Mechanical Engineering – Rotary
Mechanical Engineering is the main stream in which, Mechanical Engineering – Static and Mechanical Engineering – Rotary is subcategorised.
Here in this post we will see more about Mechanical Engineering – Rotary stream with its relevant equipment’s with its design engineering principles and brief details.
Various Types of Mechanical Engineering – Rotary Equipments
- Compressor
- Pumps
- Blowers
Air Compressor:
- This is one of the most important Mechanical Engineering Rotary Equipment used in many industries.
- Main purpose of these equipment’s are to increase air pressure by intensifying or compress free air into a smaller volume or a area.
- Mechanical Engineering Rotary Air Compressors further classified as the positive displacement and the dynamic types.
- Positive displacement compressors can be further separated into reciprocating and rotary machines.
- Typical reciprocating compressors include piston and diaphragm types.
- Mechanical Engineering Rotary compressors include sliding vane, liquid ring (or liquid piston), and screw types.
- The most widely used dynamic compressors are the centrifugal and axial flow types.
Positive Displacement Compressor
- The positive displacement compressor is a machine which is essentially a constant volume, variable pressure and suited to operate over a wide range of discharge pressures with relatively using constant capacity
- Positive displacement compressors sub classified in different types as sliding vane, liquid ring, and helical lobe compressors
Sliding Vane Compressor
- Operating principle of sliding vane compressors is by utilizing vanes are free to slide in and out of slots and mounted eccentrically in a cylindrical rotor.
- As the impeller or rotor turns, the available area between the compressor casing and the vanes reduces, which compresses air.
- The best application is for use where small, low-capacity compressors are required generally in the range of 100 cfm and up to 75 psi (2830 lpm and up to 518 kPa).
Sectional View of Sliding Vane
Mechanical Engineering Reciprocating & Rotary Screw Compressor
- A reciprocating compressor is a positive displacement machine. This is accomplished by a moving piston in a cylinder.
- Single-acting cylinder implies when only single stroke compression occurs. Whereas in double-acting compressor air is compressed on both strokes.
- The cylinders can be horizontal, vertical, or angled.
- The cylinders can be sealed and lubricated with oil when traces of oil in the discharge air will cause no problems. Oil-free machines are also available at a higher cost.
- A Rotary screw compressors use a pair of close-clearance helical lobe rotors turning in unison. As air enters the inlet, the rotation of the impellers causes the cavity in which air is trapped to become smaller and smaller, increasing pressure. The air reaches the end of the screw at high pressure and flows out smoothly at the discharge port.
Rotary Screw Compressor
Centrifugal Compressor
- Centrifugal compressors are dynamic machines that utilize impellers to impact kinetic energy to the air stream by centrifugal action.
- Once air enters inside each impeller, the velocity of the air is increased.Subsequent to this, kinetic energy is converted into potential energy, by reducing the high velocity of air in diffused section.
- Further the volute rises the pressure further and directs the air into the outlet or discharge piping.
- At relatively low pressuresCentrifugal compressors usually produce large volumes of air.
- Centrifugal compressors can have multi stages with inter-cooling between stages to achieve higher pressures.
Working of a Centrifugal Compressor
Compressor Accessories
AIR RECEIVERS: Storage of compressed air received from air compressor, is the main function of air receivers. A secondary purpose is to align pulsations from a compressor.
The requirement or need for air receiver is depends on the type of regulation the system will use.
If compressor is used continuously all the time and is having continuous or constant blow-off or use without any storage based on system requirements, in that case an air receiver may not be required.
When receiver is used to store air, it can also be used to prevent from often starting and stopping with intermittent use of air compressor, since most of the cases or applications an air compressor is regulated by starting and stopping.
Limit for starts to about 10 per hour is generally accepted practice for reciprocating compressors, with a 70 percent of maximum running time.
As stated above an air receiver work for the following basic purposes:
- Storage of air
- Equalize pressure variations or pulsations
- Accumulates en during condensate
Receivers should be designed in accordance with Mechanical Engineering codes Section VIII, Pressure Vessels Division 1, of the ASME Boiler and Pressure Vessel Code. An automatic drain valve is required for the receiver to act automatically to remove residual condensate formed inside receiver. Sometimes dryers also used to reduce condensate formation and increase dry air inside air receiver.
