AREA 3: AB STRUCTURES & ENVIRONMENT ENGINEERING & BIOPROCESS ENGINEERING & ALLIED SUBJECTS

AREA 3: AB STRUCTURES & ENVIRONMENT ENGINEERING & BIOPROCESS ENGINEERING &  ALLIED SUBJECTS  VOLUME II

WATCH SOLUTIONS HERE: https://youtu.be/P07RC3f-Lgg?si=jdtEDyFTtGGrheMI

1. A refrigerating system operates on the reversed carnot cycle. The higher temperature of the refrigerant in the system is 120°F and the lower is 10°F. The capacity is 20 Ton. Neglect losses. Determine: 

A. coefficient of performance

B. Heat rejected from the system in BTU / min

C. Net work in BTU / min

D. Net work in horsepower

2. A refrigeration system operates on the reversed carnot cycle. The minimum and maximum temperatures are 25°C and 72°C, respectively. If the heat rejected at the condenser is 6000 kJ / min, draw the T- S diagram and find:

a. Power input required

b. Tons of refrigeration developed

3. The power requirement of a carnot refrigerator in maintaining a low temperature region at 238. 9 K is 1.1 kW per ton. Find:

a. COP

b. T2

c. The heat rejected

4. A reversed Carnot cycle has a refrigerating COP of 4.

a. What is the ratio Tmax / Tmin?

b. If the work input is 6 kW, what will be the maximum refrigerating effect in kJ/min and in Tons of refrigeration?

5. A simple saturated refrigeration cycle for R-12 system operates at an evaporating temperature of  -5°C and a condensing temperature of 40°C. Determine:

 (a) the refrigerating effect per kg

 (b) the work per kg

 (c) the heat rejected at the condenser per kg

 (d) the COP. For a refrigerating capacity of 1 kW  

 (e) the total heat rejected at the condenser

 (f) total the work

 (g) the volume flow rate.

6. A refrigeration system using refrigerant 22 is to have a refrigerating capacity of 60 kW. The evaporating temperature is -10°C and the condensing temperature is 42°C. 

Determine:

 (a) the volume flow rate of the refrigerant at inlet to the compressor

 (b) the power required by the compressor, and 

 (c) the quality of refrigerant at entrance to the evaporator (fraction of the mass of vapor to the refrigerant).

7. A simple saturated refrigeration cycle for R-12 system operates at an evaporating temperature of  -5°C and a condensing temperature of 40°C. Show the effect on the COP, of installing a heat exchanger that would superheat the suction vapor from -5°C to 15°C in the heat exchanger.

8. An ammonia simple saturation cycle operates at 247.1 kPa suction pressure and 1169 kPa condenser pressure. For a load of 1688 kJ/min, determine (a) the (m3) / h of cooling water in the condenser if the water temperature is increased by 6°C (b) the compressor work and, (c) the piston displacement if the clearance is 5%. 

9. A refrigerating system is to be used to cool 45,000 kg of water from 29 to 18°C in 5hrs. The refrigerant is ammonia and the operating conditions are 616 kPa evaporating pressure and 1737 liquefaction pressure. 

Determine:

 a. the coefficient of performance

 b. the quantity of cooling water in the condenser for an increase in temp of 7°C

 c. the compressor power

 d. the volume flowrate entering the compressor. The specific heat of water is 4.187 kJ/kg °C

10. An ammonia refrigerating cycle operates at 247 kPa suction pressure and 1200 kPa condensing pressure. Other data are the following:

Refrigerating capacity = 28 kW

Compressor clearance = 5%

Compression eff. = 80%

Mechanical eff. = 75%

Actual volumetric eff. = 74%

Determine:

(a) clearance volumetric eff.

(b) the ideal and actual COP

(c) the massflowrate of ammonia

(d) the brakework.

11. A four cylinder refrigerant 12 compressor operates between evaporator and condenser temp. Of 4°C and 43°C. It is to carry a load of 20 tons of refrigeration at 1200rpm. If the average piston speed is 213 m/min and the actual volumetric efficiency is 80%, what should be the bore and stroke of the compressor?

12. Compute the humidity ratio of air at 65% relative humidity and 34°C when the barometric pressure is 101.3 Кра. Also, compute for the enthalpy of the air vapor mixture.

13. What is the specific volume of an air vapor mixture at 30°C and relative humidity of 40% at 101.3 Kpa pressure.

14. A mixture of dry air and water vapor is at a temperature of 21°C under a pressure of 101.3 kPa. The dew point temperature is 15°C. Determine the following:

a. partial pressure of water vapor

b. relative humidity

c. humidity ratio

d. Enthalpy

e. specific volume

f. degree of saturation

15. Determine the quantity of heat required to raise 14 m³/min of air at 20°C and 80% relative humidity to 35°C.

16. Determine the quantity of heat removed from 14 m³/min of air when cooled from 37°C dry bulb and 21°C wet bulb temperatures to 15°C

17. How much heat and moisture must be added to 28 m³/min of air at 24°C and 40% relative humidity to raise to 38°C dry bulb and 27°C wet bulb temperatures

18. How much heat and moisture must be removed to cool 28 m³/min of air from 35°C dry bulb and 26°C wet bulb temperatures to 21°C and 50% relative humidity.

19. Air at 33°C dry bulb and 19°C wet bulb temperatures is cooled and humidified by passing it through an air washer in which the water is continuously recirculated. The air leaves the washer at 23°C. Determine the moisture added per kg of dry air. What is the efficiency of the air washer?

20. Air at 24°C dry bulb and 15°C wet bulb temperatures enters a dehumidifier and leaves at 41°C dry bulb and 19°C wet bulb temperatures. How much moisture has been removed per kg of dry air?

21. One half cubic meter per second of air at 15°C dry bulb and 13°C wet bulb temperatures are mixed with 0.20 m³ per second of air at 25°C dry bulb and 18°C wet bulb temperatures. Determine (a) the dry bulb temperature and (b) W of the mixture when:

V₁ = 0.825 m³/kg 

W₁ = 0.0085 

V2 = 0.858 m³/kg 

W₂ = 0.011

22. Outdoor air at 35 °C dry bulb and 24 °C wet bulb temperatures is to be mixed with room air at 26 °C dry bulb temperature and 50 percent relative humidity. The final mixture is to consist of one-third outdoor air and two-thirds return air from the room. Find the resulting dry bulb temperature of the mixture.

23. An auditorium is to be maintained at a temperature of 25°C dry bulb and 19°C wet bulb temperatures. The sensible heat load is 88 kW and 58 kg per hour or moisture must be removed. Air is supplied to the auditorium at 18°C. 

Determine:

(a) the mass flow rate of supply air

(b) the sensible heat ratio when W2=0.0114 kg/kg

24. An air-conditioning plant has air temp entering the evaporator at 25.5 °C (78 °F) and leaving at 13.33 °C (56 °F). If the refrigerant is at 4.4 °C (40 °F) in the evaporator. What will be the MTD and LMTD or METD?