Tunnel laying is widely used in urban transmission network because of its large transmission current， easy management，maintenance and inspection． Optimizing the layout of multi-loop cables can make full use of its load capacity． In this paper，considering the electromagnetic field，thermal field，fluid field and the cross-bonding grounding mode，a simulation model of magnetic thermal flow and circuit coupling for a seven-circuit high voltage cables in a tunnel was established． The model was verified by infrared temperature measurement． Taking the induced voltage of metal sheath not exceeding the standard value as constraints and the minimizing the highest core temperature of cables as objective function，The phase sequence and position of the cable are optimized jointly based on memetic algorithm． After optimization，the maximum core temperature，sheath circulation loss，average circulation value and induced voltage of the cable decreased by 8. 18% ，21. 39% ，30. 62% and 8. 20% ，respectively． The result shows that the adoption of memetic algorithm，by properly increasing the horizontal distance of the tunnel cable loop and selecting the appropriate phase sequence layout，is conducive to weakening the mutual heat effect between the loop cables，reducing the circulating heat loss of the metal sheath，and improving the layout of the tunnel cable．

Aiming at the problem that the Euler-Lagrangian method can not predict the influence of the re-entrainment phenomenon on the demister performance in the numerical study，the study established a demister model based on re-entrainment phenomenon by taking wave-plate demister as the research object and coupling Euler Wall Film model on the basis of Euler-Lagrange method． Through the experimental data comparison，the model prediction curve is consistent with the experimental results． The effects of plate spacing and turning angle on the demisting performance were studied in different flow rates by the improved model． The results show that the liquid film separation at the corner is the main reason for the reduction of droplets removal efficiency at high flow rates; increasing the plate spacing and turning angle will aggravate the re-entrainment and decrease the critical velocity; below the critical velocity，the droplets removal efficiency decreases with the increase of the plate spacing，and increases with the increase of the turning angle; above the critical velocity，the droplets removal efficiency decreases with the increase of the plate spacing and the turning angle． The optimal value of the plate spacing and the turning angle is 20mm and 40°． In this situation，the droplets removal efficiency can be increased by 16. 38% ，and the pressure drop can be reduced by 9. 74% ． This result can be used to prevent the demister from re-entrainment phenomenon and improve the demister performance．

Accurate thermal conduction-based model is the key to the heat pipe-based thermal management simulation research． Based on the existing thermal conduction-based models，two conduction-based model for partially flattened heat pipes，the segmented anisotropic model and the layered segmentation model，were put forward in the present study． The results show that the segmented anisotropy model has higher accuracy in the case of low heat pipe operating temperature ( 28 ～ 38 ℃ ) ． The maximum relative error of heat pipe surface temperature is 5. 90% ． The layered and segmented model has higher accuracy in the heat pipe operating temperature range of 28 ～ 50 ℃ ． The maximum relative error of heat pipe surface temperature is 6. 51% ． And the effect of the effective thermal conductivity of the wick on the accuracy of the thermal conduction-based model was also investigated．

A new type of plate condenser which can discharge condensate in the middle was designed． The drain port was set in the middle of the condenser，which can speed up the drainage，reduce the thickness of the condensate film attached to the plate，reduce the thermal resistance of the liquid film between the vapor and the plate，and increase the phase change heat transfer coefficient of the plate condenser． The performance of the liquid-vapor separation plate condenser ( LVSPC) was compared with that of the conventional plate condenser ( CPC) ． The experimental results of 10 different test conditions show that，under the same initial conditions，compared with the CPC， the condensation heat transfer coefficient of the LVSPC is increased by 8. 3% ～51. 6%，the total heat transfer coefficient is increased by 7. 6% ～ 38. 3% ，and the total pressure drop is reduced by 2. 6% ～ 11. 4% ． The experimental results proved that the LVSPC can achieve the purpose of enhancing heat transfer and reducing pressure drop． However，due to the decrease of working fluid flow in the second condensing area，the total heat transfer of the LVSPC is approximately equal to that of CPC，and there is no obvious increase．

