Sharif Digital Repository

Microbial fuel cells (MFCs) have been a potential green energy source for a long time but one of the problems is that either the technology must be used on a large scale or special equipment have been necessary to keep the fuel cells running such as syringe pumps. Paper-based microbial fuel cells do not need to have a syringe pump to run and can run entirely by themselves when placed in contact with the fluids that are necessary for it to run. Paper-based microbial fuel cells are also more compact than traditional MFCs since the device doesn't need any external equipment to run. The goal of this paper is to develop a microbial fuel cell that does not require a syringe pump to function. This... 

The present study examines Alternating Current (AC) electroosmotic flows in a parallel plate microchannel subject to constant wall temperature. Numerical method consists of a central finite difference scheme for spatial terms and a forward difference scheme for the temporal term. Asymmetric boundary conditions are assumed for Poison-Boltzmann equation for determining the electric double layer (EDL) potential distribution. The potential distribution is then used to evaluate the velocity distribution. The velocity distribution is obtained by applying slip boundary conditions on the walls which accounts for probable hydrophobicity of surfaces. After determining the velocity distribution... 

Using reverse nonequilibrium molecular dynamics simulations the influence of intermolecular bridges on the thermal conductivity (λ) in carbon nanotube (CNT) bundles has been investigated. The chosen cross linkers (CH 2, O, CO) strengthen the transversal energy transport relative to the one in CNT bundles without bridges. The results showed that λ does not increase linearly with the linker density. The efficiency of the heat transport is determined by the number of linkers in the direction of the heat flux, the type of the linker, and their spatial ordering. The influence of a forced axial stress on the transversal λ has been also studied. The observed λ reduction with increasing axial... 

This research study presents an experimental investigation on forced convection heat transfer of an aqueous ferrofluid flow passing through a circular copper tube in the presence of an alternating magnetic field. The flow passes through the tube under a uniform heat flux and laminar flow conditions. The primary objective was to intensify the particle migration and disturbance of the boundary layer by utilizing the magnetic field effect on the nanoparticles for more heat transfer enhancement. Complicated convection regimes caused by interactions between magnetic nanoparticles under various conditions were studied. The process of heat transfer was examined with different volume concentrations... 

We study numerically the heat transfer of steady laminar flow in a square cavity filled with electrically conducting fluids, in the presence of an external uniform magnetic field. Imposing a large temperature gradient between two opposite vertical walls, there are substantial temperature and density variations in the domain. The fluid is treated as an ideal gas. Indeed, high temperature gradient thermo-buoyant cavity flows result in natural convection flow domains with high Rayleigh number. To implement the temperature variation effect, the fluid properties, including the conductivity and viscosity coefficients, are considered to vary with temperature in accordance to the Sutherland's law.... 

Oil leakage of transportation pipelines causes a change in its environmental temperature. This effect is employed to detect the leakage and its positions. The Raman Optical Time Domain Reflectometer (ROTDR) and Brillouin Optical Time Domain Amplifier (BOTDA) sensors are two of the most precise oil pipeline leak detector systems operate based on this effect. The position of leakage is determined by the time difference between the sending and backscattered laser pulses. In this paper, the transient response of BOTDA and ROTDR sensors are obtained through solution of the mass, energy and heat transfer in soil and fiber cable. It is shown that the mechanical rise time is of the order of a few... 

Pulsating heat pipes (PHPs) are interesting heat transfer devices. Their simple, high maintaining, and cheap arrangement has made PHPs very efficient compared to conventional heat pipes. Rotating closed loop PHP (RCLPHP) is a novel kind of them, in which the thermodynamic principles of PHP are combined with rotation. In this paper, effect of rotational speed on thermal performance of a RCLPHP is investigated experimentally. The research was carried out by changing input power (from 25. W to 100. W, with 15. W steps) and filling ratio (25%, 50%, and 75%) for different rotational speeds (from 50. rpm to 800. rpm with an increment of 125. rpm). The results presented that at a fixed filling... 

Both experimental and numerical studies are unanimous for enhancing Nusselt number for forced convection of nanofluids with slight difference, but there is inconsistency for natural convection heat transfer of nanofluids. In this paper attempt is made to study the effects of nanoparticles migration on the natural convection behavior of nanofluids. For analysis, a mixture model is used by including important phenomena such as Brownian motion and thermophoresis effects. These two mechanisms are taken into account to compute the slip velocities between the base fluid and nanoparticles. The governing equations are solved numerically and good agreements are observed in comparison with... 

Purpose - The purpose of this paper is to study a two-dimensional steady convective flow of a micropolar fluid over a stretching sheet in the presence of radiation with constant temperature. Design/methodology/approach - The corresponding momentum, microrotation and energy equations are analytically solved using homotopy analysis method (HAM). Findings - To validate the method, investigate the accuracy and convergence of the results, a comparison with existing numerical and experimental results is done for several cases. Finally, by using the obtained analytical solution, for the skin-friction coefficient and the local Nusselt number as well as the temperature, velocity and angular velocity,... 

Pulsating heat pipes (PHPs) are simple, cheap, and efficient heat transfer devices. They have applications in electronic cooling. In the present research, an experimental investigation is conducted on startup and steady thermal performances of open loop pulsating heat pipes (OLPHPs). Effects of working fluid, heat input, non-condensable gases (NCGs), ferrofluid concentration, magnets location, and inclination angle on the thermal performance of OLPHPs have been considered. Obtained results show that using ferrofluid can improve the thermal performance in steady state condition. Furthermore, applying a magnetic field enhances the heat transfer characteristics of ferrofluidic OLPHPs in both... 

