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Advantages and Disadvantages of Orifice Plates
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- VENTURI TUBE
- FLOW NOZZLE
- PITOT TUBE
| Advantages and Disadvantages of Orifice Plates Advantages of orifice plates include • High differential pressure generated • Exhaustive data available • Low purchase price and installation cost Disadvantages include • High permanent pressure loss implies higher pumping cost. • Cannot be used on dirty fluids, slurries or wet steam as erosion will alter the differential pressure generated by the orifice plate. VENTURI TUBE It consists of a tapered, narrowing section of pipe joined to a tapered, enlarging section. As the liquid or gas flows through the tube, its velocity increases, causing a pressure differential between the upstream and downstream flow. Fluid pressure is lowest at the point where the tube is most restricted. Venturi tubes can be round, rectangular or irregular in shape. These are used to measure the flow rate of steam, air, or other gases. 61 Field Instrumentation GEN Rev) VENTURI TUBE It produces a large differential with a minimum permanent pressure loss. It measures flows containing suspended solids. Its disadvantage is its high cost. FLOW NOZZLE In flow nozzle, the nozzle constricts the flowing stream and fluid moves faster to pass through it. The velocity increases through the nozzle and causes a drop in the internal pressure of the fluid flowing through it. Overall pressure loss in the flow nozzle is greater than in a Venturi tube because of increased turbulence at the nozzle exit. Its accuracy is greater than orifice but less than Venturi. It is costly than orifice but not as compared to Venturi. 62 Field Instrumentation GEN Rev) PITOT TUBE It is a hollow tube-within-a-tube device, designed to be pointed upstream in the fluid flow. It operates on the principle that a pressure differential exists in the fluid between the spot where the flow impinges on the front opening and the place where higher-velocity fluid speeds past the lateral openings. Pitot tube is used in clean liquids, free of solid contaminants, or its openings will clog. It must be properly positioned within the pipe where fluid velocity is average otherwise the derived flow rates will be inaccurate. Its advantages are They are inexpensive They have no moving parts They cause minimal pressure drop Annubar: An annubar is very similar to a pitot tube. The difference is that there is more than one hole into the pressure measuring chambers. The pressure in the high- pressure chamber represents an average of the velocity across the pipe. 63 Field Instrumentation GEN Rev) Annubars are more accurate than pitots as they are not as position sensitive or as sensitive to the velocity profile of the fluid. Download 3.37 Mb. Share with your friends:
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