Line Heat Sink Research Articles

Thermal recovery test for determining the thermal conductivity of the soil

This paper presents a new in-situ experimental procedure for determining a thermal conductivity of soil, as one of the thermophysical properties necessary for dimensioning vertical buried heat exchangers of geothermal heat pumps. The proposed method, called the thermal recovery test, is based on the assumption that there is a direct analogy between the hydrodynamic process of filling (recovery) the well with water from a porous aquifer after its partial or complete discharging and the process of establishment of thermal equilibrium in an infinite medium previously disturbed by a line heat sink (source). Apart from presentation the theoretical background of these two phenomena, the display of the identical theoretical logarithmic character of the change of hydrostatic pressure and soil temperature, description of the experimental procedure, the experimental results of three performed experiments are also presented. Additionally, results for the experimentally obtained values of the thermal conductivity of the soil are compared with those obtained from the thermal response test, and the advantages and drawbacks of the new thermal recovery test method are analyzed.

Heat transfer analysis describing freezing of a eutectic system by a line heat sink with convection effect in cylindrical geometry

Abstract The current article devoted to study a moving boundary problem describing freezing of a eutectic system in a semi-infinite medium in cylindrical symmetry. The solidification of the material is considered by a line heat sink of strength Q place at r = 0. The heat transfer is considered due to both mechanism, conduction and convection driven by fluid motion in the liquid region, mushy region and possibly in porous solid phase. The analysis is concerned with extended freezing temperature range between solidus and liquidus temperatures respectively. The solid fraction is considered to have a linear relationship with temperature within the mushy zone. A direct integration method is used to solve the mathematical model, resulting an exact solution of the problem is obtained. To illustrate the application of current study and validity of mathematical model, a numerical example of freezing of an Al–Cu alloy with 5% Cu is presented. In addition, the temperature distribution in each region and position of moving interfaces is shown for different Peclet number. In this work, we obtained that the process of freezing becomes fast in the presence of convection. Moreover, it is shown that for a large value of Q, strength of line heat sink, the freezing of a eutectic alloy increases rapidly. Both eutectic and solid solution alloys come under the application of current study.

Transient marangoni-buoyancy convection in rectangular tank with phase change

Transient Marangoni-buoyancy convection in an insulated rectangular tank is studied numerically using the finite volume method. The liquid is suddenly heated by a line heat source or cooled by a line heat sink being placed at the center of the free surface to initiate a thermocapillary force. Evaporation or condensation takes place on the free surface. In a low Marangoni number evaporative system, three distinct convective mechanisms are identified: surface tension-driven, buoyancy-driven and mixed convections. The effects of aspect ratio and evaporation number on flow instability and heat transfer are investigated.

Freeze Coating of a Cylindrical Object with a Binary Alloy

An analytic solution of the freeze coating of a cylindrical object with a binary alloy is obtained by modeling the object as a line heat sink. In the freeze coating with a binary alloy, there exist s an extended region where phase change occurs instead of a sharp phase interface in the freeze coating of a pure substance. In this region, which is called mushy region, the solid and the liquid phases coexist in a geometrically complicated manner. Therefore a mushy model, which can properly treat the mushy region, is adopted in the present analysis. And the effect of convection in the liquid region is also considered. The system of governing equations and boundary conditions, derived from conservation law, is analyzed through similarity transformation and numerical integration. The effect of various processing parameters on the growth rate of the freeze coating is presented.

Freeze coating of a cylindrical object with a binary alloy

An analytic solution for freeze coating a cylindrical object with a binary alloy was obtained by modeling the object as a cylindrical line heat sink. The system of governing equations and boundary conditions was solved through similarity transformation and numerical integration. The analysis includes the effects of convection in the liquid region and property variations in the mushy region. The effects of various processing parameters on the two coating thicknesses (the solid-mushy and the mushy-liquid phase interfaces) are investigated.

Freeze coating of a cylindrical object with a binary alloy

An analytic solution for freeze coating a cylindrical object with a binary alloy was obtained by modeling the object as a cylindrical line heat sink. The system of governing equations and boundary conditions was solved through similarity transformation and numerical integration. The analysis includes the effects of convection in the liquid region and property variations in the mushy region. The effects of various processing parameters on the two coating thicknesses (the solid-mushy and the mushy-liquid phase interfaces) are investigated. © 1999 Scripta Technica, Heat Trans Asian Res, 28(4): 239–254, 1999

Freeze coating of a cylindrical object with a binary alloy

An analytic solution for freeze coating a cylindrical object with a binary alloy was obtained by modeling the object as a cylindrical line heat sink. The system of governing equations and boundary conditions was solved through similarity transformation and numerical integration. The analysis includes the effects of convection in the liquid region and property variations in the mushy region. The effects of various processing parameters on the two coating thicknesses (the solid-mushy and the mushy-liquid phase interfaces) are investigated. © 1999 Scripta Technica, Heat Trans Asian Res, 28(4): 239–254, 1999

