How are heat exchangers classified?
According to the heat transfer method, it can be divided into: partition wall heat exchanger, regenerative heat exchanger, fluid connection indirect heat exchanger, direct contact heat exchanger, and multiple heat exchanger.
According to the purpose, it can be divided into: heater, preheater, superheater and evaporator.
According to the structure, it can be divided into: floating head heat exchanger, fixed tube-sheet heat exchanger, U-shaped tube-sheet heat exchanger, plate heat exchanger, etc.
One of the differences between shell and tube and plate heat exchangers: structure
1. Shell and tube heat exchanger structure:
The shell and tube heat exchanger is composed of shell, heat transfer tube bundle, tube sheet, baffle (baffle) and tube box and other components. The shell is mostly cylindrical, with a tube bundle inside, and the two ends of the tube bundle are fixed on the tube sheet. There are two kinds of hot fluid and cold fluid in heat transfer, one is the fluid inside the tube, called the tube side fluid; the other is the fluid outside the tube, called the shell side fluid.
In order to improve the heat transfer coefficient of the fluid outside the tube, several baffles are usually arranged in the tube shell. The baffle can increase the velocity of the fluid in the shell side, make the fluid pass through the tube bundle multiple times according to the specified distance, and increase the turbulence of the fluid.
The heat exchange tubes can be arranged in equilateral triangles or squares on the tube sheet. The arrangement of equilateral triangles is compact, the degree of turbulence of the fluid outside the tube is high, and the heat transfer coefficient is large. The square arrangement facilitates cleaning out of the tube and is suitable for fluids prone to fouling.
1-shell; 2-tube bundle; 3, 4-connector; 5-head; 6-tube plate: 7-baffle: 8-drain pipe
One-way shell and tube heat exchanger
Schematic diagram of a single-shell double-tube heat exchanger
2. Plate heat exchanger structure:
The detachable plate heat exchanger is made of many stamped corrugated thin plates at certain intervals, sealed by gaskets around them, and overlapped with frames and compression screws. The four corner holes of the plates and spacers form the fluid distributors and collectors. At the same time, cold fluid and hot fluid are separated reasonably so that they are separated on both sides of each plate. Flow in channels, heat exchange through plates.
One of the differences between shell and tube heat exchangers and plate heat exchangers: classification
1. Classification of shell and tube heat exchangers:
(1) The tube sheet of the fixed tube sheet heat exchanger is integrated with the tube bundles at both ends of the tube shell. When the temperature difference is slightly large and the shell side pressure is not too high, an elastic compensating ring can be installed on the shell to reduce the thermal stress.
(2) The tube plate at one end of the tube bundle of the floating head heat exchanger can float freely, completely eliminating thermal stress, and the whole tube bundle can be pulled out from the shell, which is convenient for mechanical cleaning and maintenance. Floating head heat exchangers are widely used, but their structure is complicated and the cost is high.
(3) Each tube of the U-shaped tube heat exchanger is bent into a U shape, and both ends are fixed on the same tube sheet in the upper and lower areas. With the help of the tube box partition, it is divided into two chambers: inlet and outlet. The heat exchanger completely eliminates thermal stress, and its structure is simpler than that of the floating head type, but the tube side is not easy to clean
(4) The eddy current hot film heat exchanger adopts the latest eddy current hot film heat exchange technology, and improves the heat exchange effect by changing the fluid motion state. When the medium passes through the surface of the vortex tube, it will have a strong scour on the surface of the vortex tube, thereby improving the heat transfer efficiency, up to 10000 W/m2. At the same time, the structure has the functions of corrosion resistance, high temperature resistance, high pressure resistance and anti-scaling.
2. Classification of plate heat exchangers:
(1) According to the size of the heat exchange area per unit space, the plate heat exchanger is a compact heat exchanger, mainly compared with the shell and tube heat exchanger. Traditional shell and tube heat exchangers occupy a large area.
(2) According to the use of the process, there are different names: plate heater, plate cooler, plate condenser, plate preheater.
(3) According to the process combination, it can be divided into unidirectional plate heat exchanger and multi-directional plate heat exchanger.
(4) According to the flow direction of the two media, it can be divided into parallel plate heat exchanger, counter flow plate heat exchanger and cross flow plate heat exchanger. The latter two are more commonly used.
(5) According to the gap size of the runner, it can be divided into conventional gap plate heat exchanger and wide gap plate heat exchanger.
(6) According to the corrugation wear condition, the plate heat exchanger has more detailed differences, which will not be repeated. Please refer to: corrugated form of plate heat exchanger.
(7) According to whether it is a complete set of products, it can be divided into single plate heat exchanger and plate heat exchanger unit.
