Shaft Power Generation Devices - 2

P M V SubbaraoProfessorMechanical Engineering Department

A List of Artificial Animals for Human Development !!!!

Control Mass based Power Generation Systems

• Found to be best choice for vehicular applications.

• Otto cycle is best suited for light and high speed applications.

• Diesel cycle is for high torque and low load applications.

• Not found to be good choice for electricity generation.

• Reciprocating systems are not reliable for continuous working.

• Rotating machines (control volumes) are best suitable for continuous working.

Rankine & Brayton Cycles

Process 1 2 Isentropic compressionProcess 2 3 Constant pressure heat additionProcess 3 4 Isentropic expansionProcess 4 1 Constant Pressure heat rejection

p=constant

p=constant

Schematic of Rankine & Brayton cycles

First Law Analysis of Cycle

WQ

vdpmTdsm

4123 hhhhmW net

2143 hhhhmW net

additionHeat of Rate

outputPower Net cycle theof Efficiency

23

2143

hhm

hhhhm

in

net

Q

W

23

141hh

hh

2143output Work Specific hhhh

Performance Analysis

Variation of Brayton Cycle

Complete Expansion in turbine:

Partial Expansion in turbine to create High Velocity Jet:

Air Standard Brayton Cycle for Power Plant

23

141hh

hh

1

1

212

p

pTT

Design parameter:

1

2 :Ratio Pressurep

prp

1

12

prTT

1

43

prTT

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30

th

pr

Pressure Ratio Vs Efficiency

netw

pr

Pressure Ratio Vs Specific Work output

Fuel  Natural gas

 Frequency  60 Hz

 Gross Electrical output  187.7 MW*

 Gross Electrical efficiency  36.9 %

 Gross Heat rate  9251 Btu/kWh 

 Turbine speed  3600 rpm

 Compressor pressure ratio  32:1

 Exhaust gas flow  445 kg/s

 Exhaust gas temperature  612 °C

 NOx emissions (corr. to 15% O2,dry)  < 25 vppm

GT24 (ISO 2314 : 1989)

Fuel  Natural gas

 Frequency  60 Hz

 Gross Electrical output  187.7 MW*

 Gross Electrical efficiency  36.9 %

 Gross Heat rate  9251 Btu/kWh 

 Turbine speed  3600 rpm

 Compressor pressure ratio  32:1

 Exhaust gas flow  445 kg/s

 Exhaust gas temperature  612 °C

 NOx emissions (corr. to 15% O2,dry)  < 25 vppm

9756 kJ/kWh

Analysis of Siemens Gas Turbine Power Plant

• The rated net Power output = 152 MW • Net (Irreversible) efficiency of 36.1%.

• The pressure ratio (rp) is 16:1.

• The turbine entry temperature is 12900C.• Actual(Irreversible) exhaust temperature is 550 C.

Rankine Cycle for Low Cost Power Generation

Simple Rankine cycle

23

141hh

hh

2143output, Work Specific hhhhw

Rankine Cycle for Nuclear Power Plant

Rankine Cycle for Geothermal Power Plant

Ranking Cycle for Solar Thermal Power Plant

Ranking Cycle for Biomass Thermal Power Plant

Selection of Fluids : Thermodynamics

• The selection of working fluids and operational variables is very important to obtain better system performance.

• The thermodynamic properties of working fluids will affect the system efficiency, operation, and environmental impact.

• Fluid must be selected in accordance to the temperature level of the heat source.

• Minimum temperature difference between the source and working fluid during heat addition (pinch point) is limiting factor for heat transfer

Candidate Working Substances for Rankine Cycle

Working Substances must be selectedin accordance to the heat sourcetemperature level (Tcr < Tin-source)

Selection of Fluids : Ecology

• Environmental impacts and restrictions by using organic substances

• Inflamable and/or toxic and/or GWP (Global Warming Potential) and/or ODP

• (Ozone Depletion Potential)

Optimal Design of Vapour Power Plant

pmax=10MPa

The Regenerative Cycle

T

1

2

4

5

3

s

3

4

Regeneration Through Closed Feed Water Heater (Throttled Condensate)

Thermodynamic Analysis of A Power Plant

More Cycles for Exotic Needs of Urban World …….

