Thermal Considerations Research Articles

Optimizing thermal comfort considerations with electrical demand response program implementation

Maintaining thermal comfort within an occupied building requires energy; thus, optimized solution methods for balancing energy use with indoor environmental quality (adequate thermal comfort, lighting, etc.) are needed. Current building temperature control systems do not adequately take in account the adaptive capability of the occupants, but this concept can be used advantageously during implementation of demand response. Demand response programs can affect both the occupants’ thermal comfort from temporary adjustments to space temperature settings. This paper describes ongoing research and field testing of methods to optimize building energy consumption for heating, ventilation and air conditioning applications accounting for human factors such as the thermal comfort by the occupants. Model predictive controllers could serve as powerful tools to optimize the operation of smart buildings and improve human comfort perceptions while helping to better integrate renewable energy systems with increased grid stability. Practical application: This work outlines how the operation of cooling systems can be optimized with respect to reducing peak demand while still maintaining thermal comfort within acceptable ranges.

State of Art on Minimum Quantity Lubrication in Grinding Process

Most of the machining process use cutting fluids for better cooling and lubrication, which ensures good machinability at low specific energy consumption. However, the conventional cutting fluids pose serious health hazards to operators along with environmental pollution. Furthermore, the cost incurred in the purification and disposal of cutting fluids is sometimes greater than the cutting tool. Grinding process involves higher specific energies, which give rise to high heat generation in grinding region and the penetration ability of liquid grinding fluids (flood cooling) into the contact zone becomes poor. Therefore, attention towards alternative methods of cutting fluid application has bolstered owing to the operational and environmental cost pressures. Various studies have shown that a prominent substitute to flood cooling in grinding is minimum quantity lubrication (MQL) grinding or near dry grinding (NDG). In this study, the performance parameters of MQL grinding are reviewed in terms of surface quality, grinding forces, wheel wear, thermal considerations and ecological safety. Moreover, MQL can be a viable alternative to dry and flood cooling in grinding process.

Temperature Effect on the Mechanical Properties of Very High Performance Concrete

This study aims at a better understanding of the behaviour of very high performance concretes (VHPC) subjected to high temperatures. The temperature increase within the concrete originating from the hydratation exothermic reaction of cement is emphasized by the mass effect of the structures and can lead to thermal variations of around 50°C between the heart and the structures walls. These thermal considerations are not without consequence on durability and the physical and mechanical properties of very high performance concrete, such as the compressive strength. This work is an experimental research that shows the effects of temperature on the mechanical properties of very high performance concrete (VHPC) and compares them with those of conventional concrete and HPC. Test specimens in usual concrete, HPC and VHPC are made, preserved till maturity of the concrete, and then subjected to a heating-cooling cycle from room temperature to 500°C at heating rate 0.1°C/min. Mechanical tests on the hot concrete and cooling (air and water) were realized. The results show that the mechanical characteristics of VHPC (density, compressive strength, tensile strength and elastic modulus) decrease with increasing temperature, but their strength remains higher than that of conventional concrete.

Normally-OFF GaN MIS-HEMT With F− Doped Gate Insulator Using Standard Ion Implantation

A normally-OFF GaN metal-insulator-gate high electron mobility transistors with fluorine doped gate insulator has been fabricated using standard ion implantation technique. Fluorine ions with negative charges were doped lightly into both the gate insulator and the partially recessed barrier layer, resulting in high positive threshold voltage ( ${V} _{\mathrm{ th}}$ ) for the device, meanwhile preserving low ON-resistance. Compared to the fluorine-free and recess-free device, only about 16% increase of ON-resistance was observed for the F− doped devices. The fabricated F− doped device exhibits a threshold voltage of +0.68 V at ${I} _{\mathrm{ DS}}= 5~\mu \text{A}$ /mm, a current density of 620 mA/mm, an OFF-state breakdown voltage of 800 V, and high ON/OFF current ratio of 1010. For thermal stability consideration of fluorine dopant, the ${V} _{\mathrm{ th}}$ -thermal stability test and positive bias temperature instability test were also discussed.

