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

半干式或近干式加工的一种是最小润滑量。机械加工被认为是一种生态技术。在该方法中，在几cc/h的植物油的基础上，用混合的润滑剂切割材料。在加工过程中，这种液体还可以作为冷却剂。本文通过实验和分析研究了用工业加工油和水进行雾冷却时的传热特性。重点研究了雾滴尺寸、雾滴速度和液体质量通量对雾滴冷却传热特性的影响。在常温下，用纯铜缸和工业加工油或纯水与空气的雾流进行了稳态传热实验。液体流速分别为0.3、0.9、1.8、4和l/hr；风速分别为0、40、75、120 l_N/min。实验结果表明，在每一种空气流量下，热流密度随液体流量的增加而增加。目前实验范围内的最大冷却速率为6 MW/m^2。油雾的传热机理仅为受热表面形成的液膜的冷却而不沸腾，而水雾冷却的传热机理分为非沸腾、液滴蒸发和液膜蒸发三个区域。以液体质量通量在加热器上的最大蒸发速率为研究对象，建立了水雾流的冷却极限（临界热通量- chf -）模型。油雾中的换热系数可以用向受热表面供油的显热散热量来表示。最后，通过对水雾流和油雾流的量纲分析和实验数据，导出了四种无量纲相关性。

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.