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[en] Graphical abstract: A heat pump driven, hollow fiber membrane-based two-stage liquid desiccant air dehumidification system. - Highlights: • A two-stage hollow fiber membrane based air dehumidification is proposed. • It is heat pump driven liquid desiccant system. • Performance is improved 20% upon single stage system. • The optimal first to second stage dehumidification area ratio is 1.4. - Abstract: A novel compression heat pump driven and hollow fiber membrane-based two-stage liquid desiccant air dehumidification system is presented. The liquid desiccant droplets are prevented from crossing over into the process air by the semi-permeable membranes. The isoenthalpic processes are changed to quasi-isothermal processes by the two-stage dehumidification processes. The system is set up and a model is proposed for simulation. Heat and mass capacities in the system, including the membrane modules, the condenser, the evaporator and the heat exchangers are modeled in detail. The model is also validated experimentally. Compared with a single-stage dehumidification system, the two-stage system has a lower solution concentration exiting from the dehumidifier and a lower condensing temperature. Thus, a better thermodynamic system performance is realized and the COP can be increased by about 20% under the typical hot and humid conditions in Southern China. The allocations of heat and mass transfer areas in the system are also investigated. It is found that the optimal regeneration to dehumidification area ratio is 1.33. The optimal first to second stage dehumidification area ratio is 1.4; and the optimal first to second stage regeneration area ratio is 1.286.
[en] The concept of dehumidification between air and liquid desiccant for the improvement of the efficiency of heating and cooling fluids in industrial applications was discussed. The use of solid/liquid desiccants has received much attention in recent years because liquid desiccants can take moisture from surrounding air at low temperature and then release the moisture at high temperature to provide a continuous process of dehumidification of air and regeneration of liquid desiccant. This process can be used with conventional vapor compression cycles. This paper presented a comparative numerical study between parallel and counter flow configurations that examined the effects of various parameters on heat and mass transfer for the dehumidification and cooling processes of air and regeneration rate of liquid desiccant. Ultrafine particles were added to the falling film desiccant to investigate heat and mass transfer enhancement for both parallel and counter flow channels. The Cu-volume fraction in the falling film desiccant and dispersion effect were the important parameters. A mathematical model was therefore developed to account for the addition of Cu-ultrafine particles into the film desiccant. The dehumidification and cooling rate processes were found to improve with an increase in the Cu-ultrafine particles and dispersion effect. The new hybrid AC system was shown to improve indoor air quality, reduce energy consumption, and be environmentally safe. It was concluded that although the volume fraction and dispersion factor improve the dehumidification and cooling processes of the air, the improvements are not significant due to the small thickness of the falling-film desiccant. The regeneration process did not improve for either controlling parameter because of the small thickness of the film desiccant. 14 refs., 10 figs
[en] To reasonably estimate the population dose from radon, equilibrium factor, Fp, and unattached fraction, fp, of radon progeny are important parameters. A Lucas cell and a working level monitor was used for most Fp measurement. The unattached fraction was measured by SARAD EQF3020. A detached house was chosen to measure the Fp in different rooms. The Fp value depended mainly on the ventilation rate and surface to volume ratio of the rooms. Fp and fp were measured in bedrooms of 14 other dwellings. Two hospitals were also chosen for measurement of Fp in the working place using rooms located in the basement. The average Fp for dwellings was about 0.5 and the average unattached fraction was about 0.055. The radon levels in the hospitals were higher than those in the dwellings but the equilibrium factors in the hospital were very low (about 0.06). The low Fp was attributed to the use of a dehumidifier in the hospitals. Dehumidifiers are popular for reducing fungi problem induced by the high humidity in Taiwan
[en] A draft Method of Test (MOT) has been proposed for packaged, air-to-air, desiccant-based dehumidifier systems that incorporate a thermally-regenerated desiccant material for dehumidification. This MOT is intended to function as the ''system'' testing and rating compliment to the desiccant ''component'' (desiccant wheels and/or cassettes) MOT (ASHRAE 1998) and rating standard (ARI 1998) already adopted by industry. This draft standard applies to ''packaged systems'' that: Use desiccants for dehumidification of conditioned air for buildings; Use heated air for regeneration of the desiccant material; Include fans for moving process and regeneration air; May include other system components for filtering, pre-cooling, post-cooling, or heating conditioned air; and May include other components for humidification of conditioned air. The proposed draft applies to four different system operating modes depending on whether outdoor or indoor air is used for process air and regeneration air streams . Only the ''ventilation'' mode which uses outdoor air for both process and regeneration inlets is evaluated in this paper. Performance of the dehumidification system is presented in terms that would be most familiar and useful to designers of building HVAC systems to facilitate integration of desiccant equipment with more conventional hardware. Parametric performance results from a modified, commercial desiccant dehumidifier undergoing laboratory testing were used as data input to evaluate the draft standard. Performance results calculated from this experimental input, results from an error-checking/heat-balance verification test built into the standard, and estimated comparisons between desiccant and similarly performing conventional dehumidification equipment are calculated and presented. Some variations in test procedures are suggested to aid in analytical assessment of individual component performance
