外文翻譯--在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中利用等速采樣測(cè)量粉塵濃度

內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling Z. C. Tan, Y. Zhang, S. E. Ford Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, 1304 West Pennsylvania Avenue, Room 332, Urbana, Illinois 61801. Phone: (217) 244-6316, Fax: (217) 244-0323. Email: Abstract Within this study the decay speed of centrifugal device induced rotational airflow in round ducts and its conditioning for dust concentration measurement was investigated. Tests were conducted under room conditions at average Reynolds numbers within the range of 0.7-1.14x105 . Duct diameters were 152 mm and 203 mm. Airflow in the ducts was found nonuniform and unsteady within the axial location to diameter ratio (x/D) of 10.5. The nonuniformity of axial airflow was nearly independent of the average Reynolds number. The study proved that it is impractical to decay the rotational airflow simply by using straight extension duct. A flow conditioner with minimal particle loss is needed to make the air flow uniform and steady. As a case study, a simple flow conditioner was tested. It decayed the rotational airflow to an acceptable level within x/D=2. The measured dust 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 concentrations at 5 radial locations at x/D=2 were uniform: /1% for total mass concentration, and /10% for all the particles smaller than 10 m. Keywords. Rotational airflow, airflow conditioning, dust sampling Introduction Cyclones have been widely used in many agricultural engineering applications. They were primarily used for larger particle separation (Carpenter 1986) or dust sampling at low airflow rates (Crook 1995, Lacey and Venette 1995). Although cyclones have been well industrialized and commercialized, uncertainties remain and they encourage researchers to further study the particle separation mechanism. Recent advances in this area indicate that it is very likely to be further developed for separating respirable particles at low cost and higher airflow rates (Zhang et al. 2001, Wang et al. 2002). During the investigation process, dust separation efficiency of a cyclone needs to be measured. With the increasing concern of respirable particles in environments, air-cleaning devices are often tested based on particle size (ANSI/ASHRAE 1999). Isokinetic sampling systems are often used for dust concentration measurements in ventilation ducts. In order to minimize the anisokinetic effects (Hinds 1999), the sampling nozzles should be correctly aligned to match the air velocity profile. Consequently rotational airflow exiting a cyclone has to be conditioned to an acceptab le steadiness before air velocity profile can be determined and dust concentration can be measured. In addition, uniform airflow is also preferred to reduce other sampling errors. It is a challenge to pick a representative sampling point in the rotational airflow. A multipoint sampling system could be employed. One apparent disadvantage is that many sampling heads will inference with the airflow pattern and introduce a 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 significant error factor. Another disadvantage is that more sampling points require more sampling tubes, and consequently increase particle loss in sampling tubes. Therefore, a single point sampling system is preferred. The upstream airflow is not rotational. A single sample point is acceptable. However, before a single downstream sample point can be taken, we must condition the rotational airflow to an acceptable uniformity. ANSI/ASHRAE (1999) standard requires that qualification tests shall be performed for uniformities of air velocity and aerosol in the test duct. The ANSI/ASHRAE standard also recommends bending the test duct 180 to bring the downstream sample locations relatively close to the upstream location, which allows short sample lines to the particle counter. It reduces the overall length of the test duct, facilitating its placement within the test room. However, it should be noted that this introduces another error factor. The bending could create rotational airflow. This swirl poses challenges in accurate measurements of airflow rate (McManus et al. 1985, Laribi et al. 2001), and maybe consequently, the dust concentration. Two methods are often considered for airflow conditioning. One is the use of long straight extension ducts and another is the use of flow conditioners. The rotational airflow in a duct will decay to an acceptable level provided the straight duct is sufficiently long. The question is how long it should be. If the duct is