Shell and tube heat exchangers are a type of heat exchanger that have a bundle of tubes inside a shell. Fluids at different temperatures run through the shell and the tubes. As the fluids pass through the respective chambers, heat exchange takes place between them.

Heat exchangers are devices that help in efficient heat exchange from one medium to another. The media are separated from each other with solid material so that they never mix with each other. These devices are widely used in refrigeration, air conditioning, different types of power plants and natural gas processing units. Shell and tube heat exchangers are a class of heat exchanger that is most suitable for high pressure applications. They are most popularly used in oil refineries and other units involving large chemical processes.

Structure of Shell and Tube Heat Exchangers

As the name suggests, a shell and tube heat exchanger contains a bundle of tubes inside a large pressure vessel which is referred to as the shell. The tubes on each end are attached to tube sheets. Two different fluids run through the shell and the tube heat exchanger, one through the tubes and the other outside the bundle of tubes within the shell. As the fluids flow through the system, transfer of heat takes place from the fluid that is at a higher temperature to that at a lower temperature. The fluid inside the tubes is called the tube side fluid whereas that which is flowing outside the tubes and within the shell is called the shell side fluid. This heat exchange takes place through the tube walls. The fluid that has to be heated or cooled runs through the tubes. The fluid that runs through the shell outside the tube bundle is heated or cooled depending on whether the fluid inside the tubes have to be cooled or heated. Use of a number of tubes instead of one increases the efficiency of the heat exchanger as circular surfaces of all the tubes increases the net area of transfer of heat.

Single Phase or Double Phase Heat Exchangers

The fluids can either be liquid or gas. Shell and tube heat exchangers with either only liquid or gas in both the tubes and the shell are called the one phase or single phase heat exchanger. Two phase heat exchangers involve transfer of heat between two fluids of two different phases, that is a liquid and a gas. Boilers are two phase heat exchangers in which liquids are heated to a gas. In condensers, the gas is cooled down into its liquid phase. The change in phase takes place in the shell part. Shell and tube heat exchangers can be 1, 2 or 4 pass heat exchangers. The number of passes indicate the number of times that the fluid pass through the tubes.

Designs of Shell and Tube Heat Exchangers

U-Tube Heat Exchanger: In the U-tube heat exchangers, the tubes in the tube bundle bend to form a U. The ends of the tubes open into plenums or water boxes through holes in the tube sheet. There is an inlet plenum and an outlet plenum. The fluid enters through the inlet plenum, runs the entire length of the U-tube and leaves the heat exchanger through the outlet plenum. As the fluid flows inside the U-tube, heat transfer takes place between the fluid in the tube side and that in the shell side.

Two phase U-tube heat exchangers are commonly used in nuclear power plants called pressurized water reactors. Using these heat exchangers, water that has been obtained by condensing steam is heated back to steam that is used to turn steam turbines. As the steam turbines rotate, power is generated.

Straight-Tube Heat Exchanger: As the name suggests, these heat exchangers have straight tubes. The ends open into two separate tube sheets. In case of one pass straight tube heat exchangers, one end has the inlet plenum while the other end has the outlet plenum. In case of a two pass straight tube heat exchanger, both the inlets are on the same side.

Shell and tube heat exchangers have made large-scale cooling of different media in various industries very convenient. It is important to ensure proper cleaning of the heat exchanger tubes. Although traditionally methods of hydro-blasting water was used, now more advanced techniques are being applied.

• Industrial
  • Mining - Plating heaters & coolers, analyzing heaters & coolers, strike solution cooling, quench oil coolers, sulfuric acid, hydrochloric acid, hydrogen peroxide, titanium dioxide, chloride alkaline, soda ash, steel.
  • Automotive
    • Pickling - Sulfuric and hydrochloric acid heating and cooling.
    • Rinsing – Heating rinsing water.
    • Phosphatizing – Phosphoric acid solution heating.
    • Passivating - Heat and maintain passicating bath temperature. Precutting Cooling of electrolytic bath solution (5-15% pain and water).
    • Priming & Painting – Heat and maintain paint temperature.
  • Pulp and Paper - Blowdown liquor coolers, caustic soda coolers, black liquor heating, boiler blowdown heat recovery.
  • Textile Applications - Heat recovery, caustic solution heating & cooling washers.
  • Vegetable Oil - Product heating, product cooling, product economizing, cooling water systems, hot water systems, waste water treatment.
  • Sugar - Water, juice, syrup and molasses heating. Juice demineraliztion and evoporation.

