管壳式换热器速度场及其振动情况分析毕业论文外文翻译(编辑修改稿)

管壳式换热器速度场及其振动情况分析毕业论文外文翻译(编辑修改稿)内容摘要：

w by a factor of 2–3. Surely, these considerable differences for onethroughflow will bee lower in real heat exchangers, depending on the number of flow sections. It is the object of this investigation to find a bination of the two methods A and B, getting a safe prediction of the ―measured‖ critical volume flow rates. MODEL FOR THE VELOCITY DISTRIBUTION AND THE FLOW AREAS The model does not describe the true velocity distribution, but the equivalent velocities, . the excitation force on themost endangered tube will be approximated. In figure 5, the basic data of the model for determining the distribution of the equivalent velocities and the corresponding flow areas in the second tube row are shown. L is the support length of the tubes and s is length of the chord in the second tube row. The model has been developed and tested for a central position of the inlet nozzle and for a symmetrical mode shape function. It assumes that the most endangered tube is located in the center of the nozzle. Three flow sections with partial constant velocities have been distinguished in the model: maximum flow under the inlet nozzle with the crosssectional area Fq1 and the equivalent velocity u1. All other velocities are referred to this highest value, . the velocity ratio lower positive flow with the crosssectional area Fq2 and the velocity ratio possible negative recirculation flow with the crosssectional area Fq3 and 3 D u3=u1. The flow rate in the partial section III is about 2�10% of the total flow rate, but the equivalent velocity is negligible, since the mode shape function _ is nearly zero. The reduction of the flow area by Fq3 is more important. So, the equivalent velocity u3 was assumed to be zero. The first condition is the assumption, that the true velocities each partial section r. For example, the equivalent velocity u1 in figure 5 is calculated by taking into account the velocity distribution ucr:.z/ and the mode shape function : If the reduced nozzle diameter dS=L is high, then no recirculation occurs and L2 D L. The length L2 can be determined by the ―measured‖ flow distribution. In figure 6 the velocity distribution in the tube gaps, refered to the velocity in the nozzle vS, for one geometry is illustrated. The marked line shows the velocity distribution for the most endangered tube in the tube gap No. 1. At the intersection of this line with the neutral point line, the length L2 can be found. The profiles of the velocities in the tube gaps Nos. 2 and 3 are very similar。 the values are negligibly lower. The tube gap No. 4, placed outside the nozzleprojection area shows significant lower velocity values, which reduce further for the tube gaps Nos. 5 and 6. Figure 6 contains also the values of the length L1=L and the equivalent velocities u1=vS and u2=vS, calculated by the model equations. The results for the reduced flow length L2=L of all investigated tube bundles are illustrated in figure 7. To avoid recirculation, the nozzle diameters have to exceed values dS _ .0:33 to 0:5/L, depending on the pitch ratio . The following functions for the reduced length L2 could be obtained: In order to determine the jet expansion factors X, the reduced volume flows are plotted over all variants of X. Figure 8 shows an example. The searched solutions are found for such values of the jet expansion factor, where the volume flow rate, calculated by the model, is equal to the critical volume flow rate, calculated by STARCD. There are two solutions, but the solutions at the lower X values are not。