Comprehensive analysis of various factors affecting the performance of rotary dehumidifiers

1 Preface

With the further prominent global energy and environmental issues, the superiority of dehumidification and cooling technology has begun to be recognized and gradually developed. Rotary dehumidifiers are dehumidification and cooling air conditioning technologies

A comprehensive understanding of the performance of key equipment during surgery is the foundation for selecting and configuring dehumidification, cooling, and air conditioning systems correctly. The factors that affect the performance of a rotary dehumidifier are mainly considered from two aspects: the parameters of the rotary body and the air parameters [1-3]. The optimization of the parameters of the rotary body can be completed by the equipment manufacturer, providing corresponding data and charts to describe the full performance of its product, making it easy for users to choose; The air parameters are determined by the system design engineer and are specifically applied in practical engineering.

 

    2 The influence of 2 wheel body parameters

The parameters of the wheel body in a rotary dehumidifier refer to the mass fraction of the hygroscopic agent, the thickness of the hygroscopic agent, the specific surface area of the hygroscopic agent, the particle size of the hygroscopic agent, the temperature of the hygroscopic agent, and the rotation of the wheel

Speed, sector angle of regeneration zone, etc. Some wheel body parameters are determined by the properties of the hygroscopic agent, such as the smaller the diameter of the hygroscopic agent particles, the larger the gas-solid contact area, and the reduced hygroscopicity

The distance of internal diffusion of the agent shortens the time of the regeneration stage; However, the smaller the particles, the smaller the porosity between the particles, which increases the airflow penetration resistance. Some wheel body parameters are determined by dividing

The shape of the wet wheel is determined, such as the placement of the hygroscopic agent, which can affect the contact area.

 

Some wheel body parameters are determined by the airflow during the dehumidification and regeneration processes, such as the temperature of the hygroscopic agent. The higher the temperature of the hygroscopic agent during the air treatment process, the more favorable it is to increase the hygroscopic agent

The pressure of surface water vapor accelerates the vaporization of moisture in the hygroscopic agent, and can reduce the viscosity of the solution inside the hygroscopic agent, which is conducive to the outward diffusion of moisture. However, during the regeneration process, the hygroscopic agent

The internal and external temperatures are not consistent. Generally, the surface temperature is higher than the internal temperature. Due to the opposite driving direction of the internal and external temperature and humidity differences, the overall result is a reduction in internal diffusion

The driving force is unfavorable for desorption regeneration.

 

 2.1 Effect of Moisture Absorbent Mass Fraction

The dehumidification wheel is composed of a non hygroscopic support material and a hygroscopic agent, and the percentage of hygroscopic agent in the total mass is called the hygroscopic agent mass fraction f. Research has shown that [3], in the same

Under the mass of, the f value increases, the mass of the hygroscopic agent increases, the air humidity at the dehumidifier outlet decreases, the cooling capacity of the air conditioning system increases, and the COP value also increases. Between 0 and 0.6, hygroscopic agent quality

The quantity fraction has the greatest impact on the dehumidification performance, and its influence ability is greatly weakened after exceeding 0.6. In practical applications, the f value is generally taken as 0.8-0.85, and reducing the proportion of metal support materials also

It can effectively reduce the total heat capacity of the dehumidification rotor, which is beneficial for improving the dehumidification performance of the rotor system.

 

 2.2 Impact of Runner Speed

The rotational speed of the runner is also an important factor affecting its performance, and the requirements for rotational speed are different between a total heat exchanger and a dehumidifier. Increasing the speed can enhance the heat transfer effect, but this is due to

The time that the hygroscopic agent stays in the regeneration zone becomes shorter, and it cannot be fully regenerated, which will reduce the dehumidification effect; If the rotational speed is too low, it will cause the hygroscopic agent to stay in the dehumidification zone for too long, which will cause proximity

The adsorbent in some areas of the regeneration zone loses its ability to continue dehumidification due to saturation, which will also reduce the dehumidification effect; So, considering the performance of the dehumidifier, choosing the appropriate speed is crucial

Steps for. The determination of rotational speed can be considered from aspects such as dehumidification capacity, refrigeration capacity, and COP: the dehumidification effect is best at a speed of 5 r/h, and the COP of the system is highest at a speed of 10 r/h. Therefore

The speed of the wheel should be selected between 5~10r/h [3,6-8].

