Prediction Methods for Entry Length Heat Transfer by Combined Laminar Convection in Horizontal Tubes

1982 ◽  
Vol 196 (1) ◽  
pp. 409-415 ◽  
Author(s):  
P H G Allen ◽  
O Szpiro ◽  
M W Collins
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Laminar Flow ◽  
Prediction Methods ◽  
Entry Length ◽  
Horizontal Tubes ◽  
Temperature Distributions ◽  
Constant Rate ◽  
Full Solution ◽  
Laminar Convection

Numerical prediction methods for calculating velocity and temperature distributions in heated ducts can be made accurately but are time consuming. The paper shows possible simplifications, including the neglect of the buoyancy term, and the resultant accuracy attained. The case studied is for laminar flow, entry length heat transfer in horizontal tubes with constant rate heat flux. Comparison is made between experimental results, a full solution and an approximation based on a series of truncated versions of the fully developed temperature profile. Calculations are made both with and without variation of thermophysical properties with temperature.

Computational Methods for Entry Length Heat Transfer by Combined Laminar Convection in Vertical Tubes

1977 ◽  
Vol 191 (1) ◽  
pp. 19-29 ◽  
Author(s):  
M. W. Collins ◽  
P. H. G. Allen ◽  
O. Szpiro
Keyword(s):  
Heat Transfer ◽  
Computer Time ◽  
Vertical Tube ◽  
Numerical Techniques ◽  
Temperature Dependent ◽  
Entry Length ◽  
Temperature Distributions ◽  
Temperature Dependent Properties ◽  
Laminar Convection ◽  
Vertical Tubes

Numerical techniques for the calculation of velocity and temperature distributions in heated ducts have proved accurate but expensive in computer time and capacity. It is worth investigating to what extent simplification is possible without loss of accuracy. Entry-length heat transfer to upward laminar flow with combined convection in a vertical tube is taken as typical. Comparison is made between measured values and, first, a full numerical solution for constant thermophysical properties (viscosity and thermal diffusivity), secondly, the same solution but allowing for their individual and combined variation with temperature and, thirdly, a solution which assumes a series of truncated versions of the fully developed temperature distribution to establish corresponding velocity profiles, allowing for temperature-dependent properties.

A Variational Method for Fully Developed Laminar Heat Transfer in Ducts

1959 ◽  
Vol 81 (2) ◽  
pp. 157-164 ◽  
Author(s):  
E. M. Sparrow ◽  
R. Siegel
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Variational Method ◽  
Cross Section ◽  
Cross Sections ◽  
Axial Direction ◽  
Circular Sector ◽  
Thermal Boundary Conditions ◽  
Temperature Distributions ◽  
Good Agreement

A variational method is presented for determining fully developed velocity and temperature distributions for laminar flow in noncircular ducts. The heat addition to the fluid is taken to be uniform in the axial direction, but a variety of thermal boundary conditions are considered around the periphery of the duct cross section. Several illustrative examples are given, and comparisons are made which show good agreement with available exact solutions. These examples include ducts of rectangular and circular-sector cross sections.

A Numerical Investigation of Nanofluids Thermal Behavior in Microchannels Under Laminar Flow Conditions

2015 ◽  
Author(s):  
I. P. Koronaki ◽  
M. T. Nitsas ◽  
Ch. A. Vallianos
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Laminar Flow ◽  
Volume Fraction ◽  
Constant Heat Flux ◽  
Flow Conditions ◽  
New Techniques ◽  
Pressure Drops ◽  
Nanoparticles Volume Fraction ◽  
The Heat Transfer Coefficient

Due to large amounts of heat flux developed in electronic devices, it is essential to propose and investigate effective mechanisms of cooling them. Although microchannels filled with flowing coolant are a geometry often met in such devices, new techniques need to be developed in order to increase their effectiveness. Recent studies on nanofluids, i.e. mixtures of nanometer size particles well-dispersed in a base fluid, have demonstrated their potential for augmenting heat transfer. In the present work the 2D steady state laminar flow of different nanofluids along a microchannel is examined. It is considered that the microchannel walls receive uniform and constant heat flux. The problem’s modelling has as parameters the volume fraction of nanoparticles ranging from 0 to 5% and Reynolds number varying between 50 and 500. The results of the problem’s numerical solution are used to calculate the heat transfer coefficient, the pressure drop along the microchannel and the destroyed exergy. It is found that heat transfer is enhanced due to the presence of nanoparticles. On the contrary, pressure drops faster due to nanofluids increased viscosity leading to more pump power needed. Finally, further exergy destruction is observed when nanoparticles volume fraction increases.

Three-Dimensional Numerical Simulation on the Laminar Flow and Heat Transfer in Four Basic Fins of Plate-Fin Heat Exchangers

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
Yinhai Zhu ◽  
Yanzhong Li
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Heat Exchangers ◽  
Flow Direction ◽  
Three Dimensional ◽  
Entry Length ◽  
Flow And Heat Transfer ◽  
F Factor ◽  
The One ◽  
Data Reduction Method

In this paper, four basic fins of the plate-fin heat exchangers, rectangular plain fin, strip offset fin, perforated fin, and wavy fin, are modeled and simulated by taking account of fin thickness, thermal entry effect, and end effect. Three-dimensional numerical simulations on the flow and heat transfer in the four fins are investigated and carried out at laminar flow regime. Validity of the modeling technique is verified by comparing computational results with both corresponding experimental data and three empirical correlations from literatures. Global average Colburn factor (j factor) and friction factor (f factor) and their local 1D streamwise-average distributions along the fins are presented by introducing data reduction method. The heat transfer behaviors in both the developing and developed regions are analyzed by examining variations of the local Nusselt number along the flow direction. It is found that the thermal entry length of the four fins might be expressed in the format of Le=c1 Rec2 Pr Dh, which has the same form as the one in a circular tube.

Entropy Generation Minimization of Fully Developed Internal Convective Flows With Constant Heat Flux

2003 ◽  
Author(s):  
Eric B. Ratts ◽  
Atul G. Raut
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Entropy Generation ◽  
Cross Sections ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Entropy Generation Minimization

This paper addresses the thermodynamic optimum of single-phase convective heat transfer in fully developed flow for uniform and constant heat flux. The optimal Reynolds number is obtained using the entropy generation minimization (EGM) method. Entropy generation due to viscous dissipation and heat transfer dissipation in the flow passage are summed, and then minimized with respect to Reynolds number based on hydraulic diameter. For fixed mass flow rate and fixed total heat transfer rate, and the assumption of uniform heat flux, an optimal Reynolds number for laminar as well as turbulent flow is obtained. In addition, the method quantifies the flow irreversibilities. It was shown that the ratio of heat transfer dissipation to viscous dissipation at minimum entropy generation was 5:1 for laminar flow and 29:9 for turbulent flow. For laminar flow, the study compared non-circular cross-sections to the circular cross-section. The optimal Reynolds number was determined for the following cross-sections: square, equilateral triangle, and rectangle with aspect ratios of two and eight. It was shown that the rectangle with the higher aspect ratio had the smallest optimal Reynolds number, the smallest entropy generation number, and the smallest flow length.

Sign in / Sign up

Export Citation Format

Share Document