Question Set 118

• What is the difference between machine and engine?

Engine converts heat energy to Mechanical Energy but machine converts all forms of energy to mechanical energy except heat energy.

• What is viscosity? What is newton’s law of viscosity?

Viscosity/Dynamic viscosity:

· Viscosity is the physical property that characterizes the flow resistance of simple fluids.

· Viscosity is the property of a fluid by virtue of its offers resistance to the movement of one layer of fluid over an adjacent layer.

Newton’s Law of Viscosity:

Newton’s viscosity law’s states that, the shear stress between adjacent fluid layers is proportional to the velocity gradients between the two layers.

The ratio of shear stress to shear rate is a constant, for a given temperature and pressure, and is defined as the viscosity or coefficient of viscosity.

• What are Newtonian and non-Newtonian fluids ?
  
  

Newtonian Fluid:

A fluid, whose viscosity does not change with the rate of deformation or shear stain (V/Y), is called Newtonian fluid.

A fluid which obeys Newton’s law of viscosity is termed as Newtonian fluid.

Non-Newtonian Fluid:

A fluid, whose viscosity changes with the rate of deformation or shear stain (V/Y), is called Non-Newtonian fluid.

A fluid which does not obey Newton’s law of viscosity is termed as Non-Newtonian fluid.

• What is Pump? What is turbine? / What is the difference between turbine and pump?

Pump is a device which transfers mechanical energy to fluid. Turbine does the opposite. It transfers flow energy of the fluid to the mechanical energy.

• What are turbo machines?

Turbo machines are devices which transfer energy to or from the fluid by the dynamic action of rotating blades.

• How the characteristics of a flow is determined?

By Reynolds Number .

If Re <2300 then the flow is laminar .

if 2300 <Re<4000 then the flow is transient and

if Re>4000 then the flow is turbulent .

• What is Reynolds number ?

Reynolds Number is the ratio of inertia force to viscous force . Re = ρvL/μ

• What is the difference between centrifugal pump and positive displacement pump?

In Centrifugal pump the flow rate changes with the head but in positive displacement pump the flow rate remains the same.

• What is cavitation in centrifugal pump? Why priming is done in centrifugal pump?

If the suction side develops a pressure less than the vapor pressure of the water then water will start to boil and create water bubbles and it will spoil the impeller material. It is called cavitation.

When impeller rotates it adds a rotating motion to the adjacent fluid and as a result K.E and Pressure in the fluid increases and a negative pressure is developed in the suction side of the impeller . So water/fluid flows continuously through the impeller. But when the pipe is filled with air , the impeller rotates but the pressure difference is negligible as a result no water flows through the pump. Thats why priming is done.

• What is the difference between heat engine & heat pump?

Heat Engine produces work and transfers energy from high temp. to low temp source medium. In Heat pump external work is needed to transfer energy from low to high temp. medium.