The heat pipe has the advantages of high thermal conductivity，lightness and miniaturization． This study proposed a finite-time thermodynamic model of thermoelectric coolers based on heat pipe heat dissipation and the specific calculation methods for the thermal resistance of the cold and hot junctions． In order to reflect the cooling capacity per unit area of the thermoelectric module，the refrigeration rate density analysis method and the converted area thermal resistance method were used to analyze the influence of key operating parameters and design parameters with numerical examples． In order to compare the refrigeration performance under different working conditions， the thermodynamic perfectibility was introduced and the refrigeration performance of the thermoelectric refrigerator was comprehensively analyzed． The paper also revealed the optimum current working range and temperature difference range of thermoelectric coolers and analyzed the influence of the refrigeration module filling factor，cooling temperature difference，heat pipe parameters ( evaporation section length and tube wall thickness) on the refrigeration density，coefficient of performance ( COP) and thermodynamic perfectibility of the refrigerator． Its performance was compared with that of air cooling and the results can provide theoretical guidance for the design and operation of refrigerators based on heat pipe heat dissipation．

In order to study the effect of temperature on the bolt pretension of flange structure，the bolt pretension and sealing conditions of flange in liquified natural gas ( LNG) ultra-low temperature ball valve at different temperatures were analyzed by ANSYS finite element software，and the pretension states of bolt materials with different linear expansion coefficients at room temperature and low temperature were compared． The results show that when the bolt material is B8M and XM-19，the preload force increases with the decrease of temperature，and the pretension under the low temperature conditions increases by 24. 93% and 6. 28% respectively compared with normal temperature; when the bolt material is Inconel625，the pretension decreases with the decrease of temperature，and the pretension under the low temperature condition decreases by 26. 39% compared with normal temperature． At the same time，the variation of the sealing specific pressure of the metal spiral wound gasket with temperature exhibits the same trend with the bolt pretension．

A multiphase relaxation calculation method with the adaptive process was established to analyze jetbuffer mechanism in water hammer with liquid column separation． The rationality and stability of this calculation method were verified by air-water two-phase shock tube． The internal flow mechanism of water hammer with liquid column separation was analyzed． The results show that for water hammer with liquid column separation whose secondary pressure variation value is higher than the theoretical ones，it can be divided into the direct water hammer， the buffer water hammer，and the jet water hammer． In the stage of buffer water hammer，the presence of bubbles reduces the pressure impact on the boundary，causing the water hammer wave appear buffered and the change of pressure value is smaller than the theoretical ones． In the stage of jet water hammer，the jet acceleration generated during void compression and collapse does not directly affect the pressure impact on the boundary，but it causes a secondary pressure change accumulation in the initial value after back propagation，and the change value is higher than the theoretical calculation value． The occurrence of jet water hammer affects the accuracy of value calculated by direct water hammer method，so this is the most noteworthy part of water hammer with column separation calculation．

Under severe icing conditions，the iced sub-conductor may be connected by the ice bridge to form a connected ellipse iced conductor，resulting in the increase of windward area and aerodynamic shape deterioration of conductors． In order to study the aerodynamic force characteristics of the connected ellipse iced conductor ( with the ice bridge) and the separated ellipse iced conductor ( without the ice bridge) ，the high frequency force balance wind tunnel tests were conducted． Based on the test results，the effects of aerodynamic force characteristics of two ice accretion types on galloping stability and wind-induced swing response were analyzed． The results show that: ( 1) compared with the separated ellipse iced conductor condition，the lift force curve of the connected ellipse iced two-bundled conductor has a slower drop around peak，and the mean lift force coefficient is much larger in high wind attack angle cases; ( 2) near the wind attack angle of 170°，the mean torque coefficient of the separated ellipse iced conductor is larger than that of the connected ellipse iced two-bundled conductor; ( 3) the drag forces of conductors with the two iced types both satisfied the quasi-steady assumption; ( 4) for the vertical galloping，the separated ellipse iced conductor has worse stability，and for the torsional galloping，the connected ellipse iced conductor is more disadvantageous; ( 5 ) under the same wind velocity and transmission line condition，the wind-induced response of the connected ellipse iced conductor is larger than that of the separated ellipse iced conductor，leading to greater wind-induced swing accident risk．

