1、OR-05-8-6 Feasibility Study of Using Various Instruments for Measurement of Air Motion in a Test Room Paul A. Lebbin Byron W. Jones, PhD Fellow ASHRAE M.H. Hosni, PhD Fellow ASHRAE B.T. Beck, PhD ABSTRACT The data presented in this article were collected using four different commercially available m
2、easurement instruments, which included a draft instrument, a three-dimensional hot- wire instrument, a three-dimensional sonic instrument, and stereoscopic PIV (SPIV) equipment. The test room was constructed mostly out of transparent acrylic glass to facilitate the use of the SPIV system placed outs
3、ide the test room. This approach prevented the SPIV system from interfering with the airflow structure in the test room. A stereoscopic particle image velocimetry (SPIV) system was used to measure airflow characteristics in an irregularly shaped test room. These measurements were compared with air v
4、elociq measurements obtained by a sonic anemometer instrument, hot-wire instrument, and dru3 instrument. The dimensions of the main portion of the test room were 2.1 x 2.1 x 1.7 m (7 x 7 x 5.63). The ceiling of the center portion of the test room was elevated and had dimensions of 2.1 x 1.0 x 0.4 m
5、(7.0 x 3.1 x 1.43). All of the measurements were taken at five measurement locations along the center plane of the test room. For each measurement location, numer- ous pairs of SPIK sonic, hot-wire, and draft data were collected and averaged to determine the average velocity. The normalized turbulen
6、ce intensity was calculated from the SPIV data. The equipment description, measurement procedures, and velocity data are presented in this paper. A comparison was made for the average velocities from each of the four types of measurement equipment. This comparison established the benefit of using a
7、noncontact measurement system such as the SPIV system. INTRODUCTION This paper presents the results from four different air velocity measurement instruments used in an irregularly shaped test room. The test room was constructed to obtain experimental velocity data for the project sponsor for their v
8、alidation of a CFD simulation model. This paper focuses on the air motion measurements, not the CFD validation. The objective of this paper is to identie which instruments can be used to measure air motion characteristics in such an applica- tion. This paper begins by presenting the description of t
9、he test facility used in this study. Each of the four instruments is described, and the measurement sets collected for each set of instruments are discussed. Next, the results of the measure- ment sets collected by the four measurement instruments are compared. Finally, the paper concludes with the
10、discussions of the results and conclusions drawn from the experimental results. TEST FACILITY DESCRIPTION The test facility is located at the Institute for Environmen- tal Research (IER) at Kansas State University. Two environ- mental chambers were used-one was the irregularly shaped test room where
11、 the measurements were taken and the other was a large chamber used to house the test room. The large chamber provided conditioned air to the test room such that isothermal conditions were achieved. A data acquisition and control system was used to control the environment inside the test room. When
12、the airflow inside the test room was fully developed, measurements were taken at five measurement locations with four different types of airflow measurement instruments. Paul A. Lebbin is a senior research engineer at the Institute for Environmental Research, and M.H. Hosni is department head and pr
13、ofessor, Byron W. Jones is a professor and associate dean for Research and Graduate Programs, and B.T. Beck is a professor in the Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, Kans. 02005 ASHRAE. 769 Air Flow ( 1706.9 Figure I Test room dimensions (in mm). Lar
14、ge Environmental Chamber The large chamber measured 7.3 m (24 ft) long, 1.8 m (6 ft) wide, and 2.7 m (9 ft) tall, and it is well insulated on all six sides. The chamber climate control system consists of a 10 ton chiller unit connected to an air-handling unit (MU) equipped with a blower and an eight
15、 kilowatt heater. The AHU system was configured to recirculate the air in the chamber. The environmental conditions within this chamber were controlled using an automated control system, and the steady- state conditions were achieved within an hour of starting the chambers control system. Test Room
16、The dimensions of the test room correspond to those used in the sponsors CFD model. The test room is an irregularly shaped test room that was 2.1 m (7 ft) tall, 2.1 m (7 ft) long, and 2.1 m (7 ft) deep. The schematic diagram of the test room is shown in Figure 1. The air to the test room was supplie
17、d from the upper left comer and exhausted out of the lower right comer. The test room was built out of 19.1 mm (0.8 in.) thick acrylic glass except for the floor and back wall, which were built out of plywood. The airflow was drawn through the test room with the use of a blower installed at the outl
18、et. This airflow was measured with the use of a calibrated vane anemometer installed in a long 152.4 mm (6 in.) diameter duct connected to the inlet. Before the air entered the test room, it passed through a baffle plate and a two-dimensional nozzle that spanned the entire length of the inlet. The b
19、affles and nozzle configuration provided a repeatable and uniform airflow into the test room. Data Acquisition System The type-K thermocouple temperature sensor used to monitor inlet air temperature and the 76.2 mm (3 in.) digital vane anemometer used to measure the inlet flow rate were 1066.8 I Out
20、let - Figure2 The measurement areas used in the three- dimensional SPIV measurements (dimensions in mm). 240 z . “- 4WO 4500 50W 5500 8000 6500 7000 7500 8000 Vane Anemometer (pulsmhnin) Data -Calibration Figure 3 Results of inlet vane anemometer calibration. installed in the center of a 152.4 mm (6
21、 in.) round supply duct and were connected to a commercial automated data acquisi- tion and control system that consists of hardware and software components. The temperature sensor and vane anemometer were used to monitor the inlet air temperature and volumetric flow rate, respectively. Also, the da
22、ta acquisition and control system was used to control a variable frequency drive (VFD) system that powered the fan used for airflow into the large environmental chamber. Before the measurements were taken, the temperature sensor was calibrated in a constant-temperature water bath. The vane anemomete
23、r and supply air duct assembly were cali- brated as a unit using a calibration airflow box with a bank of ASME standard nozzles (ASME 1989). The results of the inlet vane anemometer calibration are shown in Figure 3. A soft- 770 ASH RAE Transactions: Symposia ware program was written to collect data
24、 from the temperature sensor and automatically adjust the fan speed to maintain the desired average airflow rate of 4.2 m3/min (147 CFM). This airflow rate corresponds to an average air velocity of 22.8 rni s (4492 ft/min.) within the 152.4 mm (6 in.) supply air duct and an average air velocity of 0
25、.61 mis (120.0 Wmin) at the test room inlet nozzle. The temperature in the chamber was controlled to obtain isothermal conditions at a temperature of about 25C. Measuring Range Accuracy 0.05 to 1.00 m/s Measurement Instruments Draft Instrument. A single draft instrument connected to a draft transmit
26、ter was used to measure the average velocity magnitude taken over a period of 15 minutes. The air velocity and air temperature measurement range and accuracy for the draft instrument as reported by the manufacturer are listed in Tables 1 and 2, respectively. Three-Dimensional Hot-wire Velocity Instr
27、ument. The hot-wire instrument was used with a commercial anemometer-digitizer system to measure a 15-minute average air velocity. The three-dimensional hot-wire instrument is an end-flow hot-wire instrument consisting of three wires main- tained at a constant temperature of 130C. The amount of powe
28、r required to maintain this temperature for each wire was used to determine the air velocity. The resulting air velocity was only accurate if the airflow direction was within a *30“ Table 1. Velocity Measurement Range and Accuracy for the Draft Instrument (SWEMA 2004) 0.05 to 3.0 m/s (at 23C): (10 t
29、o 34C): M.O3 m/s M.O4 mis Measuring Range Accuracy: 20C 1 1.00 to 3.00ds I *3%ofreadin I *4%ofreading I 10 to 40C *0.3“C I I ., ., Measurement Resolution (mis rms) Offset Error (ds) Gain Error: (YO of reading) Table 2. Temperature Measurement Range and Accuracy for the Draft Instrument (SWEMA 2004)
30、u V W C 0.001 0.001 0.0005 0.001 *O. 04 *O. 04 *0.02 - Wind vector within *5“ 2 2 2 Wind vector within *lo“ 3 3 3 Wind vector within *20“ 6 6 6 I 10C to 40C I *0.5“C I cone angle normal to the instruments axis. Each wire, which consists of a film of metal plated onto a ceramic rod, has a low thermal
31、 mass, which allowed for fast measurement frequen- cies (-1000 Hz) that can be used to measure the turbulence of the airstream. Three-Dimensional Sonic Anemometer. The three- dimensional sonic anemometer determines the air velocity with the use of three sensors mounted on three nonorthogonal axes. U
32、nlike the hot-wire instrument, the sonic anemometer can measure air velocity vectors within a larger cone angle of h170“. The manufacturer reported accuracy of the sonic instrument is listed in Table 3. The Stereoscopic Particle Image Velocimetry (SPIV). A three-dimensional SPIV system was used to m
33、easure a 304.8 x 304.8 mm (12 x 12 in.) grid of three-dimensional air velocities inside the test room. It is equipped with two high- speed digital cameras mounted perpendicular to a thin light sheet emitted by a pair of Nd:YAG 12 mJ lasers. The cameras and lasers were controlled with a synchronizer
