Rotary Dehumidifier Research Articles

Experimental evaluation of a hydrogel composite desiccant wheel for dehumidification with high water uptake and low regeneration temperature

Rotary dehumidification, a key method for continuous solid adsorption dehumidification, is extensively utilised in various industrial and practical applications. The performance of the adsorbent within the desiccant wheel is a major determinant of its energy efficiency in practical applications. While studies on Metal Organic Frameworks (MOFs) and polymer desiccant wheels exist, the majority of rotary dehumidification systems continue to employ traditional adsorbents like silica gel and zeolite, which are plagued by low dehumidification capacity and high energy consumption issues. Super hygroscopic hydrogel, enhanced with a hygroscopic agent, has gained prominence in air treatment because of its outstanding hygroscopicity and low regeneration temperature. With the goal of integrating advanced materials into practical engineering applications and mitigating the heat and mass transfer loss and adsorption/desorption performance degradation due to volume expansion and viscous agglomeration post-water uptake in large-scale super hygroscopic hydrogel applications, this study successfully developed a hydrogel wheel, measuring 350 mm in diameter and 200 mm in thickness, using a honeycomb-shaped glass fibre paper substrate. Experimental findings demonstrate that the hydrogel desiccant wheel outperforms both the MOF and commercial low-temperature silica gel wheels under all tested environmental conditions. This advantage is particularly noticeable at 15 °C and 30 % Relative Humidity (RH), where the moisture content differential (Δd) in the hydrogel system is 2.96 g/kg, 1.89 times greater than the MOF system’s 1.56 g/kg and 5.19 times higher than the silica gel’s 0.57 g/kg. Furthermore, the controlled variable method was used to assess the impact of each operational parameter on the hydrogel wheel’s performance in both low and high moisture conditions, offering design insights for engineering applications.

Review on dehumidification technology in low and extremely low humidity industrial environments

Many industrial environments have low-humidity requirements. However, most research focuses on dehumidification systems in civil buildings, while research on industrial low humidity environments is extremely limited. This paper aims to summarize the research of dehumidification systems in low-humidity industrial environments, and provide some suggestions for the selection and improvement of dehumidification systems. Firstly, the environmental control requirements of industrial plants are reviewed and categorized into low humidity and extremely low humidity based on a relative humidity of 45 %. Then, the performance and applicability of condensation dehumidification systems, desiccant wheel (rotary dehumidifier) dehumidification systems and liquid desiccant dehumidification systems in typical industrial environments are summarized. Several preliminary system selection and configuration methods are presented. It is shown that the traditional condensation system is only suitable for low humidity plants. The desiccant wheel-based system is more capable of deep dehumidification, with a humidity ratio of less than 4 g/kg of supply air, while the liquid desiccant-based system can achieve high air volume operation of 10000 m3/h. Furthermore, their ranking under different scenarios is still outstanding issues. Evaluation indicators that weigh factors such as initial investment, operating costs, and control effectiveness need to be urgently proposed. Long term on-site testing is strongly recommended.

Experimental analysis of a CO2 closed heat pump drying system combined with rotary dehumidification for drying banana slices drying

A CO2 closed heat pump drying system combined with rotary dehumidification (HPRD) was investigated using both experimental and theoretical approaches. The advantages of HPRD over traditional CO2 closed heat pump drying systems (THPSs) for drying banana slices were analyzed. After drying, the drying kinetics and quality of banana slices were investigated. The results demonstrated that HPRD reduced the banana slice drying time during low-temperature processing while retaining more color and vitamin C content than THPS. In particular, HPRD increased the drying rate of banana slices dried at low temperatures by up to 41 % compared to the rate obtained by THPS. In addition, it increased the vitamin C content by an average of 12 % and reduced the total color difference by an average of 16 %. And the specific moisture extraction rate of HPRD increases by 26 % compared to THPS. The highest-quality banana slices, which were 3 mm thick and dried by HPRD at 43 °C, maintained a high drying rate and high drying quality. The optimal model of Henderson & Pabis predicted the drying behavior within the experimental range. The results indicated that the drying rate and quality of banana slices dried at low temperatures using HPRD were superior to those dried using THPS.

