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Study on the Characteristics of Heat Exchanger for Cold Energy Recovery in LNG Vehicles
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 104 (2016) 487 – 491
CUE2016-Applied Energy Symposium and Forum 2016: Low carbon cities & urban energy systems
Study on the Characteristics of Heat Exchanger for Cold Energy Recovery in LNG Vehicles Fayi Yana,b, *, Wei Yia, Boyan Xub, Ying Luob a Shandong University, Jingshi Road, Jinan 250061, P. R. China Shandong Jianzhu University, Fengming Road , Jinan 250101, P. R. China
b
Abstract LNG (Liquefied Natural Gas) vehicles, which are the transport of disposing of urban pollution, have the advantages of high thermal efficiency and less pollution. Another advantage of LNG vehicles is that the cold energy of the fuel LNG can be recycled for air conditioner. Based on the two fluid model, numerical simulation of the heat transfer characteristics of cold energy recovery heat exchanger in LNG vehicle are carried out. The results can provide a reference for the design of cold energy recovery heat exchanger in LNG vehicle. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-reviewofunder responsibility of of CUE Peer-review under responsibility the scientific committee the Applied Energy Symposium and Forum, CUE2016: Low carbon cities and urban energy systems. Keywords: Numerical simulation; Cold energy recovery; Heat exchanger; LNG vehicle
1. Introduction Nomenclature
U
fluid density
G u
velocity vector
p
pressure
u, v, w velocity component in three directions of x, y, z i
internal energy
* Corresponding author. Tel.: +0086-0531-86361369 E-mail address:[email protected].
1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the Applied Energy Symposium and Forum, CUE2016: Low carbon cities and urban energy systems. doi:10.1016/j.egypro.2016.12.082
488
Fayi Yan et al. / Energy Procedia 104 (2016) 487 – 491
Nowadays, automobile exhaust has become one of the main source of urban pollution. It’s more and more urgent for automobiles to apply new energy resources to replace gasoline and diesel, which increase air pollution seriously. As the fuel compare to gasoline and diesel widely used in modern vehicles, LNG has the advantages of good economy, high safety, clean emission, convenience to fill, etc. Another advantage of LNG vehicles is that the cold energy of the fuel LNG can be recycled for the use of air conditioner in automobiles or refrigerated trucks [1]. The construction of urban LNG bus with cold energy recovery for bus air-conditioning system was studied [2]. In this paper, the characteristics of heat transfer of the cold energy recovery heat exchanger in the LNG bus is studied. The cold energy recovery heat exchanger of LNG vehicle is the key heat exchange equipment in the whole cold energy recovery system. The characteristics of fluid flow and heat transfer in the heat exchanger in LNG vehicle determine the effect of LNG cold energy recovery. Concentric tube heat exchanger is of high heat transfer efficiency, compact structure etc. especially for small flow, high pressure conditions [3]. The spiral concentric tube heat exchanger was applied for cold energy recovery in LNG vehicles [4]. Garcia-valladares [5] and Quadir [6] studied the characteristics of the concentric pipe heat exchangers by numerical simulation. However, the heat transfer for refrigeration in concentric pipe heat exchangers was not concerned. In literature [7], the heat transfer of the refrigeration system in the concentric tube heat exchanger was studied, however, the spiral concentric tube heat exchanger studied in this paper was also not mentioned. In the paper, the numerical method is carried out to simulate the flow and heat transfer characteristics of the spiral concentric tube heat exchanger. The study is aimed to provide the references for the design of cold energy recovery heat exchanger in LNG vehicles. 2. Physical model The structure of the spiral concentric tube heat exchanger in the air conditioning system is shown in Fig.1. (a) and the section shape is shown in Fig.1. (b).
