# Momentum flux out momentum flux in forces acting on

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(Momentum flux out) − (Momentum flux in) = (Forces acting on fluidin control volume)Another factor is shear force which contributed by the viscosity. Theshear force can be narrowed while the vessel is relatively largecompared with the red cell size. On the other hand, it can becalculated by assuming the blood as Newtonian flow (Siggers, 2009). τ= μ ∂V/∂yIt is known that every fluid has its own viscosity. Normally, humanblood viscosity is around 0.003~0.004 Pas. μ=0.003~0.004 Pa∙sWhere τ is shear stress, and shear force can be obtained by applyingthe formula:F= τ∙ABy knowing all the relationship with fluid and blood pump, it will beeasier for people to solve the problem associated with blood pump.For example, heart failure usually occurs while the heart could notprovide the sufficient blood circulation which causes the imbalance inpump function (Behbahani et al. 2009). That is the problem with fluidmechanics and it can be solved by calculating all the data such asflow rate and pressure. With these information, the blood pump canbe built up with the exact requirement.9. Comparing Blood Pumps with Water PumpsP a g e | 12
Blood pumps and water pumps are comparable in the way that theyboth utilize mechanical strengths to move fluids, however theirpurpose and kind of operation is distinctive. Water pumps draw thewater through the pump and expel the water, in essences it makes apartial vacuum which then draws more water. While blood pumps arefunctioned either briefly, for all time or completely taken control of theheart muscles. Therefore, from these aspects and purposes the keycorrelations on these pumps include: ● Flow rate ● Durability and Materials utilized ● Power source ● Size 9.1 Flow rate The flow rate in blood pumps and water pumps diverse significantlybecause of their purpose and proposed use. Blood pumps needs highprecision and consistent flow accuracy as the heart needs toproficiently thump around 100,000 times each day at a steady rateand without fatigue to provide the body with oxygen, this isproportional to 5L/min when resting and up to 30L/min when workingout. Because of this high volume and a more prominent viscosity inblood compared with water a more prominent force per volume isneeded to pump the blood. This could be overcome by utilizing biggermotors, however this is impractical in the blood pumps thus magnetsare implanted into the impeller blades, enabling the impeller blades tobe bigger and therefore make a bigger flow rate without trading off onthe size. A change in the flow rate could be detrimental to the human body asa slower or quicker flow rate could result in Thrombosis orHaemolysis, respectively. In this way, it is imperative that bloodpumps keep up a precise flow rate as an ordinary heart does to stayaway from complications like blood damage and blood clusters.