- Email: [email protected]
Influence of cooling gallery structure on the flow patterns of two-phase flow and heat transfer characteristics
International Communications in Heat and Mass Transfer 110 (2020) 104407
Contents lists available at ScienceDirect
International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt
Influence of cooling gallery structure on the flow patterns of two-phase flow and heat transfer characteristics
T
⁎
Deng Lijun, Zhang Jian , Hao Guannan College of Electromechanical Engineering, Binzhou University, Binzhou 256600, Shandong, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Cooling gallery Visualization test Numerical simulation Area coverage Heat transfer coefficient
In research of the accurate relation between two-phase flow pattern and heat transfer characteristics in distinct cooling gallery structures, a dynamic transient visualization test bench was established recording flow of fluid real-time. Meanwhile, multiphase flow model and dynamic mesh were also employed to carry out simulation calculation concerning the dynamic characteristics of two-phase flow and heat transfer characteristics. Compared with the experimental results, the calculation results were extremely close to the actual state. It can be clearly seen that “liquid slug” of engine oil in Kidney shaped cooling gallery emerged mostly during upstroke and the half of downstroke when crankshaft angle was roughly at 90°and 270° while that in water droplet shaped cooling gallery emerged mostly near the entry and exit of engine oil during downstroke of piston. However, liquid slug of engine oil in ellipse shaped cooling gallery appeared in more locations relatively.
1. Introduction High temperature gas transfers heat with the top surface of piston by convection and radiation leading to the increase of thermal load of piston. Cooling gallery is an effective structure in heat transfer enhancement and plays a key role in the process of reducing thermal load of piston head [1,2]. It has been revealed that 50% of heat could be taken away by coolant flowing through oil chamber designed with an appropriate structure [3]. Recent years, domestic and overseas scholars have made large-scale research on structure of cooling gallery and obtained the impacts of distinct structures resulting in distribution of piston temperature field [4–11]. For instance, TAN Jiansong [12] proposed that shortening distance between cooling gallery and the top surface of piston could reduce temperature of piston head after establishing a heat transfer model between piston and its surrounding environment based on finite element method. DENG Jun [11] carried out simulations on ellipse shaped cooling gallery of a specific type of piston, considering influence of oil injection speed, and found that temperature of piston was affected primarily by bottom temperature of combustion chamber. It was also demonstrated that improving oil injection speed as well as moving up cooling gallery axially by 2 mm could increase the amount of heat exchange. In addition, YUAN Yanpeng [13] defined thermal boundary conditions in finite element analysis on the basis of performance calculation. Further more, in the study of cooling effect influenced by
⁎
Corresponding author. E-mail address: [email protected] (Z. Jian).
https://doi.org/10.1016/j.icheatmasstransfer.2019.104407
0735-1933/ © 2019 Published by Elsevier Ltd.
different locations of ellipse shaped gallery, results showed that axial locations had a more significant impact on temperature of piston, especially in reducing temperature of the head as well as the first ring groove of piston; by contrast, piston temperature field was much less affected by radial locations. In terms of study on water droplet shaped cooling gallery, LU Caiqin [14] compared two different cooling gallery locations and found that temperature of the first ring groove could be effectively cut down if cooling gallery was risen up axially. A further study was made by FENG Yaonan [15] and results indicated that moving up location of cooling gallery by 1 mm–4 mm was an effective approach in optimizing the distribution of heat flux in face of high temperature phenomenon in the first ring groove of piston. All previous studies above become the basis of following research in identifying oscillating flow characteristics of coolant and the most wide-used structures of cooling gallery at present are in shapes of kidnap, ellipse and water droplet. The formation and transition of two-phase flow patterns is an important factor affecting flow and the heat transfer [16]. Several factors influencing the heat transfer performance, such as the movement conditions of the air-oil two-phase flow inside the gallery, the instantaneous oil distributions, the relative oil velocity, the instantaneous acceleration and the velocity of the piston, the radial displacement of the secondary motion were investigated by Deng Xiwen [17,18]. For two-phase flow, Wang Jing's team [19–21]studied the dynamic flow characteristics and the transition mechanism of the flow pattern in
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
detail, based on the theories of dynamic fluctuation and system identification and technologies of data processing and data acquisition. Subsequently, Jizu Lv and Peng Wang [22–24]simplified the model, taking piston cooling gallery as the research object, and used the highspeed camera to capture the flow pattern when the crank angle varied. The effects of oscillation frequency, gas content and two-phase distribution on the turbulent flow characteristics and heat transfer mechanism were discussed. The different combinations of gas-liquid two-phase flow result in different flow patterns which is one of the most important flowing parameters in two-phase flow, and there are significant differences for flow characteristic and heat transfer in different flow patterns. In our previous investigations [25], a prediction model of convection heat transfer coefficient in oil cooling gallery was established, taking into consideration of several factors such as the structure of oil cooling gallery, physical properties of two-phase flow and characteristics of local flow in the cooling gallery under different piston diameters and engine speeds. In order to reveal various factors contributing to flow pattern of coolant as well as corresponding transformation mechanism, a dynamic transient visualization test bench was established recording real-time the flow of fluid. And test was launched only in the case of idling engine in restriction of experimental conditions. Two phase flow and heat transfer simulation of cooling gallery under various complex conditions could be carried out by using Computational Fluid Dynamics (CFD) software which seems to be currently considered as a central method of study. In this paper, dynamic and heat transfer characteristics of two phase flow in different cooling gallery structures under high engine speed were simulated and studied by using multiphase flow model and dynamic mesh technique of CFD. Besides, oil coverage, oil filling rate and variation law of heat transfer coefficient with crankshaft angle were also discussed providing the basis for the optimization of cooling gallery of piston in following research.
Fig. 1. Different section shapes of cooling gallery.
Fig. 2. The dynamic transient visualization test bench.
transparent cooling gallery, drive motor, control panel and hydraulic station(control system of engine oil circulation) as its main components. (as shown in Fig. 2). An adjustable block capable of moving in plane, fixed with injector connected with hydraulic station by pipelines, was installed on workbench. Moving block could enable both axis of injector and oil passage to keep in a line facilitating injection of coolant into oil passage. Alloy cast iron sleeve was positioned above workbench in the interior of which piston was placed. The crankshaft was fixed on the output shaft of the drive motor and link rod was fixed on the crankshaft driving piston to achieve reciprocating motion. A transparent sleeve could be found under the alloy cast iron sleeve and cooling gallery was placed inside connected to the piston by a fixed circular plate as well as a threaded rod. In addition, transparent sleeve and transparent cooling gallery were both made of visual materials in the test which enabled the observation of flowing of coolant during reciprocating motion therefore flow patterns of fluid in cooling gallery could be easily recorded and analyzed.
