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  • 1
    Electronic Resource
    Electronic Resource
    Numerical analysis of natural convection around a vertical channel in a rectangular enclosure (1996)
    Springer
    Heat and mass transfer 31 (1996), S. 313-321 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Aus numerischen Berechnungen wurde das Wärmeübergangs- und Strömungsverhalten eines aus zwei parallelen Platten gebildeten Vertikalkanals ermittelt, der sich symmetrisch angeordnet in einer rechteckigen Kammer befindet. Kanal- und Kammerwände haben gleichförmige, jedoch unterschiedliche Temperaturen. In der luftgefüllten Kammer herrscht freie Konvektion. Die dimensionslose KanalbreiteS wurde als Parameter variiert, wobei die Rayleigh-Zahlen zwischen 102 und 107 lagen. Für die beschriebene Konfiguration wurde statische Bifurkation festgestellt, welche sich im Strömungsbild durch den Übergang von der Einzel-zur Doppelwirbelstruktur und umgekehrt dokumentiert. Der Vergleich mit empirischen Beziehungen für eine vertikale Platte und einen Kanal im umbegrenzten Raum ergab, daß der Wärmeaustausch an Platte und Kanal durch den Kammereinschluß behindert wird.
    Notes: Abstract Numerical computations were performed for the heat transfer and fluid flow characteristics of an internal vertical channel composed by a pair of parallel plates situated in a rectangular enclosure, with the inner plates and the bounding wall of the enclosure maintained at uniform but different temperatures. Natural convection occurred in the air which occupied the enclosure space. The plates were symmetrically arranged. The dimensionless channel widthS was varied parametrically. The Rayleigh numbers ranged from 102 to 107. Static bifurcation was found in this configuration. The bifurcation is related to the flow pattern transition from single-vortex structure to double-vortex structure or vice versa. Comparison with the empirical correlations obtained for a vertical plate and a channel in an infinite space showed that the heat transfer process of the plates and the channel was deteriorated by the existence of the enclosure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02184044
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  • 2
    Electronic Resource
    Electronic Resource
    Natural convection in a square enclosure with an internal isolated vertical plate (1994)
    Springer
    Heat and mass transfer 29 (1994), S. 161-169 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Eine numerische Untersuchung liefert mittlere Nußelt-Zahlen an einer, in einem quadratischen Horizontalschacht freistehenden, senkrechten Platte, wobei deren Temperatur und die der umgebenden Wände jeweils konstant gehalten werden. Im Luftraum dazwischen stellte sich freie Konvektion ein. Die Position der Platte war veränderlich, ihre Höhe blieb mit 51.3% der Schachthöhe konstant. Rückte die Platte nahe an eine Schachtwand, so erhöhte sich die Nußelt-Zahl auf der dieser zugewandten Seite, während die Gesamt-Nußelt-Zahl bezüglich der Platte fast konstant bleibt. Es wird auch der Einfluß der Rayleigh-Zahl auf das Geschwindigkeitsund Temperaturfeld diskutiert. BeiRa=1.1·106 stimmten die Ergebnisse aus der Berechnung gut mit den experimentellen Befunden einer Strömungsvisualisation überein.
    Notes: Abstract Numerical computations were performed for the average Nusselt number at an internal vertical plate situated in a square enclosure, with the inner plate and the bounding wall of the enclosure maintained at uniform but different temperatures. Natural convection occurred in the air which occupied the enclosure space. The position of the inner vertical plate within the enclosure was varied parametrically. The plate height-cavity height ratio was 0.513. For narrow distance between the inner plate and the bounding wall the inner plate Nusselt number was enhanced. Aside from this, the plate average Nusselt number was remarkably insensitive to the plate position. The effect of the Rayleigh number on the velocity and temperature fields and local Nusselt numbers are also discussed. The agreement between the predicted flow pattern forRa=1.1×106 and the flow visualization result was reasonably good.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01548600
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental study of natural convection heat transfer between an outer horizontal cylindrical envelope and an inner concentric heated square cylinder with two slots (1995)
    Springer
    Heat and mass transfer 30 (1995), S. 455-459 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung In der Arbeit werden die Ergebnisse einer experimentellen Untersuchung des Wärmeübergangs bei natürlicher Konvektion zwischen einer horizontalen zylindrischen Außenhülle und einem beheizten quadratischen Prisma mit zwei Schlitzen vorgestellt. Das Prisma selbst ist hohl und weist in der oberen und unteren Begrenzungsfläche je einen horizontalen Längsschlitz auf. Das Verhältnis von SchlitzweiteS zu SeitenhöheH beträgt 0,0612 und 0,3878, das des HülleninnendurchmessersD o zur SeitenhöheH beträgt 2,653. Als Arbeitsmedium diente Luft. Die Rayleigh-Zahlen variierten zwischen 1,7·102 und 8,72·106 fürS/H=0,0612 und zwischen 1,32·102 und 6,25·106 fürS/H=0,3878. Die Ergebnisse belegen die Existenz dreier unterschiedlicher Wärmeübergangsregime in den verschiedenen Rayleigh-Zahl-Bereichen, und zwar reiner Leitungsbereich, Übergangsgebiet und Konvektionsbereich. Die Ergebnisse für den Wärmeübergang werden im Vergleich mit jenen für ein Prisma ohne Schlitze durch zwei Korrelationbeziehungen dargestellt. Es zeigt sich, daß durch Anbringung von Schlitzen am Innenprisma der Wärmeübergang wesentlich verstärkt werden kann.
