০০। A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in higher coefficient of performance.
ক) Agree
খ) Disagree
০১। A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in __________ power per tonne of refrigeration.
ক) same
খ) lower
গ) higher
০২। A boot-strap air cooling system has
ক) one heat exchanger
খ) two heat exchangers
গ) three heat exchangers
ঘ) four heat exchangers
০৩। A composite slab has two layers of different materials with thermal conductivities k1 and k2. If each layer has the same thickness, then the equivalent thermal conductivity of the slab will be
ক) k1 k2
খ) k1 + k2
গ)
ঘ)
০৪। A condenser is used in the __________ pressure side of a refrigerating system.
ক) low
খ) high
০৫। A condenser of refrigeration system rejects heat at the rate of 120 kW, while its compressor consumes a power of 30 kW. The coefficient of performance of the system will be
ক) 1/4
খ) 1/3
গ) 3
ঘ) 4
০৬। A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h1, h2 and h3 respectively. The average heat transfer coefficient for the cube is
ক) h1 + h2 + h3
খ) (h1h2h3)1/3
গ)
ঘ) none of these
০৭। A designer chooses the values of fluid flow rates and specific heats in such a manner that the heat capacities of the two fluids are equal. A hot fluid enters the counter flow heat exchanger at 100° C and leaves at 60° C. A cold fluid enters the heat exchanger at 40° C. The mean temperature difference between the two fluids is
ক) 20°C
খ) 40°C
গ) 60°C
ঘ) 66.7°C
০৮। A device used for transfering heat from one fluid to another is called heat exchanger.
ক) True
খ) False
০৯। A furnace is made of a red brick wall of thickness 0.5 m and conductivity 0.7 W/mK. For the same heat loss and temperature drop, this can be replaced by a layer of diatomite earth of conductivity 0.14 W/mK and thickness
ক) 0.5 m
খ) 0.1 m
গ) 0.2 m
ঘ) 0.5 m
১০। A good refrigerant should have
ক) high latent heat of vaporisation and low freezing point
খ) high operating pressures and low freezing point
গ) high specific volume and high latent heat of vaporisation
ঘ) low C.O.P. and low freezing point
১১। A grey body is one whose absorptivity does not vary with temperature and wave length of the incident ray.
ক) True
খ) False
১২। A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as
ক)
খ)
গ) AU Cmin
ঘ)
১৩। A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be
ক) 1 kW
খ) 2 kW
গ) 3 kW
ঘ) 4 kW
১৪। A human body feels comfortable when the heat produced by the metabolism of human body is equal to the
ক) heat dissipated to the surroundings
খ) heat stored in the human body
গ) sum of (a) and (b)
ঘ) difference of (a) and (b)
১৫। A low wet bulb temperature indicates very __________ humidity.
ক) low
খ) high
১৬। A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called
ক) dry air
খ) moist air
গ) saturated air
ঘ) specific humidity
১৭। A one tonne refrigerating machine means that
ক) one tonne is the total mass of machine
খ) one tonne refrigerant is used
গ) one tonne of water can be converted into ice
ঘ) one tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min
১৮। A perfect black body is one which
ক) is black in colour
খ) absorbs heat radiations of all wave lengths falling on it
গ) reflects all the heat radiations
ঘ) transmits the heat radiations
১৯। A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be