A heat exchanger is a device that transfers heat to achieve desired heating or cooling. An important design aspect of heat exchanger technology is the selection of the right material to conduct and transfer heat quickly and efficiently.
Copper has many desirable properties for efficient and durable heat exchangers. First and foremost, copper is an excellent heat conductor. This means that the high thermal conductivity of copper allows heat to pass through quickly. Other desirable properties of copper in heat exchangers include corrosion resistance, biofouling resistance, allowable maximum stress and internal pressure, creep impact strength, fatigue strength, hardness, thermal expansion, specific heat, antimicrobial properties, tensile strength, yield strength, high melting point, alloya ability, ease of fabrication, and ease of joining.
The combination of these properties allows copper to be determined for heat exchangers in industrial facilities, HVAC systems, cooling and vehicle radiators, and as heat sinks to cool computers, disk drives, televisions, computer monitors, and other electronic equipment. Copper is also fed to the bottom of high quality cookware because the metal does heat up quickly and distributes it evenly.
Non-copper heat exchangers are also available. Some alternative materials include aluminum, carbon steel, stainless steel, nickel alloys, and titanium.
This article focuses on useful properties and general application of copper in heat exchangers. New copper heat exchanger technology for special applications was also introduced.
Video Copper in heat exchangers
Histori
The heat exchangers using copper and its alloys have evolved along with the heat transfer technology over the last few hundred years. The copper condenser tube was first used in 1769 for the steam engine. Originally, the tubes were made of pure copper. In 1870, Muntz metal, 60% Cu-40% brass Zn alloy, was used for condensers in cooling seawater. Metal admiralty, 70% Cu-30% Zn alloy yellow brass with 1% tin added to improve corrosion resistance, introduced in 1890 for seawater service. In the 1920s, 70% Ni-30% Ni alloys were developed for naval condensers. Soon after, 2% of manganese and 2% iron copper alloys were introduced for better erosion resistance. A 90% Cu-10% Ni alloy was first available in the 1950s, initially for seawater piping. This alloy is now the most widely used copper-nickel alloy in ocean heat exchangers.
Today, steam, evaporator, and condenser rolls are made of copper and copper alloys. These heat exchangers are used in cooling and air conditioning systems, heating and industrial and central cooling systems, radiators, hot water tanks, and under floor heating systems.
Copper-based heat exchangers can be produced with copper/aluminum fins, cupro-nickel, or all copper construction. Various coatings can be applied to improve the corrosion resistance of the tube and fins.
Maps Copper in heat exchangers
The beneficial properties of copper heat exchanger
Thermal conductivity
Thermal conductivity (k, also denoted as? Or?) Is a measure of the material's ability to heat. Heat transfers across all high thermal conductivity materials occur at a higher rate than low thermal conductivity materials. In International Unit System (SI), the thermal conductivity is measured in watts per meter of Kelvin (W/(moK)). In Imperial Measurement Systems (Imperial English, or Imperial units), thermal conductivity is measured in Btu/(hroft? F).
Copper has a thermal conductivity of 231 Btu/(hr-ft-F). This is higher than all other metals except silver, precious metals. Copper has a better thermal conductivity rating of 60% than aluminum and a better 3,000% rating of stainless steels.
More information about the thermal conductivity of the selected metals is available.
Corrosion resistance
Corrosion resistance is essential in heat transfer applications where liquids are involved, such as in hot water tanks, radiators, etc. The only affordable material that has the same corrosion resistance as copper is stainless steel. However, the thermal conductivity of stainless steel is 1/30 of copper. The aluminum tube is not suitable for drinking or untreated water applications because it correlates to pH & lt; 7.0 and releases hydrogen gas.
Protective film can be applied to the inner surface of the copper alloy tube to improve corrosion resistance. For certain applications, this film is composed of iron. In a power plant condenser, a duplex tube comprising an inner titanium layer with an outer copper-nickel alloy is used. This allows the use of favorable mechanical and chemical properties of copper (eg, tense crack corrosion, ammonia attack) along with excellent titanium corrosion resistance. Duplex tubes with inner aluminum brass or copper-nickel and stainless steel or light steel outward can be used for refrigeration in oil refining and petrochemical industries.
