Sharif Digital Repository

Performance optimization of a single-effect lithium bromide water absorption refrigeration system is the subject of this paper. First, the thermodynamic model of the system wasderived based on the first and second law analysis of an absorption refrigeration cycle with LiBr-water as the working fluid pair. Then, the effects of different design parameters such as the generator inlet hot water temperature, evaporator inlet chilling water temperature and absorber and condenser inlet cooling water temperatures on the performance of the systemwere investigated. In order that, by defining the coefficient of performance (COP), exergy efficiency (Second-law efficiency) and total cost function of the... 

The Persian Gulf is one of the aquatic ecosystems which has recently been faced with different pollutions. Cooling water discharges due to various industries such as power plants can cause important disorders on the present ecosystem balance and on aquatic creatures because of their high temperature. Thermal pollution leads to their migration, creates a potential for new coming species which in turn can thoroughly change the marine ecosystem feature. In this research, thermal pollution due to the Bandar Abbas Thermal Power Plant (BATP) development plan was modeled using MIKE21 software. In order to avoid a decrease in the power plant efficiency in the development plan, the distance between... 

Lake surface temperature is an important indicator of the lake state and a driver of regional weather and climate near large lakes. The objective of this study is to use thermal imagery from the MODIS on board the Earth Observing System Terra and Aqua platforms to assess the spatial and temporal variations in Urmia lake temperature. Urmia Lake, located in northwestern Iran is one of the largest permanent hypersaline lakes in the world. The surface temperature of Urmia Lake is examined between 2008 and 2009, as dry years. MODIS-derived lake SWT then was calibrated with monthly observations. MODIS-derived lake SWT exhibits a cool bias (-0.72°C) relative to in situ temperature observations in... 

Natural nanochannels and those used for applied purposes are often several nanometers in diameter and have lengths up to micrometer scales. Since normally no pressure gradient, mechanical force or electrical field is exerted on fluids in these situations, the fluid flow within them is not single-file and can be bidirectional. For this reason, studying the behavior of bidirectional flows in the channels is of paramount importance. In this study, a comprehensive investigation on the straight and non-straight bidirectional water transfer through carbon nanotubes is conducted via extensive molecular dynamics simulations. The results indicate that by changing the length, the diameter and the... 

Poly (vinyl alcohol)/graphene oxide (PVA/GO) gamma irradiated nanocomposite films and hydrogels were prepared. In composite films, GO was initially irradiated by gamma ray in order to improve interactions between GO and PVA. The film containing 1 wt-% GO was very strong where tensile modulus and tensile yield strength were 45 and 115% higher than those of pure PVA. In the second set of experiments PVA/GO hydrogels were made by irradiating PVA/GO suspensions by gamma ray at various doses. It was an interesting finding that GO increased the gel portion of hydrogels through contribution of H-bonds between PVA and GO. The hydrogels prepared at 20 kGy had remarkable water swelling ratio that... 

Theoretical and experimental analysis of performance of a solar desalination pond as a second stage of proposed zero discharge desalination processes is considered in this work. Major purpose of this proposed process is producing salt and potable water. Experiments are conducted for brackish wastewater with different salinity content. The relation between temperature variations of brackish water, glass, and base of solar desalination pond with condensation rate are discussed. Results indicate when brackish water temperature is increasing; the average daily production of solar desalination pond is increased considerably. Results of the mathematical modeling show good agreement with... 

In this study, the aim is to investigate the application of pulsating heat pipes (PHPs) as a heat transfer tool in a solar water heater (SWH). For this purpose, an extra-long pulsating heat pipe (ELPHP) is designed, constructed and installed in a thermosyphon solar water heater. In this work the ELPHPs are made of copper tubes of internal diameter 2.0. mm. The number of meandering turns is 6 and the working fluid employed is distilled water. The lengths of condenser and evaporator sections are 0.8 and 0.96. m, respectively. The length of adiabatic section varies between 0.7 and 1.8. m. Inclination of the ELPHPs varies between 15° and 90° but is 45° for evaporator section. Four different... 

This study deals with an experimental investigation on the thermal performance of a mechanical wet cooling tower with counter flow arrangement by using multi-walled carbon nanotubes (MWNTs) and nanoporous graphene nanofluids. Stable nanofluids were prepared through two-step procedure by using water with properties taken from a working cooling tower in the South of Iran. Zeta potential revealed suitable stability of MWNTs and nanoporous graphene nanofluids. Thermal and rheological properties of the nanofluids were investigated. It was found that thermal conductivity increases by 20% and 16% at 45°C for MWNTs and nanoporous graphene nanofluids, respectively. The increase in density and... 

