Using the nomogram and charts (FIGURES 1 and 2) on pages 4 and 5, determine the diameter of a suitable air main for the distribution of 6 m3 min–1 FAD. System pressure is 6 bar, the length of the pipe run is 175 metres, and a maximum pressure drop of 0.3 bar is allowed.
The distribution main must also include the following:
Pipe flow, Q = 6m3/min
Q = 6 × 1000/60
Q = 100dm3/s
Let the initial diameter of the pipe be dmm
We, therefore, assume that the initial velocity is 15m/s
Air density at 6 bar = 1.225 × 6
= 7.36kg/m3
The initial area, A = Q/60/15
= 0.006667m2
Initial diameter, d = (4 × A/π)0.5
= 0.092m
= say 100mm
The total equivalent length LT = Lpipe + Lbends + Ltee + Lelbow + Ldiaphragm
LT = 175 + (4 × 0.8) + (2 × 7) + (6 × 10) + (2 × 6)
LT = 264.2m
From the nomogram (refer image) we get 2.2mbar/m pressure drop. Hence, total pressure drop is 2.2 × 10-3×264.2 = 0.58bar > 0.3bar
Hence we need to go for 150mm diameter pipe which is beyond the nomogram.
Describe the relevant advantages and disadvantages of using steel, copper or plastic pipe for a distribution main.
Steel pipes are available in various types depending on the percentage of carbon present.
Advantages.
Disadvantages.
Copper pipes
Advantages
Disadvantages
Plastic pipes
Plastic pipes are available in various forms such as PVC, PEX, CPVC, and PP amongst others.
Advantages
Disadvantages
Than the optimum value?
Solution.
Let us consider that for a given application the flow rate, Q is constant.
Flow rate, Q = Area × Velocity
Area, A = πr2 where r is the radius of the pipe.
Suppose, the pipe being used is small in size:
To maintain constant flow rate, Q, if the radius is less than the optimum radius the velocity of flow in the pipe will be more.
As the velocity increases the head losses due to friction in the pipe will increase. (Head loss V2)
Hence the difference in total energy at the entry and exit of the pipe will be more, that is, energy losses are higher in case of undersized pipes and the external power required to maintain the flow will be more as compared to oversized pipes (Brusselman et al, 2010).
If a pipe has a diameter less than the optimum diameter then the pressure inside the pipe will increase which may be too much for the pipe to handle and the pipe may crack or burst. So optimum value is very important while constructing a pipe.
Suppose, the value of the pipe being used is bigger than the optimum value:
Larger pipe means that diameter is more than the optimum diameter value but still carrying fluid under pressure only and always running full (Gandossi, 2013).
If flow rate, Q is the same in both the larger pipe and the optimum one and radius, R increases then velocity, V decreases. Hence, head losses caused by friction decreases.
If a pipe has a diameter exceeding the optimum diameter then the pressure inside the pipe will drop and more work has to be done to recover that lost pressure. This will lead to increase in power consumption of the pump which in turn will increase the total expenditure.
In Conclusion, the transmission losses with the use of undersized pipes are higher as compared to oversized pipes for the same length of pipes.
Calculate the minimum diameter of the pipe if the pressure drop in a system is to be limited to 0.3 bar when is delivered through a pipe of equivalent length 160 m.
Pressure drop =800 2 5 31 lQ Rd.
Given the following data
Flow rate, Q = 300lt/s
Pipe length, L = 160m
Pressure drop in the system = 0.3 bar
Solution.
Consider the pressure drop equation
Pdrop = 800lQ2/Rd531
Write the Reynold’s number equation.
Re = ρvd/µ
Here,
ρ = density of air
v = velocity
µ = viscosity
v (velocity) = Q/a
Friction factor = 64/ Re
Calculation of velocity.
v = 0.3/0.25πd2
Substitute the above values in the Reynolds equation.
Re = {1.225 × (0.3 ÷ π/4d2)}/{16.96 × 10-6}
Re = (0.0276 × 106)/d
R = 64/ Re
R = (64 × d)/ (0.0276 × 106)
R = 2318.8 × 10-6 d
Substitute the values in the pressure drop equation
Pdrop = (800 × 160 × 0.32)/ (2318.8 × 10-6)d5.31
d5.31 = (4.968 × 106)/ (0.3 × 105)
d = 2.25m
This is the minimum diameter of the pipe.
Solution.
Macro oil mist lubricator
Micro oil mist lubricator
Micro mist oil lubrication is preferable in the intake manifold of an engine and a situation where the pneumatic piping system is used. In addition, micro-mist lubrication is preferred for long pipes and cylinders with complicated shapes (Izquierdo et al, 2010).
Solution.
There are several reasons for a compressor to run hot or overheat. Such reasons include high compression ratio, high return gas temperatures, and lack of external cooling.