2. Research object The flow of gas-liquid two-phase flow in cooling gallery is supposed to be the type of small diameter flow thus compared with large diameter flow, flow patterns and conversion characteristics of two-phase flow in small diameter are likely to be more complicated. This paper carried out experimental study and numerical simulation for actual pipe of cooling gallery on the basis of previous study of horizontal “small pipe” flow and the simulation of cooling gallery, taking influence of different section shapes into account. Parameters of cooling gallery are indicated in the Table 1 below, including the distribution diagram of two-phase flow and the variation law of heat transfer coefficient in different locations during reciprocating motion of piston. Different section shapes of cooling gallery are also provided in Fig. 1. 3. Test device and experiment process 3.1. Test device
3.2. Experiment process
A dynamic transient visualization test bench was established with workbench, alloy cast iron sleeve, piston, transparent glass enclosure,
The process of test was performed as follows: (1)Install piston tooling and make sure that distance between entry of engine oil in cooling gallery and injector was exactly the same as the position of piston as it reached bottom dead center(BDC); (2)Adjust to ensure axis of injector and oil passage be in a line so as to reduce the error introduced probably by test system; (3)Start cooling system preventing high temperature of oil and ensure injection system be always in normal operation; (4)Start the hydraulic station and preheat the engine, and adjust oil injection pressure through the control panel; (5)Start the drive motor and regulate the speed to 600 r/min; (6)Test cooling galleries with different section shapes and record the variation of flow pattern by a camera.
Table 1 The parameters of cooling gallery. Items
Parameters
section shapes of cooling gallery
Kidney shape
Ellipse shape
Water droplet shape
height of a ring cavity /mm Sectional area of a ring cavity /mm2
18.0 194
18.0 197
18.0 185
2
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
In the equations, Gk is the production phase of turbulent kinetic energy caused by mean velocity gradient while Gω is the produced phase of ω. Γk and Γω are the effective diffusion coefficients of k and ω correspondingly while Yk and Yω are the turbulent dissipative phases of k and ω respectively. Besides, Dω represents the orthogonal diffusion term and both Sk and Sω are self source phases. Turbulent kinetic energies of k and ω are calculated separately by Eqs. (3) and (4).
3 (u⋅I )2 2
k=
1
ω=
k
1
Cμ
(3)
2
4l
(4)
In the equations, u is the average velocity; I is turbulence intensity; Cμ is the empirical constant and equals to 0.09 by default. 4.2. Control equation Due to the fuel injection rate and characteristics of piston movement, not only engine oil but also air existed simultaneously in the cooling gallery. Then some of engine oil occupied the space where the air is in the ring cavity. Several assumptions were proposed as follows: oil and air in the entry of cooling gallery flowed parallel; there was sufficient interphase drag forces between two-phase flow in order to avoid the occurrence of fusion; and the heat transfer between the two phases of air and oil was also ignored. In this condition, the governing equations of flow and heat transfer for cooling oil, air and internal surface were obtained as follows. component equation.
Fig. 3. The procedure of analysis.
4. Numerical simulation
∂αoil ∂α + ui oil = 0 ∂t ∂x i
Considering initial conditions and boundary conditions of the flow and heat transfer of the coolant, heat transfer hypothesis were proposed by using Computational Fluid Dynamics (CFD) software FLUENT. Without consideration of factors such as piston secondary motion and in-homogeneous properties, a governing equation based on two-phase flow oscillation characteristics was established, including process differential equations, continuity equations, momentum differential equations and energy differential equations. Combined with the Levelset+VOF model(coupling model of Level set and VOF)and turbulence model, transient numerical analysis was carried out and heat transfer characteristics of coolant was then determined. The flow-process diagram in Fig. 3 illustrates the procedure of analysis.
equation of continuity.
∂ρuj ∂ρui =0 + ∂y ∂x
∂p ∂ ⎛ ∂ui ∂ ∂ ∂ui ⎞ + μ⎜ + ρui + ρui uj = − ⎟ + ρgi + Fi ∂x i ∂x i ⎝ ∂x i ∂t ∂x i ∂x j ⎠
∂ ∂ ∂ ⎛ ∂ω ⎞ (ρω) + (ρωui ) = ⎜Γω ⎟ + Gω − Yω + Dω + Sω ∂t ∂x i ∂x j ⎝ ∂x j ⎠
(2)
(7)
In the entire solving domain,all momentum equations share the velocity field between phases. It can be seen that the momentum equation lies on volume fraction expressed by attributes ρ and μ at all phases. energy equation.
∂ ∂ ∂ ∂T ρE + ui (ρE + p) = k ∂t ∂x i ∂x i ∂x i
According to the results of studies obtained in references [26–28], the accuracy of predicting oscillation cooling effect with the application of a SST k-ω turbulence model is much higher than that of a k-epsilon turbulence model. Therefore, the SST k-ω turbulence model was employed in the simulation. The main idea was to capture the flow of viscous sublayer by making full use of the robustness of k-ω model near wall. However, k-epsilon model was applied in the main flow in the aim of avoiding the disadvantage of k-ω model being too sensitive to turbulence parameters near the entry. Indeed, SST k-ω is a two equation model combining k-ω model with k-epsilon model expressed in Eqs. (1) and (2).
(1)
(6)
momentum equation.
4.1. Turbulence model
∂ ∂ ∂ ⎛ ∂k ⎞ ∼ (ρk ) + (ρkui ) = ⎜Γk ⎟ + Gk − Yk + Sk ∂t ∂x i ∂x j ⎝ ∂x j ⎠
(5)
(8)
In the control equations above, t is time; u is speed, i = x,y,z; ɑ represents volume fraction of phase; ρ and μ are density and dynamic viscosity coefficient of fluid respectively and both are determined by the volume fraction in each control unit; g is gravitational acceleration; Fi is body force; E and T could be defined as mean mass variables. 4.3. Analysis of mesh accuracy In this paper, FLUENT is employed to solve the problem of threedimensional transient flow.The density of mesh is adjusted by changing the mesh size in the way of which the dynamic grid size is assigned to 0.5, 1.0, and 1.5 ratio of surrounding grid size. Fig. 4 illustrates the effect of grid on the flow of cooling gallery Qout. It can be seen that the deviations between numerical results and test data concerning different ratios all drop in an appropriate range of 10% which is acceptable in industrial applications. Results show that the mesh refining affects the 3
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
FA =
Soil × 100% S
(11)
In the formula, Soil is the effective erosion area of oil to the inner wall of cooling gallery; S is the internal surface area of cooling gallery. 5. Results and discussions 5.1. Comparison of numerical results with experimental results The numerical simulation of the two-phase flow in cooling gallery under an engine speed of 600 r/min was performed. Results are compared with the visualization test, selecting the flow pattern of the key position, such as the top dead centre (TDC) during the operation of the piston, and are shown in Table 2. The comparative results show a good agreement between the numerical results with the flow pattern obtained from the visualization test. Therefore, the numerical method is verified to be reliable and accurate to simulate the two-phase flow process of cooling gallery. Fig. 4. Effect of dynamic mesh refinement on the outlet flow of cooling gallery.
5.2. Influence of cooling gallery structure on characteristics of flow
accuracy of computational results. When the ratio between dynamic mesh size and surrounding mesh size a varies in the range of 0.5–1.0, a higher accuracy can be obtained. As a result, the ratio a = 1.0 is selected hence the dynamic mesh size is 2 mm for its moderate computation time and relatively high accuracy.
