FLOW RATE SENSOR

Abstract: A flow rate sensing device in which electrodes are concentrically disposed so as to form an electric field having a field strength which changes in space along the flow of a dielectric fluid, and a current sensing means measures the dielectric polarization-current produced when the dielectric fluid flows in the electric field. This device senses a highly changing flow rate, e.g., an intermittent flow, with good response and is therefore suitable for measuring the flow rate of a fuel.

Description: TECHNICAL FIELD This invention relates to a flow rate detection device for measuring a flow rate of a dielectric fluid. BACKGROUND ART As a flow meter for detecting a flow rdte of. a dielectric fluid such as a fuel or the like, there is used a vane flow meter such as shown in Figure 1. That is, in Figure 1 (1) is a flow path of a fluid, (2) a vane wheel, and (3) is a container for accommodating that vane wheel therein. When the fluid flowing through the flow path (1) strikes against the vane wheel (2), the vane wheel (2) is rotated at a speed identical to a flow speed of the fluid. Assuming that the flow speed of the fluid is designated by V in m/sec, the number N in r/sec of rotation in unit time (which is simply called hereinafter a rotation speed) of the vane wheel (2) is given by the following expression: N=Kn V (1) On the other hand, assuming that a flow rate of the fluid is designated by Qv in m /sec and a sectional area of the flow path (I) is designated by S in m3, the flow speed V in rn/sec of the fluid is given by the following expression: Qv V = -- (2) S From the expressions (1) and (2) the relationship between the flow rate Qv in m3/sec of the fluid and the rotational speed N in r/sec of the vane wheel (2) is given by the following expression: : EMI2.1 Since each of the sectional area S in m2 of the flow path (1) and Kn in the expression (2) is a constant, the rotational -speed N in r/sec of the vane wheel (2) is proportional to the flow rate Qv in m /sec of the fluid. Therefore, if the rotational speed N in r/sec is measured, the flow rate of the fluid flowing through the flow path (1) can be measured. Since conventional vane flow meters measure the rotational speed N in r/sec of the vane wheel (2) as described above, the flow rate of fluid can be accurately measured as shown in the expression (3) provided that a stream of the fluid flowing through the flow path (1) is in the steady state Cthe flow rate Ov in m3/sec being substantially constant). However where the flow rate of the fluid has suddenly changed (suddenly increased or suddenly decreased), a time delay is caused until the vane wheel (21 has a speed identical to the flow speed V in m/sec of the fluid because the vane wheel C2) has an inertia. The inertia of the vane wheel (2) can be reduced by-properly selecting the shape and material of the vane wheel (2) and devising to be small-sized.and light-weighted. However as the stoutness of the structure can not be disregarded, a reduction in inertia of the vane wheel (2) has a limit. Accordingly, in the case the stream of the fluid is suddenly varied with respect to time, for example, in the case of an intermittent stream, it is possible to.comparatively accurately measure the mean flow rate but it is impossible to accurately measure an instantaneous flow rate because a time delay occurs until. the van wheel (2) coincides with the flow speed of the fluid as described above.. DISCLOSURE OF THE INVENTION According to the. present invention, a mass flow rate of a dielectric fluid is measured by coaxially disposing electrodes for forming an electric field having an intensity spatially changed along a stream of the dielectric fluid and measuring dielectric polarization current flowing when the dielectric fluid flows through this electric field. Thus there is the effect that even a flow rate having a large change, for example, a flow rate of an intermittent stream can be detected with a good response. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side elevational sectional view of a conventional flow meter for a dielectric fluid; Figure 2 is a side elevational sectional view illustrating one embodiment of the present invention; Figures 3, 4 and 5 are views explaining the operation of the present invention; and Figure 6 is a side elevational sectional view illustrating another embodiment of the present invention BEST MODE FOR CARRYING OUT THE INVENTION Figure 2 shows one embodiment of the present invention wherein (11) is a central electrode disposed in a path of a dielectric fluid and connected to a positive pole of a high voltage DC electric source (12). C13) is a cylindrical circumferential electrode disposed around the outer periphery of the central electrode t to oppose to each other through a fluid flowing space, and consisting of two circumferential electrodes (13a) and C13bl divided in a direction of flow of the fluid. (14) is an insulating member for insulating those circumferential electrodes C13al