Heat Exchangers

Many industrial processes require heat exchangers to perform a crucial role in the design, operation and maintenance of heating systems, air-conditioning systems, vehicle operation, power generation, refrigeration, chemical processing, offshore oil rigging and engineering systems. They can also be used in the process of waste heat recovery in industrial facilities. There are a number of varieties of heat exchangers which are used according to their location and purpose. They are typically constructed with a shell and tube design or a flat plate design, in which fluids, steam and/or air flow through heat-conducting tubes or conductive plate-walled cavities. Plate heat exchangers can be configured as plate and frame heat exchangers or flat plate heat exchangers, while shell and tube heat exchangers in a tubular design may be designed as tube heat exchangers, finned tube heat exchangers, oil coolers or spiral heat exchangers. Water to water heat exchangers and marine heat exchangers typically have a shell and tube or spiral design, while air to air heat exchangers and water to air heat exchangers are generally configured in a plate, flat plate or plate and frame design.

Although tubular and plate heat exchangers are configured differently in terms of layout, they both apply the same principles of thermodynamics. The tube walls or conductive metal plates are partitions, acting as thermal conductors between the two fluids or gases while keeping the substances from intermingling. Stainless steel is commonly used as a wall or plate as it is a highly durable metal and is able to withstand the pressure and high temperatures that typically come with the heat exchange process while still acting as a conductor. A hot solution flowing on one side of the barrier transfers its heat to a cooler solution flowing on the other side, temporarily creating thermal stress within the plate or wall. Thermal energy flows in the direction of the cooler substance from the hotter in the substance's attempt to reach equilibrium on the surface. The size of the surface area of these conductive partitions affects the speed and efficiency of the process. The larger the surface area the substance is exposed to, the faster and more efficient the heat transfer; this is why plate heat exchangers are used to transfer heat between air or gases, which do not transfer heat as easily as liquids. Heat exchanger manufacturers typically construct exchangers from durable, corrosion-resistant materials such as steel, titanium, copper, bronze, stainless steel, aluminum or cast iron.

Typically power generation facilities rely on heat exchangers to keep processes from dangerously overheating and/or to recycle process heat. Other industries that integrate heat exchangers into equipment and products include aerospace, chemical, marine, semiconductor, petrochemical, electronic and automotive. Another common use for heat exchangers is the process of waste heat recovery which is used to capture excess heat from one industrial process and use it in another process requiring heat. This environmentally conscious manufacturing practice may also be used to cool process fluids, or it may be used to cool air for refrigeration and air conditioning. It saves money and energy as it uses an existing source of heat thus eliminating the need to use an electrical supply or fossil fuels to create heat. Heat exchangers are also important for process cooling and waste heat recovery in pharmaceutical, food processing, water treatment, textile manufacturing, pulp and paper and steel manufacturing processes.

Despite the many advantages of heat exchangers, including saved time and energy, increased performance and lower maintenance costs, there are some drawbacks to take note of. The materials used to manufacture heat exchangers need to be high quality and durable as the process can cause high levels of stress and pressure. One of the biggest problems with heat exchangers is corrosion. Due to the constant flowing of liquid and high humidity rates in the process of heat transfer, corrosion is common and unfortunately is very difficult to avoid. To help prevent this from creating system running problems, heat exchanger manufacturers need to use tubing and walling that is resistant to general corrosion, pitting, stress-corrosion cracking and selective leaching. Also, some liquids can build up residue over extended periods of time which then needs to be cleaned, but this is generally a straightforward process and should not cause too long of a process delay. Although they are not always known as heat exchangers, these devices are quite common and are an important element in many machines. Heat exchangers aren't always industrial process types; most mechanical, chemical and energy systems require heat transferal of some sort. For instance, a car's radiator is a type of heat exchanger responsible for transferring heat from the engine to the air. Other examples of commercial uses for heat exchangers include spa and swimming pool heating, home radiators, hot water radiators and air conditioners. Whether in commercial or industrial use, heat exchangers are vital in creating greater efficiency in terms of both energy and costs.

Heat Exchangers and Heat Exchanger Manufacturers Images Provided by Tranter, Inc.

Heat Exchanger Types

• Air-cooled heat exchangers have a central motor fan for heat removal.
  
