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MCQOPTIONS
This section includes 4791 Mcqs, each offering curated multiple-choice questions to sharpen your Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 1751. |
A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be |
| A. | lack of cooling water |
| B. | water temperature being high |
| C. | dirty condenser surface |
| D. | all of these |
| Answer» E. | |
| 1752. |
The emissivity for a black body is |
| A. | 0 |
| B. | 0.5 |
| C. | 0.75 |
| D. | 1 |
| Answer» E. | |
| 1753. |
Which of the following would lead to a reduction in thermal resistance? |
| A. | In conduction, reduction in the thickness of the material and an increase in thermal conductivity. |
| B. | In convection, stirring of the fluid and cleaning the heating surface. |
| C. | In radiation, increasing the temperature and reducing the emissivity. |
| D. | all of the above |
| Answer» E. | |
| 1754. |
The sensible heat during humidification process decreases. |
| A. | True |
| B. | False |
| Answer» C. | |
| 1755. |
The counter-current flow heat exchanger can transfer __________ heat than parallel flow heat exchanger. |
| A. | less |
| B. | more |
| Answer» C. | |
| 1756. |
The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number)n, where n is equal to |
| A. | -1/3 |
| B. | -2/3 |
| C. | 1 |
| D. | -1 |
| Answer» B. -2/3 | |
| 1757. |
The material of pipe lines for a system using ammonia as a refrigerant should be copper. |
| A. | Yes |
| B. | No |
| Answer» C. | |
| 1758. |
The wave length corresponding to the maximum energy is inversely proportional to the absolute temperature. This statement is called Planck's law. |
| A. | Yes |
| B. | No |
| Answer» C. | |
| 1759. |
Thermal conductivity of air increases with rise in temperature. |
| A. | Correct |
| B. | Incorrect |
| Answer» B. Incorrect | |
| 1760. |
The thermal diffusivity for gases is generally __________ those for liquids. |
| A. | equal to |
| B. | less than |
| C. | greater than |
| Answer» D. | |
| 1761. |
The freon group of refrigerants are |
| A. | halo-carbon refrigerants |
| B. | azeotrope refrigerants |
| C. | inorganic refrigerants |
| D. | hydro-carbon refrigerants |
| Answer» B. azeotrope refrigerants | |
| 1762. |
The super-heating in a refrigeration cycle |
| A. | does not alter C.O.P. |
| B. | increases C.O.P. |
| C. | decreases C.O.P. |
| D. | none of these |
| Answer» D. none of these | |
| 1763. |
According to Prevost's theory of exchanges, every body irrespective of its temperature continuously emit heat radiations to the surrounding bodies and at the same time receives heat radiations from the surrounding bodies. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 1764. |
The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to |
| A. | Stanton number |
| B. | Biot number |
| C. | Peclet number |
| D. | Grashoff number |
| Answer» B. Biot number | |
| 1765. |
In a boot-strap air evaporative cooling system, the evaporator is provided |
| A. | between the combustion chamber and the first heat exchanger |
| B. | between the first heat exchanger and the secondary compressor |
| C. | between the secondary compressor and the second heat exchanger |
| D. | between the second heat exchanger and the cooling turbine |
| Answer» E. | |
| 1766. |
According to Stefan-Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the |
| A. | absolute temperature |
| B. | square of the absolute temperature |
| C. | cube of the absolute temperature |
| D. | fourth power of the absolute temperature |
| Answer» E. | |
| 1767. |
A good refrigerant should have |
| A. | high latent heat of vaporisation and low freezing point |
| B. | high operating pressures and low freezing point |
| C. | high specific volume and high latent heat of vaporisation |
| D. | low C.O.P. and low freezing point |
| Answer» B. high operating pressures and low freezing point | |
| 1768. |
The thermostatic expansion valve is used in __________ type of evaporators. |
| A. | flooded |
| B. | DX coil |
| C. | dry |
| Answer» D. | |
| 1769. |
If the condenser temperature is kept constant, the coefficient of performance of a refrigeration cycle increases with the increase in evaporator temperature. |
| A. | Yes |
| B. | No |
| Answer» B. No | |
| 1770. |
When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be |
| A. | positive |
| B. | negative |
| C. | zero |
| D. | none of these |
| Answer» C. zero | |
| 1771. |
If a gas is to be liquified, its temperature must be |
| A. | increased to a value above its critical temperature |
| B. | reduced to a value below its critical temperature |
| C. | equal to critical temperature |
| D. | none of the above |
| Answer» D. none of the above | |
| 1772. |
The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as |
| A. | conduction |
| B. | free convection |
| C. | forced convection |
| D. | radiation |
| Answer» D. radiation | |
| 1773. |
The boiling point of ammonia is |
| A. | -10.5 C |
| B. | -30 C |
| C. | -33.3 C |
| D. | -77.7 C |
| Answer» D. -77.7 C | |
| 1774. |
The by-pass factor (B. P. F.) in case of sensible heating of air is (Where td1 = Dry bulb temperature of air entering the heating coil, td2 = Dry bulb temperature of air leaving the heating coil, and td3 = Dry bulb temperature of heating coil) |
| A. | <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/432-343-1.png"> |
| B. | <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/432-343-2.png"> |
| C. | <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/432-343-3.png"> |
| D. | <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/432-343-4.png"> |
| Answer» C. <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/432-343-3.png"> | |
| 1775. |
The refrigerant used for absorption refrigerators working on heat from solar collectors is a mixture of water and |
