Egidio Marotta

An advanced engine thermal management system: nonlinear control and test

Internal combustion engine thermal management system functionality can be enhanced through the introduction of smart thermostat valves and variable speed electric pumps and fans. The traditional automotive cooling system components include a wax based thermostat valve and crankshaft driven water pump. However, servo-motor driven valves, pumps, and fans can better regulate the engines coolant fluid flow to realize fuel economy gains and tailpipe emission reductions. To study these cooling system actuators, with accompanying nonlinear control strategy, a scale experimental system has been fabricated which features a smart valve, electric coolant pump, radiator with electric fan, and immersion heater. In this paper, mathematical models will be presented to describe the systems behavior. A nonlinear controller will then be designed for transient temperature tracking. Representative experimental results are presented and discussed to demonstrate the smart valves operation in maintaining the temperature within a neighborhood of the target value for various scenarios including highway mode, full power with load disturbance, and quick heat.

Flow Structure and Enhanced Heat Transfer in Channel Flow With Dimpled Surfaces: Application to Heat Sinks in Microelectronic Cooling

The use of dimple technology for improvement in friction factors and enhancement of heat transfer has been attracting the attention of many scientists and engineers. Numerical and experimental studies have shown there is a positive improvement (two-fold on average) in Nusselt number when dimpled surfaces are compared to flat plates, and this improvement is achieved with pressure drop penalties that are small when compared to other more intrusive types of turbulence promoters. When arrays of specific dimple geometry are used, pressure drop penalties are roughly equivalent to the heat transfer improvement. This, at least theoretically, will enable the design of smaller heat transfer devices such as heat sinks, which are especially appealing in those applications where size is an important design factor. A literature review of numerical modeling and experiments on flow over dimpled surfaces was performed, and key parameters and flow structure were identified and summarized. With these premises, a numerical model was developed. The model was validated with published experimental data from selected papers and fine tuned for channel flow within the laminar flow regime. Subsequently, the model was employed for a specific application to heat sinks for microelectronic cooling. This paper, then, provides a comparative evaluation of dimple technology for improving heat transfer in microelectronic systems.

Enhanced automotive engine cooling systems: a mechatronics approach

Internal combustion spark ignition and diesel engines are used worldwide to meet societys need for transportation and mobile power generation. The cooling system is responsible for thermal management of the engine block, under-hood components, and passenger compartment. The majority of production vehicles use a thermostatic valve and belt-driven water pump whose operation is fixed with respect to the coolant temperature and the engine speed, respectively. However, transient engine operation, environmental changes, and product life-cycle events should be accommodated by the cooling system to enhance thermal efficiency while maintaining engine performance and vehicle driveability. In this paper, a mechatronic thermostatic valve is presented for a continual on-line motor and CVT-based mechanical water pumps are discussed in terms of adjustable fluid flow rates. The operation of current thermostat valves are introduced followed by the design of an ECU controlled solenoid or dc servo-motor thermostat actuator. A multi-node resistor-capacitor nonlinear thermal model is presented to estimate the thermal behaviour of cylinder components. The proposed control algorithm manages the coolant flow rate to regulate engine temperature while offsetting possible abnormal combustion effects, oil lubrication issues, and anticipatory driving demands. Numerical results are presented and discussed to demonstrate the validity and functionality of the automotive mechatronic system for thermal regulation.

Thermal Periodic Contact of Exhaust Valves

Internal combustion engines generate exhaust gases at extremely high temperatures and pressures. As these heated gases exit through the exhaust valve, the valve and valve seat insert achieve comparable temperatures. To avoid damage, heat is transferred from the exhaust valve to the valve seat insert as they come into contact with each other during the opening and closing cycle. Modern engine management systems regulate the thermal process through coolant and/or airflow rates, fuel injection, and ignition timing, and exhaust gas recirculation contributions to achieve satisfactory tradeoffs between power, emissions, and efficiency for various engine speeds and loads. One of the primary functions of the engine control unit is the prevention and detection of abnormal combustion to prevent severe engine damage. The online estimation of cylinder component temperatures offers an opportunity for greater engine control measures. A nonlinear dynamic thermal model is presented to describe the transient and steady-state phenomena in the engines cylinder using a lumped parameter resistance-capacitance network. The model prediction of the engines thermal behavior establishes a foundation to explore thermal periodic contact issues. Representative experimental and numerical results will be presented and discussed.

Study of Laminar Forced Convection Heat Transfer for Dimpled Heat Sinks

An investigation was conducted to determine whether dimpled surfaces could improve the heat transfer in a heat sink under laminar airflows. This was accomplished by performing experimental and numerical investigations using two different dimple geometries: 1) circular (spherical) and 2) oval (elliptical or trenched) dimples. Dimples with a relative pitch of S/D = 1.21 and relative depth of δ/D = 0.2 (e.g., circular dimples) were machined on both sides of copper plates, then placed into a channel with airflow impinging over the leading edge of the plate. For oval dimples, similar ratios with the same total depth and circular edge-to-edge distance as the circular dimples were used. For those configurations the average heat transfer coefficient and Nusselt number ratio were determined experimentally. Heat transfer enhancements up to a 6% relative to a flat plate were consistently observed for Reynolds number (based on channel height) in the range of 500 to 1650 on both circular and oval dimples. Additionally, pressure drop, thermal performance, and flow characteristic were simulated numerically. The heat transfer coefficients in our numerical experiment were close to those of the experimental investigation for Reynolds number up to 750. The pressure drop over the dimpled plates was either equivalent to or less than that of the flat plate with no dimples.

