Ruixian Fang

System-level thermal modeling and co-simulation with hybrid power system for future all electric ship

This paper presents an approach to performing thermal-electrical coupled co-simulation of hybrid power system and cooling system of future all-electric Navy ships. The goal is to study the transient interactions between the electrical and the thermal sub-systems. The approach utilizes an existing solid oxide fuel cell (SOFC) /gas turbine (GT) hybrid electrical power model and the ship cooling system model developed on the virtual test bed (VTB) platform at University of South Carolina. The integrated system simulation approach merges the thermal modeling capacity with the electrical modeling capacity in the same platform. The paper first briefly discusses the dynamic SOFC / GT hybrid engine system combined with propulsion plant model. It then describes ship cooling system model and the interactions between the electrical and the thermal sub-systems. A simple application scenario has been implemented and analyzed to illustrate the simulation. Dynamic responses of coupled thermal-electrical systems are explored under a step change of the service load to reveal important system interactions.

Enhanced Thermal Conductivity for LWR Fuel

Abstract The thermal conductivity of the fuel in today’s light water reactors, uranium dioxide (UO2), can be improved by incorporating a uniformly distributed heat-conducting network of a higher-conductivity material: silicon carbide (SiC). The higher thermal conductivity of SiC along with its other prominent reactor-grade properties makes it a potential material to address some of the related issues when used in UO2 (97% theoretical density). This ongoing research, in collaboration with the University of Florida, aims to investigate the feasibility and development of a formal methodology for producing the resultant composite oxide fuel. Calculations of the effective thermal conductivity (ETC) of the new fuel as a function of percent SiC for certain percentages and as a function of temperature are presented as a preliminary approach. The ETCs are obtained at different temperatures from 600 to 1600 K. The corresponding polynomial equations for the temperature-dependent thermal conductivities are given based on the simulation results. The heat transfer mechanism in this fuel is explained using a finite volume approach and validated against existing empirical models. FLUENT 6.1.22 was used for the thermal conductivity calculations and to estimate the reduction in centerline temperatures achievable within such a fuel rod. Later, the computer codes COMBINE-PC and VENTURE-PC were employed to estimate the fuel enrichment required to maintain the same burnup levels corresponding to a volume percent addition of SiC.

System-Level Dynamic Thermal Modeling and Simulation for an All-Electric Ship Cooling System in VTB

A system-level dynamic simulation of a thermo-electrical coupled model for a ship cooling system was developed in the virtual test bed (VTB) platform. This paper presents dynamic simulations for two most essential cooling schemes used in the ship thermal management. One configuration is freshwater cooling with seawater as the secondary coolant. The other configuration is chilled water cooling from the ships air conditioning plants. Details of some major thermal components used in the simulations are identified. The results from these simulations clearly demonstrate the ability of the VTB environment to simulate the dynamic behavior of complex and coupled devices. The work presented in this paper provides the first step to use VTB as a potential system-level dynamic simulation platform for an all-electric ship thermal management.

Control Strategies for Start-Up and Part-Load Operation of Solid Oxide Fuel Cell/Gas Turbine Hybrid System

Control strategy plays a significant role in ensuring system stability and performance as well as equipment protection for maximum service life. This work is aimed at investigating the control strategies for start-up and part-load operating conditions of the solid oxide fuel cell/gas turbine (SOFC/GT) hybrid system. First, a dynamic SOFC/GT hybrid cycle, based on the thermodynamic modeling of system components, has been successfully developed and simulated in the virtual test bed simulation environment. The one-dimensional tubular SOFC model is based on the electrochemical and thermal modeling, accounting for voltage losses and temperature dynamics. The single cell is discretized using a finite volume method where all the governing equations are solved for each finite volume. Two operating conditions, start-up and part load, are employed to investigate the control strategies of the SOFC/GT hybrid cycle. In particular, start-up control is adopted to ensure the initial rotation speed of a compressor and a turbine for a system-level operation. The control objective for the part-load operation regardless of load changes, as proposed, is to maintain constant fuel utilization and a fairly constant SOFC temperature within a small range by manipulating the fuel mass flow and air mass flow. To this end, the dynamic electrical characteristics such as cell voltage, current density, and temperature under the part load are simulated and analyzed. Several feedback control cycles are designed from the dynamic responses of electrical characteristics. Control cycles combined with control related variables are introduced and discussed.

Performance Prediction and Dynamic Simulation of Electric Ship Hybrid Power System

A hybrid power system for future electric ship is developed in the Virtual Test Bed (VTB) computational environment for the system-level performance prediction and dynamic investigation. The power system consists of a propulsion plant and a hybrid engine subsystem. Important system components such as the compressor, gas turbine, propeller and ship are described in detail and modeled in the VTB. A physics-based one-dimensional Solid Oxide Fuel Cell (SOFC) model is introduced here specifically for higher power density and better performance. To evaluate system-level performance both statically and dynamically, the following two investigations are carried out: 1) steady-state performance of power system; 2) the transient behavior of the system under a variety of operating conditions. Simulation results show that the hybrid power system could achieve a 68% total electrical efficiency (LHV) and an electrical power output of 1.66 MW, around 30% of which is produced by the power turbine while 70% is generated in SOFC stacks.