too long, excessive space is needed to setup the measurement system, and more importantly, there might be too much particle loss on the inner surface of the duct. Studies on rotational flow have been reported since the 1950s. The majority of these studies dealt with rotational flows in burners and air mixing in combustion areas. Only few of them are about decay of rotational flows. One of the early studies on rotational flow in ducts is an analysis of rotational flow of a constant property fluid in a straight duct of circular cross-section by Talbot (1954). The subject was steady and laminar flow in ducts. Kreith and Sonju (1965) later presented the average decay of 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 tape-induced fully developed turbulent swirl in water flow through a duct. The duct was 25.4 mm in diameter and 2,540 mm long. The twisted tape inducers consisted of 0.85 mm thick galvanized steel strips. The experiments were done with Reynolds numbers from 104 to 105 . It indicated that the rate of decay depended on the axial Reynolds number: the decay rate increased as the Reynolds number decreased, but the decay was found to be independent of the initial swirl intensity. It was observed that turbulent swirl decayed to about 10-20% of its initial intensity at an axial location to diameter ratio (x/D) of 50. Recently Laribi et al. (2001) experimentally studied the decay of swirling turbulent gas (petroleum) flow in a long duct. The inner diameter of the duct was 100 mm. The swirling flow was generated by double 90-degree elbow. Tests were conducted at Reynolds number ranging from 3x104 to 1.1x105 . It was observed that the flow was fully developed at x/D=90. The decay of a swirling flow of nitrogen gas in long ducts was reported by McManus et al. (1985). Tests were conducted under ambient temperature and pressure of 40 kPa at Re=8x105 to 1.4x106 . The decay of 60 degrees of swirling across a 100 mm smooth-walled duct measured at x/D=0, 10, 33, and 70. It was found that at x/D=70, the decay was 59%. Based on 6 sets of experimental data, they gave a fit decay equation, Percent Decay =0 . 9 5 4 e x p 0 . 0 1 2 6 xD 1 where x is the axial location in the duct, D the inner diameter of the duct, and x/D the axial location to diameter ratio. From this equation, we can predict that the decay can be reduced to 10% at x/D=200. Although the exact x/D numbers are different for the rotational flow to become fully developed, the above representative studies have shown that the duct has to be very long to reduce swirl to acceptable levels. In a laboratory, it might not be a practical solution for eliminating possible measurement errors attributed to swirl simply by using long ducts. 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Objective Among the limited amount of literature on decay of rotational fluid flow, few of them are about decay of rotational airflow in long ducts, and most of them were conducted in ducts less than 100 mm in diameter. The objective of this research is to study the decay of a rotational airflow created by a rotation device (i.e. centrifugal fan or cyclone) in ducts larger than 100 mm in diameter. It will be proved that a long duct is impractical, and a flow conditioner has to be used to condition the rotational airflow. As a case study, a flow conditioner with a large open ratio and with smooth surfaces was made and its effect on flow conditioning was tested. It is also expected that researchers who measure dust emission rate downstream of exhausting fans can find useful information from the results herein. Experimental Methods Ducts used in this research were commercial galvanized steel ducts with inner diameters of D= 152 mm and 203 mm. Maximum length of the ducts was 2,100 mm. The maximum length to diameter ratio, L/D, was about 10.8 due to space limitations in the laboratory. Axial velocity profile was measured using an anemometer from TSI, Inc. The anemometers measurement range was 0 to 20.3 m/s, with an accuracy of 5.0% of reading or 0.025 m/s whichever is greater. In this paper, airflow direction is our major concern for isokinetic sampling purpose. We wanted to condition the rotational airflow into a one-dimensional airflow. Therefore, only the axial velocity profile was measured. If axial velocity is not steady or uniform, the total velocity is not steady or uniform. While rotating the anemometer during test, other velocity components were obvious if the axial flow was not steady or uniform. On the other hand, other two velocity components were not apparent when the axial flow was 