Estimation of transient wall and flow temperature distributions in a circular duct using an inverse approach

2007 ◽  
Vol 221 (11) ◽  
pp. 1353-1361
Author(s):  
S D Masouros ◽  
K Mathioudakis
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient ◽  
Circular Duct ◽  
Inverse Approach ◽  
Forced Convection Heat Transfer

Inverse methods have become a useful tool for estimating parameters that cannot be measured or calculated directly in engineering applications. Parameters characterizing unsteady heat convection in circular duct flows are associated with numerous uncertainties. This fact renders the inverse approach appropriate for the determination of these parameters. An inverse problem for transient turbulent thermally developing and thermally developed forced-convection flow in a circular duct is formulated and discussed, and a simplified direct thermal model is presented. Parameters of the model are estimated by solving a minimization problem, using temperature data from the wall surface and/or the flow. A multivariable optimization algorithm is employed for this purpose. Furthermore, a model for the forced-convection heat-transfer coefficient is proposed and its effect on the results is discussed. The validity of the proposed method is assessed using data from two different circular duct flows. The method is shown to provide a good prediction capability in computationally demanding transient heat-data sequences of different duct flows, both in terms of duct and of flow characteristics. Results show that a hyperbolic axial distribution of the forced-convection heat-transfer coefficient in the developing region of the flow is essential for good adaptation of the method to the test data.

scholarly journals Forced Convection Nanofluid Heat Transfer as a Function of Distance in Microchannels

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3021
Author(s):  
Saeid Vafaei ◽  
Jonathan A. Yeager ◽  
Peter Daluga ◽  
Branden Scherer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Crystal Phase ◽  
Convection Heat ◽  
Effective Parameters ◽  
Forced Convection Heat Transfer ◽  
Base Liquid

As electronic devices become smaller and more powerful, the demand for micro-scale thermal management becomes necessary in achieving a more compact design. One way to do that is enhancing the forced convection heat transfer by adding nanoparticles into the base liquid. In this study, the nanofluid forced convection heat transfer coefficient was measured inside stainless-steel microchannels (ID = 210 μm) and heat transfer coefficient as a function of distance was measured to explore the effects of base liquid, crystal phase, nanoparticle material, and size on heat transfer coefficient. It was found that crystal phase, characteristics of nanoparticles, the thermal conductivity and viscosity of nanofluid can play a significant role on heat transfer coefficient. In addition, the effects of man-made and commercial TiO2 on heat transfer coefficient were investigated and it was found that man-made anatase TiO2 nanoparticles were more effective to enhance the heat transfer coefficient, for given conditions. This study also conducted a brief literature review on nanofluid forced convection heat transfer to investigate how nanofluid heat transfer coefficient as a function of distance would be affected by effective parameters such as base liquid, flow regime, concentration, and the characteristics of nanoparticles (material and size).

scholarly journals Determination of Heat Transfer Coefficient for the Air Forced Cooling Over a Flat Side of Coil

2019 ◽  
Vol 15 (1) ◽  
pp. 15-20 ◽  
Author(s):  
Payam Shams Ghahfarokhi ◽  
Ants Kallaste ◽  
Anouar Belahcen ◽  
Toomas Vaimann
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Analytical Results ◽  
Flat Side

AbstractThe paper deals with the analytical and experimental determination of the forced convection heat transfer coefficients over the flat coil module. In the analytical part, the forced convection coefficients at different wind speeds are calculated based on various known equations of the forced convection heat transfer coefficient with unheated starting length. The experimental part presents the description of the test: loading the coil with DC current and measurements of the coil temperatures with thermal sensors while it was inside a wind tunnel. Based on the measurement, the convection coefficients were determined. In the final part, the experimental and analytical results are compared. It is found that the accuracy of the analytical results is more precise in highly turbulent flows.

scholarly journals Experimental and Theoretical Investigation of the Natural Convection Heat Transfer Coefficient in Phase Change Material (PCM) Based Fin-and-Tube Heat Exchanger

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 716
Author(s):  
Saulius Pakalka ◽  
Kęstutis Valančius ◽  
Giedrė Streckienė
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Energy Storage ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient

Latent heat thermal energy storage systems allow storing large amounts of energy in relatively small volumes. Phase change materials (PCMs) are used as a latent heat storage medium. However, low thermal conductivity of most PCMs results in long melting (charging) and solidification (discharging) processes. This study focuses on the PCM melting process in a fin-and-tube type copper heat exchanger. The aim of this study is to define analytically natural convection heat transfer coefficient and compare the results with experimental data. The study shows how the local heat transfer coefficient changes in different areas of the heat exchanger and how it is affected by the choice of characteristic length and boundary conditions. It has been determined that applying the calculation method of the natural convection occurring in the channel leads to results that are closer to the experiment. Using this method, the average values of the heat transfer coefficient (have) during the entire charging process was obtained 68 W/m2K, compared to the experimental result have = 61 W/m2K. This is beneficial in the predesign stage of PCM-based thermal energy storage units.

Forced Convection Heat Transfer of Nanofluids: A Review

2017 ◽  
Author(s):  
Aditya Kuchibhotla ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Specific Heat ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Convection Heat

Stable homogeneous colloidal suspensions of nanoparticles in a liquid solvents are termed as nanofluids. In this review the results for the forced convection heat transfer of nanofluids are gleaned from the literature reports. This study attempts to evaluate the experimental data in the literature for the efficacy of employing nanofluids as heat transfer fluids (HTF) and for Thermal Energy Storage (TES). The efficacy of nanofluids for improving the performance of compact heat exchangers were also explored. In addition to thermal conductivity and specific heat capacity the rheological behavior of nanofluids also play a significant role for various applications. The material properties of nanofluids are highly sensitive to small variations in synthesis protocols. Hence the scope of this review encompassed various sub-topics including: synthesis protocols for nanofluids, materials characterization, thermo-physical properties (thermal conductivity, viscosity, specific heat capacity), pressure drop and heat transfer coefficients under forced convection conditions. The measured values of heat transfer coefficient of the nanofluids varies with testing configuration i.e. flow regime, boundary condition and geometry. Furthermore, a review of the reported results on the effects of particle concentration, size, temperature is presented in this study. A brief discussion on the pros and cons of various models in the literature is also performed — especially pertaining to the reports on the anomalous enhancement in heat transfer coefficient of nanofluids. Furthermore, the experimental data in the literature indicate that the enhancement observed in heat transfer coefficient is incongruous compared to the level of thermal conductivity enhancement obtained in these studies. Plausible explanations for this incongruous behavior is explored in this review. A brief discussion on the applicability of conventional single phase convection correlations based on Newtonian rheological models for predicting the heat transfer characteristics of the nanofluids is also explored in this review (especially considering that nanofluids often display non-Newtonian rheology). Validity of various correlations reported in the literature that were developed from experiments, is also explored in this review. These comparisons were performed as a function of various parameters, such as, for the same mass flow rate, Reynolds number, mass averaged velocity and pumping power.

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