The increasing power density of electronic devices drives the need for lighter, more compact heat dissipation devices. This research determines whether a hollow heat sink filled with fluid outperforms solid heat sinks for heat dissipation. Research on the integration of a heat spreader, heat pipe, and finned heat sink as a single component is limited. The copper and aluminum heat sinks consisted of a 4 × 4 fin array with a volume of 44.5 × 44.5 × 44.5 mm3. The working fluids were water and acetone with a 50% fill volume for the hollow copper and aluminum heat sinks, respectively. Each was tested at nine operating points (varying applied heats and air velocities). The hollow copper heat sink had similar overall heat sink thermal resistance while the hollow aluminum increased by 8% when compared to the solid copper heat sink, and the hollow heat sinks had a 2–9% lower fin array thermal resistance. The weight was reduced by 82% and the mass-based thermal resistance was 77% lower than the solid copper heat sink for the hollow aluminum heat sink. The considerable decrease in mass without significant loss in thermal resistance demonstrates the potential widespread application across technologies requiring low-weight components. In addition, the hollow heat sink design provides comparable or superior thermal performance to previous flat heat pipe solutions.

The space industry is an important aspect of current and future humanity. One of the largest cost factors for space deployment is the payload weight and volumetric constraints. Additionally, many technical aspects of space missions involve high-performance thermal management. New materials and manufacturing methods are enabling more space missions than ever before and at a lower cost than ever. We are proposing a novel design of a lightweight and flexible heat pipe that can be arranged in a helical coil that is compact for orbital launch and can fully extend and deploy once in stable orbit. The use of light weight Mylar-based flexible heat pipes (FHPs) for heat mitigation has been investigated in the past. These devices can be used to cool electronics on satellites and take up less space and weight than conventional methods. The flat Mylar based flexible heat pipes being designed, fabricated, and tested within this research are being produced using a novel approach due to the complex geometry that is necessary to have heat pipes that resemble a helix.

The noise generated by high-performance vehicles like Formula SAE (FSAE) race cars, presents a significant challenge in adhering to strict competition noise regulations. In this study two muffler designs were created: muffler design 1 and 2. Each design utilized two chambers to generate destructive interference, targeting two dominant exhaust frequencies of the Honda CBR600RR engine to maximize transmission loss and reduce sound pressure levels (SPL) below the FSAE-mandated range of 103 dBC at idle and 110 dBC at all other operating conditions. For each design, the exhaust noise and muffler performance were simulated using GT-Suite, allowing for an evaluation of noise attenuation across engine speeds. Experimental testing was conducted to validate the GT-Suite model and assess the effectiveness of muffler design 1. This testing involved measuring the SPL with a calibrated microphone, both with and without the designed muffler. Muffler design 1 was based on the dominant exhaust frequencies from the engine-out simulations while muffler design 2 was based on the engine-out experimental measurements. The simulation results showed all muffler designs were below the FSAE mandated SPL at idle and the high engine speed condition. The experimental testing showed that muffler design 1 was 7 dBC above the high engine speed FSAE mandated SPL. The experimental SPLs from engine-out and muffler design 1 were -6 to 1 dBC and 1 to 11 dBC above the idle and the high engine speed test values, respectively, from the simulations. Based on the comparison of the simulation and experimental results from engine-out and muffler design 1, the experimental SPLs were predicted to be below the FSAE requirement for muffler design 2. Therefore, muffler design 2, designed from the dominating experimental exhaust frequencies, achieved superior noise reduction compared to muffler design 1.

Electrical power is the main mode of residential energy delivery in most of the world, though many communities in the U.S and in other regions of the world are too remote and isolated to benefit from a connection to utility-scale electrical power. Additionally, the conversion from heat, to electricity, to heat suffers from major conversion losses. To reduce these losses and to offer a more effective method of transferring thermal energy directly to homes, we are proposing the use of large-scale heat pipe thermal transmission arrays. A single heat pipe is limited in its length by how far the capillary pumping force allows for the working fluid to return to the evaporator. To prevent this condition, called "dry-out", we propose that smaller heat pipes connected in series may eliminate this problem. To demonstrate this concept, we performed a series of laboratory-scale experiments to show that heat pipes in series can potentially transfer energy over greater distances than the use of a singular heat pipe. Four tests were completed under steady state conditions. In the first set, both the series heat pipes, and a single long heat were found to operate at nearly equal temperatures, when measuring the condenser end. When performing the second experiment, at a different height in the heat source, results still indicated identical condenser temperatures. This indicates that two heat pipes in series have similar thermal performance as a single, equivalent length heat pipe. Overall, the goal is to deliver efficient energy to remote locations and communities using series-connected heat pipes that are paired with concentrated solar-thermal collection systems.

