Browsing by Author "Beer, Hans"

Now showing 1 - 16 of 16

Open Access
Fluid flow and heat transfer in an axially rotating pipe subjected to external convection
(1992) Weigand, Bernhard; Beer, Hans
The effects of external insulation and tube rotation on the heat transfer to a fluid flowing inside a tube are examined by analysis. The turbulent flow is assumed to be hydrodynamically fully developed. Heat transfer was found to be strongly suppressed by tube rotation. It is shown that the significance of external insulation on the Nusselt number increases with growing rotation rate of the pipe.
Open Access
Fluid flow and heat transfer in an axially rotating pipe. 2, Effect of rotation on laminar pipe flow
(1989) Reich, Gerhard; Weigand, Bernhard; Beer, Hans
The effects of tube rotation on the velocity and temperature distribution, on the friction coefficient and on the heat transfer to a fluid flowing laminar inside a tube are examined by analysis. It is demonstrated that the rotation has a destabilizing effect on a laminar pipe flow, which changes to turbulent flow. Free convection vortices, that occur, if the pipe wall is heated, disappear with a growing rotation velocity of tbe tube. For that purpose a perturbation calculation is performed. By the results of this calculation the disappearance of the free convection vortices is demonstrated evidently.
Open Access
Fluid flow and heat transfer in an axially rotating pipe: the rotational entrance
(1992) Weigand, Bernhard; Beer, Hans
The complex interactions between turbulence and rotation in the rotational entrance region of a pipe, rotating about its axis, are examined. By assuming, a universal tangential velocity profile and with the use of a modified mixing length theory, the development of the axial velocIty profile and the heat transfer coefficient along the rotational entrance length are calculated. The theoretical results are compared with experimental flndings of Reich.
Open Access
Freezing in turbulent flow inside tubes and channels
(1993) Weigand, Bernhard; Beer, Hans
A simple and quite flexible numerical model is presented to predict the steady state ice-layer formation inside a cooled two dimensional channel or a tube containing a turbulent flow. The effects of arbitrary entrance velocity distributions upon the shape of the ice-layers are examined. The presented numerical scheme is verified by comparing the predicted ice-layers with measurements and generally good agreement was found.
Open Access
Heat transfer and solidification of a laminar liquid flow in a cooled parallel plate channel: the stationary case
(1991) Weigand, Bernhard; Beer, Hans
A simple numerical model is presented to predict the steady-state ice layers on the cooled walls inside a parallel plate channel for arbitrary entrance velocity profiles. The effect of two different entrance velocity distributions (a parabolic velocity distribution and a slug flow) on the shape of the ice-layers are examined. The quality of an approximative solution given in literature was checked by comparing with the numerical results. For the case of a fully developed parabolic velocity distribution at the entrance of the cooled channel the results are compared with experimental findings of Kikuchi. A generally good agreement was found.
Open Access
Ice-formation phenomena for water flow inside a cooled parallel plate channel : an experimental and theoretical investigation of wavy ice layers
(1993) Weigand, Bernhard; Beer, Hans
A numerical model is developed for predicting steady-state ice formation inside a cooled two-dimensional channel. The study takes into account the strong interactions existing between the turbulent flow, the shape of the ice and the heat transfer at the ice-water interface which lead to the formation of wavy ice layers with one wave. The presented analysis is found to be able to predict realistic variations of the ice layer thickness for a wide range of Reynolds numbers and cooling parameters. The numerical results were verified by comparing the predicted ice layers with measurements and generally good agreement was found.
Open Access
The morphology of ice structure in a parallel plate channel
(1991) Weigand, Bernhard; Beer, Hans
An experimental study has been performed to investigate the ice formation phenomena of water flow between two horizontal cooled parallel plates. A detailed and comprehensive investigation of the morphology of the ice-structure is given. It is shown that the different shapes of ice-layers can be classified with the help of a Θc - ReD diagramm. The regions for which a certain type of ice-layer occures are clearly separated.
Open Access
A numerical and experimental study of wavy ice structure in a parallel plate channel
(1992) Weigand, Bernhard; Beer, Hans
The paper presents a numerical model for predicting steady-state ice formation inside a cooled, parallel plate channel. The study takes into account the strong interactions occuring between the turbulent flow, the shape of the ice and the heat transfer at the ice-water interface, which lead to the formation of wavy ice layers. The presented model is found to be able to predict realistic variations of the ice layer thickness for a wide range of Reynolds numbers and cooling parameters. The numerical results were verified by comparing with own measurements and good agreement was found.
Open Access
A numerical and experimental study of wavy ice-structure in an asymmetrically cooled parallel-plate channel
(1992) Weigand, Bernhard; Beer, Hans
Ice formation of flowing water in a pipe or a channel, whose wall is kept at a uniform temperature below the freezing temperature of the water, is a basic engineering problem. It Introduces many practical problems, such as pressure drop, diminution of flow rate and sometime, breakage of the pipe as a result of flow blockage by ice. The phenomenon of freezing of flowing water involves interactions between the turbulent flow, the shape of the ice layer and the heat transfer at the ice-water interface. Under certain conditions these interactions result in an instabilily of the ice layer. This instability is caused by the strong laminarization of the turbulent flow due to converging ice layers in the entrance region of the cooled channel and results in a wavy ice structure. Wavy ice layers with one wave, occuring in a parallel.plate channel subjected to symmetrically oooled walls were investigated experimentally by Seld et al. and by Weigand and Beer. More recently Weigand and Beer were able to predict numerically the shape of wavy ice layers with one wave occuring in a symmetrically cooled channel. Wavy ice layers in a parallel-plate channel with one wave in the case of asymmetrically cooled walls were investigated experimentally by Tago et al. and by Weigand and Beer. No numerical calculation of asymmetric wavy freezing fronts was done in the past. Therefore, the subject of this paper is the presentation of a numerical model for calculating steady state ice layers with one wave in the entrance region of an asymmetric cooled channel. The method is based on a work performed by Weigand and Beer. The given numerical study is supported by a detailed experimental investigation.
