International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 11, November 2017, pp. 668 675, Article ID: IJMET_08_11_068 Available online at http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=8&itype=11 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication Scopus Indexed THERMOELECTRIC COOLING RADIATOR FOR INTERNAL COMBUSTION ENGINE Nikolay Anatolyevich Khripach, Viktor Sergeevich Korotkov and Igor Arkadyevich Papkin, Moscow Polytechnic University, ul. Bolshaya Semenovskaya 38, Moscow, 107023, Russia ABSTRACT This article discusses the results of computational experiments with previously developed algorithm of development of thermoelectric energy recovery system aimed at determination of parameters of thermoelectric cooling of internal combustion engine, namely: thermoelectric radiator, its main physical and geometrical parameters, such as thermal and electric power, aerodynamic and hydraulic resistance, temperature of cooling fluid, and so on. The calculations were performed both for separate elements of the radiator and for overall radiator. On the basis of the presented calculation results 3D model of thermoelectric cooling radiator for internal combustion engine was developed with subsequent fabrication of a mockup of thermoelectric radiator. In addition, this article presents specifications of the fabricated mockup of thermoelectric radiator obtained on the basis of preliminary researching experiments, which correspond to calculations with minor error. Keywords: Thermoelectric generator, thermoelectric cooling system, direct conversion of thermal energy into electric, internal combustion engine, cooling system, heat exchanger, thermoelectric generator. Cite this Article: Nikolay Anatolyevich Khripach, Viktor Sergeevich Korotkov and Igor Arkadyevich Papkin, Thermoelectric Cooling Radiator for Internal Combustion Engine, International Journal of Mechanical Engineering and Technology 8(11), 2017, pp. 668 675. http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=8&itype=11 1. INTRODUCTION Nowadays automotive transport plays an important role in human life. Increase in vehicle fleet is related with increase in atmospheric harmful emissions. The amount of harmful emissions is restricted by established toxic regulations. The main normalized components of exhaust gases are carbon oxide (CO), hydrocarbons (HC) and nitrogen oxides (NO x ). One of the main methods to decrease toxic emissions is increase in efficiency of internal combustion engine (ICE). http://www.iaeme.com/ijmet/index.asp 668 editor@iaeme.com
Thermoelectric Cooling Radiator for Internal Combustion Engine Power efficiency of units based on thermal engines can be increased by conversion of thermal energy into electric energy. According to the equation of external heat balance of ICE [1], higher portion of heat energy generated during fuel combustion is released into atmosphere with exhaust gases and via cooling system. Thermal energy can be converted into electric energy using thermoelectric generator. At present the greatest attention is paid to thermoelectric generators producing electric energy from thermal energy of exhaust gases, that is, installed directly on vehicle exhaust system [2-3]. However, thermal energy, dissipated by ICE cooling system, can also be converted into electric energy by thermoelectric generator, which in this case can be considered as thermoelectric radiator. The main element of thermoelectric generator is the thermoelectric generator module converting heat into electricity. Operation of thermoelectric generator module is based on the Seebeck effect: occurrence of electromotive force in closed electric circuit comprised of dissimilar conductors connected in series and the contacts of which exist at different temperatures. 2. DESIGNING THERMOELECTRIC RADIATOR Initial data were determined prior to beginning of design activities, that is, dimensions of thermoelectric radiator core. After studying of existing designs of vehicle radiators as well as thermoelectric generators, which use exhaust gases and ICE cooling fluid as heat source, design features of future thermoelectric cooling radiator for ICE have been determined. The design described in [4] was taken as a basis. It was decided to select single-row, two-pass, tube-band thermoelectric radiator design, material: aluminium. Currently numerous studies are available devoted to design procedures of thermoelectric generators and recovery systems of heat energy in general [5-7], however, development of thermoelectric radiator was based on the procedure described in [8-10]. Geometric parameters of thermoelectric radiator core were determined prior to the design stage; they are summarized in Table 1. Table 1 Geometric parameters of thermoelectric radiator core Geometric parameters of thermoelectric cooling radiator core Core height, m H=436.8 10-3 Core width, m B=624 10-3 Tube width, m b=60 10-3 Parameters of elements of thermoelectric cooling radiator Front spacing, m t fr =52 10-3 Depth spacing, m t d =60 10-3 Height spacing t h =32.6 10-3 Element length, m l e =52 10-3 During design procedure the following parameters were determined: temperatures of fluid and air at input and output to/from thermoelectric radiator, fluid and cooling air flow rates, the Reynolds, Prandtl and Nusselt criteria for air and cooling fluid, aerodynamic and hydraulic resistances, as well as the required geometrical parameters of thermoelectric radiator elements for efficient cooling of ICE. The performed calculations demonstrated that thermoelectric radiator with geometric properties preset in Table 1 can efficiently cool ICE similar to standard cooling radiator. http://www.iaeme.com/ijmet/index.asp 669 editor@iaeme.com
