ABSTRACT:Comparing to pumps with moving parts water-jet pumps have a lower efficiency and surface roughness is an important factor for these types of pumps. The aim of this simulation study is to numerically determine how the scaling-up, downscaling and change in the absolute and relative roughness would impact on the energy efficiency of the pumps, using a commercial computational fluid dynamics (CFD) solver ANSYS FLUENT. In order to select the turbulence model that produces the predictions closest to the actual data from four turbulence models, a preliminary study was conducted on a full-scale jet pump. Using the transition SST model, which gives the best results among all the models, the effects of scale and roughness on the performance of the pumps were investigated in the scale range from 1/4 to 20/1. The optimum efficiencies for different area ratios over a wide range were determined according to the scale and size of roughness. It was seen that the efficiency increases significantly up to a given scale size at a constant absolute roughness, while it is generally independent of the scale size at constant relative roughness. The relative efficiency for the area ratio 5.92 reduces to 60% at the relative roughness value of 0.05. Moreover, CFD appears to be the most appropriate tool for model studies of jet pumps.

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A water jet pump is one of the best examples of a device in which liquid-jet mixing phenomena occur. Since such mixing processes are complex, the choice of turbulence model for accurate prediction of performance of the pumps is important. The aim of this numerical simulation study is to investigate effects of parameters such as the jet pump area ratio, nozzle position, and length of the mixing chamber on the pump performance and then to perform an optimization of six different water jet pumps according to these parameters, taking energy efficiency as a criterion. In the optimization procedure, the transition SST model (-Re ) was used because it provided more accurate results among the four advanced turbulence models. The numerical results obtained with the model were compared with experimental data of the jet pump with the same geometry at the boundary conditions available in the literature and it was seen that maximum deviation in the pump efficiency at the optimum operating conditions was approximately 10%. As a result, the maximum numerical efficiency is found to be 34.6% at the area ratio of 4.61 and a pressure ratio of 0.277.

Kalp yetersizliği, kalbin vücudun ihtiyacı olan yeterli kanı pompalayamadığı bir kalp rahatsızlığıdır. Sol ventrikül kalp destek pompaları, kalbin sol ventrikülünden kanın aort atar damarına pompalanmasına yardımcı olurlar. Bu çalışmada, heliko-santrifüj karışık akışlı bir sol ventrikül kalp destek pompasının tasarımı, pompa tasarım programları kullanılarak yapıldı. Hesaplamalı akışkanlar dinamiği (HAD) metodu ile pompanın hidrodinamik performansı belirlendi. Pompanın sayısal performans sonuçları kullanılarak hidrolik verime göre optimum pompa tasarımı gerçekleştirildi. Kurulan deney düzeneğinde farklı dönme hızlarında bu pompanın basıncı, debisi ve tükettiği güç ölçüldü ve ölçülen bu değerler ile deneysel hidrodinamik performans eğrileri belirlendi. Deneyde ve HAD analizinde, çalışma akışkanı kan ile aynı viskozitede olan su-gliserin çözeltisi (hacimce %40 gliserin ve %60 su) kullanıldı. Karşılaştırma yapılması için su ile de deney ve HAD analizleri yapıldı. Pompanın deneysel ve sayısal performans sonuçlarına göre, basınç farkındaki sapma oranın yüksek debilerde %1'den daha düşük ve düşük debilerde ise yaklaşık %5,7 olarak görüldü. Bu yetişkin kalp destek pompalarının sağlaması gereken 5 L/dak debideki 100 mmHg basınç değeri, 5100 dev/dak dönme hızında elde edildi. Bu noktada pompanın hidrolik verimi %52,1, genel verimi %30,9 ve maksimum cidar kayma gerilmesi 166 Pa olarak belirlendi.

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