The consequences of using the wrong heat exchanger can be serious. The interior tube acts a heat tracer which helps prevent condensate from freezing before it can be drained from the coil. Consider a waterlogging air heater frost coil. A steam distributing coil uses a tube-within-a-tube design, where the steam is delivered through the interior tube and condenses on the inside of the exterior tube (see Figure 1). If this temperature difference is relatively large, then the natural convective currents will be significant and the heat transfer coefficient will be high. What are the primary and secondary factors that affect coil design? Alternatively, if there is some flexibility regarding the piping, then either same-end or opposite-end connections may be employed, although this should be understood at the outset of the coil design process. Return to Spirax Sarco International continue to Spirax Sarco, This region has not yet joined our new website. 2 4 Air Vent 3 5 Condensate Return Safety Drain Vacuum Breaker 6 12" Min. Steam coils require numerous considerations, such as traps, pitched casing, piping flexibility, and vacuum breakers. Privacy Policy. The coil design also allows for thermal expansion and contraction without thermal stress to maximize heat transfer. Pass 850 kg/h of condensate with 1.1 bar g in the coil, i.e. So, gradually temperature is decrease until about 50 deg C. This mean Heat loss from tank shell is higher than heat release from steam coil. The DRS Marlo Coil steam heating coil is a steam to air heat transfer device intended to be used in commercial, institutional, industrial, marine, or process use. However, it may be better to size the control valve to supply the maximum (start-up) load. The seal arrangement allows a small amount of condensate to collect to act as a water seal, and prevents the occurrence of steam locking. When debris accumulates inside the fin bundle, it will contact tubes with surface temperatures in excess of 300-400oF. The last of the primary considerations in coil design is the fin density. If the airside pressure drop is quite high, then significant loss of process air may occur, and an airtight case design would be a wiser choice (Figure 3). All Rights Reserved. As a tried & true technology, it is common for Coil Replacement Company engineers to manufacture direct replacement steam distributing & heating coils … The direction of airflow is not always a critical design parameter, but this is also best known at the start of coil design. The diameter of the coil should provide sufficient length of coil for good distribution. The most commonly used type of steam jacket consists simply of an outer cylinder surrounding the vessel, as shown in Figure 2.10.4. Steam coils SPC manufacture steam coils for use against working pressures of up to 8 bar g (175 deg C). When the airstream possesses a high concentration of chlorides, it may be necessary to coat the exterior of the coil with a protective coating. the full-load condition. The control valve set (either one valve or two valves in parallel). From the perspective of the coil manufacturer, large aspect ratios are the most cost effective. With respect to non-flow type applications such as tanks, this may not be too serious from a thermal viewpoint because the contents of the tank will almost be at the required temperature, and have a huge reservoir of heat. The amount of heat required to raise the temperature of a substance can be expressed as: Imperial Units? In extreme cases the average pressure used may be as low as 40% of the inlet pressure. However, for reasons previously explained, two valves may be better. This may occur in one of 3 ways, further details of which can be found in 4. With tubes horizontal, the Basic steam coil is used for re-heat … By understanding the critical factors that determine proper coil selection, you can be confident that you have chosen a high-performing, long-lasting piece of equipment. The drain line must fall from the bottom of the condensate manifold down to the steam trap (or pump-trap). Coil choices include water cooling, water heating, steam, booster, evaporator and condenser. For these reasons side hung coils are often used in the electroplating industry. The steam manifold should be 100 mm diameter as determined by the previous velocity calculation. When the locked steam condenses and the steam trap opens, a slug of water is discharged up the riser. The maximum steam mass flowrate with the recommended heat transfer area. Critical pressure drop (CPD) will occur across the control valve during start-up, therefore the minimum steam pressure in the heating coil should be taken as 58% of upstream absolute pressure. Heating Vats and Tanks by Steam Injections, Steam Consumption of Pipes and Air Heaters, Previous - Energy Consumption of Tanks and Vats, Next - Heating Vats and Tanks by Steam Injections. The condensate level would then rise and form a temporary water seal, locking the steam between the bottom of the riser and the steam trap. As the condensate manifold is holding condensate, the heat from it will be small compared to the steam manifold and this can be ignored in the calculation. To calculate the heat transfer area, a value for the overall heat transfer coefficient, U, must be chosen. 