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Sindo Kou 《Metallurgical and Materials Transactions A》1981,12(12):2025-2030
Based on the finite difference method and the enthalpy model of Shamsundar, a computer model was developed to describe the
steady state, two-dimensional heat flow during the welding of thin plates. In order to allow accurate computations of the
weld pool configuration, the size of the mushy zone and the temperature distribution near the heat source, a grid mesh of
variable spacings was used. The heat of fusion, the size and distribution of the heat source, the temperature dependence of
thermal properties, the heat conduction in the welding direction and the surface heat loss during welding were considered.
The model was first checked with Rosenthal’s analytical solution of welding heat flow using pure aluminum for examples. Experimental
results of 6061 aluminum, including the width of the fusion zone and the thermal cycles at positions in both the fusion and
the heat affected zones, were then compared with the calculated results of the heat flow model. The agreement was very good.
Finally, in order to demonstrate systematically the quantitative effect of welding parameters such as the heat input, the
welding speed and the preheating of the workpiece, a series of computations were made based upon 6061 aluminum. 相似文献
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Zhanquan Hao Weiqing Chen Carsten Lippold 《Metallurgical and Materials Transactions B》2010,41(4):805-812
The heat transfer behavior between mold and slab changes when titania is absorbed into the mold flux during the continuous
casting of titanium-stabilized stainless steel. The trend and the extent of this effect were investigated in the laboratory.
Furthermore, to investigate the effect of titania on heat transfer, the effect of titania on the crystallization properties
of the mold flux was studied. The results showed that with an increasing titania content of mold fluxes, the heat transfer
coefficient and the heat flux of the slag film increases, whereas the heat transfer resistance decreases; the effect is that
the growth and crystallization temperature of the cuspidine crystallites in the slag are suppressed by the absorption of titania. 相似文献
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板式换热器的研究现状及进展 总被引:2,自引:0,他引:2
讨论了发展板式换热器的意义,介绍了国内外板式换热器的发展历程及现状,论述了一些目前研究采用的新技术和新方法.最后对板式换热的未来进行了展望,指出板式换热器在广泛的领域将大有作为. 相似文献
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作为一种工作机理独特的新型传热装置,脉动热管具有极高的传热效率、较高的抗烧干能力、良好的环境适应性,且结构简单、可变,成本较低,具有很高的实际应用价值,是目前传热技术领域的研究热点.本文在对脉动热管的优点、结构形式和工作原理进行总体介绍的基础上,首先从理论建模研究入手归纳了目前研究中通常采用的直管、单弯头管、部分单弯头管等结构模型和质量-弹簧-阻尼模型,质量、动量、能量方程模型以及其他数学模型,然后从实验可视化研究和计算可视化研究两方面综述了脉动热管的运行过程、工作机理以及近年来国内外在脉动热管方面的最新研究进展,从启动性能、传热性能和传热极限三方面系统介绍了管径、长度、截面形状、加热方式、充液率、倾斜角度、输入功率和工作流体种类等不同设计和使用参数对脉动热管性能的影响.进一步从设计与应用方面,对脉动热管在电子设备、太阳能集热、动力装置热管理和低温环境换热等方面的研究进行了综述,展示了脉动热管在实际应用中的效果和优势.最后对今后的研究方向与发展趋势进行了展望,指出可通过更详细的理论和仿真建模研究脉动热管的工作机理、工作性能、工作过程和优化设计方法. 相似文献
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O Plattner T Ikeda DI Sessler R Christensen M Turakhia 《Canadian Metallurgical Quarterly》1997,85(4):899-906
Forced-air warming during anesthesia increases core temperature comparably with and without thermoregulatory vasoconstriction. In contrast, postoperative forced-air warming may be no more effective than passive insulation. Nonthermoregulatory anesthesia-induced vasodilation may thus influence heat transfer. We compared postanesthetic core rewarming rates in volunteers given cotton blankets or forced air. Additionally, we compared increases in peripheral and core heat contents in the postanesthetic period with data previously acquired during anesthesia to determine how much vasomotion alters intercompartmental heat transfer. Six men were anesthetized and cooled passively until their core temperatures reached 34 degrees C. Anesthesia was then discontinued, and shivering was prevented by giving meperidine. On one day, the volunteers were covered with warmed blankets for 2 h; on the other, volunteers were warmed with forced air. Peripheral tissue heat contents were determined from intramuscular and skin thermocouples. Predicted changes in core temperature were calculated assuming that increases in body heat content were evenly distributed. Predicted changes were thus those that would be expected if vasomotor activity did not impair peripheral-to-core transfer of applied heat. These results were compared