| OCR Text |
Show In the turbulent flow field, t is nearly c viscosity t • III Substituting Eq.(l) into Eq.(S), 't H=L2/C1k 1/21 (6) equal to eddy U '0: U from assumption 2 and 1 0: L from assumption 3, above Eq.(6) can be expressed as 't H cc L2/UoL=L/Uo Hence, the scaling of keeping the resi«1ence time constant is enough to keep the macro mixing time 't H constant as same as micro mixing time. However, in the above ~erivations, an adequacy of assumption 1)-3) is not shown. Therefore, we have studied experimentally the effect of Re number on the turbulent mixing characteristics by using the cold model of free jet from circular tube nozzle which is frequently used in the practical burner and examined an adequacy of above assumptions. Consequently, we found the lower limit of Re number over which similar turbulent mixing characteristics can be maintained irrespective of Re number under the same geometrical configuration. The detai 1 of the resul t was shown in Ref .10 and resul ts were summarized as follows, 1) The analogy of the flow pattern was attained when the Reynolds number of a free jet is held above 4x104. 2) Turbulent characteristics such as relative turbulent intensi ty and integral scales are not affected by a Reynolds number of free jet over 105. 3) The rate control of turbulent mixing is the rate of turbulent energy transfer from energy containing lower-wave number eddies to higher-wave number eddies. Consequently, an adequacy of assumptions 1)-3) can be attained when the Reynolds number of a free jet was held above 105. As the results, the analogy of both the flow pattern and mixing time can be attained Simultaneously when the Reynolds number of a free jet is held above 105. 6 |
