Abdulhaiy M. Radhwan

Analysis of assisted coupled solar stills

Abstract The potential of coupled solar stills as a mean for improving solar distillation yield is investigated. A model for a simple solar still assisted by an external solar collector is presented. The governing coupled heat and momentum balance equations are solved for a quasi-steady-state condition with temperature dependent physical properties. The results show that for coupled stills the fresh water productivity increases as the solar collector area of the assisting device increases. For an ideal system, neglecting the thermal inertia, the yield is linearly dependent upon the solar insolation. The thermal inertia causes a significant drop in the system yield and deviation from linearity. The net efficiency of the coupled system is higher than that of a similar simple still by a value that depends mainly upon the system configuration and independent of the meteorological conditions. Comparison of the analysis with experimental data is satisfactory.

Cogeneration by combining gas turbine engine with organic rankine cycle

The gas turbine engine is known by its relatively low efficiency especially at part load. Therefore, to conserve energy and reduce the operating cost, waste heat is recovered by combining a heat-exchange gas turbine cycle with closed organic Rankine cycle. A computer programme was made to calculate parametrically the individual and combined cycle performances, namely the work and efficiency of each. The parameters considered were: gas turbine pressure ratio; maximum cycle temperature; fluid-air mass ratio; and type of working fluid. This analytical study shows that R113 is the optimum choice because it gives the smallest, hence the most economical, size of turbo-expander. Maximum cycle temperature and pressure ratio are relatively the most important parameters. Economic analysis indicates very good rate of return on investment, related with heat recovery by cogeneration.

Transient analysis of a stepped solar still for heating and humidifying greenhouses

Abstract This paper presents the transient analysis of a stepped solar still for heating and humidifying agriculture greenhouses (GH). The still body consists of five stepped basins insulated from the bottom with an inclined glass cover. Air from the GH enters the still from the bottom and flows between the basins and glass cover where it is heated and humidified, and then re-enters the GH from the still top. The still performance parameters, i.e., still components heat rates, air temperatures and humidity, still yield and efficiency are analyzed and presented. The results show that (1) the still daily average efficiency ( η av ) is about 63%; (2) total daily yield is about 4.92 L/m 2 out of which 0.81 L/m 2 is condensed on the glass cover and the rest (4.11 L/m 2 ) enters the GH as humidity carried by the circulating air; (3) temperature distribution for still components increases along the still and follows the sinusoidal trends as the solar intensity; (4) circulating air relative humidity increases along the still and always leaves the still at saturation conditions; and (5) decreasing air flow rate has an insignificant influence on the system productivity; however, it does influence the GH heat load.

Comparison of total energy systems using gas turbines and diesel engines for combined cooling

A gas turbine engine was used to drive the compressor of a vapour compression cycle so that the usually wasted energy in the exhaust gases was partially recovered and used in the generator of an absorption cycle. The cooling effect was therefore boosted. The degree of energy utilization was further enhanced when the energy released from the absorber and condenser of both cycles was recovered in the form of hot water, which could be used for different applications. The performance parameters for this combined system, such as the cooling effect, total heat recovered and performance effectiveness ratio, were calculated for various evaporator and condenser temperatures. It was found that a system driven by a gas turbine gives a better performance than a diesel engine system under similar operating conditions.

A case study of cogeneration for Jeddah and Yanbu petromin refineries in Saudi Arabia

Abstract The Petromin refineries in Jeddah and Yanbu, Saudi Arabia produce power and process steam separately. The Jeddah refinery gas turbines that have an installed capacity of 88 MW, run at less than 50% utilization factor. The refinery demand of steam is 70–120 tons h −1 . The electric power demand of Yanbu refinery is supplied by The Royal Commission of Yanbu at a rate of 16–25 MW. The steam consumption is 68 tons h −1 . Data were collected for the performance and requirement for both plants. An integrated system for cogeneration is proposed which consists of a gas turbine, heat recovery steam generator equipped with a supplementary duct burner and economizer. The thermal and economical analyses have proved the feasibility of the proposed system with payback periods of 23 and 36 months for Jeddah and Yanbu refineries, respectively. However, the payback period for Jeddah refinery can be reduced to 15 months if the utilization factor is improved, and the excess power generated by the gas turbines is connected to the public utility grid. In fact, it is worth mentioning that the present study is considered the first to be carried out in Saudi Arabia; more studies and investigations could lead to tremendous saving in the fuel consumption in this country.

