The function of a heat exchanger can be to exchange heat. Exchange a certain amount of heat between certain fluids within a certain period of time; It can also be used for waste heat utilization with the purpose of recovering heat; It can also be for the purpose of ensuring safety, that is, to prevent temperature rise from causing pressure rise and causing damage to certain equipment. The function of heat exchangers varies, and their design, selection, and operating conditions are also different. The basic requirement for a heat exchanger is to meet the heat transfer requirements, that is, to achieve the required heat transfer and heat medium temperature; The heat loss of the heat exchanger should be minimal, and the heat transfer efficiency should be high; The flow resistance should be small; To have sufficient mechanical strength, strong corrosion and damage resistance, and minimal maintenance workload; The structure should be reasonable and the work should be safe and reliable, that is, the thermal stress generated between components due to temperature rise will not cause the heat exchanger to rupture; To facilitate manufacturing, installation, and maintenance; Economically reasonable, the total investment for the entire life cycle of the equipment should be minimal (including initial investment costs for equipment and ancillary devices, as well as operation, maintenance, and management costs); The heat exchanger of the domestic hot water system should be easy to remove scale, and the above requirements often constrain each other, making it difficult to fully meet them at the same time. Therefore, the selection and design of heat exchangers should be focused on specific situations to meet the main requirements of engineering heat exchangers. Due to the low failure rate of heat exchangers and the seasonal load of heating, there is sufficient maintenance time. Suspending the heating of the domestic hot water system will not have a significant impact, so it is not necessary to install heat exchangers. The selection of the number of heat exchangers and the determination of their individual capacity should adapt to the staged growth of heat load and consider the reliability of heating. Heat exchangers can be divided into water water heat exchangers and steam water heat exchangers according to different heat exchange media; According to different working principles, it can be divided into partition type, direct contact type, heat storage type, and heat pipe type heat exchangers.

Surface heat exchanger

Also known as a wall mounted heat exchanger. It refers to a heat exchanger that indirectly heats through a heat transfer surface. Due to the separation of hot and cold fluids by solid walls during heat transfer, surface heat exchangers have lower heat transfer efficiency compared to direct contact heat exchangers. They are commonly used in situations where the two fluids do not mix. There are mainly forms such as tubular, volumetric, plate, spiral plate, etc.

tubular heat exchanger

It refers to a surface heat exchanger that utilizes thin-walled metal tubes for wall heat transfer. When calculating, the influence of fouling on the heat transfer surface should be considered, and the fouling correction factor should be taken into account when calculating the heat transfer coefficient.

Shell and tube heat exchanger

It refers to a tubular heat exchanger composed of a cylindrical shell and a tube bundle with tube plates assembled inside the shell. Simple structure, low cost, wide flow cross-section, easy to clean scale; But with low heat transfer coefficient and large footprint. There are several types of shell and tube heat exchangers, including fixed tube plate steam water heat exchangers, shell and tube steam water heat exchangers with expansion joints, floating head steam water heat exchangers, U-shaped shell and tube steam water heat exchangers, corrugated shell and tube steam water heat exchangers, and segmented water water heat exchangers.

Sleeve type heat exchanger

It refers to a tubular heat exchanger composed of components such as tube sleeves made from pipes.

plate heat exchanger

It refers to a surface heat exchanger in which fluids of different temperatures flow and exchange heat between multiple layers of tightly arranged thin-walled metal plates. It mainly consists of heat transfer plates, fixed cover plates, movable cover plates, positioning bolts, and clamping bolts, and the plates are sealed with gaskets. Due to the special structure of the plate surface, strong turbulence can occur in the fluid at low flow rates, thereby enhancing the heat transfer process. Plate heat exchangers have a compact structure, are easy to disassemble and clean, have a high heat transfer coefficient, are adaptable, and save materials. However, the narrow flow cross-section between the plates can easily form scale and deposits, causing blockages. When the heat resistance of the sealing gasket is poor, it is prone to leakage. This type of heat exchanger is commonly used in heating systems. When calculating plate heat exchangers, the influence of fouling on the heat transfer surface should be considered, and the fouling correction factor should be taken into account when calculating the heat transfer coefficient.

