(Luận văn thạc sĩ) nghiên cứu sự ảnh hưởng của nhiệt độ và lưu lượng đến quá trình bay hơi kênh micro dùng môi chất CO2

BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC SƯ PHẠM KỸ THUẬT THÀNH PHỐ HỒ CHÍ MINH LUẬN VĂN THẠC SĨ CHÂU VĂN KẾT ĐOÀN NGHIÊN CỨU SỰ ẢNH HƯỞNG CỦA NHIỆT ĐỘ VÀ LƯU LƯỢNG ĐẾN QUÁ TRÌNH BAY HƠI KÊNH MICRO DÙNG MÔI CHẤT Co2 NGÀNH: KỸ THUẬT NHIỆT - 60520115 SKC005133 Tp Hồ Chí Minh, tháng 04/2017 BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƢỜNG ĐẠI HỌC SƢ PHẠM KỸ THUẬT THÀNH PHỐ HỒ CHÍ MINH LUẬN VĂN THẠC SĨ CHÂU VĂN KẾT ĐOÀN NGHIÊN CỨU SỰ ẢNH HƢỞNG CỦA NHIỆT ĐỘ VÀ LƢU LƢỢNG ĐẾN QUÁ TRÌNH BAY HƠI KÊNH MICRO DÙNG MƠI CHẤT CO2 NGÀNH: KỸ THUẬT NHIỆT Mà SỐ: 60520115 Hồ Chí Minh, tháng 04/2017 BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƢỜNG ĐẠI HỌC SƢ PHẠM KỸ THUẬT THÀNH PHỐ HỒ CHÍ MINH LUẬN VĂN THẠC SĨ CHÂU VĂN KẾT ĐOÀN NGHIÊN CỨU SỰ ẢNH HƢỞNG CỦA NHIỆT ĐỘ VÀ LƢU LƢỢNG ĐẾN QUÁ TRÌNH BAY HƠI KÊNH MICRO DÙNG MƠI CHẤT CO2 NGÀNH: KỸ THUẬT NHIỆT - 60520115 Hướng dẫn khoa học: PGS.TS ĐẶNG THÀNH TRUNG NCS NGUYỄN TRỌNG HIẾU Tp Hồ Chí Minh, tháng 04/2017 %Ӝ*,È2'Ө&9¬ Ҥ27Ҥ2 TRƯỜNG ĐẠI HỌC SƯ PHẠM KỸ THUẬT THÀNH PHỐ HỒ CHÍ MINH PHIẾU NHẬN XÉT LUẬN 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biện) Tên đề tài luận văn thạc s: 1JKLrQFXVQKKQJFDQKLWYjOXOQJQTXiWUuQKED\KL NrQK0LFURGQJP{LFKW&2 Tờn tỏc Ji: &+ặ89 1.7 2ơ1 MSHV: 1521004 Ngành: WKXұW1KLӋW Khóa: 2015-2016 Định hướng: ӬQJGөQJ Họ tên nJười phản biện: 761JX\ӉQ7KӃ%ҧR Cơ quDn cônJ tác: 9LӋQ3KiWWULӇQ1 QJOѭӧQJ%ӅQYӳQJ,6(' Điện thoại liên hệ: 0906331133 I Ý KIẾN NHẬN XÉT Về hình thức & kết cấu luận văn: /XұQY QGj\67WUDQJWURQJÿySKҫQFKtQKFKLӃP58WUDQJYjSKҫQSKөOөF9WUDQJÿѭӧFFKLDWKjQK5 FKѭѫQJ&KѭѫQJ1WiFJLҧWәQJTXDQYӅWuQKKuQKQJKLrQFӭXWURQJYjQJRjLQѭӟFYӅVӱGөQJP{LFKҩW&22 WURQJKӋWKӕQJOҥQKF QJQKѭWKLӃWEӏWUX\ӅQQKLӋWORҥL0LFURWӯÿyWiFJLҧÿѭDUDOêGRYjQӝLGXQJFKӑQÿӅ WjL/971&KѭѫQJ2WiFJLҧWUuQKEj\OêWKX\ӃWYӅ&22F QJQKѭOêWKX\ӃWFKXQJYӅWUX\ӅQQKLӋW&KѭѫQJ 3WiFJLҧWUuQKEj\YӅWKLӃWNӃP{KuQKWKtQJKLӋPF QJQKѭP{SKӓQJVӕYӟLSKҫQPӅP&2062/ 0XOWLSK\VLFV&KѭѫQJ4WiFJLҧWUuQKEj\YjWKҧROXұQNӃWTXҧP{SKӓQJVӕÿҥWÿѭӧF&KѭѫQJ5OjNӃWOXұ Q YjNLӃQQJKӏ 1KuQFKXQJKuQKWKӭFYjNӃWFҩXOXұQY QOjKӧSOê Về nội dunJ: 2.1 Nhận xét tính khoa học, rõ ràng, mạch lạc, khúc chiết luận văn 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ĈӅWjLÿҥW\rXFҫXYӅQӝLGXQJPөFWLrXYjSKѭѫQJSKiSQJKLrQFӭX 3KҫQNӃWTXҧP{SKӓQJVӕÿѭӧFWUuQKEj\WѭѫQJÿӕLU}UzQJWURQJOXұQY QWX\QKLrQNӃWTXҧP{KuQKWKӵF QJKLӋPNK{QJWKҩ\ÿѭӧFWUuQKEj\WURQJOXұQY Q" 2.5 Nhận xét đánh giá nội dung & chất lượng LVTN 1ӝLGXQJÿҥW\rXFҫXFӫD/9WKҥFV 7X\QKLrQFҫQWUuQKEj\U}KѫQYӅNӃWTXҧFӫDP{KuQKWKӵFQJKLӋP F QJQKѭVRViQKJLӳDNӃWTXҧWKӵFQJKLӋPYjOêWKX\ӃWP{SKӓQJVӕ 2.6 Nhận xét đánh giá khả ứng dụng, giá trị thực tiễn đề tài 9LӋFQJKLrQFӭXWKLӃWEӏED\KѫLGҥQJPLFUROj[XKѭӟQJQJKLrQFӭXKLӋQQD\WUrQWKӃJLӟLQKҵPÿҥWÿ ѭӧF WKLӃWEӏ7 1QyLFKѭQJYj7%%+QyLULrQJQKӓJӑQYjVӱGөQJKLӋXTXҧQ QJOѭӧQJ7ѭѫQJWӵYLӋFQJKLrQ FӭXP{LFKҩWWKD\WKӃFiFP{LFKҩW&)&+)&+&)&Jk\SKiKӫ\WҫQJR]RQYjJySSKҫQOjPJLDW QJNKt QKjNtQKÿDQJOj[XKѭӟQJWҩW\ӃXFӫDWKӃJLӟLWURQJÿyFy&22QKѭOXұQY QÿDQJQJKLrQFӭX 9uYұ\ÿӅWjLVӁFzêQJK DWKӵFWLӉQYjNKҧQ QJӭQJGөQJFDRPӝWNKLKRjQWҩWNKkX5 ' 2.7 Luận văn cần chỉnh sửa, bổ sung nội dung (thiết sót tồn tại): &ҫQFKӍQKVӱDOҥLFiFKWUtFKGүQFiF7/7.FKRFiFFKѭѫQJ2 3F QJQKѭFRLOҥLSKҭQ7/7 &ҫQWUuQKEj\U}KѫQYӅNӃWTXҧFӫDP{KuQKWKӵFQJKLӋPF QJQKѭVRViQKJLӳDNӃWTXҧWKӵFQJKLӋPYjOê WKX\ӃWP{SKӓQJVӕ 3KҫQNLӃQQJKӏTXjVѫVjLFҫQEәVXQJFөWKӇYjFKLWLӃWKѫQ II CÁC VẤ0Ề CẦN LÀM RÕ (Các câu hỏi giảng viên phản biện) 7UuQKEj\U}KѫQYӅNӃWTXҧFӫDP{KuQKWKӵFQJKLӋPF QJQKѭVRViQKJLӳDNӃWTXҧWKӵFQJKLӋPYjOê WKX\ӃWP{SKӓQJVӕ TT Mục đánh Jiá 7tQKNKRDKӑFU}UjQJPҥFKOҥFNK~FFKLӃWWURQJOXұQY Q iQKJLiYLӋFVӱGөQJKRһFWUtFKGүQNӃWTXҧ1&FӫDQJѭӡLNKiFFy ÿӏQKKLӋQKjQKFӫDSKiSOXұWVӣKӳXWUtWXӋ 0өFWLrXQJKLrQFӭXSKѭѫQJSKiSQJKLrQFӭXVӱGөQJWURQJ/9 7әQJTXDQFӫDÿӅWjL iQKJLiYӅQӝLGXQJ FKҩWOѭӧQJFӫD/971 iQKJLiYӅNKҧQ QJӭQJGөQJJLiWUӏWKӵFWLӉQFӫDÿӅWjL 0žžžžНžžž±ž ž žžžØžžгž0žžžžžž (Giảng viên phản biện ghi rõ ý kiến “Tán thành luận văn” hay “Không tán thành luận văn”) 7iQWKjQKQӃXKӑFYLrQEҧRYӋWKjQKF{QJWUѭӟF+ӝLÿӗQJYjEәVXQJFiFSKҫQFzQWKLӃXQKѭÿm QrX 73+&0QJj\WKiQJQ P 56 Luận Văn Thạc Sĩ GVHD: PGS.TS Đặng Thành Trung [20] Vamadevan and Kraft,‖ Processing effects in aluminum micro-channel tube for brazed R744 heat exchangers‖, Journal of Materials Processing Technology 191 (2007) 30–33 [21] Ducoulombier et al,‖ Carbon dioxide flow boiling in a single microchannel – Part II: Heat transfer‖,Experimental Thermal and Fluid Science 35 (2011) 597– 611 [22] Pamitran et al,‖ Two-phase pressure drop during CO vaporization inhorizontal smooth minichannels‖, International Journal of Refrigeration 31 (200 8) 1375 – 1383 [23] T.L Ngo, Y Kato, K Nikitin, T Ishizuka, Heat transfer and pressure drop correlations of microchannel heat exchangers with S-shaped and zigzag fins for carbon dioxide cycles, Experimental Thermal and Fluid Science, Vol 32, 2007, pp 560-570 [24] S Barlak, S Yapici, O.N Sara, Experimental investigation of pressure drop and friction factor for water flow in microtubes, Int J Therm Sci 50 (2011)361e368 [25] G Kuang , M Ohadi, S Dessiatoun, Semi-Empirical Correlation of Gas Cooling Heat Transfer of Supercritical Carbon Dioxide in Microchannels HVAC&R Research, 14:6, 861-870 [26] Rin Yun et al., ―Numerical analysis on a microchannel evaporator designed for CO2 air-conditioning systems‖, Applied Thermal Engineering 27 (2007) 1320–1326 [27] Nguyễn Trọng Hiếu cộng ―Nghiên cứu đặc tính truyền nhiệt thiết bị bay kênh micro dùng môi chất lạnh CO phương pháp mơ số‖, Hội nghị khí tồn quố 2015, 2015, pp 631-636 [28] tranfer Batan Le et al., ―The effects of microchannel geometry on heat behaviors for two phase flow by numerical simulation‖, Hội nghị khí toàn quố 2015, 2015, pp 627-642 57 Luận Văn Thạc Sĩ GVHD: PGS.TS Đặng Thành Trung [29] Đặng Thành Trung cộng ―Nghiên cứu ảnh hưởng sơ đồ dịng chảy đến q trình bay kênh micro‖, Hội nghị khí tồn quố 2015, 2015, pp 643-648 [30] ASHRAE Handbook—Fundamentals, SI ed Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc ASHRAE 2005 [31] Kandlikar SG, Garimella S, Li DQ, Colin S, King MR, ―Heat transfer and fluid flow in minichannels and microchannels‖, Elsevier Pte Ltd., Singapore (2006) [32] Yunus A Cengel Heat Transfer, Second Edition, 2015 [33] COMSOL Multiphysics version 5.2a, Documentation, May 2015 [34] PGS.TS Nguyễn Đức Lợi ―Kỹ thuật lạnh ứng dụng‖ NXB Giáo Dục 2009 58 Luận Văn Thạc Sĩ GVHD: PGS.TS Đặng Thành Trung PHỤ LỤC 59 American Journal of Engineering Research (AJER) Research Paper Numerical Simulation on Heat Transfer Phenomena in Microchannel Evaporator of A CO2 Air Conditioning System Ketdoan V Chau, Tronghieu Nguyen, and Thanhtrung Dang Department of Thermal Engineering, Hochiminh City University of Technology and Education, Vietnam ABSTRACT: The investigation presented a numerical simulation on heat transfer behaviors in microchannel evaporator of a CO2 air conditioning system The conditions for numerical simulation were applied by the experimental data of a CO2 air conditioning cycle This cycle worked with the cooler pressure of 85 bar, evaporator pressure of 37 bar, and the CO2 flow rate of 5.2 g/s The temperature and pressure in microchannels are uniform; they are suitable with the theory of evaporating process The numerical results are in good agreement with those obtained from experimental data at the same condition In addition, the vapor quality increases from 0.50 to 0.52 when the CO2 refrigerant enters the evaporator at position of 200mm These results are in good agreement with experimental data Keywords – Numerical simulation, CO2 refrigerant, air conditioning system, heat transfer, evaporator I INTRODUCTION The CO2 air conditioning systems using microchannel heat exchangers are very interesting for scientists These topics related to environmental protection and energy efficiency Regarding to CO air conditioning using microchannel evaporator, Asadi et al [1] reviewed heat transfer and pressure drop characteristics of single and two-phase microchannels The review showed that earlier investigations were largely concentrated using experimental methods, while more recent studies (from 2003 to 2013) used numerical simulations for predicting pressure drop and heat transfer coefficients Huang et al [2] also studied non-linear fluid flow and the surface temperature changes inside the microchannel with temperature sensor molecule technology Dang et al [3, 4] studied the microchannel heat transfer of single phase flow with water as the working fluid The results showed that the influence of gravity to the heat transfer and pressure drop characteristics of the microchannel heat exchanger is negligible The difference of heat transfer coefficient between the experimental method and numerical simulation is less than 9% Zhao et al [5] investigated experimentally for the flow of CO and R134a boiling in micro-channels, with the vapor quality is from 0.05 to 0.3 They concluded that the heat transfer coefficient of CO is higher than 200% with R134a Yun et al [6] studied the boiling heat transfer characteristics of CO in the microchannel Results showed that the average heat transfer coefficient of CO is higher than 53% with R134a Gasche [7] investigated experimentally the evaporation of CO inside the tubular microphone channel with a diameter of 0.8mm The average heat transfer coefficient of 9700 W/(m °C) was achieved with a standard error 35% For the vapor quality is low (less 0.25), the slow flow is predominant; whereas, for the vapor quality is high (over 0.50), the annular flow is better Kim and Bullard [8] researched and made a very important result for the evaporation of CO2 refrigerant in the evaporator In this study, the formulas of heat transfer and pressure drops due to friction for microchannel heat exchanger according to the boiling liquid and saturated vapor were mentioned from the balance mass and balances energy equations In the two-phase flows in microchannels, Yu et al [9] studied two-phase gas-liquid flows in microchannels using experiment and lattice Boltzmann simulation The results showed that the two-phase