Heat transfer by natural convection is enhanced in system with__________________?

Byadmin March 3, 2019August 24, 2021

Heat transfer by natural convection is enhanced in system with__________________?

A. High viscosity
B. High co-efficient of thermal expansion
C. Low temperature gradients
D. Low density change with temperature

Chemical Heat Transfer

The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are _______________?

The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are _______________?

A. (COP)R = (COP)HP = 0.6
B. (COP)R = 2.5; (COP)HP = 1.5
C. (COP)R = 1.5; (COP)HP = 2.5
D. (COP)R = (COP)HP = 2.5

Read More The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are _______________?
Chemical Heat Transfer

The equation, (NSt × N2/3 Pr) = f/2, is the ____________ analogy ?

The equation, (NSt × N2/3 Pr) = f/2, is the ____________ analogy ?

A. Colburn
B. Reynolds
C. Prandtl
D. None of these

Read More The equation, (NSt × N2/3 Pr) = f/2, is the ____________ analogy ?
Chemical Heat Transfer

With increase in temperature, the thermal conductivity of non-metallic amorphous solids_________________?

With increase in temperature, the thermal conductivity of non-metallic amorphous solids_________________?

A. Decreases
B. Increases
C. Remain constant
D. First decreases upto certain temperature and then increases

Read More With increase in temperature, the thermal conductivity of non-metallic amorphous solids_________________?
Chemical Heat Transfer

In a heat exchanger, one transfer unit means___________________?

In a heat exchanger, one transfer unit means___________________?

A. A section of the exchanger in which change in temperature of one stream equals the average
driving force in the section
B. The size of the exchanger in which heat transfer rate is 1 kcal/hr
C. Both A. and B.
D. None of these

Read More In a heat exchanger, one transfer unit means___________________?
Chemical Heat Transfer

Radiation energy is emitted by all the substances, which are above____________________?

Radiation energy is emitted by all the substances, which are above____________________?

A. 0°K
B. 0°C
C. 100°C
D. Room temperature

Read More Radiation energy is emitted by all the substances, which are above____________________?
Chemical Heat Transfer

A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time ___________________?

A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time ___________________?

A. t = 283 s
B. t = 356 s
C. t = 400 s
D. t = 800 s

Read More A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time ___________________?

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