ANS:C - higher tube side heat transfer co-efficient.

The advantage of using a 1-2 shell and tube heat exchanger over a 1-1 shell and tube heat exchanger is typically a higher tube side heat transfer coefficient. Explanation:

1. 1-2 Shell and Tube Heat Exchanger: In a 1-2 shell and tube heat exchanger, the number "1" represents one shell pass and the number "2" represents two tube passes. This configuration means that the fluid flows through the tubes twice before exiting the heat exchanger.
2. 1-1 Shell and Tube Heat Exchanger: In a 1-1 shell and tube heat exchanger, both the shell side fluid and the tube side fluid each make only one pass through the heat exchanger.

Advantages of 1-2 Shell and Tube Heat Exchanger over 1-1 Shell and Tube Heat Exchanger:

• Higher Tube Side Heat Transfer Coefficient: By increasing the number of tube passes, the fluid spends more time in contact with the tube surface, leading to enhanced heat transfer. This typically results in a higher tube side heat transfer coefficient in a 1-2 configuration compared to a 1-1 configuration.
• Increased Heat Transfer Surface Area: The multiple tube passes in a 1-2 configuration increase the effective heat transfer surface area, promoting more efficient heat exchange between the fluids.
• Improved Heat Transfer Efficiency: With a higher tube side heat transfer coefficient and increased heat transfer surface area, the 1-2 shell and tube heat exchanger can achieve higher heat transfer rates and better overall heat transfer efficiency compared to the 1-1 configuration.

Therefore, the advantage of using a 1-2 shell and tube heat exchanger over a 1-1 shell and tube heat exchanger is typically a higher tube side heat transfer coefficient.