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SURGE TANKS, THIN PLATE ORIFICES, HEAD LOSSES, Sheet 733-1

작성자 Uploader : ezcivil 작성일 Upload Date: 2017-02-19변경일 Update Date: 2017-02-19조회수 View : 1543

HYDRAULIC DESIGN CRITERIA
SHEET 733-1
SURGE TANKS
THIN PLATE ORIFICES
HEAD LOSSES

1. Thin plate orifices are often used in surge tank risers to restrict the flow during load-on and load-off operations. Computation of the head losses through these orifices is of interest in the design of surge tanks.

2. A number of experiments have been made on head losses through orifices in straight pipe. When an orifice is placed in a surge tank riser close to the penstock tee, the energy loss of flow entering or leaving the riser is affected by the orifice flow. Indri’s(2) extensive study of orifices in branches has made available new data on head loss coefficients considered to be applicable to surge tank problems. The pipe used in this study was 9 cm (3.54 in.) in diameter. The orifice plates were located in the branches 125 mm (4.92 in.) from the center line of the main pipe. The test results indicate that the combined tee and orifice loss coefficients were independent of Reynolds number for Re>3×10^4.

3. HDC 733-1 presents a head loss coefficient curve for thin plate orifices in tees. The head loss coefficient is based on the combined tee and orifice head loss. Indri’s data shown in this chart indicate that a single curve is applicable to load on-load off turbine conditions. Also shown in this chart are head loss coefficient curves by Weisbach(3) and Marchetti(1) for thin plate orifices in straight pipe. These curves indicate that the location of the orifice with respect to other disturbances affects the head loss.

4. The data in HDC 733-1 are based on the equation:

HL = Ko * V^2 / (2g)

where

HL = head loss across the orifice or orifice and tee, (ft)
Ko = head loss coefficient
V = velocity in riser, (ft per sec)

The head loss coefficient is plotted as a function of the ratio of the square of the riser diameter D to the square of the orifice diameter d. A sketch of an orifice in a straight pipe is included in the chart for purposes of defining the terms involved.

5. References.

(1) Caric, D. M., ″Tehnicka hydraulika.″ Gradevenska, Knjiga, Belgrad(1952).

(2) Indri, E., ″Richerche sperimentali su modelli di strozzature per pozzi piezometrici (Experimental research on models of constrictions for surge tanks).″ L′Energia Elettrica, vol 34, No. 6 (June 1957), pp 554-569. Translation by Jan C. Van Tienhove, for U. S. Army Engineer Waterways Experiment Station, CE, Translation No. 60-3, Vicksburg, Miss., April 1960.

(3) Weisbach, J., Untersuchungen in den Gebieten der Mechanik und Hydraulik. Leipzig, 1945.

*** 참고문헌[References] ***

USACE, HYDRAULIC DESIGN CRITERIA, SHEET 733-1, SURGE TANKS, THIN PLATE ORIFICES, HEAD LOSSES
HL = Ko * V^2 / (2*g)
변수명 Variable 변수값 Value 변 수 설 명 Description of the variable


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