Numerical Simulation of the Thermal Fields Occurring in the Treatment of Malignant Tumors by Local Hyperthermia

1993 ◽  
Vol 115 (3) ◽  
pp. 247-253 ◽  
Author(s):  
K. T. O’Brien ◽  
A. M. Mekkaoui
Keyword(s):  
Heat Transfer ◽  
Transient Flow ◽  
Malignant Tumors ◽  
Blood Perfusion ◽  
Temperature Fields ◽  
Conductive Heat ◽  
Transient Heating ◽  
Local Hyperthermia ◽  
Thermal Fields ◽  
Dual Beam

Dual beam microwave heating is known to deposit heat at depth in a medium. Thus transient heating times may be reduced and more even heating may be obtained. Such a system has potential in the treatment of cancer by hyperthermia. A theoretical analysis of this situation is presented here. A simulation has been made of the thermal fields generated in the treatment of malignant tumors using local hyperthermia. The simulation utilizes the alternating direction implicit method which is particularly suited to the solution of the governing equations, and provides rapid convergence in multiple dimensions. The simulation is three dimensional in temperature, with variations occurring through two spatial coordinates and one time coordinate. The simulation can accommodate the transient flow of heat due to conductive heat transfer through tissues such as healthy tissue, malignant tumors, cartilage and bone, convective heat transfer through perfusion in the tissue and flow through the arteries, and heat generation from sources such as microwave beams. Small changes in the thermophysical properties of the tissue, and the blood perfusion rates are shown to exhibit only minor effects on the thermal fields, whereas the power of the heat sources, and the conductive flux are shown to have major effects on the thermal fields. The effects of adjacent physiological structures such as arteries and bones have also been determined. The temperature fields have been found to be weakly dependent on the increased perfusion rates encountered in the arteries except when the perfusion rate in the artery exceeds that in the tissue by at least one order of magnitude. A similar effect is noticed if the tumor is close to a bone. The greater thermal insulation exhibited by the bone restricts the flow of heat into it, and therefore causes the tissue to increase in temperature. Once the transient heating has been employed and the heating proceeds under steady-state conditions, the dual beam microwave applicator must be controlled to avoid overheating. The effect of on/off control and proportional + integral + derivative control is discussed.

scholarly journals Modelling and numerical simulation of the heat transfer and natural ventilation in storage halls

2020 ◽  
Vol 207 ◽  
pp. 01005
Author(s):  
Nina Penkova ◽  
Kalin Krumov ◽  
Boian Mladenov ◽  
Yordan Stoyanov
Keyword(s):  
Heat Transfer ◽  
Natural Ventilation ◽  
Temperature Fields ◽  
Design Stage ◽  
Temperate Climate ◽  
Heat Sources ◽  
Thermal Fields ◽  
Wind Pressures ◽  
Volume Method ◽  
Velocity Pressure

An algorithm for modelling of the heat transfer in storage halls at different combinations of open doors and smoke vents is developed. The models allow numerical simulations of velocity, pressure and temperature fields in the halls in cases of transient and steady state conditions, taking into account the indoor buoyancy, heat sources, heat transfer through the building envelopes and outdoor wind pressures. The models are solved numerically via finite volume method in order to estimate the necessity of additional heating at a design stage of a courier logistic storage hall, situated in the temperate climate zone, at the hardest winter conditions of the region. Recommendations about the organization of the heating and the cargo input are done based on the analyses of the fluid flow and thermal fields at the modelled scenarios.