Different structures of cooling gallery result in different section areas which enable the filling rate of cooling gallery to vary under the same working conditions as well as injection conditions. For reducing or eliminating the influence of filling rate, engine was tested at the speed of 600 r/min with a fixed static filling rate and flow patterns were then observed in different structures of cooling gallery. Table 3 provides the flow variation of two phase flow in cooling gallery with different cross section shapes. Some central results were obtained in comparison of the test results. Firstly, It was obvious in kidney shaped cooling gallery that oil on the right side hit the top of the oil chamber earlier during upstroke in the majority of circulations. By contrast, oil on the left side hit the bottom of the oil chamber earlier during downstroke. Therefore, the movement of oil could be considered as a reverse circulation in a plane looking from the front and exterior. Besides, oil showed an obvious wavy shape at the top of the oil chamber while different circulations at the bottom showed different states. Moreover, the liquid slug of engine oil emerged mostly when crank angle was roughly at 90°and 270°. Secondly, the liquid slug of engine oil in ellipse shaped cooling gallery appeared in more locations relatively and did not occur when the BDC and TDC were reversed. The moment of reaching at the TDC, all the oil was accumulated at the top of the oil chamber and presented an obvious and more regular wavy shape. Thirdly, for water droplet shaped cooling gallery, the liquid slug of engine oil emerged mostly during down stroke of piston. And oil close to the entry or exit of cooling gallery moved downward thus formed liquid slug in most of circulations. Meanwhile, a relatively large blank was formed in the middle. In addition, section areas of kidney shaped and ellipse shaped cooling galleries were more large and the oscillation of oil was more severe at BDC. Therefore, the coverage area of each location was more considerable and the amplitude of the wavy formed was comparatively large.
4.4. Prediction of enhanced heat transfer criteria Through the experimental research and analysis of two-phase flow in cooling gallery, it can be seen that the heat transfer enhancement is carried out by the continuous erosion of the inner wall of the oil chamber during piston motion. Thus the erosion strength of oil to wall was considered as the criterion of heat transfer. In this way, calculation of the sheer stresses of the inner wall and medium in oil chamber demonstrated that the shear stresses of the wall and the liquid medium in cooling gallery can effectively represent the erosion force of the oil on the inner wall. Besides, the speed of liquid phase (engine oil) during piston movement makes crucial contributions to the erosion strength as well. Refer to WANG Peng [29]in determining the criteria for the heat transfer of air-water two phase flow under reciprocating oscillation conditions and Eq. (9), the heat transfer of the gas-liquid (oil-air) two phase flow could be directly reflected by the shear stress between the wall and the liquid medium in cooling gallery thus the criterion is defined as in Eq. (10).
F = Fτ
(9)
The shear stress between the wall and the liquid medium in cooling gallery could also be expressed in following expression.
τ=μ
dV dH
(10)
where，μis dynamic viscosity coefficient of fluid； dV is velocity gradH dient。. In Eq. (10), the shear stresses of wall and liquid phase are defined as the shear stresses per unit area and the overall sheer force of liquid phase and wall of cooling gallery depends on the contact area between the oil and the wall of oil chamber. Therefore, the erosion area of oil to wall is another crucial factor of heat transfer enhancement. Precisely, the erosion area of the oil to the wall in cooling gallery varies with crankshaft angle and coverage area is then proposed and expressed in formula (11). The ratio of the effective erosion area of oil to the inner wall and the internal surface area of cooling gallery corresponding to the related crankshaft angle is showed in this formula.
5.3. Influence of cooling gallery structure on the heat transfer characteristics The cooling gallery was firstly divided into different sections as shown in Fig. 5. Then the surface temperature of inner wall of oil chamber in each section was set up according to the average temperature estimated by actual temperature. Fig. 6 showed the variation of both oil distribution in cooling gallery and wall heat transfer coefficient with different crankshaft angles in three section shapes. According to the chart, the area coverage of kidney shaped and ellipse shaped cooling galleries were more coherent compared with that of water droplet shaped cooling gallery. To be more exact, the oil distribution flowing through water droplet shaped cooling 4
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
Table 2 Comparison of numerical simulation results and test results of flow pattern in cooling gallery. Crank angle
30°
90°
TDC
270°
Visualization test results
umerical simulation results
Crank angle Visualization test results
Numerical simulation results
It can be seen from Fig. 6(a) that the wall coverage of the oil in the kidney and water droplet shape sections changes relatively stably, which changes obviously in the ellipse section during the commutation, and it can be seen that the dynamic erosion of the oil in the ellipse section cooling gallery is more severe. According to the principle of oscillating enhanced heat transfer, it can be concluded that the heat transfer in the ellipse section cooling gallery is higher. In addition, the method of relative analysis is mentioned in the literature [18]. According to the change of heat transfer coefficient of the oil chamber wall, the influence of different influencing factors on heat transfer can be explored. In order to analyze the influence of different cross-sectional shapes, the wall heat transfer coefficient when different cross-sectional shapes in Fig. 6(b) are extracted, Table 4 can be obtained. It can be seen from the table that the minimum and average values of the heat transfer coefficient inner wall of the ellipse cooling gallery are the largest, the heat transfer coefficient changes little, and the heat transfer effect is better. From the change of the heat transfer coefficient of the bottom of cooling gallery, the minimum and average values of the heat transfer coefficient of the ellipse cooling gallery are
gallery was largely affected by considerable variation on both the top and the internal and external of oil chamber, especially at the BDC and TDC. At these locations, erosion positions varies largely with different section shapes, affected by local structure size, contributing to the impact on heat transfer. Combined with experimental results, on the one hand, it was demonstrated that structure of cooling gallery had an impact on the flow of two-phase flow in condition of the same static filling rate but had an faint influence on wall coverage and on overall heat transfer effect. Further more, it was confirmed that the variation law of heat transfer coefficient on up wall of cooling gallery differed, resulted from the structure at reversal of BDC and TDC, which matched properly with the wall coverage variation of oil in cooling gallery. On the other hand, the structure of down wall of cooling gallery changed little thus the variation of heat transfer coefficient in different crankshaft angles was coherent as a whole. Overall, the heat transfer coefficient variation of internal and external wall of cooling gallery illustrated clearly the change of flow patterns of two-phase flow in different structures. It also showed that flow patterns of two-phase flow was extremely essential for heat transfer in cooling gallery.
5
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
Table 3 Flow patterns of two-phase flow in different oil cooling gallery section shapes.
the largest, and the variation range is large, which can be concluded that the heat transfer effect of the bottom is better, compared with the other two sections. From the change of the heat transfer coefficient of the outer wall and the top wall, the minimum and average values of the heat transfer coefficient of the kidney cooling gallery are the largest, the heat transfer coefficient changes little, and the heat transfer effect is better. It can be seen from the data in the table that the water droplet shape cooling gallery does not show its heat exchange advantage on any side. The variations of the wall coverage of the oil in the cooling gallery and the heat transfer coefficient of the oil chamber wall surface are analyzed. It can be seen that the ellipse cooling gallery has a good heat exchange effect. The above analysis also shows that the ellipse cooling gallery is beneficial to improve the structural reliability of the piston combustion bowl and the undercrown, and the kidney cooling gallery is more beneficial to improve the structural reliability of the piston top surface and the ring groove. Therefore, it is still necessary to optimize the cross-sectional shape of the cooling gallery to enhance the heat exchange effect and improve the reliability of piston. Fig. 5. The schematic diagram of the area zones of cooling gallery.
6
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
Fig. 6. The variation of both oil distribution in cooling gallery and wall heat transfer coefficient with different crankshaft angles in three section shapes.
6. Conclusions
(3) In water droplet shaped cooling gallery, oil close to the entry or exit of cooling gallery moved downward thus formed liquid slug in most of circulations resulting in the formation of a large “gas slug” in the middle.
