For flow instabilities in inverted U-tubes steam generator (SG),a dimensionless analysis is made for flow equation.Criteria of flow stabilities (characteristic Reynolds number) are derived according to small perturbation analysis.With calculation for a certain type of SG,effect of inlet fluid temperature and U-tube bend radius on the criteria are studied.It shows that the characteristic Reynolds number increases with the increase of inlet fluid temperature.Relations between U-tube bend radius under different inlet temperatures are complex.It is useful for calculation of flows as well as space distribution of reverse flow in a SG.

Contact melting around a heat source with non-isothermal wall is investigated.A theoretical model for contact melting around a horizontal cylindrical heat source,whose wall temperature varied with angle,is established.Condition of heat transfer and motion of the liquid molten in contact region are studied.Control equations of melting are established with Nusslet's liquid film theory.And analytical solution of melting velocity is obtained theoretically.It includes result published in literature about melting around the heat source with constant temperature.Melting velocity,thickness and pressure distribution of molten layer under different melting conditions are studied.Effects of temperature distribution on melting are obtained.

Melting of unfixed solid phase change material(PCM) inside a cylindrical tube was investigated.An analysis model of contact melting inside a cylinder tube with constant heat flux was established.Control equations of melting were established with Nusselt's liquid film theory,and dimensionless melting equations were obtained theoretically.Melting velocity,thickness and pressure distribution of molten layer were discussed,and they were compared with melting under Dirichlet condition to study melting law with Neumann condition.It was found that molten film thickness increases as height of solid decreases,and melting velocity decreases during melting process.Heat flux has great effect on melting while heat flux is low.