Jawaharlal Nehru Technological University Hyderabad B.Tech III Thermodynamics for Petroleum Engineers Previous Question Paper (September - 2021 - R18)

For a steady-state flow process, the mass flow rate and energy properties at any point in the control volume remain constant over time. The general energy balance equation for an open system is given by the rate of energy accumulation equal to the rate of energy in minus the rate of energy out. Under steady-state conditions, the accumulation is zero.

The energy balance is expressed as:

For a single-stream steady flow system, where ṁ is constant:

Dividing by the mass flow rate ṁ, we obtain the energy balance per unit mass:

Where q is the heat transfer per unit mass, w is the work done per unit mass, h is enthalpy, v is velocity, z is elevation, and g is the gravitational acceleration.

Joule's experiment, conducted by James Prescott Joule, was fundamental in establishing the First Law of Thermodynamics by demonstrating the equivalence between mechanical work and heat.

The experimental setup involved an insulated container filled with a known mass of water. A paddle wheel was submerged in the water and connected to a falling weight via a pulley system. As the weight descended, it turned the paddle wheel, performing mechanical work on the water through internal friction/viscous dissipation.

Joule observed that the temperature of the water increased as the weight fell. By measuring the work done by the falling weight (W = mgh) and the corresponding rise in water temperature (Q = mcΔT), he showed that the same amount of work always produced the same increase in temperature, regardless of the method used to stir the fluid.

The experiment concluded that heat and work are both forms of energy transfer and that internal energy is a state function. This provided the experimental basis for the conservation of energy principle, proving that energy cannot be created or destroyed, only converted from one form to another.