ME-801 Refrigeration and Air Conditioning - Jun 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aExplain the term "tonne of refrigeration". Discuss the advantages of the dense air refrigerating system over an open air refrigeration system.
   How to answer

   • Define 1 tonne of refrigeration as 210 kJ/min / 3.5 kW cooling effect
   • Explain basis of ice melting from 0C in 24 hrs
   • List features of dense air system - closed, high pressure, smaller size
   • Advantages over open system - no moisture entry, smaller compressor/expander, higher COP, less frost
2. 7 Marks
   bThe capacity of a refrigerator is 400 TR when working between $-12^{\circ}C$ and $35^{\circ}C$. Determine the mass of ice produced per day from water at $25^{\circ}C$. Also find the power required to drive the unit. Assume that the cycle operates on reversed Carnot cycle and latent heat of ice is 335 kJ/Kg.
   How to answer

   • Calculate reversed Carnot COP = TL/(TH-TL)
   • Calculate refrigerating effect = 400 TR in kJ/s
   • Calculate heat to remove per kg: sensible water 25C to 0C + latent 335 kJ/Kg
   • Divide total daily refrigeration by per kg to get ice mass and power = RE/COP
3. 7 Marks
   aThe temperature limits of an ammonia refrigerating system are $25^{\circ}C$ and $-10^{\circ}C$. If the gas is dry at the end of compression, calculate the coefficient of performance of the cycle assuming no under-cooling of the liquid ammonia. Use the following table for properties of ammonia:

   

   How to answer

   • Identify states: dry saturated vapour after compression at 25C condenser
   • Use entropy balance to find dryness after expansion/throttling
   • Calculate refrigerating effect = h1 - h4 and work = h2 - h1
   • Compute COP = RE / work using table values
4. 7 Marks
   bExplain the function liquid intercooler in multistage compression system.
   How to answer

   • Define liquid intercooler / flash intercooler location between stages
   • Explain subcooling of high pressure liquid by flash vapour
   • Explain reduction in flash gas and increase in refrigerating effect
   • Mention reduction in power and improved COP
5. 7 Marks
   aWhat is the basic function of a compressor in vapour compression refrigeration system? How this function is achieved in vapour absorption refrigeration system?
   How to answer

   • State compressor function: raise pressure/temperature and circulate refrigerant
   • Explain suction of low pressure vapour and discharge to condenser
   • Explain equivalent in VARS: generator + absorber + pump as thermal compressor
   • Mention pressure rise by heating and pumping solution
6. 7 Marks
   bDefine Primary refrigerant. What are the desirable properties of a primary refrigerant? Give the refrigerant number for the following: $CHClF_{2}$, $CH_{2}F-CF_{3}$ and $NH_{3}$.
   How to answer

   • Define primary refrigerant as working fluid undergoing phase change
   • List desirable properties: thermodynamic, chemical, physical, safety
   • Assign R-22 to CHClF2, R-134a to CH2F-CF3, R-717 to NH3
   • Explain numbering logic briefly
7. 7 Marks
   aAtmospheric air at dry bulb temperature of $16^{\circ}C$ and 25% relative humidity passes through a furnace and then through a humidifier, in such a way that the final dry bulb temperature is $30^{\circ}C$ and 50% relative humidity. Find the heat and moisture added to the air. Also determine the sensible heat factor of the process.
   How to answer

   • Locate initial state 16C 25% RH and final state 30C 50% RH on psychrometric chart
   • Calculate enthalpy difference for heat added per kg dry air
   • Calculate humidity ratio difference for moisture added
   • Compute sensible heat factor = sensible heat / total heat
8. 7 Marks
   bWhat is fog? Show on the psychometric chart when two air streams yield fogged state of air.
   How to answer

   • Define fog as suspended water droplets due to supersaturation
   • Explain mixing of two unsaturated streams resulting in fog
   • Sketch psychrometric chart with mixing line crossing saturation curve
   • Mark fog region and mist state
9. 7 Marks
   aWhat is the basic difference between the requirements for Comfort and Industrial air conditioning?
   How to answer

   • Define comfort AC for human occupancy vs industrial for process/product
   • Compare temperature, humidity, air motion, purity requirements
   • Compare control precision, operating hours, load variation
   • Give examples of each
10. 7 Marks
    bAn air conditioning plant is required to supply 60 $m^{3}$ of air per minute at a DBT of $21^{\circ}C$ and 55% RH. The outside air is at DBT of $28^{\circ}C$ and 60% RH. Determine the mass of water drained and capacity of the cooling coil. Assume the air conditioning plant first to dehumidify and then to cool the air.
    How to answer

    • Locate outside 28C 60% RH and supply 21C 55% RH on chart, get w and h
    • Calculate mass flow of air from 60 m3/min and specific volume
    • Mass of water drained = m_dot*(w_outside - w_supply)
    • Cooling coil capacity = m_dot*(h_outside - h_supply)
11. 14 Marks
    Write short notes on any three:

    1. i)Steam jet refrigeration.
    2. ii)Environment friendly refrigerants.
    3. iii)Leak detection methods
    4. iv)By pass factor of coil.
    How to answer

    • Explain principle, components and working for each selected topic
    • Give neat sketch / equation where relevant
    • Mention applications / advantages / limitations
    • Conclude with significance in RAC
12. 7 Marks
    aWhat is multi-stage vapour compression refrigeration system? Compare it with cascade refrigeration system.
    How to answer

    • Define multistage VCRS with multiple compression stages and intercooling
    • Define cascade with separate circuits and cascade condenser
    • Compare on refrigerant, temperature range, heat exchanger, applications
    • Mention COP and complexity differences
13. 7 Marks
    bDefine the terms:

    1. i)Cooling and dehumidification process.
    2. ii)Sensible heating and sensible cooling process.
    How to answer

    • Define cooling and dehumidification with psychrometric line and coil ADP
    • Define sensible heating as DBT rise at constant w
    • Define sensible cooling as DBT fall at constant w
    • Show processes on psychrometric sketch
14. 7 Marks
    aA machine working on a Carnot cycle operates between 305 K and 260 K Determine the C.O.P. when it is operand as

    1. i)A refrigerating machine
    2. ii)A heat pump
    3. iii)A heat engine
    How to answer

    • Write Carnot COP formulas for refrigerator, heat pump, engine
    • Substitute TH=305 K, TL=260 K
    • Compute COP_ref = TL/(TH-TL), COP_hp = TH/(TH-TL)
    • Compute engine efficiency = (TH-TL)/TH
15. 7 Marks
    bExplain the applications of refrigeration for food preservation. Explain how refrigeration controls the spoilage of food.
    How to answer

    • List refrigeration applications in food: chilling, freezing, cold storage, transport
    • Explain microbial, enzymatic and chemical spoilage factors
    • Explain how low temperature slows bacteria and enzyme action
    • Mention shelf life, nutritional and quality preservation