Sharif Digital Repository

In this research, the effect of surface characteristics on boiling heat transfer has been investigated experimentally. For this purpose, a device with the ability to automatically record the liquid temperature of the inlet and outlet of the test area, calculate the coefficient of boiling heat transfer, and heat flux has been developed. The automatic temperature stability of the working fluid and the ability to investigate the effect of surfaces with different characteristics (in terms of material and surface structure) on the boiling heat transfer parameters are the most important features of this device. The performance of the experimental setup was evaluated by the modified "Chen" equation... 

The present work numerically investigates the mass and heat transport flow of micropolar fluid in a channel having permeable walls. The appropriate boundary layer approximations are used to convert the system of flow model equations in ODEs, which are then numerically treated with the quasi-linearization method along with finite difference discretization. This technique creates an efficient way to solve the complex dynamical system of equations. A numerical data comparison is presented which assures the accuracy of our code. The outcomes of various problem parameters are portrayed via the graphs and tables. The concentration and temperature accelerate with the impacts of the Peclet numbers... 

The present work numerically investigates the mass and heat transport flow of micropolar fluid in a channel having permeable walls. The appropriate boundary layer approximations are used to convert the system of flow model equations in ODEs, which are then numerically treated with the quasi-linearization method along with finite difference discretization. This technique creates an efficient way to solve the complex dynamical system of equations. A numerical data comparison is presented which assures the accuracy of our code. The outcomes of various problem parameters are portrayed via the graphs and tables. The concentration and temperature accelerate with the impacts of the Peclet numbers... 

The objective of this paper is to provide optimization of falling film LiBr solution on a horizontal single tube based on minimization of entropy generation. Flow regime is considered to be laminar. The effect of boiling has been ignored and wall temperature is constant. Velocity, temperature and concentration distributions are numerically determined and dimensionless correlations are obtained to predict the average heat transfer coefficient and average evaporation factor on the horizontal tube. Thermodynamic imperfection due to passing lithium bromide solution is attributed to nonisothermal heat transfer; fluid flow friction and mass transfer irreversibility. Scale analysis shows that the... 

In this paper, heat and mass transfer phenomena occurring simultaneously in falling film generator of absorption chillers have been studied. The analysis is based on the laminar flow of an Li/Br solution over a horizontal single tube and tube bundle having a constant tube wall temperature. The effect of boiling has been ignored. An extensive numerical code is provided to calculate the heat transfer coefficient and the rate of evaporation. A parametric study is performed on the coefficient of heat transfer and the evaporation flux of the refrigerant. Dimensionless correlations are obtained to calculate the heat transfer coefficient on the horizontal tube and tube bundle. The comparison... 

In this paper, a theoretical analysis of the combined heat and mass transfer over cooled horizontal tubes is presented. The boundary layer assumptions are used for the transport of mass, momentum and energy equations and the finite difference method is employed to solve the governing equations in the absorber tube bundle. The effects of important parameters, such as solution flow rate, absorber pressure and tube radius, are discussed on the overall heat and mass transfer for a tube and tube bundle. © Sharif University of Technology, October 2004  

The steady-state laminar and incompressible vapor flow in four partially-beated concentric annular beat pipe (CAHP) is studied. The governing equations are solved numerically, using finite volume approach based on collocated grids. The first order upwind scheme and the QUICK scheme are used in the numerical solution. The vapor pressure distributions and velocity profiles along the annular vapor space are predicted for a number of test cases in the range of low to moderate radial Reynolds numbers. The results show that in a partially-heated annular beat pipe, as the radial Reynolds number increases, a number of recirculation zones may be created at both ends of the evaporator and condenser... 

In this paper, a numerical simulation involving fluid flow and heat transfer is presented in order to improve the understanding of rotary furnaces. The finite element model is employed to simulate the furnace rotation and analyse the energy flows inside the furnace. A transient dynamic analysis is carried out to predict the evolution and distribution of temperatures in a rotary furnace by modelling and analysing the furnace under different flame positions. The finite element modelling system ELFEN is used to develop models of the furnace. The results clearly indicate the temperature distribution for different angular velocities along with a comparison of temperature variation under different... 

A heat transfer rate was determined for polypropylene tubes in solar water heaters for the Reynolds number range 800-5600. Experiments were conducted in ambient temperatures of 34 to 37°C. Data were correlated in the form of Nusselt numbers as: Nu=0.0015 Re0.75 Pr1/3 with correlation coefficient of 0.95. Such data can be used to predict heat transfer rates in a polypropylene solar heater in Tehran where the experiments were performed. An application of the results is shown in an example. © 2003 Elsevier Ltd. All rights reserved  

In this paper the velocity and temperature fields during hot strip rolling are determined using a rigid-viscoplastic finite element method together with a microstructural model for handling dynamic phase transformation during hot deformation. Based on these fields, the strain distributions within the rolled metal at different positions in the deformation zone are estimated. The analysis is capable of considering the effects of metallurgical phase transformations as well as various process parameters such as initial strip temperature, rolling speed, lubrication on the strain inhomogeneity produced during the hot rolling process. To assess the reliability of the theoretical analysis, a... 