A Computational Model for Heat Transfer in Multichannel Microreactors

2005 ◽  
Author(s):  
S. Hardt ◽  
To Baier
Keyword(s):  
Heat Transfer ◽  
Field Model ◽  
Solid Phase ◽  
Mean Field ◽  
System Optimization ◽  
Temperature Fields ◽  
Conductive Heat ◽  
Mean Field Model ◽  
Detailed Model ◽  
The Mean

A reduced-order model is developed allowing for a fast computation of the temperature field in multichannel microreactors. The model regards the fluid and the solid phase as interpenetrating continua and incorporates heat exchange between the two phases via a heat-transfer coefficient characteristic for the channel geometry under study. The geometry of the channel walls determines the components of the thermal conductivity tensor which govern conductive heat transfer to the envelope of the reactor. The mean-field model is solved numerically for a test case inspired from practical applications. Parallel to that, a detailed model is set up with the purpose to benchmark the results of the mean-field model. This full model incorporates the geometric details of the multichannel reactor and contains consider-ably more degrees of freedom than the mean-field model, resulting in a much larger computational effort. It is found that the temperature fields computed with the two models agree reasonably well. Thus, the mean-field model appears as an efficient tool to evaluate the thermal performance of multichannel microreactors, especially in the context of parameter studies or system optimization.

Effet du maximum de densité sur la convection libre de l'eau dans une cavité fermée

1979 ◽  
Vol 6 (4) ◽  
pp. 481-493 ◽  
Author(s):  
L. Robillard ◽  
P. Vasseur
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Wall Temperature ◽  
Transient Flow ◽  
Coupled System ◽  
Flow Patterns ◽  
Maximum Density ◽  
Temperature Fields ◽  
Constant Wall Temperature ◽  
Square Enclosure

One of the most important factors affecting the rate of heat transfer by natural convection is the temperature–density relationship of the convecting fluid. The importance of this factor is greatly amplified when the heat is being transferred to a medium that has a maximum density at a given temperature. Water at low temperatures offers such a behavior, its density attaining a maximum value near 3.98 °C. thereafter decreasing with decreasing temperature. This phenomenon is responsible for unusual flow patterns in areas of water exposed to near freezing temperatures.This investigation is a theoretical analysis of the transient natural convection of water contained in a square enclosure with constant wall temperature. Initially the water is assumed to be at a uniform temperature above 0 °C, the wall temperature being suddenly applied.An alternating direction implicit finite-difference schema was used to solve the coupled system of partial differential equations. The transient flow and temperature fields, and local and overall heat transfer are greatly affected by the inversion of flow patterns caused by the maximum density. Their respective values for different flow situations are presented in this study.

Transient Hydrodynamic Phenomena and Conjugate Heat Transfer During Cooling of Water in an Underground Thermal Storage Tank

2004 ◽  
Vol 126 (1) ◽  
pp. 84-96 ◽  
Author(s):  
E. Papanicolaou ◽  
V. Belessiotis
Keyword(s):  
Heat Transfer ◽  
Storage Tank ◽  
Conjugate Heat Transfer ◽  
Transient Flow ◽  
Thermal Storage ◽  
Hot Water ◽  
Uniform Temperature ◽  
Thermal Fields ◽  
Flow And Heat Transfer ◽  
Insight Into

The flow and heat transfer phenomena inside an underground thermal storage tank, initially filled with hot water at an almost uniform temperature and then left to interact with the cold surroundings, are studied numerically. The purpose of the study is to gain insight into how these phenomena affect the heat losses to the surroundings, before a new charging process takes place. A two-dimensional numerical model to solve for the transient flow and thermal fields within the tank coupled with the heat transport through the tank walls and within the ground are employed. Natural convection is found to dominate at the early transients when a strong recirculation develops, with a Rayleigh number characteristic of turbulent flow. A low-Re k−ε turbulence model is used for the computation. As time proceeds and the temperature differences between water and surroundings decrease, the recirculation decays and the heat transfer is dominated by thermal diffusion. The ground properties are varied, mainly in order to account for different moisture contents in the ground. Comparisons are made under realistic conditions with preliminary experimental results showing satisfactory agreement.