In order to reach a more efficient and compact heat exchanger, it is essential to optimize the design, having in mind the impact of different geometrical parameters. Many of the previously cited studies in the area of heat transfer enhancement using vortex generators were confined only to defined points in the possible design space. Thus, a multiobjective optimization study is particularly suitable in order to cover this space entirely. A CFD simulation along with Pareto method were used to simulate the air flow and heat transfer and optimize the design parameters. The angle of attack of a pair of delta-winglets mounted behind each tube is varied between β = -90° and ß = +90°. Three... 

In the present research an experimental investigation is performed to explore the effects of working fluid, heat input, ferrofluid concentration, magnets location, and inclination angle on the thermal performance of an Open Loop Pulsating Heat Pipe (OLPHP). Obtained results show that using ferrofluid can improve the thermal performance and applying a magnetic field on the water based ferrofluid decreases the thermal resistance. It shows that at an inclination angle of the OLPHP to be zero, the thermal performance of the present OLPHP reduces. Best heat transfer capability was achieved at 67.5 degree relative to horizontal axis for all of working fluids. Variation of the magnets location... 

The present work investigates the thermal performance of a five turn Open Loop Pulsating Heat Pipe (OLPHP). The effects of working fluid namely water and ferrofluid, heat input, ferrofluid concentration, charging ratio, and orientation will be considered. Experimental results show that using ferrofluids can enhance the thermal performance in comparison with the case of distilled water. In addition, applying a magnetic field on the OLPHP charged with ferrofluid reduces its thermal resistance. Variation of the ferrofluid concentration results in different thermal performance of the OLPHP. Best charging ratio for the distilled water and ferrofluid without magnetic field is 60 % in most of the... 

Shell and tube heat exchanger with single twisted tube bundle in five different twist angles, are studied using computational fluid dynamics (CFD) and compared to the conventional shell and tube heat exchanger with single segmental baffles. Effect of shell-side nozzles configurations on heat exchanger performance is studied as well. Heat transfer rate and pressure drop are the main issues investigated in the paper. The results show that, for the same shell-side flow rate, the heat transfer coefficient of heat exchanger with twisted tube bundle is lower than that of the heat exchanger with segmental baffles while shell-side pressure drop of the former is even much lower than that of the... 

Pulsating Heat Pipes (PHPs) are new and promising heat transfer devices. To implement the novel idea to vary the startup performance of a PHP using ferrofluid with and without the application of magnetic field, an experimental investigation is conducted. The effects of several important parameters including working fluid, charging ratio, heat input, ferrofluid concentration, internal pressure, and application of magnetic field on the startup performance of Open Loop Pulsating Heat Pipes (Open Loop PHPs) have been considered and described in detail. Obtained results show that using ferrofluid instead of distilled water can improve the startup performance of PHPs in certain conditions.... 

Homogenous dispersing of nanoparticles in a base fluid is an excellent way to increase the thermal performance of heat transfer devices especially Heat Pipes (HPs). As a wickless, cheap and efficient heat pipe, Pulsating Heat Pipes (PHPs) are important candidates for thermal application considerations. In the present research an Open Loop Pulsating Heat Pipe (OLPHP) is fabricated and tested experimentally. The effects of working fluid namely, water, Silica Coated ferrofluid (SC ferrofluid), and ferrofluid without surface coating of nanoparticles (ferrofluid), charging ratio, heat input, and application of magnetic field on the overall thermal performance of the OLPHPs are investigated.... 

Modern turbine blades are cooled by air flowing through internal cooling passages. Three-Dimensional numerical simulation of these blade cooling passages is too time-consuming because of their complex geometries. These geometrical complexities exist as a result of using various kinds of cooling technologies such as rib turbulators (inline, staggered, or inclined ribs), pin fin, 90 and 180 degree turns (both sharp and gradual turns, with and without turbulators), finned passage, by-pass flow and tip cap impingement. One possible solution to simulate such sophisticated passages is to use the one-dimensional network method, which is presented in the current work. Turbine blade cooling channels... 

Pulsating Heat Pipes are an effective mean for heat removal with the potential for a widespread application in electronic packaging. An experimental study a Closed Loop Pulsating Heat Pipe (CLPHP) constructed of copper tubes formed into four meandering turns is presented. Once configured in a vertical orientation the lower portion of the CLPHP comes in contact with a heat source (called the evaporator) from which it will remove heat through the pulsating action of the two-phase mixture contained within the initially evacuated copper tubes eventually transfer the heat to a heat sink (known as the condenser). Heat fluxes can be measured using temperature data gathered from experiments.... 

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... 

In this article, transient hydrodynamic and heat-transfer behavior of Newtonian fluid flow in vertical parallel-plate channels partially filled with a porous medium has been investigated numerically. In this regard, the influences of macroscopic local inertial term and the viscous heating due to the viscous dissipation were taken into account in the momentum equations of porous region and the thermal energy equations, respectively. Moreover, Forchheimer-Brinkman extended Darcy model was used to model fluid flow in the porous region. In addition, an analytical solution was obtained in the case of negligible Brinkman and Forchheimer number values at the steady-state conditions. The predicted...