Performance analysis of a ball valve used for gas pipelines by introducing nondimensional parameters

The present study deals with the performance characteristics of a ball valve used for gas pipelines by introducing nondimensional parameters. The ball valve has relatively complex flow characteristics on the inside and downstream of the valve, although it has a simple structure as compared with the other valves. The nondimensional parameters, which define the valve operating conditions, are introduced to analyze the nature of the physical properties due to the valve’s complex flow. To define the valve flow conditions with respect to valve size, seven nondimensional parameters were selected: pressure ratio, volumetric flow rate ratio, mass flow rate ratio, Reynolds number, Mach number, valve flow coefficient, and inherent flow coefficient. The open-loop type experimental setup is designed to measure the pressure drop and the volumetric flow rate of the ball valve according to the opening rate (angle) of the test valve. Based on the experimental data, obtained by the data acquisition system of the test rig, useful nondimensional parameters to define the nature of the valve performance have been selected and determined. Throughout the experimental analysis of the ball valve, it was found that the nondimensional parameters of pressure ratio, Reynolds number, and Mach number have a similar tendency as related to the valve performance. It can be seen that the intrinsic characteristics of the ball valve are represented by the selected nondimensional parameters, which are defined irrespective of the valve size. The authors proposed a quadratic polynomial for the volumetric flow rate ratio, and the mass flow rate ratio, and introduced the formula for predicting the inherent flow coefficient by the cubic approximation polynomial. It is noted that the nondimensional parameters of the ball valve can be used to determine the performance characteristics with respect to the valve-opening rate and size effectively.

Theoretical study on the influence of sprayed water temperature and minimum temperature difference to the efficiency of a humidification – dehumidification desalination unit

The main content of the paper focuses on the theoretical study of the heat exchange between sprayed water and air in a humidification – dehumidification unit. The gained results [7] have been validated by using Hou data [1] and show that, in order to achieve the maximum GOR, the mass flow rate ratio between sprayed water and air depends on the sprayed water temperature and the minimum temperature difference ∆tmin. Particularly, the spayed water temperature should be from 70oC to 75oC when the minimum temperature difference ∆tmin= 5oC.

An Experimental Investigation of Full-Coverage Film Cooling Effectiveness and Heat Transfer Coefficient of a Turbine Guide Vane in a Linear Transonic Cascade

This paper experimentally investigates the film cooling performance of an enlarged turbine guide vane with full-coverage cylindrical hole film cooling in short duration transonic wind tunnel which can model realistic engine aerodynamic conditions and adjust inlet Reynolds number and isentropic exit Mach number independently. The effects of mass flow rate ratio (MFR=4.83%∼8.83%), inlet Reynolds number (Rein= 1.7×105∼5.7×105), and isentropic exit Mach number (Mais=0.81∼1.01) are investigated. There are five rows of cylindrical film cooling holes on the pressure side and four such rows on the suction side respectively. Another four rows of cylindrical holes are provided on the leading edge to obtain a showerhead film cooling. The surface heat transfer coefficient and adiabatic film cooling effectiveness are derived from the surface temperatures measured by the thermocouples mounted in the middle span of the vane surface based on transient heat transfer measurement method. Mass flow rate ratio is shown to have a significant effect on film cooling effectiveness. The increase of mass flow rate ratio increases film cooling effectiveness on pressure side, while increasing this factor has opposite effect on film cooling effectiveness on the suction side. At the same mass flow rate ratio, increasing the Reynolds number can enhance the film cooling performance, the expectation is that at low mass flow rate ratio condition increasing the Reynolds number decreases film cooling effectiveness on the pressure side. The heat transfer coefficient increases with the mass flow rate ratio increasing on both pressure and suction side. At middle and high inlet Reynolds number condition, in the region of 0.4<s<0.6 on suction side, the coolant weakens heat transfer adversely.

High Efficient Metal Powder Production by Gas Atomisation Process

The most important parameter for production of fine powders efficiently is the velocity of the atomizing gas. This can be achieved by increasing the pressure, but this way will not be economic. For that reason, to achieve supersonic velocities different nozzle designs are used in close coupled configuration for an efficient atomization. In this study, a new laval type nozzle was designed and manufactured. Using this nozzle tin powder was produced in close coupled system by using nitrogen gas at different operating conditions. The results showed that the increasing the gas pressure up to 1.47 MPa reduced the mean powder size down to 11.39 microns with a gas/melt mass flow rate ratio of 2.0. Powders are spherical in shape and have smooth surfaces.

Maximum Power Extraction From a Hot Stream in the Presence of Phase Change Under Limiting Collecting Temperatures

In this paper we consider the fundamental problem of maximizing the power extraction from a hot stream when the collecting stream experiences a phase change and there are limits imposed by the materials on the operating temperatures. It constitutes an extension of [4] where it was pointed out the existence of an optimal mass flow rate ratio of the hot stream to the collecting stream. In this work, we study the effects of the restrictions imposed by limiting temperatures on the spatial configuration, power extraction and the optimal matching of the two streams. An optimal hot-stream-to-collecting-stream mass flow rate ratio can be found when the collecting stream experiences a phase change while in contact with the hottest section of the hot stream. Associated to the optimal mass flow rate ratio there is also an optimal heat exchanger area allocation. The effects of several operating parameters on the optimal configuration are documented. This paper constitutes an illustration of how thermodynamic optimization leads to the discovery of system structure (constructal theory [1]).