Advanced Materials Research Vols. 1008-1009

Abstract: The k-distribution method applied in narrow band and wide band is extended to the full spectrum based on spectroscopic datebase HITEMP, educing the full-spectrum k-distribution model. Absorption coefficents in this model are reordered into a smooth,monotonically increasing function such that the intensity calculations are performed only once for each absorption coefficent value and the resulting computations are immensely more efficent.Accuracy of this model is examined for cases ranging from homogeneous one-dimensional carbon dioxide to inhomogeneous ones with simultaneous variations in temperature. Comparision with line-by-line calculations (LBL) and narrow-band k-distribution (NBK) method as well as wide-band k-distribution (WBK) method shows that the full-spectrum k-distribution model is exact for homogeneous media, although the errors are greater than the other two models. After dividing the absorption coefficients into several groups according to their temperature dependence, the full-spectrum k-distribution model achieves line-by-line accuracy for gases inhomogeneous in temperature, accompanied by lower computational expense as compared to NBK model or WBK model. It is worth noting that a new grouping scheme is provided in this paper.

Abstract: Based on precise mathematical principles, a narrow band k-distribution (NBK) model is developed to calculate the radiative properties of water vapor and carbon dioxide. In this model, the integral variable of radiative transfer equation (RTE) is transformed from wavenumber to non-dimensional cumulative k-distribution function, leading to a final integration with very few quadrature points. Accuracy of the model is examined by calculating radiation in gases between two cold and black parallel plates. All the parameters calculated through NBK model, including radiative flux, transmissivity as well as radiative intensity, are compared with that of line-by-line calculations, which proves the NBK model can provide exact results with great computational savings. In this paper, absorption coefficients of water vapor and carbon dioxide are obtained from the line parameters in high-resolution spectroscopic database HITEMP 2010.

Abstract: A calculation method for counter-current type coil-wound heat exchanger is presented for heat exchange process. The numerical simulation method is applied to determine the basic physical parameters of wound bundles. By controlling the inlet fluid velocity varying in coil-wound heat exchanger to program and calculate the iterative process. The calculation data is analyzed by comparison of numerical result and the unit three dimensional pipe bundle model was built. Studies show that the introduction of numerical simulation can simplify the pipe winding process and accelerate the calculation and design of overall configuration in coil-wound heat exchanger. This method can be applied to the physical modeling and heat transfer calculation of pipe bundles in coil wound heat exchanger, program to calculate the complex heat transfer changing with velocity and other parameters, and optimize the overall design and calculation of spiral bundles.

Abstract: Equilibrium molecular dynamics simulations that use the Green–Kubo method for sI CO₂-hydrate systems from medium to full occupancy were performed to estimate the corresponding thermal conductivities at temperatures that range from 233.15K to 278.15K and pressures that range from 3MPa to 100MPa. Specific potential models for water and CO₂ were adopted. The effects of guest occupancy ratios and outside thermobaric conditions on CO₂ hydrate thermal conductivity were studied. The thermal mechanism was also analyzed. The thermal conductivities of hydrates of CH₄, C₂H₆, N₂, and O₂ were estimated. The size ratio of guest diameter to cavity diameter provided an adequate basis for understanding the thermal conductivities of gas hydrates.

Abstract: A spatial cold-shield system with cryogenic phase change refrigeration was studied to decrease the surface temperature of spacecraft under 100 K and surface infrared intensity under 0.5 W/m² within 30 minutes in space. A 3-D unit and systematic model were established to simulate the real structures and the variation regularities of the major parameters under different flying periods. A simplified unit model and a systematic model were established to simulate the heat-transfer and flow-field of cold shield in cryogenic, vacuum and micro-gravitational conditions. The unit and systematic experiments were carried out to study the cryogenic phase change refrigeration in cold shield on the ground. The results indicated the simulated and experimented parameters of cold-shield were consistent with the designing conditions of spacecraft. The systematic model could make the LN₂ touching the surface easily and causing the surface temperature distributed more uniformly. The cold-shield could meet the requirement of cryogenic infrared intensity by phase change refrigeration in space.

Abstract: The small-scale experiments of water mist extinguishing cardboard fire were carried out. Thermocouples and heat radiation sensor were used to measure the fire temperature and radiation heat flux of the burning area. The variation characteristics of the combustion field radiation heat flux under different spray pressure were studied. The results show that: the spray pressure has a significant influence on the extinguishing process. Based on the experiments, The simplified model of water mist absorbing heat radiation has been established, the results of this model agree well with the results of the experiments, and is good for predicting the effect of water mist particle diameter.

Abstract: The paper presents a novel drying system which includes a superheated steam drying and a hot air drying. The conventional viscose fiber drying is experimental studied and the drying quality and energy consumption were analyzed. In the experiments, the temperature of superheated steam covered the range from 120°C to 150°C and, hot air temperature is about 80°C. A series of drying kinetics curves were determined to optimize the operation parameters. The results show that the combined drying has high energy efficiency because of the exhaust heat recovery from superheated drying period.

Abstract: An optimization was performed for a sintering waste heat power unit with all data obtained in the site and under the unit normal operating conditions. The physical and mathematical model for the process of cooling and generation is established, which makes the net power generation as an objective function of the cooling machine imported ventilation, the thickness of sinter and the main steam pressure. Optimizing for single parameter, we found that each parameter had an optimal value for the system. In order to further optimize the system's operating parameters, genetic algorithm was used to make the combinatorial optimization of the three parameters. Optimization results show that power generation capacity per ton is increased by13.10%, and net power generation is increased by 16.17%. The optimization is instructive to the operation of sintering waste heat power unit.

Abstract: A numerical simulation for heat exchanger with continuous helical baffles was carried out. The study focuses on the effects of helix angle on heat transfer characteristics. The results show that both the shell-side heat transfer coefficient and pressure drop decrease with the increase of the helix angle at certain mass flow rate. The latter decreases more quickly than the former. The tangential velocity distribution on shell-side cross section is more uniform with continuous helical baffles than with segmental baffles. The axial velocity at certain radial position decreases as the helix angle increases in the inner region near the central dummy tube, whereas it increases as the helix angle increases in the outer region near the shell. The heat exchange quantity distribution in tubes at different radial positions is more uniform at larger helix angel.

Abstract: Unsteady flow of a single six-blade ruston turbine in stirred tank is numerically simulated by using the large eddy simulation. Then the effect of the turbine installation position on mixing flow field is studied. The result shows that with a relatively low paddle installation position, mixing effect at the bottom of tank is obvious, while which go against the materials at the top layer mixing. When the paddle is installed at the top of the stirred tank, liquid splash and a concave downward liquid surface are easily caused. Finally the cavitation phenomenon is generated. When the paddle is installed from 1/3H to 2/3H, there are a uniform flow field distribution and higher average velocity flow. Large size vortex structures at the top and the bottom of the paddle are obvious which is beneficial to mix the materials.