Availability or Exergy Analysis

The concept of availability or available useful work is a convenient way to determine the thermodynamic minimum amount of energy required for doing work in a steady flow process. The availability is referred to as exergy in Europe. The availability function is defined as:

where H is the enthalpy, S is the entropy and Ta is the reference temperature (298 K). A higher value of availability indicates that more work can be extracted as compared to a lower value. For example, high pressure steam is more valuable than steam at atmospheric pressure, although the latent heat values are about equal.

The change in availability represents the amount of shaft work that can be extracted from a system as it flows from an initial to final state. It also defines the minimum work required to achieve a change in a flowing system. This available shaft work, Ws, is defined in terms of the availability change, or:

These properties are readily available from data references or process simulators and can be applied to all types of plant equipment in a process.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment