Mechanical Engineering

A simple Okra threshing machine was designed, fabricated and tested to alleviate the problems associated with Okra processing in Nigeria. It is consists mainly of five units namely, the feeding assembly, the threshing unit, separation unit, power transmission unit. The overall mean threshing and cleaning efficiencies obtained were 93.95 and 99.56% respectively. Drum speed 500rpm combine with 55mm concave clearance gave the highest Threshing efficiency of 99.99%. All speeds, concave clearance combinations gave clearing efficiency above 98%. The machine threshing and cleaning efficiencies increased with increase in drum speed and decrease with increase in concave clearance. The machine is simple to operate and maintain without formal training.

The increased demand for the development of certain materials to be used in aerospace, military and medical industries justifies the execution of an extensive investigation to enhance the properties of such materials, especially the shape memory alloys (SMAs). Copper based SMAs are constantly receiving wide attention due to their low cost and important applications. This work is an attempt to enhance the fatigue life of CuZnAl shape memory alloys. A powder metallurgy technique was adopted to prepare samples. Alloying elements such as vanadium, nickel and germanium were used to improve the mechanical properties. Porosity, SEM, EDS, microhardness, compression and fatigue tests were conducted. Alloying with (0.4%wt.V) results in a significant increase in ultimate compressive strength of (33.6 %) in comparison with the reference sample. The reference (control) sample in this work has a substantial increase in ultimate compressive strength (100%) in comparison with a previously reported value in the literature. A microhardness test supports the ultimate compressive strength result and yields an improvement of (39%). These improvements are reflected positively on the fatigue behavior. The endurance limit of alloyed sample was improved by a factor of (23.3 %) in comparison with the reference sample.

In this project we will using three type of tools ,straight cylindrical , taper cylindrical and triangular tool all made of High speed steel (Wc-Co) for the friction stir welding (FSW) aluminum alloy H20 –H20 and test the mechanical properties of the welded joint by tensile test and vicker hardness test. Finally we will compare mentioned mechanical properties and make conclusion. The result will help welding parameter optimization in different type of friction stir process. Like rotational speed ,depth of welding ,travel speed ,type of material ,type of joint, work piece dimension ,joint dimension ,tool material and tool geometry .previous investigations in different types of materials work pieces ,joint type, machining parameter and preheating temperature take placed. in this investigation 3 mentioned tool types that are popular in FSW tested and the results will complete other aspects of the process .hope this paper open a new horizon in experimental investigation of mechanical properties of friction stir welded joint with other different type of tools like oval shape probe, paddle shape probe ,three flat sided probe, and three sided re-entrant probe also other materials and alloys like titanium or steel in near future.

The thermal power plants are used to generate power. The thermal power plants are designed based on required conditions, but actually inlet conditions are not as per the designed conditions. Variations in the power outputs from power plant are always a matter of disputes. So correction curves for power and heat rate are generated. In this paper, the thermodynamic analysis of 120MW thermal power plant has been done at a different inlet pressure (123.14 bar) and at different inlet temperatures (507.78°C, 517.78°C, 527.78°C, 537.78°C, 547.78°C, 557.78°C, 567.78°C). The correction curves for power and heat rate have been generated for the combined effect of inlet pressure and different inlet temperatures. These curves indicate that if inlet conditions vary then power output and heat rate also vary.

In the present study numerical analysis of enhancement in heat transfer characteristics in a double pipe heat exchanger is studied using a holed twisted tape. The twisted tape with a constant twist ratio is inserted in a double pipe heat exchanger. Holes of diameter 1mm, 3 mm and 5 mm were drilled at regular pitch throughout the length of the tape. Numerical modeling of a double pipe heat exchanger with the holed twisted tape was constructed considering hot fluid flowing in the inner pipe and cold fluid through the annulus. Simulation was done for varied mass flow rates of hot fluid in the turbulent condition keeping the mass flow rate of cold fluid being constant. Thermal properties like Outlet temperatures, Nusselt number overall heat transfer coefficient, heat transfer rate and pressure drop were determined for all the cases. Results indicated that normal twisted tape without holes performed better than the bare tube. In the tested range of mass flow rates the average Nusselt number and heat transfer rate were increased by 85% and 34% respectively. Performance of Twisted tape with holes was slightly reduced than the normal twisted tape and it deteriorated further for higher values hole diameter. Pressure drop was found to be higher for the holed twisted tape than the normal tape.

