冷库用空气冷却器的经济性计算模型

为了优化结霜工况下翅片管式空气冷却器的结构设计,提出经济性分析计算模型。综合考虑换热性能、材料成本及运行费用,以单位制冷量的费用年值为目标函数,以费用年值最小为优化目标求解经济模型得到合理的空气冷却器的结构参数,分析了翅片间距、换热管管径、管排数变化对目标函数的影响,并通过一冷库案例进行实际测试验证。计算及试验结果表明:随着翅片间距的增大,目标函数先减小后增大,翅片间距为10时目标函数取极小值;在相同翅片间距的情况下管径越大,其目标函数值也越大;综合考虑换热管直径、翅片间距和管排数的影响,翅片间距为10,换热管外径为9.52,管排数为6时,目标函数取极小值。     

大高宽比散热片制造方案

以大高宽比散热片的制造为对象,给出了大高宽比散热片翅片的几种加工方法,介绍了每一种制造方法的基本原理和优缺点,对散热片的加工制造具有一定的应用价值。     

Airside fin efficiencies for finned-tube heat exchangers with forced convection

The heat transfer and mass transfer fin efficiencies were analyzed numerically to show that popular models for heat transfer fin efficiency for circular fins are not always reasonable.The numerical results show that the effective heat transfer area of a circular fin increases several times faster than that of a straight fin for the same tube radius.Then,a simple but accurate heat transfer fin efficiency model was developed and verified by numerical results for a wide range of fin designs.This model predicts...     

Exergo‐economic analysis of micro pin fin heat sinks

A parametric study of thermoeconomic performance over four micro pin fin heat sinks of different spacing and shapes was conducted. Unit cost per product exergy, relative cost difference, and exergo‐economic factor were utilized to evaluate the thermoeconomic performance. The effect of working fluid on the thermoeconomic performance was also investigated using R‐123 and water as working fluids. Unit costs per product exergy were obtained to evaluate the product costs (total exergy change between exit and inlet streams) in micro pin fin heat sinks at fixed mass flow rate and fixed pressure drop. The results of the thermoeconomic analysis were compared with the results of a past exergy performance study by the author. In the light of raw experimental data acquired from the past studies of the author, important differences between the results of exergy and exergo‐economic performances were observed. It was found that the unit cost of exergy change decreased as electrical power increased and the relative cost difference approached to unity at high electrical powers (greater than 20 W). Moreover, high exergo‐economic factor values (more than 0.5) were obtained at low electrical powers while exergo‐economic factors had a small value at high electrical powers. When looking at the effect of the working fluid, higher cost per Watts of the products (up to the double of R‐123) was obtained with water compared with R‐123 at both fixed mass flow rate and pressure drop. No significant effect of pin fin spacing on the unit cost of exergy change was observed at fixed mass flow rate, while higher unit costs (up to 102%) were recorded at fixed pressure drop for scarcely packed pin fin heat sinks. Finally, the unit cost of exergy change was found to be independent of pin fin shape at fixed mass flow rate, whereas at fixed pressure drop, the hydrofoil‐based pin fin heat sink had higher unit costs (up to 1.8 times as much) when compared with the unit costs of pin fin heat sinks having flow separation promoting pin fins. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical and experimental study on expansion forming of inner grooved tube

Inner grooved copper tubes have attracted more and more attention in recent years. In mass production of tube–fin heat exchanger plates in ACR (air conditioning and refrigeration) industry, mechanical expansion is a key forming process which joins the fins to the tubes. During the process, the spiral grooves inside the tube with thermally efficient geometries are deformed and the tube–fin joints are influenced by the groove layer. In this paper, tube expansion forming process is studied and effect of the groove shape on forming quality is analyzed. Experiments are performed with tubes of different groove types. FE (finite element) model of the forming process is developed. Influences of the key geometry parameters, such as groove height ratio, apex and helix angle, on strength of the grooves as well as tube wall thinning are investigated. Sections of the tube–fin joints are observed and the die geometry on the joining status is examined. The results indicate that helix angle has significant effect on groove height reduction while groove height ratio is the main factor influencing the deformation resistant force; outer diameter and radius of the front part of the expanding die influence the tube–fin joining status.     

Influence of geometrical factors and pressing mould wear on thermal-hydraulic characteristics for steel offset strip fins at low Reynolds number

Aiming at achieving a more comprehensive understanding of influence factors on thermal-hydraulic characteristics for high-pressure-direction type steel offset strip fins, this paper constructed a single fin core assembly test rig with lubricant oil as work media at low Reynolds number. Six fin schemes were experimentally investigated only varying in fin height and fin wavelength due to mould restrictions. Twenty fin schemes changing in fin width, fin angle, fin thickness and staggered fin wavelength were simulated for supplement, and the geometrical influences in fin performance were put forward. Both Taguchi method and uniform design were introduced to study the contribution of each geometrical factor to fin global thermal-hydraulic performance, verifying that fin wavelength and fin height have the most significant contributions. Based on signal to noise ratio distributions, fin geometries were optimized for 16% elevation of global performance at Reynolds number of 430, then the ‘cost-based fin performance’ was put forward and compared quantitatively, proving that above optimum fin scheme is also economical. Finally, mould wear influence in fin performance was tested in different wear periods of a vacuum heat-treated Cr12MoV mould pair, then three stages of initial wear, stable wear, and overdrive wear were defined based on pressing times. The influences were analyzed and regulations were deduced relating to mould pressing times and oil Reynolds number. The suggested lifetime for this type of mould pair is 1050 thousand pressing times. The paper intends for fin performance evaluation, optimization, and pressing mould improvement.     

冷拔外螺纹铜管凸筋高度与坯料壁厚之间的经验关系式

利用多元线性回归建立了冷拔外螺纹铜管凸筋高度与坯料壁厚之间的经验关系式。该关系式可对外螺纹铜管凸筋高度进行预测与控制，对外螺纹铜管冷拔工艺的制订具有参考价值。     

Condensation of vertical plate fins of variable cross section-limiting solutions

The purpose of the present theoretical analysis is to provide explicit solutions for the problem of condensation of vapours on the lateral surface of a long vertical plate fin of variable cross-section. The formulation yields solutions to the Limiting cases so that the results can be employed in the design of the condenser section of a flat plate heat pipe in which the fin is considered to be an essential element in transporting heat liberated by the condensing vapours. It is observed that the local and average Nusselt numbers depend on fin parameter, fin profile index, Rayleigh number and degree of subcooling.     

一种双自由度胸鳍仿生机器鱼

为提升机动性,设计一种由双自由度胸鳍和仿鲹科鱼尾部相结合的运动推进型仿生机器鱼。分别对机器 鱼的双自由度胸鳍、身体与尾部弹簧传动机构进行设计,采用Arduino 控制板及一体化的硅胶膜,基于电气系统控 制方案和防水密封方案,通过对CPG 单元进行建模与控制,给出机器鱼在不同运动形态下的控制方法,并通过实验 验证了方案的可行性。结果表明,该设计实现了双自由度胸鳍机器鱼直行、转弯、下潜的运动姿态。     

不同剖面形状的栅格壁对栅格翼气动特性的影响?

鉴于栅格翼相对于传统平板翼所体现的优越性,有必要研究其气动特性。栅格壁剖面形状作为一个重要的几何特征,采用数值模拟的方法,分别对不同的剖面形状进行气动分析。结果显示：剖面形状为菱形、四角形、六角形的栅格翼与矩形剖面的栅格翼相比能够很大程度的减小阻力,一定程度上增加升力,并且提高升阻比。流线型剖面的栅格翼中,菱形和四角形的栅格翼存在较好的气动性能。