Viscous heating effects on heat transfer characteristics of laminar compressible channel flow (original) (raw)
Related papers
Temperature-viscosity induced laminar instabilities in a gaseous heated channel
Nuclear Engineering and Design
Laminar flow instability exhibits itself as a flow rate excursion in single isolated tubes having negative pressuredrop-flow-rate derivative at constant heat addition in a gas which has a viscosity increasing with temperature in the laminar Reynolds number range. An application is in laminar flow nuclear rocket reactors. The constitutive equations for such a system were solved using seven different forms of the energy equation in a steady state isolated channel. An equation for flow rate at neutral stability is given. Parametric results are presented for a range of heat flux, flow rate and fluid state conditions. Closed form solutions and existing experimental findings were verified using numerical analysis.
International Journal of Heat and Mass Transfer, 2017
In this article, a theoretical model is developed to investigate the effects of the axial heat conduction on the laminar forced convection in a circular tube with uniform internal heat generation in the solid wall. In the current work, three different fluids, i.e. water, n-decane and air, are selected on purpose since their thermophysical properties show different behavior with temperature. The effects of the axial heat conduction with varying dynamic viscosity and/or varying thermal conductivity are investigated in a systematic manner. Results indicate that the variable-property effects could alleviate the reduction in Nusselt number (Nu) due to the axial heat conduction. For the case of Peclet number (Pe) equal to 100, wall thickness to inner diameter ratio of 1 and solid wall to fluid thermal conductivity ratio of 100, the maximum Nu deviation between constant and variable properties are up to 7.33% at the entrance part for water in the temperature range of 50℃, and 4.45% at the entrance part for n-decane in the temperature range of 120℃, as well as 2.20% at the ending part for air in the temperature range of 475℃, respectively. In addition, the average Nu deviation for water, n-decane and air are 3.24%, 1.94% and 1.74%, respectively. Besides, Nu decreases drastically with decreasing Pe when Pe≤500 and with increasing solid wall to fluid thermal conductivity ratio (sf k) when sf k ≤100. It is also found that variable properties have more obvious effects on the velocity profile at the upstream part while more obvious effects on the temperature profile at the downstream part.
Analysis of the transient compressible vapor flow in heat pipe
1989
The transient compressible one-dimensional vapor flow dynamics in a heat pipe is modeled. The numerical results are obtained by using the implicit non-iterative Beam-Warming finite difference method. The model is tested for simulated heat pipe vapor flow and actual vapor flow in cylindrical heat pipes. A good comparison of the present transient results for the simulated heat pipe vapor flow with the previous results of a two-dimensional numerical model is achieved and the steady state results are in agreement with the existing experimental data. The transient behavior of the vapor flow under subsonic, sonic, and supersonic speeds and high mass flow rates are successfully predicted. The one-dimensional model also describes the vapor flow dynamics in cylindrical heat pipes at high temperatures.
Universal Journal of Applied Science, 2017
In this work, we have numerically studied the heat transfer of viscoelastic fluid flow inside a planar channel with 1:3 abrupt expansion. For modeling rheological behavior of non-creeping flow related to the viscoelastic fluid which includes both the effects of shear-thinning and elasticity, the constitutive equation of exponential Phan Thien-Tanner (EPTT) is used. Also, thermal boundary condition of constant temperature at the walls and inlet of channel with internal heat generated by the viscous dissipation are considered. Because of high temperature differences in the current study, the fluid properties such as fluid viscosity, relaxation time, specific heat capacity and thermal conductivity have a function of temperature. For coupling the variables of velocity, pressure and temperature, the PISO algorithm is employed and finite volume method (FVM) imposed on the collocated grid to discretize the governing equations. The main propose of the present study is to examine the effects of elastic property on the size of recirculation regions, temperature distribution, local and mean Nusselt numbers.
Comparative Study between Heat Transfer through Laminar Flow and Turbulent Flow
A common situation encountered by an engineer is heat transfer to fluid flowing through a tube. This can occur in heat exchangers, boilers, condensers, evaporators, and a host of other process equipment. The study of heat transfer can be done either in laminar flow or in turbulent flow. Both conditions show different performance characteristics of the heat transfer. In this paper, comparative study of heat transfer in both conditions is done. Under turbulent flow conditions, the increase in heat transfer rate is more significant than that under laminar flow conditions. This is due to the increase in the Reynolds number of the flowing fluid in turbulent flow. The turbulent effects become a dominant factor over secondary flow at higher Reynolds number.
