# Tpc 431 The Refrigeration Cycle Lesson 4 Air Properties And Simple Psychrometrics

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Questions: 10 | Attempts: 53

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• 1.

### Saturated air at 80 F can hold 0.022 lb of moisture for each pound of dry air.  If the temperature is doubled, how much moisture can it hold

• A.

Half as much

• B.

The same amount

• C.

Twice as much

• D.

More than twice as much

D. More than twice as much
Explanation
When the temperature is doubled, the air can hold more moisture. This is because warmer air has a higher capacity for holding moisture. Since the original air was already saturated at 80 F, doubling the temperature would result in the air being able to hold more than twice as much moisture.

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• 2.

### Dry-bulb temp is a measure of the ______ of the air

• A.

Latent heat

• B.

Moisture content

• C.

Sensible heat

• D.

Total heat

C. Sensible heat
Explanation
The dry-bulb temperature is a measure of the sensible heat of the air. Sensible heat refers to the heat energy that can be sensed or measured by a thermometer. It is the heat energy associated with the temperature of the air, without considering any moisture content or latent heat. Therefore, the dry-bulb temperature is a measure of the sensible heat of the air.

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• 3.

### Wet-bulb temp can be measured with a(n)

• A.

Digital multimeter

• B.

Manometer

• C.

Ordinary thermometer

• D.

Sling psychrometer

D. Sling psychrometer
Explanation
A sling psychrometer is used to measure the wet-bulb temperature. This instrument consists of two thermometers, one of which has a wet bulb covered with a moistened wick. When the sling psychrometer is swung in the air, the moisture on the wet bulb evaporates, causing the temperature to decrease. By comparing the readings of the wet bulb thermometer and the dry bulb thermometer, the wet-bulb temperature can be determined. Therefore, a sling psychrometer is the correct instrument for measuring the wet-bulb temperature.

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• 4.

### When air is fully saturated, which of the following is true

• A.

The dewpoint, dry-bulb and wet-bulb temps are the same

• B.

The difference between dry-bulb and wet-bulb temp is greatest

• C.

The sensible heat content is greatest

• D.

The specific volume is greatest

A. The dewpoint, dry-bulb and wet-bulb temps are the same
Explanation
When air is fully saturated, the dewpoint, dry-bulb, and wet-bulb temperatures are the same. This is because the air is holding as much moisture as it can at that temperature, and any additional cooling will cause the excess moisture to condense as dew. Therefore, the dewpoint temperature, which is the temperature at which the air becomes saturated and condensation occurs, is equal to the dry-bulb and wet-bulb temperatures when the air is fully saturated.

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• 5.

### The dewpoint temp of air is a direct indication of

• A.

Moisture content

• B.

Relative humidity

• C.

Total heat

• D.

Volume

A. Moisture content
Explanation
The dewpoint temperature of air is a direct indication of moisture content because it is the temperature at which air becomes saturated and can no longer hold all the moisture it contains. When the air temperature drops to the dewpoint, water vapor in the air condenses into liquid water, forming dew or fog. Therefore, the dewpoint temperature is a measure of how much moisture is present in the air.

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• 6.

### The specific humidity of air is independent of

• A.

Dewpoint temperature

• B.

Dry-bulb temperature

• C.

Moisture content

• D.

Wet-bulb temperature

B. Dry-bulb temperature
Explanation
The specific humidity of air refers to the amount of moisture present in the air. It is defined as the ratio of the mass of water vapor to the total mass of the air sample. The specific humidity is independent of the dewpoint temperature, moisture content, and wet-bulb temperature because these factors are related to the state of the air (such as saturation and cooling), while specific humidity only considers the actual amount of water vapor present. However, the specific humidity is affected by the dry-bulb temperature, which is the temperature of the air measured with a regular thermometer. As the dry-bulb temperature increases, the air can hold more water vapor, resulting in an increase in specific humidity.

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• 7.

### Enthalpy of moist air is a measure of

• A.

Latent heat of the water vapor

• B.

Sensible heat of the air and water vapor mixture

• C.

Sensible heat of the water vapor

• D.

Total heat of the air and water vapor mixture

B. Sensible heat of the air and water vapor mixture
Explanation
The enthalpy of moist air is a measure of the sensible heat of the air and water vapor mixture. Enthalpy is the total energy content of a substance, including both its internal energy and the work done by or on the substance. In the case of moist air, it refers to the total heat content of the air and water vapor mixture, taking into account the sensible heat, which is the heat energy associated with the temperature of the air and water vapor. Therefore, the correct answer is the sensible heat of the air and water vapor mixture.

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• 8.

### The horizontal scale of the psychrometric chart indicates

• A.

Dewpoint temp

• B.

Dry-bulb temp

• C.

Moisture content

• D.

Wet-bulb temp

B. Dry-bulb temp
Explanation
The horizontal scale of the psychrometric chart indicates the dry-bulb temperature. The dry-bulb temperature is the temperature measured by a regular thermometer and represents the actual air temperature. It is an important parameter in psychrometrics as it helps determine the state of the air and its ability to hold moisture. By using the dry-bulb temperature along with other parameters, such as the wet-bulb temperature and dewpoint temperature, one can analyze the moisture content and other properties of the air on the psychrometric chart.

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• 9.

### The vertical scale on the psychrometric chart indicates

• A.

Dry-bulb temp

• B.

Moisture content

• C.

Volume per pound of dry air

• D.

Wet-bulb temp

B. Moisture content
Explanation
The vertical scale on the psychrometric chart indicates moisture content. This means that it shows the amount of water vapor present in the air. The psychrometric chart is a graphical representation of the properties of moist air, and the moisture content is an important parameter in understanding the behavior and characteristics of air. By using the chart, one can determine the relative humidity, dew point, and other properties related to moisture in the air.

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• 10.

### The total heat content of air depends on its

• A.

Dry-bulb temp

• B.

Relative humidity

• C.

Specific humidity

• D.

Wet-bulb temperature

D. Wet-bulb temperature
Explanation
The total heat content of air depends on its wet-bulb temperature. Wet-bulb temperature is a measure of the lowest temperature that can be achieved by evaporating water into the air. It takes into account both the dry-bulb temperature (the temperature of the air) and the relative humidity (the amount of moisture in the air). As water evaporates, it absorbs heat from the air, lowering the temperature. Therefore, the wet-bulb temperature provides a more accurate representation of the heat content of the air compared to just the dry-bulb temperature or the humidity levels.

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• Mar 21, 2023
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• Jul 22, 2020
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