Performance analysis of three-stage liquid desiccant deep dehumidification processor driven by heat pump

A new type of a heat pump driven three-stage lithium bromide liquid desiccant deep dehumidification processor is presented,which can dehumidify the outdoor humid air to a rather dry state,even when there is no available indoor exhaust air.The test results show that with an outdoor air temperature of 28 to 31 ℃ and an outdoor air humidity ratio of 11 to 14 g/kg,the supply air temperature and the supply air humidity ratio are 1.6 to 2.6 ℃ and 2.6 to 3.0 g/kg,respectively,and the coefficient of performance（COP）of the processor is 1.8.During the test,a liquid pipeline link problem leading to mixture losses of hot and cold liquid desiccants is found.These pipelines are modified.Then,the performance of the modified processor is investigated.And the experimental results show that with an outdoor air temperature of 25 to 32 ℃ and an outdoor air humidity ratio of 18 to 21 g/kg,the supply air temperature and the supply air humidity ratio are 3.2 to 4.0 ℃ and 3.4 to 3.6 g/kg,respectively,and the COP is 2.8.Finally,a mathematical model of the processor is established.The comparison of the simulation results and the test results of the processor exhibits that the pipeline modification improves the performance by about 20%.

Liquid drying of BeO gelcast green bodies using ethanol as liquid desiccant

BeO gelcast green bodies were dried by liquid drying method with liquid desiccant ethanol.Effects of ethanol concentration,solids loading and aspect ratio of green body on the moisture and shrinkage of green bodies were studied through measuring mass and dimension.Additionally,liquid drying stress was analyzed and a model of the initial stage drying stress was established.The results show that higher ethanol concentration,lower solids loading and higher aspect ratio of gelcast green bodies increase the drying rate.Increasing the ethanol concentration decreases the shrinkage rate.Liquid drying stress is generated due to a non-uniform drying rate.During the process of liquid drying,the inner drying stress of the green body changes from compressive stress to tensile stress,while the outer drying stress changes from tensile stress to compressive stress.

Performance analysis on a novel water chiller using liquid desiccant

A new type of liquid desiccant water chiller for applications on air-conditioning and refrigeration is introduced.The system can be driven by low-grade heat sources with temperatures of 60 to 80 ℃,which can be easily obtained by a flat plat solar collector,waste heat,etc.A numerical model is developed to study the system performance.The effects of different parameters on performance are discussed,including evaporating temperature,regenerating temperature,ambient condition,and mass flow rates of closed moist air and regenerating air.The results show that an acceptable performance of a cooling capacity of 2.5 kW and a coefficient of performance of 0.37 can be achieved in a reference case.The regenerating temperature and the humidity ratios of ambient air are two main factors affecting system performance,while the temperature of ambient air functions less.In addition,the mass flow rate of regenerating air and closed moist air should be carefully determined for economical operation.

Improvement of conventional liquid desiccant dehumidification technology

A new system of liquid desiccant dehumidification,called ultrasound atomization dehumidification system,is proposed.In this system,a packed bed is replaced by ultrasound atomization technology,so high resistance and liquid desiccant consumption caused by the packed bed are avoided.A mathematical model is established to predict the efficiency and the liquid consumption of the dehumidification process under ideal conditions.Through comparing the simulation results with the experimental data of a conventional packed-bed dehumidifier,it is found that the liquid desiccant consumption of the conventional packed-bed dehumidifier is much greater than that under ideal conditions.In the proposed system,the dehumidification process occurs on the surfaces of the micron liquid desiccant droplets produced with the irradiation of ultrasound,so there is a greater contact area created with the same quantity of the liquid desiccant;moreover,the power consumption is lower because there are no nozzles and no solution pump.It can be seen that this new system is closer to ideal conditions when compared with the conventional liquid desiccant dehumidification system.

A new solar coupling regeneration method for liquid desiccant air-conditioning system

A new solar coupling regeneration system is proposed in order to improve the reliability of solar desiccant regeneration system.The new system makes comprehensively use of the solar energy and can also be appropriate for energy-storage in a night operation mode when the electric power supply is at its valley.Comparison of the performance of the new system,the solar thermal regeneration system and the solar electrodialysis regeneration system are made and the influential factors of the performance of the new system are investigated.The results reveal that the new system will be more energy efficient than the solar thermal regeneration system and the solar electrodialysis regeneration system.