Experiment: Heat Transfer in Laminar Flow
The experiment is designed to determine the convection coefficient of heat transfer when the test fluid or fluid being cooled is flowing in the laminar flow regime. It also aims at verifying the Seider-Tate equation to find the convection coefficient. The flow is exhibited by fluids having high viscosity, e.g. oil. The experiment involves the calculation of the heat dissipated by the test fluid depending upon the temperatures that are measured. The test fluid side convection coefficient is calculated from the calculated value of overall heat transfer coefficient. The experiment, coupled with the experiment in the turbulent flow domain, will help us in understanding as to how the turbulent fluid flow is better for heat transfer than a laminar fluid flow. Introduction: A laminar flow in a pipe or circular conduit can be defined as one which has a Reynolds' number (Re < 2100). The laminar low domain is characterized by negligible turbulences and a planar flow. There is a lack of eddy currents in the flow which leads to a lesser convection coefficient than a turbulent regime flow. The formation of a boundary layer is very prominent in a laminar flow. This boundary layer also leads to the formation of a thermal boundary layer which acts as a thermal resistance.
Numerical investigation of turbulent flow and heat transfer in flat tube
Journal of Thermal Analysis and Calorimetry, 2018
In this study, the heat transfer and friction characteristics of four different rib geometries-45 angled, Vshaped, W-shaped and M-shaped ribs in a two-pass stationary channel have been numerically investigated. The aspect ratio (Height to Width) of the cooling channel was 1:1 (square). The rib pitch-to-rib height ratio (p/e) and the rib-height-to-channel hydraulic diameter ratio (e/D h) were 16 and 0.125 respectively. The Reynolds number was varied from 20,000 to 70,000. For the computations, the Reynolds averaged NaviereStokes (RANS) equations were solved with the commercial software ANSYS Fluent using the realizable version of k-ε (RKE) model. The heat transfer results were benchmarked with experiments on a test rig with similar geometries and flow conditions. Detailed analysis of the flow characteristics in the two-pass channel was carried out so as to understand the interaction of the ribinduced secondary flows and the bend-induced secondary flows and their contribution to heat transfer enhancement. The heat transfer enhancement provided by V-shaped ribs was 7% higher than 45 ribs, 28% higher than W-shaped ribs and 35% higher than M-shaped ribs. However, the pressure penalty for Vshaped ribs was 19% higher than 45 ribs, 24% higher than W-shaped ribs and 28% higher than M-shaped ribs. On comparing the overall thermal hydraulic performance, V-shaped and 45 ribs were observed to perform significantly better than W-shaped and M-shaped ribs.
2006
Heat transfer analysis of Viscoelastic fluids in noncircular channel has complication because of nonlinear behavior of fluid consistency equation and channel geometry. In this paper a weak secondary flow is shown using generalized model CEF and numerical solution. Numerical solution is based on the Artificial Compressibility (Chorin method) and using staggered mesh. The effect of secondary flow on the forced and natural heat convection is studied. Effect of fast secondary flows at forced and free convection was assimilated. Quantities of static pressure and temperature distributions were obtained. Computer program was used for 3-D CFD technique.
Laminar flow in horizontal circular tubes with a constant heat flux boundary condition has been extensively investigated, however, some questions still remain regarding the effect of free convection on thermal developing flow. What further complicates the effects of free convection on developing flow, is the local transition from laminar to turbulent flow along the tube length above the critical Reynolds number. The purpose of this study was to investigate the effects of free convection on the development of the local heat transfer characteristics in a smooth horizontal circular tube heated with a constant heat flux, and is work in progress. An experimental setup was designed, built and validated against literature. The test section had an innder diameter of 11.5 mm and a maximum length-to-diameter ratio of 872. Heat transfer measurements were taken at Reynolds numbers between 500 and 10 000 at different heat fluxes. A total of 186 mass flow rate measurements and 20 274 temperature measurements were taken. Water was used as the test fluid and the Prandtl number ranged between 3 and 7. Three different regions were identified for developing laminar flow. Furthermore, it was found that the available correlations to calculate the laminar thermal entrance length are restricted to forced convection conditions, since the thermal entrance length decreased with increasing free convection effects. In the transitional flow regime, it was found that the laminar-turbulent transition occurred faster with increasing free convection effects and Reynolds number.
2011
Steady laminar forced convection heat transfer in the thermal entrance region of a circular pipe including viscous dissipation has been studied assuming the flow to be hydrodynamically fully developed and thermally developing. The circular pipe is subjected to constant wall temperature. Two entry temperatures have been considered. 1) A temperature that varies with the radial coordinate obtained in an adiabatic pipe due to viscous dissipation while the flow is hydrodynamically developing. This temperature is termed as the dissipative entry temperature. 2) A uniform temperature equal to the bulk mean value of the dissipative entry temperature. It has been shown that the difference in the Nusselt numbers and heat transfer obtained with these two entry temperatures is insignificant. Thus, the simplicity of classical assumption of uniform entry temperature can be retained when the entry temperature has been chosen as the bulk mean of the dissipative entry temperature.