access deny [1301]
Research field: Water and Energy
Expert: Jamal Darand
Phone: +2182884941
Address: Mechanical Eng. Dpt.
access deny [1026]
The cleanroom is a controlled space used in various industries such as electronics, and medical and military industries. One of the most important tests to evaluate the performance of the cleanroom is recovery test. Recovery test determines the time period during which a cleanroom returns to its designated cleanliness level after an instant or a period of deliberate or unintentional contamination. In this paper, a thorough investigation of recovery period has been implemented. In the study, air change rate and its pattern were investigated using the Eulerian and Lagrangian approaches as well as LES, DES, and κ-oj SST turbulent models. Simulation results were evaluated through control volume analysis. Parameters such as the air change rate,
Considering water level and pressure variation in drum of a?natural circulation heat recovery steam generator (HRSG) is very crucial to design?HRSGs; in other words, if a sudden change occurs in input heat rate, steam and feed water flow rate, drum water level would increase or decrease rapidly. Therefore, due to their important role, drum inlet parameters, such as steam quality and pressure should be accurately controlled. In this study, a dynamic simulation of HRSG was carried out to investigate dynamic behavior of important key parameters involved in the steam generating process. The rate of produced pure water by brine concentration plant under varying gas turbine load and consequently input heat rate to the HRSG’s risers
In this paper, thermo-economic evaluation of hybrid solar-conventional energy supply in a zero liquid discharge plant has been conducted. The zero liquid discharge plant includes a brine concentrator and a crystallizer. Brine concentrator and crystallizer utilize falling film and forced circulation evaporators respectively. The plant was studied thermo-economically in capital of Iran, Tehran city weather conditions. The plant performance and economics were investigated in four design (winter, spring, summer and autumn design) conditions based on the seasonal weather data and compared with the conventional energy supply system. It was concluded that the design proposed based on average weather conditions shows no economic advantage over the
Stirling engines have recently been studied theoretically via two different methods, thermodynamic analysis and CFD simulation. Evidently, second order thermodynamic analysis is simpler and less time consuming than CFD. However CFD considers more details as well as the engine geometry and consequently reflects more details about the flow field and losses phenomena. In this paper, numerical simulation of a typical Stirling engine was conducted by OpenFoam open source software. Dynamic mesh was used to simulate moving pistons and the working fluid was considered compressible. Volume averaging technique was applied to simulate flow in the regenerator as a porous media. The well-established PIMPLE algorithm was used to handle pressure coupling
Presence of salts in water has been one of the biggest problems of industrial equipment such as evaporators, boilers, and pipes. These salts gradually form scales on evaporators and boilers tubes and reduce their efficiency. Pretreatment processes are conducted to remove these salts; with sedimentation tanks being one of the essential equipment used in these processes. This study numerically simulates multiphase flows in the sedimentation tanks using Discrete Phase Model (DPM). Various important parameters, such as sedimentation tank entrance and existence of baffle in the case of non-homogenous injected particles are studied. The results indicated that the bottom entrance tank provides maximum sedimentation efficiency of 70.3%. In addition
This paper aims to study the operating mechanism of Stirling Pulse Tube Refrigerators (PTRs) by tracing the characteristics of working gas elements at the cold end of the system using both Eulerian and Eulerian-Lagrangian (EL) methods. The main objective of the investigation is to demonstrate non-symmetry effects in the pulse tube section of the system. Elemental cyclic-enthalpy transfer of Simple (S), Double-Inlet (DI) and Multi-Mesh regenerator (MM) PTRs are also investigated to demonstrate the effects of DI and MM systems on the refrigeration mechanism of PTRs. It is shown that the elemental cyclic-enthalpy transfer of SPTR is less than that of DIPTR, MMPTR and MMDIPTR. Also, its elemental cyclic-temperature reduction is more than the ot
In this paper, dynamic simulation of a Multi-Effect Distillation process has been conducted via deriving, discretizing, and solving PDEs governing its tube-bundle behavior. Possessing a complex process and different heat transfer mechanisms has limited recent researches to steady-state simulations. A detailed examination was performed on existing correlations of falling film evaporation on horizontal tubes and condensation inside them. A couple of appropriate correlations were selected and applied to calculate the transferred heat. Results showed that during start-up and feeding the main steam to the process, vapor quality almost drops linearly inside tubes. Moreover, during initial time steps, steam condenses quickly and forms a mass of su
In the present work the transient behavior of ejectors is explored experimentally and numerically. The main goal is to achieve an appropriate numerical model for predicting transient phenomena in ejectors. To validate the numerical results, an experimental test rig was built up and a set of experiments was performed. Results showed a good agreement between experiments and numerical simulations and the average deviation of about 16 percent was achieved. Furthermore, employing the validated numerical model a vacuum steam ejector was simulated numerically. Two different linear motive flow pressure profiles were applied to simulate the ejector performance. Results showed that as the slope of the motive flow pressure profile increases as much as
Wind turbines are used in a variety of applications with different performance requirements. Investigating the influence of scaling on wind turbine characteristics can pave the way to utilize the experience gained from a smaller turbine for a larger one. In this paper, the effects of wind turbine size on aerodynamic characteristics of a rotor blade are examined using CFD simulation. NREL phase VI wind turbine rotor was simulated in order to validate the results and ensure the accuracy of the CFD model. A 2?MW wind turbine was then chosen as a large turbine and a scaled down model of its rotor was simulated numerically. The results of the simulation were introduced to Similarity Theory relations in order to predict the aerodynamic characteri