Development of rotary dehumidifier with silica-gel-based composite desiccant

The desiccant dehumidification system's key component, the desiccant wheel, can perform effectively using composite desiccant materials. Evaluation of the desiccant wheel's performance using composite desiccant material is the primary goal of this study. Authors have compared the performance of two desiccant wheels; one is packed with traditional Silica-gel, and the other is a composite of Silica-gel and calcium chloride in a ratio of 3:2 by weight. A rotary wheel is developed with rectangular channels parallel to the wheel's axis. The novelty of this research lies in the improved design of the desiccant wheel. Unlike other techniques involving pressure losses and ineffective space utilization, this design offers better space utilization and fewer pressure losses. In addition, wheel fabrication is less costly and easily reusable with other desiccants. Three performance indicators were evaluated through experimentation: dehumidification capability, moisture removal capacity, and dehumidification coefficient of performance. Results show that the Parallel channel desiccant wheel achieves 25% higher dehumidification capability and 55% greater moisture removal capacity. The specific humidity of the air is reduced by 35% using the composite desiccant wheel. Comparing the composite desiccant to traditional Silica-gel, its dehumidification coefficient of performance is 40% higher.

Investigation on the control strategy of new spray cooling system based on PV/T and heat recovery in sow houses: As a case study in Nanchang, China

The uncertain cooling effect and additional huge primary energy consumption caused by humidity regulation are currently the main problems of traditional air-conditioning systems in sow houses. In order to address the above problems, a new spray cooling system is proposed based on PV/T and heat recovery in sow houses in this paper. Compared with traditional spray cooling systems, the cooling efficiency of new system can be improved and its energy consumption can be reduced due to solar dehumidification and heat recovery. Meanwhile, the mathematical models are established for its key equipment and their reliability is verified according to literature data. The results show that the maximum error is less than 7.2% for the models. The main operating parameters affecting the system characteristics are determined through simulation. The results show that with the changes in the set inlet temperature of second heat exchanger (IHET), the set subcooled temperature (SCT) and the set superheated temperature (SHT) of sensible heat exchanger, the total energy consumption and gain of new system are changed by 2%–11.9%, while they are changed by 54.5%–86% with the changes in the set inlet relative humidity of rotary dehumidifier (IRH) and the set inlet temperature of spray device (ISDT). In other words, the total energy consumption and gain of new system are slightly affected by IHET, SCT and SHT, but significantly affected by IRH and ISDT. The annual control strategy is further proposed for the new system. In cooling season, supply air of sow house will be dehumidified, heat exchanged with exhaust air and cooled, and the optimal setting ranges of operating parameters are IRH = 70%, SCT = 18 °C, SHT = 26 °C and ISDT = 22–24 °C. In heating season, it will be heat exchanged with exhaust air and heated, and the optimal setting ranges of operating parameters are SCT = 19 or 20 °C, SHT = 26–28 °C and IHET = 22–24 °C. The above research will provide guidance for the improvement of traditional spray cooling systems and the operating control of new system.

Performance evaluation of a rotary dehumidifier with molecular sieve desiccant using coupled regeneration mode: Experimental investigation

The increasing demand for energy-efficient and environmentally friendly air conditioning systems has led to the development of innovative technologies such as desiccant cooling systems. This study presents a comprehensive experimental analysis of the dehumidification and thermal performance of a rotary dehumidifier with molecular sieve desiccant designed to effectively remove moisture from the air by utilizing coupled regeneration mode (complete waste heat liberated out of condenser and electric rod heat). Various experiments were conducted to investigate different performance parameters including moisture removed from air by adsorption, moisture added to air by regeneration, dehumidification effectiveness, regeneration effectiveness, moisture removal capacity (MRC), regeneration rate (RR) at different process air inlet temperatures ranging (28–34 °C) and at different regeneration air inlet temperatures ranging (55–62 °C). These experiments were conducted at same air velocity for both adsorption and regeneration segments of rotary solid desiccant wheel using molecular sieve. The results showed that the performance of the desiccant wheel was affected by inlet temperature and humidity ratio for adsorption and regeneration segments. The findings emphasize the system's ability to provide efficient dehumidification and cooling while simultaneously promoting sustainable energy practices. Moreover, the waste heat recovery system significantly contributes to the overall efficiency improvement of the rotary dehumidifier with molecular sieve desiccant, making it an environmentally friendly alternative to conventional air conditioning technologies.

Enhanced Water Sorption Performance of Polyacrylamide & Glass Fiber Paper Composites: Investigation and Comparison of Application in Desiccant Wheels.

