Abnormal Evaporation Phenomena Associated with Excessive or Insufficient Refrigerant in Low-Temperature Heat Pump Evaporators

I. Insufficient Refrigerant Charge (Refrigerant Deficiency)

Heating capacity on the heating side decreases significantly.

Insufficient refrigerant circulation results in inadequate heat dissipation from the compressor. The heating temperature of the heat exchange plates or tube bundles fails to rise, leading to a low saturated evaporation temperature of the feed solution and persistently insufficient steam production. Under the same feed conditions, concentration efficiency plummets.

Vacuum in the evaporation chamber fluctuates easily, and the boiling point shifts

Insufficient heating leads to unstable steam production and fluctuating vapor pressure. The vacuum controller frequently cycles on and off to regulate, resulting in unstable operating conditions.

Excessively low compressor low-pressure and extremely high suction superheat

The refrigerant completely vaporizes prematurely in the evaporator heat exchange section. Without liquid refrigerant returning to cool the compressor cylinder, the compressor discharge temperature skyrockets, causing frequent high-temperature protection shutdowns.

Insufficient heat exchange in the condenser, unbalanced condensation load

A small amount of refrigerant cannot adequately remove the heat from the secondary vapor, resulting in poor condensation efficiency. The system accumulates a large amount of non-condensable vapor, causing the vacuum to continuously deteriorate and increasing mist entrainment.

Accelerated compressor wear and increased energy consumption

The lack of liquid refrigerant returning to the oil sump for cooling leads to poor lubrication and reduced compression efficiency; to maintain the set heating temperature, the compressor runs at high frequency continuously, resulting in a significant increase in electricity consumption per unit of water produced.

Failures are more pronounced under low-temperature winter conditions

At low ambient temperatures, the refrigerant’s saturated pressure is even lower. After a refrigerant shortage, heating capacity drops dramatically, and the system may even fail to reach the required evaporation temperature for extended periods.

II. Refrigerant Overcharge

Liquid accumulation in the condenser, with heat exchange area occupied by liquid refrigerant

Excess liquid refrigerant accumulates on the condenser side, reducing the effective heat exchange area. Secondary vapor cannot fully condense, causing system pressure to build up, vacuum levels to continuously drop, and the boiling point of the material to rise.

Compressor Suction of Liquid, Risk of Liquid Slugging

Excess refrigerant cannot fully vaporize in time; liquid refrigerant flows directly back into the compressor, causing liquid slugging that damages valves and bearings. Over time, this leads to irreversible compressor damage.

Excessive High-Pressure Levels, Frequent High-Pressure Shutdowns

Large refrigerant volume increases system saturated pressure, easily triggering high-pressure alarms during operation. This results in intermittent equipment start-stops and erratic evaporation.

Uncontrolled heating temperature, localized overheating and dry walls

Under high pressure, the wall temperature of the heat exchange plates fluctuates wildly. Even slight irregularities in the spray liquid film can cause dry walls, leading to rapid coking and salt scale buildup.

Simultaneous increase in load on circulation pumps and vacuum pumps

Poor condensation, significant fluctuations in steam production, and erratic vapor flow cause the vacuum pump to operate under continuous high load, resulting in a substantial increase in overall system power consumption.

Throttle valve icing/blockage and failure of flow regulation

Excess refrigerant causes abnormal pressure and temperature in the throttling section, leading to frost buildup and blockage of the throttling device, loss of control over refrigerant circulation flow, and severe fluctuations in evaporation capacity.