mecanica de fluidos ii.- mec2249. trabajo...

MECANICA DE FLUIDOS II.- MEC2249. TRABAJO PRACTICO 3. Se pide al estudiante resolver los ejercicios que se exponen a continuación, de manera crítica y sistemática, aplicando conceptos, ecuaciones y haciendo las consideraciones e hipótesis que fueren necesarias. .

P1. A sketch of the arithmetic mean radius blade sections of an axial-flow water

turbine stage is shown in Fig. P1. The rotor speed is 1500 rpm. (a) Sketch and

label velocity triangles for the flow entering and leaving the rotor row. Use V for

absolute velocity, W for relative velocity, and U for blade velocity. Assume flow

enters and leaves each blade row at the blade angles shown. (b) Calculate the

work per unit mass delivered at the shaft.

P2.- An inward flow radial turbine (see Fig. P2) involves a nozzle angle, α1, of 60o

and an inlet rotor tip speed, U1 of 9 m/s. The ratio of rotor inlet to outlet

diameters is 2.0. The radial component of velocity remains constant at 6 m/s

through the rotor, and the flow leaving the rotor at section (2) is without angular

momentum. (a) If the flowing fluid is water and the stagnation pressure drop

across the rotor is 110 kPa, determine the loss of available energy across the rotor

and the efficiency involved. (b) If the flowing fluid is air and the static pressure

drop across the rotor is 0.07 kPa, determine the loss of available energy across

the rotor and the rotor efficiency.

P3.- A 37-cm-diameter centrifugal pump, running at 2140 r/min with water at

20°C, produces the following performance data:

(a) Determine the best efficiency point. (b) Plot CH versus CQ. (c) If we desire to

use this same pump family to deliver 7000 gal/min of kerosene at 20°C at an input

power of 400 kW, what pump speed (in r/min) and impeller size (in cm) are needed? What head will be developed?

P4. - Water at 20°C is to be pumped through 2000 ft of pipe from reservoir 1

to 2 at a rate of 3 ft3/s, as shown in Fig. P4. If the pipe is cast iron of diameter

6 in and the pump is 75 percent efficient. Consider this problem as an exercise

in pump selection. Select an impeller size and rotational speed from the Byron

Jackson pump family (Table P1) to deliver a flow rate of 3 ft3/s to the system

of Fig. P1 at minimum input power. Calculate the horsepower required.

P5. - The system of Fig. P6 is designed to deliver water at 20°C from a

sea-level reservoir to another through new cast iron pipe of diameter

38 cm. Minor losses areΣK1 = 0.5 before the pump entrance and ΣK2 =

7.2 after the pump exit. (a) Select a pump from either Fig. 11.7a or

11.7b, running at the given speeds, that can perform this task at

maximum efficiency. Determine (b) the resulting flow rate, (c) the

brake horsepower, and (d) whether the pump as presently situated is

safe from cavitation.

Fig. P4

Fig. P5

TABLE P1: Tests by the Byron Jackson Co. of a 14.62-in-

diameter centrifugal water pump at 2134 r/min.

Fig. P1

Fig. P2


P6.- You are asked to consider a pump geometrically similar to the 9-in-diameter Taco pump of Fig. P11.34 to deliver 1200

gal/min at 1500 r/min. Determine the appropriate (a) impeller diameter, (b) BEP horsepower, (c) shutoff head, and (d)

maximum efficiency. The fluid is kerosene, not water

P7.- El supervisor de April le pide encontrar una bomba de

reemplazo que incremente el caudal por la tubería del

problema 14-41 (Yunus Cengel, pag. 808) por un factor de

2 o mayor. April busca en algunos folletos en línea y

encuentra una bomba con los datos de operación que se

muestran en la tabla P4. Las dimensiones y parámetros son

los mismos que en el problema

14-41 (Yunus Cengel), sólo se

cambia la bomba. a) Efectúe un

ajuste de curva de mínimos

cuadrados (análisis de regresión)

de Hdisponible contra Q2, y calcule los

valores de mejor ajuste de los

coeficientes H0 y a que traducen

los datos tabulados de la tabla P4

en la expresión parabólica

Hdisponible = H0 - aQ2. Grafique los

datos como los valores numéricos y el ajuste de curva como

una línea para comparación. b) Use la expresión obtenida

en el inciso a) para estimar el caudal de operación de la

nueva bomba si se reemplazara la bomba existente con

todo lo demás igual. ¿Logró su objetivo April? c) Construya

una gráfica de la carga hidrostática neta requerida y la carga

hidrostática neta disponible como funciones de caudal e

indique el punto de operación sobre la gráfica.

P8.- Performance data for a very small (D= 8.25 cm) model water turbine, operating with an available head of 49 ft, are as

follows:

(a) What type of turbine is this likely to be? (b) What is so different about these data compared to the dimensionless

performance plot in Fig. 11.22d? Suppose it is desired to use a geometrically similar turbine to serve where the available head

and flow are 150 ft and 6.7 ft3/s, respectively. Estimate the most efficient (c) turbine diameter, (d) rotation speed, and (e)

horsepower.

TABLA P4


ANEXOS

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