Analysis of refrigerant-charged solar collectors with phase change

Abstract This paper presents a mathematical model for natural circulation refrigerant-charged solar collector plates with phase change. The model accounts for the thermal nonequilibrium vapor generation process along fully charged collector tubes. The local vapor generation rate is determined by solving the steady one-dimensional two-phase energy conservation equations in finite difference form along the flow path. The integral momentum balance around the circulation loop determines the circulation flow rate, which shows dependency on the solar flux and the pressure of the heat carrying refrigerant inside the loop. Calculations have been made for a system fully charged by R-11, with temperature-dependent thermophysical properties. The effect of solar insolation, for a controlled pressure system, on the vaquality, ad circulation rate is presented and discussed. Performance of the system is studied for a range of the independent variables, solar flux up to 1000 W m−2, and refrigerant saturations temperatures up to 80°C.

Laminar Natural Convection in a Square Enclosure with Discrete Heating of Vertical Walls

أجريت دراسة عددية لانتقال الحرارة بالحمل الحر في حيز مربع معبأ بالهواء بوضع سخان جزئي ومباشر على جدار. إن الحيز كان في وضع عمودي وقد تم إبقاء جزء من جدار عمودي في درجة حرارة ثابتة بينما بقية الجدار وكذلك الجدار المقابل في درجة حرارة أقل. وقد عزلت الجوانب العليا والسفلى من الحيز. وقد حلت المعادلات التفاضلية ذات البعدين الخاصة حفظ المادة والطاقة وكمية الحركة باستخدام طريقة الفروقات المحدودة لعدة قيم لرقم رالي تتراوح بين 210ـ 610 . ودرست التغيرات في درجة الحرارة وحقول السريان مع زيادة رقم رالي وذلك لعدة مواضع للسخان. وقد وجد من الدراسة أن المناطق الباردة المجاورة للسخان والتي تم إبقاؤها فيدرجة حرارة أقل تساعد على تكوين خلايا دوران ثانوية والتي تعتمد على رقم رالي وعلى موضع السخان. وبوجود التسخين الجزئي والمناطق الباردة على جدار واحد يتميز السريان بوجود طبقات متاخمة تحيط هذه المناطق بخلايا دوران منفصلة. وتتأثر التغيرات في رقم نوسلت المحلي بهذا النمط من السريان ويكون متوسط رقم نوسلت أكبر من ذلك عندما يكون شريط التسخين موضوعا على جدار معزول. وقد وجد أن المكان الأمثل ـ في نطاق رقم رالي ـ هو منتصف الجدار S/L=0.5. وهذه النتيجة دعمت بنتائج تجار ب سابقة.

Laminar Natural Convection in a Square Enclosure with Discrete Heating of Vertical Walls@@@انتقال الحرارة بالحمل الحر الانسيابي في حيز مربع عند تسخين جزئي لجدران عمودية

أجريت دراسة عددية لانتقال الحرارة بالحمل الحر في حيز مربع معبأ بالهواء بوضع سخان جزئي ومباشر على جدار. إن الحيز كان في وضع عمودي وقد تم إبقاء جزء من جدار عمودي في درجة حرارة ثابتة بينما بقية الجدار وكذلك الجدار المقابل في درجة حرارة أقل. وقد عزلت الجوانب العليا والسفلى من الحيز. وقد حلت المعادلات التفاضلية ذات البعدين الخاصة حفظ المادة والطاقة وكمية الحركة باستخدام طريقة الفروقات المحدودة لعدة قيم لرقم رالي تتراوح بين 210ـ 610 . ودرست التغيرات في درجة الحرارة وحقول السريان مع زيادة رقم رالي وذلك لعدة مواضع للسخان. وقد وجد من الدراسة أن المناطق الباردة المجاورة للسخان والتي تم إبقاؤها فيدرجة حرارة أقل تساعد على تكوين خلايا دوران ثانوية والتي تعتمد على رقم رالي وعلى موضع السخان. وبوجود التسخين الجزئي والمناطق الباردة على جدار واحد يتميز السريان بوجود طبقات متاخمة تحيط هذه المناطق بخلايا دوران منفصلة. وتتأثر التغيرات في رقم نوسلت المحلي بهذا النمط من السريان ويكون متوسط رقم نوسلت أكبر من ذلك عندما يكون شريط التسخين موضوعا على جدار معزول. وقد وجد أن المكان الأمثل ـ في نطاق رقم رالي ـ هو منتصف الجدار S/L=0.5. وهذه النتيجة دعمت بنتائج تجار ب سابقة.