High compression ratio
High compression ratios are the result of either lower than normal suction pressure or higher than normal discharge pressures. Change in suction pressure will affect the compression ratio more rapidly than changes in the discharge pressure. For this reason, it is important to keep the suction pressure at its high possible value and also keeping the discharge pressure within normal operating conditions is still important (Brusselman et al, 2010).
When the returning gas temperatures are high the, an overheating will occur in a multi-stage reciprocating compressor.
Low suction pressure.
Usually, the compression process roughly follows the constant entropy line on the pressure-enthalpy diagram. With a constant discharge pressure, when the process of compression begins on a constant entropy line of a higher value, the resultant temperature of discharge is higher. Starting the process of compression on a higher constant entropy line occurs in two ways, that is, lower suction pressure and higher suction temperature. It is therefore important to operate the system with the highest possible suction pressure (Comba et al, 2011).
An increase in suction temperature results in a corresponding increase in discharge temperature. This means that the higher the suction temperature the higher the discharge temperature thus leading to overheating.
Hydraulic system performance checklist
|
No. |
Checklist. |
Good condition. |
Poor condition. |
Remarks. |
|
1 |
Check the lubricant tank oil level |
|||
|
2 |
Check the hydraulic tank level |
|||
|
3 |
Check the pressure of the hydraulic system. |
|||
|
4 |
Check the clamping stock |
|||
|
5 |
Check the clamping devices |
|||
|
6 |
Check the clamping pressure of the hydraulic system for chuck/fixture |
|||
|
7 |
Check the chuck function |
|||
|
8 |
Lubricate the clamping device if any manual. |
|||
|
9 |
Check the coolant supply. |
|||
|
10 |
Check the selectable zero offset entries |
|||
|
11 |
Clean the oil filters |
|||
|
12 |
Observe the oil pipe connections. |
Solution.
The unique characteristics of fire-resistant fluids make it necessary to carefully consider the modifications required before converting to a fire-resistant fluid or when converting from one type of fire-resistant fluid to another.
When changing the fluid in a hydraulic system from a mineral oil based hydraulic fluid to a fire resistant fluid, the following precautions should be taken as discussed.
All of these fluids have a higher specific gravity than does mineral oil based fluid. As a result, the pump inlet may need to be enlarged to avoid cavitation. Long inlet lines must be avoided, and inlet fluid strainers should be no finer than 60 mesh.
It may also be necessary to design and install additional filtration circuits on the discharge and return lines because fire-resistant fluids tend to suspend contamination much more readily than mineral base oils (Izquierdo et al, 2010).
Before installing the fire-resistant fluid, the entire system must be flushed thoroughly to remove any residual contamination. Adding Varsol to the system and operating all of the circuits before draining the original hydraulic oil can help to dislodge sediment and sludge, which should be removed prior to the installation of the new fire-resistant fluid.
Make certain that compatibility tests are performed to ensure that seals, packing material and hoses will not deteriorate prematurely after the conversion is completed.
Synthetic fire-resistant fluids, such as phosphate ester, are not compatible with most standard sealing materials. Also, keep in mind that water glycol fire-resistant fluid will attack components with aluminium, zinc or magnesium materials (Comba et al, 2011).
The most important thing to remember when considering a conversion to a fire-resistant fluid is to become aware of all of the potential problems that can occur. Then carefully investigate all of the available options before rushing into a decision that could prove to be very costly.
Changing to a fire resistant fluid generally requires draining of existing fluid and thorough cleaning and flushing of the system to assume minimal contamination.
If the system contains painted surfaces, compatibility of the fluid with the paint should be verified as well as compatibility with seals, holes and other components of the system (Izquierdo et al, 2010).
In some cases, it is necessary to change the suction pipe size and filters to accommodate the fluid being used.
For any additional precautions, the specific manufacturers of both the system components and the fluid should be consulted.
Maintenance procedure objectives should include the following;
References.
Brusselman, E., Moens, M., Steurbaut, W., and Nuyttens, D., 2010. Evaluation of hydraulic, pneumatic and mechanical agitation for the spray application of Steinernema carpocapsae (Rhabditida: Steinernematidae). Biocontrol Science and Technology, 20(4), pp.339-351.
Comba, S., Di Molfetta, A. and Sethi, R., 2011. A comparison between field applications of nano-, micro-, and millimetric zero-valent iron for the remediation of contaminated aquifers. Water, Air, & Soil Pollution, 215(1-4), pp.595-607.
De Volder, M. and Reynaerts, D., 2010. Pneumatic and hydraulic microactuators: a review. Journal of Micromechanics and microengineering, 20(4), p.043001.
Gandossi, L., 2013. An overview of hydraulic fracturing and other formation stimulation technologies for shale gas production. Eur. Commisison Jt. Res. Cent. Tech. Reports.
Izquierdo, D., Azcona, R., Del Cerro, F.L., Fernandez, C. and Delicado, B., 2010, February. Electrical power distribution system (HV270DC), for application in more electric aircraft. In Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE (pp. 1300-1305). IEEE.
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