Numerical simulation of liquid desiccant evaporator driven by heat pump

The standard k-ε turbulence model and discrete phase model (DPM) were used to simulate the heat and mass transfer in a liquid-desiccant evaporator driven by a heat pump using FLUENT software, and the temperature field and velocity field in the device were obtained. The performance of the liquid-desiccant evaporator was studied as the concentration of the inlet solution varied between 21% and 30% and the pipe wall temperature between 30 and 50 ℃. Results show that the humidification rate and the humidification efficiency increased with the inlet air temperature, the solution flow rate, the solution temperature, and the pipe wall temperature. The humidification rate and humidification efficiency decreased with increasing moisture content in inlet air and the concentration of inlet solution. The humidification rate increased substantially but the humidification efficiency decreased as the inlet air flow rate increased. The error between the simulations and experimental results is acceptable, meaning that our model can provide a theoretical basis for optimizing the performance of a humidifying evaporator.

A Bubble Column Dehumidifier using Ionic Liquid Desiccant for Low-Humidity Industries: Insights into Transfer Processes Integrating Experiment and CFD Modelling

Liquid desiccant deep dehumidification(LDDD)is an excellent energy-saving technology for low-humidity industries.Ionic liquids(ILs)are favored as optimal working fluids for LDDD,owing to their low vapor pressure,non-crystallization,and non-corrosion.The combined application of IL desiccant with the bubble column has been proven to effectively improve deep dehumidification.The present work focuses specifically on the insights into air-liquid transfer processes in bubble column dehumidifier using ionic liquid desiccant.The effect of operating parameters on volumetric transfer coefficient is examined based on the experimental platform.Meanwhile,the bubble swarms meso-scale flow structure is predicted using computational fluid dynamics coupled with a population balance model(CFD-PBM).Besides,the structure-activity relationship between meso-scale flow structure and transfer performance is investigated.The results indicated a notable phenomenon of bubble aggregation/breakage in the moist air-IL desiccant bubbly deep dehumidification(MA-ILD BDD)system,with a specific interfacial area is basically less than 40 m^(-1).Meanwhile,a decrease in solution temperature,correlated with a significant increase in viscosity,leads to larger turbulent eddies and a slower breakage rate.Notably,a high transfer potential difference enhances heat and mass transfer coefficients at lower solution temperatures,with the mass transfer coefficient at 4℃ being approximately three times that at 10℃.As the superficial velocity changes,the specific interfacial area and heat and mass transfer coefficients have a positive synergistic effect on volumetric transfer coefficient.However,this synergistic effect is reversed with variations in solution temperature.This study aims to clarify the air-liquid transfer mechanism in bubble column dehumidifierusingILdesiccant.

Efficiency comparison and performance analysis of internally-cooled liquid desiccant dehumidifiers using LiCl and CaCl2 aqueous solutions

Internally-cooled dehumidifiers are efficient liquid desiccant dehumidifiers, whose performance is mainly determined by the device structure and operating conditions. Based on energy and mass conservation in the air, solution, and cooling water in the device, mathematical models are built and their theoretical performance is simulated and analyzed in this paper. A novel measure of dehumidification efficiency is introduced to evaluate the performance of internally-cooled dehumidifiers, in which the equilibrium humidity ratio of the inlet solution is calculated according to the minimum temperature in the inlet solution and the cooling water. Numerical simulations show that a counter flow between air and solution is always the most efficient, followed by cross flow, and parallel flow is the least efficient. Cooling water with the same flow direction as the solution performs better than that with a counter flow, with approximately a 5% improvement in efficiency. Compared with Ca Cl2, the dehumidification efficiency of a Li Cl solution is greater by 60%, while its exergy efficiency is less by 16%. Dehumidification efficiency can be improved with the number of air-solution heat transfer units(NTUa-s) increasing, and reduced with the air mass flow rate raised. With NTUa-s increasing, exergy efficiency can be improved, and an increase in mass flow rate of cooling water results in a decrease of efficiency. Higher solution concentration and lower inlet temperature of solution and air can achieve both higher dehumidification efficiency and exergy efficiency.

Recent progress in liquid desiccant dehumidification and air-conditioning:A review

This paper presents a literature review on the recent research progress in liquid desiccant dehumidification and air conditioning systems.The physical features of various liquid desiccant materials and their dehumidification performances have been summarized.With the aim to improve the dehumidification characteristics,mixed sol-vents desiccants have become research hot topics recently.Various types of dehumidifiers and their integration with liquid desiccant dehumidification system have been reviewed.The combination of liquid desiccant dehumid-ification system with solar collector,vapour compression system,heat pump system,CHP system,etc.have been grouped and compared.It is shown that the majority of the recent research work for liquid desiccant dehumid-ification systems has concentrated on numerical simulations,a considerable amount of works are still required for the practical investigations of innovative material(mixed solvents)and hybrid systems.