Fig.1.(a) structure of the heat exchanger; (b) section of the heat exchanger
The detailed size and material of the heat exchanger is shown in Table 1. The effective length of the heat exchanger is 8.7 m, and the axis can be simplified to be a spiral. Table 1. Structure of the spiral concentric tube heat exchanger Parameters of the heat exchanger
Internal diameter (mm)
Wall thickness (mm) Material
Outer tube
16
1.5
Cold pressed carbon steel
Inner tube
11
1
Copper
489
Fayi Yan et al. / Energy Procedia 104 (2016) 487 – 491
The fuel LNG enters into the inner tube and the refrigerant enters into the interlayer of the heat exchanger, in which the large temperature difference and countercurrent heat exchange happens. Glycol aqueous solution(HOCH2CH2OH) is a colorless, tasteless, non-electrolytic, non-burning, low-volatile and corrosive liquid. Glycol aqueous solution as the refrigerant is commonly used in the central airconditioning, LNG cold recovery system. In the paper, a certain mixing concentration of water and glycol aqueous solution is chosen to study the heat exchange characteristics of the heat exchanger for cold energy recovery in LNG vehicles. 3. Study method The large temperature difference and countercurrent heat exchange is conducting between the cold media and the low temperature LNG in the cold energy recovery system of the heat exchanger for LNG vehicles. The process of the heat exchange is a typical subcooled flow boiling. The basic form of the double fluid model in the circular tube of the spiral concentric tube heat exchanger is established for the recovery of the cold energy of the LNG. And the closed equation including wall heat flux partitioning model, mathematical model of bubble departure diameter area and bubble diameter in main area of the heat and mass transfer in the two phases of gas and liquid is described. The mathematical models established in the paper are embedded into the CFD software to simulate the process of the flow and the heat transfer of the heat exchanger. The regularities of distribution of gas volume fraction and the heat transfer characteristics of the two phase between the gas and the liquid are obtained. The main results mainly include gas volume fraction distribution and velocity distribution, surface heat transfer coefficient distribution, and the influence of the wall heat flux on heat transfer coefficient. 4. Numerical simulation The fluid flows in the heat exchanger can be considered as compressible Newton fluid. The fundamental mass equation, the momentum equations, and the energy conservation equation are as follows, Mass equation, wU G div ( Uu ) wt
(1)
0
Momentum equations, wU div( U u ) wt
0
w( U u ) div( Uuu ) wt
(2)
wp div( Pgradu) SMx wx
w ( U v) wp div( U vu ) div( Pgradv) SMy wt wy
(3)
(4)
490
Fayi Yan et al. / Energy Procedia 104 (2016) 487 – 491
w( U w) div( U wu ) wt
wp div( Pgradw) SMz wz
(5)
Energy conservation equation, w( Ui) G G div ( Uiu ) pdivu div (kgrad T ) ) S wt
(6)
The temperature distribution of the glycol aqueous solution in the subcooled area of the LNG is shown as Fig. 3. The experimental study was conducted. The experimental layout is shown as Fig. 4.
the heat exchanger
Fig. 3 temperature distribution in the subcooled area
Fig. 4 experimental layout
From the simulation result, the maximum temperature distributes in the outer tube, in which the glycol aqueous solution flows, and the maximum temperature is 298 K. The maximum LNG temperature, which is 147.5 K, distributes in near the inner tube wall. According to the experimental results, the maximum temperature of glycol aqueous solution is 306.7 K in the outer tube and the he maximum temperature of the LNG in the inner tube is 144.2 K. Compared to the simulation results and the experimental results, the margin of error is under 3 per cent. The simulation method in the paper proves to be effective. The further experimental results show that the temperature of the glycol aqueous solution for air supply of the bus air conditioner is 17.1ćˈwhich can meet the refrigeration requirement in the urban bus. From the results of the temperature distributions of Fig. 3, to choose glycol aqueous solution with a volume fraction of 20% and the heat exchange is carried out under the condition of volume flow rate of 7L/min, the thickness of the ice layer in the casing tube heat exchanger is about 1mm. The corresponding ice layer fill rate is about 9%. The results can well meet the design requirements that the glycol aqueous solution will not be frozen to block the fluid flow in the tube because of large temperature difference heat transfer. 5. Conclusions
