ecen 5007 - quiz #2 - answers

7/31/2019 ECEN 5007 - Quiz #2 - Answers

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ECEN 5007 SOLAR THERMAL POWER PLANTS

Answers to Quiz #2 covering Lectures 3 to 6

July 27, 2012

Manuel J. Blanco, Ph.D., Dr.Ing. - Manuel A. Silva, Dr.Ing.

TWTH 17:00-19:30 - Class Room: ECCR 1B55

Office Hours: TWTH 15:30-16:30


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Quiz # 2 Lectures 3 6 CORRECT ANSWERS (1)

1) State the First Law of Thermodynamics for a closed system. What physicalmagnitude this Law defines?

Energy is conserved in any non-relativistic process

For a closed system:

U = Q + W

Where:

U : internal energy (J) Q: heat (J) W: work (J)2) Write the expression of the efficiency of the ideal heat engine Carnot cycle.

The maximum 1st Law efficiency for a heat engine is the efficiency of the Carnot cycle. This

efficiency is given by the following expression:

N = 1-TC/THWhere TH is the temperature of the hot temperature reservoir, and TC is the temperature ofthe cold temperature reservoir.The 2nd Law efficiency of the Carnot Cycle is 1.


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3) What kind of working fluid is used in a Brayton cycle?

The working fluidof a Brayton cycle (gas turbine cycle) is a gas (usually air)

4) The concentration of the solar radiation is limited by:a. The temperature of the heat transfer fluidb. The temperature of the absorber surfacec.

The apparent size of the sund. It is not limited at all

5) Explain the concepts of point-focus and line-focus concentrating systems.Point focus or 3-D concentrators ideally concentrate collected rays on a point (focal

point)

Line focus or 2-D concentrators ideally concentrate collected rays on a line (focal

line)

1) What are the limits for the concentration of solar radiation for point-focus and line-focus concentrating systems?

2) Provide a concise explanation of the convenience of high concentration ratios forsolar thermal power systems.

3 Which of the concentratin solar thermal technolo ies is currentl more



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6). What are the limits for the concentration of solar radiation for point-focus and line-focus concentrating systems?

7). Provide a concise explanation of the convenience of high concentration ratios for

solar thermal power systems.

High concentration ratios permit to achieve high absorber efficiencies at high

temperatures by keeping the radiation losses low reducing the area of the absorber

8). Which of the concentrating solar thermal technologies is currently morestandardized?

Parabolic trough


Cmx,linefocus =1/sinS 215

Cmx,po int focus =1/sin2

S 46, 200

ecen 5007 - quiz #2 - answers

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