How are heat exchangers made?
We interviewed our Engineering Director, Nic Zeoli, to learn how heat exchangers are made – starting with the design process all the way through to the final delivery of the product.
Heat exchangers are units designed to either cool or heat a primary substance. Find out more by reading: What is a heat exchanger?
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At Sterling TT, we specialise in heat exchangers for industrial applications – from power generation to chemical processing. This doesn’t necessarily mean large units (although it can!), but more specifically bespoke designs. We make just 1 or 2 units per order – rather than mass-producing heat exchanger products.
Our process of making a heat exchanger is therefore unique to each product, and we never manufacture the same product twice. Even when making the same model for the same application, industry standards will usually have changed since we made the first, and therefore, the specific product will be slightly different.
In addition, every heat exchanger serves a different specific purpose. The shape, design and manufacturing process is unique to the heat exchanger and the application for which it’s designed. Therefore, each manufacturing process is slightly different according to the requirements of that particular unit. However, they do all have some things in common…
If you’re unsure of any of the terminology in this article, use our heat exchanger glossary.
Designing the heat exchanger
The first step in making a heat exchanger is always the design, and this starts with data from the user, our client.
Each heat exchanger we make is different. Understanding these differences lies in the data that a client provides to us. This then allows us to design a bespoke heat exchanger that is fit for purpose.
The data includes everything from the specified hot and cold media and the amount of heat the heat exchanger must transfer, to space and noise constraints. We work with our clients and discuss any aspects that help us identify the best solution.
It’s also important to consider any phase-changing media, which is common in chemical plants or the food industry. The ambient conditions are essential for understanding constraints, and we need to know whether the media involved is likely to result in fouling.
All the data we collect from the user ensures we can design a heat exchanger that delivers results efficiently within the specific context the user needs it.
The thermal model
The precise design process varies according to each type of heat exchanger and each unit we’re making, but we always use a thermal model unique to Sterling TT.
This thermal model is a complex algorithm developed by our experienced engineers. We use it during the design process to calculate the parameters of the heat exchanger to transfer heat under specific conditions.
Sterling TT has been in the heat exchanger business for over 100 years, and this experience informs the unique thermal model we use. It’s why clients continue to be satisfied with our final products!
While the actual mechanics are very complex, in summary, the thermal model is developed internally using wind tunnel testing. A small mock-up of a heat exchanger is tested within the wind tunnel, measuring the amount of wind that is transferred in specific conditions.
We then use the user’s initial data to apply the best fit to the model.
Because this is a small version, we then use algorithms to scale up the model to the right size specifications so it will fit within our heat exchanger unit.
Please be aware that this is a simplified version and the thermal model in actuality involves many more steps and complexities!
There are various operating conditions that we must take into account in the design stages when making a heat exchanger.
1. Internal size
This describes the actual diameters of the internal parts, which directly affects the heat transfer coefficient, plus the physical size of the unit.
2. Mechanical aspects
A heat exchanger is a pressure vessel, meaning it contains one or more fluids at certain pressures. In the design process of making a heat exchanger, we need to verify that the thickness of the material is appropriate for the operating pressures.
2. National standards
Every country has a national code for vessel pressure. Worldwide, Asme VIII is perhaps one of the most widely accepted.
As a company, we work with all international standards including American, European, Japanese and everything in between.
Beyond national and international standards, it’s common for customers to also have their own standards. For example, units designed for the North Sea will need more checking and higher control standards, and the material needs to be of extremely high quality.
Noise is another primary consideration. Many coolers (a form of heat exchanger designed to remove heat from the primary medium), involve a fan that circulates air through the finned surface. Fans are naturally very noisy!
Noise tolerance depends on where the user will need the heat exchanger. For example, if it will be in an area where staff work, noise may need to be below a certain level, such as less than 72 dB A.
To achieve this, a variety of techniques can be incorporated when making the heat exchanger. For example, we can add a silencer in front of the propeller.
All sorts of adjustments can be made to reduce noise levels. This has to be considered in the design stage, though, so other elements can be modified to ensure efficiency isn’t lost.
For example, in one heat exchanger design, air flow might have to have a certain static pressure, but this generates too much noise. We would reduce the velocity of the fan to lower the vortex generation, and therefore the noise is reduced. If the noise is still too loud, we could then change the profile of the blade and the geometry of the impeller to achieve the optimum design.
