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- Thermodynamics
- Applications of thermodynamics
Section summary
- An artifact of the second law of thermodynamics is the ability to heat an interior space using a heat pump. Heat pumps compress cold ambient air and, in so doing, heat it to room temperature without violation of conservation principles.
- To calculate the heat pump's coefficient of performance, use the equation
.
- A refrigerator is a heat pump; it takes warm ambient air and expands it to chill it.
Conceptual questions
In some Northern European nations, homes are being built without heating systems of any type. They are very well insulated and are kept warm by the body heat of the residents. However, when the residents are not at home, it is still warm in these houses. What is a possible explanation?
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Why do refrigerators, air conditioners, and heat pumps operate most cost-effectively for cycles with a small difference between
and
? (Note that the temperatures of the cycle employed are crucial to its
.)
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Grocery store managers contend that there is
less total energy consumption in the summer if the store is kept at a
low temperature. Make arguments to support or refute this claim, taking into account that there are numerous refrigerators and freezers in the store.
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Problem exercises
What is the coefficient of performance of an ideal heat pump that has heat transfer from a cold temperature of
to a hot temperature of
?
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Suppose you have an ideal refrigerator that cools an environment at
and has heat transfer to another environment at
. What is its coefficient of performance?
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What is the best coefficient of performance possible for a hypothetical refrigerator that could make liquid nitrogen at
and has heat transfer to the environment at
?
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(a) What is the best coefficient of performance for a heat pump that has a hot reservoir temperature of
and a cold reservoir temperature of
? (b) How much heat transfer occurs into the warm environment if
of work (
) is put into it? (c) If the cost of this work input is
, how does its cost compare with the direct heat transfer achieved by burning natural gas at a cost of 85.0 cents per therm. (A therm is a common unit of energy for natural gas and equals
.)
(a) 4.61
(b)
(c) To transfer
, heat pump costs $1.00, natural gas costs $1.34.
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(a) What is the best coefficient of performance for a refrigerator that cools an environment at
and has heat transfer to another environment at
? (b) How much work in joules must be done for a heat transfer of 4186 kJ from the cold environment? (c) What is the cost of doing this if the work costs 10.0 cents per
(a kilowatt-hour)? (d) How many kJ of heat transfer occurs into the warm environment? (e) Discuss what type of refrigerator might operate between these temperatures.
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Suppose you want to operate an ideal refrigerator with a cold temperature of
, and you would like it to have a coefficient of performance of 7.00. What is the hot reservoir temperature for such a refrigerator?
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An ideal heat pump is being considered for use in heating an environment with a temperature of
. What is the cold reservoir temperature if the pump is to have a coefficient of performance of 12.0?
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A 4-ton air conditioner removes
(48,000 British thermal units) from a cold environment in 1.00 h. (a) What energy input in joules is necessary to do this if the air conditioner has an energy efficiency rating (
) of 12.0? (b) What is the cost of doing this if the work costs 10.0 cents per
(one kilowatt-hour)? (c) Discuss whether this cost seems realistic. Note that the energy efficiency rating (
) of an air conditioner or refrigerator is defined to be the number of British thermal units of heat transfer from a cold environment per hour divided by the watts of power input.
(a)
(b) 40 cents
(c) This cost seems quite realistic; it says that running an air conditioner all day would cost $9.59 (if it ran continuously).
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Show that the coefficients of performance of refrigerators and heat pumps are related by
.
Start with the definitions of the
s and the conservation of energy relationship between
,
, and
.
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Questions & Answers
how does Neisseria cause meningitis
is the branch of biology that deals with the study of microorganisms.
studies of microbes
Louisiaste
when we takee the specimen which lumbar,spin,
How bacteria create energy to survive?
Bacteria doesn't produce energy they are dependent upon their substrate in case of lack of nutrients they are able to make spores which helps them to sustain in harsh environments
_Adnan
But not all bacteria make spores, l mean Eukaryotic cells have Mitochondria which acts as powerhouse for them, since bacteria don't have it, what is the substitution for it?
Muhamad
they make spores
Louisiaste
what is sporadic nd endemic, epidemic
the significance of food webs for disease transmission
Abreham
food webs brings about an infection as an individual depends on number of diseased foods or carriers dully.
Mark
explain assimilatory nitrate reduction
Assimilatory nitrate reduction is a process that occurs in some microorganisms, such as bacteria and archaea, in which nitrate (NO3-) is reduced to nitrite (NO2-), and then further reduced to ammonia (NH3).
Elkana
This process is called assimilatory nitrate reduction because the nitrogen that is produced is incorporated in the cells of microorganisms where it can be used in the synthesis of amino acids and other nitrogen products
Elkana
Examples of thermophilic organisms
Give Examples of thermophilic organisms
Shu
advantages of normal Flora to the host
Prevent foreign microbes to the host
Abubakar
they provide healthier benefits to their hosts
ayesha
They are friends to host only when Host immune system is strong and become enemies when the host immune system is weakened . very bad relationship!
Mark
cell is the smallest unit of life
Fauziya
cell is the smallest unit of life
Akanni
cell is the structural and functional unit of life
Hasan
is the fundamental units of Life
Musa
what are emergency diseases
There are nothing like emergency disease but there are some common medical emergency which can occur simultaneously like Bleeding,heart attack,Breathing difficulties,severe pain heart stock.Hope you will get my point .Have a nice day ❣️
_Adnan
define infection ,prevention and control
Innocent
I think infection prevention and control is the avoidance of all things we do that gives out break of infections and promotion of health practices that promote life
Lubega
Heyy Lubega hussein where are u from?
_Adnan
which site have a normal flora
Many sites of the body have it
Skin
Nasal cavity
Oral cavity
Gastro intestinal tract
Safaa
skin,Oral,Nasal,GIt
Sadik
How can Commensal can Bacteria change into pathogen?
Sadik
How can Commensal Bacteria change into pathogen?
Sadik
what are the advantages of normal Flora to the host
Micheal
what are the ways of control and prevention of nosocomial infection in the hospital
Micheal
part of a tissue or an organ being wounded or bruised.
Wilfred
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Source:
OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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