Solution Dehumidification Research Articles

Multi-objective optimization of solar-driven hollow fiber membrane dehumidification system based on MOPSO

The solar-driven hollow fiber membrane dehumidification (SHFMD) system is a renewable, energy-saving, and highly effective dehumidification system. It provides an effective solution to the problem of air-entrained liquid droplets during the traditional solution dehumidification process. The system's mathematical model was established and the reliability of the mathematical model was verified by experimental data. To enhance the comprehensive performance of the system, the multi-objective particle swarm optimization (MOPSO) algorithm is used in this paper to optimize the multi-objective parameters of the system. The objective function is the total exergy destruction of the system and the dehumidification capacity of the system. The optimization variables are cold water temperature, cold water flow rate, solution flow rate, air flow rate, and hot water flow rate. The optimization is performed using the multi-objective particle swarm optimization (MOPSO) algorithm to obtain the Pareto front, and the points of the Pareto front are normalized. Finally, the optimal trade-off point of the Pareto frontier is obtained. Each operating parameter of the optimal point of the Pareto front is also analyzed. The results show that the air flow rate and cold water flow rate have the most influence on the conflict between the total exergy destruction of the system and the dehumidification capacity of the system.

Marine temperature and humidity regulation combined system: performance analysis and multi-objective optimization

The efficient and environmentally friendly air conditioning system plays a vital role in cost reduction and efficiency improvement within the shipping industry. This study focuses on a specific ocean-going container ship equipped with the 8S90ME-C10.2 marine diesel engine as its main propulsion system. Firstly, the cooling load of 149.56 kW and a wet load of 18.04 g/s for the container ship were calculated to determine an energy-efficient and comfortable air conditioning scheme. Secondly, a novel combined system, integrating temperature and humidity solution dehumidification with enhanced transcritical CO2 refrigeration using injection subcooling, was proposed. The regenerator for solution dehumidification and the generator for injection refrigeration utilized the main cylinder liner cooling water as a heat source. Based on the system modeling, numerical simulation, and result validation, comprehensive analyses and quantitative evaluations were conducted to investigate the sensitivity of temperature and humidity regulation parameters, system performance, components exergy efficiency, and economics. Finally, employing a multi-objective optimization algorithm, the optimal operating conditions and corresponding objective functions for the system were obtained: exhaust pressure of 9.43 MPa, regeneration temperature of 91.08 °C, subcooling degree of 19.48 °C, coefficient of refrigeration performance of 3.697, exergy loss of 84.136 kW, and an annual operating cost of $111,300. This combined system exhibits high efficiency, environmental friendliness, and comfort, making it well-suited to handle the fluctuating heat and humidity loads during the ocean-going container ship through varying sea climates.

Study on the optimal solution recirculation ratio of liquid desiccant dehumidification system based on matching rate evaluation

The recirculation of dehumidification and regeneration solutions has shown promising moisture removal rates and energy-saving effects in liquid desiccant dehumidification systems. The different combinations of dehumidification solution recirculation ratio and regeneration solution recirculation ratio under varying operating conditions can have different impacts on the system. Nevertheless, the system performance under full operating conditions has not been comprehensively studied. To address this research gap, this study proposes a liquid desiccant dehumidification system with a solution recirculation structure, defines a new evaluation index — matching rate, and conducts a parameterized study and optimization of the steady-state performance of the liquid desiccant dehumidification system with a solution recirculation structure within the range of solution recirculation ratios under all operating conditions, by integrating the system cooling capacity and energy effectiveness ratio. The performance of the system is studied by varying seven key parameters: dehumidification solution recirculation ratio, regeneration solution recirculation ratio, total solution mass flow rate, dehumidification solution inlet temperature, regeneration solution inlet temperature, and ambient air temperature-humidity ratio. The results show that under design conditions, the solution recirculation ratio within the full operating range can process air to a range of 17.8℃～18.5℃ and 12.5 g/kg～17.4 g/kg. The maximum system cooling capacity, energy effectiveness ratio and matching rate values are 21.5 kW, 0.21 and 0.42 respectively. The recommended (dehumidification solution recirculation ratio, regeneration solution recirculation ratio) schemes for high, medium and low demand of system cooling capacity are (0.7～0.9, 0～0.5), (0.4～0.6, 0～0.7) and (0～0.3, 0.4～0.7) respectively, based on the requirements of system cooling capacity.