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 steady and uniform. Samples were taken at different axial locations (x/D). At each location, velocities were measured at different radial locations. The rotational airflow was generated with an in-line centrifugal fan. The airflow rate was adjusted with a variable transformer. The transformers maximum output settings were 120 V and 140 V. It could be adjusted from 0% to 100% of each maximum output. In this project, seven voltage levels of fan power were used: 90% and 100% of 140V, and 60%, 70%, 80%, 90% and 100% of 120V. For each power level and each x/D in duct, axial air velocities at up to 13 evenly distributed points were measured, with increase of 12.7 mm or 25.4 mm (see Figure 5). To verify the conditioning effect of the simple airflow conditioner, dust spatial distribution downstream was measured using an isokinetic sampling system. Particle concentrations were measured using APS 3321 (TSI, Inc.). The sampling points were 2D downstream of the flow conditioner, and their relative radial locations are shown in Figure 1. The corresponding radial locations of #1, #2, #3, #4 and #5 are 1/3 R, 1/6 R, 1/6 R, 7/12 R, and 5/6 R, respectively. 10 samples were taken at each of the 5 radial locations. The tests were conducted under Reynolds number of Re=2.2x104 . Figure 1. Particle sampling locations Standard Arizona test dust was dispersed using a turntable dust generator. The size distribution of particles entering the air stream is shown in Figure 2. As seen in the graph, 95% by volume are less than 12 m with a mass median of 4.8 m. 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Figure 2. Particle size distribution Results and Discussion In this paper, a coordinate system as illustrated in Figure 3 is used. Axial direction is x, and radial direction is r. The length, radius and diameter of the duct are L, R, and D, respectively. At any axial location x, the velocity at different radial location r is Vr. The velocity on the centerline is Vc. The average velocity at x is V. Figure 3. Illustration of the parameters referred in this paper In this paper, dimensionless parameters including Reynolds numbers, nonuniformity parameter, and dimensionless velocity are used for data analysis. For airflow inside a uct, Reynolds number is defined as (ANSI/ASME 1979), Re=Vlv 2 where: V is the average fluid velocity (m/s)., l a characteristic dimension of the 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 system in which the flow occurs (m), and v the kinematic viscosity of the fluid (m2 /s). The characteristic dimension is the inner diameter of the duct, D. The kine matic viscosity is 1.5x10-5 m2 /s for room air at 20 oC and 1 atm. Average Reynolds numbers are calculated using the averaged axial velocities. The average Reynolds numbers in ducts in our tests were within the range of 0.7-1.14x105. 1. Effect of centrifugal device location The airflow pattern inside a duct created by pushing air into a duct is different from pulling air out. Curves in Figure 4 are dimensionless velocities, the velocity at r over the average velocity (Vr/V), against dimensionless radial location, radial location r over the radius of the duct (r/R). For the example cases in Figure 4, the average Reynolds number was 1.14x105 . The effects under other operation conditions were similar. When the fan was pulling air out of the duct, Vr/Vs at all the measured locations, even at x/D=0.46, were very close 1. It indicates that airflow was uniform. However, when the duct was downstream the device, Vr/Vs at most of the measured points are way off unity, even at x/D=8.8. It indicates that downstream centrifugal device does not create strong rotational flow in duct, but upstream centrifugal device does. Figure 4. Effect of device location (pulling air out of and pushing air in duct) (r is 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 the radial location, R is the Radius of the duct, Vr is the velocity at r, V is the average velocity, x is the axial location, and D is the diameter of the duct). Since the rotational effect was negligible when the duct was upstream of our fan, only those cases where the duct was downstream of the fan are presented below. An example velocity profile is first given to visualize the airflow inside the ducts with and without flow conditioner. Then the uniformity and steadiness of the airflow are compared. At the end, as a case study, the dust concentration distrib ution after the flow conditioner is presented. 