flow has more advantages on the heat transfer and transmission quality than single-phase flow Cheng and Thome [10] researched on the evaporation temperature of CO refrigerant in the micro-channel evaporator With the two-phase flow, CO2 heat transfer coefficient is higher and the pressure drop is lower than that of R236fa Pettersen [11] studied about two-phase flow in microchannel tubes using CO refrigerant The results showed that the heat transfer is much influenced by the vapor quality, especially in volume flow and temperature Thome and Ribatski [12] reviewed two-phase flow and flow boiling heat transfer and pressure drop of CO in macro- and micro-channel The review addresses flow boiling heat transfer experimental studies, macro- and www.ajer.org Page 174 American Journal of Engineering Research (AJER) micro-scale heat transfer prediction methods for CO2 Ducoulombier et al [13] studied carbon dioxide flow boiling in a single microchannel However, this study mentioned about pressure drop only Yun et al [14] carried out two experiments for two-phase flow in microchannel, using R410A refrigerant The hydraulic diameters are 1.36 and 1.44 mm As the saturation temperatures were maintained at 0, and 10 °C, the mass flux was varied from 200 to 400 kg/m 2s, heat flux from 10 to 20 kW/m2 However, this study did not use CO2 as the working fluid Cheng et al [15] researched the updated model of CO flow in the pipe diameters from 0.6 to 10 mm, mass velocities from 50 to 1500 kg /m 2s, heat fluxes from 1.8 to 46 kW/m and saturation temperatures from -28 to 25 0C However, studies in [14, 15] did not mention the complete CO air conditioning cycle using microchannel evaporator Schael and Kind [16] studied the flow patterns and heat transfer characteristics of CO2 in the micro fin tube and compared with smooth pipes The results showed that the thermal conductivity in micro-channel fins tube is significantly higher than the smooth tube From literature reviews above, there are no more numerical studies on heat transfer phenomena in microchannel evaporator of a complete CO2 air conditioning system They did not indicate phase transition of CO2 air conditioning cycle clearly So, it is essential to investigate heat transfer phenomena on microchannel evaporator of a CO2 air conditioning system by using numerical simulation II METHODOLOGY 2.1 Mathematical Model The governing equations describing the microchannel evaporator consist of the continuity equation, momentum equations, and energy equation [3, 15, 16] Fluid properties equations in 3D Cartesian coordinates can be shown by:  (u. )u    pI (T ) u ( u )T  33.(u) (T )( u) I  kI  F   . k p     (u. ) k    k T k C p u  T q Q Q p Qvd q  k T Equations for solid can be shown by: C p u  T q Q Qted q  k T Equations for change phase can be shown by: C p u T q Q Q p Qvd q  k T    (1 ) phase1 phase2   phase1C p , phase1 C p K  k  (1 ) K phase1  m  (1   )    phase 2 phase1 (1 )phase2 Equations for wall:   phase1 phase www.ajer.org Page 175 American Journal of Engineering Research (AJER) u.n  T  (u ) u  u tang u (u.n )n k n 0, Equations for inlet:    k (u.n )d bc dS m  (U  / T ) ,  C3/ k 3/ 2 ref LT Equations for outlet:     pl (T ) u  k n 0, n  nqC p Initial conditions for temperature: T  T0 Initial conditions for heat flux: -n.q=q0 where p is pressure, p0 is pressure