and C13bZ from each other, C15al and Cl5b) are current detecting resistances serially connected between said circumferential electrodes (13al and ±13b), (16) a voltmeter, and (17) is a housing supporting each of said electrodes (11) and (131 and comprised of an insulating member (l82 and C191 are an inflow port and an outflow port for the dielectric fluid connected to a flow path of the fluid not shown. Still more the middle point of said resistances (15a) and (15b) is connected to ground and a voltage across said electric source (2) is applied between said electrodes (11) and (13). Also said electrodes (11) and (13a) and (13b) are constructed so that sections perpendicular to the stream of the fluid are circular-shaped. Then the description will be made in conjunction with the operation of Figure 2 constructed in this way. Applied between the central electrode (11) and the circumferential electrodes (13a) and C13b) connected to ground through the detecting resistances (15a) and C1551 respectively is a voltage by means of the electric source (121 and an electric field is formed in the path of the fluid surrounded by the central electrode (11) and the circumferential electrodes (13a) and (13b). The shapes of those central electrode (11) and circumferential electrodes a3al and a3bl are formed so that by considering that a distribution of electric fields on the side of the inflow port (18) for the fluid is rendered symmetric with respect to that on the side of the outflow port Cl9) therefor about the insulating member (14), the electric field intensity is strongest adjacent to the insulating member (14) and weakest adjacent to the inflow port (18) and outflow port (19) for the fluid with the electric field intensity therebetween spatially slowly changed. Assuming that E(2) designates an electric field intensity formed at each part in the path of the fluid Ke a specific dielectric constant and ò designates a dielectric constant of a vacuum, a dielectric polarization intensity P at each part in the path of the fluid is given by the following expression: - eg (Ke - 1) E (z) t41 In Figure 3 there are illustrated the shapes and dispositions of the central electrode (11) and the circumferential electrodes (13a) and (13b), the electric field intensity E at each part in the path of the fluid and the dielectric polarization intensity P of the dilelectric to locally correspond to one another. That is, Figure 3(a) shows the shapes and disposition of the central electrode (11) and the circumferential electrodes (13al and C13bl Interelectrode distances between the central electrode t112 and the circumferential electrodes cl3ai and C13b) are rendered largest adjacent to the inflow port (18) and the outflow port (19) for the fluid and smallest adjacent to the insulating member (14) on the central part while the interelectrode distances therebetween are rendered linearly changed. Figure 3(b) corresponds to the shapes and disposition of the electrodes shown in Fogure 3 Ca) and qualitatively illustrates a distribution of the electric field intensities at each part. The electric field intensity within the path of the fluid is weakest adjacent to the inflow port (18) and the outflow port (19) for the fluid and strongest adjacent to the insulating member (14) on the central part with the electrid field intensity therebetween slowly changed. Figure 3(c) corresponds to the distribution of the electric field intensities shown in Fi.gure 3(b) and illustrates a distribution of dielectric polarization intensities at each part. Since the specific dielectric constant of the dielectric is a constant, the dielectric polarization intensity is proportional to the electric field intensity as shown by the expression (4). Accordingly the distribution of the dielectric polarization intensities becomes identical to that of the electric field intensities. Figure 3(dl illustrates the distribution of the dielectric polarization intensities shown in Fiogure 3Ccl by modelling that distribution with the polarization of positive and negative charges composing dielectric molecules Before the dielectric fluid enters the region of the electric field, the dielectric molecules are neutral but when the dielectric fluid enters the region of the electric field, the polarization of the positive and negative charges becomes strong in proportion to the electric field intensity and the polarization becomes strongest adjacent to the insulating member (14) on the central part. When the central part is passed by and the electric field intensity becomes weak, the polarization of the positive and negative charges becomes weak. When leaving the region of the electric field, the dielectric becomes again neutral. Figure 3 shows the distribution of the polarization intensities of the dielectric fluid which is the same in spite of whether the dielectric fluid is moving or stationary. However, perceiving the individual molecules, the polariza-tion intensities of the individual molecules are constant with the