(1) Engine oil in kidney shaped cooling gallery showed an obvious wavy shape at the top of the oil chamber while different circulations at the bottom showed different states. Besides, the liquid slug emerged mostly during upstroke and the half of down stroke near crankshaft angle. (2) The liquid slug of engine oil in ellipse shaped cooling gallery appeared in more locations relatively. The moment of reaching at the TDC, all the oil was accumulated at the top of the oil chamber and presented in a regular wavy shape.
Acknowledgement This project is supported by National Natural Science Foundation of China (Grant No. 51705028); Scientific Research Project of Colleges and Universities of Shandong Province (Grant No. J17KA025), Research Funding of Binzhou University(Grant No. BZXYZZJJ201703), PhD 7
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
Water droplet shape 2949 637 2313 1779
Research Funding of Binzhou University (Grant No. 2018Y12). References
Kidney shape 2949 660 2289 1870 Kidney shape 3071 581 2490 1661 Kidney shape 2894 889 2006 1918 Water droplet shape 3747 152 3595 1518 Kidney shape 3663 313 3350 1703 section shapes Max. value Min. value Amplitude Mean value
Ellipse shape 3734 208 3526 1519 Top wall Statistical result
Table 4 Comparison of heat transfer coefficient of each region of gallery.
Outer wall
Ellipse shape 2639 757 1882 1792
Water droplet shape 2903 716 2188 1582
Inner wall
Ellipse shape 2788 867 1921 1786
Water droplet shape 2801 549 2252 1533
Bottom wall
Ellipse shape 3180 667 2513 1901
[1] D.C. Luff, T. Law, P.J. Shayler, et al., The effect of piston cooling jets on diesel engine piston temperatures, emissions and fuel consumption [J], SAE Int. J. Engines 5 (3) (2012) 1300–1311. [2] H. Zhang, Z. Lin, J. Xing, Temperature field analysis to gasoline engine piston and structure optimization[J], J. Theore. Appl. Inf. Technol. 48 (2) (2013). [3] G. Mahle, Pistons and Engine Testing[M], Vieweg Teubner Verlag (2011). [4] N. Thiel, H.J. Weimar, H. Kamp, et al., Advanced piston cooling efficiency: A comparison of different new gallery cooling concepts[R], SAE Technical Paper, 2007. [5] Y. Wu, Z. Xudong, L. Xiaobin, Research of cooling duct of piston in heavy duty automobile diesel engine[J], Diesel Engine 31 (6) (2009) 31–33. [6] K. Robinson, IC Engine Coolant Heat Transfer Studies[D], University of Bath, 2001. [7] Е.А. Лазарев, М.Л. Перлов, Yuan Jie, Evaluation of the shape and position of the cross section of the cooling oil cavity for the piston of a diesel engine[J], Vehicle Engine 3 (1983) 42–46. [8] L. Chuang, Z. Yi, C. Qiang, Influence upon temperature field distribution by different shape of cooling gallery[J]. Coal mine, Machinery 37 (3) (2016) 82–85. [9] H. Shanshan, Research on the influence factors of the piston structure strength and heat transfer of diesel engine[D], Kunming Uni. Sci. Technol. (2013) 34–43. [10] X. Ma, C. Ma, W. Guo, The structure design of diesel engine piston to meet euro-III emission regulation[J], Inter. Combust. Engine Powerplant 2 (2006) 11–13. [11] Deng Jun, Qian Zuoqin, The Cooling Oil Path Effecting on the heat transfer in Piston [A], China Science and Technology Paper Online, 2011. [12] Jiansong Tan, Xiaoli Yu, High strength engine piston cooling simulation [J], J. China Ordnance. 27 (1) (2006) 97–100. [13] Yuan Yanpeng, Wang Yue, Zhang Weizheng, et al., A Study on the Effect upon the Piston Temperature Field through Changing the Position of the Cooling Gallery [J], Trans. Beijing Inst. Technol. 28 (7) (2008) 585–588. [14] Lv Caiqin, Su Tiexiong, Influence of piston oil cooling gallery position to the piston strength [J], Inter. Combust. Engine. 1 (2009) 4–9. [15] Feng Yaonan, Zhang Yi, Influence of the position of the oscillating oil chamber on the temperature field of the diesel engine [J], Equip. Manuf. Technol. 6 (2009) 11–13. [16] P. Hanafizadeh, A. Hojati, A. Karimi, Experimental investigation of oil–water two phase flow regime in an inclined pipe [J], J. Pet. Sci. Eng. 136 (2015) 12–22. [17] X. Deng, J. Lei, J. Wen, et al., Numerical investigation on the oscillating flow and uneven heat transfer processes of the cooling oil inside a piston gallery[J], Appl. Therm. Eng. 126 (2017). [18] X. Deng, J. Lei, J. Wen, et al., Impact of piston secondary motion on oscillating flow and heat transfer of oil inside piston cooling gallery of diesel engine[J], Trans. Chin. Soc. Agri. Eng. 14 (2017) 93–100. [19] J. Wang, Research on the Dynamic Behavior of Gas-Liquued Two-Phase Flow [M], Shanghai Jiao Tong University press, Shang Hai, 2012. [20] Y.P. Liu, Study on the flow regime transition in horizontal gas-oil flow and the characteristics of gas-liquid interface [D], Shang Hai: Shanghai Jiao Tong University, (2008). [21] R. Kong, S. Kim, S. Bajorek, et al., Effects of pipe size on horizontal two-phase flow: flow regimes, pressure drop, two-phase flow parameters, and drift-flux analysis[J], Exp. Thermal Fluid Sci. 96 (2018) 75–89. [22] J. Lu, P. Wang, M. Bai, J. Li, K. Zeng, Experimental visualization of gas–liquid twophase flow during reciprocating motion [J], Appl. Therm. Eng. 79 (2015) 63–73. [23] P. Wang, J. Lv, M. Bai, K. Zeng, The reciprocating motion characteristics of nanofluid inside the piston cooling gallery [J], Powder Technol. 274 (2015) 402–417. [24] P. Wang, K. Han, S. Yoon, et al., The gas-liquid two-phase flow in reciprocating enclosure with piston cooling gallery application [J], Int. J. Therm. Sci. 129 (2018) 73–82. [25] Z. Jian, D. Lijun, L. Shiying, et al., Steady Heat Transfer Prediction Model for Oil Cooling Gallery in the Piston of Internal Combustion Engine [J], Trans. Csice 36 (2018) 258–266. [26] Z. Hairong, Z. Weizheng, Y. Yanpeng, et al., Comparison of turbulence models for multiphase-flow oscillating heat transfer enhancement[J], Num. Heat Transf. Part B: Fundam. 66 (3) (2014) 268–280. [27] Hairong Zhu, Zhang WeiZheng, Yuan Yanpeng, Comparative study on numerical model of turbulent heat transfer in multiphase flow[J], Vehicle Engine 6 (2014) 8–12. [28] Z. Hairong, Z. WeiZheng, Y. Yanpeng, Study on oscillating cooling effect of Hightlyintensified piston considering turbulence model difference[J], Chin. Inter. Combust. Engine Eng. 37 (2) (2016) 78–82. [29] P. Wang, R. Liang, Y. Yu, et al., The flow and heat transfer characteristics of engine oil inside the piston cooling gallery[J], Appl. Therm. Eng. 115 (2017) 620–629.
