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Suppose you stand with one foot on ceramic flooring and one foot on a wool carpet, making contact over an area of 80 . 0 cm 2 with each foot. Both the ceramic and the carpet are 2.00 cm thick and are 10. C on their bottom sides. At what rate must heat transfer occur from each foot to keep the top of the ceramic and carpet at 33 . C ?

A man consumes 3000 kcal of food in one day, converting most of it to maintain body temperature. If he loses half this energy by evaporating water (through breathing and sweating), how many kilograms of water evaporate?

2.59 kg

(a) A firewalker runs across a bed of hot coals without sustaining burns. Calculate the heat transferred by conduction into the sole of one foot of a firewalker given that the bottom of the foot is a 3.00-mm-thick callus with a conductivity at the low end of the range for wood and its density is 300  kg/m 3 size 12{"300"`"kg/m" rSup { size 8{3} } } {} . The area of contact is 25 . 0  cm 2 size 12{"25" "." 0`"cm" rSup { size 8{2} } } {} , the temperature of the coals is 700º C size 12{"700"°C} {} , and the time in contact is 1.00 s.

(b) What temperature increase is produced in the 25 . 0  cm 3 size 12{"25" "." 0`"cm" rSup { size 8{3} } } {} of tissue affected?

(c) What effect do you think this will have on the tissue, keeping in mind that a callus is made of dead cells?

(a) What is the rate of heat conduction through the 3.00-cm-thick fur of a large animal having a 1 . 40-m 2 size 12{1 "." "40-m" rSup { size 8{2} } } {} surface area? Assume that the animal’s skin temperature is 32 . C , that the air temperature is 5 . 00º C size 12{ - 5 "." "00"°C} {} , and that fur has the same thermal conductivity as air. (b) What food intake will the animal need in one day to replace this heat transfer?

(a) 39.7 W

(b) 820 kcal

A walrus transfers energy by conduction through its blubber at the rate of 150 W when immersed in 1 .00ºC water. The walrus’s internal core temperature is 37. C size 12{"37" "." 0°C} {} , and it has a surface area of 2 .00 m 2 . What is the average thickness of its blubber, which has the conductivity of fatty tissues without blood?

The figure shows a walrus on an ice bank near the water. The tusks the walrus are visible.
Walrus on ice. (credit: Captain Budd Christman, NOAA Corps)

Compare the rate of heat conduction through a 13.0-cm-thick wall that has an area of 10 . 0  m 2 size 12{"10" "." 0`m rSup { size 8{2} } } {} and a thermal conductivity twice that of glass wool with the rate of heat conduction through a window that is 0.750 cm thick and that has an area of 2 . 00  m 2 size 12{2 "." "00"`m rSup { size 8{2} } } {} , assuming the same temperature difference across each.

35 to 1, window to wall

Suppose a person is covered head to foot by wool clothing with average thickness of 2.00 cm and is transferring energy by conduction through the clothing at the rate of 50.0 W. What is the temperature difference across the clothing, given the surface area is 1 . 40  m 2 size 12{1 "." "40"`m rSup { size 8{2} } } {} ?

Some stove tops are smooth ceramic for easy cleaning. If the ceramic is 0.600 cm thick and heat conduction occurs through the same area and at the same rate as computed in [link] , what is the temperature difference across it? Ceramic has the same thermal conductivity as glass and brick.

1 . 05 × 10 3 K size 12{1 "." "05" times "10" rSup { size 8{3} } `K} {}

One easy way to reduce heating (and cooling) costs is to add extra insulation in the attic of a house. Suppose the house already had 15 cm of fiberglass insulation in the attic and in all the exterior surfaces. If you added an extra 8.0 cm of fiberglass to the attic, then by what percentage would the heating cost of the house drop? Take the single story house to be of dimensions 10 m by 15 m by 3.0 m. Ignore air infiltration and heat loss through windows and doors.

(a) Calculate the rate of heat conduction through a double-paned window that has a 1 . 50 -m 2 area and is made of two panes of 0.800-cm-thick glass separated by a 1.00-cm air gap. The inside surface temperature is 15 . C size 12{"15" "." 0°C} {} , while that on the outside is 10 . C size 12{ - "10" "." 0°C} {} . (Hint: There are identical temperature drops across the two glass panes. First find these and then the temperature drop across the air gap. This problem ignores the increased heat transfer in the air gap due to convection.)

(b) Calculate the rate of heat conduction through a 1.60-cm-thick window of the same area and with the same temperatures. Compare your answer with that for part (a).

(a) 83 W

(b) 24 times that of a double pane window.

Many decisions are made on the basis of the payback period: the time it will take through savings to equal the capital cost of an investment. Acceptable payback times depend upon the business or philosophy one has. (For some industries, a payback period is as small as two years.) Suppose you wish to install the extra insulation in [link] . If energy cost $1.00 per million joules and the insulation was $4.00 per square meter, then calculate the simple payback time. Take the average Δ T for the 120 day heating season to be 15. C .

For the human body, what is the rate of heat transfer by conduction through the body’s tissue with the following conditions: the tissue thickness is 3.00 cm, the change in temperature is 2 . 00º C size 12{2 "." "00"°C} {} , and the skin area is 1 . 50  m 2 size 12{1 "." "50"`m rSup { size 8{2} } } {} . How does this compare with the average heat transfer rate to the body resulting from an energy intake of about 2400 kcal per day? (No exercise is included.)

20.0 W, 17.2% of 2400 kcal per day

Questions & Answers

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
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Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, College physics ii. OpenStax CNX. Nov 29, 2012 Download for free at http://legacy.cnx.org/content/col11458/1.2
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