Heat Transfer

231. In counter flow compared to parallel flow,

1. LMTD is greater
2. Less surface area is required for a given heat transfer rate
3. Both (A) and (B)
4. More surface area is required for a given heat transfer rate

232. In evaporators, lowering the feed temperature

1. Increases the heating area required
2. Reduces the economy
3. Both (A) and (B)
4. Decreases the heating area required

233. In forced circulation, the heating element is injected

1. Internally
2. Externally
3. Both (A) and (A)
4. Neither (A) nor (B)

234. In forced convection, the heat transfer depends on

1. Re, Pr
2. Re, Gr
3. Mainly Gr
4. Re only

235. In forced convection, the Nusselt number is a function of

1. Re and Pr
2. Re and Gr
3. Pr and Gr
4. Re and Sc

236. In Fourier's law, the proportionality constant is called the

1. Heat transfer co-efficient
2. Thermal diffusivity
3. Thermal conductivity
4. Stefan-Boltzmann constant

237. In Joule's experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms^-2. Neglecting the heat capacity of agitator, the temperature of water (in °C) is

1. 40.5
2. 34.4
3. 26.8
4. 25

238. In natural convection heat transfer, the correlating parameter is the

1. Graetz number
2. Eckert number
3. Grashoff number
4. Bond number

239. In pipe flow, heat is transferred from hot wall to the liquid by

1. Conduction only
2. Forced convection only
3. Forced convection and conduction
4. Free and forced convection

240. In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred

1. Through a metallic wall
2. By direct contact of hot flue gas with air
3. By heating an intermediate material (like chequor bricks) and then heating the air from this hot material
4. None of these