Final Examination - ME20-5ME-2 A.Y

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12/22/2020

Final Examination - ME20-5ME-2/ A.Y. 2020-2021 - University of Batangas

ME20-5ME-2/ A.Y. 2020-2021 Final Examination

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Question 1 This is a type of dryer that consists of a vertical shaft in which the wet feed is introduced at the top and falls downward over baffles while coming in contact with the hot air that rises and exhaust at the top. This dryer is used for drying palay, wheat, and grains.

Response: Tower dryer

Question 2 A dryer is to deliver 1,000 kg/hr of cassava with 2% moisture and 20% moisture in the feed. Determine the regain at 20% moisture. _____ % Response: 20.4

Question 3 The Weather Bureau records for a certain data indicated a temperature of 28°C. Barometric pressure is 100 kPa and relative humidity is 75%. Determine the density of water vapor. https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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_____ kg/m3 Response: 1.12

Question 4 Eight hundred kg of dry air per hour is saturated at 45°C then heated to 105°C, passed through an adiabatic dryer and discharged at 51°C. Determine the water evaporated from material in the dryer. _____ kg/hr Response: 18.56

Question 5 Air at 33°C DB and 19°C WB is cooled and humidified by passing through an air washer in which water is continuously recirculated. The air leaves the air washer at 23°C DB. Determine the moisture added per kg d.a. _____ x10^-3 Response: 4.10

Question 6 The humidity ratio corresponding to any given dew point temperature varies with the total barometric pressure, increasing as the barometric pressure Response: Decreases

Question 7 A dancing hall is to be maintained at a temperature of 27°C DB and 20°C WB temperatures. The sensible heat load is 130 kW and 70 kg per hour of moisture must be removed. Air is supply to the hall at 16°C. Find the latent heat load. _____ kW Response: [none]

Question 8 Heat added to or removed from a substance that cause a change of temperature: Response: Latent heat

Question 9 A dryer is to deliver 1,000 kg/hr of cassava with 2% moisture and 20% moisture in the feed. Determine the regain at 2% moisture. _____ % Response: 2.04

Question 10 Copra enters dryer containing 70% moisture and leaves at 7% moisture. Find the moisture removed on each pound on solid in final product. _____ https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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Response: 2.26

Question 11 The process of simultaneous heating and humidifying ratio is known as: Response: Heating and humidifying

Question 12 Calculate the load on the cooler coil which cools 1.8 kg/s of moist air at a state of 21°C DB, 15°C WB and 1 atmosphere, by 5°C. The enthalpy of air entering is 41.84 kJ/kg and air leaving is 36.845 kJ/kg. _____ Hp Response: 12.05

Question 13 The following data relate to a conference room for seating 80 persons.

Inside Design Conditions

22°C DB, 55% RH

Outside Design Conditions

38°C DB, 28°C WB

Sensible and latent heat loads per person

75 W and 45 W, respectively

Lights and fans load

12,000 W

Sensible heat gain through glass, wall, ceiling etc.

12,000 W

Air infiltration

18 m3/min

Fresh air supply

80 m3/min

By-pass factor of the coils

0.1

If two-third of recirculated room air and one-third of fresh air are mixed before entering the cooling coils, determine the grand total heat load. _____ kW Response: [none]

Question 14 The following data relate to a conference room for seating 80 persons.

Inside Design Conditions

22°C DB, 55% RH

Outside Design Conditions

38°C DB, 28°C WB

Sensible and latent heat loads per person

75 W and 45 W, respectively

Lights and fans load

12,000 W

https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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Sensible heat gain through glass, wall, ceiling etc.

12,000 W

Air infiltration

18 m3/min

Fresh air supply

80 m3/min

By-pass factor of the coils

0.1

If two-third of recirculated room air and one-third of fresh air are mixed before entering the cooling coils, determine the apparatus dew point temperature. _____ °C Response: [none]

Question 15 Copra enters dryer, containing 65% water and 35% solids, and leaves with 10% water and 90% solids. Find the mass of water removed in kilogram on each slug of original product. _____ kg Response: 0.61

Question 16 Raw cotton has been stored in a warehouse at 29°C, 50% RH and regain at 6.6%. The cotton goes through a mill and passes through the weaving room kept at 31°C and 70% RH. For 200 kg of cotton from warehouse, how many kg should appear in woven cloth neglecting thread losses? Regain of finished cotton cloth at 70% is 8.1%. _____ kg Response: 202.8

Question 17 Eight hundred kg of dry air per hour is saturated at 45°C then heated to 105°C, passed through an adiabatic dryer and discharged at 51°C. Determine the total kg per hour of water in air before heating. _____ Response: 52.04

Question 18 A machine or equipment used in drying processes.