Network Temperatures and Flow Rate: Case Study of District Heating in Canberra, Australia

The purpose of this paper is to highlight the relevance of district heating (DH) in the country where, in general, there is no such system and, specifically, to develop and implement a helpful approach for designing a DH network combining thermal and hydraulic considerations to simulate the energy behaviour of such network. The nonlinear model of the supply and return temperatures describes the dynamics of a DH system with an appropriate accuracy. The results of the generated scenarios are partial load values obtained for each category. The data on the daily heating power demand was transformed into an outdoor temperature dependence curve used to compute the flow rate for each of the scenario. Under the designed condition, the flow is determined and regulation approaches are elaborated. The resulting flow is quite stable. Taking into account the deficiencies of conventional evaluation for DH networks, this study excludes the hypothesis of constant outdoor temperature, and analyzes the influence of outside temperature on the heat losses and electricity consumption for DH networks based upon the state-space method. The obtained results are achieved without significant investments into a DH system just by adjusting and controlling temperatures and flow rates of a heat radiator circulating in the network.

RF and Thermal Considerations of a Flip-Chip Integrated 40+ Gb/s Silicon Photonic Electro-Optic Transmitter

We demonstrate a flip-chip integrated electro-optic transmitter incorporating a high-swing CMOS driver and silicon photonic Mach–Zehnder modulator, and discuss the RF and thermal characteristics of the assembly. The transmitter showed a dynamic extinction ratio of 8 dB, which is the highest to date for 40+ Gb/s-class transmitters using CMOS drivers with silicon modulators. The input reflection coefficient of the module was mostly determined by the input electrical lines, solder bumps, and driver, while the electro-optic transfer function was mostly set by the Mach–Zehnder modulator. Despite the high power consumption of the driver and modulator (553 mW) and the close proximity between the electronic and photonic dies, the thermal simulations show that heat can be efficiently sunk from the bottom side of the silicon photonic die.

Do ring-necked snakes choose retreat sites based upon thermal preferences?

Biochemical reaction rates are highly sensitive to temperature, and the body temperatures of ectotherms covary with their immediate environment. Therefore, ectotherms should choose microhabitats that permit the maintenance of physiological function. While some previous studies have found that squamate reptiles choose retreat sites that allow them to maintain physiologically optimal body temperatures, this research has been limited in context and taxonomic scope. We sought to test these empirical patterns by studying the properties of retreat sites in the context of physiological preferences and tolerances in a population of semifossorial ring-necked snakes (Diadophis punctatus). We measured environmental temperature distributions of retreat sites, field body temperatures, thermal preferences, and both upper voluntary temperature and critical thermal minima of snakes. We found that ring-necked snakes are under larger and warmer rocks, but that body temperatures in the field do not match thermal preferences measured in the laboratory. Specifically, we found aggregated ring-necked snakes (those occurring with multiple conspecifics) select rocks providing environmental temperatures averaging 3°C higher than their preferred temperature. By contrast, solitary snakes select rocks that allowed them to maintain their body temperatures very close to their preferred temperatures. These results imply that there is substantial within and among-species variation in the role of thermal considerations in retreat-site selection. Our work also highlights the complex tradeoffs between physiological and ecological requirements that organisms must navigate in heterogeneous habitats.

Inorganic Thin Film Deposition and Application on Organic Polymer Substrates

This review details the emerging area of inorganic thin film coatings on polymer substrates, from examples of applications through to the fabrication processes and the underlying growth mechanism(s). Of particular focus is the use of physical vapor deposition to deposit thin metal and/or metal oxide films onto polymeric materials. This primary focus highlights an area of research, that is, gaining in popularity, as researchers attempt to provide insight into the adaption of a well‐established manufacturing process to be compatible with the ever expanding range of polymer substrates. The motivation for doing so comes from the evolution of existing industry (i.e., the semi‐conductor sector) to fabricate new devices (i.e., flexible electronics). In addition, the research challenges faced in achieving evaporated and sputtered thin film coatings on polymeric substrates, such as mechanical and thermal considerations will be discussed.