Conjugate Heat Transfer Analysis Using the Discrete Green's Function

2020 ◽  
Author(s):  
Davis Hoffman ◽  
John Eaton
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Green’S Function ◽  
Green's Function ◽  
Conjugate Heat Transfer ◽  
Temperature Fields ◽  
Heat Transfer Analysis ◽  
Transient Heating ◽  
Discrete Green’S Function ◽  
Linear Algebraic Equations

Abstract Conjugate heat transfer problems generally require a coupled solution of the temperature fields in the fluid and solid domains. Implementing the boundary condition at the surface of the solid using a discrete Green's function (DGF) decouples the solutions. A DGF is determined first considering only the fluid domain with prescribed thermal boundary conditions, then the temperature distribution in the solid is calculated using standard numerical methods. The only compatibility requirement is that the DGF must be specified with the same discretization as the surface of the solid. The method is demonstrated for both steady-state and transient heating of a thin plate with laminar boundary layers flowing over both sides. The resulting set of linear algebraic equations for the steady-state problem or linear ordinary differential equations for the transient problem are easily solved using conventional scientific programming packages. The method converges with nearly second-order accuracy as the discretization resolution is increased.

scholarly journals Investigation of temperature fields in the air environment above wood subjected to thermal degradation

2019 ◽  
Vol 70 (4) ◽  
pp. 319-327
Author(s):  
Elena Pivarčiová ◽  
Štefan Barcík ◽  
Jaroslava Štefková ◽  
Emil Škultéty
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Coefficient ◽  
Quantitative Analysis ◽  
Thermal Boundary Layer ◽  
Thermal Loading ◽  
Beech Wood ◽  
Temperature Fields ◽  
Thermal Fields ◽  
The Heat Transfer Coefficient

The paper deals with the visualization of thermal fields above the sample body while observing thermal loading of wood. Via holographic interferometry, thermal fields were visualized in a non-contact manner and the values were recorded in 0, 3, 7 and 15 minutes or earlier in case of degradation. In real time, the ongoing processes were recorded in the thermal boundary layer above the surface of sample bodies in dimensions of 43 mm × 40 mm × 10 mm of beech wood in three different directions: longitudinal, radial, tangential cut. The temperatures of isothermal curves above the heated samples and coefficients of heat transfer α were determined by a quantitative analysis of holographic interferograms. The heat transfer coefficient α ranged within 4.6-7.4 W/m2K. The simulation of heat transfer for the selected samples was prepared by the Fluent programme. Consequently, the measured values from the experiments were compared with the calculated values. There is a correlation between the measured and calculated values.

CONVERGENCE OF A NUMERICAL SCHEME FOR A NONLINEAR COUPLED SYSTEM OF RADIATIVE-CONDUCTIVE HEAT TRANSFER EQUATIONS

2004 ◽  
Vol 14 (07) ◽  
pp. 943-974 ◽  
Author(s):  
FATMIR ASLLANAJ ◽  
GERARD JEANDEL ◽  
JEAN RODOLPHE ROCHE
Keyword(s):  
Heat Transfer ◽  
Numerical Scheme ◽  
Coupled System ◽  
Fixed Point Problem ◽  
Conductive Heat Transfer ◽  
Dirichlet Boundary Conditions ◽  
Temperature Fields ◽  
Point Problem ◽  
Conductive Heat ◽  
Nonlinear Coupled System

In this paper, we prove the convergence of a numerical scheme for one-dimensional coupled system of nonlinear partial and ordinary integro-differential equations. This system describes the steady-state coupled radiative-conductive heat transfer for a non-grey anisotropically absorbing, emitting and scattering medium, with axial symmetry and nonhomogeneous Dirichlet boundary conditions. The convergence proof follows from monotonicity arguments and the application of a discrete fixed-point problem, involving only to the temperature fields.

scholarly journals Influence of thermo-gravitational convection to temperature fields in small surroundings of the heat source

2018 ◽  
Vol 194 ◽  
pp. 01028
Author(s):  
Alexander Kondakov
Keyword(s):  
Mathematical Modeling ◽  
Heat Transfer ◽  
Temperature Field ◽  
Heat Source ◽  
Velocity Fields ◽  
Temperature Fields ◽  
Conductive Heat ◽  
Gravitational Convection ◽  
Temperature And Velocity Fields ◽  
The Impact

The mathematical modeling of temperature and velocity fields in the system “the heat source - environment - the object of heating” was conducted. The impact assessment of thermo-gravitational convection to the temperature field in comparison with the model of conductive heat transfer was done.

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