Question

Using a thermometer, measure the temperature of the main food compartment of your refrigerator, and check if it is between 1 and 4°C. Also, measure the temperature of the freezer compartment, and check if it is at the recommended value of 218°C.

Answer 1

A hypothetical engine that works on the reversible Carnot cycle is known as Carnot heat engine. The series of processes in the Carnot cycle is given as:-

• Reversible isothermal heat absorption or addition.

• Reversible adiabatic work done.

• Reversible isothermal heat rejection.

 • Reversible adiabatic work supply. Therefore, an engine which works on Carnot cycle is Carnot heat engine. The basic steady-flow components to describe the working of the Carnot heat engine are turbine, pump and two heat exchangers. Draw the Carnot heat engine with steady-flow components.

 

 

Draw the p-v and T-S diagrams of Carnot cycle as shown in the following figure.

 

Execution of Carnot cycle in heat engine:-

• Four steps to execute the Carnot cycle in Carnot heat engine.

 

• Reversible isothermal heat absorption or addition:

In this process, the heat is supplied to the engine at steady temperature in the heat exchanger due to which the pressure of the working source reduces and the volume taken by the working source increases. The transfer of heat in this process is given as Q1.

 

• Reversible adiabatic work done:

The steady-flow component of the heat engine that executes the above procedure is the turbine. Therefore, the working source is expanded in the turbine adiabatically and results in zero heat transfer during this process. The pressure and temperature of the working source minimizes and the volume taken by the working source increases. The work done by the working source in the turbine is given as WT.

 

• Reversible isothermal heat rejection:

In this process, the heat exchanger completes the process of heat rejection to the system at t2. Also, the working source pressure maximizes and the volume taken by the working source minimizes. The heat transfer taken place in this process is given as Q2.

 

• Reversible adiabatic work supply:

The steady-flow component that executes the above procedure is the pump. Thus, the working source compressed adiabatically in the pump that results in zero heat transfer. In this process, the temperature and the process of the working source maximizes at the cost of volume. The work transfer taken place in this process is given as Wp. Therefore from the first law of thermodynamics, write the equation of cyclic heat engine as:

 

ΣQnet = ΣWnet

Q1 – Q2 = WT - Wp

 

Here, net heat transfer is Qnet, and network transfer is Wnet.

 

Show the Carnot heat engine with reversed direction as in Figure (2).

 

In Figure (2), heat is received from the reservoir at T2 and heat is supplied to the reservoir at T1. Process is done through the working source in the pump and work is regularly done on the working source in the turbine. Therefore, if the directions of heat and work interactions are reversed, then all the transfers of energy connected with that process are reversed in path but stay in the equal magnitude. In heat engine of reversed type, the quantities WT, Wnet, Wp, Q1 and Q2 continues with equal magnitude but the paths are reversed.

A hypothetical engine that works on the reversible Carnot cycle is known as Carnot heat engine. The series of processes in the Carnot cycle is given as:-