What Is A Heat Exchanger And What's The Effect?
A heat exchanger is a device that transfers some heat from a hot fluid to a cold fluid, also known as a heat exchanger.
Heat exchanger is used widely, in the daily life of heating heating radiator, condenser in the turbine unit and the oil cooler on the space rocket, etc., are all heat exchanger. It is also widely used in industries such as chemicals, oil, power and atomic energy. Its main function is to guarantee the specific temperature required by the process, and is also one of the main equipment for improving energy efficiency.
A heat exchanger is a single device, such as a heater, a cooler, and a condenser. It is also part of a process equipment, such as the heat exchanger in ammonia.
Because of the limitation of manufacturing process and scientific level of the early heat exchanger can only use simple structure, and the heat transfer area is small, large and heavy volume, such as coil heat exchanger, etc. With the development of the manufacturing process, and gradually form a pipe heat exchanger, it not only has a large heat transfer area per unit volume, and the heat transfer effect is better also, in the industrial production for a long time to become a kind of typical heat exchanger.
The plate heat exchanger was introduced in the 1920s and applied to the food industry. The heat exchanger, which is made of plate tube, is compact and heat transfer, so it develops in various forms. In the early 1930s, Sweden made its first helix heat exchanger. The British brazing method was then used to create a plate-fin heat exchanger made from copper and its alloy materials for heat dissipation of aircraft engines. In the late 1930s, Sweden made the first shell heat exchanger for pulp mills. During this period, the heat exchanger of the new material was noticed in order to solve the heat exchange problem of the strong corrosive medium.
About the '60 s, because of the space technology and the rapid development of advanced science, an urgent need to all kinds of high performance of compact heat exchangers, coupled with the stamping, brazing and seal the development of technology, such as heat exchanger manufacturing technology further perfect, in order to impel the vigorous development of the compact of the plate heat exchanger and a wide range of applications. In addition, since the '60 s, in order to adapt to change under the condition of high temperature and high pressure heat and the need of energy saving, the typical tube and shell heat exchanger has been further development. In the mid-1970s, the heat pipe heat exchanger was created in order to strengthen the heat transfer in the research and development of the heat pipe.
Heat exchangers can be divided into three types: mixed type, heat storage and wall type. ZHCOOLER heat exchanger is subdivided into,Aluminum bar plate heat exchanger, the Car Radiator, the Mixer oil cooler, cold, and Copper coil aluminum fin radiator, such as application scope is more accurate.
The hybrid heat exchanger is a heat exchanger, which is a direct contact of cold, hot fluid, and a heat exchanger, which is also called a contact heat exchanger. Due to the need to be separated in time due to the mixing of two fluids, this heat exchanger is suitable for heat exchange between two fluids. Cooling tower used in the chemical plants and power plants, for example, hot water to spray, by the cold air inhaled from bottom to top, on the surface of the water film that filler or droplets and droplet surface, heat transfer of the hot water and cold air touch each other, hot water is cooling, cold air is heated, then depend on the density difference between the two fluid itself to separation in a timely manner.
Regenerative heat exchanger is the use of cold and hot fluid flows through the regenerator regenerator alternately (stuffing) surface, and thus for the heat exchange heat exchanger, such as coke oven preheated air below the regenerator. These heat exchangers are mainly used to recover and utilize heat from high temperature exhaust. The same kind of equipment, which is used for the purpose of recovering cold, is used in air separation devices.
Recuperative heat exchanger in cold and hot fluid separated by a solid partition, and the heat exchange with the partition of the heat exchanger, so also called on the surface of heat exchanger, the most widely used this kind of heat exchanger.
According to the structure of heat transfer surface, the wall heat exchanger can be divided into pipe, plate and other type. The tubular heat exchanger is used as a heat transfer surface on the surface of the pipe, including the coil heat exchanger, sleeve heat exchanger and tube heat exchanger, etc. The plate heat exchanger with the plate as the heat transfer surface, including the plate heat exchanger, spiral plate heat exchanger, plate fin heat exchanger, plate heat exchanger and umbrella plate heat exchanger, etc.; Other types of heat exchangers are heat exchangers designed to meet certain special requirements, such as surface heat exchanger, rotary disc heat exchanger and air cooler.
The relative flow of the fluid in the heat exchanger is usually in both the downstream and the current. At the same time, the temperature difference between the two fluid at the entrance is the largest, and the temperature difference is minimized along the heat transfer surface. In the current, the temperature difference between the two fluid surfaces of the heat transfer surface is more uniform. When the temperature of the inlet and inlet of the cold and hot fluid is certain, when the two kinds of fluid have no phase change, the average temperature difference of the reverse flow is the least.
In the case of the same heat transfer, the average temperature difference between the heat transfer and the heat transfer is decreased. If the heat transfer area is not changed, the consumption of heating or cooling fluid can be reduced by using reverse flow. The former can save the cost of the equipment, the latter can save the cost of the operation, so in the design or the production use should use the counter-current exchange heat as far as possible.
When one or both cold and hot fluid with phase change (boiling or condensation), due to emit or absorb only when phase change latent heat of vaporization, the temperature of the fluid itself is not change, so the import and export of fluid temperature is equal, when the temperature difference between the two fluid has nothing to do with the flow of fluid selection. In addition to flow and reverse flow, there are also flows and flows.
In the heat transfer process, it is an important problem to reduce heat resistance in the wall heat exchanger to improve the heat transfer coefficient. Thermal resistance is mainly derived from the partition on both sides of the viscosity in the thin layer on the surface of the heat transfer fluid (called boundary layer), and the heat exchanger used in the wall on both sides of the formation of the dirt layer, metal wall thermal resistance is relatively small.
Increase fluid flow velocity and disturbance, reduce the thin boundary layer, reduce heat resistance and increase the heat factor. But increasing the flow rate increases the energy consumption, so the design should be reasonable in reducing heat resistance and reducing energy consumption. In order to reduce the heat resistance of dirt, we can try to delay the formation of dirt and wash the heat surface regularly.
Conventional heat exchangers are made of metal, including carbon steel and low alloy steel, mostly for manufacturing medium and low voltage heat exchanger. Stainless steel can also be used as a high, low temperature material except for different corrosion-resistant conditions. Copper, aluminum and its alloys are used to make cryogenic heat exchangers. Nickel alloys are used for high temperature conditions; Non-metallic materials in addition to the gasket parts made, some have begun to corrosion resistant heat exchanger used in non-metal materials, such as graphite heat exchanger, fluorine plastic heat exchanger heat exchanger and glass, etc.
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