AFTER COOLERS: Since aftercoolers also consists of Rotating elements, it’s also classified in Mechanical Engineering Rotary. Generally after coolers are used in multistage air compressors, and utilized in between the compressor stages. After compression of air inside compressor, an after cooler is used to lower the temperature of compressed air immediately.
Since air cools to ambient temperature conditions, after cooler is important to the lower air temperature which removes moisture that would otherwise condense elsewhere in the system.
COMPRESSED AIR DRYERS: Compressed air dryers are basically moisture dryer. Moister separator or filter is used to remove larger droplets from large volumes of water. To reduce further water vapor content requirement, compressed air dryers are used.
FILTERS AND SEPARATORS: The function of any filter or separator is to reduce or remove impurities or impurities, other than water vapor, in the air stream to an acceptable or determined level.
Filters operate by having the air stream pass through a porous, granular, or other type of medium.
A separator is generally an inert mechanical device that eliminates large particles of a liquid, such as water and oil.
Typical Air Compressor Schematic:
Typical After Cooler & Separator Schematic:
Pumps:
What is a pump?
Pump is a another equipment of Mechanical Engineering – Rotary stream. A pump is a device that raises, elevates or transfers fluids from one device to other device or unit. Even it cannot be used only for transfer of fluid, it can be used to maintain constant flow rate or constant pressure.
Mechanical Engineering Rotary Pumps further Classifications.
Dynamic pumps and Positive displacement pumps are the two main categories of pumps.
These two categories also have many sub classification of pumps.
Pump Applications.
Pumps are used for a multiple applications. Here is a list of a some of the applications:
Drainage Systems– Pumps are used in drainage to regulate the level of water in a safe area.
Sewage Systems – Used for collection and treatment of sewage.
Irrigation –For irrigation pumps are used for water transfer from wells or bore wells to agricultural land for farming.
Chemical Industry–Various units needs transportation of fluids internally, for which pumps are being used.
Oil & Gas and Petroleum Industry– At every phase of this industry pumps are used during production, transportation even during refining.
Medical Sector–In any hospitals, small pumps are used to fluids in and out of the body. Even in pharma sector plants also pumps are used for transportation and during production.
Important factors in deciding on the right pump.
There are various factors on which pump selection is decided. Basic factors are like fluid process characteristics, Layout to suit in the type, required cycle life, cost of energy, some of the cases code requirements for specific applications, material of construction to be used etc.
Types of Pump
Positive-displacement pumps: Basic principle of this pump is forcing a fixed volume of fluid from the inlet pressure segment of the pump into the discharge area of the pump.
Positive displacement pumps are larger in size than same size or capacity dynamic type of pumps.
Normally these pumps are used in hydraulic systems with higher pressure range up to 5000 psi.
The main advantage of this type of pumps can achieve high power density i.e. power per unit weight using hydraulic power. Additionally they can have infinite pressures to move fluids with static displacement per revolution and within mechanical boundaries.
Reciprocating Pumps: These type of pumps use intake stroke by piston for suction of liquid into the cylinder through suction valves and discharged under positive pressure from outlet valve during its discharge stroke.
The discharge from a reciprocating pump is pulsating and changes only when the speed of the pump is changed. This is because the intake is always a constant volume.
Metering Pumps: These type of pumps are used where precision control of very low flow rates are required. Flow rates are normally less than 1/2 gallon per minute. They are usually used to regulate additives to the main flow stream. Based on its function these are also called controlled-volume pumps or proportioning pumps.
Metering pumps are designed for clean service using diaphragm or packed plunger style as dirty liquid can easily block the valves and nozzle connections.
Rotary Pumps: A rotary pump traps fluid in its closed casing and discharges a smooth flow. These type of pumps are used to handle almost any fluid or liquid including viscous liquids, that does not contain solid, hard and abrasive entities. They are also simple in design and efficient in handling flow conditions that are usually considered to low for economic application of centrifuges.
Dynamic Pumps: Dynamic pumps are unique category of pumps under which there are multiple classes, which includes: centrifugal and axial.
