Law of Degradation of Energy:
The available energy of a system decreases as its temperature or pressure
decreases and approaches that of the surroundings. When heat is transferred from a system. its temperature decreases and hence the quality of its energy deteriorates. The degradation is more for energy loss at a higher temperature than that at a lower temperature. Quantity-wise energy loss may be the same. but quality-wise the losses are different. While tire first law states that energy is
always conserved quantity-wise, the improved emphasizes that energy always degrades quality-wise. When gas is throttled adiabatically from a high to low pressure, the enthalpy (or energy per unit mass) remains the same, but there is a degradation of energy or available work. The same holds good for pressure drop due to friction of a fluid flowing through an insulated pipe. Energy is always conserved, but its quality is always degraded.