Demands for more powerful and smaller electronic devices have increased the energy dissipation requirements. Accurate determination of the thermal performance of small-sized heat sinks is necessary for innovation within the heat dissipation sector. This study designed, developed, and tested an apparatus for determining the thermal performance of mini heat sinks (MHS). The test apparatus consisted of a wind tunnel, fan, heater, heater block, five temperature sensors, air velocity sensor, and a data acquisition system. A robust dataset was created by testing the heater without an MHS and testing two different MHS materials of polycarbonate (PC) and aluminum (AL) and having 16-21 repeat tests. Linear and polynomial approximations for the temperature profile were explored. For the steady-state tests, the mean and 90% confidence interval were calculated to determine statistically significant differences. The temperature gradient at the interface, rate of heat transfer, and the thermal resistances from the polynomial fit had higher variation than the linear fit. The experimentally determined heater surface temperature had a 90% confidence interval of +/- 0.3 to +/- 0.7 degrees C. The 90% confidence intervals for the thermal resistances were 1.0 to 1.5 K/W for linear and 2.3 to 6.0 K/W for polynomials. Statistically significant differences in the temperature gradient at the interface, rate of heat transfer, and thermal resistances between the bare, PC, and AL were found. Due to heat losses, the linear fit had greater precision, but the polynomial fit had greater accuracy.

Thermal Energy Storage materials, integrated with phase-change materials (PCMs), enable near-isothermal heat extraction through thermosyphons, reducing production costs and carbon emissions. Thermosyphons, with high thermal conductivities, efficiently transfer heat through evaporation, convection, and condensation, are widely utilized for various applications. Conventional PCM thermosyphons often lack sufficient contact surface areas for optimized PCM solidification. This paper proposes a thermosyphon design inspired by fractal geometry found in biological structures, specifically the corn plant, suitable for additive manufacturing. By utilizing fractal geometry, these thermosyphons promise enhanced heat exchange through increased exterior surface area and internal liquid wicking structures. A prototype, designed for household use, has been modeled with empirical and analytical methods, focusing on capillary pressure and effective thermal conductivity. Operating at 1 kW while submerged in a low-temperature wax-based PCM (melting temperature 40 degrees C), it comprises one main vertical tube and six base tubes with leaves. Full-scale production will utilize stainless steel powder additive manufacturing, incorporating radially and axially patterned rectangular channel cubes for the wicking structure. Analytical modeling confirms the system's viability with an excess pressure of 2353 Pa, showing that capillary pressure will efficiently drive liquid flow despite liquid viscous pressure losses. This innovation holds promise for significant contributions to industry and building heating system decarbonization efforts.

An ideal thermal interface materials (TIM) will minimize the resistance to the flow of heat from a heat generating object, such as an integrated circuit chip, to a heat dissipating object, such as a heat sink. Indium (In) foils, films, and preforms have been widely used as TIM in applications with high power density where efficient heat transfer is required. The use of In as TIM is limited by the propensity for voids to occur at the bond interface, the terminal thermal conductivity of In at ~86 W/mK, and In pump out during operation. This paper presents a novel approach to increasing the thermal conductivity of an In solder TIM1 by 1.54-fold, to 133 W/mK. This thermal enhancement is made possible through the incorporation of vertically (z-axis) oriented carbon fibers with extremely high thermal conductivity (900 W/mK). Beyond improvements to thermal performance, the novel approach is expected to be a "drop-in" solution which also reduces voiding and In pump out.

