International Journal of Applied Engineering Research ISSN 0973-4562 Volume 13, Number 2 (2018) pp. 1385-1407 © Research India Publications. http://www.ripublication.com 1385 A Comparison of Mixed Convection Heat Transfer in Upward Stepped Tilted Constant Area Pipe between Air and Diesel Exhausted Gas Samheri A. Almuradi Ph. D. Associate Prof., Lecturer and General Supervisor of Applied Research Lab., Mech. Eng. Dept., Faculty of Engineering, Al-Mustansiriyah University, Baghdad, Iraq, P.O. Box (46049), Baghdad, Iraq. Orcid: 0000-0002-9138-0840 Abstract The widespread diesel engines usage has many advantages, such as electricity generating units with 500 kVA and above, which mainly takes a great attention in countries and places suffering from a large lack of daily supplying electricity. These may need to about 12 units to cover one populated kilometer. These engines play an important role in environmental pollution problems all over the world. Pollutions generated from exhaust emissions are the main responsible factor for environmental pollutions, and they lead to many problems of health. Many policies have been imposed worldwide in recent years to reduce negative effects of diesel engine emissions on human health and environment. Many research efforts have been carried out on both diesel exhaust pollutant emissions and aftertreatment emission control technologies. The aftertreatment systems convert the pollutant gases separately into non-pollutant compounds. Studies show that its function depends on exhaust gas temperature and velocity. This paper deals with a comparison of laminar mixed heat transfer in circular different inclination pipe with 0, 45 and 90 degrees angle between fresh air and diesel exhaust gas (DEG). They are examined at a constant heat flux of 115 and 816 W-m -2 for 450 and 2008 Reynolds numbers. The results show a clear increase in temperature distribution and a clear decrease in local Nusselt number grow with the exhaust gas pipe inclination increase. This will help to modify the aftertreatment design parameters, their inclination and more generally the most important a trial to solve such environmental problem. Keywords: Laminar flow, Mixed convection, Stepped tilted pipe, Air, Diesel exhaust gas. INTRODUCTION Air Nowadays Global warming, change in climate and protection of the environment from air pollution took the whole world attention. World organizations like (EPA, IPCC, OECD, IEA, EEA, etc.) are working hard to minimize and eliminate the pollution of air and any change takes place in climate and explains their causes and cooperate with all industrial and non- industrial countries to find more extensive solutions and force participants to issue laws and rules. They reported that about 20–30 % of pollutant emissions originate from transport and industrial sources these emissions have a direct effect on global warming and climate change. Some countries suffer from a lake in electricity refuge to use small generating units. Therefore these units become the first source for pollutant emissions in addition to its higher effect come from its unmovable sources in comparison with transport ones. They invented and developed technological devices (control systems) that get rid of emissions prevent the effects of these pollutant emissions. Some of these control devices are (OECD 2002, IPCC 2007, OECD 2011, EPA 2012, IEA 2012 and EEA 2012) Ibrahim et al. [1]. Diesel Engine Prasad and Bella [2] explained that recent Diesel fuel engines are used extensively. Advantages of engines using diesel fuels on gasoline fuel engines are, 1. Low-operating costs. 2. Its thermal and overall efficiency. 3. High durability and reliability. 4. Power source of commercial transport in all its kinds. 5. Industrial units such as small electricity generating units. Sydbom et al. [3], Lloyd and Cackette [4], Whichmann [5], Lewtas [6] and Burr and Gregory [7] showed its disadvantages as, 1. Environmental pollutants source. 2. Containing a higher amount of particulate matter and NOx emissions. 3. Environmental and health problems. 4. Causing acid rains. 5. Lowering ozone level. 6. Reducing visibility. 7. Causing lung damage and respiratory problems when direct exposure.