Fayi Yan et al. / Energy Procedia 104 (2016) 487 – 491
The physical model of the cold energy recovery heat exchanger in LNG vehicles is established. Based on the double fluid model, the numerical simulations of the fluid flow and the heat exchange in the heat exchanger are carried out. From the results obtained in the paper, the cold medium, the fluid flow velocity can meets the requirements of the cold energy recovery. Acknowledgements This work is supported by Natural Science Foundation of Shandong Province (ZR2013EEQ017) and Postdoctoral Science Foundation of Shandong University. References [1] Yannick Zaczek, Nicolas Lambert. Liquefied Natural Gas Terminal Siting in a Highly Seismic Region on the Mexican Pacific Coast[M]// Robert HackRafig AzzamRobert Charlier. Engineering Geology for Infrastructure Planning in Europe: Springer Berlin / Heidelberg; 2004˖641 [2]Yan Fayi, Xu Boyan. The Project Design for Cold Energy Recovery of LNG Vehicle Air-conditioning System[J]. Advanced Material Research, 2013,773(6): 43-46 [3] Ke Rubai. Experiment and analysis of gas heat transfer reinforcement method and theory of casing heat exchanger [J]. Journal of Refrigeration,1989 (4):4-8 [4] Wang Qiang. Study on Automobile Air-conditioning System Applying the Cold Energy of Green Auto Fuel-Liquefied Natural Gas [D]. Xi’an: Xi’an Jiaotong Universityˈ2003 [5] O. Garcia-valladares. Numerical simulation of triple concentric pipe heat exchangers[J]. International Journal of Thermal sciences.2004, 43(10): 979-991. [6] Quadir G. A., Badruddin I., A., Ahmed N. J. Salman. Numerical investigation of the performance of a triple concentric pipe heat exchanger[J]. International Journal of Heat and Mass Transfer. 2014, 75(1): 165–172. [7] Liu Yao, Lin Wensheng. Analysis of carbondioxide anti- sublimation heat transfer in natural gas flow in a tube heat exchanger under the third class boundary condition[J]. CRYOGENICS. 2012,187(3):42-46
Biography Fayi Yan, Doctor of Philosophy, majoring in mechanical engineering, whose main research area is new energy vehicle technology.
491
ScienceDirect Energy Procedia 104 (2016) 487 – 491
CUE2016-Applied Energy Symposium and Forum 2016: Low carbon cities & urban energy systems
Study on the Characteristics of Heat Exchanger for Cold Energy Recovery in LNG Vehicles Fayi Yana,b, *, Wei Yia, Boyan Xub, Ying Luob a Shandong University, Jingshi Road, Jinan 250061, P. R. China Shandong Jianzhu University, Fengming Road , Jinan 250101, P. R. China
b
Abstract LNG (Liquefied Natural Gas) vehicles, which are the transport of disposing of urban pollution, have the advantages of high thermal efficiency and less pollution. Another advantage of LNG vehicles is that the cold energy of the fuel LNG can be recycled for air conditioner. Based on the two fluid model, numerical simulation of the heat transfer characteristics of cold energy recovery heat exchanger in LNG vehicle are carried out. The results can provide a reference for the design of cold energy recovery heat exchanger in LNG vehicle. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-reviewofunder responsibility of of CUE Peer-review under responsibility the scientific committee the Applied Energy Symposium and Forum, CUE2016: Low carbon cities and urban energy systems. Keywords: Numerical simulation; Cold energy recovery; Heat exchanger; LNG vehicle
1. Introduction Nomenclature
U
fluid density
G u
velocity vector
p
pressure
u, v, w velocity component in three directions of x, y, z i
internal energy
* Corresponding author. Tel.: +0086-0531-86361369 E-mail address:[email protected].
