Reversed Carnot Cycle MCQ Quiz in తెలుగు - Objective Question with Answer for Reversed Carnot Cycle - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Explanation

A reversed Carnot cycle using air as a working medium (or refrigerant) is shown on p-v and T-S diagrams in figures below.

The four processes of the reversed Carnot cycle are as follows.

1-2: Isentropic compression process

2-3: Isothermal expansion process

3-4: Isentropic compression process

4-1: Isothermal expansion process 

Hence the reversed Carnot engine consists of two isentropic processes and two isothermal processes.

Explanation:

Carnot cycle:

• The Carnot cycle consists of 4 processes
  • 1-2 isothermal heat addition
  • 2-3 reversible adiabatic expansion
  • 3-4 isothermal heat rejection
  • 4-1 reversible adiabatic compression
• A cycle is said to be reversible only when each process in a cycle is reversible.
• Carnot cycle consists of 2 isothermal and 2 adiabatic processes.
• An isothermal process is a very slow process and the adiabatic process is a very fast process and the combination of a slow process and fast process are very difficult.
• So a Carnot cycle is also known as an impractical cycle. It is used only to compare other actual cycles.

Brayton cycle:

Brayton cycle is a theoretical cycle for gas turbines. This cycle consists of two reversible adiabatic or isentropic processes and two constant pressure processes. The heat addition and rejection takes place at constant pressure.

• Isentropic compression (in a compressor)
• Constant-pressure heat addition
• Isentropic expansion (in a turbine)
• Constant-pressure heat rejection

Explanation:

The Reversed Carnot Cycle:

• The reversed Carnot cycle is a theoretical thermodynamic cycle that forms the basis for understanding the operation of refrigerators and heat pumps. This cycle is essentially the Carnot cycle operating in reverse. While the Carnot cycle describes the most efficient process for converting heat into work (as used in heat engines), the reversed Carnot cycle describes the most efficient process for transferring heat from a colder area to a hotter area using work input, which is the principle behind refrigeration and heat pumping systems.

In a reversed Carnot cycle, the main goal is to transfer heat from a low-temperature reservoir to a high-temperature reservoir. The cycle consists of four thermodynamic processes:

1. Isentropic Compression: In this process, the working fluid (often a refrigerant) is compressed isentropically, meaning there is no change in entropy. This compression increases the temperature and pressure of the fluid.
2. Isothermal Heat Rejection: The working fluid, now at a higher temperature, releases heat to the high-temperature reservoir (e.g., the surrounding environment). This process occurs at a constant temperature.
3. Isentropic Expansion: The fluid undergoes isentropic expansion, reducing its pressure and temperature. This process prepares the fluid for absorbing heat in the next step.
4. Isothermal Heat Absorption: Finally, the working fluid absorbs heat from the low-temperature reservoir (e.g., the space to be cooled). This process also occurs at a constant temperature.

The reversed Carnot cycle is idealized and assumes no irreversibilities, which means it represents the maximum possible efficiency for any refrigeration or heat pump system. Real-world systems, such as vapor-compression refrigeration cycles, are modeled on the reversed Carnot cycle but include inefficiencies like friction, pressure drops, and non-ideal gas behavior.

Applications:

The reversed Carnot cycle is the theoretical foundation for:

• Refrigerators: Devices that transfer heat from the interior of a refrigerator (low temperature) to the surrounding environment (high temperature) to maintain a cool interior.
• Heat Pumps: Systems that transfer heat from a cold source (e.g., the ground or air in winter) to a warm space (e.g., the interior of a building) for heating purposes.

Explanation:

Energy stored in battery (E) = [Power produced by generator - Heat transfer to surrounding] × time

E = [6 – 0.3] × 2 × 3600 = 41040 KJ

Explanation:

The Carnot Cycle:

The Carnot cycle is a theoretical thermodynamic cycle proposed by Nicolas Léonard Sadi Carnot in 1824. It is considered the most efficient cycle possible for a heat engine operating between two temperature reservoirs. The Carnot cycle consists of four reversible processes: two isothermal processes and two adiabatic (isentropic) processes. These processes are:

• Reversible Isothermal Expansion: During this process, the working substance (usually a gas) expands isothermally (at constant temperature) while absorbing heat from a high-temperature heat reservoir. The gas does work on the surroundings, and the temperature remains constant.
• Reversible Adiabatic Expansion: In this process, the gas continues to expand, but no heat is exchanged with the surroundings (adiabatic process). The gas does work on the surroundings, and its temperature decreases.
• Reversible Isothermal Compression: The gas is compressed isothermally while rejecting heat to a low-temperature heat reservoir. The surroundings do work on the gas, and the temperature remains constant.
• Reversible Adiabatic Compression: Finally, the gas is compressed adiabatically, meaning no heat is exchanged. The surroundings do work on the gas, and its temperature increases, bringing it back to the initial state.