Energy, exergy, economic and environmental analysis of a solar-driven hollow fibre membrane dehumidification system

Solar-driven hollow fibre membrane dehumidification systems are already being used for air dehumidification, as they have the advantage of saving energy and preventing dehumidification solution droplets from entering the process air. Mathematical models of the system were built, which were validated with experimental data. An analysis of energy, exergy, economic and environmental was accomplished. Effects of critical parameters, including the flow rate of air, solution, hot-water and cold-water, and the cold-water temperature on the system's energy and exergy under the design conditions, were investigated theoretically. Economic and environmental aspects of the system were compared with a traditional refrigeration dehumidification system. The energy analysis indicates that the system has a higher coefficient of performance and dehumidification capacity in July and August. The exergy analysis indicates that the exergy efficiency is lower in May, June and July. The economic analysis shows the initial investment in the system is 641.65 $ higher than the traditional refrigeration dehumidification system, and the higher portion would be paid back with electricity savings in 6.08 years. The annual CO2 emissions of the solar-driven hollow fibre membrane dehumidification system is 0.2642 tCO2, which is 68.89% lower than the traditional refrigeration dehumidification system.

Research on energy-saving conventional submarine air-conditioning system based on heat and humidity load calculation

The built-in air-conditioning and ventilation system of modern conventional submarines still adopts duct ventilation, which has high working noise, high energy consumption, poor dehumidification effect, and is mainly inter-cooled. For the air quality, hot and humid environment and comfort requirements in the submarine cabin. This project proposes an energy-saving cold storage air-conditioning system suitable for submarines. It adopts the air control method of temperature and humidity independent processing, and combines solution dehumidification and cold storage technology to independently control the temperature and humidity of the cabin, so as to achieve the purpose of efficient dehumidification and energy saving. The system makes full use of the limited space inside the submarine, reduces the energy consumption of refrigeration, improves the underwater endurance and concealment, and provides a healthy and comfortable air environment for the crew of the submarine, which has important strategic value.

Improvement of low-grade heat utilization: Sensitivity mechanism of saturated vapor pressure–temperature in dehumidified materials

Low-grade heat exists widely in industrial processes and nature, but it is difficult to harvest and utilize due to the limitation of existing technology. In this paper, a new concept for improving low-grade heat utilization efficiency is proposed, which relies on absorption refrigeration or solution dehumidification air conditioning system to achieve heat-driven regeneration at a lower temperature by using a multi-component liquid desiccant solution with stronger saturated vapor pressure–temperature sensitivity. It is proved that the regeneration temperature can be reduced by increasing the P-T sensitivity of the dehumidified materials. Further, the paper quantifies the description of the P-T sensitivity and reveals the mechanism of the sensitivity as follows: the higher the charge concentration of ions, the stronger the ion-water molecule dipole interaction, resulting in the lower the concentration of dehumidification solution is required, and thus the stronger the P-T sensitivity. Finally, experimental verification shows that compared with typical LiBr solution as a liquid desiccant, the regeneration temperature of the solution dehumidification system can be reduced by 7.9 ℃ by using a multicomponent solution with higher P-T sensitivity as a liquid desiccant, which also proves that low-grade heat at a lower temperature can be recovered by using the method recommended in this paper.

Directional vapor transported and water-proof nanofibrous membranes for liquid desiccant dehumidification systems

The membrane-based liquid desiccant dehumidification system is a newly developed method in the field of air dehumidification. In this study, double-layer nanofibrous membranes (DLNMs) with directional vapor transport and water repellency for liquid dehumidification were fabricated by a simple electrospinning process. Specifically, the combination of thermoplastic polyurethane nanofibrous membrane and polyvinylidene fluoride (PVDF) nanofibrous membrane forms a cone-like structure in DLNMs, resulting in directional vapor transportation. The nanoporous structure and rough surface of PVDF nanofibrous membrane provide waterproof performance for DLNMs. Compare with the commercial membranes, the proposed DLNMs have a significantly higher water vapor permeability coefficient, which is as high as 539.67 g·μm m−2·24 h·Pa. This study not only provides a new route to construct a directional vapor transport and waterproof membrane, but also demonstrates the huge application prospect of the nanofibrous membrane formed by electrospinning in the field of solution dehumidification.