8
Contents lists available at ScienceDirect
International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt
Influence of cooling gallery structure on the flow patterns of two-phase flow and heat transfer characteristics
T
⁎
Deng Lijun, Zhang Jian , Hao Guannan College of Electromechanical Engineering, Binzhou University, Binzhou 256600, Shandong, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Cooling gallery Visualization test Numerical simulation Area coverage Heat transfer coefficient
In research of the accurate relation between two-phase flow pattern and heat transfer characteristics in distinct cooling gallery structures, a dynamic transient visualization test bench was established recording flow of fluid real-time. Meanwhile, multiphase flow model and dynamic mesh were also employed to carry out simulation calculation concerning the dynamic characteristics of two-phase flow and heat transfer characteristics. Compared with the experimental results, the calculation results were extremely close to the actual state. It can be clearly seen that “liquid slug” of engine oil in Kidney shaped cooling gallery emerged mostly during upstroke and the half of downstroke when crankshaft angle was roughly at 90°and 270° while that in water droplet shaped cooling gallery emerged mostly near the entry and exit of engine oil during downstroke of piston. However, liquid slug of engine oil in ellipse shaped cooling gallery appeared in more locations relatively.
1. Introduction High temperature gas transfers heat with the top surface of piston by convection and radiation leading to the increase of thermal load of piston. Cooling gallery is an effective structure in heat transfer enhancement and plays a key role in the process of reducing thermal load of piston head [1,2]. It has been revealed that 50% of heat could be taken away by coolant flowing through oil chamber designed with an appropriate structure [3]. Recent years, domestic and overseas scholars have made large-scale research on structure of cooling gallery and obtained the impacts of distinct structures resulting in distribution of piston temperature field [4–11]. For instance, TAN Jiansong [12] proposed that shortening distance between cooling gallery and the top surface of piston could reduce temperature of piston head after establishing a heat transfer model between piston and its surrounding environment based on finite element method. DENG Jun [11] carried out simulations on ellipse shaped cooling gallery of a specific type of piston, considering influence of oil injection speed, and found that temperature of piston was affected primarily by bottom temperature of combustion chamber. It was also demonstrated that improving oil injection speed as well as moving up cooling gallery axially by 2 mm could increase the amount of heat exchange. In addition, YUAN Yanpeng [13] defined thermal boundary conditions in finite element analysis on the basis of performance calculation. Further more, in the study of cooling effect influenced by
⁎
Corresponding author. E-mail address: [email protected] (Z. Jian).
https://doi.org/10.1016/j.icheatmasstransfer.2019.104407
0735-1933/ © 2019 Published by Elsevier Ltd.
different locations of ellipse shaped gallery, results showed that axial locations had a more significant impact on temperature of piston, especially in reducing temperature of the head as well as the first ring groove of piston; by contrast, piston temperature field was much less affected by radial locations. In terms of study on water droplet shaped cooling gallery, LU Caiqin [14] compared two different cooling gallery locations and found that temperature of the first ring groove could be effectively cut down if cooling gallery was risen up axially. A further study was made by FENG Yaonan [15] and results indicated that moving up location of cooling gallery by 1 mm–4 mm was an effective approach in optimizing the distribution of heat flux in face of high temperature phenomenon in the first ring groove of piston. All previous studies above become the basis of following research in identifying oscillating flow characteristics of coolant and the most wide-used structures of cooling gallery at present are in shapes of kidnap, ellipse and water droplet. The formation and transition of two-phase flow patterns is an important factor affecting flow and the heat transfer [16]. Several factors influencing the heat transfer performance, such as the movement conditions of the air-oil two-phase flow inside the gallery, the instantaneous oil distributions, the relative oil velocity, the instantaneous acceleration and the velocity of the piston, the radial displacement of the secondary motion were investigated by Deng Xiwen [17,18]. For two-phase flow, Wang Jing's team [19–21]studied the dynamic flow characteristics and the transition mechanism of the flow pattern in
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
detail, based on the theories of dynamic fluctuation and system identification and technologies of data processing and data acquisition. Subsequently, Jizu Lv and Peng Wang [22–24]simplified the model, taking piston cooling gallery as the research object, and used the highspeed camera to capture the flow pattern when the crank angle varied. The effects of oscillation frequency, gas content and two-phase distribution on the turbulent flow characteristics and heat transfer mechanism were discussed. The different combinations of gas-liquid two-phase flow result in different flow patterns which is one of the most important flowing parameters in two-phase flow, and there are significant differences for flow characteristic and heat transfer in different flow patterns. In our previous investigations [25], a prediction model of convection heat transfer coefficient in oil cooling gallery was established, taking into consideration of several factors such as the structure of oil cooling gallery, physical properties of two-phase flow and characteristics of local flow in the cooling gallery under different piston diameters and engine speeds. In order to reveal various factors contributing to flow pattern of coolant as well as corresponding transformation mechanism, a dynamic transient visualization test bench was established recording real-time the flow of fluid. And test was launched only in the case of idling engine in restriction of experimental conditions. Two phase flow and heat transfer simulation of cooling gallery under various complex conditions could be carried out by using Computational Fluid Dynamics (CFD) software which seems to be currently considered as a central method of study. In this paper, dynamic and heat transfer characteristics of two phase flow in different cooling gallery structures under high engine speed were simulated and studied by using multiphase flow model and dynamic mesh technique of CFD. Besides, oil coverage, oil filling rate and variation law of heat transfer coefficient with crankshaft angle were also discussed providing the basis for the optimization of cooling gallery of piston in following research.
Fig. 1. Different section shapes of cooling gallery.
Fig. 2. The dynamic transient visualization test bench.
transparent cooling gallery, drive motor, control panel and hydraulic station(control system of engine oil circulation) as its main components. (as shown in Fig. 2). An adjustable block capable of moving in plane, fixed with injector connected with hydraulic station by pipelines, was installed on workbench. Moving block could enable both axis of injector and oil passage to keep in a line facilitating injection of coolant into oil passage. Alloy cast iron sleeve was positioned above workbench in the interior of which piston was placed. The crankshaft was fixed on the output shaft of the drive motor and link rod was fixed on the crankshaft driving piston to achieve reciprocating motion. A transparent sleeve could be found under the alloy cast iron sleeve and cooling gallery was placed inside connected to the piston by a fixed circular plate as well as a threaded rod. In addition, transparent sleeve and transparent cooling gallery were both made of visual materials in the test which enabled the observation of flowing of coolant during reciprocating motion therefore flow patterns of fluid in cooling gallery could be easily recorded and analyzed.
2. Research object The flow of gas-liquid two-phase flow in cooling gallery is supposed to be the type of small diameter flow thus compared with large diameter flow, flow patterns and conversion characteristics of two-phase flow in small diameter are likely to be more complicated. This paper carried out experimental study and numerical simulation for actual pipe of cooling gallery on the basis of previous study of horizontal “small pipe” flow and the simulation of cooling gallery, taking influence of different section shapes into account. Parameters of cooling gallery are indicated in the Table 1 below, including the distribution diagram of two-phase flow and the variation law of heat transfer coefficient in different locations during reciprocating motion of piston. Different section shapes of cooling gallery are also provided in Fig. 1. 3. Test device and experiment process 3.1. Test device
3.2. Experiment process
A dynamic transient visualization test bench was established with workbench, alloy cast iron sleeve, piston, transparent glass enclosure,
The process of test was performed as follows: (1)Install piston tooling and make sure that distance between entry of engine oil in cooling gallery and injector was exactly the same as the position of piston as it reached bottom dead center(BDC); (2)Adjust to ensure axis of injector and oil passage be in a line so as to reduce the error introduced probably by test system; (3)Start cooling system preventing high temperature of oil and ensure injection system be always in normal operation; (4)Start the hydraulic station and preheat the engine, and adjust oil injection pressure through the control panel; (5)Start the drive motor and regulate the speed to 600 r/min; (6)Test cooling galleries with different section shapes and record the variation of flow pattern by a camera.