Experimentation of a Membrane-based Concentration Gradient Energy Storage of Liquid Desiccant Solutions Driven by Solar Energy

Solar energy storage is an indispensable and sustainable utilization mode of renewable energy;environment friendly,large-capacity,low heat loss,and long-term storage are critical to improving the integration of solar energy supply.Traditional thermal energy storage mode cannot achieve long-term storage due to the heat loss even under the excellent thermal insulation measures.In this work,a solar-powered membrane-based concentration gradient energy storage of liquid desiccant solutions is presented.In the membrane distillation process driven by solar energy under the right solar radiation conditions,the liquid desiccant solution is concentrated gradually and long-term stored as the concentration gradient energy.To this end,the measured temperature of solar hot water is in the range of 40°C to 90°C from May to September,2018,in Xi’an,China.And then,the LiBr solution(50 wt%),the LiCl solution(35 wt%),and the CaCl_(2)solution(40 wt%)were membrane-based concentrated in the temperature range of 42°C to 63°C,separately.The results showed that the water vapor pressure difference decides the water vapor transferred across the membrane pores from the liquid desiccant side to the air side.The energy storage density of liquid desiccant solutions increases along with the increases in temperature and the membrane area.Consequently,when the LiBr,LiCl,and CaCl_(2)solutions are concentrated from 50%to 55%,from 35%to 40%,and from 40%to 45%,separately,the concentration energy storage density is 245 kJ/kg,350 kJ/kg,and 306 kJ/kg,which is equivalent to or even higher than ice storage capacity.Due to the two independent closed cycle of the liquid desiccant solution and air,the liquid desiccant solution’s concentration gradient energy storage can be long-term stored environment-friendly without any insulation measures.

Numerical study on dehumidifying process in falling film dehumidifier

A counter flow model of simultaneous heat and mass transfer of a vapor absorption process in a falling film dehumidifier is developed. The governing equations with appropriate boundaries and interfacial conditions describing the dehumidifying process are set up. Calcium chloride is applied as the desiccant. The dehumidifying process between falling liquid desiccant film and process air is analyzed and calculated by the control volume approach. Velocity field, temperature distribution and outlet parameters for both the process air and desiccant solution are obtained. The effects of inlet conditions and vertical wall height on the dehumidification process are also predicted. The results show that the humidity ratio, temperature and mass fraction of salt decrease rapidly at the inlet region but slowly at the outlet region along the vertical wall height. The dehumidification processes can be enhanced by increasing the vertical wall height, desiccant solution flow rates or inlet salt concentration in the desiccant solution, respectively. Similarly, the dehumidification process can be improved by decreasing the inlet humidity ratio or flow rates of the process air. The obtained results can improve the performance of the dehumidifier and provide the theoretical basis for the optimization design, and the ooeration and modulation of the solar liquid desiccant air-conditioning systems.

Design of quaternary ammonium type-ionic liquids as desiccants for an air-conditioning system

The liquid desiccant air-conditioning system allows reducing energy consumption compared to the conventional compressor-type air conditioners.In order to develop desiccant materials for air conditioners,we have investigated the dehumidification capability of quaternary ammonium Ionic Liquids(ILs)and the equilibrium water vapor pressure of aqueous solutions of these ammonium salts.Among the seven tested types of ILs,2-hydroxyN,N,N-trimethylethan-1-aminium dimethylphosphate([Ch][DMPO4])displayed the best dehumidification capability and the lowest equilibrium water vapor pressure.Furthermore,the 80%aqueous solution of[Ch][DMPO4]exhibited a less corrosive effect on four types of metals,i.e.,steel(hot dip zinc-aluminum alloy plated steel),copper(C1100P),aluminum(A5052),and stainless steel(SUS:SUS304).It should be noted that this[Ch][DMPO4]is not only non-toxic but also exhibits a stable nature;the aqueous solution produced no odor after storing for over 1 year under ambient conditions.

Effectiveness and Humidification Capacity Investigation of Liquid-to-air Membrane Energy Exchanger under Low Heat Capacity Ratios at Winter Air Conditions

In this research,a novel small-scale single-panel liquid-to-air membrane energy exchanger has been used to numerically investigate the effect of given number of heat transfer units(4.5),different cold inlet air temperature(1.7,5.0,10.0℃)and different low heat capacity ratio(0.4,0.5,0.6,0.7,0.8,0.9)on the steady-state performance of the energy exchanger.This small-scale energy exchanger represents the full-scale prototypes well,saving manufacturing costs and time.Lithium chloride is used as a salt solution in the system and the steady-state total effectiveness of the exchanger is evaluated for winter inlet air conditions.The results show that total effectiveness of the energy exchanger decreases with heat capacity ratio in the mentioned range.Maximum numerical total effectiveness of 97%is achieved for the energy exchanger.Increasing the heat capacity ratio values on given inlet air temperature,the humidification capacity of energy exhanger is also investigated in this paper.The humidification performance increases with heat capacity ratio.The highest humidification performance(4.53 g/kg)can be reached when inlet air temperature is 1.7℃,and heat capacity ratio is 1.0 in winter inlet air conditions in the range of low heat capacity ratio.