Correct Option Analysis:

The correct answer is:

Option 3: Reversible Isobaric Condensation

This option is correct because the Carnot cycle does not involve any isobaric (constant pressure) processes. The Carnot cycle consists solely of isothermal and adiabatic processes. Therefore, reversible isobaric condensation does not constitute part of the Carnot cycle.

Important Information:

To further understand the analysis, let’s evaluate the other options:

Option 1: Reversible Isothermal Heat Addition

This option describes the first process of the Carnot cycle, where the working substance absorbs heat from a high-temperature reservoir at a constant temperature. This is a fundamental part of the Carnot cycle and is essential for its operation.

Option 2: Reversible Adiabatic Expansion

This option accurately describes the second process of the Carnot cycle. During reversible adiabatic expansion, the gas expands without exchanging heat with the surroundings, and its temperature decreases. This process is crucial for the Carnot cycle.

Option 4: Reversible Isothermal Heat Rejection

This option accurately describes the third process of the Carnot cycle, where the working substance releases heat to a low-temperature reservoir at a constant temperature. This process is essential for completing the cycle.

Conclusion:

The Carnot cycle is a theoretical model that defines the maximum possible efficiency of a heat engine operating between two temperature reservoirs. The cycle consists of two isothermal processes (heat addition and rejection) and two adiabatic processes (expansion and compression). Reversible isobaric condensation is not a part of the Carnot cycle, making option 3 the correct answer. Understanding the Carnot cycle is fundamental in thermodynamics and helps in analyzing the efficiency of real-world heat engines.

Explanation:

Vapour compression cycle:

• The Vapor Compression Refrigeration Cycle involves four components:
  1. Compressor
  2. Condenser
  3. Expansion valve/throttle valve
  4. Evaporator.
• It is a compression process, whose aim is to raise the refrigerant pressure, as it flows from an evaporator.
• The high-pressure refrigerant flows through a condenser/heat exchanger before attaining the initial low pressure and going back to the evaporator.
  • Process 1-2: Isentropic compression of saturated vapour in compressor
  • Process 2-3: Isobaric heat rejection in condenser.
  • Process 3-4: Isenthalpic expansion of saturated liquid in expansion device.
  • Process 4-1: Isobaric heat extraction in the evaporator.

​​Additional Information

Carnot cycle:

• The Carnot cycle consists of 4 processes
  • 1-2 isothermal heat addition
  • 2-3 reversible adiabatic expansion
  • 3-4 isothermal heat rejection
  • 4-1 reversible adiabatic compression
• A cycle is said to be reversible only when each process in a cycle is reversible.
• Carnot cycle consists of 2 isothermal and 2 adiabatic processes. An isothermal process is a very slow process and the adiabatic process is a very fast process and the combination of a slow process and fast process are very difficult.
• So a Carnot cycle is also known as an impractical cycle. It is used only to compare other actual cycles.

Joule cycle

Gas turbines operate on the Brayton cycle/Joule cycle. The Joule cycle consists of four internally reversible processes:

• Isentropic compression (in a compressor)
• Constant-pressure heat addition
• Isentropic expansion (in a turbine)
• Constant-pressure heat rejection

Concept:

Refrigerator:

COP of a reversed Carnot cycle

where, T_L = Lower Temperature, T_H = Higher temperature

Calculation:

Given:

T_H = 273 + 35°C = 308 K

T_L = 273 + (-15°C) = 258 K

Explanation:

Bell–Colleman cycle or Reversed Brayton cycle:

where,

Process 1-2: Isentropic compression

Process 2-3: Constant pressure heat rejection

Process 3-4: Isentropic expansion

Process 4-1: Constant pressure heat absorption 

T-S diagram represents a reversed Brayton cycle used in the air conditioning of aeroplanes where the air is used as a refrigerant.

Reversed Carnot cycle:

Vapour Compression Refrigeration cycle:

Concept:

Reverse Carnot cycle (Gases Refrigerant):

Processes in Reverse Carnot cycle:

Process 1 – 2: Isentropic Compression

Process 2 – 3: Isothermal Condensation

Process 3 – 4: Isentropic Expansion

Process 4 – 1: Isothermal Evaporation

COP_R= = =

Calculation:

Given:

Q_L= 2 kW, T_L= 200 K, T_H= 300 K, COP_R=?, P_in=?

Now, we know that

COP_R=  = 

= 

∴ P_in= 1 kW

And

COP_R=  =  = 2