20. Heat and Temperature

Heat Transfer

Physics - Energy - Heat Transfer - Convection

The blood plays an important role in removing heat from the body by bringing this energy directly to the surface where it can radiate away. Nevertheless, this heat must still travel through the skin before it can radiate away. Assume that the blood is brought to the bottom layer of skin at 37.0°C and that the outer surface of the skin is at 30.0°C. Skin varies in thickness from 0.50 mm to a few millimeters on the palms and soles, so assume an average thickness of 0.75 mm. A 165-lb, 6-ft-tall person has a surface area of about 2.0 m2 and loses heat at a net rate of 75 W while resting. On the basis of our assumptions, what is the thermal conductivity of this person’s skin?

Heat Exchange

Suppose that the rod in Fig. 17.24a is made of copper, is 45.0 cm long, and has a cross-sectional area of 1.25 cm^2 . Let TH = 100.0°C and TC = 0.0°C. (a) What is the final steady-state temperature gradient along the rod? <img class="fr-dib" src="https://lightcat-files.s3.amazonaws.com/problem_images/84d05b92f33d906e-1678285742880.jpg" style="width: 274px;">

A rigid container holds <math display="inline"><mrow><mn>12</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">g</mi></mrow></math> of <math display="inline"><mrow><msub><mi mathvariant="normal" class="MathML-Unit">O</mi><mn>2</mn></msub></mrow></math> gas at <math display="inline"><mrow><mn>30</mn><mo>&#x00B0;</mo><mi mathvariant="normal" class="MathML-Unit">C</mi></mrow></math>. How much energy must be added to the gas to bring its temperature to <math display="inline"><mrow><mn>50</mn><mo>&#x00B0;</mo><mi mathvariant="normal" class="MathML-Unit">C</mi></mrow></math>?

Physics - Energy - Heat Transfer - Conduction

300⁢g of water at 40°C is in an insulated cup. What mass of copper at 500°C must be added to heat the water to 60°C?

Conduction -Convection- Radiation-Heat Transfer

Physics - Heat Transfer - Thermal Radiation

Heat Transfer L1 p4 - Conduction Rate Equation - Fourier's Law

An electric kitchen range has a total wall area of 1.40 m^2 and is insulated with a layer of fiberglass 4.00 cm thick. The inside surface of the fiberglass has a temperature of 175°C, and its outside surface is at 35.0°C. The fiberglass has a thermal conductivity of 0.040 W/m K. (a) What is the heat current through the insulation, assuming it may be treated as a flat slab with an area of 1.40 m^2 ?

<math display="inline"><mrow><mn>650</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">J</mi></mrow></math> is transferred into the system.

<math display="inline"><mrow><mn>250</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">J</mi></mrow></math> is transferred out of the system.

<math display="inline"><mrow><mn>250</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">J</mi></mrow></math> is transferred into the system.

There is not enough information to answer this question.

<math display="inline"><mrow><mn>650</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">J</mi></mrow></math> is transferred out of the system.

<math display="inline"><mrow><mn>450</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">J</mi></mrow></math> of work are done on a gas in a process which decreases the thermal energy by <math display="inline"><mrow><mn>200</mn><mo rspace="thickmathspace">&#x2062;</mo><mi mathvariant="normal" class="MathML-Unit">J</mi></mrow></math>. How much heat energy is transferred to or from the system?

The emissivity of tungsten is 0.350. A tungsten sphere with radius 1.50 cm is suspended within a large evacuated enclosure whose walls are at 290.0 K. What power input is required to maintain the sphere at 3000.0 K if heat conduction along the supports is ignored?

A cubic Styrofoam cooler containing ice on a hot day is shown in the following figure. The thickness of each wall of the cooler is 15 mm, with a side length of 1 m. If it is 40°C outside, how long will 2 kg of ice last in the cooler? Assume that during the melting process, the temperature inside the cooler remains at 0°C and that no heat enters from the bottom of the cooler. Note that the latent heat of fusion for water is 334 kJ/kg and the thermal conductivity of Styrofoam is 0.033 W/mK.<img src="https://static.studychannel.pearsonprd.tech/courses/physics/thumbnails/images/65cefef8"alt=""/>

Radiation

Two rods, one made of brass and the other made of copper, are joined end to end. The length of the brass section is 0.300 m and the length of the copper section is 0.800 m. Each segment has cross-sectional area 0.00500 m^2 . The free end of the brass segment is in boiling water and the free end of the copper segment is in an ice–water mixture, in both cases under normal atmospheric pressure. The sides of the rods are insulated so there is no heat loss to the surroundings. (b) What mass of ice is melted in 5.00 min by the heat conducted by the composite rod?

If the intensity of sunlight measured at the Earth’s surface is 1400 W/m2 , what is the surface temperature of the Sun? Treat the Sun like a true blackbody. Note that the distance from the Earth to the Sun is 1.5 x 1011 m and the radius of the Sun is 696 million meters.

Introduction to Heat Transfer

Conduction

Heat Transfer [Conduction, Convection, and Radiation]

A spherical pot contains 0.75 L of hot coffee (essentially water) at an initial temperature of 95°C. The pot has an emissivity of 0.60, and the surroundings are at 20.0°C. Calculate the coffee’s rate of heat loss by radiation.

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