Thermoelectric Model of a Tubular SOFC for Dynamic Simulation

A one-dimensional transient model of a tubular solid oxide fuel cell stack is proposed in this paper. The model developed in the virtual test bed (VTB ) computational environment is capable of dynamic system simulation. This model is based on the electrochemical and thermal modeling, accounting for the voltage losses and temperature dynamics. The single cell is discretized using a finite volume method where all the governing equations are solved for each finite volume. The temperature, the current density, and the gas concentration distribution along the axial direction of the cell are presented. The dynamic behavior of electrical characteristics and temperature under the variable load is simulated and analyzed. For easy implementation in the VTB platform, the nonlinear governing equations are discretized in resistive companion form. The developed model is validated with experimental results and can be used for dynamic performance evaluation and design optimization of the cell under variable operating conditions and geometric condition.

Thermal modeling and simulation of the chilled water system for future all electric ship

A system-level model for a combatant ships chilled water system is described and developed in this paper. Some major thermal components related to dynamic aspects are identified in detail. Given the vital heat load for each compartment and equipment, the steady state performances are evaluated for the normal two-loop alignment. Dynamic behaviors are also investigated at different operating conditions. Several extreme cases such as pipe rupture in the vital branch and time to overheat are also studied to evaluate the system survivability. The work presented in this paper continuous the efforts for using Virtual Test Bed as a potential system-level dynamic simulation platform for an all-electric ship thermal management.

Active Heat Transfer Enhancement in Single-Phase Microchannels by Using Synthetic Jets

The present work experimentally investigates the effect of synthetic jets on the heat transfer performance in a microchannel heat sink. The heat sink consists of five parallel rectangular microchannels measuring 500 μm wide, 500 μm deep, and 26 mm long each. An array of synthetic jets with 100 μm diameter orifices is placed right above the microchannel with a total of eight jet orifices per channel. Microjets are synthesized from the fluid flowing through the microchannel. Periodic disturbances are generated when the synthetic jets interact with the microchannel flow. Heat transfer performance is enhanced as local turbulence is generated and penetrates the thermal boundary layer near heated channel wall. The effects of synthetic jets on microchannels heat transfer performance are studied for several parameters including the channel stream flow rate, the synthetic jets strength and operating frequency. It shows that the synthetic jets have higher heat transfer enhancement for microchannel flow at lower channel flow rates. A maximum of 130% heat transfer enhancement is achieved for some test cases. The pressure dynamics introduced by the synthetic jets are also investigated. The synthetic jets cause a minor increase in the pressure drop.

Experimental Heat Transfer Enhancement in Single-phase Liquid Microchannel Cooling with Cross-flow Synthetic Jet

The present study experimentally investigated a new hybrid cooling scheme by combination of a microchannel heat sink with a micro-synthetic jet actuator. The heat sink consisted of a single rectangular microchannel measured 550 µm wide, 500 µm deep and 26 mm long. The synthetic jet actuator with a 100 µm diameter orifice was placed right above the microchannel and 5 mm downstream from the channel inlet. Micro jet is synthesized from the fluid flowing through the microchannel. Periodic disturbance is generated when the synthetic jet interacts with the microchannel flow. Heat transfer performance is enhanced as local turbulence is generated and propagated downstream the microchannel. The scale and frequency of the disturbance can be controlled by changing the driving voltage and frequency of the piezoelectric driven synthetic jet actuator. The effects of synthetic jet on microchannel heat transfer performance were studied based on the microchannel flow Reynolds number, the jet operating voltage and frequency, respectively. It shows that the synthetic jet has a greater heat transfer enhancement for microchannel flow at lower Reynolds number. It also shows that the thermal effects of the synthetic jet are functions of the jet driving voltage and frequency. We obtained around 42% heat transfer enhancement for some test cases, whereas the pressure drop across the microchannel increases very slightly. The paper concludes that the synthetic jet can effectively enhance single-phase liquid microchannel heat transfer performance and would have more promising enhancements if multi-jets are applied along the microchannel.

Evaluation of gas turbine engine dynamic interaction with electrical and thermal system

In navys future all-electric ship design, the gas turbine engine is dedicated to electrical power generation. The power is then sent to a common electrical bus for allocation to both propulsion and non-propulsion electrical loads. Thus the gas turbine engine is dynamically coupled with the electrical system, and even with the thermal system, which is usually critical for the electrical system design. It has becoming increasingly important to understand the interactions that exist between the operation of the engine and the behavior of the electrical and thermal systems. This paper presents a co-simulation approach for cross-disciplinary simulations. Such an approach is implemented by integrating a twin-shaft gas turbine model, with a power generation and distribution system, and a thermal system. In this study, the thermal system is mainly used to manage the heat generated by the power converters in the electrical system. This paper discusses potential interactions that could take place during a dynamic disturbance of the fuel flow to the gas turbine engine. Preliminary simulation results for the dynamics of gas turbine power generation, power redistribution between the electrical loads, temperatures of power converters are presented to demonstrate the modeling and simulation capability, as well as illustrating the opportunities for further research.