In this type, two fluids with different temperatures, one of which flows through the tubes (the tube side fluid) and the other flows outside the tubes but inside the shell (the shell side fluid). The heat transfer rate associated with a spiral tube is higher than that for a straight tube. If you continue to use this site we will assume that you are happy with it. We are launching courses in Pipeline Design and Business & Project Development soon. place simultaneously. That is why heat exchangers are widely used for heat up or cooling down a fluid stream in a processing plant. Shell and Tube Heat Exchangers are some of the most popular types of exchangers due to its flexibility. In the sections below, a review of each of these heat transfer modes is presented. More heat is transferred in a counterflow arrangement than in a parallel flow heat exchanger. And the transfer of heat takes. This exchanger usually consists of two concentric pipes; The inner pipe acts as the conductive barrier, where one fluid flows in the inner pipe, and the other fluid flows in the annulus between pipes. Direct-contact heat exchangers (DCHEs) make … In these units, the streams flow at right angles to each other. Compact heat exchangers are used in aircraft & automobile industries. Fouling also increases the pressure drop across heat exchangers. It should have a definite corrosion rate. In a direct-contact exchanger, two immiscible fluids under different temperatures come into direct contact, exchange heat, and are then separated. The fluid may be in direct contact or separated by a solid wall so that they don’t get mixed. Shell and coil type heat exchanger consists of a helical coil. Thus, there is no direct contact between thermally interacting fluids. The simplest heat exchanger is when the hot and cold fluids move in the same or opposite directions. Thermal expansion is no problem, but cleaning is almost impossible. Most direct contact heat exchangers fall under the Gas- Liquid category, where heat is transferred between a gas and liquid in the form of drops, films or sprays. This type of exchanger is widely used in the food industry because it can quickly be taken apart to clean. This heat exchanger also referred to as a surface heat exchanger, can be further classified into direct-transfer type, storage type, and fluidized-bed exchangers. Increasing the number of passes increases overall effectiveness, but it also increases the pressure drop on the multi-pass side. The plates are arranged alternatively so that hot fluid flows in 1, 3 and 5 numbered plate while cold fluid flows in 2, 4 & 6 numbered plates. Condensers and evaporators are used in distillation processes, refrigeration and power plants. To understand heat exchanger thermodynamics, a good starting point is to learn about the three ways in which heat can be transferred – conduction, convection, and radiation. Flow rates determine the flow area. Here the fluid flows through the exchanger along its length once. Double-pipe exchangers are generally used for small-capacity applications because they are cheap for both design and maintenance. 4 SELECTION PARAMETERS FOR HEAT EXCHANGER: https://en.wikipedia.org/wiki/Heat_exchanger, http://thepipingtalk.com/2019/11/types-of-heat-exchanger-according-to-construction/, Very high heat transfer rates are achievable, Due to the absence of a heat transfer surface, the fouling problem is less. The heat exchanger is considered as a single-pass unit if both fluids make one pass in the exchanger. In the Parallel/Co-current flow arrangement, the hot and cold fluids enter at the same end, flow in the same direction, and leave at the same end. High-pressure drop results in high pumping power, which ultimately increases the cost. Each of the plates is separated by a gasket which seals the plates and arranges the flow of fluids between the plates. Flow in a double-pipe heat exchanger can be co-current or countercurrent. Very often this heat transfer is accompanied by mass transfer. This arrangement lets the hot and cold fluid exchange heat while not mixing. (1982) Industrial Heat Exchangers-A Basic Guide, Hemisphere Publishing Corporation. Shell and Coil type of heat exchanger. The hot fluid flow in one channel and just next to it the cold fluid.
In the Heat exchanger, heat flows from hot stream to the cold one. On the other hand, the pressure drop also creates turbulence, which increases the heat transfer coefficient. In an indirect-contact heat exchanger, the fluid streams remain separate, and the heat transfers continuously through an impervious wall. These units comprise of a large approximately cylindrical shell (usually over 100 m in … : Cooling towers, jet condensers for water vapour, and other vapors utilizing water spray. The pressure is one of the parameters which determines the thickness of components. Example- cooling towers, scrubbers etc. The major components of this exchanger are tubes (or tube bundle), shell, frontend head, rear-end head, baffles, and tube sheets. The fouling of heat exchangers may be defined as the deposition of unwanted material on heat transfer surfaces, impacting its performance. Heat exchanger are classified according to their construction features as below, SOLAR POWERED RAINWATER HARVESTING SYSTEM. Based on the heat transfer process, heat exchangers are classified as indirect contact and direct contact. Higher is the pressure; higher is the thickness of pressure retaining components. In direct contact heat exchangers, heat transfer takes place between two immiscible fluids like a gas and a liquid coming into direct contact. This heat exchanger also referred to as a surface heat exchanger, can be further classified into direct-transfer type, storage type, and fluidized-bed exchangers. This is less efficient than countercurrent flow but does provide more uniform wall temperatures. In a direct-contact exchanger, two immiscible fluids under different temperatures come into direct contact, exchange heat, and are then separated. This system handles fluids at different pressures, higher pressure fluid is typically directed through tubes, and lower pressure fluid is circulated through a shell side. After flowing through one full length, if the flow direction is reversed and fluid flows through an equal or different-sized section, it is considered to have made a second pass. In this type, efficiency lies between countercurrent flow and co-current flow exchangers. It is an important parameter in heat exchanger design. The plates are either smooth or have some form of a groove. For obtaining a higher flow area, flow rates should be kept quite high. In direct contact type heat exchangers the two fluids are not separated by the wall and come into direct contact, exchange heat and are then separated. This type of exchangers is generally used for low pressure & low-temperature application. They are simple, but they have low efficiency with the large space occupied in large scales. Typical applications of a direct-contact exchanger involve a mass transfer in addition to heat transfer, such as in evaporative cooling and rectification; means this exchanger involves phase change of working fluid, which enhances the heat transfer rate, this can be further classified into Immiscible Fluid Exchangers. The streams flow parallel to each other and in the same direction. Fouling increases the resistance to fluid flow and lowers the overall heat transfer coefficient of heat exchangers. 3. heaters. Tubular Exchangers are used in the industrial paint system to maintain temperature. MOC for the heat exchanger depends on the types of fluids or vapours handled. Gas-Liquid Exchangers, Liquid-Vapor Exchangers. Here both fluids flow parallel perpendicular to each other. This heat exchanger consists of two concentric pipes of different diameters. In a direct contact heat exchanger, the exchange of heat takes.
The fluids can be either liquids or gases. They are used for gas-to-liquid and gas-to-gas heat transfer applications mostly when the operating temperature or pressure is very high, or fouling is a significant problem. As there is no extra wall or barrier for heat transfer, closer temperatures are attained. Compared with the traditional direct-contact heat exchanger, heat transfer means has more advantages due to a more simple design, low temperature driving force and higher heat transfer efficiency [2, 3]. The heat exchanger’s thermal effectiveness is the ratio of the heat transfer rate to the maximum possible heat transfer rate. The material should exhibit strength to withstand operating temperature and pressure. place by direct mixing of hot and cold fluids. Similar to the plate exchanger, the spiral exchanger is compact and requires less installation and maintenance space. 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. This type of flow arrangement allows the largest change in both fluids’ temperature and therefore is most efficient.
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