I would like to ask about the actual exam questions from the 2010 Chemical Engineering examination
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On the morning of the first day last year, question number 3 read as follows: What is the amount of heat (in kJ) required to raise 1 mole of carbon dioxide from 400 K to 1100 K? Which of the following values is the correct answer? It is known that the average heat capacity of carbon dioxide between 298 and 400 K is Cp1-=39.23 J/(mol•K); at 400 K, its true heat capacity is Cp1=41.05 KJ/(Kmol•K), and at 1100 K, it is Cp2=55.65 KJ/(Kmol•K). The options are A 30.7, B 34.9, C 1 r7, D 44.8. What is the solution to this problem? Thank you in advance.
C: 44.8 + 55.65*(1100/1000) – 41.05*(400/1000) = 44.795; I’m not sure if this is correct.
Reply to 3# kzhren: I thought about it too, but I felt there was a problem with it. Thinking in this way is equivalent to designing a process in which CO2 is first cooled from 400 K to 0 K, and then heated from 0 K to 1100 K. However, I believe it is inappropriate to use the specific heat capacity at 400 K instead of the average heat capacity over the range 0–400 K, and to use the specific heat capacity at 1100 K instead of the average heat capacity over the range 0–1100 K.
The calculation proceeds as follows: the average specific heat capacity at 298–1100 K is CPi = (41.05 + 55.65)/2 = 48.35; then Q = 48.35 * (1100 – 298) – 39.23 * (400 – 298) = 34.8
Can anyone answer question 32? 32. For a steam pipe with a length of 1000 m and an outer diameter of 114 mm, where the outer wall temperature is 180°C, and insulation material with a thermal conductivity of 0.2 W/(m·K) is used with an insulation thickness of 50 mm, what value is closest to the total heat loss of the pipe in KW when the surface temperature of the insulation layer is 50°C? A. 240 B. 260 C. 280 D. 300
OP, what’s the correct answer to this question?