Heat Exchangers Selection Rating And Thermal Design Scribd Pdf
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- Heat Exchanger Rating Hysys Manual Pdf
- Understanding Heat Exchangers
- Heat Exchanger Design
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Heat Exchanger Rating Hysys Manual Pdf
Romina Ronquillo. Heat exchangers are devices designed to transfer heat between two or more fluids—i. Depending on the type of heat exchanger employed, the heat transferring process can be gas-to-gas , liquid-to-gas , or liquid-to-liquid and occur through a solid separator, which prevents mixing of the fluids, or direct fluid contact.
Other design characteristics, including construction materials and components, heat transfer mechanisms, and flow configurations, also help to classify and categorize the types of heat exchangers available. Finding application across a wide range of industries, a diverse selection of these heat exchanging devices are designed and manufactured for use in both heating and cooling processes. This article focuses on heat exchangers, exploring the various designs and types available and explaining their respective functions and mechanisms.
Additionally, this article outlines the selection considerations and common applications for each type of heat exchanging device. The design of a heat exchanger is an exercise in thermodynamics, which is the science that deals with heat energy flow, temperature, and the relationships to other forms of energy. In the sections below, a review of each of these heat transfer modes is presented. Conduction is the passing of thermal energy between materials that are in contact with one another.
Temperature is a measure of the average kinetic energy of molecules in a material — warmer objects that are at a higher temperature are exhibiting more molecular motion.
When a warmer object is brought in contact with a cooler object one that is at a lower temperature , there is a thermal energy transfer between the two materials, with the cooler object becoming more energized and the warmer object becoming less energized. This process will continue until thermal equilibrium has been achieved.
The rate at which heat energy is transferred in a material by thermal conduction is given by the following expression:. Air and other gases generally have low thermal conductivities, while non-metallic solids exhibit higher values and metallic solids generally showing the highest values. 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. The convective heat transfer coefficient h c is a function of the properties of the fluid, similar to the thermal conductivity of the material mentioned earlier regarding conduction. Thermal radiation is a mechanism of heat energy transfer that involves the emission of electromagnetic waves from a heated surface or object.
Unlike conduction and convection, thermal radiation does not require an intermediate medium to carry the wave energy. All objects whose temperature is above absolute zero It is also a function of the temperature of the material.
This transfer of heat results in a decrease in temperature for F 1 and an increase in temperature for F 2. Depending on whether the application is aimed towards heating or cooling a fluid, this process and devices that employ it can be used to direct heat towards or away from a system, respectively. As outlined above, all heat exchangers operate under the same basic principles. However, these devices can be classified and categorized in several different ways based on their design characteristics.
The main characteristics by which heat exchangers can be categorized include:. The flow configuration, also referred to as the flow arrangement, of a heat exchanger refers to the direction of movement of the fluids within the heat exchanger in relation to each other.
There are four principal flow configurations employed by heat exchangers:. Cocurrent flow heat exchangers , also referred to as parallel flow heat exchangers, are heat exchanging devices in which the fluids move parallel to and in the same direction as each other.
Although this configuration typically results in lower efficiencies than a counter flow arrangement, it also allows for the greatest thermal uniformity across the walls of the heat exchanger.
Countercurrent flow heat exchangers , also known as counter flow heat exchangers, are designed such that the fluids move antiparallel i. The most commonly employed of the flow configurations, a counter flow arrangement typically exhibits the highest efficiencies as it allows for the greatest amount of heat transference between fluids and, consequently, the greatest change in temperature.
In crossflow heat exchangers , fluids flow perpendicularly to one another. The efficiencies of heat exchangers which employ this flow configuration fall between that of countercurrent and cocurrent heat exchangers. Hybrid flow heat exchangers exhibit some combination of the characteristics of the previously mentioned flow configurations. For example, heat exchanger designs can employ multiple flow passes and arrangements e. These types of heat exchangers are typically used to accommodate the limitations of an application, such as space, budget costs, or temperature and pressure requirements.
While in the previous section, heat exchangers were categorized based on the type of flow configuration employed, this section categorizes them based on their construction. The construction characteristics by which these devices can be classified include:. Heat exchangers can be classified as recuperative heat exchangers and regenerative heat exchangers.
The difference between recuperative and regenerative heat exchanger systems is that in recuperative heat exchangers commonly called recuperators , each fluid simultaneously flows through its own channel within the heat exchanger. On the other hand, regenerative heat exchangers , also referred to as capacitive heat exchangers or regenerators, alternately allow warmer and cooler fluids to flow through the same channel.
