Question

Steam at a pressure of 1.5 MPa and 250°C isexpanded through a turbine at first to a pressureof 0.4 MPa. It is then reheated at constant pressureto the initial temperature of 250°C and is finallyexpanded to 0.1 bar. Using Mollier chart, estimatethe quality of steam before reheat, the work doneper kg of steam flowing through the turbine andamount of heat supplied during the process ofreheat. Compare the work output when theexpansion is direct from 15 bar to 0.1 bar withoutany reheat.​

Answer 1

Given :

Heat gained = 4.5 × 10⁵ J

Heat released = 2 × 10⁵ J

To Find :

Percentage efficiency of steam engine and work done per cycle..

Solution :

❒ Efficiency of a heat engine/steam engine is given by, η = 1 - (Q₂ / Q₁)

Where,

η denotes efficiency

Q₂ denotes heat released to the sink

Q₁ denotes heat extracted from the source

By substituting the given values;

➛ η = 1 - (Q₂ / Q₁)

➛ η = 1 - (2 × 10⁵ / 4.5 × 10⁵)

➛ η = 1 - 0.44

➛ η = 0.56

Percentage efficiency = 56%

❒ Work done per cycle :

We know that work done is measured as the change in energy.

➠ W = Q₁ - Q₂

➠ W = (4.5 × 10⁵) - (2 × 10⁵)

➠ W = 2.5 × 10⁵ J