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- Physics 101
- 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
Explain why heat pumps do not work as well in very cold climates as they do in milder ones. Is the same true of refrigerators?
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?
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
.)
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.
Can you cool a kitchen by leaving the refrigerator door open?
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
?
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?
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
?
In a very mild winter climate, a heat pump has heat transfer from an environment at
to one at
. What is the best possible coefficient of performance for these temperatures? Explicitly show how you follow the steps in the
Problem-Solving Strategies for Thermodynamics .
(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.
(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.
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?
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?
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).
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
.
Questions & Answers
I'm interested in biological psychology and cognitive psychology
what does preconceived mean
How can I develope my cognitive domain
why is communication effective
Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.
it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.
miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
please i need answer
Wekolamo
because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).
Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!
ARC
A child is a member of community not society elucidate ?
Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?
compare and contrast skinner's perspective on personality development on freud
Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning
war
explain how nature and nurture affect the development and later the productivity of an individual.
nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
Samuel
I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
and having a good philosophy of the world is like a sandwich and a peanut butter 👍
Jonathan
generally amnesi how long yrs memory loss
interpersonal relationships
What would be the best educational aid(s) for gifted kids/savants?
treat them normal, if they want help then give them.
that will make everyone happy
Saurabh
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Source:
OpenStax, Physics 101. OpenStax CNX. Jan 07, 2013 Download for free at http://legacy.cnx.org/content/col11479/1.1
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