2. Axial velocity profile Axial velocity patterns were similar for all 7 average Reynolds numbers (fan levels). Figure 5 is an example that illustrates the axial velocity profile in ducts with and without flow conditioner at different x/D. The corresponding average Reynolds number was 1.14x105 (140V x 100% fan power). The flow conditioner was made of galvanized steel sheet metal. It had 4 vanes with L/D=2. When a flow conditioner is used, we have to take into consideration the particle loss on the flow conditioner. Particle loss on the flow conditioner should be minimized as much as possible. Therefore, the open area of the conditioner should to be as large as possible, and the surfaces should be as smooth as possible. Flow conditioners that are made up of multiple small tubes (i.e. 1 mm diameter) were not considered. The sheet metal is about 1 mm thick with smooth surface. The open ratio of a conditioner in a 152 mm duct is about 98.3%. Considering the large open ratio and smooth surface of the vanes, and small downstream particles, it is expected that the pressure drop and particle loss were minimal. This should be verified. 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Figure 5. Decay of rotational airflow in a long duct without and with a flow conditioner 3. Nonuniformity As mentioned above, at each axial location (x/D), velocities at about 10 radial locations (r/Rs) were measured. Then we have an average velocity (V) and a standard deviation ( ) for each x/D. A nonuniformity parameter was defined to quantitatively compare the rotational effect at different x/Ds under different operational conditions. The nonuniformity parameter is defined as the standard deviation over the average value of the velocities. The higher the standard deviation over the average, the higher the level of nonuniformity is. Figure 6 shows some examples of the variation of /V with average Reynolds number. In most cases of rotational airflow, /V dropped slightly with average Reynolds number. For conditioned airflow, the variation is negligible. For any fixed point in the duct, the value of /V did not change significantly with fan power. This also explained that the velocity profile mentioned above was similar at different average Reynolds numbers (velocities). Therefore, only the average /V was used for each Reynolds number to quantitatively illustrate the nonuniformity at each x/D. Figure 7 is based on this idea. 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Figure 6. Nonuniformity of velocity under test conditions (V is the average velocity, is standard deviation of velocity. x/D is the axial location over diameter of the duct) Figure 7 compares the nonuniformity of airflow in duct. Each point in Figure 7 is the average of 7 values of /Vs as shown in Figure 6. Within the accuracy in the tests, /V of air velocities at any axial location in round ducts was higher than 0.1 (or 10%) (for x/D2/3) is always less than 0.1. The experimental results here show that airflow approached uniformity level of 0.05 (5%) after x/D=1.5. On the other hand, even with a flow conditioner, it is not recommended to take samples right after the conditioner. Taking samples at x/D1.5 after the flow conditioner is a safe choice, unless it is impractical like in the situations reported by Marsh et al. (2003). The fitting curve gives the relationship between /V and x/D as, 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 0 .3 30 .0 8 1 xVD 2 0.89R 4 Figure 7. Nonuniformity of velocity over x/D for flow with and without flow conditioner (V is the average velocity, is standard deviation of velocity. x/D is the axial location over diameter of the duct) 4. Steadiness Another parameter to evaluate the effect of the flow conditioner is flow steadiness. In this paper steadiness of the flow is characterized using centerline dimensionless velocity, Vc /V. Where, Vc is air velocity at the centerline, and is the average velocity at x/D. It shows the velocity change along the duct. For tested conditions without flow conditioner, the centerline axial velocity keeps increasing along the duct length (see Figure 5). Figure 8 gives an example when average Reynolds number is 1.14x105 . It shows that the centerline velocity approached the average velocity as x/D increased. For airflow without flow conditioner, the axial velocity kept increasing and approaching steady state, but it did not reach steady state within our test conditions (x/D10.5). For flow after conditioner, the centerline velocity number reached the average velocity quickly after x/D=1.5. It indicates that the flow conditioner made the 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 rotational air flow quickly approach steady state. Figure 8. Steadiness over x/D for flow with and without flow conditioner (Vc/V is the velocity at the centerline over average velocity at x, and x/D the axial location over diameter of the duct) Overall, the tests confirmed that it is impractical to decay the rotational airflow in ducts to an acceptable level simply by using long ducts. 