Heat transfer quiz 2018

HEAT TRANSFER QUIZ

Q. 1 A hot liquid is to be cooled in a 1-1 shell and tube heat exchanger from 80 ⁰C to 50 ⁰C. Cooling water enters the tube side at 30 ⁰C, and exits at 45 ⁰C. The properties of the liquids are constant. Also, the overall heat transfer coefficient is same for counter-current and co-current modes. The percentage saving in heat transfer area for counter-current option with respect to the area of cocurrent option is ______________ (rounded off to third decimal place).

Q. 2.Economy of evaporators used for concentrating sugarcane juice is

Q. 3 Segmental baffles in a 2-4 shell and tube heat exchanger

change the flow pattern of the tube side fluid and increase the overall heat transfer co- efficient
increase the heat transfer coefficient in the shell side and support the tubes
help to reduce the thermal expansion of the tubes and increase the heat transfer coefficient in the tube side
increase the number of passes in the shell side and increase the heat transfer coefficient in the tube side

Q. 4 The wall of a pipe of radius 1 m is at a uniform temperature of 200 ⁰C, and is covered by insulation of thickness 0.1 m. The ambient air outside the insulated pipe is at 20 ⁰C and has heat transfer coefficient of 10 Wm^-2 K^-1. The thermal conductivity of the insulation material is 0.05 Wm^-1 K^-1.If the heat transfer occurs at steady state, the temperature (in ⁰C) of the outer surface of insulation is ...................... (rounded off to second decimal place).

Q. 5 Vapour bubbles are formed in the nucleate boiling regime at a frequency of 10 bubbles per second per nucleation site. There are 100 nucleation sites per m² of heating area. The latent heat of vapourization and the density of vapour under the operating condition are 1000 kJ / kg and 1 kg/m³ respectively. The diameter of each bubble is 10^-3 m. Assume that the entire heat supplied is used for vapour generation. The heat flux (in Watt per m² of heating area is............(rounded off to third decimal place)..

Q. 6 An insulated storage tank contains 1000 kg liquid of specific heat 10 kJ kg^-1 K^-1. The liquid is heated by saturated steam, condensing in helical coil at a temperature of 180 ⁰C. The heat transfer area of the coil is 0.1 m² . If the overall heat transfer coefficient is constant at 1000 Wm^-2 K^-1, then the time (in hours) required to raise the temperature of the liquid in the tank from 20 ⁰C to 80 ⁰C is ................(rounded off to second decimal place).