Sharif Digital Repository

In this work, the parametric study of a vapor compression refrigeration system integrated with a PCM storage tank for increasing the condenser sub-cooled temperature has been conducted based on the hottest day in Tehran city. The effects of various parameters such as comfort zone temperature, condenser and evaporator temperatures, and changes in heat transfer coefficient relative to the thickness of the ice formation in the PCM tank have been considered for simulating the desired system in the EES software. The focus of this study is to figure out the system's performance according to the changes in the effective parameters of the PCM storage tank. The results indicate that adding the PCM... 

In this study, the combination of a vapor compression cycle with a phase change material (PCM) storage tank has been assessed experimentally during the hottest day based on Tehran city climatic conditions. The temperature conditions for outdoor (condenser, compressor, etc.) and indoor (evaporator) air conditioning (AC) units are provided with the help of two separate test chambers and a controller system. The desired system has been surveyed based on two scenarios. In each scenario, the system is evaluated for the conventional AC system (with no PCM involved) and the AC plus PCM unit (conventional AC + PCM storage tank). Based on scenario 1 operating strategy, the results show that adding... 

Depending on the type of dopant metal, many kinds of zircon based pigments are produced and blue vanadium pigment is the most important one of them. In this study, blue zircon ceramic pigments were synthesized from intermediate product, resulting from decomposition of zircon sand with NaOH. In this regard, various amounts of sulfuric acid, water, NH4VO3 as colorant, NaF as mineralizer and extra quartz were added to the prepared Na 2ZrSiO5. Role of quartz was to omit the repercussions of presence of free zirconia in the composition. The main objective of this work is to assess various reactions at different temperatures during blue pigment synthesis. Phase analysis was done by X ray... 

Incremental launching is a widespread bridge erection technique which may offer many advantages for bridge designers. Since internal forces of deck vary perpetually during construction stages, simulation and modeling of the bridge behavior, for each step of launching, are tedious and time consuming tasks. The problem becomes much more complicated in construction progression. Considering other load cases such as support settlements or temperature effects makes the problem more intricate. Therefore, modeling of construction stages entails a reliable, simple, economical and fast algorithmic solution. In this paper, a new Finite Element (FE) model for study on static behavior of bridges during... 

Introduction: Research evidence indicates that maladaptive reorganization of the brain plays a critical role in amplifying pain experiences and pain chronification; however, no clear evidence of change exists in brain wave activity among patients with chronic low back pain (CLBP). The objective of this study was to assess brain wave activity in patients with CLBP, compared to healthy controls. Methods: Twenty-five patients with CLBP and twenty-four healthy controls participated in the study. A quantitative electroencephalography device was used to assess brain wave activity in eyes-open and eyes-closed (EO and EC) conditions. The regional absolute and relative power of brain waves were... 

In this survey, the integration of a vapor compression cycle with a phase change material (PCM) storage tank has been evaluated experimentally during the hottest days of five cities with different weather conditions: Tehran, Ramsar Hamedan, Bushehr, and Ahvaz. The temperature conditions for outdoor (condenser, compressor, etc.) and indoor (evaporator) air conditioning units are provided with the help of two separated test chambers and a controller system. The desired system has been examined based on two scenarios. In each scenario, the system is assessed for the conventional air conditioning (AC) system (with no PCM involved) and the AC plus PCM unit. Based on scenario 1 operating strategy,... 

Absorptive characteristics of polyaniline synthesized in different solvents were studied. Water and mixture of water with other solvents were implemented for polyaniline synthesis. Synthesized polyanilines in powder shape is used as an adsorbent to remove toxic hexavalent chromium from aqueous solutions. Experiments were conducted in batch mode. Removal mechanism involving polyaniline is the combination of surface adsorption and reduction. The kind of solvent used at synthesizing stage can affect the capacity of produced polyanilines for removal of heavy metals including chromium. Synthesized polyaniline in water had the maximum chromium removal efficiency. The morphology study of... 