 

  2.3 Impact of sector angle in regeneration zone

The regenerative sector angle of the wheel reflects the proportion of dehumidification and regenerative hygroscopic agents. From the perspectives of dehumidification, system performance, and system cooling capacity, the influence of the regenerative sector angle jR

It's different. From the perspective of dehumidification, under certain air flow rates in the dehumidification and regeneration zones, a small fan angle in the regeneration zone will prevent the adsorbent from fully regenerating and reduce the dehumidification effect

； However, if the regeneration area is too large, it will reduce the dehumidification area, and the adsorbent will not be fully cooled, which will also reduce the dehumidification performance. Therefore, there must be an optimal ratio.  

In practical applications, the requirement for the sector angle jR of the regeneration zone should take into account the following considerations: the adsorbent regeneration is easy and can be fully regenerated; Handling air at the outlet

Humidity can also be lowered very low; The dehumidifier has a high coefficient of performance and consumes less energy per unit of cooling capacity; The refrigeration capacity of the refrigerator is relatively large. Only by meeting the above comprehensive requirements can we

To better determine the sector angle of the regeneration zone. In general, due to the high temperature of the regenerated air, the regeneration area of the runner accounts for about 1/4 of the total area of the runner, i.e. the sector angle jR of the regeneration area is 900

。 If the temperature and flow rate of the regeneration air are changed to enable effective regeneration, it is necessary to change the sector angle of the dehumidification wheel regeneration area [3,5,10].

 

 3 The influence of 3 air parameters on dehumidification performance

The air in the rotary dehumidification cooling air conditioning system includes treated air and regenerated air. The parameters of the treated air (temperature, humidity, flow rate, etc.) directly affect the dehumidification of the rotary dehumidifier

Performance, and the parameters of the regenerated air (temperature, humidity, flow rate, etc.) directly affect the regeneration performance of the dehumidifier, which in turn affects the adsorption and dehumidification performance of the dehumidifier. Therefore, these two are interrelated

Constrained [10-12]. Understanding the effects of various parameters in two types of air is beneficial for configuring appropriate systems for efficient and energy-saving operation.

 

3.1 Impact of Handling Air Parameters

For both fresh air and recirculating air conditioning systems, the processed air ultimately needs to be sent into the air conditioning area, and its parameters directly affect the effectiveness of the air conditioning and the energy consumption of the system. Therefore, people are concerned about

The impact of air parameters on air conditioning systems is highly valued and corresponding research has been carried out.  

3.1.1 Impact of processing air temperature at the inlet

The inlet temperature of the dehumidifier for handling air is influenced by the system form: the inlet temperature of the fresh air system is generally the outdoor temperature; The temperature of the return air system is the temperature of the air-conditioned room;

The hybrid system can achieve an appropriate temperature by adjusting the ratio of fresh and return air. It is necessary to understand the hygroscopic properties of hygroscopics at different temperatures.  

By analyzing the adsorption isotherm of adsorbents at different temperatures, it can be known that under the same pressure, the higher the temperature, the lower the adsorption capacity of the adsorbent; Moisture absorption of hygroscopic agents

Performance also decreases with the increase of air temperature. In practical engineering, it is hoped to improve the performance of the dehumidification wheel by reducing the temperature of the inlet air. Can be reduced through pre cooling measures

The processing air temperature at the inlet of the dehumidification wheel enables the wheel to dehumidify lower temperature air. Pre cooling will significantly improve the performance of the dehumidification and cooling air conditioning system: for the same initial air

The conditions and final treatment requirements can increase the cooling capacity by about 13% and COP by 4% after adopting pre cooling measures [3]. However, pre cooling requires the provision of a cold source and heat exchanger, which increases the initial operation of the system

Capital; After pre cooling, the temperature difference between the pre cooled air and the cooling air decreases, reducing the power of heat transfer; The impact of these adverse factors on the performance of the cooling and air conditioning system should be comprehensively considered.

