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Unformatted text preview: 1 ME 416 Computer Assisted Design of Thermal Systems Fan Calculations Adiabatic Fan Using a Constant c P The actual power will be given by W = W s ideal act & & The ideal power will be calculated from ( ) 2 v 2 v + T- T c m = W 2 1 2 2 1 2s avg P, ideal & & - & & where c P,avg should be evaluated at the average temperature of the inlet and outlet, but since the temperature rise is quite small for a fan can be evaluated at the inlet temperature. The ideal exit temperature, T 2s , is calculated from the isentropic condition with P P T = T k 1- k 1 2 1 2s where k is the ratio of specific heats. The ideal power calculation can then be carried out followed by the actual power calculation. The actual exit temperature is then calculated from T = T + c W m- v 2 v 2 2a 1 P,avg act 2 2 1 2 1 & & - ME 416 CAD of Thermal Systems 2 Adiabatic Fan Using the Air Tables As before the actual power will be given by & & W = W act ideal s The ideal power now will be calculated from & & W = m h- h + v 2 v 2 ideal 2s 1 2 2 1 2 - & Again the ideal exit state is fixed from the isentropic condition, but using the air tables we now solve for the temperature part of the entropy, or s o depending on the book you are using, 2s 1 2 1 = + R ln P P & Then from the air table the value of the enthalpy, h...
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- Fall '07