We study the problem of wildfire surveillance using autonomous unmanned aerial vehicles (UAVs). The objective of the UAVs is to find the maximum number of locations that are under fire, assuming that the UAVs can share their observations. We propose a deep recurrent Q-learning technique that uses these observations to make decisions for the robots, i.e., where to move next. The prohibitively large state space underlying the decision policy motivates a neural network approximation, but prior work used only convolutional layers to extract spatial fire information from the current observations. Our network also incorporates a recurrent module to capture temporal information from the history of observations. Experiments involving two simulated fixed-wing aircraft feature a more realistic physics-based wildfire propagation model than the discrete wildfire models of prior work. Results show that our proposed technique uses about 20 times less memory than the approach of prior work, while performing comparably in terms of finding the fire's locations.

Performance of thermal interface materials (TIMs), such as thermal pastes and mats, hinders the advance of integrated circuit (IC) devices. Current state-of-the-art TIMs suffer from low thermal conductivity, thick cross sections, and poor long-term performance. Gallium (Ga) and gallium-based alloys and amalgamations, in liquid and solid form, have demonstrated up to three times greater thermal conductivity than conventional TIMs, but rapidly alloy with and destroy aluminum (Al) components, which are commonly found in IC devices. In this work, we investigate the use of thin-film barrier layers on Al to prevent Ga alloying and characterize their performance through accelerated Ga exposure experiments and scanning electron microscopy. It is found that 100-nm-thick layers of the common passivation materials niobium and 304 stainless steel do not sufficiently prohibit Ga migration, but a 100 nm layer of titanium (Ti) does. No alloying is evident in Ti-coated Al samples after exposure to a liquid Ga alloy droplet at 300 °C for 168 h, 250 thermal cycles from room temperature to 150 °C with 30-min dwell, or 50 thermal cycles from room temperature to 300 °C with 2-min dwell. The results present a clear and direct path to the use of Ga and Ga alloys as TIMs through the addition of a thin inexpensive barrier layer on Al components and may enable future IC device technologies.

Thermal properties of geological materials are required for analysis and design of energy geostructures. In Florida the weathered limestone bedrock, which has highly variable engineering properties, can be found near the ground surface and its thermal properties will need to be incorporated into the design of such systems. Thermal conductivity values for split tension sized specimens were determined using a specially designed thermal apparatus. The apparatus is capable of determining four thermal conductivity values for each specimen, which provided a measure of variability of the measurements. Thermal conductivities ranged between 2.65 and 3.75 W/m-K with specimen measurement standard deviations and coefficient of variations as high as 0.415 W/m-K and 11.1%, respectively. The variability of the results can be attributed to both dissolution, which would decrease thermal conductivity, and dolotomitization, which would increase thermal conductivity. Thermal conductivity values are in the lower range of values reported in the literature.

This paper investigates the effect of the addition of natural gas (NG) and engine load on the cylinder pressure, combustion process, brake thermal efficiency, and methane combustion efficiency of a heavy-duty NG-diesel dual fuel engine. Significantly increased peak cylinder pressure (PCP) was only observed with the addition of NG at 100% load. The addition of a relatively large amount NG at high load slightly retarded the premixed combustion, significantly increased the peak heat release rate (PHRR) of the diffusion combustion, decreased the combustion duration, and advanced combustion phasing. The accelerated combustion process and increased heat release rate (HRR) at high load were supported by the increased NOx emissions with the addition of over 3% NG (vol.). By comparison, when operated at low load, the addition of a large amount of NG decreased the PHRR of the premixed combustion and slightly increased the PHRR during the late diffusion combustion. Improved brake thermal efficiency was only observed with the addition of a relatively large amount of NG at high load. The improved thermal efficiency was due to a decrease in combustion duration and the shifting of the combustion phasing toward the optimal phasing. The overall combustion efficiency of the dual fuel operation was always lower than diesel-only operation as indicated by the excess emissions of the unburned methane and carbon monoxide from dual fuel engine. This deteriorated the potential of dual fuel engine in further improving the brake thermal efficiency although the combustion duration of dual fuel engine at high load was much shorter than diesel only operation. The addition of NG at low load should be avoided due to the low combustion efficiency of NG and the decreased thermal efficiency. Approaches capable of further improving the in-cylinder combustion efficiency of NG should enable further improvement in the brake thermal efficiency.

