Heat exchanger is a device used to transfer heat between fluids at different temperatures.
There are several common forms as follows:
Shell – and – tube heat exchanger
- Structural features
- It mainly consists of components such as the shell, tube bundle, tube sheet, and head. The tube bundle is installed inside the shell, and both ends of the tube bundle are fixed on the tube sheet. One fluid flows inside the tubes, and the other fluid flows outside the tubes within the shell, and heat is exchanged through the tube wall.
- For example, in common chemical production, the shell is generally cylindrical, and the material can be carbon steel, stainless steel, etc., depending on the operating environment and medium. The tube bundle usually consists of many parallel tubes, and the tubes can be plain tubes or tubes with heat – transfer – enhancing structures such as fins.
- Working principle
- Heat is transferred from the fluid with a higher temperature to the fluid with a lower temperature through the tube wall. When the hot fluid flows inside the tubes, its heat is conducted to the cold fluid on the shell side through the tube wall; conversely, if the cold fluid is inside the tubes, the heat – exchange process is similar.
- For example, in the crude oil pre – heating process in an oil refinery, the high – temperature heated crude oil flows in the tube side, while the cold crude oil that needs to be pre – heated flows in the shell side. Heat is transferred through the tube wall to increase the temperature of the cold crude oil.
- Application fields
- It is widely used in many industrial fields such as chemical engineering, petroleum, power, and food. In chemical production, it is used for heating or cooling various reaction materials; in petroleum refining, it is used for pre – heating crude oil, cooling bottom products of fractionating towers, etc.; in the power industry, it is used for steam condensation and water heating.
Plate heat exchanger
- Structural features
- It mainly consists of a set of metal plates with corrugated shapes stacked together. Sealing gaskets are used between the plates to form fluid channels. There are holes at the four corners of the plates for distributing and collecting fluids.
- For example, the material of the plates can be stainless steel, titanium alloy, etc., and the corrugated shapes can be herringbone, horizontal straight corrugations, etc. These corrugations can not only increase the heat – transfer area but also enhance the turbulence of the fluid, improving the heat – transfer efficiency.
- Working principle
- Two fluids flow in adjacent plates respectively, and heat is transferred through the plates. Since the plates are very thin and have good thermal conductivity, heat can be transferred quickly between the two fluids.
- For example, in a heating, ventilation, and air – conditioning (HVAC) system, hot water and cold water flow on both sides of the plates of the plate heat exchanger to achieve heat exchange for adjusting the indoor temperature.
- Application fields
- It is often used in industries with high hygiene requirements and the need for efficient heat exchange, such as the food and beverage industry (e.g., sterilization and cooling of milk and juice), HVAC systems, and the pharmaceutical industry (e.g., heating and cooling of liquid medicines).
Double – pipe heat exchanger
- Structural features
- It is composed of two tubes of different diameters nested together. An annular passage is formed between the inner tube and the outer tube, and the two fluids flow in the inner tube and the annular passage respectively.
- For example, the inner and outer tubes can be concentric. The inner tube generally transports the fluid with a higher temperature or that requires special treatment, and the outer tube protects and isolates it, and at the same time serves as the passage for the other fluid.
- Working principle
- Heat is transferred between the two fluids through the wall of the inner tube. Although the contact area between the inner and outer tubes is relatively small, the flow velocity of the fluid in the double – pipe can be relatively high, which helps to increase the heat – transfer coefficient.
- For example, in some small – scale chemical experimental devices or special working conditions with high temperature and high pressure, the double – pipe heat exchanger can adjust the flow rate and temperature of the fluids in the inner and outer tubes to achieve heat exchange.
- Application fields
- It is often used for heat exchange of fluids with high temperature, high pressure, and small flow rates, or in occasions where the two fluids need to be strictly separated. For example, in some fine – chemical processes for temperature control of reaction materials, and in small – scale refrigeration devices as evaporators or condensers.
Finned – tube heat exchanger
- Structural features
- Fins are installed on the outer surface (or inner surface) of the heat – exchange tube. The fins can be in various shapes such as circular and rectangular. The material is usually the same as or matched with that of the heat – exchange tube and is closely connected to the heat – exchange tube.
- For example, in an air – liquid heat exchanger, it is common to install aluminum fins on the outer surface of the tube bundle to increase the heat – transfer area on the air side because the heat – transfer coefficient of air is relatively low.
- Working principle
- The heat – transfer process is enhanced by increasing the contact area with the fluid through the fins. Heat is conducted between the fins and the heat – exchange tube, and then transferred between the fluids inside and outside the heat – exchange tube.
- For example, in the condenser and evaporator of an air – conditioner, when the refrigerant flows inside the tube, there are fins outside the tube. Air is blown through the fins by a fan, and heat is efficiently transferred between the refrigerant and the air.
- Application fields
- It is mainly applied to heat exchange between gases and liquids, such as in air – conditioners, refrigeration equipment, and automobile radiators. It effectively solves the problem of low heat – transfer coefficient on the gas side and improves the heat – transfer efficiency of the entire heat exchanger.