Flow Characteristics Of System Research Articles

Effect of slot-shaped pins on heat transfer performance in the extended jet impingement cooling

In this study, effects of heat transfer performance on the roughened target surface with slot-shaped pins (SSP) were numerically investigated using an in-line array of extended jet impingement cooling models. The influence of pin heights on convective heat transfer for variable nozzle lengths, different pin arrangements, and Reynolds numbers (Re) in a rectangular channel flow was examined. The pins were located in a staggered and circular pattern. The numerical solution procedure has been verified by comparing numerical results with the available experimental data in the literature. The simulations were conducted with shear stress transport k-ω with low-Re correction turbulence model considering boundary conditions. The numerical model reasonably predicted heat transfer and pressure drop for flat plates and roughened plates with pins. Average Nusselt numbers on the surface were determined numerically using the model validated with experimental data for different dimensionless pin heights Hp/Dj (0.167, 0.417, and 0.667), various pin arrangements (R1, R2, R3), dimensionless nozzle lengths Gj/Dj (1.0, 2.0, and 6.0), and Re numbers (16250, 27100, and 32500). Numerical results were compared with the orifice plate; in other words, the conventional jet impinging configuration (Gj/Dj= 6.0 and Hp/Dj= 0). When the system's flow characteristics and performance evaluation criterion were considered, optimum geometric parameters for all Re were determined as Hp/Dj= 0.167 and R1_Gj/Dj= 1.0. Obviously, pin-roughened surfaces strongly affect the mean convective heat transfer and the homogeneity of the local heat transfer in extended jet impinging cooling systems. In this way, the negative effect of thermal stresses on the interested surface can be reduced, and the life of the material can be extended. Since the development of additive manufacturing technologies makes it possible to use these geometries in the internal cooling channels of gas turbine blades, a significant contribution will be made to the literature as a result of this study.

Experiment investigation on flow characteristics of open natural circulation system

Experimental research on flow characteristics of open natural circulation system was performed, to figure out the mechanism of the open natural circulation behaviors. The influence factors, such as the heating power, the inlet subcooled and the level of cooling tank on the flow characteristics of the system were examined. It was shown that within the scope of the experimental conditions, there are five flow types: single-phase stable flow, flash and geyser coexisting unstable flow, flash stable flow, flash unstable flow, and flash and boiling coexisting unstable flow. The geyser flow in flash and geyser coexisting unstable flow is different from classic geysers flow. The flow oscillation period and amplitude of the former are more regular, is a newly discovered flow pattern. By drawing the flow instability boundary diagram and sorting out the flow types, it is found that the two-phase unstable flow is mainly characterized by boiling and flash, which determine the behavior of open natural circulation respectively or jointly. Moreover, compared with full liquid level system, non-full liquid level system is more prone to boiling phenomenon, and the range of heat flux density and undercooling degree corresponding to unstable flow is larger.

Air-Assisted Injection System for Aviation Heavy Fuel Engine

According to the system requirement of a certain type of aviation piston engine, the reconstruction and matching of fuel injection system is carried out. The schematic design of the air-assisted injection assembly and the improvement of pressure regulator assembly are completed. After that, the air-assisted direct injection system is studied experimentally. The results reveal the effect of injection parameters and injection pressures on the system flow characteristics and spray characteristics. The effects of gasoline and kerosene on the actual engine performance are compared. The test results show that the self-designed air-assisted direct injection system can meet the system fuel injection requirements. In addition, the effect of injection pressure on the spray width is more noticeable than other spray characteristics.

Network structures and systems: I. Flows characteristics of complex networks

Structural and functional directions of complex network systems research are considered. The network system is defined as a complex network where flows occur. The classification of network systems is carried out on the basis of continuity and the level of orderliness of flows. Flow characteristics of network systems are introduced along with the structural characteristics of complex networks. The problem of critical loading of network components is studied. Problems of dimension and adequacy of models of network systems are considered. It is shown how the system's flow characteristics allow us to identify and exclude fictitious nodes and links from its structure and determine the hidden elements of the system. It was investigated how on the basis of the analysis of flows processes in the system the structure of scale-free networks changed not only during the growth stage, but also during the whole life cycle of the corresponding network system. The problem of isolated zones of network systems is considered and the algorithm is proposed for finding alternative ways for flows in order to bypass inaccessible components of the network.

The Characteristics of Porous Solar Wall Heating System with Localized UFAD

In this paper, the physical models of the porous solar wall heating system with localized underfloor air distribution (UFAD) are established. Based on Brinkman-Forchheimer Extended Darcy and energy two-equation models for saturated porous medium, the influences of the structure of underfloor space on the heat transfer and flow characteristics of the system are simulated, analyzed and compared.The results show that the underfloor space with rational partition is good for improving the heat transfer and flow characteristics of system, and maintaining the cable system in the underfloor space.

Visualization by light transmission of oil and water contents in transient two-phase flow fields

The difficulty of determining transient fluid contents in a soil–oil–water system is hampering an understanding of the system's flow characteristics. In this paper, we describe a light transmission method (LTM) which can rapidly obtain oil and water contents throughout a large two-dimensional flow field of silica sand. By appropriately coloring the water with 0.005% FD&C blue #1, the hue of the transmitted light is found to be directly related to the water content within the porous media. The hue provides a high resolution measurement of the water and oil contents in transient flow fields (such as unstable flow). Evaluation of the reliability of LTM was assessed by checking the mass balance for a known water injection and its utility in visualizing a whole flow field was exemplified for unstable fingered flow by comparing fluid contents to those obtained with synchrotron X-ray radiation.

Control Valves: System Flow Characteristics and Controllability

A theoretical examination is made of the relationship between a control valve and the plant in which it is installed; the effect of valve size and characteristic on the relationship is described. From the theoretical basis, practical rules are devised for use at the design stage, also for later changes that may be necessary once the plant is in operation. Some well known practical difficulties are described, together with means of evading or overcoming them.