Results 11 - 20 of 209
Results 11 - 20 of 209. Search took: 0.019 seconds
|Sort by: date | relevance|
[en] As fusion research facilities and power plants are sure to require a large atmospheric-detritiation system (ADSs) to mitigate the tritium releases and to recover the heavy water vapor. The best available technology for these systems is the oxidized-and-adsorb process, where tritiated species are converted to tritium oxide (HTO) and adsorbed onto an atmospheric-detritiation dryer (ADD). Conventional ADDs use synthetic zeolites as the adsorbent and rely on a thermal swing cycle. This permits a continuous detritiation of a gas by using multiple desiccant beds, each bed being regenerated following a period of moisture removal (adsorption). The performance of a desiccant dryer depends on the simultaneous transfer of the mass and energy between the flowing gas and solid desiccant. In designing a fixed bed dryer and preparing an advanced dryer control, it is necessary to quantify the bed utilization and dynamic behavior against inlet humidity and flow rate. In this study, a quantitative evaluation based on an adsorption test was carried out to evaluate the adsorption characteristics and the operating performance of an atmospheric detritiation dryer
[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] Goal of this contribution is to draw a picture about some general issues for using solar thermal energy for air conditioning of buildings. The following topics are covered:-A basic analysis of the thermodynamic limits for the use of heat cooling in combination with solar thermal energy is drawn; thereby fundamental insights about control needs for solar thermal driven cooling are obtained. -A short overview about the state-of-the-art of available technologies, such as closed thermal driven cooling cycles (e.g., absorption, adsorption) and open cooling cycles (e.g., desiccant employing either solid or liquid sorbents) is given and needs and perspectives for future developments are described. -The state-of-the-art of application of solar assisted air-conditioning in Europe is given and some example installations are presented. -An overview about new developments of open and closed heat driven cooling cycles for application in combination with solar thermal collectors is given and some of these new systems are outlined more in detail
[en] This study reports the hydrogen production from using photocatalyst. In particular we focus on the role of synergism on the reaction rate. The results reveal that the presence of nano Fe in bentonite-water systems exhibit higher photoactivity than pure one for the photolysis. As bentonite was used Dash-Salakhli bentonite clay. For hydrogen production the photocatalyst is composed of nano-size metal such as Fe. The presence of the montmorillonite and nanometal particles together results in considerable enhancement of the reaction rate when compared to per one alone. In this work the influence of Fe nanoparticles in the bentonite-water systems on the photocatalytic activities was investigated. Experimental results of FT-IR spectroscopy and SEM images show that the increase in activity is related to change in the lattice parameters and surface events.
[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] Highlights: • Five configurations of a DEC system are analyzed in five climate zones. • DEC system model configurations are developed in Dymola/Modelica. • Performance analysis predicted a suitable DEC system configuration for each climate zone. • Results show that climate of Vienna, Sao Paulo, and Adelaide favors the ventilated-dunkle cycle. • While ventilation cycle configuration suits the climate of Karachi and Shanghai. - Abstract: Performance of desiccant evaporative cooling (DEC) system configurations is strongly influenced by the climate conditions and varies widely in different climate zones. Finding the optimal configuration of DEC systems for a specific climatic zone is tedious and time consuming. This investigation conducts performance analysis of five DEC system configurations under climatic conditions of five cities from different zones: Vienna, Karachi, Sao Paulo, Shanghai, and Adelaide. On the basis of operating cycle, three standard and two modified system configurations (ventilation, recirculation, dunkle cycles; ventilated-recirculation and ventilated-dunkle cycles) are analyzed in these five climate zones. Using an advance equation-based object-oriented (EOO) modeling and simulation approach, optimal configurations of a DEC system are determined for each climate zone. Based on the hourly climate data of each zone for its respective design cooling day, performance of each system configuration is estimated using three performance parameters: cooling capacity, COP, and cooling energy delivered. The results revealed that the continental/micro-thermal climate of Vienna, temperate/mesothermal climate of Sao Paulo, and dry-summer subtropical climate of Adelaide favor the use of ventilated-dunkle cycle configuration with average COP of 0.405, 0.89 and 1.01 respectively. While ventilation cycle based DEC configuration suits arid and semiarid climate of Karachi and another category of temperate/mesothermal climate of Shanghai with average COP of 2.43 and 3.03 respectively
[en] We prepared organic (self-assembled monolayer (SAM))–inorganic (TiO2) multilayer barrier films on polyethylene terephthalate substrate using atomic layer deposition and molecular layer deposition methods in the same deposition chamber. The water permeation was mainly blocked by the inorganic TiO2 layer. While the lag time was proportional to the thickness of the TiO2 layer, the steady-state permeation rate was relatively independent of the thickness. The multilayer approach was effective in extending the lag time due to both the tortuous path effect and the internal desiccant effect. Water permeation occurred sequentially in the organic–inorganic multilayer barriers by water accumulation in the organic SAM layers. The water vapor transmission rate was 7.0 × 10−4 g/m2·day during the lag time of 155 h at 60 °C and a relative humidity of 85% with 5-dyad barrier film. - Highlights: ► TiO2 and self-assembled monolayer (SAM) are grown by layer-by-layer deposition. ► We showed that the SAM layer is beneficial due to its internal desiccant effect. ► Water vapor transmission rate of the film is measured by electrical Ca test.
[en] A man-portable personal cooling garment based on the concept of vacuum desiccant cooling (VDC) was developed. It was demonstrated with cooling pads that a cooling capacity of 373.1 W/m2 could be achieved in an ambient environment of 37 °C. Tests with human subjects wearing prototype cooling garments consisting of 12 VDC pads with an overall weight of 3.4 kg covering 0.4 m2 body surface indicate that the garment could maintain a core temperature substantially lower than the control when the workload was walking on a treadmill of 2% inclination at 3 mph. The exercise was carried out in an environment of 40 °C and 50% relative humidity (RH) for 60 min. Tests also showed that the VDC garment could effectively reduce the metabolic heat accumulation in body with subject wearing heavily insulated nuclear, biological and chemical (NBC) suit working in the heat and allow the participant to work safely for 60 min, almost doubling the safe working time of the same participant when he wore NBC suit only. - Highlights: ► Heat stress mitigation is important for workers health, safety, and performance. ► Vacuum desiccant cooling (VDC) a novel concept for personal cooling. ► VDC garment man-portable and more efficient than commercial ice/pad vest. ► VDC garment suitable for personal cooling with NBC suit.
[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] A frequently used method in determining the radium concentration of water is the radon emanation method. When radon gas is transferred to the Lucas-cell usually CaCl2 is used to remove the water traces. When the background of the system was measured using ultra clear distilled water the results were astonishing. The detailed investigation has shown that the unwanted radon originated from the CaCl2, contained about 1000 Bq/kg of 226Ra. Depending on the time interval between two measurement, the radon deriving from the CaCl2 disturbed the measurements. (author)