Start-up timing behavior of single-loop oscillating heat pipes based on the second-order dynamic model

Oscillating heat pipes have the potential to combine with the grinding wheel to enhance heat transfer in grinding process to avoid thermal damage of workpiece and grinding wheel. Since the time of grinding process is short, it raises a requirement for a good start-up behavior of oscillating heat pipes inside grinding wheel. In order to understand the start-up behavior, a new method is proposed based on the second-order dynamic theory to represent and evaluate start-up process. Several parameters (i.e., rising and settling time, percent-overshoot) are defined to value quantitatively the start-up process. Accordingly, three start-up modes are discovered with respect to the evaporator temperature, which are over-damped, under-damped and transient start-up modes. The start-up behavior is discussed with both pure fluids and nanofluids. Results show that as the heating power increases, the start-up speed enhances, and over-damped start-up mode develops to under-damped or transition start-up mode. The start-up speed of DI water is faster at low heating power, while acetone and nano-diamond solution without dispersant show faster start-up speed at high heating power. This methodology will help to compare the start-up timing of the OHP experiments in literatures, providing a more robust way to analyze start-up data.