Question 14.11: Design of a New Geometrically Similar Pump After graduation,...
Design of a New Geometrically Similar Pump
After graduation, you go to work for a pump manufacturing company. One of your company’s best-selling products is a water pump, which we shall call pump A. Its impeller diameter is D_{ A }=6.0 cm , and its performance data when operating at \dot{n}_{ A }=1725 rpm \left(\omega_{ A }=180.6 rad / s \right) are shown in Table 14–2. The marketing research department is recommending that the company design a new product, namely, a larger pump (which we shall call pump B) that will be used to pump liquid refrigerant R-134a at room temperature. The pump is to be designed such that its best efficiency point occurs as close as possible to a volume flow rate of \dot{V}_{B}=2400 cm ^{3} / s and at a net head of H_{B}=450 cm (of R-134a). The chief engineer (your boss) tells you to perform some preliminary analyses using pump scaling laws to determine if a geometrically scaled-up pump could be designed and built to meet the given requirements. (a) Plot the performance curves of pump A in both dimensional and dimensionless form, and identify the best efficiency point. (b) Calculate the required pump diameter D_{ B } , rotational speed \dot{n}_{ B } , and brake horsepower bhp _{ B } for the new product.
TABLE 14–2 |
Manufacturer’s performance data for a water pump operating at 1725 rpm and room temperature (Example 14–11)* |
\begin{array}{ccc}\dot{V}, cm ^{3} / s & H, cm & \eta_{\text {pump }}, \% \\\hline 100 & 180 & 32 \\200 & 185 & 54 \\300 & 175 & 70 \\400 & 170 & 79 \\500 & 150 & 81 \\600 & 95 & 66 \\700 & 54 & 38\end{array} |
* Net head is in centimeters of water. |
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