Dynamic pumps operating principle is todevelop a high fluid velocity and converting the high velocity to pressure in a diffusing flow opening.
Dynamic pumps usually have cons over lower efficiencies than positive displacement pumps, but having pros as lower maintenance requirements.
However dynamic pumps are also able to operate at equally high speeds and with high fluid flow rates.
Centrifugal Pumps: A centrifugal pump involves of an impeller and an inlet or suction of pump is at its centre. These are organisedsuch that when the impeller take turns, liquid is discharged by centrifugal force into a casing surrounding the impeller.
Velocity of fluid is gradually reduced inside the casing which leaves the impeller. And subsequent velocity is converted to pressure, further which is used to discharge the fluid or liquid from the pump.
Some of the benefits of centrifugal pumps are,
- Smooth flow through the pump.
- Uniform pressure in the discharge pipe.
- Low cost
- An operating speed that allows for direct connection to steam turbines and electric motors.
Most of the worlds pump production, centrifugal pumps are produced or designed choice more than 80% of pumps, considering its suitability for handling large bulks of liquids than the positive-displacement pump.
Centrifugal Pump for Petroleum, Petrochemical and Natural Gas industries follows ANSI/API STANDARD 610 and Identical ISO 13709 – 2009.
Pump Standards include API 610, API 685, ISO5199 / 2858, ASME / ANSI B73.1 & B73.2, API 674, API 682, API 671
Axial Flow Pumps: Another name for Axial flow pumps are propeller pump. Working principle of axial flow pumps is by propelling or lifting action of vanes on the fluid or liquid, which develops pressure.
These pumps are mostly used in wet-pit drainage, low-pressure irrigation, as well as storm-water applications.
Generally, these pumps are used in single or even multi stages. Single stage is vertical single-stage axial and mixed-flow pumps are used on the other hand, sometimes considering economy two-stage axial-flow pumps are preferred.
Horizontal axial-flow pumps are used for pumping large volumes against low pressures and usually employ siphoned action.
For high pressure use, these pumps can be arranged to operate siphoned action, unless the back pressure at upstream of siphon with hydraulic gradient above the pump.
A turbine pump is a type of centrifugal pump and mainly used to pump water from bore wells or deep wells or other underground and man-made frames of water for water distribution.
Same as a centrifugal pump consists of a pump shaft, a revolving device as an impeller, and a motor or an engine.
Unlike other pumps, these pumps also having stages and consist of multiple semi-open or enclosed impellers.A metal plate named shroud supports, the vanes of the impeller in an open or semi-open impeller, however in an enclosed impeller, the shroud encloses the impeller vanes. The pump also has a water intake point and a water discharge point.
In this type of pumps, motor is usually placed above the water level, whereas submersible type of pumps are used based on the application or requirements.
Total head is the total energyreserved by the pump to move water from the supply — i.e., the supply tank or reservoir to the point of discharge. Powerful pumps can exceed or having high head around several hundred feet or over 70 meters.
On operation, water enters the centre of the rotating impeller, which is known as the “eye” of the impeller.
Steel rod which transfers power from motor or rotary engine to impeller is called pump shaft.
Further, water is augmented and pushed out alongside the vanes of one impeller to the next if any, and finally to discharge the pump.
In this manner, electric power is transformed to mechanical energy, leading the water to flow under a specific pressure. As a result of this mechanism, more water enters the pump from the water source.
Industrial fans and blowers
These also classified as a Mechanical Engineering Rotary equipment. Primary function of industrial fans and blowers are to provide anoutsized flow of air or gas to various processes of various industries.
This is attained by revolving a number of blades, connected to a hub and shaft, and compelled by a motor or turbine.
The flow rates of these fans range from approximately 200 to 2,000,000 cubic feet (5.7 to 57000 cubic meters) per minute.
Another name of fan is called as a blower that operates where the resistance to the flow is primarily on the downstream side of the fan.
There are various uses or application for continuous flow of air or gas which fans or blowers generate including exhaust, combustion, ventilation, aeration, particulate transport, cooling, air-cleaning, and drying etc.
The industries where these are used include electrical power stations, pollution controls, metal manufacturing and processing, cement production, mining, oil & gas or petrochemical, food processing, cryogenics, and clean rooms.