COOLING TOWER

COOLING tower-: In power plants, cooling towers are employed for cooling the warm water from the condensers so that the same water after cooling can be reused for condensing the steam. 

                             In other words, a cooling tower is a specialized heat exchanger in which air and water are brought into direct contact with each other in order to reduce the water's temperature . As this occurs, a small volume of water is evaporated,  reducing the temperature of the water being circulated through the tower.

              The use of cooling towers becomes essential where plenty of cooling water is not available from river or sea for direct cooling. A cooling tower can be considered as an enclosed device used for the evaporation cooling of water by contact with the air. In cooling towers,  the cooling takes place partly by an exchange of latent heat resulting from the evaporation of some of the circulating water, and partly by the transfer of sensible heat. Although the cooling effect can be produced by cooling pond , spray pond, atmospheric tower , spray filled tower. 

The types of cooling towers used in thermal power stations are : 

( 1 ) Atmospheric ( Natural draught chimney ) type cooling tower .                                            ( 2 )Mechanical draught type cooling towers. 

The cooling towers can also be classified as wet cooling towers or dry cooling towers.

Wet cooling tower -: In wet cooling towers the cooling takes place by evaporation but huge quantity of water goes along with hot air into atmosphere. 

Dry cooling tower -: In this type of cooling towers,  the cooling takes place by surface heat exchange, there being no drift losses ; of course, the initial cost is very high. 

REFRIGERATION AND AIR CONDITIONING MCQ -: 05

Q.1 On high side of ammonia absorption system allowable pressure is of the order of ______ .

A. 1 - 2 bars

B. 5 - 6 bars

C. ATM pressure 

D. 10 bars

And -: B

Q.2 The ______ temperature is the temperature above which a gas will never liquefy .

A. Atmospheric temperature 

B. Dew point temperature 

C. Wet bulb temperature 

D. Critical temperature 

And-: D

Q.3 The refrigerant for a refrigerator should have _____ .

A. High latent heat 

B. High sensible heat 

C. Low latent heat

D. Low sensible heat

And-: A

Q.4 At which pressure above which a liquid will remain liquid 

A. Absolute pressure 

B. Critical pressure 

C. Atmospheric pressure 

D. Low pressure 

And -: B

Q.5  In a flooded evaporator refrigerator  , an accumulator at suction of compressor is used to ____.

A. Collect vapour 

B. Increase refrigeration effect 

C. Collect liquid refrigerant and prevent it from going to compressor. 

D. None of the above 

Ans -: C

Q.6 In vapour compression cycle the higher temperature occurs at _____ .

A. Evaporator 

B. Condenser discharge 

C. Compressor discharge 

D. Expansion system

Ans -: C

Q.7 In which type of refrigeration system aqua ammonia is used as a refrigerant?

A. Compression 

B. Absorption 

C. Indirect 

D. None of the above 

Ans -: B

Q.8 The flow of refrigerant is controlled by which device?

A. Evaporator 

B. Compressor 

C. Condenser 

D. Expansion valve 

And -: D

Q.9 what is the effect of supercharging in a refrigeration cycle?

A. Decrease COP

B. Increase COP

C. Higher efficiency 

D. More refrigeration effect 

Ans -: A

Q.10  which temperature indicate the amount of moisture in air ?

A. Dew point temperature 

B. Critical temperature 

C. Dry bulb temperature 

D. Wet bulb temperature 

And -: D

Q.11 Generally cooling towers are installed where __.

A. For very big plant

B. Water is scarce

C. Water is available in plenty 

D. All of the above 

Ans -: B

Q.12 The percentage loss of drift in cooling towers is ____ .

A. 1 to 5 %

B. 10 to 15 %

C. 10 to 20 %

D. 25 to 50 %

Ans -: C

Q.13 Water is cooled by _____ in cooling towers system.

A. Condensation 

B. Evaporation 

C. Fusion

D. Sublimation 

And-: B

Q.14 Pure humidification can be achieved by passing air through the spray water maintained at _________ .

