Modeling Coupled Conduction–Convection Ice Formation on Horizontal Axially Finned and Unfinned Tubes

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Hassan M. S. Al-Sarrach ◽  
Ghalib Y. Kahwaji ◽  
Mohamed A. Samaha
Keyword(s):  
Natural Convection ◽  
Liquid Interface ◽  
Ice Formation ◽  
Finite Difference Schemes ◽  
Freezing Process ◽  
Liquid Region ◽  
Water Density ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
The Impact

The freezing of water around immersed unfinned and finned horizontal tubes is simulated numerically. The impact of natural convection as well as the water density inversion with temperature is considered. The equations governing both fluid flow and heat transfer around the tubes and through the solid–liquid interface are solved using finite difference schemes. To follow the moving solid–liquid boundary, dynamic grid generation is performed using the elliptic partial differential equation method with iterative interpolating smoothing to avoid divergence. For validation, the present results for unfinned tubes are compared with experimental studies reported in the literature. The present numerical simulations are aimed at improving our understanding of the parameters affecting the freezing process around both finned and unfinned tubes. The results showed that the flow patterns are similar in both tube configurations with one main vortex in the liquid region when there is no inversion in the water density. The presence of fins complicates the distribution of local Nusselt number along the solid–liquid interface in comparison with the unfinned tube. The impact of natural convection on the rate of ice formation is limited to the initial period of the freezing process. The results also show the freezing enhancement when utilizing fins. An accumulated ice mass correlation is developed for each tube configuration. This model can be used to optimize the design of both finned and unfinned tubes in energy storage systems, which are viable tools for air conditioning load shifting and leveling.

Microstructural Perturbations in Directionally Solidified Al-In, Al-Bi and Zn-Bi Monotectic Alloys

1981 ◽  
Vol 12 ◽  
Author(s):  
B. Toloui ◽  
A. J. Macleod ◽  
D. D. Double
Keyword(s):  
Melting Point ◽  
Temperature Gradient ◽  
Growth Velocity ◽  
Liquid Interface ◽  
Liquid Region ◽  
Directionally Solidified ◽  
Lower Melting Point ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Oscillatory Instabilities

ABSTRACTStudies have been made of the microstructures developed in directionally solidified monotectic Al-In, Al-Bi and Zn-Bi alloys, as a function of growth velocity and temperature gradient. With increasing growth velocity and decreasing gradient the microstructures show transitions from regular rod-like arrangements of the lower melting point phase, through arrays of aligned droplets to coarse irregular droplet dispersions. Intermediate stages show rods with longitudinal shape perturbations of a classic Rayleigh-type instability. The changes are discussed in terms of oscillatory instabilities at the solid-liquid interface (enhanced by increasing growth velocity and decreasing temperature gradient) coupled with ripening effects in the solid + liquid region behind the interface.

Study on the Natural Convection and Formation of Periodic Diphase Dendrite in Al-La Alloys

2010 ◽  
Vol 129-131 ◽  
pp. 1308-1312
Author(s):  
Ya Hong Zheng ◽  
Yan Lin Wang ◽  
Zi Dong Wang
Keyword(s):  
Crystal Growth ◽  
Natural Convection ◽  
Concentration Distribution ◽  
Concentration Field ◽  
Growth Direction ◽  
Liquid Interface ◽  
Dendrite Morphology ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Interface Edge

In the crystal growth process, the temperature distribution and concentration distribution at the solid-liquid interface edge are always the hot problems. In this paper, we study the concentration distribution at the solid-liquid interface edge under the natural convection conditions, we find that the concentration field is oscillating exponential decline or rose along the crystal growth direction. We also study the dendrite morphology of Al-La alloys using the experimental method, the results show that the microstructure of Al-35%La alloys is different from the common microstructure of hypereutectic alloy during the conventional casting process, the first crystalline phase is Al11La3, which composition is discontinuous along the growth direction, the main dendrite is composed of α-Al alternating with Al11La3, the results of SEM and XRD show that the chemical composition along the main dendrite exhibits periodic behavior, therefore, this microstructure is named as periodic diphase dendrite structure.

Natural Convection Influenced Ice-Water Systems Contained Between Concentric Spheres

2001 ◽  
Author(s):  
D. A. Sinton ◽  
B. R. Baliga
Keyword(s):  
Natural Convection ◽  
Liquid Phase ◽  
Computational Study ◽  
Water Systems ◽  
Liquid Interface ◽  
Two Dimensional ◽  
Concentric Spheres ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Ice Water

Abstract A computational study of natural convection influenced ice-water systems contained in the annular space between two concentric isothermal spheres is presented. An adaptive-grid control-volume finite element method (CVFEM) formulated for the solution of two-dimensional planar and axisymmetric problems was used in the computer simulations. The grid was designed to delineate the solid-liquid interface using a structured adaptation technique. In this study, attention is limited to three different two-dimensional axisymmetric, steady state, pure ice-water systems, with buoyancy-driven natural convection in the liquid phase: two of these systems involve ice adjacent to the inner sphere, and one system involves ice adjacent to the outer sphere. The dimensionless parameters are the following: a modified Rayleigh number, a density inversion parameter, the Prandtl number, radius ratio, and a temperature ratio. The results presented include solid-liquid interface shapes, streamlines and temperature contours in the liquid phase, and dimensionless local heat flux distributions along the surfaces of the inner and outer spheres, and the interface.

scholarly journals The impact of grafted surface defects on the on-surface Schiff-base chemistry at the solid–liquid interface