An Urban world that was present till the end of first decade of the 20th century.

• Only fresh foods that could be grown locally were available, and they had to be purchased and used on a daily basis.

• Meat was bought during the daily trip to the butcher's; the milkman made his rounds every morning.

• If you could afford weekly deliveries of ice blocks—harvested in the winter from frozen northern lakes—you could keep some perishable foods around for 2 or 3 days in an icebox.

• New York was a virtual ghost town in the summer months.

• Homes were built with natural cooling in mind.

• Ceilings were high, porches were deep and shaded, and windows were placed to take every possible advantage of cross-ventilation

The Necessity (mother) Delivered a Dangerous Baby

• Three American corporations launched collaborative research to develop a less dangerous method of refrigeration; their efforts lead to the discovery of Freon.

• In just a few years, compressor refrigerators using Freon would became the standard for almost all home kitchens.

• Only decades later, would people realize that these chlorofluorocarbons endangered the ozone layer of the entire planet

Urban Life after the end of first decade of the 21st century.

• Fresh foods of all kinds were available just about anywhere in the country all year round.

• The milkman was all but gone and forgotten, and the butcher now did his work behind a counter at the supermarket.

• Indeed, many families concentrated the entire week's food shopping into one trip to the market, stocking the refrigerator with perishables that would last a week or more.

• New York is a busy town in the summer months.• Buildings are totally isolated from fresh air.

Creation of Artificial Temperature/Quality

Performance Index

The performance of refrigerators and heat pumps is expressed in terms of coefficient of performance (COP), defined as

COPQ

W

COPQ

W

RL

net in

HPH

net in

Desired output

Required input

Cooling effect

Work input

Desired output

Required input

Heating effect

Work input

,

,Under the same operating conditions, the COPs are related by

COP COPHP R 1

Why not use the reversed Rankine cycle for Refrigeration ?

• Very costly to expand the liquid using a turbine with very low or negligible power output!?!

• May become negative under irreversible conditions.

• Cheaper to have irreversible expansion through an expansion valve.

Thermodynamics of Ideal VCR Cycle

• Ideal Vapor-Compression Refrigeration Cycle

• Process Description

• 1-2 Isentropic compression

• 2-3 Constant pressure heat rejection in the condenser

• 3-4 Throttling in an expansion valve

• 4-1 Constant pressure heat addition in the evaporator

The P-h diagram is another convenient diagram often used to illustrate the refrigeration cycle.

Samsung Split A/c Model No : AQ24UUA

Cooling Capacity : 7.03kW

Power Consumption (Cooling) : 2,600Watts

Refrigerant Type R22

The refrigerant leaves the evaporator at 7.2oC Condenser pressure : 2.71 MPa.

Heat Pump Systems

•The gas power cycle can be used as refrigeration cycles by simply reversing them. •Of these, the reversed Brayton cycle, which is also known as the gas refrigeration cycle, is used to cool aircraft. • Further Modification this cycle is used to obtain very low (cryogenic) temperatures. •The work output of the turbine can be used to reduce the work input requirements to the compressor. •Thus, the COP of a gas refrigeration cycle is

COPq

w

q

w wRL

net in

L

comp in turb out

, , ,

Gas Refrigeration Systems

Air Standard Refrigeration Cycle for Aircraft Cooling

1

Air Craft Engine Bleed for Refrigeration System

Air Craft Engine Refrigeration System

Air to Cabin

Absorption Refrigeration Systems

Compression to Absorption Refrigeration Systems

Thermoelectric Refrigeration Systems A refrigeration effect can also be achieved without using any moving parts by simply passing current through a closed circuit made up of two dissimilar materials.

This effect is called the Peltier effect, and a refrigerator that works on this principle is called a thermoelectric refrigerator.