On heat transfer in tubes

Modelowanie ustalonych procesów przepływowo-cieplnych w kotle fluidalnym

“…gdzie Nu oznacza liczbę Nusselta, która jest wyznaczana z wykorzystaniem korelacji Gnielinskiego [1,4,7], obowiązującej dla zakresów liczb Reynoldsa 3·10 3 ≤ Re ≤ 10 7 i Prandtla 0,5 ≤ Pr ≤ 200:…”

Determining heat transfer correlations for transition and turbulent flow in ducts

“…(10) in conjunction with the formulas (11) and (12). Furthermore, the friction factor was calculated from the formula (29) with experimental data by Buyukalaca et al [2] and Eiamsa-Ard et al [4] and the method of calculation proposed by Gnielinski [8] An inspection of the results shown in Fig. 2 indicates that for small Reynolds numbers the use of the experimental velocity distribution (14) given by Reichardt to calculate the friction factor ξ for small Reynolds numbers gives very satisfactory results.…”

“…There are only a few heat transfer correlations for internal flows in pipes and ducts which are valid in transition and turbulent regions [3,[5][6][7][8]12]. Based on the suggestion of Hausen, Gnielinski [5] superseded the Reynolds number Re by the term (Re -1000) in the heat transfer correlation to include the transitional region.…”

“…It turned out, however, that in the range of Reynolds numbers from Re = 4000 to 20000 values of Nusselt numbers calculated using the interpolation formula proposed by Gnielinski are too large. For this reason, he changed his formula [8]. A linear interpolation between the Nusselt numbers at Re = 2300 and Re = 4000, was proposed.…”

“…The Nusselt number for Re = 2300 is calculated from wellknown correlations for the laminar flow and for Re = 4000 the Nusselt number is determined using the modified Pietukhov correlation in which Re was replaced by (Re-1000). The disadvantage of all interpolation functions proposed by Gnielinski [6][7][8] is the need to specify the value of the Reynolds number for the end of the interval, in which the flow is transitional. Experimental studies show that in the range of Reynolds numbers: 2300 < Re < 20000 the Nusselt numbers are much smaller than those calculated from the correlations used for turbulent flow.…”