Search

This study investigates the performances of a self-sufficient greenhouse powered by a solar humidification–dehumidification desalination unit. It aims to achieve an overall integrated system that produces enough fresh water to cover the irrigation demand as well as the air humidification needs of the greenhouse. The humidification–dehumidification operation was numerically simulated using the developed model along with the greenhouse microclimate. The greenhouse model was validated through an experimental real-scale greenhouse. To make the proposed system more flexible, an auxiliary control system is used to easily monitor the greenhouse needs and ensure its satisfaction. The findings revealed that the integrated system, with its two main subsystems and its regulation device, successfully ensures the greenhouse irrigation, the humidification needs and provides an optimal plant growth. For the case study, i.e. cucurbit greenhouse situated at El Hamma (Tunisia), the desalination system can cover more than 200% of the greenhouse water irrigation needs while keeping the greenhouse inside air at a humidity level of 60% at least. The maximum productivity and the best energy efficiency are respectively 5.1 m3/day and 63.25%.

The lower productivity of the conventional solar still requires bringing modifications to this system. The proposed modification in this work consists of coupling water spray and ambient air injection, which may enhance the water–air surface contact area as it plays a crucial role in the performance in such a device and, consequently, increases the still performances. Response surface methodology (RSM) model is derived from an experimental test set up using the design of experiment procedure to investigate the binary interaction effects of the operating parameters, i.e., spraying height, inlet water temperature, and water and air flowrates. Based on RSM results, a simple polynomial statistical model is stated in this investigation to determine and maximize the amount of evaporated water from solar still based on the four considered input factors. An excellent fitting is attained between the predicted results derived from the statistical model and the experimental results. The performance of this model was also validated using the variance analysis approach. The findings indicate that the main influencing parameters in the order of impact on the system productivity is ambient air mass flow, saltwater temperature, sprayed water mass flow and sprayer height. The binary interaction effects of the variables were considered and illustrated for design recommendations. Within the studied ranges, the hourly productivity varies from 1.91 to 7.9 kg/h m2for a water temperature between 40 and 70 °C.

An innovative design approach consists of using a saline water spray humidifier to improve the performance of the humidification–dehumidification water desalination system, where hot water was sprayed from the top and air was supplied from the bottom of the humidifier. Before scaling a unit of this type, it is necessary to get sufficient information about the heat and mass transfer process that occurs in the unit. A prototype desalination unit has been developed and used to fulfill the main objective of this research which is to evaluate the mass and heat transfer coefficients in the humidifier. As well, the effect of salt water flow rate, water temperature, air flow rate and position of the water spray are examined in order to optimize the operating conditions. A quadratic model estimating the performance of the humidifier was developed and validated using the design of experiment analysis and variance approach. A response surface methodology was used to correlate and assess the influence of each parameter and its interactions with the others. The results indicate that the effect of air flow rate and inlet water temperature on mass and heat transfer is greater than the height of the sprayer and the saline water flow rate. Binary interaction effects of the variables were taken into account and provided for the design recommendations.

Vacuum membrane distillation is a thermal desalination process characterized by a low operating temperature which gives the possibility to coupling with renewable energy. New systems for producing drinking water from seawater using vacuum membrane distillation coupling with solar energy were simulated. The study of different configurations has allowed us to present the processing advantages and disadvantages of each configuration, and enabled us to suggest recommendations on the choice of the configuration according to the type of membrane and application context. In this work, two types of coupling configuration for the type of collectors were investigated. The models concerning the hollow fiber module, the cylindro-parabolic solar collector (CPC) and salinity gradient solar pond (SGSP) were developed. The simulation of the module model allows for the study of the effect of various parameters such us the temperature, velocity and salinity. Then the coupling between this model and the solar collector model was achieved. The solving of models equation allows the determination of each coupling configuration production along the year. The simulation shows that the production of the integrated module in a solar pond is the most productive configuration confirming the interest of the module integration. This system allows the production to reach about 32.5 m3/y.

AbstractIn isolated and arid areas, especially in the almost Maghreb regions, the abundant solar radiation intensity along the year and the available brackish water resources are the two favorable conditions for using solar desalination technology to produce fresh water. In this paper, a theoretical correlation named the “Lewis number” correlation is developed and used for the calculation of a simple and a hybrid solar distiller mass flow rate. Uses of single glass cover for periodically oriented still or double glass cover for fixed still are studied. Calculated results are compared with those obtained experimentally. It was found that the theoretical mass flow rate is in good agreement with that obtained experimentally.

In isolated and arid areas, especially in the almost Maghreb regions, the abundant solar radiation intensity along the year and the available brackish water resources are the two favorable conditions for using solar desalination technology to produce fresh water. In this paper, a theoretical correlation named the “Lewis number” correlation is developed and used for the calculation of a simple and a hybrid solar distiller mass flow rate. Uses of single glass cover for periodically oriented still or double glass cover for fixed still are studied. Calculated results are compared with those obtained experimentally. It was found that the theoretical mass flow rate is in good agreement with that obtained experimentally.

AbstractThe object of this study is the comparison between two configurations of hollow fiber module for seawater vacuum membrane distillation. The first one is a module membrane in series with a solar compound parabolic collector (CPC). The second configuration is a hollow fiber module integrated in a cylindrical absorber of CPC. A model describing the operation of a hollow fiber module, with and without recycling, will be developed. This model determines the instantaneous variation of the temperature of each element of the installation with the distillate flow variation. A comparison of each module production is carried out. A mathematical model describing the performances of different configurations for membrane hollow fibers shows that: (1) The permeate flow for the integrated configuration is always higher than that of not integrated. It can be multiplied by two and even more. (2) The recycling of concentrate makes it possible to improve the production. This is due to the high level temperature at the exit of the module. (3) The energy recovery from the distillate will make it possible to increase the production and to reduce the plant size.

The object of this study is the comparison between two configurations of hollow fiber module for seawater vacuum membrane distillation. The first one is a module membrane in series with a solar compound parabolic collector (CPC). The second configuration is a hollow fiber module integrated in a cylindrical absorber of CPC. A model describing the operation of a hollow fiber module, with and without recycling, will be developed. This model determines the instantaneous variation of the temperature of each element of the installation with the distillate flow variation. A comparison of each module production is carried out. A mathematical model describing the performances of different configurations for membrane hollow fibers shows that: (1) The permeate flow for the integrated configuration is always higher than that of not integrated. It can be multiplied by two and even more. (2) The recycling of concentrate makes it possible to improve the production. This is due to the high level temperature at the exit of the module. (3) The energy recovery from the distillate will make it possible to increase the production and to reduce the plant size.

AbstractSeveral papers deal with membrane distillation of seawater and mainly focus on the choice of membranes and comparison of this technique with other desalination techniques, but there are very few studies that quantitatively estimate the potential of this technology coupled with solar energy. The objective of this work is to develop a model describing the operation of a desalination membrane powered by solar energy. This model determines the performance of the unit over time and for any day of the year. This model is established from the balance equations of mass and heat on the different units (membrane, exchanger, condenser, and field of solar collectors). The model is used to evaluate the evolution of the distillate flow rate and temperature changes for different flows. The model also allows to estimate the productivity of the unit during the year. The simulation of the operation of the unit shows that the daily production of distilled water is between 63 and 188 kg/m2for the days of 21 December and 21 June.

AbstractIn arid coastal regions, the lack of potable water coincides often with high solar insolation. In this case, coupling of the desalination systems with solar energy is of great importance. Among the desalination systems, the membrane distillation technique holds numerous advantages. The present work focuses on the vacuum membrane distillation coupled with solar energy. The aim is to simulate a novel membrane configuration in order to enhance the permeate product. This novel membrane is composed of hollow fiber wound in helically coiled shape. Two-dimensional Navier–Stokes equations are written and then solved using the finite element method. For a pitch of 32.2 mm and a coil radius of 95.7 mm, the simulation results of the permeate product are 0.2685 kg/h and 7.688 10−3 kg/sm² for the permeate flux. These values present an enhancement when compared to the linear hollow fiber configuration at the same operating conditions. This enhancement is about 28% for the permeate flow rate.

Several papers deal with membrane distillation of seawater and mainly focus on the choice of membranes and comparison of this technique with other desalination techniques, but there are very few studies that quantitatively estimate the potential of this technology coupled with solar energy. The objective of this work is to develop a model describing the operation of a desalination membrane powered by solar energy. This model determines the performance of the unit over time and for any day of the year. This model is established from the balance equations of mass and heat on the different units (membrane, exchanger, condenser, and field of solar collectors). The model is used to evaluate the evolution of the distillate flow rate and temperature changes for different flows. The model also allows to estimate the productivity of the unit during the year. The simulation of the operation of the unit shows that the daily production of distilled water is between 63 and 188 kg/m2for the days of 21 December and 21 June.

