Counter flow — the two fluids enter at opposite ends of the heat exchanger and flow counter to one another. In this design, the temperature differences are less but more constant over the length of the exchanger. It is possible that the fluid being heated may leave the exchanger at a higher temperature than the exit temperature of the heating fluid.
This is the most efficient design because of higher temperature differential over length of the exchanger. There can be more than one method of heat transfer in a heat exchanger. Heat transfer will occur using one or more modes of transfer, conduction, convection, or radiation. Proper implementation of heat exchangers in multi-process systems, like oil refineries, requires a consideration of the network of heat flows on a systems level. Sophisticated software is available to aid the designer in this process.
Fouling mitigation is also a consideration of design and can include the consideration of various technologies, velocities, bypasses for cleaning individual HX during the operation, and the incorporation of spare heat exchangers. Similarly, software is available for managing heat exchanger fouling. Based on process conditions and component selection, some software packages can predict the rate at which heat exchangers are likely to experience fouling. Software packages are also available to monitor fouling by examining heat exchanger performance over time.
Estimates of the costs of cleaning heat exchangers versus the economic benefits in terms of reduced energy use are also calculated. Cooling ponds may be used to allow warm water to naturally cool through evaporative loss to the atmosphere.
The water in the pond can then be recirculated into the plant as cooling water. These ponds may offer secondary recreational purposes such as fishing, boating, or swimming. Make up water is required to account for evaporative losses. A large amount of land is required for this option. Direct venting of steam may reduce the need for process water cooling but this option ignores the primary reasons for cooling which is to improve system efficiency and conserve process quality water and results in additional make up water and water treatment chemicals.
This option is generally not used except in start-up, emergency venting and shut down operations. Heat Exchangers require regular maintenance to operate at high efficiency and usually require a rigorous overhaul schedule. Much of this effort is aimed at countering the effects of fouling, wherein solids like foreign particles or precipitates accumulate on heat exchanger surfaces, inhibiting heat transfer and restricting fluid flow.
Chemical additives can also prevent the precipitation of particles and may be a cost effective means of fouling prevention. Overhauls can range from simple preventative maintenance activities i. This down time should also be taken into consideration when sizing the heat exchangers and designing the process network.
Many heat exchangers operate at high pressures and temperatures or with hazardous fluids and adequate operating procedures must be followed to avoid personnel risks and system outages. New equipment designs and any repairs should comply with applicable codes. Many heat exchanger designs are available in numerous materials and can be customized for specific applications as well as standard designs that are available with minimal lead time at lower costs.
Heat exchangers could be classified in many different ways. Generally, industrial heat exchangers have been classified according to construction, transfer processes, degrees of surface compactness, flow arrangements, pass arrangements, phase of the process fluids and heat transfer mechanisms as seen in Figure 1.
Classification of industrial heat exchanger [ 12 ]. The design concepts of heat exchanger must meet normal process requirements specified through service conditions for combinations of un-corroded and corroded conditions and the clean and fouled conditions. One of the critical criteria of heat exchanger design is the exchanger must be designed for ease of maintenance, which usually means cleaning or replacement of parts, tubing, fittings, etc. Hence, a heat exchanger design should be as simple as possible particularly if heavy fouling is expected.
By minimize temperature in conjunction with the choice of fluid velocity and reducing the concentration of foulant precursors, will reduce the incidence of potential fouling. Moreover, highest flowing velocity should be allowed under the constraints of pressure drop and erosion from the flow. In addition, material selection within constrained cost retards the build-up of deposits and allows shorter residence time.
It should also be compatible in terms of pH, corrosion and not only just heat exchanger, but also in terms of heat equipment and transfer lines of the heat exchanger. Fouling is always defined as the formation and accumulation of unwanted materials deposit onto the processing equipment surfaces. These normally very low thermal conductivity materials form an insulation on the surface which can extremely deteriorate the performance of the surface to transfer heat under the temperature difference for which it was designed [ 13 ].
On top of this, fouling increases the resistance to fluid flow, resulting in higher pressure drop across the heat exchanger. Many types of fouling can occur on the heat transfer surfaces, for examples, crystallization fouling, particulate fouling, corrosion fouling, chemical reaction fouling, biological fouling and solidification fouling [ 14 ]. Fouling can have a very costly effect in the industries which eventually increases fuel usage, interrupts operation, production losses and enhances maintenance costs [ 15 ].
The fouling is formed in five stages which can be summarized as initiation of fouling, transport to the surface, attachment to the surface, removal from the surface and ageing at the surface [ 16 ]. There are a few parameters influencing the fouling factors, such as pH [ 9 ], velocity [ 17 ], bulk temperature of fluid [ 18 ], temperature of the heat transfer surface, surface structure [ 19 ] and roughness [ 20 , 21 ]. The overall fouling process is usually considered to be the net result of two simultaneous sub processes: a deposition process and a removal process as shown in Figure 2.
