7,000 lb/hr of aniline is to be heated from 100 to 150 °F by
cooling 10,000 lb/hr of toluene with an initial temperature
of 185 °F in 2- by 1-in IPS double pipe hairpin exchangers
15 ft long. Pressure drops of 10 psi are allowable, and a dirt
factor of 0.005 is required. (b) How many hairpin sections
are required? (c) How shall they be arranged? (c) What is the
final dirt factor?

. For quick preparation of a cup of hot chocolate in a cafeteria, cocoa powder and sugar

are added in a cup of water and the solution is heated by direct steam injection. If the

initial temperature of all the ingredients is 15 ℃, the final temperature is 95℃, the mass

of the solution is 150g initially, and the heat capacity of the solution is 3.8 kJ/kg ℃,

calculate how much saturated steam at 110 ℃ will be used. State your assumptions.

A large cylindrical vessel is used as a batch reactor and is perfectly mixed.
The liquid inside is heated to keep the reactants at an elevated temperature.
Heat is lost through the portion of the vessel walls that is in contact with the liquid
contents, corresponding to an area of 25.9 m2
. The overall heat-transfer
coefficient, U, is 200 W m-2 K-1
.
The temperature of the ambient surroundings is 15 ºC, the mass of liquid in the
tank is 12.7 x 103
 kg, and its specific heat capacity is 3000 J kg-1 K-1. There is no
flow into or out of the tank. The contribution of any chemical reactions to the heat
balance is very small, and should be neglected.
(a) Determine the rate of heating required to keep the contents of the tank at a
steady-state temperature of 100 ºC.
[2 marks]
(b) At a given moment (at t=0), it starts to rain. This causes an increase in the
rate of heat loss from the tank, manifested in a 10% increase in the overall
heat-transfer coefficient. The ambient temperature has not changed.
i. What is the steady-state gain in the temperature of the tank
contents, in response to changes in U? 

Read all the following statements and mark the statement as your answer that best defines the heat capacity of a sample.

1. It is the amount of heat required to raise the temperature of unit mass by 1 ℃

2. It is the amount of heat required to raise the temperature of a substance by 1 ℃.

3. It is the amount of heat required to raise the temperature of a body by 100 ℃.

4. None of these