Nikolay Anatolyevich Khripach, Viktor Sergeevich Korotkov and Igor Arkadyevich Papkin On the basis of calculations of heat exchange in thermoelectric radiator the coefficient of heat transfer was determined, according to which the element parameters of thermoelectric radiator core were adjusted (cooling tubes, plates and bands). Table 2 summarizes geometrical parameters of core elements of thermoelectric radiator. Table 2 Geometric parameters of core elements of thermoelectric radiator Parameters of cooling tubes of thermoelectric cooling radiator Tube height, m c=6 10-3 Tube wall thickness, m Δ tube =1 10-3 Parameters of air cooled bands of thermoelectric cooling radiator Band height, m f h =7,5 10-3 Band thickness, m Δ b =0,2 10-3 Front spacing, m t fr =1,6 10-3 Horizontal spacing, m l h =9,5 10-3 Band base thickness, m Δ bas =1 10-3 After designing procedure electric power of thermoelectric radiator was determined. According to the dimensions of developed thermoelectric radiator core H-288-14-06-L2 thermoelectric generator modules were selected; their geometrical properties and specifications are summarized in Table 3. Table 3 Geometrical properties and specifications of H-288-14-06-L2 TEG module Properties Geometrical parameters of thermoelectric generator module - width, mm; - length, mm; - height, mm Maximum temperature of hot side: - short time, C; - long time, C. Value 52 55 3.3 200 150 Output parameters at the temperature on hot side and cold side 150 C and 50 C, respectively (ΔT mod =100 C) - current I mod, A; - voltage U mod, V; - power P mod, W; - Efficiency η mod, %. 2.4 6.5 15.7 4.2 Heat conductance of module hot side and cold side λ mod, W/(m K) 1.2 Thermoelectric generator modules are located at both large sides of tubes, hot sides in contact with them, along the first fluid pass, since exactly during the first fluid pass it is possible to provide the temperature gradient between hot and cold sides of thermoelectric generator module required for electricity production. On the basis of dimensions of thermoelectric radiator core, the amount of thermoelectric generator modules was 168 pieces, located on the seven tubes of the first fluid pass. It was decided to place aluminum plates on the 8-th tube, simulating thermoelectric generator modules, which can be replaced for thermoelectric generator modules for production of electricity. Calculated electric power of thermoelectric radiator was 817.7 W. http://www.iaeme.com/ijmet/index.asp 670 editor@iaeme.com
Thermoelectric Cooling Radiator for Internal Combustion Engine The thermoelectric radiator operates as follows. Cooling fluid circulates in the tubes of rectangular cross section, whereas the incoming air flow passes via the undulated band in frontal and horizontal projections. In order to improve heat transfer between fluid in tubes and air flow in thermoelectric radiator, the undulated band is equipped by two soldered aluminum plates with the thickness of 1 mm from above and below. The hot sides of thermoelectric generator modules mechanically contact with cooling tubes, and the cold side with the bases of undulated cooling band. Thermoelectric radiator of such design provides reliable operation in modern petrol and diesel vehicle engines, and is characterized by high cooling efficiency for cooling fluid. It should be mentioned that the radiator of such design is easy in fabrication and operation as well as characterized by high maintainability and replaceability of thermoelectric generator module upon failures. 3. 3D MODEL OF THERMOELECTRIC RADIATOR On the basis of designing procedure 3D model of thermoelectric radiator was developed comprised of: two tanks, one is for input and output of cooling fluid, the other is for bypassing of cooling fluid from the upper portion of thermoelectric radiator into the bottom one; two cross members aimed at provision of rigidity of thermoelectric radiator; tubes intended for circulation of cooling fluid as well as for heating of hot side of thermoelectric generator modules; undulated bands intended for cooling of thermoelectric radiator as well as for cooling of cold side of thermoelectric generator modules; bases of undulated bands intended for increase in contact area with cold sides of thermoelectric generator modules; Thermoelectric generator modules the hot sides of which are in direct contact with tubes, where cooling fluid circulates, and the cold sides contact with bases of cooling bands. 3D model of thermoelectric cooling radiator is illustrated in Figure 1. Figure 1 3D model of thermoelectric cooling radiator Aerodynamic properties of the thermoelectric radiator obtained in design experiments were validated using the developed 3D model of thermoelectric radiator. This was aided by computational model of thermoelectric radiator cell comprised of a tube, two thermoelectric generator modules and two undulated bands with bases. The width of http://www.iaeme.com/ijmet/index.asp 671 editor@iaeme.com
