What Factors Affect The Dehumidification Efficiency of A Desiccant Wheel Dehumidifier?

What Factors Affect The Dehumidification Efficiency of A Desiccant Wheel Dehumidifier?

Types of Desiccant Materials

The desiccant media filling the desiccant wheel (e.g., silica gel, molecular sieves, lithium chloride composite materials) exhibit significant performance differences:

Silica gel wheel: Suitable for medium-to-low temperature, high-humidity environments (5-35°C, 60% RH and above). Features rapid moisture absorption but poor high-temperature resistance (deteriorates at regeneration temperatures exceeding 140°C). Efficiency declines in high-temperature, low-humidity scenarios.

Molecular Sieve Desiccant Wheel: Suitable for high-temperature, low-humidity environments (35-50°C, ≤40% RH). Offers greater desiccation depth (can reduce humidity below 10% RH) and withstands high regeneration temperatures (stable up to 180°C), but desiccation speed is slower than silica gel.

Lithium Chloride Composite Wheel: Features large moisture absorption capacity (1.5-2 times that of silica gel), but pores can clog easily from airborne dust and oil contamination. Lithium chloride exhibits mild corrosivity, necessitating precision filtration; otherwise, efficiency degrades rapidly over extended use.

Rotary Desiccant Wheel Structural Parameters

Specific Surface Area: A larger surface area of the wheel's honeycomb-like internal channels (typically measured in “m²/m³”) allows more thorough air contact, enhancing moisture absorption efficiency (e.g., high-quality wheels can reach 2500-3000 m²/m³, while low-efficiency wheels only achieve around 1500 m²/m³).

Rotation Speed: The wheel must rotate slowly (typical speed: 8-12 revolutions per hour) to ensure thorough moisture absorption in the adsorption zone and complete desiccation in the regeneration zone. Excessively high speeds result in incomplete moisture absorption, while excessively low speeds prolong dwell time in the regeneration zone, wasting energy and reducing overall processing capacity.

Desiccant Wheel Degradation and Contamination

Long-term operation may cause efficiency decline due to:

Dust Clogging: Airborne particles (e.g., metal dust in shipyards, cotton fibers in workshops) adhere to channel surfaces, reducing active surface area;

Oil Contamination: In environments with oil mist (e.g., machining shops), oil coats the desiccant material, neutralizing its moisture-absorbing capacity;

Material Degradation: Frequent high-temperature regeneration (exceeding rated temperatures) or prolonged exposure to corrosive gases causes desiccant material to disintegrate and pores to collapse, shortening service life from 5-8 years to 2-3 years.

Airflow Volume and Velocity

Airflow Matching: Set appropriate airflow volume based on the dehumidification space's volume and initial humidity (e.g., a 100㎡ workshop requires 500-800m³/h). Insufficient airflow results in inadequate air residence time within the desiccant wheel, leading to incomplete moisture absorption. Excessive airflow increases velocity (exceeding 2.5 m/s), shortening contact time with desiccant material and potentially dislodging loosely adsorbed moisture from the wheel surface, thereby reducing efficiency.

Air Resistance Loss: Excessively long or sharply curved intake ducts reduce actual airflow entering the wheel below rated capacity. Compensate by increasing fan power; otherwise, efficiency may drop by 10%-20%.

Regeneration Air Temperature and Volume

After absorbing moisture, the wheel requires “high-temperature regeneration air” to remove water vapor (the “desorption process”). Regeneration conditions directly determine the wheel's “recovery capacity”:

Regeneration Temperature: Must reach the desorption threshold of the desiccant material (silica gel: 120-140°C; molecular sieve: 150-180°C). If the temperature is too low (e.g., only 100°C for silica gel regeneration), moisture cannot be completely desorbed, and the wheel's moisture absorption capacity will “saturate and decay” after repeated use. If the temperature is too high (e.g., exceeding 160°C for silica gel), it will accelerate material aging and actually shorten its lifespan.

