Process Heat Transfer. Principles, Applications...
Understanding how heat is transferred from the outdoors into your home and from your home to your body is important for understanding the challenge of keeping your house cool. Understanding the processes that help keep your body cool is important in understanding cooling strategies for your home.
Process Heat Transfer. Principles, Applications...
The First Law of Thermodynamics states that energy can neither be created nor destroyed. Heat exchangers are devices built for efficient heat transfer from one fluid to another. They are widely used in engineering processes and include examples such as intercoolers, preheaters, boilers and condensers in power plants. Heat exchangers are becoming more and more important to manufacturers striving to control energy costs.
Process Heat Transfer Rules of Thumb investigates the design and implementation of industrial heat exchangers. It provides the background needed to understand and master the commercial software packages used by professional engineers for design and analysis of heat exchangers. This book focuses on the types of heat exchangers most widely used by industry, namely shell-and-tube exchangers (including condensers, reboilers and vaporizers), air-cooled heat exchangers and double-pipe (hairpin) exchangers. It provides a substantial introduction to the design of heat exchanger networks using pinch technology, the most efficient strategy used to achieve optimal recovery of heat in industrial processes.
Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.
Heat convection occurs when the bulk flow of a fluid (gas or liquid) carries its heat through the fluid. All convective processes also move heat partly by diffusion, as well. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". The former process is often called "forced convection." In this case, the fluid is forced to flow by use of a pump, fan, or other mechanical means.
Heat transfer is a process function (or path function), as opposed to functions of state; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process.
Thermal engineering concerns the generation, use, conversion, storage, and exchange of heat transfer. As such, heat transfer is involved in almost every sector of the economy.[6] Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.
The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection. In this case the fluid is forced to flow by using a pump, fan or other mechanical means.
Convective heat transfer, or simply, convection, is the transfer of heat from one place to another by the movement of fluids, a process that is essentially the transfer of heat via mass transfer. Bulk motion of fluid enhances heat transfer in many physical situations, such as (for example) between a solid surface and the fluid.[10] Convection is usually the dominant form of heat transfer in liquids and gases. Although sometimes discussed as a third method of heat transfer, convection is usually used to describe the combined effects of heat conduction within the fluid (diffusion) and heat transference by bulk fluid flow streaming.[11] The process of transport by fluid streaming is known as advection, but pure advection is a term that is generally associated only with mass transport in fluids, such as advection of pebbles in a river. In the case of heat transfer in fluids, where transport by advection in a fluid is always also accompanied by transport via heat diffusion (also known as heat conduction) the process of heat convection is understood to refer to the sum of heat transport by advection and diffusion/conduction.
The blackbody limit established by the Stefan-Boltzmann equation can be exceeded when the objects exchanging thermal radiation or the distances separating them are comparable in scale or smaller than the dominant thermal wavelength. The study of these cases is called near-field radiative heat transfer.
Phase transition or phase change, takes place in a thermodynamic system from one phase or state of matter to another one by heat transfer. Phase change examples are the melting of ice or the boiling of water.The Mason equation explains the growth of a water droplet based on the effects of heat transport on evaporation and condensation.
Melting is a thermal process that results in the phase transition of a substance from a solid to a liquid. The internal energy of a substance is increased, typically with in heat or pressure, resulting in a rise of its temperature to the melting point, at which the ordering of ionic or molecular entities in the solid breaks down to a less ordered state and the solid liquefies. Molten substances generally have reduced viscosity with elevated temperature; an exception to this maxim is the element sulfur, whose viscosity increases to a point due to polymerization and then decreases with higher temperatures in its molten state.[25]
A heat exchanger is used for more efficient heat transfer or to dissipate heat. Heat exchangers are widely used in refrigeration, air conditioning, space heating, power generation, and chemical processing. One common example of a heat exchanger is a car's radiator, in which the hot coolant fluid is cooled by the flow of air over the radiator's surface.[34][35]
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases and clouds , and is re-radiated in all directions, resulting in a reduction in the amount of thermal radiation reaching space relative to what would reach space in the absence of absorbing materials. This reduction in outgoing radiation leads to a rise in the temperature of the surface and troposphere, until the rate of outgoing radiation again equals the rate at which heat arrives from the Sun.[42]
Thermal energy storage includes technologies for collecting and storing energy for later use. It may be employed to balance energy demand between day and nighttime. The thermal reservoir may be maintained at a temperature above or below that of the ambient environment. Applications include space heating, domestic or process hot water systems, or generating electricity.
This course focuses on developing design checklists and rules-of- thumb to help engineers avoid common problems in process heat transfer. It surveys common heat exchanger types used in the process industry including shell-and-tube, air-cooled, plate-frame, and plate- fin exchangers. Fundamentals of heat transfer and pressure drop are provided for single-phase, boiling, and condensing services. Selection criteria for common applications are discussed, guidelines for thermal design are provided, and detailed examples are summarized. Industry case studies of thermal design and operational problems are presented and lessons learned discussed.
A copy of Process Heat Transfer: Principles, Applications, and Rules of Thumb, by Robert Serth and Thomas Lestina, is included with the course and serves as the primary reference for course material. Engineers who have recently graduated and more experienced engineers who are responsible for design and operation of process heat exchangers will find this course valuable.
HTRI, a leading source of process heat transfer technology, research, software and services, is offering a two-day course covering selection criteria for common applications and guidelines for thermal design. The Process Heat Exchangers: Applications and Rules-of-Thumb Short Course will take place at HTRI headquarters in Navasota, Texas, on Feb. 1-2, 2016, and is open to engineering students and engineers who are new to the workforce.
About HTRIHTRI is a leading global source of process heat transfer technology, research, software and services. Incorporated in 1962, the company conducts research on heat transfer and fluid flow at its multimillion dollar Research and Technology Center located near Houston, Texas, USA. HTRI technology has been used for decades by companies worldwide to help design, operate and maintain heat exchangers. For more information, visit www.htri.net.
Convection is the transfer of thermal energy from a surface by way of the motion of a fluid such as air or water that has been heated. Most fluids expand when heated and therefore will become less dense and rise relative to other parts of the fluid that are cooler. So, when the air in a room is heated, it rises to the ceiling because it is warmer and less dense, and transfers heat energy as it collides with the cooler air in the room, then becoming denser and falling again towards the floor. This process creates a natural or free convection current. Convection can also occur through what is termed forced or assisted convection, such as when heated water is pumped through a pipe such as in a hydronic heating system. 041b061a72