ABSTRACT: 0.6 and number holes 9, 16

ABSTRACT:

The multi-hole orifice plate is one of the effective devices for measuring flow rate accurately. In this study, an experimental and numerical investigation of the flow characteristics behavior caused by a water flow through a multi-hole orifice configuration is reported. A circular centered single hole orifice and a multi-hole orifices are used for the test.  Orifices of interest for present study have an area ratio of 0.36, the equivalent diameter ratio of 0.6 and number holes 9, 16 and 25. Discharge coefficients for flow through multi-hole orifices are evaluated. Parameters investigated were hole numbers, orifice pressure drop and Reynolds number. In the present work, k-? turbulence model has been used to predict velocity fields, pressure loss and discharge coefficient around this device. Advantages gained by using multiple holes in an orifice plate instead of single hole are discussed. It is shown that number of holes, hole diameter and aspect ratio influences the discharge coefficients. Tests were conducted under laboratory conditions. The experimental results were compared with numerical modeling and appropriate conclusions are discussed.

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Key Words- Multi-hole orifice, Equivalent diameter ratio, Discharge coefficient, Reynold’s Number

 

 

 

1.    Introduction

Flow measurement is one of the most complex and demanding tasks in industry. Even today there does not exist a universal measuring instrument for all applications. Orifice plates are mainly used as a device of flow measurement for fluid delivery systems is based on the measurement of the pressure difference created when forcing the fluid to flow through a restriction in the pipe. The multi-hole orifice plates or perforated plates are assumed to be composed of a number of individual orifices acting independently and parallel will have flow characteristics different compared to the flow characteristics of a single hole orifice plate having same flow area 1. This is basically because of the flow restriction due to the small flow area of each hole.

Tianyi Zhao et al.2 investigated the key factors affecting multi-hole orifices throttle or flow control characteristics. Shanfang Huang et al. 3 presented the discharge coefficient of a perforated orifice with t = 3 and t/D is 0.1, 0.21, 0.31, Stefano Malavasi et al 4 has conducted two experimental campaigns to investigate the dissipation characteristics of multi-hole orifices under cavitation-free conditions. B. Laribi and M. Mehdi 5 presents a numerical experimentation on the perforated plate flow conditioner with a 90° double bend and a valve 50% closed. The simulation is done with air as fluid in 100 mm pipe diameter with Reynolds numbers 104, 105 and 106. D. Maynes G. J. Holt  J. Blotter 6  experimentally investigated the loss coefficient and cavitation caused by water flow through perforated plates. Plates with beta ratio = 0.11 to 0.6, and t/d = 0.25 to 0.33 were considered. Akshay Dandwate et al. 7 compared orifice plates with various geometry on the basis of their coefficient of discharge with the help using simulations done with k-? and SST model on CFX as a solver.

 

 

A literature review shows that a great deal of work has been done on the pressure drop characteristics of orifice plates in pipe flows. The performance characteristics of the multi hole orifice meter are limited in the open literature. whatever little information available shows that for an orifice plate whose axis is coincident with that of duct or for a multi-hole orifice plate with regularly spaced holes, the factors influencing flow characteristics of the multi hole plates are area ratio of the plate (m), the number of holes and its distribution on the plate. Past research has also shown that the value of Cd is primarily considered to be a function of aspect ratio (t/d), equivalent diameter ratio (? = d/D) and nature of flow defined using the pipe/hole Reynolds number (Re).

The paper therefore addresses the problem of relating flow rate to pressure drop and the discharge coefficient prediction by experiments and numerical simulations through single orifice over multi hole orifice geometries and operating conditions. The main objective is to validate the numerical simulations with experimental data to predict pressure loss, velocity fields and discharge coefficient Cd. The present paper is subdivided into three sections. The experimental setup is first presented. Numerical models are then detailed. Comparison of experimental results with numerical simulations is done in the last section

2. Experimental arrangement and measurements:

To measure pressure drop across multi hole orifice plates at known flow rates experiments were conducted. Experimental test section consists of 30 D upstream and 50 D downstream side of the orifice. At a location 50mm upstream and 25.4mm downstream from the orifice flange pressure taps were used to measure pressure differences across the orifice using water –mercury manometer. By means of the collecting tank the discharges were measured volumetrically. Systematic procedure was used in making the orifice plates and experiments were conducted at room temperature. Twenty square edged orifice plates were studied during this work. All holes were drilled on a vertical drill press with plates backed by wooden blocks to prevent excess burring. After drilling, the plates were drawn across No. 0 emery paper on a flat surface to knock off the burrs.

Data for each orifice plate were collected by strict set of test procedures to ensure the collection of repeatable and accurate data. Air was removed from the system by the help of knob providing for the purpose whenever the orifice plate was changed. Once the air was removed the system was run for approximately 15 minutes in the maintenance configuration. About seven to eight data points were taken for each orifice plate, corresponding to a pressure drop across the orifice meter using mercury manometer. To check the consistency of the data five to six runs were made independently on the same plate to get a good sample of the data. The coefficient of discharge Cd was obtained for all the orifice plates.

The physical data and other dimensions for all the orifices used for the computations and experiments are summarized in Table 1.

Table 1: The relevant parameters in these experiments/Computations

Number of holes

Diameter of the hole mm

Aspect Ratio t/d

Equivalent Diameter Ratio d/D

1.5 mm thickness of the Orifice plate

1

30

0.05

0.6

9

10

0.15

0.6

16

7.5

0.2

0.6

25

6

0.25

0.6

Overall Range: 0.05