Transient Conjugate Heat Transfer in a Circular Duct for Power-Law Fluid with Viscous Dissipation

The study of unsteady forced convection heat transfer in tubes imposed to cyclic variations has been motivated by heat exchanger applications. This study investigates the heat transfer behavior associated with a thermal transient in a forced convection. In this analysis, the effects of the duct wall heat capacity and convection from the ambient are considered, while axial conduction is neglected. The fluid inlet temperature is varied periodically with time. Incompressible, hydrodynamically developed laminar flow of non-Newtonian fluid flow is assumed. The transient conjugate heat transfer problem for fully-developed laminar flow of non-Newtonian fluids in circular duct is studied by numerical analysis. Control volume based finite difference method is adopted in the numerical procedure for the integration of the governing equations. For the non-Newtonian fluid part, power-law model is used. Heat generation from viscous dissipation is also taken into account and is represented by Brinkman number. The study investigates the effects of non-dimensional parameters on wall, fluid and bulk temperatures. In this dissertation, special focus is placed on the effects of the flow index, Brinkman, and Nusselt numbers

Forced convection to laminar flow of liquid egg yolk in circular and annular ducts

The steady-state heat transfer in laminar flow of liquid egg yolk - an important pseudoplastic fluid food - in circular and concentric annular ducts was experimentally investigated. The average convection heat transfer coefficients, determined by measuring temperatures before and after heating sections with constant temperatures at the tube wall, were used to obtain simple new empirical expressions to estimate the Nusselt numbers for fully established flows at the thermal entrance of the considered geometries. The comparisons with existing correlations for Newtonian and non-Newtonian fluids resulted in excellent agreement. The main contribution of this work is to supply practical and easily applicable correlations, which are, especially for the case of annulus, rather scarce and extensively required in the design of heat transfer operations dealing with similar shear-thinning products. In addition, the experimental results may support existing theoretical analyses.(CNPq) National Council for Scientific and Technological Development(FAPESP) São Paulo Research Foundatio

Combined Convection of Packer Fluid Flow between Vertical Parallel Plates

Packer fluid whose function is to prevent or tremendously reduce the heat transfer rate which would occur from the production tubing area to the production casing region is being studied in recent decades because of its wide applications in Oil & Gas Industry. Reduction of heat transfer rate can lead to the minimization of trapped annular pressures and reduction of contents of hydrates resolvable in production fluids. This paper utilizing ANSYS Fluent gives numerical solution for the combined convection problem of this packer fluid. Because of the geometry of the tubing-to-casing annulus, it is modeled as vertical and long parallel plates in ANSYS Fluent geometry part where the width of the duct is small comparable to the length of the duct. The flow is assumed to lie in laminar region and ANSYS Fluent laminar flow model is utilized. How different parameters including aspect ratio, temperature difference and inlet velocity will have effects on the convective heat transfer rate are analyzed respectively by measuring and calculating dimensionless parameters including Nusselt number, Reynolds number, Prandtl number, Grashof number and Rayleigh number. Numerical results characterize the convective heat transfer performance of the packer fluid

Investigation Of Laminar Convective Heat Transfer And Pressure Drop Of SiO2 Nanofluid In Ducts Of Different Geometries

Engineers are seeking alternatives to conventional heat transfer fluids and in an attempt to improve their thermal transport properties, they added thermally conductive solids into the conventional fluids resulting in a fluid called nanofluid. Nanofluid was suggested as an alternative solution to the problem and many publications reported its potential for heat transfer enhancement. This thesis describes the experimental study of 9.58% by vol. silica/water nanofluid flow through different flow geometries which are circular, hexagonal and rectangular ducts of close hydraulic diameter. The experiments are performed at uniform heat flux condition. The aim of this thesis is to determine experimentally the best duct geometry for optimal thermal performance in nanofluids. The effect of the cross-section of the flow geometry on the enhancement capability of nanofluid is the focus of this research and four different geometries of relatively equal hydraulic diameters were studied. This study compares the result from the different duct geometries in order to identify the best flow channel for optimal heat transfer using nanofluids. Based on the test data, the thermal performance comparisons are made under three constraints (similar mass flow rate and Reynolds number). It was observed from the comparisons that the rectangular duct showed the highest heat transfer capability through a higher Nusselt number and heat transfer coefficients at for the silica/water nanofluid flow. The circular duct was next to the rectangular duct in thermal performance. There was no significant change in friction factor between the ducts for both water and nanofluid flow