Plate-fin heat exchanger
One of the differences between shell and tube and plate heat exchangers: Features
1. Features of shell and tube heat exchanger:
(1) High efficiency and energy saving, the heat transfer coefficient of the heat exchanger is 6000-8000W/(m2·k).
(2) All stainless steel production, long service life, up to 20 years.
(3) Changing laminar flow to turbulent flow improves heat transfer efficiency and reduces thermal resistance.
(4) Fast heat transfer, high temperature resistance (400 degrees Celsius), high pressure resistance (2.5 MPa).
(5) Compact structure, small footprint, light weight, easy installation, saving civil construction investment.
(6) The design is flexible, the specifications are complete, the practicability is strong, and the money is saved.
(7) It has a wide range of application conditions and is suitable for pressure, temperature range and heat exchange of various media.
(8) Low maintenance cost, simple operation, long cleaning cycle and convenient cleaning.
(9) Adopt nano-thermal film technology, which can significantly improve the heat transfer coefficient.
(10) Widely used in thermal power, industrial and mining, petrochemical, urban central heating, food and medicine, energy electronics, machinery and light industry and other fields.
(11) The copper tube with cooling fins rolled on the outer surface of the heat transfer tube has high thermal conductivity and large heat transfer area.
(12) The guide plate guides the shell-side fluid to flow continuously in the broken line in the heat exchanger. The distance between guide plates can be adjusted for optimum flow. The structure is firm, and it can meet the heat transfer of shell-side fluid with large flow rate or even super large flow rate and high pulsation frequency.
2. Features of plate heat exchanger:
(1) High heat transfer coefficient
Since different corrugated plates are reversed, complex channels are formed, so that the fluid between the corrugated plates flows in a three-dimensional swirling flow, and turbulent flow can be generated at a low Reynolds number (generally Re=50-200), so heat transfer The coefficient is relatively high, and it is generally considered that the red color is 3-5 times that of the shell-and-tube type.
(2) The logarithmic average temperature difference is large, and the temperature difference at the end is small
In a shell and tube heat exchanger, there are two fluid flows on the tube side and the tube side respectively. Generally, they are cross-flow and have a small logarithmic mean temperature difference correction factor. Most plate heat exchangers are parallel or countercurrent flow, and the correction factor is generally around 0.95. In addition, the hot and cold fluid flow in the plate heat exchanger is parallel to the flow of the hot and cold fluid in the heat exchanger.
The hot surface and no bypass make the temperature difference at the end of the plate heat exchanger small, and the heat transfer to water can be less than 1°C, while the shell and tube heat exchanger is generally 5°C.
(3) Small footprint
The plate heat exchanger has a compact structure, and the heat transfer area per unit volume is 2-5 times that of the shell-and-tube heat exchanger. Unlike the shell-and-tube heat exchanger, it does not require a maintenance location for the extraction of the tube bundle. Therefore, in order to achieve the same heat transfer capacity, the floor area of the plate heat exchanger is about 1/5-1/8 of that of the shell and tube heat exchanger.
(4) It is easy to change the heat exchange area or process combination
As long as a few plates are added or removed, the purpose of increasing or reducing the heat transfer area can be achieved. By changing the plate layout or replacing multiple plate types, the required process combination can be realized, and the heat exchange area of the shell and tube heat exchanger can be adapted to the new heat exchange conditions. It is almost impossible to increase the heat transfer area of a shell and tube heat exchanger.
(5) light weight
The plate thickness of the plate heat exchanger is only 0.4-0.8 mm, and the tube thickness of the shell-and-tube heat exchanger is 2.0-2.5 mm. Shell and tube heat exchangers are much heavier than plate heat exchanger frames. Plate heat exchangers generally only account for about 1/5 of the weight of the shell and tube.
(6) Low price
The material of the plate heat exchanger is the same, the heat exchange area is the same, and the price is 40%~60% lower than that of the shell and tube heat exchanger.
(7) Easy to make
The heat transfer plate of the plate heat exchanger has been stamped and processed, which has a high degree of standardization and can be mass-produced. Shell and tube heat exchangers are usually handmade.
(8) Easy to clean
As long as the pressure bolts of the frame plate heat exchanger are loosened, the tube bundle of the plate heat exchanger can be loosened, and the plate heat exchanger can be removed for mechanical cleaning. This is very convenient for the heat exchange process of equipment that needs to be cleaned frequently.
(9) Small heat loss
In the plate heat exchanger, only the shell plate of the heat exchange plate is exposed to the atmosphere, the heat loss is negligible, and no insulation measures are required.
