Compressors have a limited stable operating range, due to occurrence of rotating stall and surge, so many techniques were introduced to increase its stability and more enhancements still are needed for optimum performance. Two different techniques for enhancing the compressor stability are investigated in the present work. The first technique makes use of splitters with different lengths located at various positions through the diffuser passages. In the second, radial grooves with different geometric parameters are manufactured through the compressor front casing matching with the diffuser passages and the vaneless regions. Influences of various geometric parameters on the stability of the compressor using the two techniques are studied. Enhancement in the flow and pressure coefficients at stall initiation of about 22.5 % and 4.4 % respectively, could be achieved by providing the compressor with diffuser splitters. Providing the compressor with radial grooves achieves an enhancement in the flow coefficient at stall initiation reaches to 45.5 %. The flow coefficient at stall initiation resulted from the use of the radial grooves technique is given in a form of streamlines in terms of the grooves width and depth. The grooves width and depth required for optimum flow stability could be predicted from these streamlines for similar compressors. The present experimental results show an acceptable agreement with those obtained by another author using similar compressor

Compressors have a limited stable operating range, due to occurrence of rotating stall and surge, so many techniques were introduced to increase its stability and more enhancements still are needed for optimum performance. Two different techniques for enhancing the compressor stability are investigated in the present work. The first technique makes use of splitters with different lengths located at various positions through the diffuser passages. In the second, radial grooves with different geometric parameters are manufactured through the compressor front casing matching with the diffuser passages and the vaneless regions. Influences of various geometric parameters on the stability of the compressor using the two techniques are studied. Enhancement in the flow and pressure coefficients at stall initiation of about 22.5 % and 4.4 % respectively, could be achieved by providing the compressor with diffuser splitters. Providing the compressor with radial grooves achieves an enhancement in the flow coefficient at stall initiation reaches to 45.5 %. The flow coefficient at stall initiation resulted from the use of the radial grooves technique is given in a form of streamlines in terms of the grooves width and depth. The grooves width and depth required for optimum flow stability could be predicted from these streamlines for similar compressors. The present experimental results show an acceptable agreement with those obtained by another author using similar compressor

The present work deals with one of the new techniques of saline water desalination. It is based on the humidification of ambient air and then dehumidification of this humid air to produce fresh water. Solar ponds as a source of hot saline water are well adapted for coupling with the unit. A computer programs were designed to investigate the performance characteristics at different operating conditions. The important design descriptions and the operating parameters of such units are identified. The effects of the operating parameters on the unit performance characteristics are studied. The productivities obtained from simple and modified models are qualitatively compared with the experimental values. Due to the simplicity of this technique, it may be a good candidate and is recommended if one looks for a solution for fresh water needs of small communities living in rural areas.

A proposed model is introduced for predicting the performance characteristics of an inward flow hydraulic turbine at design and off-design conditions. The model simulates the flow through the turbine runner based on fundamental principles. The incidence loss at the runner inlet, which commonly exists under off-design conditions is taken into account for both positive and negative incidence angles. The runner internal loss and the draft tube loss, which exist even under design conditions are taken into consideration through the use of simple and reasonable empirical expressions. The model is developed for studying the effect of the operating and the geometric parameters on the turbine performance under design and off-design conditions. The energy losses at the runner entrance due to incidence and that occur at the runner exit are minimized. An alternative optimization method is adopted to obtain the best possible efficiency of the turbine. Moreover, new charts are obtained and can be used for maximizing the efficiency of the radial turbine at different operating conditions. The obtained results from the proposed model show an acceptable agreement with the available published experimental and theoretical data

A theoretical model is developed for the effect of the operating parameters and the geometric parameters on the Kaplan turbine performance under design and off-design conditions. In the theoretical model, the incidence loss at the runner inlet that exists under off-design conditions for both positive and negative incidence angles is taken into account. The runner internal loss and the draft tube loss, which exist even under design conditions, are also taken into consideration through the use of simple and reasonable empirical expressions. The experimental works were carried out to validate the theoretical results. An optimization technique is adopted to obtain the operating parameters that achieve the best possible efficiency of a Kaplan turbine. A chart is deduced for detecting the suitable values of the operating parameters that achieve efficiency higher than 88% for different geometric parameters of the axial flow turbine, constant runner inlet blade angle. Comparisons of the obtained results with the present experimental and available published works show an acceptable agreement