• Power
  • Power - Auxiliary cooling circuit isolation, co-generation applications, geothermal applications, lubrication oil cooling, diesel engine cooling, heat recovery.
  • HVAC - Cooling tower isolation, free cooling, heat pump systems, sea water isolation, thermal storagesystems, pressure Interceptor.

• Petroleum
  • Refinery – Brine cooling, crude oil/water interchanger, treated crude oil / untreated crude oil interchanger.
  • MTBE - Product heating, cooling & interchanging, jacket water cooling, condensing.
  • Alkylotion - Cooling, hearing of corrosive fluids, Isobutene condenser and reactor interchanger.
  • Oil & Gas – Sea water coolers, crude oil heat treatment.
  • Dehydration/Desolving - Crude oil interchanger, water/crude oil interchanger, water interchanger, crude oil cooling.
  • Desulphurization – Lean/rich fluid interchanger & cooling, acid gas condensor.
• Hydrocarbon Processing
  • Methanol - Prehearing, water cooling, liquid product cooling.
  • Propylene Oxide - Sodium hydroxide cooling, reaction mixture cooling, heat recovery from reactor bottom liquid.
  • Ethylene Glycol – Product cooling, reactor feed heater and interchanger.
  • Ethylene Oxide - Lean/rich cycle water interchanger, lean cycle water cooler.
  • Ethylene-Propylene - water cooling & heating, propylene condensers, propylene cooling, naphtha preheating.
  • Formaldehyde - Methanol preheating, formalin cooling, water cooling.
• Polymer
  • Acrylic Fibers - Heating & cooling of solvents, reactor cooling.
  •  Nylon - Water cooling & heating, nylon salt cooling, condensers and interchangers.
  • Polyester - Glycol cooling, solvent heating.
  • Polyethylene - Pelleter water & cooling water systems.
  • Polyol - Water heating & cooling, reactor feed heating & cooling, polyol product cooling, polyol mix heating.
  • Polypropylene - Circulating, pellet, refrigerated and feed matercooling, condensers and interchangers.
  • Polyurethane - Heating & cooling of polyol and isocyanate.
  • PVC - Reactor jacket water cooling.
  • Viscose - Heating & Cooling of NaOH, viscose and different acides, heating of spin bath solution.
• Pharmaceutical – Product heating & cooling, cooling water systems, hot water systems, condensers & interchangers.

MX Machinery’s standard air-cooler design, like our reputation for superior quality and performance, has been honed over many years to be the very best available on the international marketplace. Much of this results from the use of the patented core, resulting in class-leading levels of performance and durability. The ability to specify virtually any combination of tube and fin material, including copper-alloys, stainless steel and titanium etc., gives engineers the freedom to balance budget and longevity considerations.

The MX Machinery manufacturing process also imparts the ability to incorporate many enhancements such as louvers, air turbulators and vortex generators. Our expertise in the use of vortex clean air technology reduces pressure loss and fin fouling, resulting in lower maintenance costs and reduced energy consumption.

Benefits

An absolute refusal to compromise on quality and durability pays dividends in greatly improved characteristics:

Unmatchable levels of choice
Extended operating life
Ease of maintenance
Superior heat transfer
Improved operating efficiency
Very low pressure drop
Product consistency
Vibration resistance

Example Applications

Common applications include:

Charge air coolers
Alternator air coolers
Boiler feed pump heaters/coolers
Diesel generator air coolers
Gas circulator motor air coolers
Generator air coolers
Heating coils
Main engine charge air coolers
Motor air coolers
Scavenge air coolers
Waste heat recovery units

Spiral Tube (Coiled Tube) Heat Exchangers are widely used in swimming pool equipment, aquarium chiller, marine refrigerant units, Air source heat pump,water source heat pump, aquaculture, pharmacy, the food industry , electroplating industry and some heat recovery from the waste water or exhaust gas.

