Start-up behavior of oscillating heat pipe in grinding wheel under axial-rotation conditions

Abstract

• Start-up timing behavior of AR-OHP is characterized and studied. • AR-OHP filled with acetone has a fast start-up speed followed by methanol & water. • Start-up mode turns from over-damped to under-damped/ transient mode with increase of cooling. • Centrifugal acceleration improves AR-OHP flow motion and increases start-up time. • Start-up mode becomes over-damped mode @ a =738m/s 2 and benefits temperature control. High efficiency grinding of difficult-to-machine materials can generate a good amount of heat in a short time. If the heat is not timely transferred, the accumulation of heat will cause a high grinding temperature and can be harmful to the machining quality. The oscillating heat pipes (OHP) are designed in the grinding wheel to directly transfer out grinding heat when axial rotating with the grinding wheel. To avoid sudden burnout of the workpiece in high efficiency grinding, the OHPs in the grinding wheel are supposed to dissipate a high heat flux in a very short time, therefore, such OHPs should start-up very quickly. The start-up speed of the OHP plays an important role in the grinding efficiency and quality, while the study on the start-up behavior of the OHP under axial-rotation is insufficient. Given that, the start-up process of the OHP under axial-rotation is here described and characterized, and the insurgence of the start-up is evaluated by the settling time and the rising time. Besides, the influences of the working fluids, cooling conditions, and centrifugal accelerations are studied. As expected for other kinds of OHP, also for the present OHP, the OHP filled with acetone has the shortest start-up time (20s), followed by the OHP filled with methanol (45s), while the water as the working fluid has the longest start-up time (46.5s). Along with the increase of cold air pressure, the settling and the rising time decreases significantly, e.g., for acetone, the settling time decreases by 59% - 87%. The centrifugal acceleration promotes the OHP flow motion and heat transfer, in turn, increases the start-up time. Besides, the start-up behavior turns from under-damped mode to over-damped mode, which has no temperature overshoot and is beneficial to the temperature control for thermal management in axial-rotation scenarios.