 

3.1.2 Impact of air humidity treatment at the inlet

The impact of imported air humidity can be analyzed from the following aspects [7,11]:

(1) When the dry bulb temperature is the same, the higher the relative humidity of the air, the greater its moisture content. The partial pressure of water vapor in the air is closer to the partial pressure of saturated water vapor, which is similar to the surface of the hygroscopic agent

The increase in air pressure difference increases the driving force for dehumidification, which can increase the dehumidification capacity of the equipment.  

(2) When the moisture content is the same, the partial pressure of water vapor in the air is a constant value. At this time, the higher the relative humidity of the air, the lower its dry bulb temperature, and the saturated water vapor on the surface of the dehumidifying wheel

The lower the vapor pressure, the more conducive it is to the dehumidification process.  

(3) When the relative humidity is the same, the higher the moisture content of the air, the higher the dry bulb temperature of the air. The increase in the temperature of the processed air will cause the temperature of the saturated air on the surface of the dehumidification wheel to rise

High, resulting in an increase in the partial pressure of saturated water vapor, which is unfavorable for air dehumidification; However, an increase in air moisture content will correspondingly increase the partial pressure of water vapor in the air,

This is a favorable factor for dehumidification; Therefore, the impact on the dehumidification process needs to be comprehensively considered.  

It can be seen that in dehumidification and cooling air conditioning systems, using the moisture content of the air as the standard for measuring air humidity is relatively accurate, and the moisture content directly corresponds to the dew point temperature of the air. Therefore

The dew point temperature of the air is suitable as a control for air humidity.

 

3.1.3 Impact of Handling Air Flow Rate

The lower the air flow rate, the longer the contact time between the air and the hygroscopic agent, and the more sufficient the heat and mass exchange between the two, but the amount of processed air per unit area is smaller. Increase air volume

The flow rate will increase the convective heat transfer coefficient and mass transfer coefficient, which is a favorable factor for convective mass transfer between air and hygroscopic agents; But the increase in wind speed also shortens the contact time between the two

It may cause the processed air to exit the wheel before being effectively dehumidified, which is detrimental to dehumidification and may result in the air not reaching the predetermined humidity. Therefore, the appropriate air flow rate is also

The important parameters of this type of air conditioning system are generally set at approximately 0.2 seconds for the passage time of the processed air in the dehumidification wheel with a reasonable design, and the total number of heat transfer units (NTU) in the wheel is approximately

10[10]。 The impact of processing air flow rate on practical engineering applications is mainly reflected in the determination of processing air flow rate: after the specification of the dehumidification wheel is determined, the processing air flow rate should not be

Exceeding the rated flow rate of the runner too much.

 

3.2 Impact of Regenerated Air Parameters

The desorption and regeneration performance of the hygroscopic agent in the dehumidification wheel is mainly reflected in two aspects: firstly, the drying state that the hygroscopic agent can ultimately reach, which depends on the equilibrium moisture content of the hygroscopic agent; Secondly

The regeneration rate to reach the final dry state, which includes the vaporization rate on the surface of the hygroscopic agent and the diffusion and transfer rate of water inside the hygroscopic agent, depends on the main of the two rates mentioned above

The impact part is mainly dominated by processes with lower rates; The equilibrium moisture content and regeneration rate are interdependent, and people focus on the influence of regeneration rate in application research.

The regeneration process of the adsorbent in the rotary dehumidifier is essentially the process of driving water out of the adsorbent and entering the regenerated air. The regeneration process of the hygroscopic agent is mainly affected by both the hygroscopic agent and the hot air

The influence of surface factors. The influence of hygroscopic agent parameters on the performance of dehumidifiers is mainly reflected in: the shape of the hygroscopic agent, the placement method of the hygroscopic agent, the temperature of the hygroscopic agent, etc; Influence of Hot Air Parameters on Dehumidifier Performance

The impact of energy is mainly reflected in temperature, moisture content, flow rate, and contact with moisture absorbents. In practical applications, it is easier to control the parameters of regenerated air, so people

Pay more attention to the impact of regenerated air on the performance of dehumidifiers: When the moisture content of the air remains constant, increasing the temperature of the air not only enhances the ability to vaporize and remove moisture, but also improves the effectiveness of moisture absorbents

