2004级流体力学与传热期中考试题(双语班)

Midterm Examination for Fluid Mechanics and Heat Transfer Grade 2004

Name Student No. Class Score

1.(10 points) True or false

(1)( ) When a fluid passes through a pipe, the total mechanical energy in section

1 (inlet) is always equal to that in section

2 (outlet).

(2)( ) When the developed head H is the same, one pump can not develop more

volume flow rate than that two same pumps which work in parallel.

(3)( ) In a laminar flow, the frictional loss is proportional to velocity square.

(4) ( ) A reciprocating pump is not subject to air binding.

(5) ( ) There are three types of flow, that is, laminar, transitional and turbulent flow.

2.(30 points) Fill in the blanks or choose the correct answer

(1) The orifice meter belongs to , flow rate meter; while the rotameter is , flow rate meter.

A) constant pressure drop; B) constant area; C) variable pressure drop; D) variable area

(2) ( ) In order to avoid the cavitation, which of the following methods is feasible?

A)increase the operating temperature;

B)decrease the diameter of suction pipe;

C)install the valve or fittings in the suction pipeline;

D)reduce the frictional loss in the suction pipeline

(3) The orifice meter is used to measure ; the rotameter is utilized to

measure ; the Pitot tube is used to measure .

A.average velocity in the orifice;

B.volume flow rate in the orifice;

C.average velocity in annular space between the float and tube wall;

D.volume flow rate in annular space between the float and tube wall;

E.local velocity in the pipe;

F.average velocity in the pipe

(4) The methods of adjusting volume flow rate of centrifugal pump are

1) ; 2) ;

(3) .

The most common used way in practice is ( ). (5) To avoid cavitation, the pressure at the centrifugal pump inlet must exceed the vapor pressure by a certain value called the .

(6) 1atm= mH2O= N/m2；

1cp= P= N·s/m2.

(7) When the temperature of fluid to be transported increases, the maximum suction lift will ( ). If the velocity of suction pipe decreases, the maximum suction lift will ( ).

(8) The viscosity of a gas with temperature increasing, and viscosity of a liquid usually significantly when the temperature is raised.

(9) In the boundary layer, there exist . Outside the boundary layer, potential flow survives.

(10) When the pipe installation changes from horizontal to vertical position and the velocity keeps unchanged, the frictional loss will be .

A. increased;

B. decreased;

C. the same;

D. uncertain