Q. Two rods A and B of the same length and diameter protrude from a surface at 120 degree Celsius and are exposed at air at 25 degree Celsius. The temperatures measured at the end of the rods are 50 degree Celsius and 75 degree Celsius. If thermal conductivity of material A is 20W/ m K, calculate it for B.

View solution

Q. An centrifugal pump which circulates a hot liquid metal at 500 degree Celsius is driven by a 3600 rpm electric motor. The motor is coupled to the pump impeller by a horizontal steel shaft of dia 25 mm. Let us assume the motor temperature as 60 degree Celsius with the ambient air at 25 degree Celsius, what length of shaft should be specified between the motor and the pump? It may be presumed that the thermal conductivity of the shaft material is 35W/m K, and that the convective film coefficient between the steel shaft and the ambient air is 15.7W/square m K

View solution

Q. The utility of fin in dissipating a given quantity of heat is generally assessed on the basic of how many parameters?

View solution

Q. A copper steel rod (k = 55 W/m degree) has been attached to a plane wall which is maintained at a temperature of 350 degree Celsius. The rod is 8 cm long and has the cross-section of an equilateral triangle with each side 5 mm. Determine the heat dissipation from the rod if it is exposed to a convection environment at 25 degree Celsius with unit surface conductance 100 W/m² degree. Consider end surface loss to be negligible

View solution

Q. For an infinitely long fin, the efficiency of fin is given by

View solution

Q. For a fin of finite length with an insulated end, the fin efficiency is given as

View solution

Q. For an infinitely long fin, the effectiveness of fin is given as

View solution

Q. For a straight rectangular fin of thickness δ and width b, choose the correct option

View solution

Q. “Effectiveness of fin is the ratio of the fin heat dissipation with fin to that of no fin”. Choose the correct answer

View solution

Q. Three fins of equal length and diameter but made of aluminum, brass and cast iron is heated to 200 degree Celsius at one end. If the fins dissipate heat to the surrounding air at 25 degree Celsius, the temperature at the free end will be least in

View solution

Q. Two long rods A and B of the same diameter have thermal conductivities k and 4k and have one of their end inserted into a furnace at 400 K. At 9.5 m away section from the furnace, the temperature of rod B is120 degree Celsius. So find out at what end from the furnace end, the same temperature would be reached in the rod A?

View solution

Q. The following factors need consideration for the optimum design of fins

(i) Cost

(ii) Space considerations

(iii) Weight considerations

Choose the correct option

View solution

Q. A heating unit is made in the form of a vertical tube of 50 mm outside diameter and 1.2 m height. The tube is fitted with 20 steel fins of rectangular section with height 40 mm and thickness 2.5 mm. The temperature at the base of fin is 75 degree Celsius, the surrounding air temperature is 20 degree Celsius and the heat transfer coefficient between the fin as well as the tube surface and the surrounding air is 9.5 W/m² K. If thermal conductivity of the fin material is 55 W/m K, find the amount of heat transferred from the tube with fin

View solution

Q. The fins would be effective for heat conduction if the ratio P k/h A C is

View solution

Q. Consider the following statements pertaining to heat transfer through fins

(i) They must be arranged at right angles to the direction of flow of working fluid

(ii) The temperature along the fin is variable and accordingly heat transfer rate varies along the fin elements

(iii) Fins are equally effective irrespective whether they are on the hot side or cold side of the fluid

(iv) Fins are made of materials that have thermal conductivity higher than that of wall

Identify the correct statements

View solution

Q. An increase in fin effectiveness is caused by high value of

(i) Convective coefficient

(ii) Thermal conductivity

(iii) Circumference

(iv) Area

Identify the correct statement

View solution

Q. Choose the correct option regarding fin efficiency and fin effectiveness

View solution

Q. The handle of a saucepan, 30 cm long and 2 cm in diameter, is subjected to 100 degree Celsius temperature during a certain cooking operation. The average unit surface conductance over the handle surface is 7.35 W/m² degree in the kitchen air at 24 degree Celsius. The cook is likely to grasp the last 10 cm of the handle and hence the temperature in this region should not exceed 38 degree Celsius. What should be the thermal conductivity of the handle material to accomplish it? The handle may be treated as a fin insulated at the tip

View solution

Q. Let us assume a square section fin split longitudinally and used as two fins. This will result in

View solution

Q. Mark the false statement regarding effectiveness of fin

View solution