dielectric fluid put in the stationary state whereas the polarization intensities of the individual molecules change upon the flowing of the dielectric fluid because of changes in polarization intensities acting upon the individual melecules. In Figure 4 there is illustrated a situation in which the polarization intensity changes with the flowing dielectric fluid by a model for the polarization of positive and negative charges of the molecule with the individual molecules perceived. Figure 4(a) illustrates a situation of the molecule of the dielectric fluid before it enters the region of the electric field. In this region no electric field exists in the path so that the positive and negative charges of the molecule are not polarized and the melecule is neutral. Figure 4(b) illustrates a situation of the molecule of the dielectric fluid in which it has entered the region of the electric field through the inflow port (18). In this region the electric field acting on the molecule becomes strong upon the molecule flowing to the side of the outflow port (19). Thus the positive and negative charges of the molecule are moved in the direction of the arrow ( in the Figure to advance the polarization. In other words, when the dielectric fluid flows to the side of the outflow port (19), a dielectric polarization current flows through between the central electrode (11) and the circumferential electrode (13a). Figure 4tic) illustrates a situation of the molecule of the dielectric fluid in which it have come adjacent to the insulating member (14) on the central part. In this region the electric field intensity is strongest so that the polarization intensity of the melecule is strongest but the electric field intensity acting on the molecule of the dielectric fluid does not change even when the molecule flows to the side of the outflow port (19). Thus the polarization intensity of the molecule does not change and the dielectric polarization current does not flow. Figure 4(d) illustrates a situation of the molecule of the dielectric fluid in which it has further flowed to the side of the outflow port (19). On the contrary of the region shown in Figure 4(b) when the molecule of the dielectric fluid flows to the side of the outflow port (19) in this region, the electric field intensity acting on the molecule becomes weak so that the positive and negative changes of the molecule are moved in the direction of the arrow ( b ) in the Figure to return the polarization. In other words, when the dielectric fluid flows to the side of the outflow port (19), a dielectric polarization current in the sense reversed from that illustrated in the region shown in Figure 4(b), that is to say, a negative one flows through between the central electrode (11) and the circumferential electrode (13bl. Figure 4(e) shows a situation of the dielectric fluid in which it has come outside of the region of the electric field through the outflow port (19). In this region no electric field exists so that the polarization of the positive and negative changes of the dielectric disappears and the dielectric fluid becomes neutral. Figure 5 shows a course on which the dielectric polarization current flows through between the central electrode (11) and the circumferential electrodes (13a) and (l3b) in the process in which the dielectric fluid enters the region of the electrid field through the inflow port (18) for the fluid and flows through the region of the electric field until it flows out from the outflow port (19). In a region in which the polarization intensity is increased the dielectric polarization current from the central electrode (11) flowing into the circumferential electrode (13a) passes through the current detecting resistances (15a) and t15b) and enters the circumferential electrode (13b) while in a region in which the polarization intensity is decreased, it enters the central electrode (11) through the circumferential electrode (13b) as a negative dielectric polarization current. At that time, if the voltmeter (16) measures a voltage developed across the current detecting resistances (15a) and C15br then this permits the measurement of a dielectric polarization current flowing when the dielectric fluid flows through the electric field whose intensity spatially varies along the stream of the dielectric fluid. Still more when the dielectric fluid changes in sense of the stream, the dielectric polarization current also varies in sense. Thus the sense of the stream can be decided. This dielectric polarization current Ip is determined by the voltage V applied between the central electrode (11) and the circumferential electrodes (13a) and 13(b), a radius of an internal electrode (the voltage applied circumferential electrode (11) a radius r0 of an outer electrode (the circumferential electrode (13)) and a volume flow rate Gv of the dielectric fluid and it is given by the following expression: EMI12.1 In the expression (5) a specific polarizability (Xe - 1) of the dielectric is proportional to a