التحقق العملي من تحسين انتقال الحرارة وقدرة الضخ لأنبوب مبادل حراري باستخدام رغوة معدنية متدرجة ومتعددة الطبقات

الباحث

نور محسن جاسم

المشرف

اخلاص محمد فياض - مؤيد رزوقي حسن

الجامعة

الجامعة التكنولوجية

الكلية / القسم

قسم الهندسة الميكانيكية / الهندسة الميكانيكية

الشهادة

دكتوراه

السنة

2022

لغة الرسالة

انكليزي

الكلمات المفتاحية

Metal foam;Heat transfer enhancement;Pumping power;Heat exchanger tube

High porosity metal foam is a novel material recently utilized in the applications of heat exchangers. It is characterized by high specific surface area, lightweight, good thermal conductivity, high permeability and hardness, and durability. This study used the copper metal foam as an extended area for heat exchanger tube bundles in a staggered arrangement. The thermal and hydraulic performance of metallic foam has been compared with that of the copper finned tube heat exchanger. The study is carried out under high- temperature conditions of tube wall with constant properties of the inlet air at ambient temperature and within a range of airflow velocity of 1 to 5 m/s. The first part of this study is based on a numerical simulation to study foam heat exchanger performance at partially filling with a single layer. The study includes the effect of foam layer height on heat transfer and pressure drop. The thermal performance was compared with different properties of copper foam at a porosity of 90-95 and a pore density of 10-20PPI for the five foam specimens having dimensionless height foam of (λfoam= 0.2, 0.43, 0.6, 0.81, and 0.91). The effect of varying the pore density (from 10 to 20 PPI) on the thermal performance at a constant porosity (95%) was also investigated. Also, numerical simulation investigated the effect of varying the porosity (from 90 to 95%) on thermal performance at constant pore density (10PPI). The results of the effect of the geometrical configuration, where the air duct is fully or partially filled with dimensionless foam height (λfoam=0.91), for different characteristics of the copper foam, were also presented in this simulation. Finally, the double-layered foam test with fixed porosity of 95%, while the pore density was varying (10PPI and 20PPI) and the variable position. Also, the effect of porosity change (95% and 90%) with fixed pore density (10ppi) compared with a single layer of (95% and 90%). In the second part of this study, the experimental work is then conducted on the single-layer foam with a fixed porosity of 95% with a variable pore density of 10 PPI and 20 PPI. The experimental test also examined the effect of foam layer gradient on thermal performance. Whereas, the double-layer foam was examined at constant porosity (95%) and variable pore density (10- 20PPI). The results show that the pressure drop of the highest foam height, 0.91 (with porosity 90%, and 20PPI), can be as high as almost with range (6) and (10) for lower and higher air velocity, respectively, times that of the copper finned tube heat exchanger. In comparison, the Nusselt number increased from 2.43 to 3.02 times. The results of increasing pore density (from 10 to 20) PPI with constant porosity (0.95) of copper foam with different dimensionless heights on the performance evaluation criteria showed that the dimensionless height of (λfoam=0.43) of 10PPI had the highest performance values (1.10) at high Reynolds number. The performance of the dimensionless foam height (λfoam=0.91) of porosity (90%, and 10PPI) reaches about 1.51 at high Reynold number. Increasing the porosity and thickness of the foam significantly improves the thermal performance of the heat exchanger. Considering that the two options require an increase in cost on the one hand and an increase in the volume and weight of the exchanger on the other hand. The performance evaluation criteria (PEC) of the foam heat exchanger with fully filling metal foam (second configuration), with fixed porosity of 95%, is lower than partially filling metal foam heat exchanger (first configuration) at about (0.07- 0.16) for 10 and 20PPI, respectively. This means that there is a small increase in heat transfer rate in the second configuration compared to the high increase associated with the mechanical power required to pump the working fluid. The full-filling of constant pore density with different porosity (90-95%) was displayed. It was noticed that the second configuration of the copper metal foam with pore density 10PPI has a lower thermal performance than the first configuration by about (0.06-0.08) for porosity (95% -90%) respectively, at a high Renold number. By comparing the thermal performance of double layers foam, it was noticed that the order of 10/20PPI (with porosity 95%) is greater than the performance of single foam 10PPI and 20PPI by 1.07 -1.10, respectively. While comparing the performance of the double foam 90/95% (with pore density 10PPI), it was noted that it improved the thermal performance and was very close to the single foam 90%, where the difference is about 0.04. In contrast, the double-foam 95/90% has low thermal performance because the percentage of increase in heat transfer is less than that of pressure increase. The comparison showed that the experimental results agreed with the numerical solution with a difference between them for the friction factor and Colburn factor values by 16% and 6%, respectively.

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