Shape of an evaporating completely wetting extended meniscus

The microscopic details of fluid flow and heat transfer in the contact line region of an evaporating curved liquid film were experimentally and theoretically evaluated. The evaporating film thickness profiles were measured optically using null ellipsometry and image analyzing interferometry. These thickness profiles were analyzed using the augmented Young-Laplace equation to obtain the pressure field. Using the liquid pressure field, the evaporative mass flux profile was obtained from a Kelvin -Clapeyron model for the local vapor pressure. A correlation for the local slope (apparent contact angle) at a film thickness of 6 = 20 nm as a function of a dimensionless contact line heat sink was thereby obtained for a group of completely wetting fluids. This change in local slope leads to a decrease in the maximum value of the possible capillary suction at the base of the meniscus. A complementary macroscopic interfacial force balance was also used to describe the effects of viscous losses and interfacial forces on the local values of the apparent contact angle and curvature that are functions of the film thickness and heat flux. These two perspectives give a complete description of an evaporating, nonpolar, completely wetting curved film in the contact line region.

A Dimensionless Number for the Contact Line Evaporative Heat Sink

The main driving force for flow in very thin films can be the gradient in the van der Waals force. This phenomenon was used by Wayner et al. (1976) to develop an equation for the interline heat transfer coefficient of an evaporating wetting film. Buried in this development is a dimensionless group that can enhance, when properly viewed, the understanding of the evaporation process in the contact line region where the film thickness becomes vanishingly thin. This process is crucial in systems that rely on heat transfer in ultrathin films such as evaporating drops on solid surfaces and evaporating menisci in heat pipes. Herein, the authors discuss the significance and use of this dimensionless contact line heat sink number.

SOLIDIFICATION OF A BINARY ALLOY FROM A COLD WIRE OR PIPE: MODELING OF THE MIXED-PHASE REGION

This paper presents a theoretical study of the heat and mass transfer phenomena occurring during the solidification of a binary alloy from a thin cold wire or pipe modeled as a line heat sink. The study accounts for the existence of a mixed-phase region (mushy zone) separating the solid from the liquid regions. The mushy zone consists of a complex mixture of liquid and dendrites, whose composition depends on both position and time and cannot be prescribed a priori. The growth rate of the mushy zone (which has a paramount effect on the structure of the resulting solid) depends on the heat and mass transport processes that govern the solidification phenomenon. The results of this study illuminate the dependence of the temperature, concentration, and liquid fraction distributions in the mushy zone on several dimensionless groups of the problem. The study also found that the growth rate or even the very existence of the mixed-phase region is controlled by the values of these dimensionless groups.

GROWTH OF A SOLID FROM A LINE HEAT SINK IN A BINARY ALLOY

This paper presents a numerical study on the growth of a solid from a line heat sink immersed in a binary alloy. The numerical model takes into account macroscopically the existence of a mushy zone separating the solid region from the liquid region. This zone consists of a mixture of liquid and dendrites. Interesting results shed light on the dependence of the thickness and the temperature of the mushy zone on several important dimensionless groups representing the physical parameters of the problem. It is found that the effect of some of these groups on the solidification process is significant and difficult to predict a priori. The mushy zone disappears when the values of the problem parameters are outside certain ranges.

Growth of a Solid from a Line Heat Sink in a Binary Alloy

Growth of a Solid from a Line Heat Sink in a Binary Alloy

Exact Solution for Freezing in Cylindrical Symmetry with Extended Freezing Temperature Range

The problem of solidification by a line heat sink in an infinite medium with cylindrical symmetry for a substance having an extended freezing temperature range between the solidus and liquidus temperatures is solved exactly for two different cases characterizing the distribution of the solid fraction within the two-phase zone. In one of the models, the solid fraction is assumed to vary linearly with the temperature and in the other solidification within the two-phase zone is assumed to have a linear relationship with the distance. The analysis is applicable for both eutectic and solid solution alloys.

Erratum: “Frozen Region Formed around a Line Heat Sink under a Uniform Stream of an Incompressible Fluid”

Erratum: “Frozen Region Formed around a Line Heat Sink under a Uniform Stream of an Incompressible Fluid”

Frozen Region Formed around a Line Heat Sink under a Uniform Stream of an Incompressible Fluid

In the present paper is studied a frozen region formed around a line heat sink under a uniform stream of an incompressible fluid. The diameter and the geometrical shape of the frozen region are obtained in terms of strength of the heat sink and the uniform velocity at infinity in the ultimate steady state that the system will reach. The results are compared with the experimental values given by Takashi in his practical investigation of the soil-freezing method in engineering construction.