Mohammad Abutayeh

Theoretical and Experimental Simulation of Passive Vacuum Solar Flash Desalination

Experimental and theoretical simulations of a novel sustainable desalination process have been carried out. The simulated process consists of pumping seawater through a solar heater before flashing it under vacuum in an elevated chamber. Vacuum is passively created and then maintained by the hydrostatic balance between pressure inside the elevated flash chamber and outdoor atmospheric pressure. Experimental simulations were carried out using a pilot unit built to depict the proposed desalination system. Theoretical simulations were performed using a detailed computer code employing fundamental physical and thermodynamic laws to describe the separation process, complimented by experimentally based correlations to estimate physical properties of the involved species and operational parameters of the proposed system setting it apart from previous empirical desalination models. Experimental and theoretical simulation results matched well, validating the developed model. Feasibility of the proposed system rapidly increased with flash temperature due to increased fresh water production and improved heat recovery. In addition, the proposed desalination system is naturally sustainable by solar radiation and gravity, making it very energy efficient.

Experimental Simulation of Solar Flash Desalination

ABSTRACT Experimental simulations of a sustainable desalination process have been carried out using a small pilot unit at different operating conditions to enhance process analysis and modeling. The proposed desalination process, which employs solar heating and creates vacuum in an innovative passive way, has been theoretically simulated in earlier work. It entails flowing seawater through a condenser to preheat it then through a heater before flashing it in a vacuumed evaporator connected to the condenser where the flashed hot vapor is condensed by the incoming cold seawater forming fresh water. Flashing seawater at higher temperatures increases the vaporization and the production rate of fresh water. In addition, the accumulating non-condensable gases that are slowly eroding the vacuum will decrease the overall vaporization with time which reduces the production rate of fresh water. Keywords : solar flash desalination. INTRODUCTION Water demand is rising due to growing populations, while fresh water reserves are diminishing due to consumption and pollution. Desalination is the rational way to meet this rising water demand since oceans constitute an inexhaustible source of water. Moreover, energy demand is also rising due to worldwide development, but the traditional sources of energy are limited. Environmental, economic, and social troubles are unfolding over the consumption and control of these limited supplies. Solar radiation is an attractive source of energy due to its renewability and availability for free [1]. The objective of this study is to experimentally simulate the proposed solar flash desalination process and analyze its controlling variables. The simulation is achieved using a small pilot unit built to depict the proposed desalination system.

Solar Flash Desalination Under Hydrostatically Sustained Vacuum

A new desalination scheme has been proposed. The system consists of a saline water tank, a concentrated brine tank, and a fresh water tank placed on ground level plus an evaporator and a condenser located several meters above the ground. The evaporator-condenser assembly, or flash chamber, is initially filled with saline water that later drops by gravity, creating a vacuum above the water surface in the unit without a vacuum pump. The vacuum is maintained by the internal hydrostatic pressure balanced by the atmospheric pressure. The ground tanks are open to the atmosphere, while the flash chamber is insulated and sealed to retain both heat and vacuum. A theoretical simulation of the proposed model was carried out using a detailed model built by employing the fundamental physical and thermodynamic relationships to describe the process and was complimented by reliable empirical correlations to estimate the physical properties of the involved species and the operational parameters of the proposed system. The simulation results show that running the system at higher ,flash temperatures with a fixed flash chamber size will result in faster vacuum erosion leading to less overall evaporation.

Performance model of Shams I solar power plant

A performance model for Shams I solar power plant in Abu Dhabi has been developed using spreadsheets. The solar field of the plant is composed of 192 loops, where each loop contains 4 parabolic trough collector assemblies tracking the sun on a single axis. These solar collectors focus sunlight onto a heat transfer fluid flowing in their focal line, causing its temperature to rise. The hot fluid is then used to generate steam via a heat exchanger network in a separate Rankine cycle loop. The pressurized solar-generated steam is then fed to a turbine, where a generator connected to its shaft is used to produce electricity by the work of the expanding steam. The developed spreadsheet requires certain inputs to quantify electric power generation, such as solar radiation, ambient temperature, humidity, wind speed, time of day, day of year, and other geographical and optical constants. A simulation based on the data of a typical metrological year for Abu Dhabi found that the plant will generate 225 GWh of net electricity. Highest generation was accomplished in the summer months of May and June, while lowest generation was realized in the winter months of January and December. The model is very flexible in that it can be easily modified to model different operating periods with different time increments.

