ENERGY CONVERSION
EFFICIENCY
BY ENGR JTM
At the end of the lesson, the students should have:
• Explained where energy is "lost" in conversions.
• Computed the efficiency of an energy conversion
given input and output.
• Identified system by-products and explained how
they can be used effectively to increase overall
system efficiency.
• The first law of thermodynamics states that energy
can be neither created nor destroyed during a
process; it can only change forms.
ENERGY BALANCE
• The net change (increase or decrease) in the total
energy of the system during a process is equal to the
difference between the total energy entering and the
total energy leaving the system during that process.
• It indicates how well an energy conversion or transfer
process is accomplished.
EFFICIENCY OF WATER HEATER
• The ratio of the energy
delivered to the house
by hot water to the
energy supplied to the
water heater
Source: The McGrawHill Companies,
Inc./Christopher
Kerrigan,
photographer
HEATING VALUE OF FUEL
• The amount of heat
released when a unit
amount of fuel at room
temperature is
completely burned and
the combustion
products are cooled to
the room temperature
COMBUSTION EFFICIENCY
ANNUAL FUEL UTILIZATION
EFFICIENCY
• The efficiency of space heating systems of residential and
commercial buildings is usually expressed in terms of the
annual fuel utilization efficiency, or AFUE, which accounts
for the combustion efficiency as well as other losses such
as heat losses to unheated areas and start-up and cooldown losses.
GENERATOR EFFICIENCY
• The effectiveness which
is the ratio of the
electrical power output
to the mechanical
power input.
Source:
https://www.maderelectricinc.com/blog/
7-signs-your-generator-needs-repairs
EFFICIENCY OF A POWER PLANT
• The ratio of the net
shaft work output of
the turbine to the heat
input to the working
fluid.
• The effects of other factors
are incorporated by defining
an overall efficiency for the
power plant as the ratio of the
net electrical power output to
the rate of fuel energy input.
• The ratio of the energy converted to light to the
electrical energy consumed.
• More common to express the effectiveness of this
conversion process by lighting efficacy which is
defined as the amount of light output in lumens per
W of electricity consumed.
Source: https://justenergy.com/blog/types-light-bulbshistory-buying-guide/
EFFICIENCY OF FLUID SYSTEMS
• The degree of perfection of the conversion process
between the mechanical work supplied or extracted
and the mechanical energy of the fluid is expressed
by the pump efficiency and turbine efficiency
EFFICIENCY OF FLUID SYSTEMS
is the rate of decrease in the mechanical energy
of the fluid, which is equivalent to the
mechanical power extracted from the fluid by
the turbine Wturbine,e, and we use the absolute
value sign to avoid negative values for
efficiencies.
Electric power is to be generated by
installing a hydraulic Turbine–generator
at a site 70 m below the free surface of
a large water reservoir that can
supply water at a rate of 1500 kg/s
steadily . If the mechanical power output
of the turbine is 800 kW and the electric
power generation is 750 kW, determine
the turbine efficiency and the combined
turbine–generator efficiency of this
plant. Neglect losses in the pipes.
z1 = 70m
z2 = 0 m
mass flow rate = 1500 kg/s
Welect,out(turbine) = 800 kW
Welect,out(turbine -generator) = 750 kW
At a certain location, wind is blowing
steadily at 7 m/s. Determine the
mechanical energy of air per unit mass
and the power generation potential of a
wind turbine with 80-m-diameter blades
at that location. Also determine the actual
electric power generation assuming an
overall efficiency of 30 percent. Take the
air density to be 1.25 kg/m3.
1. A geothermal pump is used to pump brine
whose density is 1050 kg/m3 at a rate of 0.3 m3/s from
a depth of 200 m. For a pump efficiency of 74 percent,
determine the required power input to the pump. Disregard
frictional losses in the pipes, and assume the geo ther mal
water at 200 m depth to be exposed to the atmosphere.
2. A water pump delivers 6 hp of shaft power when
operating. If the pressure differential between the outlet and
the inlet of the pump is measured to be 1.2 psi when the
flow rate is 15 ft3/s and the changes in velocity and elevation
are negligible, determine the mechanical efficiency of
this pump.
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