In the case of a shell and tube heat exchanger, the logarithmic mean temperature difference ______________________?

• A. Is always less than arithmetic average value
• B. Is always more than arithmetic mean value and the geometric mean value
• C. Is always less than arithmetic mean value, but more than geometric mean value
• D. May be either more or less than geometric mean and arithmetic mean value depending upon whether the flow of stream is co-current or counter-current