density p of the dielectric and given by the following expression: : EMI13.1 Accordingly assuming that Gm designates a mass flow rate of the dielectric fluid, the dielectric polarization current 1p is given by the following expression: EMI13.2 In the expressions (6) and (7) Kp is a constant inherent to the dielectric, and r. and r0 are contstants as determinated by-the size and shape of the voltage V applied electrode (li) and the current detecting electrode (135. Thus assuming that the voltage V applied between the voltage applied electrode Cll) and the current detecting electrode (13) is constant, the dielectric polarization current 1p becomes proportional to the mass flow rate Gm of the dielectric fluid. That is, the flow meter according to the present invention is a mass flow meter for a dielectric fluid. Figure 6 shows another embodiment of the present invention. In the embodiment shown in Figure 2 through 5 the electrodes are arranged coaxially and the circumferential electrode (13) is divided with the current detecting resistances (15a) and (15b) connected therebetween in order to form the electric field having an intensity spatially changed along the stream of the dielectric fluid but the effect of the present invention is not damaged even by dividing the central electrode Cll), coupling two electrodes (ill) and Cllb) to each other through the insulating member (i4) and connecting the current detecting resistances (1spa) and (15b) between those electrodes (lla) and (llb) as in another embodiment shown in Figure 6. Furthermore the generation and neutralization of the polarization can be caused on the dielectric fluid through the utilization of a change in electric field intensity developed in the vicinity of either end of a direction of a stream of the fluid flowing through between a pair of equidistant coaxial electrodes without obtaining a change in electric field due to a variation in distance between the respective electrodes (11) and (13). As described above ,and according to the present invention, the electrodes for forming the electric field having an intensity changed spatially along the stream of the dielectric fluid are arranged coaxially and the dielectric polarization current flowing when the dielectric fluid flows through this electric field is measured thereby to measure the mass flow rate of the dielectric fluid resulting in the following effects: Ci) Since movable mechanical portions are not included structually and temporally delaying elements due to inertias and others do not exist, the response is fast and not only the mean flow rate of the dielectric fluid but also an instantaneous flow rate of an intermittent stream can be faithfully measured with a good accuracy. (ii) Since the dielectric polarization current is inverted in sense in accordance with a direction of flow of the dielectric fluid, the sense of flow of the dielectric fluid can be decided in accordance with the polarity of the dielectric polarization current. (iii) Since the electric field formed in the path of the dielectric fluid is formed of a pair of electrodes put in coaxial arrangement, the axis symmetry can be made about the axis of the central electrode and a disturbance of the electric field attributing to the shape and disposition of the electrodes does not exist adjacent to a maximum of the electric field intensity. Thus it becomes possible to effect the stable measurement with a high accuracy. (iv) The path of the dielectric fluid is surrounded by the circumferential electrode and no disturbance of the electric field due to the intrusion of an external electric field exists adjacent to a maximum of the electric field intensity. Thus it becomes possible to effect the stable measurement with a high accuracy. (v) Since the path of the dielectric fluid can be render circular, there is provided a flow meter for dielectric fluids small-sized and small in pressure loss. (vi) Since the structure is simple and includes no movable portion, there is provide a flow rate detection device inexpensive and high in reliability. INDUSTRIAL APPLICABILITY The present invention is not restricted to a flow meter for detecting a flow rate of a fuel and so far as the flow rate of dielectric fluids in concerned, it is similarly applicable to devices for measuring it.

Claims: CLAIM (11 A flow meter comprising electric field forming means disposed in a flow path of a dielectric fluid and having a central electrode and a circumferential electrode radially opposing to an outer periphery of said central electrode to form an electric field in the flow path of said dielectric fluid having an intensity changed along a stream thereof by applying a voltage between said individual electrodes, and current detecting means for detecting a dielectric polarization current flowing when the dielectric fluid flows through the interior of said electric field.

Inventors: UEYAMA, YOSHIJI MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1982
Main classification: G01F1
IPC codes: G01F1