All questions of Applications for UPSC CSE Exam

The best capacity control method suitable for domestic refrigerant compressor is On and Off control.

Explanation:
On and Off control is the most suitable capacity control method for domestic refrigerant compressors. This method involves turning the compressor on and off to maintain the desired temperature in the refrigeration system. Here are the reasons why On and Off control is the best option:

1. Simplicity:
On and Off control is a simple and straightforward method. It does not require any complex control mechanisms or additional components. The compressor is either running at full capacity or completely turned off, making it easy to implement and understand.

2. Energy Efficiency:
In domestic refrigeration systems, the load demand can vary significantly throughout the day. On and Off control allows the compressor to operate only when cooling is required. This helps in conserving energy by reducing the runtime of the compressor when it is not needed.

3. Cost-effectiveness:
Since On and Off control does not involve any additional control components, it is a cost-effective solution for domestic refrigeration systems. The simplicity of this method reduces the overall system cost and maintenance requirements.

4. Reliability:
On and Off control is a reliable method as it does not rely on complex control mechanisms that can fail or malfunction. The compressor operates at full capacity when it is on, providing efficient cooling performance.

5. Temperature Control:
On and Off control allows for precise temperature control in the refrigeration system. When the desired temperature is reached, the compressor turns off, and when the temperature rises above the set point, the compressor turns on again. This ensures that the temperature is maintained within the desired range.

In conclusion, On and Off control is the best capacity control method for domestic refrigerant compressors due to its simplicity, energy efficiency, cost-effectiveness, reliability, and temperature control capabilities.

One Tonnes of Refrigeration (TR) is equal to 210 kJ/min.

Explanation:

- One Tonnes of Refrigeration (TR) is a unit of power used in refrigeration and air conditioning industries.
- It is defined as the amount of cooling required to freeze one metric tonne (1000 kg) of water from 0°C to -1°C in 24 hours.
- TR is commonly used to rate the capacity of refrigeration and air conditioning systems.
- The conversion factor from TR to kJ/min is 210.
- Therefore, one TR is equal to 210 kJ/min.

Formula:

- The formula to calculate the cooling capacity in TR is given as: Q = m × Cp × ΔT / 24
- Where Q is the cooling capacity in TR, m is the mass of water to be frozen (in kg), Cp is the specific heat of water (4.18 kJ/kg°C), and ΔT is the temperature difference (in °C) between the initial and final temperatures of water.
- For example, if we want to freeze 1000 kg of water from 0°C to -1°C in 24 hours, the cooling capacity required will be:
Q = 1000 × 4.18 × (0-(-1)) / 24 = 34.9 kJ/min
- To convert this cooling capacity in TR, we need to divide it by 211. That is:
Q(TR) = 34.9 / 210 = 0.166 TR

Conclusion:

- One Tonnes of Refrigeration (TR) is equal to 210 kJ/min.
- It is used to rate the capacity of refrigeration and air conditioning systems.
- The formula to calculate the cooling capacity in TR is Q = m × Cp × ΔT / 24.
- To convert the cooling capacity in TR to kJ/min, we need to multiply it by 210.

Correct nomenclature for ethylene is R 150

Explanation:
The nomenclature system used for naming refrigerants is called the "Refrigerant Numbering System" or the "R-number system". This system was developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and is widely used in the industry.

Refrigerant R 150:
R 150 is the correct nomenclature for ethylene. Ethylene is a hydrocarbon compound with the chemical formula C2H4. It is a colorless gas with a sweet odor and is commonly used as a refrigerant in low-temperature applications.

Significance of R-number:
The R-number assigned to a refrigerant provides important information about its chemical composition, thermodynamic properties, and environmental impact. The R-number system helps in identifying and categorizing different refrigerants based on their characteristics.

Other options:
- R 740: This nomenclature is not correct for ethylene. R 740 refers to carbon dioxide (CO2), which is another commonly used refrigerant.
- R 1150: This nomenclature is not correct for ethylene. R 1150 refers to ethane (C2H6), which is also a hydrocarbon compound but has different properties compared to ethylene.
- R 12: This nomenclature is not correct for ethylene. R 12 refers to dichlorodifluoromethane (CCl2F2), which is an ozone-depleting refrigerant commonly known as Freon-12.

Conclusion:
The correct nomenclature for ethylene is R 150. It is important to use the correct nomenclature when working with refrigerants to ensure proper identification and handling.

The Bank of Tubes at the Back of a Domestic Refrigerator

The bank of tubes at the back of a domestic refrigerator of the vapor compression type is known as the condenser tubes. These tubes play a crucial role in the refrigeration cycle by facilitating the transfer of heat from the refrigerant to the surrounding environment.

Explanation:

Refrigeration Cycle
To understand the function of the condenser tubes, it is essential to have a basic understanding of the refrigeration cycle. The refrigeration cycle is a continuous process that involves the circulation of refrigerant through various components of the refrigeration system. These components include the compressor, condenser, expansion valve, and evaporator.