| A. | carbon dioxide |
| B. | sulphur dioxide |
| C. | lithium bromide |
| D. | R-12 |
| Answer» D. R-12 | |
| 1776. |
In a black body, all radiations are rejected. |
| A. | True |
| B. | False |
| Answer» C. | |
| 1777. |
Planck's law holds good for all coloured bodies. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 1778. |
The capacity of a domestic refrigerator is in the range of |
| A. | 0.1 to 0.3 TR |
| B. | 1 to 3 TR |
| C. | 3 to 5 TR |
| D. | 5 to 7 TR |
| Answer» B. 1 to 3 TR | |
| 1779. |
The condition of refrigerant after passing through the condenser in a vapour compression system is |
| A. | saturated liquid |
| B. | wet vapour |
| C. | dry saturated vapour |
| D. | superheated vapour |
| Answer» B. wet vapour | |
| 1780. |
The difference between dry bulb temperature and dew point temperature, is called |
| A. | dry bulb depression |
| B. | wet bulb depression |
| C. | dew point depression |
| D. | degree of saturation |
| Answer» D. degree of saturation | |
| 1781. |
The expression is used for calculating |
| A. | relative humidity |
| B. | humidity ratio |
| C. | degree of saturation |
| D. | pressure of water vapour |
| Answer» C. degree of saturation | |
| 1782. |
In mechanical refrigeration system, the refrigerant has the maximum temperature |
| A. | in evaporator |
| B. | before expansion valve |
| C. | between compressor and condenser |
| D. | between condenser and evaporator |
| Answer» D. between condenser and evaporator | |
| 1783. |
The leakage in a refrigeration system using freon is detected by |
| A. | halide torch |
| B. | sulphur sticks |
| C. | soap and water |
| D. | all of these |
| Answer» B. sulphur sticks | |
| 1784. |
Logarithmic mean temperature difference is the same as the arithmetic mean temperature difference. |
| A. | Agree |
| B. | Disagree |
| Answer» C. | |
| 1785. |
In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature |
| A. | which lies between the dry bulb and wet bulb temperatures of the incoming stream |
| B. | which lies between the wet bulb and dew point temperatures of the incoming stream |
| C. | which is lower than the dew point temperature of the incoming stream |
| D. | of adiabatic saturation of incoming stream |
| Answer» D. of adiabatic saturation of incoming stream | |
| 1786. |
Kirchhoff's law states that |
| A. | the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature |
| B. | the wave length corresponding to the maximum energy is proportional to the absolute temperature |
| C. | the ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body |
| D. | none of the above |
| Answer» D. none of the above | |
| 1787. |
Film coefficient is defined as the ratio of |
| A. | thermal conductivity to the equivalent thickness of the film of fluid |
| B. | temperature drop through the films of fluids to the thickness of film of fluids |
| C. | thickness of film of fluid to the thermal conductivity |
| D. | thickness of film of fluid to the temperature drop through the films of fluids |
| Answer» B. temperature drop through the films of fluids to the thickness of film of fluids | |
| 1788. |
Dew point temperature is the temperature of air recorded by a thermometer, when the moisture present in it begins to condense. |
| A. | Correct |
| B. | Incorrect |
| Answer» B. Incorrect | |
| 1789. |
The temperature below which a gas is always liquified, is known as critical temperature. |
| A. | Correct |
| B. | Incorrect |
| Answer» C. | |
| 1790. |
In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40 C and an evaporator temperature of 5 C, the heat rejection factor is about |
| A. | 1 |
| B. | 1.25 |
| C. | 2.15 |
| D. | 5.12 |
| Answer» C. 2.15 | |
| 1791. |
The undesireable property of a refrigerant is |
| A. | non-toxic |
| B. | non-flammable |
| C. | non-explosive |
| D. | high boiling point |
| Answer» E. | |
| 1792. |
The dry bulb temperature during sensible heating of air |
| A. | remains constant |
| B. | increases |
| C. | decreases |
| Answer» C. decreases | |
| 1793. |
The coefficient of performance of a domestic refrigerator is __________ as compared to a domestic air-conditioner. |
| A. | same |
| B. | less |
| C. | more |
| Answer» C. more | |
| 1794. |
In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = By-pass factor) |
| A. | B.P.F. - 1 |
| B. | 1 - B.P.F. |
| C. | <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/432-352-1.png"> |
| D. | 1 + B.RF. |
| Answer» C. <img src="/_files/images/mechanical-engineering/heat-transfer-refrigeration-and-air-conditioning/432-352-1.png"> | |
| 1795. |
The coefficient of performance (C.O.P.) is the reciprocal of the efficiency of a heat engine. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 1796. |
The emissive power of a body depends upon its |
| A. | temperature |
| B. | physical nature |
| C. | wave length |
| D. | all of these |
| Answer» E. | |
| 1797. |
The horizontal and non-uniformly spaced lines on a psychrometric chart indicates |
| A. | dry bulb temperature |
| B. | wet bulb temperature |
| C. | dew point temperature |
| D. | specific humidity |
| Answer» D. specific humidity | |
| 1798. |
An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m2). The critical thickness of insulation will be |
| A. | 25 mm |
| B. | 40 mm |
| C. | 160 mm |
| D. | 800 mm |
| Answer» B. 40 mm | |
| 1799. |
A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be |
| A. | 1.33 |
| B. | 2.33 |
| C. | 3.33 |
| D. | 4.33 |
| Answer» C. 3.33 | |
| 1800. |
Radiation is the process of heat transfer in which heat flows from a __________ , in a straight line, without affecting the intervening medium. |
| A. | cold body to hot body |
| B. | hot body to cold body |
| C. | smaller body to larger body |
| D. | larger body to smaller body |
| Answer» C. smaller body to larger body | |