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