Abstract: An experimental study was performed on wavy-finned-tube used in forced draft direct air-cooled steam condenser (DACSC) under actual working conditions of the power generating unit. Tests were carried out to study the air side heat transfer characteristics of wavy-finned-tube in actual operating conditions of DACSC, such as: air temperature, air face velocity, environmental temperature, exhaust pressure of steam turbine and temperature of exhaust steam. The air-side heat transfer characteristics of wavy-finned-tube heat exchangers were tested and analyzed by varying air face velocity .One empirical correlations for predicting the h-factor was developed.
Abstract: This paper investigates the condensation performance of a novel type of two-phase closed thermosyphon with internal helical microfin. The length of the thermosyphon is 1500 mm, with the filling ratio of 60%. A series of experiments were conducted for the novel and conventional thermosyphons. The results show that the internal helical microfins could not only ameliorate the thermal response characteristic but also improve the condensation heat transfer coefficient by 116.87% for the higher heat input. A correlation was developed to predict the condensation heat transfer coefficient of the novel thermosyphon.
Abstract: The effects of micro-particle diameters (i.e. dp=0.4~1.1mm) and low fluid velocities (v=5ml/min, 3ml/min and 1ml/min) on the heat transfer behavior of water flowing through a micro-particle packed bed as a reactor of thermal biosensor were investigated experimentally under constant wall temperature conditions (i.e. 60°C). The effective thermal parameter is smaller with decreasing the particle diameter and fluid velocities. This is mainly due to the poor thermal conductivity of the filling materials which leads to a larger thermal resistance and hydraulic resistance. As such, it is very important to select a filling material with better thermal conductivity to enhance heat transfer, which is favorable to completely detect the heat created during the enzyme-catalyzed reaction. Comparing the correlations of both this work and those published in the literature, there are considerable discrepancies among them due to different experimental conditions. The two-dimensional heat transfer model that predicts the temperature distributions agree reasonably well with actual measurements except a slight over-prediction in the region close to the inlet.
Abstract: A frosting test bench was designed, and unsteady frosting on vertical plate surface was dynamically described with liquid nitrogen as working medium under natural convection conditions. The variation of frost thickness was analyzed, and the flow state of moist air and temperature distribution near the vertical plate were described. The experimental results show the unsteady frosting of vertical plate surface under natural convection and cryogenic condition actually includes several steps: formation of frost crystals, growth of frost crystals and growth of frost layer. The initial frosting rate is large, but the rate decreases as time goes on until the frost layer thickness is unchanged. Moist air conducts a top-down flow near the vertical plate, and the rest of moist air flows into the main flow. The temperature of moist air decreased systematically along the tangential direction of vertical plate from top to bottom and along the normal direction of vertical plate from far to vertical plate surface.
Abstract: Integral analysis of heat transfer of a laminar falling liquid film along a vertical heated plate with specified heat flux boundary condition was investigated. The temperature distribution of liquid film was obtained by utilizing an integral analysis method, which was compared with numerical solution and other researcher’s results. In this analysis a new concept of thermal changing point was put forward. It’s found that the Nusselt number has a characteristic relationship with thermal changing point, which is obtained by calculation. When the film flow distance is less than thermal changing point, the Nusselt number decreases rapidly. When the film flow distance is greater than or equal to thermal changing point, the Nusselt number reaches to a fixed value. A larger Peclet number or lower initial temperature generally leads to a larger Nusselt number in entrance region, whereas the wall heat flux is found to have no influence on the Nusselt number.
Abstract: A model of boiling heat transfer system was established by introducing disjoining pressure produced by three phase molecular interactions and Lie algebra analysis for a developed bubble in micro channel and simulation of chaotic movement of the obtained interface dynamic system was carried out in this paper. Experiments for 0.6 mm2 mm rectangular micro channel were carried out to obtain the pressure time serials. Power spectrum density analysis for this serials shows that the system is in chaotic state if the frequency is above 7.39Hz.The result indicates that high heat transfer performance of micro channel phase change system may relate to the characteristics of chaos.
Abstract: A new wide band k-distribution model has been developed and used to investigate infrared radiation signatures of liquid rocket plume in some detectors’ working spectrum regions, in which the temperature and the gas molar concentration fields are solved using engineering empirical formulations. Based on the line parameters in HITEMP database, absorption coefficient variables of water vapor and carbon dioxide corresponding to 12-point Gauss-Lobatto quadrature points are derived and expressed as a simple formulation. The absorption coefficient variables of mixture are obtained by summing the absorption coefficient variables of individual gas species under the hypothesis that the k-distributions are statistically uncorrelated. Its validity for the numerical prediction of liquid rocket plume radiation is verified by comparison with line-by-line approach (LBL). Compared with line-by-line calculations, the maximum relative errors of the new band model are less than 10 % in the detectors’ working spectrum regions, while the computational time of the new band model is less than 1/1000 of LBL. The effects of fly parameter on infrared radiation signatures of liquid rocket plume are studied using the new model. The results showed that the integral radiation intensities of liquid rocket plume increase with the nozzle exit temperature, Mach number and the ratio of nozzle exit pressure to atmospheric pressure. The radiation intensity variation trend for liquid rocket plume with altitude is different for different detectors’ working spectrum regions.
Abstract: Adopting standard k-ε turbulent model and mixture flow model, settling process and decant process was simulated using 3-d numerical simulation in M-ICAR(Mixture-Intermittently Cycle Aeration Reactor) process to analyze the changes of sludge phase volume fraction. The simulation results showed that the changes of feeding wastewater had great influence on sludge settle ability in decant process, and the position of decanter needed optimized; it had no influence on sludge settle ability in settling process. For considering the lowest hydraulic retention time, the research controlled maximum feeding wastewater for 1610m3/h. Internal recycle had no influence on sludge settle ability. Two methods were proposed: the first one, the water level of decanter was set 3.9m (sludge volume fraction of this suspended area was less than 0.05), feeding velocity was 0.07 m/s; the second, keep the water level of decanter 3.75 m, reduce feeding velocity (preliminary setting feeding velocity 0.06 m/s). The two methods had no influence on sludge settle ability.
Abstract: A supercritical water oxidation (SCWO) reactor containing a hydrothermal flame as heat source is simulated by computational fuild dynamics (CFD) simulation. Methanol solution and oxygen are fed separately into the reactor as fuel and oxidizer, and at the same time the cold waste water is also fed into the reactor. The combustion of methanol is simulated by the eddy dissipation concept (EDC) model with an Arrhenius law kinetic. This simulation is conducted to study the behavior of the hydrothermal flame at different inlet fuel temperatures and the relationship between the ignition temperature and methanol mass fraction.