11/08/2021 | Industrial Wastewater | 8 MINUTE READ
A Comprehensive Overview of Heat Exchangers
Among the most important pieces of technology that are used by many different industries is a heat exchanger. A heat exchanger is designed to transfer heat from one type of media to another. The various media that heat exchangers accommodate include liquid, gas, and a combination of the two. It’s possible for the media to be separated directly by a wall to make sure that the media don’t mix together or come into contact with one another in any way.
In many cases, heat exchangers are used to enhancing how energy efficient a system is by moving heat from one area of the system that doesn’t require it to another area that would benefit from the added heat. Heat exchangers are used in a wide range of different systems, which include everything from air conditioners and refrigerators to boilers and power plants. The exact application that the heat exchanger is used for depends on the system it’s tied to.
To understand exactly how a heat exchanger works, let’s take a look at what happens when a furnace burns propane fuel or natural gas. In this situation, the byproducts created from the exhaust or combustion process will be taken through the heat exchanger. These byproducts will heat the metal while the gas is pushed towards the furnace’s exhaust outlet. While this occurs, the hot metal will directly heat the air that’s currently circulating around the heat exchanger’s exterior. The following article provides an in-depth overview of how heat exchangers work and the different types of heat exchangers that could be used in your facility.
Types of Heat Exchangers
There are three distinct types of heat exchangers that you can use, which include plate and frame heat exchangers, shell and tube heat exchangers, and scraped surface heat exchangers. Heat exchangers with a plate and frame design use corrugated parallel plates to effectively control how cold and hot fluids flow over plate surfaces.
Shell and tube exchangers work by transferring heat via fluids that go through tubes and a sizable shell vessel. These exchanges are able to handle fluids with an ample amount of particulate. As for scraped surface heat exchangers, these systems are used specifically for extremely viscous or sticky products. A scraped surface heat exchanger is particularly effective at transferring heat because of the scraping blades that ensure the product never settles on interior surfaces.
Plate and Frame Heat Exchangers
Plate and frame heat exchangers are outfitted with corrugated parallel plates that have been separated by gaskets. This design allows the exchanger to control how the hot and cold fluids flow over plate surfaces. The system has a very simplistic mechanical design that allows for a quick cleaning as well as easy capacity changes with the addition or removal of different plates.
In the event that the fluids that flow through the exchanger are somewhat viscous or contain a small number of particulates, having relatively wide gaps between the plates should help you maintain your flow requirements. Different plates will have different chevron angles to them, which allows the heat exchanger to maintain heat transfer at differing pressure drops.
Plates with wide streams have fewer contact points to them, which reduces blockages. As such, these systems have proven to be effective when used in raw juice applications. Your system may also consist of double-walled plates, which help to prevent different media from mixing together if ever one of the plates is cracked. Plate and frame heat exchangers are commonly used for products with very little viscosity, which means that there are hardly any particulates in the substance. Some of these products include milk, beer, ice cream, and beer wort.
Shell and Tube Heat Exchanger
Shell and tube heat exchangers are comprised of a series of tubes as well as a larger shell that surrounds all of the tubes. Certain fluids will pass through the tubes. At the same time, other fluids will be contained in the shell vessel. When this heat exchanger is operating properly, heat can be transferred from one fluid to another. The inner tubes are able to process viscous fluids that contain a moderate amount of particulate, which makes them more effective for viscous fluids in comparison to plate and frame exchangers.
There are many different types of shell and tube heat exchangers, which include everything from mono-tube heat exchangers to multi-tube heat exchangers. Mono-tube heat exchangers are the simplest option available to you. These systems are equipped with a single inner tube alongside an external shell. Mono-tube heat exchangers are mainly used for products that contain large particles or high-fiber ingredients.
On the other hand, multi-tube heat exchangers can perform heating, heat recovery, and cooling of products that have relatively low viscosity. It’s also possible for these heat exchangers to have a single-tubesheet or double-tubesheet design. Shell and tube heat exchangers are commonly used for products with low or medium amounts of viscosity. Purees, gels, and lotions are some of the products that these heat exchangers can accommodate.
Scraped Surface Heat Exchanger
As mentioned previously, a scraped surface heat exchanger is designed specifically for products that are considered to be sticky or highly viscous. These systems are unique because they are outfitted with scraping blades that make sure that the product never settles on interior surfaces. The product will initially enter the scraped surface heat exchanger from the bottom of the tube. Cooling or heating fluids will then travel in a standard counter-current flow.
The blades contained in this type of heat exchanger will get rid of any product on the channel wall, which means that the heat transfer will be consistent. These blades can be made from different materials depending on the exact application that the heat exchanger is being used for. No matter what material the blades are made from, they are always designed to gently handle the product, which ensures that the heat exchanger doesn’t compromise product consistency and quality.
Keep in mind that these exchangers can be mounted horizontally or vertically depending on your preference. The rotors and product will move in the same direction before the product exits from the top of the exchanger, which is done to make sure that the rotors don’t damage the product. Scraped surface heat exchangers are used for a wide range of different applications across many industries. These applications include:
Viscous products – Peanut butter, ketchup, bread dough, baby food, shampoos, and skin lotions
Particulate products – Jams, preserves, meats, pet foods, and poultry
Sticky products – Process cheese, toothpaste, gelatin, and caramel
Heat-sensitive products – Cream cheeses, egg products, and fruit purees
Phase-changing products – Sugar concentrates, tea extracts, frostings, shortening, beer, wine, lard, and fondant
Flow Configurations of Heat Exchangers
There are three separate types of flow configurations that heat exchangers can have, which include parallel flow, counterflow, and crossflow.
Parallel flow involves two fluids entering the heat exchanger from the same location, which means that they will flow in the same direction and will be parallel to one another during this process. The temperature differences between the two fluids are relatively large around the inlet area. Once the fluids reach the outlet, the two fluids will have a similar temperature.
Counterflow involves two fluids being placed in the heat exchanger at opposite ends. As such, the fluids will flow counter to one another. Even though the temperature differences between these two fluids will be lower when compared to other configurations, they will also remain constant throughout the process. The counter-flow configuration is considered to be the most efficient option that you can use with a heat exchanger.
Crossflow involves two separate fluids flowing perpendicular to one another. It’s important to understand that some heat exchangers are able to use multiple flow configurations in one system.
Implementing Heat Exchangers
If you want to properly implement heat exchangers in systems that are based on multiple processes, a network of heat flows must be implemented. In these situations, implementing heat exchangers can be difficult.Multi-process systems are necessary for oil refineries and similar facilities. When a designer is working on implementing heat exchangers in a facility, there are several different types of software that can aid them during the design stage. The most important consideration during the design stage is to properly mitigate fouling, which will require numerous technologies and bypasses. Software can also be used to manage heat exchanger fouling.
Depending on the product you’re using, it’s possible for software to predict the rate of fouling for your heat exchangers. Some types of software will measure heat exchanger performance over an extended period of time to determine if fouling has occurred at a notable level. When considering the implementation of heat exchangers, it’s important to compare the reduction in energy costs that occur when using a heat exchanger to the cleaning costs that are necessary for system maintenance. These calculations can also be made by software.
Heat exchangers have proven to be invaluable for a wide range of industrial processes. By efficiently transferring heat from one liquid to another, the system should be more economical in its operation, which can help you keep energy costs down.
Posted by Sensorex on November 8, 2021
Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.