Thermal Anemometer Research Articles

Evaluation of Aldehydes, Polycyclic Aromatic Hydrocarbons, and PM2.5 Levels in Food Trucks: A Pilot Study.

Background: The food truck industry has rapidly expanded in the United States and kitchen environments can contain harmful contaminants from cooking emissions. The objective of this study was to examine the levels of aldehydes, polycyclic aromatic hydrocarbons (PAHs), and Particulate Matter (PM)2.5 generated from cooking process in food trucks. Methods: Area sampling was performed twice at two participating food trucks during work shifts. Nine aldehydes and eighteeen PAHs were analyzed according to the relevant standard methods while PM2.5 was measured with a real time monitor. Ventilation performance of the food truck exhaust hoods was also investigated using a thermal anemometer. Findings: Formaldehyde was the only aldehyde detected in all samples with a concentration range of 7.16 to 53.68 µg/m3. No PAHs were detected above the limit of quantification. Average PM2.5 concentrations ranged from 0.65 to 7.03 mg/m3. Food Trucks 1 and 2 have an average exhaust flow rate of 211 and 215 L/s per linear meter of hood, respectively. Conclusions/Application to practice: Overall, Food Truck 2 had consistently higher levels of aldehydes and PM2.5 with comparable ventilation performance as Food Truck 1. The higher exposure levels of Food Truck 2 could possibly be attributed to a larger volume of food orders and the heavy duty cooking equipment with an exhaust flow rate below the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommendations. Although more investigations need to be performed, the findings could be used to raise awareness of food truck workers and health practitioners to reduce potential exposure risks.

Evaluation of wind gust at pedestrian space with a small thermistor anemometer in wind tunnel experiment

Evaluation of wind gust at pedestrian space with a small thermistor anemometer in wind tunnel experiment

Design of highly-sensitive fiber thermal anemometer based on reflective photonic crystal fiber loop mirror

• A reflective fiber loop mirror is firstly used in flow rate sensing. • The proposed sensor exists an infinite temperature-sensitivity point, which can be adjusted. • The fiber thermal anemometer has high sensitivity and long-distance sensing capability. A highly-sensitive fiber thermal anemometer was proposed and numerically designed based on reflective fiber loop mirror (RFLM). One ethanol-infiltrated birefringent photonic crystal fiber (BPCF) was imbedded in the RFLM as the sensing head, whose output interference spectrum was sensitive to surrounding temperature. Laser was used to heat the BPCF to a fixed temperature, but the temperature changed with the variation of surrounding flow rate. Therefore, the flow rate could be measured by monitoring the wavelength shift of the output spectrum. Through numerical analyses on the characteristics of the RFLM, the relationship between the flow rate and the temperature of the BPCF was numerical studied and then the structure parameters of the BPCF were optimized. Finally, numerical results showed that the maximum detectable flow rate could be enlarged to 20.8 m/s with the detection limit of 0.3 m/s, when the laser power was 100 mW. In addition, the defined quality parameter Q demonstrated that the sensitivity was improved to about 20 times.

Evaluation of thermal comfort in outdoor public space: Case of study: City of Annaba –Algeria-

Outdoor public spaces play an important role in the articulation of a city. The thermal comfort of these spaces has become a problem because of climate variations. Our work aims to study thermal comfort in outdoor public spaces in order to tackle the variability between microclimatic parameters which were taken from several field stations. Furthermore, it aims to identify the effect of the different factors and thermal conditions on both the microclimate and the external thermal comfort. A comparative study between three public spaces of the city of Annaba (course, square and garden) has been conducted. The method adopted for this research is based on the measurement of microclimatic parameters. The measurement took place during August 2016. It was performed by a thermal hygrometer to cover air temperature and relative humidity. Then, a thermal anemometer was used in order to estimate wind speed, every 2 hours from 06:00am until 08:00pm. The obtained results confirm the variability of the thermal environment in an urban environment and the impact of vegetation, urban morphology and water on outdoor thermal comfort.