1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the Applied Energy Symposium and Forum, CUE2016: Low carbon cities and urban energy systems. doi:10.1016/j.egypro.2016.12.082
488
Fayi Yan et al. / Energy Procedia 104 (2016) 487 – 491
Nowadays, automobile exhaust has become one of the main source of urban pollution. It’s more and more urgent for automobiles to apply new energy resources to replace gasoline and diesel, which increase air pollution seriously. As the fuel compare to gasoline and diesel widely used in modern vehicles, LNG has the advantages of good economy, high safety, clean emission, convenience to fill, etc. Another advantage of LNG vehicles is that the cold energy of the fuel LNG can be recycled for the use of air conditioner in automobiles or refrigerated trucks [1]. The construction of urban LNG bus with cold energy recovery for bus air-conditioning system was studied [2]. In this paper, the characteristics of heat transfer of the cold energy recovery heat exchanger in the LNG bus is studied. The cold energy recovery heat exchanger of LNG vehicle is the key heat exchange equipment in the whole cold energy recovery system. The characteristics of fluid flow and heat transfer in the heat exchanger in LNG vehicle determine the effect of LNG cold energy recovery. Concentric tube heat exchanger is of high heat transfer efficiency, compact structure etc. especially for small flow, high pressure conditions [3]. The spiral concentric tube heat exchanger was applied for cold energy recovery in LNG vehicles [4]. Garcia-valladares [5] and Quadir [6] studied the characteristics of the concentric pipe heat exchangers by numerical simulation. However, the heat transfer for refrigeration in concentric pipe heat exchangers was not concerned. In literature [7], the heat transfer of the refrigeration system in the concentric tube heat exchanger was studied, however, the spiral concentric tube heat exchanger studied in this paper was also not mentioned. In the paper, the numerical method is carried out to simulate the flow and heat transfer characteristics of the spiral concentric tube heat exchanger. The study is aimed to provide the references for the design of cold energy recovery heat exchanger in LNG vehicles. 2. Physical model The structure of the spiral concentric tube heat exchanger in the air conditioning system is shown in Fig.1. (a) and the section shape is shown in Fig.1. (b).
Fig.1.(a) structure of the heat exchanger; (b) section of the heat exchanger
The detailed size and material of the heat exchanger is shown in Table 1. The effective length of the heat exchanger is 8.7 m, and the axis can be simplified to be a spiral. Table 1. Structure of the spiral concentric tube heat exchanger Parameters of the heat exchanger
Internal diameter (mm)
Wall thickness (mm) Material
Outer tube
16
1.5
Cold pressed carbon steel
Inner tube
11
1
Copper
489
Fayi Yan et al. / Energy Procedia 104 (2016) 487 – 491
The fuel LNG enters into the inner tube and the refrigerant enters into the interlayer of the heat exchanger, in which the large temperature difference and countercurrent heat exchange happens. Glycol aqueous solution(HOCH2CH2OH) is a colorless, tasteless, non-electrolytic, non-burning, low-volatile and corrosive liquid. Glycol aqueous solution as the refrigerant is commonly used in the central airconditioning, LNG cold recovery system. In the paper, a certain mixing concentration of water and glycol aqueous solution is chosen to study the heat exchange characteristics of the heat exchanger for cold energy recovery in LNG vehicles. 3. Study method The large temperature difference and countercurrent heat exchange is conducting between the cold media and the low temperature LNG in the cold energy recovery system of the heat exchanger for LNG vehicles. The process of the heat exchange is a typical subcooled flow boiling. The basic form of the double fluid model in the circular tube of the spiral concentric tube heat exchanger is established for the recovery of the cold energy of the LNG. And the closed equation including wall heat flux partitioning model, mathematical model of bubble departure diameter area and bubble diameter in main area of the heat and mass transfer in the two phases of gas and liquid is described. The mathematical models established in the paper are embedded into the CFD software to simulate the process of the flow and the heat transfer of the heat exchanger. The regularities of distribution of gas volume fraction and the heat transfer characteristics of the two phase between the gas and the liquid are obtained. The main results mainly include gas volume fraction distribution and velocity distribution, surface heat transfer coefficient distribution, and the influence of the wall heat flux on heat transfer coefficient. 4. Numerical simulation The fluid flows in the heat exchanger can be considered as compressible Newton fluid. The fundamental mass equation, the momentum equations, and the energy conservation equation are as follows, Mass equation, wU G div ( Uu ) wt
(1)
0
Momentum equations, wU div( U u ) wt
0
w( U u ) div( Uuu ) wt
(2)
wp div( Pgradu) SMx wx
w ( U v) wp div( U vu ) div( Pgradv) SMy wt wy
(3)
(4)
490
Fayi Yan et al. / Energy Procedia 104 (2016) 487 – 491
w( U w) div( U wu ) wt
wp div( Pgradw) SMz wz
(5)
Energy conservation equation, w( Ui) G G div ( Uiu ) pdivu div (kgrad T ) ) S wt
(6)
The temperature distribution of the glycol aqueous solution in the subcooled area of the LNG is shown as Fig. 3. The experimental study was conducted. The experimental layout is shown as Fig. 4.
