The Workhorse of Ammonia Refrigeration Part 1 of 2: Shell and Tube Heat Exchangers | Blog No. 110
- Jordan Barga
- 2 days ago
- 4 min read
If you’ve spent any time around industrial ammonia refrigeration, you’ve seen a shell-and-tube heat exchanger. It is one of the most common ways to transfer heat between two fluids without letting them mix, and it appears throughout ammonia systems.
Shell-and-tube heat exchangers show up all over industrial ammonia refrigeration because they can serve many duties in one durable package. You may see them as water-cooled condensers, where hot, high-pressure ammonia vapor is condensed to liquid while cooling water runs through the tubes. Even though evaporative condensers are common in newer plants, shell-and-tube condensers still appear where a cooling tower and circulating water system are used. They are also widely used as evaporators, often called “chillers,” to cool water, glycol, or brine. In these units, ammonia boils on one side while the secondary fluid flows on the other.
They are also commonly used as oil coolers on rotary screw compressors. In some systems, cooling water removes heat from the oil; in others, liquid ammonia does the cooling through a thermosyphon loop, where the ammonia absorbs heat and circulates by natural flow. On the high-pressure side, they may act as liquid subcoolers or heat recovery units. In large two-stage systems, they can also provide interstage cooling, helping cool discharge gas or further cool liquid between compression stages.
What it is:
A shell-and-tube exchanger consists of a bundle of tubes enclosed within a larger cylindrical shell. One fluid flows through the tubes, while the other flows around the outside of the tubes inside the shell. Heat moves through the tube walls from the warmer fluid to the cooler one.
Shell-and-tube exchangers are designed so fluids can pass through the equipment more than once without the need for multiple footprints. On the tube side, internal dividers send the fluid through numerous tubes to increase the surface area in which heat transfer occurs. These tubes can form a U-shape so that the fluid passes the length of the shell multiple times before exiting the exchanger. This back-and-forth movement allows for the fluids to have more interaction, which allows more heat to be transferred in the same amount of space. On the shell side, baffles steer the flow across the tube bundle instead of straight through the shell, helping to distribute heat more evenly. In ammonia refrigeration systems, ammonia typically flows on the shell side, while water or glycol runs through the tubes.
As a rule of thumb, heat exchangers work best when the flow stays steady and the surfaces stay clean. Even a thin layer of oil, scale, or debris can reduce heat transfer and increase pressure drop, so filtration and routine cleaning matter. Small changes in temperatures or flow rates can shift capacity more than people expect, so it is important to trend outlet temperatures and pressure drop instead of guessing. Finally, treat isolation valves, vents, drains, and relief protection as part of the exchanger, not accessories, as they make safe maintenance possible.
Why the ammonia industry likes it
This design is popular in ammonia systems because it can handle high pressures, phase change (boiling or condensing), and large temperature differences. When ammonia condenses, it releases significant energy; when it boils, it absorbs significant energy. Shell-and-tube exchangers are well-suited for both duties.
Shell-and-tube exchangers are known for being:
Rugged: Thick walls and strong construction support long-term industrial service.
Flexible: Designs can accommodate liquid-to-liquid, vapor-to-liquid, condensing, and boiling applications.
Serviceable: Many designs allow the tube bundles to be removed for cleaning, inspection, or repair.
This serviceability is critical in refrigeration plants, where downtime is costly and reliability is essential.
The Process Safety (PSM) connection
In a PSM-covered facility, heat exchangers are not just equipment; they are pressure vessels that can leak, foul, or fail if neglected. A few practical risk points to keep in mind:
Tube leaks = cross-contamination. If water or glycol is in service with ammonia, a tube failure can contaminate the secondary loop and create unexpected hazards for operators downstream.
Fouling reduces capacity and changes operating conditions. As tubes foul, pressures and temperatures can drift. That can push compressors harder, reduce cooling capacity, and create nuisance trips, or worse, hide developing problems.
Vibration and corrosion. Flow-induced vibration can wear tubes at supports, while corrosion can thin walls over time.
From a PSM perspective, shell-and-tube heat exchangers fall squarely under Mechanical Integrity. This includes routine inspection, trending approach temperatures and pressure drops, scheduled cleaning, and thorough repair documentation. When operating conditions change, such as new loads, different water quality, or material upgrades, the Management of Change (MOC) process should treat heat exchanger impacts as critical, not secondary.
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For a comprehensive training on Anhydrous Ammonia, click here for our PSM Academy Ammonia Awareness training, to learn and earn a certificate of completion. Training is in English and Spanish. Use code SDS20 for a 20% discount on the entire purchase. For more information, email us at academy@machapsm.com.For a comprehensive training on Anhydrous Ammonia, click here for our PSM Academy Ammonia Awareness training, to learn and earn a certificate of completion. Training is in English and Spanish. Use code SDS20 for a 20% discount on the entire purchase. For more information, email us at academy@machapsm.com.
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