Cavitating flows are highly complicated because it is a rapid phase change phenomenon, which often occurs in the high-speed or rotating fluid machineries. It is well known that the cavitating flows rise up the vibration, the noise and the erosion. Therefore, the research on the cavitating flows is of great interest. Numerical method is highly important approach for studying the cavitating flow. The propeller is the predominant propulsion device used in ships. The performance of propeller is conventionally represented in terms of non-dimensional coefficients, i.e., thrust coefficient (KT), torque coefficient (KQ) and efficiency and their variation with advance coefficients (J). It is difficult to determine the characteristics of a full-size propeller in open water by varying the speed of the advance and the revolution rate over a range and measuring the thrust and torque of the propeller. Therefore, recourse is made to experiments with models of the propeller and the ship in which the thrust and torque of the model propeller can be conveniently measured over a range of speed of advance and revolution rate. Experiments are very expensive and time consuming, so the present paper deals with a complete computational solution for the flow using STAR-CCM+ software. When the operating pressure was lowered below the vapor pressure of surrounding liquid it simulates cavitating condition. In the present work, STAR-CCM+ software is also used to solve advanced phenomena like cavitation of propeller. The simulation results of cavitation and open water characteristics of propeller are compared with experimental predictions, as obtained from literature [1].

Small air conditioning units are usually used for small and medium scale residential buildings. Therefore, more energy efficiency and lower cost are needed along with reliable control for the air conditioning units. An experimental investigation has been carried out to study the performance of a direct expansion air conditioning unit under abnormal surrounding ambient conditions. To facilitate variation of refrigerant flow rate according to the evaporator load, a suitable thermostatic expansion valve and liquid refrigerant reserve was used. The influence of evaporator airflow and its temperature on the air conditioning unit performance and compressor power consumption has been investigated. The performance of air conditioning unit is simulated using the TRANSYS Simulation Program. The model is validated by real operating data from the system. It has been found that a 14.28 % reduction in compressor power consumption is achieved by decreasing the condenser inlet air temperature from 50 to 35 ºC. The cooling capacity of the evaporator was increased by 32.2 % with decreasing the condenser inlet air temperature from 50 to 35 ºC, Also it was increase by 7.56 % with increasing the evaporator entering air volume flow rate from 300 to 600 m3/hr. It can be concluded that the COP increases by 19.84 % with increasing the condenser inlet air temperature from 50 to 35 ºC. The modeled results of the air conditioner’s COP show agreed well with the corresponding measured data, the uncertainty was within ±11.9 %.

Shot-peening is a cold-working process primarily used to improve the fatigue life and strength of metallic structural components. In this work, the shot-peening time (SPT) effect on fatigue life of 7075-T651 Al-alloy was investigating at room temperature stress ratio R=-1 and reversed bending. An increase in shot-peening time (SPT) resulted in an increase in fatigue life improvement percentage (FLI %). For 5 SPT, reducing the applied stress, increasing (FLI%) while at 10 and 15 SPT reducing the applied stress reducing the (FLI%).

In this work, an experimental study was carried to obtain the fatigue damage for aluminum alloy, 2024-T4 under rotating bending loading and stress ratio R= -1. The experiments were done at RT(room temperature) ,25oC ,and 200oC. A modified damage stress model was suggested to predict the fatigue life under elevated temperature which has been formulated to take into account the damage at different load levels. The microstructure and hardness of aluminium alloy after fatigue-creep interaction testing have been investigated. Attention has been paid to the role of the microstructure and hardness on the fatigue-creep strength of aluminum alloy. It has been shown that, there is a little effect of microstructure in the cyclic response of aluminum alloy, while the hardness has a significant effect on the fatigue-creep strength. This is described numerically.

This paper describes the study of coefficient of thermal expansion (CTE) of as-cast and heat treated aluminium 7075/ SiC composites. These composites were subjected to different aging durations. The stir casting technique is used to prepare the castings. Castings were machined in accordance with ASTM standards followed by heat treatment process. All the castings were aged to different periods of 1hr, 3hr, 5hr at an aging temperature of 175 oC. Coefficient of thermal expansion tests were performed in both as-cast and heat treated conditions. In each case the coefficient of thermal expansion values were found to increase with increase in aging durations. Solution heat treatment at 530 oC followed by artificial aging at 175 oC found to increase in dimension change of every specimen tested. The coefficient of thermal expansion curves exhibited some residual strains, which were decreased with the increase in aging durations.