Biofouling resistance
Copper and nickel-copper alloys have high natural resistance to biofouling compared to alternative materials. Other metals used in heat exchangers, such as steel, titanium, and aluminum, are ready. Protection against biofouling, especially in marine structures, can be achieved over long periods with copper metal.
Copper-nickel alloys have been proven for years in seawater pipelines and other marine applications. These alloys reject biofouling in the open ocean where they do not allow microbial slime to build and support macrofouling.
The investigators attribute copper resistance to biofouling, even in temperate waters, to two possible mechanisms: 1) sequence of colonization that inhibits through the release of slow copper ions during corrosion, thus inhibiting the adhesion of the microbial layer to the ocean surface; and/or, 2) separating layers containing corrosive products and larvae of macro-encrusting organisms. The latter mechanism prevents the completion of the pelagic larval stage on the metal surface, rather than killing the organism.
Antimicrobial properties
Due to the strong antimicrobial properties of copper, the copper fins can inhibit the growth of bacteria, fungi, and viruses normally formed in air conditioning systems. Therefore, the surface of the copper-based heat exchanger is cleaner for longer periods of time than the heat exchangers made of other metals. These benefits offer a highly expanded service life of heat exchangers and contribute to improving air quality. The heat exchanger made separately from the antimicrobial copper and aluminum in a full-scale HVAC system has been evaluated for its ability to limit microbial growth under normal flow rate conditions using a single-pass outside the air. Commonly used aluminum components develop stable biofilms of bacteria and fungi within four weeks of operation. During the same period of time, antimicrobial copper was able to limit the burden of bacteria associated with a copper heat exchanger of 99.99% and a mushroom load of 99.74%.
Copper fin fuels have been deployed on buses in Shanghai to kill and kill bacteria, viruses and fungi that originally thrived on non-copper fins and allowed to circulate around the system. The decision to replace aluminum with copper follows an antimicrobial test by the Shanghai Disease Control and Prevention Center (SCDC) from 2010 to 2012. The study found that the microbial level on the copper fin surface is significantly lower than that of aluminum, thus helping to protect the health of bus passengers.
More information about the benefits of antimicrobial copper in HVAC systems is available.
Grooving ease in
The internal grooved copper tubes with smaller diameters are more thermally efficient, materially efficient, and easier to bend and burn and if not working with them. In general it is easier to make deep grooved tubes of copper, a very soft metal.
Common applications for copper heat exchangers
Industrial facilities and power plants
Copper alloys are widely used as heat exchangers in fossils and nuclear steam power plants, chemical and petrochemical plants, marine services, and desalination plants.
The greatest use of copper alloy heat exchangers on a per unit basis is in utility power plants. These plants contain surface condensers, heaters, and coolers, all of which contain copper pipes. The main surface condenser receiving steam-turbine discharge uses the most copper.
Nickel copper is a group of alloys commonly specified in heat exchangers or condenser tubes in evaporators from desalination plants, process industry factories, thermal power generation air conditioning zones, high pressure water feeders, and marine pipelines piping. The alloy composition may vary from 90% Cu-10% Ni to 70% Cu-30% Ni.
The condenser and tube heat exchanger from brass admiralty arsenic (Cu-Zn-Sn-As) once dominated the market of industrial facilities. Aluminum brass then rose in popularity due to improved corrosion resistance. Today, aluminum-brass, 90% Cu-10% Ni, and other copper alloys are widely used in tubular heat exchangers and piping systems in seawater, brackish water and fresh water. Aluminum-brass, 90% Cu-10% Ni and 70% Cu-30% Ni alloys show good corrosion resistance in seawater de-aeration of hot and saltwater in multi-stage flash desalination plants.
The fixed tube of liquid-cooled heat exchanger is particularly suitable for marine and hard applications can be assembled with brass shell, copper tube, brass baffles, and forged integral hollow brass tip.