    Notes: Abstract This paper presents the results of an experimental study of natural convection heat transfer between a horizontal cylindrical envelope and an internal concentric heated square cylinder with two slots. The internal cylinder was a hollow one with horizontal slots on its top and bottom surfaces. The ratio of slot widthS to the side heightH was 0.0612 and 0.3878. The ratio of the envelope inner diameterD o to the side heightH was 2.653. Air was used as the working fluid. The range of Ray-leigh number was 1.77×102∼8.72×106 forS/H=0.0612 and 1.32×102∼6.25×106 forS/H=0.3878. The results show that there are three different heat transfer regimes in different Ray-leigh number regions, i.e. pure conduction regime, transition regime and convection regime. The average heat transfer results were correlated into two empirical equations. Comparison was made with the non-slotted case. It is found that slots of the internal cylinder can significantly enhance the heat transfer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01647451
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  • 4
    Electronic Resource
    Electronic Resource
    Numerical analysis of natural convection around a vertical channel in a rectangular enclosure (1996)
    Springer
    Heat and mass transfer 31 (1996), S. 313-321 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung  Aus numerischen Berechnungen wurde das Wärmeübergangs- und Strömungsverhalten eines aus zwei parallelen Platten gebildeten Vertikalkanals ermittelt, der sich symmetrisch angeordnet in einer rechteckigen Kammer befindet. Kanal- und Kammerwände haben gleichförmige, jedoch unterschiedliche Temperaturen. In der luftgefüllten Kammer herrscht freie Konvektion. Die dimensionslose Kanalbreite S wurde als Parameter variiert, wobei die Rayleigh–Zahlen zwischen 102 und 107 lagen. Für die beschriebene Konfiguration wurde statische Bifurkation festgestellt, welche sich im Strömungsbild durch den Übergang von der Einzel–zur Doppelwirbelstruktur und umgekehrt dokumentiert. Der Vergleich mit empirischen Beziehungen für eine vertikale Platte und einen Kanal im umbegrenzten Raum ergab, daß der Wärmeaustausch an Platte und Kanal durch den Kammereinschluß behindert wird.
    Notes: Abstract  Numerical computations were performed for the heat transfer and fluid flow characteristics of an internal vertical channel composed by a pair of parallel plates situated in a rectangular enclosure, with the inner plates and the bounding wall of the enclosure maintained at uniform but different temperatures. Natural convection occurred in the air which occupied the enclosure space. The plates were symmetrically arranged. The dimensionless channel width S was varied parametrically. The Rayleigh numbers ranged from 102 to 107. Static bifurcation was found in this configuration. The bifurcation is related to the flow pattern transition from single-vortex structure to double-vortex structure or vice versa. Comparison with the empirical correlations obtained for a vertical plate and a channel in an infinite space showed that the heat transfer process of the plates and the channel was deteriorated by the existence of the enclosure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002310050061
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  • 5
    Electronic Resource
    Electronic Resource
    Natural convections in conjugated single and double enclosures (1995)
    Springer
    Heat and mass transfer 30 (1995), S. 175-182 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Es wird der Wärmetransport durch freie Konvektion in Einzel- und Doppelhohlräumen numerisch untersucht, welche von Wänden endlicher Dicke und niedriger Wärmeleitfähigkeit gebildet werden. An deren vertikalen Außenseite soll die Randbedingung 3. Art herrschen, während Boden- und Deckenseite als adiabat vorausgesetzt seien. Das untersuchte Problem ist durch einen dominanten horizontalen Temperaturgradienten charakterisiert, sowie den Umstand, daß die Randbedigungen auf den Berandungen der Hohlräume nicht von vornherein festgelegt werden können. Numerische Ergebnisse lassen das charakteristische Übertragungsverhalten solcher Hohlräume erkennen und zeigen den Einfluß der thermischen Randbedingungen auf die natürliche innenseitige Konvektion. Ferner wurde gefunden, daß freie Konvektionsvorgänge in Doppelhohlräumen grundsätzlich nicht anders als in Einzelhohlräumen ablaufen, abgesehen davon, daß diese auf unterschiedlichen Temperaturniveaus stattfinden.
