I. Classification of heat exchangers
Traditionally, heat exchange equipment can be divided into three categories:
1, hybrid heat exchanger
The direct interaction and mixing between hot and cold fluids can exchange heat. This kind of heat exchanger is simple in structure, but cheap, and often made into a tower shape.
Allow two completely mixed media with different temperatures to complete heat transfer in the process of direct contact.
For example: cold water tower (cooling tower), granulating tower, airflow drying device, fluidized bed, etc.
2. AC heat exchanger
In this kind of heat exchanger, the energy transfer is completed by the regenerator such as checker bricks or fillers. Let the hot fluid pass through to store the heat in the regenerator, and then let the cold fluid pass through to take away the heat. Due to the alternating input of two fluids, it is inevitable that a small amount of fluids will mix with each other, resulting in "pollution" of fluids.
Regenerative heat exchanger has compact structure, low price and large heat transfer area per unit volume, which is more suitable for gas-gas heat exchange. It is mainly used for raw gas conversion and air waste heat in petrochemical production. The structural feature of rotary regenerative heat exchanger is to realize continuous operation. The regenerator in a heat exchanger is generally in a fan-shaped box assembled by a die plate or a wire mesh, and its outside is sealed with a metal shell, rotating at a low speed of 1 ~ 4 rpm for continuous heat exchange.
3. Partition heat exchanger
The so-called baffle heat exchanger means that two fluids with different temperatures flow in a space separated by a fixed wall (called heat transfer surface), and heat is transferred through heat conduction and convection heat transfer on the wall. The fluids participating in heat exchange will not be mixed, and the transfer process is continuous and stable. The heat transfer surface of baffle heat exchanger is mostly made of metal with good thermal conductivity. In some cases, due to the need of anticorrosion, it is also made of nonmetal (such as graphite, polyethylene, etc.). This is the most widely used heat exchanger in industrial manufacturing. Cold fluid and hot fluid are separated by a solid wall, and heat is transferred through the wall. According to the shape and structural characteristics of heat transfer surface, it can be divided into:
(1) tube heat exchanger:
Such as sleeve type, spiral pipe type, shell-and-tube type and heat pipe type.
(2) Plate heat exchanger:
Such as plate type, spiral plate type, plate and shell type, etc.
(3) Extended surface heat exchanger:
Such as plate-fin type, tube-fin type and enhanced heat transfer tubes.
Second, the type of heat exchanger is introduced
1, jacketed heat exchanger
The structure is shown in the figure below. Jacket space is the passage of heating medium and cooling medium. This kind of heat exchanger is mainly used for heating or cooling the reaction process. When heated by steam, the upper nozzle of steam enters the jacket and the condensed water flows out from the lower nozzle. As a cooler, the cooling medium (such as cooling water) enters from the lower nozzle of the jacket and flows out from the upper nozzle.
Jacket heat exchanger has a simple structure, but the heating surface is limited by the container wall, and the heat transfer surface is small and the heat transfer coefficient is not high.
2. Spray heat exchanger
The structure and operation of the spray heat exchanger are shown in the following figure. This kind of heat exchanger is often used as a cooler. Hot fluid flows from bottom to top in the pipeline, and cold water flows out from the top shower pipe, evenly distributed on the serpentine pipe, flowing from top to bottom along its surface in the form of thin film, and finally flowing into the water tank for discharge. Spray heat exchanger is usually placed in outdoor air circulation. Evaporation of cooling water in the air can also take away some heat and enhance the cooling effect. Its advantages are convenient maintenance and good heat transfer effect. The disadvantage is that spraying is not easy to be uniform.
3. Sleeve heat exchanger
The basic components of double-tube heat exchanger are formed by coaxial nesting of straight tubes with different diameters. If the pipeline is too long, the middle of the pipeline will bend downward, which will make the fluid distribution in the annulus uneven.
The advantages of double-tube heat exchanger are simple structure, the inner tube can withstand high pressure, and the heat transfer area can be increased or decreased as needed. If the diameters of the two tubes are properly selected, both fluids can obtain proper flow velocity, and the two fluids can carry out strict countercurrent. Its disadvantages are many indirect heads, easy leakage of joints and small heat transfer area per unit heat exchanger volume. Therefore, it is suitable for occasions with small flow, small heat transfer area and high pressure requirements.
All kinds of heat exchangers and some kinds of heat exchangers are introduced in detail above, hoping to help you.