• Heat Exchanger Pdf

A furnace is a device used for high-temperature heating. The name derives from Latin word fornax, which means oven. The heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace, or through induction heating in induction furnaces.

1. In all versions of the Heat Transfer interface, the Thin Layer, Thin Film, and Fracture nodes can be used on boundaries to model layered shells made of solid, fluid, and porous materials (with any number of layers) using the Layered Material technology.
2. PETROLEUM TECHNOLOGY QUARTERLY. SPECIAL FEATURES. In refinery heat exchangers typically. Figure 1 Production of the SHE heat-transfer body.

In American English and Canadian English usage, the term furnace refers to the household heating systems based upon a central furnace, otherwise known either as a boiler, or a heater in British English. Furnace may also be a synonym for kiln, a device used in the production of ceramics.

In British English, a furnace is an industrial furnace used for many things, such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants, for example as the heat source for fractional distillation columns. The term furnace can also refer to a direct fired heater, used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking, and is part of the standard English names for many metallurgical furnaces worldwide.

• 1Categories
  • 1.5Furnace types

Categories[edit]

Furnaces can be classified into four general categories, based on efficiency and design.

Natural draft[edit]

Heat exchangers are important heat transfer apparatus in oil refining, chemical engineering, environmental protection, electric power generation etc.

The first category of furnaces are natural draft, atmospheric burner furnaces. These furnaces consisted of cast-iron or riveted-steel heat exchangers built within an outer shell of brick, masonry, or steel. The heat exchangers were vented through brick or masonry chimneys. Air circulation depended on large, upwardly pitched pipes constructed of wood or metal. The pipes would channel the warm air into floor or wall vents inside the home. This method of heating worked because warm air rises.

The system was simple, had few controls, a single automatic gas valve, and no blower. These furnaces could be made to work with any fuel simply by adapting the burner area. They have been operated with wood, coke, coal, trash, paper, natural gas, fuel oil as well as whale oil for a brief period at the turn of the century. Furnaces that used solid fuels required daily maintenance to remove ash and 'clinkers' that accumulated in the bottom of the burner area. In later years, these furnaces were adapted with electric blowers to aid air distribution and speed moving heat into the home. Gas and oil-fired systems were usually controlled by a thermostat inside the home, while most wood and coal-fired furnaces had no electrical connection and were controlled by the amount of fuel in the burner and position of the fresh-air damper on the burner access door.

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Forced-air[edit]

The second category of furnace is the forced-air, atmospheric burner style with a cast-iron or sectional steel heat exchanger. Through the 1950s and 1960s, this style of furnace was used to replace the big, natural draft systems, and was sometimes installed on the existing gravity duct work. The heated air was moved by blowers which were belt driven and designed for a wide range of speeds. These furnaces were still big and bulky compared to modern furnaces, and had heavy-steel exteriors with bolt-on removable panels. Energy efficiency would range anywhere from just over 50% to upward of 65% AFUE. This style furnace still used large, masonry or brick chimneys for flues and was eventually designed to accommodate air-conditioning systems.

Forced draft[edit]

The third category of furnace is the forced draft, mid-efficiency furnace with a steel heat exchanger and multi-speed blower. These furnaces were physically much more compact than the previous styles. They were equipped with combustion air blowers that would pull air through the heat exchanger which greatly increased fuel efficiency while allowing the heat exchangers to become smaller. These furnaces may have multi-speed blowers and were designed to work with central air-conditioning systems.

Condensing[edit]

The fourth category of furnace is the high-efficiency, or condensing furnace. High-efficiency furnaces can achieve from 89% to 98% fuel efficiency. This style of furnace includes a sealed combustion area, combustion draft inducer and a secondary heat exchanger. Because the heat exchanger removes most of the heat from the exhaust gas, it actually condenses water vapor and other chemicals (which form a mild acid) as it operates. The vent pipes are normally installed with PVC pipe versus metal vent pipe to prevent corrosion. The draft inducer allows for the exhaust piping to be routed vertically or horizontally as it exits the structure. The most efficient arrangement for high-efficiency furnaces include PVC piping that brings fresh combustion air from the outside of the home directly to the furnace. Normally the combustion air (fresh air) PVC is routed alongside the exhaust PVC during installation and the pipes exit through a sidewall of the home in the same location. High efficiency furnaces typically deliver a 25% to 35% fuel savings over a 60% AFUE furnace.

