In this chapter, some basic concepts of thermal-fluid sciences are introduced and discussed. The physical sciences that deal with energy and the transfer, transport, and conversion of en- ergy are referred to as thermal-fluid sciences, and they are studied under the subcategories of thermodynamics, heat trans- fer, and fluid mechanics.
Thermodynamics is the science that primarily deals with en- ergy. The first law of thermodynamics is simply an expression of the conservation of energy principle, and it asserts that en- ergy is a thermodynamic property. The second law of thermo- dynamics asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing qual- ity of energy. Determining the rates of heat transfer to or from a system and thus the times of cooling or heating, as well as the
variation of the temperature, is the subject of heat transfer. The basic requirement for heat transfer is the presence of a temper- ature difference. A substance in the liquid or gas phase is referred to as a fluid. Fluid mechanics is the science that deals with the behavior of fluids at rest (fluid statics) or in motion (fluid dynamics), and the interaction of fluids with solids or other fluids at the boundaries.
When solving a problem, it is recommended that a step-by-step approach be used. Such an approach involves stat- ing the problem, drawing a schematic, making appropriate as- sumptions, applying the physical laws, listing the relevant properties, making the necessary calculations, and making sure that the results are reasonable.