Reactor scale study of self-heating and self-ignition of torrefied wood in contact with oxygen

This experimental work aims at investigating the potential development of self-heating when torrefied wood chips enter into contact with oxygen. Two kilograms of dried beech chips have been torrefied under nitrogen in a cylindrical reactor at 250 °C or 285 °C. The temperature was then leveled down between 100 °C and 160 °C and nitrogen flow was replaced by oxygen-containing flow. Influences of oxygen volumetric fraction and sweeping gas flow rate were investigated. Temperatures at different bed locations and gaseous product volumetric fractions at the bed output were monitored continuously. In some of the experiments a limited temperature rise was observed while in others a temperature runaway occurred. Thermal considerations indicate a clear enhancement of self-heating propensity with the severity of torrefaction. Gas phase analysis and molecule oxygen balance reveal an adsorption mechanism pathway and a higher rate of oxygen adsorption for the severely torrefied wood. Lowering the oxygen volumetric fraction or increasing the flow rate decrease self-heating behavior and was used to stop self-ignition of the bed.

Thermal-aware correlated two-level scheduling of real-time tasks with reduced processor energy on heterogeneous MPSoCs

Abstract With the exponential increase in power density and the relentless scaling of transistors in VLSI circuits over the past decades, modern high-performance processors fall into a predicament of high energy consumption and elevated chip temperature. Such increased energy consumption and chip temperature could induce significant economic, ecological, and technical problems. Thus, energy-efficient task scheduling with thermal consideration has become a pressing research issue in sustainable computing systems, especially for battery-powered real-time embedded systems with limited cooling techniques. This paper tackles the above challenge through scheduling tasks leveraging correlated optimizations at two different scales. Precisely, a two-level thermal-aware energy-efficient scheduling algorithm for real-time tasks on DVFS-enabled heterogeneous MPSoC systems is developed considering the constraints of task deadlines, task precedences, and chip peak temperature limit. At the processor level, a multi-processor model supporting dynamic voltage/frequency scaling is transformed to a virtual multi-processor model supporting only one fixed frequency level. At the core level, real-time tasks are assigned to individual cores of the virtual processor under the constraints of task precedence and peak temperature limit. Through nicely interleaving optimizations at both levels, high quality task scheduling solutions can be computed efficiently. Extensive simulations of synthetic real-time tasks and real-life benchmarks are performed to validate the proposed algorithm. Experimental results demonstrate the effectiveness of the proposed algorithm as compared to the benchmarking schemes.

Enabling fast charging – Battery thermal considerations

Battery thermal barriers are reviewed with regards to extreme fast charging. Present-day thermal management systems for battery electric vehicles are inadequate in limiting the maximum temperature rise of the battery during extreme fast charging. If the battery thermal management system is not designed correctly, the temperature of the cells could reach abuse temperatures and potentially send the cells into thermal runaway. Furthermore, the cell and battery interconnect design needs to be improved to meet the lifetime expectations of the consumer. Each of these aspects is explored and addressed as well as outlining where the heat is generated in a cell, the efficiencies of power and energy cells, and what type of battery thermal management solutions are available in today's market. Thermal management is not a limiting condition with regard to extreme fast charging, but many factors need to be addressed especially for future high specific energy density cells to meet U.S. Department of Energy cost and volume goals.

