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GGRA03H3 Lecture : lecture 5

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2 Nov 2010

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Document Summary

Development that improves the long-term health of human and ecological systems. Contested ideas (varying between opinions and ideas) Cities are complicated/complex systems (lots of things happening at the same time) Policy: help maintain/govern the city on different levels. Investment in rebuilding of our city as city system: inefficient in energy uses. Ability to maintain sustainable life with low/shared uses. Sustainable development = development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Inter-generational equity: inequitable for g3eneration to use up cheap resources. Intra-generation equity: disparities in wealth increasing, poor countries are unable to use a lot of resources, but are more damaging. Transfrontier responsibility: if developed world makes/uses all of the resources/pollution, catch up. Green infrastructure & buildings (e: 25-50%, c: 33-39%, w: 40%, s: 70%) urban sustainability issues [measures of ecological footprint]

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Related Questions

8. Have you ever worn something from a culture other than your own? This includes thing like hairstyles, clothes and accessories.

Yes. Not only me, at present most of the people, all over the world are doing the same. In this world we live in a together in a society with people from different places, different customs, and backgrounds. As we live together, we grow together, we also learn about other cultures and we accept them. There is a mutual two way exchange of cultural behaviors. This process is usually called "Acculturation". Also with technologies like television, internet, social media, etc. There is a widespread of information which is easily accessible to everyone. People following other cultures is most commonly evident in their dressing style (fashion). For example, long ago in India, ancestors used to wear Kurtas and dhotis. Where as we can see now present generation wearing jeans, t-shirts, and shirts of different patterns which is originally adopted from western culture.

9. If yes, did you know the meaning, significance and importance of that symbol?

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

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