Originally I wrote Bhagavad-gétä As It Is in the form in which it is presented now. When this book Bhagavad-Git ESSENTIALS OF MARKETING. methods, equations, and data described in this book, but they do not guarantee them for any Function and configuration of heat exchangers HEAT. EXCHANGERS. Selection, Rating, and. Thermal Design. Third Edition. H International Standard Book Number (eBook - PDF).
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A heat exchanger is a device that is used to transfer thermal energy (enthalpy) between . of these exchangers but are beyond the scope of this book. PROCESS DESIGN OF SHELL AND TUBE HEAT EXCHANGER, CONDENSER AND .. petroleum fractions are available in the text book (; page ). Heat exchangers are off-the-shelf equipment targeted to the efficient transfer of heat from a hot fluid flow to a cold fluid flow, in most cases through an.
A second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required.
A set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned, etc. Several thermal design features must be considered when designing the tubes in the shell and tube heat exchangers: There can be many variations on the shell and tube design.
Typically, the ends of each tube are connected to plenums sometimes called water boxes through holes in tubesheets.
The tubes may be straight or bent in the shape of a U, called U-tubes. Tube diameter: Using a small tube diameter makes the heat exchanger both economical and compact. However, it is more likely for the heat exchanger to foul up faster and the small size makes mechanical cleaning of the fouling difficult. To prevail over the fouling and cleaning problems, larger tube diameters can be used.
Thus to determine the tube diameter, the available space, cost and fouling nature of the fluids must be considered.
Tube thickness: The thickness of the wall of the tubes is usually determined to ensure: There is enough room for corrosion That flow-induced vibration has resistance Axial strength Hoop strength to withstand internal tube pressure Buckling strength to withstand overpressure in the shell Tube length: heat exchangers are usually cheaper when they have a smaller shell diameter and a long tube length.
Thus, typically there is an aim to make the heat exchanger as long as physically possible whilst not exceeding production capabilities.
However, there are many limitations for this, including space available at the installation site and the need to ensure tubes are available in lengths that are twice the required length so they can be withdrawn and replaced. Also, long, thin tubes are difficult to take out and replace. Tube pitch: when designing the tubes, it is practical to ensure that the tube pitch i. A larger tube pitch leads to a larger overall shell diameter, which leads to a more expensive heat exchanger.
Tube corrugation: this type of tubes, mainly used for the inner tubes, increases the turbulence of the fluids and the effect is very important in the heat transfer giving a better performance.
Tube Layout: refers to how tubes are positioned within the shell. The triangular patterns are employed to give greater heat transfer as they force the fluid to flow in a more turbulent fashion around the piping. Square patterns are employed where high fouling is experienced and cleaning is more regular. Baffle Design: baffles are used in shell and tube heat exchangers to direct fluid across the tube bundle.
They run perpendicularly to the shell and hold the bundle, preventing the tubes from sagging over a long length. They can also prevent the tubes from vibrating.
The most common type of baffle is the segmental baffle. The semicircular segmental baffles are oriented at degrees to the adjacent baffles forcing the fluid to flow upward and downwards between the tube bundle. Baffle spacing is of large thermodynamic concern when designing shell and tube heat exchangers. Baffles must be spaced with consideration for the conversion of pressure drop and heat transfer.
Having baffles spaced too closely causes a greater pressure drop because of flow redirection. Consequently, having the baffles spaced too far apart means that there may be cooler spots in the corners between baffles. It is also important to ensure the baffles are spaced close enough that the tubes do not sag. The other main type of baffle is the disc and doughnut baffle, which consists of two concentric baffles.
An outer, wider baffle looks like a doughnut, whilst the inner baffle is shaped like a disk. This type of baffle forces the fluid to pass around each side of the disk then through the doughnut baffle generating a different type of fluid flow. Fixed tube liquid-cooled heat exchangers especially suitable for marine and harsh applications can be assembled with brass shells, copper tubes, brass baffles, and forged brass integral end hubs.
Conceptual diagram of a plate and frame heat exchanger. A single plate heat exchanger An interchangeable plate heat exchanger applied to the system of a swimming pool Plate heat exchangers[ edit ] Main article: Plate heat exchanger Another type of heat exchanger is the plate heat exchanger.