• Air to air heat exchangers replace stale indoor air with fresh air from outside.
• Brazed plate heat exchangers are made up of specially formed plates, vacuum brazed together.
  
• Flat plate heat exchangers transfer heat through flat, corrugated plates.
• Gasketed plate heat exchangers are the most common. Elastomer gaskets are used in the plates, which contain the pressure and control the flow of each medium.
  
• Marine heat exchangers are designed for use on boats.
• Oil coolers are heat exchangers that are specifically designed for the transfer of heat, or thermal energy, by carrying the oil through cooling units in order to cool.
• Plate and frame heat exchangers use plates clamped together in frames.
• Plate heat exchangers use corrugated plates that are mounted on a frame and fastened together. They are designed so that the flows of hot and cool liquids run counter to each other, and are used when temperature and pressure demands are moderate.
• Semi-welded or hybrid plate exchangers consist of pairs of plates that are laser welded together into cassettes. These allow one fluid to flow in a welded channel and the other to flow in a gasketed channel.
• Spiral heat exchangers are made with a shell and tube heat exchanger design that consists of a spiral body made from two flat surfaces, typically metal strips, which are coiled to form two spiral channels.
• Tube-and-shell heat exchangers, or tube heat exchangers, consist of tubes that are run through a large circular tank, called the shell. Tube-and-shell (or tubular) heat exchangers are used in applications where the pressure and temperature demands are high, and when the fluid contains particles that block the channels of a plate heat exchanger.
• Waste heat recovery is any method that recaptures waste heat that was discharged as a byproduct of one process and puts it to use in another process.
• Water to air heat exchangers are devices used to transfer process heat from water into the air.
• Water to water heat exchangers transfer heat energy from one liquid to another without bringing the two liquids into direct contact.
• Welded plate heat exchangers are fully welded and require no gaskets. These are usually constructed of one material, generally stainless steel.

Heat Exchanger Terms

1, 2, 4 Pass - The number of times, one, two or four, the liquid passes through the tube bundles of heat exchangers. Anything greater than a one pass is considered a multi-pass unit.
 
Baffle Plate - Plate the tubes pass through for support that provides a blocked path for the shell side flow, which forces the flows across the tubes and improves the performance of heat transfers. These heat exchangers are shaped in various ways, but are basically segmental.
 
Baffle Spacing - The space between the tube bundle baffle plates that is adjusted to maximize effectiveness of heat exchangers.
 
Bonnet - Like a channel with straight tubes but without a removable cover. These heat exchangers do not have divider walls and are found at each end of heat exchangers.
 
Bonnet Assembly - Manages the tube side liquid for circulation through heat exchanger tubes. This can also hold the tube side inlet and outlet connections and/or pass ribs.
 
Box Linear Style - Tubes of heat exchangers parallel to each other from the inlet to the outlet manifold.
 
Bundle Assembly - The tubing assembly in removable bundle heat exchangers. This typically includes tubes, tube sheets, baffles, spacers and tie rods.
 
Capscrew - A threaded bolt that holds the bonnet onto the core of some types of heat exchangers.
 
Channel - A kind of front end with a removable cover from which the tube side flows in and out. A dividing wall separates the inlet and outlet flow.
 
Channel Assembly - Same function as a bonnet assembly, except that the cover is removable and provides access to the ends of the tubes.
 
Collector - What the tubes in heat exchangers drain into.
 
Core Assembly - The shell and tube assembly in fixed tube sheet heat exchangers.
 
Coupling - The parts that connect the piping to the heat exchangers, come in many varieties.
 
Cover/Cover Assembly - Used to cover openings on heat exchangers. Covers are different from end plates because they can be removed to clean the interior of the tube side, without distressing any piping.
 
Cradle Assembly - The part used to support heat exchangers and to secure it to the mounting surface when welded or strapped to the shell. Cradles may be fixed or moveable.
 
Design Pressure - Calculations of part thickness and design of heat exchangers based on the most severe conditions or highest operating pressures seen by heat exchangers, to make the pressure slightly higher.
 
Dome - A type of nozzle connection that provides a larger nozzle opening between the pipe size and tube bundles of heat exchangers, typically to prevent tube erosion due to high inlet velocities.
 