The water sorption and desorption properties of solid adsorbent materials are crucial in rotary dehumidification systems. Metal organic frameworks (MOFs) and hydrogels are mostly at the laboratory stage due to factors like the synthesis process and yield. In this study, we utilized an eco-friendly and large-scale synthesis method to prepare polyacrylamide (PAM) hydrogels (yielding approximately 500 mL from a single polymerization). Subsequently, PAM was then coated onto glass fiber paper (GFP), which serves as a commonly employed substrate in desiccant wheels. By incorporating the hygroscopic salt LiCl and optimizing the content of each component, the water sorption performance of the composite was notably improved. The water sorption and desorption performances, as well as cycling stability, were evaluated and compared with composites containing aluminum fumarate, LiCl, and GFP (AlFum-LiCl&GFP). The results revealed that PAM-LiCl&GFP outperformed AlFum-LiCl&GFP in terms of sorption capacity throughout various relative humidity (RH) levels. It achieved a water uptake of 1.06 g·g-1 at 25 °C and 30% RH, corresponding to a water sorption rate coefficient K of 15.32 × 10-4 s-1. Furthermore, the lower desorption temperature (60 °C) resulting in a desorption ratio of 82.6%, along with the excellent cycling stability and effective performance as a desiccant wheel module, provide evidence for the potential application of PAM-LiCl&GFP in desiccant wheels.

Investigation of angular aspects of a novel four-sector rotary dehumidifier configuration for HVAC applications

In buildings and industries, different humidity and temperature ranges may be required to fulfill the requirement. Desiccant-based air conditioning is more widely used to control the latent load using solar or waste heat efficiently. This work divides a rotary solid desiccant wheel into four sections: two process sections and two regeneration sections. Air from one process section (P1) is used in a cooling application with the aid of a cooling unit, while air from the other process section (P2) is used for warm and dry air applications. Furthermore, the input conditions and positioning of the regeneration sections (R1 and R2) are such that there is less carryover heat to the P1 section and more carryover heat to the P2 section, which is advantageous for both applications. The major objective of the present work is to investigate the optimal angular divisions of these four sections using a two-dimensional mathematical model. The developed mathematical model results are reported in good agreement with the experimental results of the literature. The optimal rotational speed of the wheel is computed as 15 revolutions per hour, and the optimal regeneration angles for R2 and R1 of the desiccant wheels are 100–110° and 115–125°, respectively.

Performance evaluation of a ventilated roof desiccant bed by direct use of solar energy for zero-energy buildings

Indoor dehumidification is usually achieved by mechanical cooling resulting in significant consumption of high-grade energy resources such as electricity. Conventional rotary dehumidification systems also require the use of high-grade energy to heat the desiccant and regenerate it. Utilization of renewable energy for indoor dehumidification is highly of concern. Ventilated roof desiccant bed system is a novel dehumidification method which can regenerate itself automatically with low-grade energy usage by taking advantage of solar energy and natural ventilation directly. Using renewable energy as an alternative, it can reduce the building energy consumption, which is beneficial to achieve nearly zero energy building (nZEB) target. This study establishes the heat and moisture transfer model of the ventilated roof desiccant bed while the moisture transfer model is validated by using the reference data. The flow-field characteristics in the airflow channels are numerically analyzed, and the regeneration process of the desiccant bed in a typical day is also simulated. Results show that both the temperature and air velocity in the channel are increasing from the inlet to the outlet. The air velocity increment can reach 0.5 m/s, and the temperature can rise about 6 °C under the same boundaries. On a typical day, the regeneration process of the ventilated roof desiccant bed lasts for approximately 3 h, and 80 g of water is desorped per unit. It means that about 18 units are sufficient to remove the moisture produced in 8 h by a man. The research results can provide data reference for the design of the system, and thus facilitates the realization of engineering application.

Experimental study and performance analysis on a closed-cycle rotary dehumidification air conditioning system in deep underground spaces

High temperature and high humidity are challenges threatening human health in deep underground spaces. A rotary dehumidifying air conditioning system is an appealing way to solve this problem with free cooling and free heating from different depths of groundwater. A closed-cycle rotary dehumidification air conditioning system in deep underground spaces is proposed. The process and regeneration channels in this proposed system are merged into an optimal channel by recovering heat and harvesting water from the regenerated air. The effects of working conditions, such as the flow configuration of the chilled water, the chilled water supply temperature, the ambient air humidity and the regeneration temperature, on the energy and exergy performance are experimentally investigated. The recommended the flow configuration of the chilled water is 1:5:4. Under typical operating conditions (32 °C, 14 g kg −1 ), the moisture removal of the system driven by 80 °C hot air, reaches 4.9 kW, the thermodynamic coefficient is 1.1, and the exergy efficiency approaches 50.05%. This closed-cycle system with heat and water recovery improves the energy and exergy performance, which is an effective technology option for being applied in deep underground spaces.