LCL Filter Design of a 50-kW 60-kHz SiC Inverter with Size and Thermal Considerations for Aerospace Applications

To achieve high power density, increasing the switching frequency of the power converter has become a trend. The LCL filter is a major contributor of the overall weight of a high-power-density converter (HPDC), especially the inverter-side inductor, which requires to suppress higher frequency harmonic contents at the inverter side. This paper describes a comprehensive design flow of the LCL filter for a 50-kW, 60-kHz two-level silicon carbide (SiC) inverter for high-power aerospace applications with space constraint and harsh ambient temperature environment. To meet the space constraint requirement and reduce the inductor size, specific design attention is made on a customized amorphous cored inductor with a comprehensive study on the relationships of inductor weight, core width, and total surface area with respect to air gap length. To overcome the harsh ambient temperature environment, a liquid cooling system of the amorphous cored inductor is also described.

Power scaling in quantum cascade lasers using broad-area stripes with reduced cascade number

For many applications, optical emission power of many watts in the midinfrared part of the optical spectrum is required. Quantum cascade lasers for these applications typically contain 30 to 40 cascades and have laser ridge widths of about 10 μm. These lasers cannot, however, be readily scaled up in power. This paper demonstrates a path for further power scaling that is based on broad stripes with fewer than 15 cascades. Although the confinement factor Γ for this design approach is lower than for designs with 30 to 40 cascades, the ability to efficiently extract heat from the top and bottom of the lasers more than offsets the Γ disadvantage. We expect this approach to deliver tens of watts of power with high beam quality leading to high brilliance. The paper discusses the design approach, thermal conduction considerations, and confinement factor. Room temperature cw operation of broad-area lasers based on this approach is demonstrated and described.

Thermal considerations in the cryogenic regime for the BNL double ridge higher order mode waveguide

Brookhaven National Laboratory (BNL) has proposed to build an electron ion collider (EIC) as an upgrade to the existing Relativistic Heavy Ion Collider (RHIC). A part of the new design is to use superconducting radio frequency (SRF) cavities for acceleration, which sit in a bath of superfluid helium at a temperature of 2 K. SRF cavities designed for the BNL EIC create a standing electromagnetic wave, oscillating at a fundamental frequency of 647 MHz. Interaction of the charged particle beam with the EM field in the cavity creates higher order modes (HOM) of oscillation which have adverse effects on the beam when allowed to propagate down the beam tube. HOM waveguides are thus designed to remove this excess energy which is then damped at room temperature. As a result, these waveguides provide a direct thermal link between room temperature and the superconducting cavities adding a static thermal load. The EM wave propagating through the warmer sections of the waveguide creates an additional dynamic thermal load. This study calculates these thermal loads, concluding that the dynamic load is small in comparison to the static load. Temperature distributions are mapped on the waveguide and the number of heat intercepts required to efficiently manage thermal loads have been determined. In addition, a thermal radiation study has been performed and it is found that this contribution is around three orders of magnitude smaller than the static conduction and dynamic loads.

Manufacture and Initial Thermo-Fluid Measurements on a Heat Sink Module for Potential Applications in a DEMO

The necessity to handle heat loads in the MW/m2 range has become increasingly prevalent in a number of industries. Termed high-heat flux cooling, some of the most challenging conditions in this field occur at the first wall and divertor regions of a fusion tokamak. Steady-state heat fluxes here may reach values in excess of 10 MW/m2 in some areas for a first stage DEMO. The situation is exasperated further by the environment within the machine, which severely alters material properties with time. Even coolant choice itself can have an impact beyond thermal considerations through tritium inventory and neutron activation. Successfully addressing these issues is of critical importance to the development of commercial fusion power. A number of heat sink modules utilising jet impingement in a flat plate geometry were manufactured using diffusion bonding. Each sample produced was subject to leak and hydrostatic pressure measurements, together with further non-destructive analyses. Thermo-fluid measurements were performed on the components in a purpose built facility employing water as the coolant at pressures of up to 200 bar. To replicate the thermal boundary conditions a resistive thin-film heater technique was utilised. This allowed heat fluxes in the MW/m2 range to be applied to the modules. The results indicate that the concept may be a viable alternative heat sink candidate for first wall or divertor applications in a DEMO, but that further research is required to optimise certain aspects of the design.