Experimental Study of a Solar Thermal Desalination Unit

Scarcity of potable water causes a serious problem in arid regions of the world where freshwater is becoming insufficient and expensive. Warm regions in the Middle East and North Africa are considered among the severest water shortage places. The objective of this project is to study the potential of using solar energy to run existing multi-stage flash (MSF) desalination units in the Arabian Gulf. One problem with MSF is the low efficiency of the system because of the bulk energy required for heating. Exploitation of solar energy in thermal desalination processes is a promising technology because of the ubiquitous nature of sun’s energy. Experimental studies were conducted on a single flash desalination unit. The pilot unit demonstrates the use of solar radiation as the thermal energy input. The process starts by preheating seawater through a vacuumed condenser. Seawater, then, flows inside a circulation tank to be indirectly heated by a heat transfer fluid. The heat transfer fluid circulates inside a flat plate solar collector facing south to absorb solar energy. After raising its temperature, seawater goes through an expansion valve and flashes in a vacuumed chamber to form brine and vapor. The vapor transfers to the condenser and condenses to form potable water by losing its latent heat of vaporization to incoming seawater. The flow rate of the working fluid is controlled via a control valve based on a set point temperature reference. The experiments were carried out using different values of the controlling variables to enhance analysis and validate results.Copyright

Solar Distillation and Drying

Extracting fresh water from seawater or brackish water requires a great deal of energy, both thermal and mechanical. Renewable energy driven processes are becoming more viable despite their expensive infrastructure because they employ free natural energy sources and release no harmful effluents to the environment. Solar radiation is usually chosen over other renewable energy sources in distillation systems because its heat can be directly applied to drive such systems without the adverse energy conversion losses.

Improved Modeling of Solar Flash Desalination Using Support Vector Regression

AbstractAccurate prediction of heat-transfer rates in condensers is a challenging task because of phase-change dynamics. This is further complicated if noncondensable gases are present since they t...

Accurate Prediction of Preheat Temperature in Solar Flash Desalination Systems Using Kernel Ridge Regression

AbstractThermal desalination systems consist of phase-change operations to separate freshwater from bulk seawater. Solar desalination systems involve partial vaporization of seawater, known as flashing, using solar heat then condensation of flashed steam to produce fresh water. The latent heat of the condensing steam is usually utilized to preheat seawater, thus increasing the energy efficiency of the desalination systems. Evaluating the feasibility of a solar desalination system requires accurate determination of seawater preheat temperature exiting the condenser to enter the evaporator. Determining this temperature is very challenging due to the complicated phase-change dynamics and the existence of noncondensable gases in the condenser that were dissolved in seawater. The preheat temperature depends on several factors such as seawater flow rate, system vacuum, and flashed vapor temperature. This study utilizes the kernel ridge regression (KRR) method to predict the preheat temperature as a function of ...

Adapting Steady State Solar Power Models to Include Transients

Quite a few computer programs have been developed to model power plant performance. These software codes are geared towards modeling steady state operations which is usually sufficient for conventional power plants. Solar thermal power plants undergo lengthy transient start–up and shut–down operations due to the sporadic nature of solar radiation; therefore, valid modeling of their performance must address those unsteady state operations.A novel scheme has been developed to fine–tune steady state solar power generation models to accurately take account of the impact of those transient operations. The suggested new scheme is implemented by adjusting solar radiation input data and has been shown to significantly improve modeling accuracy by moving modeled results closer to matching real operating data.Copyright

Modeling microparticles' path in DEP-FFF microfludic devices

This article documents the development of a dynamic model for predicting the trajectory of microparticles in a DEP-FFF microfluidic device. The electrode configuration is such that the top and bottom surfaces support multiple finite sized electrodes in the range of few micrometers. The electric potential inside the microchannel takes the form of Laplace equation while the equations of motion are based on Newtons second law. The forces considered include that due to inertia, drag, gravity, buoyancy and dielectrophoresis. All governing equations are solved using finite difference method with a spatial step size of 0.5 μm and temporal step size of 10-4s. In addition, a parametric study is carried out in order to understand the individual influence of operating and geometric parameters on the path of microparticles. The parameters considered include microparticle radius, actuation voltage, volumetric flow rate and microchannel height. It is found that all parameters influence the transient trajectory of microparticles while only a few parameters influence the final levitation height of microparticles.