NUMERICAL ANALYSIS OF DEVELOPING TURBULENT FLOW IN A CLOSED COMPOUND CHANNEL

The study of turbulence characteristics in compound channels is still focus of attention. A lot of experimental results have been produced. Main results have revealed a mixing layer formation between main subchannel and the gap region, implying the flow might be ruled by local scales. The outcomes have pointed to the instabilities of mixing layer are responsible for large structures formation between main channel and narrow gap. Furthermore, the periodical behavior of these structures seems to be ruled by mean mixing layer characteristics, as velocity difference, velocity of convection and mixing layer thickness. By using ANSYS-CFX-12, with unsteady Reynolds Average Navier-Stokes and as turbulence model Spalart-Allmaras (SA), a compound channel was studied. Numerical results predicted velocity profile with high vorticity peaks and flow instabilities starting at L/Dh = 15

NUMERICAL INVESTIGATION OF HEAT TRANSFER IN A TURBULENT FLOW IN CHANNELS WITH GAP

Turbulent flow in channels with gap is still a challenge for engineering. The velocity fluctuations and the appearance of coherent structures have been playing a major role in forced convective heat transfer process between the warm tube walls and the cooling fluid. In this paper numerical simulation of non-isothermal turbulent flow in a rectangular channel containing only one tube was performed. Unsteady Reynolds Navier-Stokes along with the energy equation were applied to model the problem. In order to overcome the closure problem the turbulence was modeled applying SAS model. The simulated geometry consists of a heated cylindrical tube, placed 10 mm from the bottom wall of the rectangular duct. The fluid flows externally to the heated tube along the mainstream direction. The channel’s length was based on the tube diameter, yielding L/D equal 80

USING BEM TO PREDICT THE EFFECTIVE THERMAL CONDUCTIVITY FOR HETEROGENEOUS MATERIALS

This work presents a study on the effective thermal conductivity in material with heterogeneous composition in two dimensions. The Boundary Elements Method (BEM) is used to solve the steady state potential equations. The sub regions technique was implemented in order to take into account the effects of these inclusions inside the domain. In the numerical implementation, the inclusions are randomly generated in a Representative Volume Element (RVE) domain. The Average Field Theory is used to predict the effective properties (macroscopic) of the material with heterogeneous composition. The material is characterized by a specified volume fraction as well as the inclusion’s size. The samples are composed of square domains with defined number of randomly distributed inclusions and submitted to a condition of unidirectional heat conduction. Each set of samples is analyzed several times in order to guarantee statistical stability of the result

Scalar Quantum Field Theory in Disordered Media

A free massive scalar field in inhomogeneous random media is investigated. The coefficients of the Klein-Gordon equation are taken to be random functions of the spatial coordinates. The case of an annealed-like disordered medium, modeled by centered stationary and Gaussian processes, is analyzed. After performing the averages over the random functions, we obtain the two-point causal Green's function of the model up to one-loop. The disordered scalar quantum field theory becomes qualitatively similar to a $\lambda\phi^{4}$ self-interacting theory with a frequency-dependent coupling

Formal analogies between gravitation and electrodynamics

We develop a theoretical framework that allows us to compare electromagnetism and gravitation in a fully covariant way. This new scenario does not rely on any kind of approximation nor associate objects with different operational meaning as it's sometime done in the literature. We construct the electromagnetic analogue to the Riemann and Weyl tensors and develop the equations of motion for these objects. In particular, we are able to identify precisely how and in what conditions gravity can be mapped to electrodynamics. As a consequence, many of the gemometrical tools of General Relativity can be applied to Electromagnetism and vice-versa. We hope our results would shed new light in the nature of electromagnetic and gravitational theories.Comment: 9pages, submitted to General Relativity and Gravitatio

