Some considerations in the thermal energy recovery of engine exhaust with thermoelectric module

• Main Authors: Chi-Hung Lin, 林繼弘
• Other Authors: 盧昭暉
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/33029346629659879437

碩士 === 國立中興大學 === 機械工程學系所 === 98 === This paper focuses on recovering the thermal energy of vehicle exhaust to convert heat to generate power by thermoelectric module and discusses the power conversion efficiency. The entire system includes heat exchanger, fins, and thermoelectric modules. The fin was set inside the heat exchanger, the thermoelectric modules were attached on the surface of the fin, and part of the exhaust heat was absorbed by the fins. Heat transfers to one side of the thermoelectric modules, and the coolant water flows from the other side through the thermoelectric module. The thermoelectric module generates electricity with the temperature differences. In this article, we established the model by using the normal thermoelectric module chip. First, we use the temperature of heat exchanger wall calculated by the exhaust flow rate and the exhaust temperature as the temperature of the hot side of the thermoelectric module. Then we calculate the heat transfer rate of the hot side and cool side, and the transferring efficiencies. In this article there are two type engines to be evaluated, one is 2835c.c diesel engine and the other one is 124.6c.c motobike inject engine and install three different type heat exchangers. We found the power generation efficiencies are 7.9% & 0.52% when the thermoelectric modules load resistance factor m = 1, heat exchanger Type_A & Type_B which internal sectional areas are both 47.4cm2 , the exhaust temperatures are 800K & 673K, temperatures of coolant water are 313K & 298K, and the output power efficiencies are 446.2W & 0.65W. The major internal losses of thermoelectric modules are thermal transfer losses and the loss of the resistance. If we increase the exhaust temperature to 1000K, then the generation power can be increased to 881.73 & 2.65W; increasing the coolant water temperature to 363K, then the generation power are reduced to 356.56W & 0.43W. The output efficiencies will be increased to 528.49W & 57.15W if the number of the fin increases. The output efficiency will be 519.22W & 0.99W when the length of exhaust pipe increases. In this article we use the designing of heat exchanger Type_B to carry on the experiment, in result when the engine at 4500RPM, the exhaust gas which inlet heat exchanger is 724K and the exhaust gas temperature of heat exchanger outlet is 410K. We found the output voltage of TEG system is 6.48V and power generation efficiency is 3.11W, the temperature alone the heat exchanger is 442.5K, the temperature of coolant water is 320K. The heat energy recovery efficiency of whole system is 0.38%. The key aspect to effect the efficiency are the quantity of TEM, the length of heat exchanger, the number of the fin and the operation conditions of engine.