In view of the diversity of domestic solid waste calorific value，there will be some problems such as fuel calorific value is not suitable for the incinerator introduced from abroad． In this study，the adaptability modification of a 350 t /d grate waste incinerator in Guangdong was carried out and based on the bed FLIC calculation software and computational fluid dynamics software Fluent，the combustion in garbage incinerators of different structures was simulated to predict the distribution features and fuel adaptability of the temperature field，velocity field and the gas composition of the front wall folding flame angle and arch u-shaped angle of furnace． The results show that: eliminating the front wall flame angle and the U-shaped angle of the rear arch makes the combustion area of the furnace move down; when the high temperature area is between the grate and the secondary air outlet，the furnace combustion is more sufficient，effectively reducing the output of NOx，saving the amount of out of stock reductant and resulting more suitable mixed combustion of sludge and garbage． Besides，adding 5% LD-40 sludge can effectively reduce the production of CO，CO2 and furnace temperature and slow down the high temperature corrosion phenomenon． The average error between the numerical simulation results and the measured temperature is less than 5% ．

With the wide application of renewable energy and the development of distributed generation technology， more and more microgrids operate independently in island mode，and the requirements for microgrid construction are also higher and higher． As an important part of microgrid construction，Microgrid power planning needs to configure power according to the resource characteristics of different regions． Based on the background of“wind / photovoltaic /battery”standalone microgrids，this paper proposed an optimal power configuration method for standalone microgrids based on the characteristics of wind and solar resources． An optimization model with the objective of minimizing the annual generation cost and considering the constraints of power output and energy storage battery capacity was established and solved by linear programming algorithm． Considering the randomness of the wind and photovoltaic output，the wind and photovoltaic output scenario was simulated by the generative adversarial network algorithm，and the scene was reduced by the improved K-medoids clustering algorithm． In order to analyze the characteristics of wind and solar resources，an evaluation system including wind power resources，photovoltaic resources and wind solar complementary indicators was constructed，and the subjective and objective combination weight method based on“entropy weight-complex correlation coefficient-order relationship analysis”was proposed． Fuzzy evaluation and grey evaluation methods were used to comprehensively evaluate the level of wind and solar resources in 30 provinces of China． Finally，according to the evaluation results，five representative regions were selected for example analysis． The results show that there is a corresponding relationship between the evaluation level of wind power resource evaluation index and the proportion of wind turbine configuration capacity． The study can provide reference for the planning of standalone microgrids power supply．

Inverter compressor operating in low frequency range shows apparent speed fluctuation． It is the periodic load torque disturbance that brings about speed offset． The poor performance of periodic load disturbance is caused by the small gain of disturbance observation ( DOB) ． To solve this problem，a periodic disturbance observer ( PDOB) was proposed to estimate load disturbance and compensate current in this paper and attenuate speed deviation in low frequency range． Load disturbance is compensated by PDOB based on internal model theorem，including fundamental and related harmonic components． Adaptive notch filter based on Steiglitz-McBride method was constructed to estimate the fundamental frequency of periodic disturbance． Experiments were carried out on inverter compressor platform and results show that speed fluctuation of can be effectively suppressed by the proposed method comparing with general DOB．

To study the flow heat transfer characteristics of Al2O3-HITEC molten salt-based nanofluids in heating tubes with constant heat flux，a computational fluid dynamics ( CFD) simulation was carried out with the singlephase thermal dispersion model． The effects of nanoparticle additions with different mass fractions on the heat transfer performance of molten salt were analyzed，and the heat transfer performance variations were discussed from the respect of the thermal physical properties of the fluid． Comparisons of results show that the thermal dispersion model can be used to simulate the heat transfer performance of molten salt-based nanofluids． Simulations show that the temperature inside the tube with various nanofluids is lower than that with pure molten salt，and the temperature drop is the most obvious with the particle concentration of 0. 063% ． The temperature distributions at the four sections show that under the wall heat flux boundary，the temperature of molten salt with or without nanoparticles increases radially，while the temperature of molten salt-based nanofluids is lower than that of the pure molten salt，indicating nanofluids absorb and take away more heat energy． Moreover，compared with that of pure molten salt，the heat transfer performance of molten salt-based nanofluids increases，proving that the nanoparticle additions can improve the heat transfer performance of molten salt． However，the improvement is not proportional to the increase of nanoparticle concentration． Instead，the nanofluids with a mass fraction of 0. 063% show the greatest heat transfer enhancement，and the heat transfer coefficient in the fully developed region is 6. 5% higher than that of pure molten salt． Finally，the drastic change of specific heat capacity is found playing a key role in the change of heat transfer performance through analyzing the physical properties of molten salt and molten salt-based nanofluids．

