Industrial heat exchangers. Learn the different types of heat exchangers used and how they work along with worked examples.
Industrial Heat Exchangers Explained, Learn about the different types of heat exchangers used and how they work with examples.
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Almost all industrial facilities depend on the transfer of thermal energy to generate electricity, control systems and work environments, and even manufacture products. So how do engineers control this? That is what we are going to cover in this article, which is kindly sponsored by Super Radiator Coils, one of the leaders in the production of heat exchangers for the commercial, industrial and even nuclear markets. All engineering design, performance, testing, and manufacturing is done in-house at one of its three divisions in Chaska, Minnesota, Richmond, Virginia, and Phoenix, Arizona. When it has to be perfect, it has to be great.
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A heat exchanger is simply a device used to transfer heat energy between two fluids without mixing. The fluids can be liquids or gases or even a mixture of one or the other.
Take this oil, for example. We need to raise its temperature, but we don't want to apply a flame directly to the storage unit. Instead, we're going to boil water and run it through a simple heat exchanger. The oil is also normally recycled through the heat exchanger where it will safely absorb the heat from the water. Thermal energy is transferred from the hot water through the metal wall and into the oil.
Water and oil never meet or mix. They are still completely apart. There must be a temperature difference for heat to be transferred and heat always goes from hot to cold. We could also cool the oil by pumping cold water through the heat exchanger. The cold water will now absorb the heat energy from the oil.
We see heat exchangers being used everywhere in air conditioning units, engine cooling radiators in cars, and even in the back of refrigerators. However, industrial heat exchangers are a bit different because they often work in extreme environments such as nuclear power plants, oil refineries, food processing plants, and factories, all of which involve working at high pressure and temperature. Therefore, these units are built more solidly and with stronger materials. Work environments are usually corrosive, so they are chemically treated to solve them. These heat exchangers or handle fluids such as water, steam, air, refrigerants, oil, chemical products, gases, food, etc.
There are five main types of industrial heat exchangers, although there are many variations of each design. Let's first look at a thin tube heat exchanger, which is probably the most common design usage.
thin tube heat exchanger
A typical thin tube heat exchanger looks like this. We see that there is an entrance and an exit. Both of us are located on the same side. These connections are usually flanged, but can be threaded or welded depending on the application and the pressures of the working fluid. Between the inlet and the outlet there is a tube that will contain and direct one of the working fluids, for example, hot water. The tubes will be covered with many thin sheets of metal called fines. The thin ones increase the surface area of the tube wall, allowing more heat to be transferred to the other fluid.
For example, ambient air will pass out of this tube between the boxes. The two fluids will never mix. Heat passes from the hot water through the tube wall and into the air. The heat from the water moves through the pipe wall and into the fins. The fins increase the surface area and allow for more interaction with the Airstream, which improves heat transfer.
In some designs, the fluid will simply flow along the length of the tube. Other designs will pass fluid through multiple tubes at the same time. These will be connected to both an inlet and outlet header to facilitate distribution through the tubes. For example, these are used in a gas turbine power plant to cool intake air, which will be drawn into the turbine and burned.
This allows the turbine to perform optimally in hot and humid conditions. A chiller pumps cold water into the heat exchanger, which is then circulated through the tubes. Warm ambient air passes out of these tubes. Thermal energy is transferred from hot air to cold water. The air will come out cooler and enter the turbine.
The water comes out hotter and returns to the cooler, where the unwanted heat will be expelled into the atmosphere.
Shell and tube heat exchangers
Shell and tube heat exchangers will look like this. With this design, we normally find the inlet and outlet of a fluid at the end of the heat exchanger, called the header. We then have another inlet and outlet for fluid two in the main body, known as the shell. Inside the unit we have the tubes. These are folded and wrapped to begin and end at the tube sheet, which sits between the shell and head.
Usually the tubes will also pass through baffles, which are sheets of metal. We'll see how it works in a moment. The manifold, together with the tubes, can be removed for cleaning, repair and maintenance. Inside the headstock is a sheet of metal called a divider or bulkhead. This separates the ends of the tubes, allowing fluid to flow in and out of the heat exchanger tubes.