Propene induced reversible deactivation effects in diesel oxidation catalysts

By applying different transient test protocols in a lab reactor, it is demonstrated that in the presence of C3H6 a Pt/Pd based oxidation catalyst experiences a persistent deactivation that can be attributed to the accumulation of propene partial oxidation products on the catalyst surface. The deactivation can be reversed by treating the catalyst at higher temperature in a hydrocarbon free atmosphere. The three most important scenarios giving rise to the activation/deactivation phenomenon are:(1) Consecutive heat-up/cool-down cycles: If several consecutive heat-up/cool-down cycles are performed with a catalyst pretreated in a propene free oxidative atmosphere, a lower ignition temperature is observed during the first heating ramp than during the following cycles. The effect can be explained by a reversible blocking of active sites by hydrocarbon (HC) intermediates, which are formed during the ignition branch, then entirely are removed after the HC ignition is completed and finally are formed again during the extinction branch, providing a deactivated state of the catalyst for the following ignition. The deactivation can be completely reversed either by a conditioning in an oxidizing HC free gas mixture at temperatures above 110°C or a conditioning in N2 above 140°C. The deactivation effect is more pronounced under conditions that lead to a low light-off temperature and completely disappears at conditions leading to higher light-off temperatures, i.e. high CO concentrations or high space velocities.(2) Light-off tests with varying temperature ramp rate: For faster ramp rates, CO/propene ignition is observed at lower inlet temperatures. This is the opposite behavior than would be expected based on thermal considerations and can be explained by a higher accumulation of HC intermediates during the slower ramp.(3) Transient observation of the deactivation effect: If an initially clean catalyst is operated at a constant temperature in the light-off range, a transient decrease in CO/HC conversion is observed that can be attributed to the gradual build-up of the blocking HC intermediates.A kinetic model is presented which considers not only the standard CO and hydrocarbon oxidation kinetics, but also the formation of site blocking intermediates by partial oxidation of propene and the removal of these blocking intermediates either by total oxidation with O2 or by thermal desorption. The model nearly quantitatively reproduces the experimental results of the different test protocols.

Electric and Hybrid-Electric Marine Ferries for Public Transportation Networks

Coastal cities and regions rely on marine vessels to ensure safe and timely transport of people within their public transportation networks. Local emissions of particulate matter and noise pollution are of increasing concern for growing cities. The UN forecasts the percentage of people living in cities will rise from 54 percent in 2014 to 66 percent in 2050 [1] when global population is forecast to reach 9.7 billion. Hence, the infrastructure built today will have to serve the growing communities of tomorrow. Li-ion battery systems within electric and hybrid-electric marine vessels offer a low cost to greatly reduce local and global emissions of particulate matter and harmful gases within vessels which are traditionally powered by combustion of fossil fuels. In this work, design considerations of Li-ion batteries within marine vessels are presented, including cathode/anode requirements, safety, and thermal management considerations. Use of a thermal, electric, aging model is implemented for a first assessment of the dimensioning of a Li-ion battery system within a marine vessel, with a specific focus on the choice of lithium titanate as anode versus the conventional graphitic anode. 1. World Population Prospects, 2014, United Nations. Figure 1

Prediction of sliding speed and normal force effects on friction and wear rate evolution in a dry oscillating-fretting PTFE/Ti-6Al-4V contact

