__Objective: __

To
determine the shock factors for a 45 split and a double bend from the
measurement of pressure losses due to shock, and quantities in the duct.

__Introduction:__

Shock
losses occur in the fluid flow whenever there is a change in the direction of
flow, or change in the cross-sectional for the flow is encountered. The loss of
pressure due to the formation of eddies and flow separation at the shock
sources is expressed in terms of velocity pressure for the fluid. If

P_{s}
is the shock pressure loss in mm. w.g. then,

** P _{s }= X * P_{v}**

Where
P_{v} is the velocity head (mm w.g.) for the flow specified either
before or after the shock source. The shock factor ‘X’ is unique for the flow
regime encountered defined by the Reynolds number). However, for the general
flow conditions encountered in the underground mines, the shock factor may be
treated constant for each shock source. The value for ‘X’ may be derived
essentially through the scale model studies.

The experimental duct setup has a 45
split and a double bend. Three shock factors are determined from the setup:

Ø
Shock
factor due to split with respect to the flow in the straight branch.

Ø
Shock
factor due to split with respect to the floe in the deflected branch.

Ø
Shock
factor due to the double bend.

__Instruments:__

Experimental
duct setup, Askania minimeter, four inclined tube manometers, two pitot static
tubes, scale and calipers.

__Procedure: __

(1)
Measure
the diameters of the main branch and the deflected branch.

(2)
Place
one pitot static tube in one portion of each split such that its nose is at the
center of the air duct and facing the air stream.

(3)
Connect
the manometer as follows:

·
Askania
minimeter to the Pitot-static tube in deflected branch to measure the velocity
head at the center of the duct.

·
One
inclined manometer to the Pitot-static tube in the main branch to measure the
velocity head.

·
One
inclined manometer between the static pressure portals across the double bend.

·
One
inclined manometer across the split between the inlet and the straight branch
static pressure portals.

·
One
inclined manometer across the split between the inlet and deflected branch
static pressure portals.

(4)
Level
the Askania minimeter and the four manometers and take their initial readings.

(5)
With
the fan running, once the flow is stabilized, take the first set of
observations.

(6)
Obtain
6 to 8 sets of readings for varying flow conditions. Adjusting the throttles on
the outlet of the splits varies the flow in the splits.

__Computations:__

Calibrate
the inclined tube observations with the ‘calibration charts’ available. The
average velocity head values are obtained in the splits as follows:

Average velocity head = velocity
head on the center where ‘m’ is the method factor assumed to be 0.85. Plot
three graphs as follows:

Ø
Static
pressure drop across the split with respect to the straight branch against
average velocity pressure in the straight branch.

Ø
Static
pressure drop across the split with respect to the deflected branch against
average velocity pressure in the deflected branch.

Ø
Static
pressure dorp across the double bend against the average velocity pressure in
the deflected branch.

Pass
a best-fit straight line through the points marked for each case, and the sope
of this line indicates the respective shock factor.

The shock factors for the split are
given by empirically derived relationships as follows:

For the straight branch

**X
= 0.5{(Q/Q _{m})-1}^{2}**

For
the deflected branch

**X
= (Q/2Q _{d})^{2} + {(Q/Q_{d})-1}+ X_{d}**

Where
Q, Q_{m} and Q_{d} refer to the total, straight branch and
deflected branch airflow rates, and X_{d} is computed from the shock
loss formulae.

Convert
the average velocity heads obtained into quantity flow rates (assuming the sir
density of 1.15 kg/m) and verify the applicability of the above empirical
relationships.

Ø
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