Reduced Coolant Flow Research Articles

Design and Cooling Performance of Additively Manufactured Ceramic Turbine Vanes

Abstract Ceramic materials are of significant interest in aviation and power generation gas turbine engines due to their low density and ability to withstand high temperatures. Increased cycle thermal efficiency and higher specific power output is possible by incorporating ceramic components that enable high turbine inlet temperatures and lower required cooling airflow levels. However, ceramics can be difficult and costly to form into the complex shapes used in gas turbine components, often requiring specialized multi-step processes. Furthermore, ceramic components in the hottest areas of a gas turbine, such as vanes or blade shroud seals, will still likely require cooling which is challenging to implement in conventional ceramic manufacturing approaches. Therefore, this study presents a multidisciplinary approach that investigates the design, fabrication, and overall cooling effectiveness evaluation of additively manufactured (AM), polymer derived ceramic (PDC) turbine vanes. A thermo-mechanically optimized vane design was generated, ceramic additive manufacturing of the complex cooling configuration was developed, and quantification of the increase in overall cooling effectiveness was performed in a 1X scale, high-speed facility using infrared thermography. This study produced a PDC AM process, capable of printing complex internal cooling schemes in 1X scale turbine vanes. It was found that the optimized vane more than doubled the overall cooling effectiveness observed in the baseline design, which reasonably agreed with thermomechanical optimization model predictions. Additionally, the optimized ceramic vane outperformed an identical metal vane, in terms of area averaged cooling effectiveness, suggesting that the ceramic vane could operate at reduced coolant flowrates to achieve comparable levels of cooling performance.

Experimental Study of Impact of In-Service Deterioration on Aerodynamic Performance of High-Pressure Nozzle Guide Vanes

AbstractIn this paper we experimentally evaluate the impact of in-service deterioration on the aerodynamic performance of heavily film-cooled high-pressure nozzle guide vanes from large civil jet engines. We study 15 mid-life to end-of-life parts removed from operational engines, and compare their performance to those of new parts. Deterioration features included: increased surface roughness; thermal barrier coating spallation; damaged film cooling holes; and trailing edge burn-back. We characterize and present statistics for the surface roughness. Aerodynamic measurements were performed in the high technology readiness level Engine Component AeroThermal (ECAT) facility at the University of Oxford, at engine-representative conditions of exit Mach number, exit Reynolds number, coolant-to-mainstream pressure ratio, and turbulence intensity. We present detailed experimental measurements of the coolant capacity characteristics, downstream loss, and downstream flow structures. The results show that service time has the following effects on high-pressure nozzle guide vanes: increased equivalent sandgrain roughness of (up by 1056% change); reduced coolant flow capacity (maximum change of −6.27% for film cooling holes and −24.7% for the trailing edge slot); increased overall mixed-out kinetic energy loss coefficient by (up to 33% change); leads to greater downstream flow angle variation (change of −6 deg). This is one of the first significant studies of its type in the open literature, and is an important step towards whole-life engine performance assessment.

Assay of nuclear grade primary sodium in the fast breeder test reactor for radionuclides and corrosion elements

Periodic assay of primary sodium used as a coolant in the fast breeder test reactor (FBTR) at Kalpakkam is necessary and pre-requisite for the safe and continuous operation of the reactor. Contamination of nuclear grade purity of the primary sodium is monitored either online or offline for the radionuclides and chemical impurities to ascertain the integrity of the various components. Chemical elements which can entrain into sodium due to the corrosion of structural materials is troublesome as they might clog the coolant channels resulting in to a reduced coolant flow which further leads to fuel clad failure. The corrosion elements present in the primary sodium were determined by ICP-OES and their activation products were assayed by high resolution gamma spectrometry. In case of fuel clad rupture, the fission products such as 137Cs, 134Cs, 136Cs, 131I, 90Sr, 125Sb etc. along with actinides U and Pu are released into primary sodium. This paper reports actinides, fission products, corrosion elements as well as their activation products and concentration levels present in the primary sodium of FBTR. Activity variation of one of the long-lived fission products, viz. 137Cs over the period of time, before and after fuel clad rupture is profiled and discussed.

