过程装备与控制工程专业毕业(设计)论文外文资料翻译

过程装备与控制工程专业毕业(设计)论文外文资料翻译内容摘要：

i is inside surface area of test tubes, Rwall is the thermal resistance of the tube wall. The tube side heat transfer coefficients αi were obtained by Wilson plot technique.(10) 武汉工程大学邮电与信息工 程学院毕业设计 6 It is found that the constants in correlation 13 and 14 are slightly larger than the wellknown constant of the Dittus−Boelter correlation remended to calculate heat transfer coefficient in smooth tube for turbulent flow. The reason is that microribs are formed in the inner surface of test tubes when the fin tubes are manufactured by the extrusion process, and heat transfer coefficients of the tube side are improved. The shellside Nusselt number can be obtained depending on the shellside heat transfer coefficient from the following equation: dr is the outer diameter of the fin tube at the fins root, λoil is the oil thermal conductivity. The shellside Reynolds number and Euler number are defined as follows: where umax is the maximum velocity of oil through the tube bundle. To find it, the minimum cross section area Amin must be evaluated. This is given as where Di is the shell inside diameter, dc is the central tube outside diameter, S is the baffle spacing, and PT is tube pitch. An uncertainty analysis of the experimental results has been carried out. Experimental uncertainties in the shellside Nusselt and Euler number were estimated by the procedure described Kline and McClitock.(11) The highest uncertainties of Nu and Eu are 177。 % and %, respectively. 4 Results and Discussion Experiments were performed under the condition that the shellside pressure drops were lower than 100 kPa. Figure 4 shows the variation of the shellside Nusselt number (Nu) with product of Reynolds and Prandtl number (RePr) for helically baffled heat exchangers with low fin and ribshaped fin tubes. It can be observed from Figure 4 that Nu increases with the increasing of RePr for both low fin and ribshaped fin tubes, and Nu increases more rapid with RePr for ribshaped fin tubes than lowfin tubes. Based on RePr range, the shellside Nusselt number of the helically baffled heat exchanger with ribshaped fin tubes is − times as large as that of the helically baffled heat exchanger with lowfin tubes. The heat transfer rate is enhanced because the outside surface area of ribshaped fin tubes is larger than that of lowfin tubes, and ribshaped fin tubes have repeatedly interrupted flow passages along 武汉工程大学邮电与信息工 程学院毕业设计 7 the circumferential direction of tube outside surface that create successive entrance regions resulting in the periodic boundary layer disruptions and promoting vortex shedding. Furthermore, this threedimensional finned geometry of the ribshaped finned tube is able to induce highly threedimensional vorticity and good crossflow mixing. Figure 4. Variation of Nu with Re •Pr. The variation of the shellside Euler number (Eu) with RePr for helically baffled heat exchangers with low fin and ribshaped fin tubes is shown in Figure 5. The same trend in the variation of Euler number is also observed for different values of RePr. The shellside Euler number of helically baffled heat exchanger with ribshaped fin tubes is about 10% higher than that of helically baffled heat exchanger with lowfin tubes. Figure 5. Variation of Eu with RePr. Compared the experimental data in Figure 4 with Figure 5, it can be found that the increase in heat transfer is significantly greater than that of the increase in pressure drop at constant RePr for ribshaped fin tubes. The following correlations are suggested for Nu and Eu (as described in literature(12)), on the shell side of shellandtube heat exchanger with one shell pass and two tube passes in the form of On the basis of experimental results, suggested values of a and m are given in Table 2. These correlations are suggested for the range of RePr for different tubes as follows. For lowfin tubes: For ribshaped fin tubes: Equations 19 and 20 give very good agreements with experimental results for ribshaped fin and lowfin tubes。 the standard deviations (Δav) are shown in Table 3. 武汉工程大学邮电与信息工 程学院毕业设计 8 Table 3. Standard Deviations of Equations 19 and 20 Δav % correlation lowfin tube ribshaped fin tube eq 19 eq 20 5 Conclusions This paper presents the experimental work carried out to pare the shellside Nusselt and Euler numbers of a helically baffled heat exchanger with ribshaped fin tubes to those with lowfin tubes for oil cooling using water as a coolant. Both the values of Nu and Eu increase with the increasing RePr for a helically baffled heat exchanger bined with ribshaped fin tubes and lowfin tubes, and Nuincreases more rapidly with an Re •Pr increase for ribshaped fin tubes than lowfin tubes. Based on the constant RePr, the values of Nu and Eu of a helically baffled heat exchanger with ribshaped fin tubes are about − and times as large as that of a helically baffled heat exchanger with lowfin tubes, respectively. The increase in heat transfer is significantly greater than that of the increase in pressure drop for ribshaped fin tubes. A simple correlation was presented for the determination of the shellside Nusselt。