Experimental study of natural convection heat transfer inside smooth and rough surfaces of horizontal equilateral triangular channels with a uniformly heated surface are performed. The effect of smooth and rough surface of average roughness, ra = 0.02μm, on the heat transfer characteristics are studied. The local and average heat transfer coefficients and Nusselt number are obtained for smooth and rough channel at different Rayleigh numbers from 6.45 × 105 to 4.45 × 106. The findings show that the values of temperature difference between the inside surface and ambient air increase with increase of axial distance from both ends of the channel until a maximum value at the middle of the channel. The results show a higher values of local (Nux) for rough channel along the axial distance compared with the smooth channel. The average Num of rough channel is higher than Num of smooth channel by about 7%. The results obtained are correlated using dimensionless groups for both rough and smooth surfaces of the equilateral horizontal triangular channels

This study presents two different Fault Ride Through (FRT) techniques to keep and restore stability of Fixed Speed Wind Generation system (FSWGs) installed in standalone Micro-Grid (MG). The first technique is an electrical FRT and is implemented by inserting a series resistance with the terminals of FSWGs during fault to maintain reasonable value of terminal voltage and consequently help stability restoration. The second controller is a mechanical FRT controller and is performed by change the gear ratio of wind generation systems to spill part of extracted mechanical power and consequently improving stability issue. Obtained results proved that each controller able to maintain the stability of FSWGs under the most severe disturbance conditions (400 ms three phase fault at FSWGs terminals). The first controller is faster than the second controller in restoring FSWGs stability. Superior results and performances are obtained when the two FRT techniques are employed simultaneously. Without employing any one of the two FRT techniques, FSWGs is not able to maintain or restore its stability after fault clearing. Consequently, MG will lose one of its micro-sources and cannot keep its stability during the standalone mode, unless load shedding strategy is activated. The two proposed controllers are simple, effective, and economical attractive.

In this paper a mathematical model for swash plate compressor is presented. Using this model, the description of the swash plate motion and the average power input to the compressor was derived as a function of the compressor geometry and angular speed under different operating conditions. The performance of an automotive air conditioning system provided with a swash compressor type is experimentally studied. The theoretical and experimental studies of the swash plate compressor indicate that the average power acting on the swash compressor mainly depends upon the swash plate inclination angle, rotational speed and system pressure. It is concluded that, small value of the swash plate inclined angle is necessary for decreasing the power lost due to friction between the slipper and the swash plate and decreasing the shaft power required for the swash compressor. Also, in the design case when a long stroke and minimum shaft power for the swash plate compressor are required, the present analysis is very important for selecting the suitable inclined angle and the stroke length of the swash compressor. The experimental results show that low rotational speed, high cooling capacity and low shaft power per unit refrigerant mass flow rates are required for high values of coefficient of performance and volumetric efficiency. The coefficient of performance relative to that obtained for the corresponding Carnot cycle is parabolically decreased by increasing the shaft power per unit refrigerant mass flow rates. The shaft power values obtained from the theoretical results agree with those obtained from a simulated program prepared by the manufacture company of the swash compressor [8] under different operating conditions.

Cavitation erosion resistance of steels is important in many applications. The investigation of such resistance, under different conditions, should be very useful. Cavitation erosion tests were carried out on carbon steel AISI-1045 using an ultrasonic induced cavitation facility. Cavitation erosion pits and their effect on the localized corrosion were investigated in detail in three different corrosive media: distilled water, tap water, and 3% NaCl water. The results of the investigation using SEM indicated the formation of three types of pits on cavitating specimen surfaces: corrosion pits, erosion pits, and erosion-corrosion pits. The corrosion pits have different shapes, however, the lamellar structure is the dominant structure, and has a large size of about 100 μm. The erosion pits that were formed by the cavitation microjet impacts have sizes of a few micrometers. The erosion-corrosion pits were similar to the corrosion pits, except the erosion pits formed on the corrosion pit surface due to dissolution. The eroded surface removal was the largest in the case of saline water.