Air-Cooled Heat Exchangers. These are devices for rejecting heat from a fluid directly into ambient air, instead of rejecting heat to water and then rejecting it to air, as with shell and tube heat exchangers. They do not require water. They may be as small as an automobile radiator or large enough to reject heat from a power plant. They require, at a minimum, one or more bundles of heat transfer surface and air-moving devices, such as a fans or blowers.
Things to Consider: Thermal duty and design margins, Process pressure drop, Design ambient conditions, Process physical properties, Materials of construction, Fintube type, Tubing dimensions, Temperature limitations, Airside design clearances, Noise, Fan characteristics, Fan drives, Header types, Arrangement, Airside fouling, Control panel.
Carbon/Graphite Heat Exchangers. Several types of carbon/graphite are manufactured that are identical in operation to their metal counterparts. These heat exchangers can be used with many acids and with combustion gases, and they are resistant to most organic and inorganic media. The graphite material offers excellent corrosion protection, low pressure drops, high efficiency, large heat exchange areas, and resistance to stress and pressure surges.
Things to Consider: Application, Maximum working pressure, Temperature range, Liquid flow rate, Gas/air flow rate, Primary exchanger material, Connection types, NEMA rating, ASME certification, Dimensions, Weight, Warranty.
Clamp-On Dimple Jacket Heat Exchanger. These jackets consist of hemispherical dimples pressed into a thin plate, which is then wrapped around and clamped onto the vessel. They are frequently used to heat or to cool process vessels in the chemical process industries. They have better heat-transfer characteristics than conventional jackets due to the turbulence generated by the dimples. They can be fitted to both cylindrical and dished portions of a process vessel. Dimple jackets typically give high pressure ratings, have a low to moderate pressure drop, and are moderate in cost.
Things to Consider: Heat transfer media, Process temperature, Stress corrosion cracking risk, Water volume rate, Use of steam, Maximum 300 psig design pressure with steam, Transfer fluid temperature, Design according to ASME code, Heat transfer coefficients, Reynolds number.
Clamp-on Plate Heat Exchangers. These heat exchangers offer a convenient way to add heating or cooling to the exterior of tanks or vessels. The plates are fitted to the tank exterior to provide moderate heating or cooling. Because they do not directly contact the substance within the vessel or tank, they cannot contaminate the product. The clamp on plates should be installed with a heat transfer mastic to increase their overall performance.
Things to Consider: Application, Maximum working pressure, Temperature range, Liquid flow rate, Gas/Air flow rate, Primary exchanger material, Connection types, NEMA rating, ASME certification, Dimensions, Weight, Warranty.
Direct Steam Injector Heat Exchangers: This is a static heat pump, with no rotating machinery or refrigerating fluid, that uses steam for its driving energy. Low pressure thermal wastes go through an exchanger evaporator where part of the heat is turned into latent heat of vaporization, which produces low pressure steam. This steam is compressed in an ejection compressor by the driving steam. At the ejection-compressor outlet, the steam is condensed in an exchanger and releases its latent heat.
Things to Consider: Efficiency, Integral steam modulation valve, Broad operating range, Pressure drop, Fit with existing piping and space, Clean steam supply/pressure, Temperature controller, Temperature sensor, Heating tank, Vapor exhaust, Control valves, Air supply/pressure, Transducer, Control signal.
Electric Heat Exchanger. Similar in concept to shell and tube heat exchangers, except the heat source is from an electrical element rather than a heated fluid. This type of heat exchanger has an electric heating element placed inside of a tube designed to specifically accommodate the process pressure and temperature of the fluid to which the heat is being transferred. Special fittings at the end of the tubes enable electrical and fluid connections. The intimate contact of the heated tube with the fluid to be heated results in high-energy efficiency and fast response. These exchangers are capable of precise temperature control.
Things to Consider: Application, Maximum working pressure, Temperature range, Liquid flow rate, Gas/Air flow rate, Primary exchanger material, Connection types, NEMA rating, ASME certification, Dimensions, Weight, Warranty.
Glass Heat Exchanger. Any heat exchanger in which glass replaces metal, such as shell-and-tube, cascade, double-pipe, bayonet, and coil exchangers. These heat exchangers, usually manufactured from borosilicate glass, have many desirable characteristics for laboratory applications. They provide long service life, product purity, smooth interior surfaces, and transparency. They are impervious to almost every corrosive and reagent known, are virtually unaffected by heat and thermal expansion, and do not burn or emit toxic fumes.
