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Regeneration of dehumidizers is the most important stage in the working cycle of desiccant system. The lower regeneration temperature will be favorable for the energy efficiency of the whole system. Ultrasonic technology may be a promising method of dehydration applied to the regeneration of desiccant. As a non-heating method, the power ultrasonic...
Contexts in source publication
Context 1
... the sound source can be considered as a point source in a free space, and the sound intensity decreases inversely with the square of the distance from the point source. However, the ultrasonic transducers are usually shaped as horn, paraboloid or ellipsoid. The sound radiation can be regarded as coming from a plane source. According to the Huygens-Fresnel principle [24], the pattern of sound intensity distribution can be schematically illustrated as shown in Fig. 2. The sound intensity is constant within the zone near the sound source (called the Fresnel zone), whereas outside this zone (called the Fraunhofer zone), the sound intensity decreases in the same way as for a point source. The length of the near zone, L, can be approximately determined by Eq. ...
Context 2
... Solid-side. As shown in Fig. 2, the three main transport mechanisms on solid-side are the ordinary, Knudsen and surface diffusion. The ordinary diffusion occurs when the molecules of the gas collide with each other more often than with the pore walls of a porous medium, and the Knudsen diffusion occurs when the gas molecules collide more frequently with pore walls than with each other [28]. For water vapor-air mixtures, the ordinary diffusion coefficient (D ord : m 2 /s) and the Knudsen coefficient (D K : m 2 /s) can be written, respectively, by Eqs. (6) and (7) ...
Context 3
... schematic curves of dehydration under different drying conditions are supposedly shown in Fig. 20. The curve marked with '&' (C1) corresponds to the drying conditions as follows: with ultrasonic radiation (U), t1 in the drying air temperature (RT); the curve with 'd' (C2) to the conditions as follows: no ultrasonic radiation (NU), t2 in the drying air temperature (RT); and the curve with '*' (C3) has the following conditions: no ultrasonic radiation (NU), t1 in the drying air temperature (RT). The other conditions, e.g. the air flow rate and humidity, are the same for all the three ...
Context 4
... possible generalization of a new technology to the practice mainly depends, to a large extent, on its environmental impact and economic benefit. For the environmental impact, the possible harm to human body done by high-intensity ultrasonic radiation must be seriously assessed. Exposure to ultrasound can be either through direct contact, a coupling medium, or the air (airborne ultrasound). Limits for exposure from each mode should be treated separately. In general, direct contact exposure to high intensities of liquid-borne ultrasound is not allowed. So, the limits for human exposure to airborne ultrasound are emphasized. In Grigor'eva's work, the author thought airborne ultrasound is considerably less hazardous to man in comparison with audible sound, and proposed 120 dB be adopted as an acceptable limit for the acoustic pressure for airborne ultrasound [84]. After 2 years, Acton [85] proposed a criterion below which auditory damage and/or subjective effects were unlikely to occur as a result of human exposure to airborne noise from industrial ultrasonic sources over a working day. He based his criterion on the belief that it is the high audible frequencies present in the noise from ultrasonic machines, and not the ultrasonic frequencies themselves, that are responsible for producing subjective effects. He extended this criterion to produce a tentative estimate for an extension to damage risk criteria, giving levels of 110 dB in the one-third octave bands centered on 20, 25, and 31.5 kHz. In his another paper published in 1974, Acton argued that additional data obtained for industrial exposures confirmed that the levels set in the proposed criterion were at approximately the right level, and that there did not seem to be any necessity to amend them [86]. The International Radiation Protection Associa- tion (IRPA) [87] has drafted the first international limits for human exposure to airborne acoustic energy having one-third octave bands with mid frequencies from 8 to 50 kHz, which is shown in Fig. 21 [88]. Measures should be taken to avoid the potential hazards caused by high-intensity ultrasound, e.g. persons exposed to high levels of noise associated with ultrasonic equipment should be protected either by wearing devices like earmuffs, or by acoustic barriers constructed around the equipment to reduce the noise ...
Context 5
... ultrasonic effects in mass transfer processes are influenced by both the intensity and frequency. Intensity is directly related to the energy applied. In order to utilize ultrasonic energy more efficiently, it is necessary to investigate the influence of intensity on the effects of drying process. Garcia- Perez et al. [56] made an experimental study on the convective drying of carrot and lemon peel by applying ultrasound (21.7 kHz) with different levels of acoustic power density (0,4,8,12,16,21,25,29,33 and 37 kW/m 3 ). The effective moisture diffusivities of carrot and lemon peel under different levels of acoustic energy were obtained by this study (see Fig. 11). It shows that the higher intensity in ultrasonic power results in a higher moisture diffusivity in lemon peel. But for carrot, there appears to be a threshold of intensity (about 12 kW/m 3 ) above which the ultrasonic effects on the moisture diffusivity can become significant. Yao et al. [57] have investigated the moisture diffusivity in silica gel (initial moisture ratio is about 0.33) with and without ultrasound under different drying air temperatures. Fig. 12 shows the influence of acoustic power intensity ( f = 26 kHz) on the moisture diffusivity in silica gel. As seen from Fig. 12, the moisture diffusivity increases with increasing power intensity of the ultrasound. The energy-saving rates brought by ultrasound ( f = 21 kHz) with different power inten- sities were also analyzed. The results (see Fig. 13) indicate that within the range from 0 to 60 W, the higher ultrasonic power tends to result in the higher energy-saving rate (ESR) in silica gel regeneration. The ESR brought by ultrasound may be influenced by other factors, e.g. the drying air temperature. As shown in Fig. 13, the ESR drops as the drying air temperature ...
Context 6
... ultrasonic effects in mass transfer processes are influenced by both the intensity and frequency. Intensity is directly related to the energy applied. In order to utilize ultrasonic energy more efficiently, it is necessary to investigate the influence of intensity on the effects of drying process. Garcia- Perez et al. [56] made an experimental study on the convective drying of carrot and lemon peel by applying ultrasound (21.7 kHz) with different levels of acoustic power density (0,4,8,12,16,21,25,29,33 and 37 kW/m 3 ). The effective moisture diffusivities of carrot and lemon peel under different levels of acoustic energy were obtained by this study (see Fig. 11). It shows that the higher intensity in ultrasonic power results in a higher moisture diffusivity in lemon peel. But for carrot, there appears to be a threshold of intensity (about 12 kW/m 3 ) above which the ultrasonic effects on the moisture diffusivity can become significant. Yao et al. [57] have investigated the moisture diffusivity in silica gel (initial moisture ratio is about 0.33) with and without ultrasound under different drying air temperatures. Fig. 12 shows the influence of acoustic power intensity ( f = 26 kHz) on the moisture diffusivity in silica gel. As seen from Fig. 12, the moisture diffusivity increases with increasing power intensity of the ultrasound. The energy-saving rates brought by ultrasound ( f = 21 kHz) with different power inten- sities were also analyzed. The results (see Fig. 13) indicate that within the range from 0 to 60 W, the higher ultrasonic power tends to result in the higher energy-saving rate (ESR) in silica gel regeneration. The ESR brought by ultrasound may be influenced by other factors, e.g. the drying air temperature. As shown in Fig. 13, the ESR drops as the drying air temperature ...
Context 7
... with the square of the distance from the point source. However, the ultrasonic transducers are usually shaped as horn, paraboloid or ellipsoid. The sound radiation can be regarded as coming from a plane source. According to the Huygens-Fresnel principle [24], the pattern of sound intensity distribution can be schematically illustrated as shown in Fig. 2. The sound intensity is constant within the zone near the sound source (called the Fresnel zone), whereas outside this zone (called the Fraunhofer zone), the sound intensity decreases in the same way as for a point source. The length of the near zone, L, can be approximately determined by Eq. ...
Context 8
... Solid-side. As shown in Fig. 2, the three main transport mechanisms on solid-side are the ordinary, Knudsen and surface diffusion. The ordinary diffusion occurs when the molecules of the gas collide with each other more often than with the pore walls of a porous medium, and the Knudsen diffusion occurs when the gas molecules collide more frequently with pore walls ...
Context 9
... But for carrot, there appears to be a threshold of intensity (about 12 kW/m 3 ) above which the ultrasonic effects on the moisture diffusivity can become significant. Yao et al. [57] have investigated the moisture diffusivity in silica gel (initial moisture ratio is about 0.33) with and without ultrasound under different drying air temperatures. Fig. 12 shows the influence of acoustic power intensity ( f = 26 kHz) on the moisture diffusivity in silica gel. As seen from Fig. 12, the moisture diffusivity increases with increasing power intensity of the ultrasound. The energy-saving rates brought by ultrasound ( f = 21 kHz) with different power inten- sities were also analyzed. The ...
Context 10
... diffusivity can become significant. Yao et al. [57] have investigated the moisture diffusivity in silica gel (initial moisture ratio is about 0.33) with and without ultrasound under different drying air temperatures. Fig. 12 shows the influence of acoustic power intensity ( f = 26 kHz) on the moisture diffusivity in silica gel. As seen from Fig. 12, the moisture diffusivity increases with increasing power intensity of the ultrasound. The energy-saving rates brought by ultrasound ( f = 21 kHz) with different power inten- sities were also analyzed. The results (see Fig. 13) indicate that within the range from 0 to 60 W, the higher ultrasonic power tends to result in the higher ...
Context 11
... schematic curves of dehydration under different drying conditions are supposedly shown in Fig. 20. The curve marked with '&' (C1) corresponds to the drying conditions as follows: with ultrasonic radiation (U), t1 in the drying air temperature (RT); the curve with 'd' (C2) to the conditions as follows: no ultrasonic radiation (NU), t2 in the drying air temperature (RT); and the curve with '*' (C3) has the following conditions: no ...
Context 12
... were at approximately the right level, and that there did not seem to be any necessity to amend them [86]. The International Radiation Protection Associa- tion (IRPA) [87] has drafted the first international limits for human exposure to airborne acoustic energy having one-third octave bands with mid frequencies from 8 to 50 kHz, which is shown in Fig. 21 [88]. Measures should be taken to avoid the potential hazards caused by high-intensity ultrasound, e.g. persons exposed to high levels of noise associated with ultrasonic equipment should be protected either by wearing devices like earmuffs, or by acoustic barriers constructed around the equipment to reduce the noise ...
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Citations
... Daou et al. [15] 2006 Demonstration of the feasibility and the energy saving effect of desiccant cooling systems Mei et al. [16] 2008 Techniques, configurations, components, performance improvement for LDAS Yao [17] 2010 Ultrasonic dehydrator for the desiccant regeneration Cheng et al. [18] 2013 Solar regeneration methods for LDAS Mohammad et al. [19] 2013 Liquid desiccant dehumidification systems combined with evaporative cooling technologies Yin et al. [20] 2014 Models, system configurations, component design and renewable energy utilization of LDAS Luo et al. [8] 2014 ...
Liquid desiccant air-conditioning system (LDAS) becomes an attractive option for reducing the energy consumption of conventional air-conditioning systems. Despite lots of published papers on LDAS in various aspects, there is not yet a comprehensive and up-to-date review on the properties of liquid desiccants, while the selection of liquid desiccant plays essential role in the overall performance of LDAS. In this paper, a state-of-the-art review on the properties in regard of energy and environmental performance is delivered for present and potential liquid desiccants, including vapor–liquid equilibrium, specific heat capacity, safety concerns. The current situations and future concerns of liquid desiccant investigation can be obtained, while different kinds of liquid desiccant candidates can be compared and evaluated comprehensively. Existing liquid desiccant of halide salt faces severe drawback of corrosiveness in long-term use. Compared with existing liquid desiccants, the candidates of weak acid salt, ionic liquid and deep eutectic solvent behave low toxicity and friendly corrosiveness, whereas their weak moisture absorption ability, high cost or high viscosity is the bottleneck for further applications. Therefore, the mixture of them can be regarded as a promising candidate in LDAS applications, but the fundamental properties are urged to be measured. The work in this paper provides momentous reference and guidance for the exploration of new liquid desiccant as well as the evaluation of future prospect of LDAS.
... Therefore, all desiccants must be regenerated by a high temperature and low water content air flow, thus allowing these desiccants to resume activity and sustain a higher efficiency. This regeneration /reactivation air can be produced by utilization of solar energy (Angrisani et al., 2011) (Zhang et al., 2017) (Ge et al., 2014) (Dezfouli et al., 2014), local heating, thermal waste heat (Angrisani et al., 2014) (De Antonellis et al., 2012, ultrasonication (Yao, 2010) (Yao et al., 2011), or bioenergy, which are all low-grade energy sources. ...
Desiccant dehumidification systems are thermally regenerated systems that can be used either as standalone or as complementary additives for conventional cooling systems. One of their best competitive qualities is the potential to utilize low-grade heat sources for the regeneration process, thus decreasing electrical power consumption and scaling back the emissions of greenhouse gasses. However, up till now, desiccant dehumidification systems saw limited practical applications, due to their relatively high capital costs and low efficiency. To enhance the commercial competitiveness of desiccant dehumidification systems and expand their fairly tiny niche market, it was necessary to improve the system's performance and reliability and reduce their costs. A detailed discussion of the current designs configurations and the main differences between them may help future researchers to come up with novel, innovative designs, to overcome the system's drawbacks and make them actual viable alternative competitors in the dehumidification market. Consequently, this paper presents and analyzes the development of those configurations in the following three main aspects: packed bed, fluidized bed, and rotating desiccant wheel.
... For instance, LiCl impressive thermal and electric conductivities engender it to be applicable across different regeneration techniques while none-ionic DES are not advisable for electrochemical regeneration like electrodialysis. 121 There are three main techniques for liquid desiccant regeneration 122 : thermal regeneration, non-thermal regeneration, and hybrid thermal and non-thermal regeneration techniques. ...
... Therefore, energy saving capacity of non-thermal regeneration is found to be promising. Ultrasonic regeneration was investigated by Yao et al. 122 where ultrasound power was used for the regeneration of a desiccant solution. It involves solution atomization into droplets of about 40-50 μm to release vapor into the mist chamber as illustrated in Figure 10. ...
Liquid desiccant air dehumidification has gained substantial attention recently due to its attractive energy‐saving capability, high moisture retention, and low regeneration temperature. However, there are still unresolved limitations in liquid desiccant air conditioning systems (LDACs). Among on‐going studies are the search for greener desiccant solvents, high‐performance membrane, and regeneration techniques hybridization. This review discusses up‐to‐date development of the performance influential components of LDACs, such as desiccant properties, regeneration techniques, membranes, energy sources, and hybrid system configurations. The corrosive nature of conventional halide salt solutions, non‐biodegradability and high viscosity property of most ionic liquids necessitate the search for alternative solvents in LDACs. Deep eutectic solvents (DES) properties, such as non‐corrosive, hygroscopic, biodegradable, and low viscosity idealize promising alternative desiccant solutions. Therefore, DES may be usefully explored and further investigated in LDACs to establish the degree of their capacities in replacing conventional desiccants. Non‐thermal regeneration techniques and nanoparticle enhanced membranes were also found to improve the overall energy performance of the LDAC system. Non‐thermal regeneration techniques can operate below 40°C and reduce energy utilization between 10% and 50% in indoor space cooling. The coefficient of performance (COP) of this regeneration category is capable of being as high as 6, which is an indication of its promising energy‐saving propensity.
Highlights
• Review on liquid desiccant materials and the potential of deep eutectic solvents as bio‐desiccants for air dehumidification.
• Nanoparticles enhanced ion exchange membrane tendency to eliminate membrane fouling and improve regeneration performance.
• Non‐thermal liquid desiccant regeneration techniques eliminate re‐cooling energies requirement in LDACs.
... Yao et al. [25] reviewed the studies related to ultrasonic dehydration which are important in regeneration of silica gel dehumidifiers in air conditioning systems. They have discussed mass transfer enhancement by ultrasound in solid-gas and liquid gas systems. ...
The paper presents a brief review of the literature reported over the past six decades on Process Intensification using pulsation and vibration. The review encompasses gas-liquid and miscible as well as immiscible liquid-liquid systems operating in batch, semi-batch and continuous flow mode. In the paper, pulsations have been categorized as imparted to the system through mechanical vibration, ultrasound and thermally induced pulsation. Modes of mechanical vibration include flow pulsation, vibration of the entire device and vibration induced through coils and inserts. The effects of the above techniques on mixing, mass transfer, heat transfer and flow hydrodynamics have been summarized. The studies discussed herein contribute directly or indirectly to enhanced process and energy savings. The grey areas identified in the “Conclusion section” is expected to assist in enriching the research on process intensification by the application of pulsation and vibration.
... Previous research uncovered that ultrasonic waves are able to be applied to reduce energy consumption and improve efficiency in various industries. A frequency range of 20 to 40 kHz activates the liquid's bonding breakage, and bubbles are formed from the cavitation phenomena, which affect the mechanical properties and chemical substances [24][25]. This form of energy is widely used in optimizing the efficiency of the extraction of various substances [26][27] and can be applied to emulsification processes [28]. ...
This report presents a study on the use of ultrasonic waves in solar ethanol distillation to investigate the performance of
ultrasonic waves at a frequency of 30 kHz and at 100 Watts that were installed in the inlet area of a 10-litre distillation tank.
Based on the non-continuous distillation process (batch distillation), the experiment demonstrated that using ultrasonic waves
in solar ethanol distillation caused the average concentration of hourly distilled ethanol to be higher than that of a normal
system (solar ethanol distillation without ultrasonic wave) at the same or higher distillation rate and hourly distillation volume.
The ultrasonic wave was able to enhance the separation of ethanol from the solution (water-ethanol mixture) through solar
distillation. The amount of pure ethanol product from each distilled batch was clearly larger than the amount of product
obtained from a normal system when the initial concentration of ethanol was lower than 50%v/v (% by volume), where an
average of approximately 40% and 20% are obtained for an initial ethanol concentration of 10%v/v and 30%v/v, respectively.
Furthermore, the distillation rate varied based on the solar radiation value.
... The smaller the diameter of desiccant droplets, the higher the contact surface area between desiccant solution and air streams, and thus the higher the mass transfer coefficient. It can be seen from Fig. 14(b) that the mass transfer coefficient of a LiBr desiccant solution droplet in an air stream of 40°C increases with the decrease of the liquid droplets diameter, with significant increase when the diameter decreases below 50 μm [142]. ...
... A conceptual schematic diagram for an ultrasonic-atomization dehumidifier ([60]), and (b) the relation between the mass transfer coefficient and diameter of liquid droplet[142]. ...
The air conditioning market has witnessed a significant development in liquid desiccant air conditioning (LDAC) technologies over the past few decades. Many previous studies have confirmed that technical and economical deficits associated with conventional air conditioning systems can be eliminated using LDAC technologies. As a result, LDAC technologies – both equipment and systems – have become hot topics for research, which has resulted in hundreds of research papers in the scientific literature. The objective of this paper is to present a comprehensive overview of LDAC equipment and systems, and to identify gaps in the literature to be considered by future research.
... Therefore, the efficiency of thermal regeneration is limited. Yao [15] described the basic idea of a ultrasonic dehydrator for liquid desiccant regeneration. This non-thermal regeneration method can potentially improve the energy efficiency of the liquid desiccant dehumidification system due to the lower regeneration temperature. ...
... This non-thermal regeneration method can potentially improve the energy efficiency of the liquid desiccant dehumidification system due to the lower regeneration temperature. However, Yao [15] also acknowledged that the ultrasonic regeneration may bring environmental hazard issue and the energy savings due to the use of the ultrasonic regenerator for liquid desiccant were not reported. Al-Sulaiman et al. [16] studied the reverse osmosis (RO) process for regenerating calcium chloride liquid desiccant in a cooling system with two-stage evaporative coolers. ...
This study evaluates the potential of using electrodialysis (ED) technology to regenerate the aqueous lithium chloride (LiCl) solution, a commonly used liquid desiccant in liquid desiccant air conditioning (LDAC) systems. Experiments were performed using an ED system with ten cell pairs of ion-exchange membranes. A range of tests were carried out to examine the effects of the circulation flow rate, supplied current density, solution initial concentration and the concentration difference between the regenerated and spent solutions on the performance of ED for regenerating LiCl liquid desiccant solutions. The results showed that the regeneration capability of the ED stack decreased with the increase of the circulation flow rate. Regeneration performance in terms of the concentration enrichment increased as the supplied current density increased and the solution initial concentration decreased. It is also shown that the concentration difference between the regenerated and spent solutions is critical for the regeneration performance of ED. The ED stack can continuously increase the concentration of the regenerated solution when the concentration difference between the regenerated and spent solutions is below 5.86% (wt/wt), under the supplied current density of 57.1 mA/cm2, circulation flow rate of 100 L/h, and the initial concentrations of the solutions in the regenerated and spent tanks of 28.77 and 23.96% (wt/wt), respectively. The current efficiency of the ED in two hours running for all experiments was in the range of 55.17-73.54%. The results obtained from this study would be useful for the ED regenerator design and system integration.
... These enhanced effect of ultrasound in the field of power ultrasound is due to the cavitation phenomena [17]. Acoustic cavitation is defined as the formation of gas-filled micro-bubbles or cavities in liquid once the pressure of the spot decreases below the saturation vapor pressure of the dissolved gas in the liquid [18,19]. The growth and collapse of these cavities (micro bubbles) under proper conditions create drastic local conditions (high temperature and pressure). ...
... Also, ultrasound produces cavitation, which generates high-frequency vibration and decreases the thickness of the boundary layer (Zhi et al. 2007). Furthermore, ultrasound produces disturbance heat radiation and thus increases the water concentration gradient and water diffusion coefficients (Yao 2010). During the drying process, water at the wood surface should move through the boundary layer by diffusion and then evaporate to the drying media. ...
Ultrasound was applied to enhance mass transfer within the boundary layer during wood vacuum drying. Fast growing poplar (Populus tomentosa) was used as the specimen in this work. The water migration rates and the mass transfer coefficients were studied at temperatures of 35 and 50 degrees C, absolute pressures of 0.03, 0.06, and 0.1 MPa, and ultrasound power-frequency groups of 60 W-28 kHz, 100 W-28 kHz, and 100 W-20 kHz, respectively. The results indicated that ultrasound could markedly increase the water migration rates within the boundary layer. The water migration rates increased with increasing ultrasound power and frequency. The mass transfer coefficients within the boundary layer for specimens treated with ultrasound were much higher than those of the control group, and the mass transfer coefficients increased with decreasing absolute pressure. Ultrasound could be applied in the wood drying industry as a means of saving time and energy.
... Meanwhile, a part of the ultrasonic energy is directly adsorbed and bring about a temperature rise ("heating effect") in drying material, which increases the water vapor pressure in the evaporation zone. The respective contribution to drying enhancement of these two effects and additionally a "synergistic effect" will be discussed in this paper to help further understanding the mechanism of drying enhancement brought by ultrasound [20][21][22][23][24] . ...
... This model was validated by experimental data, and the estimated in this way material coefficients enabled estimation of the contribution ratio of "vibration effect" and "heating effect". It can be stated that the drying efficiency 24 increases mainly owing to special "vibration effect" and owing to "heating effect" involved by ultrasounds. This is a very positive outcome as far as it concerns drying of temperature sensitive biological materials. ...
The aim of this work is to promote ultrasound as an energy source that is suitable for the enhancement of drying processes, and in particular of biological materials. The study aims at a more profound recognition of the interaction between ultrasonic (US) waves and the tissues of fruits and vegetables, which may contribute to an intensification of moisture removal during their drying. Absorption of acoustic energy causes heating and structural changes of the drying material due to a series of rapid material compressions and decompressions. The research hypothesis is based on the expectation that the ultrasound waves may enhance moisture removal from the fruits and vegetables during drying due to a special “heating effect”, “vibration effect”, and “synergistic effect”. Convective ultrasonic-assisted drying tests were conducted experimentally on a new hybrid dryer with ultrasonic equipment, and the effects of ultrasonic enhancement by drying are presented based on a drying model and assessed numerically.