Table 1 The parameters of cooling gallery. Items
Parameters
section shapes of cooling gallery
Kidney shape
Ellipse shape
Water droplet shape
height of a ring cavity /mm Sectional area of a ring cavity /mm2
18.0 194
18.0 197
18.0 185
2
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
In the equations, Gk is the production phase of turbulent kinetic energy caused by mean velocity gradient while Gω is the produced phase of ω. Γk and Γω are the effective diffusion coefficients of k and ω correspondingly while Yk and Yω are the turbulent dissipative phases of k and ω respectively. Besides, Dω represents the orthogonal diffusion term and both Sk and Sω are self source phases. Turbulent kinetic energies of k and ω are calculated separately by Eqs. (3) and (4).
3 (u⋅I )2 2
k=
1
ω=
k
1
Cμ
(3)
2
4l
(4)
In the equations, u is the average velocity; I is turbulence intensity; Cμ is the empirical constant and equals to 0.09 by default. 4.2. Control equation Due to the fuel injection rate and characteristics of piston movement, not only engine oil but also air existed simultaneously in the cooling gallery. Then some of engine oil occupied the space where the air is in the ring cavity. Several assumptions were proposed as follows: oil and air in the entry of cooling gallery flowed parallel; there was sufficient interphase drag forces between two-phase flow in order to avoid the occurrence of fusion; and the heat transfer between the two phases of air and oil was also ignored. In this condition, the governing equations of flow and heat transfer for cooling oil, air and internal surface were obtained as follows. component equation.
Fig. 3. The procedure of analysis.
4. Numerical simulation
∂αoil ∂α + ui oil = 0 ∂t ∂x i
Considering initial conditions and boundary conditions of the flow and heat transfer of the coolant, heat transfer hypothesis were proposed by using Computational Fluid Dynamics (CFD) software FLUENT. Without consideration of factors such as piston secondary motion and in-homogeneous properties, a governing equation based on two-phase flow oscillation characteristics was established, including process differential equations, continuity equations, momentum differential equations and energy differential equations. Combined with the Levelset+VOF model(coupling model of Level set and VOF)and turbulence model, transient numerical analysis was carried out and heat transfer characteristics of coolant was then determined. The flow-process diagram in Fig. 3 illustrates the procedure of analysis.
equation of continuity.
∂ρuj ∂ρui =0 + ∂y ∂x
∂p ∂ ⎛ ∂ui ∂ ∂ ∂ui ⎞ + μ⎜ + ρui + ρui uj = − ⎟ + ρgi + Fi ∂x i ∂x i ⎝ ∂x i ∂t ∂x i ∂x j ⎠
∂ ∂ ∂ ⎛ ∂ω ⎞ (ρω) + (ρωui ) = ⎜Γω ⎟ + Gω − Yω + Dω + Sω ∂t ∂x i ∂x j ⎝ ∂x j ⎠
(2)
(7)
In the entire solving domain,all momentum equations share the velocity field between phases. It can be seen that the momentum equation lies on volume fraction expressed by attributes ρ and μ at all phases. energy equation.
∂ ∂ ∂ ∂T ρE + ui (ρE + p) = k ∂t ∂x i ∂x i ∂x i
According to the results of studies obtained in references [26–28], the accuracy of predicting oscillation cooling effect with the application of a SST k-ω turbulence model is much higher than that of a k-epsilon turbulence model. Therefore, the SST k-ω turbulence model was employed in the simulation. The main idea was to capture the flow of viscous sublayer by making full use of the robustness of k-ω model near wall. However, k-epsilon model was applied in the main flow in the aim of avoiding the disadvantage of k-ω model being too sensitive to turbulence parameters near the entry. Indeed, SST k-ω is a two equation model combining k-ω model with k-epsilon model expressed in Eqs. (1) and (2).
(1)
(6)
momentum equation.
4.1. Turbulence model
∂ ∂ ∂ ⎛ ∂k ⎞ ∼ (ρk ) + (ρkui ) = ⎜Γk ⎟ + Gk − Yk + Sk ∂t ∂x i ∂x j ⎝ ∂x j ⎠
(5)
(8)
In the control equations above, t is time; u is speed, i = x,y,z; ɑ represents volume fraction of phase; ρ and μ are density and dynamic viscosity coefficient of fluid respectively and both are determined by the volume fraction in each control unit; g is gravitational acceleration; Fi is body force; E and T could be defined as mean mass variables. 4.3. Analysis of mesh accuracy In this paper, FLUENT is employed to solve the problem of threedimensional transient flow.The density of mesh is adjusted by changing the mesh size in the way of which the dynamic grid size is assigned to 0.5, 1.0, and 1.5 ratio of surrounding grid size. Fig. 4 illustrates the effect of grid on the flow of cooling gallery Qout. It can be seen that the deviations between numerical results and test data concerning different ratios all drop in an appropriate range of 10% which is acceptable in industrial applications. Results show that the mesh refining affects the 3
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
FA =
Soil × 100% S
(11)
In the formula, Soil is the effective erosion area of oil to the inner wall of cooling gallery; S is the internal surface area of cooling gallery. 5. Results and discussions 5.1. Comparison of numerical results with experimental results The numerical simulation of the two-phase flow in cooling gallery under an engine speed of 600 r/min was performed. Results are compared with the visualization test, selecting the flow pattern of the key position, such as the top dead centre (TDC) during the operation of the piston, and are shown in Table 2. The comparative results show a good agreement between the numerical results with the flow pattern obtained from the visualization test. Therefore, the numerical method is verified to be reliable and accurate to simulate the two-phase flow process of cooling gallery. Fig. 4. Effect of dynamic mesh refinement on the outlet flow of cooling gallery.
5.2. Influence of cooling gallery structure on characteristics of flow
accuracy of computational results. When the ratio between dynamic mesh size and surrounding mesh size a varies in the range of 0.5–1.0, a higher accuracy can be obtained. As a result, the ratio a = 1.0 is selected hence the dynamic mesh size is 2 mm for its moderate computation time and relatively high accuracy.
