Heat exchanger , also known as heat exchanger is a device designed to transfer heat between two or more fluids. Its basic working principle is to transfer part of the heat from the hot fluid to the cold fluid, thereby heating the cold fluid or cooling the hot fluid, without allowing the two fluids to mix directly. Heat exchangers play a crucial role in the chemical, petroleum, power, food, and many other industrial production fields. They can be used as heaters, coolers, condensers, evaporators, and reboilers, among other functions, with a very wide range of applications.

Botte salt-containing wastewater evaporator or production salt solution evaporator often uses stainless steel or titanium shell-and-tube heat exchangers, which are wall-type heat exchangers. When used for heating, they are called heaters; when used for cooling, they are called condensers. Plate heat exchangers or other types of heat exchangers are also used for preheating or other parts of evaporation systems, all aiming to achieve good heat exchange functionality.

They can be classified according to different standards, mainly including the following methods:

1. Classification by structure

1. Shell-and-tube heat exchanger: This is the most traditional and widely used type, consisting of a shell, tube bundle, tube sheet, and head. One fluid flows inside the tubes, while the other fluid flows in the shell outside the tubes. Depending on the tube bundle structure, it can be further divided into various forms such as fixed tube sheet type, floating head type, and U-tube type.

2. Plate heat exchanger: It is made up of a series of thin metal plates stacked together, with flow channels formed between the plates for fluid passage. Compared with shell-and-tube type, it is usually more compact, lighter, and has higher heat exchange efficiency, but its ability to withstand pressure and temperature is lower.

1. Spiral plate heat exchanger: Two spiral metal plates are interlaced to form spiral channels, and the fluid flows in opposite directions in these channels to achieve efficient heat exchange.

2. Plate-fin heat exchanger: Suitable for heat exchange between gases, it consists of many thin metal plates and fins, providing a large surface contact area.

3. Double-pipe heat exchanger: Simple structure, one pipe is inserted into another pipe, and the inner and outer fluids flow separately for heat exchange.

2. Classification by heat transfer principle

1. Wall-type heat exchanger: Heat exchange is carried out through a solid wall between fluids, such as the shell-and-tube and plate types mentioned above.

2. Mixed heat exchanger: Hot and cold fluids directly contact and mix for heat exchange, such as cooling towers.

3. Regenerative heat exchanger: Uses the heat capacity of solid materials to store heat and then release it to another fluid, such as a rotary regenerator.

3. Classification by application

• Heater: Mainly used for heating fluids.

• Cooler: Used to lower the fluid temperature.

• Condenser: Condenses gas into liquid.

• Evaporator: Evaporates liquid into gas.

• Reboiler: Heats the liquid during distillation to cause partial evaporation.

4. Classification by materials used

It can be mainly divided into two categories: Metal material heat exchangers and Non-metal material heat exchangers 。

4.1 Metal material heat exchangers: Metal materials, due to their good thermal conductivity and mechanical properties, are widely used in heat exchanger manufacturing. Common metal materials include:

• Stainless steel: Strong corrosion resistance, high temperature resistance, high strength, and is the most widely used material.

• Carbon steel: High strength, relatively low cost, but poor corrosion resistance, suitable for non-corrosive media.

• Copper and copper alloys: Good thermal conductivity and corrosion resistance, suitable for low temperature and low pressure environments, but high cost.

• Aluminum and aluminum alloys: Lightweight, good thermal conductivity, also suitable for low-temperature conditions, not suitable for corrosive media.

• Titanium and titanium alloys: Extremely high corrosion resistance and temperature resistance, suitable for extreme corrosion, high temperature, and high pressure environments, but expensive.

• Nickel and its alloys: Suitable for use in high-temperature, high-pressure, and corrosive environments.

4.2 Non-metal material heat exchangers: Non-metal material heat exchangers are mainly used in the processing of corrosive media. Although their thermal conductivity is low and the heat transfer efficiency is not as good as metal materials, they have good corrosion resistance. Common non-metal materials include:

• Graphite: Good corrosion resistance and thermal stability, suitable for strong acids, alkalis, and other corrosive media.

• Glass: Corrosion-resistant, can be used in specific chemical processes, but brittle.

• Plastics: Such as polypropylene (PP), polyvinyl chloride (PVC), and fluoroplastics, these are lightweight and corrosion-resistant, suitable for certain chemical industries.

• Ceramics: High temperature and corrosion resistant, but may be limited in mechanical strength and thermal shock.

• Rubber: Good elasticity and corrosion resistance, but usually used as sealing materials or gaskets, not as main structural materials.

Each type of heat exchanger has its specific application scenarios and advantages and disadvantages. Selecting the appropriate type of heat exchanger requires considering fluid characteristics, required heat transfer efficiency, operating conditions (such as temperature, pressure), maintenance convenience, cost, and other factors. Structural differences mainly lie in the design of fluid channels, material selection, sealing methods, etc., to meet the heat transfer requirements under different operating conditions.