Non Intrusive Exhaust Gas Heat Recovery System for an. Automobile: An Experimental Investigation. Author, co-author (Do NOT enter this information. It will beΒ ...
13CVI-0097
Non Intrusive Exhaust Gas Heat Recovery System for Automobile: An Experimental Investigation
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ABSTRACT A parallel flow concentric tube heat exchanger is designed to recover exhaust heat by using the exhaust pipe as the tube side and the concentric tube as the shell side. The heat exchanger which is also called the primary heat exchanger is welded concentrically to the intermediate exhaust pipe forming a double pipe heat exchanger. The shell side pipe consists of Cold Water inlet and Hot Water outlet while the tube side pipe carries the hot exhaust gases. The water flowing in the shell side gets heated due to conduction and convection and is circulated through the Hot Water outlet to produce Hot Water on demand. The same Hot Water is simultaneously circulated to the annular chamber of the secondary heat exchanger, thereby transferring the heat to the Hot Box.
INTRODUCTION Amid the economic uncertainties and a declining sales, a demand for new technologies and innovative features that will enhance the pleasure of driving to the customer is inevitable. As the expectations of the conscious consumption customer increases, there is an increasing emphasis on value for money [1]. In other words, a car with luxurious features at a competitive cost is the key to woo customers in this highly competitive automotive industry. Increasingly customers are being given the opportunity to customize their purchase, while the automakers are becoming more adroit at understanding which customers create the most value for them. Another dimension is the fact that cars are evolving into electric appliances. Today, 22 percent of a car is electronic content. In ten years, that will be 40 percent. Connectivity will promote extended relationships with auto owners fostering a greater customer-centric focus [2].
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One way to enhance relationship of car with its owners is by providing features that will augment the pleasure of driving a car at no additional cost or minimal cost. This can be best done by making use of the sunk energy of the vehicle that get wasted otherwise. For example, the heat energy from the heated coolant and the exhaust gases. Extraction of heat energy from the former will mean higher pumping requirement to drive the flow of the coolant in the annular chamber of the Hot Box and a reduced cooling efficiency of the cooling system whereas the later can be done in a nonintrusive manner and without any impact on the back pressure of the exhaust system. Moreover, the coolant oil used in the cooling system may lead to contamination of the Hot Box [3]. Therefore, heat recovery from the exhaust system with water as the heat exchanger medium is found to be a more pragmatic and hygienic proposition. The Exhaust gas heat recovery system discussed in this paper harnessed the thermal energy of the exhaust gases and used it for heating water to provide Hot Water on demand and the same Hot Water can be use for heating a closed container called Hot Box. The unique feature of this feature is that the heat exchange takes place without the need for bypassing the exhaust gases and thereby without increasing the exhaust back pressure and hence without any adverse impact on the volumetric efficiency of the engine.
THERMAL LOSSES FROM EXHAUST SYSTEM Typical thermal efficiencies of Diesel Internal Combustion Engines are in the range of 32-33 per cent in which the thermal losses from exhaust system alone contributes to about 33 per cent as shown in figure 1. Therefore, a mechanism for
effective utilization of the heat loss from exhaust system is an important aspect of energy recovery system.
Figure 2. Parallel flow Double Pipe Heat Exchanger
Location
Figure 1.Thermal losses from Exhaust System
The Primary Heat Exchanger is a retrofitted part that is adapted into existing exhaust system of the vehicle. The functions of various components of the exhaust system like the Catalytic converter and muffler cannot be compromised. Hence, determination of the position of the Primary Heat Exchanger in the exhaust system is a critical aspect of the design. It is a well known fact that the performance of catalytic converter depends on the exhaust gas temperature among other parameters [6]. The Primary Heat Exchanger is located downstream at a distance of about 700 mm from the outlet of the Catalytic Converter at the Intermediate Pipe as shown in figure 3 and figure 4.