Spiral plate heat exchanger

It refers to a surface heat exchanger composed of two parallel metal plates rolled into two spiral channels, with two fluids flowing and exchanging heat on both sides of the spiral plates. Spiral plate heat exchangers have a compact structure and generally have a higher heat transfer coefficient than shell and tube heat exchangers. Compared with plate heat exchangers, they have a wider flow cross-section and are less prone to blockage. Its main disadvantage is that it cannot be disassembled and cleaned.

Hybrid heat exchanger

Also known as direct contact heat exchanger. It refers to the heat exchange and mass exchange between two fluids at different temperatures in direct contact. Its heat transfer efficiency is relatively high, mainly including water spray and nozzle heat exchangers.

Water immersed heat exchanger

It refers to a hybrid heat exchanger in which water flows down in a dispersed state through the fine pores on several stages of the drip tray and directly contacts with steam. It is mainly composed of a shell and an ice shower tray. The heated water is injected from the upper part and divided into fine streams through the sieve holes on the water shower tray. The steam is injected from the mU or lower part of the shell and condenses and releases heat when it comes into contact with the heated water. The heated hot water is sent out from the lower part of the heat exchanger. Compared with surface heat exchangers, water spray heat exchangers have higher heat transfer efficiency, smaller heat transfer area, and compact equipment under the same design heat load conditions; However, pure condensed water cannot be recycled, so the application will increase the capacity of the heat source water treatment equipment and consider the issue of utilizing excess condensed water in the system. This type of heat exchanger not only has the function of heat exchange, but also serves as a water storage tank (which can replace the expansion tank of the heating system) and a pressure regulating function (which can use the steam pressure inside the shell to regulate the system).

Nozzle type heat exchanger

The heat exchanger refers to the mixture of heated water flowing through the nozzle and directly contacting the steam sprayed in from many oblique small holes on the nozzle wall. It mainly consists of a shell, nozzle, drain plug, mesh cover, and packing. When heated water passes through a Laval shaped nozzle, steam is sprayed into the water through small holes on the nozzle wall from the outside of the nozzle, and the two quickly mix in high-speed flow, heating the water. The nozzle type heat exchanger has a small volume, simple manufacturing, easy installation, sensitive adjustment, large heating temperature difference, and stable operation. However, the heat transfer is not large, and it is generally only used for hot water supply and small hot water heating systems. When used in heating systems, it is often set on the outlet side of the circulating water pump.

Steam water heat exchanger

It refers to a heat exchanger that uses steam as the heating medium and whose medium is being heated.

Water water heat exchanger

It refers to a heat exchanger where both the heating medium and the heated medium are water.

Volumetric heat exchanger

It refers to a heat exchanger with a large cross-sectional area and low water flow velocity for the heated water, which not only exchanges heat but also has the function of storing hot water. It mainly consists of a shell and a U-shaped bent pipe bundle connected in parallel, through which steam or hot water flows. The size of the shell is determined by the water storage capacity. When calculating, the influence of fouling on the heat transfer surface should be considered, and the heat transfer coefficient should be calculated by considering the thermal resistance of scale. The main feature is that it also serves as a water storage tank. Easy to remove scale, but with a much lower heat transfer coefficient than shell and tube heat exchangers, mainly used in hot water supply systems.

Quick Heat Exchanger

It refers to a heat exchanger where both the heating medium and the heated medium flow at a high velocity to achieve strong heat exchange. High thermal efficiency, compact structure, small footprint, but high head loss, unable to store hot water for regulating use. If the water usage is uneven or the pressure of the heat medium is unstable, the water temperature is difficult to adjust; When the water quality is poor, the heat exchanger is severely scaled and difficult to clean. Commonly used in hot water supply systems.

Heat pipe heat exchanger

It refers to a heat exchanger that utilizes the principle of heat pipes to achieve heat exchange. A heat exchange tube bundle consisting of several heat pipes is placed inside the shell through a central partition. A central heat pipe heat exchanger refers to a heat exchanger that uses the principle of heat pipes to achieve heat exchange. A heat exchange tube bundle composed of several heat pipes is placed inside the shell through a middle partition. The middle partition forms hot and cold fluid channels with the heating section, cooling section, and corresponding inner cavity of the shell. The hot and cold fluids flow continuously across the heat tube bundle in the channel to achieve heat transfer. Mostly used in waste heat recovery projects.