Design and validation of a nanoscale cross-wire probe (X-NSTAP)

A nano-sized crossed thermal anemometer (X-NSTAP) was developed and validated for measurements of two-components of velocity at high Reynolds numbers. The new sensor design is based on the single-component nanoscale thermal anemometry probe (NSTAP) previously used to acquire streamwise velocity measurements at high Reynolds numbers. The new sensor can, simultaneously, measure two components of velocity with a spatial resolution of $$42\times 42\times 50 \, \upmu {\text {m}}$$ , an order of magnitude smaller in each dimension than conventional cross-wires. The new X-NSTAP design features several structural and manufacturing modifications to improve the aerodynamic performance of the sensor compared to previous nanoscale cross-wire designs. The effects of different manufacturing modifications were evaluated using dye visualizations over scale models of the sensor tip. The pitch sensitivity of the final sensor design was evaluated in an open-loop wind-tunnel and was comparable to the single-component NSTAP design. The X-NSTAP was then deployed in the Princeton Superpipe to acquire axial and radial velocity measurements up to friction Reynolds numbers, $$Re_\tau = 24{,}000$$ with good agreement to existing studies.

Wind direction sensor based on thermal anemometer for olfactory mobile robot

A wind direction sensor has been implemented for many applications, such as navigation, weather, and air pollution monitoring. In an odor tracking system, the wind plays the important role to carry gas from its source. Therefore, the precise, low-cost, and effective wind direction sensor is required to trace the gas source. In this study, a new design of wind direction sensor has been developed using thermal anemometer principle with the main component of the positive temperature coefficient thermistor. Three anemometers each of which has different directions are used as inputs for the neural network to determine the direction of the wind automatically.The experimental results show that the wind sensor system is able to detect twelve wind directions. A mobile robot equipped with this sensor system can navigate to a wind source in the open air with a success rate of 80%.This system is expected to increase the success rate of the mobile robot in searching for dangerous leaking gas in the open air.

Temperature compensation of NTC thermistors based anemometer

Thermal anemometers based on self-heated thermistors with negative temperature coefficients are a robust, sensitive and low-cost alternative to standard hot-wire anemometers in wind turbine characterization and optimization. However, changes in ambient temperature greatly affect the accuracy in wind speed measurements of these devices. In this paper, a temperature compensation method incorporating two thermistors with negative temperature coefficients is experimentally investigated. A temperature compensated anemometer circuit is proposed. The effectiveness of the implemented temperature compensation method is verified over a span of 16 ℃ for two different air velocities. To account for a possible thermistor mismatch, a correction procedure is proposed and verified. In the end, it is shown that the air temperature can be reconstructed from the uncompensated anemometer outputs as well.

Visualization of the shielding gas flow in SLM machines by space-resolved thermal anemometry

PurposeThe purpose of this paper is to introduce an approach in measuring the shielding gas flow within laser powder bed fusion (L-PBF) machines under near-process conditions (regarding oxygen content and shielding gas flow).Design/methodology/approachThe measurements are made sequentially using a hot-wire anemometer. After a short introduction into the measurement technique, the system which places the measurement probe within the machine is described. Finally, the measured shielding gas flow of a commercial L-PBF machine is presented.FindingsAn approach to measure the shielding gas flow within SLM machines has been developed and successfully tested. The use of a thermal anemometer along with an automated probe-placement system enables the space-resolved measurement of the flow speed and its turbulence.Research limitations/implicationsThe used single-normal (SN) hot-wire anemometer does not provide the flow vectors’ orientation. Using a probe with two or three hot-films and an improved placement system will provide more information about the flow and less disturbance to it.Originality/valueA measurement system which allows the measurement of the shielding gas flow within commercial L-PBF machines is presented. This enables the correlation of the shielding gas flow with the resulting parts’ quality.

