Heat and Thermodynamics II - SS1 Physics Past Questions and Answers - page 6
The Carnot cycle is an idealised thermodynamic cycle used in refrigeration systems. Which of the following is true about the Carnot cycle?
It operates in a closed-loop configuration.
It consists of four processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.
It has a higher coefficient of performance (COP) compared to other refrigeration cycles.
It operates based on the principle of thermal equilibrium.
The coefficient of performance (COP) of a refrigeration system is defined as:
The ratio of heat absorbed by the refrigerant to the work input
The ratio of work output to the heat input
The ratio of heat absorbed by the refrigerant to the work output
The ratio of heat removed from the refrigerated space to the work input
Which of the following statements about the Carnot cycle is correct?
It can achieve 100% efficiency in converting heat into work.
It operates in a single process of compression.
It is not based on any reversible processes.
It is a non-ideal cycle with low efficiency.
Explain the working principle of a refrigeration system and the role of each component in the system.
A refrigeration system works by removing heat from a refrigerated space, thereby cooling it down. The key components of a refrigeration system include the compressor, condenser, expansion valve, and evaporator. The compressor pressurises the refrigerant, increasing its temperature and pressure. The high-pressure refrigerant then flows to the condenser, where it releases heat to the surroundings and condenses into a liquid.
The liquid refrigerant passes through the expansion valve, which reduces its pressure, causing it to evaporate and absorb heat from the refrigerated space. The gaseous refrigerant then enters the evaporator, where it completes the cycle by absorbing heat and turning it back into a low-pressure gas. This cycle is repeated continuously to maintain the desired cooling effect.
Describe the Carnot cycle and its significance in refrigeration systems.
The Carnot cycle is an idealised thermodynamic cycle used as a benchmark for the performance of refrigeration systems. It consists of four processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression. In the isothermal expansion process, the refrigerant absorbs heat from the refrigerated space at a constant temperature, resulting in an increase in volume.
The adiabatic expansion process follows, where the refrigerant expands further without any heat exchange with the surroundings, resulting in a decrease in temperature and pressure. The isothermal compression process occurs next, during which the refrigerant rejects heat to the surroundings at a constant temperature, decreasing its volume.
Finally, the adiabatic compression process takes place, where the refrigerant is compressed without any heat exchange, resulting in an increase in temperature and pressure. The Carnot cycle is significant because it represents the maximum theoretical efficiency that a refrigeration system can achieve when operating between two temperature reservoirs. It provides a reference point for evaluating the performance of real refrigeration cycles and serves as a basis for improving their efficiency.