Advanced Materials and Manufacturing Technology Developments for Extreme Environment Gas Turbine Applications

Abstract Electrical power generation is becoming increasingly reliant on gas turbines with multiple fuel capability, with research advances focusing on increased efficiency/power output and reduced emissions. Increasing gas turbine efficiency primarily requires higher operating temperatures and reduced coolant flow in the turbine flow path, which makes it challenging to increase component performance, as these will encounter high stresses and large temperature gradients. Current nickel-based alloys, which operate at operate at extreme environments, are exposed to stress caused by temperature or static/dynamic loading like creep and fatigue, oxidation and corrosion, wear, and damage due to vibrations. Higher turbine inlet temperatures are currently managed with internal/film cooling and thermal/environmental barrier coatings for hot section parts. Comprehensive solutions are needed to translate to achieve ultrahigh efficiencies, lower parts cost, reduced scrape rate, and life cycle savings. The paper discusses material developments coupled with innovative manufacturing approaches to be married with advanced design strategies to realize the needed improvements for hot gas path components. The case studies for combustion and turbine components will be presented to demonstrate the structure property relationships and improved component performance at lower cost.

Implementation and optimization of minimum quantity lubrication for machining LM4 aluminium alloy

The cooling method employed in machining processes plays a vital role in the surface quality and the efficiency of the process. Dry machining is being performed for flat milling operation on LM-4 alloy. This has resulted in poor surface roughness and increased tool wear rate. The other type of cooling installed in the industry is the flood coolant method which uses enormous coolant flow rate. Hence the scope of our project is to enhance the surface finish with reduced coolant flow rate and tool wear rate by introducing the Minimum Quantity Lubrication system which sprays a mixture of compressed air and lubricant in a form of mist at the point of operation i.e. tool workpiece interface. The optimized air pressure, siphon height and coolant concentration ratio are determined based on the results obtained from the surface roughness tests and the coolant flow rate measurements. Both single objective and multi objective optimization are done with the help of Taguchi analysis and Grey relational analysis respectively. Finally, this optimized MQL system is implemented in the Industry and its results are found to be in tune with our project outcome.

ЭКСПЕРИМЕНТАЛЬНЫЕ И РАСЧЕТНЫЕ ИССЛЕДОВАНИЯ ТЕПЛООБМЕНА ПРИ КИПЕНИИ ЖИДКИХ МЕТАЛЛОВ НА МОДЕЛЯХ ТВС БЫСТРЫХ РЕАКТОРАХ В АВАРИЙНЫХ РЕЖИМАХ

Studies of the boiling of alkali metals show that, compared with boiling water, the process of boiling liquid metals has significant features. Cooling of a fuel assembly in accident conditions when accident protection is triggered and circulation pumps are switched off (ULOF) leads to the study of fuel elements cooling at reduced coolant flow rates or even tipping circulation in fuel assemblies. There is only limited data on the boiling of sodium in fuel assemblies in these regimes. The results of a series of experiments on heat transfer and stability of circulation during boiling of a sodiumpotassium alloy on single fuel assembly models and in a parallel fuel assembly system with natural coolant circulation performed at JSC “SSC RF - IPPE” are presented. The results of comparing the data of the calculated and experimental studies are presented. The influence of the surface roughness of the fuel rods on the heat transfer and flow regimes during boiling of a liquid metal in bundles is demonstrated. The results of experimental studies of heat transfer during boiling of sodium in natural and forced convection regimes in a fuel assembly model with a “sodium cavity” located above the reactor core intended to compensate for the positive sodium void reactivity effect in emergency situations with sodium boiling are also presented. It is shown that it is possible to provide continuous sodium cooling of fuel element simulators in fuel assemblies under these conditions. The results of the generalization of data on heat transfer during boiling of liquid metals in bundles and a cartogram of the regimes of two-phase flow during boiling of liquid metals in bundles are presented. The objectives of further research are discussed.