Further heating up and increasing the diffusion rate of moisture between the surface and interior of the hygroscopic agent is beneficial for both the constant rate and deceleration drying stages, but each hygroscopic agent has a maximum allowable temperature value

； The lower the moisture content of the air, the stronger the ability to remove moisture from the hygroscopic agent, and the greater the driving force of the drying process, resulting in a higher drying rate; Improving the flow rate of hot air can effectively

Strengthening the drying process is beneficial for both heat and mass transfer, but with high air flow rates and short contact time with moisture absorbents, the effective utilization rate of heat energy is reduced; Good contact between air and hygroscopic agents

It is conducive to the uniform drying of the hygroscopic agent, reasonable arrangement of airflow, and obtaining a larger gas-solid contact area, which can effectively strengthen the regeneration process. The following focuses on exploring the temperature and humidity of regenerated air

The influence of parameters such as flow rate on the performance of rotary dehumidifiers.

 

3.2.1 Impact of Regenerated Air Temperature at the Inlet

The temperature of the regenerated air is an important parameter that directly affects the performance of the rotary dehumidifier. If the regeneration temperature is lower, the main process in the rotary dehumidifier is full heat exchange; With temperature

As the temperature increases, the trend of desorption and regeneration of the hygroscopic agent in the wheel gradually becomes apparent, until the entire process is controlled by the desorption and regeneration trend. People hope to fully utilize low-grade heat sources for production

Low grade energy may not have a high temperature, which limits the extent to which the regenerated air is heated, in order to desorb and regenerate energy for the runner. How does the temperature of regenerated air affect the performance of a rotary dehumidifier

When the temperature of the raw air drops to what value, the main thing that can still be ensured is the dehumidification process, which is a concern for people. So, to determine the impact of regeneration air temperature on the performance of rotary dehumidifiers,

How to determine whether the heat and mass transfer process in the runner is a total heat exchange process or a moisture desorption regeneration process, and where the regeneration temperature at the boundary point between the two is the focus of this study

One.

   

In a rotary type total heat exchanger, the main process of two streams of air is to transfer moisture from the treated air to the regenerated air, and to increase the temperature on the low-temperature side. At this time, the rotary dehumidification

The mathematical model should be changed to that of a total heat exchanger; Moreover, since the most suitable fan angle jR for the total heat exchange process is 1800, if it is still set according to the dehumidification process at this time

The sector angle jR of the regeneration zone is 900, which cannot efficiently carry out the total heat exchange process; In addition, the rotational speed of the runner used as a total heat exchanger is much faster than the required rotational speed of the dehumidification runner

[19]。 These are all issues that must be considered when studying the dehumidification process of the wheel.  

 

   

Hygroscopic agents may work at different regeneration temperatures, and the performance of dehumidifiers is a concern for people. The regeneration process of hygroscopic agents is divided into preheating period, constant rate drying, and deceleration

The influence of temperature varies in different stages such as drying. The temperature of the regenerated air is higher than the temperature of the hygroscopic agent at this time, and the hygroscopic agent is heated by the air, while the hygroscopic agent is outward

As the water evaporates, the temperature also increases. When the surface temperature of the hygroscopic agent is equal to the wet bulb temperature of the air, it reaches a stable state. For the same hygroscopic agent, if the regeneration air

An increase in temperature will cause the surface temperature of the hygroscopic agent to rise. After the surface temperature of the hygroscopic agent rises, the evaporation pressure on its surface also increases, that is, the water vapor of the air in contact with the surface of the hygroscopic agent

The increase in vapor pressure can increase the speed of regeneration and shorten the regeneration time. For non isothermal adsorption systems, the concepts of "temperature wave" and "concentration wave" can be used to analyze

Adsorption drying process. In general, temperature is faster than mass transfer, meaning that the "temperature wave" moves before the "concentration wave". The front velocity of temperature waves is independent of temperature, and in an ideal situation

The author believes that the key to determining whether the main process in the runner is total heat exchange or dehumidification desorption regeneration is to look at the dew point temperature of the processed air at the outlet of the runner dehumidifier and the air conditioning system

The dew point temperature of the air supply state point corresponding to the regeneration air temperature can serve as the boundary point between the two. If the dew point temperature of the processed air at the outlet is lower than the dew point temperature of the air supply state point of the air conditioner, turn to

The main process carried out in the wheel is the process of moisture absorption desorption regeneration; If the dew point temperature is higher than the air supply state point, it can be considered that the main process being carried out is the total heat exchange process, and this air conditioning system cannot achieve the designed humidity

Degree control requirements; Therefore, the parameter control of the rotary dehumidification and cooling air conditioning system should be based on this.