Copper alloy tubes can be supplied either with bright metal surfaces (CuNiO) or with a thin and strongly attached oxide layer (aluminum brass). This finish allows the formation of a protective layer. The surface of the protective oxide is best achieved when the system is operated for several weeks with clean, oxygen-containing cooling water. While a protective layer is formed, support measures may be performed to improve the process, such as adding iron sulphate or intermittent tube cleaning. The protective film formed on Cu-Ni alloys in seawater is mature to about three months at 60 ° F and becomes increasingly protective with time. The film is resistant to contaminated water, irregular speed, and other harsh conditions. More details are available.
Biofouling resistance of Cu-Ni alloys allows heat exchange units to operate for several months between mechanical cleaning. However, cleaning is required to restore the original heat transfer capability. Chlorine injection may extend mechanical cleansing intervals for up to a year or more without adverse effects on Cu-Ni alloys.
More information about copper alloy heat exchangers for industrial facilities is available.
Solar hot water system
Solar water heaters can be a cost effective way to generate hot water for homes in many areas of the world. Copper heat exchangers are important in solar thermal heating and cooling systems due to high copper heat conductivity, resistance to atmospheric and water corrosion, sealing and solder incorporation, and mechanical strength. Copper is used both in receivers and in primary circuits (pipes and heat exchangers for water tanks) of solar hot water systems.
Different types of solar collectors for residential applications are available by direct circulation (ie, heating the water and bringing it directly to the house for use) or indirect circulation (ie, pumping the heat transfer fluid through the heat exchanger, which then heats the water flowing into the house) system. In a solar hot water heater evacuated with an indirect circulatory system, the evacuated tube contains an outer glass tube and a metal absorbent tube attached to the fins. Solar thermal energy is absorbed in the evacuated tube and converted into usable heat. The evacuated glass tube has a double layer. Inside the glass tube there is a copper pipe. It is a closed hollow copper tube containing a small amount of heat transfer fluid (mixture of water or glycol) under low boiling pressure at very low temperatures. Hot copper pipes transfer heat energy from inside a solar tube to a copper canopy. When the solution circulates through the copper canopy, the temperature rises.
Other components in a copper-containing solar thermal system include a solar thermal exchange tank and a solar pumping station, along with pumps and controllers.
HVAC System
Air conditioning and heating in buildings and motor vehicles are the two largest applications for heat exchangers. While copper tubes are used in most cooling and air conditioning systems, typical air conditioning units today use aluminum fins. This system can infect bacteria and form and develop smells and fouling that can make them work poorly. Strong new requirements including demands for increased operating efficiency and the reduction or elimination of harmful emissions increase the role of copper in modern HVAC systems.
The antimicrobial properties of copper can improve the performance of HVAC systems and associated indoor air quality. After extensive testing, copper became a US registered material to protect heating and air conditioning equipment against bacteria, fungi, and fungi. In addition, tests funded by the US Department of Defense indicate that all copper air coolers suppress the growth of bacteria, fungi, and fungi that cause odors and reduce the energy efficiency of the system. Units made with aluminum have not shown this benefit.
Copper can cause a galvanic reaction in the presence of other alloys, which cause corrosion.
Gas water heaters
The water heater is the second largest energy use in the home. Gas-water heat exchangers that transfer heat from gas fuel to water between 3 and 300 kilowatts of thermal (kWth) have extensive residential and commercial use in water heating and heating boiler applications.
Increased demand for energy-efficient compact water heating systems. Tankless gas water heaters produce hot water when needed. Copper heat exchangers are the preferred material in these units due to their high thermal conductivity and ease of fabrication. To protect these units in acidic environments, durable coatings or other surface treatments are available. The acid-resistant layer is able to withstand temperatures of 1000 ° C.
Forced air cooling and cooling
Air source heat pumps have been used for residential and commercial heating and cooling for years. These units rely on air-to-air heat exchange through evaporator units similar to those used for air conditioning. The most commonly used air-to-air heat exchangers for forced air heating and cooling systems, such as with indoor and outdoor wood stoves, boilers, and stoves. They can also be suitable for liquid cooling applications. Copper is specified in the supply manifold and back and in the tube rolls.