The calorific value, flash point and cetane number were investigated for binary and multi-blends of biodiesel from cotton, jatropha and neem with diesel. A binary blend is a fuel mixture comprising biodiesel from one feedstock and diesel, while a multi-blend consists of biodiesel from two or more feedstocks and diesel fuel. Blends were made of B5, B10, B15, B20, B25 and B30 for binary blends of each biodiesel, and a replication of those blend levels for the mixed blends of cotton, neem and jatropha with fossil diesel. The calorific value of the biodiesel/diesel samples was measured using a bomb calorimeter, the flash point was determined by the ASTMD93 method using a Pensky-Martens closed cup tester and the cetane number was determined using a portable cetane/octane meter. It was established that most of the fuel samples have heating values above the American Society for Testing and Materials (ASTM) minimum and close to that of petro-diesel. All 28 fuel samples are consistent with the ASTM standards for flash point and cetane number, they are devoid of carbon deposits and inferior cooking in the CI engines, and they have the shortest ignition delay when burned in the CI engines; hence, they are suitable for use in CI engine operations. Statistical analyses of the experimental data carried out using SPSS software indicate that the data contributed equally in each category to all of the properties, and there are no significant differences between the experimental values.

Energy is a driving force for automotive applications. Reducing the energy demand of the vehicle is one method of increasing the fuel economy of a vehicle. Heavy-duty commercial vehicles have large frontal areas that provide large amounts of aerodynamic drag at highway speeds. Reducing the aerodynamic drag lowers the engine demand and therefore increases the fuel economy of the vehicle. This study tested the fuel economy and the front air velocity of a 10.7 m box truck trailing another box truck by distances of 3.1 times the truck length, 4.7 times the truck length, and 6.3 times the truck length at a highway speed of 28 m/s. The distance of 6.3 times the vehicle length was considered ‘safe’ for trailing another vehicle, whereas the distances of 3.1 times the truck length and 4.7 times the truck length were not considered safe by the United States Fire Administration. The results showed significant reductions in the air velocity in front of the trailing vehicle of 8.5%, 6.5%, and 3.8% for trailing distances of 3.1 times the vehicle length, 4.7 times the vehicle length, and 6.3 times the vehicle length respectively. The fuel economy of the trailing truck increased significantly by 7.4–8.0%, 8.2–9.0%, and 6.5%–7.7%, for trailing distances of 3.1 times the vehicle length, 4.7 times the vehicle length, and 6.3 times the vehicle length respectively. Based on a road load analysis, these fuel economy improvements indicated a reduction in the drag coefficient of the trailing vehicle of 8–10%. Therefore, a box truck trailing another box truck at a safe distance results in a reduction in the aerodynamics drag and a significant increase in the fuel economy.

Reactivity controlled compression ignition (RCCI) is a form of dual-fuel combustion that exploits the reactivity difference between two fuels to control combustion phasing. This combustion approach limits the formation of oxides of nitrogen (NOX) and soot while retaining high thermal efficiencies associated with compression-ignition (CI) engines. Theoretical and applied research has been conducted by researchers at several other institutions detailing RCCI combustion characteristics, exhaust emissions, fuel efficiency, and operability. However, the discussion of fuel property effects on RCCI combustion has been limited. Previous research on fuel properties that influence RCCI combustion have predominantly focused on the low reactivity fuel. The research presented herein was performed to determine the influences that high reactivity fuel properties have on RCCI combustion characteristics, exhaust emissions, fuel efficiency, and the operable load range.;A General Motors 4-cylinder, 1.9 liter, light-duty CI engine was converted to run on diesel fuel (high reactivity fuel) and compressed natural gas (CNG) (low reactivity fuel). The engine was operated at 2100 revolutions per minute (RPM), which is near its intermediate speed and where previous low temperature combustion (LTC) research has been performed. Two different loads were imposed on the engine, 3.6 bar brake mean effective pressure (BMEP) and 6 bar BMEP. A preliminary parametric study was conducted at each load to determine which engine control parameters had the largest effect on RCCI combustion, exhaust emissions, and fuel efficiency. From this study, a test matrix was developed that varied intake manifold air pressure (IMAP) and the location of 50 percent mass fraction burned (CA50) for the 3.6 bar BMEP load condition. At the 6 bar BMEP load condition a test matrix that varied the direct injection (DI) start of injection (SOI) timing and CA50 was developed. CA50 was controlled by adjusting the ratio of CNG to diesel (percentage CNG). The engine was operated at each point of these test matrices with nine different diesel fuels that had varying fuel properties, including cetane number (CN), aromatic content (AC), and distillation temperatures. The results from these tests were used to identify high reactivity fuel property effects on RCCI combustion characteristics, exhaust emissions, fuel efficiency, and the operable load range.;Results from the experiment demonstrated that CN of the diesel fuel had a dominant effect on nearly all facets of RCCI combustion, exhaust emissions, and fuel efficiency. RCCI operation with diesel fuels whose CN was lower than 33 resulted in substantially higher NOX emissions and in-cylinder pressure rise rates (PRRs) that limited the operable load range, compared to fuels with a CN ranging from 44 to 54. High CN diesel fuels with a low AC (<23%) required the largest percentage CNG to maintain combustion phasing, 70.5% to 78.6% of total fuel energy input as CNG at 3.6 bar BMEP and 73.4% to 83.0% at 6 bar BMEP. High CN, low AC diesel fuels also operated at the highest fuel conversion efficiency, 27.3% to 30.2% at 3.6 bar BMEP and 38.0% to 39.4% at 6 bar BMEP. Furthermore, in-cylinder PRR decreased as CN of the diesel fuel increased which would allow for higher engine loads to be achieved.

