CEE 310 Fluid Mechanics
Lab 2 Pressure, Pressure Forces and Buoyancy

Purpose

A)To become familiar with methods of pressure measurement.

B)To study the effect of pressure forces on a plane surface.

Experiment (A) Use of a Water-Over-Mercury Manometer

I. Objective:

(1) To use the water-over-mercury ‘U’ tube manometer to determine the pressure at a point.

(2) To compare the reading of a manometer with a Bourdon Gauge.

II. Equipment:

Deadweight Pressure Gauge Calibrator.
Mercury Manometer.
Bourdon Type Pressure Gauge.

The Bourdon gauge has a glass cover plate so the internal mechanisms are visible. The pressure element is a

curved, hollow metallic tube closed at one end, while the other end is connected to the pressure to be measured.

When the internal pressure is increased, the tube straightens out a small amount, pulling on a linkage to which is

attached a pointer that moves across a metallic scale. The dial reads zero when the inside and outside of the bent

tube are at the same pressure, Figure (2).

III. Procedure:

1)Ensure that the tube connecting the manometer and Bourdon Gauge and the respective limb of the manometer, are fully primed with water.

2)Level the deadweight pressure gauge calibrator.

3)Fill cylinder of deadweight calibrator with water; read Bourdon gauge and manometer levels.

4)Insert the deadweight piston; read gauge and manometer levels. Rotate piston to avoid sticking.

5)Load up piston with ½ kg mass and read gauge and manometer levels.

IV. Data:

Room temperature, T=_______________ ^oC

Barometric pressure,p_atm = ______________

Zero pressure conditions:

Bourdon Gauge reading,p_b=_______________KN/m²

Height of mercury in column 1Hm₁=_______________mm

Height of mercury in column 2, Hm₂=_______________mm

Initial height offset:DH_o= (Hm₂-Hm₁)DH_o=_______________ mm

Pressure based on manometer values,p_m=________________ KN/m²

Pressure calculated based on F/A,p_c= _______________ KN/m²

Case A – Deadweight Piston Only:

Bourdon Gauge reading, p_b=_______________KN/m²

Height of mercury in column 1, Hm₁=_______________mm

Height of mercury in column 2, Hm₂=_______________mm

Net offset: DH_A=(Hm₂-Hm₁)-DH_oDH_A=_______________ mm

Pressure based on manometer values,p_m=________________ KN/m²

Pressure calculated based on F/A,p_c= _______________ KN/m²

Case B – Deadweight Piston and ½ kg Weight:

Bourdon Gauge reading, p_b=_______________KN/m²

Height of mercury in column 1, Hm₁=_______________mm

Height of mercury in column 2, Hm₂=_______________mm

Net offset: DH_B =(Hm₂-Hm₁)-DH_oDH_B=_______________ mm

Pressure based on manometer values,p_m=________________ KN

Pressure calculated based on F/A,p_c= _______________ KN/m²

Constants:

Specific gravity of mercury,S = _________________

Mass of deadweight piston = 0.500 Kg

Diameter of deadweight piston = 17.6 mm

Area of deadweight piston = 2.45E-04 m²

Calculated Pressure = Force/Area

V. Questions:

1.How does the pressure measured with the manometer and the Bourdon gauge compare the calculated pressure?

2.Calculate the ABSOLUTE pressure for the deadweight piston only case.

3.What are the potential sources of error in the experiment?

Experiment B. Pressure Forces on a Vertical Plane Surface

I. Objective:

To measure the moments due to the water pressure force acting on a vertical plane surface and compare

with the moments calculated by the principles of hydrostatics.

II. Equipment:

Torroid tank device.

III. Procedure:

(1)Measure the dimensions a, b, and d of the torroid (see Figures 1a - c).

(2)Measure the distance, L, from the knife-edge axis to the balance pan.

(3)Adjust the counter-balance weight until the balance arm is horizontal.

(4)Place a mass on the balance pan. Fill the tank until the balance arm is horizontal. Record the water level on the scale. (Note: overfilling and slowly draining may achieve fine adjustment of the water level).

(5)Repeat the procedure for several different masses, noting the corresponding water levels.Record the data below.

IV. Data:

a = __________ b = __________ d = __________ L = __________.

1. Partial Immersion (y < d)

Mass (gm) y (cm) Applied Moment
(N-m)
Calculated Moment
(N -m)
% Difference

50

100

150

2. Complete Immersion (y > d)

Mass (gm) y (cm) Applied Moment
(N-m)
Calculated Moment
(N -m)
% Difference

250

300

400

Note: Lab Requirements

Note:The analysis required for this lab is more than for previous labs.Allow extra time to do the calculations.Present your work in an organized fashion using quality engineering sketches to define your coordinate system and explain your method of solution.

Compute the applied moments, due to the masses loaded onto the balance arm.
Derive an expression for the moment created about the torroid pivot, by the hydrostatic force, for both the partial and complete immersion cases. (Note: these are two different equations). Evaluate your equations for each load as the “calculated moment”.
Compare the applied and the calculated moments. Do they agree? Explain any significant differences.
The pressure forces acting on the curved surfaces do not contribute to the moment about the pivot. Why? Explain briefly.

Mass (gm)	y (cm)	Applied Moment (N-m)	Calculated Moment (N -m)	% Difference
50
100
150