This paper is aimed to investigate the influence of axial heat conduction on conjugate heat transfer for oscillating flow at the pulse tube section of Pulse Tube Cryocoolers (PTCs) via a numerical approach. Finite volume technique with collocated arrangement of grids has been employed to discretize momentum and energy equations. The well-established SIMPLE algorithm was followed for handling the pressure–velocity coupling. The set of individual algebraic equations was solved by the Strongly Implicit Procedure (SIP). Strouhal number (St), wall thickness and solid to fluid conductivity ratio (ksf) are three important parameters which affect the conjugate heat transfer in oscillating flow in pulse tubes. It is shown that the overall Nusselt
Laminar mixed convection of Aluminium oxide (Al 2 O 3)–water nanofluid flow in an inclined annulus using a single-phase approach was numerically studied. Constant heat flux boundary conditions were applied on the inner and outer walls. All the thermophysical properties of nanofluid, such as, viscosity, heat capacity, thermal conductivity, and thermal expansion coefficient, except density in the body force term were assumed to be constant. Based on Boussinesq’s hypothesis, density was assumed to be a linear function of temperature. The nanofluid properties were calculated in terms of constant properties of nanoparticles and the base fluid. Using the finite volume method the continuity, momentum, and energy equations were numerically solv
In recent years, wind energy experienced faster growth compared with the other renewable energies. The interaction between fluid and structure becomes more important as the wind turbine size and its power production capacity increases. In the present research, the effect of wind speed and blade materials on static deformation of a small size horizontal axis wind turbine blade is investigated. The shaft torque and root flap bending moment values obtained from simulation are in a good agreement with experimental data. Results demonstrated that the deformation of the blade increases as the wind speed grows, although the increase rate has declined in the mean wind speed range because of the occurrence of separation phenomenon on the blade surfa
In this research, subsonic flow in a MHD (Magneto-Hydro-Dynamic) generator has been simulated and its influence on efficiency and power generation of a triple combined cycle has been investigated. A 2D variable cross-section Faraday channel with segmented electrodes was utilized as a MHD generator model. MHD flow assumed to be ideal with low magnetic Reynolds number. The proposed triple cycle consists of an open MHD channel as a topping cycle, a gas turbine as a middle generator and a steam turbine as a bottoming cycle. A code including the equations, governing the triple cycle behavior, has been developed to analyze the performance of the combined cycle based on MHD generator. The optimum efficiency of 71.32% was attained for the triple cy
Multi-effect distillation is one of the thermal desalting systems. MEDs have recently come to notice more than other systems because of their high energy utilizing and performance. High complicity and possessing different heat transfer mechanisms have distinguished them from other desalination systems such as Multi-stage flash. In MEDs although formation of thin fallingfilm layer on horizontal rows of tube-bundle increases heat transfer, however the risk of precipitation will be high especially on lower rows where film thickness is the least. Falling-film evaporation is a self-compensation phenomenon; the more the evaporation, the thinner the film, and subsequently the more the evaporation. In present work, an applicable algorithm is propos
During the last two decades, inertance tube pulse tube cryocoolers (ITPTC) applications in astronautics instruments gained momentum due to their high reliability. Moreover, significant efforts were made in order to improve ITPTCs operation. Investigations showed that most losses occur in the regenerator part. Due to complexity of physics of these losses, effects of the regenerator efficiency on the cryocooler performance were investigated in this work. Tocalculate heat transfer between solid matrix and acting fluid in the regenerator, Dual Energy Equation (DEE) model was used. Calculation of entropy flow inside the regenerator showed that almost 85% of the energy losses are due to viscous and inertial losses besides most of the energy losse
In recent years, vertical tube falling film evaporators have been widely used in desalination industries. In this paper mathematical modeling of a multiple effect evaporators (MEE) system has been carried out for brackish water desalination. The system includes a set of forward feed vertical tube evaporators with thermal vapor compression (TVC) and a condenser. Modeling has led to calculation of several parameters such as overall heat transfer coefficients, entrainment ratio and recovery of the process which is restricted by scale formation. A scaling prediction chemical model has been employed to calculate the allowable rate of recovery for prevention of scale formation. Physical properties of streams have been assumed as functions of temp
In the present paper, a two-dimensional compressible oscillating flow in the tube section of a pulse tube refrigerator system is modeled, based on the successive approximation method. In this respect, the variables are expanded up to second-order terms. For pulse tubes with an outer adiabatic surface, the conservation equations of mass, momentum, energy, and the equation of state for the ideal gas are applied. The effects of operating frequency and taper angle on the temperature distribution, heat transfer behavior, and time-averaged enthalpy flow during a cycle are investigated. Increasing the frequency leads to a higher heat transfer rate in the pulse tube. The enthalpy flow, as the cooling performance representative of the pulse tube, re
So far, several combined cycles have been proposed with MHD generator as a topping cycle and gas turbine or steam turbine as bottoming cycles. Triple cycle which is examined in this study is a modification of all dual cycles has been proposed in different papers. Most of available cycles are dual. High temperature of hot gases exhausted from the MHD generator, was the motivation to consider the performance of triple cycles in this paper. The MHD generator is employed as a topping cycle, Brayton (gas turbine) as an intermediate and Rankine cycle (steam turbine) as a bottoming. Combined cycle analysis showed that, efficiency of the proposed triple combined cycle is 65%. Efficiency of proposed cycle is greatly more than that of a dual one. In