Humidification Process Research Articles

Exploration on mechanical test method of improved loess under dry-wet cycles

The stability of loess subgrade is affected by many factors. Dry-wet cycle is a common factor that causes damage to the strength of loess subgrade. In order to study the influence of dry-wet cycle on the stability of loess subgrade, reveal the mechanism of dry-wet cycle damage to the strength of loess subgrade It is necessary to sample the loess soil samples in this area, and perform compaction test, dry-wet cycle test, unconfined compression test and scanning electron microscope test on the soil sample to analyze the influence of dry-wet cycle on the strength and microstructure of loess soil. . In this way, the potential relationship between the microstructure and the strength of the soil can be obtained. The results show that the loess drywet cycle causes the loess's tensile strength and compressive strength to decrease with the increase of the number of dry-wet cycles. The dry-wet cycle effect gradually reduces the shear structural strength of the undisturbed loess and eventually disappears. Scanning electron microscope tests found that the humidification process caused slight movement of the particles, while the drying process resulted in permanent deformation of small pores.

Experimental Investigation of a Small Scale Humidification Dehumidification Desalination Unit

A psychrometric energy process desalination unit has been experimentally tested. The system is based on humidification and dehumidification process where seawater is heated and then sprayed to humidify the incoming air in the humidification chamber. The humidified air enters the dehumidification chamber and is cooled by the incoming cold seawater. The moisture is condensed out and the pure water is accumulated at the base of the chamber, and the dehumidified air is discharged to the outside. The seawater was heated to temperature between 60 - 90°C using a 2.4kW electric heater. Performance data on temperature, seawater mass flow rate, air flow rate and the amount of fresh water produced were obtained, and the maximum coefficient of performance (COP) of the system was calculated based on the data obtained. The result achieved indicates the system had a maximum fresh water production of 13kg/h with a maximum COP of 3.6. The initial test shows that the system has great potential with room for improvements and further optimisation.

Performance Improvement of Membrane Energy Exchanger Using Ultrasound for Heating, Ventilation, and Air Conditioning Application

Abstract Air conditioning (AC) systems consume the maximum proportion of the total electricity used in the building sector. The demand for AC systems is expected to increase exponentially in the coming years due to various reasons such as climate change, and an increase in affordability and living floor space. A membrane-based liquid desiccant AC system along with energy recovery ventilating equipment is considered as a prospective alternative to the conventional air conditioning system (CACS). It has the potential to meet the increasing current and future AC demand in a sustainable manner. Its efficiency and energy-saving potential with respect to CACS depend on the performance of the membrane-based dehumidifier, regenerator, and energy recovery ventilating equipment, commonly referred to as membrane energy exchangers (MEEs). MEE is an indirect exchanger type in which a membrane separates the working streams. This intermediate membrane creates an additional resistance for the heat and mass transfer processes in the MEE. To reduce the resistance, this study experimentally and numerically investigate the influence of ultrasound on the performance of the MEE for dehumidification, humidification (applicable for membrane-based evaporative cooling and desiccant regeneration devices), and energy recovery processes. It is found that the vibration due to ultrasound has the potential to improve the mass transfer performance of MEE by the resistance at the air-membrane interface.

Effects of salts and its mixing ratio on the corrosion behavior of 316 stainless steel exposed to a simulated salt-lake atmospheric environment

The effect of mixed salts and mixing ratio on the corrosion behavior of 316 stainless steel exposed to a simulated salt-lake atmosphere has been firstly investigated. 316 stainless steel was mainly analyzed by the evolution of surface morphologies, composition of corrosion products, statistics of pits depth and width and electrochemical measurements. The results indicated a layered double hydroxides (LDH) was detected in the corrosion products formed on 316 stainless steel surface under different salt deposition conditions, except under single NaCl deposition condition. When the mole fraction of NaCl was 0.75 in mixed MgCl2 – NaCl salts, the corrosion rate of 316 stainless steel was the fastest. The width of the pits formed on the surface of 316 stainless steel under mixed MgCl2 - NaCl salts deposition conditions was smaller than that under single MgCl2 deposition condition. The differences in corrosion rate and pit width size of 316 stainless steel under mixed MgCl2 - NaCl salts deposition conditions and single MgCl2 deposition condition were related to diffusion barrier provided by the neighboring NaCl crystals precipitated in thin liquid film during the humidification process and dehydration process.

Research on the effectiveness of the key components in the HAT cycle

Humid Air Turbine (HAT) cycle is considered to be one of the most advanced gas turbine cycles due to its high efficiency, flexible operation, low NOX emissions, and low investment cost. The heat recovery determines the temperature field distribution of the humidification process, which is critical to the performance of the HAT cycle. However, so far, the effect of heat recovery of heat exchangers on cycle performance is still a research gap. Filling up the research gap is of great significance to the full utilization of the thermodynamic potential of the HAT cycle. This paper built a humid air turbine cycle with additional heat exchangers (aftercooler, regenerator, economizer) based on a humid air turbine test rig. A comprehensive thermodynamic analysis of the effectiveness of the heat exchanger components had been carried out. To conclude, the water–air ratio, aftercooler effectiveness and regenerator effectiveness can effectively affect the humidification performance and efficiency. The above analysis provided a theoretical reference for the actual transformation and performance enhancement of the test rig. In addition, research on the influence of the water–air ratio on the HAT cycle at different power outputs showed that the optimal water–air ratio gradually decreases with the increase of power output. The effect of the pressure ratio on the HAT cycle was clarified by comparison with a simple regenerative cycle. Finally, exergy analysis of the HAT cycle was carried out based on different optimization strategies. For the humid air turbine of 4 MW-class, increasing recuperator effectiveness is one of the effective techniques to enhance exergy recovery as well as efficiency, and improving the proportion of exergy utilized for water evaporation can augment specific work output. The maximum efficiency of 48.5% was obtained where its corresponding exergy efficiency reaches 44.4%. The maximum specific work output of 560.6 kJ/kg was achieved with an exergy efficiency of 38.0%.

Coupling effect of key parameters of heat recovery components on the HAT cycle performance

Humid Air Turbine (HAT) cycle that uses a water-air mixture as a working fluid has a significant advantage in the distributed generation technologies and combined heat and power. The feature of the HAT cycle is that air humidification is carried out at a variable temperature. This cycle is considered as one of the optimal humidified gas turbine cycles to achieve the energy cascade utilization. However, most studies typically use the method of a single variable to investigate the coupled process of humidification and heat recovery, which limits the further performance improvement of the HAT cycle. Herein, we study the interactions among air humidification, heat recovery and system performance to elaborate the effects of interactive variables on the HAT cycle performance. Considering the complexity of the interaction of water-air ratio, aftercooler effectiveness and recuperator effectiveness, a thorough numerical analysis was carried out from the following perspectives: the thermodynamic correlation between components and systems was investigated by controlling a single parameter; the interaction of multiple variables was performed with identical turbine inlet temperature (TIT) and pressure ratio (PR) conditions; and the coupling relationship between interactive variables with a variation of TIT and PR conditions. A thorough analysis revealed that the variables that significantly impact the HAT cycle efficiency are successively RE, W/A, and AE. The analysis of the coupling effects of interactive variables under different TITs is consistent with the above results. As the PR increases, the W/A and AE have a more significant effect on HAT cycle efficiency and the effect of RE on the HAT cycle efficiency greatly diminishes. The HAT cycle efficiency, specific work output, and heat recovery achieved 43.9%, 556 kJ/kg, 5505.33 kW, where its corresponding TIT, PR, W/A, AE, RE values are 1280 °C, 8, 1.5,0.75, 0.9, respectively. Overall, a thorough analysis of interactive variables is of great significance to fully understand the effect of heat recovery on the efficiency enhancement and specific work output improvement from the thermodynamic perspective.

Sustainable Energy Techniques Adapted in Buildings to Regulate Moisture Transport and Enhance Thermal Comfort: A Review

Heating ventilation air conditioning (HVAC) design mainly deals with moisture and its control. The moisture may be present inside ducts, conditioned spaces, or outdoors. The process of humidification and dehumidification requires equipment for mass and heat transfer, where the transfer of energy and mass takes place at varying concentrations and temperatures. The exchange of mass or heat depends on the type of flow and is conceivably in the form of gas to liquid or liquid–vapor. This paper aims to review the effect of moisture in the buildings and modulate its effect with several humidifying and dehumidifying techniques as sustainable techniques depending upon the external weather conditions to maintain thermal comfort. Various humidification and dehumidification techniques have been discussed with both their merits, limitations, applications and future scope to meet sustainable energy demands.

Multidisciplinary approach as a key for paleoenvironmental interpretation in a Weichselia-dominant interval from the late Aptian Codó Formation (Parnaíba Basin, Brazil)

The presence of the fern Weichselia in a restricted sedimentary interval of a drilling core in the Parnaíba Basin (Brazil) was used as a lead for paleoenvironmental interpretation integrating paleobotanical, palynofacies, palynological, organic petrography and clay mineralogy analyses. The fern paleobiogeography was amplified and its association with terrestrial bryophyte gametophytes (Muscites) indicated depositional conditions corresponding to marginal areas of freshwater bodies subjected to frequent flooding under the general fluvial-deltaic conditions so far accepted for the intermediary portion of the Codó Formation. The high dominance of non-opaque phytoclasts and very scarce autochthonous non-marine palynomorphs pointed to a shallow water body linked to marginal areas of fluvial systems in the river outlets, channel margins in estuarine systems, and/or shallow floodplain lakes connected/open to fluvial canals. The very scarce marine palynomorphs (dinoflagellate cysts) suggest a limited influence from unstable environments on coastal margins or estuarine canals. The terrestrial vegetation surrounding the depositional setting, deciphered by palynological analysis, reflected distinct environmental conditions prevailing simultaneously in 1) humid areas dominated by fern communities, and 2) dry-xerophytic areas dominated mainly by Araucariaceae and Cheirolepidiaceae gymnosperms, both as components of a wider Aptian paleoenvironment within the periequatorial latitudes in South America. The results were supported by clay mineralogy that showed abundance of detrital kaolinite over montmorillonite and suggest the dominance of a climatic humidification process and a less expressive semiarid climate in a regional context.

Oral Hygiene Care to Prevent Ventilator-Associated Pneumonia in Critically Ill Patients.

Oral Hygiene Care to Prevent Ventilator-Associated Pneumonia in Critically Ill Patients.

Experimental Evaluation of PVA as Novel Humidifier Material for Humidification-Dehumidification Applications

Abstract The humidification-dehumidification (HDH) desalination technique is a promising technology to harness fresh water, resulting in a decline of scarcities of remote and arid area water. The humidifier unit is one of the major functional elements in an HDH desalination system. The efficiency of any HDH desalination system predominantly depends on the individual humidification and dehumidification process potential. Therefore, improvement in the humidification (or) dehumidification process potential can substantially improve the system’s overall performance. In this work, an attempt has been made to utilize polyvinyl alcohol (PVA) as novel humidifier material for the humidification process. The experimental study was carried out considering diverse inlet air velocities of 3, 2, and 1 m/s. Different cases with and without air preheating were experimented to evaluate the humidification potential of PVA material when utilized in an HDH desalination system powered by waste heat and ambient conditions. The results revealed that the rate of evaporation from PVA material was predominantly influenced by the ambient air temperature compared with other system parameters. Furthermore, comparatively, it was found that, with the use of PVA as humidifier material, average increases in relative humidity of about 19 and 10 % were achieved for higher air velocity of 3 m/s in the cases with and without air preheating, respectively. Thus, it was identified that PVA can be utilized as an effective humidifier material for efficient humidification processes in HDH desalination systems.

A study on vapor transport characteristics in hollow-fiber membrane humidifier with empirical mass transfer coefficient

Proton exchange membrane fuel cells are used in vehicles as a power source that generates electrical energy from hydrogen fuel and oxygen. Proton diffusion through the membrane module requires a certain level of water content in the supply air to maintain its performance. Therefore, water management plays an essential role in fuel cell operation. For large cells, external humidifiers are commonly installed to deliver the desired amount of water to the reactant gasses. This study investigated the performance of a hollow-fiber membrane humidifier through water transport in the membrane module using a mass exchanger model and various operating variables. In the humidifier, water particles from the high-concentration side, or wet air flow, transfer through the membrane to the dry air flow, which has a lower concentration rate. The vapor transport depends on the membrane's physical characteristics and the flow properties on both sides. These influences are represented by a parameter called the overall mass transfer coefficient, which is estimated by experiments. Then, the effectiveness–NTU (number of transfer units) approach is employed to analyze the mass transfer in the humidifier as a mass exchanger model. The analogy between heat transfer and mass transfer helps in applying the traditional effectiveness–NTU method from heat transfer analysis to a mass transfer analysis with additional information from experiments. In this study, a best fit equation is generated from experimental data and employed mass transfer calculations at varying temperatures, humidities, and flow rates. The results suggest that the wet air's relative humidity is the most crucial operating parameter that influences the dry air humidity. The dry air flow rate has more significant effects on the humidification process than the wet flow. In the case of geometric parameters, the length, number of membranes, and type of arrangement are discussed.

Regularities of distribution of the relative air humidity in the volume textile fiber material in the production of yarn

Methods for calculating the moistening of textile fibers in the process of yarn production when processing with conditioned air with certain technological parameters based on mathematical modeling and numerical methods are presented. There are appropriate mathematical models, adequately describing the process of distribution of the relative air humidity in the porous medium under consideration. A mathematical model of the process of moistening porous of a textile material in the form of the Cauchy problem for a second-order differential equation for the purpose of numerical modeling of the change in the relative humidity of conditioned air in the volume of a compactly formed semi-finished product of textile production. The classical instability of the problem is shown, methods of its solution are considered, the problem is numerically solved for various options of technological conditions for organizing the humidification process. Numerical calculations have shown that the relative humidity of the air flow decreases monotonically with distance from the surface to a certain limiting value. At the same time, an increase in the specific surface area of a capillary-porous medium leads to a more intense drop in the relative humidity of the conditioned air in a moving air stream. The results of numerical studies show that with an increase in the flow rate of conditioned air, the depth of penetration of moisture into the volume of a porous medium increases, i.e. more moisture settles on the last layers of the volume. Consequently, to optimize the process, one should choose an air flow rate that provides a sufficient intensity of material moistening with deep penetration of moisture into the volume of a porous medium. Mathematical models of changes in the air flow rate in the volume of a porous medium according to linear and exonential laws are presented. It is shown that taking into account the drop in velocity according to the exponential law allows one to obtain good agreement between the calculated and experimental data. Physical and mathematical modeling of the non-stationary process of moisture distribution in a textile material during its humidification with conditioned air for the case of diffusion kinetics of the humidification reaction in the form of a boundary value problem for the diffusion equation has been carried out. On the basis of physical concepts of the processes occurring at the boundary of a porous medium and in its volume, modeling equations and boundary conditions for the problem of calculating the unsteady distribution of moisture in a porous medium are formulated.

The Effect of Electrode Moisture and Polarity On SMAW Welding of Low Carbon Steel

Welding using moist electrodes and the choice of polarity is expected to affect the defects that usually arise in the welding results of ST 37 low carbon steel. To find out how big the influence of electrode humidity and polarity on defects in low carbon steel welding results, a study was carried out using fluid as an electrode moisturizing element. The electrode humidification process is carried out by allowing the electrodes to be contaminated by humidity for 3 days, 6 days and 9 days, before welding the base metal. After welding with these electrodes, metallographic testing is carried out to observe the macrostructure and microstructure of the welding results. From the test results, it is found that the humidity of the electrode does not affect the defects that arise in the welding results of low carbon steel as long as it does not damage the flux of the electrode.

Comfort rules for face masks among healthcare workers during COVID-19 spread.

The outbreak of Coronavirus disease 2019 (COVID-19) made imperative the use of protective devices as a source control tool. As there is no definite antiviral treatment and effective vaccine, the only efficient means of protecting and mitigating infectious contagion has been the use of personal protective equipment, especially by healthcare workers. However, masks affect the humidification process of inhaled air, possibly leading to a basal inflammatory state of the upper airways. This is a single-center observational study conducted at the University Hospital of Catania from April 1, 2020, to June 31, 2020. We analyzed the role of protective masks on the elimination of upper airways complaints in healthcare workers of the University Hospital of Catania. We evaluated 277 subjects through a self-administered 17 item questionnaire based on respiratory, work performance and health-related quality of life domains. A higher prevalence of nasal and ocular symptoms, perceived reduced work performance, difficulty in concentrating, and sleep disorders were found. After two weeks adhering to a list of good practices that we recommended, significant reversibility of the symptoms investigated and work performance enhancement were observed. Despite clinical complaints related to personal protective equipment, effective amelioration through usage rules is easily obtained. Given the essential use of protective masks, healthcare workers have to adhere to appropriate work and safety prevention rules.

Numerical investigation on supersaturation phenomenon of humid air in the humidification process

In order to improve the safety and stability of pneumatic equipment, in this paper, the supersaturation phenomenon of humid air and its formation, evolution mechanism during the humidification process, are revealed and evaluated in detail with the defined evaluation criterion. In term of the finite difference method, the integrated mathematical models for humidification process are established, considering the unsaturated, saturated and supersaturated state of humid air. The influence laws of the specified critical parameters on the supersaturation characteristics of humid air are obtained at off-design conditions. The simulation results first reveal that the effects of specific surface area of porous media on the supersaturation phenomenon is affinitive with the liquid-gas ratio. It is found that a lower value both of inlet water temperature and inlet relative humidity will slightly weaken the entrainment ratio, while the inlet air temperature has a significant reaction to it, with a minimum value of 1.5 × 10−3 kgkg−1 at the conditions of Twi = 70°C, φi = 0.5 and Tai = 30°C. It is also obtained that raising the inlet wet-bulb temperature is effective to reduce the entrainment ratio. Furthermore, in the process of the development of supersaturation phenomenon, the entrainment ratio increases rapidly at the humid air outlet for all the cases, which are of great value for humidity control in aerodynamic systems.

Performance evaluation of a solar and vacuum assisted multi-stage humidification-dehumidification desalination system

This study compares the freshwater productivity of a three-stage vacuum humidification-dehumidification (VHDH) desalination system to a single-stage VHDH system. Experimental study on a multi-stage humidification in sub-atmospheric pressure condition confirmed its superiority over previous multi-stage humidification-dehumidification processes. The variation of the desalination rate was measured experimentally using the three-stage vacuum humidification and heating modes. The results showed that the maximum desalination rate of the unit was 1.8 kg.h−1 per 1 m2 of solar water heater area with minimum specific power consumption (SPC) of 0.1 kW h.kg−1 when the maximum solar intensity was 1106 W.m-2 in July 2020. This investigation indicated that the system had high freshwater productivity and low SPC compared to a single-stage VHDH system. The system performance was improved when the operation was further optimized using the response surface methodology (RSM). The optimal values of saline water to air mass flow rate ratio (sw/a) and humidifier pressure (PH) of 1.77 and 33 kPa led to the maximum freshwater productivity. In all operating conditions, through converting the single-stage humidification to two-stage and three-stage humidification processes, the humidity ratio was enhanced by about 51 % and 19 %, respectively. The optimal freshwater productivity could be realized only when multi-stage vacuum humidification was utilized at isothermal heating mode in all stages and the cost was $0.002 per liter.

Effectiveness of a built-in air duct desalination machine with absorption process

Because there is no mature potable desalination machine specifically designed to provide a sustainable water supply to vessels, this paper proposes a built-in air duct desalination machine based on humidification and dehumidification processes. The machine is powered by waste heat exhausted from the vessel’s diesel engines. The humidifier and dehumidifier are stacked so that the structure is compact. The dehumidification process is fulfilled based on the freshwater absorption process. The operating principle and structural design of the machine are introduced. A series of steady state experiments are conducted to assess the effects of heating temperature, hot seawater spray flow rate, and cold water spray flow rate on freshwater production and gained output ratio. The results show that the machine can obtain a freshwater productivity of 19.6 kg/h with gained output ratio of 0.53 when the heating temperature is 90 °C, the hot water spray flow rate is 1 t/h, and the cold water spray flow rate is 1.2 t/h. The freshwater production per volume unit per hour can reach up to 10.5 kg/(m3h). Owing to its superimposed structure, the rising driving force of the water vapor can be fully utilized, and 60% of the normal water productivity can be achieved when the fan is turned off.

Usage of solar greenhouse evaporator to enhance dehydration and potable water extraction from tannery effluent

The main objective of the present work is to treat tannery effluent with a total dissolved content of 150 g/L using solar energy by humidification and dehumidification process using a roof even type greenhouse evaporator. This system not only helps to effectively treat the tannery effluent by increasing its total dissolved solids content to 350 g/L but also helps to generate potable water from tannery effluent by using solar energy. In this study, the performance of the effluent was tested in six different modes. It was found that the tannery effluent total dissolved solids content increased to 350 g/L in just 2.5 days when the greenhouse evaporator was operated in Mode 6 which is the shortest duration when compared to other modes of operation. The specific fuel consumption of the roof even type greenhouse system to treat tannery effluent is 22.55 kW h/ m3 which is 8.3 % of the energy consumed by the zero liquid discharge plant. Meanwhile, the land area required to dehydrate 1 m3 of tannery effluent got decreased by 43 % when the roof even type greenhouse evaporator was used.

Study of loose bulk cargo storage conditions and water transportation

When transporting such cargos as mineral fertilizers by water, they absorb moisture, which stimulates cargo self-heating and ultimately leads to dangerous temperature limits. When transporting ANP fertilizer in holds, its equilibrium moisture content can change significantly, which can lead to the cargo damage. The article presents the findings on the processes of hydrothermal moistening of porous bodies on the example of ANP fertilizer associated with the phenomena of sorption and desorption. There is no analytical description of moistening processes of porous bodies associated with these phenomena in the scientific literature. The optimal conditions for storage and transportation of bulk materials have been determined on the example of ANP fertilizer transported through the Novorossiysk seaport. As a result of the study, the moisture content intervals associated with various types of absorption were established. Thus, in the range of ⱷ from 0% to 16% moisture content, monomolecular adsorption prevails, which corresponds to the normal moisture content of ANP fertilizer. In the range of ⱷ from 16% to 54%, polymolecular adsorption predominates, and at the value of ⱷ greater than 87%, a smooth transition from predominantly polymolecular adsorption to capillary condensation occurs, which will negatively affect the process of humidification and cargo caking.

Desalinated water and hydrogen generation from seawater via a desalination unit and a low temperature electrolysis using a novel solar-based setup

This study investigates the proficiency of employing solar energy in a novel setup geared towards simultaneous production of desalinated water and hydrogen wielding parabolic trough solar collectors (prime mover) in three solar radiation approaches; low radiation, high irradiation and no radiation. Targeted for coastal areas, this setup generates electricity using an organic Rankine cycle; utilizing its waste heat, a desalination unit applying humidification and dehumidification processes, yields desalinated water. Subsequently, hydrogen is produced through exploiting a proton exchange membrane electrolyser as a low temperature electrolyser fed by electricity and water. One of the cardinal points of this system is the production of hydrogen by means of electricity and desalinated water obtained from previous stages. With the purpose of determining the efficiency of this setup, a parametric study has been conducted grounded on the effect of important parameters on production rates and different efficiencies. Ensuing, multi-objective optimization is set forth by implementing a genetic algorithm in order to effectuate the optimal design state. The results indicated that the desalination rate in the three solar radiation approaches mentioned are 1.76 kg/s, 1.07 kg/s and 1.36 kg/s, respectively, and the hydrogen production rate are 4.33 g/s, 2.62 g/s and 3.54 g/s, correspondingly.