Different structures of cooling gallery result in different section areas which enable the filling rate of cooling gallery to vary under the same working conditions as well as injection conditions. For reducing or eliminating the influence of filling rate, engine was tested at the speed of 600 r/min with a fixed static filling rate and flow patterns were then observed in different structures of cooling gallery. Table 3 provides the flow variation of two phase flow in cooling gallery with different cross section shapes. Some central results were obtained in comparison of the test results. Firstly, It was obvious in kidney shaped cooling gallery that oil on the right side hit the top of the oil chamber earlier during upstroke in the majority of circulations. By contrast, oil on the left side hit the bottom of the oil chamber earlier during downstroke. Therefore, the movement of oil could be considered as a reverse circulation in a plane looking from the front and exterior. Besides, oil showed an obvious wavy shape at the top of the oil chamber while different circulations at the bottom showed different states. Moreover, the liquid slug of engine oil emerged mostly when crank angle was roughly at 90°and 270°. Secondly, the liquid slug of engine oil in ellipse shaped cooling gallery appeared in more locations relatively and did not occur when the BDC and TDC were reversed. The moment of reaching at the TDC, all the oil was accumulated at the top of the oil chamber and presented an obvious and more regular wavy shape. Thirdly, for water droplet shaped cooling gallery, the liquid slug of engine oil emerged mostly during down stroke of piston. And oil close to the entry or exit of cooling gallery moved downward thus formed liquid slug in most of circulations. Meanwhile, a relatively large blank was formed in the middle. In addition, section areas of kidney shaped and ellipse shaped cooling galleries were more large and the oscillation of oil was more severe at BDC. Therefore, the coverage area of each location was more considerable and the amplitude of the wavy formed was comparatively large.
4.4. Prediction of enhanced heat transfer criteria Through the experimental research and analysis of two-phase flow in cooling gallery, it can be seen that the heat transfer enhancement is carried out by the continuous erosion of the inner wall of the oil chamber during piston motion. Thus the erosion strength of oil to wall was considered as the criterion of heat transfer. In this way, calculation of the sheer stresses of the inner wall and medium in oil chamber demonstrated that the shear stresses of the wall and the liquid medium in cooling gallery can effectively represent the erosion force of the oil on the inner wall. Besides, the speed of liquid phase (engine oil) during piston movement makes crucial contributions to the erosion strength as well. Refer to WANG Peng [29]in determining the criteria for the heat transfer of air-water two phase flow under reciprocating oscillation conditions and Eq. (9), the heat transfer of the gas-liquid (oil-air) two phase flow could be directly reflected by the shear stress between the wall and the liquid medium in cooling gallery thus the criterion is defined as in Eq. (10).
F = Fτ
(9)
The shear stress between the wall and the liquid medium in cooling gallery could also be expressed in following expression.
τ=μ
dV dH
(10)
where，μis dynamic viscosity coefficient of fluid； dV is velocity gradH dient。. In Eq. (10), the shear stresses of wall and liquid phase are defined as the shear stresses per unit area and the overall sheer force of liquid phase and wall of cooling gallery depends on the contact area between the oil and the wall of oil chamber. Therefore, the erosion area of oil to wall is another crucial factor of heat transfer enhancement. Precisely, the erosion area of the oil to the wall in cooling gallery varies with crankshaft angle and coverage area is then proposed and expressed in formula (11). The ratio of the effective erosion area of oil to the inner wall and the internal surface area of cooling gallery corresponding to the related crankshaft angle is showed in this formula.
5.3. Influence of cooling gallery structure on the heat transfer characteristics The cooling gallery was firstly divided into different sections as shown in Fig. 5. Then the surface temperature of inner wall of oil chamber in each section was set up according to the average temperature estimated by actual temperature. Fig. 6 showed the variation of both oil distribution in cooling gallery and wall heat transfer coefficient with different crankshaft angles in three section shapes. According to the chart, the area coverage of kidney shaped and ellipse shaped cooling galleries were more coherent compared with that of water droplet shaped cooling gallery. To be more exact, the oil distribution flowing through water droplet shaped cooling 4
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
Table 2 Comparison of numerical simulation results and test results of flow pattern in cooling gallery. Crank angle
30°
90°
TDC
270°
Visualization test results
umerical simulation results
Crank angle Visualization test results
Numerical simulation results
It can be seen from Fig. 6(a) that the wall coverage of the oil in the kidney and water droplet shape sections changes relatively stably, which changes obviously in the ellipse section during the commutation, and it can be seen that the dynamic erosion of the oil in the ellipse section cooling gallery is more severe. According to the principle of oscillating enhanced heat transfer, it can be concluded that the heat transfer in the ellipse section cooling gallery is higher. In addition, the method of relative analysis is mentioned in the literature [18]. According to the change of heat transfer coefficient of the oil chamber wall, the influence of different influencing factors on heat transfer can be explored. In order to analyze the influence of different cross-sectional shapes, the wall heat transfer coefficient when different cross-sectional shapes in Fig. 6(b) are extracted, Table 4 can be obtained. It can be seen from the table that the minimum and average values of the heat transfer coefficient inner wall of the ellipse cooling gallery are the largest, the heat transfer coefficient changes little, and the heat transfer effect is better. From the change of the heat transfer coefficient of the bottom of cooling gallery, the minimum and average values of the heat transfer coefficient of the ellipse cooling gallery are
gallery was largely affected by considerable variation on both the top and the internal and external of oil chamber, especially at the BDC and TDC. At these locations, erosion positions varies largely with different section shapes, affected by local structure size, contributing to the impact on heat transfer. Combined with experimental results, on the one hand, it was demonstrated that structure of cooling gallery had an impact on the flow of two-phase flow in condition of the same static filling rate but had an faint influence on wall coverage and on overall heat transfer effect. Further more, it was confirmed that the variation law of heat transfer coefficient on up wall of cooling gallery differed, resulted from the structure at reversal of BDC and TDC, which matched properly with the wall coverage variation of oil in cooling gallery. On the other hand, the structure of down wall of cooling gallery changed little thus the variation of heat transfer coefficient in different crankshaft angles was coherent as a whole. Overall, the heat transfer coefficient variation of internal and external wall of cooling gallery illustrated clearly the change of flow patterns of two-phase flow in different structures. It also showed that flow patterns of two-phase flow was extremely essential for heat transfer in cooling gallery.
5
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
Table 3 Flow patterns of two-phase flow in different oil cooling gallery section shapes.
the largest, and the variation range is large, which can be concluded that the heat transfer effect of the bottom is better, compared with the other two sections. From the change of the heat transfer coefficient of the outer wall and the top wall, the minimum and average values of the heat transfer coefficient of the kidney cooling gallery are the largest, the heat transfer coefficient changes little, and the heat transfer effect is better. It can be seen from the data in the table that the water droplet shape cooling gallery does not show its heat exchange advantage on any side. The variations of the wall coverage of the oil in the cooling gallery and the heat transfer coefficient of the oil chamber wall surface are analyzed. It can be seen that the ellipse cooling gallery has a good heat exchange effect. The above analysis also shows that the ellipse cooling gallery is beneficial to improve the structural reliability of the piston combustion bowl and the undercrown, and the kidney cooling gallery is more beneficial to improve the structural reliability of the piston top surface and the ring groove. Therefore, it is still necessary to optimize the cross-sectional shape of the cooling gallery to enhance the heat exchange effect and improve the reliability of piston. Fig. 5. The schematic diagram of the area zones of cooling gallery.
6
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
Fig. 6. The variation of both oil distribution in cooling gallery and wall heat transfer coefficient with different crankshaft angles in three section shapes.
6. Conclusions
(3) In water droplet shaped cooling gallery, oil close to the entry or exit of cooling gallery moved downward thus formed liquid slug in most of circulations resulting in the formation of a large “gas slug” in the middle.