In-Plane Thermal Conductivity in Thin Carbon Fiber Composites

The objective of this study was to determine whether fiber type, fiber angle, and filler material affected the in-plane thermal conductivity of thin (7-15 mils thickness) carbon fiber composites. Two sets of samples were tested: low thermal conductivity samples made with polyacrylonitrile-based fibers (k = 6.8 W/m .K) in Fiberglast epoxy resin, and high thermal conductivity samples fabricated with coal-pitch-based fibers (k = 620 W/m . K) in cyanate ester resin. Samples were fabricated from 0/90 woven cloths and warped to obtain a range of fiber-pattern angles from 25/ - 25 to 65/ - 65. The filler effect on thermal conductivity was evaluated on additional samples prepared with 10% volume fraction of graphite powder in the matrix. Thermal conductivity of the low thermal conductivity samples was in the range of 15-20 W/m . K and showed up to a 15 % improvement when the angle of the fibers was varied. High thermal conductivity samples showed thermal conductivities between 60 and 150 W/m . K, with an improvement up to 60% when the angle of the fibers relative to the heat flux direction was changed from 0/90 to 25/-25. The samples with graphite powder did not show any enhancement in thermal performance. As potential alternatives, unidirectional tape and eGrafs Spreadershield® foils were also tested, showing good thermal performance.

The Development of a Bonded Fin Graphite/Epoxy Heat Sink for High Performance Servers

IBM’s has recently introduced a high performance server that utilizes multichip modules that dissipate very high heat loads. Each multichip module consists of four microprocessor chips encased by a copper cap that serves to spread the heat load over an area of roughly 113 mm × 113 mm. The module is air cooled by a single aluminum alloy bonded-fin fan sink. For applications requiring the microprocessors to operate at higher frequencies, the aluminum heat sink, with its lower thermal conductivity, cannot provide sufficient cooling; therefore, a copper heat sink must be employed. However, copper alloys have the disadvantage of a significant weight penalty (density ∼ 8.9 g/cm3 ), being 3.3 times heavier than aluminum (density ∼ 2.7 g/cm3 ), and is significantly more costly to manufacture. A novel approach for an improved heat sink has been developed using a new natural graphite-based/epoxy composite material. This material has low density (∼1.9 g/cm3 ) and anisotropic thermal conductivity (∼370 W/m-K in two directions, ∼ 7 W/m-K in the third direction). Bonded fin manufacturing methods have been developed to produce a heat sink that exploits the material’s high thermal conductivity when used in combination with a copper spreader module, such as used in the IBM server. Convective heat sink thermal performance approaching that of copper (e.g. 0.030 °C/W) has been achieved at a fraction of copper’s weight. Therefore, additional hardware required to allow the copper heat sinks to withstand shock and vibration standards, was not necessary with the lightweight graphite solution. Mechanical issues involved with using the lower strength graphite materials in a metal retrofit situation had to be resolved. Solutions included the use of aluminum end plates to provide edge protection to the heat sink with metal stiffeners inserted into the base for extra structural integrity. A variety of mechanical attachment methods was evaluated to join the graphite to the copper heat spreader. Lapping procedures were developed for the graphite heat sink to provide the required flatness necessary to minimize the temperature drop across the interface.Copyright

Characterization/Modeling of Wire Screen Insulation for Deep-Water Pipes

The amount of oil consumption has been rapidly increas ing around the world; consequently , industries have expanded to offshore exploration in to deep sea waters . At sea floor depths , pipe insulation is essential to prevent the blockage with in the pipe due to paraffin build -up within crude oil . To maintain a proper inner crude oil temperature , ab ove the paraffin formation point, insulation techniques have been used to overcome the thermal issue , but these technologies still have limitations. In this study, the objective was to develop an analytical model for a wire screen joint which contained bo th nonconforming and conforming interfaces , and then compare the predicted results to experimental measured data for validation. The experimental study for this novel insulation techn ology consisted of a coaxial pipe fabricated from P110 -4140 steel with a low conductivity wire screen (Stainless Steel) as the interstitial insulation material inserted at the annulus .

Thermal Performance of Silicon-Die/Water-Cooled Heat-Sink Assembly: Experimental Investigation

The heat flow across a high-powered silicon-die and water-cooled heat-sink assembly is a very important thermal challenge in many microelectronic applications. A single silicon thermal-die/water-cooled experimental facility was fabricated, and a successful experimental program was conducted. Heretofore, unpublished experimental thermal resistance data are presented for two commercially important interstitial materials over a pressure range of 103.4-210.4 kPa (15-30 psi). These results were then compared to thermal resistance data for helium gas, which was flowing at the interface between the two contacting solids. The pressure range employed represents actual operating conditions in an important microelectronic application, which involves chip functionality testing such as silicon burn-in and extended run-in functional operations.

Thermal Modeling of a Multilayer Insulation System

An analytical investigation of a novel multilayer insulation concept was conducted using an extended analytical model. This model was developed to accommodate a multilayer screen wire insulation system with interstitial shim layers. The goal of this study was to provide a simplified model for evaluating this insulation system, which included either a single or multilayer composite structure in order to predict optimal performance. With the present model, the feasibility and performance characteristics of the insulation concept were predicted. The thermal predictions have demonstrated a very good comparison with previously published experimental data. By adding a radiative resistance to the model, improved performance predictions of overall thermal resistance/conductance were possible, leading to the extension of single layer analytical model to multiple-layered cases. From the parametric study, the key thermophysical property of the screen wire was found to be the wires thermal conductivity. The present model provided excellent performance prediction capability for other screen wire materials, and these results were also validated with a comparison to previously published experimental results.