The fluid will flow through the manifold to and around the tubes and then back to the manifold. Fluid two will enter the shell and surround the outside of the tubes. The baffles will partially block the flow, forcing the fluid to rotate several times. This creates a turbulent flow and ensures that the fluid two mixes with itself, providing maximum heat transfer. For example, we can find this in a pharmaceutical factory with a boiler that supplies steam in the casing that surrounds the tubes. A chemical is then pumped through the tubes, and the chemical absorbs the heat from the steam through the tube wall.
Thus, this product will leave the heat exchanger much hotter. During this time, the vapor will begin to condense into a liquid and return to the boiler to capture more heat and repeat the cycle. Also, they are used in refrigeration applications like this industrial chiller. We have water flowing through the tubes and hot coolant in the hull. The water will absorb the heat from the refrigerant to transport it to the cooling tower, where it will be released into the atmosphere.
The water comes back cooler to recover more of the unwanted heat energy from the chiller. We have already explained in detail how coolers work, check out these articles HERE.
double tube
Double tube or tube-in-tube heat exchangers will look like this.
This is similar to the shell and tube heat exchanger in that we basically have a tube that goes back and forth between an inlet and an outlet multiple times. This is surrounded by a shell that has another entrance and another exit. A metal frame will hold the unit in place. Usually all of these will be made of stainless steel. One fluid will flow through the tube and another will flow through the cover.
The two fluids are separated by the vessel wall and transfer heat energy through this tube wall. Different configurations result in different temperature and heat transfer profiles. In this design, the curve at each end is not used for heat transfer and heat can be wasted here. However, manufacturing this heat exchanger is cheaper and obviously easier. Other designs like this hairpin heat exchanger, often found in oil refineries, will encapsulate the elbow to fully utilize the surface area for heat transfer.
This version typically uses multiple tubes to maximize surface area for increased heat transfer. Although this also increases resistance, it is a fairly simple and very common heat exchanger design, especially in food processing and pharmaceutical production. For example, we might have a dairy product flowing through the tube, then we have hot water or maybe even steam flowing in the opposite direction through the cover, which will heat the product to a certain temperature before it mixes with other products. ingredients. . then bottled.
industrial heat exchanger
Industrial plate heat exchangers look like this. They consist of a thick metal cover on the front and rear of the unit, which is usually made of mild steel. There are two inputs and two outputs, which are normally flanged connections. In most designs we find the four ports located on the faceplate, as this allows the heat exchanger to be easily expanded or reduced to accommodate a future change in operation. Most heat exchangers do not have this capability.
Between the end covers we find a series of plates that are thin sheets of metal with a pattern stamped on them. Usually these will be made of stainless steel. These patterns will help direct the fluids and create a highly turbulent flow, which increases heat transfer. Between each of these plates is a joint called a gasket. This is usually made of rubber. These gaskets separate the plates, creating a thin channel between them, through which fluid can flow.
On each board, the gasket will block two of the four ports, meaning only one fluid can flow in and out. The next plate will allow the second fluid to pass through. This alternates throughout the heat exchanger and keeps the two fluids completely separate. Only thermal energy will pass through the sheets. The entire unit is held together with long bolts, which compress the joints to form a very tight seal.
These heat exchangers are very common for heating and cooling. For example, an incineration plant burns household waste to produce heat. This creates steam, which drives a turbine and generates electricity. The residual thermal energy then goes through a plate heat exchanger to heat a district heating network and other buildings will then be connected to this heat network also through a plate heat exchanger to meet their own heating needs. . This will be in lieu of using your own individual boiler.
spiral heat exchanger
Spiral heat exchangers look like this. We have a flanged inlet on the front side with the outlet located at the top. Then we have an inlet for another fluid also at the top, with the outlet located at the rear. Behind the end plates we find two sheets of metal on the inside, which wrap around the inside to form a channel through which the fluids will now flow. The channel completely separates the two fluids.
The first fluid is seen entering the heat exchanger and filling the chamber, then flowing around the channel at the outlet. Meanwhile, on the other side, the second fluid enters from the top, circulates through the channel and enters the chamber, from where it exits. The two fluids enter and leave at different temperatures. This type of heat exchanger is not used as often, however, because the design has only one channel for fluid to flow through, the velocity remains high, making it more difficult to clog. While plate and even tube heat exchangers divide the flow into several paths.
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