34、and computer system. Particles consisting of white 20 micron diameter hollow plastic spheres were used to seed the airflow. The hollow spheres were chosen for their slow settling rate, which was much slower than the air velocities measured inside the test room and their ability to accurately follow
35、the flow in this application (Richardson 1999). The particles were injected well before the inlet to the test room to allow for uniform mixing of the seeds in the inlet air. Measurement Locations All of the measurements inside the test room were taken at five different measurement locations. They ar
36、e simply named measurement locations #1, #2, #3, #4, and #5, as shown in Table 4. The test room Cartesian coordinates and the measurement locations are shown in Figure 1. Since the three- dimensional SPIV measurements result in numerous air veloc- ity vectors over an area, the area of measurement wa
37、s centered and focused on the measurement location point. The areas and locations of measurement by the SPIV system are shown in Figure 2. EXPERIMENTAL RESULTS Prior to each of the experiments, the test room airflow control system was allowed to run for an extended period of Table 3. Measurement Res
38、olution and Errors for the Sonic Anemometer (Campbell 1998) ASHRAE Transactions: Symposia 771 Table 4. Location of Measurement Points inside the Test Room Measurement Location Location in Room Cartesian Coordinates - x (mm) y (mm) (mm) 1 #1 #2 I #5 I 1447.8 I 609.6 I 0.0 I 685.8 1219.2 0.0 685.8 609
39、.6 0.0 time to ensure that the airflow structure inside the test room was fully developed (i.e., well after any thermal or momentum transients from initial start-up). The velocity measurements were only sampled when such fully developed conditions were achieved. #3 #4 Draft Instrument The experiment
40、s started with the use of only a draft instrument to measure the air velocities at each of the five measurement locations in the test room. Using the draft instrument by itself eliminated the issue of instrument-to- instrument interference. Also, when the three-dimensional hot-wire instrument or the
41、 sonic instrument was used, the draft instrument was also used to measure the air velocity, which allowed for the direct comparison of air velocity measurements between two different instruments. The simul- taneous use oftwo instruments required the instruments to be separated by 152.4 mm (6 in.) on
42、 the test room z-axis, which is perpendicular to the airflow stream. For each measurement location, the draft instrument was always positioned at -76.2 mm (- 3in.) on the z-axis. All other instruments, if used in conjunction with the draft instrument, were positioned at 76.2 mm (+ 3 in.) on the z-ax
43、is. To ensure that the air velocity does not vary significantly across this distance, the draft instru- ment was used to measure the 15-minute averaged air velocity and the corresponding standard deviation at both positions at the five measurement locations. The results of these measure- ments are p
44、resented in Figure 4. 1066.8 914.4 0.0 1447.8 1219.2 0.0 Three-Dimensional Hot-wire Instrument When compared to the draft and three-dimensional sonic instmments, the thee-dimensional hot-wire instrument has the capability of measuring air velocities at a very high frequency (-1000 Hz), which could p
45、rovide more information about the turbulence intensity of the air. The draft and the three-dimen- sional hot-wire were used simultaneously to measure the air velocities at each of the five measurement locations. They were positioned 152.4 mm (6 in.) apart on the z-axis for each measurement locations
46、. Since the three-dimensional hot-wire instrument requires a measurement cone angle of 30“ about the length of the instrument, the instrument was positioned in the direction of the now, as observed in previous smoke visu- alization tests. The plot of the 15-minute averaged air velocity E O 150 - 2 -
47、$ O100 a D 2 O 050 Ow0 I 2 3 4 5 Measurement Location Figure 4 Comparison of averaged measured velocities from the drap instrument for each of theJive measurement locations and two instrument locations. and the corresponding standard deviation obtained by both instruments at all five measurements ar
48、e presented in Figure 5. Three-Dimensional Sonic Instrument Like the hot-wire air velocity measurements, the three- dimensional sonic instrument collected air velocity measure- ments alongside the draft instrument at each of the five measurement locations. The spacing between the two instru- ments w
49、as the same (152.4 mm). Given the large size of the electronics box for the sonic instrument, it was positioned with the box orientatedperpendicular to the airflow to minimize the disturbance of the airflow. The plot of the 15-minute averaged air velocity and the corresponding standard deviation obtained by both instruments are presented in Figure 6. Three-Dimensional SPIV During the SPIV measurements, no instruments were used inside the test room, as it required the use of 20 micron size particles to seed the airflow, which would foul the sensors of any instruments used inside.
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