature and high heat flow sensor was developed to meet the requirements of high heat flow measurement under ultra-high temperature conditions on the surface of high speed aircraft. This type of sensor is based on the measurement principle of circular foil heat flow sensor. Cooling water is introduced through structural design optimization to ensure that the structure, measurement accuracy, sensitivity, linearity and other indicators of the sensor do not change at ultra-high temperature of 1600°C, so as to achieve extremely high heat flow measurement on the surface of the aircraft. Through the test verification, the heat flow sensor can withstand 1600°C, heat flow measurement range up to 1000KW/m2, measurement accuracy is better than 5%.

Whole building retrofit using vacuum insulation panels and energy performance analysis

Vacuum insulation panels (VIPs), due to their high thermal performance, provide an attractive alternative to traditional building insulation materials, especially as an option for retrofitting old, poorly insulated buildings. This article describes the complete retrofit of all exterior walls of a single-story building in a cold climate using VIPs. A recently-developed low-cost VIP, called modified atmosphere insulation (MAI), was used in this study. Two buildings of near-identical construction were studied, with one remaining unaltered and serving as the baseline while the other served as the retrofit building. The VIPs or MAI panels proved to be a feasible and durable option for retrofitting building envelopes. Thermal performance of both buildings was analyzed using in-situ temperature and heat flow sensors. Numerical models of the two buildings were created, benchmarked using experimental data and used for predictions of annual energy savings due to the addition of MAI panels to the exterior walls. The models predicted significant reduction in the annual heating energy consumption in the retrofitted building compared to the baseline building.