Vibration is a factor that primarily impacts noise levels. For example, a shell and tube heat exchanger is a common type of design. In this, the tubes can vibrate. If this exceeds the allowed parameters, we can introduce elements that stiffen the position of the tubes or alter the geometry of the bundle.
5. Environmental conditions
Environmental conditions, known as ambient conditions, affect the design considerably. For example, if the heat exchanger will be used in marine conditions, the salt in the atmosphere can cause corrosion or fouling, so the materials we use in the design need to withstand this.
Alternatively, a heat exchanger might be used in an environment with a lot of dust in the atmosphere. This could affect our design; we could ensure various parts are reachable within the unit so it can be cleaned regularly.
The fluid used within the machine also impact the design. Firstly, their physical properties dictate the heat transfer coefficient – and therefore impact the geometry and type of material we need to use to ensure high efficiency. Secondly, different materials might not be compatible with the chemical composition and the fluid’s operating parameters like the velocity, which needs to be reduced to safeguard the unit’s longevity.
All these factors mean the design of each heat exchanger is extremely different and bespoke every time.
We also use various modern software to help with the design. Perhaps two of the most well-known are Aspen and HTRI. We also use our own models, and each designer has considerable training and experience.
Manufacturing the heat exchanger
Once the design is done, it goes to production. The engineers who designed the heat exchanger complete a thorough handover with the production team. This team then uses the manufacturing drawings to make the heat exchanger.
Because we make industrial heat exchangers, where each unit is unique, we don’t mass produce our products.
The actual making of the heat exchanger could include a huge number of different manufacturing processes and techniques.
To name just a few, these include:
- metal drilling
- laser cutting
- water jet cutting
- metal forming
- various forms of welding
- tube expansion
At Sterling TT, all the specialist components of the heat exchanger are made in house.
On occasions where the heat exchanger requires non-core parts, we have a long-standing relationship with manufacturing partners. They might manufacture the parts that aren’t specialist to heat exchangers, such as fabrication of the housing or making larger support frames.
As a company, our strength lies in our relationships. By maintaining strong relationships with our supply chain, we make sure that we can produce heat exchangers of a wide variety, for a range of industrial settings.
Checking for errors
While the engineers always complete a handover with the manufacturing team, a heat exchanger could have hundreds of individual parts which means there is a possibility of error.
The CAD model also doesn’t calculate how the final parts come together, which can mean certain elements can’t be reached by the person manufacturing the unit, for example.
If an element has got an error, it is costly and rarely viable to remake it and any associated parts. Therefore, the engineer continues to work on a solution that suits the products’ specifications without any cost to heat transfer efficiency.
This means that the engineers and manufacturing team have to continually work together to develop solutions as the heat exchanger is made.
At Sterling TT, new engineering graduates always start with a period on the shop floor to understand how heat exchangers are made and gain experience.
It helps to develop a real-life understanding of how designs come together. For example, a bolt that needs fastening can’t be reached by hand, which might not be able to be seen on the CAD. This process ensures our engineers understand the manufacturing element of making a heat exchanger to make the process from design to production as smooth as possible.
Once we have produced the parts, they undergo thorough testing and inspection to provide our clients with safe and reliable heat exchangers.
If they pass, we ship them to the clients alongside a user manual and all the associated certifications.
Transporting the final heat exchangers
Once the heat exchanger has been made, the parts get transported to the user.
There are various important considerations in this part of the process. For example, some heat exchangers, particularly larger models, can’t be transported in a single piece requiring multiple shipments. This means we must consider how the user will assemble the heat exchanger on site.
We communicate with the client to ensure they understand the requirements of unloading and setting up the unit. For example, a client might not have a crane on site that can handle their heat exchanger. They would need to be prepared with a lifting beam, mobile crane and associated equipment.
We discuss all this information before the unit goes out.
Making a heat exchanger: summary
The process of how a heat exchanger is made is complex, involving multiple stages and experienced professionals before arriving at the final product. It’s also unique to each bespoke heat exchanger that we manufacture.
At the centre of our work at Sterling TT is relationships. We work hard to build a lasting relationship with our clients and thus can provide the highest levels of service and quality of the final product.
Many thanks to Nic Zeoli, our Engineering Director, for his insight into how heat exchangers are made.