5. Particle Concentration Steadiness and Uniformity Steadiness at each location as illustrated in Figure 1 was characterized by the standard deviation over the average concentration( / ) of the 10 samples. Steadiness of particle concentration at each of the 5 locations is shown in Figure 9. For each location, as seen in the graph, the standard deviation of the average particle concentration is less than 15% with majority less than 10%. The steadiness of the turntable might also have contributed to the variation. 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Figure 9. Steadiness downstream the flow conditioner (Re=2.3x105 ) ( is standard deviation and is the average particle concentration； dp is the particle diameter) At each radial location, there is an average particle concentration calculated from the 10 samples. Then the average particle concentration at the axial location (x/D=2) is calculated based on the 5 concentrations at the 5 radial locations. The average particle size distribution at x/D=2 is shown in Figure 10. Each error bar marks the corresponding standard deviation ( ). The corresponding standard deviation over average ( / ) is also shown in the same graph on the right y-axis. As seen in the graph, / is less than 10% for any particle that is smaller than 10 m. A higher / is associated with lower particle concentrations. Note that at lower particle concentration, the sampling efficiency of APS 3321 is low, and it introduces errors. This is out of the scope of this paper and will be addressed separately. On the basis of mass concentration, the average concentration of the 5 locations was =8.42 mg/m3 with a standard deviation of =0.075 mg/m3 , which indicates that / is less than 1%. 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Figure 10. Uniformity downstream the flow conditioner (5 locations, Re=2.3x105 ) 6. Comparison with previous studies Results in this paper also expanded the database of study of rotational flow in long ducts. A comparison of previous tests with ours is shown in Table 1. Table 1 Comparison of test conditions with previous studies Table 1 shows that rotational flow exists in many general engineering applications. Rotational flow could be created by, but not limited to, 1) bending vanes, such as vanes used in cyclones, 2) sudden changes in flow direction, including 90 bends (McManus et al. 1985) and double 90 elbows (Laribi et al., 2001), and 3) air flow downstream of a centrifugal device such as a centrifugal fan. The rotational airflow will affect the accuracy in airflow rate measurement using an orifice meter (Laribi et al., 2001) as well as dust concentration measurements using isokinetic sampling techniques, as addressed in this paper. 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Summary and Conclusions This research investigated decay of centrifugal device created rotational airflow in round ducts under room condition. An example velocity profile was first given to visualize the airflow inside the ducts with and without flow conditioner. Then the uniformity and steadiness of the airflow were compared. As a case study, the dust concentration distribution after the flow conditioner was presented. The following conclusions can be drawn from this study: 1. Centrifugal device has negligible effect in creating rotational flow on upstream airflow in round ducts. The same device can create very strong nonuniform and unsteady rotational airflow in downstream ducts. 2. Once a rotational airflow is created in a duct, it is impractical to lessen it to an acceptable level simply by using long ducts. 3. The nonuniformity parameter of the airflow at certain point in a duct is nearly independent of the average Reynolds number. When / 0.05 , the airflow is considered uniform. 4. A simple flow conditioner can significantly reduce the airflow swirl. The flow conditioner with length to diameter ration (L/D) of 2 lessens the rotational airflow to an acceptable level quickly within x/D=2. Dust concentrations at 5 radial locations at x/D=2 downstream the conditioner was observed uniform ( / 0.01). On the other hand, it is not recommended to take samples right after the flow conditioner. References ANSI/ASME MFC-1M-1979. Glossary of terms used in the measurement of fluid flow in pipes. ANSI/ASHRAE Standard 52.2-1999. Method of testing general 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 ventilation air-cleaning devices for removal efficiency by particle size. Carpenter, G. A. 1986. Dust in Animal indoor environments-Review of Some Aspects, Journal of Agricultural Engineering Research. 