A porous composite membrane for spontaneous moisture adsorption

Highly humid air is harmful to human health. The solution dehumidification can easily cause salt solution droplets release into the air while membrane dehumidification requires a significant driving force. This work aims to investigate the moisture adsorption performance of as-synthesized composite porous membranes in the absence of pressure driving force. Here, a series of PVDF/PVA/CaCl2 membranes were prepared. An open core-shell skeleton with a porous surface and PVA aggregated core was obtained, which serves as a permeation channel for mass transfer. Due to the uniform distribution of CaCl2 adsorption sites, the hydrophilic nature of PVA, and the porous structure, the membranes exhibited outstanding hygroscopic properties with the highest initial moisture adsorption rate of 0.053 g·g−1·min−1 and moisture adsorption capacity of 2.36 g·g−1 in the spontaneous state. The water vapor adsorption data of the M-4-5 sample was best fitted using the double constant kinetic model. Moreover, the core-shell skeleton provided excellent strength and a stable structure. The maximum dry strength of the composite membrane was 1.6 MPa and the maximum wet strength was 0.92 MPa. This work provides a new concept for designing the dehumidified membrane material, especially for non-pressure-driven condition.

Experimental investigation on the performance of a boiler system with flue gas dehumidification and combustion air humidification

The temperature of the return water in heating networks is a key parameter for heat recovery from flue gas. At high the return water temperature, the conventional systems for boiler flue gas heat recovery do not perform well. This paper presents a more effective total heat recovery system by dehumidifying flue gas and humidifying combustion air. An experimental bench for flue gas waste heat recovery based on the combination of combustion air humidification and solution dehumidification was built to verify the feasibility of using potassium a formate aqueous solution (the concentration of the second dehumidifier was measured at 66%) to recover flue gas waste heat. The experimental results demonstrate that when the return water temperature of the heating network is as high as 52.5 °C, the boiler thermal efficiency increases by 9.1%. When the return water temperature of the heating network is 42–57 °C, the final relative humidity of the exhaust flue is 50–70% and the white plumes are remarkably eliminated. The equivalent thermal efficiency increases by >3% after the cooling tower is turned on. Compared with the existing waste heat recovery system, the experimental system developed in this study achieves a better waste heat recovery effect under the working conditions of a higher return water temperature of the heating network. Thus, this system holds promise for future applications as an energy-efficient, cost-effective, and environmentally-friendly system for waste heat recovery from district heating systems.

Modeling and measurements of Soret and Dufour effects on the water vapor transfer in membrane-based desiccant solution dehumidification dual-chamber system

In order to study the mutual influences of temperature gradient and concentration gradient in the coupled heat and mass transfer process of membrane-based desiccant solution dehumidification, an air-solution dual-chamber system was built. The reduced heat of transfer without concentration gradient is defined, qm2∗=-rmmrmq, to derive thermal diffusivity DSr, and then derive the corresponding Onsager coefficients rqm2(rmq2) and rmm2. The expression of the total entropy production with respect to temperature gradient and chemical potential varying with concentration is given as σ=-λ2Jm2∙T2∙dTdx3+[λJm12∙(dlnT)2+∂μ/∂cT∙Dm]∙Jm1∙Jm1+Jm2. There should be a certain temperature gradient to enable the thermal diffusion process to occur by qualitative analysis. The hydrophilic-hydrophobic alumina porous ceramic membrane grafted with fluoroalkylsilane (FAS) was prepared. The improved time lag method was applied in air-solution compartments to obtain the water vapor diffusivity in large temperature difference. The thermal conductivities of the membrane under different temperature gradients were measured. The Soret number and the Dufour number are calculated by the discretization method. A transient two-dimensional mathematical model was established to describe the Soret term affecting the mass transfer process and the Dufour term affecting the heat transfer process. In model validation section, the deviation in the latter part is explained from the perspective of the intrinsic resistance of the membrane material influenced by air inlet temperature. The phenomenon of the occurrence of additional mass flux caused by the temperature gradient in the coupled heat and mass transfer process was revealed by the simulation results of water vapor concentration and temperature distribution.

