NUMERICAL CALCULATION OF THREE-STREAM MIXING FLOW WITH WALL COOLING

The flow and the temperature in the threestream mixing flow of the lobed nozzle mixer-ejector with double-wall diffuser are numerically investigated. The domain of computation is divided into sub-domalns according to the shapes of the double-plate and lobed nozzle. The three-dimensional body-fitted coordinated grids are generated respectively in these sub-domains by solving Lapalace's equations. Grids are dense on the boundaries and orthogonal at the lobe. The grids of all sub-domains compose the whole grid of the domain. In order to avoid the divergence of the computation as the serious non-orthogonality of the grid from the lobe, the co-located grid, SIMPLEC and Chen-Kim modified k-εturbulence model are applied. The great viscosity, the linear and simultaneous cooperation under-relaxation factors are used to solve the coupling of the fluid and solid. Results show that the air is ejected into the double wall section to form the cooling flow. The wall temperature of the double-wall diffuser is lower than that of the single-wall diffuser. The average wall temperature goes down as the diffuser angle increases at the range of 0～5°,otherwise, the result at the range of 5～10°is opposite.

Process and Component Analysis on S-CO_(2)Cooling Wall in the Coal-fired Boiler Power System

The supercritical carbon dioxide(S-CO_(2))cooling wall in coal-fired boiler suffers from severe fragile crisis due to the high temperature of S-CO_(2).The analysis of both heat transfer at process scale and cooling wall arrangement at component scale were carried out in present work.At the process scale,the difference in heat transfer performance between the smooth tube and the rifled tube were identified,especially the location of maximum outer wall temperature of cooling wall.The 1-D mathematical model for thermal-hydraulic analysis of S-CO_(2)furnace cooling wall tubes was then developed.At the component scale,the coupled model of combustion and S-CO_(2)heat transfer is employed for studying the thermal-hydraulic performance of rifled-spiral(R-S)and smooth-spiral(S-S)cooling wall arrangements.The maximum outer wall temperature of R-S cooling wall is 16.38℃lower while the pressure drop increases by 2.33 times compared with the S-S cooling wall.Considering the pressure drop penalty on cycle efficiency of S-CO_(2)boiler power system,the R-S cooling wall is not recommended,while the S-S cooling wall should be carefully arranged in S-CO_(2)boilers.

A New Structure of Cooling Wall Tube for Supercritical CO_(2)Coal-Fired Power Plants

In terms of developing supercritical CO_(2)(sCO_(2))coal-fired power plants,enhancing cooling wall performance is one of significant factors to improve system performance.In this paper,a new cooling wall tube structure is proposed to match the non-uniform heat flux(NUH)with the thermal resistance by changing the cooling wall tube eccentricity.A three-dimensional multi-physical coupling model of cooling wall is constructed to compare the novel structure to the conventional structures.The properties of fluid dynamics,thermal stress,coupled heat transfer and cooling wall deformation are analyzed.In contrast to the traditional structure,the maximum temperature and circumferential temperature difference(CTD)of the proposed structure can be reduced by 2%and 27.4%,respectively.The essential working parameters related to the performances of the cooling wall tube are discussed.The maximum temperature of the new structure is reduced by 8-13 K and the maximum thermal stress is reduced by about 10%-15%under all the simulated working conditions when the eccentricity changes from 0 to 0.2.The proposed structure can effectively reduce the maximum temperature and circumferential temperature gradient under NUH.Consequently,a novel insight is put out for the design and optimization of the cooling wall tube in coal-fired power plants.

Novel Matching Strategy for the Coupling of Heat Flux in Furnace Side and CO_(2)Temperature in Tube Side to Control the Cooling Wall Temperatures

Required by the supercritical carbon dioxide(s CO_(2))coal-fired power cycle,s CO_(2)entering a boiler has a high temperature and can cause overheating of tubes.To eliminate the pressure drop penalty effect,the s CO_(2)boiler consists of several modules,each having different heat flux received from the furnace side(q)and different CO_(2)temperature in the cooling wall tube(T_f).We aim to search for the best matching strategy coupling furnace side and tube side to obtain the lowest temperature of tubes.By theoretically analyzing the wall temperature influenced by q,T_f and a comprehensive thermal resistance C,two matching methods are introduced:the heat flux-temperature matching(HTM)which matches higher q with lower T_f,and the heat flux-heat flux matching(HHM)that matches higher q with higher allowable-heat-flux at the temperature limit of tubes.HTM is a conventional method but HHM is newly proposed here.We show that,if C is identical for different modules,the two methods coincide;otherwise,HHM is recommended.For a s CO_(2)boiler driving 1000 MWe power plant,smaller cooling wall temperatures are obtained by HHM than HTM.Based on HHM,the mid-partition wall,heat transfer enhancement,and downward flow are comprehensively used,decreasing the wall temperature significantly.

Performance Analysis of Cooling Wall of Supercritical CO_(2) Coal-Fired Plants

Using supercritical CO_(2)(S-CO_(2)) instead of water steam as heat transfer fluid for coal-fired power plants is another way to further improve the power generation efficiency. In this paper, a multi-field coupling model that integrates fluid flow, heat transfer and thermal stress is proposed to solve the complex problem. The effects of the key operating parameters on the performances of the cooling wall are numerically investigated. More details of the characteristics of fluid dynamics, thermal stress, pressure drop, coupled heat transfer and the whole flow and temperature fields in the S-CO_(2) cooling wall are revealed and discussed. A comparison study is made between the cooling wall tube and waterwall tube. Both temperature and thermal deformations of cooling wall tube are much higher than that of water. Numerical simulation results indicate that inclination angle has little effects on the temperature distribution, while increase of pressure drop is obvious as the inclination angle increases. Increasing tube diameter can effectively reduce both the pressure drop and the temperature of the cooling wall tube. As a result, a new insight is introduced for the design of S-CO_(2) power cycle.

Numerical study on indoor environment and thermal comfort in train station waiting hall with two different air-conditioning modes

With the increasing size of the waiting hall,the large-area use of transparent envelope materials makes the interior surface temperature of the envelope too high,which puts forward higher requirements for the control of environment and thermal comfort indoors.In this paper,the characteristics of indoor temperature distribution,relative humidity distribution and thermal comfort under the all air system(AAs)and the radiant floor cooling and wall cooling combined with air supply system(RC/ASs)were investigated in the large spaces.The computational fluid dynamics(CFD)method was used,and the performance of the CFD model was validated by comparing the measured results with CFD simulation results in the AAs.The numerical results clearly showed that the temperature and relative humidity indoors could satisfy the design requirement both in the AAs and RC/ASs.The indoor air distribution in most areas under the RC/ASs was more uniform based on the indoor heat and humidity requirements under the cooling load of measured day.In the AAs,the total cooling capacity of air conditioning unit was the highest when indoor thermal comfort was the best,that meant that to achieve the best working condition,the air-conditioning system need high energy consumption.Meanwhile,the RC/ASs addressed the problem that the temperature around the seated passengers in the waiting area was relatively high in the AAs.This paper will provide reference for the air conditioning system design in the similar large spaces in the future.