33: 227-241. Crook, B. 1995. Inertial samplers: biological perspectives, in Bioaerosols Handbook (edited by Cox and Wathes), chapter 9, Florida: CRC Press, Inc. Hinds, W. C. 1999. Aerosol Technology: Properties, Behavior and Measurement of Airborne Particles. New York: Wiley. Kreith, F. and O. K. Sonju. 1965. The decay of a turbulent swirl in a pipe. Journal of Fluid Mechanics. 22(2): 257-271. Lacey, L. and J. Venette. 1995. Outdoor air sampling techniques, in Bioaerosols Handbook (edited by Cox and Wathes), chapter 16, Florida: CRC Press, Inc. Laribi, B., Wauters, P., and M. Aichouni. 2001. Experimental study of the decay of swirling turbulent pipe flow and its effect on orifice meter performance. Proceedings of the FEDSM2001, 2001 ASME Fluid Engineering Conference. May 29-June 1, 2001. New Orleans, USA. FEDSM2001-18039: 93-96. Marsh, L. S., S. W. Gay, G. L. Van Wicken, and T. Crouse. 2003. Performance evaluation of the SanScent air scrubber for removal of dust, ammonia, and hydrogen sulfide from the exhaust air of a swine nursery. ASAE paper #034052. ASAE 2003 annual meeting. July 27-30, 2003. Las Vegas, NV. McManus, S. E., B. R. Bateman, J. A. Brenham, I. V. Pantoja, and D. Mann. 1985. The decay of swirling gas flow in long pipes. American Gas Association Operating Section Distribution/Transmission Conference, Boston, MA. May 1985. Talbot, L. 1954. Laminar swirling pipe flow. Journal of Applied Mechanics. Transactions of ASME. 21(76): 1-7. Wang, L., C.B. Parnell and B.W. Shaw. 2002. Performance Characteristics of 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 Cyclones in Cotton-Gin Dust Removal. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Volume IV. Manuscript # BC 02 001. Zhang, Y., X. Wang, G. L. Riskowski, S. E. Ford, and L. L. Christianson. 2001. Particle separation efficiency of a uniflow deduster with different types of dusts. ASHRAE Transactions. 107 (2): 93-98. Nomenclature d p Particle diameter ( m) D Duct diameters (m) l Characteristic dimension (m) L Length of the duct, length of the flow conditioner (m) r Radial location (m) R Radius of the duct (m) r/R Dimensionless radial location Re Reynolds numbers V Average fluid velocity (m/s) Vc Velocity along the center line (m/s) Vr Velocity at radial location at r (m/s) x Axial location of the duct (m) x/D Axial location to diameter ratio Standard deviation of velocity (m/s), particle concentration (number/cm3 ) Average value particle concentration (number/cm3 ) / Non-uniformity of velocity or particle concentration v Kinematic viscosity of the fluid (m2 /s). 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 在 具有 旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中 利用等速采樣測(cè)量粉塵濃度 Z.C. 譚， Y.張， S.E.福特 伊利諾斯 州 厄巴納 市賓夕法尼亞西大街第 1304 號(hào) 伊利諾斯大學(xué)烏爾班納原野分校 農(nóng)業(yè)及生物工程系 332 室 61801 電話： (217) 244-6316，傳真： (217) 244-0323， Email: 摘要 在這項(xiàng)研究中離心設(shè)備的 速度 衰變引起了 圓 形輸送 管 道中 氣流 的 旋轉(zhuǎn)，并 調(diào)節(jié) 被 研究 測(cè)量 的 粉塵濃度。 在平均雷諾數(shù) 為 0.7-1.14x105 范圍內(nèi)的房間 條件 下進(jìn)行測(cè)試。 管道 直徑 為 152 mm 和 203 mm。發(fā)現(xiàn)輸送管道在直徑比率 (x/D)為 10.5的軸向位置內(nèi)氣流的不均勻 性 和不平穩(wěn) 性 。 軸向氣流 的 不一致 幾乎不依賴于平均雷諾數(shù) 。 研究證明通過使用 延長(zhǎng)直管道，衰變的 旋轉(zhuǎn) 氣流是 不存在 的 。帶有最小微粒 損失 的液體調(diào)節(jié)器是需要使氣流均勻和穩(wěn)定。作為一個(gè) 研究 實(shí)例，測(cè)試 一個(gè)簡(jiǎn)單 的 流量 調(diào)節(jié)器，它在 x/D=2 之內(nèi)把旋轉(zhuǎn)氣流衰變成一個(gè)可以接受的標(biāo)準(zhǔn)。在x/D=2 的 5 個(gè)輻射狀位置的被測(cè)量粉塵濃度是一致的：大多數(shù)微粒的 /1%和所有較 10 m更小的微粒的 /10%。 關(guān)鍵詞：旋轉(zhuǎn)氣流，氣流調(diào)節(jié)，粉塵取樣 前言 旋風(fēng) 分離器 曾經(jīng)廣泛地用于許多農(nóng)業(yè)的工程應(yīng)用 。 他們主要以低的氣流率(彎曲 1995， 花邊 和 Venette 1995 )用于較大的微粒分 離 (木匠 1986 )或者 粉塵內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 取樣 。 雖然旋風(fēng) 分離器已充分 被工業(yè)化 和 商業(yè)化 ，但是它們的不確定性仍然激勵(lì)研究者進(jìn)一步研究微粒的分離機(jī)制。 最新進(jìn)展 在這方面表明 ，它是十分有可能以低的費(fèi)用和較高的氣流率 （張等人， 2001 年，王等人 2002 年） 在 分離 可吸入微粒中得到更進(jìn)一步的發(fā)展 。在調(diào)查過程中，需要測(cè)量一臺(tái)旋風(fēng)分離器的粉塵分離效率。 有了在環(huán)境中可吸入微粒增加的關(guān)注，空氣清潔設(shè)備經(jīng)常基于微粒大小進(jìn)行測(cè)試（ 美國(guó)國(guó)家標(biāo)準(zhǔn)學(xué)會(huì) /美國(guó)采暖、制冷與空調(diào)工程師協(xié)會(huì)標(biāo)準(zhǔn) 1999 年 ）。等速取樣系統(tǒng)粉塵濃 度測(cè)量方法常用于通風(fēng)導(dǎo)管中，為了最大限度地減少 非同流態(tài)影響（漢斯 1999 年）， 取樣噴管應(yīng)該正確地 對(duì)齊匹配空氣速度概況。因此，旋轉(zhuǎn)氣流旋風(fēng)分離器具有一個(gè)可以接受的穩(wěn)定性之前，要求空氣流速概況可以判定及粉塵濃度可測(cè)。 此外，一致的氣流也傾向于減少其它取樣誤差。