A. Dry bulb temperature 

B. Wet bulb temperature 

C. Dew point temperature 

D. Atmospheric temperature 

And -: A

Q.15 As warm air cools , it's relative humidity ________.

A. Increase and then decrease 

B. Decrease 

C. Increase 

D. Decrease and then increase 

And -: C

Wet bulb and Dew point temperature

Wet bulb temperature -: The wet bulb temperature is the temperature read by a thermometer covered in water-soaked cloth ( wet bulb thermometer ) over which air is passed. If the bulb of an ordinary thermometer is surrounded by a wick wetter with water and air passed around it ; water at surface will being to evaporate. The vaporisation takes heat -leatent heat of vaporisation and the wick is cooled . The temperature finally reached when cooling stops is known as wet bulb temperature. At wet bulb temperature,  the heat from the air to water surface equals the haet taken from the surface to vaporise water.

                  At 100 % relative humidity , the wet bulb temperature is equal to the air temperature ( dry bulb temperature) and it is lower at lower humidity. A wet bulb temperature indicates a temperature close to the true ( thermodynamic ) temperature. The wet bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only.

Dew point temperature -: The dew-point temperature is the temperature at which moisture will condense out of the air for a given specific humidity and pressure, as air moisture temperature is reduced. It is important to note that dew point temperature remains constant as long as there us no change in moisture. 

                   The dew-point temperature is always lower than Or equal to the air temperature. If the air temperature cools to the dew point, or if the dew point raises to equal the air temperature, then dew , fog or coouds being to form. At this point where the dew point temperature equals the air temperature, the relative humidity us 100%.

At 100% humidity, wet bulb temperature is equal to the dry bulb temperature. Drier is the air , more will be the difference between dry bulb and wet bulb temperature.

REFRIGERATION MCQ 04

Q.1 While changing from a liquid phase to vapour phase, fluids _______ heat.

A. Convert

B. Extract 

C. Absorb

D. No changes in heat

Ans-: C

Q.2 In reversed carnot cycle working on vapour, work done during isothermal process is _____ .

A. Maximum 

B. Minimum 

C. Increase 

D. Zero

Ans -: D

Q.3 The heat , which can be added or removed from a substance without a change in state is called ?

A. Sensible heat

B. Leatent heat

C. Extra heat

D. None of the above 

Ans -: A

Q.4 At which temperature , centigrade and Fahrenheit scale have same reading ?

A. - 45 °

B. - 40 °

C. - 100 °

D. - 273 °

Ans -: B

Q.5 Usually the quantity of free air per person in air conditioning system is taken as ______ .

A. 1.2 m^3 / min

B. 1.2 m^3 / sec

C. 0.2 m^3 / he

D. 1.12 m^3 / min

And-: A

Q.6 The dry bulb temperature is ____ , in spray humidification process .

A. Raised

B. Same

C. Lowered 

D. Zero

Ans -: C

Q.7 During evaporative cooling process the wet bulb temperature is ___.

A. Remain constant

B. Increased 

C. Decreased 

D. Zero

Ans -: A

Q.8 Which of the following is commonly used liquid absorbent ?

A. Silica gel

B. Ethylene glycol 

C. Activated alumina

D. None of the above 

Ans -: B

Q.9 One of the reasons for an evaporator to not cool may be ?

A. Frozen oil

B. Leaking refrigerant 

C. Faculty thermostat 

D. Insufficient lubricant in refrigerant 

And-: A

Q.10 The refrigerator which does not require compressor in known as ____.

A. Carnot refrigerator 

B. Tubo-refrigerator

C. Electrolux refrigerator 

D. Vapour absorption refrigerator 

And-: C

HUMIDITY

Humidity-: Humidity is the amount of water vapour in the air. If there is a lot of water in the air , the humidity will be high.

                               In simple words , humidity means water vapour in the air, but not to be liquid droplets in the fog , clouds,or rain. Higher Humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. The gaseous state of water, is generally invisible to the human eye. Humidity indicate the likelihood for precipitation, dew or fog to be present.  The amount of water vapour needed to achieve saturation increase as the temperature increases.

