Industrial heating and cooling require one essential element – controlled and efficient heat exchange. Whether it is chemical, food, material processing, or even large-scale air conditioning, the right exchanger can sometimes affect the energy efficiency, equipment performance, maintenance, and other factors.
One of the common solutions in the industry is a plate heat exchanger that has a compact construction and allows delivering a high ratio of surface area per unit volume. Still, any exchanger has its advantages and disadvantages, which need to be carefully evaluated in relation to specific operating conditions. This article addresses some of the key questions about plate, shell-and-tube, air-cooled, and other types of heat exchangers.
Heat Exchanger Overview
The heat exchanger is often a critical part of any system where the temperature of a fluid needs to be controlled by transferring the excess heat to another fluid. The two fluids can be gaseous or liquid and do not necessarily need to be in physical contact.
In any fluid-flow system, heat exchangers allow recovering much of energy that would otherwise be lost. A heat exchanger can take many forms such as shell-and-tube, plate-and-frame, brazed plate, air-cooled, spiral, and others. The overall effectiveness depends on the properties and operating conditions of a fluid, including temperatures, pressure, fouling tendency, and maintenance needs. Shell-and-tube heat exchangers are widely used in high-pressure applications, requiring more compact and durable equipment. Meanwhile, plate systems have a large surface area exposed to fluids that allows effective heat exchange.
Common Factors to Consider When Selecting a Heat Exchanger
When choosing the right heat exchange equipment for a specific application engineers should start the selection process by defining the requirements rather than focusing on a specific model. Some of the most common factors to consider are:
- Fluid types and their temperatures.
- Fluids’ corrosive nature, viscosity, fouling tendency.
- Pressure and flow rates.
- Available space for installing the exchanger.
- Maintenance and cleaning requirements.
Considering these factors will ensure a good match of fluid and operational conditions. If the engineers define these criteria, the process of selecting the equipment will be faster and more efficient.
Selecting a Heat Transfer Equipment for Performance
As mentioned above, the exchanger can be matched to the application in terms of its ability to fulfill operational requirements. Thermal performance is, of course, a necessity, but not the sole criterion that determines the effectiveness of the exchanger.
For example, in a process with relatively clean liquid, the plate heat exchanger could provide an exceptionally high ratio of heat transfer surface area to volume. Meanwhile, where there are solids in suspension and the need for cleaning, these advantages would be offset by the inability to access hard-to-reach areas. Additionally, materials of construction are also significant when choosing a system.
Stainless steels can resist some acidic solutions, but the concentration and temperature of the fluid as well as the presence of chlorides and the pressure of the system must be considered as factors that may degrade the material. Furthermore, an exchanger’s geometry selected by engineers must be matched to the required pressure drop of a fluid flow. Finally, a balance must be achieved between the exchanger’s effectiveness, its compactness, pressure drop, maintenance, and service life.
When Do You Need a Custom Heat Exchanger?
Many standard exchanger configurations are optimal for most cases. However, there are situations when a customized solution is a better choice. For example, if there are special fluid properties, space limitations, and requirements related to thermal approaches or connections. The customization can be related to size and layout, materials of construction, and heat transfer characteristics of the exchanger. It is essential to create a solution that will meet the specific requirements of the client rather than just following a standard catalog design.
Besides, a properly done custom heat exchanger can often streamline the production process of a client to match their specific product. Before designing the exchanger it is critical to provide the necessary operating data, and engineers should also think about future changes in conditions. It is always a good idea to have a system in place today that will be able to increase its heat-transfer performance tomorrow if production volumes rise, for example.
Heat Transfer Equipment Comparison, Advantages, and Disadvantages
The industrial heat transfer equipment market consists of hundreds of companies that offer their products. Plate, shell-and-tube, spiral, and s are just a few types of heat exchangers that can be selected depending on various factors. The table below compares the key criteria that are used when choosing a heat exchanger type for a specific fluid application.
Type of Exchanger Advantages Disadvantages
Plate Good for clean liquids; Easy to inspect, clean, and inspect; Compact construction. Less suitable for viscous or particulate-laden fluids; Risk of deposits reducing the performance; Higher fouling reduces effectiveness by lowering the effective surface area.
Spiral Effective heat transfer; Single channel allows for large temperature differentials; Large number of applications. Challenging to inspect and clean.
Air-cooled Lower maintenance cost; No need for cooling water. Often has a higher pressure drop; Less energy efficient compared to other exchangers.
Shell-and-tube Wide range of applications; Can handle extreme pressures. Often requires additional equipment.
While plate heat exchangers can offer a combination of high thermal efficiency and a relatively compact design, shell-and-tube exchangers are often chosen when extremely high pressures are involved. Spiral ones are beneficial for highly fouling fluids because of simplicity and large temperature differences, and air-cooled exchangers are needed when cold water is unavailable.
Improving Exchanger Performance and Service Life by Maintaining It
Even the best heat exchanger in the world will perform poorly under dirty conditions. As soon as the deposits start to appear on the outside of the exchanger surface, the thermal performance decreases as the thermal resistance increases. Additionally, vibration and other issues can cause cracking and leaking, corrosion, and other problems. The critical aspect is to keep the exchanger under regular cleaning and maintenance according to the operating conditions.
Heat exchanger maintenance is highly dependent on the type and fluid being processed. The primary tasks of maintaining and cleaning heat exchangers include checking temperatures and pressures at the inlet, outlet, and interstage. These characteristics will show whether there is a decrease in the performance of the exchanger. Furthermore, regular inspection of flows and leakages is of equal importance.
In regards to cleaning, a particular exchanger must be maintained in such a way that the integrity of the material is not compromised. For example, aggressive solvents or improper mechanical cleaning can damage the plates of a plate heat exchanger, lowering its overall performance. As mentioned before, the maintenance schedule should include all aspects of heat exchanger servicing.
Making the Most Economical Choice When Selecting a Heat Exchanger
Some equipment manufacturers provide a large number of options for a given heat exchanger. At the same time, the ratio of equipment cost to operating costs and maintenance needs often becomes critical for a buyer. The most reliable way to ensure a good choice for an application is to look at all fluid properties and operating conditions and then find the equipment that has a balance of these criteria.
Conclusion
Choosing the equipment is an engineering task that depends mainly on the conditions at which it operates. A plate heat exchanger can be the most optimal choice for one application, while for others, a shell-and-tube, air-cooled, or brazed exchanger might be a better choice. Additionally, a properly designed custom heat exchanger could meet the unique requirements of a particular fluid and application. In any case, considering all factors when choosing equipment can help to get the best value.
Frequently Asked Questions
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What is a plate heat exchanger used for?
A plate heat exchanger is used to transfer heat between two fluids over a plate surface, enabling applications like heating and cooling processes.
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When do I need a custom heat exchanger?
A custom heat exchanger may be needed when there are specific requirements about its size, connections, materials, and other factors.
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How are the spiral heat exchangers different from other types?
A spiral heat exchanger is a type of heat exchanger where the flow of the fluid is in a spiral shape inside the exchanger rather than in a corrugated plate design.
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What factors should I consider when selecting a heat exchanger?
Some of the most common factors to consider when selecting a heat exchanger are fluid properties, temperatures, flow rates, pressure, fouling tendency, system space, maintenance, and other factors.