Open Access
On the universality of the velocity profiles of a turbulent liquid flow in an axially rotating pipe
(1994) Weigand, Bernhard; Beer, Hans
If a fluid enters an axially rotating pipe, it receives a tangential component of velocity from the moving wall, and the flow pattern change according to the rotational speed. A flow relaminarization is set up by an increase in the rotational speed of the pipe. It will be shown that the tangential- and the axial velocity distribution adopt a quite universal shape in the case of fully developed flow for a fixed value of a new defined rotation parameter. By taking into account the universal character of the velocity profiles, a formula is derived for describing the velocity distribution in an axially rotating pipe. The resulting velocity profiles are compared with measurements of Reich [10] and generally good agreement is found.
Open Access
A perturbation analysis of transient freezing of a laminar liquid flow in a cooled two-dimensional channel
(1993) Weigand, Bernhard; Höhn, Werner; Beer, Hans
he paper shows the applicability of a regular perturbation method for predicting the transient development of the ice layer thickness inside a cooled planar channel subjected to laminar flow. Applying the perturbation expansion to the conservation equations, closed-form solutions for the velocity and temperature distributions in the fluid for an arbitrarily shaped channel could be derived under the assumption that the axial variation in solid layer thickness is small. The distributions obtained for the steady-state ice layer thickness and the velocity were checked by numerical calculations and generally good agreement was found.
Open Access
Solidification of flowing liquid in an asymmetric cooled parallel-plate channel
(1992) Weigand, Bernhard; Beer, Hans
An experimental study has been performed to investigate the ice-formation phenomena of water flow between two horizontal parallel plates, with the lower wall kept at a temperature below the freezing temperature of the liquid. A detailed and comprehensive investigation of the morphology of the ice-structure is given.
Open Access
A theoretical and experimental investigation of smooth- and wavy ice layers in laminar and turbulent flow inside an asymmetrically cooled parallel-plate channel
(1993) Weigand, Bernhard; Beer, Hans
The present paper shows the adaption of the numerical model originally developed by Weigand and Beer [14] for calculating steady-state ice layers inside an asymmetrically cooled parallel-plate channel. The investigation shows the characteristics in ice formation behaviour due to asymmetrically cooled walls. Further, a simple analytical model is presented for calculating smooth ice layers in turbulent flow. The study is supported by own measurements of the freezing fronts inside an asymmetrically cooled channel. A comparison between theoretical calculations and measurements shows generally good agreement.
Open Access
Transient freezing of liquids in forced laminar flow inside a parallel plate channel
(1992) Weigand, Bernhard; Beer, Hans
A simple analytical approximative solution was given for calculating the time dependent development of the ice-layers at the cooled walls inside a parallel plate channel. By ignoring the effect of acceleration, resulting from converging ice-layers in the axial direction, an analytical solution for the variation of the ice-layer thickness with time and axial position could be obtained. The approximative solution was checked by numerical calculations and good agreement was found.
Open Access
Wärmeübertragung in einem axial rotierenden, durchströmten Rohr im Bereich des thermischen Einlaufs. T. 1, Einfluß der Rotation auf eine turbulente Strömung
(1989) Weigand, Bernhard; Beer, Hans
Der Einfluß der Rotation auf das Temperaturprofil und die Wärmeübergangszahl einer turbulenten Rohrströmung im Bereich des thermischen Einlaufs wird theoretisch untersucht und mit Meßwerten verglichen. Es wird angenommen, daß das Geschwindigkeitsprofil voll ausgebildet ist. Die Rotation hat aufgrund der radial ansteigenden Zentrifugalkräfte einen ausgeprägten Einfluß auf die Unterdrückung der turbulenten Bewegung. Dadurch verschlechtert sich die Wärmeübertragung mit steigender Rotations-Reynoldszahl und die thermische Einlauflänge nimmt beträchtlich zu.
Open Access
Wärmeübertragung in einem axial rotierenden, durchströmten Rohr im Bereich des thermischen Einlaufs. T. 2, Einfluß der Rotation auf eine laminare Strömung
(1989) Weigand, Bernhard; Beer, Hans
Der Einfluß der Rotation auf das Temperaturprofil und die Wärmeübergangszahl einer laminaren Rohrströmung im Bereich des thermischen Einlaufs wird theoretisch untersucht. Es wird angenommen, daß das Geschwindigkeitsprofil voll ausgebildet ist. Die Rotation hat einen destabilisierenden Einfluß auf die Laminarströmung, die umschlägt und turbulent wird. Aufgrund der Anfachung der Turbulenz durch die Rotation verbessert sich die Wärmeübertragung mit steigender Rotations-Reynoldszahl und die thermische Einlauflänge nimmt beträchtlich ab.