A Comprehensive Examination of Combustion of Magnesium-Water Mixtures

Analysis of effective thermal conductivity and tortuosity modeling in membrane distillation simulation

BackgroundPennes Bio Heat Transfer Equation (PBHTE) has been widely used to approximate the overall temperature distribution in tissue using a perfusion parameter term in the equation during hyperthermia treatment. In the similar modeling, effective thermal conductivity (Keff) model uses thermal conductivity as a parameter to predict temperatures. However the equations do not describe the thermal contribution of blood vessels. A countercurrent vascular network model which represents a more fundamental approach to modeling temperatures in tissue than do the generally used approximate equations such as the Pennes BHTE or effective thermal conductivity equations was presented in 1996. This type of model is capable of calculating the blood temperature in vessels and describing a vasculature in the tissue regions.MethodsIn this paper, a countercurrent blood vessel network (CBVN) model for calculating tissue temperatures has been developed for studying hyperthermia cancer treatment. We use a systematic approach to reveal the impact of a vasculature of blood vessels against a single vessel which most studies have presented. A vasculature illustrates branching vessels at the periphery of the tumor volume. The general trends present in this vascular model are similar to those shown for physiological systems in Green and Whitmore. The 3-D temperature distributions are obtained by solving the conduction equation in the tissue and the convective energy equation with specified Nusselt number in the vessels.ResultsThis paper investigates effects of size of blood vessels in the CBVN model on total absorbed power in the treated region and blood flow rates (or perfusion rate) in the CBVN on temperature distributions during hyperthermia cancer treatment. Also, the same optimized power distribution during hyperthermia treatment is used to illustrate the differences between PBHTE and CBVN models. Keff (effective thermal conductivity model) delivers the same difference as compared to the CBVN model. The optimization used here is adjusting power based on the local temperature in the treated region in an attempt to reach the ideal therapeutic temperature of 43°C. The scheme can be used (or adapted) in a non-invasive power supply application such as high-intensity focused ultrasound (HIFU). Results show that, for low perfusion rates in CBVN model vessels, impacts on tissue temperature becomes insignificant. Uniform temperature in the treated region is obtained.ConclusionTherefore, any method that could decrease or prevent blood flow rates into the tumorous region is recommended as a pre-process to hyperthermia cancer treatment. Second, the size of vessels in vasculatures does not significantly affect on total power consumption during hyperthermia therapy when the total blood flow rate is constant. It is about 0.8% decreasing in total optimized absorbed power in the heated region as γ (the ratio of diameters of successive vessel generations) increases from 0.6 to 0.7, or from 0.7 to 0.8, or from 0.8 to 0.9. Last, in hyperthermia treatments, when the heated region consists of thermally significant vessels, much of absorbed power is required to heat the region and (provided that finer spatial power deposition exists) to heat vessels which could lead to higher blood temperatures than tissue temperatures when modeled them using PBHTE.

New effective thermal conductivity model for the analysis of whole thermal storage tank

Application of the thermal pyrolysis model to predict flame spread over continuous and discrete fire load

Two-dimensional finite element thermal simulations of large rail casks designed to transport spent nuclear fuel assemblies were performed for normal conditions. Two different effective thermal conductivity models, developed by other investigators, were implemented within the basket openings that support the fuel assemblies. The effective thermal conductivity models affect the peak cladding temperature directly by influencing the temperature difference between the hottest cladding at the cask center and the walls that surround it. It also affects it indirectly by influencing the center basket wall temperature. The fuel assembly heat generation rates that cause the peak cladding temperature to reach the allowed limit were determined for both effective thermal conductivity models. At those generation rates the basket wall temperatures in the periphery of the package were highly nonuniform. The basket wall temperatures determined in this work will be used in future studies to develop improved thermal models of fuel assemblies.

New effective thermal conductivity model for the analysis of unconstrained melting in an entire thermal storage tank

Combustion of micron-sized aluminum particle, liquid water, and hydrogen peroxide mixtures

An effective thermal conductivity model of geological porous media for coupled thermo-hydro-mechanical systems with multiphase flow

The article is devoted to the study of the patterns of combustion of lean methaneair mixtures in marine internal combustion engine. Literature review shows that the implementation of combustion technology for a homogeneous lean methaneair mixture will increase the compression ratio, reduce fuel consumption and improve the environmental engine performance. However due to an increase in misfires and a decrease in the speed of flame propagation, the combustion of lean methaneair mixtures remains an unresolved problem. The article studies the influence of the excess air coefficient (from 1 to 1.4) on the turbulent combustion regime (assessed by the Karlowitz and Damkoehler criteria), the completeness and rate of fuel combustion. It was revealed that depletion of the air fuel mixture under conditions of intense turbulence leads to an increase in the Karlowitz criterion and a decrease in the Damköhler criterion. This indicates that the rate of chemical reactions in the flame front decreases, as a result of which the combustion process is characterized by stretching and rupture of the flame front. Therefore, to intensify the combustion of lean methaneair mixtures, it is advisable to increase the average speed of the vortex flow, and not the intensity of turbulence. A study of the influence of the excess air coefficient on the completeness and rate of fuel combustion showed that depletion of the mixture leads to a decrease in the completeness of fuel combustion from 93.5 % (at α=1) to 83 % (at α=1.4). The combustion rates also decrease and their maximum values shift from 13° (at α=1) to 24° (at α=1.4) degrees after top dead center. Therefore for efficient engine operation on lean mixtures, it is necessary to increase the fuel combustion rate through additional swirling of the gasair mixture or the use of combustion promoters.

A general effective thermal conductivity model for composites reinforced by non-contact spherical particles

The context of this work is the enhancement of the thermal conductivity of polymer by adding conductive particles. It will be shown how we can use effective thermal conductivity models to investigate effect of various factors such as the volume fraction of filler, matrix thermal conductivity, thermal contact resistance, and inner diameter for hollow particles. Analytical models for lower bounds and finite element models will be discussed. It is shown that one can get some insights from effective thermal conductivity models for the tailoring of conductive composite, therefore reducing the amount of experimental work.

Monodisperse monocomponent fuel droplet heating and evaporation

This study aimed to estimate the performance of a storage cooling system for roving personal air conditioning where a phase change material (PCM) was used as a condenser. The modeling on direct expansion air conditioning requires two-phase analysis. We applied 1-D two phase flow method for refrigerant inside tubes and effective thermal conductivity model outside tubes for PCM. Results were compared with those of a previous experience model which assumed a fixed ratio of super-heating region (10%), two-phase region (80%), and sub-cooling region (10%). The desired system discharge power was 600 Wh. Results showed that the previous experience method had an over-estimated performance due to the assumption of constant temperature applied over whole tube length while the current model coupled with 1-D two phase model and effective thermal conductivity model could cover the detailed heat transfer involved in the roving personal air-conditioning including developing a two-phase region.

Thermal management of water-based carbon nanotubes enclosed in a partially heated triangular cavity with heated cylindrical obstacle

Multiphase Flow Dynamics, Volume 1: Fundamentals; Volume 2: Thermal and Mechanical Interactions