25-09-2014, 10:42 AM
WASTE HEAT RECOVERY SYSTEM
WASTE HEAT.docx (Size: 2.28 MB / Downloads: 18)
ABSTRACT
The increasingly worldwide problem regarding rapid economy development and a relative shortage of energy, the internal combustion engine exhaust waste heat and environmental pollution has been more emphasized heavily recently. Out of the total heat supplied to the engine in the form of fuel, approximately, 30 to 40% is converted into useful mechanical work; the remaining heat is expelled to the environment through exhaust gases and engine cooling systems, resulting in to entropy rise and serious environmental pollution, so it is required to utilized waste heat into useful work.
The recovery and utilization of waste heat not only conserves fuel (fossil fuel) but also reduces the amount of waste heat and greenhouse gases damped to environment. The study shows the availability and possibility of waste heat from internal combustion engine, also describe loss of exhaust gas energy of an internal combustion engine. Possible methods to recover the waste heat from internal combustion engine and performance and emissions of the internal combustion engine. Waste heat recovery system is the best way to recover waste heat and saving the fuel.
INTRODUCTION
Recent trend about the best ways of using the deployable sources of energy in to useful work in order to reduce the rate of consumption of fossil fuel as well as pollution. Out of all the available sources, the internal combustion engines are the major consumer of fossil fuel around the globe. Out of the total heat supplied to the engine in the form of fuel, approximately, 30 to 40% is converted into useful mechanical work.
The remaining heat is expelled to the environment through exhaust gases and engine cooling systems, resulting in to entropy rise and serious environmental pollution, so it is required to utilized waste heat into useful work. The recovery and utilization of waste heat not only conserves fuel, usually fossil fuel but also reduces the amount of waste heat and greenhouse gases damped to environment. Such a waste heat recovery would ultimately reduce the overall energy requirement and also the impact on global warming.
PROBLEM DEFINITION
The internal combustion diesel engine expels waste heat (exhaust), which causes environmental pollution and it has been more emphasized heavily recently. Out of the total heat supplied to the engine in the form of fuel, approximately, 30 to 40% is converted into useful mechanical work; the remaining heat is expelled to the environment through exhaust gases and engine cooling systems.
So in order to reduce the heat exhaust from I C engine, the heat content in the exhaust gas must be recovered so as to reduce its effect on environment.
LITERATURE REVIEW
Presently waste heat recovery from exhaust gas, has become a topic of discussion over the globe, in order to reduce the global temperature rise, we must reduce the heat lost to the environment.
In market we can see variety of waste heat recovery systems that can be fitted to the exhaust of the engines, the recovered heat can be used to heat or to boil water, that water can be used further.
There are different methods of the exhaust gas heat recovery namely for space heating, refrigeration and power generation. The mass flow rate of exhaust gas is the function of the engine size and speed, hence larger the engine size and higher the speed the exhaust gas heat is larger. So heat recovery system will be beneficial to the large engines comparatively to smaller engines.
The heat recovery from exhaust gas and conversion in to mechanical power is possible with the help of Rankine, Stirling and Brayton thermodynamic cycles, vapour absorption cycle. These cycles are proved for low temperature heat conversion in to the useful power. Engine exhaust heat recovery is considered to be one of the most effective means and it has become a research hotspot recently. For example, Doyle and Patel [14] have designed a device for recovering exhaust gas heat based on Rankine cycle on a truck engine.
The commissioning experiment of 450 kilometers showed that this device could save fuel consumption by 12.5%. Cummins Company has also done some research on waste heat recovery on truck engines, and the results showed that engine thermal efficiency could improve by 5.4% through exhaust heat recovery. James C. Conklin and James have designed a six-stroke internal combustion engine cycle with water injection for in-cylinder exhaust heat recovery which has the potential to significantly improve the engine efficiency and fuel economy.
DOUBLE PIPE HEAT EXCHANGER
A double pipe heat exchanger, in its simplest form is just one pipe inside another larger pipe. One fluid flows through the inside pipe and the other flows through the annulus between the two pipes. The wall of the inner pipe is the heat transfer surface. The pipes are usually doubled back multiple times as shown in the diagram at the left, in order to make the overall unit more compact.
SPIRAL HEAT EXCHANGER
A series of spacers are welded onto two or four sheets of metal which are then wrapped around a cylinder, thus creating two or four identical channels with a single passage; the concentric shape of the spacing and the internal threaded stud generate turbulence even at low Reynolds numbers.
PLATE HEAT EXCHANGER
Plate Heat Exchangers consist of corrugated plates (the working part), which are clamped together between a fixed and a movable frame cover plate to retain the fluid media (the pressure vessel part) The 'hot' and 'cold' fluid media flow in alternate channels which are formed by the plate corrugations and separated by the plate material and the gaskets in the 'port' area. Double gaskets with a tell-tale leak route protect the fluids from intermixing.
CONCLUSION
The heat exchanger we have designed have the capability of recovering the 31.05% of waste heat coming out of the diesel engine.
By increasing the thermal conductivity of the inside pipe, the heat transfer rate can be increased.
Effectiveness of the heat exchanger can be increased by increasing the surface contact between inside pipe and fluid.