【正文】 tion is considerably reduced when the two rows of three cells each are separated by a distance of two cells. Further separation does not reduce recirculation much. By placing two rows of three cells each side by side, recirculation is relatively high as shown in figure . 內(nèi)蒙古工業(yè)大學(xué)本科畢業(yè)論文 18 Figure : Recirculation in cooling tower consisting of two rows of three cells located side by side. If the two rows of three cells are separated by one cell width only a relatively small reduction in maximum recirculation is experienced as is shown in figure . Based on these results it may be concluded that a row of induced draft cooling tower cells should be arranged inline with the prevailing wind direction. A high air outlet velocity and the addition of a diffuser will also tend to reduce recirculation. Bender et al. [97BE1] numerically analyzed the air flow into a counterflow induced draft cooling tower consisting of two adjacent cells of the type shown in figure (b) with a view to reducing or eliminating ice formation at the tower inlet during windy periods in winter. The dimensions of the tower they studied were m (width), m (length) and m (height) with an intake height of m. The stack or diffuser diameter was m and its height was m. Ice buildup tends to be most prevelant at the windward facing intake where the entering air flow rate is higher than on the leeward intake. By placing a 10 percent porous wall m in height, m in front of the cooling tower inlet, the air flow entering on either intake was found to be essentially the same. Tesche [96TEl] conducted model tests to determine the effect of recirculation and interference on the performance of rows of induced draft hybrid cooling tower cells (similar to the unit or cell shown in figure ). His results are applicable in cases where the wind velocity distribution is given by Vw/Vwr = (Z/Zr). It is found that the recirculation of individual cells in a row consisting of twelve ceils varies as shown in figure . All wind speeds are specified at 10 m above ground level. 內(nèi)蒙古工業(yè)大學(xué)本科畢業(yè)論文 19 Figure : Recirculation in cooling tower consisting of two rows of three cells separated by one cell width. Figure : Re, circulation in a row consisting of twelve hybrid cooling tower cells. The lowest recirculation is observed when the wind blows in the direction of the major axis of the cell row. The influence of the number of cells under these conditions is shown in figure . 內(nèi)蒙古工業(yè)大學(xué)本科畢業(yè)論文 20 Figure : Recirculation as a function of number of cells in row. The influence of the ratio of wind speed to plume exhaust speed Vw/Vp on recirculation is shown in figure . A maximum recirculation occurs at a wind speed of 5 m/s. Figure : Recirculation as function of speed ratio. When two rows of six ceils each are placed next to each other with their major axes in parallel, the resultant average interference for different spacings between them is shown in figure . The interference for rows of twelve cells are shown in figure . 內(nèi)蒙古工業(yè)大學(xué)本科畢業(yè)論文 21 Figure : Interference for two rows of six cells at different spacings. Figure : Interference for two rows of twelve ceils at different spacings. Recirculating plume air increases the effective wetbulb temperature at the inlet to the cooling tower as shown in figure . Since this increase is not only a function of the wetbulb temperature of the ambient air, but also of the thermodynamic state of the plume air, figure is at best an indication of the trend in wetbulb temperature change. 內(nèi)蒙古工業(yè)大學(xué)本科畢業(yè)論文 22 Figure : Increase in wetbulb temperature due to recirculation. 內(nèi)蒙古工業(yè)大學(xué)本科畢業(yè)論文 1 空冷熱交換器和空冷塔 (本文譯自 MR KROGER 的空冷熱交換器和空冷塔一書 包括 ， ， ） 回流： 熱空氣在空冷換熱器中會出現(xiàn)回流現(xiàn)象，因此，會降低冷卻效率，圖 所示，為一個“ X”型空冷熱交換器，在無風(fēng)的情況下，有浮力的水蒸氣在換熱器中垂直上升。 回流分析： 考慮到空冷熱交換器中回流現(xiàn)象的發(fā)生，對此，要進(jìn)行系統(tǒng)的分析。 1211 2/ ao pvp ?? ? () 2處的凈壓可以表示為 ()， 2/2222 vpp aa ??? () 此時(shí)， ()。考慮到換熱器在出口處會形成一條特殊的蒸汽線，它會從 1處和回流蒸汽的出口處分開，蒸汽現(xiàn)進(jìn)入 2 位置，還有一些進(jìn)入換熱器下 Hr處，如果考慮黏度的影響，蒸汽在混合和換熱時(shí)，外界環(huán)境可以忽略， Bernoulli的公式可以在 1與 2之間應(yīng)用 ()?，F(xiàn)在報(bào)道的一些文章，是應(yīng)用數(shù)字分析的方式來解決回?zé)醿?nèi)蒙古工業(yè)大學(xué)本科畢業(yè)論文 2 流動的問題。s equation can be applied between 1 and 2 to give )(2/)(2/ 222211 rioorioo HHgvpHHgvp ??????? ???? () It is reasonable to assume that the total pressure at I is approximately equal to the stagnation pressure of the ambient air at that elevation . 1211 2/ ao pvp ??? () At2 the static pressure can be expressed as 2/2222 vpp aa ??? () 內(nèi)蒙古工業(yè)大學(xué)本科畢業(yè)論文 3 Furthermore, for the ambient air far from the heat exchanger 21 2 araa pgHp ?? ? () Substitute equations (), () and () into equation () and find gvHr 4/22? () Due to viscous effects the velocity at the inlet at elevation Hi is in practice equal to zero. The Velocity gradient in this immediate region is however very steep and the velocity peaks at a value that is higher than the mean inlet velocity. Examples of numerically determined inlet velocity distributions for different outlet velocities and heat exchanger geometries are shown in figure [95DU1]. Since most of the recirculation occurs in this region the velocity v2 is of importance but difficult to quantify analytically. For 1)2/( ?ii HW it will be assumed that v2 can be replaced ap