Performance Evaluation of an Evaporative Cooling Pad for Humidification-Dehumidification Desalination

The perfect combination of renewable energy and desalination technologies is the key to meeting water demands in a cost-effective,efficient and environmentally friendly way.The desalination technique by humidificationdehumidification is non-conventional approach suitable for areas with low infrastructure(such as rural and decentralized regions)since it does not require permanent maintenance.In this study,this technology is implemented by using solar energy as a source of thermal power.A seawater desalination unit is considered,which consists of a chamber with two evaporators(humidifiers),a wetted porous material made of a corrugated cellulose cardboard and a condenser(dehumidifier).The evaporation system is tested with dry bulb temperature and relative air humidity data.The results of numerical simulations indicate that higher inlet air velocities(from 0.75 to 3 m/s)lead to a decrease in theΔT,ΔRH,and effectiveness.With the air remaining within the evaporator for 30 cm,the temperature differential increases to 5.7°C,accompanied by a 39%rise in relative humidity contrast.These changes result in a significant enhancement in humidification efficiency,achieving a remarkable efficiency level of 78%.However,a wettability value of 630 m^(2)/m^(3)leads to a smaller reduction of these parameters.Increasing the pad thickness,particularly to 0.3 m,improves performance by boostingΔT,ΔRH,and effectiveness,especially for pads with a wettability of 630 m^(2)/m^(3),for which superior performances are predicted by the numerical tests.

Development and Experiment of Multi- functional Wood Dehumidification Dryer

A multi functional wood dehumidification dryer has been developed recently. The dryer can carry out air dehumidification by using only one refrigeration system, in which heat supplying and moisture air are exhausted by changing the position of several air dampers. In this paper, the work principles and characteristics of the dehumidification dryer are introduced, and the testing results about the thermal engineering performance of the dehumidification dryer, as well as the experiment results of drying several species of lumbers are expounded.

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 dehumidification-assisted evaporative supercooling method for ice slurry production

Due to the fact that the conventional ice slurry production system using supercooled water suffers from ice block and depends heavily on electric power,a novel ice slurry production system is proposed.The new system consists of two major parts：the evaporative supercooling process and the liquid dehumidification process.The classical diffusion-control equation is improved by introducing an impact factor into the simulation analysis in the evaporative supercooling process.Meanwhile,experiments are carried out by adopting the particle analyzer to detect the radii and the velocities of the droplets,and an infrared camera to examine the temperature profile of the physical process.It is found that the theoretical conclusion agrees well with the experimental results.Compared with the conventional system,the new system can alleviate the burden on electric power and raise efficiency.These improvements are essentially attributed to the reutilization of the inner waste heat generated from the system itself.

Solid Desiccant Dehumidification Techniques Inspired from Natural Electroosmosis Phenomena

Electroosmosis has been shown to be an effective means of different applications in various fields such as Micro-Electro-Mechanical systems （MEMS） and biomimetics applications. This paper aims to prove the concept that the electroosmosis phenomena can also be cooperated into larger scale applications in the building service industry like dehumidification or damping proof. The electroosmotic flow inside a porous medium is validated experimentally to further understand the dehumidification mechanism of combined techniques. An experimental test validates that the condensation from the porous medium can be obtained by electroosmotic force generated by external electric field, especially for specific desiccant powders like zeolite and diatomaceous earth. With a range of volts from 5 V to 20 V applying between the testing plates, the maximum flow rate through the cross section in the testing plate achieved during the peak period is 1.35 laL＇min 1. These promising phenomena can act as an alternative way for energy choice in dehumidification industrial field. Further researches on new regeneration methods for solid desiccant dehumidification are required to make the system simple, energy-saving and suitable for small air conditioning units.

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.

Experimental Investigation of a Vertical Tubular Desalination Unit Using Humidification-Dehumidification Process

A vertical tubular desalination unit with shell and tube structure was built to perform humidification and dehumidification simultaneously on the tube and shell side of the column, respectively. The effects of several operating conditions on the productivity and thermal efficiency of the column were investigated. The results show that both the productivity and thermal efficiency of the column enhance with the elevation of the inlet water temperature. The flow rates of water and carrier gas both have optimal operating ranges, which are 10-30 kg·h^-1 and 4-7kg·h^-1 for the present column, respectively. Meanwhile, the increase of external steam flow rate will promote the productivity of the column but reduce its thermal efficiency.

