Browsing by Author "Gomaa, Abdalla"

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Correlations for heat transfer coefficient and pressure drop in the annulus of concentric helical coils
(SPRINGER, 2014) Gomaa, Abdalla; Aly, Wael I. A.; Omara, M.; Abdelmagied, Mahmoud
Heat transfer and pressure drop characteristics in the annulus of concentric helical coils heat exchangers were experimentally investigated. The effects of coil curvature ratio, flow configuration, number of turns and addition of surfactant were investigated. Five test coils were designed and manufactured to study the effect of different parameters on heat transfer and pressure drop. The liquids used in the present study were water and oleyldihydroxy- etheyl-amine-oxide (ODEAO, C22H45NO3 = 371) non-ionic aqua surfactant solution flowing through the annulus side. The inner side Reynolds number range 11,000-27,000 and the annulus side range 5,000-19,000. The results showed that the annulus Nusselt number decreases as annulus curvature ratio increases and increases when number of turns decrease. Moreover, the friction factor increases with the curvature ratio and also increases as number of turns decreases. Both Nusselt number and friction factor decrease when ODEAO concentration increases.
Enhancement of cooling characteristics and optimization of a triple concentric-tube heat exchanger with inserted ribs
(ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER, 2017-10) Elsaid, Ashraf Mimi; Halim, M. A; Gomaa, Abdalla
Experimental and numerical investigation of the triple concentric-tube heat exchanger with inserted ribs has been carried out. The purpose is to evaluate the performance characteristics of the triple tube heat exchanger with rib inserts. The investigation key design parameters involve water mass flow rate, flow pattern, temperature variation, rib height and rib pitch. Numerical CFD modeling is developed using FLUENT commercial code and validation criteria is done to extend the study parameters with extra ranges. The results revealed that, the insertion of ribs to the inner annulus fluid flow of the triple tube heat exchanger participate a significant enhancement of the convective heat transfer. Higher performance index is obtained at higher rib pitch and lower rib height. A set of empirical expressions with the dimensionless design parameters have been predicted based on the obtained data. (C) 2017 Elsevier Masson SAS. All rights reserved.
Performance characteristics of a chilled water spirally coiled finned tube in cross flow for air conditioning applications
(SAGE PUBLICATIONS LTD, 2013) Gomaa, Abdalla; Aly, Wael I; Elsaid, Ashraf Mimi
In the present study, the thermo-fluid characteristics of a spirally coiled finned tube in cross flow were experimentally investigated. This investigation covered different design parameters such as curvature ratio, air velocity, flow direction, fin pitch and flow rate of chilled water on performance characteristics of the spirally coiled finned tube. The purpose was to evaluate this kind of the spirally finned-tube cooling coils with particular reference to bare coiled tube. Six test specimens were designed and manufactured with curvature ratios of 0.027, 0.03, 0.04, tube pitches of 18, 20, 30 mm and fin pitches of (33, 22, 11 mm). Experiments were carried out in a pilot wind tunnel with air Reynolds number ranging from 35,500 to 245,000. Two types of chilled water flow directions entering the spiral coil were tested at Reynolds number ranging from 5700 to 25,300, the first was inward flow direction and the other was to outward flow direction. The results revealed that the inward flow direction has significant enhancement effect on the Nusselt number compared with outward flow direction by 37.0% for tube pitch of 18 mm and curvature ratio of 0.027. The decrease of fin pitch enhances the Nusselt number by 21.92% on expense of friction factor by 10.9%. In the case of spirally coiled bare tube, the decreasing of the curvature ratio increases air side Nusselt number by 33.69% on expense of friction factor by 18.36%. General correlations of Nusselt number and air friction factor for bare and finned spirally coiled tube were correlated based on reported experimental data.
Performance characteristics of wet air-conditioning cooling coils with different fin patterns
(TAYLOR & FRANCIS INC., 2015) Gomaa, Abdalla; Abd El Aziz, Gamal B.; Radwan, Momen I.
In the present study, the thermal performance and pressure drop characteristics of wet air-conditioning cooling coils are investigated under the hot arid climate of Cairo. The effect of fin patterns, fin pitch, and air velocity on the heat transfer performance of direct expansion cooling coils is presented. Five test specimens of cooling coils are tested involving flat, corrugated, and louvered fins. In addition, different fin pitches are considered for louvered-fin cooling coils. Reynolds number for the air side ranged from 65 to 1200, corresponding to face velocity of 0.43-6.65 m/s. Four methods of performance criteria are presented to interpret how different fin geometries of cooling coils could affect the overall performance of the air-conditioning unit. At a certain value of pressure drop of 50 Pa, the air heat transfer coefficient for louvered fins is higher than that of corrugated and flat fin cooling coils by 29.4% and 47%, respectively. The energy efficiency ratio for louvered fins is higher than that of corrugated and flat fin cooling coils by 9% and 17.4%. The air-conditioning system having a cooling coil with lower fin pitch and enhanced fin surfaces is more energy cost effective.
Thermal performance criteria of elliptic tube bundle in crossflow
(ELSEVIER, 2009) Ibrahim, Talaat A.; Gomaa, Abdalla
In this work, the thermofluid characteristics of the elliptic tube bundle in crossflow have been investigated. Experimental and numerical investigations of the turbulent flow through bundle of elliptic tubes heat exchanger are carried out with a particular reference to the circular tube bundle. The investigation covers the effects of key design parameters of Reynolds numbers (5600-40,000), minor-to-major axis ratios (0.25, 0.33. 0.5 and 1) and flow angles of attack (0-150 degrees). Five bundles of elliptic tube heat exchangers with different axis ratios were designed and manufactured in staggered manner. Numerical CFD modeling using finite volume discretization method was conducted to predict the system performance extensively. Four methods were presented to resort a metric that expresses the thermal performance criteria of the elliptic tube bundle. The results indicated that, increasing the angle of attack clockwise until 90 degrees enhances the convective heat transfer coefficient considerably. The maximum thermal performance under constraint of a fixed pumping power or a mass flow rate was obtained at a zero angle of attack and the minimum thermal performance occurred at an angle of attack equals 90 degrees. The best thermal performance of the elliptic tube heat exchanger was qualified with the lower values of Reynolds number, axis ratio and angle of attack. (c) 2009 Elsevier Masson SAS. All rights reserved.