Engineering in Kenya

# What is a fluid machine for Fluid Mechanics in Mechanical Engineering?

Posted by on Feb 2, 2018 in Mechanical Engineering | 0 comments

A fluid machine  for Fluid Mechanics in Mechanical Engineering is a device that converts the energy stored by a fluid in to mechanical energy or work. The machine functioning in Fluid Mechanics in Mechanical Engineering depends on the change of volume of the amount of fluid within the machine or a certain amount of it. There is a physical displacement of the boundary of the certain amount of fluid hence it is called a positive displacement machine in Fluid Mechanics in Mechanical Engineering. Engineering in Kenya has more articles.

Fluid Mechanics in Mechanical Engineering

# Other Definitions in Fluid Mechanics in Mechanical Engineering

Fluid machines are classified based on fluid flow direction, there are three types of machines  used in Fluid Mechanics in Mechanical Engineering ;

• Radial flow machines  where the main direction of flow is perpendicular to the axis of the machine  that is  in radial direction.
• Axial flow machines where the direction of flow is parallel to the axis of the machine.
• Mixed flow machines   where the fluid direction in is perpendicular and the fluid direction out is axial, or vice versa.
• A turbine in Fluid Mechanics in Mechanical Engineering is a machine that converts the mechanical energy of a running fluid into energy which can then be utilized in running a generator for power plant.
• The difference between reaction and impulse turbines is as follows
• If the frontal of the turbine possesses both pressure energy and kinetic energy, then the turbine is a reaction turbine. If the energy available is only kinetic energy, then the turbine is an impulse turbine in Fluid Mechanics in Mechanical Engineering.

A radial flow reaction turbine has four partsmainly;

• Casing
• Guide vane
• Runner
• Draft tube.

The purpose of the guide vane mentioned in Fluid Mechanics in Mechanical Engineering is to convert a part of the pressure energy of the fluid at the entrance to kinetic energy and then direct the fluid on the number of blades.

• The draft tube mentioned in Fluid Mechanics in Mechanical Engineering is a conduit pipe which connects the runner exit to the trail race, when the fluid is being finally discharged from the turbine. The draft tube is mostly used in the reaction turbine. The primary function of a draft tube is to reduce the velocity of the discharged fluid to minimize loss of kinetic energy in Fluid Mechanics in Mechanical Engineering.

## Complex Definitions in Fluid Mechanics in Mechanical Engineering

What are Homologous units?

• When using scale models in designing turbo machines, geometric similarity in the units used is vital as well as geometric similarity in the velocity diagrams at the entrance and the exit from the impellers. Two geometrically similar units which have similar vector diagrams are known as homologous units.

Define specific speed.

• Specific speed (Ns) of a turbine in Fluid Mechanics in Mechanical Engineering is defined as the speed of some unit of series of a certain size that it produces unit power with a unit head. This definition is based on power. Based on discharge, the specific speed of a pump is defined as the speed of a certain unit of series of such size that it delivers a unit discharge and at unit speed in Fluid Mechanics in Mechanical Engineering.

Specific speed has its own relevance. Based on power, specific speed is inversely proportional to a head across the machine. Therefore, high specific speed corresponds to low head across it and vice versa. Based on discharge, specific speed is directly proportional to discharge through the pump/ power produced by the machine. Therefore, high specific speed corresponds to high discharge/ high power produced by the machine and vice versa.

There are three major forms of turbines in Fluid Mechanics in Mechanical Engineering;

• Low head turbine e.g. Kaplan turbine
• Medium head turbine e.g. Francis turbine
• High head turbine e.g. Pelton wheel.

What is a positive displacement pump?

• A positive displacement pump is one that pushes the fluid physically from an enclosed space. The positive displacement pumps can be either the rotary type or reciprocating type. The reciprocating pump is well suited for relatively low capacities and high heads. It has a cylinder, suction valve, piston, delivery pipe, suction pipe, connecting rod mechanism and a crank shaft as its main components in Fluid Mechanics in Mechanical Engineering.

Give the difference between single acting and double acting reciprocating pumps.

A single acting pump has one delivery valve and one suction valve. On the reverse stroke of the piston, the suction valve opens and fluid gets into the cylinder space. On the opposite stroke, the suction valve closes and now delivery valve opens. The fluid is forced through the delivery pipe.

A double acting pump has two delivery valves and two suction valves, one in the front and one at the rear. On the reverse stroke, the suction valve at the front opens and delivery valve at the rear opens and fluid is forced through it. When the piston moves forward, the suction valve at the rear opens and delivery valve at the front opens and fluid is forced through it.

What is an indicator diagram of a reciprocating pump?

An indicator diagram of a reciprocating pump in Fluid Mechanics in Mechanical Engineering is the diagram which shows a pressure head in the cylinder corresponding to any position during the reverse/ suction and forward/ delivery strokes.

### Conclusion on Fluid Mechanics in Mechanical Engineering

What is an air vessel?

An air vessel is an enclosed chamber connected on the suction or delivery or both sides of the reciprocating pump to obtain a more laminar flow in Fluid Mechanics in Mechanical Engineering.

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