The adsorption of chromium compounds from solutions by a composite of polyaniline/poly ethylene glycol (PANi/PEG) was investigated in this study. Experiments were conducted in batch mode under various operational conditions including agitation time, solution pH, PANi/PEG dose and initial concentration of chromium salts. Results showed that concentration of PEG at synthesizing stage has a significant effect on the capacity of produced composite for removal of chromium. Morphologically, PANi/PEG composite is closely dependent on the concentration of PEG. Maximum removal of hexavalent chromium was experienced when 2. g/L of PEG was used in synthesis of PANi/PEG. Removal of hexavalent chromium... 

A vapor-compression cooling system utilizing PCM is studied whereby the electricity consumption peak load is shifted. More specifically, the dynamic performance of the cooling system with and without PCM is evaluated and is presented with details on the hottest day of the year in Tehran, Iran. The proposed system uses the cooling energy to freeze or “discharge” the PCM during nighttime when the cooling load is minimally needed and uses the stored cooling energy during the peak load hours by melting or “charging” the PCM. This leads to better performance during the peak load hours when higher cooling loads are required. Oleic acid was chosen as PCM. The simulation was performed in EES... 

In this study, a vapor-compression cooling system utilizing different phase change materials (PCMs) has been studied whereby the electricity consumption peak load is shifted. More specifically, the dynamic performance of cooling systems with and without using PCM is evaluated for the hottest day of the year. The proposed system uses the cooling energy to freeze, or “discharge” the PCM during nighttime when the cooling load is minimally needed and uses the stored thermal energy during the peak load hours by melting, or “charging” the PCM. This leads to better performance during peak load hours when higher cooling loads are needed. Different PCMs including oleic acid, SP224A, CL, CaCl2·6H2O... 

In this paper, a new control strategy and power management for a stand-alone PV/battery hybrid power system has been suggested. The solar cell arrays provide energy in the steady-state and the battery provides energy in transient states. Here, a charge controller system based on the MPP tracking technology, suitable for using in the islanded micro grid that contains a solar panel and a battery is designed. The charge controller includes a unidirectional DC-DC converter as an interface circuit between the solar panel and the DC bus, a bidirectional DC-DC converter as an interface circuit between the battery and the DC bus with a control system and power management in different states of... 

During construction of one of the Sahand cooling towers due to slip forming performance some imperfections were raised mostly between elevation of +30 and +40 meter. It was evaluated that some points of the shell should be repaired. In constructing the cooling tower from elevation +40 to +60 meter these imperfections were removed and the cooling tower was constructed with no problem until the elevation +130 meter. In this paper reasons of generation of geometric imperfections in Sahand cooling tower are clearly shown and possible ways for preventing them are discussed. Applied repairing method for Sahand cooling tower is explained in detail. Geometrical imperfections of the constructed... 

Elastic joints in 2-mass drive systems, may lead to torsional oscillation which is usually rectified by reducing the bandwidth of control system. In order to improve the control performance, feedback signals from all the states are required. All the states of a drive system with a flexible coupling cannot be easily measured so it is usually necessary to estimate some of the system states using appropriate observers. In this paper, the measurement noise and disturbances of the system are well rejected using a proposed modified Luenburger observer. Compared to the classic observers, a significant improvement in the quality of the state estimation of a two mass system is obtained at a wide... 

In the endurance time (ET) method, structures are subjected to a specially designed intensifying ground acceleration function and their performance is judged based on their response at various excitation levels. A range of equivalent intensities can be covered in a single numerical or experimental simulation, thus significantly reducing the computational demand as compared to full nonlinear response-history analyses. The applied excitation intensity at various times has been correlated with those of the scaled ground motions. Response spectra of seven ground motions on stiff soil were used to produce intensifying acceleration functions that at each time window produce a response spectrum... 

In the present study, the fluid characteristics of triangular turbulent jet flow are considered experimentally and numericafly. The results of spatially developed three- dimensional jet, issued from an equilateral triangular nozzle are presented. The jet is discharged to both bounded and unbounded domains. Because of the wind tunnel set up restrictions, the experimental study has done just for the bounded domain. The hot-wire anemometry is used for experimental study. A numerical method employing control volume approach with collocated grid arrangement which couples the velocity and pressure fields with SIMPLEC algorithm is introduced to discrete the governing equations of fluid flow. The...