What is first law of Thermodynamics?
What is a Thermodynamic cycle?
Types of Thermodynamic cycles
What is a Refrigeration Cycle?
Types of Refrigeration cycles
What is a Refrigeration System?
Principle of working of a Refrigeration System
Other Refrigeration systems
2. OVERVIEW
• What is first law of Thermodynamics?
• What is a Thermodynamic cycle?
• Types of Thermodynamic cycles
• What is a Refrigeration Cycle?
• Types of Refrigeration cycles
• What is a Refrigeration System?
• Principle of working of a Refrigeration System
• Other Refrigeration systems
3. FIRST LAW OF THERMODYNAMICS
• The law of conservation of energy states that the total energy of an isolated
system is constant; energy can be transformed from one form to another, but
cannot be created or destroyed. The first law is often formulated by stating that
the change in the internal energy of a closed system is equal to the amount of
heat supplied to the system, minus the amount of work done by the system on
its surroundings.
4. WHAT IS A THERMODYNAMIC CYCLE?
• A thermodynamic cycle consists of a linked sequence of thermodynamic
processes that involve transfer of heat and work into and out of the system, while
varying pressure, temperature, and other state variables within the system, and
that eventually returns the system to its initial state.
• In the process of passing through a cycle, the working fluid (system) may convert
heat from a warm source into useful work, and dispose of the remaining heat to a
cold sink, thereby acting as a heat engine
• Conversely, the cycle may be reversed and use work to move heat from a cold
source and transfer it to a warm sink thereby acting as a heat pump.
5. AN IDEAL THERMODYNAMIC CYCLE-
• Thermodynamic cycles are often represented mathematically as quasistatic
processes in the modelling of the workings of an actual device.
6. TYPES OF THERMODYNAMIC CYCLES
POWER CYCLES-
• Thermodynamic power cycles are
the basis for the operation of heat
engines, which supply most of the
world's electric power and run the
vast majority of motor vehicles.
• Power cycles can be organized into
two categories: real cycles and ideal
cycles.
• EXAMPLES- Otto cycle (gasoline
engines), Diesel cycle (diesel
engines), Brayton cycle (gas
turbines), stirling cycle (hot air
engines)
HEAT PUMP CYCLES
• Thermodynamic heat pump cycles
are the models for household heat
pumps and refrigerators.
• The most common refrigeration
cycle is the vapour compression
cycle, which models systems using
refrigerants that change phase.
• The most common refrigeration
cycle is the vapour compression
cycle, which models systems using
refrigerants that change phase.
7. WHAT IS A REFRIGERATION CYCLE?
• Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and
mathematical models for heat pumps and refrigerators.
• A heat pump is a machine or device that moves heat from one location (the
'source') at a lower temperature to another location (the 'sink' or 'heat sink') at a
higher temperature using mechanical work or a high-temperature heat source.
• Thus a heat pump may be thought of as a "heater" if the objective is to warm the
heat sink or a "refrigerator" if the objective is to cool the heat source.
• An air conditioner requires work to cool a living space, moving heat from the
cooler interior (the heat source) to the warmer outdoors (the heat sink). Similarly,
a refrigerator moves heat from inside the cold icebox (the heat source) to the
warmer room-temperature air of the kitchen (the heat sink).
9. TYPES OF REFRIGERATION CYCLES
Vapour-compression cycle
• The vapor compression refrigeration cycle
has four components: evaporator,
compressor, condenser, and expansion (or
throttle) valve.
• The most widely used refrigeration cycle is
the vapor-compression refrigeration cycle.
• In an ideal vapor-compression refrigeration
cycle, the refrigerant enters the compressor
as a saturated vapor and is cooled to the
saturated liquid state in the condenser.
• It is then throttled to the evaporator pressure
and vaporizes as it absorbs heat from the
refrigerated space.
10.
11. 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
12. Vapour Absorption cycle
• In the early years of the twentieth century, the vapor absorption cycle using
water-ammonia systems was popular and widely used but, after the
development of the vapor compression cycle, it lost much of its importance
because of its low coefficient of performance (about one fifth of that of the
vapor compression cycle).
• the vapor absorption cycle is used only where heat is more readily available
than electricity, such as waste heat provided by solar collectors, or off-the-grid
refrigeration in recreational vehicles.
• The absorption cycle is similar to the compression cycle, except for the method
of raising the pressure of the refrigerant vapor.
• In the absorption system, the compressor is replaced by an absorber which
dissolves the refrigerant in a suitable liquid, a liquid pump which raises the
pressure and a generator which, on heat addition, drives off the refrigerant
vapor from the high-pressure liquid
13. • In an absorption refrigerator, a suitable combination of refrigerant and absorbent is
used. The most common combinations are ammonia (refrigerant) and water
(absorbent), and water (refrigerant) and lithium bromide (absorbent).
14. Gas Refrigeration cycle
• When the working fluid is a gas that is compressed and expanded but does not
change phase, the refrigeration cycle is called a gas cycle.
• Air is most often this working fluid. As there is no condensation and evaporation
intended in a gas cycle, components corresponding to the condenser and
evaporator in a vapor compression cycle are the hot and cold gas-to-gas heat
exchangers.
• For given extreme temperatures, a gas cycle may be less efficient than a vapor
compression cycle because the gas cycle works on the reverse Brayton cycle
instead of the reverse Rankine cycle.
15. OTHER REFRIGERATION CYCLES
Cascade Refrigeration Systems
Very low temperatures can be achieved by operating two or more vapor-
compression Systems in series, called cascading. The COP of a refrigeration system
also increases as a result of cascading.
16. Multipurpose Refrigeration Systems
A refrigerator with a single compressor can provide refrigeration at several
temperatures by throttling the refrigerant in stages.
Liquefaction of Gases
Another way of improving the performance of a vapor-compression refrigeration
system is by using multistage compression with regenerative cooling. The vapor-
compression refrigeration cycle can also be used to liquefy gases after some
modifications.
Thermoelectric Refrigeration Systems
A refrigeration effect can also be achieved without using any moving parts by simply
passing a small 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
17. • To conclude, the principle of refrigeration is very specific because the refrigerant
undergoes a cycle which can be divided into four parts:
• The compressor turns the low pressure vapour into high pressure vapour.
• The condenser turns the gaseous refrigerant into a liquid.
• The expansion valve reduces the pressure of the high pressure liquid.
• The evaporator turns the gas-liquid mixture into a low pressure vapour.
• Mechanical vapor compression systems take a large place in the field of
refrigeration.