Spriral/Coiled Titanium tube heat exchangers

Tube Material: Titanium
Shell: PVC or Steel

Titanium has the super strong corrosion resistant ability. The Titanium heat exchangers use seamless pure titanium tubes as heat conductor, which can be used for a long time thus are cost-saving for after-sale services.

With good properties, Titanium heat exchangers are widely applied in swimming pools, marine central air conditioning units, aquariums, aquaculture, cool water irrigation, pharmacy, the food industry, electroplating industry and some heat recovery from the waste water or exhaust gas.

Spriral/Coiled Copper tube heat exchangers

Tube Material: Copper T2/TP2, Nickel-Copper 90/10, copper Bfe 10-1-1, BFe30-1-1 for option.
Shell: Steel

Features:

1. Using high efficiency rifled tube,heat exchange area is 3.6 times than the smooth type.
2. Fins inside & outside tubes induce turbulence flow of refrigerant and water, making the product high efficiency.
3. The compact helix structure of the coil ensures sufficient heat exchange between the gas and water.

• Spriral/Coiled Copper Tube in shell condensers
• Spriral/Coiled Copper Tube in shell evaporators
• Spriral/Coiled Double-wall Copper tube in shell heat exchangers
• Spriral/Coiled Nickel-copper tube in shell heat exchangers
• Industrial Chiller heat exchangers

The plate heat exchanger (PHE) is a specialized design well suited to transferring heat between medium- and low-pressure fluids. Welded, semi-welded and brazed heat exchangers are used for heat exchange between high-pressure fluids or where a more compact product is required. In place of a pipe passing through a chamber, there are instead two alternating chambers, usually thin in depth, separated at their largest surface by a corrugated metal plate. The plates used in a plate and frame heat exchanger are obtained by one piece pressing of metal plates. Stainless steel is a commonly used metal for the plates because of its ability to withstand high temperatures, its strength, and its corrosion resistance. The plates are often spaced by rubber sealing gaskets which are cemented into a section around the edge of the plates. The plates are pressed to form troughs at right angles to the direction of flow of the liquid which runs through the channels in the heat exchanger. These troughs are arranged so that they interlink with the other plates which forms the channel with gaps of 1.3–1.5 mm between the plates.

The plates produce an extremely large surface area, which allows for the fastest possible transfer. Making each chamber thin ensures that the majority of the volume of the liquid contacts the plate, again aiding exchange. The troughs also create and maintain a turbulent flow in the liquid to maximize heat transfer in the exchanger. A high degree of turbulence can be obtained at low flow rates and high heat transfer coefficient can then be achieved.

A plate heat exchanger consists of a series of thin, corrugated plates which are mentioned above. These plates are gasketed, welded or brazed together depending on the application of the heat exchanger. The plates are compressed together in a rigid frame to form an arrangement of parallel flow channels with alternating hot and cold fluids.

As compared to shell and tube heat exchangers, the temperature approach in a plate heat exchangers may be as low as 1 °C whereas shell and tube heat exchangers require an approach of 5 °C or more. For the same amount of heat exchanged, the size of the plate heat exchanger is smaller, because of the large heat transfer area afforded by the plates (the large area through which heat can travel). Expansion and reduction of the heat transfer area is possible in a plate heat exchanger.

Evaluating plate heat exchangers

All plate heat exchangers look similar on the outside. The difference lies on the inside, in the details of the plate design and the sealing technologies used. Hence, when evaluating a plate heat exchanger, it is very important not only to explore the details of the product being supplied, but also to analyze the level of research and development carried out by the manufacturer and the post-commissioning service and spare parts availability.

An important aspect to take into account when evaluating a heat exchanger are the forms of corrugation within the heat exchanger. There are two types: intermating and chevron corrugations. In general, greater heat transfer enhancement is produced from chevrons for a given increase in pressure drop and are more commonly used than intermating corrugations.

