Performance Analysis of Thermoelectric Based Automotive Waste Heat Recovery System with Nanofluid Coolant
Abstract
:1. Introduction
2. Mathematical Model
- (1)
- The heat transfer process is steady;
- (2)
- All the TEMs in the system are in series. Geometric configurations properties of P-type and N-type materials are identical, and physical properties of each P-type legs are identical, as well as the N-type legs;
- (3)
- Air between TEMs and heat exchangers are omitted because it is quite small. Thermal radiation is not taken into consideration. Contact resistance between TEMs and heat exchangers, thermal resistance perpendicular to flow direction of fluid, and Thomson effect are also omitted;
- (4)
- The external load resistance is equal to the internal resistance;
- (5)
- Thermoelectric material used in this study is Bi2Te3, its thermoelectric parameters are constants, and Table 1 presents the basic calculation parameters.
3. Results and Discussion
3.1. Comparison between Cu-EG Nanofluid and EG-W
3.2. Comparison between Different Cu-EG Nanofluid Concentrations
3.3. Analysis of Total Area of TEMs
3.4. Effect of Hot Side Heat Transfer Coefficient of TEMs
4. Conclusions
- (1)
- Compared to conventional EG-W coolant, Cu-EG nanofluid can attain a lower cold side temperature of TEMs and a larger temperature difference between hot and cold end of TEMs under equal mass flow rate, which will effectively improve power output and thermoelectric conversion efficiency for the TEG system;
- (2)
- Cu-EG nanofluid as coolant can decrease the optimal total area of TEMs and increase the power output compared with EG-W coolant under equal mass flow rate. This finding will bring significant advantages for the optimization and arrangement of TEMs in the system. When the arrangement space of TEMs for the system is sufficient, less TEMs are required when using Cu-EG nanofluid as coolant, which will save thermoelectric materials and the cost. When the arrangement space of TEMs is limited, Cu-EG nanofluid as coolant can make system output more power compared to EG-W coolant under the same amount of TEMs;
- (3)
- Power output enhancement under Cu-EG nanofluid coolant is larger than that of EG-W coolant as the increase of hot side heat transfer coefficient of TEMs. From the perspective of synergy effect on heat transfer enhancement for the hot side of the TEMs, Cu-EG nanofluid as coolant for the cold side of the TEMs is also superior to EG-W coolant.
Acknowledgments
Author Contributions
Conflicts of Interest
Nomenclature
Nomenclature | |
Specific heat of exhaust (kJ kg−1 K−1) | |
Specific heat of coolant (kJ kg−1 K−1) | |
Diameter of tube (m) | |
dp | Diameter of nanoparticle (mm) |
h | Height of TEM leg (mm) |
Heat transfer coefficient of hot side (W m−2 K−1) | |
Heat transfer coefficient of cold side (W m−2 K−1) | |
i | Direction of x coordinate |
j | Direction of y coordinate |
Thermal conductivity of basic fluid (W m−1 K−1) | |
Thermal conductivity of nanoparticle (W m−1 K−1) | |
Thermal conductivity of nanofluid (kJ m−3 K−1) | |
l | Length of TEM leg (mm) |
Mass flow rate of exhaust (kg/s) | |
Mass flow rate of coolant (kg/s) | |
Number of TE modules in x direction | |
Number of TE modules in y direction | |
Heat flow density for hot side (W/m2) | |
Heat flow density for cold side (W/m2) | |
Resistance for a P-N junction (Ω) | |
Electrical load resistance (Ω) | |
Temperature of cold fluid (K) | |
Temperature of exhaust (K) | |
Hot side temperature of TEM (K) | |
Cold side temperature of TEM (K) | |
Average speed of nanofluid (m/s) | |
w | Width of TEM leg (mm) |
Greek Symbols | |
Seebeck coefficient of N-type material (V/K) | |
Thermal diffusivity coefficient of nanofluid (m2/s) | |
Seebeck coefficient of P-type material (V/K) | |
Thermal conductivity of P-type material (W m−1 K−1) | |
Thermal conductivity of N-type material (W m−1 K−1) | |
Density of nanoparticle (kg/m3) | |
Density of nanofluid (kg/m3) | |
Density of base fluid (kg/m3) | |
Resistivity of P-type material (Ω·m) | |
Product of density and specific heat capacity for base fluid (kJ m−3 K−1) | |
Product of density and specific heat capacity for nanoparticle (kJ m−3 K−1) | |
Product of density and specific heat capacity for nanofluid (kJ m−3 K−1) | |
Kinematic viscosity of nanofluid (m2/s) | |
Dynamic viscosity of basic fluid (Pa s) | |
φ | Concentration of nanofluid |
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Semiconductor Parameters | Value |
---|---|
Seebeck coefficient of P-type leg | 2.037 × 10−4 V K−1 |
Seebeck coefficient of N-type leg | −1.721 × 10−4 V K−1 |
Resistivity of P-type leg | 1.314 × 10−5 Ω m |
Resistivity of N-type leg | 1.119 × 10−5 Ω m |
Thermal conductivity of P-type leg | 1.265 W m−1 K−1 |
Thermal conductivity of N-type leg | 1.011 W m−1 K−1 |
Length of P- and N-type leg | 5 mm |
Width of P- and N-type leg | 5 mm |
Height of P- and N-type leg | 5 mm |
Parameters | Value |
---|---|
Inlet temperature of cold fluid | 298 K |
Specific heat capacity of Cu-EG nanofluid | 2775 J kg−1 K−1 |
Specific heat capacity of EG-W | 3400 J kg−1 K−1 |
Specific heat capacity of exhaust gas | 1020 J kg−1 K−1 |
Heat transfer coefficient of Cu-EG nanofluid | 204 W m−2 K−1 |
Heat transfer coefficient of EG-W | 152 W m−2 K−1 |
Heat transfer coefficient of exhaust gas | 80 W m−2 K−1 |
Mass flow rate of exhaust gas | 0.03 kg s−1 |
Mass flow rate of cold fluid | 0.03 kg s−1 |
Concentration φ | Heat Transfer Coefficient (W·m−2·K−1) | Specific Heat Capacity (J·kg−1·K−1) | Density (kg·m−3) | Thermal Diffusivity (m2·s−1) | Dynamic Viscosity (Pa·s) |
---|---|---|---|---|---|
1% | 176 | 3160 | 1136 | 1.15 × 10−7 | 0.00183 |
2% | 191 | 2955 | 1215 | 1.19 × 10−7 | 0.00187 |
3% | 204 | 2775 | 1293 | 1.22 × 10−7 | 0.00192 |
4% | 215 | 2615 | 1371 | 1.26 × 10−7 | 0.00197 |
5% | 225 | 2473 | 1450 | 1.30 × 10−7 | 0.00202 |
6% | 234 | 2346 | 1528 | 1.34 × 10−7 | 0.00208 |
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Li, Z.; Li, W.; Chen, Z. Performance Analysis of Thermoelectric Based Automotive Waste Heat Recovery System with Nanofluid Coolant. Energies 2017, 10, 1489. https://doi.org/10.3390/en10101489
Li Z, Li W, Chen Z. Performance Analysis of Thermoelectric Based Automotive Waste Heat Recovery System with Nanofluid Coolant. Energies. 2017; 10(10):1489. https://doi.org/10.3390/en10101489
Chicago/Turabian StyleLi, Zhi, Wenhao Li, and Zhen Chen. 2017. "Performance Analysis of Thermoelectric Based Automotive Waste Heat Recovery System with Nanofluid Coolant" Energies 10, no. 10: 1489. https://doi.org/10.3390/en10101489