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Article
The effects of Reduced Temperature and Pressure on Natural Convection in Rectangular Cavity Filled with a Supercritical Water: a Benchmark Numerical Solution
تأثير درجة الحرارة والضغط المنقصين على انتقال الحرارة بالحمل الطبيعي داخل تجويف مستطيل مملوء بالماء الخفيف(SCW)

Author: Younis M. Najim يونس محل نجم
Journal: AL-Rafidain Engineering Journal (AREJ) مجلة هندسة الرافدين ISSN: 18130526 Year: 2011 Volume: 19 Issue: 3 Pages: 55-68
Publisher: Mosul University جامعة الموصل

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Abstract

AbstractIn this paper, natural convection heat transfer of supercritical water in rectangular enclosure has been investigated in various values of reduced temperature (0.955 1.205) and pressure (1.2 2.0). The right and left sides of enclosure considered to be isotherm with a temperature difference of , while the lower and upper sides of the enclosure was thermally insulated. The width of enclosure is 0.004m. Calculations were performed for Rayleigh number ( ), Prandtl number ( ). The values of Ra and Pr are governed by the fluid temperature and pressure which are controlled by reduced temperature( ) and reduced pressure ( ). Streamlines, isotherms and mean Nusselt numbers are presented. It is found that the temperature distribution and flow field are affected by the reduced temperature and pressure. The results also show that the maximum Nusselt number could be obtained at the same specification of geometry and temperature difference increases as the pressure reach the critical pressure. Keyword: Natural convection, supercritical Water, reduced temperature and pressure

ألخلاصةفي هذا البحث، تم دراسة تأثير درجة الحرارة والضغط المنقصين على انتقال الحرارة بالحمل الطبيعي داخل تجويف مستطيل مملوء بالماء الخفيف (SCW)، حيث اشتملت الدراسة على مدى من درجات الحرارة المنقصة بينما كانت القيم للضغط المنقص ، وقد اعتبرت درجة حرارة جانبي التجويف الأيمن والأيسر ثابتتين وبفرق درجات حرارة مقداره 0.0323K، أما الجانبان العلوي والسفلي فقد فرضا على أنهما معزولين عزلاً حرارياً. وفقا لذلك فان قيم رالي كانت وقيم براندتل ، يتم احتساب الخواص الفيزيائية للماء الخفيف عند درجة الحرارة والضغط ، وبالتالي فان المتغيرين الرئيسيين في هذه الدراسة هما درجة الحرارة والضغط المنقوصين ( ). حيث أظهرت النتائج تأثراً كبيراً في توزيع درجات الحرارة وجريان الماء الخفيف (SCW) وانتقال الحرارة بهذين المتغيرين. كما بينت النتائج أيضا أن القيم القصوى لعدد نسلت تزداد كلما اقترب ضغط الماء الخفيف(SCW) من الضغط الحرج تحت نفس الظروف.


Article
A WIDE RANGE FORMULA FOR COMPRESSION FACTOR FUNCTION OF REDUCED PROPERTIES

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Abstract

This paper presents an effort aimed at developing a new formula to calculate compression factor within acceptable error range. A formula has been generalized to permit calculation of the compression factor as a function of reduced properties: reduced temperature TR and reduced pressure PR. The new correlations show improvement in temperature and pressure range which offers flexibility for estimating compression factor for a wide range of reduced temperature; TR=1-5 and reduced pressure ;PR=0.5- 6.5. This correlation provides accurate and computationally reliable prediction of the compression factor (Z) with an average absolute error (AAE) 4.6 % for 169 data points.

البحث الحالي يمثل محاولة لايجاد علاقة لحساب معمل الانضغاطية وبنسبة خطأ معقولة. تم تطبيق العلاقة لحساب معامل الانضغاطية لمدى واسع بالاعتماد على الخواص التناسبية : درجة الحرارة التناسبية (TR ) والضغط التناسبي (PR ) . العلاقة الجديدة حسنت المدى التطبيقي لدرجة الحرارة والضغط والذي ادى لحساب معمل الانضغاطية وفي مدى واسع لدرجة الحرارة التناسبية (TR=1-5 ) والضغط التناسبي (PR=0.5- 6.5). الموديل الجديد يوفر التنبؤ الدقيق والموثوق لحساب معمل الانضغاطية وبمعدل نسبة خطأ مطلق ((4.6 % الخاصة في (169) نقطة عملية.


Article
Prediction and Correlations of Residual Entropy of Superheated Vapor for Pure Compounds

Authors: Mahmoud O. Abdullah --- Sarmad T. Najim --- Shahad Z. Atta
Journal: Iraqi Journal of Chemical and Petroleum Engineering المجلة العراقية للهندسة الكيمياوية وهندسة النفط ISSN: 19974884/E26180707 Year: 2012 Volume: 13 Issue: 2 Pages: 11-27
Publisher: Baghdad University جامعة بغداد

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Abstract

Prediction of accurate values of residual entropy (SR) is necessary step for the calculation of the entropy. In this paper, different equations of state were tested for the available 2791 experimental data points of 20 pure superheated vapor compounds (14 pure nonpolar compounds + 6 pure polar compounds). The Average Absolute Deviation (AAD) for SR of 2791 experimental data points of the all 20 pure compounds (nonpolar and polar) when using equations of Lee-Kesler, Peng-Robinson, Virial truncated to second and to third terms, and Soave-Redlich-Kwong were 4.0591, 4.5849, 4.9686, 5.0350, and 4.3084 J/mol.K respectively. It was found from these results that the Lee-Kesler equation was the best (more accurate) one compared with the others, but this equation is sometimes not very preferable. It was noted that SRK equation was the closest one in its accuracy to that of the Lee-Kesler equation in calculating the residual entropy SR of superheated vapor, but it was developed primarily for calculating vapor-liquid equilibrium and to overcome this problem, efforts were directed toward the possibility of modifying SRK equation to increase its accuracy in predicting the residual entropy as much as possible. The modification was made by redefining the parameter α in SRK equation to be a function of reduced pressure, acentric factor, and polarity factor for polar compounds in addition to be originally function of reduced temperature and n parameter –which is also function of acentric factor– by using statistical methods. This correlation is as follows: This new modified correlation decreases the deviations in the results obtained by using SRK equation in calculating SR when comparing with the experimental data. The AAD for 2791 experimental data points of 20 pure compounds is 4.3084 J/mol.K while it becomes 2.4621 J/mol.K after modification. Thus SRK equation after this modification gives more accurate results for residual entropy of superheated vapor of pure 20 compounds than the rest of the equations mentioned above.

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