9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
Effects of Vibration and Flow Pattern on Coriolis Flow Meter Chun-Lin Chiang, Chun-Min Su, Yi-Lin Ho, Yi-Huan Kao Center for Measurement Standards, Industrial Technology Research Institute, Taiwan 30, Ta Hsueh Road, Hsinchu, Taiwan, R.O.C., 300 Corresponding Author:
[email protected] Abstract Coriolis flow meter is widely used to measure the mass flow rate in many fields of research and industry because of its highly accurate measurement performance and superbly repeatable characteristic. The working principle of Coriolis flowmeter relies on the Coriolis Effect generated by the fluid flowing through the vibrating tubes. Therefore, the measurement accuracy of a Coriolis flow meter might be influenced by the vibration surrounding a Coriolis flow meter, the flow pulsation, and the fluid distribution between the vibration tubes. The presented work studies the impacts of possible vibration, and asymmetric flow pattern induced by the water flowing through a partially closed ball valve on a Coriolis flow meter. When a partially closed ball valve and the Coriolis flow meter are installed in series, the vibration caused by the water flow hitting a partially closed ball valve would result in a clear measurement error and a negative effect on the short-term repeatability of the Coriolis flow meter is observed. The installation of two rubber sections surrounding the Coriolis flow meter is effective to isolate the vibration as a noise on the measurement result. A possible asymmetric flow pattern is progressed and results in a clear measurement inaccuracy when the water flows through a partially closed upstream ball valve with an inadequate separation between the ball valve and the Coriolis flow meter. The measurement result and the short-term repeatability of the Coriolis flow meter are further worse and deteriorated with the combined effect of vibration and asymmetric flow pattern when the further partially closed upstream ball valve is connected to the Coriolis flow meter via a short stainless steel pipe section. 1. Introduction The utilization of a highly accurate, repeatable, stable flow meter is necessary for several scenarios, such as: the real-time petroleum fuel metering, the trace of measurement standard among calibration laboratories, and the inter-comparisons among national laboratories [ 1 ]. Coriolis flow meter is commonly believed as a candidate fitting for that. When the fluid passing through a vibrating tube has been applied Coriolis force generated by a signal generator, the tube will twist to increase its angular momentum. As a consequence, a phase angle difference between the inlet and the outlet of the vibrating tube is created, and the amount of fluid through the vibrating tube is determined by the phase angle difference. Under a wellinstalled condition, the flow measurement accuracy of a Coriolis flow meter is claimed to be up to 0.1 % or even up to 0.05 % with a specific manufacturer-tuning. The short-term repeatability and the long-term reproducibility are capable of remaining within 0.05 % and 0.2 %, respectively, which represents the superior stable and reliable characteristics of a Coriolis flow meter. This is the reason why a Coriolis flow meter is commonly employed in academic researches and industrial applications and selected as a measurement standard in many calibration laboratories. However, the measurement result of a Coriolis flow meter was reported to be sensitive to the external vibration and the internal flow fluctuation [ 2]. The literatures published by Clark and Cheesewright [ 3] and Cheesewright et al. [ 4] both mentioned that the external mechanical vibration at certain frequency applied on the vibrating tube of a Coriolis flow meter might result
9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
in the measurement error. The measurement error is proportional to the intensity of external vibration and independent of the flow rate. A Coriolis flow meter is much subjected to the external vibration at the drive frequency, as compared to the non-drive frequency, and the measurement error due to the non-drive frequency is preventable by a robust phase difference algorithm. From the ISO 10790 document [ 5], a zero setting depending on the type of Coriolis flow meter is recommended to maintain the performance of a flow meter within the specification after a re-located installation. The experimental result done by Ridder et al. [ 6] showed that the frequency of external vibration might be detected by the sensor of Coriolis flow meter, which could influence the flow measurement result. The studies done by Vetter and Notzon [ 7] and Clark and Cheesewright [ 8] indicated that the flow pulsations might lead to the measurement error of a Coriolis flow meter. Therefore, in order to minimize the impacts of the external vibration and the internal flow fluctuation, the installation mechanism of a Coriolis flow meter should feature the characteristic of absorption of mechanical stress. This presented work is intended to investigate the installation effect of a Coriolis flow meter to understand the impacts of vibration and flow pattern on the flow measurement result of a Coriolis flow meter. A nondimensional parameter, meter factor, is designated to evaluate the measurement result quantitatively, and the associated phenomenological descriptions are provided and discussed as well. 2. Experimental Setup A 150 mm (6 inch) Coriolis