The reliability of experimental data are important for heat exchanger design and evaluation. In the present paper, we extended the concept of Critical Heat Balance Error (CHBE) to a general imbalanced heat exchanger with thermal capacity ratio great than 1. Based on the principle of positive entropy generation in experiment, were analytically expressed the CHBE under the influence of different thermal capacity ratios. Interestingly, we found the same analytical expression as previous research which is, CHBE = −(1 − τ)(1 − ε), where ε and τ are heat exchanger efficiency and inlet temperature ratio, respectively. Therefore, we claim this analytical filter can be used for a general heat exchanger with any thermal capacity configuration.

We study the separation process of gaseous H 2 O/CH 4 mixtures using nanoporous graphene membranes via molecular dynamics simulations. We run the simulation in an equilibrium system 10 times with different initial atomic velocities to overcome the inefficiency brought by the low pressure of the system. The results show that the H 2 O molecules can permeate the graphene membrane with a linearly time-dependent crossing number. The permeance of the H 2 O molecules reaches to 9.5×10 −4 mol/m 2 sPa, far exceeding that of the polymer gas separation membranes. High selectivity of H 2 O over CH 4 is also observed. In summary, this study demonstrates that the specific NPG cloud be adopted as an efficient membrane in natural gas dehydration.

The process of submicron particle movement in laminar boundary layers is present in many practical applications such as the particles depositing on the turbine blade and mist droplets depositing on the surface of aircrafts. Although great progress has been made on this issue during the last decades, many underlying mechanisms still remain unclear. Here, we developed a theoretical model to understand how submicron particles will behave when they enter a supersonic laminar boundary layer above an adiabatic plate along with the main stream. In this model, we used the Lagrangian method to track the particles and calculate their trajectories, and the Eulerian method was used to calculate the flow field. Because of the large velocity and temperature gradient near the wall and the small size of the particle in this question, four forces (e.g., drag force, Saffman lift force, thermophoretic force and Brownian force) acting on the particle are considered. The effects of entering position, Mach number, the size and density of particles are investigated. We discovered that there are three particle movement patterns when they enter the supersonic boundary layer, and that the drag force and Saffman lift force play dominating roles on which pattern will happen in this process. Moreover, the results also reveal that the particle tends to move towards the wall as the diameter and the density of the particle and the Mach number of main flow increases. Finally, we suggested a dimensionless number to describe the three patterns of particle motion. This research provides a better understanding of the particle movement process in the supersonic laminar boundary layer, which can be a useful guidance for the industrial processes involving this phenomenon.

The pressure drop is considerably significant for the differential pressure meter to measure the flow rate of the two-phase flow. Little is known about the pressure drop characteristics of the V-Cone meter when it is used to measure the wet gas flow. The objective of this paper is to investigate the two-phase pressure drop of the V-Cone meter and develop a correlation for predicting its pressure drop. A V-Cone meter with the equivalent diameter ratio of 0.55 was investigated experimentally. The experimental fluid was air and water. The test pressure ranged from 0.1 MPa to 0.4 MPa, and the gas and liquid mass flow rate ranged from 100 Nm 3 /h to 500 Nm 3 /h and from 0.05 m 3 /h to 2.2 m 3 /h, respectively. The experimental results showed that the existing correlations, which are developed for the orifice plate meter and the Venturi meter, are not applicable for the V-Cone meter to predict the pressure drop. The two-phase mass flow coefficient, K , was used to develop the two-phase pressure drop correlation. The influences of the Lockhart-Martinelli parameter, the gas densiometric Froude number and the operating pressure on K were investigated. The new pressure drop correlation can accurately predict the pressure drop of the V-Cone meter for the wet gas. The relative error of the pressure drop is less than ± 9.0% at the 95.1% confidence level and the average relative error is 3.88%. The pressure drop prediction correlation provides a reference for developing the correlation of the wet gas measurement.

Swirling gas-liquid two-phase flow patterns and pressure drop in vertical pipes of a large diameter are widely present in practical applications but not well documented in experimental studies. This paper presented an experimental study on gas-liquid two phase flow patterns and pressure drop inside a vertical pipe of 62mm in inner diameter (ID) containing a helical tape insert. Experimental results were obtained in a vertical visualization test section with a length of 7m, liquid mass velocities ranging from 0.3 to 1000 kg/(m 2 ·s), and gas mass velocities from 3.2 to 900kg/(m 2 ·s). Considering the decay of the swirl flow, the swirling flow regime map at different cross sections ( z/D = 16, 32 and 64) were concluded, and their effects on the pressure drop were investigated.

An experimental study was conducted on the pressure drop of single phase and air-water two-phase flow in the bed of rectangular cross sections filled with uniform spheres densely. In the present flow-regime model, the bed was subdivided into a near-wall region and a central region. And a new empirical correlation for the prediction of single-phase flow pressure drops was proposed based on the model. The correlation can be used to predict the single phase pressure drop for both great tube-to-particle diameter ratio packed beds and small tube-to-particle diameter ratio packed beds and for the pebble beds packing with spherical particles and non spherical particles. A new empirical correlation for the prediction of two-phase flow pressure drops was proposed based on the gas phase relative permeability as a function of the gas phase saturation and the void fraction. The correlation fit well also for both experimental data points of spherical particles and non spherical particles.

