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1 | |
The relationships that predict heat transfer are based on empirical observations and depend on ideal conditions. |
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| | A) | True |
| | B) | False |
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2 | |
The quantity of heat transferred through a slab of area 4 ft² is greater than the quantity of heat conducted through an area of 8 ft², assuming that all other parameters are constant. |
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| | A) | True |
| | B) | False |
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3 | |
When a radiator is used to heat a room, the principal method of heat transfer warming the room is convection. |
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| | A) | True |
| | B) | False |
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4 | |
Air-conditioning outlets in the ceiling are more efficient than those on the floor. |
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| | A) | True |
| | B) | False |
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5 | |
All objects emit electromagnetic radiation, regardless of their temperature or the temperature of their surroundings. |
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| | A) | True |
| | B) | False |
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6 | |
An object that absorbs a large percentage of incident radiation will be a poor emitter of radiation. |
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| | A) | True |
| | B) | False |
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7 | |
Because of a similarity in the definition of heat units, the thermal conductivities are the same numerically in the engineering system and the metric system of units. |
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| | A) | True |
| | B) | False |
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8 | |
A body at the same temperature as its surroundings radiates and absorbs heat at the same rate. |
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| | A) | True |
| | B) | False |
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9 | |
In a composite wall of two or more different materials, the same number of calories is transferred per unit area per unit time through each material after time is allowed for steady flow to be established. |
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| | A) | True |
| | B) | False |
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10 | |
The units of thermal conductivity in the metric system may be written cal * cm/(cm2 * s * C°), but the numerical value would be different. |
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| | A) | True |
| | B) | False |
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11 | |
Which of the following geometries will result in the largest convection coefficient? |
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| | A) | Vertical plate |
| | B) | Horizontal plate, facing upward |
| | C) | Diagonal plate |
| | D) | Horizontal plate, facing downward |
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12 | |
When the temperature of an object is doubled, its rate of radiation is increased by a factor of |
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| | A) | 2 |
| | B) | 4 |
| | C) | 8 |
| | D) | 16 |
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13 | |
The dead airspace between the walls of a calorimeter cup and its outside container minimizes heat loss due to |
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| | A) | conduction |
| | B) | convection |
| | C) | radiation |
| | D) | contamination |
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14 | |
The rate at which heat flows through a solid plate of some materials does not depend on the |
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| | A) | temperature difference |
| | B) | thickness |
| | C) | specific heat |
| | D) | area |
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15 | |
The direction of heat flow is always from |
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| | A) | high temperature to low temperature |
| | B) | high pressure to low pressure |
| | C) | high density to low density |
| | D) | a point of higher emissivity |
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16 | |
Which of the following does not indicate heat flow as a quantity of heat per unit time? |
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| | A) | kA Δt/L |
| | B) | hA Δt |
| | C) | H |
| | D) | eσT4 |
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17 | |
The thermal conductivity of a plate is 0.01 kcal/s * m * C°. The plate is 2 cm thick and has a cross section of 4000 cm². If one side is at 150°C and the other at 50°C, the number of kilocalories transferred every second is approximately |
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| | A) | 10 kcal |
| | B) | 20 kcal |
| | C) | 40 kcal |
| | D) | 80 kcal |
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18 | |
The convection coefficient for a vertical plate is 12.7 X 1-4 kcal/s * m² * C° when the difference of temperature between the plate and its surroundings is 810°C. How much heat is transferred by convection from each side of the plate in 1 h if the area is 20 cm²? |
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| | A) | 0.206 cal |
| | B) | 12.4 cal |
| | C) | 7410 cal |
| | D) | 8410 cal |
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19 | |
A body having an emissivity of 0.2 and a surface area of 0.2 m² is heated to 727°C. The power radiated from the surface is approximately |
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| | A) | 634 W |
| | B) | 1134 W |
| | C) | 1830 W |
| | D) | 2268 W |
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20 | |
The units Btu/(h * ft² * F°) are appropriate for the |
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| | A) | convection coefficient |
| | B) | thermal conductivity |
| | C) | rate of radiation |
| | D) | emissivity |
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21 | |
Two types of convection that apply to most heating systems are convection and convection. |
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22 | |
For the common laboratory calorimeter, heat losses resulting from are minimized by a dead airspace. The rubber ring prevents heat losses by , and radiation losses are minimized by the . |
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23 | |
Heat is transferred from the sun to the earth by means of . |
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24 | |
The rate at which thermal radiation is emitted from a surface varies directly with the power of the . |
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25 | |
The of a body is a measure of its ability to absorb or emit thermal radiation, and it may vary from a value of to a value of . |
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26 | |
The convection coefficient is not a property of the solid or fluid but depends primarily on the of the solid. The convection coefficients for a wall, a floor, and a ceiling are largest for the and lowest for the . |
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27 | |
The British units commonly used for thermal conductivity are the , and the metric units are the . |
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28 | |
Copper has about twice the thermal conductivity of aluminum, but its specific heat is a little less than half that of aluminum. A rectangular block is made from each material, so that they have identical masses and the same surface area at their bases. Each block is heated 300°C and placed on top of a large cube of ice.The block will sink deeper into the ice because it has a higher . The block will stop sinking first because it has a higher . |
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29 | |
The warm air over a burning fire will rise under the influence of currents. |
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30 | |
On a cold day, a piece of iron feels colder to the touch than a piece of wood at the same temperature because the iron has a higher . |
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