Higher Convective Coefficient Research Articles

Analysis of the surface roughness and cutting tool wear using a vapor compression assisted cooling system to cool the cutting fluid in turning operation

One of the major challenges in machining is controlling the temperature in the cutting region. Cutting fluids can be used to prolong tool life because of their cooling and lubricating abilities. The properties of the cutting fluid and the manner in which it is applied will vary to prevent problems caused by thermal distortions within the parts. Temperature control during machining makes it possible to meet the tolerances for shape, size, and finish required in the parts’ specifications. Among the various cooling methods used in machining, the most notable are nanofluids, cryogenic systems, and refrigerated compressed air. This study presents a vapor compression refrigeration system to cool the cutting fluid in the liquid state. This method is advantageous due to its reduced cost and ease-of-application when compared to cryogenic systems. In addition, the liquid has a higher convective coefficient than compressed air, making the thermal exchange more efficient. In this study, the vapor compression refrigeration system is used to stabilize the temperature of the cutting fluid during machining of SAE 1045 steel with a CNC lathe. Ten test bodies were machined during the study, five using the fluid temperature control system and five without. The machining parameters used in the experiment were: cutting speed =180 m/min, feed rate =0.2 mm/rotation and depth =1 mm. The results were evaluated by analyzing temperature evolution, surface finish through medium roughness Ra, and tool wear by means of scanning electron microscopy. Among the principal conclusions reached, it was verified that refrigerated cutting fluid presented better performance with regard to surface finish and tool wear, showing that the proposed method is an excellent alternative to cryogenic systems and those that use refrigerated compressed air.

Numerical Analysis of Natural Convection and Radiation for Tube Solar Receiver With Glass Window

Conjugate laminar natural convection heat transfer and air flow with radiation of tube solar receiver with glass window were numerically investigated. The discrete ordinate method was used to solve the radiative transfer equation. And the three-dimensional steady-state continuity, Navier–Stokes, and energy equations were solved. The temperature difference based on environment and high temperature surface of receiver is varied from 100 K to 1000 K. The influence of the surface emissivity, heating temperature, convective coefficient, and convective temperature of environment on the heat transfer from the receiver with glass window has also been investigated. The numerical results indicated that the highest temperature of glass window increases and the high temperature area becomes wide, with the temperature of heating wall and surface emissivity increasing. Adopting higher convective coefficient of glass window can reduce the peak magnitude of temperature distribution on glass window of tube receiver up to 45%.

Hybrid liquid metal–water cooling system for heat dissipation of high power density microdevices

The recent decades have witnessed a remarkable advancement of very large scale integrated circuits (VLSI) and electronic equipments in micro-electronic industry. Meanwhile, the ever increasing power density of microdevices leads to the tough issue that thermal management becomes rather hard to solve. Conventional water cooling is widely used, but the convective coefficient is not high enough. Liquid metal owns much higher convective coefficient and has been identified as an effective coolant recently, but the high cost greatly precludes its large scale utilization. In this paper, a hybrid liquid metal–water cooling system which combines the advantages of both water and liquid metal cooling was proposed and demonstrated. By utilizing a liquid metal “heat spreader” in front of the water cooling module, this system not only owns more excellent cooling capability than that based on water alone, but also has much lower initial cost compared with absolute liquid metal cooling system. A series of experiments under different operation conditions have been performed to evaluate the cooling performance of this hybrid system. The compared results with absolute water cooling and liquid metal cooling system showed that the cooling capability of the new system is competitive with absolute liquid metal cooling, but the initial cost could be much lower. The theoretical thermal resistance model and economic feasibility also have been analyzed and discussed, which shows that the hybrid liquid metal–water cooling system is quite feasible and useful.