Components of Heat Recovery System The heat recovery system consists of the following components, figure 2 and figure 3: 1. Primary Heat Exchanger 2. Connectors 3. Hot Water Pump 4. Cold Water Inlet 5. Hot Water Outlet 6. Hot Box or Secondary Heat Exchanger 7. Exhaust Pipe 8. Control Valve 9. Electrical switch 10. Hoses
Figure 3.Loation of Heat Exchanger in the Exhaust System
Primary Heat Exchanger Selection of Heat Exchanger A recuperative indirect-contact-type of heat exchanger where the heat transfer occurs through a separating wall in which the Cold water recovers some of the heat from the Hot exhaust is the most appropriate type of heat exchanger which meets the customer requirement. The double pipe heat exchanger is a parallel flow concentric tube heat exchanger because the Cold Water and the Hot Exhaust Gas flow in the same direction. The heat exchanger medium flows in the shell side tube and the exhaust gas flows in the tube side tube [4][5], figure 2.
Figure 4. Heat Exchanger in the Intermediate Pipe of Exhaust System
Diameter The outer diameter of the Primary Heat Exchanger which acts as the Shell side pipe in this case is determined by the available packaging space without compromising on the critical clearances of the existing vehicle. Whereas, the diameter of the tube side pipe is the existing intermediate pipe of the vehicle. With these constraints, the outer diameter of the Primary Heat Exchanger is 120 mm and the Outer pipe
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diameter of the Exhaust Pipe is 55.5 mm which is equivalent to a hydraulic diameter of 64.5 mm. Length Within the packaging limit of the vehicle, the length of the Primary Heat Exchanger is optimized using AMESim [7] so that the water temperature is within the desired range as shown in Table 1 and figure 5 and figure 6. Table 1.Optimization of Heat Exchanger length Proposals 1 2 3 4 5 6 7 8 9
Length (mm) 500 450 400 350 300 250 200 150 100
Volume (L) 4.4 4 3.5 3.1 2.6 2.2 1.7 1.3 0.8
Temperature (o C) 208 198 186 173 158 140 121 98 73
Hot Box or Secondary Heat Exchanger The Secondary Heat Exchanger or Hot Box consists of an annular chamber for the hot water to circulate and transfer heat to the inner chamber of the Hot Box. Fins are added to enhance the rate of heat transfer from the water into the Inner Chamber as shown in figure 7. The Water Inlet of the Hot Box is connected to the Hot Water outlet of the Primary Heat Exchanger via the electronic water pump and a T Junction connector. The other side of the T junction is fitted with a control valve to provide Hot Water on demand at the Hot Water Outlet. The circulated Hot Water from the annular chamber of the Hot Box is re-circulated back to the Primary Heat Exchanger through the Water Outlet of the Hot Box. The Water outlet is also connected to a T Junction connector in which the other side of the junction is connected to the cold water inlet. The flow from Hot Box to the Primary Heat Exchanger and Cold Water Inlet to the Primary Heat Exchanger is by gravity.
Figure 7.Hot Box
Working of Hot Box
Figure 5.Optimization of length of Primary Heat Exchanger
The primary heat exchanger is welded concentrically to the exhaust pipe forming a double pipe heat exchanger. The inlet side of the primary heat exchanger is connected to the Cold Water Cup (Cold Water Inlet) and the outlet side of the primary heat exchanger is connected to the Hot Water Cup (Hot Water Outlet) and the secondary heat exchanger through a T junction connector via Hot Water Pump. The secondary heat exchanger is called Hot Box. The flow of the Hot water and hence the temperature of Hot Box is controlled by a switch which is connected to the Hot Water Pump. The hot water dispenser is controlled by a control valve located in the hot water outlet hose.
Figure 6. Primary Heat Exchanger Page 3 of 5
Test Set Up
Experimental Testing
The intermediate pipe of the existing exhaust system is replaced with a new intermediate pipe fitted with the primary heat exchanger as shown in figure 8. The inlet and outlet of the primary heat exchanger is connected to the Cold water Inlet and Hot Water Outlet and Hot Box through pneumatic hoses as shown in figure 9. Two types of thermocouples are used for temperature measurement. K-type thermocouple is used for measuring the Water and Hot Box temperature and stem-type thermocouple is used for measuring the exhaust gas temperature.