Geothermal Direct Heat Cooling (DX)
The geothermal heat pump technology, known as "ground source," "earth-coupled," or "direct exchange," relies on refrigerant circulation through buried copper pipes for heat exchange. These units, which are much more efficient than their air source counterparts, depend on the firmness of ground temperature below the frost zone for heat transfer. The most efficient heat source heat pumps use ACR, Type L or special-size copper tubes grown to the ground to transfer heat to or from the conditioned space. Flexible copper tubes (typically 1/4-inch to 5/8-inches) can be buried in deep vertical holes, horizontally in a relatively shallow grid pattern, in a vertical fence-like arrangement in a deep-medium trench, or as a custom configuration. More information is available.
Electronic system
Copper and aluminum are used as heat sinks and heat pipes in electronic cooling applications. Heat sinks are passive components that cool semiconductor and optoelectronic devices by dissipating heat into the surrounding air. Heat sinks have a higher temperature than the surrounding environment so that heat can be transferred into the air through convection, radiation, and conduction.
Aluminum is the most widely used heat sink material because it is cheaper. Copper heat sinks are a necessity when higher levels of thermal conductivity are required. An alternative to all-copper or all-aluminum heat sinks is the joining of aluminum fins to the copper base.
Heat sinks are copper die-cast and fastened together on a plate. They spread heat rapidly from heat sources to copper or aluminum fins and into the surrounding air.
The heat pipe is used to remove heat from the central processing unit (CPU) and the graphics processing unit (GPU) and to the heat sink, where heat energy is dissipated into the environment. Copper and aluminum pipes are used extensively in modern computer systems where increased power requirements and associated heat emissions result in greater demands on cooling systems.
The heat pipe usually consists of pipes or tubes that are sealed at both hot and cold ends. The heat pipe utilizes evaporative cooling to transfer heat energy from one point to another by evaporation and condensation of working liquid or coolant. They are fundamentally preferable to heat conduction at a greater distance than heat sinks because their effective thermal conductivity is some of the larger magnitude order than equivalent solid conductors.
When it is desired to maintain junction temperatures below 125-150 ° C, copper/water heat pipes are usually used. Copper/methanol heat pipes are used if the application requires hot pipe operation below 0 Â ° C.
New technology
CuproBraze
CuproBraze is a copper alloy heat exchanger technology developed for applications that must withstand harsh conditions. This technology is perfect for higher temperature and environmental pressures required in cleaner diesel engines mandated by global environmental regulations.
Applications for CuproBraze include cooling air charge, radiator, oil cooler, climate control system, and heat transfer cores. CuproBraze is well suited for filling air coolers and radiators in capital-intensive industries where machines have to operate for long periods of time under harsh conditions without premature failure. For this reason, CuproBraze is perfect for off-road vehicles, trucks, buses, industrial machinery, generators, locomotives, and military equipment markets. This technology is also suitable for light trucks, SUVs, and passenger cars.
CuproBraze is an alternative to soldered copper/plate fin brass, soldered brass copper fin of serpentine, and serpentine aluminum brazing fin. This technology allows the copper brazing serpentine fins to be used in copper-brass heat exchanger designs. It's cheaper to produce than soldered serpentine fin designs. They are also stronger, lighter, longer lasting, and have stronger joints.
internal grooved
The benefits of smaller internal grooved copper tubes for heat transfer are well documented.
Smaller coil diameters have better heat transfer rates than conventional coil sizes and they can withstand the higher pressures required by a new generation of environmentally friendly refrigerants. Smaller coil diameters also have lower material costs because they require less coolant, fin, and coil; and they allow the design of air conditioners and air conditioners that are smaller and lighter and efficient because the evaporator and condenser rolls are smaller and lighter. MicroGroove uses the inner surface of the tube to increase the surface to volume ratio and increase turbulence to mix the refrigerant and homogenize the entire tube.
References
Source of the article : Wikipedia
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