ANS:B - Backward feed

For cold viscous feed, the most suitable feeding arrangement in a heat exchanger would be backward feed. Here's why:

1. Backward Feed: In a backward feed arrangement, the coldest fluid enters the coldest end of the heat exchanger and flows in the opposite direction of the hot fluid. This configuration is beneficial for handling cold and viscous feeds because it allows the cold fluid to gradually heat up as it moves through the heat exchanger, reducing the risk of thermal shock and facilitating heat transfer in viscous fluids.
2. Forward Feed: Forward feed, on the other hand, involves introducing the coldest fluid at the hottest end of the heat exchanger and allowing it to flow parallel to the hot fluid. This arrangement may not be as suitable for cold and viscous feeds because it can result in rapid temperature changes and potentially cause issues with heat transfer in viscous fluids.
3. Mixed Feed and Parallel Feed: Mixed feed and parallel feed arrangements involve combining hot and cold fluids at different points within the heat exchanger. These arrangements are generally not preferred for handling cold and viscous feeds as they may not provide the gradual heating and optimal heat transfer conditions required for such fluids.