    Notes: Abstract The natural convection in single and double conjugated enclosures are numerically investigated. The single and double enclosures are formed by low conductance walls with finite thickness. The outside vertical surfaces of the conducting walls are of the third kind of boundary condition while the top and bottom outside surfaces are adiabatic. The problem studied is characterized by a dominant horizontal temperature gradient and the thermal boundary conditions at the cavity surfaces can not be specified in priori. Numerical results reveal the characteristics in such kind of enclosures and show the importance of the thermal boundary conditions on the natural convection in enclosures. It is also found that the natural convections in the conjugated double enclosures are basically the same, with a major difference in their fluid temperature levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01476527
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  • 6
    Electronic Resource
    Electronic Resource
    Experimental study on the pressure drop and heat transfer characteristics of tubes with internal wave-like longitudinal fins (1999)
    Springer
    Heat and mass transfer 35 (1999), S. 65-73 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Experiments were performed to determine the heat transfer and pressure drop characteristics in the entrance and fully developed regions of tubes with internal wave-like longitudinal fins. The test tube has a double-pipe structure, with the inner tube as an insertion. The wave-like fins are in the annulus and span its full width. Experiments were conducted for two cases: one with the inner tube blocked (no air flowing through it) and the other with the inner tube unblocked. The outer tube was electrically heated. Local and average heat transfer coefficients and friction factors were measured. The friction factor and Nusselt number correlations in the fully developed region were obtained in the Reynolds number range of 9×102 to 3.5×103. It has been found that the wave-like fins enhance heat transfer significantly with the blocked case being superior. In addition, the in-tube heat transfer process is characterized by an earlier transition from laminar to turbulent flow and Reynolds number-dependent thermal entrance length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002310050299
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of outflow boundary condition on convective heat transfer with strong recirculating flow (1994)
    Springer
    Heat and mass transfer 29 (1994), S. 463-470 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Es werden drei verschiedene Methoden herangezogen, um die Erfüllung der Ausflußbedingung bei der Berechnung des konvektiven Wärmeübergangs von einem zweidimensionalen Fluidstrahl an die Wände eines rechteckigen Hohlraumes zu erzwingen. Diese seien kurz bezeichnet als: (1) lokales Massenerhaltungsprinzip, (2) Einkomponentenprinzip, (3) Vollausbildung des Strömungsprofils. Unter Verwendung dieser drei Prinzipien ermittelte numerische Lösungen wurden mit experimentell (Naphtalin-Sublimationsmethode) gefundenen Ergebnissen verglichen. Es zeigte sich, daß Methode (3) ungeeignet ist, Methode (2) gute Ergebnisse für den Hohlraumboden liefert, aber an den Seitenwänden qualitativ von den Versuchsdaten abweicht und daß Methode (1) die beste Übereinstimmung bewirkt. Bei Problemen, welche starke Rezirkulationsströmungen am Austritt des zur Berechnung vorgegebenen Kontrollraumes erwarten lassen, sollte daher dieser Methode der Vorzug gegeben werden.
