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Note for Turbo Machines - TM by Kamal Raj

  • Turbo Machines - TM
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1. Principals of Turbo machines, D. G. Shepherd, The Macmillan Company (1964). 2. Fluid Mechanics & Thermodynamics of Turbo machines, S. L. Dixon, Elsevier (2005). 3. Turbo machine, B.K.Venkanna PHI, New Delhi 2009. 4. Text Book of Turbo machines, M. S. Govindgouda and A. M. Nagaraj, M. M. Publications, 4Th Ed, 2008. MODULE: 1 INTRODUCTION Definition of a Turbo machine A turbo machine is a device in which energy transfer occurs between a flowing fluid and rotating element due to dynamic action. This results in change of pressure and momentum of the fluid. Parts of a turbo machine Fig: 1.1. Schematic cross-sectional view of a turbine showing the principal parts of the turbomachine. The principle components of a turbo machine are: 1. Rotating element (vane, impeller or blades)– operating in a stream of fluid. 2. Stationary elements – which usually guide the fluid in proper direction for efficient energy conversion process. 3. Shaft – This either gives input power or takes output power from fluid under dynamic conditions and runs at required speed. 4. Housing – to keep various rotating, stationery and other passages safely under dynamic conditions of the flowing fluid. E.g. Steam turbine parts and Pelton turbine parts. Classification of turbo machines 1. Based on energy transfer a) Energy is given by fluid to the rotor - Power generating turbo machine E.g. Turbines b) Energy given by the rotor to the fluid – Power absorbing turbo machineE.g. Pumps, blowers and compressors 2. Based on fluid flowing in turbo machine

Text from page-3

a) Water b) Air c) Steam d) Hot gases e) Liquids like petrol etc. 3. Based on direction of flow through the impeller or vanes or blades, with reference to the axis of shaft rotation a) Axial flow – Axial pump, compressor or turbine b) Mixed flow – Mixed flow pump, Francis turbine c) Radial flow – Centrifugal pump or compressor d) Tangential flow – Pelton water turbine 4. Based on condition of fluid in turbo machine a) Impulse type (constant pressure) E.g. Pelton water turbine b) Reaction type (variable pressure) E.g. Francis reaction turbines 5. Based on position of rotating shaft a) Horizontal shaft – Steam turbines b) Vertical shaft – Kaplan water turbines c) Inclined shaft – Modern bulb micro Comparison between positive displacement machines andTurbo machines Comparison between positive displacement machines andTurbo machines Turbo machines It creates Thermodynamic & Dynamic action b/w rotating element & flowing fluid, energy transfer takes place if pressure and momentum changes It involves a steady flow of fluid & rotating motion of mechanical element They operate at high rotational speed Change of phase during fluid flow causes serious problems in turbomachine Efficiency is usually less It is simple in design Due to rotary motion vibration problems are less E.g. Hydraulic turbines, Gas turbines, Steam turbines etc. Positive displacement machines It creates Thermodynamic &Mechanical action b/w moving member&static fluid, energy transfer takes place with displacement of fluid It involves a unsteady flow of fluid & reciprocating motion They operate at low speed Change of phase during fluid flow causes less problems in Positive displacement machines Efficiency is higher It is complex in design Due to reciprocating motion vibration problems are more E.g. I.C engines, Reciprocating air compressor, pumps etc. Effect of Reynolds Number Just like flow in pipes with friction, with decreasing Reynolds number, the loss factor increases at first slowly, thenmore and more rapidly in Turbo machines.

Text from page-4

The majority of ordinary turbo machines, (handling water, air, steam or gas) are found to operate in fully rough region. The critical Reynolds number, at which the flow becomes fully rough, varies with the size of the machine (it dependson relative roughness) and its exact location for a given machine is difficult to predict. The understanding of boundary layer and its separation is of importance in losseffects. The graph shows the loss factor in head and efficiency of a moderate size centrifugal pump Unit Quantities Unit quantities are unit flow, unit power and unit speed which are under considerations of unit meter in connection with hydraulic turbines. In other words, the unit quantities are defined for the head of 1m.

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