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This experimental study explores the effect of using compound technique (passive techniques (packing the shell side with small cylindrical aluminium pieces) and active techniques (air injection or bubble generation) were securitized. It is conducted for both configurations (parallel and counter) flow with applying both techniques (compound) at the same conditions in a double pipe heat exchanger. The main objective of this study is to indicate the effect of employing the two techniques simultaneously and compare the outcomes without and with the passive (packing) method under the same conditions. The heat transfer of heat exchanger in terms of cost and size has been For this purpose the test rig is prepared by designing and making a suitable heat exchanger equipped with flow meters and thermocouples for measuring flow rates and temperatures (Tin and Tout) of both fluids (hot and cold) . The hot fluid is heated in a small tank by electrical heater with temperature controller from (TEquipment). The results show that the performance parameters of the heat exchanger enhanced about (15%) for case of applying the both techniques together and (25)% for case of using active method only.

Due to the upsurge of awareness of the depletion of fossil fuel feedstock and environmental issues, biodiesel has become a more attractive choice. Biodiesel's productivity is deemed a fruitful and significant research field since its relevance obtains from the increased oil prices and environmental benefits. This paper presents a study of Alfa waste cooking oil used to produce biodiesel oil via the transesterification process. The investigation includes various variables such as transesterification time, catalyst ratio, temperature, and biodiesel yield. Two catalysts (NaOH and KOH) have been utilized in this study. The engine test was carried out at constant load with increasing speed to compare different fuels' performance relative to mineral diesel. The produced biodiesel was categorized according to ASTM D6751. The highest conversion and yield of biodiesel in the transesterification method were scrutinized using the KOH catalyst compared to the NaOH catalyst. The maximum conversion and yield of biodiesel are 97.76 and 94.4%, respectively, with optimum operating conditions of 60 oC reaction temperature, 3 hours reaction time, and KOH catalyst at 4% weight. Consequently, the engine test outcomes revealed similar biodiesels trends compared to diesel in terms of engine brake power and brake specific fuel consumption with increasing engine speed.

This paper presents a modified multilevel inverter with a few number of semiconductorswitches and increasing number of output levels. One stage of the proposed inverter leads to getseven levels in the output voltage, while, forty-nine levels can be obtained when using two stages.Only six semiconductor switches are required for each stage. Standard DC sources are used, so, DC-DC converter is not required to get the desired output standard voltage. Total harmonic distortion in the output waveform of the two stage inverter is very low, so, using filter to improve output waveform is unnecessary. This topology is valid for all types of loads. Simulation results are presented for one stage and two stage inverters proposed. Experimental results are included for the one stage inverter to verify the theoretical results.