在旋轉(zhuǎn)氣流中選擇一個(gè)典型的取樣點(diǎn)是個(gè)難題，使用一個(gè)多點(diǎn)取樣系統(tǒng)，其中一個(gè)明顯的缺點(diǎn)是，許多采樣頭必須與氣流樣式的結(jié)論，并采用一個(gè)有效的誤差因素。另一個(gè)不利條件是更多取樣點(diǎn)要求更多的管子，并因此增加取樣管子中的微粒損失。因此，優(yōu)先選擇單點(diǎn)取樣系統(tǒng)。在進(jìn)入端 的氣流不是旋轉(zhuǎn)的，一個(gè)單點(diǎn)取樣系統(tǒng)是可以接受的。然而，在一個(gè)單一出口端取樣點(diǎn)被采用之前，我們必須以旋轉(zhuǎn)氣流可接受的一致性為條件。 美國(guó)國(guó)家標(biāo)準(zhǔn)學(xué)會(huì) /美國(guó)采暖、制冷與空調(diào)工程師協(xié)會(huì) （ 1999 年） 標(biāo)準(zhǔn)要求，為了空氣流速的一致性和測(cè)試導(dǎo)管的 氣溶膠 必須做資格測(cè)試。 美國(guó)國(guó)家標(biāo)準(zhǔn)學(xué)會(huì) /美國(guó)采暖、制冷與空調(diào)工程師協(xié)會(huì)標(biāo)準(zhǔn) 也建議把 測(cè)試導(dǎo)管折彎 180 ，使下游取樣位置較為接近上游的位置，允許短的采樣線對(duì)微粒計(jì)數(shù)。它減少測(cè)試導(dǎo)管的整體長(zhǎng)度，有利于其在測(cè)試房間之內(nèi)的安置。然而，值 得注意的是 這采用另一個(gè)誤差因素，折彎能夠造成旋轉(zhuǎn)氣流。 在精確測(cè)量的氣流率（麥克馬納斯等人， 1985 年，拉里比等人， 2001 年） 中，也許因粉塵濃度使這個(gè)渦流狀態(tài)帶來各種挑戰(zhàn)。 經(jīng)常被考慮的兩種氣流調(diào)節(jié)方法。一種是使用長(zhǎng)的直延長(zhǎng)導(dǎo)管和另一種是使內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 用 流量 調(diào)節(jié)器。提供足夠長(zhǎng)的直導(dǎo)管，旋轉(zhuǎn)氣流在導(dǎo)管將衰減到可以接受的標(biāo)準(zhǔn)。問題是管道應(yīng)該多長(zhǎng)，如果導(dǎo)管過長(zhǎng)， 需要 過多 的 空間 安裝 測(cè)量系統(tǒng)，以及更重要的是，在導(dǎo)管的內(nèi)表面可能會(huì)有太多的微粒損失。 關(guān)于旋流的研究從 20 世紀(jì) 50 年代 就有 報(bào)告 了，這些研究的大多數(shù)是在燃燒器的旋流處 理和空氣混合燃燒領(lǐng)域。這些研究中只有極少數(shù)是關(guān)于旋流的衰變，其中一項(xiàng)關(guān)于旋流的早期 研究，是由 塔博 （ Talbot） (1954)在圓形橫截面直導(dǎo)管內(nèi)定值流體屬性的旋流的分析。 主題是在管 道 的平穩(wěn)和層流 ， 克萊特 (kreith)和sonju （ 1965 ） 后來提出磁帶引起的平均衰變?cè)谒┻^導(dǎo)管的混亂旋動(dòng)中得到充分發(fā)展。導(dǎo)管直徑是 25.4mm 和長(zhǎng) 2， 540mm，扭轉(zhuǎn)的磁帶電感器包括了 0.85mm厚度的 鍍鋅 鋼小條 ，實(shí)驗(yàn)完成的 雷諾數(shù) 從 104 到 105 ，它表明衰變 的比率 依賴于軸的 雷諾數(shù) ： 衰變率隨雷諾數(shù)有所減少，但衰變被發(fā) 現(xiàn) 不依賴 于初始渦流強(qiáng)度 ，據(jù)指出， 混亂旋 流衰變約 10-20%，其初始強(qiáng)度在軸向位置以直徑比（ x/D）為 50。最近拉里比等 人（ 2001）在一長(zhǎng)管道的實(shí)驗(yàn)研究混亂旋流燃?xì)猓ㄓ停┑牧髁浚?管道的內(nèi)徑是 100mm，由雙 90 度彎頭產(chǎn)生旋流， 測(cè)試進(jìn)行 的 雷諾數(shù)從 3x104 到 1.1x105 。據(jù) 觀察所得，這股巨流，在 x/D=90 得到充分開發(fā)。 據(jù)麥克馬納斯等人（ 1985）發(fā)表在長(zhǎng)管道中氮?dú)怏w的一種旋流衰變，在 Re=8x105 to 1.4x106下，根據(jù)環(huán)境溫度和壓力為 40kPa 進(jìn)行測(cè)試 ， 旋流橫截面 100mm 光滑管壁的 60 度的衰變?cè)?x/D=0, 10, 33,和 70 處測(cè)量，人們發(fā)現(xiàn) x/D=70 時(shí)，衰變是 59%，基于 6套實(shí)驗(yàn)的數(shù)據(jù)，他們給出適宜的衰變方程， Percent Decay =0 . 9 5 4 e x p 0 . 0 1 2 6 xD 1 其中 X導(dǎo)管軸向位置， D 是管道的內(nèi)徑，和 x/D 是軸向位置的直徑比率。從這個(gè)方程，我們可以預(yù)測(cè)在 x/D=200 處衰變可降低至 10% 。 雖然精確的 x/D 數(shù)據(jù)是對(duì)不同的旋流得到充分發(fā) 展，上述的典型研究顯示，該導(dǎo)管要很長(zhǎng)，以減少渦流到可以接受的標(biāo)準(zhǔn)，在實(shí)驗(yàn)室里，通過使用長(zhǎng)的導(dǎo)管簡(jiǎn)單消除可能的測(cè)量誤差，它可能不是一個(gè)實(shí)用的解決辦法。 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 宗旨 在有關(guān)液體旋流的衰變的數(shù)量有限的文獻(xiàn)之中，他們中很少幾個(gè)是關(guān)于在長(zhǎng)導(dǎo)管中旋轉(zhuǎn)氣流的衰變的，而他們中大多數(shù)是在直徑少于 100mm 的導(dǎo)管中實(shí)施的。本調(diào)查的目的是研究通過一個(gè)旋轉(zhuǎn)裝置（即離心風(fēng)機(jī)或旋風(fēng)分離器）在直徑大于 100mm 的管道中形成一個(gè)衰變旋轉(zhuǎn)氣流，它將證明在一長(zhǎng)導(dǎo)管中使用流量調(diào)節(jié)器來決定旋轉(zhuǎn)氣流是不切實(shí)際的。作為一個(gè)案例研究，流量調(diào)節(jié)器制成一個(gè)大開 放比率和光滑表面及其對(duì)流量調(diào)節(jié)的影響進(jìn)行了測(cè)試。人們還預(yù)計(jì)，研究人員測(cè)量排氣風(fēng)扇下游的粉塵排放率，從如下研究結(jié)果中可以找到有用的資料。 實(shí)驗(yàn)方法 在這項(xiàng)研究中采用的管道是內(nèi)徑為 D=152mm 和 203mm 商業(yè)鍍鋅鋼 導(dǎo)管。管道的最大長(zhǎng)度是 2100mm，最大長(zhǎng)徑比由于受實(shí)驗(yàn)室中空間的限制， L/D 約為 10.8。軸向流速剖面測(cè)量采用 TSI 公司的風(fēng)速計(jì)，該風(fēng)速計(jì) 的測(cè)量范圍為 0 至 20.3m/s，讀數(shù)精度為 5.0%或 0.025m/s 以較高者為準(zhǔn)。 在本文中，我們主要關(guān)注的目的是在氣流方向上等速取樣。我們希望把旋轉(zhuǎn)氣流狀態(tài)變成一維氣流，因此，只測(cè)量軸向剖面流速。如果軸向速度并不穩(wěn)定或不一致，其總速度也就不穩(wěn)定或不一致。當(dāng)在實(shí)驗(yàn)期間旋轉(zhuǎn)風(fēng)速計(jì)，如果軸向流量不穩(wěn)定或不一致，則其他分量是顯而易見的。另一方面，當(dāng)軸向流量穩(wěn)定并一致，則其他兩個(gè)分量并不明顯。樣本送往不同的軸向位置（ x/D），在每一個(gè)位置測(cè)量不同徑向位置的流速。 一臺(tái)同軸離心風(fēng)機(jī)產(chǎn)生旋轉(zhuǎn)氣流后，用一個(gè)可變的變壓器調(diào)整氣流率 ,該變壓器的最大輸出設(shè)置為 120V 和 140V，它的最大輸出功率可以從 0%至 100%進(jìn)行調(diào)整。在這個(gè)項(xiàng)目中， 7 個(gè)電壓等級(jí)的風(fēng)機(jī)功率分別是： 140V 的有 90%和 100%，120V 的有 60%、 70%、 80%、 90%和 100%。每個(gè)功率等級(jí)和在管道中每個(gè) x/D，在多達(dá) 13 個(gè)均勻分布點(diǎn)用 12.7mm或 25.4mm 的增量進(jìn)行軸向風(fēng) 速測(cè)量（參見圖 5）。 檢驗(yàn)一個(gè)簡(jiǎn)單的氣流調(diào)節(jié)器的調(diào)節(jié)效果，采用等速取樣系統(tǒng)測(cè)量分布在下游空間的粉塵。采用 APS 3321 測(cè)量微粒濃度（ TSI 公司），采樣點(diǎn)是流量調(diào)節(jié)器的內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 二維下游，以及它們的相對(duì)徑向位置如圖 1 所示。 #1、 #2、 #3、 #4和 #5 的對(duì)應(yīng)的 徑向位置 分別為 1/3 R， 1/6 R， 1/6 R， 7/12 R 和 5/6 R， 10 個(gè)樣本，分別采用了在 5個(gè)徑向位置的每一個(gè)。測(cè)試是 在 雷諾數(shù) Re=2.2x104 下進(jìn)行的。 圖 1.微粒取樣位置 亞利桑那 州 標(biāo)準(zhǔn) 使用轉(zhuǎn)盤粉塵發(fā)電器分散粉塵，進(jìn)入空氣系統(tǒng)的微粒的大小分配如圖 2所示。在曲線圖中看出， 95%的體積小于 12 m，大部分體積為 4.8 m。 圖 2.微粒分布圖 結(jié)果與討論 在本文中 ，使用坐標(biāo)系統(tǒng)如圖 3所示。軸向方向是 X，和徑向方向是 R，導(dǎo)管的長(zhǎng)度、半徑和直徑分別是 L、 R 和 D。任何位置 X 在不同徑向位置 R 的速度是 Vr。這個(gè)速度在中線是 Vc。平均速率在 X 處是 V。 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 圖 3.例證在本文中提到的參量 在本文中，無量綱參數(shù)包括 雷諾數(shù) 、非均勻性參數(shù)和用于數(shù)據(jù)分析的無因次速率。