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- Heat and heat transfer methods
- Radiation
Summary
- Radiation is the rate of heat transfer through the emission or absorption of electromagnetic waves.
- The rate of heat transfer depends on the surface area and the fourth power of the absolute temperature:
where
is the Stefan-Boltzmann constant and
is the emissivity of the body. For a black body,
whereas a shiny white or perfect reflector has
, with real objects having values of
between 1 and 0. The net rate of heat transfer by radiation is
where
is the temperature of an object surrounded by an environment with uniform temperature
and
is the emissivity of the
object .
Conceptual questions
Satellites designed to observe the radiation from cold (3 K) dark space have sensors that are shaded from the Sun, Earth, and Moon and that are cooled to very low temperatures. Why must the sensors be at low temperature?
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Why are thermometers that are used in weather stations shielded from the sunshine? What does a thermometer measure if it is shielded from the sunshine and also if it is not?
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Problems&Exercises
At what net rate does heat radiate from a
black roof on a night when the roof’s temperature is
and the surrounding temperature is
? The emissivity of the roof is 0.900.
Note that the negative answer implies heat loss to the surroundings.
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(a) Cherry-red embers in a fireplace are at
and have an exposed area of
and an emissivity of 0.980. The surrounding room has a temperature of
. If 50% of the radiant energy enters the room, what is the net rate of radiant heat transfer in kilowatts? (b) Does your answer support the contention that most of the heat transfer into a room by a fireplace comes from infrared radiation?
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Radiation makes it impossible to stand close to a hot lava flow. Calculate the rate of heat transfer by radiation from
of
fresh lava into
surroundings, assuming lava’s emissivity is 1.00.
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(a) Calculate the rate of heat transfer by radiation from a car radiator at
into a
environment, if the radiator has an emissivity of 0.750 and a
surface area. (b) Is this a significant fraction of the heat transfer by an automobile engine? To answer this, assume a horsepower of
and the efficiency of automobile engines as 25%.
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Find the net rate of heat transfer by radiation from a skier standing in the shade, given the following. She is completely clothed in white (head to foot, including a ski mask), the clothes have an emissivity of 0.200 and a surface temperature of
, the surroundings are at
, and her surface area is
.
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Suppose you walk into a sauna that has an ambient temperature of
. (a) Calculate the rate of heat transfer to you by radiation given your skin temperature is
, the emissivity of skin is 0.98, and the surface area of your body is
. (b) If all other forms of heat transfer are balanced (the net heat transfer is zero), at what rate will your body temperature increase if your mass is 75.0 kg?
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Questions & Answers
number of sport play by 50 student construct discrete data
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Solve the mean of variance
Step 1: Find the mean. To find the mean, add up all the scores, then divide them by the number of scores. ...
Step 2: Find each score's deviation from the mean. ...
Step 3: Square each deviation from the mean. ...
Step 4: Find the sum of squares. ...
Step 5: Divide the sum of squares by n – 1 or N.
kenneth
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What is the life teble
anas
statistics is the analyzing of data
how do you calculate mean
diveving the sum if all values
Shaynaynay
let A1,A2 and A3 events be independent,show that (A1)^c, (A2)^c and (A3)^c are independent?
data collected all over the world
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construct a less than and more than table
The sample of 16 students is taken. The average age in the sample was 22 years with astandard deviation of 6 years. Construct a 95% confidence interval for the age of the population.
Bhartdarshan' is an internet-based travel agency wherein customer can see videos of the cities they plant to visit. The number of hits daily is a normally distributed random variable with a mean of 10,000 and a standard deviation of 2,400
a. what is the probability of getting more than 12,000 hits?
b. what is the probability of getting fewer than 9,000 hits?
Bhartdarshan'is an internet-based travel agency wherein customer can see videos of the cities they plan to visit. The number of hits daily is a normally distributed random variable with a mean of 10,000 and a standard deviation of 2,400.
a. What is the probability of getting more than 12,000 hits
Akshay
Sorry i want to learn more about this question
Bright
a= 0.20233
b=0.3384
Sufiyan
How do I interpret level of significance?
It depends on your business problem or in Machine Learning you could use ROC- AUC cruve to decide the threshold value
Shivam
how skewness and kurtosis are used in statistics
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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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