with those obtained previously in a similar study of anesthetized volunteers. Body heat content increased 159 +/- 35 kcal (mean +/- SD) more during forced-air than during blanket warming (P < 0.001). Both peripheral and core temperatures increased significantly faster during active warming: 3.3 +/- 0.7 degrees C and 1.1 +/- 0.4 degrees C, respectively. Nonetheless, predicted core temperature increase during forced-air warming exceeded the actual temperature increase by 0.8 +/- 0.3 degree C (P < 0.001). Vasoconstriction thus isolated core tissues from heat applied to the periphery, with the result that core heat content increased 32 +/- 12 kcal less than expected after 2 h of forced-air warming (P < 0.001). In contrast, predicted and actual core temperatures differed only slightly in the anesthetized volunteers previously studied. In contrast to four previous studies, our results indicate that forced-air warming increases core temperature faster than warm blankets. Postanesthetic vasoconstriction nonetheless impeded peripheral-to-core heat transfer, with the result that core temperatures in the two groups differed less than might be expected based on systemic heat balance estimates. Implications: Comparing intercompartmental heat flow in our previous and current studies suggests that anesthetic-induced vasodilation influences intercompartmental heat transfer and distribution of body heat more than thermoregulatory shunt vasomotion. 相似文献
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From the normal mammary tissue of a Holstein cow in late lactation, a heat shock protein (90 kDa) was purified by ammonium sulfate fractionation and five-step column chromatography. From 70 g of tissue, 9.5 mg of this heat shock protein were obtained; samples had 98% purity and 19% recovery. The molecular mass of the 90-kDa heat shock protein was estimated to be 86 kDa by SDS-PAGE. Analysis of the amino-terminal amino acid sequence suggested that the protein had been purified as a mixture of two isoforms. The contents of the heat shock protein in cytoplasmic fractions of mammary tissues from Holstein heifers and cows at lactation and involution were measured by quantitative immunoblot analysis using rabbit antiserum raised against the purified heat shock proteins. The contents of the heat shock protein were higher in tissues from lactating cows than in those from heifers and involuting cows. The elevated concentrations of cytoplasmic 90-kDa heat shock protein in lactating tissue suggested that this protein is involved in mammary differentiation and lactation. 相似文献
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除尘系统以余热锅炉为核心,通过50t电炉第4孔将高温烟气从烟道吸出,经烟道进入燃烧沉降室,CO等可燃物燃烧、大颗粒沉降后进入余热锅炉,经热交换烟气温度降到150℃,之后进入除尘器净化,由风机排入大气。使用过程中解决了热管在线清灰、蓄热器能量平衡等一系列核心技术问题,特别是冲击波吹灰技术,从根本上解决了热管在线清灰,保证热管清洁。实现了除尘及除尘烟气热量的循环再利用和清洁生产,系统产蒸汽20t/h,年效益2000万元。 相似文献
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将发生炉煤气生产流程中高竖管改造为热管废热锅炉,介绍了工艺流程,分析了温度、阻力降、积灰等对系统的影响及应对措施,每年可产生效益120万元。 相似文献
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介绍了梅钢4号烧结机余热回收系统的工艺流程,依据传热学理论分析了余热锅炉实际蒸汽发生量低的现象。结果表明,产汽量下降的根本原因是余热锅炉热风流速低与受热面积灰严重。提出了相应的解决方案,实践证明方案有效,为其他钢铁企业解决类似问题提供了借鉴。 相似文献
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1. Noradrenaline (NA) was microinjected into the anterior hypothalamic/preoptic area(AH/POA) of unanaesthetized cats held at ambient temperatures of 10, 22 or 35 degrees C. Loci in which injection of NA caused body temperature changes were also found to be sensitive to the febrile action of PGE1. 2. At all ambient temperatures, NA caused a dose-dependent fall in body temperature. However the mechanisms by which these temperature changes were brought about varied at different ambient temperatures. In cats maintained at the higher ambient temperature, NA activated heat loss mechanisms whereas in the cats maintained in the 10degrees C environment, the major effect of NA injection was an inhibition of heat conservation and heat production mechanisms. 3. We conclude that NA acts in cats not only as an inhibitor of heat conservation and production, but also acts in an excitatory manner on an active heat loss pathway within the AH/POA. 相似文献
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T Kusumoto Y Maehara H Baba I Takahashi H Kusumoto S Ohno K Sugimachi 《Canadian Metallurgical Quarterly》1993,68(2):259-263
