Centrifugal Compressor Question Answers Mechanical Engineering
Q.1) What is mean by power absorbing devices?
Power Absorbing Devices PUMPS The normal duty of the pump is to lift liquid from low level to high level and/or to transfer it from one place to another. o It can be defined as a device that converts the mechanical energy of a motor into hydraulic energy (Pressure + kinetic).
Q.2) What is a centrifugal compressor?
Centrifugal compressors increase the kinetic energy of the gas with a high-speed impeller and then convert this energy into increased pressure in a divergent outlet passage called the diffuser. Centrifugal compressors are particularly suited for compressing large volumes of gas to moderate pressures.
Q.3) Give the advantages and applications of centrifugal pumps.
The biggest advantage of centrifugal pumps is their aforementioned simplicity. They don't require any valves or many moving parts. This makes them easy to produce with many different materials. It also allows them to move at high speeds with minimal maintenance.
Early applications include the use of the windmill or watermill to pump water. Today, the pump is used for irrigation, water supply, gasoline supply, air conditioning systems, refrigeration (usually called a compressor), chemical movement, sewage movement, flood control, marine services, etc.
Q.4) Give the classification of rotary compressors.
The rotary compressors are classified into screw type, vane type-lobe type, scroll type, and other types. The screw compressors are efficient in low air pressure requirements. The compressed air delivery is continuous and quiet in operation than a reciprocating compressor.
Q.5) Draw centrifugal compressor and elements of the centrifugal stage.
Centrifugal compressors, sometimes called radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery
Q.6) Discuss the component of the impeller.
An impeller is a rotating component in a centrifugal pump that is equipped with vanes or blades that rotate and moves the fluid in a pump. These vanes or blades are coupled to a shaft. In the axial impeller, fluid moves axially to the shaft. In radial flow impeller, fluid moves perpendicularly to the shaft.
Q.7) Discuss the diffuser of the centrifugal compressor.
The diffuser is an important element of a compressor or pump. Its purpose is to reduce the velocity of the flow leaving the impeller resulting in an increase in pressure. The diffuser can be simply depicted as a nonrotating channel whose flow area increases in the direction of flow.
Q.8) Define slip factor.
The slip factor is a measure of the fluid slip in the impeller of a compressor or a turbine, mostly a centrifugal machine. Fluid slip is the deviation in the angle at which the fluid leaves the impeller from the impeller's blade/vane angle. Being quite small in axial impellers(inlet and outlet flow in the same direction), slip is a very important phenomenon in radial impellers and is useful in determining the accurate estimation of work input or the energy transfer between the impeller and the fluid, rise in pressure and the velocity triangles at the impeller exit.
Q.9) Define work factors.
In general, the work factor is a quantitative system of measurement that gives valuable insights to complex information which is uniquely held as national security information. In cryptography, a work factor is defined as the amount of effort required to break down a cryptosystem.
Q.10) Define pressure coefficient.
A pressure coefficient is a dimensionless number that describes the relative pressures throughout a flow field in fluid dynamics. The pressure coefficient is used in aerodynamics and hydrodynamics. Every point in a fluid flow field has its own unique pressure coefficient.
Q.11) Define prewhirl.
In this study, prewhirl is introduced to alleviate the compressibility effect at the convex side of the eye to avoid the formation of shock waves and the consequent losses. However, this caused a reduction of work-absorbing capacity W and pressure ratio R.
Q.12) Explain the surging and chocking of the centrifugal compressor.
Surge is a violent flow reversal that occurs when the process restricts the compressor flow below a certain minimum value. Choke occurs when the process does not create enough restriction to the compressor flow and the compressor operates at its maximum flow for a given performance level.
Q.13) Difference between fan and blower.
The main differences between Fan and Blower are The fan is used to flow gas or air, in open space whereas The blower is mostly used to flow gas in a specific direction.
Q.14) Explain vaneless and vanes diffuser.
Vaneless diffusers have a wider flow range but lower pressure recovery and efficiency, whereas vaned diffusers have higher pressure recovery and efficiency, but a narrower flow range. The diffuser is usually followed by a volute or a collecting chamber which leads the flow to one single exit.
Q.15) Why centrifugal compressors are not suitable for aircraft applications?
Centrifugal compressors are impractical, compared to axial compressors, for use in large gas turbines and turbojet engines propelling large aircraft, due to the resulting weight and stress, and to the frontal area presented by the large diameter of the radial diffuser.
Q.16) Explain the construction and working of the axial flow compressor.
Axial Flow Compressor - In these compressors, the flow of air is in the axial direction. It consists of alternately placed rows of stator blades and rotor blades. The rotor blades are mounted on the rotor while the stator blades are attached to the casing.
Q.17) Differentiate between turbine and compressor blades.
Turbine blades have large camber (so that the flow can be deflected a lot to extract much work), whereas compressor blades have little camber because otherwise, the boundary layer would separate.
Q.18) Define the degree of reaction.
The degree of reaction or reaction ratio is defined as the ratio of the static pressure drop in the rotor to the static pressure drop in the stage or as the ratio of static enthalpy drop in the rotor to the static enthalpy drop in the stage.
Q.19) Define flow coefficient.
The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an orifice valve or other assembly and the corresponding flow rate.
Q.20) What is the blade loading coefficient?
Blade loading is the single most important aerodynamic design parameter in turbomachinery blades, it defines both the amount of work made or extracted, by the blade and the distribution of such work from hub to tip/shroud
Q.21) What are the materials used for the compressor?
With a piston air compressor, the type of material involved refers to the metal used in the pump or shaft that surrounds the piston. These compressors are typically constructed of one of two materials – cast iron or aluminum.
Q.22) Differentiate between centrifugal and axial flow compressor.
A typical axial compressor consists of a drum, to which blades of specific geometry are attached. Contrary to centrifugal compressors, axial flow compressors do not change the direction of the gas: the gas typically enters and exits the compressor in an axial direction (parallel to the axis of rotation).
The centrifugal is short and of large diameter and the airflow through the compressor is turned from the axial direction to the radial and then back to the axial. On the other hand, the axial compressor derives its name from the substantially unidirectional flow of the air.
An axial fan is one in which the extracted air is forced to move parallel to the shaft about which the blades rotate. Centrifugal fans extract air at right angles to the intake of the fan and spin the air outwards to the outlet by deflection and centrifugal force.