    Notes: Abstract Three practices of treating outflow boundary condition were adopted in computations for convective heat transfer of a two-dimensional jet impinging in a rectangular cavity. The three practices were local mass conservation method, local one-way method and fully developed assumption. The numerical solutions of the three methods were compared with test data obtained via, naphthalene sublimation technique. It was found that the fully developed assumption was inappropriate, and the local one-way method could provide reasonably good results for the cavity bottom, while for the lateral wall the results with this method qualitatively differed from the test data. The solution with the local mass conservation method was the best. It thus suggested that for a problem expected with a strong recirculating flow at the exit of the computation domain, the local mass conservation method be adopted to treat the outflow boundary condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01539498
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of rib angle orientation on local mass transfer distribution around sharp 180 deg turn with rib-turbulators mounted in entire two-pass channels (1997)
    Springer
    Heat and mass transfer 32 (1997), S. 325-332 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Der lokale Stoffübergang in einem relativ kurzen (L/D = 4) 180∘-Umlenkkanal mit turbulenzerzeugenden Rippen wurde unter Einsatz der Naphtalin-Sublimationstechnik untersucht. Das Verhältnis von Rippenhöhe zu hydraulischem Durchmesser betrug e/D = 0,05 und das von Rippenabstand zu Rippenhöhe p/e = 10. Die Experimente wurden mit 5 verschiedenen Anstellwinkeln (α=90∘,45∘,60∘,−45∘,−60∘) und bei drei Reynolds-Zahlen (3,0·104, 6,0·104, 9,0·104) durchgeführt. Ripppenwinkel und Rippenorientierung zeigten wesentlichen Einfluß auf die lokalen und mitt-leren Sherwood-Zahlen, wobei die höchsten Werte bei α=60∘ auftraten; dann folgten immer niedrigere für 45∘,90∘ und −45∘. Berechnungsgleichungen für mittlere Sherwood-Zahlen in den 3 Segmenten vor, in und nach der 180∘– Umlenkung werden mitgeteilt.
    Notes: Abstract The local mass transfer distributions around sharp 180 deg turn with rib-turbulators in a relatively short (L/D=4) two-pass, square channel were determined via the naphthalene sublimation technique. The rib height-to-hydraulic diameter ratio (e/D) was 0.05 and the rib pitch-to-height ratio (p/e) was 10. Experiments were conducted for five attack angles (α=90,45,60,−45, and −60 deg), and for three Reynolds numbers (3.0×104, 6.0×104 and 9.0×104). Results show that the rib-roughened wall Sherwood numbers after the turn are higher than those in the turn region, which, in turn, are higher than those before the turn due to the ribs installed in the turn region. While in the previous studies, the ratio Sh/Sh 0 in the turn region was found to be lower than that in the before turn region, because of the absence of rib in the turn region. The rib angle and rib orientation have significant effect on both the local and average Sherwood number ratios. The average Sherwood number ratios (Sh m /Sh 0) for α = 60 deg have the highest values, then comes the case of α = 45 deg, and the Sherwood number ratios (Sh m /Sh 0) for α = 90 and −45 deg are the lowest. Correlations for the average rib-roughened wall Sherwood number ratios for the before-turn, in-turn and after-turn segments are provided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002310050129
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  • 9
    Electronic Resource
    Electronic Resource
    An improved numerical algorithm for solution of convective heat transfer problems on nonstaggered grid system (1998)
    Springer
    Heat and mass transfer 33 (1998), S. 273-280 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In this paper, a SIMPLE-like algorithm on co-located grid system has been developed. The ability to suppress the spurious pressure field is achieved via introducing the pressure difference between adjacent two grid points into the convection-diffusion finite difference scheme, and the interfacial velocity is obtained by simple linear interpolation. The differencing scheme, discretization of governing equations and solution procedure of the algorithm are described in detail. In order to check the validity of the algorithm, several test cases which have analytical or benchmark solutions are presented. Good agreements are obtained between the numerical and the corresponding analytical or benchmark solutions. The ability of the improved algorithm to suppress the spurious pressure field is demonstrated via a 3-D example.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002310050189
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  • 10
    Electronic Resource
    Electronic Resource
    Automatic generation of unstructured grids with Delaunay triangulation and its application (1999)
    Springer
    Heat and mass transfer 35 (1999), S. 361-370 
    Details
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract This paper is consisted of two parts. In the first part, a method is described which generates two-dimensional triangle mesh using the Delaunay triangulation criterion. An automatic algorithm was proposed which combines several advantages of the existing methods. Local mesh refinement can also be easily performed with this method. Examples of generated grids were presented for several convex, non-convex and multi-connected domains to demonstrate the effectiveness and feasibility of the proposed method. In the second part, the turbulent heat transfer in an annular space finned by wave-like longitudinal fins was numerical simulated. The proposed technique was adopted to generate the grid in the cross-section. The standard K-ɛ model in conjuction with wall function method was used to simulate the fluid flow and heat transfer in the complex geometry. The discretization of the governing equations was described. The computational results were compared with the authors' test data and the agreement was reasonably good.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002310050337
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