An ion mass transfer model of electrodialysis regenerator for inorganic salt liquid desiccants

The solution dehumidification air-conditioning system shows great energy-saving potential in humid area, which is significant to the energy consumption in buildings as air-conditioning costs more than half energy in buildings under this climate. The electrodialysis regeneration is suitable for liquid desiccant in humid area as this method needs no heat and mass transfer with environmental air, and the heating and cooling of liquid desiccant are also not needed in this regeneration approach. In order to improve the mass transfer coefficient in electrodialysis regenerator, the ion mass transfer mechanism of liquid desiccant with ultra-high concentration is investigated in this paper. An ion mass transfer model of electrodialysis regenerator for inorganic salt liquid desiccant with ultra-high concentration is established based on the Nernst-Plank equation, which can be solved by the finite difference method. The current coefficient model is corrected and the accuracy of the ion mass transfer model of electrodialysis regenerator is verified by the experiment. Theoretical research shows that when the dehumidification requirement is met, the initial solution concentration, operating current and circulation flow rate should be reduced to achieve better performance of solution dehumidification air conditioning system.

Study on flow and heat and mass transfer characteristics of cross-flow poly propylene hollow fiber membrane module

ABSTRACT Hollow fiber membrane solution dehumidification technology is a new type of dehumidification technology combining solution dehumidification and membrane separation. It is currently widely used in the field of air conditioning dehumidification. In this study, membrane dehumidification technology was applied to low-temperature flue gas dehumidification, and a model of regularly arranged hollow fiber membrane modules was established on the basis of a conjugate heat and mass transfer model. The accuracy of the model was verified by comparing it with literature and experimental data, applying a random arrangement of components. Numerical simulation is carried out by COMSOL software. The flue gas velocity, temperature and water vapor concentration field in the module are coupled together, and the flue gas flow and heat and mass transfer characteristics are affected by the distance between the membrane filament tubes. The dehumidification and cooling efficiency of the randomly arranged hollow fiber membrane module can reach 68.3% and 39.1%,respectively, which Close to 72.1% and 48.7% of regularly arranged components. And the components can be optimized based on the model.

Experimental Study on the Regeneration Process of the Dehumidification System of Lithium Bromide Solution Based on Computer

Dehumidification is a common problem in production and life. solution dehumidification method is to use salt solution with strong hygroscopicity as dehumidifier, the salt solution is in direct communicate with the treated air because of the pressure variance between the water vapor force on the side of the salt solution and the water vapor force of the treated air, the moisture is driven to transfer between the air and the hygroscopic solution, thus the change of air humidity is realized. In short, the high concentration of lithium bromide and other aqueous solutions absorb the water vapor in the atmosphere by the force difference between the water vapor and the treated air, thus completing the dehumidification process of the air. After the solution absorbs water in the air, it needs to be concentrated and regenerated to restore moisture absorption capacity. Many scholars at home and abroad have studied the solution dehumidification system. Florida Solar Energy Center Swami proposed a system for regeneration of solutions using roofs as solar absorbing surfaces in 1998. Nelson dehumidification performance of Li Cl solution as dehumidifier was studied. Due to the fact that the surface vapor pressure, specific heat capacity, corrosion and other physical and chemical properties of lithium bromide are better than those of lithium chloride and calcium chloride under the same PH and equal concentration, I have studied the regeneration process of dehumidification system of lithium bromide solution based on computer.

Research on performance of mine dehumidification and cooling system based on heat pump

A heat pump-based mine solution dehumidification and cooling system is used in deep mines, which can not only reduce the temperature and humidity of the working face, but also recycle the low-grade heat energy and improve the utilization rate of energy.Under the condition of long distance air supply, within the range of 10m from the heading face, the equivalent temperature of the air can fall to 24.7 °C, the cooling range is 5.6 °C, and the relative humidity decreases by 23.79%. Compared with the original cooling system, the COP value of the system can reach 3.43 under the same working conditions, 19% higher than the original cooling equipment.