Both recuperators and regenerators can be further separated into different categories of exchangers, such as direct or indirect and static or dynamic, respectively. Of the two types indicated, recuperative heat exchangers are more commonly employed throughout industry.
Recuperative heat exchangers employ either direct contact or indirect contact transfer processes to exchange heat between fluids. In direct contact heat exchangers , the fluids are not separated within the device and heat transfers from one fluid to another through direct contact. On the other hand, in indirect heat exchangers , the fluids remain separated from one another by thermally conductive components, such as tubes or plates, throughout the heat transfer process.
The components first receive heat from the warmer fluid as it flows through the heat exchanger, and then transfer the heat to the cooler fluid as it flows through. Some of the devices which employ direct contact transfer processes include cooling towers and steam injectors , while devices that employ indirect contact transfer processes include tubular or plate heat exchangers.
There are two main types of regenerative heat exchangers—static heat exchangers and dynamic heat exchangers. In static regenerators also known as fixed bed regenerators , the heat exchanger material and components remains stationary as fluids flow through the device, while in dynamic regenerators the material and components move throughout the heat transfer process.
Both types are at risk of cross-contamination between fluid streams, necessitating careful design considerations during manufacturing. In one example of the static type, warmer fluid is run through one channel while cooler fluid runs through another for a fixed period of time at the end of which, through the use of quick-operating valves, flow is reversed such that the two fluids switch channels. An example of the dynamic type typically employs a rotating, thermally conductive component e.
As the component rotates, any given section alternately passes through the warmer steam and cooler streams, allowing for the component to absorb heat from the warmer fluid and transfer the heat to the cooler fluid as it passes through.
Figure 2, below, depicts the heat transfer process within a rotary-type regenerator with a countercurrent flow configuration. There are several types of components which can be employed in heat exchangers, as well as a wide range of materials used to construct them.
The components and materials used depend on the type of heat exchanger and its intended application. Some of the most common components used to construct heat exchangers include shells, tubes, spiral tubes coils , plates, fins, and adiabatic wheels.
Further detail on how these components function within a heat exchanger will be provided in the next section see Types of Heat Exchangers. While metals are highly suitable—and commonly used—for constructing heat exchangers due to their high thermal conductivity, as in the case of copper , titanium , and stainless steel heat exchangers, other materials, such as graphite, ceramics, composites, or plastics, may offer greater advantages depending on the requirements of the heat transfer application.
There are two types of heat transfer mechanisms employed by heat exchangers—single-phase or two-phase heat transfer. In single-phase heat exchangers , the fluids do not undergo any phase change throughout the heat transfer process, meaning that both the warmer and cooler fluids remain in the same state of matter at which they entered the heat exchanger.
For example, in water-to-water heat transfer applications, the warmer water loses heat which is then transferred to the cooler water and neither change to a gas or solid. On the other hand, in two-phase heat exchangers , fluids do experience a phase change during the heat transfer process. The phase change can occur in either or both of the fluids involved resulting in a change from a liquid to a gas or a gas to a liquid.
Typically, devices that employ a two-phase heat transfer mechanism require more complex design considerations than ones that employ a single-phase heat transfer mechanism.
Some of the types of two-phase heat exchangers available include boilers, condensers, and evaporators. Based on the design characteristics indicated above, there are several different variants of heat exchangers available. Some of the more common variants employed throughout industry include:. The most common type of heat exchangers, shell and tube heat exchangers are constructed of a single tube or series of parallel tubes i.
Other design characteristics available for this type of heat exchanger include finned tubes , single- or two-phase heat transfer, countercurrent flow, cocurrent flow, or crossflow arrangements, and single, two, or multiple pass configurations.
Some of the types of shell and tube heat exchangers available include helical coil heat exchangers and double pipe heat exchangers, and some of the applications include preheating , oil cooling , and steam generation. A form of shell and tube heat exchanger, double pipe heat exchangers employ the simplest heat exchanger design and configuration which consists of two or more concentric, cylindrical pipes or tubes one larger tube and one or more smaller tubes. As per the design of all shell and tube heat exchangers, one fluid flows through the smaller tube s , and the other fluid flows around the smaller tube s within the larger tube.
The design requirements of double pipe heat exchangers include characteristics from the recuperative and indirect contact types mentioned previously as the fluids remain separated and flow through their own channels throughout the heat transfer process.