Too low or too high operating temperature and excessive temperature fluctuations will adversely affect the output performance and durability of proton exchange membrane fuel cells． Therefore，effective thermal management is the essential to the stable and efficient output of proton exchange membrane fuel cells． In this study，a 1. 5mmthick vapor chamber was used as a heat dissipation structure in the thermal management of a proton exchange membrane fuel cell stack，and 80 thermocouples were installed on a cathode graphite plate with 5 single cells to obtain the internal surface temperature of cells，so as to explore the temperature distribution characteristics of the stack under different load currents． It’s found that，during the loading process of 0 ～ 8A，the maximum temperature difference of the cathodic side within each single cell is less than 1. 0 ℃，and local temperature fluctuation only occurs at inlet ports． In addition，the temperature distribution uniformity of the stack with vapor chamber is better than that of the ordinary water-cooled stack under the same operating condition．

Closed-loop control method of electrostatic precipitator outlet dust concentration was studied to solve the problems of high energy consumption of dry electrostatic precipitator in 1000 MW coal-fired units and the failure to achieve closed-loop control of concentration． Firstly，for dry electrostatic precipitator with a five-field structure，a concentration control method combining feedforward control of the first three-stage electric fields and closed-loop control of the last two-stage electric field was proposed． The IMC-PID parameter setting method was used to set the PID ( Proportional Integral Derivative) controller parameters，and a disturbance observer was added to the PID controller to enhance the anti-disturbance ability of the system． Finally，the method of fuzzy weighted switching was used to achieve smooth switching between the control functions of each load point model． The simulation and experimental results show that the proposed control method can realize the fixed value control of electrostatic precipitator outlet dust concentration and has good performance．

With the development of social economy，the production of all kinds of garbage is increasing rapidly， and the research on efficient and clean utilization of pyrolysis gas of garbage is gradually carried out． This study used FLUENT software to simulate the MILD combustion of MSW pyrolysis gas in the burner，and the effects of fuel nozzle diameter，air nozzle diameter，distance between fuel nozzle and air nozzle，air nozzle distribution and thermal value fluctuation on the combustion and NO emission in the burner were explored． The results show that the change of jet velocity indicated by the change of air nozzle diameter has the most significant effect on combustion， and the increase of jet velocity can achieve better MILD combustion effect by turbulence and entrainment． And there is an optimal value of 8mm of air nozzle diameter in this study． The increase of fuel jet velocity has less effect on combustion effect，the high speed of fuel jet is conducive to fuel jet rigidity and combustion zone extension，and there is an optimal value of 8 mm of fuel nozzle diameter in this study． The diffusion process and the size of return area can be influenced by the distance between air and fuel nozzle，which can be matched with the aperture to obtain an optimal value when the nozzle spacing is 15mm． The uniformity of the air jet distribution affects the combustion effect，but has little effect on NO emission，so 4 air nozzles are suitable． The burner can satisfy the MILD combustion with the calorific value of the pyrolysis gas fluctuating at 20% ．

Based on the research of the power capture optimization method for the direct-drive wave power generation system，a state switching control method based on a linear generator was proposed in this paper． Based on the characteristic that the speed of the linear generator in the no-load state is higher than that in the power generation state，the linear generator is controlled to switch between the no-load state and the power generation state，thereby increasing the speed of the linear generator in the power generation state． Therefore，the captured power is further improved． The results show that，compared with other power capture optimization methods，the proposed method has excellent performance in power capture．