نشریه مهندسی مکانیک تبدیل انرژی
سال دوم شماره 4 (پیاپی 5، پاییز و زمستان 1390)

The main goal of this paper is reducing emissions of nitrogen oxides and soot in the combustion chamber by injecting water in theintake air through a chamber (relative humidity). In this regard, an axially symmetric turbulent combustion chamber with fuel gas (methane) and non-premixed, derived from laboratory studies [9], has been considered. The other two-equation model of turbulence k-Ɛ, in both standard and realizable and to calculate the rate of reaction of combustion the Eddy Dissipation model (EDM) and the probability density function (PDF) were applied. The results of modeling showed that the most accurate model for turbulent flow, k-Ɛ realizable and for combustion, PDF. To reduce emissions, the relative humidity of the intake air in six different values ​​from zero to 100 percent have been examined. Results showed that by increasing the relative humidity, considered mildly reduced inlet air temperature and the resulting sharp decline in pollutants such as nitrogen oxides and soot seen compartment. while this value to NO and soot are respectively 5/67 and 8/71 percent. Failure to reduce thermal efficiency and a drastic reduction of NO and soot, showing the effectiveness of this method is to reduce emissions.

In the current study, the modeling and simulation of energy consumption for a two-story building with green roof in three different climates of Iran (Bandar Abbas: hot and humid, Tehran: mild and dry, and Tabriz: dry and cold) have been performed. This simulation aimed at investigation of the effects of the green roofs on reduction of thermal loads on the building and its role in reducing heat flux through the roof of the building. As the method, the building has been modeled by a software. This three-dimensional model by Energy Plus simulation software has been done. Simulation has been performed for different times of a year. For each of the three cities, a typical building with asphalt roof and a complete identical building with vegetation on its roof instead of asphalt, on its last layer, have been simulated and the results have been compared. The heat pumps have been used to provide heating and cooling loads on the building. The results of the simulation indicated that by the use of green roof, the annual baseline electricity consumption for heating and cooling loads were reduced up to 16.3%, 12.5% and 23% in Tehran, Tabriz and Bandar Abbas, respectively. According to the results, the use of green roofs in the tropical regions (Bandar Abbas) is more efficient compared to cold regions (Tabriz). The reason behind this phenomenon is the effect of the green roof as a cooler on the performance of the studied building's cooling system. The sensitivity analysis have shown that the energy consumption of described building is strongly dependent on soil thickness and vegetation density on the green roof structure as the more the soil thickness is, the better thermal insulator will be, and the higher the vegetation density is, the more powerful it will be, to prevent radiation from the sun.

The aim of present study is to investigate porous domestic vertical walls effects on reducing natural convection heat transfer in square cavity through Lattice Boltzmann methods. It is assumed upper and down cavity walls are thermal insulation and right side had constant temperature and cold, and left side constant and heated temperature. The left and right walls consisted of thermal differentiation as 1. In order to modelling natural heat transfer process in cavity, Lattice Boltzmann method used. And Brinkman equations used to model porous space. The current study attempt to consider natural heat transfer for Prandtl number was 0.7 and Rayleigh number was  , and it showed that porous walls may be reduce heat transfer and control it. The porosity of the separators, in addition to the effect of the heat transfer reducer, creates a smaller change in the overall shape of the flow pattern than the solid walls. Also, effect of porous wall distance from a wall in constant temperature and height considered and revealed that what time natural heat transfer in hole has minimum or maximum extent through domestic vertical porous walls.

This paper present, Based on the experimental results, two new non-dimensional parameters, namely thermal conductivity ( ) and dynamic viscosity ( ) are introduced. These new non-dimensional parameters indicate the enhancement of thermal conductivity and dynamic viscosity of nanofluids by utilizing nanoparticles, and they facilitates the general survey of convective enhancement of nanofluids. Using the presented non-dimensional parameters, the effect of working temperature of nanofluid, type of base fluid, size and type of nanoparticles have been studied on the heat transfer enhancement of nanofluids. The results show that utilizing nanofluid can lead to deterioration or enhancement of heat transfer. On the other hand, Decrease of the size of nanoparticles can lead to enhancement of heat transfer.