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

Analysis of heat transfer and fluid flow thermodynamic irreversibilities is realized on an example of a counter flow double pipe heat exchanger utilizing turbulent air flow as a working fluid. During the process of mathematical model creation and for different working and constructing limitations, total thermodynamic irreversibility is studied. The present work proves that the irreversibility is occurred due to unequal capacity flow rates (flow imbalance irreversibility). It is concluded that the heat exchanger should be operated at effectiveness greater than 0.5 and the best design will be achieved when  approach from one where low irreversibility is expected. A new equation is adopted to express the entropy generation numbers for imbalanced heat exchangers of similar design with smallest deviation from the exact value. The results obtained from the new equation are compared with the exact values and with that obtained by another author

The aim of the present work is to increase the limit of stability and improve the performance of an actual aircraft turbocharger compressor with different casing modifications. Three schemes of modifications in the shroud side of the compressor casing through the vaneless region; circumferential groove, protrude and combined of groove and protrude, were studied. The time variations of wall static pressure were observed using couple of pressure transducers with high frequency response in the vaneless region at different compressor operating conditions. Stall initiation and surge triggering were detected by analyzing both of the fluctuations of pressure signals and the power spectrum density (PSD) which deduced by using the Fast Fourier Transformation analysis (FFT). The number and speed of stall cells relative to the impeller speed were investigated. The flow angles, that are representing the stall initiation for the original compressor, were studied theoretically and experimentally. Both the theoretical and the experimental results were compared with those experimentally obtained by another author and show good agreements. The present measurements show that the inception of unsteady flow which leads to rotating stall initiation hence surge trigger appears at the vaneless region between the impeller exit and the diffuser vane leading edge. The modified casing by one way of the three-presented schemes can be used to increase the limit of stability for low speed compressor at different operating conditions. The compressor with groove height Hg = 0.2 and depth Tg = 0.2 gives about 55% and 39% improvement in stall margin, but unfortunately with decrease in the pressure coefficient at low flow rates. While the compressor achieves improvement between 14% and 26% in the range of stable operating based on surge margin and about 13% in pressure coefficient. Modification utilizing combination of groove and protrude achieves improvements of about 28% in stall margin, 22% in surge margin and 4% in maximum pressure coefficients

Gas turbine cycle technologies will play a major role in future power generation and several well-justified concepts have been developed or are the subject of major feasibility studies. In the present work, gas turbine cycles are modified with steam injection between the combustion chamber exit and the gas turbine inlet. Heat recovery steam generators, utilizing the exhaust gases, provide these cycles with the injected steam at saturated vapor. The thermodynamic characteristics of the various cycles are considered in order to establish their relative importance to future power generation markets. The irreversibility of the different composing units of the cycles and the variation of gas properties due to steam injection as well as changes in the interrelation of component performance parameters are taken into account. The isentropic temperature ratio and maximum to minimum cycle temperature ratio are varied over some ranges that slightly exceed their practically acceptable bounds in order to comprehensively investigate their effects on cycle characteristics. The performance characteristics for various modified and regeneration cycles are presented at the same values of the operating parameters. The present modified cycles with steam injected cycles achieve an additional power output and higher efficiencies, resulting in a lower specific cost. At the chosen values of the operating parameters, the enhancement achieved in the overall efficiency for the simple, reheat (with steam injection at high and low pressures) and partial oxidation (with steam injection at high and low pressures) gas turbine cycles are of about 20~30%, 120~200%, 10~12%, 120~260%, 20% respectively. The present modified cycles technique can be considered among the possible ways to improve the performance of gas turbine cycles based power plants at feasible costs. This concept can be used for similar core engines

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

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