HEAT TRANSFER IN BIOPROCESS Question Papers (Regular, 2008)

SET : 1

1. A plate of thickness L and thermal conductivity k is exposed to a fluid at a temperature Tα1 with a heat transfer coefficient h1 on one side and Tα2 and h2 on the other side. Determine the one dimensional temperature distribution in the plate. Assume steady state and constant conductivity.

2. Fuel oil on a tank is to be heated from 288.5 K to 316 K by means of steam coil. The oil has a poutr point below 288.5 K. This oil stands in the tank and circulates only by natural convection. Exhaust steam is used and it leaves the coil at atmospheric pressure but not cooled below 373 K. The film heat transfer coefficient for fuel oil is 18.26 W/m²K and the heat transfer coefficient for condensation steam is 4070 W/m²K. The fouling factors for oily steam is 0.215 m²K/W and for fuel oil is 0.123 m²K/W. The coil is required to heat 2250 kg/h of specific heat 3.35 Kj/KgK. The inside diameter of pipe is 40 mm and the outside diameter 48 mm. Caculate,

a) The over all co-efficient of heat transfer

b) The heat transfer surface area.

3. You are anxious to drink your cup of coffee; however, it is too hot. If you stir the coffee with a spoon and set it in a circular motion, will it cool at a faster rate? Explain in detail.

4. What is the difference between film wise condensation and drop wise condensation?

5. In an extended surface heat exchanger, the heat transfer area increased by 50% by putting a sleeve on a cylindrical pipe, and the overall heat transfer coefficient decreased by 10%. The heat transfer coefficient of the pipe is 0.75 KW/m²C, and the temperature difference is 50 C. Find the heat transfer rate for the extended surface heat exchanger for unit area of the cylindrical pipe.

6. What is the boiling point elevation of salt solution and driving force for heat transfer?

Data : salt solution boils at a temperature of 380 K (107 C) and boiling point of water at a pressure in the vapour soace is 373 K (100 C)

Temperature of condensing steam is 399 K (126 C)

7. Distinguish between sterilization and pasteurization.

Explain about continuous sterilization process.

A certain fermentation medium was sterilized in a fermenter. The heating-up took 30 min from 100 C and the cooling took 15 minutes from 121 C to 100 C. The ∆ factor value is ∆_1̊/min =12.55. The thermal death constant K_{121 C} is 2.54 min^-1. The ∆ for sterilization is 43.5. Find ∆_holding and holding period.