The influence of liquid bulk viscosity on the dynamics of a single cavitation bubble is numerically studied via Gilmore model with a new modified boundary condition at bubble interface. In order to more accurately describe the interior gas thermodynamics, a hydrochemical model is used. The numerical results for an argon bubble in water and aqueous H2SO4 show that including the liquid bulk viscosity slightly affects the bubble dynamics in collapse phase. This effect becomes significant only at high ultrasonic amplitudes and high viscosities. Moreover, the maximum pressure value inside the bubble is much more influenced than the maximum temperature. This finding lends support to results of... 

Supercritical water was used for simultaneous fragmentation and reduction of graphene oxide (GO) sheets into water-dispersible graphene quantum dots (GQDs) with tunable sizes. Transmission electron microscopy (TEM) demonstrated that by increasing the temperature above the critical point of water, the average size and thickness of the GQDs were decreased and the size uniformity and production yield were increased. The results of thermal conductivity measurement of GQD nanofluids with different weight fractions indicated that the GQDs prepared at supercritical condition could enhance the thermal conductivity of water by 65% as compared to 35% for the GQDs synthesized at sub-critical... 

The purpose of the present study is to investigate the thermal performance of a photovoltaic/thermal system, integrated with phase change materials in porous medium. For this purpose, a metal foam was employed as porous medium and the performance of five different PCMs, as organic and inorganic, were examined as well. Moreover, the effects of different key parameters such as the mass flow rate, solar irradiance, inlet water temperature and inclination were studied. Finally, the simulation results were compared with a water-cooled photovoltaic/thermal without incorporating PCMs and porous medium, and thermal performance of the three PV/T cases were reported. The highest thermal efficiency of... 

Direct reduction of iron process in steel industry has special production conditions. Low quality cooling water, low cold and high hot cooling water temperature, space limitation for new equipment installation, high value-added of product and severe effect of cooling water temperature on production rate are of these conditions. Considering technical and economic constraints and limitations, this situation makes this process an attractive case study for converting the existing wet cooling tower to hybrid cooling system. In this paper, based on integration of process, dry and wet cooling system and ambient conditions profiles, a new method for designing hybrid cooling system has been proposed.... 

In this study, a latent heat storage unit and built-in condenser were integrated with a solar still. Storage of dissipated latent heat of vapor during the day and using it after sunset prolongs system operation. During the day, the entire solar radiation was consumed to heat the saline water and only the heat coming from the condensation of vapor was stored in the phase change material (PCM). The dissipated heat from the condenser body was transferred to the PCM and stored. Additionally, the existence of PCM on the outer surfaces of the condenser prevented the rise of condenser wall temperature during the day and kept the condenser temperature low. After sunset, the heat stored in the PCM... 

In this study, a numerical and empirical scheme for increasing cooling tower performance is developed by combining the particle swarm optimization (PSO) algorithm with a neural network and considering the packing’s compaction as an effective factor for higher accuracies. An experimental setup is used to analyze the effects of packing compaction on the performance. The neural network is optimized by the PSO algorithm in order to predict the precise temperature difference, efficiency, and outlet temperature, which are functions of air flow rate, water flow rate, inlet water temperature, inlet air temperature, inlet air relative humidity, and packing compaction. The effects of water flow rate,... 

In this study, a numerical and empirical scheme for increasing cooling tower performance is developed by combining the particle swarm optimization (PSO) algorithm with a neural network and considering the packing’s compaction as an effective factor for higher accuracies. An experimental setup is used to analyze the effects of packing compaction on the performance. The neural network is optimized by the PSO algorithm in order to predict the precise temperature difference, efficiency, and outlet temperature, which are functions of air flow rate, water flow rate, inlet water temperature, inlet air temperature, inlet air relative humidity, and packing compaction. The effects of water flow rate,... 

Remote sensing is an effective tool for capturing spatial and temporal variations of water surface temperature (WST) in large lakes. The WST of Urmia Lake in northwestern Iran was examined from 2007 to 2010, using MODIS land surface temperature (LST) products. Spatial and temporal (diurnal, monthly, seasonal and inter-annual) variations of Urmia Lake WST were also investigated. Results indicate that the MODIS-derived WSTs are in a good agreement with the in situ data (R2=0.92 and bias=-0.27). Spatial analysis of WST revealed that there are three thermal zones along the lake: the shallow region in barriers of the causeway, islands and the shoreline; the south part; and the deep north parts....