Regrigeratio cycle
- 1. REFRIGERATION CYCLES GUIDED BY- PRESENTED BY-
- 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).
- 8. AN IDEAL HEAT PUMP
- 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.
- 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.
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