1. Compressor: The compressor is responsible for compressing the low-pressure refrigerant vapor coming from the evaporator and raising its temperature and pressure.
2. Condenser: The condenser is where the hot refrigerant vapor from the compressor is condensed into a high-pressure liquid. This process releases heat to the surrounding environment.
3. Expansion Valve: The expansion valve controls the flow of the high-pressure liquid refrigerant into the evaporator.
4. Evaporator: In the evaporator, the low-pressure liquid refrigerant evaporates, absorbing heat from the area being cooled.

Function of the Condenser Tubes
The condenser tubes are located at the back of the refrigerator and are responsible for transferring heat from the hot refrigerant vapor to the surrounding environment. This heat transfer process causes the refrigerant to condense into a high-pressure liquid.

Heat Transfer
The condenser tubes are designed to facilitate efficient heat transfer. The hot refrigerant vapor flows through these tubes, while the cooler air from the surrounding environment passes over the tubes. As the air comes into contact with the hot tubes, heat is transferred from the refrigerant to the air.

Condensation Process
As the heat is transferred, the refrigerant undergoes a phase change from a vapor to a liquid state. This condensation process releases a significant amount of heat energy, which is why the condenser tubes are located at the back of the refrigerator to allow for proper heat dissipation.

Conclusion
In conclusion, the bank of tubes at the back of a domestic refrigerator of the vapor compression type is known as the condenser tubes. These tubes are responsible for transferring heat from the hot refrigerant vapor to the surrounding environment, causing the refrigerant to condense into a high-pressure liquid. This is an essential step in the refrigeration cycle, allowing the refrigerator to cool and maintain low temperatures inside.

Solid CO2, also known as dry ice, is produced by the pressure snow chamber method. This method involves the conversion of gaseous carbon dioxide (CO2) into a solid state under high pressure.

Explanation:
1. Pressure Snow Chamber Method:
The pressure snow chamber method is a process used to produce solid CO2. In this method, gaseous carbon dioxide is compressed to a high pressure of about 5 to 10 MPa (megapascals). When the gas is compressed to such high pressures, it undergoes a phase change directly from a gas to a solid, bypassing the liquid phase. This solid form of carbon dioxide is known as dry ice.

Advantages of the Pressure Snow Chamber Method:
- The pressure snow chamber method allows for the direct conversion of gaseous carbon dioxide into a solid state without the need for intermediate steps.
- It is a relatively simple and efficient process for producing solid CO2.
- The high-pressure conditions ensure that the solid CO2 is produced in a dense and compact form, making it suitable for various applications.

Applications of Solid CO2:
Solid CO2 (dry ice) has several applications, including:
- Cold storage and transportation: Solid CO2 is commonly used for preserving and transporting perishable goods that require low temperatures.
- Cleaning and blasting: Dry ice blasting is a non-abrasive cleaning method that uses solid CO2 pellets to remove dirt, grime, and contaminants from surfaces.
- Special effects: Solid CO2 is used in the entertainment industry for creating smoke and fog effects in theatrical productions and concerts.
- Food and beverage industry: Solid CO2 is used for chilling and freezing food products, as well as in carbonation processes for beverages.

In conclusion, solid CO2 is produced by the pressure snow chamber method, which involves compressing gaseous carbon dioxide to high pressures to directly convert it into a solid state. This method is efficient and provides solid CO2 in a dense and compact form for various applications.

Refrigeration Load of Domestic Refrigerator

Definition of Refrigeration Load

Refrigeration load is defined as the amount of heat that needs to be removed from a space or substance in order to achieve a desired temperature.

Refrigeration Load of Domestic Refrigerator

The refrigeration load of a domestic refrigerator is the amount of heat that needs to be removed from the interior of the refrigerator in order to keep the temperature low enough to preserve food and beverages.

Calculation of Refrigeration Load

The refrigeration load of a domestic refrigerator can be calculated by determining the heat gain into the refrigerator and then calculating the amount of heat that needs to be removed to maintain the desired temperature. Factors that contribute to the heat gain into the refrigerator include:

- Ambient temperature
- Insulation quality
- Door opening frequency
- Type and quantity of food stored

Answer Explanation

The refrigeration load of a domestic refrigerator is typically less than 0.25 ton. This is because the size of a domestic refrigerator is relatively small compared to commercial refrigeration systems, and the amount of heat gain into the refrigerator is relatively low due to the insulation quality and infrequent door opening. Therefore, the amount of heat that needs to be removed is also relatively low.

Explanation:
The wet bulb depression is a measure of the difference between the dry bulb temperature and the wet bulb temperature. It represents the cooling effect of evaporation on the wet bulb temperature.

The wet bulb depression is zero when the relative humidity is equal to 1.0 or 100%. This means that the air is saturated with moisture and cannot hold any more water vapor. When the air is saturated, the wet bulb temperature is equal to the dry bulb temperature.

Why is the wet bulb depression zero when the relative humidity is 1.0?

