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【单选题】
关于对流传热系数，一般来说，下列说法正确的是（ ）。A.
对于同一流体，强制对流时的对流传热系数要大于自然对流时的对流传热系数
B.
对于同一种流体，有相变时的对流传热系数一般小于无相变时的对流传热系数
C.
在稳态的间壁式换热中，、外流体的对流传热系数之比等于、外径之比
D.
流体在稳态流动换热时，对流传热系数沿不发生改变
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举一反三
【单选题】External shunts are sometimes used with ammeters to _______.
A.
increase meter sensitivity
B.
permit shunts with larger resistances to be utilized
C.
prevent damage to the meter movement from heat generated by the shunt
D.
enable the construction of a compact meter with a virtually unlimited range
【单选题】Ammeters and voltmeters used in sinusoidal AC power systems indicate which of the following values of the waveforms measured?
A.
Peak value
B.
Boot-mean-square value
C.
Average value
D.
Maximum value
【单选题】Ammeters and voltmeters used in sinusoidal AC power systems including which of the following values of the waveforms measured?
A.
Peak value
B.
Root mean square value
C.
average value
D.
Maximum value
【单选题】In the sinusoidal steady-state circuit, the readings of ammeters A 1 and A 2 are 3A and 4A, respectively, then the reading of A is A .
A.
5A
B.
7A
C.
1A
D.
-1A
【单选题】Ammeters must have a resistance, while voltmeters must have a resistance.
A.
high...low
B.
low...high
C.
low...low
D.
high...high
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