المستودع الرقمي لـقسم الهندسة الميكانيكية والصناعية

An efficient way to reduce the energy required for conditioning buildings and therefore to reduce CO2 emission is the use of proper thermal insulation in buildings' external walls. This measure requires data from metrological stations that can be used in the optimization of the thermal insulation. The main objectives of this study are to construct thermal climatic zones for Libya and to specify the optimum insulation thickness for external walls for the different zones. This work is comprehensive as the metrological data from all existing 33 weather stations has been collected and used for identifying thermal zones. For the optimization of the construction of external walls, the most commonly used local wall structures are investigated: hollow concrete block, limestone block and hollow brick. In addition, four thermal insulation materials: extruded polystyrene, expanded polystyrene, rock wool and foamed polyurethane are used with every wall type. Optimum insulation thickness, energy savings, energy cost and payback periods were estimated for the 33 locations using life cycle cost analysis. A map is constructed for the thermal zones based on degree-day values for the entire country. The results show that limestone blocks with expanded polystyrene insulation form the optimum wall construction as it provides the minimum total cost for all locations. Depending on the Degree-day values, the optimum insulation thickness varies between 5.4 and 15.3 cm across the country with energy saving varies between 28 and 178 $/m2. Using the optimum thickness, the average CO2 emissions can potentially be reduced by about 85%. Finally, a contour map represents the optimum thickness of expanded polystyrene is presented in this work. arabic 12 English 80
Samah Khlifa Otman Alghoul, (1-2021)

This paper presents valuable potential savings from fuel and financial expenses of a steam boiler being studied at Elkhmus power plant, Libya. For this research, a visual basic program was developed and being applied for analyzing the gathered data. Key findings pointed to an acceptable level of savings throughout the entire operations within the studied section of the power plant. The highest level of findings was found to be the increasing of thermal gain along with the total efficiency of the boiler as a result of using the exhaust temperature for heating-up the feed water to the boiler. It was clearly found that the increase of the total efficiency has a direct impact on saving the amount of consumed fuel, and thereby the financial expenses were saved by an average of about 11.6% arabic 16 English 78
Rajab HOKOMA, Nabil M. Muhaisen, Omran Alshogi(1-2014)

This paper is concerned with calculating boiler efficiency as one of the most important types of performance measurements in any steam power plant. That has a key role in determining the overall effectiveness of the whole system within the power station. For this calculation, a Visual-Basic program was developed, and a steam power plant known as El-Khmus power plant, Libya was selected as a case study. The calculation of the boiler efficiency was applied by using heating balance method. The findings showed how the maximum heat energy which produced from the boiler increases the boiler efficiency through increasing the temperature of the feed water, and decreasing the exhaust temperature along with humidity levels of the of fuel used within the boiler. arabic 15 English 78
Rajab HOKOMA, Nabil M. Muhaisen(1-2012)

تناولت هذه الورقة دراسة للوضع الحالي لأعمال الصيانة بشركة الواحة للنفط بغرض التحقق من مستوى التطبيق الفعلي لأساليب الصيانة الإنتاجية الشاملة في الشركة، هدفت الدراسة للتعرف على أوجه القصور في تنفيذ أعمال الصيانة الحالية لاقتراح ما يلزم استخدامه من مفاهيم حديثة لأعمال الصيانة، بغرض تحقيق النجاح والرفع من مستويات الأداء لكافة الاعمال المنفذة في الشركة. اعتمدت الدراسة استخدام استمارة استبيان تم تصميمها خصيصاً لهذا الغرض، بالإضافة إلى إجراء بعض المقابلات الشخصية مع من لهم علاقة بأعمال الصيانة في الحقول التابعة للشركة، اضافة الى استخدام أسلوب الملاحظة المباشرة لكشف بعض المعوقات والاخطاء في تخطيط وتنفيذ العمليات بالشركة. تمثلت المساهمة العلمية لهذه الورقة في تقديم حقيقة من أرض الواقع على مدى الفهم والدراية للأساليب الحديثة لأعمال الصيانة، واستناداً على ما تم تحليله من بيانات أوضحت النتائج وجود انخفاض في مستويات الأداء لأعمال الصيانة، وضعف ملحوظ في برامج التدريب والتطوير، وعدم وضع استراتيجيات مناسبة لبرامج الصيانة المخططة، وانخفاض مستوى السيطرة والتحكم في تنفيذ العمليات، كذلك وجود تدني في مستوى الجودة في عمليات الصيانة والإنتاج. كما اقترحت الدراسة على متخذي القرار ضرورة اتخاذ إجراءات فورية فعالة، ووضع استراتيجية لتنفيذ نظام الصيانة الإنتاجية الشاملة، والاهتمام أكثر ببرامج التدريب والتطوير، كما أشارت الدراسة الى ضرورة إدخال ثقافة التحسين والتطوير المستمر والتعريف بها لكل العاملين.
أ.د. رجب عبدالله حكومة, المعتصم بالله المبروك أحمد العكاري(1-2019)