Effects of rotation on coolant passage heat transfer. Volume 1: Coolant passages with smooth walls

An experimental program was conducted to investigate heat transfer and pressure loss characteristics of rotating multipass passages, for configurations and dimensions typical of modern turbine blades. The immediate objective was the generation of a data base of heat transfer and pressure loss data required to develop heat transfer correlations and to assess computational fluid dynamic techniques for rotating coolant passages. Experiments were conducted in a smooth wall large scale heat transfer model

Fluid and thermal behaviour of multi-phase flow through curved ducts

Fluid flow through curved ducts is influenced by the centrifugal action arising from duct curvature and has behaviour uniquely different to fluid flow through straight ducts. In such flows, centrifugal forces induce secondary flow vortices and produce spiralling fluid motion within curved ducts. Secondary flow promotes fluid mixing with intrinsic potential for thermal enhancement and, exhibits possibility of fluid instability and additional secondary vortices under certain flow conditions. Reviewing published numerical and experimental work, this thesis discusses the current knowledge-base on secondary flow in curved ducts and, identifies the deficiencies in analyses and fundamental understanding. It then presents an extensive research study capturing advanced aspects of secondary flow behaviour in single and two-phase fluid flow through curved channels of several practical geometries and the associated wall heat transfer processes.As a key contribution to the field and overcoming current limitations, this research study develops a new three-dimensional numerical model for single-phase fluid flow in curved ducts incorporating vortex structure (helicity) approach and a curvilinear mesh system. The model is validated against the published data to ascertain modelling accuracy. Considering rectangular, elliptical and circular ducts, the flow patterns and thermal characteristics are obtained for a range of duct aspect ratios, flow rates and wall heat fluxes. Results are analysed for parametric influences and construed for clearer physical understanding of the flow mechanics involved. The study formulates two analytical techniques whereby secondary vortex detection is integrated into the computational process with unprecedented accuracy and reliability. The vortex inception at flow instability is carefully examined with respect to the duct aspect ratio, duct geometry and flow rate. An entropy-based thermal optimisation technique is developed for fluid flow through curved ducts.Extending the single-phase model, novel simulations are developed to investigate the multiphase flow in heated curved ducts. The variants of these models are separately formulated to examine the immiscible fluid mixture flow and the two-phase flow boiling situations in heated curved ducts. These advanced curved duct flow simulation models are validated against the available data. Along with physical interpretations, the predicted results are used to appraise the parametric influences on phase and void fraction distribution, unique flow features and thermal characteristics. A channel flow optimisation method based on thermal and viscous fluid irreversibilities is proposed and tested with a view to develop a practical design tool

Viscous Heating Effects on Heat Transfer Characteristics of an Explosive Fluid in a Converging Pipe

Viscous dissipation is the production of heat due to the slip of fluid layers and can raise the temperature of the fluid that is affected by high shear stresses. This raise of temperature in fluids with explosive properties can cause the explosion during the processing. The present paper investigates the temperature distribution of an explosive fluid beside the wall of a converging tube. This study has been done by using the computational fluid dynamics and OpenFOAM software. The studied cases contain the fluid with two viscosities (50 and 500 kg/m × s) and two inlet conditions (constant and developed velocity profile). The results of this study show that at the end of a converging pipe, duo to the viscous dissipation effects, the temperature rise for high viscosity fluid is more intensive and this is a dangerous fact for high viscosity explosive fluids discharging. Also, it has been considered that the constant inlet velocity is safer in comparison with the developed profile, as the slope of temperature rise is less