Water Desalination Using a Humidification-Dehumidification Technique—A Detailed Review

Solar humidification-dehumidification desalination technology has been reviewed in detail in this paper. This review would also throw light on the scope for further research and recommendations in active distillation system by humidification and dehumidification (HDH). Also in this article, a review has been done on different types of (HDH) systems. Thermal modeling was done for various types of humidification and dehumidification(HDH) distillation system. From the present review, it is found that the humidification-dehumidification desalination process HDH will be a suitable choice for fresh water production when the demand is decentralized. HDH is a low temperature process where total required thermal energy can be obtained from solar energy. Capacity of HDH units is between that produced by conventional methods and solar stills. Moreover, HDH is distinguished by simple operation and maintenance. Also from the present condensed review, it was observed that an increase in evaporator and condenser surface areas significantly improves system productivity. But prior to implementing any techniques in design improvement, it is necessary to optimize the MEH unit by optimizing its component size to understand the effect of feed water and air flow rates. Although a fair amount of simulation studies have been conducted in the past, further design simulation is required to fully understand the complicated effects of air and water flow rates, the optimum size of individual components or modules of the unit and to generate a comprehensive model for the system.

Membrane-based air dehumidification:A comparative review on membrane contactors,separative membranes and adsorptive membranes

This review compares the different types of membrane processes for air dehumidification.Three main categories of membrane-based dehumidification are identified–membrane contactors using porous membranes with concentrated liquid desiccants,separative membranes using dense membrane morphology with a pressure gradient to drive the separation of moisture from air,and adsorptive membranes using nanofibrous membranes which adsorb and capture moisture to realise dehumidification.Drawing upon the importance of dehumidification and humidity control for urban sustainability and energy efficacy,this review critically analyses and recognizes the three unique categories of membrane-based air dehumidification technologies.Essentially,the discussion is broken into three sections-one for each category-discriminating in terms of the driving force,membrane structure and properties,and its performance indicators.Readers will notice that despite having the same objective to dehumidify air,the polymers used amongst each category differs to suit the operating requirements and optimize dehumidification performance.At the end of each section,a performance table or summary of dehumidifying membranes in its class is provided.The final section concludes with a comparative review of the three categories on membrane-based air dehumidification technologies and draw inspiration from parallel research to rationalise the potential and innovative use of promising materials in membrane fabrication for air dehumidification.

Simplified Calculation of Flow Resistance of Suspension Bridge Main Cable Dehumidification System

To calculate the flow resistance of a main cable dehumidification system,this study considers the air flow in the main cable as the flow in a porous medium,and adopts the Hagen–Poiseuille equation by using average hydraulic radius and capillary bundle models.A mathematical derivation is combined with an experimental study to obtain a semi-empirical flow resistance formula.Additionally,Fluent software is used to simulate the flow resistance across the main cable relative to the experimental values.Based on the actual measured results for a Yangtze River bridge,this study verifies the semi-empirical formula,and indicates that it can be applied in actual engineering.

Thermodynamic performance assessment of vacuum membrane-based dehumidification and air carrying energy radiant air-conditioning system(VMD-ACERS)

Temperature and humidity independent control(THIC)air-conditioning system is a promising technology.In this work,a novel temperature and humidity independent control(THIC)system is proposed,namely VMD-ACERS,which integrates vacuum membrane-based dehumidification and air carrying energy radiant air-conditioning system.This work establishes a novel coefficient of performance(COP)model of VMD-ACERS.The main parameters affecting the COP of conventional fan coil unit cooling system(FCUCS)and VMD-ACERS are investigated.The performance of FCUCS and VMD-ACERS are compared,and the energy-saving potential of VMD-ACERS is proved.Results indicate that,for FCUCS,the importance ranking of parameters is basically stable.However,for VMD-ACERS,the importance ranking will be affected by FCU and refrigerant.The most important parameters of VMD-ACERS are condensation temperature and permeate side pressure.On the contrary,superheating,subcooling are relatively less important parameters.For VMD-ACERS,it is not necessary to pursue the membrane with very high selectivity,because the selectivity of membrane would also be a less important parameter when it reaches 500.The COP of VMD-ACERS is higher than that of FCUCS when the permeate side pressure is higher than 8 k Pa.The VMD-ACERS solves two technical problems about power-saving and thermal comfort of conventional THIC,and can extend the application of THIC air-conditioning system.

