The tubular heat exchanger is also called a shell-and-tube heat exchanger/shell-and-tube heat exchanger, and its English name is a tubular heat exchanger.
Tube heat exchanger structure
The shell-and-tube heat exchanger is composed of a casing, a heat transfer tube bundle, a tube sheet, a baffle (baffle) and a pipe box, and has a relatively simple structure and high heat exchange efficiency. The casing is mostly cylindrical, and a tube bundle is installed inside, and both ends of the bundle are fixed on the tube sheet. The flow of the material medium between the bundles of shells creates a heat and cold exchange. The two types of hot and cold fluids for heat exchange, one flowing in the tube, called the tube-flow fluid, and the other flowing outside the tube, called the shell-side fluid. In order to increase the heat transfer coefficient of the fluid outside the tube, a number of baffles are typically installed in the housing. A multi-plate baffle increases the thermal coefficient of the fluid process, and the baffle increases the shell-side fluid velocity, forcing the fluid to pass laterally through the tube bundle multiple times over a specified path, enhancing fluid turbulence. The heat exchange tubes can be arranged on the tube sheets in an equilateral triangle or square. The equilateral triangles are arranged in a compact manner, the fluid outside the tube is highly turbulent, and the heat transfer coefficient is large; the square arrangement is convenient for cleaning outside the tube, and is suitable for fluids that are easy to scale.
Tube-type heat transfer analysis
We all know that any heat transfer can only be done by heat conduction, convection heat transfer, radiation conduction, and the heat transfer mode of shell-and-tube heat exchangers is usually directly understood to be convective heat transfer.
(1) Heat conduction is because the molecules in the higher temperature part of the object collide with adjacent molecules due to thermal vibration to generate thermal energy, and the heat energy is transmitted to the lower temperature part of the heat transfer mode, and the particles in the object do not have relative displacement.
(2) Convective heat transfer is the exchange of heat with a surface of a fluid as it flows through a solid surface, causing a relative displacement of the particles in the heat exchange fluid.
(3) Radiation conduction is a way of transmitting thermal energy by electromagnetic waves, which is continuously spread out.
The three heat transfer methods that we are familiar with rarely seldom exist alone, and tend to be accompanied by each other at the same time.
Shell-tube heat exchanger tube-side shell-side operation mechanism
The shell-and-tube heat exchanger fluid is referred to as one tube pass per pass through the tube bundle; the tube-and-tube heat exchanger fluid is referred to as a shell side per pass through the housing. In order to increase the fluid velocity in the pipe, partitions may be provided in the pipe boxes at both ends, and all the pipes are divided into several groups. This way the fluid passes through only a portion of the tube at a time and thus travels back and forth multiple times in the tube bundle, which is referred to as multi-tube. Similarly, in order to increase the flow rate outside the tube, a longitudinal baffle can also be installed in the housing to force the fluid to pass through the housing space multiple times, which is called a multi-shell process. Multi-tube and multi-shell can be used together. Since the temperature of the fluid inside and outside the tube is different, the temperature of the shell and the bundle of the heat exchanger is also different. If the two temperatures differ greatly, a large thermal stress will be generated in the heat exchanger, causing the tube to bend, break, or pull off the tubesheet. Therefore, when the temperature difference between the tube bundle and the casing exceeds 50 °C, appropriate compensation measures should be taken to eliminate or reduce the thermal stress.
Tube-and-tube heat exchanger through medium wall heat exchange
A partition wall heat exchanger is commonly used in chemical production. It uses a metal wall to separate fluids of two different temperatures, and a higher temperature fluid transfers heat to the wall by convective heat transfer. Through the heat conduction in the partition wall, the heat is transferred to the lower temperature fluid by convection, the higher temperature fluid is cooled, and the lower temperature fluid is heated, thereby achieving the purpose of the two fluid heat exchange process. The tubular heat exchanger is a partition wall heat exchanger that is closed on the wall surface of the tube bundle in the casing as a heat transfer surface. The heat exchanger has a simple structure and reliable operation, can be manufactured by using various structural materials (mainly metal materials), can be used under high temperature and high pressure, and is a widely used type.
Therefore, in summary, the working principle of the tube-and-tube tube side and the principle of the tube-and-tube heat exchanger are summarized by the structure, thermal analysis, operation mechanism and the heat transfer of the medium. The shell heat exchanger is generally understood.