Conservation equations of mass, momentum and energy have been solved numerically along with a two-equation-based k-ɛ turbulent model to determine the air entrainment into a mixing pipe. Two different louvered pipe configurations (one with entrance face closed to atmosphere while the other was opened) were used to entrain air into the mixing pipe and by changing various design parameters, the resulting effects were studied. For both the configurations, the opening area and the number of nozzles (assumed exhaust pipe) had significant effect in bringing down the exhaust temperature especially the configuration with its entrance face opened to atmosphere. Temperature as low as 309 K (approx.) was successfully achieved in the analysis. Nozzle protrusion length also proved to be an important parameter among other parameters like nozzle pitch circle diameter, inclination angle and pipe diameter.
Top1. Introduction
Transportation is an important part of the daily life. During ancient times, horses were the mode of transportation. From the invention of wheel, the mode of transportation took a whole new turn and got inclined towards carts. Since then, many developments have taken place to make this process more comfortable. All those modes of transportation used human or animal power. Moreover, the travelling also took time. With the passage of time, considerable research works were conducted by many investigators so that the travelling time can be reduced making the journey more comfortable. Thus vehicles came into action. Brilliant minds like Nikolaus A. Otto, Sir Dougald Clerk, George Brayton, Gottlieb Daimler, Rudolf Diesel and Daimler made various engine designs so that they could be employed on these vehicles.
Technology, nowadays have advanced to an even higher level. Compare to earlier times, the engines are now more fuel efficient and reliable. In the current times, vehicles have been the easiest mode of transportation for every individual and thus have become an important part of today’s lifestyle. They have made the world easier in eve ry aspect. But every coin has two sides. On one hand, the life style has become easier, while on the other hand a huge price is being paid for it. The heavy and continuous usage of vehicles has led to deterioration of not only the environment but also one’s health. Every year the temperature of the planet is increasing causing many undesirable environmental changes. Global warming is being one of the most dangerous one. All these just because of the hot exhaust gases from the vehicles running all over the world every day and night. Jie (2011) studied the effects of exhaust gases on local as well as global scale showing their effect on the ecosystem. Locally viewing, these gases enter the respiratory systems which may become fatal to asthma patients and in the long run will affect the rest too in one way or another. These gases have a tendency to rise up, thereby creating adverse effects on the environment like ozone layer depletion and smog formation. The climatic conditions are also changing creating an inhospitable environment for all the life forms in the planet. So, a major challenge is faced by all of us. Therefore, some major steps have to be taken so as to control this degradation.
A simple step of cooling the exhaust gases prior to its release into the atmosphere can be applied to take care of such environmental issues. If fresh atmospheric air, which is at a lower temperature than the exhaust gases, is sucked in without using any external power or source, then it can be used for cooling of these exhaust gases. A louvered pipe surrounding the exhaust pipe will do the purpose of entraining the atmospheric air into the pipe. This works on Bernoulli’s principle creating low pressure inside the louvered pipe by high speed jet action of the exhaust gas. Since, the exhaust gases travel at a greater speed while coming out of the exhaust pipe, they create a low pressure inside the pipe which thereby sucks in atmospheric air into the ventilated pipe as shown in the Figure 1. As the exhaust gases are hot, the exhaust pipe material should have high thermal resistance or should be stable at high temperatures. Now if theses exhaust gases are cooled down to a lower temperature, relatively lower price material can be employed for making the exhaust pipe. This in turn will cut the fabrication cost of the vehicles for large scale production. If sufficient cooling of these gases is achieved, then there is a chance of reducing the rate of increment in the local environmental temperature. The present work was numerically done so that an optimum design can be made that would suck maximum air from the atmosphere into the louvered pipe. Practically, it can be applied to any vehicle of any size.
Figure 1. Entrainment of atmospheric air into the louvered pipe for configuration A and configuration B
The numerical analysis was aimed to obtain an optimum design which would effectively help in bringing down the temperature of the exhaust gas. For this purpose, two different pipe configurations were used. The first design was named as Configuration A. In this design, the air was admitted to enter the pipe only through the louvers on the pipe. The second was Configuration B, where the air entered the pipe via entrance face of the pipe as well as the louvers.