There are three types of humility-:

1. Absolute humidity 

2. Relative humidity 

3. Specific humidity 

1. Absolute humidity -: Absolute humidity is the measure of water vapour or moisture in the air, regardless of temperature.  It is expressed as grams of moisture per cubic meter of air ( g/m^3). 

                    In other words , the total mass of water vapour present in a given volume of the mass of the air known as " absolute humidity ". It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly 30 grams per cubic meter when the air is saturated at 30 °C. It is the mass of water vapour divided by the volume of the air and water vapour mixture, which can be expressed as -

Absolute humidity = mH2O / V(net)                                                                 

The absolute humidity changes as air temperature or pressure changes , if the volume is not fixed.

2. Relative humidity -: Relative Humidity is actual amount of moisture in air at any given temperature,  divided by the greatest amount of moisture the same air could hold without condensation. Relative humidity could also be expressed by moisture, divided by the highest vapour pressure ( saturation condition ) possible under the same conditions. 

                 Highest pressure that water vapour can have without condensation,  i.e. ,100 % relative humidity at various atmospheric temperature. 

3. Specific humidity -: Specific humidity is the ratio of the mass of water vapour to the total mass of the air parcel. Specific humidity is approximately equal to the mixing ratio,which defined as the ratio of the mass of water vapour in an air parcel to the mass of dry air for the same parcel. As the temperature decreasing the amount of the water vapour needed to reach saturation also decreases. As the temperature of a parcel of air become lower it Will eventually reach the point of saturation without adding or losing water mass.

                                     

REFRIGERATION MCQ-: 03

Q.1 ______ leatent heat of vaporisation is desirable in a refrigerant.

A. Low

B. High

C. Minimum 

D. Maximum 

Ans -: B

Q.2 The maximum temperature of a refrigerant at which it can be condensed into liquid known as ____ .

A. Boiling temperature 

B. Desirable temperature 

C. Critical temperature 

D. Refrigeration temperature 

Ans -: C

Q.3 Refrigeration compressor designed to oprate with R22 refrigerant and can't be oprated with R12 , because  Condensing pressure of R22 at any given temperature is ________ than that of R12.

A. Higher

B. Lower

C. Equal

D. None of these 

Ans-: A

Q.4 What is the name of combined process of cooling and humidifying ?

A. Vaporisation 

B. Condensation 

C. Evaporative cooling

D. None of these 

Ans -:C

Q.5 What is the value of sensible heat factor for humidification or dehumidification process ?

A. 1.5

B. 2

C. 1.5

D. Zero

Ans -: D

Q.6 In gas refrigeration cycle, ______ cycle is used .

A. Compression cycle 

B. Bell-coleman / Brayton cycle 

C. Expansion cycle 

D. Evaporation cycle 

Ans -: B

Q.7 Which refrigeration cycle is used in aircraft?

A. Water refrigeration cycle 

B. Air refrigeration cycle 

C. A + B

D. None of these 

Ans -: B

Q.8 How can we detect leakage of Freon in a refrigeration system?

A. Using freon detector 

B. Using a halide torch

C. Using Freon meter

D. All of the above 

Ans -: B

Q.9 One tone of refrigeration is equal to ___ .

A. 3.5 kW

B. 4.5 kW

C. 1.15 kW

D. 5.2 kW

Ans -: A

Q.10 In a refrigerant moisture is removed by which device?

A. Dehumidifier 

B. Evaporator 

C. Heat exchanger 

D. Driers 

Ans -: D

Q.11 In domestic refrigerator back side tubes are used , are known as _____ .

A. Capillary tube 

B. Evaporating tube

C. Condenser tube

D. None of these 

Ans -: C

Q.12 The coefficient of performance of a domestic refrigerator is ____.

A. More than 1

B. Less than 1

C. 100 %

D. Zero

Ans-: A

Q.13 In which type of refrigeration system only have droplets of liquid in the evaporator?

A. Flooded type 

B. Dry type

C. Low side float system 

D. Capillary tube type 

Ans -: B

Q.14 The rate at which refrigeration is produced and is expressed in tons of refrigeration known as _____ .

