Work procedure

1.Fill in reservoir 1 with water (Fig. 4.2).

2.Open quickly the tank choke and put calibrating tank 3 under the stream.

3.Open faucet for filling tank 1 with water and fix its level as H.

4.Measure H, and coordinates X and Y of some flow points with two rulers. Determine coefficients with formula 4.3

5.Measure time T and volume of water W in the calibrating tank.

6.Determine actual , and theoretical flow rates and coefficient .

7.Determine flow contraction coefficient by formula .

8. Calculate resistance coefficient .

9. Put results of measurements and calculations into table 4.1.

10. Compare these results with those given in the manual. Make conclusions.

Table4.1

Pressure head H, cm
Ordinate Y, cm
Abscissa X, cm
Speed Coefficient
Time for filling the calibrating tank T, s
Measured volume W, cm3
Actual flow rate , cm3/s
Theoretical flow rate , cm3/s
Rate Coefficient
Flow contraction Coefficient
Coefficient of resistance

2. Discharge coefficients of liquid flow through cylindrical nozzles

Nozzle is a short tube attached to the hole in a thin wall. Cylindrical nozzles are short cylindrical tubes of the length of three - four diameters. Cylindrical nozzles may be of external (Fig. 4.4, a) and internal (Fig. 4.4, b) shape.

The jet, on entering the pipe, is being contracted and then stars expending and fulfilling the pipe.

Fig. 4.4. Scheme of liquid efflux through cylindrical nozzles

In the liquid flow the nozzle forms a contraction section where vacuum occurs. Presence of vacuum is explained by the speed value at the contracted section 1-1 comparing to the speed at the flow outlet (section 2-2), and therefore pressure in the contracted section is less than atmospheric.

At large Pressure Head (H  14 m for water) the flow regime changes suddenly. The flow jet tears away of the wall and flow efflux starts to be of orifice type. The similar phenomena are observed in short mouthpieces when atmospheric pressure bursts into the vacuum zone.

At the first regime of operation the area of flow cross-section (2-2) equals to the area of nozzle cross-section (ε=1) and speed is less in the nozzle than in the orifice because of losses.

Liquid flow rate through nozzles shows to be greater than that through the orifices. The nozzle sucks in liquid and makes speed increase. Taking into account that for nozzle = 1, one has .

The experiments stated, that discharge coefficient for external cylindrical nozzle is = 0,81...0,82.

In internal cylindrical nozzle coefficient gets a lower value because of more difficult entrance conditions and is equal to 0,71. Flow contraction in internal nozzle is greater than in external, therefore changing of flow running shape starts at some lower pressure head H.

Liquid flow rate through mouthpieces is determined by formula 4.6 and liquid speed - by formula 4.1.