The First Law of Thermodynamics for Open Systems: Derivation and Sample Problem

Abstract

The material presented in this lecture is adapted from Chapter 3 of T&M. First, we will derive the First Law of Thermodynamics for Open Systems. Second, we will use this law to solve Sample Problem 5–1, an illuminating problem where the gas in the ullage volume of a fuel storage tank is first pressurized by gas entering from an external gas storage tank until its pressure reaches a desired value. Subsequently, the pressurized gas is used to partially empty the fuel which flows into a missile to be launched for strategic purposes. Third, we will discuss the selection of the optimal model systems when modeling the pressurization and the emptying steps. Fourth, we will describe the pressurization step using the well-mixed gas model. Fifth, we will describe the fueling step using the two-layer (or stratified) gas model. Finally, we will show how to solve the First Law of Thermodynamics for an Open System during the pressurization and the fueling steps.