METHODS FOR INCREASING THE EFFICIENCY OF A DUAL-CHANNEL OPTO-ELECTRONIC SIGHT

The actual task of the aiming equipment manufacturers is to develop autonomous models of optical sights capable of independently measuring and analyzing input parameters in combat conditions and on their basis to make corrections to the guidance system and aiming mechanisms. The aim of the study was to investigate methods for increasing the efficiency of the dual-channel opto-electronic sight of the DNS-1 model for small arms by analyzing the degree of influence of external environmental factors determining the trajectory of a bullet flight and the accuracy of its hit into the target.The variant of the practical implementation of the DNS-1 sight with an integrated ballistic computer, taking into account: wind speed and direction, target location angle, ambient temperature, relative humidity and atmospheric pressure is considered. Evaluation of the rigidity and stability of the sight design was made when fastening it to the receiver along the «swallowtail» guide and on the «Picatinny» bar. In the variant with Picatinny rail, the loads are smaller and distributed more evenly along the line of the body of the sight. Calculations of the trajectory of the bullet from the cartridge 7Н10 with a caliber of 5.45 mm for the AK74Н at distances of 300 and 1000 m were carried out. At a distance of 300 m and at a value exceeding 53.2 cm, the throwing angle remains practically unchanged and lies within 0.2°. For long distances up to 1000 m, the ballistic angle increases to 3°. A method for measuring wind load using a thermal anemometer based on the Dantec Dynamics 55P11 sensor is proposed. Optimization of the anemometer housing design was performed and wind load simulation was performed, wind field velocity distribution was obtained in the aerodynamic blowdown of the anemometer assembly in the range from 2 to 20 m/s. A method is proposed for measuring the angle of the target site using an accelerometer based on the SCA830-D07 sensor with an accuracy of 0.00179°.The presented research results show the possibility of creating a complex automated fire control system for small arms.

Sliding mode analysis applied to improve the dynamical response of a spherical 3D wind sensor for Mars atmosphere

The objective of this paper is to show how the structure of a thermal wind anemometer can be tuned to ensure a fast response when the sensor works in closed loop configuration (constant temperature operation). If the thermal filter associated to the sensor structure has only one significative time constant, the resulting system time response, working in closed loop, is enhanced beyond the natural limit imposed by its own thermal circuit. This effect is theoretically explained using the theory of sliding mode controllers. Experimental corroboration is presented by comparing the results obtained with two prototypes of a spherical wind sensor for Mars atmosphere. It will be shown that in case of having only one significant time constant, the time response in closed loop is much faster than the value associated with that time constant. It will be experimentally shown that this effect is lost when the thermal filter has more than one significant time constant. Diffusive representation is used to obtain arbitrary-order models of the thermal structures of the sensors.

Dead-beat control based thermal compensation for micromachined thermal gas gyroscope

Micromachined thermal gas gyroscopes take advantages of simple structure, low cost, high shock resistance, and large measurement range by using thermally driven gas stream instead of solid proof mass as moving and sensitive element compared with conventional silicon or quartz gyroscopes. However, they suffer from temperature susceptibility, which degrades performances of the gyroscopes. It is important to investigate thermal mechanism behaving in sensor and build an effective thermal compensation method to guarantee the sensor accuracy. In this paper, Finite-Element-Model (FEM) simulation method is used to study the thermal behavior and the relationship between the thermal drift of the gyroscope and the working temperature of the heaters that thermally drives gas motion is established. On this basis, we propose a real-time thermal compensation scheme based on Alternating Dead-Beat Control (ADBC). ADBC is used to alternatively modulate the heaters to implement fast, small-overshoot, and precise temperature control so as to keep the working condition of the sensor steady. Experiments validate that the thermal compensation scheme is effective to eliminate the temperature drifts in scale factor and zero bias of the sensor, meanwhile improves the gyroscope sensitivity. Predictably, the ADBC based compensation methodology can be applied for other thermal sensors (e.g. thermal accelerometers, thermal anemometers).

Full scale measurements of the operation of fire ventilation in a road tunnel

The main aim of the research performed was to check the operation of a ventilation system in a conventionally operated road tunnel in Southern Poland. The length of the examined tunnel is 678m and it has a gradient of 4%. It includes longitudinal ventilation. The measurements of normal and reversed velocity of air flows (which were forced by the fans) were conducted at two cross-sectional profiles inside the tunnel. A set of fourteen thermal anemometers was applied there. In addition, at the intake and exit portals the wind direction, wind velocity and temperature were recorded during the tests. The fans worked according to the emergency operation pattern. The results were compared to estimated critical velocity and the correct functioning of the ventilation system was confirmed. The results showed a significant influence of the naturally caused airflows. Numerical simulations were performed to determine the air velocity resulting from this effect. CFD Ansys Fluent was used to solve the simplified model of the tunnel. The results confirmed that the combination of the stack effect and wind influence is crucial.

