Measurement concepts
A versatile system was built to cater to different measurement needs and develop an innovative hot-wire probe automatic positioning-based concept for a multipoint duct airflow measurement device. Figure 1 illustrates the system's overview, which comprises four distinct subsystems. These subsystems are further explained in next Sections, providing detailed insights into the final configuration method employed during testing. Additionally, the subsequent section provides a comprehensive outline of the system's operation and the equipment utilized.
The assembly was programmed to perform the airflow velocity measurement of 5032 points. In order to deduct the uniformity index based on measured velocity at standard air condition, the uniformity index is given by Eq. 1. and the standard deviation is given by Eq. 2 (Zhang et al., 2017)(Sharma et al., 2015).
$${\gamma }_{u}=1-\frac{1}{\text{2n}}\sum _{i=1}^{n}\frac{\sqrt{{\left({u}_{i}-\stackrel{-}{u}\right)}^{2}}}{\stackrel{-}{u}} \left(1\right)$$
where \({{\gamma }}_{{u}}\) is the experimental uniformity index; \(\stackrel{-}{{u}}\) the measured outlet average velocity \({n}\) the number of measurement points.
$$\stackrel{-}{u}= \frac{\sum _{i=1}^{n}{u}_{i}}{n} \left(2\right)$$
$$Std=\sqrt{\frac{\sum _{i=1}^{n}{\left({u}_{i}-\stackrel{-}{u}\right)}^{2}}{n}} \left(3\right)$$
Measurement uncertainty
This study also aimed to evaluate the type A and B uncertainties associated with airflow and mass flow measurements. It was acknowledged that no measurement can be perfectly precise, necessitating the expression of uncertainty in the estimated values. While the study assumed that the uncertainties related to air density calculation and cross-section measurement had minimal impact on the results, the primary focus was on assessing the uncertainty associated with airspeed measurements.
Type A uncertainty was quantified using the statistically estimated sample standard deviation of the mean, denoted as \({u}_{A}\left(x\right)\) (4) (Biol et al., 2010)(Fojtlín et al., n.d.). Formula (4) was considered valid under the following conditions: 1. The variable \(x\) follows a normal probability distribution, and 2. The data were derived from independent observations conducted under the same conditions. Our previous experience provided evidence supporting the assumption of a normal probability distribution for the data.
$${{u}_{A}\left(x\right)=k}_{uA}.{\left[\sum _{i=1}^{n}{\frac{1}{n\left(n-1\right)}\left({x}_{i}- \stackrel{-}{x}\right)}^{2}\right]}^{\frac{1}{2}} \left(4\right)$$
The type A uncertainty of variable x, denoted as \({u}_{A}\left(x\right)\), is determined using the statistically estimated sample standard deviation. It takes into account the number of independent observations \(\left(n\right)\), the individual values of \({x}_{i}\), the mean value of \(x\), and the safety factor \({k}_{uA}\).
In this study, the outlets measurements involved 5032 observations, resulting in a safety factor \({k}_{uA}=4.36\) .
On the other hand, the type B uncertainty, \({u}_{B}\left(x\right)\), is evaluated using methods other than statistical data analysis. For this study, only the uncertainty arising from the limited precision of the anemometer W410D2 (which ensures accuracy with a rating of 0.2 + 2% FS (Full Scale) in m/s) was considered, while other sources of type B uncertainty were omitted.
The expanded combined uncertainty was expressed as follows.
$$U=k.u=k.\sqrt{{ {u}_{A}\left(x\right)}^{2}+{ {u}_{b}\left(x\right)}^{2}} \left(5\right)$$
Where \(k\) is the coverage factor, \(k=2\) was applied to achieve 95% level of confidence; \(u\) is the combined uncertainty
he uncertainty of an indirect independent measurement depends on the individual uncertainties associated with each quantity involved in the calculation. When determining the final uncertainty \(\left({u}_{x}\right)\) of a quantity \(x\), which is a function of various quantities \(\left(a, b,c,\dots ,\right)\), the calculation follows the following procedure.