Regeneration Airflow: Typically 15%-25% of the treated airflow. Insufficient airflow prevents high-temperature air from fully contacting the wheel, leaving localized moisture residue. Excessive airflow dilutes the regeneration zone temperature, reducing desorption efficiency while increasing energy consumption.

“Zone Sealing” Between Treated and Regeneration Air

The wheel comprises a “moisture-absorption zone” (where process air flows and moisture is adsorbed) and a “regeneration zone” (where high-temperature air flows and moisture is carried away). These zones require strict sealing (separated by sealing strips and partitions). Poor sealing (e.g., aged sealing strips, excessive installation gaps) can lead to:

Moist air from the absorption zone infiltrating the regeneration zone, diluting regeneration effectiveness;

High-temperature regeneration air infiltrating the moisture absorption zone, heating the treated air (causing increased outlet air temperature; if used in temperature-controlled applications, additional cooling is required, indirectly reducing dehumidification efficiency).

Environmental Humidity (Moisture Content)

This is the most direct influencing factor: the higher the environmental moisture content (e.g., during the rainy season at 90% RH and 25°C, with moisture content around 22g/kg of dry air), the stronger the “driving force” for desiccant wheel moisture absorption (larger vapor concentration difference), resulting in greater moisture adsorption per unit time and higher dehumidification efficiency. Conversely, at low ambient humidity (e.g., winter conditions at 30% RH and 10°C, with a moisture content of approximately 2.5g/kg dry air), the moisture absorption driving force weakens, significantly reducing efficiency (at this point, reliance on the molecular sieve wheel's “deep moisture absorption” characteristic becomes necessary).

Ambient Temperature

Temperature affects efficiency in a “two-way” manner:

As temperature rises (e.g., 35°C vs. 25°C): Air can hold more moisture. If humidity remains constant, the moisture content increases, allowing the wheel to adsorb more water vapor and improving efficiency.

Excessively low temperatures (e.g., below 5°C): Although air moisture content is low, the adsorption capacity of moisture-absorbing materials decreases (e.g., silica gel's moisture capacity at 0°C is only 60% of its capacity at 25°C). Additionally, moisture in the air may condense into water on the wheel surface, clogging channels and reducing efficiency (requiring a preheating device).

Air Contaminant Levels

If the air contains significant dust, oil, or corrosive gases (e.g., metal dust in shipyards, acid/alkali mists in chemical plants):

Dust clogs the wheel's honeycomb channels, reducing contact area;

Oil residues form a “hydrophobic film” that isolates the desiccant material from moisture;

Corrosive gases degrade the desiccant material structure (e.g., lithium chloride wheels decompose when exposed to acidic gases), causing rapid efficiency decline. Therefore, primary + medium-efficiency filters (or even high-efficiency filters) must be installed in such scenarios. Otherwise, dehumidification efficiency will drop by over 30% within 3-6 months.

Equipment Installation and Maintenance

Installation Inclination: If the wheel is not installed horizontally (with an inclination exceeding 3°), it will cause uneven force distribution during rotation. This leads to increased friction between certain areas and the sealing strip, resulting in reduced sealing performance.

Lack of Maintenance: Failure to regularly clean filters, inspect regeneration heating elements (e.g., reduced heating efficiency due to scale buildup), or calibrate wheel speed causes “hidden degradation.” While appearing to operate normally, actual dehumidification efficiency declines by 20%-50%.

Load Matching

The dehumidifier's “rated dehumidification capacity” (e.g., 10kg/h@25℃, 80% RH) must match actual dehumidification requirements. If the unit is “underpowered for the task” (e.g., a 10kg/h unit used in a workshop requiring 20kg/h), it cannot reduce environmental humidity to the target value. This appears as “low efficiency” but is actually a selection error. Conversely, if the unit is “overpowered,” it wastes energy and causes excessive regeneration cycles, accelerating wheel aging.