Heat and mass transfer characteristics and dehumidification performance improvement of an evaporatively-cooled liquid dehumidifier

In this paper, an evaporatively-cooled dehumidifier and its experimental test rig is introduced. By using the LiCl and CaCl2 solutions with mass concentration of 0.35 and 0.45 as liquid desiccants, the dehumidification performance improvement compared to adiabatic falling-film dehumidification and the heat and mass transfer characteristics of LiCl and CaCl2 solutions under evaporatively-cooled conditions are analyzed. The results indicate: the dehumidification rate under evaporatively-cooled condition is about 20% higher than that under adiabatic condition and the improving extent of dehumidification performance of the evaporatively-cooled dehumidifier appears more obviously under higher environmental temperature and humidity and lower solution concentration and higher solution temperature. Meanwhile, the dehumidification rate of LiCl is about 73% higher than that of CaCl2 under the same solution concentration, and the CaCl2 with mass concentration of 0.45 shows the parallel dehumidification performance with LiCl. As for the enthalpy effectiveness, CaCl2 with mass concentration of 0.35 is the highest. By changing the air, solution, and evaporative cooling air parameters, it is found that the heat and mass transfer coefficient is most significantly affected by air flow rate, and the heat transfer coefficient increases with the increase of solution flow rate but the mass transfer coefficient decreases. Moreover, four correlations on heat and mass transfer characteristics are given. In summary, the evaporatively-cooled devices can do effectively improve the solution dehumidification performance and the study results of this paper are beneficial to the industrial application of that device.

Air-conditioning and refrigeration: Current status and future perspectives

Air-conditioning and refrigeration systems are essential facilities of health care, transportation and food preservation, which make people able to live and work at the coldest and warmest climates in the planet. These technologies have been applied to a wide range of scenarios, including the distributed air-conditioning, food, medicine, health and sport for people’s daily life, and centralized air-conditioning, heat pump and cryogenics in commercial and industrial applications. In the near future, global warming, urbanization and pursuit of higher living standard will continue to push the demand of air-conditioning. Food preservation for the increasing global population and fresh food e-commerce require more cold storage. Space detection, low-temperature imaging and cryogenic medical treatment will push the cryogenics forward. Except for these listed applications, there are also many other driven forces for the next-step development of air-conditioning and refrigeration, which make its future progress complicated. A comprehensive summary of the current status is necessary for air-conditioning and refrigeration, which will also provide us the basis to analyze its future perspectives. Three typical air-conditioning and refrigeration technologies are introduced at first. These include the refrigeration/heat pump, temperature-humidity control and cryogenics. Vapor compression refrigeration, absorption refrigeration, adsorption refrigeration, ejector refrigeration, solid state refrigeration, refrigeration without thermodynamic cycles and heat pumps are introduced for the first topic, which focuses on the temperature manipulation in normal temperature range. Condensation dehumidification, solution dehumidification, solid desiccant dehumidification and evaporative cooling are introduced for the second topic, which focuses on the interaction of temperature and humidity of air. Gas liquefaction and cryocooler are introduced for the third topic, which focuses on the thermal energy removal under low temperature. Conventional and emerging applications of these technologies are introduced afterwards. The refrigeration and dehumidification could support a wide range of application including air-conditioning, data center cooling, solar cooling, electrical vehicle thermal management and food/drug preservation. The applications of heat pumps include the clean heating supply and industrial heat recovery. The cryogenics could be applied for air liquefaction, liquefied natural gas, hydrogen storage, cryobiology/cryomedicine and big science project. Based on the previous analysis, future challenges on efficiency enhancement, eco-friendly refrigeration and application promotion are presented at last. The efficiency enhancement is driven by the numerous equipments of air-conditioning and refrigeration in use, which consume a large portion of total power consumption of mankind. It could be achieved through the innovation on heat exchanger, thermodynamic cycle and intelligent control. The eco-friendly refrigeration is driven by the environmental protection policies. Low GWP and ODP refrigerants including HFOs and natural refrigerant will be effective solutions. Small-sized heat exchanger with less refrigerant charge is also important. The application promotion is driven by the fact that air-conditioning and refrigeration have already become the basic technology supporting the emerging technologies. Except for the traditional applications, the air-conditioning and refrigeration technologies are becoming fundamental technologies for many multidisciplinary fields, including the data center cooling, electrical vehicle thermal management, clean heating, industrial waste heat recovery, cryobiology/cryomedicine, and big science project.