(1) Engine oil in kidney shaped cooling gallery showed an obvious wavy shape at the top of the oil chamber while different circulations at the bottom showed different states. Besides, the liquid slug emerged mostly during upstroke and the half of down stroke near crankshaft angle. (2) The liquid slug of engine oil in ellipse shaped cooling gallery appeared in more locations relatively. The moment of reaching at the TDC, all the oil was accumulated at the top of the oil chamber and presented in a regular wavy shape.
Acknowledgement This project is supported by National Natural Science Foundation of China (Grant No. 51705028); Scientific Research Project of Colleges and Universities of Shandong Province (Grant No. J17KA025), Research Funding of Binzhou University(Grant No. BZXYZZJJ201703), PhD 7
International Communications in Heat and Mass Transfer 110 (2020) 104407
D. Lijun, et al.
Water droplet shape 2949 637 2313 1779
Research Funding of Binzhou University (Grant No. 2018Y12). References
Kidney shape 2949 660 2289 1870 Kidney shape 3071 581 2490 1661 Kidney shape 2894 889 2006 1918 Water droplet shape 3747 152 3595 1518 Kidney shape 3663 313 3350 1703 section shapes Max. value Min. value Amplitude Mean value
Ellipse shape 3734 208 3526 1519 Top wall Statistical result
Table 4 Comparison of heat transfer coefficient of each region of gallery.
Outer wall
Ellipse shape 2639 757 1882 1792
Water droplet shape 2903 716 2188 1582
Inner wall
Ellipse shape 2788 867 1921 1786
Water droplet shape 2801 549 2252 1533
Bottom wall
Ellipse shape 3180 667 2513 1901
[1] D.C. Luff, T. Law, P.J. Shayler, et al., The effect of piston cooling jets on diesel engine piston temperatures, emissions and fuel consumption [J], SAE Int. J. Engines 5 (3) (2012) 1300–1311. [2] H. Zhang, Z. Lin, J. Xing, Temperature field analysis to gasoline engine piston and structure optimization[J], J. Theore. Appl. Inf. Technol. 48 (2) (2013). [3] G. Mahle, Pistons and Engine Testing[M], Vieweg Teubner Verlag (2011). [4] N. Thiel, H.J. Weimar, H. Kamp, et al., Advanced piston cooling efficiency: A comparison of different new gallery cooling concepts[R], SAE Technical Paper, 2007. [5] Y. Wu, Z. Xudong, L. Xiaobin, Research of cooling duct of piston in heavy duty automobile diesel engine[J], Diesel Engine 31 (6) (2009) 31–33. [6] K. Robinson, IC Engine Coolant Heat Transfer Studies[D], University of Bath, 2001. [7] Е.А. Лазарев, М.Л. Перлов, Yuan Jie, Evaluation of the shape and position of the cross section of the cooling oil cavity for the piston of a diesel engine[J], Vehicle Engine 3 (1983) 42–46. [8] L. Chuang, Z. Yi, C. Qiang, Influence upon temperature field distribution by different shape of cooling gallery[J]. Coal mine, Machinery 37 (3) (2016) 82–85. [9] H. Shanshan, Research on the influence factors of the piston structure strength and heat transfer of diesel engine[D], Kunming Uni. Sci. Technol. (2013) 34–43. [10] X. Ma, C. Ma, W. Guo, The structure design of diesel engine piston to meet euro-III emission regulation[J], Inter. Combust. Engine Powerplant 2 (2006) 11–13. [11] Deng Jun, Qian Zuoqin, The Cooling Oil Path Effecting on the heat transfer in Piston [A], China Science and Technology Paper Online, 2011. [12] Jiansong Tan, Xiaoli Yu, High strength engine piston cooling simulation [J], J. China Ordnance. 27 (1) (2006) 97–100. [13] Yuan Yanpeng, Wang Yue, Zhang Weizheng, et al., A Study on the Effect upon the Piston Temperature Field through Changing the Position of the Cooling Gallery [J], Trans. Beijing Inst. Technol. 28 (7) (2008) 585–588. [14] Lv Caiqin, Su Tiexiong, Influence of piston oil cooling gallery position to the piston strength [J], Inter. Combust. Engine. 1 (2009) 4–9. [15] Feng Yaonan, Zhang Yi, Influence of the position of the oscillating oil chamber on the temperature field of the diesel engine [J], Equip. Manuf. Technol. 6 (2009) 11–13. [16] P. Hanafizadeh, A. Hojati, A. Karimi, Experimental investigation of oil–water two phase flow regime in an inclined pipe [J], J. Pet. Sci. Eng. 136 (2015) 12–22. [17] X. Deng, J. Lei, J. Wen, et al., Numerical investigation on the oscillating flow and uneven heat transfer processes of the cooling oil inside a piston gallery[J], Appl. Therm. Eng. 126 (2017). [18] X. Deng, J. Lei, J. Wen, et al., Impact of piston secondary motion on oscillating flow and heat transfer of oil inside piston cooling gallery of diesel engine[J], Trans. Chin. Soc. Agri. Eng. 14 (2017) 93–100. [19] J. Wang, Research on the Dynamic Behavior of Gas-Liquued Two-Phase Flow [M], Shanghai Jiao Tong University press, Shang Hai, 2012. [20] Y.P. Liu, Study on the flow regime transition in horizontal gas-oil flow and the characteristics of gas-liquid interface [D], Shang Hai: Shanghai Jiao Tong University, (2008). [21] R. Kong, S. Kim, S. Bajorek, et al., Effects of pipe size on horizontal two-phase flow: flow regimes, pressure drop, two-phase flow parameters, and drift-flux analysis[J], Exp. Thermal Fluid Sci. 96 (2018) 75–89. [22] J. Lu, P. Wang, M. Bai, J. Li, K. Zeng, Experimental visualization of gas–liquid twophase flow during reciprocating motion [J], Appl. Therm. Eng. 79 (2015) 63–73. [23] P. Wang, J. Lv, M. Bai, K. Zeng, The reciprocating motion characteristics of nanofluid inside the piston cooling gallery [J], Powder Technol. 274 (2015) 402–417. [24] P. Wang, K. Han, S. Yoon, et al., The gas-liquid two-phase flow in reciprocating enclosure with piston cooling gallery application [J], Int. J. Therm. Sci. 129 (2018) 73–82. [25] Z. Jian, D. Lijun, L. Shiying, et al., Steady Heat Transfer Prediction Model for Oil Cooling Gallery in the Piston of Internal Combustion Engine [J], Trans. Csice 36 (2018) 258–266. [26] Z. Hairong, Z. Weizheng, Y. Yanpeng, et al., Comparison of turbulence models for multiphase-flow oscillating heat transfer enhancement[J], Num. Heat Transf. Part B: Fundam. 66 (3) (2014) 268–280. [27] Hairong Zhu, Zhang WeiZheng, Yuan Yanpeng, Comparative study on numerical model of turbulent heat transfer in multiphase flow[J], Vehicle Engine 6 (2014) 8–12. [28] Z. Hairong, Z. WeiZheng, Y. Yanpeng, Study on oscillating cooling effect of Hightlyintensified piston considering turbulence model difference[J], Chin. Inter. Combust. Engine Eng. 37 (2) (2016) 78–82. [29] P. Wang, R. Liang, Y. Yu, et al., The flow and heat transfer characteristics of engine oil inside the piston cooling gallery[J], Appl. Therm. Eng. 115 (2017) 620–629.
8