2. The high salinity content of air on coasts near oceans can also be destructive to stainless steels, and this should be accounted for in the material selection. Steam coil construction is available for high and low pressure applications and is a very effective way to heat air. Because water expands upon freezing, tubes that contain condensate can be forced to expand until they burst. On the product side of the coil a thermal boundary layer will exist in which there is a temperature gradient between the surface and the bulk fluid. If one valve is to be used, this valve must ensure the maximum heat load is catered for, while maintaining the required steam pressure in the coil to assist the drainage of condensate from it at start-up. DRS Marlo Coil must be contacted for advice before any changes from the The factors that affect the coil design can be separated into two categories: primary factors which are essential to the operation of the coil, and secondary, nonessential factors which can be used to tune or optimize the performance or price of the coil. Proven. - Check the Units Converter! This will ensure that there are no weak points in the tank lining, where there is a risk of leakage of corrosive liquids. The steam trap remains closed until the locked steam condenses, during which time the coil continues to waterlog. Steam coils are also built according to steam pressure through the tubes and headers. One solution would be to run a bank of parallel pipes between steam and condensate manifolds, set at different heights to encourage condensate to run The range of figures shown in Table 2.10.1 demonstrates the difficulty in providing definitive ‘U’ values. Whether your application is used to preheat air going into a combustion chamber at a coal-fired power plant, dry cereal before packaging, heat air in an air handler, or some other type of application, we have the solution for you. Although corrosion can occur anywhere on the coil, it is typically in high-stress areas such as welds or in microscopic cracks that form in tubes that have been expanded. Whether bottom or side coils are used, it is essential that they are arranged with adequate coverage so that the heat is distributed evenly throughout the bulk of the liquid. Channeling the steam from the header to the other rows in the series has the same purging effect. We use cookies to give you the best experience on our website. Steam Heating Coils Generally constructed from copper tubes mechanically expanded into aluminium plate fins with self spacing collars to ensure efficient heat transfer. Often, vacuum breakers are also needed in the system. E.g. These coils should also have a fall to the bottom with a water seal and a small bore dip-pipe.This arrangement has the advantage that it is often easier to install, and also easier to remove for periodic cleaning if required. If the process involves articles being dipped into the liquid, it may not be convenient to install the coil at the bottom of the tank - it may be damaged by the objects being immersed in the solution. The recommended overall heat transfer coefficients will apply to typical conditions and installations. length vs height, materials, fin spacing, air flow, orientation, etc. Do not use steam-distributing type coils or multiple-pass basic steam coils. This will vary considerably with the thermal and transport properties of both fluids and a range of other conditions. If the control valve were sized on mean values, steam pressure in the coil at start-up will tend to be lower and the coil may flood. The same basic design is used for both Clayton fired and unfired industrial steam generators (heat … The coil has been sized on mean heat transfer values. Any reduction in heat transfer at this part of the heating process may therefore have little immediate effect on the tank contents. (a) Consider the maximum heating capacity of the coil Q̇(coil), Part 5 A recommendation for installation, including coil diameter and layout. This design is ideal when the airside pressure drop is relatively low and completely sealing off the process air from the ambient air is not a paramount concern. You can be assured of proper heating / cooling and airflow without paying for … A recommendation for installation, including coil diameter and layout. HC Coils Steam Heating Coils are engineered with heavy gauge copper tubes and connection manifolds to withstand the normal operating stresses of a correctly installed steam system. How efficiently and effectively a workpiece is heated is determined by the induction coil. In flow type applications the product or fluid is heated when it constantly flows over … When the seal is ultimately broken, a smaller volume of water will return to the heating coil than with an unrestricted large bore riser, but as the water seal arrangement requires a smaller volume of condensate to form a water seal, it will immediately re-form. Steam enters through the supply connection and into the internal distribution tubes. Assisted circulation (such as stirring) that will induce forced convection, will also result in higher coefficients. This is mainly due