![]() Liquids are generally considered to be incompressible. A floating body displaces its own weight of the fluid in which it floats.Ĭompressibility is the measure of the change in volume a substance undergoes when a pressure is exerted on the substance. If the body weighs less than that of the displaced liquid, the body will rise to the surface eventually floating at such a depth that will displace a volume of liquid whose weight will just equal its own weight. If a body weighs more than the liquid it displaces, it sinks but will appear to lose an amount of weight equal to that of the displaced liquid, as our rock. When a body is placed in a fluid, it is buoyed up by a force equal to the weight of the water that it displaces. The amount of this buoyant effect was first computed and stated by the Greek philosopher Archimedes. Boats rely on this buoyant force to stay afloat. When we lift a rock from a stream bed, it suddenly seems heavier on emerging from the water. ![]() When we go swimming, our bodies are held up almost entirely by the water. We all have had numerous opportunities of observing the buoyant effects of a liquid. In actuality, liquids can be slightly compressed at high pressures, resulting in a slight increase in density and a slight decrease in specific volume of the liquid.īuoyancy is defined as the tendency of a body to float or rise when submerged in a fluid. Since liquids are considered incompressible, an increase in pressure will result in no change in density or specific volume of the liquid. As the temperature of the fluid increases, the density decreases and the specific volume increases. Both density and specific volume are dependant on the temperature and somewhat on the pressure of the fluid. Density and specific volume are the inverse of one another. Density, on the other hand, is the mass of a substance per unit volume. ![]() The specific volume of a substance is the volume per unit mass of the substance. Mass was defined as the quantity of matter contained in a body and is to be distinguished from weight, which is measured by the pull of gravity on a body. Common units for pressure are pounds force per square inch (psi). Pressure was defined as the force per unit area. It can be used to predict the direction that heat will be transferred. Temperature was defined as the relative measure of how hot or cold a material is. ![]() These included temperature, pressure, mass, specific volume and density. Several properties of fluids were discussed in the Thermodynamics section of this text. Essentially, fluids are materials which have no repeating crystalline structure. This includes liquids, gases and even some materials which are normally considered solids, such as glass. The third is the conservation of mass (leading to the continuity equation) which will be explained in this module.Ī fluid is any substance which flows because its particles are not rigidly attached to one another. The second is the conservation of energy (leading to the First Law of Thermodynamics) which was studied in thermodynamics. The first is the principle of momentum (leading to equations of fluid forces) which was covered in the manual on Classical Physics. The basic principles of fluid flow include three concepts or principles the first two of which the student has been exposed to in previous manuals. Even though this type of analysis would not be sufficient in the engineering design of systems, it is very useful in understanding the operation of systems and predicting the approximate response of fluid systems to changes in operating parameters. These basic concepts can be applied in solving fluid flow problems through the use of simplifying assumptions and average values, where appropriate. Unlike solids, the particles of fluids move through piping and components at different velocities and are often subjected to different accelerations.Įven though a detailed analysis of fluid flow can be extremely difficult, the basic concepts involved in fluid flow problems are fairly straightforward. Fluid flow systems are also commonly used to provide lubrication.įluid flow in the nuclear field can be complex and is not always subject to rigorous mathematical analysis. Examples of this are the cooling water circulated through a gasoline or diesel engine, the air flow past the windings of a motor, and the flow of water through the core of a nuclear reactor. Frequently, when it is desired to remove heat from the point at which it is generated, some type of fluid is involved in the heat transfer process. The continuity equation expresses the relationship between mass flow rates at different points in a fluid system under steady-state flow conditions.įluid flow is an important part of most industrial processes especially those involving the transfer of heat. Understanding the quantities measured by the volumetric flow rate and mass flow rate is crucial to understanding other fluid flow topics.
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