Molecular Physics | Thermodynamics Answers

A hot plate 1 m × 1.5 m is maintained at 300°C. Air at 25°C blows over the

plate. If the convective heat transfer coefficient is 20 W/m2°C, calculate the rate of heat transfer

A wire 1.5 mm in diameter and 150 mm long is submerged in water at

atmospheric pressure. An electric current is passed through the wire and is increased until the

water boils at 100°C. Under the condition if convective heat transfer coefficient is 4500 W/m2°C

find how much electric power must be supplied to the wire to maintain the wire surface at 120°C ?

When 0.5 kg of water per minute is passed through a tube of 20 mm

diameter, it is found to be heated from 20°C to 50°C. The heating is accomplished by condensing

steam on the surface of the tube and subsequently the surface temperature of the tube is main￾tained at 85°C. Determine the length of the tube required for developed flow.

Take the thermo-physical properties of water at 60°C as :

ρ = 983.2 kg/m2, cp = 4.178 kJ/kg K, k = 0.659 W/m°C, ν = 0.478 × 10–6 m2/s.

The volume of a liquid is 25.5ml. A student measures the volume and finds it to be 25.2ml, 25.1ml, 24.9ml and 25.3ml in the first, second, third, and fourth trial respectively. Which of the following statements is true for his measurements?

a. They have poor precision

b. They have poor accuracy

c. They are neither precise nor accurate

d. They have good precision

the mass of an unknown substance is 2.86g. which of the following sets of measurement represents the value with both accuracy and precision?

a. 1.78 g, 1.80 g, 1.76 g, 1.81 g

b. 1.98 g, 2.02 g, 1.96 g, 2.01 g

c. 2.85 g, 2.86 g, 2.84 g, 2.81 g

d. 2.81 g, 1.98 g, 2.40 g, 2.78 g

When 0.5 kg of water per minute is passed through a tube of 20 mm

diameter, it is found to be heated from 20°C to 50°C. The heating is accomplished by condensing

steam on the surface of the tube and subsequently the surface temperature of the tube is main￾tained at 85°C. Determine the length of the tube required for developed flow.

Take the thermo-physical properties of water at 60°C as :

ρ = 983.2 kg/m2, cp = 4.178 kJ/kg K, k = 0.659 W/m°C, ν = 0.478 × 10–6 m2/s

Water flows inside a tube 45 mm in diameter and 3.2 m long at a velocity

of 0.78 m/s. Determine the heat transfer co-efficient and the rate of heat transfer if the mean

water temperature is 50°C and the wall is isothermal at 70°C. For water at 50°C take k = 0.66 W/

mK, ν = 0.478 × 10–6 m2/s and Prandtl number = 2.98