Measurement of Air Flow Rate Through Perforated Floor Tiles in a Raised Floor Data Center

In a raised floor data center, cold air from a pressurized subfloor plenum reaches the data center room space through perforated floor tiles. Presently, commercial tool “Flow Hood” is used to measure the tile air flow rate. Here, we will discuss the operating principle and the shortcomings of the commercial tool and introduce two other tile air flow rate measurement tools. The first tool has an array of thermal anemometers (named as “Anemometric Tool”), and the second tool uses the principle of temperature rise across a known heat load to measure the tile air flow rate (named as “Calorimetric Tool”). The performance of the tools is discussed for different types of tiles for a wide range of tile air flow rates. It is found that the proposed tools result in lower uncertainty and work better for high porosity tiles, as compared to the commercial tool.

家庭用エアコンを対象としたCOP測定実験によるカタログAPFの精度検証

INTRODUCTION As the Coefficient of Performance (COP) of heat pump devices varies significantly according to the heating and cooling load and ambient temperature, when selecting a suitable device, it is very important to consider the thermal performance of the house and the local weather conditions. It is common to select a home-use air conditioners according to the room floorage in Japan. The heating and cooling load value per unit floorage from 1964 has not been revised, and is still used in the case of the present air-conditioner selection (maximum heating load per floorage: 275 W/m2). However, this is not the best method for highly insulated houses and leads to problems for energy conservation. In this study, we developed a calorie meter to carry out temperature adjustment, and used it in analysis of the relationships among COP, heating and cooling load and outside air temperature. COP Matrix is constructed by a database of the measurement results. Furthermore, heat load calculation was performed using the insulation efficiency and the local condition of detached housing as analysis variables. As a result of the heat load calculation, Annual Performance Factor (APF) in actual environmental conditions is computed through correlation with the created COP Matrix. The APF calculated from experiment results is compared with the catalogue APF in order to clarify the characteristics of home-use air-conditioners considering the local conditions and heat load conditions. RESEARCH METHODS The indoor chamber of the calorie meter is 3 m wide, 3 m deep, and 2.7 m high. The outdoor chamber is 2 m wide, 2 m deep, and 2 m high. One temperature and humidity sensor and one thermistor anemometer are installed in the inlet of the inside air conditioner unit. Two temperature-and-humidity sensors are installed in the outlet of the inside air conditioner unit. One temperature-and-humidity sensors are installed in the inlet of the outside air conditioner unit, the temperature at this point is the outside temperature. Furthermore, in order to examine experimental accuracy, two thermocouples are separately installed in the inlet and three thermocouples are separately installed in the outlet of the inside air conditioner unit. A COP matrix is created from the relationship of COP, heating and cooling load and outside air temperature. In order to consider the change of APF calculated from experiment results, analysis was performed by changing the insulation efficiency according to the Standard Model issued by the Architectural Institute of Japan (AIJ). We used the meteorological data of the AIJ extended AMeDAS meteorological data. Analysis was performed by heat load simulation software TRNSYS. COP was calculated by collation with the computed COP matrix. RESULTS The COP of cooling is lower when output is relatively low. The COP of heating is higher when the outdoor air temperature is relatively high. And there is a tendency for COP to rise as the flow rate of the inside unit increases. COP matrix in automatic flow rate is similar to COP matrix in relatively small flow rate. Although the APF of an air conditioner in the catalogue is 5.6, which computed from COP matrix in case1-1 (Tokyo) is 2.9, which is about 0.5 times rather than catalogue value. The year cumulative power consumption in the catalogue is about 2,000 kWh, which computed from COP by the COP matrix in case1-1 (Tokyo) is about 3,200kWh, which is about 1.6 times rather than catalogue value. The APF of heating and cooling become lower when insulation efficiency is relatively high. Because the heating load and cooling load is reduced, the frequency of the ON-OFF operation which COP is relatively low is increased.

EURAMET project No. 1225: intercomparsion of very low air speed standard facilities (0.05 m/s to 1 m/s)

For the first time a EURAMET comparison of standard facilities in the field of low air speed is presented. The air velocities range from 0.05 m/s up to 1 m/s. Two different thermal anemometers are used as Transfer Standards (TS), namely a ball-type and a planar-type anemometer. Due to their construction it is possible to analyze different components of the flow vector. Orientation-dependent measurements which are investigated in addition might also deliver information concerning the components of the flow vector. A Comparison Reference Value (CRV) is calculated with the help of the chi-squared test according to the procedure A presented by Cox [1] [2] and the degree of equivalence of the laboratory data to the CRV is determined. Both TS show reasonable results and a high degree of equivalence. Furthermore the degree of equivalence of the laboratory data to each other is investigated in detail.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Rugged constant-temperature thermal anemometer.