at the outlet, u is velocity field, T is temperature, Q is heat transfer rate, Qi is internal heat generation, k is thermal conductivity,  is dynamic viscosity,  is density, u is velocity in the x-direction, v is velocity in the y-direction, w is velocity in the z-direction, q is heat flux, c is specific heat, m is mass flow rate, S is area, k is turbulent kinetic energy, n is normal vector, is turbulent dissipation rate, utang is velocity field, LT is turbulence length scale, lT is Turbulent intensity, Uref is is velocity Reference, K is Average viscous stress, α is thermal diffusivity and θ is phase indicator 2.2 Design and numerical simulation The heat transfer process of this microchannel evaporator is carried out between the CO refrigerant and air Fig shows the dimensions of the evaporator The material for this heat exchanger is aluminum, used as a substrate with the thermal conductivity of 237 W/(mºC), density of 2,700 kg/m 3, and specific heat at constant pressure of 904 J/(kgºC) Fig Dimensions of the microchannel evaporator www.ajer.org Page 176 American Journal of Engineering Research (AJER) The evaporator has six passes (29 channels in the total) Microchannels have a square cross-section with the side of 900m The total heat transfer area of this evaporator is 2.5 m To simplify the numerical simulation for the microchannel evaporator, the sample for simulation is the microchannel section from the inlet of evaporator to the position of 200 mm, as indicated in Fig.1 The dimensions of the microchannel section for simulation are shown in Fig.2 Numerical study of the behavior of the microchannel section of evaporator with 3D was done by using the COMSOL Multiphysics software, version 5.2a The mesh diagram of the microchannel section of evaporator is shown in Fig.3 The nodalization of this model was done by using 244329 mesh elements The solution time of this model was 1505 seconds; the number of degrees of freedom was 287833 (plus 58627 internal DOFs); a relative tolerance was 10-6 Fig Grid mesh diagram of the microchannel section of evaporator III RESULTS AND DISCUSSION The simulation conditions were based on the thermodynamic parameters of the CO2 air conditioning system in Fig The principle of CO2 air conditioning cycle was indicated in [17] Fig The thermodynamic points of the cycle on p-h diagram www.ajer.org Page 177 American Journal of Engineering Research (AJER) Fig Temperature profiles of the microchannel section of the evaporator This cycle operated with the cooler pressure of 85 bar, evaporator pressure of 37 bar (corresponding with the evaporating temperature of 5 C), and the CO2 flow rate of 5.2 g/s The numerical results in Fig show temperature profiles of the microchannel section It is observed that the temperature in microchannels is uniform; it is suitable with the theory of evaporating process The numerical results in Fig are in good agreement with those obtained from experimental data at the same condition (as shown in Fig 6) Fig A picture of microchannel evaporator using thermal camera Fig Pressure profiles of the microchannel section of the evaporator www.ajer.org Page 178 American Journal of Engineering Research (AJER) The pressure profiles of microchannel section of evaporator are shown in Fig The pressure value in microchannels is also uniform with the values