These exchangers are composed of many thin, slightly separated plates that have very large surface areas and small fluid flow passages for heat transfer. Advances in gasket and brazing technology have made the plate-type heat exchanger increasingly practical.
In HVAC applications, large heat exchangers of this type are called plate-and-frame; when used in open loops, these heat exchangers are normally of the gasket type to allow periodic disassembly, cleaning, and inspection. There are many types of permanently bonded plate heat exchangers, such as dip-brazed, vacuum-brazed, and welded plate varieties, and they are often specified for closed-loop applications such as refrigeration. Plate heat exchangers also differ in the types of plates that are used, and in the configurations of those plates.
When compared to shell and tube exchangers, the stacked-plate arrangement typically has lower volume and cost. Another difference between the two is that plate exchangers typically serve low to medium pressure fluids, compared to medium and high pressures of shell and tube.
A third and important difference is that plate exchangers employ more countercurrent flow rather than cross current flow, which allows lower approach temperature differences, high temperature changes, and increased efficiencies. Plate and shell heat exchanger[ edit ] A third type of heat exchanger is a plate and shell heat exchanger, which combines plate heat exchanger with shell and tube heat exchanger technologies. The heart of the heat exchanger contains a fully welded circular plate pack made by pressing and cutting round plates and welding them together.
Nozzles carry flow in and out of the platepack the 'Plate side' flowpath. The fully welded platepack is assembled into an outer shell that creates a second flowpath the 'Shell side'. Plate and shell technology offers high heat transfer, high pressure, high operating temperature , uling and close approach temperature.
In particular, it does completely without gaskets, which provides security against leakage at high pressures and temperatures. Adiabatic wheel heat exchanger[ edit ] A fourth type of heat exchanger uses an intermediate fluid or solid store to hold heat, which is then moved to the other side of the heat exchanger to be released. Two examples of this are adiabatic wheels, which consist of a large wheel with fine threads rotating through the hot and cold fluids, and fluid heat exchangers.
Plate fin heat exchanger[ edit ] Main article: Plate fin heat exchanger This type of heat exchanger uses "sandwiched" passages containing fins to increase the effectiveness of the unit.
The designs include crossflow and counterflow coupled with various fin configurations such as straight fins, offset fins and wavy fins. Plate and fin heat exchangers are usually made of aluminum alloys, which provide high heat transfer efficiency. These have been used in the nuclear industry as a method for exchanging heat in a sodium system for large liquid metal fast breeder reactors since the early s, using an HCHE device invented by Charles E.
Boardman and John H. Patil et al. Haraburda method from the United States. However, these are based upon assumptions of estimating inside heat transfer coefficient, predicting flow around the outside of the coil, and upon constant heat flux. A modification to the perpendicular flow of the typical HCHE involves the replacement of shell with another coiled tube, allowing the two fluids to flow parallel to one another, and which requires the use of different design calculations.
Each of the two channels has one long curved path. A pair of fluid ports are connected tangentially to the outer arms of the spiral, and axial ports are common, but optional. The main advantage of the SHE is its highly efficient use of space. This attribute is often leveraged and partially reallocated to gain other improvements in performance, according to well known tradeoffs in heat exchanger design.
A notable tradeoff is capital cost vs operating cost. A compact SHE may be used to have a smaller footprint and thus lower all-around capital costs, or an oversized SHE may be used to have less pressure drop, less pumping energy , higher thermal efficiency , and lower energy costs. The distance between the sheets in the spiral channels is maintained by using spacer studs that were welded prior to rolling.
Once the main spiral pack has been rolled, alternate top and bottom edges are welded and each end closed by a gasketed flat or conical cover bolted to the body. This ensures no mixing of the two fluids occurs. Any leakage is from the periphery cover to the atmosphere, or to a passage that contains the same fluid.
Spiral heat exchangers are often used in the heating of fluids that contain solids and thus tend to foul the inside of the heat exchanger. The low pressure drop lets the SHE handle fouling more easily.