In arid coastal regions, the lack of potable water coincides often with high solar insolation. In this case, coupling of the desalination systems with solar energy is of great importance. Among the desalination systems, the membrane distillation technique holds numerous advantages. The present work focuses on the vacuum membrane distillation coupled with solar energy. The aim is to simulate a novel membrane configuration in order to enhance the permeate product. This novel membrane is composed of hollow fiber wound in helically coiled shape. Two-dimensional Navier–Stokes equations are written and then solved using the finite element method. For a pitch of 32.2mm and a coil radius of 95.7 mm, the simulation results of the permeate product are 0.2685 kg/h and 7.688 10−3 kg/sm² for the permeate flux. These values present an enhancement when compared to the linear hollow fiber configuration at the same operating conditions. This enhancement is about 28% for the permeate flow rate.

This work focuses on solar energy coupled with vacuum membrane distillation (VMD) for brackish water desalination. VMD is an evaporative process, using porous and hydrophobic membranes, permit to obtain the gaseous permeate, under vacuum, from the aqueous liquid feed. The aim of this work was to simulate the influence of operating conditions (feed flow, feed temperature) and hollow fibers membrane characteristics (pitch and curvature radius) on the permeate flow rate. The model formulation takes into consideration the variation of the physical characteristics of brackish solution and the water permeability of membrane. We used in this case a membrane module, composed of hollow fiber wound in helically coiled shape and placed in the absorber of the parabolic trough concentrator. Two dimensional Navier–Stokes equations were written and were solved with the finite element method. For the pitch of 32.2mm and the coil radius of 95.7 mm, the simulation results of the permeate product are 0.2685 kg/h and 7.688 10-3kg/s m2for the permeate flux.

Evaluation of inner glass, outer glass water and basin temperatures as well as yield of a simple solar distiller (SSD) still is performed. Numerical computation based on the Runge-Kutta method is used. Experimental results and those calculated are then compared in terms of the above-mentioned parameters. Results concern the climatic conditions of Gabès (south east region of Tunisia). Effects of different parameters, namely the orientation and the use of single or double glass cover of the SSD still are studied. It is important to notice the significant effects on daily yield due to the studied operating parameters. It was found that the double glass cover use provides higher values of temperatures as well as the still productivity.

This work focuses on solar energy coupled with vacuum membrane distillation (VMD) for brackish water desalination. VMD is an evaporative process, using porous and hydrophobic membranes, permit to obtain the gaseous permeate, under vacuum, from the aqueous liquid feed. The aim of this work was to simulate the influence of operating conditions (feed flow, feed temperature) and hollow fibers membrane characteristics (pitch and curvature radius) on the permeate flow rate. The model formulation takes into consideration the variation of the physical characteristics of brackish solution and the water permeability of membrane. We used in this case a membrane module, composed of hollow fiber wound in helically coiled shape and placed in the absorber of the parabolic trough concentrator. Two dimensional Navier–Stokes equations were written and were solved with the finite element method. For the pitch of 32.2 mm and the coil radius of 95.7 mm, the simulation results of the permeate product are 0.2685 kg/h and 7.688 10-3kg/s m2for the permeate flux.

Evaluation of inner glass, outer glass water and basin temperatures as well as yield of a simple solar distiller (SSD) still is performed. Numerical computation based on the Runge-Kutta method is used. Experimental results and those calculated are then compared in terms of the above-mentioned parameters. Results concern the climatic conditions of Gabès (south east region of Tunisia). Effects of different parameters, namely the orientation and the use of single or double glass cover of the SSD still are studied. It is important to notice the significant effects on daily yield due to the studied operating parameters. It was found that the double glass cover use provides higher values of temperatures as well as the still productivity.

The present study is based on the use of three correlation groups which are: the Lewis number, the Dunkle and the ‘Kumar and Tiwari’ correlations for evaluating mass transfer in two types of solar stills. Theoretical results are compared with those obtained experimentally for a Simple Solar Distiller and a Hybrid Simple Solar Distiller/Heat pump stills. Experimental results and those calculated by Lewis number correlation show good agreements. Theoretical results obtained using Dunkle and ‘Kumar and Tiwari’ correlations are not satisfactory with the experimental ones.

The present study is based on the use of three correlation groups which are: the Lewis number, the Dunkle and the ‘Kumar and Tiwari’ correlations for evaluating mass transfer in two types of solar stills. Theoretical results are compared with those obtained experimentally for a Simple Solar Distiller and a Hybrid Simple Solar Distiller/Heat pump stills. Experimental results and those calculated by Lewis number correlation show good agreements. Theoretical results obtained using Dunkle and ‘Kumar and Tiwari’ correlations are not satisfactory with the experimental ones.