Transport phenomena

Transport phenomena (TP) is a branch of engineering science that focuses on mass transport, energy transport, and fluid dynamics. These three areas are similar in behavior in that they all involve moving something, whether that is mass, heat, or momentum. Transport phenomena is used by chemical and mechanical engineers and researchers to understand the processes of making and synthesizing materials. This allows them to choose the best ways to make various materials, develop models for testing these processes, and improve the processes. Transport phenomena also helps provide understanding of some everyday experiences, such as how blood flows through the body, how pollutants move in large bodies of water, and why bubbles sometimes go down in a beverage instead of up.

Background

Engineers who deal with transport phenomena can be working in a variety of fields and with a number of different materials and substances. However, the study of transport phenomena focuses more on the things that are similar about these fields and substances than on the ways they are different. This is possible because the three main areas that encompass these fields and substances hold many concepts and ideas in common.

Each area—mass transport, energy transport, and fluid dynamics—involves a transfer of something from one location to another. Mass transport, as the name implies, involves the way mass moves from one place to another. For example, when milk is added to coffee, it starts in one spot but eventually spreads throughout the beverage even before it is stirred. Energy transport refers to the transfer of heat. This can happen in several ways. The warmth that is felt when moving from shade into sun is an example of radiation of heat, the heat rising from hot pavement is an example of convection heat, and the heat felt when a hand is rested on a hot stove is conduction heat. Fluid transfer is concerned with how fluids move. This happens as molecules push and bump against each other, causing momentum to shift in the fluid. This momentum can result in a laminar flow—a smooth movement from place to place—or in turbulence—a rough, choppy movement.

In each case, the theories of transport phenomena mean that matter moves from an area where there is a lot of something to an area where there is less of it. For example, if salt is added to a glass of water, it will spread throughout the whole glass. Eventually the water will have an equal amount of salt throughout and will have reached the maximum amount of mass transfer. Similarly, when a blacksmith heats a piece of iron and then drops it into water, the heat from the iron transfers to the water; the iron cools toward the water's temperature and the water heats up from the transfer of heat. At some point, both will reach the same temperature and the heat transfer will end. Fluid mechanics is similar and applies to both gases and fluids. Both tend to move from the areas of highest pressure to the areas of lower pressure. This is why a wide river will generally flow smoothly but become choppier and rougher when it narrows.

While people have noticed these phenomena for centuries, it was not until the eighteenth century that anyone began studying the technical and mathematical reasons these things occur. Daniel Bernoulli was a Swiss mathematician who studied fluid mechanics. While he completed his calculations based on a nonexistent fluid that did not change in any way, his theoretical formulas help researchers and engineers understand the properties of water and air. For example, he theorized that if water was flowing from a larger pipe to a smaller pipe, it would have to speed up or less water would be able to get through the smaller pipe. Bernoulli's work helped expand the understanding of pressure and flow in water and gases, including air. This is important in developing aerodynamic vehicles that move efficiently on land, in the air, and in water.

Overview

Engineers have developed a number of mathematical ways to look at transport phenomena. All of their equations and theories are based on two key principles: mass and energy cannot be destroyed, and the way energy, mass, or fluids transfer momentum is in proportion to some instigating or driving force. Several standard equations have been developed to calculate how substances will respond. These include Newton's law of fluid mechanics, Fourier's law of heat transfer, and Fick's law of mass transfer.

Developed by Isaac Newton, the fluid mechanics law takes into account the viscosity—or thickness—of the liquid, the velocity or speed at which it is moving, and the sheer stress that is being applied to the fluid. Fourier's law, named after French mathematician Jean-Baptiste Joseph Fourier, takes into account the temperature, the area available for the heat to transfer to, the amount of heat flowing per unit of time, and how easily the material conducts heat. Fick's law of mass transfer, developed by Adolf Fick, factors in the diffusivity of one substance in the other, how much of the mass there is, and how quickly the mass flows into each unit of available space in relation to the average speed at which it moves.

While transport phenomena is thought of as a part of engineering, it is very much part of everyday life. Cooking a meal uses the principles of heat and mass transfer. Opening a window to cool a room or air out an unpleasant odor is an example of mass transfer. Washing dishes or using soap in a bath or to clean laundry utilizes principles from fluid mechanics, as the soap changes how water molecules move. The way blood flows through the human body is another everyday example of fluid mechanics.

Bibliography

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