around 37 bar; it also is suitable with the theory of evaporating process The numerical results in Fig are in good agreement with those obtained from experimental data in Fig However, in Fig 4, the pressures at the outlets of the evaporator are lower than those obtained from the inlet ones It is due to pressure drop of the heat exchanger and suction force of the compressor In this experiment, the liquid and flash refrigerant had the vapor quality of 0.5; this value was used to simulate The numerical results in Fig show the phase change in the microchannels It is observed that the vapor quality increases from 0.50 to 0.52 when the CO2 refrigerant enters evaporator at position of 200mm These results are in good agreement with experimental data (the experimental data of vapor quality at the position of 200 mm was estimated about 0.53) It is noted that the results in Figs 5-8 have rarely seen in literature reviews These numerical results will be valuable to investigate the evaporation and condensation in microchannels, especially for CO2 refrigerant Fig Phase transition in the microchannels IV CONCLUSION A numerical simulation on heat transfer behaviors in microchannel evaporator of a CO air conditioning system was done The numerical results were compared with experimental data of a CO air conditioning cycle This cycle operated with the cooler pressure of 85 bar, evaporator pressure of 37 bar (corresponding with the evaporating temperature of 5C), and the CO2 flow rate of 5.2 g/s The temperature and pressure in microchannels are uniform; they are suitable with the theory of evaporating process The numerical results of temperature and pressure are in good agreement with those obtained from experimental data at the same condition In this study, the vapor quality increases from 0.50 to 0.52 when the CO refrigerant enters evaporator at position of 200 mm These results are in good agreement with experimental data It is noted that the numerical results have rarely seen in literature reviews ACKNOWLEDGEMENTS The supports of this work by the project No.B2015.22.01 (sponsored by Vietnam Ministry of Education and Training) are deeply appreciated REFERENCES 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[16] Arndt-Erik Schael, Matthias Kind, Flow pattern and heat transfer characteristics during flow boiling of CO in a horizontal micro fin tube and comparison with smooth tube data, International Journal of Refrigeration, 28, 2005, 1186–1195 [17] Tankhuong Nguyen, Tronghieu Nguyen, Thanhtrung Dang, and Minhhung Doan, An experiment on a CO2 air conditioning system with Copper heat exchangers, International Journal of Advanced Engineering, Management and Science, Vol 2, 2016, 2058-2063 www ajer org Page 180 ... tài tập trung nghiên cứu, đánh giá ảnh hưởng nhiệt độ lưu lượng đến trình bay kênh micro sử dụng môi chất CO tiến hành thay đổi điều kiện nhiệt độ CO đầu vào lưu lượng CO2 kênh micro phương pháp... Comsol 5.2a Từ đó, nghiên cứu ảnh hưởng nhiệt độ lưu lượng đến trình bay dùng mơi chất CO2 để tìm giá trị nhiệt độ lưu lượng tối ưu cho hiệu suất trao đổi nhiệt thiết bị bay kênh micro 1.3.2 Mong... DỤC VÀ ĐÀO TẠO TRƢỜNG ĐẠI HỌC SƢ PHẠM KỸ THUẬT THÀNH PHỐ HỒ CHÍ MINH LUẬN VĂN THẠC SĨ CHÂU VĂN KẾT ĐOÀN NGHIÊN CỨU SỰ ẢNH HƢỞNG CỦA NHIỆT ĐỘ VÀ LƢU LƢỢNG ĐẾN QUÁ TRÌNH BAY HƠI KÊNH MICRO DÙNG MÔI