The present work numerically investigates the mass and heat transport flow of micropolar fluid in a channel having permeable walls. The appropriate boundary layer approximations are used to convert the system of flow model equations in ODEs, which are then numerically treated with the quasi-linearization method along with finite difference discretization. This technique creates an efficient way to solve the complex dynamical system of equations. A numerical data comparison is presented which assures the accuracy of our code. The outcomes of various problem parameters are portrayed via the graphs and tables. The concentration and temperature accelerate with the impacts of the Peclet numbers... 

In this research, the effect of surface characteristics on boiling heat transfer has been investigated experimentally. For this purpose, a device with the ability to automatically record the liquid temperature of the inlet and outlet of the test area, calculate the coefficient of boiling heat transfer, and heat flux has been developed. The automatic temperature stability of the working fluid and the ability to investigate the effect of surfaces with different characteristics (in terms of material and surface structure) on the boiling heat transfer parameters are the most important features of this device. The performance of the experimental setup was evaluated by the modified "Chen" equation... 

Olefin industry came to a commercialization maturity, but still energy consumption, coke formation and thermal cracking optimization seem hot debates. The typical use of static mixers or fins inside the pipes itself leads to significant pressure drop, leading to higher power consumption and lower selectivity of olefins production. Herein we propose an innovative approach, i.e., accelerated sinusoidal heat transfer through mixing at viscous sublayer pipe-fluid interface. CFD simulation by SOLIDWORKS, ANSYS FLUENT computer-aided computations visualized hydrodynamic wave effects on heat transfer in corrugated tube taking bare tubes as reference. The length and outside diameter of tube were... 

Pool boiling heat transfer as a promising heat transfer mechanism that can provide ample heat dissipation for thermal management applications has been granted much attention. This study puts forward the idea of applying an Inner Corrugated Hollow Conical Frustum (ICHCF) to ameliorate pool boiling heat transfer. The performance of the ICHCF is experimentally investigated for both the stationary and rotating cases. Furthermore, the effect of various geometrical parameters such as the ICHCF height, thread depth, thread pitch, the gap between the ICHCF and boiling surface, and the rotational speed of the ICHCF are studied. Twelve different ICHCFs were fabricated and tested for the purpose of... 

The effect of a permanent magnetic field on the heat transfer characteristics of hybrid graphene-magnetite nanofluids (hybrid nanofluid) under forced laminar flow was experimentally investigated. For this purpose, a reduced graphene oxide-Fe3O4 was synthesized by using two-dimensional (2D) graphene oxide, iron salts and tannic acid as the reductant and stabilizer. Graphene sheets acted as the supporting materials to enhance the stability and thermal properties of magnetite nanoparticles. The thermo-physical and magnetic properties of this hybrid nanofluid have been widely characterized and it shows that the thermal conductivity increased up to 11%. The hybrid nanofluid behaves as a Newtonian... 

The boiling phenomena in a quiescent fluid is the nucleate pool boiling which has attracted much interest in the thermal management studies. This paper investigates the effect of the installed Twisted Tape Fins (TTFs) on the heat transfer from a surface with a temperature above the water saturation point to a coil condenser. Four different arrangements of TTFs (1, 3, 5, and 9 TTFs) are fabricated and their boiling performance in distilled water at atmospheric pressure is experimentally tested. It was observed that the increase in the boiling heat transfer coefficient of the plate with nine TTFs compared to that of the plain one is 15.5%. Furthermore, the effect of TTFs heights on the heat... 

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... 

In this study, the effects of ferrofluids on the forced convective heat transfer in a tube with a round cross section under constant heat flux in the laminar flow regime are investigated experimentally. For this purpose, an experimental setup was designed and built. Furthermore, the effects of an external magnetic field on the forced convective heat transfer were examined for various Reynolds numbers and volume concentrations. The parameters of magnetic field strength, magnetic field arrangement, the constancy or oscillation of the magnetic field and also its oscillatory mode were examined. As a result of the experimental studies, in the absence of a magnetic field enhancement in convective... 

The paper studies the effects of solid and liquid steel properties on the heat transfer coefficient (HTC) in electric arc furnaces (EAFs). Mathematically speaking, the HTC is a function of solid and liquid steel properties. Different velocities of the bath cause different flow paths around the solid particles and therefore different HTCs - a computational issue that has not been addressed yet. Therefore, a simplified calculation model is proposed, intended for HTC estimation according to the EAF conditions. Although many studies investigated this topic, most of them either assume unconventional conditions for the EAF operation, are computationally complex or focus on a specific case; and... 

The overall heat transfer coefficient (OHTC) of air in a double-pipe helical heat exchanger is studied and experimentally investigated. In order to increase the rate of heat transfer in the annulus section, a copper-wire fin is soldered on the outside area of the internal tube. The literature correlations’ results are presented against the experimental data by changing mass flow rate and temperature, and consequently changing the Reynolds number. Further, a new method is suggested to obtain the heat transfer coefficients of double-pipe helical heat exchangers for the internal tube and the annulus section by combining two of the previously proposed approaches and making subsequent...