When the relative humidity is 1.0, it means that the air is holding the maximum amount of water vapor it can at a given temperature. The air is saturated with moisture, and any additional water vapor will condense into liquid water.

In this saturated condition, there is no evaporation occurring from the wet bulb. Evaporation is a cooling process, and it lowers the temperature of the wet bulb. However, when the air is already holding as much moisture as it can, there is no more room for evaporation to take place. As a result, the wet bulb temperature is equal to the dry bulb temperature, and the wet bulb depression is zero.

Significance of wet bulb depression:

The wet bulb depression is an important parameter in determining the comfort level and heat stress in a given environment. It provides an indication of the cooling effect of evaporation and the potential for heat transfer through sweating.

When the wet bulb depression is high, it means that there is a significant difference between the dry and wet bulb temperatures. This indicates that evaporation is occurring and the air has the potential to provide cooling. This is desirable in hot and humid conditions as it helps in dissipating heat from the body.

On the other hand, when the wet bulb depression is low or zero, it indicates that the air is already saturated with moisture and evaporation is not occurring. This can lead to discomfort and heat stress as the body's ability to cool down through sweating is limited.

In conclusion, the wet bulb depression is zero when the relative humidity is equal to 1.0 or 100%. This means that the air is saturated with moisture and there is no room for evaporation. Understanding the wet bulb depression is important in assessing the comfort level and heat stress in a given environment.

Thermoelectric refrigeration system is based on Peltier effect.

Explanation:
Thermoelectric refrigeration system works on the principle of Peltier effect. This effect was discovered by Jean Charles Athanase Peltier, a French physicist in the year 1834. According to the Peltier effect, when a current flows through a junction of two different materials, heat is either absorbed or evolved at the junction depending on the direction of current flow.

Working of thermoelectric refrigeration system:
The thermoelectric refrigeration system consists of a thermoelectric module which is made up of two different materials such as n-type and p-type semiconductors. These two materials are connected electrically in series and thermally in parallel. When a current is passed through the thermoelectric module, one side of the module gets heated and the other side gets cooled. The cooling effect is due to the absorption of heat from the surrounding medium.

Advantages of thermoelectric refrigeration system:
- It is a compact and lightweight system.
- It does not require any moving parts for its operation.
- It can operate in any orientation.
- It is highly reliable and requires low maintenance.

Applications of thermoelectric refrigeration system:
- It is used in small-scale refrigeration applications such as electronic devices, cooling of laser diodes, and medical refrigeration.
- It is also used in spacecraft and satellites where conventional refrigeration systems cannot be used due to the absence of gravity.

Conclusion:
Thus, the thermoelectric refrigeration system is based on the Peltier effect, where the cooling effect is due to the absorption of heat from the surrounding medium. This system is highly reliable, lightweight, and requires low maintenance, making it suitable for small-scale refrigeration applications.

Psychrometric Chart

The psychrometric chart is a graphical representation of the thermodynamic properties of air-water vapor mixtures. It is a valuable tool used by engineers and scientists to analyze and design systems involving air conditioning, heating, and ventilation. The chart provides information about various properties of moist air, such as temperature, humidity, specific volume, and enthalpy.

Statements and Analysis

Let's analyze each statement and determine whether it is correct or not.

1. Constant relative humidity lines are uphill straight lines to the right.
This statement is incorrect. Constant relative humidity lines on the psychrometric chart are not straight lines. They are curved lines that slope upwards to the right. This is because as temperature increases, the absolute humidity (amount of moisture in the air) required to maintain a constant relative humidity decreases. Therefore, the constant relative humidity lines curve upwards towards the right.

2. Constant wet bulb temperature lines are downhill straight lines to the right.
This statement is correct. Constant wet bulb temperature lines on the psychrometric chart are straight lines that slope downwards to the right. The wet bulb temperature represents the lowest temperature that can be achieved by evaporative cooling. As the moisture content in the air increases, the wet bulb temperature decreases. Therefore, the constant wet bulb temperature lines slope downwards towards the right.

3. Constant specific volume lines are downhill straight lines to the right.
This statement is incorrect. Constant specific volume lines on the psychrometric chart are not straight lines. They are curved lines that slope downwards to the right. The specific volume of air-water vapor mixture decreases as the humidity ratio (mass of water vapor per unit mass of dry air) increases. Therefore, the constant specific volume lines curve downwards towards the right.

4. Constant enthalpy fines are coincident with constant wet bulb temperature lines.
This statement is correct. Constant enthalpy lines on the psychrometric chart coincide with constant wet bulb temperature lines. Enthalpy is a measure of the total heat content of the air-water vapor mixture. The enthalpy value remains constant along a given line. Since the wet bulb temperature is directly related to the enthalpy of the air, the constant enthalpy lines align with the constant wet bulb temperature lines.

Conclusion

Based on the analysis, the correct statements are:

2. Constant wet bulb temperature lines are downhill straight lines to the right.
4. Constant enthalpy fines are coincident with constant wet bulb temperature lines.

Therefore, the correct answer is option 'D' - 2 and 4.