Quinn Leland

Design of a Thermal Management System for Directed Energy Weapons

A generic model was developed that can provide an estimate of the mass and volume and characterize the usefulness of thermal energy storage (TES) for various thermal management (TM) applications in advanced military aircraft. Conceptual design for low thermal duty cycle electronic heat sink applications was described. The criteria are presented for selecting a design for different end-applications. A thermal resistance model has been developed to analyze and optimize the design. It can be concluded that the heat sink design for the high-energy laser (HEL) system can have a high heat storage ability of 20 MJ, a volume storage density of 86 MJ/m 3 and a mass storage density of 77 kJ/kg. The airborne active denial (AAD) system heat sink design can have a high heat storage ability of 25 MJ, a volume storage density of 76 MJ/m 3 and a mass storage density of 69 kJ/kg. Nomenclature A = surface area of TES chambers (m 2 ) a = vapor chamber width (m) b = vapor chamber length (m) D = width of vapor channel (m) Dh = hydraulic diameter of vapor channel (m) keff = effective thermal conductivity of carbon foam and PCM (W/m⋅K) kfoam = thermal conductivity of the carbon foam (W/m⋅K) kl = thermal conductivity of the working fluid in liquid state (W/m⋅K) kPCM = thermal conductivity of PCM (W/m⋅K) kwall = thermal conductivity of the TES chamber wall (W/m⋅K) kc = thermal conductivity of the vapor chamber plate (W/m⋅K) G = mass flux (kg/m 2 .s) N = number of TES chambers mPCM = total mass of PCM present in the VCTES system (kg) mtot = total mass of VCTES heat sink (kg) Prl = liquid Prandtl number, µl cp,l / kl Pred = reduced pressure, P/Pcritical Psat = normal pressure (gage)/vapor saturation pressure (atm) (=P) Q = total heat absorption capacity of the VCTES heat sink (MJ) Qm = heat storage capacity per unit mass (MJ/kg)

Design of a Dual Latent Heat Sink for Pulsed Electronic Systems

A conceptual design of a dual latent heat sink basically intended for low thermal duty cycle electronic heat sink applications is presented. In addition to the concept, end-application-dependent criteria to select an optimized design for this dual latent heat sink are presented. A thermal resistance model has been developed to analyze and optimize the design, which would also serve as a fast design tool for experiments. The model showed that it is possible to have a dual latent heat sink design capable of handling 7 MJ of thermal load at a heat flux of 500 W/cm 2 (over an area of 100 cm 2 ) with a volume of 0.072 m 3 and a weight of about 57.5 kg. It was also found that, with such high heat flux absorption capability, the proposed conceptual design can have a vapor-to-condenser temperature difference of less than 10°C with a volume storage density of 97 MJ/m 3 and a mass storage density of 0.122 MJ/kg.

Lumped Node Thermal Modeling of EMA with FEA Validation

Abstract : The development of electromechanical actuators (EMAs) is the key technology to build an all-electric aircraft. One of the greatest hurdles to replacing all hydraulic actuators on an aircraft with EMAs is the acquisition, transport and rejection of waste heat generated within the EMAs. The absence of hydraulic fluids removes an attractive and effective means of acquiring and transporting the heat. To address thermal management under limited cooling options, accurate spatial and temporal information on heat generation must be obtained and carefully monitored. In military aircraft, the heat loads of EMAs are highly transient and localized. Consequently, a FEA-based thermal model should have high spatial and temporal resolution. This requires tremendous calculation resources if a whole flight mission simulation is needed. A lumped node thermal network is therefore needed which can correctly identify the hot spot locations and can perform the calculations in a much shorter time. The challenge in forming an accurate lumped node thermal network is to determine all the suitable thermal resistances and capacitances of the thermal network. In this paper we present an FEA-based lumped node network and its simulation of a mission profile. This model is based on a detailed FEA model to locate the hot spots, to determine the network parameters and to verify its effectiveness. The model can also deal with the nonlinear behavior of the EMA system introduced by phase-change materials (PCM) if thermal energy storage is needed, and temperature-dependent magnetic properties. This model can also be incorporated into lumped node magnetic and electric model to develop a full multi-physics, multi-scale simulation engine. This engine can accurately analyze the complete EMA system in a systematic scale and whole-mission duration.

High-Performance Electromechanical Actuator Dynamic Heat Generation Modeling

All-electric aircraft is a high-priority goal in the avionics community. Both increased reliability and efficiency are the promised implications of this move. But, thermal management has become a significant problem that must be resolved before reaching this goal. Electromechanical actuators (EMAs) are of special concern. Advanced analysis technologies such as the finite element method (FEM) and intelligent control systems such as field-oriented control (FOC) are being used to better understand the source of the heat and to eliminate as much of it as possible. This paper describes the nonlinear, lumped-element, integrated modeling of a permanent magnet (PM) motor used in an EMA. The parameters, including nonlinear inductance, rotor flux linkage, and thermal resistances and capacitances, are tuned using FEM models of a real, commercial actuator. The FOC scheme and the lumped-element thermal model are also described.

Novel nonlinear inductance modeling of permanent magnet motor

Power management has become a significant concern that must be addressed before the realization of an all-electric aircraft. Electromechanical actuators (EMAs) for flight control surfaces are of special concern. They demand high power with highly variable duty cycles and are extremely flight-critical. Dynamic, nonlinear, lumped-element modeling of permanent magnet motors provides the means to simulate with high fidelity and speed the behavior of EMAs over any given mission profile. This paper focuses on a successful technique of dynamic, nonlinear inductance modeling which is at the heart of modeling the whole EMA.

Development and Experimental Validation of a Micro/Nano Thermal Ground Plane

Heat pipes are commonly used in electronics cooling applications to spread heat from a concentrated heat source to a larger heat sink. Heat pipes work on the principles of two-phase heat transfer by evaporation and condensation of a working fluid. The amount of heat that can be transported is limited by the capillary and hydrostatic forces in the wicking structure of the device. Thermal ground planes are two-dimensional high conductivity heat pipes that can serve as thermal ground to which heat can be rejected by a multitude of heat sources. As hydrostatic forces are dependent on gravity, it is commonly known that heat pipe and thermal ground plane performance is orientation dependent. The effect of variation of gravity force on performance is discussed and the development of a miniaturized thermal ground plane for high g operation is described. In addition, experimental results are presented from zero to −10g acceleration. The study shows and discusses that minimal orientation or g-force dependence can be achieved if pore dimensions in the wicking structure can be designed at micro/nano-scale dimensions.Copyright

Dynamic Heat Generation Modeling of High Performance Electromechanical Actuator

All-electric aircraft is a high priority goal in the avionics community. Both increased reliability and efficiency are the promised implications of this move. But thermal management has become a significant issue that must be resolved before reaching this goal. Advanced analysis technologies such as finite element method and intelligent control systems such as field oriented control are being used to better understand the source of the heat and to eliminate as much of it as possible. This paper addresses the motivation behind allelectric aircraft and gives an overview of some of the considerations in cooling, simulation and modeling, and control, with an example of one control scheme which is being developed.

METAL HYDRIDE HEAT STORAGE TECHNOLOGY FOR DIRECTED ENERGY WEAPON SYSTEMS

Directed Energy Weapon (DEW) systems in a pulse operation mode dissipate excessively large, transient waste heat because of their inherent inefficiencies. The heat storage system can store such a pulsed heat load not relying on oversized systems and dissipate the stored heat over time after the pulse operation. A compressor-driven metal hydride heat storage system was developed for efficient, compact heat storage and dissipation of the transient heat from the DEW systems. The greater volumetric heat storage capacity of metal hydride material was realized into more compact design than conventional Phase Change Material (PCM) systems. Other exclusive advantages of the metal hydride system were fast thermal response time and active heat pumping capability required for precision temperature control and on-demand cooling. This paper presented the operating principle and heat storage performance results of the compressor-driven metal hydride heat storage system through system modeling and prototype testing. The modeling and test results showed that the metal hydride system can store the average heat of 4.4kW during the heat storage period of 250 seconds and release the stored heat during the subsequent regeneration period of 900 seconds.

HIGH PERFORMANCE HEAT STORAGE AND DISSIPATION TECHNOLOGY

High power solid state laser systems operating in a pulse mode dissipate the transient and excessively large waste heat from the laser diode arrays and gain material. The heat storage option using Phase Change Materials (PCMs) has been considered to manage such peak heat loads not relying on oversized systems for real-time cooling. However, the PCM heat storage systems suffer from the low heat storage densities and poor thermal conductivities of the conventional PCMs, consequently requiring large PCM volumes housed in thermal conductors such as aluminum or graphite foams. We developed a high performance metal hydride heat storage system for efficient and passive acquisition, storage, transport and dissipation of the transient, high heat flux heat from the high power solid state laser systems. The greater volumetric heat storage capacity of metal hydrides than the conventional PCMs can be translated into very compact systems with shorter heat transfer paths and therefore less thermal resistance. Other exclusive properties of the metal hydride materials consist of fast thermal response and active cooling capability required for the precision temperature control and transient high heat flux cooling. This paper discusses the operating principle and heat storage performance results of the metal hydride heat storage system through system analysis and prototype testing. The results revealed the superior heat storage performance of the metal hydride system to a conventional PCM system in terms of temperature excursion and system volume requirement.

Characterization of Paraffin-Graphite Foam and Paraffin- Aluminum Foam Thermal Energy Storage Systems

The steady-state and transient response of paraffin-graphite and paraffin-aluminum foam Thermal Energy Storage (TES) systems was investigated. The samples used were Pocofoam, Poco HTC porous graphite, and Duocel aluminum foam from ERG Aerospace. The phase change material used was 99% pure docosane. Heat fluxes of 1.1 to 9.3 W/cm 2 were applied and the thermal response was measured. Experimental determinations of thermal conductivity and thermal contact resistance were made. An analytical model was developed to predict the response of the samples. A heuristic Design Parameter is also proposed as a predictor of the efficiency of a TES system.