 

 

3.2.2 Impact of Regenerated Air Humidity at the Inlet

The regeneration process of the hygroscopic agent is actually the drying process of the hygroscopic agent. At this time, the power that drives the transfer of water vapor from the hygroscopic agent to the regenerated air is the partial pressure of water vapor on the surface of the hygroscopic agent and the regeneration

The difference in partial pressure of water vapor in the air. The research on the influence of the humidity of the imported regenerated air on the performance of dehumidifiers is not comprehensive, and the influence of this factor should be combined with the influence of temperature

Let's consider together, this is because the temperature of the regenerated air is higher than that of the hygroscopic agent, which transfers heat to the hygroscopic agent, causing the temperature of the hygroscopic agent to increase simultaneously. Partial pressure of water vapor in regenerated air

Mainly related to atmospheric pressure and air moisture content [4].

 

In the equation:

Pw: Partial pressure of water vapor (Pa)

B: Atmospheric pressure (Pa)

d: Air moisture content [kg (kg dry air) -1]

When the atmospheric pressure and moisture content in the air remain constant, increasing the temperature of the air does not change the partial pressure of water vapor, but the partial pressure of saturated water vapor increases, resulting in

The relative humidity of the air decreases, that is, the degree of unsaturation of the air increases, which makes the hot air used for regeneration have a stronger ability to accept water vapor; At this point, it becomes mainly regenerative air

The effect of temperature on the desorption and regeneration performance of the runner. If the temperature of the regenerated air remains unchanged, reducing the relative humidity of the air will result in a decrease in the partial pressure of water vapor in the air, which will increase the correlation with the hygroscopic agent

The difference in water vapor pressure between the air in contact with each other enhances the driving force for water transfer. At this point, the essence of reducing the relative humidity of the regenerated air is the need for dehumidification, or

Mix outdoor fresh air with circulating air to obtain a lower relative humidity (moisture content). The process of heating regenerated air is an isothermal heating process, usually before heating

Change its moisture content. Compared to the dry bulb temperature, the humidity of the regenerated air has a smaller impact on the performance of the dehumidification wheel, and the control is also more complex. But understanding the humidity of regenerated air

The impact can provide reference for the technical measures adopted by the rotary dehumidification air conditioning system in different regions and at different times.

 

3.2.3 Impact of Regeneration Air Flow Rate
The flow rate of the regeneration air directly affects the regeneration rate of the hygroscopic agent. The convective heat transfer coefficient increases with the increase of the flow rate, and the heat transfer coefficient also increases with the increase of the flow rate, so that the total
The regeneration process time has been shortened; Moreover, the flow rate of regenerated air can be adjusted to adapt to changes in the flow rate and state parameters of the processed air. In short, the increase in regeneration air flow rate strengthens
The regeneration process accelerates the regeneration speed of the runner, but at this time, without changing the sector angle of the regeneration area, the regenerated runner area may be heated, increasing the temperature of the hygroscopic agent, thereby affecting
The progress of moisture absorption process; Moreover, considering the energy consumption of the system, an increase in flow rate will lead to an increase in the demand for regenerative heat, resulting in a decrease in heat transfer efficiency on the regenerative side of the runner and a decrease in the COP of the system; place
Under rated operating conditions, careful consideration should be given to changing the air flow rate. If the regeneration air flow rate is changed, parameters such as the sector angle of the regeneration zone and the temperature of the regeneration air should be adjusted accordingly. In practical applications
It is not feasible for users to change the sector angle of the regeneration zone, so methods of adjusting the temperature of the regeneration air are often used.  