Furnace types[edit]

Single-stage[edit]

A single-stage furnace has only one stage of operation, it is either on or off.^[1] This means that it is relatively noisy, always running at the highest speed, and always pumping out the hottest air at the highest velocity.

One of the benefits to a single-stage furnace is typically the cost for installation. Single-stage furnaces are relatively inexpensive since the technology is rather simple.

Two-stage[edit]

A two-stage furnace has to do two stage full speed and half (or reduced) speed. Depending on the demanded heat, they can run at a lower speed most of the time. They can be quieter, move the air at less velocity, and will better keep the desired temperature in the house.

Modulating[edit]

A modulating furnace can modulate the heat output and air velocity nearly continuously, depending on the demanded heat and outside temperature. This means that it only works as much as necessary and therefore saves energy.

Heat distribution[edit]

The furnace transfers heat to the living space of the building through an intermediary distribution system. If the distribution is through hot water (or other fluid) or through steam, then the furnace is more commonly called a boiler. One advantage of a boiler is that the furnace can provide hot water for bathing and washing dishes, rather than requiring a separate water heater. One disadvantage to this type of application is when the boiler breaks down, neither heating nor domestic hot water are available.

Air convection heating systems have been in use for over a century. Older systems rely on a passive air circulation system where the greater density of cooler air causes it to sink into the furnace area below, through air return registers in the floor, and the lesser density of warmed air causes it to rise in the ductwork; the two forces acting together to drive air circulation in a system termed 'gravity-fed'. The layout of these 'octopus’ furnaces and their duct systems is optimized with various diameters of large dampered ducts.

By comparison, most modern 'warm air' furnaces typically use a fan to circulate air to the rooms of house and pull cooler air back to the furnace for reheating; this is called forced-air heat. Because the fan easily overcomes the resistance of the ductwork, the arrangement of ducts can be far more flexible than the octopus of old. In American practice, separate ducts collect cool air to be returned to the furnace. At the furnace, cool air passes into the furnace, usually through an air filter, through the blower, then through the heat exchanger of the furnace, whence it is blown throughout the building. One major advantage of this type of system is that it also enables easy installation of central air conditioning, simply by adding a cooling coil at the outlet of the furnace.

Air is circulated through ductwork, which may be made of sheet metal or plastic 'flex' duct, and is insulated or uninsulated. Unless the ducts and plenum have been sealed using mastic or foil duct tape, the ductwork is likely to have a high leakage of conditioned air, possibly into unconditioned spaces. Another cause of wasted energy is the installation of ductwork in unheated areas, such as attics and crawl spaces; or ductwork of air conditioning systems in attics in warm climates.

Home furnaces[edit]

A home furnace is a major appliance that is permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boiler or residential hot water boiler. The most common fuel source for modern furnaces in North America and much of Europe is natural gas; other common fuel sources include LPG (liquefied petroleum gas), fuel oil and in rare cases coal or wood. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning.

Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient.^[2] Waste gas and heat are mechanically ventilated through PVC pipes that can be vented through the side or roof of the house. Fuel efficiency in a gas furnace is measured in AFUE (Annual Fuel Utilization Efficiency).

Heat Exchanger Pdf

Metallurgical furnaces[edit]

In metallurgy, several specialized furnaces are used. These include:

• Furnaces used in smelters, including:
  • The blast furnace, used to reduceiron ore to pig iron
  • Steelmaking furnaces, including:
• Furnaces used to remelt metal in foundries.
• Furnaces used to reheat and heat treat metal for use in:
  • Rolling mills, including tinplate works and slitting mills.
  • Forges.

Industrial furnaces[edit]

An industrial furnace or direct fired heater, is an equipment used to provide heat for a process or can serve as reactor which provides heats of reaction. Furnace designs vary as to its function, heating duty, type of fuel and method of introducing combustion air. However, most process furnaces have some common features.

