Ahmed M. Hamed

The effect of inlet parameters on the performance of packed tower-regenerator

An investigation on the operation of packed tower for the regeneration of liquid desiccant is presented. A theoretical model demonstrating the effect of the system parameters is described. The experimental results are plotted to illustrate the effect of air and liquid parameters on the output variables. The regeneration process is shown to be highly dependent on the air inlet conditions, namely, temperature, humidity and flow rate. Also, the effects of the liquid temperature, concentration and flow rate is discussed. Data obtained were correlated to estimate the rate of water evaporation (regeneration rate) from values of variables that influence the rate of mass transfer in the column.

Theoretical and experimental study on the transient adsorption characteristics of a vertical packed porous bed

This paper presents a theoretical and experimental study of the transient adsorption characteristics of vertical packed porous bed. The theoretical model describes the effect of independent parameters (time and vertical distance through the bed) on the vertical gradient of adsorbable fluid in the bed. A simplified analytical solution, for specific operating conditions, is also presented. In the experimental study, porous granules of burned clay are applied as a desiccant carrier in the fixed bed. The granules of the packed bed are impregnated with liquid calcium chloride solution to form the porous adsorbing surface. The isothermal adsorption of water vapour from atmospheric air using the prepared bed is experimentally studied. Transient values of the mass of adsorbed water vapour, solution concentration and vapour pressure through the bed layers are evaluated from the experimental measurements. The model output, which show the effect of dimensionless relative time (Tr) on the potential ratio (C−C∗)/(C−C∗0), is compared with the experimental results and good agreement is found.

Application of a solar desiccant/collector system for water recovery from atmospheric air

An integrated desiccant/solar collector system for production of fresh water from atmospheric air is described. The solar driven system provided about 1.5 l of fresh water per square meter per day. The system involves the absorption of water vapor from ambient air during the night and simultaneous desiccant regeneration and water vapor condensation during the day. To enhance the mass transfer surface, a thick corrugated layer of cloth was used as a bed to carry the liquid absorbent. In the nocturnal phase of operation, air is allowed to penetrate the desiccant bed. The airflow is driven by fans supported on one side of the desiccant/solar collector unit. In this study, the effects of different parameters on the absorption and regeneration processes are discussed, and operational conditions for the proposed equipment evaluated. Radiation intensity, ambient temperature, bed temperature and temperature of the glass surface were recorded. Also, the productivity of the system during the day and under the given operation conditions was plotted. A mathematical model was prepared and its output compared with the analyzed experimental data.

Absorption-regeneration cycle for production of water from air-theoretical approach

Description and analysis of the theoretical cycle for absorption of water vapour from air with subsequent regeneration, by heating is presented. Properties of the desiccant (CaCl2) applied in the study are correlated in a simplified form, which can be used in computational analysis of the cycle performance. To predict the effect of ambient conditions on the operating limits of the cycle, heat and mass balance equations are developed. In addition, an expression for the efficiency of the simple cycle is introduced. Theoretical analysis shows that strong and weak solution concentration limits play a decisive role in the value of cycle efficiency. The limits of regeneration temperature and mass of strong solution per kg of produced vapour are found highly dependent on the operating concentration of the desiccant.

Desorption characteristics of desiccant bed for solar dehumidification/humidification air conditioning systems

Theoretical and experimental investigation on the desorption characteristics of a packed porous bed is presented in this study. The granules of burned clay are applied as a desiccant carrier. Calcium chloride is used as the working desiccant. The theoretical model defines the transient gradient of air stream parameters (humidity and temperature) as well as desiccant concentration in the bed. In the experimental study, transient concentration gradient in the bed is evaluated by weight method. The bed is divided into seven separate layers. Air stream at low temperature and nearly constant inlet parameters are used for desorption purposes. Concentration gradient in the bed is found highly dependent on the mass transfer rate. For the specified operating conditions and stated assumptions, experimental measurements shows acceptable agreement with the analytical solution.

Experimental investigation on the natural absorption on the surface of sandy layer impregnated with liquid desiccant

This paper presents an investigation on the natural absorption of water vapour of the gaseous-air mixture on the horizontal surface of a sandy layer impregnated with calcium chloride as the working desiccant. Seven layers with different values of desiccant to sand mass ratio in the range from 0.1 to 0.4 are studied. Isothermal absorption is assumed in this analysis. The effect of desiccant concentration as well as Grashof number on the mass transfer coefficient is discussed. Also, the effect of the mixing ratio (desiccant/sand) in the bed on the rate of absorption is demonstrated. Experimental results show that the mass transfer coefficient is highly affected by the desiccant concentration in the bed. Also, it is found that the potential of mass transfer rapidly decreases with a decrease in mixing ratio.

Mass transfer in vertical cloth layers impregnated with calcium chloride for recovery of water from air

This paper presents an investigation on the absorption/regeneration mass transfer through parallel plates of cloth layers. Cloth layers impregnated with calcium chloride solution are subjected to absorption of water vapour from a flowing air stream with subsequent regeneration by a hot stream. Concentration range of desiccant from 0.2 to 0.5 is applied in this study. Experimental measurements are used to evaluate the mass transfer coefficient and Sherwood number. An attempt to fit the Sherwood number as a function of the Reynolds number, for the operating range of the Schmidt number, has been made. Scatter of the experimental values of the Sherwood number is observed and discussed in this work.

Study on the Performance of a Fluidized Air Dehumidifier

Transient adsorption/desorption characteristics of solid desiccant particles in fluidized bed have been presented. The system operates in batch mode and the atmospheric air with controlled inlet humidity and temperature is dehumidified by the applied desiccant. Also, heated air is used for regeneration purposes. A simplified analytical solution, with isothermal adsorption assumption, is demonstrated. In the experimental study, spherical particles of silica gel about 3 mm in diameter are used as the working desiccant in the fluidized bed. The experimental system is equipped with the necessary control valves to facilitate operation in adsorption and desorption modes, respectively. To control the humidity of inlet air, a humidifier is designed and fitted in a proper location in the system. Also, the system is well instrumented to measure the inlet and outlet air parameters as well as bed temperatures during the operation modes. Transient values of the mass of adsorbed water in the bed, rate of adsorption and water content in silica gel particles are evaluated from the experimental measurements. Also, numerical values of the volumetric mass transfer coefficient are plotted and discussed for different operating conditions. Model output, which shows the dependence of the dimensionless value of water content in the bed [(w*i − w)/(w*i − wo )] on the dimensionless time, is compared with the experimental results. Good agreement is found at the first period of adsorption, when the adsorption is nearly isothermal. Successive increase in bed temperature, due to the heat of adsorption, results in increase in discrepancy between the model and the experimental data. Accordingly, the isothermal model could be applied with reasonable degree of reality for systems with shorter adsorption/desorption cycles. The effect of air inlet humidity on the system operation has been highlighted. The drop in air humidity is highly affected by its inlet value. It is found that, the maximum decrease in air humidity occurs at the beginning of adsorption for the different inlet values. Also, the rate of water vapor adsorption increases with the increase in the inlet humidity.Copyright