[en] An experimental study has been conducted to investigate the performance of a liquid desiccant air dehumidifier equipped with a structured packing made of wood for three different densities using triethylene glycol (TEG) as the liquid desiccant. The structured packing densities used were 77, 100 and 200 m2/m3. The performance of the dehumidifier was expressed in terms of the moisture removal rate and the dehumidifier effectiveness under different air and desiccant parameters, i.e. the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. In general, the trend in the dehumidifier performance was similar to that reported by other investigators using random packing. The effect of packing density on moisture removal rate and dehumidifier effectiveness is assessed. The differences in the effectiveness of different packing densities are attributed to the wetting condition. Lower effectiveness of the column is shown with the packing density of 200 m2/m3 compared to the other two packing densities when the air flow rate, inlet concentration and desiccant flow rate are increased. However, higher effectiveness is shown when either the inlet temperature of the air or desiccant is increased
[en] The performance of an air dehumidifier using triethylene glycol (TEG) as desiccant under hot and humid conditions was investigated. The performance of the dehumidifier was evaluated and expressed in terms of the moisture removal rate and the dehumidifier effectiveness. A packed bed column (dehumidifier) was employed, with low packing density (77 m2/m3), to provide direct contact between the air and the TEG. Two different structured packings were used, wood and aluminum. The experiments covered a wide range of parameter space that included the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and inlet TEG concentration. The liquid flow rate investigated is much less than that covered in previous studies (<1 kg/m2 s). The trend of the dehumidifier performance was similar to that reported in the literature using high density and random packing. The results were compared to the Chung and Luo correlation, which over predicted the effectiveness. The Martin and Goswami correlation failed to predict the effectiveness under the conditions of this study. In the present study, it was found that the moisture removal rate increased with increasing inlet TEG concentration, TEG flow rate and air flow rate. This was seen for both the wood and the aluminum packings. In addition, the moisture removal rate is increased with increasing the inlet air temperature for the aluminum packing only. The effectiveness of the column was increased by increasing the TEG flow rate and inlet TEG temperature for the two packings
[en] An Air Handling Unit(AHU) has been usually designed by manual calculations. Drawing works together with design calculations should be redone for every designing work, and also be needed to make some corrections of them. In order to design the AHU more efficiently, an AHU program has been developed. The developed program on the Windows environment is operated by the Graphic User Interface(GUI) realized using the Visual Basic Interpreter. The program provides calculation sheet of coils, weights and pressures in a MS-Excel file format as well as design drawing of the AHU in a auto CAD file format idealized by AutoLISP. Those files of the commercial softwares make easier for a designer to transfer design results to the another company for bid via e-mail
[en] Establishment of tritium recovery system is necessary to prevent its leakage to the working area. The catalytic oxidation and adsorption is the most reliable method to recover tritium released into the working area of those facilities. Therefore, there is a necessity that the tritium recovery system with large-scale and higher integrity is developed and constructed. For this purpose, it is required to obtain and accumulate updated database for chemical engineering design based on most recently commercial and available catalysts and absorbents. In this work, we selected a catalyst and an adsorbent, and examined their adsorption characteristics for water vapor and performance of catalytic oxidation of hydrogen. Adsorption isotherms were studied with a volumetric gas adsorption instrument. Various adsorption models were tested to correlate the experimental isotherms. Breakthrough experiments were also performed to assess adsorption performances. Furthermore, numerical simulations were performed based on the obtained experimental results. (author)
[en] Heat and mass transfer processes in a cross flow liquid desiccant dehumidifier, in which wet durable honeycomb paper constitutes the packing material, is investigated in this paper. The device is expected to be used in hot and humid areas to control the indoor humidity environment. A mathematical model, able to determine the heat and mass transfer between the air and the falling film of liquid desiccant, is developed, and the analysis on Nusselt and Sherwood numbers at the liquid-air interface is performed considering the solution of 40% H2O/CaCl2. Also obtained is the theoretical Nusselt number under assumed conditions and the relevant analysis, as well as the comparison between the two results
[en] Highlights: • A novel solar driven multi-stage bubble column humidifier is developed and tested. • Single stage, two stage, and three stage configuration were tested. • Average day round absolute humidity is increased by 9% for 2 stage configuration. • Average day round absolute humidity is increased by 23% for 3 stage configuration. • Air absolute humidity increases up to 26% with the integration of Fresnel lens. - Abstract: In this study, a novel solar heated multi-stage bubble column humidifier is designed and tested. The overall objective of this work is to investigate the main operating parameters of the new humidifier. The study addresses the significance of the perforated plate geometric features, optimum balance of air superficial velocity and water column height, and the influence of inlet water temperature and inlet air relative humidity on the performance of the humidifier. The day round performance of the humidifier is investigated in single stage, two stage, and three stage configuration, in which each configuration was tested with and without the integration of the Fresnel lens. Findings show that the average day round absolute humidity, without Fresnel lens, increased up to 9% for the two stage configuration and 23% for the three stage configuration as compared to the single stage configuration of the humidifier. The integration of the Fresnel lens further increased the absolute humidity up to 25% as compared to the results obtained without the integration of the Fresnel lens under the same prevailing conditions, which is significant. Moreover, the current humidifier shows a higher humidification efficiency in the climatic conditions that have a lower inlet air relative humidity. Furthermore, the finding demonstrates that the newly developed multi-stage bubble column humidifier has better performance as compared to the conventional single stage bubble column humidifier. The findings from this study are of pivotal importance to understand the optimum operating conditions of the humidifier for its possible integration with the dehumidifier. Consequently, an improved humidification-dehumidification desalination system attained.