 

4. Impact of Work Environment
Rotary dehumidifiers can be applied in different regions, and the impact of environmental changes on their performance is also a concern. This mainly discusses atmospheric pressure and air cleaning process
The impact of factors such as degree. In this case, the movement speed of temperature waves within the column is constant; In practice, due to the presence of thermal resistance, the front edge continuously widens, and with different waveforms
The temperature of moves forward.

 

4.1 Impact of atmospheric pressure
The performance of dehumidifiers is affected by changes in atmospheric pressure, and the performance of dehumidifiers varies under different atmospheric pressures [6]. The analysis of the impact of atmospheric pressure on the system mainly focuses on suction
Considering the adsorption characteristics of wet agents, changes in air parameters, and performance curves of fans, the influence of pressure varies for systems with mass and volume flow rates as standards
of
When the atmospheric pressure drops from 1 atm to 0.8 atm:
(1) A system based on mass flow rate: the performance of the heat exchanger remains unchanged, the heat exchange performance of the evaporative cooler improves, the dehumidification performance of the dehumidifier decreases, and all regeneration and dehumidification agents are affected
In terms of COP and cooling capacity, both increased by 6-8%, system resistance increased by 20%, corresponding energy consumption increased by 44%, resulting in a total COP decrease of 4%.  
(2) System based on volumetric flow rate: The performance of the heat exchanger has been improved by 2-4%, the heat transfer performance of the evaporative cooler has been improved, and the dehumidification performance of the dehumidifier has decreased, which affects all regenerations
Compared to dehumidifiers, COP increased by 8%, cooling capacity decreased by 14%, and system resistance remained unchanged, resulting in a 5% increase in total COP.  
These situations indicate that when using rotary dehumidification and cooling air conditioning systems in different regions, the impact of local atmospheric pressure on system performance should be considered, and it should be clear whether to use mass flow rate as the standard or not
Based on volumetric flow rate. China has a vast territory, and the location of use of rotary dehumidifiers directly affects the performance characteristics of dehumidifiers.  

 

4.2 Impact of Air Cleanliness
The cleanliness of the air and regenerated air processed by the dehumidifier directly affects the performance of the desiccant, mainly because the adsorbent in the rotary dehumidifier not only adsorbs moisture in the air, but also empties the air
The adsorption of small particles in the gas is a characteristic of the adsorbent itself, which will lead to the deterioration of the hygroscopic agent. The deterioration of the adsorbent will directly affect the dehumidification performance of the rotary dehumidifier
According to the degree of deterioration of the hygroscopic agent, the COP and cooling capacity of the dehumidification and cooling air conditioning system will be reduced by 10% to 35% [9]. Within a certain range of degradation, the following methods can be used to eliminate its impact:
(1) Air filtration: Setting an air filter can effectively remove dust from the air entering the dehumidifier, but the setting of the air filter increases the resistance of the air system
The residual pressure of the machine needs to be increased accordingly, which increases the initial investment and operating costs. After adding air filtration equipment, it is necessary to pay attention to regular cleaning and replacement, although it may increase some costs,
However, it is necessary to extend the service life of dehumidification equipment.  
(2) Deep regeneration of hygroscopic agents: Achieving regeneration of hygroscopic agents at high temperatures can drive away dust particles, but this is not the fundamental method because if regeneration is carried out without treatment
The discharged air into the atmosphere will cause new pollution; Moreover, increasing the temperature of the regenerated air requires a higher grade of energy and a higher cost. Excessive temperatures of the regenerated air can also
It can affect the performance of the hygroscopic agent.  
(3) Adjusting operating parameters: such as accelerating the speed of the dehumidifier, the adjustment depends on the type of absorbent, the type of attenuation, and the method of regeneration.  

 

5 Conclusion
In summary, there are many factors that affect the performance of a rotary dehumidifier, but the body parameters of the dehumidifier are mostly determined by the equipment manufacturer, and their variability is not significant; work
Design personnel should mainly consider the impact of air parameters and application environment, and clarify that the dew point temperature after dehumidification is an important parameter that needs to be controlled. Only with a comprehensive understanding of wheel dehumidification
Only the performance of the machine can reasonably configure the dehumidification and cooling air conditioning system.