ICAR AIEEA PG Dairy Technology 14 July 2023 Shift-1 Paper

In a vapour compression refrigeration plant, the liquid receiver is a pressure vessel installed immediately downstream of the condenser. It serves as a surge tank and bulk storage reservoir for excess liquid refrigerant during operational load fluctuations and holds the entire refrigerant charge during pump-down maintenance.

Option analysis:

• Compressor: Compresses low-pressure vapor to high pressure, does not store liquid refrigerant.
• Condenser: Heat exchanger where vapor condenses to liquid.
• Evaporator: Heat exchanger where liquid boils to absorb heat.
• Receiver: Correct, specialized storage tank for holding liquid refrigerant.

Commercial batch and continuous ice cream freezers (scraped surface freezers) operate on the Vapour Compression Refrigeration System (VCRS). Liquid refrigerant (typically ammonia $R-717$ or modern halocarbons) expands directly into the jacket surrounding the freezing cylinder, boiling at temperatures of $-25^\circ\text{C}$ to $-30^\circ\text{C}$ to rapidly freeze the agitated ice cream mix.

Option analysis:

• Vapour absorption refrigeration system: Heat-driven refrigeration system, rarely used in commercial freezing freezers.
• Vapour expansion refrigeration system: Incomplete and non-standard terminology.
• Vapour compression refrigeration system: Correct, universal thermodynamic refrigeration cycle used in ice cream freezers.
• Vapour evaporation refrigeration system: Incorrect non-standard term.

Throttling and expansion devices in refrigeration systems include: capillary tubes, thermostatic expansion valves (TEV), automatic expansion valves (constant pressure valves), high-side float valves, low-side float valves, and electronic expansion valves (EEV). There is no such device as a 'Centrifugal expansion valve' in refrigeration technology.

Option analysis:

• Low side float valve: Standard expansion device used in flooded evaporators.
• Centrifugal expansion valve: Correct, non-existent device in refrigeration systems.
• Capillary tube: Universal fixed-orifice expansion device in domestic refrigerators.
• Thermostatic expansion valve: Standard superheat-controlled expansion valve in commercial refrigeration.

One ton of refrigeration (TR) is defined as the rate of heat extraction needed to freeze $1\text{ short ton}$ ($2000\text{ lb}$ or $907.18\text{ kg}$) of pure water at $0^\circ\text{C}$ into ice at $0^\circ\text{C}$ in $24\text{ hours}$:

$$1\text{ TR} = \frac{2000\text{ lb} \times 144\text{ BTU/lb}}{24\text{ hours}} = 12000\text{ BTU/h} = 200\text{ BTU/min}$$

Converting to SI metric units:

$$1\text{ TR} = 210.98\text{ kJ/min} \approx 211\text{ kJ/min} = \frac{210.98}{60}\text{ kJ/s} = 3.5167\text{ kW}$$

Option analysis:

• $1\text{ TR} = 311\text{ kJ/min} = 5.5167\text{ kW}$: Incorrect values.
• $1\text{ TR} = 111\text{ kJ/min} = 4.5167\text{ kW}$: Incorrect values.
• $1\text{ TR} = 411\text{ kJ/min} = 2.5167\text{ kW}$: Incorrect values.
• $1\text{ TR} = 211\text{ kJ/min} = 3.5167\text{ kW}$: Correct standard thermodynamic equivalents.