Plate heat exchangers are widely used in refrigeration, heat pump systems, industrial cooling, and energy recovery applications due to their high heat transfer efficiency and compact structure. However, under low-temperature operating conditions, if system control or operating conditions are improper, freezing of the process medium may cause severe mechanical damage to the plate heat exchanger, leading to internal leakage or cross-contamination between circuits.
Leakage caused by freezing is typically characterized by sudden occurrence, severe damage, and irreversibility. It represents a high-risk failure mode that requires special attention during the operation of plate heat exchangers.
Freezing in a plate heat exchanger usually occurs when one or more of the following conditions are present simultaneously:
Cooling water, softened water, or low-concentration antifreeze solutions
Actual freezing point higher than the design assumption
Flow rate too low
Local blockage
Uneven flow distribution in channels
Transient low flow velocity during start-up or shutdown
Excessive refrigerant supply
Delayed response of temperature control valves
Antifreeze protection logic not activated
Inside a plate heat exchanger, even if the overall outlet temperature has not dropped below 0°C, localized areas on the plates may still reach temperatures below the freezing point, forming so-called “cold spots.” This is the most common yet most easily overlooked trigger for freezing.
During freezing, water expands in volume by approximately 9%.
Within the narrow flow channels of a plate heat exchanger, this volumetric expansion generates extremely high localized mechanical stress.
Because the plates are relatively thin (typically 0.3–0.6 mm) and form complex flow channels through corrugated patterns, once freezing occurs:
The expansion force of ice acts directly on the plate surface
The plates undergo plastic deformation
Microcracks or permanent deformation may form in areas of stress concentration
Freezing does not usually occur uniformly, but rather:
Initiates in localized regions
Propagates along low-flow or stagnant zones
This can result in:
Local bulging or indentation of plates
Irreversible changes in inter-plate spacing
Abnormal stress on gasket sealing lines (for gasketed plate heat exchangers) or on welds/brazed joints (for welded or brazed plate heat exchangers)
Even after the ice melts, the plates cannot return to their original geometry, thereby creating latent leakage risks.
Leakage caused by freezing typically exhibits the following characteristics:
Damage limited to one or a small number of plates
Leakage points are localized rather than randomly distributed
Initial leakage may be minor
Leakage gradually worsens with continued operation
In brazed or fully welded plate heat exchangers, once the plates are damaged by ice expansion, the unit is generally not repairable and must be replaced as a whole.
Unlike general corrosion or fatigue failure, freezing represents an instantaneous mechanical damage mechanism:
It may occur during a single start-up or a short abnormal operating event
Total operating hours may be relatively low
Leakage may only become apparent after the freezing event
Therefore, the occurrence of leakage after a short operating period does not rule out freezing as the root cause.
In practical applications, freezing-related leakage is often associated with the following factors:
Actual operating medium differs from the design medium (e.g., water used instead of antifreeze)
Insufficient antifreeze concentration
Excessive cooling capacity with delayed regulation
Frequent start-stop cycles or low-load operation
Internal fouling or blockage leading to reduced local flow rates
To prevent leakage caused by freezing in plate heat exchangers, the following aspects should be carefully addressed:
Antifreeze type and concentration
Consideration of actual operating conditions, not only theoretical values
Avoid operation below the manufacturer’s specified minimum flow
Prevent local stagnation
Low-temperature interlocks
Shutdown of cooling source
Forced circulation pump operation
Outlet temperature design should include sufficient safety margin
Continuous operation close to the freezing point should be avoided
Leakage caused by freezing in plate heat exchangers is essentially a form of mechanically induced damage resulting from phase change. Its occurrence is closely related to operating conditions, control logic, and medium properties.
Once freezing occurs, even if normal operation is subsequently restored, irreversible damage may already exist within the plate structure. This damage can later develop into leakage during continued operation. Therefore, freezing should not be regarded as a negligible transient anomaly, but rather as a high-risk condition that must be actively prevented during both the design and operation stages.
This is a very relevant question. The key conclusion can be summarized in one sentence, followed by a breakdown from a design perspective: freezing is directly related to plate heat exchanger design, but not in a simplistic “good design versus bad design” sense.
Plate heat exchangers are inherently more susceptible to freezing than shell-and-tube heat exchangers due to their structural characteristics.
Certain design parameters can significantly amplify or mitigate the risk of leakage caused by freezing.
Plate heat exchanger plates are typically only 0.3–0.6 mm thick.
This thin design is intended to:
Improve heat transfer efficiency
Reduce thermal resistance
Increase turbulence
However, the trade-off is:
Reduced resistance to mechanical deformation
Stress generated by ice expansion can easily exceed the yield strength of the plate material
A single freezing event may cause permanent plastic deformation
By comparison:
Shell-and-tube heat exchangers use thicker tubes with larger diameters and therefore exhibit much higher resistance to freezing damage.
The internal flow channels of a plate heat exchanger are extremely narrow:
Typical channel gap: 2–4 mm
Corrugated patterns create numerous contact points
While this is advantageous for heat transfer, under freezing conditions it means:
Ice has no room to expand
Expansion force acts directly on the plates
Stress is highly concentrated at:
Chevron peaks
Contact points
Welded or brazed joints
This is the structural reason why freezing can directly rupture plates.
One frequently overlooked area in plate heat exchanger design is the distribution zone, which is characterized by:
Proximity to the ports
Lower flow velocity than the main heat transfer area
These zones are prone to:
Localized low temperature
Stagnant flow
Formation of cold spots
If:
The distribution area is relatively large, or
The operating flow rate is low
Freezing often initiates in these regions. This is fully consistent with cases where leakage is concentrated in adjacent channels rather than randomly distributed.
From a design standpoint:
Multiple-pass arrangements (2-pass / 4-pass):
Advantage: higher velocity and heat transfer coefficient
Risk: higher pressure drop and more complex flow distribution
Single-pass arrangements (1-pass):
Lower pressure drop
More prone to low-flow operation under low-load conditions
If:
The design is valid at rated flow conditions
Actual operation frequently occurs at low load or low flow
Then the operating point may enter a “freezing-sensitive zone,” even though the design itself is not incorrect.
The freezing margin represents a critical interface between design and operation.
In many designs:
Outlet temperature is very close to 0°C
Antifreeze concentration is selected close to the theoretical freezing point
Under actual operating conditions:
Instrumentation inaccuracies
Control delays
Load fluctuations
Local plate temperatures may easily fall below the freezing point.
If the design does not include:
Adequate freezing safety margin
Minimum flow verification
Then freezing risk is effectively embedded at the design stage.