Things to Consider: Application, Maximum working pressure, Temperature range, Liquid flow rate, Gas/Air flow rate, Primary exchanger material, Connection types, NEMA rating, ASME certification, Dimensions, Weight, Warranty.
Helical Coil Heat Exchangers. These heat exchangers, including a sister type called a spiral heat exchanger, refer to a helical tube configuration that are coiled to form the two channels in a counter-flow arrangement. Each channel has one long curved path. These compact units present a small footprint, have less pressure drop, less pumping energy, higher thermal efficiency, and lower energy costs. Due to their flow characteristics, they are virtually self cleaning. They are often used in such applications as pasteurization, digester heating, heat recovery, pre-heating, and effluent cooling.
Things to Consider: Application, Maximum working pressure, Temperature range, Liquid flow rate, Gas/Air flow rate, Primary exchanger material, Connection types, NEMA rating, ASME certification, Dimensions, Weight, Warranty.
Plate and Frame Heat Exchangers. These heat exchangers are fabricated from a series of thin, corrugated plates which are gasketed, welded, or brazed together depending on the application. These plates transfer heat between two fluids. Because the fluids are spread over a large surface area, the transfer of heat is facilitated and the temperature changes more rapidly. The plates are compressed together in a rigid frame to form a network of parallel flow channels with alternating hot and cold fluids. They are easily dismantled for inspection and cleaning.
Things to Consider: Application, Maximum working pressure, Temperature range, Liquid flow rate, Gas/Air flow rate, Operating temperature below 150C, Primary exchanger material, Connection, NEMA rated, ASME certified, Dimensions, Weight, Warranty.
Heat Exchanger, Point-of-Use Cooler. These devices, which cool the processed media for immediate local use or local sampling, are specifically designed for taking high quality chemical, conductivity and microbiological samples quickly and safely from clean/pure steam, water for injection, and other high purity media systems. These sanitary machines are usually made from stainless steel components.
Things to Consider: Application, Maximum working pressure, Temperature range, Liquid flow rate, Gas/Air flow rate, Primary exchanger material, Connection types, NEMA rating, ASME certification, Dimensions, Weight, Warranty.
Sanitary Shell & Tube Heat Exchangers. These heat exchangers are identical in operation to standard shell and tube exchangers. The differences are found in the elements of design such as the selection of materials, usually stainless steel or other high-allow material; the use of highly polished surfaces to minimize product buildup; and the implementation of design features that allow free-draining and easy cleaning.
Things to Consider: MAWP (PSI at specified temperature), MDMT (degrees F at specified pressure), (ASME Section VIII Div 1 standard, TEMA standard, CGMP standard, Double tubesheet type, Product contact surfaces type 316L stainless, Product contact surfaces cleanable wih no pockets or crevices, Drainable in designated mounting orientation, Tri-clamp style fittings on all product connections, Process materials on tube side, Heating/cooling medium on shell side, Welding in accordance with section IX of the ASME Boiler and Pressure Vessel Code, Welding of GTAW (tig) or GMAW (mig) types, Tubesheet to tube joints welded and/or expanded, Product contact tube to tubesheet joints seal welded, Finish specification (quantified by Ra or RMS), Electropolishing, Installation must provide clearance at stationary head end to permit withdrawal of the tube bundle or at opposite end to permit removal of shell, Foundation engineered to withstand settling, Provisions for valve and bypasses for inpection and repairs, Thermometer well and pressure gauge connections, Vent valves, Drains, Safety relief devices according to ASME code, Warranty.
Shell & Tube Heat Exchangers. These heat exchangers are fabricated using two sets of tubes. One set contains the fluid that must be either heated or cooled. The second set contains the fluid that runs over the tubes that are being heated or cooled and provides the heat or absorbs the heat required. A set of tubes is called a tube bundle, and can be made up of several types of tubes: plain, longitudinally finned, etc. Shell and Tube heat exchangers are robust due to their shape, and are typically used for high pressure applications.
Things to Consider: Phase changes in system, Zones in system, Flowrates and operating pressures in system, Physical properties of streams, Allowable pressure drops and velocities in exchanger, Heat duty of the system, Exchanger area, Geometric configuration, Heat transfer coefficient, Materials of construction, Ease of maintenance, Heat integration overall, Warranty.