flow meter with two vibrating tubes, which has a maximum capability of flow rate of 133,000 kg/min is employed in this work to study the possible installation effects, including the vibration created by the hit of water on a ball valve and the asymmetric flow pattern. The baseline experimental configuration is briefly shown as Figure 1. Water is pumped into the 150 mm (6 inch) stainless steel pipe line by a speed-adjustable centrifugal pump. The tested Coriolis flow meter is installed after a 6 meter (20 feet) long straight section to ensure that a fully developed flow has been reached. Water will flow through a ball valve which is installed at the 2,200 mm downstream of the tested Coriolis flow meter, and then it will be collected in a 6,000 liter tank and weighted by a balance to obtain the water flow rate by weighting method with knowing the duration of collection period. The operating temperature is uncontrolled and remains around 20 ℃ ~ 25 ℃. For understanding of the impact of vibration, an inferred vibration is naturally induced by allowing the water flow to hit a partially closed ball valve. The reflected flow wave will result in a vibration source. A modified configuration with two rubber sections with lengths of 30 cm (1 foot) are installed right before and after the tested Coriolis flow meter, respectively, to isolate the vibration, which has been studied in this work as well. For investigating the other possible installation effect, a ball valve is added at the upstream of flow meter to control the flow rate as the downstream ball valve remains fully opened. In this case, an asymmetric flow pattern might be resulted when the upstream manual ball valve is partially opened. A flow disturber suggested by OIML R49-2 document [ 9] has a half opening area is also employed in this work to generate an asymmetric flow pattern. The investigated flow rate is ranged from around 3,000 kg/min to 5,000 kg/min by varying the degree of upstream or downstream ball valve opening or the loading of centrifugal pump, respectively. Each test condition has been conducted 2 to 4 times to ensure the repeatability of measurement result.
9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
Fig.1: schematic of experimental configuration 3. Results and Discussion 3.1 Effect of a Partially Closed Downstream Ball Valve Figure 2 shows the results of meter factor for three different investigated flow rates in the baseline experimental configuration with a fully opened downstream valve. The values of meter factor are very approaching to 1 to show the highly accurate characteristic of this tested Coriolis flow meter. The meter factor is defined as Eq. (1). For each investigated flow rates, the data points almost overlap each other to indicate that the excellent feature of short-term repeatability. However, when the flow rate is reduced from around 5,000 kg/min to 4,000 kg/min by closing the downstream valve partially instead of by lowering the pump loading, the meter factor values jump to the range of 1.0560 to 1.0718. It means not only an apparent flow measurement error around 5 % to 7 % but also a deteriorated short-term repeatability which is evident by the large variation of meter factor in this configuration. A hypothesis is proposed to explain this situation. When the water flows toward downstream and hits the downstream partially closed ball valve, a reflected flow wave might create a vibration as a signal noise to deteriorate the performance of the tested Coriolis flow meter. However, a detailed research to understand the source for degrading the flow meter performance is not established completely in this work. In order to isolate the impact of vibration as a signal noise on the Coriolis flow meter, a modified configuration with two rubber sections with lengths of 30 cm (1 foot) installed right before and after the flow meter is employed. The effective isolation of vibration is obtained by showing a highly similar measurement result from the configuration with a fully opened, complete stainless steel pipe line and the configuration having a partially closed downstream ball valve and two short rubber sections surrounding the flow meter. meter factor = 𝑚𝑠 ⁄𝑚𝑚 ; 𝑚𝑠 : 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑚𝑚𝑚𝑚 𝑓𝑓𝑓𝑓 𝑟𝑟𝑟𝑟, 𝑚𝑚 : 𝑚𝑚𝑚𝑚 𝑓𝑓𝑓𝑓 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑏𝑏 𝑓𝑓𝑓𝑓 𝑚𝑚𝑚𝑚𝑚
Eq. (1)
9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
Fig. 2: the influence of opening of downstream valve 3.2 Effect of a Partially Closed Upstream Ball Valve For studying the effect of a partially closed upstream ball valve, the downstream ball valve keeps as fully opened status among all the test conditions discussed in this section. When the valve located at 3,250 mm upstream of the flow meter is fully opened, the resulted meter factor is around 1.0002 to 1.0007 within the investigated flow rate range, as shown in Figure 3. This is very consistent with the reported result as mentioned above. The fully opened upstream ball valve is shown as in Figure 4 (a). However, the meter factors increase by around 0.0020, when the upstream ball valve becomes partially closed, as displayed in Figure 4 (b), and remains the same degree of closing among all three test conditions along with adjusting the pump loading to reach the corresponding flow rates. Since the distance between the upstream valve and the flow meter is 21.67 D, where D is the inner diameter of pipe, and should be long enough to