2018 ◽  
Vol 54 (71) ◽  
pp. 9905-9908 ◽  
Author(s):  
Nerea Bilbao ◽  
Yanxia Yu ◽  
Lander Verstraete ◽  
Jianbin Lin ◽  
Shengbin Lei ◽  
...  
Keyword(s):  
Schiff Base ◽  
Surface Defects ◽  
Single Layer ◽  
Liquid Interface ◽  
Covalent Organic Frameworks ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
The Impact

We investigate the effect of covalently modified graphitic surfaces on the formation of single-layer covalent organic frameworks (sCOFs) at the solid–liquid interface.

scholarly journals Effect Of Natural Convection On Directional Solidification Of Pure Metal

2015 ◽  
Vol 60 (2) ◽  
pp. 835-841 ◽  
Author(s):  
T. Skrzypczak ◽  
E. Węgrzyn-Skrzypczak ◽  
J. Winczek
Keyword(s):  
Natural Convection ◽  
Directional Solidification ◽  
Stokes Equation ◽  
Pure Copper ◽  
Pure Metal ◽  
Liquid Interface ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Solid Liquid Interface ◽  
Solid Liquid

AbstractThe paper is focused on the modeling of the directional solidification process of pure metal. During the process the solidification front is sharp in the shape of the surface separating liquid from solid in three dimensional space or a curve in 2D. The position and shape of the solid-liquid interface change according to time. The local velocity of the interface depends on the values of heat fluxes on the solid and liquid sides. Sharp interface solidification belongs to the phase transition problems which occur due to temperature changes, pressure, etc. Transition from one state to another is discontinuous from the mathematical point of view. Such process can be identified during water freezing, evaporation, melting and solidification of metals and alloys, etc.The influence of natural convection on the temperature distribution and the solid-liquid interface motion during solidification of pure copper is studied. The mathematical model of the process is based on the differential equations of heat transfer with convection, Navier-Stokes equation and the motion of the interface. This system of equations is supplemented by the appropriate initial and boundary conditions. In addition the continuity conditions at the solidification interface must be properly formulated. The solution involves the determination of the temporary temperature and velocity fields and the position of the interface. Typically, it is impossible to obtain the exact solution of such problem. The numerical model of solidification of pure copper in a closed cavity is presented, the influence of the natural convection on the phase change is investigated. Mathematical formulation of the problem is based on the Stefan problem with moving internal boundaries. The equations are spatially discretized with the use of fixed grid by means of the Finite Element Method (FEM). Front advancing technique uses the Level Set Method (LSM). Chorin’s projection method is used to solve Navier-Stokes equation. Such approach makes possible to uncouple velocities and pressure. The Petrov-Galerkin formulation is employed to stabilize numerical solutions of the equations. The results of numerical simulations in the 2D region are discussed and compared to the results obtained from the simulation where movement of the liquid phase was neglected.

Interface Shape and Melt Flow Near the Solid-Liquid Interface During Horizontal Unidirectional Solidification

2003 ◽  
Author(s):  
T. M. Guo ◽  
H. Li ◽  
M. J. Braun ◽  
G.-X. Wang
Keyword(s):  
Natural Convection ◽  
Flow Velocity ◽  
Video Camera ◽  
Unidirectional Solidification ◽  
Liquid Interface ◽  
Melt Flow ◽  
Long Distance ◽  
Heating And Cooling ◽  
Solid Liquid Interface ◽  
Solid Liquid

Generally, unindirectional solidification experiments of transparent alloys are conducted using thin film samples sandwiched between two glass slides with a small channel height[1]. In such systems, natural convection and melt flow can be assumed negligible and the solification process is diffusive in nature [2,3]; these physical realities allow fundamental simplifications in theoretical/numerical modeling, without losing physical significance. However, natural convection and melt flow do exist in all actual solidification processes and have a significant effect on interface morphology and microstructure formation and development. Recognizing the latter, a great deal of effort went in recent years towards the investigation of the effect of melt flow on interface dynamics and morphology [3–5]. The objective of this paper is to study the natural convection and melt flow near the solid-liquid interface during horizontal unidirectional solidification. In particular, the authors are interested in the melt flow and solid-liquid interface under various channel heights (H) and temperature differences across the hot and cold ends (ΔT) of the samples. A horizontal unindirectional solidification experimental system was constructed. The samples used here are rectangular ampoules made of borosilicate glass that is 3.2 mm thick (on bottom and top sides) and 2.3 mm thick (on the vertical sides). The channel formed in the sample is 75 mm long and 50 mm wide. Three ampoules with channel heights of 1, 3.2 and 5 mm, respectively, are used in these experiments. The ampoules are filled with succinonitrile (99% pure) seeded with polyamide tracer particles (5 μm in diameter, density ρ=1030 kg/m3); the latter are used to resolve and visualize the fluid velocity in the melt. Surface temperatures of the sample on the hot end and cold end are measured with J-type thermocouples. The unidirectional solifification setup is mounted on a microscope stage so that the interface can be observed from the top with the regular microscope. A long distance microscope (LDM) affixed either to a photo- or video- camera is used to observe the vertical shape of the interface, as well as to qualitatively and quantitatively assess the flow. During experiments, the sample is allowed to reach both thermally and flow-wise a steady state situation. The heating and cooling systems are adjusted to make the solid-liquid interface stay at the center of the gap between the heating and cooling chambers for case of observation. The density of polymide particle being close to that of succinonitrile melt allows an almost neutrally buoyant behavior of the tracing particles and thus minimizes the error in flow velocity calculations as well as enhances confidence in the observed qualitative flow patterns. With the help of proprietary computer software, the flow velocity is obtained by evaluating the difference in successive two images of the same particle at time intervals consistent with the sampling speed of video-camera (0.033 sec).

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