The Experiment and Simulation of Solid Desiccant Dehumidification for Air-Conditioning System in a Tropical Humid Climate

The aim of this research was to study and design a solid desiccant dehumidification system suitable for tropical climate to reduce the latent load of air-conditioning system and improve the thermal comfort. Different dehumidifiers such as desiccant column and desiccant wheel were investigated. The ANSYS and TRASYS software were used to predict the results of dehumidifiers and the desiccant cooling systems, respectively. The desiccant bed contained approximately 15 kg of silica-gel, with 3 mm average diameter. Results indicated that the pressure drop and the adsorption rate of desiccant column are usually higher than those of the desiccant wheel. The feasible and practical adsorption rate of desiccant wheel was 0.102 kgw/h at air flow rate 1.0 kg/min, regenerated air temperature of 55?C and at a wheel speed of 2.5 rpm. The humidity ratio of conditioning space and cooling load of split-type air conditioner was decreased to 0.002 kgw/kgda (14%) and 0.71 kWth (19.26%), respectively. Consequently, the thermal comfort was improved from 0.5 PMV (10.12% PPD) to 0.3 PMV (7.04% PPD).

Energy conservation research of dehumidification system for main cable anticorrosion of suspension bridge

The necessity of the main cable anticorrosion for suspension bridge is described, and operating principles and composition of main cable dehumidification system are analyzed. An idea using the waste heat of high temperature outlet air of dehumidification system to heat up regeneration air of rotary-type dehumidifier is put forward in this paper. The concrete scheme is to install a heat exchanger on air-out pipeline of roots blower and air-in pipeline of regeneration electric heater of rotary dehumidifier. Air preheated by the heat exchanger enters regeneration electric heater of rotary-type dehumidifier. Energy conservation of main cable dehumidification system for the Yangtze River highway bridge is calculated, and the results show that energy conservation rate can reach 44 %.

Industrial Application of a Deep Purification Technology for Flue Gas Involving Phase-Transition Agglomeration and Dehumidification

A moist plume forms when the flue gas emitted from wet desulfurization equipment exits into the ambi- ent air, resulting in a waste of water resources and visual pollution. In addition, sulfur trioxide （SO3）, water with dissolved salts, and particles in the wet flue gas form secondary pollution in the surrounding atmosphere. In this study, a deep purification technology for flue gas involving phase-transition agglom- eration and dehumidification （PAD） is proposed. This deep purification technology includes two technical routes： the integrated technology of phase-transition agglomeration and a wet electrostatic precipitator （PAW）; and the integrated technology of phase-transition agglomeration and a mist eliminator （PAM）. Industrial applications of PAW and PAM were carried out on 630 and 1000 MW coal-fired units, respectively. The results show that the average amount of recycled water obtained from wet flue gas by means of PAD is more than 4 g.（kg.℃）-1 Decreasing the wet flue gas temperature by 1.5-5.3 ℃ allows 5%-20% of the moisture in the flue gas to be recycled; therefore, this process could effectively save water resources and significantly reduce water vapor emissions. In addition, the moist plume is effectively elim- inated. With the use of this process, the ion concentration in droplets of flue gas is decreased by more than 65%, the SO3 removal efficiency from flue gas is greater than 75%, and the removal efficiency of par- ticulate matter is 92.53%.

Experimental Investigation of Modified Polypropylene Shell-Tube Column Using Humidification-Dehumidification Desalination Process

The polypropylene tubes with surface modification were installed in a baffled shell-tube column to conduct the thermally coupled humidification and dehumidification desalination process. The effects of several operating parameters （feed water temperature, water flow rate, carrier air flow rate, and external steam flow rate） on the productivity and thermal efficiency of this column were investigated experimentally. The results show that the feed water temperature has a positive effect on the productivity and thermal efficiency, while the flow rates of external steam, feed water, and carrier air should be optimized within the ranges of 0.006-0.020 kg·m^-2·s^-1 , 0.005-0.015 kg·m^-2·s^-1, and 0.7-1.3kg·m^-2·s^-1, respectively; the flow rates of feed water and carrier air are greatly controlled by the wetting state of the tubes. In comparison with the previous desalination column installing the coppery tubes, the present column can reach nearly the same production capacity of distilled water, which demonstrates the feasibility of applying such a plastic column to the humidification and dehumidification desalination process.

Improving thermal comfort of high-temperature environment of heading face through dehumidification

In order to improve the thermal environment of high-temperature heading face,moisture content of supply air is reduced by dehumidification, and the relative humidity ofenvironment air of the heading face is also decreased.First, according to the coefficient ofperformance of dehumidifier, the capacity of dehumidification was calculated.Second, inthe engineering example of the heading face, quantitative changes of WBGT (Wet BulbGlobe Temperature) were compared between with dehumidification and without dehumidification.Based on WBGT standards, the thermal comfort of high-temperature environmentof heading face was evaluated between with dehumidification and without handling.Reducingthe relative humidity of airflow through dehumidification, the thermal comfort of ahigh-temperature environment of heading face can improve greatly.Even if dry bulb temperatureof airflow is not decreased, the thermal comfort of heading face environment isalso improved to some extent.

