Study on Thermalhydraulic Effects of Nuclear Steam Superheat for a Generic 1200-MWel Pressure-Channel Reactor

Current generation water-cooled Nuclear Power Plants (NPPs) have significantly lower thermal efficiencies than their thermal counterparts; due, partially, to their lower turbine-inlet steam temperature. Nuclear steam superheat can be implemented in a generic pressure-channel nuclear reactor to increase the temperature of the steam at the inlet of the turbine, and thus increase the thermal efficiency of a NPP. A heat flux is computed specifically for a stable SuperHeated Steam (SHS) and Pressurized Water (PW) 520 pressure-channel reactor core configuration, from which a unique temperature profile for each coolant (as a bulk fluid) is calculated. Using the coolant temperature profile of each coolant, the sheath temperature distribution is calculated, using Fourier’s law, and the fuel pellets’ axial and radial temperature profiles are determined using an analytical solution to the temperature distribution in a solid with uniform heat generation. Properties of the coolant, sheath, and fuel were calculated based on the temperature (and pressure, in the case of coolant) along the heated length of a channel. The effects on the flow rates and the differences in the required channel powers, due to the addition of the SHS channels, were also considered. To ensure safe operating parameters, the maximum sheath and fuel centerline temperatures were shown to be much lower than the operating limits. The implementation of steam superheat in a generic 1200-MWel pressure-channel nuclear reactor allows for an increase in the temperature of steam at the inlet of a turbine from ∼319°C to ∼550°C, and ultimately an increase in the thermal efficiency of the NPP by about 5–7%.

Numerical Investigation on the Flow and Heat Transfer Characteristics of the Superheated Steam in the Wedge Duct With Pin-Fins

By using the CFX software, the three-dimensional flow and heat transfer characteristics in the cooling duct with pin-fin in the blade trailing edge were numerically simulated. The effects of pin-fin arrangements, Reynolds number, steam superheat degrees, streamwise pin density and convergence angle of the wedge duct on the flow and heat transfer characteristics were analysed. The results show that the Nusselt number on the endwall and pin-fin surfaces as well as the pin-fin row averaged Nusselt number increase with the increasing of Reynolds number, while it decreased with the with the increasing of X/D. The pressure drop increases with the increasing of Reynolds number while decreases with the increasing of X/D in the wedge duct. The degree of superheat has little effect on the pressure loss in the wedge duct. A comprehensive analysis and comparison show that the highest thermal performance is reached in the wedge duct when the value of X/D is 1.5.

Numerical Investigation of Heat Transfer and Flow Characteristics in a Steam-Cooled Square Ribbed Duct

In order to increase entry gas temperature and improve the efficiency of gas turbine, steam is used as a coolant instead of air. Much research has been carried out on the closed circuit steam cooling of vanes substituted with film-cooling using compressor air in recent years. Furthermore, by studying the steam flow and heat transfer characteristics in rib ducts, this investigation focuses on establishing the basis of steam cooling technology application in complex flow field of internally-cooled turbine vane. In this paper, a report and assessment of RSM method based on SSG turbulence model is performed with commercial computational fluid dynamics software ANSYS CFX. The numerical results of heat transfer coefficient and friction factors in square channels with 90 degree rib turbulators for Reynolds numbers of 10 000, 30 000 and 60 000 are compared with the experimental data from Han’s. It is found that the obtained heat transfer coefficient distributions and friction factors match well with SSG turbulence model. In addition, the heat transfer distribution and pressure drop of steam-cooled ducts are predicted under the same work conditions by using dry real gas model. The Reynolds number could be correlated with the Nusselt number. The impact of steam physical properties on heat transfer performance are researched detailedly by respectively changing the steam superheat and entry pressure. The results indicate that the RSM method with a suitable turbulence model is valuable for the air-cooled and steam-cooled duct with the acceptable engineering accuracy (less than 20%). Comparing the cooling efficiency between steam and air under the same operation condition, the advantage of using cooling steam is evident than using cooling air. Furthermore, the efficiency of the whole gas turbine system will be greatly improved through using the closed loop steam cooling system. Changing the steam superheat and entry pressure, it has little effect on the steam flow and heat transfer characteristics. Increasing the steam overheat would raise the friction factor. Contrarily, enhancing the entry pressure would decrease the friction factor.