GEOG 4891 Lecture 1: Home Work No 1, Paper Report Format

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1 Jun 2020

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The problems solved by this study are: The underlying physical and/or theoretical principles used in the: (so on if required) solutions are, (so on if required, (so on if required, (so on if required, assumptions and limitations: The assumptions and limitations of the solutions/results are: Reasonability of assumptions and limits: practical applications: The practical applications of the solutions are: (so on if required, discussion: Discussing the authors" view of the solutions/results. My own view of the solutions/results: (so on if required, (so on if required, (so on if required, recommendations/extensions: The solutions/results could be extended or improved by:

Related Questions

Students are designing an experiment to demonstrate the conversionof mechanical energy into thermal energy. They have designed theapparatus shown in the figure above. Small lead beads of total massM and specific heat c (heat capacity is used in Q = mc?T) fill thelower hollow sphere. The valves between the spheres and the hollowtube can be opened or closed to control the flow of the lead beads.Initially both valves are open.

a. The lower valve is closed and a student turns the apparatus 180Â°about a horizontal axis, so that the filled sphere is now on top.This elevates the center of mass of the lead beads by a verticaldistance h. What minimum amount of work must the student do toaccomplish this?

b. The valve is now opened and the lead beads tumble down thehollow tube into the other hollow sphere. If all of thegravitational potential energy is converted into thermal energy inthe lead beads, what is the temperature increase of the lead?

c. The values of M, h, and c for the students' apparatus are M =3.0 kg, h = 2.00 m, and c = 128 J/(kg Â· K). The students measurethe initial temperature of the lead beads and then conduct 100repetitions of the "elevate and drain" process. Again, assume thatall of the gravitational potential energy is converted into thermalenergy in the lead beads. Calculate the theoretical cumulativetemperature increase after the 100 repetitions.

d. Suppose that the experiment were conducted using smallerreservoirs, so that M was one tenth as large (but h was unchanged).Would your answers to parts (b) and (c) be changed? If so, in whatway, and why? If not, why not?

e. When the experiment is actually done, the temperature increaseis less than calculated in part (c). Identify a physical effectthat might account for this discrepancy and explain why it lowersthe temperature.

Vapor cycles
5EM - Thermodynamics
September 2010
1 The T-S diagram
The temperature-entropy diagram is an alternative to the well knownpressure-
volume diagram. Before using it to analyze different vapor cycles,we need
to understand it properly.
1. Plot the following transformations for ideal gases in a T-Sdiagram
(a) Isothermal expansion
(b) Isobaric expansion
(c) Isometric heating
(d) Reversible adiabatic expansion
(e) Irreversible adiabatic expansion
2. Repeat the last question, but this time do it for a realsubstance,
starting in the compressed liquid1 region and ending in thesuperheated
region, when possible. Indicate the boundaries of eachregion.
3. We know that under certain circumstances the area under theplot
in a P-V diagram represents the work performed during theprocess.
What does it represent in this case? Under what assumptions isyour
answer true? Compare examples 6.1 and 6.2.
2 Thermal machines
We understand by thermal machine a device capable of transformingther-
mal energy (heat) into mechanical energy (work). We already knowthat
these machines have a limited efficiency which, in the two-sourcesmodel, is
obtained by Carnotâs cycle.
(Compressed liquid is sometimes also called subcooled liquid)
2.1 Carnot cycle
This cycle, although efficient, is impractical. To begin with, theextreme
temperatures of the cycle should be within the sources temperaturesfor a
finite heat flow to exist.
1. Given the temperature of the sources, draw the cycle accordingto the
named limitation.
2. Show that this leads to lower efficiency than the theoreticallimit.
3. Assume that heat flow from/to the sources is proportional to thetem-
perature difference between them and the working fluid, anddemon-
strate that a higher power output is related to a decreasedefficiency.
2.2 Rankine cycle
Out of the several practical possibilities, Rankine cycle and itsvariations is
widely used, especially for electric power generation.
1. Draw the basic cycle in a T-S diagram and explain it.
2. What does the efficiency of the cycle depend on? Comparewith
Carnotâs.
3. What are the differences between the ideal cycle and the realone?
4. Describe how it is modified by superheating and/or reheating.Explain
te benefits.
2.3 Problems
After answering the previous questions solve the followingexercises from the
book: 8.2, 8.4, 8.5, 8.13, 8.19, 8.20
3 Frigorific machines
3.1 Reverse Carnot cycle
We have already studied Carnot cycle in detail as the ideal thermalmachine.
Now we will take is as the starting point to understand thecharacteristics
of frigorific machines.
1. Draw the ideal cycle in a T-S diagram and explain it.
2. Show that this cycle has a theoretical efficiency Ã =Tcold/Thot-Tcold
3. What are the difficulties in implementing such cycle in actualdevices?
3.2 Actual refrigerators
1. Why is the turbine replaced by an expansion valve in mostcases?
2. Plot the actual cycle and explain the differences with the idealcase.
3. How do cascade and multistage systems improve the performanceof
the refrigerator?
4. What aspects are important in the choice of a refrigerant fluid?Justify
3.3 Problems
After answering the previous questions solve the followingexercises from the
book: 10.2 10.7, 10.8, 10.9, 10.22, 10.23 10.1D

GEOG 4891 Lecture 1: Home Work No 1, Paper Report Format

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