Fuel flows into the burner and is burnt with air provided from an air blower. There can be more than one burner in a particular furnace which can be arranged in cells which heat a particular set of tubes. Burners can also be floor mounted, wall mounted or roof mounted depending on design. The flames heat up the tubes, which in turn heat the fluid inside in the first part of the furnace known as the radiant section or firebox. In this chamber where combustion takes place, the heat is transferred mainly by radiation to tubes around the fire in the chamber.

See also[edit]

• Fire test furnaces
• Geothermal heat pump (Geothermal systems)

Notes[edit]

1. ^Homebuilding, Fine (2017-05-09). Home Repair Wisdom & Know-How: Timeless Techniques to Fix, Maintain, and Improve Your Home. Hachette Books. ISBN9780316362887.
2. ^Johnson, Bill; Standiford, Kevin (2008-08-28). Practical Heating Technology. Cengage Learning. p. 116. ISBN141808039X.

References[edit]

• Gray, W.A.; Muller, R (1974). Engineering calculations in radiative heat transfer (1st ed.). Pergamon Press Ltd. ISBN0-08-017786-7.
• Fiveland, W.A., Crosbie, A.L., Smith A.M. and Smith, T.F. (Editors) (1991). Fundamentals of radiation heat transfer. American Society of Mechanical Engineers. ISBN0-7918-0729-0.CS1 maint: Multiple names: authors list (link) CS1 maint: Extra text: authors list (link)
• Warring, R. H (1982). Handbook of valves, piping and pipelines (1st ed.). Gulf Publishing Company. ISBN0-87201-885-7.
• Dukelow, Samuel G (1985). Improving boiler efficiency (2nd ed.). Instrument Society of America. ISBN0-87664-852-9.
• Whitehouse, R.C. (Editor) (1993). The valve and actuator user's manual. Mechanical Engineering Publications. ISBN0-85298-805-2.CS1 maint: Extra text: authors list (link)
• Davies, Clive (1970). Calculations in furnace technology (1st ed.). Pergamon Press. ISBN0-08-013366-5.
• Goldstick, R.; Thumann, A (1986). Principles of waste heat recovery. Fairmont Press. ISBN0-88173-015-7.
• ASHRAE (1992). ASHRAE Handbook. Heating, ventilating and air-conditioning systems and equipment. ASHRAE. ISBN0-910110-80-8. ISSN1078-6066.
• Perry, R.H. and Green, D.W. (Editors) (1997). Perry's Chemical Engineers' Handbook (7th ed.). McGraw-Hill. ISBN0-07-049841-5.CS1 maint: Multiple names: authors list (link) CS1 maint: Extra text: authors list (link)
• Lieberman, P.; Lieberman, Elizabeth T (2003). Working Guide to Process Equipment (2nd ed.). McGraw-Hill. ISBN0-07-139087-1.

External links[edit]

• Furnaces, Incinerators, Kilns at Curlie

A shell and tube heat exchanger is a class of heat exchanger designs.^[1][2] It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell (a large pressure vessel) with a bundle of tubes inside it. One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed of several types of tubes: plain, longitudinally finned, etc.

• 2Shell and tube heat exchanger design

Theory and application[edit]

Two fluids, of different starting temperatures, flow through the heat exchanger. One flows through the tubes (the tube side) and the other flows outside the tubes but inside the shell (the shell side). Heat is transferred from one fluid to the other through the tube walls, either from tube side to shell side or vice versa. The fluids can be either liquids or gases on either the shell or the tube side. In order to transfer heat efficiently, a large heat transfer area should be used, leading to the use of many tubes. In this way, waste heat can be put to use. This is an efficient way to conserve energy.

Heat exchangers with only one phase (liquid or gas) on each side can be called one-phase or single-phase heat exchangers. Two-phase heat exchangers can be used to heat a liquid to boil it into a gas (vapor), sometimes called boilers, or cool a vapor to condense it into a liquid (called condensers), with the phase change usually occurring on the shell side. Boilers in steam engine locomotives are typically large, usually cylindrically-shaped shell-and-tube heat exchangers. In large power plants with steam-driven turbines, shell-and-tube surface condensers are used to condense the exhaust steam exiting the turbine into condensate water which is recycled back to be turned into steam in the steam generator.

