An elderly woman is rushed to the hospital because she is having a heart attack. The emergency room doctor informs her that she needs immediate coronary artery (a vessel that wraps around the heart) bypass surgery because one coronary artery has 75 percent blockage (caused by atherosclerotic plaque). This surgery involves using an artificial graft (typically made of Dacron) to divert blood from the coronary artery around the blockage and reattach to the coronary artery beyond the blockage site as illustrated in Figure P8-163. The coronary artery diameter is 5.0 mm and its length is 15.0 mm. The bypass graft diameter is 4.0 mm and its length is 20.0 mm.

The flow rate within the bypass graft is 0.45 liters per minute (recall 1 ml equals 1 cm³). Blood has a density of 1060 kg/m³ and a dynamic viscosity of 3.5 centipoise. Assume that the Dacron and coronary artery have the same material properties and ignore any minor losses. Assume the friction factor is the same in both tubes. Ignoring the plaque in determining the head loss for the coronary artery, calculate the velocity through the small gap between the plaque and the coronary artery.

FIGURE P8–163

Transcribed Image Text:

Bypass graft Coronary Artery