Guo Chaohong

Nano-Metal Film Thermal Conductivity Measurement by using the Femtosecond Laser Pump and Probe Method

Heat management at nanoscale is a critical issue across many areas of science and engineering, where the size effect of thermal properties plays an important role. We measure the transient thermoreflectance signals of thin metal films with thicknesses from 50 to 200nm by using the femtosecond laser pump and probe method, and the experimental data are combined with the parabolic two-step model to enable us to measure thermal conductivity of the thin metal films. The measurement results of Ni and Al films show that, in the thickness range from tens to hundreds of nanometer, the thermal conductivity increases with the increasing thicknesses of the films, which agrees well with the previous conclusions.

Study of the circulation theory of the cooling system in vertical evaporative cooling generator

The article briefly states the current development of evaporative cooling generator and its advantages comparing with generators of traditional cooling. Vertical evaporative cooling generator, which adopts Close-Loop-Self-Cycle with no-pump and free convection boil in the hollow stator bar, is one of the great developments in generator design. This article emphasizes the importance of cooling system in generator; expatiates the circulation theory in two aspects, energy and flow; and analyzes the essential reason, motivity and stability of Close-Loop-Self-Cycle. The article points out that the motivity of the circulation is the heat absorbed by coolant. After absorbing heat the coolant will have the ability of doing work because of the phase change. In another words, it is the buoyancy causing by density difference leads to the Close-Loop-Self-Cycle. This conclusion is validated by experimental data.