Yang Fei Rao

Transient characteristics of He II forced flow heated at the center of a pipe line

Numerical analysis is performed with the two-fluid model and the simplified model of Kashani et al. to study one-dimensional forced convection heat transfer of He II in a pipe heated at the midpoint along its length. An entropy transport equation derived from the theory of Khalatnitkov is incorporated into the two-fluid model. The numerical results obtained with the two models are compared with each other and with experimental data to investigate the validity of the models. In the range of parameters of concern in this paper, good agreement is observed for temperature distributions and internal convection heat fluxes obtained numerically and experimentally. Explanation is provided for the relationship between the two-fluid model and the simplified model. Conditions are discussed under which the simplified model will produce results that are in close agreement with the two-fluid model. Some interesting characteristics of transient flow and heat transfer are also presented.

A numerical model on transient, two-dimensional flow and heat transfer in He II

Abstract A new numerical model is developed to study the unique features of flow and heat transfer in superfluid helium or He II. The model, called the simplified model, is derived from the original two-fluid model. It consists of a conventional continuity equation, a momentum equation for the total fluid in the form of a modified Navier-Stokes equation, and an energy equation in the form of the conventional temperature-based energy equation, in which the heat flux due to Gorter-Mellink internal convection is properly incorporated. To verify the validity of the simplified model, the analytical results by the simplified model are compared with those by the original two-fluid model in the analysis of one-dimensional heat transfer in a vertical He II duct heated at the bottom boundary. To demonstrate the capability of the present model for multi-dimensional problems, two-dimensional analysis is performed for internal-convection heat transfer in an He II pool with one of the walls partially heated. The two-dimensional results obtained by the present model are also compared with that by the modified two-dimensional model by Ramadan and Witt.

Numerical study of flow and heat transfer of superfluid helium in capillary channels

Abstract A modified two-fluid model is adopted to study flow and heat transfer of superfluid helium in a microchannel with a diameter as small as that of a superleak in a fountain effect pump. Variable properties of superfluid helium and energy dissipations due to the two-fluid mutual friction and the friction at the channel wall are fully taken into consideration. It is found that the normal fluid component flow is not trivial even in a channel with diameter of a micrometre, and that there exists an optimum diameter for the maximum mass flow rate. The flow of superfluid helium through a channel with different temperatures at the ends differs considerably from that of a Newtonian fluid. The strong dependence of the thermodynamic properties on temperature and pressure, as well as the internal-convection mechanism are found to be the causes of the unique flows.

On the Mechanism of the Geysering in a Double Tube Thermosyphon

An experimental study has been carried out to investigate into a two-phase flow instability called the “geysering”. The regions are divided by the frequency and amplitude of pressure fluctuations caused by periodical bubble nucleations and its expansions. Experiments are conducted with a double tube closed thermosyphon which is made of glass to make visual observation possible. As the working fluid R113 is adopted. The mechanism of the geysering is described based on the visual observation of the phenomena as well as on the transients of temperature distributions of the outer tube.