Sharif Digital Repository

In this study, a novel idea of storing the latent heat of condensing vapor in solar stills by means of phase change materials (PCMs) as a thermal storage is experimentally investigated. During the daytime, the generated water vapor by the solar energy, is conducted to an external condenser filled with PCM to be condensed. The wasted latent heat is absorbed by PCM and thereby stored. It is worth noting that there is no direct contact between the saline water and the PCM, therefore, the solar energy is not directly stored in the PCM. In the evening, the energy stored in the PCM is transferred as heat to the saline water by heat pipes and enables the desalination process to continue. Several... 

In this study, the theoretical investigation of a novel heat pump assisted humidification-dehumidification desalination system has been carried out. The conventional dehumidifier of the humidification-dehumidification system was removed and the evaporator of the heat pump was utilized for direct dehumidification of air. Besides, the heat pump condenser was used as the saline water heater of the humidification-dehumidification cycle. First, the sizes of the components were calculated at design conditions for fixed input operational conditions namely the ambient air temperature, relative humidity, and inlet saline water temperature. However, the input operating conditions vary at off-design... 

A new design for heat pump integrated humidification-dehumidification (HDH-HP) desalination cycles was proposed in the current experimental study. An evaporative condenser was designed and fabricated instead of a separate humidifier, heater, and air/water-cooled condensers find in previous HDH-HP systems. Meanwhile, the air dehumidification process in this work directly occurred inside the heat pump evaporator. The effect of several operating parameters such as ambient wet-bulb temperature, spraying saline water and airflow rates, compressor speed, superheat, and evaporator saturation temperature control modes of the electronic expansion valve (EEV) on freshwater production and GOR were... 

A hybrid HDH desalination system integrated with a heat pump was experimentally studied. In this system, heat pump's heating was used to raise the temperature of the air entering the humidifier and its cooling effect was used for dehumidification of humid air and freshwater production. In other words, heat pump's condenser works as the heater of the HDH cycle and its evaporator works as the coolant for the dehumidifier of HDH cycle. The effects of different parameters such as mass flow rate of inlet saline water (relative humidity of the air passing the dehumidification section), volume flow rate of the air passing the dehumidification section and ambient air temperature on freshwater... 

In this study, a novel Magnetically Variable Conductance Thermosyphon Heat Pipe (MVCTHP) was investigated experimentally. The possibility of deactivating a portion of evaporator length and subsequently altering heat pipe resistance by positioning a steel ball inside the evaporator and moving it by an external magnet was studied. The effect of various ball positions in the evaporator and inclination angles on heat pipe performance was studied at 30, 60, 90 and 120 W. The results indicated that at a given heat input, moving the ball away from the beginning of the evaporator of heat pipe increases its thermal resistance. Furthermore, by increasing heat input, MVCTHP performance for various ball... 

In this article, a novel solar still which is equipped with thermoelectric modules to utilize the heat of vapor condensation is experimentally investigated. The use of thermoelectric modules as devices for generating electricity from the temperature difference between two environments (hot vapor steam and cold ambient air) as well as taking outstanding advantages of evacuated tubes as collectors with high performances in adverse climatic conditions, led to utilizing of the energy dissipated due to vapor condensation and a considerable increase in the performance of the system. The effect of using the generated electricity to operate a small propeller fan for inducing forced convection was... 

In common solar stills, a portion of the produced vapor undesirably condenses on the sidewalls and runs down to be mixed with saline water in the basin. This results in lower distillate output of the system. The aim of this study was to improve the condensation process of a solar still without complicating its structure to collect the water condensed on sidewalls. The proposed solar still was made of two containers nested one inside the other such that the smaller container, containing saline water, fitted easily into the larger container. There was a thin gap between the two in which condensed liquid on sidewalls, ran down and was collected from the bottom of the larger container. The... 

In this study, the application of data-driven methods for performance prediction of a heat pump assisted humidification-dehumidification (HDH-HP) desalination system was investigated for the first time. Although HDH-HP desalination systems have been widely studied both theoretically and experimentally, the application of data-driven models as a powerful predictive tool has not yet been investigated in these systems. To fill this gap, three data-driven models (MLPANN, RBFANN, and ANFIS) were applied using 180 experimental samples. The gain output ratio (GOR), heat transfer rates of the evaporator Q̇e, and evaporative condenser Q̇c, were considered as outputs. The results indicate that the... 

Low-temperature geothermal heat sources have the highest share of geothermal energy in the world. Utilization of these heat sources for energy and freshwater generation can play an important role in meeting energy and freshwater demands. To do so, this study aims to propose a novel trigeneration cycle powered by low-temperature geothermal sources. The proposed system, which is an integration of Kalina and humidification-dehumidification (HDH) cycles, is used for the generation of electricity, heating, and freshwater. For the Kalina cycle, an evaporative condenser is used. It also acts as a humidifier and heater of the humidification-dehumidification desalination cycle, resulting in a... 

Water and energy supply are two of the key issues human beings must address to attain sustainable development. Humidification-dehumidification technology has been proven to be a cost-effective approach to fulfill the freshwater demand. Particular attention has been given to coupling the humidification-dehumidification cycles with refrigeration, power and other desalination technologies with the aim of enhancing the performance of the combined cycle as well as increasing the amount of produced freshwater, cooling effect, power, etc. This paper provides a comprehensive review of the state-of-the-art investigations in terms of humidification-dehumidification technologies and their integration... 

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit... 

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive... 

There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas  

By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only...