What can be ignored when making energy balance for an adiabatic gas turbine?

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BlackTom AI · Accepted Answer

When performing an energy balance for an adiabatic gas turbine, we focus on the primary energy transfers involved in converting chemical or thermal energy into shaft work, while keeping track of what can be neglected to simplify the model.
Option a: change of gravitational potential energy. In many gas-turbine analyses, the turbine is treated as a system with negligible vertical height change between inlet and outlet, so the potential energy term (m g z) is small compared to the flow work and enthalpy terms. Therefore, for many practical engineering calculations, the change in gravitational potential energy is ignored without significantly impacting accuracy.
Option d: heat losses. By definition, an adiabatic process involves no heat transfer across the system boundary, i.e., Q = 0. In an ideal adiabatic gas turbine, external heat losses are neglected, and the energy balance does not include a heat loss term. In real systems, there may be small unavoidable heat losses, but in the idealized adiabatic assumption they are ignored to simplify the model.
If one were to question the remaining energy terms, the core components typically considered are inlet and outlet enthalpy (or internal energy) and shaft work, along with any potential changes in kinetic energy if flow speeds change significantly. Misconceptions to watch for include treating heat losses as significant in an adiabatic model, or assuming large altitude changes where gravitational potential could become non-negligible. Similarly, assuming that all energy changes go into shaft work without accounting for losses would be an incomplete energy balance, even in adiabatic conditions.
In summary, both the change in gravitational potential energy and heat losses are commonly neglected in the ideal adiabatic gas-turbine energy balance, which aligns with standard simplifying assumptions used in first-order analyses.

BH20A0720 Engineering Thermodynamics - Blended teaching 2.9.2024-15.12.2024 Quiz 3

What can be ignored when making energy balance for an adiabatic gas turbine?

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