As illustrated in Figure 3 , the growth of these deposits causes the heat transfer performance of heat exchanger to decline with time. This problem affects the energy consumption of industrial processes and eventually causes industrial breakdown due to the heat exchanger failure as seen in Figure 4. Overall fouling process [ 22 ]. Fouling resistance against time curves [ 22 ]. Heavy build-up of deposition on heat exchanger piping [ 24 , 23 ].
Environment features such as soil, atmosphere, water or aqueous solutions commonly attack general metal and alloys. The deterioration of these metals is known as corrosion. It is agreeable that corrosion happens due to electrochemical mechanism. Premature failures in various equipment are caused by corrosion in most commercial processes and engineering operations, leading to unwanted issues. This includes pricey breakdown, un-schedule shutdown and increases in maintenance cost. This downtime worsens in fields such as chemical industries, oil refining, sea and land electric power plant, paper manufacture, air conditioning, refrigerator, food and liquor manufacturing.
Hence, general info and mechanism of corrosion will bring great interest to public and industry [ 24 ]. The corrosion process is affected by various parameters as show in Figure 5. Hence, these criteria should take consideration into the design basics of heat exchangers. Factor influencing corrosion [ 25 ]. Apart from the high cost of heat exchanger fouling, very few work have been reported to accurate determine economic penalties causes by fouling.
Therefore, these attribute cost to difference aspect of heat exchanger design and operation. However, reliable knowledge of fouling economics is desirable in order to evaluate the cost efficiency of various mitigation strategies [ 26 , 27 ]. The total fouling-related costs involve the following:. Capital expenditure. Excessive surface area required to overcome the heavy fouling conditions, costs for stronger foundation, provision for extra spaces and increased transportation and installation costs.
Energy costs. Costs for extra fuel required if fouling leads to extra fuel burning in heat exchanging equipment to overcome the effect of fouling. Maintenance costs. Costs for removal of fouling deposits, costs for chemicals or other operating costs for antifouling devices. We use cookies to personalize content, to provide better marketing, and to analyze our traffic. You consent to our use of Cookies if you continue to use this website. Search Close Search Bar. They provide the exact combination of temperature and holding time, for precise pasteurization and ultra-high temperature treatment and regeneration in a variety of applications: Milk and cheese milk pasteurization Ultra-high temperature sterilization Beverage and energy drink pasteurization Standard and pulpy juice pasteurization Beer wort heating and beer cooling Liquid egg processing Bottled water treatment Soups, sauces and starch heating Ketchup and mustard heating and cooling.
Pharmaceutical, food, and beverage operations realize the value of heat exchangers in several ways: Heat exchangers heat the cleaning fluids that remove residues from systems components. Heat exchangers create consistent temperatures for pasteurizing and Clean-in-place CIP. They heat water for effective rinsing of food production equipment tanks and piping. They can be placed on skids for small-footprint, flexible CIP equipment positioning.
Heat exchangers themselves are CIP'able because their designs induce turbulence when systems maintain sufficient flow rate. They transfer heat without contaminating the heated fluids. Energy savings: regenerative heat transfer conserves energy by re-using heated fluids to heat fluids in repeatable cycles.
Greater efficiencies in processing also result in lower water consumption worth thousands of dollars per site P. Advantages of Each Type of Heat Exchanger To meet the heating and cooling needs of such an array of applications and products, heat-exchanger designs have evolved to meet a range of site-specific temperature-modulation requirements. Plate-and-Frame Heat Exchangers Highly efficient and typically have a small footprint allowing a more compact system design. Shell-and-Tube Heat Exchangers Simple, low-maintenance in-line heating option.
Scraped-Surface Heat Exchangers Used in processing are more costly than other options, but they are the right choice for products that are viscous or sticky or include large particulates. Flexible plate and frame heat exchangers Because plate and frame heat exchangers are designed to increase or decrease in capacity depending on application, they are among the most versatile heat exchangers available.
Efficient heat transfer of shell and tube heat exchangers Processors use shell-and-tube heat exchangers for general product heating and cooling. Double-duty scraped-surface heat exchangers By performing heating duties while also scraping interior surfaces to prevent fouling, scraped-surface heat exchangers add value to systems by keeping them running longer between cleaning.
Heating cleaning fluids that remove residues from systems components Heat exchangers play an important role in maintaining correct cleaning fluid temperatures for clean-in-place. In all sanitary applications including pharmaceuticals and food processing, cleaning and sanitation must occur at sufficient intervals to prevent equipment fouling, reactions, and cross contamination, and temperature regulation is a key factor in maintaining temperatures during each interval.
Download Infographic Heat exchangers are CIP'able CIP effectiveness is determined by cleaning time, strength of cleaning chemicals, the temperature of cleaning chemicals, and the amount of turbulence, so heat exchangers have a key role to play in operational productivity and effectiveness.
Being able to fit into virtually any design makes them highly versatile, and therefore highly beneficial, thermal management solutions. Among their many benefits , however, three of the most important include the ability to save a maximum amount of space, their reduced impact on the environment, and their reduced need for energy and routine maintenance costs.
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