End Plate - Covers welded to heat exchangers. The majority of end plates are used on bonnet assemblies.
 
End Zone - The first baffle space on a tube bundle, occurring between the tube sheet and the first baffle plate. It is adjusted to maintain the baffle plates within the two shell side nozzles.
 
Ferrule - A small copper or stainless steel piece of tubing that is crimped or squeezed onto the tie tube, up against the last baffle, and locks the baffles into position.
 
Fixed Tube Sheet - A tube sheet that is an essential part of the core shell assembly of heat exchangers.
 
Floating Tube Sheet - Placed at one end of a removable tube bundle and allowed to move freely with the expansion and contraction of the tube bundle due to temperature changes in operation. It always has a smaller diameter than the immobile tube sheets.
 
Gasket - A device used between two parts that helps prevent leakage in heat exchangers.
 
Impingement Plate - A small perforated-plate or bar assembly in the shell-side nozzle that can also be attached directly to the bundle. This protects and prolongs tube life by breaking up and slowing down the shell side fluid, which slows the erosion of the tubing.
 
In and Out End - The side of heat exchangers that contains the tube side inlet and outlet connections in a multi-pass unit.
 
Lantern Ring - A metal or nylon ring on some packed joint heat exchangers that holds the packing rings in place.
 
Operating Pressure - The pressure of heat exchangers during operation and while in use.
 
Packed End - The end of heat exchangers, which contains the packed joint and the packing rings.
 
Pass Lane - A lane in a tube layout where there are no tubes and where the pass ribs mate.
 
Pass Rib - A separator plate inside a bonnet or channel that merges with the pass lane surface, used to form multi-pass heat exchangers. By arranging the ribs, a designer can direct the flow of the tube side substance.
 
Protector Rod - Protects the parts of heat exchangers (tubes, tube sheets and bonnets) from corrosion by acting as a sacrificial anode so that when water is flowing through the tube side it is consumed instead of other parts of heat exchangers.

Range Temperature - The temperature difference of a single fluid as it flows through heat exchangers.
 
Removable Bundle - heat exchangers with a removable tube bundle from the shell casing. This provides easy cleaning of the shell side and also a more feasible way of replacing depleted tubes.
 
Reversing End - The end of multi-pass heat exchangers where the tube side fluid reverses its flow. This usually contains only small vent and drain connections.
 
Shell - The container where the tube bundle is placed and is the conduit for one of the fluids in heat exchangers.
 
Shell Assembly - The assembly into which the tube bundle is placed. It also houses the shell side connections.
 
Shell Head - A formed plate that is welded to the shell (or bonnet) pipe. It comes in many styles and shapes, including flanged and dished, elliptical, ellipsoidal and hemispherical.
 
Shell Side - The part of heat exchangers where the fluid circulates around the tubes.
 
Spacer - Tubing that holds the baffle plate in place.
 
Stacking - Two or more heat exchangers connected together side by side or one on top of the other. Interconnecting piping hooks these heat exchangers together.
 
Stationary Tube Sheet - The tube sheet at one end of a removable bundle that has a larger diameter than the floating tube sheet. The stationary tube sheet is held in a permanent position between the bonnet and shell flanges.
 
Stuffing Box Flange - A flange used at a packed end joint. When a packed joint is tightened, the packing ring is forced into this by the lantern ring/lantern gland.
 
Support Foot - Bolted to heat exchangers using bonnet to shell flange bolting.
 
Test Pressure - Test that detects leaks on the joints of heat exchangers.
 
Tie Rods - Bars mounted between the tube sheets to support the baffles.
 
Tie Tube - A tie tube takes the place of the tie rod in small diameter heat exchangers, and serves the same purpose.
 
Tube - A flow channel for one of the fluids in heat exchangers. These heat exchangers are often parallel within the shell to provide a large surface area for heat transfers.
 
Tube Layout - Shows the positioning of the tubes inside heat exchangers and the locations of the tie rods.
 
Tube Sheet - The apparatus that the tubes are affixed into that holds them in place. It also provides a seal between the tube-side and shell-side liquid.
 
Tube Side - The fluid that circulates through the inside of the tubes of heat exchangers.