To construct a model of the microscopic near-wall region in a macroscopic pool boiling system, the present work introduced the effect of the solid wall at the bottom of the simulation system and the infinite liquid region outside it as extra potential. Molecular dynamics simulation results showed that thermodynamics properties of near-wall region was influenced by the interaction strength and deviated from the bulk liquid region. Vapor embryo nucleated at a position several nanometers away from the solid surface. With the increase of Hamaker constant, the vapor embryo occurred at a position farther away from the solid wall.

An experimental study was conducted on the air-water two-phase flow patterns and pressure drop in the bed of rectangular cross section containing spheres of regular distribution. Three kinds of glass spheres with different diameters (3mm, 6mm and 8mm) were used for the establishment of the test section. By means of visual observations of the two-phase flow through the test section, it was discovered that five different flow patterns occur in the experimental parameter ranges, namely bubbly flow, bubbly-slug flow, slug flow, slug-annular flow and annular flow. A correlation for bubble and slug diameter in packed beds was proposed, which is an extension of the Tung/Dhir model, Jamialahmadi’s model and Schmidt’s model. Three correlations were proposed to calculate the void friction of flow regime transition in bubble flow, slug flow and annular flow based on the bubble model in the pore region. The experimental result shows that the modified Tung and Dhir’s model of flow pattern transition is a better agreement with the experimental data compared with Tung and Dhir’s model.

In the present research, a visual experiment was carried out on the flow regimes of the porous channels in the spherical fuel element nuclear reactor. Boiling two-phase flow in different porous channels composed of particles with diameters of 4mm, 6mm and 8mm were studied respectively, and four different flow regimes occur within the experimental parameter range: bubbly flow, bubbly-slug flow, slug flow and slug-annular flow. The effects of heat flux, mass flux and particle diameter on the flow regimes were obtained. Bubbles and slugs deform, coalesce and break up more frequently, and increase in both number and size with the increase of the heat flux; bubbles and slugs tend to decrease in number and size with higher mass flux and particles of smaller diameters. At higher mass flux, a higher heat flux is needed to get the same flow regime that occurs at lower mass flux; with particles of smaller diameter, a higher heat flux is needed to get the same flow regime as that of particles of larger diameter. The flow regime map and flow regime transition have been proposed by modifying the void fractions of Tung/Dhir model.

The thermosolutal convection and solute segregation of Hg 1-x Cd x Te alloy during the vertical Bridgman single crystal growth have been numerically analyzed. Based on the thermal properties changed with the temperature and concentration, the coupling laws between temperature and solute gradients in the melt and the effects of thermosolutal convection on the solute segregation are studied in the paper. The main results obtained are as followed. Firstly, the stabilizing solute gradient will damp the convection caused by temperature gradient in the melt. But the damping effect of solute gradient will be significant only when the absolute value of the solute Rayleigh Number increases to the thermal Rayleigh Number. Secondly, when the solute gradient is large, the upper flow in the melt will be a sideway diffusive instability flow and evolve to a twocell construction. Thirdly, the solute distribution in the melt is mainly determined by the flow intensity and construction and the solute segregation near the solidification interface will be improved as the intensity of the lower flow decreases.

In order to reveal the law of double-diffusive convection of multi-compound solution in cylindrical cavity, experimental study on solidification of NH 4 Cl-H 2 O hypereutectic solution has been performed by using particle image velocimetry (PIV). The influencing factors of flow patterns and intensity are also analyzed. The results show that: 1) There are two approximately symmetric main convection cells in the liquid which are down along the sidewall and up along the center of the cylindrical cavity. Meanwhile, there are also two secondary cells on the bottom corner of cylindrical cavity, which flow in contrary direction to that of the main ones; 2) Due to the release of water during the solidification process, solute layers and diffusive interface are developed in the liquid and will be disappeared in the end; 3) The cooling temperature and the initial concentration have significantly effects on the flow velocity, solute layers and diffusive interface.

The pressure drop and boiling heat transfer of steam water two-phase flow were studied in a small horizontal helically coiled tube once-through steam generator of 9-mm inside diameter with 292-mm coil diameter and 30-mm pitch. Experiments were performed at a range of qualities up to 0.95, a system pressure range of 0.5∼3.5MPa, a mass flux range of 236∼943kg/m 2 s and a heat flux range of 0∼900kW/m 2 . Based on the experimental results, a new two-phase frictional pressure drop correlation was developed on the basis of Chisholm’s B -coefficient method. In the present experimental range, boiling heat transfer was found to be dependent not only on mass flux but also on heat flux. This result implies that both the nucleation mechanism and the convection mechanism have the same importance to forced convective boiling heat transfer in small horizontal helically coiled tube over the full range of qualities (pre-critical heat flux qualities of 0.1∼0.9) which is contrary to situations in larger helically coiled tube where the convection mechanism dominates at qualities typically > 0.1. Traditional single parameter Lockhart-Martinelli type correlations failed to satisfactorily predict present experimental data and in this paper a new flow boiling heat transfer correlation was put forward to better predict the experimental data of the present study.