Nikolay Anatolyevich Khripach, Viktor Sergeevich Korotkov and Igor Arkadyevich Papkin this cell corresponds to that of a thermoelectric generator module. The computational model of the developed thermoelectric radiator cell is illustrated in Fig. 2. Figure 2 Computational model of thermoelectric radiator cell In order to determine aerodynamic properties of the cell, maximum air flow rate in channel was pre-calculated during designing of thermoelectric radiator, it was 37 m/s (133.2 km/h). Variations of air flow velocity and pressure in thermoelectric radiator cell upon verification of aerodynamic properties are illustrated in Figs. 3 and 4. Figure 3 Variation of air flow speed in thermoelectric radiator cell Figure 4 Pressure variation in thermoelectric radiator cell During experiments the pressure at input to thermoelectric radiator cell was determined equaling to 103696 Pa, and the pressure at output from thermoelectric radiator cell was determined equaling to 101325 Pa. http://www.iaeme.com/ijmet/index.asp 672 editor@iaeme.com
Thermoelectric Cooling Radiator for Internal Combustion Engine Aerodynamic resistance of thermoelectric radiator cell obtained upon simulation was 2731 Pa, which corresponded to calculated aerodynamic resistance of air channel obtained upon design procedure of thermoelectric radiator. 4. FABRICATION OF THERMOELECTRIC RADIATOR The following elements of thermoelectric radiator were fabricated on the basis of the developed 3D model: tanks, made of aluminum billet by cutting. The holes for mounting of tubes with gaps were also made in the tanks by cutting; cross members, also fabricated from aluminum billets by cutting; tubes for fluid cooling; bands of air cooling; band bases made of aluminum sheets by laser cutting with the thickness of 1 mm. A thermoelectric radiator was assembled of the prefabricated elements. Firstly, using fastening elements, the tanks and the cross-members were joined between themselves, which formed the frame of thermoelectric radiator providing the required rigidity of the design. For the sake of convenience, the tanks were equipped with detachable lids via which all tubes for fluid circulation were installed. After assembling, the tubes and the tanks were sealed. The thermoelectric generator modules were installed in the tubes. In order to improve heat transfer, both sides of the modules were coated with hot binder characterized by heat transferring and adhesive properties. As mentioned above, the undulated band was joined with the bases by soldering, the resulted sandwiches were installed into the thermoelectric radiator. The fabricated thermoelectric cooling radiator for internal combustion engine is illustrated in Figure 5. Figure 5 Thermoelectric cooling radiator for internal combustion engine After fabrication of the thermoelectric radiator the air tightness of joints of its elements was examined, namely: tubes, tanks, and tank lids. Calculated hydraulic resistance of thermoelectric radiator was 1117.36 Pa, thus, in order to check the air tightness, water was supplied under the pressure of 1500 Pa aiming at obtaining of reliable result. The fabricated thermoelectric radiator withstood the preset pressure, then preliminary experiments were performed on engine test stand. http://www.iaeme.com/ijmet/index.asp 673 editor@iaeme.com
Nikolay Anatolyevich Khripach, Viktor Sergeevich Korotkov and Igor Arkadyevich Papkin 5. PRELIMINARY TESTING OF THERMOELECTRIC RADIATOR Preliminary studies were performed according to the procedure used for validation of specifications of thermoelectric radiator for compliance with calculations, such as: electric power of thermoelectric cooling radiator for internal combustion engine; temperature of cooling fluid at input and output to/from thermoelectric radiator; cooling fluid flow rate via thermoelectric radiator; cooling air flow rate via thermoelectric radiator; aerodynamic resistance of thermoelectric radiator; hydraulic resistance of thermoelectric radiator. The obtained specifications of thermoelectric radiator as well as their calculated values are summarized in Table 4. Table 4 Calculated parameters and specifications of thermoelectric radiator obtained in experiments # Properties Calculations Measurements 1 Electric power, W 817.7 815.4 2 Cooling fluid temperature at input to thermoelectric radiator, C 99.45 100.2 3 Cooling fluid temperature at output from thermoelectric radiator, C 87.65 87.9 4 Cooling fluid flow rate via thermoelectric radiator, kg/s 1.84 1.85 5 Air flow rate via thermoelectric radiator, kg/s 5.66 5.51 6 Aerodynamic resistance of thermoelectric radiator, Pa 2371.3 2374.8 7 Hydraulic resistance of thermoelectric radiator 1117.36 1118.6 6. CONCLUSION This article discussed step-by-step development of thermoelectric cooling radiator starting from designing, calculations development and fabrication of 3D model. Preliminary tests were performed after fabrication of the model used for development of specifications of thermoelectric radiator, which validated calculations with minor error. Electric power of thermoelectric radiator according to the results of preliminary tests was 815.4 W, aerodynamic resistance of thermoelectric radiator was 2374.8 Pa, deviation from calculations was less than 5%. ACKNOWLEDGMENTS This work was supported by the grant No. 14.577.21.0184 dated October 27, 2015, of the Ministry of Education and Science of the Russian Federation. Unique identifier: RFMEFI57715X0184. REFERENCES [1] Bourhis, G. and Leduc, P. Energy and Exergy Balances for Modern Diesel and Gasoline Engines. Oil & Gas Science and Technology - Rev. IFP, 65(1), 2010, pp. 39-46. http://www.iaeme.com/ijmet/index.asp 674 editor@iaeme.com
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