在 開普敦大學(xué) 里面，氣流的 雷諾數(shù) 被定 義為（ 美國(guó)國(guó)家標(biāo)準(zhǔn)學(xué)會(huì) /機(jī)場(chǎng)地面活動(dòng)目標(biāo)顯示設(shè)備 1979） ： Re=Vlv 2 其中： V 是平均的流體速度（ m/s）， L是流量重現(xiàn)（ m）系統(tǒng)的一個(gè)典型尺寸和 V是流體（ m2 /s）的運(yùn)動(dòng)學(xué)黏度， D是管道內(nèi)徑的特征尺寸。在 20 oC 和 1 atm的室內(nèi)空氣速度為 m2 /s 的運(yùn)動(dòng)學(xué)黏度 是 1.5x10-5 m2 /s。用平均軸向速度計(jì)算平均雷諾數(shù) ，在我們的實(shí)驗(yàn)導(dǎo)管內(nèi)平均 雷諾數(shù) 的范圍是 0.7-1.14x105。 1. 離心設(shè)備位置的效果 在造成氣流模式的管道里面，空氣輸入管道與排出空 氣的不同。在圖 4 中曲線的無因次速度，流速在 r 以上的平均速度（ Vr/V），對(duì)無量綱徑向位置，導(dǎo) 管（ r/R）半徑超過 r的徑向位置。例如，例圖 4中，平均 雷諾數(shù) 是 1.14x105 ，在其它操作條件下面的結(jié)果是相似的。當(dāng)風(fēng)扇從管道里排除空氣，在 x/D=0.46 時(shí)所有被測(cè)位置 Vr/Vs 是非常接近 1 的 ，它表明氣流是一致的。然而，當(dāng)管道下游設(shè)備，在 x/D=8.8 時(shí) Vr/Vs在大多數(shù)測(cè)量點(diǎn)是一致的，它表明下游的離心設(shè)備沒有造成強(qiáng)有力的旋轉(zhuǎn)流管，但上游的離心設(shè)備不會(huì)造成。 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 圖 4.設(shè)備位置的作用（空氣從導(dǎo)管里排除和推入） （ r 是徑 向位置， R 是管道的半徑，Vr 是在 r 處的速度， V 是平均速度， X 是軸向位置， D 是管道的直徑 ） 當(dāng)管道是在上游時(shí)，我們的風(fēng)扇旋轉(zhuǎn)效應(yīng)是可以忽略的。只有那些情況下，風(fēng)扇下游的管道下面呈現(xiàn)出來，一個(gè)例子速度剖面，首先給導(dǎo)管內(nèi)部和流量調(diào)節(jié)器外可視化氣流，然后比較氣流的均勻性和穩(wěn)定性。在去年底，作為一個(gè)案例研究，流量調(diào)節(jié)器呈現(xiàn)粉塵濃度分布。 2. 軸向流速剖面圖 軸的速度模式 對(duì)所有 7 個(gè)平均的 雷諾數(shù) （風(fēng)機(jī)標(biāo)準(zhǔn)）是相似的。圖 5是一個(gè)例子，說明了 在管道中軸向速度剖面和無流量調(diào)節(jié)器，在不同的 x/D 相應(yīng)的平均雷諾數(shù) 是 1.14x105 (140V x 100% 風(fēng)扇電源 )。流量調(diào)節(jié)器是鍍鋅合金鋼板制成，它有 4個(gè) L/D=2 的葉片。當(dāng)我們使用流量調(diào)節(jié)器時(shí)，我們必須考慮到流量調(diào)節(jié)器的微粒損失。應(yīng)該盡量減小流量調(diào)節(jié)器的微粒損失。所以，調(diào)節(jié)器的開放區(qū)域應(yīng)該可能的大，并且表面應(yīng)該盡可能的光滑。流量調(diào)節(jié)器是彌補(bǔ)了多重小管（即1mm 直徑）進(jìn)行考慮。表面光滑的 1mm 厚合金鋼板，在一 152mm 口徑的管道中調(diào)節(jié)器的開口比率為 98.3%?？紤]到大的開口比率及表面光滑的葉片，以及下游的小微粒，但預(yù)計(jì)到壓力降和微粒損失 甚微 ，這應(yīng)加以核實(shí)。 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 圖 5.有沒有 流量調(diào)節(jié)器在長(zhǎng)管道中旋轉(zhuǎn)氣流的衰變 3. 不均勻性 如上所述，在每個(gè)軸向位置（ x/D），測(cè)量大約 10 個(gè)徑向位置（ r/R）的速度。于是，對(duì)于每 x/D 我們有一個(gè)平均速度（ V）和標(biāo)準(zhǔn)差（ ）。不均勻性參數(shù)的定義是在不同的 x/Ds根據(jù)不同的運(yùn)行條件 以定量比較旋轉(zhuǎn)效應(yīng)。不均勻參數(shù)定義為標(biāo)準(zhǔn)偏差超過平均值的速度。較高的標(biāo)準(zhǔn)差以上的平均值來說，等級(jí)越高的不均勻度越高。 圖 6.的一些例子顯示 /V 的變動(dòng)與平均 雷諾數(shù) ，在大 多數(shù)情況下的旋轉(zhuǎn)氣流，其 /V 與 雷諾數(shù) 略為下降。對(duì)于經(jīng)過調(diào)整的氣流，其變化是微不足道的。對(duì)于任何固定點(diǎn)導(dǎo)管，其 /V 的值與風(fēng)機(jī)電源沒有明顯改變。這也說明以上提到的速度剖面在不同的平均 雷諾數(shù) （速度） 相似。因此，只有 /V 的平均值用于每個(gè) 雷諾數(shù) 在 x/D 的數(shù)量說明了非均勻性。圖 7 就是基于這種想法的。 圖 6.速度不均勻的條件下測(cè)試（ v 是平均速度，是速度的標(biāo)準(zhǔn)差； x/D 是超過導(dǎo)管直徑的軸向位置 ） 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 圖 7 比較導(dǎo)管內(nèi)氣流的不均勻性，每一個(gè)點(diǎn)在圖 7 中的 7個(gè) /Vs的平均值如圖 6 所示。在測(cè)試的準(zhǔn)確性之內(nèi)，在圓形管道的任何軸向位置空氣流速的 /V高于 0.1（或 10%）（因?yàn)?x/D2/3）總是小于 0.1，實(shí)驗(yàn)結(jié)果表明，在經(jīng)x/D=1.5 之后 氣流接近均勻標(biāo)準(zhǔn)的 0.05（ 5%）。在另一方面，即使以流量調(diào)節(jié)器不建議采取經(jīng)過調(diào)節(jié)后的樣本。流量調(diào)節(jié)器在 x/D1.5 時(shí)獲取樣本是一個(gè)安全的選擇，除非它是像瑪稀等人（ 2003）報(bào)告中的形勢(shì) 一樣不切實(shí)際。擬合曲線 /V 和 x/D 給出的關(guān)系， 0 .3 30 .0 8 1 xVD 2 0.89R 4 圖 7.對(duì)于用與不用流量調(diào)節(jié)器，超過 x/D 時(shí)速度的不均勻性（ v 是平均速度，是標(biāo)準(zhǔn)偏差速度， x/D 是超過導(dǎo)管直徑的軸向位置） 4. 穩(wěn)定性 另一個(gè) 參數(shù)是評(píng)價(jià)流量調(diào)節(jié)器對(duì)流量 穩(wěn)定性的影響，在本文中流量穩(wěn)定性的特點(diǎn)是采用中線 Vc /V 的無因此速度，在中線處 Vc 是空氣的 速度，也是在 x/D處平均速度，它顯示出長(zhǎng)導(dǎo)管中速度的變化。在沒有流量調(diào)節(jié)器的實(shí)驗(yàn)條件下，內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S. Ford. !Decay of Rotational Airflow with Flow Conditioner in Larger Diameter Ducts for Dust Concentration Measurement using Isokinetic Sampling!. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript BC 03 007. Vol. V. December 2003. Z.C. 譚， Y. 張， S.E.福特 !為測(cè)量粉塵濃度，在具有旋轉(zhuǎn)氣流衰變和流量調(diào)節(jié)器的大直徑管道中使用等速采樣 !國(guó)際農(nóng)業(yè)工程：國(guó)際 農(nóng)業(yè)工程學(xué)會(huì)雜志科學(xué)的研究和發(fā)展。公元前 2003年 12 月手稿第 5 卷， 編號(hào) 03 007 。 沿長(zhǎng)導(dǎo)管中心線的軸向速度不斷增加（見圖 5）。 圖 8.給出當(dāng)平均 雷諾數(shù) 為 1.14x105 時(shí)的一個(gè)實(shí)例，它表明中線的速度接近當(dāng) x/D 增加時(shí)的平均速度。對(duì)于沒有流量調(diào)節(jié)器的氣流，軸向速度不斷增加，并接近穩(wěn)定狀態(tài)。但在我們的實(shí)驗(yàn)條件下（ x/D10.5），它并沒有達(dá)到穩(wěn)定狀態(tài)。對(duì)于經(jīng)過調(diào)節(jié)后的流量，在 x/D=1.5 后，中心線速度的數(shù)值很 快達(dá)到平均速度。它表明流量調(diào)節(jié)器使得旋轉(zhuǎn)空氣流快速的接近穩(wěn)定狀態(tài)。 圖 8.對(duì)于流量有無流量調(diào)節(jié)器穩(wěn)定性超過 x/D（ Vc/V 是在中線以上的平均速度超過導(dǎo)管直徑的軸向位置 x 和 x/D 處的速度） 總之，實(shí)驗(yàn)證明，它是通過使用簡(jiǎn)單的長(zhǎng)導(dǎo)管使導(dǎo)管中衰變的旋轉(zhuǎn)氣流達(dá)到可接受的標(biāo)準(zhǔn)是不現(xiàn)實(shí)的。 5. 微粒濃度穩(wěn)定性和一致性 通過標(biāo)準(zhǔn)偏差超過平均濃度 ( / )的 10 個(gè)樣本，在圖 1 顯示的每一個(gè)位置的穩(wěn)定性特點(diǎn)。在圖 9 中所示的 每 5 個(gè)位置的微粒濃度的穩(wěn)定性。對(duì)于每個(gè)位置，在曲線中看出，平均微粒 濃度小于 15%與大多數(shù)不到 10%的標(biāo)準(zhǔn)偏差。轉(zhuǎn)臺(tái)的穩(wěn)定性可能有助于這一變化。 內(nèi)蒙古科技大學(xué)畢業(yè)設(shè)計(jì)外文翻譯 _ Z. Tan, Y. Zhang, and S.