In heat exchanger design, one transfer unit means

• A. Condition when the change in temperature of 1?C numerically equals the average driving force.
• B. The equivalent length of tubes in case the heat exchange was for a temperature difference of 1?C
• C. One fluid exchanging with another fluid of the same chemical composition
• D. The section of heat exchanger where heat transfer surface area is one square metre
• E. The section of heat exchanger which will cause temperature drop of one degree centigrade