Results 1 - 10 of 171
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[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] A theoretical model is developed to simulate the heat and mass transfer processes in a cross flow dehumidifier/regenerator using liquid desiccant. The model depends on NTU as input parameter, and NTU can be correlated based on the corresponding experimental data. The model is able to predict the air and desiccant parameters inside the dehumidifier/regenerator, as well as the outlet parameters, with known inlet parameters. The calculated results are compared with the experimental findings. For the total 284 groups of dehumidification experimental data with different module sizes, the average absolute discrepancies for enthalpy effectiveness and moisture effectiveness are 7.9% and 8.5%, respectively. For the 82 groups of regeneration experimental results, the average discrepancies for enthalpy and moisture effectiveness are 5.8% and 6.9%, respectively. The distributions of desiccant outlet temperatures are measured during both the dehumidification and regeneration processes, and the temperatures predicted by the theoretical model agree well with the experimental results
[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] 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)
[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] 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.