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#21
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"Threeducks" > wrote in message ... | | A system does not contain "heat". Heat is simply a method of | transfering energy between the system and it's surroundings. I thought that *any* material with a temperature above "absolute zero" contains "heat". |
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#22
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"Daniel J. Stern" > wrote in message n.umich.edu... | On Fri, 24 Sep 2004, Kathy and Erich Coiner wrote: | | > > An air conditioner generates neither heat nor cold. All it does is *move* | > > heat. | | > But it moves the energy at less than 100% efficiency. That means there is | > some extra work that shows up as heat. | | Sure, but the fact remains, an aircon does not "generate" heat or cold. | | > You have a closed,well insulated room with a refrigerator in it. It is | > running and you hold the door open. What happens to the air temp in the | > room? | | Of course the ambient temp increases. | | Now here's a fun one: It is common knowledge that there is no such thing | as a 100 percent efficient machine. Given that, consider an electric space | heater with a 20-foot electric cord and a high-speed motor-driven blower. | Is the efficiency of such a device 100 percent, or some lesser figure? | Support your answer. No for several reasons: o Losses in the generation of electricity at the power plant o Losses due to electrical transmission line losses between the generator and the heater o Losses in step-down transformers along the electrical transmission route. o Losses at each connection point, switch/fuse/breaker |
#23
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Daniel J. Stern wrote:
> On Thu, 23 Sep 2004, motsco_ _ wrote: > > >>An air conditioner generates more HEAT than COLD > > > An air conditioner generates neither heat nor cold. All it does is *move* > heat. > > It does naturally generate heat due to the energy lost in moving the energy in the hot air. Otherwise it would consume almost zero watts... |
#24
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On Fri, 24 Sep 2004, James C. Reeves wrote:
> | Now here's a fun one: It is common knowledge that there is no such thing > | as a 100 percent efficient machine. Given that, consider an electric space > | heater with a 20-foot electric cord and a high-speed motor-driven blower. > | Is the efficiency of such a device 100 percent, or some lesser figure? > | Support your answer. > > No for several reasons: > > o Losses in the generation of electricity at the power plant > o Losses due to electrical transmission line losses between the > generator and the heater > o Losses in step-down transformers along the electrical > transmission route. > o Losses at each connection point, switch/fuse/breaker "No" is not a valid answer; the question is not of the yes/no variety. Also, we're talking about efficiency at converting the electricity *at the wall socket* into heat. |
#25
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On Fri, 24 Sep 2004, James C. Reeves wrote:
> | > | On Wed, 22 Sep 2004, Burt Squareman wrote: > | > | > The A/C system in an `89 old Honda is completely dead. > | Find and get an automotive swamp cooler. They were popular before car A/C > | became common. > Swamp coolers are relatively ineffective So are clapped-out '89 Hondas. Perfect match. |
#26
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"Daniel J. Stern" > wrote in message n.umich.edu... | On Fri, 24 Sep 2004, James C. Reeves wrote: | | > | | > | On Wed, 22 Sep 2004, Burt Squareman wrote: | > | | > | > The A/C system in an `89 old Honda is completely dead. | | > | Find and get an automotive swamp cooler. They were popular before car A/C | > | became common. | | > Swamp coolers are relatively ineffective | | So are clapped-out '89 Hondas. Perfect match. | Good point! ;-) |
#27
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"James C. Reeves" > wrote > I thought that *any* material with a temperature above "absolute zero" contains > "heat". Except for my ex-wife. |
#28
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On Fri, 24 Sep 2004 03:54:20 GMT, "Kathy and Erich Coiner"
> wrote: >This is a thought problem we sometimes give to mechanical engineering job >applicants. > >You have a closed,well insulated room with a refrigerator in it. It is >running and you hold the door open. >What happens to the air temp in the room? > >Erich If you let the condensate down the drain instead of evaporating inside the room, you have the most efficient heater. Bye, Leon |
#29
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On Fri, 24 Sep 2004 19:18:42 -0400, Max > wrote:
>Daniel J. Stern wrote: >> On Thu, 23 Sep 2004, motsco_ _ wrote: >> >> >>>An air conditioner generates more HEAT than COLD >> >> >> An air conditioner generates neither heat nor cold. All it does is *move* >> heat. >> >> > >It does naturally generate heat due to the energy lost in moving the >energy in the hot air. > >Otherwise it would consume almost zero watts... No, the a/c is a heat pump. Think about it as a pump pumping water between two tanks. It takes energy to pump water up to the higher tank. The pump is also inefficient. Bye, Leon |
#30
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"James C. Reeves" wrote: > > "Threeducks" > wrote in message > ... > | > | A system does not contain "heat". Heat is simply a method of > | transfering energy between the system and it's surroundings. > > I thought that *any* material with a temperature above "absolute zero" contains > "heat". No, a material can not contain heat. Heat, as Threeducks said, applies only to thermal energy in transit. From Halliday / Resnick: Fundamentals of Physics, 3rd edition, Wiley 1988: Page 464: "Heat is energy that flows between a system and its environment by virtue of a temperature difference that exists between them" Page 465: "Both heat and work represents energy-in-transit between a system and its environment. Heat and work, unlike temperature, pressure and volume, are not intrinsic properties of a system. They have meaning only as they describe energy transfers into or out of a system, adding or subtracting from the system's store of internal energy. (...) It is without meaning to say: "This system contains 450 J of heat" or "This system contains 385 J of work"" |
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