다중효용 담수 설비의 증기이젝터 진공장치에 관한 수치해석

Advanced MED process for most economical sea water desalination

The efficacy of seawater desalination has a profound impact in terms of reducing the water demand-supply gap especially in dry and arid countries. In UAE, 90% of the country’s water supply relies solely on desalinated water where a high share of the desalination plant’s output is aimed towards water supply for residential buildings. The hospitality sector consumes 50% more than the global average. The purpose of this paper is to determine the technical and economic viability for the integration of a concentrated photovoltaic thermal (CPV/T) system with a hybrid reverse osmosis (RO) and multi effect desalination (MED) plant. The system was designed to meet the water demand of a luxurious beach resort located in Fujairah. The resort accommodates about 110 occupancies per day. The estimated water consumption is 51m3/hr. The proposed system was analyzed with the aid of numerical simulation and reverse engineering calculations. The capacity of the CPV/T module, which represents the electrical and thermal energy output supplied to the RO and MED plant was determined using TRNSYS software. The results showed an efficient solar system providing electricity of 3500 kWh/year and thermal energy of 14,100 kWh/year, that is required to meet the water consumption of the hotel. In addition, the proposed system proved to be economically feasible, achieving a payback period of 3.6 years under an average lifetime of 20 years.

Water is one of the most stressed resources on the planet. The limited availability of fresh water and the high cost of transportation have led to an increased interest in water desalination technologies. The two main categories of desalination techniques are membrane desalination and thermal desalination. Membrane technologies include pressure driven and electrical driven membranes. On the other hand, thermal desalination includes: multi-effect desalination (MED), multi-stage flash (MSF) desalination, and mechanical vapor compression desalination. Multi-effect desalination plants are usually made of a series of evaporators (also known as effects). In each effect, hot steam flows inside the tubes and evaporates the seawater that falls on the outside of the tubes. The vapor formed at each effect flows to the next effect and acts as the heating medium for the falling seawater. The prevailing flow mode of the falling seawater (i.e. droplet, jet, or sheet) influences heat and mass transfer as well as dry out in the evaporators of Multi-Effect Desalination (MED) plants. The objective of this paper is to predict and discuss the prevailing falling film flow modes in the evaporators of MED plants, under different operating conditions. The paper demonstrates the transitional Reynolds numbers between the main falling film modes for seawater. This closes a gap in the literature where there is a dearth of mode transition data for seawater. The effect of fluid properties and tube geometry on the transitions is discussed in details. The accuracy of the predicted transitional Reynolds numbers is evaluated via uncertainty quantification techniques.

Numerical investigation on characteristics of falling film in horizontal-tube falling film evaporator

Presented is an investigation of the wind-tunnel nozzle effects on the thermal performance within passenger vehicle underhood area. The Lattice-Boltzmann Equation (LBE) based flow solver is coupled with the system tool to solve for airflow and temperature distribution around the passenger vehicle in the wind tunnel. Several simulations with different nozzle sizes were performed. The simulation results are compared with airflow, temperature, and heat exchangers heat rejection measurements in the thermal wind tunnel. Good agreement is observed confirming that nozzle geometry dominates the airflow around the vehicle. The results show that different nozzle sizes can produce flows that have almost the same macroscopic characteristics while at the same time have subtle differences that can be very important for the vehicle design.

scarcity. Underground water is mostly saline and other sources are small seasonal rivers and dams that collect rain water for sprawling population. Desalination plants can alleviate this problem to an extent. This paper examines various desalination plants, provides detailed technical discussion of Passive Vacuum Flash Type Solar Thermal technology and compares it with Concentrating Solar Desalination technology. Comprehensive levelised cost of water calculations are laid out for conventional Reverse Osmosis (RO) plant, Photovoltaic (PV) RO plant, conventional thermal Multi Effect Desalination (MED) plant and solar thermal MED plant. PVRO with cost of PKR 0.39 per gallon is the most suitable option.