Mathematical investigation of two-stage dehumidification from single rotary dehumidifier with and without precooling

A one-dimension mathematical model has been developed to investigate the performance of two-stage dehumidification using a single rotary dehumidifier of four sectors. To obtain two-stage dehumidification, the outlet stream of process 1 has been supplied into process 2 and a precooler is also introduced to enhance the performance. The performance of two-stage dehumidification using four sectors with and without precooling has been compared with the single-stage dehumidification using two-sector. The results of this study indicate that the total moisture removal of two-stage-dehumidifier using four sectors with precooling is significantly higher than single-stage-dehumidifier using two sectors, but only a little higher than the Two-stage dehumidifier using four sectors without precooling. The introduction of a precooler not only decreases the exit temperature but also increases the total moisture removal. Hence, this study recommends that a two-stage dehumidifier using four sectors can be used for better performance in place of a single-stage dehumidifier using a two-sector for the same size or space of the wheel in a variety of applications.

Experimental Study and Performance Analysis on a Closed-Cycle Rotary Dehumidification Air Conditioning System in Deep Underground Spaces

Experimental Study and Performance Analysis on a Closed-Cycle Rotary Dehumidification Air Conditioning System in Deep Underground Spaces

Review on nanoporous inorganic desiccant materials in the context of application in rotary dehumidifiers

Desiccants play a major role in dehumidifiers operated using desiccant wheels. Performance improvement of desiccant wheels is mostly depending on the desiccants. Good desiccant materials should have high adsorption capacity and low regeneration temperature. Researchers in the past have made several attempts to review desiccant materials that possess good adsorption capacities and low regeneration temperature but not many have reviewed the class of nanoporous inorganic desiccant materials. This class of desiccants covers three novel types – Aluminosilicate zeolites, Aluminophosphate-based molecular sieves, and Aerogels. Detail review of nanoporous inorganic desiccants is presented in this paper in the context of the applicability of desiccants in the dehumidifiers operated using desiccant wheels. Authors have attempted to cover a work of researchers who have synthesized and utilized this novel class of desiccants for dehumidification. It is important to note that nanoporous inorganic desiccants have high adsorption capacity than conventional desiccants such as Silica-gel, activated carbon, zeolites, etc., and also, it possesses regeneration temperatures in the range of 50 to 90 °C which can be easy to achieve using low-grade energy or waste heat.

Design of Solar Powered Desiccant based Air Handling Unit

Using an air handling unit (AHU) is a suitable method to meet the ventilation requirements in a conditioned space. This paper proposes two novel design configurations of AHUs, which ensure that the excess load on the AHU cooling coil is minimized using air to air heat recovery units, a desiccant based rotary dehumidifier, and an evaporative cooler. The proposed design is also capable of harvesting surplus water in the process. The impact assessment of the proposed designs is illustrated taking the example of a typical high-humidity design case. Simplified mathematical models were used to analyze the power-saving and moisture harvesting potential of the two configurations. Calculations show that both the configurations reduce the excess load on the cooling coil by a significant amount, while also co-producing surplus water for domestic use.

Retracted] Microcomputer Control System of Bridge Dehumidification Based on Energy Consumption Optimization and Wireless Communication

At present, with the development of wireless communication and microcomputer control system, the design and construction level of long‐span bridges in China are also improving. How to improve the durability of bridge structure has become a major scientific and technological problem in bridge design and construction. This paper studies a microcomputer control system of bridge dehumidification based on energy consumption optimization and wireless communication. It compares three kinds of dehumidification and anticorrosion methods of bridge engineering, namely, freezing dehumidification system, rotary dehumidification system, and hybrid dehumidification system. In the hardware design of microcomputer control system of dehumidification system, ATmega128 bit main control chip and aluminum designer are used to draw the power circuit. Then, the MCU program of the air dehumidifier is written, and the power of the air dehumidifier is controlled by the PWM signal generated by the timer 0 of the MCU. The air dehumidifier is divided into three tap positions corresponding to three duty cycles, and the power of the air dehumidifier is changed according to the input tap position.

An overview on use of desiccant dehumidifiers in modern air-conditioning

The solid desiccant based dehumidifier used in conjunction with the conventional HVAC combines the dehumidification of solid desiccant system and with the cooling capacity of the conventional air conditioning system. This hybrid cooling system provides thermal comfort to the occupants of the conditioned space. The hybrid systems main appeal lies in the fact that, it consumes much lesser high grade electrical energy as compared to the dedicated standalone traditional air conditioning systems. The electrical energy usage is possible still lower by use of primary energy sources for to supply the thermal energy needed for the desiccant regeneration. For this purpose freely available renewable solar energy or industrial waste heat can also be used for the regeneration heat source. Sometimes it is also possible to provide condenser waste heat for the part of desiccant reactivation heat supply may increase the overall performance of the system. It was also found that this cooling system with use of air to air waste heat recovery wheel performed better than without it in terms of dehumidification as well as cooling performance. The present study report important literature survey on the dehumidification potentials of desiccant integrated hybrid cooling system operating in hot and humid climates. Keywords: Hybrid air-conditioning; Rotary desiccant dehumidifier; Heat recovery wheel; Regeneration heat; Renewable solar energy; Waste heat