Advantages and disadvantages of plate heat exchangers

Advantages

• Compactness- The units in a plate heat exchanger occupy less floor space and floor loading by having a large surface area that is formed from a small volume. This in turn produces a high overall heat transfer coefficient due to the heat transfer associated with the narrow passages and corrugated surfaces.
• Flexibility- Changes can be made to heat exchanger performance by utilizing a wide range of fluids and conditions that can be modified to adapt to the various design specifications. These specifications can be matched with different plate corrugations.
• Low Fabrication Costs- Welded plates are relatively more expensive than pressed plates. Plate heat exchangers are made from pressed plates, which allow greater resistance to corrosion and chemical reactions.
• Ease of Cleaning- The heat exchanger can be easily dismantled for inspection and cleaning (especially in food processing) and the plates are also easily replaceable as they can be removed and replaced individually.
• Temperature Control- The plate heat exchanger can operate with relatively small temperature differences. This is an advantage when high temperatures must be avoided. Local overheating and possibility of stagnant zones can also be reduced by the form of the flow passage.

Disadvantages

• The main weakness of the plate and frame heat exchanger is the necessity for the long gaskets which holds the plates together. Although these gaskets are seen as drawback, plate-and-frame heat exchangers have been successfully run at high temperatures and pressures.
• There is a potential for leakage. The leaks that occur are sent to the atmosphere and not between process streams.
• The pressure drop that occurs through a plate heat exchanger is relatively high and the running costs and capital of the pumping system should be considered.
• When loss of containment or loss of pressure occurs, it can take a long time to clean and reinitialise this type of exchanger as hundreds of plates are common in larger builds.
• The narrow spacing between plates can become blocked by particulate contaminants in the fluid, for example oxide and sludge particles found in central heating systems.
• for the reason above most manufacturers will only guarantee their units for 12 months, furthermore replacement plate and gasket sets can be as much as the plate to buy initially.

Plate heat transfer equation

The total rate of heat transfer between the hot and cold fluids passing through a plate heat exchanger may be expressed as: Q = UA∆Tm where U is the overall heat transfer coefficient, A is the total plate area, and ∆Tm is the temperature difference. U is dependent upon the heat transfer coefficients in the hot and cold streams.

(From Wikipedia)

The plate heat exchanger is formed up by a set of corrugated metal plates. The corrugated plates are mounted in a frame with a fixed plate on one side and a movable pressure plate and pressed together with tightening bolts. The corrugated plates serve not only to raise the level of turbulence, but also provide numerous supporting points to withstand the pressure difference between the media. The plate heat exchangers are widely applied in the following applications.

1. Metallurgical Industry
2. Power Generating Industry
3. Chemical Engineering Industry
4. HVAC Industry
5. Light Industry And Textile/Paper Industry
6 .Electronics Industry
7. Automotive Industry
8. Pharmaceutical Industry
9. Food Processing Industry
10. District Heating

Features and Advantages

High heating transferring coefficient: as the flowing made in the plate pack forms up turbulence at low Re and the smooth plates have little possibility of forming scale, the plate heat exchanger has a heat transferring coefficient over 5000W/m2k, which is 2-4 times that of the shell-and-tube exchanger.
High heat recovery rate: Thanks to the high heat-transferring coefficient, the heat transferring temperature difference can be very low Therefore, it is very well suited to low energy level heat recovery. Normally heat recovery using a plate heat exchanger can be as high as9 0%.
Great flexibility
Compact structure
Easy maintenance

Material of gasket from designated material supplier protection groove for the gasket “roof type” gasket profile high temperature solidifying epoxy resin glue, or glue free gasket

Fixation and sealing: functions of fixation and sealing of the clip-on gasket are separate. Therefore, even if fixation goes wrong the gasket retains its sealing function.

Welded Plate Heat Exchangers applyinng in industries of heat supply, air conditioning, chemicals, machinery, metallurgy, steel, medicines, food, oil field, shipbuilding, light industry and so on.

Working temperature up to 500 degree Celsius.
Working pressure up to 4.0MPa.

Material: 304, 316L, 310S, 254MO, C-276, TA1, N6