Abstract— Horizontal-Axis Wind Turbine (HAWT) small scaled is widely employed for generating electricity for domestic uses due to higher efficiencies among other turbines. Three-Blade HAWTs power performance can be further improved by optimizing lift (CL), drag (CD) coefficients and thus power (CP) coefficient. In this study, Taguchi design of experiments (DOE) of L9 orthogonal array (OA) with three parameters and one interaction, namely airfoil, angle of attack, interaction (between the airfoil and the attack angle), and Reynolds number with three value levels are used to determine the single quality (CL, CD, CP) optimization. For multi-qualities optimization, the Grey-based Taguchi is employed which combines the Taguchi DOE orthogonal array with grey relational analysis to determine the grey relational grade, which can convert the multi-response grey relational grade into single grey relational grade, thus the optimal design parameters can be achieved. The Q-Blade software is used to determine lift and drag coefficients and empirical equation used for power coefficient. The obtained results show that the most influence design parameter on airfoil coefficients is Reynolds number with 72.6% contribution followed by attack angle with 16.8%, interaction with 9.1% and airfoil with 1.5%. The F-value indicates that Reynolds number and angle of attack give at least 97.5% and 90% confidence respectively, for this specific set of experiments. arabic 14 English 86
Abdulhamed M. Hwas, Ali M. Hatab(12-2020)

Almost all Libyan industries (both private and public) have struggled with many difficulties during the past three decades due to many problems. These problems have created a strongly negative impact on the productivity and utilization of many companies within Libya. This paper studies the current awareness and implementation levels of Just-In-Time (JIT) within the Libyan Textile private industry. A survey has been applied in this study using an intensive detailed questionnaire. Based on the analysis of the survey responses, the results show that the management body within the surveyed companies has a modest strategy towards most of the areas that are considered as being very crucial in any successful implementation of JIT. The results also show a variation within the implementation levels of the JIT elements as these varies between Low and Acceptable levels. The paper has also identified limitations within the investigated areas within this industry, and has pointed to areas where senior managers within the Libyan textile industry should take immediate actions in order to achieve effective implementation of JIT within their companies. arabic 17 English 88
ٌRajab HOKOMA(7-2010)

Supply Chain Management (SCM) is the integration between manufacturer, transporter and customer in order to form one seamless chain that allows smooth flow of raw materials, information and products throughout the entire network that help in minimizing all related efforts and costs. The main objective of this paper is to develop a model that can accept a specified number of spare-parts within the supply chain, simulating its inventory operations throughout all stages in order to minimize the inventory holding costs, base-stock, safety-stock, and to find the optimum quantity of inventory levels, thereby suggesting a way forward to adapt some factors of Just-In-Time to minimizing the inventory costs throughout the entire supply chain. The model has been developed using Micro- Soft Excel & Visual Basic in order to study inventory allocations in any network of the supply chain. The application and reproducibility of this model were tested by comparing the actual system that was implemented in the case study with the results of the developed model. The findings showed that the total inventory costs of the developed model are about 50% less than the actual costs of the inventory items within the case study. arabic 14 English 67
Rajab HOKOMA, Faraj Farhat El Dabee(9-2012)

This paper is designed to present an experimental study being recently conducted for investigating the effect of some fuel additives on the performance of spark ignition within a benzene engine. Three types of additives were added separately (Gasoline Additive, Gasoline Booster, and Octane Booster) to pure gasoline with a volumetric ratio 1:6, 1:7, and 1:8 respectively. Four separate laboratory experiments being conducted using an internal combustion engine at rotational speed ranges from 600 to 3000 rpm, where the three mixtures and the pure gasoline itself were used. The findings showed that there was a positive effect on the engine performance as the brake power increases by 8%, 13% and 23% at the use of Gasoline Additive, Gasoline Booster, and Octane Booster respectively as compared with using only the pure gasoline. The brake thermal efficiency (ɳth) was also affected positively showing its maximum value of about 8% for Octane Booster, and with a minimum value for using Gasoline Additive at about 4.7%. In addition, this study showed that the value changes in the brake specific fuel consumption for Gasoline Additive, Gasoline Booster, and Octane Booster was at the levels of 1%, 2%, and 5% respectively compared with using only the pure gasoline. Furthermore, the results also showed that the use of Octane Booster gave the highest level of air fuel ratio arabic 18 English 97
ٌRajab HOKOMA, Nabil M. Muhaisen(1-2017)