allow that the water flow reaches a nearly fully-developed condition before approaching flow meter. Thus, the vibration induced due to the water flow hitting the upstream ball valve might be the reason to cause the measurement result error. For the other investigated case with flow rate of around 4,000 kg/min, the upstream ball valve is further partially closed, as shown in Figure 4 (c), along with increasing the pump loading, as the red solid circles shown in Figure 3. The meter factor of flow meter which increases to 1.0327 to 1.0363 is around 3 % higher than that of the case without any obstruction. Furthermore, a noticeably splashing noise has been heard by the people who stand next to the upstream ball valve and might be attributed to that there are several eddies, vorticities, and cavitation created because of the largely sudden area change in the flow channel by the further closed upstream valve. Those locally far-upstream eddies, vorticities, and cavitation might generate a pressure fluctuation, as an internal vibration source, transported downstream along the water flowing to result in the measurement error of a Coriolis flow meter, although those eddies, vorticities, and cavitation might be disappeared before approaching the Coriolis meter since the indicated density from the Coriolis meter remains stable and the separation is around 21.67 D. The degree of vibration increases with increasing the degree of upstream valve closing, which results in the measurement error of this Coriolis flow meter increased might be drawn.
9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
Additionally, a more predominant impact of vibration because of the partially closed downstream ball valve (discussed in Section 3.1) as compared to that due to the partially closed upstream ball valve is observed. It might be firstly attributed to that the separation, more or less acting as a damper, between the tested flow meter and the downstream ball valve is shorter than that between the flow meter and the upstream ball valve. The difference of interior geometry between the two ball valves could be the other more critical reason for that. The downstream ball valve utilizes the concave surface of a crescent part to withstand the coming flow to control the flow rate, on the contrary, the upstream ball valve has a full port design.
Fig. 3: the influence of opening of upstream valve
(a)
(b) Fig. 4: different degree of closing of upstream ball valve
(c)
When the ball valve is moved to the position 600 mm upstream of the flow meter, and the rubber sections (soft pipe) are inserted surrounding the flow meter in order to isolate the vibration induced by the water hitting the upstream ball valve. The values of meter factor for this configuration with soft pipe gets dropped from around 1.0028 to 1.0016 in the flow rate range from about 3,000 kg/min to 4,000 kg/min, as compared to those from the cases without soft pipe, as shown in Figure 5. Whereas, the value of meter factor of 1.0016 is still slightly higher than that from the fully opened case. It might be because of the asymmetric flow pattern resulted from the water flowing through a partially closed valve. In addition, the distance between the valve and the flow meter is not long enough, about only 4D, to allow the flow pattern reshape to
9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
a symmetric one. The asymmetric flow pattern might cause the distribution of flow amount passing through two separate vibrating tubes of the Coriolis flow meter is not even to cause the slight measurement inaccuracy. The other series of test has been conducted by installed a flow disturber, as shown in Figure 6, suggested by OIML R49-2 document at the same position to generate a more specifically asymmetric flow pattern. Regardless the opening orientation, the value of meter factor is increased around 0.1 %, as shown in Figure 7. Therefore, a resulted measurement error because of an asymmetric flow pattern ranged around 0.1 % to 0.2 % by the means of a flow disturber or a partially closed ball valve could be concluded. The value of measurement error is only slightly beyond or barely within the specification claimed by the manufacturer, thus to use a Coriolis flow meter with an imperfect coming flow condition might be acceptable in many industrial fields but should not be recommend as a measurement standard for the calibration laboratories. For realizing the combined effect of vibration and flow pattern, the test condition with flow rate of around 4,000 kg/min via a setting with a further partially closed valve at 600 mm upstream of flow meter and removed soft pipes has been conducted. The indicated flow rate by the Coriolis meter is about 11 % less, i.e. an 11 % higher meter factor, as compared to those of the well-installed configurations. And the variation of indicated flow rate is around 3 %, which also represent an unfavorable short-term repeatability. Moreover, the resulted measurement error of 11 % should be majorly contributed by the vibration duo to a further partially closed upstream valve since the measurement error of an imperfect flow pattern is only around 0.1 to 0.2 %. The impact of vibration could be even more significant when the vibration source, as a further partially closed valve in this study, moves closer to the tested flow meter. The performance benchmark of the tested Coriolis flow meter accompanied with an upstream ball valve is tabulated in Table 1.
