We were discussing the concept of control volume system and concept of specific enthalpy in the field of thermal engineering in
our previous posts, where we have seen the fundamentals of a control volume
system as well as the specific heat and types of specific heat also.
Let us go ahead to discuss the concept of a heat
engine and a heat pump in thermodynamics.Â
We will see here the fundamentals of heat engine and after that we will see the principle of heat pump in our next post. We will finally find out here the thermal efficiency of a heat engine.
We will see here the fundamentals of heat engine and after that we will see the principle of heat pump in our next post. We will finally find out here the thermal efficiency of a heat engine.
So let us first see here the concept of a heat engine
Heat engine is basically defined as a device which
will be operated in a thermodynamic cyclic process and will convert the heat
energy or thermal energy in to mechanical energy. Following figure, displayed
here, indicates the fundamentals of a heat engine.
Heat
engine
So as we have studied above, during definition of a
heat engine, that heat engine will provide mechanical energy i.e. work energy or
we may say that output of a heat engine will be mechanical energy i.e. work
energy.
As we know that heat engine converts thermal energy
or heat energy in to mechanical energy, therefore we can say that thermal
energy or heat energy will be termed as the input energy to a heat engine.
As we can see above in figure, heat engine will have
three important terms and these are as mentioned below
- Thermal reservoir at higher temperature or source of heat energy
- Working media or substance
- Thermal reservoir at lower temperature or sink of heat energy
According to the second law of thermodynamics, heat
energy will be given by higher temperature thermal reservoir i.e. from the
source of heat to heat engine and heat engine will convert a part of input heat
energy in to useful work energy and rest part of input heat energy will be
directed towards the sink of heat i.e. lower thermal reservoir.
Efficiency of a heat engine
Let us determine the efficiency of a heat engine, before going for calculation we need to know the each term used here and these
are as mentioned below.
Temperature of hot thermal reservoir is TH
Temperature of cold thermal reservoir is TC
Heat energy provided by source of heat or hot
thermal reservoir is QH
Useful work energy produced by heat energy is W
Rest quantity of heat energy rejected to sink of
heat or cold thermal reservoir is QC
Efficiency of a heat engine will be determined by
the ratio of output term i.e. useful work energy to the input term i.e. input
heat energy. Efficiency of a heat engine could be easily written as displayed
in following figure.
Heat
engine efficiency
We will come again with another important topic i.e.
heat pump in thermodynamics in our next post.
Do you have suggestions? Please write in comment
box.
Reference:
Engineering thermodynamics by P. K. Nag
Basic thermodynamics by Prof. S.K. Som
Image courtesy: Google
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