the heat exchanger
Fig. 3 temperature distribution in the subcooled area
Fig. 4 experimental layout
From the simulation result, the maximum temperature distributes in the outer tube, in which the glycol aqueous solution flows, and the maximum temperature is 298 K. The maximum LNG temperature, which is 147.5 K, distributes in near the inner tube wall. According to the experimental results, the maximum temperature of glycol aqueous solution is 306.7 K in the outer tube and the he maximum temperature of the LNG in the inner tube is 144.2 K. Compared to the simulation results and the experimental results, the margin of error is under 3 per cent. The simulation method in the paper proves to be effective. The further experimental results show that the temperature of the glycol aqueous solution for air supply of the bus air conditioner is 17.1ćˈwhich can meet the refrigeration requirement in the urban bus. From the results of the temperature distributions of Fig. 3, to choose glycol aqueous solution with a volume fraction of 20% and the heat exchange is carried out under the condition of volume flow rate of 7L/min, the thickness of the ice layer in the casing tube heat exchanger is about 1mm. The corresponding ice layer fill rate is about 9%. The results can well meet the design requirements that the glycol aqueous solution will not be frozen to block the fluid flow in the tube because of large temperature difference heat transfer. 5. Conclusions
Fayi Yan et al. / Energy Procedia 104 (2016) 487 – 491
The physical model of the cold energy recovery heat exchanger in LNG vehicles is established. Based on the double fluid model, the numerical simulations of the fluid flow and the heat exchange in the heat exchanger are carried out. From the results obtained in the paper, the cold medium, the fluid flow velocity can meets the requirements of the cold energy recovery. Acknowledgements This work is supported by Natural Science Foundation of Shandong Province (ZR2013EEQ017) and Postdoctoral Science Foundation of Shandong University. References [1] Yannick Zaczek, Nicolas Lambert. Liquefied Natural Gas Terminal Siting in a Highly Seismic Region on the Mexican Pacific Coast[M]// Robert HackRafig AzzamRobert Charlier. Engineering Geology for Infrastructure Planning in Europe: Springer Berlin / Heidelberg; 2004˖641 [2]Yan Fayi, Xu Boyan. The Project Design for Cold Energy Recovery of LNG Vehicle Air-conditioning System[J]. Advanced Material Research, 2013,773(6): 43-46 [3] Ke Rubai. Experiment and analysis of gas heat transfer reinforcement method and theory of casing heat exchanger [J]. Journal of Refrigeration,1989 (4):4-8 [4] Wang Qiang. Study on Automobile Air-conditioning System Applying the Cold Energy of Green Auto Fuel-Liquefied Natural Gas [D]. Xi’an: Xi’an Jiaotong Universityˈ2003 [5] O. Garcia-valladares. Numerical simulation of triple concentric pipe heat exchangers[J]. International Journal of Thermal sciences.2004, 43(10): 979-991. [6] Quadir G. A., Badruddin I., A., Ahmed N. J. Salman. Numerical investigation of the performance of a triple concentric pipe heat exchanger[J]. International Journal of Heat and Mass Transfer. 2014, 75(1): 165–172. [7] Liu Yao, Lin Wensheng. Analysis of carbondioxide anti- sublimation heat transfer in natural gas flow in a tube heat exchanger under the third class boundary condition[J]. CRYOGENICS. 2012,187(3):42-46
Biography Fayi Yan, Doctor of Philosophy, majoring in mechanical engineering, whose main research area is new energy vehicle technology.
491