Simple preparation of high concentration Nd3+-modified NaY zeolites with lower desorption activation energy of water

High concentration Nd3+-modified zeolite NaY with 22.6 wt% Nd element contained has been successfully prepared by a simple re-doping method via 4-fold ion-exchange and subsequent calcination treatments. This re-doping method not only provides a way to incorporate as high contend Nd cations within zeolite, but also proves the ion migration theory from experimental prospective. The obtained Nd-NaY zeolites are characterized by X-ray powder diffraction (XRD), Inductive coupled plasma (ICP), Scanning electron microscopy (SEM), etc, illustrating the Nd3+ cations can migrate into the sodalite cages from supercages, which leads to the lattice distortion of zeolite structure. With the addition of more Nd3+ ions, the average pore of the Nd-NaY zeolites has increased slowly while the specific surface area decreases. We found the values of reduce desorption activation energy (Ed) of water decrease gradually with the introduction of Nd3+ cations when it used as adsorptive materials. When the Nd3+ content of zeolite reaches 22.6 wt %, the value of Ed of water decreases to 154.7 kJ/mol. This research provides highly application value to reduce water molecules desorption activity energy as potential adsorptive materials in rotary dehumidification wheel.

In Situ Synthesis and Performance of Aluminum Fumarate Metal–Organic Framework Monolithic Adsorbent for Water Adsorption

The monolithic adsorbent is a key part of an adsorptive rotary dehumidification system. It is usually prepared by dip-coating the adsorbent on glass fiber paper. In this study, a new in situ strategy for synthesis of an aluminum fumarate (A520) metal–organic framework monolithic adsorbent on glass fiber paper is introduced. The influences of the mole ratio of fumaric acid to H2O, the reaction temperature and time on the crystal phase, the pore structure, and the adsorption performance of the monolithic adsorbent are systematically discussed. The morphology of the adsorbent was characterized by scanning electronic microscopy, and the adsorption and desorption performances were evaluated by dynamic vapor sorption and differential thermogravimetric analysis. The results showed that under the conditions of a mole ratio of fumaric acid to H2O of 0.02, reaction temperature of 50 °C, and reaction time of 60 min, the obtained A520 monolith exhibited the highest BET surface area (740.15 m2·g–1) and high adsorption capacity (0.3906 g·g–1). The monolithic adsorbent carries about 76% A520 powder with the advantages of a facile fabrication process, high adsorption capacity, rapid adsorption rate, and low desorption temperature, providing guidance for the fabrication of a highly efficient desiccant dehumidification wheel.

Comparative analysis of different design of rotary dehumidifier

AbstractA one‐dimensional mathematical model has been developed to do the comparative analysis of four design of the desiccant wheel. The mathematical model has been validated with experimental results and shows good agreements with experimental results. In this study, a two‐sector desiccant wheel is modified into a three‐sector wheel by introducing a purge section in the desiccant wheel. Similarly, a four‐sector desiccant wheel is reformed into a six‐sector wheel by installing two purge section in the desiccant wheel and comparative study of these designs have been carried for given ranges of operating conditions. The effect of purge conditions has been also investigated and found that in all operating conditions six‐sector design is a better choice for optimum MRC and ∆T.

Simulation environment design for the investigation of damping and dewing mechanisms in the 12kV high-voltage switchgear

The phenomenon of dampness and dewing inside the switchgear can improve the occurrence of serious equipment faults. Based on it, this paper, starting from the occurrence mechanism of dampness and dewing of the switchgear, summarizes the main techniques that can prevent and control them, and the merits and demerits of them are analysed. After that, based on the mechanism investigation of damping and dewing of 12kV switchgear, a simulation environment is designed in order to investigate the mechanism of damping and dewing the 12kV switchgear. Firstly, the entire simulation environment factors are given. Then, the prototype of this switchgear is designed, including base configuration and sensor installation configuration. In addition, the simulation environment of the distribution room, the switchgear with load operating conditions, several commonly used anti-dampness and anti-dewing methods of 12kV switchgear, and the rotary dehumidifier are designed. Lastly, prospects are given. This paper can provide some references for studying of damp-proofing and anti-dewing of 12kV switchgears.