$$x=f\left(a,b,c\dots \right) \left(6\right)$$
$${u}_{x}=\sqrt{{\left(\frac{\partial f}{\partial a}{u}_{a}\right)}^{2}+{\left(\frac{\partial f}{\partial b}{u}_{b}\right)}^{2}+{\left(\frac{\partial f}{\partial c}{u}_{c}\right)}^{2}+\dots } \left(7\right)$$
Materials
In our experimental setup, we utilized a combination of hardware components controlled by an Arduino microcontroller ATMEGA 2560 for precise positioning of a Chinese-made W410D2 analog hot-wire anemometer. The device consisted of a 3-meter stroke Belt Linear Motion Slide and a 600 mm stroke worm screw linear motion slide, which provided robust and accurate movement along the desired axes. The Arduino microcontroller served as the control unit, executing custom code to command the stepper motors responsible for the linear motion slides, ensuring precise positioning of the anemometer probe. The experiment was conducted with the support of a personal computer equipped with an i7 processor and 16GB of RAM, running under the Microsoft Windows operating system. The computer played a crucial role in data acquisition, analysis, and providing a graphical user interface for controlling the positioning system. Figures 4 and 5 visually depict the configuration of the experimental device, highlighting the interconnection between the various components and their respective roles in the setup.
-The hot-wire anemometer probe with his inbuild analogic to digital electronic board.
The W410D2 analog hot-wire anemometer, a China-made model, is a versatile airflow measurement device offering a range of desirable characteristics (Li et al., 2018). Powered by a DC supply of 10 to 30VDC, it consumes a maximum of 0.6W. Capable of measuring airflow in various mediums such as air, nitrogen, and smoke exhaust, the W410D2 ensures accuracy with a rating of 0.2 + 2% FS (Full Scale) in m/s. It operates reliably in humid conditions ranging from 0 to 95% RH (Relative humidity) and can withstand temperatures between − 10 to + 50 degrees Celsius. The anemometer provides both a current signal output (4 to 20 mA) and a voltage signal output (0 to 5V) for easy integration with analog systems. With a high resolution of 0.1 m/s, it covers a wide range of airflow velocities from 0 to 30 m/s. The W410D2 boasts a quick response time of 2 seconds and exceptional long-term stability, maintaining a deviation of less than 0.1 m/s per year. Overall, the JT400 analog hot-wire anemometer combines reliable performance, versatility, and accurate airflow measurements, making it an excellent choice for this research.
- Probe positioning actuator
The 2D positioning device is a versatile and precise system designed to enable accurate movement along the X and Y axes. It incorporates a 3-meter stroke Belt Linear Motion Slide Stage Guide Actuator, specifically equipped with a powerful Nema 34 Motor (Figure***), to control the movement along the X axis. The Nema 34 Motor provides substantial power and torque, ensuring efficient and reliable positioning(Silva et al., 2017). Its belt-driven mechanism guarantees precise control and repeatability, allowing for precise and smooth movement. For the Y axis, the device features a 600 mm stroke worm screw linear motion slide actuator powered by a compact Nema 16 motor. This actuator enables fine adjustments and micro-movements along the Y axis, enhancing overall precision and resolution. The Nema 16 motor ensures smooth and controlled motion, contributing to the device's accuracy. With these combined components, the 2D positioning device offers exceptional control and performance for a wide range of applications requiring precise and reliable positioning along both axes.
- Data acquisition system
For data acquisition from the hot-wire probe, we utilize an Arduino Mega 2560 microcontroller board, which is based on the ATmega2560 microcontroller. The Arduino Mega 2560 offers an array of features including 54 digital input/output pins, with 15 of them capable of functioning as PWM outputs. It also provides 16 analog inputs, 4 UARTs for hardware serial communication, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. With these components, the Arduino Mega 2560 is a comprehensive platform that supports the microcontroller's functionality. It can be easily connected to a computer using a USB cable or powered by an AC-to-DC adapter or battery. Furthermore, the Mega 2560 is compatible with shields designed for the Uno, Duemilanove, or Diecimila boards, offering additional flexibility and expandability for various applications (Munitxa, 2016).
Methods
- Computer and data analysis software
To acquire velocities data, we developed a customized code utilizing the Arduino programming language to interface with the microcontroller and control the stepper motors accurately. The code incorporated an algorithm that allowed us to position the anemometer probe at 5032 different locations based on specified abscissa and ordinate coordinates. To capture the measured velocity data, we utilized PLX-DAQ, an Excel add-in that facilitated real-time data acquisition (Fig. 5). PLX-DAQ allowed us to record and save the measured velocity values into an Excel table, along with the corresponding coordinates of each measurement point (Shreesha & Gudi, n.d.). This enabled us to automate the precise positioning of the anemometer probe at multiple locations and efficiently collect and organize velocity data for further analysis and interpretation as shown in Fig. 4. The acquired data was plotted using OriginPro and can be further analyzed and compared with the numerical results obtained using Ansys Fluent, providing valuable insights into the airflow characteristics.