Biodiesel considerably decrease the CO and CO2 emissions and its blends reduce NOX emissions. In this work, binary blends of biodiesel from Cotton, Jatropha and Neem with diesel were prepared in form of B5C, B10C, B15C, B20C, B25C and B30C for Cotton at 5%, 10%, 15%, 20%, 25% and 30% respectively. This was similarly done for Jatropha and Neem biodiesel designated as B5J and MON, etc. A set of multi-blends of all the 3biodiesel with diesel were also prepared. The fuel samples were used to run a Cusson's 4-cylinder, stationary diesel engine with data logger system. The exhaust emissions of fuel during the combustion process were measured using IMR 1400 gas analyser to detect the composition of flue gases at 1500 rpm, 2000 rpm, and 2500 rpm engine speeds. It was found that, B2OC has the lowest exhaust temperature, lowest percentage losses, highest combustion efficiency, and lowest NOX and CO2 emissions, but highest SO2 emissions although with negligible percentage. The binary biodiesel blends are better than the multi-blends in terms of exhaust emissions reduction. (C) 2017 Elsevier Ltd. All rights reserved.

This paper compares the effects of the addition of hydrogen (H2) or natural gas (NG) on the combustion of a heavy-duty diesel engine converted to operate under gaseous fuel-diesel dual fuel combustion mode. The parameters examined include the start of combustion (SOC), heat release process, peak heat release rate (PHRR), and combustion duration. Significant positive effects on the combustion process were only observed with the addition of a relatively large amount of H2 or NG. When operated at low load, the addition of a large amount of H2 or NG reduced the heat release rate (HRR) of the premixed combustion. By comparison, the addition of a relatively large amount of H2 or NG at high load significantly increased the PHRR of the diffusion combustion. The addition of H2 has more significant impact on the PHRR than NG. The addition of NG retarded the SOC while the impact of the addition of H2 on SOC was relatively mild. The significant variation in HRR and its phasing make it necessary to further optimize the combustion of a dual fuel engine. The impact of the addition of gaseous fuel on the brake thermal efficiency was also examined and discussed. The increased thermal efficiency was only observed with the addition of relatively large amount of H2 or NG at medium to high load. The improved thermal efficiency was due to the decrease in combustion duration and the shifting of the combustion phasing toward the optimal one. The decreased thermal efficiency observed at low load was due to the low combustion efficiency of the gaseous fuel supplemented.

Gas dividers are important in emissions measurement since they continuously and accurately mix two gases to create a known gas concentration that is needed in the multi-point calibration of gas analyzers. A novel gas divider was designed using nonlinear laminar flow induced from the density change along the capillary channels due to the high-pressure drop (relative to the inlet gas pressure). The minor losses from entrance and exit effects can be ignored due to the high pressure loss from Hagen-Poiseuille's law relative to the minor losses. Small diameter wires inside of a tube were used to create capillary channels through which gas could flow. The gas divider, using nonlinear laminar flow, showed lower measurement uncertainty at high (90%) dilution levels than using linear laminar flow due to the higher-pressure drop at the same volumetric flow rates. Experiments showed the expected gas concentration from using the gas divider to be within 2% of the measured gas concentrations.