Shell and tube heat exchanger design[edit]

There can be many variations on the shell and tube design. Typically, the ends of each tube are connected to plenums (sometimes called water boxes) through holes in tubesheets. The tubes may be straight or bent in the shape of a U, called U-tubes.

In nuclear power plants called pressurized water reactors, large heat exchangers called steam generators are two-phase, shell-and-tube heat exchangers which typically have U-tubes. They are used to boil water recycled from a surface condenser into steam to drive a turbine to produce power. Most shell-and-tube heat exchangers are either 1, 2, or 4 pass designs on the tube side. This refers to the number of times the fluid in the tubes passes through the fluid in the shell. In a single pass heat exchanger, the fluid goes in one end of each tube and out the other.

Surface condensers in power plants are often 1-pass straight-tube heat exchangers (see surface condenser for diagram). Two and four pass designs are common because the fluid can enter and exit on the same side. This makes construction much simpler.

There are often baffles directing flow through the shell side so the fluid does not take a short cut through the shell side leaving ineffective low flow volumes. These are generally attached to the tube bundle rather than the shell in order that the bundle is still removable for maintenance.

Counter current heat exchangers are most efficient because they allow the highest log mean temperature difference between the hot and cold streams. Many companies however do not use two pass heat exchangers with a u-tube because they can break easily in addition to being more expensive to build. Often multiple heat exchangers can be used to simulate the counter current flow of a single large exchanger.

Selection of tube material[edit]

To be able to transfer heat well, the tube material should have good thermal conductivity. Because heat is transferred from a hot to a cold side through the tubes, there is a temperature difference through the width of the tubes. Because of the tendency of the tube material to thermally expand differently at various temperatures, thermal stresses occur during operation. This is in addition to any stress from high pressures from the fluids themselves. The tube material also should be compatible with both the shell and tube side fluids for long periods under the operating conditions (temperatures, pressures, pH, etc.) to minimize deterioration such as corrosion. All of these requirements call for careful selection of strong, thermally-conductive, corrosion-resistant, high quality tube materials, typically metals, including aluminium, copper alloy, stainless steel, carbon steel, non-ferrous copper alloy, Inconel, nickel, Hastelloy and titanium.^[3]Fluoropolymers such as Perfluoroalkoxy alkane (PFA) and Fluorinated ethylene propylene (FEP) are also used to produce the tubing material due to their high resistance to extreme temperatures.^[4] Poor choice of tube material could result in a leak through a tube between the shell and tube sides causing fluid cross-contamination and possibly loss of pressure.

Applications and uses[edit]

The simple design of a shell and tube heat exchanger makes it an ideal cooling solution for a wide variety of applications. One of the most common applications is the cooling of hydraulic fluid and oil in engines, transmissions and hydraulic power packs. With the right choice of materials they can also be used to cool or heat other mediums, such as swimming pool water or charge air.^[5] One of the big advantages of using a shell and tube heat exchanger is that they are often easy to service, particularly with models where a floating tube bundle (where the tube plates are not welded to the outer shell) is available.^[6]

Design and construction standards[edit]

• Standards of the Tubular Exchanger Manufacturers Association (TEMA), 9th edition, 2009
• EN 13445-3 'Unfired Pressure Vessels - Part 3: Design', Section 13 (2012)
• ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, Part UHX

See also[edit]

• Boiler or Reboiler
• Fouling or scaling
• NTU method as an alternative to finding the LMTD

References[edit]

1. ^Sadik Kakaç & Hongtan Liu (2002). Heat Exchangers: Selection, Rating and Thermal Design (2nd ed.). CRC Press. ISBN0-8493-0902-6.
2. ^Perry, Robert H. & Green, Don W. (1984). Perry's Chemical Engineers' Handbook (6th ed.). McGraw-Hill. ISBN0-07-049479-7.
3. ^'Shell and Tube Exchangers'. Retrieved 2009-05-08.
4. ^'PFA Properties'(PDF). http://www.fluorotherm.com/. Fluorotherm Polymers, Inc. Retrieved 4 November 2014.External link in website= (help)
5. ^'Applications and Uses'. Retrieved 2016-01-25.
6. ^Heat Exchanger Shell Bellows Piping Technology and Products, (retrieved March 2012)

External links[edit]