Investigation of Semi/Near-Dry Machining for Ecology in Thermal Engineering

一种半干式或近干式加工是最小润滑量。这项加工有望成为一项生态技术。在这种方法中，材料是用以几毫升/小时的植物油为基础混合的润滑剂进行切割的。这些液体在加工过程中也作为冷却剂。本文通过实验和分析相结合的方法，对工业加工油和水冷却雾化过程中的换热特性进行了研究。重点研究了雾化冷却过程中的换热问题，重点考察了液滴尺寸、液滴速度和液体质量流量对换热特性的影响。在常温下，利用纯铜圆柱体和工业加工油或纯水与空气的雾化流动进行了稳态换热实验。液体流量分别为0.3、0.9、1.8、4和L/小时，空气流量分别为0、40、75和120 L N/min。在本实验范围内，最大冷却速率为6 mW/m2。油雾的换热机理仅为液膜冷却，受热表面没有沸腾，而细水雾冷却的换热机理可分为三个区域：非沸腾、液滴蒸发和液膜蒸发。以加热器上液体质量流量的最大蒸发速率为研究对象，建立了细水雾流动的冷却极限(临界热流密度CHF-)模型。油雾换热系数可以用油滴对被加热表面的显热的放热能力来很好地表达。最后，通过对细水雾流动和油雾流动的量纲分析和实验数据，得到了四个无因次换热关联式。

A kind of semi or near dry machining is Minimum Quantity Lubrication. The machining is expected as an Ecological technology. In the method, material is cut with lubrication blended on the basis of vegetable oils of a few cc/h. The liquid also serves as coolant during the machining. In this study, heat transfer characteristics in mist cooling with commercial machining oil and water were investigated experimentally and analytically. Especially, the heat transfer in the mist cooling was examined focusing on the effects of droplet size, droplet velocity and liquid mass flux on the heat transfer characteristics.Steady state experiments of heat transfer were conducted using a pure copper cylinder and mist flow of commercial machining oil or pure water with air at room temperature. Liquid flow rates were 0.3,0.9,1.8,4 and l/hr, respectively ; each air flow rate was 0,40,75 and 120 l_N/min.Experimental results showed that heat fluxes increased with an increasing liquid flow rate for every air flow rate. Maximum cooling rate in the present experimental range was 6 MW/m^2. The heat transfer mechanism in oil mist was only cooling of liquid film without boiling formed on a heated surface, whereas the heat transfer mechanism in water mist cooling was classified into three regions: non-boiling, evaporation of droplets and evaporation of the liquid film. A cooling limit (critical heat flux-CHF-) model of water mist flow was presented by focusing on maximum evaporation rate of liquid mass flux on a heater. The heat transfer coefficient in oil mist was well expressed by the heat removal capacity on sensible heat of supplying oil-droplets to the heated surface. Finally, four dimensionless correlations of heat transfer were derived from a dimension analysis and experimental data for both the water mist flow and the oil mist flow.