INVESTIGATION OF CONJUGATED HEAT TRANSFER FOR A RADIAL TURBINE WITH IMPINGEMENT COOLING

Radial turbine is widely used in micro-turbines, turbochargers, small jet engines and expanders, and the pursue of high system efficiency has resulted in elevated turbine inlet temperatures for some of its applications, threatening its reliability. There are, however, few cooling studies on radial turbines. This paper studies the jet impingement cooling of a turbocharger radial turbine. A small amount of air (coolant), which could come from compressor discharge cooled by an intercooler, is injected through a few jet holes on the heat shield of the turbine onto the upper part of turbine backdisc, to cool the rotor blades and the backdisc. Parameters that may affect the cooling were studied by a Conjugated Heat Transfer (CHT) numerical simulation using steady flow calculations. The influences to the cooling effects by different coolant-to-turbine mass flow ratios, Coolant-to-turbine inlet temperature ratio, number of the jets etc. were analysed by a steady flow simulation. The simulation results show that, when four jet holes are placed at blade leading edge radius, using 1.0% ~ 3.0% of the main gas mass flow of coolant, the average temperature on leading edge, inducer hub and backdisc surface is reduced by 2K ~ 17K,27K ~ 65K and 51K ~ 70K respectively. Turbine efficiency is mostly reduced little over 1% point.

Numerical Investigation of Conjugated Heat Transfer of the Plate-Type Fuel Assembly in the Research Reactor

In nuclear reactors, the research of conjugated heat transfer between the fuel and coolant in the fuel assembly is fundamental for improving the safety, reliability and economy. The numerical approach based on Computational Fluid Dynamics (CFD) can be used to realize the rapid analysis of the conjugated heat transfer. Besides, the numerical simulation can provide detailed physical fields that are useful for the designing and optimizing of the fuel assembly. The plate-type fuels are generally used to enhance heat transfer in research reactors with high power density. In this study, a standard plate-type fuel assembly in the research reactor was taken into consideration. The solid-fluid conjugated heat transfer of the fuel assembly and coolant was numerically investigated. In the fluid region, the subcooled flow boiling simulation model was established by implementing the Rensselaer Polytechnic Institute model into the Euler multi-phase flow method. The results show that the conjugated heat transfer of the fuel assembly and coolant can be simulated using the model established in this work. The influence of fluid velocity, power density and the width of the flow channel on the temperature distribution and the conjugated heat transfer was investigated and discussed.