Optimization studies on blood pumps that require complex designs are gradually increasing in number. The essential design criteria of centrifugal blood pump are minimum shear stress with maximal efficiency. The geometry design of impeller sidewall gaps (blade tip clearance, axial gap, radial gap) is highly effective with regard to these two criteria. Therefore, unlike methods such as trial and error, the optimal dimensions of these gaps should be adjusted via a heuristic method, giving more effective results. In this study, the optimal gaps that can ensure these two design criteria with The Bees Algorithm (BA), which is a population-based heuristic method, are investigated. Firstly, a Computational Fluid Dynamics (CFD) analysis of sample pump models, which are selected according to the orthogonal array and pre-designed with different gaps, are performed. The dimensions of the gaps are optimized through this mathematical model. The simulation results for the improved pump model are nearly identical to those predicted by the BA. The improved pump model, as designed with the optimal gap dimensions so obtained, is able to meet the design criteria better than all existing sample pumps. Thanks to the optimal gap dimensions, it has been observed that compared to average values, it has provided a 42% reduction in aWSS and a 20% increase in efficiency. Moreover, original an approach to the design of impeller sidewall gaps was developed. The results show that computational costs have been significantly reduced by using the BA in blood pump geometry design.
The use of substitute fluid with similar rheological properties instead of blood is important due to ethical concerns and high blood volume consumption in pump performance test before clinical applications. The performance of a centrifugal blood pump with hydrodynamic journal bearing is experimentally tested using Newtonian 40% aqueous glycerin solution (GS) and non-Newtonian aqueous xanthan gum solution of 600 ppm (XGS) as working fluids. Experiments are performed at four different rotational speeds which are 2700, 3000, 3300, and 3600 rpm; experiments using GS reach between 8.5% and 37.2% higher head curve than experiments using the XGS for every rotational speed. It was observed that as the rotational speed and flow rate increase, the head curve difference between GS and XGS decreases. This result can be attributed to the friction reduction effect when using XGS in experiments at high rotation speed and high flow rate. Moreover, due to different fluid viscosities, differences in hydraulic efficiency were observed for both fluids. This study reveals that the use of Newtonian fluids as working fluids is not sufficient to determine the actual performance of a blood pump, and the performance effects of non-Newtonian fluids are remarkably important in pump performance optimizations.
Using fuzzy logic methods, some complex experiments that are not possible due to critical limitations can be simulated in a short time. In this study, experimental data of Newtonian 40% aqueous glycerin solution (GS) and non-Newtonian 600[Formula: see text]ppm aqueous xanthan gum solution (XGS) working fluids were used to model the hydraulic performance of a centrifugal blood pump. A novel fuzzy logic-based model (FLM) for modeling the hydraulic performance of the pump model is proposed. In the proposed model, there are two inputs which are flow rate and impeller rotational speed and one output which is head pressure. In FLM, the range for flow rate is 1–7.8[Formula: see text]L/min in GS and 1–8[Formula: see text]L/min in XGS, and for head pressure 50–245[Formula: see text]mmHg in GS and 50–215[Formula: see text]mmHg in XGS. In addition, impeller rotational speed range is 2700–3600[Formula: see text]rpm for both fluids. The estimated results with FLM were validated with the experimental results and it was seen that the FLM was compatible with the experimental results with an accuracy of 96.25%. These results imply that the developed FLM is acceptable and can be used to assist in determining the performance of blood pumps.
ÖZ:Bu çalışmada büyük ölçekli pompaların tasarımında kullanılan konvansiyonel yöntemle tasarlanan prototip bir santrifüj kalp destek pompasının HAD yazılımları aracılığıyla santrifüj pompa karakteristiklerinin belirlenmesi ve bu karakteristiklerin deneysel olarak doğrulanması yapıldı. Ayrıca HAD simülasyonuyla pompanın cidarlarındaki kayma gerilmeleri incelendi. Pompanın tasarım parametreleri olarak 5 lt/dak debi, 3000 dev/dak dönme sayısı ve 100 mm-Hg basınç farkı seçildi. Tasarlanan pompa çarkının katı modellemesi oluşturularak hızlı prototipleme cihazlarıyla imalatı yapıldı. Katı modeli oluşturulan pompa salyangozu alüminyum bloktan CNC dik işlem merkezinde imal edildi. Pompanın performans deneylerinde akışkan olarak; su ve akışkan özellikleri kana benzer olan hacimce %40 gliserin-%60 su çözeltisi kullanıldı. Tasarım dönme sayısı ve debisinde yaklaşık 72 mm-Hg'lik bir toplam basınç farkı elde edildi. Akışkan olarak su kullanılan testlerde HAD simülasyonuyla belirlenen pompa performansı sonuçları ile deneysel sonuçlar arasında iyi bir uyum olduğu görüldü. Akışkan olarak su-gliserin çözeltisi kullanılan deneysel sonuçlarla HAD simülasyon sonuçları arasında yaklaşık %15 sapma olduğu görüldü. HAD simülasyonlarıyla yapılan analizlerde; su için 664.7Pa, su-gliserin çözeltisi için 1271 Pa kayma gerilmesi değerleri bulundu. Gelecek çalışmalarda bu kayma gerilmesi değerlerinin azaltılması üzerine yoğunlaşılacaktır. Anahtar Kelimeler: HAD, Kalp Destek Pompası,LVAD, Santrifüj Pompa Numerical and Experimental Investigation of A Centrifugal Heart Assist Pump PrototypeABSTRACT: In this study, pump characteristics of a prototype centrifugal ventricular assist pump, which is designed with conventional design method of large scale pumps, have been determined by CFD software and these characteristics are confirmed experimentally. Also shear stresses on the walls of the pump were inspected with CFD simulations. As design parameters; 5 L/min flow rate, 3000 rpm motor speed and 100 mm-Hg pressure rise have been selected. Solid model of the designed pump was prepared and manufactured by rapid prototyping machine. Volute of the pump was manufactured from aluminum block at CNC milling machine. At performance tests of the pump, water and 40% glycerin60%water solution, which have similar rheological properties with blood, were used as working fluid. At design speed and flow rate, 72 mm-Hg of pressure rise has been obtained. For tests which water used as fluid, a fine agreement between CFD determined and experimental pump performance results has been seen. For tests which water-glycerin solution used as fluid, there is nearly 15% of deviation between CFD determined and experimental pump performance results. At CFD simulations shear stress value for water was 664.7 Pa and 1271 Pa for glycerin solution. Upcoming researches will be focused on decreasing this shear stress level.
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