We have examined the enhancement of cytotoxic effects of cis-diammine-1,1-cyclobutane dicarboxylate platinum(II) (carboplatin) by hyperthermia in HeLa cells using different regimes of timing and sequence. The results were compared with those obtained with cis-diamminedichloroplatinum(II) (cisplatin). We found that cisplatin simultaneously combined with heat was the most cytotoxic toward HeLa cells of the various timing and sequencing conditions studied. On the other hand, for carboplatin, drug treatment immediately following or during heat exposure showed the greatest effect. Intracellular platinum concentration in HeLa cells treated with heat before carboplatin showed a 2.75-fold increase over that in cells treated with the drug alone. The ratios for carboplatin given before, or during heating, were 0.67 and 1.42 respectively. Simultaneous exposure of cells to cisplatin and heat led to a 1.64-fold enhancement in cisplatin accumulation, compared to 0.92- and 1.24-fold increase for cells treated with cisplatin before and after heat respectively. Although each drug exposure prior to heat was less cytotoxic toward HeLa cells than any other heat/drug combination sequences, the platinum concentration was less than seen with each drug alone. Even though heat exposure prior to and during carboplatin showed a similar toxicity, platinum concentration in cells treated with heat prior to carboplatin was higher than that in cells treated with heat and carboplatin simultaneously. Thus, increased cytotoxicity cannot always be explained on the basis of intracellular platinum concentration. It is clear however that, differing from cisplatin, exposure of cells to heat prior to or during carboplatin administration results in the greatest cell kill. 相似文献
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The influence of the temperature at which Listeria monocytogenes had been grown (4 or 37 degrees C) on the response to heat shocks of different durations at different temperatures was investigated. For cells grown at 4 degrees C, the effect of storage, prior to and after heat shock, on the induced thermotolerance was also studied. Death kinetics of heat-shocked cells is also discussed. For L. monocytogenes grown at 37 degrees C, the greatest response to heat shock was a fourfold increase in thermotolerance. For L. monocytogenes grown at 4 degrees C, the greatest response to heat shock was a sevenfold increase in thermotolerance. The only survival curves of cells to have shoulders were those for cells that had been heat shocked. A 3% concentration of sodium chloride added to the recovery medium made these shoulders disappear and decreased decimal reduction times. The percentage of cells for which thermotolerance increased after a heat shock was smaller the milder the heat shock and the longer the prior storage. 相似文献
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MM Petersen PT Nielsen A Lebech S Toksvig-Larsen B Lund 《Canadian Metallurgical Quarterly》1999,14(1):77-81
BACKGROUND: It has been rarely reported that heat stress induces an early phase of protection against oxidative damage, whereas a delayed phase of protection is shown in heat stress. To explore the early effect of heat stress against oxidative damage, we evaluated the changes in contractility, lipid peroxidation, and ultrastructure induced by hydrogen peroxide (H2O2) with or without heat stress (HS) in human skeleton muscle. METHODS: Thirty-two muscle samples were obtained from the vastus lateralis muscle of 7 subjects. These specimens were divided into three groups based on form of treatment: HS (n = 13), non HS (n = 14), and control group (n = 5). The control group was performed under identical conditions without H2O2. Specimens in the HS group were incubated at 42 degrees C for 20 min, while those in the non-HS and control groups were maintained at 37 degrees C. RESULTS: The control group showed no significant change in contractile force. Although contractile force significantly decreased 30 min after H2O2 administration in both the HS and non-HS groups, only the HS group showed apparent recovery of contractile force 60 min after H2O2 administration. Lipid peroxidation was lower in the HS group than in the non-HS group. Ultrastructural examination revealed less mitochondrial damage in the HS group compared with the non-HS group. CONCLUSION: We found that human skeleton muscle escaped cellular damage induced by H2O2 in the early phase after heat stress. These data suggest evidence for an early effect of heat stress against ischemia/reperfusion injury in human muscle. 相似文献