to the small volume in the heat exchanger. However, further along the length of the coil the steam velocity may be lower, and the coil may be running partially full of water. Steam coils are used in a wide variety of air heating applications. The steam tubes are pitched toward the condensate header to promote condensate removal. Part 1. Steam circulates in the outer jacket, and condenses on the wall of the vessel. This will help steam to flow and push condensate through the coils. This design ensures that air passing over the last row is at … The U-factor is usually developed from past experience.T is a difference in temperature. However, FPI should not be viewed as a parameter to be maximized if the coil stays under the maximum allowable air pressure drop. This module will deal with indirect heating. Because of the difficulties in providing accurate ‘U’ values, and to allow for future fouling of the heat exchange surface, it is usual to add 10% to the calculated heat transfer area. It is most important to be aware of potential corrosion of pressure parts such as tubes and headers, but corrosion of fins can also occur and result in the depleted performance of the coil. Data Mass of Batch (M) lb. In the application, the steam and condensate headers would each be 2.8 m long. The selection and sizing of the condensate removal device will be very much influenced by the condensate backpressure. This minimizes the number of joints that need to be welded, which is usually the largest driver of labor costs in heat exchanger manufacturing. When an airstream is unfiltered, it is good practice not to exceed 8 fins per inch; if there are a lot of particulates in the airstream then 5 fins per inch or less is a wiser maximum fin density. Enter your name, email address and a message. (Mean heat load = 367 kW). Pass the condensate load when steam pressure in the coil equals the condensate backpressure, i.e. Submerged steam coils - A widely used form of heat transfer involves the installation inside a tank of a steam coil immersed in a process fluid. Other factors such as aspect ratio, orientation, or casework design can be tuned to optimize performance and/or cost of the equipment. It may be difficult to accommodate this length of large bore heating pipe to install in a 3 m × 3 m tank. Steam moves from the boiler to the point of use and releases energy at a constant temperature when it condenses. To achieve the mean coil temperature, an average steam pressure of approximately 75% of the inlet pressure may be used. This equation can be used to determine a total amount of heat energy for the whole process, but it does not take into account the rate of heat transferwhich is: 1. amount of heat energy transferred per unit time In non-flow type applications a fixed mass or a single batch of product is heated. When tubes are installed vertically the Basic Steam coil provides excellent freeze protection. The consequences of using the wrong heat exchanger can be serious. Part 5. The presence of any lift will result in waterlogging of a proportion of the coil length, and possibly waterhammer, noise and leaking pipework. If articles are to be dipped into the tank, it may not be possible to use any sort of agitator to induce forced convection and prevent temperature gradients occurring throughout the tank. By understanding the critical factors that determine proper coil selection, one can be confident that they have chosen a piece of equipment that will be both reliable and high-performing. When approaching the control temperature, the larger valve would be set to shut down, allowing the smaller valve to give good control. Reliable. Options include: The use of tank coils is particularly common in marine applications where cargoes of crude oil, edible oils, tallow and molasses are heated in deep tanks. conditions: If the steam trap is only sized on the first condition, it is possible that it may not pass the stall load (the condition where the product approaches its required temperature and the control valve modulates to reduce steam pressure). The least expensive option is to leave the headers exposed outside of the case, with the casework surrounding only the fin bundle (Figure 2). Some of the choices, such as method of steam delivery, materials of construction, or fin spacing can be critical to the safe operation of the heat exchanger. There needs to be correctly designed traps, and they need to be installed in the correct place and depth in the system. One of the most important requirements of a steam coil design is to allow for thermal expansion without creating stress and wear on the tubes. Our Daikin Hi-F (high-efficiency) fins maximize heat transfer with less fins to lower your initial cost. 24" minimum if safety drain is used. The steam supply and condensate return headers and connections are normally at opposite ends of the coil. Arbitrarily selecting 32 mm pipe as a good compromise between robustness and workability: It is necessary to confirm the steam velocity through the connecting tubes: On the basis of proportionality of heat transfer area, the steam header will condense: The design and layout of the steam coil will depend on the process fluid being heated.