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[en] Pre-anthesis assimilation of stem reserves is considered as an important source for grain filling during post anthesis abiotic stresses that inhibit photosynthesis. Twenty one Pakistani wheat genotypes were evaluated for stem reserve utilization (SRU) using potassium iodide (0.4%) induced desiccation stress 14 days after anthesis. Evaluated genotypes differed significantly (p<0.01) for percent reduction in kernel weight under chemical desiccation stress. Percent reduction in kernel weight ranged from 26.19% to 50.72%. Minimum reduction was observed in C-271 (26.19%) showing highest stem reserve utilization while maximum reduction in kernel weight was recorded in Maxi-Pak (50.72%) presenting least SRU. A significant negative correlation (R2=0.452) between percent reduction in kernel weight and plant height was observed. In conclusion, tested genotypes vary considerably in stem reserve utilization when subjected to post-anthesis chemical desiccation inhibiting the photosynthesis. The genotypes with better SRU based kernel growth in the absence of photosynthesis may also provide relative tolerance to drought. This technique therefore, can be used to indirectly screen the wheat genotypes for better performance under terminal drought conditions. (author)
[en] Highlights: ► A solar desiccant cooling/heating system is simulation studied. ► The mean deviation is about 10.5% for temperature and 9.6% for humidity ratio. ► The 51.7% of humidity load and 76% of the total cooling can be handled. ► About 49.0% of heating load can be handled by solar energy. ► An optimization of solar air collector has been investigated. - Abstract: To increase the fraction of solar energy might be used in supplying energy for the operation of a building, a solar desiccant cooling and heating system was modeled in Simulink. First, base case performance models were programmed according to the configuration of the installed solar desiccant system and verified by the experimental data. Then, the year-round performance about the system was simulated. Last, design parameters of solar air collectors were optimized that include collector area, air leakage and thermal insulation. Comparison between numerical and experimental results shows good agreement. During the simulation, the humidity load for 63 days (51.7%) can be totally handled by the two-stage desiccant cooling unit. For seasonal total heating load, about 49.0% can be handled by solar energy. Based on optimized results, the thermal energy subsystem functioned to its expected performance in solar energy collection and thermal storage
[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] 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] 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 effects on the performance of an air-detritiation dryer (ADD) of inlet-gas humidity and residual tritiated water (HTO) left on the desiccant following regeneration were demonstrated. Residual HTO significantly reduced the detritiation factor (DFSP) of an ADD from clean-bed values. In addition, HTO/H2O separation occurred in the ADD, with H2O leading HTO. HTO roll-up may also have occurred. Finally, an increase in the inlet-gas humidity at constant inlet HTO concentration decreased the DFSP while increasing the humidity-reduction factor (HRFSP)
[en] In this work a novel energy efficient air-conditioning system utilizing lithium chloride (LiCl) solution as liquid desiccant has been proposed and simulated. The simulation of this system is mainly formulated with two packed columns, one for regenerating the weak desiccant and the other for the dehumidification of ambient air. The air is first dehumidified in the dehumidifier and then sensibly cooled in the indirect and direct evaporative coolers. First and second laws of thermodynamics have been used to analyze the effect of five key variables on the performance of the system. High efficiency could be achieved if proper values of these variables are selected.
[en] Highlights: • Multi-objective optimization of desiccant wheels is investigated. • Response surface method is used for establishing novel regression models. • Effects of operating variables on corresponding responses are comprehensively evaluated. • Optimum values of input variables have been derived to minimize process outlet temperature and humidity ratio. • A valuable equation for determination of Pareto-optimal points has been proposed. - Abstract: A two-step computational framework based on the combination of response surface methodology and multi-objective optimization is proposed to model the outlet-air state of desiccant wheels and subsequently optimize their operation. Regeneration temperature, surface area ratio, rotational speed, and wheel diameter are considered as decision parameters in the genetic algorithm. The central composite design and response surface methods have been employed to design experiments, establish predictive empirical models, and determine interactive effects of decision variables on response variables—process outlet temperature and humidity ratio. Several experiments have been performed to verify applicability of the proposed methodology and validate obtained results. A value of the coefficient of determination exceeding 0.95 demonstrates high reliability and accuracy of the modeling process involved in the proposed methodology. Results obtained demonstrate greater dominance of the surface area ratio compared to other decision variables in terms of their influence on response variables. After successful validation against experimental data, the developed models have been considered as a combination of two objective functions. A fast and elitist non-dominated sorted genetic algorithm II-based optimization technique has been employed to simultaneously determine optimum values of decision variables. A Pareto-optimum front has been presented to select the best value of each decision parameter from available points of optimum operation, and a valuable equation for Pareto-optimal points has been deduced for each material to assist designers develop an optimum design of desiccant cooling systems.
[en] Soil radon is employed to trace residual NAPL (Non-Aqueous Phase Liquid) contamination because it is very soluble in these substances and is strongly depleted over polluted volumes of the subsoil. The solubility of radon into NAPL vapors, generally poorly considered, is investigated here, either as growth of radon exhalation from a material contaminated with increasing volumes of kerosene, or as radon partition between liquid kerosene, water and total air, considered ad the sum of kerosene vapors plus air. - Highlights: • Laboratory simulation of recent NAPL spills was carried out • Kerosene vapors enhance soil radon exhalation and transport • The use of desiccants emphasizes radon preferential dissolution into NAPL vapors • Radon partitioning among liquid kerosene, water and total air is investigated • Radon partition coefficients between liquid and vaporized kerosene were estimated
[en] Microwave heating is expected to be a novel regeneration method of desiccant rotor in desiccant humidity conditioner, because it has advantages of direct and rapid heating of material. In this study, desorption experiments were conducted by using the practical desiccant rotor coated with zeolite in the microwave power ranging from 200 to 800 W and desiccant rotor length of 60-180 mm. As a result, both desorption ratio in a desorption equilibrium and initial desorption rate were found to increase linearly with microwave power. Concerning the effect of rotor length, it was found that initial desorption rate and desorption ratio at 600 s also increased with rotor length. However, experimental desorption ratio in a desorption equilibrium was much lower than estimated value, which was calculated on the basis of change in relative humidity involved by temperature increase of rotor, and the deviation increased with microwave power and rotor length. From the temperature measurement in the rotor, a noticeable temperature distribution was observed in the radial and axial directions of rotor even though water desorption attained an equilibrium state. Consequently, it was indicated that nonuniform heating of the rotor mainly caused decrease in desorption ratio. - Research highlights: → Water desorption of zeolite desiccant rotor was conducted with microwave heating. → Initial desorption rate and equilibrium ratio rose linearly with microwave power. → Initial desorption rate and equilibrium ratio increased with rotor length. → Experimental desorption ratio was much lower than theoretically estimated value. → A big temperature distribution existed in the radial and axial directions of rotor.