Static Static testing is performed to measure the temperature if the Hot water temperature and Hot Box temperature is measured under idle condition for which the RPM is 750. Temperature measurements are in degree Celsius. Table 2. Results of Static testing Initial 34 34 31 31 31
T1 T2 T3 T4 33 T5
Figure 8.Location of Primary Heat Exchanger in actual vehicle
where T T1 T2 T3 T4 T5
After 15 minutes 95 90 37 34 39
Temperature in degree Celsius Exhaust gas temperature before heat exchanger Exhaust gas temperature after heat exchanger Hot Box temperature Cold water temperature Hot water temperature
Dynamic Dynamic testing is done under two conditions. One in slow driving at 10 kilometer per hour and other in Highway driving condition up to a maximum speed of 120 kilometer per hour as shown in Table 3, Table 4 and figure 10. Table 3. Results of Dynamic testing at 10 kmph
T1 T2 T3 T4 33 T5
Initial 36 38 36 33 36
After 15 minutes 121 111 45 35 50
Table 4. Results of Dynamic testing at Highway Driving
Figure 9.Location of Water Inlet, Water Outlet, Electrical Switch, Control Valve and Hot Box
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T1 T2 T3 T4 33 T5
Initial 36 38 36 31 36
After 15 minutes 348 336 82 33 94
Temperature in deg C
350 300 250 200 150 100 50 0
T1
The potential of making potable Hot Water is evident due to the fact that the Heat Recovery from Exhaust System is without using the engine coolant or bypassing the exhaust gases which can cause unhygienic contamination to Hot Water.
T2 T5 T3 0
2000
4000
6000
Seconds
Figure 10.Temperature of Hot Box in Highway Driving condition
Moreover, the main advantage of this system is in its ability to recover exhaust gas heat without increasing exhaust system back pressure and hence no effect on engine performance. The location of the Primary Heat Exchanger after the Catalytic Converter is another added advantage since it do not disturb the emission criteria of the vehicle.
REFERENCES 1.
Log mean temperature difference(LMTD) The Log mean temperature difference for a parallel flow double pipe heat exchanger is given by [5] βπππ =
βπ2 β βπ1 ππ
2.
3.
βπ2 βπ1
4.
Where βπ1 = π1 β π4 βπ2 = π2 β π5
5.
6.
The log mean temperature difference for the three cases are as given below Testing Condition Static At 10 kmph Highway driving
LMTD 55.85 72.75 276.89
SUMMARY/CONCLUSIONS The advantages of the technology lies in its possibility to be implemented in the existing vehicle as it requires no or less modification of the surrounding systems. The system can be easily integrated with any of the existing cup holders inside the vehicle.
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7.
Tohmatsu, Deloitte Touche. "A New Era: Accelerating towards 2020βAn Automotive Industry Transformed." (2009). Benko, Cathleen, and Warren McFarlan. "Metamorphosis in the auto industry." Strategy & Leadership 31, no. 4 (2003): 4-8. Akao, YΕji. Quality function deployment: integrating customer requirements into product design. Productivity Press, 1990. KakaΓ§, SadΔ±k, Anchasa Pramuanjaroenkij, and Hongtan Liu. Heat exchangers: selection, rating, and thermal design. CRC press, 2012. Incropera, Frank P., Adrienne S. Lavine, and David P. DeWitt. Fundamentals of heat and mass transfer. John Wiley & Sons Incorporated, 2011. Ehsan, M., M. Z. Shah, M. Hasan, and S. M. R. Hasan. "Study of Temperature Profile in automotive exhaust systems for retrofitting catalytic converters." In Proceedings of the International Conference on Mechanical Engineering (ICME2005). Imagine, L. M. S. "Lab AMESim."
ACKNOWLEDGMENTS The authors would like to acknowledge the support of the Mr. K Sudharsan and his team from the Validation Department of Mahindra Research Valley, Chennai for their support. We also thank Mr Pund S and Loganathan Balasubramanian from the Intellectual Property Cell of Mahindra Research Valley for their continuous support in filing the patent.
