A. Al-Salaymeh

Effect of Channel Aspect Ratio on the Flow Performance of a Spiral-Channel Viscous Micropump

We investigate the effect of channel aspect ratio on the flow performance of a newly introduced spiral-channel viscous micropump. An approximate 2D analytical solution for the flow field, which ignores channel curvature but accounts for a finite wall height, is first developed at the lubrication limit. A number of 3D models for spiral pumps with different aspect ratios are then built and analyzed using the finite volume method. Numerical and analytical results are in good agreement and tend to support one another The results are compared with an approximate 2D analytical solution developed for infinite aspect ratio, which neglects the effect of side walls, and assumes uniform velocity distribution across the channel width. The error in this approximation was found to exceed 5% for aspect ratios less than 10. Pressure and drag shape factors were introduced to express the effect of the pressure difference and boundary velocity on the flow rate at various aspect ratios for both moving and stationary walls

Theoretical and experimental investigations of a wide-range thermal velocity sensor

This paper describes a two-wire thermal velocity sensor operating with an electrically heated upstream wire and a downstream wire acting as a resistance thermometer. The sensor can be operated in such a way that the phase shift between the periodic (sinusoidal) voltage that drives the first wire and the detected second signal is controlled by a combination of convection, diffusion and the finite thermal response time of the wires. This yields an effective operating range of 0.05?m?s-1?U?25?m?s-1 and corresponds to a bandwidth of 1-500. This wide velocity range is confirmed theoretically and experimentally for a number of sensors. The paper provides detailed analytical and numerical investigations which are well verified by experiments. The resultant design work also aimed at a sensor that can be manufactured industrially and can therefore be produced at low cost. Our immediate application is the measurement of flow velocities (or volume flow rates) in slowly changing unidirectional flows. This sensor design is briefly described and the description involves the mechanical part of the sensor as well as the electronics. Calibration of the first automatically manufactured sensors is shown. It is demonstrated that their performance is as good as those of the sensors that the authors have designed and built during their initial development work.

Thermal wakes measurement in electronic modules in the presence of heat transfer enhancement devices

Abstract This paper reports the thermal wake measurements in electronic modules in the presence of heat transfer enhancement devices. The enhancement devices consist of various sizes and shapes of ribs, secondary air flow injections through cylinders and “film cooling-like” injection devices. The effects of such devices on the thermal wake and the pressure drop characteristics of an array of rectangular modules at different values of Reynolds number in the range 4.0×103–1.6×104 have been investigated. Generally, it was found that using sizes and shapes of ribs as well as the presence of secondary air flow injection cylinders and film cooling-like injection hole devices tends to results in a significant attenuation in the thermal wake, in particular in the region downstream of the enhancement devices, depending on the location of the active module in the array. A maximum attenuation in the thermal wake of 33%, 30% and 25% for the rectangular, triangular and cylindrical ribs occurs at the sixth row, respectively, when the active module is located just upstream of the rib-enhancement devices. The film cooling-like enhancement devices tend to have higher attenuation in the thermal wake than the rib enhancement devices for the same location of the active module downstream of these devices, but with very much smaller pressure drop.

Experimental in situ investigations of turbulence under high pressure

In tube injection systems applied in high‐pressure processing of packed biomaterials and foods, the pressure‐transmitting medium is injected into the vessel to increase the pressure up to 1000 MPa, generating a submerged liquid‐free jet. The presence of a turbulent‐free jet during the pressurization phase and its positive influence on the homogeneity of the product treatment has already been examined by computational fluid dynamics investigations. However, no experimental data have supported the existence and properties of turbulent flow under high‐pressure (HP) conditions up to 400 MPa. This contribution presents the development of two experimental setups: HP‐laser Doppler anemometry and HP‐hot wire anemometry. For the first time the time‐averaged velocity profiles of a free jet during pressurization up to 300 MPa at different Reynolds numbers (Re) have been obtained. In this article, the dependence of the velocity profiles on the Re is discussed in detail. Moreover, the relaminarization phenomenon of the turbulent pipe flow most likely caused by the compressibility effects and viscosity changes of the pressure‐transmitting medium is examined.

A theoretical study of the performance of wind-driven pumps under Jordanian climatic conditions

The utilization of renewable energy resources such as wind energy has increased recently due to the rising concern regarding global warming and the associated impact upon climate change, the increasingly rapid depletion of fossil fuel resources and the desire to maximize security of fuel supply. This study deals with autonomous wind pump applications for remote areas in Jordan. The performance of roto-dynamic wind-driven pumps under normal operating conditions has been estimated based on the mathematical model proposed by Mathew and Pandey for the integrated output of wind-driven roto-dynamic pumps. The effects of the specific speed and specific diameter ratios and the gear ratio on the size of the pump selected have been investigated. Specifications and the performance of piston pumps have also been investigated under the same conditions for comparison purposes. It is clear that the roto-dynamic wind-driven pumps offer better performance than the piston pumps.

Impact of connecting renewable energy plants on the capacity and voltage stability of the national grid of Jordan

This paper presents the impact of connecting large scale renewable energy plants (REPs) comprising photo voltaic plants (PVPs) and wind power plants (WPPs) to the national grid of Jordan. The candidate geographical sites with valuable wind speed, solar irradiation, and space availability are considered. Load flow analysis has been carried out to investigate the capacity of the transmission network to integrate REPs. Transmission network upgrading to increase the network capacity is also studied. Moreover, the impact of increasing the penetration levels of PVPs and WPPs, during normal conditions, on the voltage stability has been analyzed. All simulation studies have been implemented using the professional DIgSILENT software package. The load flow simulation results show that congestion management, based on line flow capacity constraints, requires that maximum power generation of the REP shall not increase beyond 10% of the annual peak demand of Jordan. However, higher penetration levels can be reached provided that network upgrading is implemented. Network upgrading to accommodate up to 1600 MW of RE generation by 20202 is proposed. Furthermore, voltage stability analysis shows that the voltage profile and the dynamic voltage behavior depend significantly on the grids short circuit capacity at the point of connecting the REP. P-V curves have been developed to determine the maximum generation that could be connected at different points on the grid before reaching a voltage collapse. It was also found that the maximum generation size can be doubled by introducing voltage and reactive power control capability.

Development of a two‐wire thermal flow sensor for industrial applications

Thermal flow sensors with a wide dynamic range are at present not available in spite of the large demand which exists for such sensors in practical fluid flow measurements. In this paper, it is shown that the velocity range of a “time‐of‐flight” thermal flowmeter for slowly changing flows can be increased by using wires (or other heating/sensing elements) with large thermal inertia (time constant) and heating the sending wire with a continuous sinusoidal current, instead of discrete, very short, square‐wave pulses as in the usual pulsed‐wire anemometer. The device described here uses two parallel wires of 12.5μm diameter and its usable speed range is 0.05 to 25m/s. Although the present thermal flowmeter can be applied as a point measurement device, the main applications are in pipe flow, especially at very low flow rates. The high sensitivity at low flow rates makes the device especially suitable for this purpose.