Fresh water production is one of the main concerns in the new century. Population grows fast and potable water resources are decreased. In the other hand energy crises would also be another issue that must be well addressed by the politicians and also scientists. Developing desalination plant with using renewable energy (particularly solar energy) is one of the important options to overcome these concerns. Thus many researchers have been working on different desalination plants to find the best conditions and to realize the most efficient performances for different cycles. Different approaches have been used to achieve the most efficient conditions or to find the optimum operation and design conditions. Some of the researchers used parametric study approach while many other adopted different conventional optimization algorithms for these tasks. The algorithms such as gradient based algorithm, genetic algorithm, search and pattern algorithm and neural network method have been used in the field of desalination. For instance; Ophir and Lokiec (2005) described the design principles of a MED plant and various energy considerations that result in an economical MED process and plant. Kamali and Mohebbinia (2007) showed that parametric study as one of the optimization methods on thermo-hydraulic data strongly helps to increase GOR value inside MED-TVC systems. Shamel and Chung (2006) used parametric study to find the optimum condition of a Reverse Osmosis (RO) system for sea water desalination. Metaiche et al (2008) developed optimization software, Desaltop, for RO system for water desalination. They used genetic algorithm to find suitable operating parameters and also to find appropriate type of membrane. Al-Shayji (1998) used neural network method for optimization of large-scale commercial desalination plants. Djebedjian et al. (2008) used genetic algorithm for optimization of a reverse osmosis desalination system. Mussati et al. (2003) used an evolutionary algorithm for the optimization of Multi Stage Flash (MSF) system. Finding the optimum conditions is a major challenge on the desalination plant studies. The plant performance depends on several different variables and constraints that need exhausting efforts to find the optimum conditions. This chapter introduces Design of Experiment (DOE) method as a statistical tool for optimization of desalination systems. Thus two different desalination plants; Multi-Effect Desalination (MED) system and solar desalination using humidification–dehumidification cycle (SDHD) have been considered to show the ability of DOE method for optimizing such systems. These both desalination plants could use the low graded heating energy sources

Through numerical simulation, key issues concerning the plasma jet features as well as the sizes of nozzle for supersonic atmosphere plasma spraying (SAPS) were analyzed in this paper. Numerical results were compared with the experimental measurements and a good agreement has been achieved. Due to the effect of mechanical compression, the increasing sizes ofr1,r2,r3andr4(r1,r2,r3andr4are the sizes of nozzle) lead to a decrease in temperature and velocity of plasma jet. But large size ofr5can increase the external temperature and velocity of plasma jet, which benefit particles accelerating at the far downstream region. A new nozzle was designed based on the simulation results. Compared to the temperature and velocity of plasma jet in the original nozzle, the maximum temperature and velocity of plasma jet in new structure are increased by about 9.8% and 44.5%, which is a benefit to the particles to reach a higher speed and surface temperature.

Heat and mass transfer processes between a water spray and ambient air – II. Simulations

In multi-effect desalination (MED) plants, the evaporators are usually of horizontal falling film type. For this kind of evaporators, high heat transfer coefficient can be achieved over low temperature difference and low spray density/liquid load. The current operating temperature range of MED plants is from 65 to 40 °C and researchers are trying to widen this range (85–5 °C), in order to enhance desalted water productivity. In this study, review of heat transfer coefficient correlations for falling films was carried out. The heat transfer coefficient prediction by different studies was compared with respect to film Reynolds number and working temperature. It was found that the empirical correlations by Fujita and Tsutsui, and Danilova et al. were better in evaluating heat transfer coefficient for MED application. It was concluded that increasing the top brine temperature (TBT) of MED evaporator is more beneficial than decreasing the lower temperature. The estimated heat transfer coefficient at 5 °C was 30–65% was less than that of heat transfer coefficient at 85 °C.KeywordsFalling filmHeat transfer coefficientHorizontal tubeMED

Techno-economic analysis of a combined concentrated solar power and water desalination plant

Performance enhancement of a multi-effect desalination plant: A thermodynamic investigation

Thermodynamic optimization of multi-effect desalination plant using the DoE method

Multiple scattering of light by the fluctuations of the director in a nematic liquid crystal (NLC) aligned by a magnetic field is considered. A peak of coherent backscattering is calculated by numerical simulation. Since the indicatrix of single scattering for a liquid crystal (LC) is known exactly, the calculations are carried out without any simplifying assumptions on the parameters of the liquid crystal. Multiple scattering is simulated as a random walk of photons in the medium. A peak of coherent backscattering in such a medium is very narrow; therefore, the so-called semianalytical method is applied. The parameters of the backscattering peak obtained by numerical simulation are compared with the available experimental data and with the results of analytical approximations. It turns out that the experimental data are in good agreement with the results of simulation. The results of numerical simulation adequately describe the anisotropy and the width of the backscattering peak.

Multi-effect desalination (MED) uses less energy and has a smaller footprint than other thermal desalination systems. The MED plant consists of cascaded horizontal-tube falling film exchangers (HFFE), offering improved heat transfer at lower liquid loads. The MED plant’s current working temperature range is 40 °C–65 °C, for which 6–8 HFFE can be used. However, this limit can be extended to 5 °C–85 °C by using new antiscalants and an adsorption vapor compression system. Thus, more HFFE can provide enhanced water production. Furthermore, the heat transfer studies for this range are limited. Therefore, this work presents a 2-D computational fluid dynamics (CFD) model in Ansys fluent v19.0 to examine the film thickness, the temperature distribution, and the heat transfer coefficient for working temperatures of 5 °C, 65 °C, and 85 °C at various liquid loads. It is found that the heat transfer is improved at higher temperatures and liquid loads by 21 %–37 %, which indicates lower energy requirements and better distillate productivity.