A Review Study of Experimental and Theoretical Humidification Dehumidification Solar Desalination Technology

Most of the desalination technologies consume a huge quantity of energy resulting from petroleum products in the form of heat or electrical energy. Solar desalination is a promisingly sustainable freshwater production technology. Solar desalination humidification dehumidification process showed the best approach as it is of the highest overall energy efficiency. In this review paper, a detailed study of the previous work is performed on solar humidification dehumidification desalination techniques experimentally and theoretically. Also in this review, different types of HDH systems were mentioned. The review showed that the humidification dehumidification desalination systems are suitable for decentralized demand. On the other hand, capacity of HDH units is not as large as conventional methods or small as solar stills. Finally, this study threw light on the scope of the parameters which have a considerable influence on increasing the freshwater output of the HDH systems as feed water flow rate, air flow rate, and design of the evaporator, condenser, and packing material. A brief economical study and a comparison of the costs per liter are performed for various humidification dehumidification desalination systems presented in this study.

Optimized Operation of a Solar-Driven Thermoelectric Dehumidification System for Fresh Water Production

The work presents a parametric analysis of the performance of a solar-driven thermoelectric system to dehumidify air and produce fresh water. The system is combined with a solar distiller humidifying ambient air to enhance distillate output to meet the specified fresh water needs for a residential application. The presented system is a totally renewable energy-based system taking advantage of the clean solar energy. A model is developed to simulate the air dehumidification process using TEC （thermoelectrically cooled） channels. An optimization problem for setting system operational parameters is formulated to meet the fresh water requirement of 10 liters per day for a typical residential application in the Lebanese coastal humid climate. Using five TEC channels of length of 1.2 m and area of 0.07 - 0.05 m^2 integrated with 1.2 m^2 solar distiller is capable of meeting the water demand, where the air mass flow rate introduced to each TEC channel is optimally set at 0.0155 kg/s. The optimal electrical current input to the TEC modules from the photovoltaic solar panels varied depending on the month and is set at 2.2 A in June, 2.1 A in July and 2.0 A in August, September and October per each TEC module.

4种用于温室除湿的亲水翅片管蒸发器热湿传递性能分析

温室冬季高效除湿需求已经成为制约中国温室产业高质量发展的技术难题之一。为了提高温室用冷冻除湿系统中亲水翅片管蒸发器的热湿传递性能,该研究建立了低温高湿工况下平翅片、带涡产生器平翅片、波纹翅片、开缝翅片4种亲水翅片管蒸发器空气侧的数值传热模型,采用蒸发器的换热量Q、努塞尔特数Nu、摩擦因子f、单位翅片面积析湿量和强化传热因子JF等评价参数,对比分析了低温高湿工况下4种亲水翅片管蒸发器空气侧热湿传递性能。结果表明,与平翅片相比,带涡产生器平翅片、波纹翅片、开缝翅片空气侧的Nu、Q和f均高于平翅片,且开缝翅片的Q和f在相同条件下均最大;4种翅片的f随入口风速的增大而大幅度减小,而相对湿度对f的影响较小;单位翅片面积析湿量均随入口风速和相对湿度的增大而增大,波纹翅片的除湿能力最优;在入口风速1~4 m/s和相对湿度80%~95%条件下,波纹翅片管蒸发器的JF因子平均值最大,其热性能最优;在冬季寒冷地区低温高湿的温室中,推荐选用波纹亲水翅片管蒸发器对温室内空气进行除湿。该研究可为温室低温高湿环境下除湿系统用亲水翅片管蒸发器的设计与应用提供参考。

一种新型溶液除湿空调系统能耗及应用分析

传统空调系统通常采用温湿度联合处理的方式,该方式存在舒适性差、能源消耗大等问题。针对以上问题,提出一种利用复合直接蒸发冷却制冷水的溶液除湿空调系统,该系统可以有效节省功耗,符合节能减排的发展趋势。在研究过程中,以某办公楼为研究对象,利用TRNSYS仿真软件建立该系统,研究其在制冷季7—9月的能耗,分析其节能性及适用性。结果表明:当空调新风系统使用太阳能热水作为再生热源时,总供热能耗为6.1×10^(5)kW·h,总耗功为8.73×10^(4)kW·h。相比于传统空调系统,节能率达到55.2%,为降低空调系统能耗提供了新思路。