Wyniki wyszukiwania - Biblioteka Nauki

1

Analytical solutions of heat transfer for laminar flow in rectangular channels

100%

Mikielewicz J. , Rybiński W.

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nr 4

2

An Integrated Approach of Profi le Studies for Surface Water Velocity on a Steep Slope in a Rectangular Channel

86%

Ayalew A. T. , Koshuma A. E. , Ayele M. n. A. , Dirate D. D.

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2022

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tom Vol. 16, no 2

74--80

EN

The flow velocity of water and its accurate surface profile estimation is important parameter as changes in climate increases the uneven rainfall patterns causing flood in downstream. It is important to know the velocity profile in steep open channel flows for solving the soil erosion, flooding and sediment transport problems in rivers or streams on steep slopes. A fixed bed laboratory experiment for a rectangular channel with steep slope is conducted to find the velocity profiles and surface profiles at different sections. Velocity profiles are presented at different sections in rectangular channel with steep slope. The outcome of the laboratory based experimental investigation shows that the velocity and surface profiles are influenced by the depth of flow of water and channel bed slope respectively.

3

Grawitacyjny spływ wody w kanałach prostokątnych wymiennika ciepła

86%

Bednarski J. , Rajski K.

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tom R. 48, nr 12

16--17

PL

W artykule przedstawiono proces grawitacyjnego spływu wody w prostokątnych kanałach zraszanego wymiennika ciepła. Omówiono trzy podstawowe rodzaje takiego przepływu dwufazowego. Występujące zjawisko opisano za pomocą równania różniczkowego cząstkowego wraz z odpowiednimi warunkami brzegowymi. Omówiono wyniki przeprowadzonych obliczeń numerycznych. Na ich podstawie opracowano korelacje pozwalające określić grubość filmu wodnego oraz jego prędkość średnią w zależności od występującego strumienia objętościowego wody oraz od jej lepkości dynamicznej.

EN

The paper discusses process of gravity -driven water flow in the rectangular channels of the plate-type sprinkled heat exchanger. The three basic types of such two-phase flow have been presented. The occurring phenomenon has been described by the partial differential equation with appropriate boundary conditions. The results of the numerical calculations have been discussed. The correlations for determining the average speed and the thickness of the water film (depending on the volume flow and the dynamic viscosity of water) have been obtained.

4

A simplifed approach for the evaluation of groundwater fow in stream–aquifer interaction

86%

Saxena M. , Singh R. K.

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tom Vol. 69, no. 1

231--241

EN

Stream–aquifer interaction process plays an important role in modulating food wave propagation in a channel. The most elementary understanding of stream–aquifer interaction can be interpreted by the fux direction between a surface water body and the underlying aquifer. At the time of foods, stream stage rises, and the water gets infltrated into the aquifer, and this process gets reversed at the time when the stream stage gets declined. Therefore, an integrated mechanism between the surface and subsurface fows is particularly important for models, where the response of the system is based on simultaneous interactions between these two major fow domains. In this study, numerical simulation of a food wave has been demon strated considering stream–aquifer interaction. The calibration has been executed on a hypothetical food event accessed by routing a known stage hydrograph for a channel reach having a rectangular cross section which fully penetrates the adjoining aquifer given by Zitta and Wiggert (Water Resour Res 7:1341–1345, 1971). A simplifed mathematical approach, based on Darcy’s law, has been presented here for the solution of groundwater fow equations. The results obtained from the adopted procedure are also compared with the solution proposed by Zitta and Wiggert in 1971. The NSE and RMSE (m3 /s) estimate assessed for the simulated hydrographs using the proposed methodology with respect to the procedure adopted by Zitta and Wiggert (Water Resour Res 7:1341–1345, 1971) is 0.9983 and 0.8544, respectively. Therefore, the use of Simpson’s (3/8)- rule is not suggestible due to its complicated calculation and its sensitivity, and it is better to use the proposed simplifed approach for the evaluation of lateral fow.

5

Analytical solutions of heat transfer for laminar flow in rectangular channels

72%

Rybiński W. , Mikielewicz J.

Archives of Thermodynamics

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2014

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tom Vol. 35, no. 4

29--42

EN

The paper presents two analytical solutions namely for Fanning friction factor and for Nusselt number of fully developed laminar fluid flow in straight mini channels with rectangular cross-section. This type of channels is common in mini- and microchannel heat exchangers. Analytical formulae, both for velocity and temperature profiles, were obtained in the explicit form of two terms. The first term is an asymptotic solution of laminar flow between parallel plates. The second one is a rapidly convergent series. This series becomes zero as the cross-section aspect ratio goes to infinity. This clear mathematical form is also inherited by the formulae for friction factor and Nusselt number. As the boundary conditions for velocity and temperature profiles no-slip and peripherally constant temperature with axially constant heat flux were assumed (H1 type). The velocity profile is assumed to be independent of the temperature profile. The assumption of constant temperature at the channel’s perimeter is related to the asymptotic case of channel’s wall thermal resistance: infinite in the axial direction and zero in the peripheral one. It represents typical conditions in a minichannel heat exchanger made of metal.