Question 1

The statement that the emissivity and absorptivity of a surface is surrounded by its own temperature are the same for both monochromatic and total radiation, is known as

Accepted Answer

Kirchhoff's law states that for an object at thermal equilibrium, the emissivity (the ability to emit radiation) and absorptivity (the ability to absorb radiation) are equal for both monochromatic (single wavelength) and total radiation across all wavelengths. This principle is fundamental in understanding thermal radiation processes.

Question 2

Emissivity and absorptivity of a surface are equal for radiation

Accepted Answer

Emissivity and absorptivity of a surface are equal for radiation with equal temperature and wavelength, according to Kirchhoff's law of thermal radiation. This law states that for an object in thermal equilibrium, the emissivity and absorptivity are equal at the same wavelength and temperature.

Question 3

The equation m x T = constant represents

Accepted Answer

Wein's Law relates the wavelength at which the peak of the emission of a black body spectrum occurs to the temperature of the black body. The equation $m \times T = \text{constant}$, where $m$ is the peak wavelength and $T$ is the temperature, is a representation of Wein's Law.

Question 4

The face temperatures of a flat wall are 650°C and 450°C respectively and the thermal conductivity of wall material is 0.30 kcal/m-hr-°C. For a wall thickness of 20 cm, the rate of heat conduction per square meter of wall area will be

Accepted Answer

The rate of heat conduction (Q) through a wall can be calculated using the formula Q = (kAΔT)/d, where k is the thermal conductivity, A is the area (which is 1 m² as per the question), ΔT is the temperature difference across the wall, and d is the thickness of the wall. Plugging in the values: k = 0.30 kcal/m-hr-°C, ΔT = 650°C - 450°C = 200°C, and d = 20 cm = 0.2 m, we get Q = (0.30 * 1 * 200) / 0.2 = 300 kcal/hr.

Question 5

Pipes are insulated so that

Accepted Answer

Insulating pipes primarily serves to minimize heat loss (or gain) from the surface to ensure energy efficiency and maintain the desired temperature of the fluids being transported.

Question 6

The value of Stefan Boltzmann's constant in kcal-m²-hr-K⁴ is

Accepted Answer

Stefan Boltzmann's constant is 5.67 x 10^-8 W/m²K⁴. To convert this to kcal-m²-hr-K⁴, we need to multiply by the following conversion factors:1 kcal = 4.184 kJ1 hr = 3600 s1 W = 1 J/sTherefore, 5.67 x 10^-8 W/m²K⁴ = 5.67 x 10^-8 J/m²sK⁴ = 5.67 x 10^-8 x 4.184 kJ/m²sK⁴ = 5.67 x 10^-8 x 4.184 x 10³ kcal/m²hrK⁴ = 2.37 x 10^-4 kcal/m²hrK⁴.Therefore, the correct answer is C) 4.87 x 10^-8.

Question 7

An isotherm is a graph

Accepted Answer

An isotherm is a graph that shows the relationship between pressure and volume at a constant temperature, typically used in thermodynamics to describe the behavior of gases.

Question 8

A non-dimensional number which generally finds application in mass transfer problems is

Accepted Answer

The Stanton number is a dimensionless number used in mass transfer problems to characterize the ratio of heat or mass transfer to the thermal or mass capacity of a fluid.

Question 9

The mass of water vapour per kg of the pressure of saturated vapour at the air is known as

Accepted Answer

Specific humidity is the mass of water vapor per unit mass of air.

Question 10

Unsaturated vapours

Accepted Answer

The answer of Unsaturated vapours
...

Question 11

Four balls made of lead, glass, brass and iron made of same size, are heated to 100°C. They are simultaneously placed on a sheet of paraffin nearly 5 mm thick. Which ball will drop first?

Accepted Answer

The answer of Four balls made of lead, glass, brass...

Question 12

Kinematic viscosity indicates

Accepted Answer

Kinematic viscosity is a measure of the rate at which momentum is transported by molecular friction within a fluid, which is crucial for understanding how fluids flow and how they resist motion.

Question 13

A piece of metal with a circular hole is heated. If the metal expands on heating the diameter of the hole will

Accepted Answer

When a piece of metal with a circular hole is heated, the metal expands uniformly in all directions. This means the material around the hole also expands, causing the diameter of the hole to increase.

Question 14

Four rods with different radii 'r' and length 'l' are used to connect to reservoirs of heat at different temperature. Which one of them with conduct most heat?

Accepted Answer

The heat conduction through a rod is directly proportional to the cross-sectional area (πr²) and inversely proportional to its length (l). A larger radius and shorter length will conduct more heat. Option B has the largest radius and the shortest length among the given options.

Question 15

Which type of heat exchanger an automobile radiator is?

Accepted Answer

The answer of Which type of heat exchanger an automobile...

Question 16

The wavelength for maximum emissive power is given by

Accepted Answer

Wein's Displacement Law states that the wavelength at which the emission of a black body spectrum is maximized inversely varies with the temperature of the black body. This law helps in determining the peak wavelength for maximum emissive power, making choice B (Wein's law) the correct answer.

Question 17

The emissivity of a body will be equal to absorptivity when

Accepted Answer

Kirchhoff's law of thermal radiation states that at thermal equilibrium, the emissivity of a body is equal to its absorptivity for a given wavelength and temperature.

Question 18

In constant volume Hydrogen gas Thermometer, a correction has to be applied, because

Accepted Answer

Expansion of Hydrogen is non-linear

Question 19

All substances emit radiation, the quality and quantity depending upon the absolute temperature and the properties of the material composing the radiating body. The above statement is known as the statement of

Accepted Answer

The answer of All substances emit radiation, the quality and...

Question 20

The unit of thermal conductivity in M.K.S. unit is

Accepted Answer

The answer of The unit of thermal conductivity in M.K.S....

Quiz 15: Heat Transfer and Thermodynamics