TABLE OF CONTENTS This chapter aims to clarify the concept of population balance model or population balance equation, terms that are used almost interchangeably in this book. This is followed by a short narrative of the strengths and weaknesses of these models.
Population balance is not a well-defined concept in science and engineering, but means slightly different things to different people. During the fall of 2004, a Web search on the term "population balance model" gave more than 1 million hits, and a casual perusal of some of the Web pages obtained in this search makes clear this confusion of connotations. In this book, population balance models will connote the equations or sets of equations that model the dynamics of the distribution of states of a population of cells or particles.
Population balances are models describing how the number of individuals in a population and their properties change with time and with the conditions of growth. In engineering, population balances are used to model not just populations of living cells, but also populations of inanimate particles, such as the size and number of crystals in a crystalizer or the size, number, and composition of droplets in an aerosol.
Although an engineering concept, there is a population balance notion that is known to most people and that is the population pyramid. Age pyramids are histograms depicting the number of people in each of a set of age classes. Often, these histograms are split into two...