Response: Dryer

Question 19 Which of the following types of air dryers works by absorbing moisture on a solid desiccant or drying material such as activated alumina, silicon gel or molecular sieve?

Response: Deliquescent dryer

Question 20 https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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2.5 m3/s of humid air at a state of 28°C DB, 21°C WB and 101.325 kPaa flow across a cooler coil and leaves ar 12.5°C DB and 0.0083 kg vapor per kg dry air. If the apparatus dew point temperature (ADP) is 8.5, compute for the contact factor. _____ Response: [none]

Question 21 The following data is available for designing an air-conditioning system for a restaurant: Inside design conditions

26°C DB, 55% RH

Outdoor conditions

36°C DB, 27°C WB

Minimum temperature of air supplied to room

16°DB

Total amount of fresh air supplied

1550 m3/hr

Total infiltration air

390 m3/hr

Seating chairs for dining

45

Employees serving the meals

5

Sensible heat gain per person

60 W

Latent heat gain per sitting person

45 W

Latent heat gain per employee

75 W

Sensible heat added from meals

0.16 kW

Latent heat added from meals

0.28 kW

Total heat flow through walls, roof and floor

5.9 kW

Solar heat gain through glass

1.9 kW

Equipment sensible heat gain

2.75 kW

Equipment latent heat gain

0.65 kW

Determine the by-pass factor. _____ Response: [none]

Question 22 Cooling and dehumidifying process is commonly used for: Response: Summer air conditioning

Question 23 https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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Air motion also plays important role in Response: Cooling

Question 24 When measuring ____________ of air, the bulb of the thermometer should be shaded to reduce the effect of direct radiation Response: Dry bulb temperature

Question 25 The relationship of water vapor in the air at the dew point temperature to the amount that should be in the air if the air were saturated at the dry-bulb temperature is: Response: Relative humidity

Question 26 Copra enters dryer, containing 65% water and 35% solids, and leaves with 10% water and 90% solids. Find the mass of water removed in kilogram on each slug of bone-dry material. _____ kg Response: 1.75

Question 27 Compute the heat gain for a window facing southeast at 32° north latitude at 10 AM on August 21. The window is regular double glass with 13-mm air space. The glass and inside draperies have a combined shading coefficient of 0.45. The indoor design temperature is 25°C, and the outdoor temperature is 37°C. Window dimensions are 2 m wide and 1.5 m high. _____ W Response: 744.6

Question 28 An air-vapor mixture has a dry bulb temperature of 20°C and a humidity ratio of 0.025 kg/kgd.a., calculate the enthalpy of the moist air. _____ kJ/kg d.a Response: 83.58

Question 29 A 10 kg/s of air enters the theater at 16°C. The theater is to be maintained at 27°C DB and 20°C WB. If the sensible heat ratio is 0.80, what is the latent heat load of the theater? _____ kW Response: [none]

Question 30 The following data is available for designing an air-conditioning system for a restaurant: https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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Inside design conditions

26°C DB, 55% RH

Outdoor conditions

36°C DB, 27°C WB

Minimum temperature of air supplied to room

16°DB

Total amount of fresh air supplied

1550 m3/hr

Total infiltration air

390 m3/hr

Seating chairs for dining

45

Employees serving the meals

5

Sensible heat gain per person

60 W

Latent heat gain per sitting person

45 W

Latent heat gain per employee

75 W

Sensible heat added from meals

0.16 kW

Latent heat added from meals

0.28 kW

Total heat flow through walls, roof and floor

5.9 kW

Solar heat gain through glass

1.9 kW

Equipment sensible heat gain

2.75 kW

Equipment latent heat gain

0.65 kW

Determine the dew point temperature of the cooling coil. _____ °C Response: [none]

Question 31 An air-vapor mixture has a DB temperature of 30°C and a humidity ratio of 0.015 kg/kg d.a. Calculate the enthalpy. _____ kJ/kg d.a Response: [none]

Question 32 If the sensible heat ratio is 0.80 and the cooling load is 100 kW, what is the amount of sensible heat? _____ kW Response: 80

Question 33 A certain material enters the dryer containing 40% solid and leaves with 5% water. Find the mass of the final product if the original product is 1 kg/s. _____ kg/s https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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Response: [none]

Question 34 Is the ratio of the mass water-vapor in air and the mass of air if it is saturated is called: Response: Humidity ratio

Question 35 A type of dryer that may have the flames from combustion impinging on the material being dried; or the gases of combustion may be mixed with additional air so that mixture in contact with the material is reduced in temperature.