Fig. 5: the influence of flow pattern created by a partially closed upstream ball valve
9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
Fig. 6: flow disturber (OIML R49-2)
Fig. 7: the influence of flow pattern created by a flow disturber Table 1: benchmark of Coriolis flow meter accompanied with an upstream ball valve position of upstream ball valve
3250 mm
600 mm
degree of ball valve opening
fully opened
partially closed
further partially closed
fully opened
partially closed
partially closed
further partially closed
soft pipes
without
without
without
without
without
with
without
avg. meter factor
1.0004
1.0026
1.0337
1.0005
1.0028
1.0016
1.1129
4. Conclusions A preliminary benchmark regarding the effects of vibration and asymmetric flow pattern has been established by studying the degree of upstream or downstream valve closing, the flow
9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
disturber, and the installation of soft pipes as the vibration dampers. The main conclusions of this study reached have been highlighted as follows: 1. For a complete stainless steel pipe line configuration, when the water flow hits a partially closed ball valve which is located at either upstream or downstream, the vibration induced by a reflected flow wave might result in a clear flow measurement error of a Coriolis flow meter. A further partially closed upstream ball valve might generate eddies, vorticities, and cavitation after the ball valve and lead to an obvious measurement error. The measurement error increases with increasing the degree of ball valve closing, i.e. the degree of vibration. 2. The installation of two rubber sections right before and after the Coriolis flow meter is an effective method to isolate the vibration as noise for the measurement result. 3. An asymmetric flow pattern approaching a Coriolis flow meter might be the other factor of measurement inaccuracy when a ball valve is located at the upstream of the flow meter with an inadequate separation between them. However, the measurement error due to asymmetric flow pattern is around 0.1 % and might be still acceptable in general uses. 4. With a combined effect of vibration and asymmetric flow pattern, the measurement result indicates a very significant measurement error around 10 % and an adverse short-term repeatability of the Coriolis flow meter. In order to further understand the correlation between the vibration induced by the fluid flowing through a partially closed valve and the measurement result of a Coriolis flow meter, a more detailed research as future work is still progressed. Nomenclature avg. average D inner diameter of pipe D.V. downstream (ball) valve mm mass flow rate measured by a flow meter ms standard mass flow rate obtained by weighting method U.V. upstream (ball) valve w/ with w/o without [1] Meng, T., Wang, C., Gao, F, Xing, C., and Zhang, L., Design and experimental analysis of
transfer standard in water flow comparison, Proceedings of FLOMEKO, Paris, France, 2013. [2] Bobovnik, G., Kutin, J., Mole, N., Štok, B., and Bajsić, I., Influence of the design parameters on the installation effects in Corolis flowmeters, Proceedings of FLOMEKO, Paris, France, 2013. [3] Clark, C. and Cheesewright, R., The influence upon Coriolis mass flow meters of external vibrations at selected frequencies, Flow Measurement and Instrumentation, Vol. 14, pp. 33-42, 2003. [4] Cheesewright, R., Belhadj, A., and Clark, C., Effect of mechanical vibrations on Coriolis mass flow meters, Journal of Dynamic Systems, Measurement, and Control, Vol. 125, pp. 103-113, 2003. [5] ISO 10790:1999 Measurement of fluid flow in closed conduits – Guidance to the selection, installation, and use of Coriolis meters (mass flow, density, and volume flow measurements), 1999. [ 6 ] Ridder, L. V. D., Hakvoort, W. B. J., Dijk, J. V., and Lotters, J. C., and Boer, A. D., Quantitative estimation of the influence of external vibrations on the measurement error of a
9th ISFFM
Arlington, Virginia, April 14 to 17, 2015
Coriolis mass flow meter, Proceedings of 11th International Conference on Vibration Problems, Lisbon, Portugal, 2013. [7] Vetter, G. and Notzon, S., Effect of pulsating flow on Coriolis mass flowmeters, Flow Measurement Instrument, Vol. 5, pp.263-273, 1994. [8] Clark, C., Cheesewright, R., The effect of flow pulsations on coriolis mass flow meter, Journal of Fluids and Structures, Vol. 12, pp. 1025-1039, 1998. [9]OIML R49-2:2013(E), Water meters for cold potable water and hot water, 2013
