mechanical engineering

Comparison Between Reciprocating and Rotary Compressors Comparison between Reciprocating and Rotary Compressors can be done in aspects like pressure ratio, handled volume, speed of compressor, vibrational problem, size, air supply, purity of compressed air, compression efficiency, maintenance, mechanical efficiency, lubrication, initial cost, flexibility and suitability. S.no Aspect Reciprocating Compressors Rotary Compressors 1 Pressure Ratio Discharge Pressure of air is high. The pressure ratio per stage will be in the order of 4 to 7. Discharge pressure of air is low. The pressure ratio per stage will be in the order of 3 to 5. 2 Handled Volume Quantity of air handled is low and is limited to 50m 3 /s. Large measure of air handled can be handled and it is about 500 m 3 /s. 3 Speed of Compressor Low speed of compressor. High speed of compressor. 4 Vibrational Problem Due to reciprocating section, greater vibrational problem, the parts of machine are poorly bal

Centrifugal Pump Efficiency The performance of a centrifugal pump can be known by finding the following efficiencies: Mechanical efficiency Hydraulic efficiency Volumetric efficiency Overall efficiency 1. Mechanical efficiency of a centrifugal pump (η m ): Mechanical efficiency of a centrifugal pump (η m ) is the ratio of theoretical power that must be supplied to operate the pump to the actual power delivered to the pump. Mechanical efficiency can be used to determine the power loss in bearings and other moving parts of a centrifugal pump. It determines the actual power that must be supplied to a centrifugal pump for desired result. 2. Hydraulic efficiency of a centrifugal pump (η H ): Hydraulic efficiency of a centrifugal pump (η H ) is defined as the ratio of the useful hydrodynamic energy in fluid to Mechanical energy supplied to rotor. 3. Volumetric efficiency of a centrifugal pump (η v ): Volumetric efficiency of a centrifugal pump (η v ) is define

Comparison between Impulse Turbine and Reaction Turbine Impulse and reaction turbine are compared below presented in picture and tabular form. Schematic diagram summarising the differences between impulse turbine and reaction turbine, where the rotor is the rotating part and the stator is the stationary part of the machine. Image source:  Emoscopes (Wikimedia Commons) Differences between Impulse and Reaction Turbines: S.No Impulse Turbine Reaction Turbine 1 In impulse turbine all hydraulic energy is converted into kinetic energy by a nozzle and it is is the jet so produced which strikes the runner blades. In reaction turbine only some amount of the available energy is converted into kinetic energy before the fluid enters the runner. 2 The velocity of jet which changes, the pressure throughout remaining atmosphere. Both pressure and velocity changes as fluid passes through a runner. Pressure at inlet is much higher than at outlet. 3 Water-tight casing is not

Hydraulic Turbines: Introduction and Classification Hydraulic turbines are Machines which convert hydraulic energy in to mechanical energy. Uses the  potential energy and  kinetic energy  of water and rotate the rotor by dynamic action of water. Classification of Hydraulic turbines: 1) Based on type of energy at inlet to the turbine: Impulse Turbine  : The energy is in the form of kinetic form. e.g: Pelton wheel, Turbo wheel. Reaction Turbine  : The energy is in both Kinetic and Pressure form. e.g: Tubular, Bulb, Propellar, Francis turbine. 2) Based on direction of flow of water through the runner: Tangential flow:  water flows in a direction tangential to path of rotational, i.e. Perpendicular to both axial and radial directions. Radial outward flow  e.g : Forneyron turbine. Axial flow :  Water flows parallel to the axis of the turbine. e.g: Girard, Jonval, Kalpan turbine. Mixed flow :  Water enters radially at outer periphery and leaves axially. e.g : Moder

Comparison Between Reciprocating and Centrifugal Compressors Comparison between reciprocating and  centrifugal compressors  can done in aspects like mechanical efficiency, cost, noise, pressure ratio, multi stage possibility, volume handled, maintenance required or not, weight of compressor, operation speed, isentropic efficiency, higher compression efficiency condition and suitable operation conditions. S.no Reciprocating Compressors Centrifugal Compressors 1 Reciprocating compressors have poor mechanical efficiency due to large sliding parts. Centrifugal compressors have better mechanical efficiency due to absence of sliding parts. 2 Installation cost for setting up reciprocating compressors is higher. Installation cost for setting up centrifugal compressors is lower. 3 Reciprocating compressors produce greater noise and vibrations. Centrifugal compressors have comparatively salient operation. 4 Pressure ratio up to 5 to 8. Pressure ratio up to 4. 5 Higher pres

Differences Between Centrifugal and Axial Flow Compressors Comparison between  centrifugal compressor  and axial flow compressors can be done in aspects like air flow direction, maintenance cost, torque requirement, multi staging suitable or not, pressure ratios conditions, frontal area, isentropic efficiency and performance at part load. S.no Centrifugal Compressors Axial Flow Compressors 1 In centrifugal compressors air flows radially in the compressor In Axial flow compressors air flows parallel to the axis of shaft 2 Low maintenance and running cost High maintenance and running cost 3 Low starting torque is required Requires high starting torque 4 Not suitable for multi staging Suitable for multi staging 5 Suitable for low pressure ratios up to 4 Suitable for only multi staging ratio of 10 6 For given mass flow rate, it requires a larger frontal area. For a given mass flow rate, it requires less Frontal area. 7 Isentropic efficiency is 80 to 82% Isentropic

Comparison of Electrical, Hydraulic and Pneumatic Systems Comparison of electrical, hydraulic and pneumatic systems can be done in aspects like energy source, energy storage, energy cost, distribution system, linear actuators, rotary actuators and controllable force. S.no Aspect Electrical Hydraulic Pneumatic 1 Energy source Usually from outside supplier Electric motor or diesel driven Electric motor or diesel driven 2 Energy storage Limited (batteries) Limited (accumulator) Good (reservoir) 3 Distribution system Excellent, with minimal loss Limited basically a local facility Good. Can be treated as a plant wide service  4 Energy cost Low cost Moderate cost High cost 5 Linear actuators Short motion via solenoid. Otherwise via mechanical conversion Cylinders. Very high force Cylinders. Medium force 6 Rotary actuators AC and DC motors. Good control on DC motors. AC motors cheap Low speed. Good control. Can be stalled Wide spread range. Accurate speed control dif