Performance analysis of vacuum membrane distillation regenerator in liquid desiccant air conditioning system

In order to solve the problem of poor regeneration performance of the solar solution dehumidification air conditioning regeneration system under high temperature and high humidity weather conditions. In this paper, a novel vacuum membrane distillation (VMD) solution regeneration method was proposed for a solution desiccant air conditioning system, and a theoretical study of this novel regenerator is performed. Through the analysis of heat and mass transfer, the mathematical model of VMD regeneration is established, and the mathematical model is verified by experiments. The results indicated that VMD regenerator not only could increase the regenerate rate but also could exhibit higher energy utilization efficiency. At the same concentration, the VMD regenerator has a higher regeneration performance, and the regeneration rate is 1.6–2.4 times that of the internal heat type regenerator, and the 4.5–6 times that of the adiabatic regenerator.

Modeling and performance analyses of a batch-wise liquid desiccant air conditioning system

Numerous efforts have been made and reported to improve the energy efficiency of liquid desiccant air conditioning (LDAC) in recent studies. This study proposes a novel batch-wise operation strategy for LDAC that desiccant solutions in dehumidifier and regenerator are circulating independently and exchanging intermittently to get a full utilization of solution dehumidification capacity, cooling and heating energy. System models, including heat and mass transfer models of dehumidifier and regenerator, heat exchanger models and solution transfer model, are developed and verified to analyze and estimate the performance of proposed batch-wise strategy. The maximum relative errors between experimental and model predicting results are within 9.69% for outlet air temperature and within 7.97% for outlet air relative humidity. Performance and energy efficiency of proposed strategy are analyzed and compared with normal on-going solution exchange strategy. According to the simulation results, dehumidification rate and regeneration rate can be improved by average of 5.00% and 3.50% due to multiple solution usages in dehumidifier and regenerator. Moreover, the proposed batch-wise strategy demonstrates considerable energy savings with up to 16.81% and 18.60% from dehumidifier and regenerator, respectively.

A Shell of Wireless Sensor Network Node for High-Temperature and High-Humidity Environment: Modeling, Simulation, and Experimental Analysis

With more and more applications of wireless sensor network technology in intelligent management of greenhouse, high-temperature and high-humidity resistance of wireless sensor nodes are becoming more and more important. This paper takes the wireless sensor nodes of the greenhouse as the research object. Aiming at the characteristics of high-temperature and high-humidity environment in summer, solid–liquid phase change material (stearic acid/lauric acid/graphite powder = 0.18:0.67:0.15) is selected as the cooling solution, the mixed desiccant of silica gel and clay is the dehumidification solution, and the high-temperature and high-humidity resistant shell of wireless sensor node is designed; the COMSOL software is used to simulate the high-temperature and high-humidity performance of the wireless sensor nodes. The results show that the maximum temperature of the node with the shell is kept below 45 °C and the relative humidity is kept within 60.9%; the experimental results of high-temperature and high-humidity environment show that the designed greenhouse wireless sensor nodes have obvious high-temperature and high-humidity resistance and can meet the requirements of wireless sensor nodes working in high-temperature and high-humidity environment of the greenhouse in summer.

Experimental analysis of a novel internally-cooled dehumidifier with self-cooled liquid desiccant

With respect to air dehumidification, an internally-cooled dehumidifier is more efficient than an adiabatic dehumidifier. In the present study, a new method to control the increase in the temperature of the liquid dehumidifier solution was presented. A self-cooled liquid desiccant solution was defined and prepared. Anhydrous ethanol was added into the lithium chloride (LiCl) aqueous solution as the vaporizable coolant to control the increase in the temperature of the solution. A working hypothesis for the self-cooled solution dehumidification was established with a main feature wherein the heat exchangers in conventional internally-cooled dehumidifier were replaced by using self-cooled liquid desiccant solution. Its performance was compared and experimentally investigated. An environmental chamber and a visible experimental setup were established. Experimental results under different operating conditions were obtained. The performance indices including moisture removal rate and dehumidification efficiency were analysed. When compared with conventional LiCl liquid desiccant solution, the current analysis indicated that the self-cooled solution is superior with respect to the above performance indices.