Self-cleaning water filters are used to keep the system clean and running without the need to shut down or replace cartridges and bags. The Spiral heat exchanger is good for applications such as pasteurization, digester heating, heat recovery, pre-heating see: For sludge treatment, SHEs are generally smaller than other types of heat exchangers.
Due to the many variables involved, selecting optimal heat exchangers is challenging. Hand calculations are possible, but many iterations are typically needed. As such, heat exchangers are most often selected via computer programs, either by system designers, who are typically engineers , or by equipment vendors. To select an appropriate heat exchanger, the system designers or equipment vendors would firstly consider the design limitations for each heat exchanger type.
Though cost is often the primary criterion, several other selection criteria are important:. Small-diameter coil technologies are becoming more popular in modern air conditioning and refrigeration systems because they have better rates of heat transfer than conventional sized condenser and evaporator coils with round copper tubes and aluminum or copper fin that have been the standard in the HVAC industry.
Small diameter coils can withstand the higher pressures required by the new generation of environmentally friendlier refrigerants. Two small diameter coil technologies are currently available for air conditioning and refrigeration products: Choosing the right heat exchanger HX requires some knowledge of the different heat exchanger types, as well as the environment where the unit must operate.
Typically in the manufacturing industry, several differing types of heat exchangers are used for just one process or system to derive the final product. With sufficient knowledge of heat exchanger types and operating requirements, an appropriate selection can be made to optimise the process. Online monitoring of commercial heat exchangers is done by tracking the overall heat transfer coefficient. The overall heat transfer coefficient tends to decline over time due to fouling.
By periodically calculating the overall heat transfer coefficient from exchanger flow rates and temperatures, the owner of the heat exchanger can estimate when cleaning the heat exchanger is economically attractive.
Integrity inspection of plate and tubular heat exchanger can be tested in situ by the conductivity or helium gas methods. These methods confirm the integrity of the plates or tubes to prevent any cross contamination and the condition of the gaskets.
Mechanical integrity monitoring of heat exchanger tubes may be conducted through Nondestructive methods such as eddy current testing. Fouling occurs when impurities deposit on the heat exchange surface. Deposition of these impurities can decrease heat transfer effectiveness significantly over time and are caused by:. This model was originally proposed in by Kern and Seaton. Crude Oil Exchanger Fouling.
Fouling occurs on the crude side of these exchangers due to asphaltene insolubility. The nature of asphaltene solubility in crude oil was successfully modeled by Wiehe and Kennedy. Cooling Water Fouling. Cooling water systems are susceptible to fouling.
Cooling water typically has a high total dissolved solids content and suspended colloidal solids. Localized precipitation of dissolved solids occurs at the heat exchange surface due to wall temperatures higher than bulk fluid temperature. Cooling water is typically on the tube side of a shell and tube exchanger because it's easy to clean. To prevent fouling, designers typically ensure that cooling water velocity is greater than 0.
Other approaches to control fouling control combine the "blind" application of biocides and anti-scale chemicals with periodic lab testing. Plate and frame heat exchangers can be disassembled and cleaned periodically. In large-scale cooling water systems for heat exchangers, water treatment such as purification, addition of chemicals , and testing, is used to minimize fouling of the heat exchange equipment.
Other water treatment is also used in steam systems for power plants, etc. A variety of companies have started using water borne oscillations technology to prevent biofouling. Without the use of chemicals, this type of technology has helped in providing a low-pressure drop in heat exchangers.
The human nasal passages serve as a heat exchanger, with cool air being inhaled and warm air being exhaled. Its effectiveness can be demonstrated by putting the hand in front of the face and exhaling, first through the nose and then through the mouth.
Air exhaled through the nose is substantially cooler. In species that have external testes such as humans , the artery to the testis is surrounded by a mesh of veins called the pampiniform plexus.
This cools the blood heading to the testes, while reheating the returning blood. Arteries to the skin carrying warm blood are intertwined with veins from the skin carrying cold blood, causing the warm arterial blood to exchange heat with the cold venous blood. This reduces the overall heat loss in cold waters.
Heat exchangers are also present in the tongue of baleen whales as large volumes of water flow through their mouths. The carotid rete is a counter-current heat exchanging organ in some ungulates. The blood ascending the carotid arteries on its way to the brain, flows via a network of vessels where heat is discharged to the veins of cooler blood descending from the nasal passages.