Dry fretting wear tests were performed on a semicrystalline polytetrafluoroethylene PTFE cylinder rubbing on a flat Ti-6Al-4V surface at room temperature. Various sliding speeds and normal loads were imposed for test durations from 5×104 to 106 cycles. The purpose of the investigation was to evaluate how sliding speed and normal load influence friction and wear rate evolution for gross slip fretting-reciprocating sliding conditions. Analysis confirmed an initial transient regime related to the progressive formation of a PTFE transfer film on the titanium counterface, followed by a linear steady-state wear regime. Focusing on the steady-state wear regime, a rising staircase evolution versus sliding speed was observed for both friction and Archard's wear rate. This continuous “sigmoid” wear rate evolution was related to friction heating, inducing transition from micro to macro surface-ploughing wear damage. In addition, a discontinuous cracking wear component was observed from a threshold sliding speed (vth=12mm/s), due to friction-induced thermal activation of the crystalline phase transition then the principal transition (associated with the glass transition) of the PTFE polymer. The analysis also showed that an increase in normal load induced a parallel reduction in the coefficient of friction and parallel increase in wear rate. These parallel evolutions suggest no direct interaction between sliding speed and normal force. Hence the normal force effect can be analyzed using a (P/Pref)n weight function, where the n exponent quantifies the relative effect of normal load versus friction and PTFE wear rate. These results, which are discussed regarding former research works of Tanaka, are correlated with PTFE thermo-mechanical response, friction thermal considerations and competition between several wear processes. Finally, global wear rate could be formulated, including sigmoid (ploughing wear), bell shape (cracking wear) and weighted (normal force effect) functions. Good correlation between experiments and predictions confirmed the stability of this formulation.

Diamond‐based concept for combining beams at very high average powers

AbstractEver since the laser's invention, there has been great interest in increasing beam output power without detriment to its coherence. Despite great advances having been obtained through the use of a diverse range of approaches, steady‐state beam powers above ten kilowatts remain a significant challenge for solid‐state lasers due to the heightened impact of detrimental nonlinear effects such as thermal lensing. Multiplexing several lasers using beam combination represents a method for surpassing the power barriers of single lasers. Here we propose and demonstrate a novel approach to beam combination and power scaling based on Raman conversion in diamond. Power from multiple non‐collinear pump beams is efficiently transferred onto a single Stokes beam in a single‐pass amplifier. Using three mutually‐independent nanosecond pulsed beams from a free‐running‐linewidth 1064 nm laser, 69% of the total peak pump power of 6.7 kW was transferred onto a TEM00 Stokes seed pulse at 1240 nm in a 9.5 mm long diamond crystal. Compared to other beam combination techniques, diamond beam combination has advantages of relaxed constraints on pump beam mutual coherence, while enabling narrowband output. Thermal considerations for extending from low duty‐cycle to continuous wave operation and higher power levels are discussed. image

Thermal stabilization and permanent deformation resistance of LWA/PCM-modified asphalt road surfaces

This paper presents the results of attempts at reducing the problem of solar overheating of asphalt road pavement surfaces, resulting in weakening and accelerated destruction of the aforementioned structures.To protect pavement surfaces against periodic overheating, standard asphalt mixture AC 16 W 35/50, used for binder course, has been modified by replacing one of the aggregate fractions from the mineral mixture with lightweight aggregate (LWA) soaked in phase-change material (PCM). This modified asphalt mixture, placed under the thin standard asphalt wearing course without any modification (no LWA and no PCM), serves as a temperature and permanent deformation stabilizer of the asphalt surface layer.To ensure maintaining the highest possible resistance to permanent deformation the newly design asphalt mixture has been verified with the rutting tests. Two different asphalt packet layers have been tested. First the configuration contained only the binder course and the second test configuration-double-layered ones – comprised of binder course covered by thin wearing course.To verify the correctness of conclusions drawn from theoretical thermal considerations, experimental temperature simulation tests were conducted under laboratory conditions on two asphalt specimens with dimensions of 0.30×0.30×0.10m. The first one, standard AC 16 W 35/50, served as reference specimen, while the second one, PCM AC 16 W 35/50 containing LWA with PCM (LWA/PCM), was tested. In both cases a binder course was covered by a wearing course from stone mastics asphalt SMA without LWA/PCM. The simulations have confirmed that 3% wt. addition of PCM, in relation to the weight of the asphalt mixture for binder course, reaches a reduction in surface temperature of about 4°C in moderate laboratory conditions, within the tested temperature range between 30 and 60°C.