In recent years increasing the heat transfer coefficient has been the main problem of the researchers and increasing the internal heat transfer coefficient has a special importance. For receiving to this goal different methods were used. One of these methods for increasing the internal heat transfer is using different shapes of disks in tube. Of course using these disks in tube will cause to increase the pressure loss. In this investigation have been tried to study the effect of wooden disks, that were placed in a tube with fixed wall temperature in regular space, on heat transfer and pressure loss in the range of Reynolds number between 4000 to 40000. Also with defining the Performance Evaluation Criterion (P.E.C.) as a relation between heat transfer and pressure loss economic use of disks have been studied. For receiving to this goal two groups of disks including ring-shaped and not hollow disks have been considered. According to the earned results ring-shaped disks have better P.E.C. than not hollow disks. In this investigation angle of disks relative to the flow direction have been studied. According to the earned results disks that have placed at angle 45 relative to flow direction have a better P.E.C. than vertical disks. In all disks in the mentioned range of Reynolds number increasing the Reynolds number will cause to decreasing P.E.C. and the maximum value of P.E.C. happens near Re=4000. The maximum values of P.E.C. are 1.85 in elliptical hole disks and 1.91 in rectangular hole disks
