Natural Convection Heat Transfer in Horizontal Cylindrical Cavities: A Computational Fluid Dynamics (CFD) Investigation

2013 ◽  
Author(s):  
Daniele Ludovisi ◽  
Ivo A. Garza
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Power Plants ◽  
Convection Heat Transfer ◽  
Weather Conditions ◽  
Freezing Temperature ◽  
Cold Weather ◽  
Pipe Surface ◽  
Cfd Models ◽  
Different Diameters

Many processes in power plants involve the storage and transfer of fluids including water in outdoor pipelines. Under extreme cold weather conditions, water can freeze if allowed to cool down to the freezing temperature. Installing insulation and maintaining adequate flow rate can sometimes prevent problems. However, during extended non-processing times, there are circumstances where cool down cannot be avoided and heat tracing along the piping becomes a necessity. In many instances, the need for the installation of heat tracing is simply determined based on pipe size. However, by performing accurate calculations, it is possible to determine if the need for heat tracing is real or not, thus saving on installation and maintenance costs. Correlations for the estimation of the heat transfer coefficient in horizontal cavities are not sufficiently documented in literature. In the present work, two-dimensional CFD models are used to investigate the natural convection in water-filled horizontal pipes of different diameters. The analysis has been carried out based on the assumption of a uniform pipe surface temperature. The Nusselt number is estimated as a function of the Rayleigh number and shown not to be strongly dependent on the Prandtl number. The analysis and the results of the numerical investigation are presented and compared to experimental data and other correlations available in literature. The documented correlation has an expanded range of applicability to high and low Rayleigh numbers, is supported by numerical and experimental results and is expressed in a simple form.

Natural Convection From Horizontal Wires to Viscoelastic Fluids

1986 ◽  
Vol 108 (4) ◽  
pp. 790-795 ◽  
Author(s):  
M. L. Ng ◽  
J. P. Hartnett ◽  
E. Y. Kwack
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Shear Rate ◽  
Convection Heat Transfer ◽  
Viscoelastic Liquid ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Nusselt Numbers ◽  
Prandtl Numbers ◽  
Different Diameters

Natural convection heat transfer from horizontal wires of three different diameters (0.0254, 0.0508, and 0.0826 cm) to a pool of viscoelastic liquid was studied. Aqueous solutions of Natrosol and Polyox constituted the viscoelastic test fluids. The experimental Nusselt numbers were found to agree with the correlations recommended by Fand and Brucker for Newtonian fluids if the zero shear rate viscosity is used in the Rayleigh and Prandtl numbers.

Experimental Investigation of Natural Convection Heat Transfer From a Horizontal Array of Three Heated Cylinders

2005 ◽  
Author(s):  
Asim Chatha ◽  
Ahmad Fakheri
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Different Diameters

An experimental study was performed to determine the natural convection heat transfer characteristics of a row of three horizontal heated cylinders of two different diameters (0.625 in. and 1.50 in.) with various cylinder-spacing arrangements. As a result, it was found that the heat transfer characteristics are strongly dependent on the spacing between the cylinders and the Rayleigh number Ra. The results of this study show that as the inter-cylinder spacing between a single row of three horizontal heated cylinders is reduced, the natural convection heat transfer coefficient and the heat transfer from each cylinder initially increase and then decrease beyond those for infinitely apart cylinders. Therefore, the array’s total rate of heat transfer increases because of two factors: the enhanced heat transfer coefficient, and the ability to add more cylinders in a fixed volume. This type of behavior has not been reported before experimentally and should be useful in the design of heat exchangers to reduce their sizes.

scholarly journals KARAKTERISTIK PERPINDAHAN PANAS KONVEKSI ALAMIAH ALIRAN NANOFLUIDA AL2O3-AIR DI DALAM PIPA ANULUS VERTIKAL

2016 ◽  
Vol 18 (1) ◽  
pp. 21
Author(s):  
Reinaldy Nazar
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Power Plants ◽  
Convection Heat Transfer ◽  
Thermal Characteristics ◽  
Heat Transfer Fluid ◽  
Empirical Correlations ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Vertical Annulus

ABSTRAK KARAKTERISTIK PERPINDAHAN PANAS KONVEKSI ALAMIAH ALIRAN NANOFLUIDA AL2O3-AIR DI DALAM PIPA ANULUS VERTIKAL. Hasil beberapa penelitian menunjukan bahwa nanofluida memiliki karakteristik termal yang lebih baik dibandingkan dengan fluida konvensional (air). Berkaitan dengan hal tersebut, saat ini sedang berkembang pemikiran untuk menggunakan nanofluida sebagai fluida perpindahan panas alternatif pada sistem pedingin reaktor. Sementara itu, konveksi alamiah di dalam pipa anulus vertikal merupakan salah satu mekanisme perpindahan panas yang penting dan banyak ditemukan pada reaktor riset TRIGA, reaktor daya generasi baru dan alat konversi energi lainnya. Namun disisi lain karakteristik perpindahan panas nanofluida di dalam pipa anulus vertikal belum banyak diketahui. Oleh karena itu penting dilakukan secara berkesinambungan penelitian-penelitian untuk menganalisis perpindahan panas nanofluida di dalam pipa anulus vertikal. Pada penelitian telah dilakukan analisis numerik menggunakan program computer CFD (computational of fluids dynamic) terhadap karakteristik perpindahan panas konveksi alamiah aliran nanofluida Al2O3-air konsentrasi 2% volume di dalam pipa anulus vertikal. Hasil kajian ini menunjukkan terjadi peningkatan kinerja perpindahan panas (bilangan Nuselt- NU) sebesar 20,5% - 35%. Pada moda konveksi alamiah dengan bilangan 2,4708e+09 £ Ra £ 1,9554e+13 diperoleh korelasi empirik untuk air adalah dan korelasi empirik untuk nanofluida Al2O3-air adalah   Kata kunci: Nanofluida Al2O3-air, konveksi alamiah, pipa anulus vertikal     ABSTRACT THE CHARACTERISTICS OF NATURAL CONVECTIVE HEAT TRANSFER OF AL2O3–WATER NANOFLUIDS FLOW IN A VERTICAL ANNULUS PIPE. Results of several research have shown that nanofluids have better thermal characteristics compared to conventional fluid (water). In this regard, currently developing ideas for using nanofluids as an alternative heat transfer fluid in the reactor coolant system. Meanwhile the natural convection in a vertical annulus pipe is one of the important mechanisms of heat transfer and is found at the TRIGA research reactor, the new generation nuclear power plants and other energy conversion devices. On the other hand the heat transfer characteristics of nanofluids in a vertical annulus pipe has not been known. Therefore, it is important to do research continuously to analyze the heat transfer nanofluids in a vertical annulus pipe. In the research has been carried out numerical analysis by using computer code of CFD (computational of fluids dynamic) on natural convection heat transfer characteristics of nanofluids flow of Al2O3-water 2% volume in the vertical annulus pipe. The results showed an increase in heat transfer performance (Nusselt numbers - NU) by 20.5% - 35%. In natural convection mode with Rayleigh numbers 2.4708e+09 £ Ra £ 1.9554e+13 obtained empirical correlations for water is and empirical correlations for Al2O3-water nanofluids is .   Keywords: Al2O3-water nanofluids, the natural convection, the vertical annulus pipe

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