Here we report a robust thermal anemometer which can be easily built. It was conceived to measure outdoor wind speeds and for airspeed monitoring in wind tunnels and other indoor uses. It works at a constant, low temperature of approximately 90 °C, so that an independent measurement of the air temperature is required to give a correct speed reading. Despite the size and high thermal inertia of the probe, the test results show that this anemometer is capable of measuring turbulent fluctuations up to ∼100 Hz in winds of ∼14 m/s, which corresponds to a scale similar to the length of the probe.

Omnidirectional thermal anemometer for low airspeed and multi-point measurement applications

Current control strategies for livestock and poultry facilities need to improve their interpretation of the Thermal Environment (TE) that the animals are experiencing in order to provide an optimum TE that is uniformly distributed throughout the facility; hence, airspeed, a critical parameter influencing evaporative and convective heat exchange must be measured. An omnidirectional, constant temperature, Thermal Anemometer (TA) with ambient dry-bulb temperature (tdb) compensation was designed and developed for measuring airspeeds between 0 and 6.0ms−1. An Arduino measured two analog voltages to determine the thermistor temperature and subsequently the power being dissipated from a near-spherical overheated thermistor in a bridge circuit with a transistor and operational amplifier. A custom wind tunnel featuring a 0.1m diameter pipe with an access for TA insertion was constructed to calibrate the TA at different temperatures and airspeeds, at a constant relative humidity. The heat dissipation factor was calculated for a given airspeed at different ambient temperatures ranging from 18°C to 34°C and used in a unique fourth-order polynomial regression that compensates for temperature using the fluid properties evaluated at the film temperature. A detailed uncertainty analysis was performed on all key measurement inputs, such as the microcontroller analog to digital converter, TA and tdb thermistor regression statistics, and the calibration standard, that were propagated through the calibration regression. Absolute combined standard uncertainty associated with temperature corrected airspeed measurements ranged from 0.11ms−1 (at 0.47ms−1; 30.3% relative) to 0.71ms−1 (at 5.52ms−1; 12.8% relative). The TA system cost less than $35USD in components and due to the simple hardware, this thermal anemometer is well-suited for integration into multi-point data acquisition systems analyzing spatial and temporal variability inside livestock and poultry housing.

Liquid Flow Meter based on a Thermal Anemometer Microsensor

Liquid Flow Meter based on a Thermal Anemometer Microsensor

A micro-scale hot wire anemometer based on low stress (Ni/W) multi-layers deposited on nano-crystalline diamond for air flow sensing

A linear array of microscale thermal anemometers has been designed, fabricated and characterized. The sensitive element consists of a self-compensated-stress multilayer (Ni/W) patterned to form a wire with length, width, and thickness close to 200 μm, 5 μm and 2 μm respectively. The wire is deposited and supported by prongs made of nano-crystalline diamond (NCD) of about 2 μm in thickness. Due to its high Young’s modulus, NCD allows a very high mechanical toughness without the need for thicker support for the hot wire. Also, depending on grain size, the NCD is able to present thermal conductivity smaller than 10 W mK−1, providing good thermal insulation from the substrate and less conductive end losses to the prongs. The sensor was characterized experimentally. Its electrical and thermal properties were obtained first in the absence of fluid flow. The results confirm the effectiveness of thermal insulation and the mechanical robustness of the structure. The fluidic characterizations were performed and analysed in the case of an airflow with velocities of up to 30 m s−1.

Self‐calibrating closed‐loop circuit for configurable constant voltage thermal anemometers

A new circuit is described which applies a configurable voltage across an RTD while the current flowing through it is measured with a current mirror. The circuit also allows working with voltages above the IC supply voltage to cope with the high power RTD dissipation normally required in thermal anemometers. The circuit is periodically calibrated to cancel the errors and amplifier offset and therefore improves measurement accuracy. Experimental measurements of the circuit fabricated using 0.35 μm AMS technology show the functionality and improved power efficiency.