Results 1 - 10 of 129
Results 1 - 10 of 129. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] This paper presents a study on the regeneration performance characteristics of an internally heated regenerator applicable to a liquid desiccant system. The internally heated regenerator used in this study was designed and manufactured to provide better regeneration performance. An experimental setup was established to examine the regeneration performance. LiCl aqueous solution was used as working fluid. Variables to evaluate regeneration performance characteristics of the internally heated regenerator were dry bulb temperature, relative humidity and velocity of regeneration air, mass flow rate, temperature and concentration of the LiCl aqueous solution. The experimental conditions were chosen by using a 1/2 fractional factorial DOE. Regeneration rate and regeneration effectiveness were taken as results. From the results, solution concentration and regeneration air relative humidity have strong effects on the regeneration rate. The regeneration effectiveness was affected mostly by regeneration air velocity.
[en] Long term ex situ conservation depends on seeds response to desiccation and storage temperatures. This was the objective of this work. Moisture content (MC) of fresh seeds was assessed in oven at 103 Celsius degrade weighting the samples at regular intervals till constant weight. Seed tolerance to desiccation and temperatures was evaluated with 5 germination experiments: fresh seeds (10-12%MC); 3-5% MC and 3-5% MC stored 3 months at 25, 5 y -20 Celsius degrade, in two treatments: control and scarification. Moisture content was 11% in both species. In P. nigra seed germination was higher than 80% in scarified seeds in all experiments. Germination in the control seeds decreased with desiccation and storage. The storage temperature did not affect germination. The Z. mistol germination of fresh endocarps was low (<35%) and increased with the reduction in MC. In summary, P. nigra and Z. mistol are tolerant to desiccation and storage temperatures tested and can therefore be considered as probably orthodox.
[en] Highlights: • A ground-coupled desiccant assisted air conditioning system is evaluated experimentally. • The evaluation is carried out for steady state operation and the cooling period as a whole. • The suitability of the system to provide comfort conditions is examined demonstrated. • Energy comparisons with other air-conditioning systems are performed. • The performance of the borehole heat exchangers for cooling is evaluated. - Abstract: In a pilot installation at Hamburg University of Technology the coupled operation of an open cycle desiccant assisted air conditioning system with borehole heat exchangers is investigated. The paper presents experimental data recorded during the cooling period 2014. Results show that the electricity demand of the system can be reduced to the parasitic consumption of the fans, wheels and pumps. An electric energy efficiency ratio of 6.63 is achieved, enabling electricity savings of more than 70% compared to a conventional reference system and 54% compared to a desiccant assisted hybrid system relying on an electric chiller. Comfort conditions can be maintained during the whole cooling period. The borehole heat exchangers work highly efficient, exhibiting a seasonal performance factor of 192.
[en] Highlights: •Thermodynamic principles are applied to systematically compare three technologies. •Merits and limits of standalone versus integrated designs are identified. •Effect of climate conditions on performance and technology selection is evaluated. •Integrated desiccant/membrane technologies outperform current state-of-the-art VCS. -- Abstract: Recently, next-generation HVAC technologies have gained attention as potential alternatives to the conventional vapor-compression system (VCS) for dehumidification and cooling. Previous studies have primarily focused on analyzing a specific technology or its application to a particular climate. A comparison of these technologies is necessary to elucidate the reasons and conditions under which one technology might outperform the rest. In this study, we apply a uniform framework based on fundamental thermodynamic principles to assess and compare different HVAC technologies from an energy conversion standpoint. The thermodynamic least work of dehumidification and cooling is formally defined as a thermodynamic benchmark, while VCS performance is chosen as the industry benchmark against which other technologies, namely desiccant-based cooling system (DCS) and membrane-based cooling system (MCS), are compared. The effect of outdoor temperature and humidity on device performance is investigated, and key insights underlying the dehumidification and cooling process are elucidated. In spite of the great potential of DCS and MCS technologies, our results underscore the need for improved system-level design and integration if DCS or MCS are to compete with VCS. Our findings have significant implications for the design and operation of next-generation HVAC technologies and shed light on potential avenues to achieve higher efficiencies in dehumidification and cooling applications.
[en] Regenerator is major component of liquid desiccant regeneration system. The influence of operating parameters; air flow rate, solution flow rate and concentration of desiccant is investigated experimentally on the performance parameters; outlet specific humidity, evaporation rate, air outlet temperature, mass transfer coefficient and effectiveness of the regenerator. Air and desiccant solution flow in counter direction with celdek pads as packing material. It is concluded that evaporation rate increases with increasing solution temperature, air flow rate and solution flow rate whereas same decreases with increasing concentration of desiccant. The effectiveness of regenerator is increased by 99 % with increase in air flow rate. A comparison of present finding with those available in the literature is presented in the last. Simulation results have revealed good agreement between the present experimental results.
[en] Highlights: ► Effects of irreversible processes on the performance of desiccant cooling cycle are identified. ► The exergy destructions involved are classified by the properties of the individual processes. ► Appropriate indexes for thermodynamic evaluation are proposed based on thermodynamic analyses. - Abstract: Thermodynamic analyses of desiccant cooling cycle usually focus on the overall cycle performance in previous study. In this paper, the effects of the individual irreversible processes in each component on thermodynamic performance are analyzed in detail. The objective of this paper is to reveal the elemental features of the individual components, and to show their effects on the thermodynamic performance of the whole cycle in a fundamental way. Appropriate indexes for thermodynamic evaluation are derived based on the first and second law analyses. A generalized model independent of the connection of components is developed. The results indicate that as the effectiveness of the desiccant wheel increases, the cycle performance is increased principally due to the significant reduction in exergy carried out by exhaust air. The corresponding exergy destruction coefficient of the cycle with moderate performance desiccant wheel is decreased greatly to 3.9%, which is more than 50% lower than that of the cycle with low performance desiccant wheel. The effect of the heat source is similar. As the temperature of the heat source increases from 60 °C to 90 °C, the percentage of exergy destruction raised by exhaust air increases sharply from 5.3% to 21.8%. High heat exchanger effectiveness improves the cycle performance mainly by lowering the irreversibility of the heat exchanger, using less regeneration heat and pre-cooling the process air effectively
[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] 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.