Heat Transfer and Pressure Drop Characteristics of Water in the Transitional Flow Regime of Horizontal Smooth Tubes at Constant Wall Temperature

2010 ◽  
Author(s):  
J. P. Meyer ◽  
A. Du Preez
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Regime ◽  
Wall Temperature ◽  
Reynolds Numbers ◽  
Transitional Flow ◽  
Maximum Efficiency ◽  
Constant Wall Temperature ◽  
Pressure Losses ◽  
Nusselt Numbers

Owing to design limitations, heat exchangers are frequently forced to operate in the transitional flow regime, however, there exists no accurate measurements for both heat transfer and pressure drop in this region. In order to optimize a heat exchanger for maximum efficiency and minimum pressure losses, it is required to design it for the transitional flow regime. Therefore, the purpose of this study is to obtain accurate Nusselt numbers and pressure drop coefficients for water flowing through a horizontal smooth tube with a constant wall temperature. Heat transfer and pressure drop measurements were conducted on a 5.33 mm tube at Reynolds numbers ranging from 1 000 to 5 000.

Measurement and Analysis of Laminar Heat Transfer Coefficients in Micro and Mini-Scale Ducts and Channels

2014 ◽  
Author(s):  
Y. S. Muzychka ◽  
M. Ghobadi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Fully Developed Flow ◽  
Transfer Rates ◽  
Heat Transfer Coefficients ◽  
Advantages And Disadvantages ◽  
Nusselt Numbers

Heat transfer in micro and mini-scale ducts and channels is considered. In particular, issues of thermal performance are considered in systems with constant wall temperature at low to moderate Reynolds numbers or small dimensional scales which lead to conditions characteristic of thermally fully developed flows or within the transition region leading to thermally fully developed flows. An analysis of two approaches to representing experimental data is given. One using the traditional Nusselt number and another using the dimensionless mean wall flux. Both approaches offer a number of advantages and disadvantages. In particular, it is shown that while good data can be obtained which agree with predicted heat transfer rates, the same data can be problematic if one desires a Nusselt number. Other issues such as boundary conditions pertaining to measuring thermally developing and fully developed flow Nusselt numbers are also discussed in detail.

scholarly journals Constant-Wall-Temperature Nusselt Number in Micro and Nano-Channels1

2001 ◽  
Vol 124 (2) ◽  
pp. 356-364 ◽  
Author(s):  
Nicolas G. Hadjiconstantinou ◽  
Olga Simek
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Conduction ◽  
Flow Regime ◽  
Wall Temperature ◽  
Slip Flow ◽  
Constant Wall Temperature ◽  
Slip Flow Regime ◽  
Axial Heat ◽  
Axial Heat Conduction

We investigate the constant-wall-temperature convective heat-transfer characteristics of a model gaseous flow in two-dimensional micro and nano-channels under hydrodynamically and thermally fully developed conditions. Our investigation covers both the slip-flow regime 0⩽Kn⩽0.1, and most of the transition regime 0.1<Kn⩽10, where Kn, the Knudsen number, is defined as the ratio between the molecular mean free path and the channel height. We use slip-flow theory in the presence of axial heat conduction to calculate the Nusselt number in the range 0⩽Kn⩽0.2, and a stochastic molecular simulation technique known as the direct simulation Monte Carlo (DSMC) to calculate the Nusselt number in the range 0.02<Kn<2. Inclusion of the effects of axial heat conduction in the continuum model is necessary since small-scale internal flows are typically characterized by finite Peclet numbers. Our results show that the slip-flow prediction is in good agreement with the DSMC results for Kn⩽0.1, but also remains a good approximation beyond its expected range of applicability. We also show that the Nusselt number decreases monotonically with increasing Knudsen number in the fully accommodating case, both in the slip-flow and transition regimes. In the slip-flow regime, axial heat conduction is found to increase the Nusselt number; this effect is largest at Kn=0 and is of the order of 10 percent. Qualitatively similar results are obtained for slip-flow heat transfer in circular tubes.

scholarly journals Numerical investigation of fluid flow and heat transfer around a circular cylinder utilizing nanofluid for different thermal boundary condition in the steady regime

10.30544/292 ◽  
2017 ◽  
Vol 23 (2) ◽  
pp. 131-141
Author(s):  
Rafik Bouakkaz ◽  
F. Salhi ◽  
Y. Khelili ◽  
M. Ouazzazi ◽  
K. Talbi
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Reynolds Numbers ◽  
Uniform Heat Flux ◽  
Constant Wall Temperature ◽  
Steady Regime ◽  
Volume Fractions ◽  
Thermal Boundary Conditions ◽  
Nusselt Numbers ◽  
Volume Method

In this work, steady flow-field and heat transfer through a copper–water nanofluid around a circular cylinder, under the influence of both the standard thermal boundary conditions i.e. uniform heat flux (UHF) and constant wall temperature (CWT) was investigated numerically by using a finite-volume method for Reynolds numbers of 10 to 40. Furthermore, the range of nanoparticle volume fractions (φ) considered is 0 ≤ φ ≤ 5%. The variation of the local and the average Nusselt numbers with Reynolds number, and volume fractions are presented for the range of conditions. The average Nusselt number is found to increase with increasing the nanoparticle volume fractions.

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