However, there is some flexibility in the design of double pipe heat exchangers, as they can be designed with cocurrent or countercurrent flow arrangements and to be used modularly in series, parallel, or series-parallel configurations within a system.
For example, Figure 4, below, depicts the transfer of heat within an isolated double pipe heat exchanger with a cocurrent flow configuration. Also referred to as plate type heat exchangers , plate heat exchangers are constructed of several thin, corrugated plates bundled together. Each pair of plates creates a channel through which one fluid can flow, and the pairs are stacked and attached—via bolting, brazing, or welding—such that a second passage is created between pairs through which the other fluid can flow.
The standard plate design is also available with some variations, such as in plate fin or pillow plate heat exchangers. Plate fin exchangers employ fins or spacers between plates and allow for multiple flow configurations and more than two fluid streams to pass through the device. Pillow plate exchangers apply pressure to the plates to increase the heat transfer efficiency across the surface of the plate. Some of the other types available include plate and frame , plate and shell , and spiral plate heat exchangers.
Boilers, condensers, and evaporators are heat exchangers which employ a two-phase heat transfer mechanism. As mentioned previously, in two-phase heat exchangers one or more fluids undergo a phase change during the heat transfer process, either changing from a liquid to a gas or a gas to a liquid. Condensers are heat exchanging devices that take heated gas or vapor and cool it to the point of condensation, changing the gas or vapor into a liquid.
On the other hand, in evaporators and boilers , the heat transfer process changes the fluids from liquid form to gas or vapor form. Heat exchangers are employed in a variety of applications across a wide range of industries.
Consequently, there are several variants of heat exchangers available, each suitable for the requirements and specifications of a particular application.
Beyond the variants mentioned above, other types available include air cooled heat exchangers , fan cooled heat exchangers , and adiabatic wheel heat exchangers. While there are a wide variety of heat exchangers available, the suitability of each type and its design in transferring heat between fluids is dependent on the specifications and requirements of the application.
Those factors largely determine the optimal design of the desired heat exchanger and influence the corresponding rating and sizing calculations. Some of the factors that industry professionals should keep in mind when designing and choosing a heat exchanger include:. The specific type of fluids—e.
Understanding Heat Exchangers
Romina Ronquillo. Heat exchangers are devices designed to transfer heat between two or more fluids—i. Depending on the type of heat exchanger employed, the heat transferring process can be gas-to-gas , liquid-to-gas , or liquid-to-liquid and occur through a solid separator, which prevents mixing of the fluids, or direct fluid contact. Other design characteristics, including construction materials and components, heat transfer mechanisms, and flow configurations, also help to classify and categorize the types of heat exchangers available. Finding application across a wide range of industries, a diverse selection of these heat exchanging devices are designed and manufactured for use in both heating and cooling processes. This article focuses on heat exchangers, exploring the various designs and types available and explaining their respective functions and mechanisms. Additionally, this article outlines the selection considerations and common applications for each type of heat exchanging device.
The heat capacity of the oil is 1. What is the total amount of heat transferred? Morrison, MichiganDesign of a heat exchanger is an iterative trial error process. Make an initial estimate of the overall heat transfer coefficient, U, based on the fluids involved. Heat Exchangers Heat exchangers are used to transfer heat between two sources.
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Heat Exchanger Design
Молодые люди поднялись по ступенькам, и двигатель автобуса снова взревел. Беккер вдруг понял, что непроизвольно рванулся вперед, перед его глазами маячил только один образ - черная помада на губах, жуткие тени под глазами и эти волосы… заплетенные в три торчащие в разные стороны косички. Красную, белую и синюю. Автобус тронулся, а Беккер бежал за ним в черном облаке окиси углерода. - Espera! - крикнул он ему вдогонку. Его туфли кордовской кожи стучали по асфальту, но его обычная реакция теннисиста ему изменила: он чувствовал, что теряет равновесие.
Не знаю, о ком вы говорите, - поправил его Беккер, подзывая проходившую мимо официантку. Он купил две бутылки пива и протянул одну Двухцветному. Панк изумленно взглянул на бутылку, потом отпил изрядный глоток и тупо уставился на Беккера. - Чего вы от меня хотите, мистер. Беккер улыбнулся: - Я ищу одну девушку.
Download as PDF or read online from Scribd S. (Sadik) Heat exchangers: selection, rating, and thermal design / Sadik Kakay, Hongtan Liu~.
Всю ответственность я беру на. Быстрее. Хейл выслушал все это, не сдвинувшись с места и не веря своим ушам.