07流体力学与传热期末考试题(含答案).

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华南理工大学期末考试

2007《流体力学与传热英文》试卷

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一．(38 points) True or false or fill the black or choose the correct answer

(1)In SI system, the dimension of viscosity is ( M/Lq ), and its unit is ( kg/ms ).

(2) ( T ) If the volume flow rate Q increases, the developed head H of centrifugal pumps will decrease.

(3) ( F )When the gas temperature increases, its viscosity will decrease.

(4) ( F ) Water need not to be added during the start of centrifugal pump because it has priming function.

(5) If water with density r=1000kg/m3, viscosity µ=0.001Pa.s and u=1m/s flows through a pipe with di=0.001m, its Re=(1000), f (Fanning

(maximum velocity)=( 2 m/s); If the pipe factor)=( 0.016), u

max

length is 2m, its pressure drop Dp=(128000 Pa).

(6) A single spherical solid particle settles freely in static liquid, in which the settling obeys Stoke's Law (laminar flow). If the diameter of particle increases, the settling velocity u

will ( be up ); when the

t

will ( be down ).

temperature decreases, u

t

(7) The revolution n of centrifugal pump increase, its volumetric flow rate Q will increases , its developed head H will increase .

(8) Orifice meter measures ( C ) to get mass flow rate of fluid in

a pipe, rotameter measures ( A ) to get mass flow rate of fluid in a pipe. The former ( E ) keeps constant, and the later ( D ) keeps unchanged.

A Volume flow rate;

B Local velocity;

C Average velocity;

D Pressure drop;

E cross section area

(9) The pressure of 10 m H

2

O is equal to 735.7 mmHg. If

atmospheric pressure is 1 atm and the reading of centrifugal pump outlet gauge is 5000Pa(N/m2)= 106300 N/m2 (absolute pressure).

(10) When the flow rate is fixed, the maximum suction lift Z

a will increase if the diameter of suction pipe increases. When

the flow rate is fixed, Z

a

will decreases if a valve and some fittings are set up in the suction pipe.

(11) The expression of Newton's Law of cooling is ( hADt ).

(12)

If the temperature drop DT o between the saturated vapor and pipe wall is double in a vertical tube, the condensation heat transfer film coefficient h will increase to ( A ) of original value.

A) 2-1/4 ; B) 21/4 ; C) 23/4 ; D) 2

(13) Based on the temperature distribution as shown in figure, which has largest temperature drop A , and which has the largest thermal conductivity C if the thickness of each layer is the same?

A) layer A; B) layer B; C) layer C

(14) The removal of uncondensable gas in the condensing vapor will ( B )

A increase condensing film coefficient h;

B decrease condensing film coefficient h;

C do not change condensing film coefficient h;

D be uncertain.

(15) A flat wall thickness b=0.1m and heat transfer area A=2m2 consists of some material with conductivity k=0.1 w/m×K, heat transfer rate q will be 200 (w) when the temperature difference between both sides of wall is 100 K. If heat resistance is double and temperature drop between both sides of wall keeps constant, heat transfer rate q will be 100 (w).

(16) If h

i is much smaller than h

o

and wall heat resistance is ignored,

overall heat transfer coefficient U will be approximately equal to ( A ); in order to enhance heat transfer, the best way is to increase ( ).

A h

i ; B h

o

; C average of h

i

and h

o

; D uncertain