Dryout avoidance control for multi-evaporator vapor compression cycle cooling

Two-phase cooling systems (e.g., pump-loops, vapor compression cycles) present a promising approach to the cooling of modern high power electronic systems. Such systems can achieve high coefficient of heat transfer but may incur dangerously high temperature when the imposed heat flux exceeds the critical heat flux (CHF). This paper presents a new control strategy that provides robust CHF avoidance in two-phase cooling for multiple evaporators under dynamic heat loads. This approach operates near the CHF to allow reduced coolant flow rates and greater system efficiency compared with the typical, and more conservative, open-loop or worst-case control strategies. The control architecture consists of two loops: an outer loop to determine evaporator mass flow rate demand, and an inner loop to supply and distribute the coolant using system actuators. Each control loop is implemented with feedforward based on static models as well as proportional–integral (PI) feedback controllers, and the decentralized approach allows scalable control design without the need for high fidelity nonlinear dynamic models. Simulations and corresponding experimental controller validations were conducted using a three-evaporator vapor compression cycle (VCC) testbed with transient imposed heat flux. The full closed-loop system is shown to be able to operate near CHF while avoiding CHF under transient heat flux, demonstrating both efficiency and robustness.

A feasibility study on the use of the MOOSE computational framework to simulate three-dimensional deformation of CANDU reactor fuel elements

Horizontally oriented fuel bundles, such as those in CANada Deuterium Uranium (CANDU) reactors present unique modeling challenges. After long irradiation times or during severe transients the fuel elements can laterally deform out of plane due to processes known as bow and sag. Bowing is a thermally driven process that causes the fuel elements to laterally deform when a temperature gradient develops across the diameter of the element. Sagging is a coupled mechanical and thermal process caused by deformation of the fuel pin due to creep mechanisms of the sheathing after long irradiation times and or high temperatures. These out-of-plane deformations can lead to reduced coolant flow and a reduction in coolability of the fuel bundle. In extreme cases element-to-element or element-to-pressure tube contact could occur leading to reduced coolant flow in the subchannels or pressure tube rupture leading to a loss of coolant accident. This paper evaluates the capability of the Multiphysics Object-Oriented Simulation Environment (MOOSE) framework developed at the Idaho National Laboratory to model these deformation mechanisms. The material model capabilities of MOOSE and its ability to simulate contact are also investigated.

Analysis of the Chernobyl Reactor Accident (I) Nuclear and thermal hydraulic characteristics and follow-up calculation of the accident

A follow-up calculation was made on the accident of Reactor No. 4 of the Chernobyl Nuclear Power Plant based on the literature and accident reports published by the USSR. The analysis code system used had models peculiar toa pressure tube type reactor, of which the accuracy had been verified by the experimental facilities at the O-arai Engineering Center and the tests made at the “Fugen” Nuclear Power Plant. The analysis data were prepared based on plant specifications and its operation history obtained from those published literature and accident reports. The analysis was composed of (1) a calculation of the nuclear and thermal-hydraulic characteristics, and the graphite heating and temperature distributions which were the basic data for the follow-up calculation of the accident, (2) an analysis of the plant behavior before the test started, using these basic characteristics, and (3) a follow-up calculation of the power increase which occurred after the test started. The analytical results were found to agree well with the data published by the USSR. It was confirmed from these analyses that the main factors causing the accident were the increased enthalpy at the core entrance caused by the test made at low power level and the increased void fraction due to reduced coolant flow rate, in addition to the nuclear characteristics and performance of the control system peculiar to the Chernobyl Nuclear Power Plant.

General Features of Advanced Pressurized Water Reactors with Improved Fuel Utilization

The main feature of an advanced pressurized water reactor (APWR) with improved fuel utilization is a plutonium-enriched tight lattice core integrated in an unchanged primary system of a common pres...

Analysis of the Static Power Coefficient of EBR-II with Reduced Coolant Flow

This study of EBR-II operating behavior, which began with a reexamination of the thermal analysis of fuel pins under varying rates of coolant flow, incorporates the recent interpretations of the bowing behavior of the subassemblies. The nonlinear bowing effects are combined with the linear expansion effects in equations that express the power-reactivity decrement as a function of both power and flow. Comparison with experiments indicates agreement to within a few inhours. Differentiation of the equations leads to expressions for power and flow coefficients of reactivity. The reduced flow data are used to determine an effective average thermal expansion coefficient for the fuel.