Heat exchangers are widely used in industry both for cooling and heating large scale industrial processes. The type and size of heat exchanger used can be tailored to suit a process depending on the type of fluid, its phase, temperature, density, viscosity, pressures, chemical composition and various other thermodynamic properties. In many industrial processes there is waste of energy or a heat stream that is being exhausted, heat exchangers can be used to recover this heat and put it to use by heating a different stream in the process.
This practice saves a lot of money in industry, as the heat supplied to other streams from the heat exchangers would otherwise come from an external source that is more expensive and more harmful to the environment. In waste water treatment, heat exchangers play a vital role in maintaining optimal temperatures within anaerobic digesters to promote the growth of microbes that remove pollutants. Common types of heat exchangers used in this application are the double pipe heat exchanger as well as the plate and frame heat exchanger.
In commercial aircraft heat exchangers are used to take heat from the engine's oil system to heat cold fuel. Tubular heat exchangers and plate heat exchangers are still the most widely applied product types. A simple heat exchange   might be thought of as two straight pipes with fluid flow, which are thermally connected.
Assume a steady state, so that the temperature profiles are not functions of time. Assume also that the only transfer of heat from a small volume of fluid in one pipe is to the fluid element in the other pipe at the same position, i. By Newton's law of cooling the rate of change in energy of a small volume of fluid is proportional to the difference in temperatures between it and the corresponding element in the other pipe:.
This change in internal energy results in a change in the temperature of the fluid element. The time rate of change for the fluid element being carried along by the flow is:.
The differential equations governing the heat exchanger may now be written as:. Note that, since the system is in a steady state, there are no partial derivatives of temperature with respect to time, and since there is no heat transfer along the pipe, there are no second derivatives in x as is found in the heat equation. These two coupled first-order differential equations may be solved to yield:.
Define the average temperatures in each pipe as:. Choosing any two of the temperatures above eliminates the constants of integration, letting us find the other four temperatures. We find the total energy transferred by integrating the expressions for the time rate of change of internal energy per unit length:.
By the conservation of energy, the sum of the two energies is zero. From Wikipedia, the free encyclopedia. Shell and tube heat exchanger, 2-pass tube side 1—2 crossflow. Shell and tube heat exchanger, 2-pass shell side, 2-pass tube side countercurrent. Main article: Shell and tube heat exchanger.
Plate heat exchanger. Plate fin heat exchanger.
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March Learn how and when to remove this template message. Micro heat exchanger. Further information: Countercurrent exchange in biological systems. Architectural engineering Chemical engineering Cooling tower Copper in heat exchangers Heat pipe Heat pump Heat recovery ventilation Jacketed vessel Log mean temperature difference LMTD Marine heat exchangers Mechanical engineering Micro heat exchanger Moving bed heat exchanger Packed bed and in particular Packed columns Pumpable ice technology Reboiler Recuperator , or cross plate heat exchanger Regenerator Run around coil Steam generator nuclear power Surface condenser Toroidal expansion joint Thermosiphon Thermal wheel , or rotary heat exchanger including enthalpy wheel and desiccant wheel Tube tool Waste heat.
Applications, Heat Exchangers: Selection, Rating and Thermal Design 2nd ed. CRC Press. Constructal design of circular multilayer microchannel heat sinks. Journal of Thermal Science and Engineering Applications, 11 1 , Heat Exchanges: Selection, Design and Construction. New York: Longman Scientific and Technical. Distillation Design 1st ed. Perry's Chemical Engineers' Handbook 6th ed. Applied Thermal Engineering. Journal of Heat Transfer.
International Journal of Refrigeration. Chemical Engineering. Retrieved 14 July July Consider Helical-Coil Heat Exchanger". McGill University. June April September Experimental Thermal and Fluid Science. Saunders Retrieved The Microgroove advantage; http: Microchannel air-cooled condenser; Heatcraft Worldwide Refrigeration; April ; http: Wiehe and R. Retrieved 18 August Burggren; Kathleen French; Roger Eckert Eckert animal physiology: