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The effects of the air-to-dehydrated desiccant mass flow rate ratio in the dehumidifier on the performance of the liquid desiccant air-conditioning system.
Source publication
This paper is concerned with performance investigation and comparison between two novel configurations (type A and type B) of liquid desiccant air-conditioning system driven by low grade thermal energies. Both of these configurations, compared with other liquid desiccant systems, may have some outstanding advantages: leading to improved indoor air...
Contexts in source publication
Context 1
... the analysis of Section 5.5, we change the mass flux of air m a in the dehumidifier while keeping the other variables stable. Fig. 8 shows the effects of changing the m a /m d in the dehumidifier on system performances of both the two type configurations. Fig. 8(a) describes that the t 10 and d 10 of both the type A and type B configurations rise with the increase of the m a /m d in the dehumidifier. One of the two main reasons is that the moisture content absorbed ...
Context 2
... the analysis of Section 5.5, we change the mass flux of air m a in the dehumidifier while keeping the other variables stable. Fig. 8 shows the effects of changing the m a /m d in the dehumidifier on system performances of both the two type configurations. Fig. 8(a) describes that the t 10 and d 10 of both the type A and type B configurations rise with the increase of the m a /m d in the dehumidifier. One of the two main reasons is that the moisture content absorbed by the solution increases with the rise of m a in dehumidifier, which results in the decrease of the concentration of the outlet ...
Context 3
... Fig. 8(b), one can see that the Q cd of the two type configurations increases with the rise of the m a /m d in dehumidifier. The Q cd of the two type configurations is approximately equal, due to the very small discrepancies of both the t 10 and d 10 between the type A and type B configurations. One can also see that the COPs of the two type ...
Context 4
... solution (state 4) is used to preheat the weak solution (state 1), making the temperature of state 2 of type B configuration lower than that of type A configuration. As a result, the difference between t 2 and t 3 increases, the Q gen absorbed by the weak solution in the heater of type B configuration is larger than that of type A configuration. Fig. 8(c) describes that the Ex Qcd of the two type configurations increases with the rise of the m a /m d in the dehumidifier. That is because although the humid air exergy difference between the supply air and ambient air decreases, the m a increases rapidly, then the product of m a and the humid air exergy difference increases. Because the ...
Context 5
... the discrepancies of both the t 10 and d 10 between the type A and type B configurations are very small, the Ex Qcd of the two type configurations is approximately equal. From Fig. 8(c), we can also see that the h LD of the two type configurations rises as the m a /m d in the dehumidifier increases. When the m a /m d in the dehumidifier is above 6.16, the h LD of type A configuration is more than that of type B configuration. ...
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Citations
... The results demonstrate the technology's potential and clarify specific recommendations for using such systems. The performance of two unique liquid desiccant air-conditioning system configurations (types A and B) powered by low-grade thermal energy is investigated and compared in the research by Tu et al. [37] . Compared to other liquid desiccant systems, both of these arrangements may have some notable benefits, such as better indoor air quality, a small footprint, and efficient use of space exhaust air to chill the process air. ...
Air conditioning systems have become an integral part of society, and their utilization is increasing day by day.
Most air conditioning systems use the vapor compression refrigeration (VCR) principle, which is a 190-year-old
technology and has undergone significant changes to improve its performance and efficiency. However, the
major drawback of VCR is its high energy consumption and use of highly polluting refrigerants. In this 21st
century, energy conservation and environmental protection are the need of the hour. To mitigate the challenges,
the search for alternative cooling systems that are eco-friendly and have less energy consumption is gaining wide
attention. Liquid desiccant systems are gaining popularity due to less energy consumption and being ecofriendly. Therefore, this study attempts to review the recent developments in liquid desiccant technology by
focusing on internal cooling strategies. As the internal cooling improves the overall performance of the liquid
desiccant by controlling the liquid temperatures. Therefore, this review highlights the various methods, configurations and mathematical simulations in internal cooling, which are less explored in the available literature.
... The effectiveness of systems using liquid desiccant dehumidification followed by direct and indirect evaporative cooling systems was studied by Abdalla and Kamal [24]. Tu et al. [25] and Tu and Ren [26] investigated liquid desiccant dehumidification followed by evaporative cooling systems. Woods and Kozubal [27] conducted sensitivity and parametric analysis to find key design parameters using a numerical model and found an existing compromise between the coefficient of performance and dimensions of a liquid desiccant-based M-cycle airconditioner. ...
Air-conditioning of buildings is more energy-consuming with widely used vapour compression refrigeration systems in hot and humid areas. Alternatively, evaporative cooling does not show much effect in sultry regions because of increased humidity despite the minimum energy consumption. Indirect evaporative cooling is a promising alternative to direct evaporative cooling systems, but it suffers from low cooling effectiveness and is unsuitable for highly humid regions. Considering the above facts an alternative liquid desiccant-assisted modified M-cycle cooling system is proposed and examined numerically in the present work. The proposed cooling and dehumidification system is a simple unit incorporating chemical dehumidification and regenerative evaporative cooling in a single unit. A simultaneous heat and mass transfer model is developed for the numerical analysis. The numerical code is written in MATLAB and is validated with results available in the literature. Further, numerical analysis was carried out for the effect of various parameters on the performance of the proposed cooling system. The study shows an improvement of 19.2% in dew point effectiveness by incorporating an intermediate opening in the plate separating the product air and working air channels.
... A hybrid system COP (COP hybrid ) is proposed to evaluate the space cooling and dehumidification energy efficiency of the integrated system of the desiccant cooler and the PV/T panels, indicating the real-time grid electricity consumption under time-varying cooling and dehumidification capacity after whole building energy retrofit, which is defined in Eq. (43). ...
The heat and mass transfer of liquid desiccant for dehumidification and cooling has been investigated in recent years as a promising energy-efficient technology to improve indoor thermal comfort. Limited studies, however, investigated integration strategies and energy performance of such systems in real buildings with performance correlations in building energy simulation software. This research considers a low-rise Greek apartment building constructed in 1981 as a case study. The optimal system sizing is determined via parametric analysis in the numerical modelling stage as: 1) air mass flow rate of 57 m³/h; 2) solution mass flow of 2.0 l/min; 3) solution inlet temperature of 14 °C; 4) solution concentration of 40%. Besides, the thermal and electrical COP correlations are derived from the inlet air temperature and relative humidity, with maximum value of 0.51 and 7.32 (inlet air temperature: 35 °C and relative humidity: 90%). The results show that by integrating two photovoltaic thermal (PVT) panels and a 300L water-based thermal storage tank into the desiccant cooler, such a hybrid system could achieve maximum COP value of 4.21 in the case study. Besides, the summer supply air thermal unacceptable level is reduced by at least 65% from 2535 h to 884 h.
... A hybrid system COP (COP hybrid ) is proposed to evaluate the space cooling and dehumidification energy efficiency of the integrated system of the desiccant cooler and the PV/T panels, indicating the real-time grid electricity consumption under time-varying cooling and dehumidification capacity after whole building energy retrofit, which is defined in Eq. (43). ...
... The exergy efficiency can be used to compare the same solution [28]; nevertheless, it can also be used under different operational conditions and has been considered a proper tool to evaluate two different solutions [29]. The exergy efficiency may be evaluated according to Equations (10) and (11). ...
In this paper, an energy and exergy analysis is applied to the air dehumidification unit of a liquid desiccant system in an industrial gelatin conveyor dryer. The working fluid is a binary solution of lithium chloride (LiCl) in water. Dry air is used in order to decrease the amount of liquid in the gelatin. Therefore, the environmental air must have its absolute humidity reduced from about 12 g/kg to the project target, which is 5 g/kg. The process is a cycle using an absorption desiccant unit (LiCl in water), where the weak solution absorbs water vapor from the air. In the regenerator, condensation of the solution (desorption) from the moist air occurs. As a result, the steam consumption of the desorber and electrical power used for the vapor compression chiller (with ammonia, NH3, as working fluid) are the primary sources of cost for the factory. To improve the plant’s energy and exergy behaviors, the process is evaluated using a mathematical model of the system processes. In addition, we evaluate the substitution of the vapor compression chiller by an absorption unit (lithium bromide (LiBr) in water). The performance indicators of the compression vapor systems showed the best results. Even when using the condenser’s energy to pre-heat the solution, the installed system proved to be more effective.
... Significant energy is required to reach the apparatus dew point (ADP) and further cooling below the ADP is required to compensate the bypass effect of the evaporator coils [5]. The dehumidified air must then be reheated to the required comfort level and this leads to extra energy waste [6]. Numerous issues have been associated with conventional coolers, starting with their relatively high costs, their operational costs, and maintenance costs; it has likewise been understood that recently the demand on using air conditioning for cooling has been increasing due to climate change and due to increase in the urban heat island impact, particularly in populated territories. ...
Desert coolers have attracted much attention as an alternative to mechanical air conditioning systems, as they are proving to be of lower initial cost and significantly lower operating cost. However, the uncontrolled increase in the moisture content of the supply air is still a great issue for indoor air quality and human thermal comfort concerns. This paper represents an experimental and numerical investigation of a modified desert air cooler into a liquid desiccant air conditioner (LDAC). An experimental setup was established to explore the supply air properties for an adapted commercial desert cooler. Several experiments were performed for air–water and air–desiccant as flow media, at several solutions to air mass ratios. Furthermore, the experimental results were compared with the result of a numerical simplified effectiveness model. The outcomes indicate a sharp reduction in the air humidity ratio by applying the desiccant solutions up to 5.57 g/kg and up to 4.15 g/kg, corresponding to dew point temperatures of 9.5 °C and 12.4 °C for LiCl and CaCl2, respectively. Additionally, the experimental and the numerical results concurred having shown the same pattern, with a maximal deviation of about 18% within the experimental uncertainties.
... Min et al [4] introduced two novel configurations of desiccant liquid air conditioning system and investigated their performances. A comparison between these configurations with other desiccant liquid systems to improve indoor air qualities was carried. ...
Contrary to the conventional air conditioning systems, the liquid desiccant cooling (LDC) systems are considered efficient systems to control the indoor air conditions. In addition, the LDC technologies are more adequate for the hot and humid climates. In this paper, we present an analytical investigation at assessing the feasibility of a LDC technology under Mediterranean climate. The mathematical equations including the sensible and latent heat transfer equations in both air stream and desiccant solution are presented. The impacts of climatic and operating parameters on the supplied air qualities, moisture removal rate (MRR) and sensible heat ratio (SHR) are evaluated. As a consequence, this study provides a solution to investigate the feasibility of this type of air conditioning technologies under hot and humid climate.
... As for an adiabatic dehumidifier/regenerator, there are three flow arrangements for the device, namely counter flow, cross flow and parallel flow according to the relative flow direction between air and solution. It was generally agreed by scholars [6][7][8] that counter flow shows the most superior dehumidification/regeneration performance, while the parallel flow performances the poorest under same condition. Such performance difference can be analyzed and explained through parameter variances diagram, exergy analysis and unmatched coefficients [9,10]. ...
... (7), namely the exergy destruction (ΔEx) equals to the difference between input exergy and output exergy, which can further transfer into Eq. (8). ...
In the present study, performance comparison and exergy analysis of different flow types in internally-cooled liquid desiccant dehumidifiers (ICDs) were conducted. Moisture removal rate, exergy efficiency and unmatched coefficient are adopted, to analyze performance of ICDs under different flow types. Sensitivity analysis of each operating parameters as well as their influence on the performance difference among different flow types were carried out. Finally, the design suggestion on choosing flow types for ICD was given. It was found that counter flow arrangement between air and cooling media has shown higher moisture removal rate and lower exergy destruction among all flow types. It was proved that more evenly distributed heat and mass transfer driving force can help decrease the device exergy destruction as well as improving the overall device performance. Thus, the performance of ICD can be improved by decreasing the desiccant solution mass flow rate, lowering the desiccant solution inlet temperature. As for further dehumidifier design, flow type with counter flow between air and cooling media and cross flow between air and desiccant solution is recommended.
... Therefore, new air-conditioning technologies are required. The liquid desiccant air-conditioning (LDAC) system is developed and regarded as a promising alternative for lower energy consumption, less pollution and more flexible humidity control [4,5]. In LDAC systems, the extra moisture is removed by liquid desiccant absorption and the sensible and latent heat can be handled separately. ...
... According to the previous researches [33,37], in the numerical experiments, the values of other important settled parameters are as follows: room exhaust air temperature, 26.0 C; room exhaust air relative humidity, 60%; dehydrated desiccant mass flow rate, 0.38 kg/s; NTU of each sub-model, 3.0. ...
... The Coefficient of Performance (COP) of the system is defined as the cooling capacity Q cd divided by regeneration heat Q gen as follows [33,37]: ...
Liquid desiccant dehumidification systems are widely used in many industries including HVAC. Special attention has been paid to the liquid desiccant air conditioning (LDAC) system performance analyses. However, the studies, such as factor analysis and performance optimization of LDAC system, have not received enough attention. This paper focuses on the factor analysis and optimization of the operational parameters of a LDAC system that has been described in previous work. Firstly, through the process of factor analysis, the most important factors and pair-wise interactions can be selected, when is used as the target variable. Secondly, the optimum values for these factors that optimize are found by using the method of orthogonal design. Thirdly, a sectioned polynomial regression model is developed to describe the relationship between the and independent variables inclusive of the factors in the optimal combinations and the outdoor air parameters. With the variation of outdoor air parameters, the optimal values of and could also be predicated on the regression model. The accuracy of the regression model is also analyzed. Finally, according to the same analytical method, the operational parameters are analyzed and their levels are optimized when the COP is used as the target variable.