Response: Indirect type dryer

Question 36 An air-vapor mixture has a DB temperature of 30°C and a humidity ratio of 0.015 kg/kg d.a. Determine the vapor pressure if the barometric pressure is 101 kPaa. _____ kPaa Response: 2.38

Question 37 A stream of outdoor air is mixed with a stream of return air in an air conditioning system that operated at 101.325 kPa barometric pressure. . The flow rate of outdoor air is 3 kg/s and its conditions are 35°C DB and 0.0159 kg/kg d.a. The flow rate of return air is 2 kg/s and its conditions are 24°C DB and 0.00925 kg/kg d.a. Determine the volume flow rate of the mixture. _____ m3/s Response: 58.78

Question 38 A copra drying plant is designed to dry 1000 kg/hr of fresh coconut meat containing 30% water. The raw copra from the dryer contains 5% water. Fresh air is at 27°C and 40% RH and barometric pressure of 98 kPa. The air is heated to 110°C before entering the adiabatic drying chamber and leaves the dryer at 75°C. Assuming 100% heat transfer efficiency in the air-preheater, determine the enthalpy of air leaving the dryer. _____ kJ/kg d.a Response: [none]

Question 39 Air whose condition is such that any decrease in temperature will result in condensation of water vapor into liquid.

Response: saturated air

Question 40 The ratio of the mass of water vapor in the air per unit mass of dry to the mass of water vapor requires for saturation of the same air sample https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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Response: Absolute humidity

Question 41 Air in an occupied room is at temperature of 20°C DB and has moisture content of 0.00738 kg/kg d.a. When air at 20°C DB is fully saturated, it can hold 0.01475 kg vapor per kg dry air. . Calculate the enthalpy of the moist air. From steam tables, at 20°C, Psat = 2.339 kPaa. _____ kJ/kg d.a Response: [none]

Question 42 In a sensible heating process the final humidity ratio is: Response: Decreased

Question 43 Eight hundred kg of dry air per hour is saturated at 45°C then heated to 105°C, passed through an adiabatic dryer and discharged at 51°C. Determine the final kg per hour of water in air when discharged. _____ Response: 70.60

Question 44 Wet material, containing 220% moisture (dry basis) is to be dried at the rate of 1.8 kg/s in a continuous dryer to give a product containing 10% (dry basis). Find the moisture removed, kg/hr. _____ Response: 3524.76

Question 45 A copra drying plant is designed to dry 1000 kg/hr of fresh coconut meat containing 30% water. The raw copra from the dryer contains 5% water. Fresh air is at 27°C and 40% RH and barometric pressure of 98 kPa. The air is heated to 110°C before entering the adiabatic drying chamber and leaves the dryer at 75°C. Assuming 100% heat transfer efficiency in the air-preheater, determine the amount of steam required by the dryer when condensing saturated steam to saturated liquid at 150 kPaa. _____ kg/hr Response: [none]

Question 46 A classroom that normally contains 40 people is to be air- conditioned with window air-conditioning units of 4 KW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 KJ/hr. There are 10 light bulbs in the room, each with a rating of 100 watts. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000 KJ/hr. If the room air is to be maintained at a constant temperature of 21°C, determine the number of window air- conditioning units required. _____ Response: 2 https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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Question 47 The following data is available for designing an air-conditioning system for a restaurant: Inside design conditions

26°C DB, 55% RH

Outdoor conditions

36°C DB, 27°C WB

Minimum temperature of air supplied to room

16°DB

Total amount of fresh air supplied

1550 m3/hr

Total infiltration air

390 m3/hr

Seating chairs for dining

45

Employees serving the meals

5

Sensible heat gain per person

60 W

Latent heat gain per sitting person

45 W

Latent heat gain per employee

75 W

Sensible heat added from meals

0.16 kW

Latent heat added from meals

0.28 kW

Total heat flow through walls, roof and floor

5.9 kW

Solar heat gain through glass

1.9 kW

Equipment sensible heat gain

2.75 kW

Equipment latent heat gain

0.65 kW

Determine refrigeration load on the coil in tons of refrigeration. _____ TR Response: [none]

Question 48 Air in an occupied room is at temperature of 20°C DB and has moisture content of 0.00738 kg/kg d.a. When air at 20°C DB is fully saturated, it can hold 0.01475 kg vapor per kg dry air. Calculate the percent saturation of the room air. _____ % Response: [none]

Question 49 A window, facing southeast at 32° north latitude at 10 AM on August 21, is regular double glass with 13-mm air space.

Window dimensions are 2 m wide and 1.5 m high. The window has a 0.5-m overhang at the top of the window. How far will the shadow extend downward? _____ m https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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Response: [none]

Question 50 How much heat must be added to 28 m³/min of air at 24°C and 40% RH to raise it to 38°C DB and 37°C WB. _____ kW Response: 22.73

https://ubian.ub.edu.ph/student_take_quiz_assignment/display/19039682?part=51&results=204715638#

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