CONSTRUCTAL DESIGN APPLIED TO A FINNED CHANNEL UNDER FORCED CONVECTION FLOWS WITH DIFFERENT IMPOSED PRESSURE DROPS

This paper aims to numerically study the heat transfer in a two dimensional finned channel under laminar, incompressible and forced convective flow with adiabatic walls. The main purpose is to maximize the convection heat transfer by changing the fin’s dimensions by means of Constructal Design. Numerical computations are performed for different Bejan numbers ranging from 0.182 up to 18.2. For all simulations the Prandlt number is kept constant, Pr = 0.71. The fluid motion throughout the channel is caused by imposition of pressure difference between inlet/outlet surfaces. Concerning heat transfer, it is caused by the difference of temperature between the inlet stream of fluid and the heated fins placed at the channel surfaces. The first fin is positioned in the lower surface of the channel while the second one is placed in the upper one. The problem is submitted to three constraints, the channel area (H × L), area of two fins and occupancy areas for the fins. It is considered here that both fins have the same fraction area (ratio between the fins and occupancy areas) f = 0.2. The problem is submitted to three degrees of freedom: H/L (ratio between height and length of channel), H3/L3 and H4/L4 which represent the ratio between the height and length of the first and second fin, respectively. Here, the second fin remains unchanged, being its dimensions H4/L4 = 2.0, whereas the first one is free to modify its dimensions, H3/L3. The channel dimensions are also constant. The solutions are sought using the conservation equations of mass, momentum and energy being these ones discretized through the Finite Volume Method (FVM). Results showed the importance of Constructal Design application for thermal improvement of the problem. Thermal efficiency differences of 5 times where achieved when comparing the best and worst cases. Other important observation is concerned with the effect of ratio H3/L3 over heat transfer ratio (q) which varied significantly from a case where a pressure drop is imposed in the channel to other case where the driven force is caused by imposition of velocity field at the channel inlet

SIMULATION AND PERFORMANCE ANALYSIS OF A HYBRID ROCKET ENGINE WITH SELF-PRESSURIZING OXIDIZER

There are many challenges to simulate and design a hybrid engine, such as the dimensioning of the feed lines and tanks, propulsive performance calculations, and simulations of the expected behavior in the combustion chamber and the oxidizer tank during the engine operation. In this work, methods are assembled in a concise and complete analysis of the Gluon hybrid rocket engine, developed by PION Labs, with a blowdown pressurization system, using N2O as oxidizer and a paraffin-based fuel. For that, a study will be presented on the peculiar characteristics of the oxidizer and its behavior during the phases of operation of the rocket engine. Then, the main equations that describe the operation of the rocket engine, including the combustion chamber, injection plate, feed lines, and the oxidizer tank are presented, and the performance indicators calculations of the engine are shown and discussed. Finally, simulation results of the combustion chamber and the oxidizer tank during engine firing will be presented, leading to the concluding remarks on the data obtained

Uso de proexadiona cálcica não afeta a capacidade produtiva e qualidade dos frutos em pomares de macieira cobertos com tela antigranizo.

O Brasil é o terceiro produtor de frutas e o décimo produtor mundial de maçã. As condições climáticas do Sul do Brasil favorecem a produção de maçãs, porém alguns problemas como o alto vigor vegetativo geram desequilíbrio na eficiência produtiva, agravando-se com o uso da cobertura de tela antigranizo, devido ao sombreamento. A utilização de práticas de controle de crescimento em conjunto com o uso de fitorreguladores, como a proexadiona cálcica (PCa), é uma alternativa eficaz para controlar o desenvolvimento vegetativo e garantir a produção

Uso de tidiazuron como alternativa para aumento de formação de brotações em pomares de macieiras no Brasil.

A maçã é a principal fruta de clima temperado comercializada no Brasil. Porém, alguns entraves no sistema produtivo desta fruta causam perdas na produtividade brasileira. Entre elas, a deficiência de brotação de ramos produtivos em macieiras. Para uma ótima produtividade, objetiva-se durante a formação das plantas em pomares de macieira a uniformidade de brotação com técnicas mecânicas e/ou químicas. Porém, mesmo com as técnicas atuais de manejo utilizadas, existem locais na planta onde a brotação é deficiente e se faz necessário medidas corretivas para induzir a formação de novas brotações. Sendo assim, o trabalho teve como objetivo induzir a formação de brotações em macieiras com aplicação de tidiazuron (TDZ)