6 - Macroscopic Balances

Abstract

This chapter discusses macroscopic balances. With the macroscopic balances and appropriate experimental data, one can determine flow rates and pressure differences, but not velocity fields and pressure fields; one can determine inter-phase heat transfer rates and average temperatures of process streams entering and leaving control volumes, but cannot determine the details of the temperature field. Also, these are helpful in determining mass flow rates, but not the density field. Most of the time it is the pressure drop, flowrate, and inter-phase heat transfer rate that one really needs, and the pressure field, velocity field, and temperature field is often something one can do without. The interest in liquid metals as heat transfer fluids stem from their high thermal conductivity and high boiling points . This allows liquid metals to be used at high temperatures and relatively low pressures . The obvious disadvantage to the use of liquid metals is their toxic nature, for example, mercury is quite poisonous, and their difficult handling characteristics, for example, sodium reacts violently with water and reacts with air at elevated temperatures.