A. Power of refrigerator 

B. Capacity of refrigerator 

C. C.O.P. of refrigerator 

D. None of these 

Ans -: B

Q.15 At -15° C carbon dioxide ( CO2 ) has low specific volume in order of _____ .

A. 0.52 m^2/ kg

B. 0.016 m^3/ kg

C. 0.025 m^3 / kg

D. 1.57 m^2 / kg

Ans -: B

Q.16 As compared to ammonia,  freon-12 has _____ specific volume.

A. Large

B. Same

C. Small

D. Very high 

Ans -: C

Q.17 Absorption system normally uses which refrigerant?

A. CO2

B. SO2

C. Ammonia 

D. CFC

Ans -: C

Q.18 In ammonia absorption plant,  cooling water is required for which equipment?

A. Absorber

B. Condenser 

C. Separator 

D. All of the above 

Ans -: D

Q.19 Generally oil separator is installed between _____ in refrigeration system. 

A. Compressor and condenser 

B. Evaporator and flow control device 

C. Compressor and Evaporator 

D. None of these 

Ans -: A

Q.20 What is the use of brine agitator in ice plant ?

A. Increase COP

B. Increasing refrigeration effect

C. Obtain uniform temperature of brine

D. All of the above 

Ans -: C

REFRIGERATION MCQ-: 02

Q.1 Air refrigerator cycle works on ____ cycle.

A. Bell-coleman

B. Air cooling cycle 

C. Carnot cycle 

D. Raynold cycle 

Ans -: A

Q.2. Fluid ____ heat while changing from a liquid phase to vapour phase .

A. Remove

B. Convert

C. Absorb 

D. Increase

Ans -: C

Q.3 What is the boiling temperature  of carbon dioxide?

A. 31° C

B. 78.5 ° C

C. - 78.5 ° C

D. -48.5  ° C

Ans -: C

Q.4 What is the boiling temperature of ammonia?

A. - 33° C

B. - 45° C

C. 75 ° C

D. 22.5 ° C

Ans-: A

Q.5 Operating pressure of Freon- 12 is ____ .

A. 5 kgf/cm^2

B. 8 kgf/cm^2

C. 10 kgf/cm^2

D. 22 kgf/cm^2

Ans -: B

Q.6 Sulphur dioxide ( SO2 ) has low working pressure _____ .

A. 5.5 kgf/cm^2

B. 7.5 kgf/cm^2

C. 4.5 kgf/cm^2

D. 1.8 kgf/cm^2

Ans -: C

Q.7 As compared to Freon-12 , freon-22 has _____.

A. High specific volume 

B. Low specific volume 

C. Equal specific volume 

D. None of these 

Ans -: B

Q.8 Freon-12 is mostly used in which type of plants?

A. Commercial 

B. Domestic 

C. Never used

D. A + B

Ans-: B

Q.9 Sulphur dioxide has a critical temperature of ______ .

A. 157.2 ° C

B.  225.5 ° C

C. 100 ° C

D.  127.5 ° C

Ans-: A

Q.10 What happed , when SO2 contact with moisture?

A. Highly toxic 

B. Corrosive 

C. Non- corrosive 

D. A + B

Ans-: D

Q.11 Carbon dioxide has critical temperature in the order of _____ .

A. 52 ° C

B. 25 ° C

C. 31 ° C

D. 125 ° C

Ans -: C

Q.12 Ammonia is mostly used in ____ .

A. Domestic purpose 

B. Large commercial installation 

C. A + B

D. None of the above 

Ans-: B

Q.13 The ratio of the refrigeration obtained to the net work done on the system in the cycle known as _____ .

A. Refrigeration ratio

B. Work done

C. Coefficient of performance of refrigerant 

D. Refrgerant quality 

Ans-: C

Q.14 Compression refrigeration system also known as _____ .

A. Flood refrigeration system 

B. Mechanical refrigeration system 

C. Dry refrigeration system 

D. None of these 

Ans -: B

Q. 15 The ratio of actual and theoretical coefficient of performance is known as ____ .

A. Relative Coefficient of performance 

B. Refrigeration C.O.P.

C. Total work done

D. None of these 

Ans -: A