Refrigeration and Air conditioning — Summer 2023

How to calculate the Total Equivalent Warming Impact (TEWI) of refrigerant?

Enlist requirement for working fluid to use as a refrigerant in vapour compression cycle.

Differentiate all-air, all-water and air-water air conditioning system with neat sketch.

List out the different method of improving the COP of simple compression refrigeration cycle

Enlist various methods for food preservation. How does Cold Storage Work?

Calculate the power needed to compress 20 kg/min of ammonia from saturated vapour at 1.4 bar to a condensing pressure of 10 bar by two stage compression with intercooling by liquid refrigerant at 4 bar. Assume saturated liquid to leave the condenser and dry saturated vapour to leave the evaporator. Also determine the power needed when intercooling is not employed. Use following properties: Enthalpy, h Entopy, s (kJ/kg Point (kJ/kg) K) Saturated vapour at low pressure compressor inlet 1400 5.75 Superheated vapour at low pressure compressor exit 1525 - Saturated vapour leaving intercooler 1428 5.39 Superheated vapour at high pressure compressor exit 1550 - Saturated liquid at condenser exit 284 -

Why is compound refrigeration system employed when condenser temperature to evaporator temperature range is very large? Explain the difference between compound vapour compression system with flash cooling and flash intercooling.

Why air cycle refrigeration is most suitable for aircraft refrigeration compared to vapour compression refrigeration system?

Explain the factor affecting human comfort.

In a Bell-Coleman refrigeration plant, the air is drawn from cold chamber at 1 bar and 10°Cand compressed to 5 bar. The same is cooled to 25°Cin the cooler before expanding in the expansion cylinder to cold chamber pressure of 1 bar. Calculate theoretical COP of the plant and the theoretical rate refrigeration effect per kg of air. The compression and expansion be assumed isentropic. Assume =1.41 and Cp=1.009 kJ/kg°C.

How the human body reacts to changes in temperature of environment?

Discuss the latent heat loss from human body and how it varies with dry bulb temperature and activity of human beings.

Why regenerative system is useful at high flight speeds compared to simple cooling cycle? Explain regenerative cooling system with diagrammatic layout and T-s representation.

Under what situation the vapour absorption system of refrigeration is preferred to vapour compression system of refrigeration?1

Discuss the influence of suction temperature on compressor power, capacity and COP of reciprocating refrigerant compressor when condenser temperature is fix.

What are desirable characteristics of absorbent and absorbent refrigerant combination in vapour absorption refrigeration cycle? Explain working of Li-Br vapour absorption refrigeration system with neat sketch.

Explain the function of capillary tube in a vapour compression refrigeration system. Under what situations is this used.

Why a minute leak in hermatic compressor based refrigeration system can affect the windings of the compressor motor?

The following data apply to Vapour absorption refrigeration system. Capacity =25 ton, Evaporator temperature = - 20°C Temperature of condensed NH from condenser = 20°Cexit from the operator dry saturated3 Pressure maintained in generator = 11.67 bar Temperature of strong aqua-ammonia solution = 70°C Temperature of week aqua-ammonia solution = 100°C Enthalpy of 1 kg anhydrous NH released from generator = 1930 kJ/kg3 Mass concentration of strong aqua-ammonia =0.35 Mass concentration of week aqua-ammonia = 0.25 Mean specific heat of aqua-ammonia solution = 4.7 kJ/kg°C Assume the enthalpy of strong and weak solution as that of NH liquid at -50°Ci.e. 200kJ/kg. Heat given by 1 kg steam is 2021.953 kJ/kg. Enthalpy at inlet of generator at - 20°C = 1655 kJ/kg, Enthalpy after generator at 11.67 bar = 1930 kJ/kg and Enthalpy at evaporator inlet = 520 kJ/kg. The mass of ammonia fed to evaporator is 4.625 kg/min. Heat of absorption in the generator is given by Q =804-586x -5950x absorbed w w Neglecting any heat loss to surroundings, determine the required steam per hour for heat input to the generator from outside source at 4 bar and 0.9 dry if the temperature at the exit of the condensate is 120°C.

List out different factors affecting the grill performance of air distribution system.

Illustrate the differences between unitary and central air conditioning system.

Arectangular duct section of 500 mm x 350 mm size carries 75 m3/min of air having density of 1.15 kg/m3. Determine the equivalent diameter of a circular duct if 1) the quantity of air carried in both the cases is same and 2) the velocity of air in both the cases is same. If friction factor f=0.01 for sheet metal, find the pressure loss per 100 m length of the duct.

Why all water air conditioning system for commercial use is compact and less expensive than all air system?

Explain the effect of duct heat gain or loss on the temperature of supply air.

An office for seating 30 occupants is to be maintained at 22°C DBT and 55% RH. The outdoor conditions are 36°C DBT and 27°C WBT. The various loads in the office are:  Sensible heat gain per occupants : 83 W  Solar heat gain : 8500W  Latent heat gain per occupant : 100W  Lighting load : 2600W  Sensible heat load from other sources : 12000W  Infiltration load : 15m3/min Assuming 40% fresh air and 60% of re-circulated air passing through the evaporator coil and the bypass factor of 0.12 Calculate: 1) Dew point temperature of the coil 2) Capacity of the plant