Thermal Design Considerations Research Articles

Thermal design considerations for a L-PBF built metal component: effects of Inter-Layer Cooling Time, Preheating Temperature and Gas Flow

The paper aims to investigate some important thermal effects that could affect the Additive Manufacturing (AM) process of Laser Powder Bed Fusion. This analysis starts with investigating the variation of the material substrate temperature due to a variation of the Interlayer Cooling-Time (ILCT); then, the paper analyzes the effect of Preheating temperature on the material microstructure of the first building layers. Finally, we assess the effect of variation in gas flow speed as a function of part position on the building platform. In addition, in this work, the previously mentioned thermal aspects are evaluated in detail under particular geometrical and printing conditions considered the most critical for the L-PBF process. All cases studied are performed on IN718 superalloy specimens. In particular, for ILCT investigation, 60 microns layered specimens are printed for Preheating temperature analysis 40 and 60 layered specimens and for gas flow speed evaluation 40 microns one. All the results are evaluated through a porosity and melt pool analysis. The results obtained in this work highlight a critical range for low ILCT, 2-6 seconds, for part integrity that could be affected by overheating effects. To avoid this criticality, inserting ghost parts during the printing or reducing the laser power value is suggested. Concerning the preheating temperature effect, the first 1.2 mm of printed layers are found to be critical and affected by melt pool instability. In this case, a sacrificial substrate used in the first layers could save the quality of a few layers height part. The gas flow analysis highlights how some areas of the building platform are affected by particular thermal conditions negatively influencing material printability. To minimize this issue as much as possible, modify the job layout to avoid printing parts in the critical zones.

Urban thermal map design considerations: color, shading, and resolution

ABSTRACT While satellite-based remote sensing techniques are often used for studying and visualizing the heat distribution in cities, they are limited in terms of spatial resolution, view bias, and revisit times. In comparison, modern Unmanned Aerial Vehicles (UAVs) equipped with infrared sensors allow very fine-scale (cm) data to be collected over smaller areas. We present a user study (n = 66) that outlines how satellite and drone-sourced thermal pseudo-color images compare in terms of map reading performance on three representative map reading tasks, how the choice of colormap affects map reading, and how a new shading augmentation to thermal maps based on high-resolution digital surface models can support interaction. Additionally, users provided explicit preferences indicating an inclination toward the shading augmentation, for the recently designed rainbow-style colormap turbo, and the cmocean thermal/FLIR ironbow colormap. However, we detail how user preferences and map reading performance are not always well aligned and are linked to issues of information content and visual clutter.

A Review on Thermal Design of Liquid Droplet Radiator System

Liquid Droplet Radiator (LDR) system is regarded as a quite promising waste heat rejection system for aerospace engineering. A comprehensive review on the state-of-the-art of LDR system was carried out. The thermal design considerations of crucial components such as working fluid, droplet generator and collector, intermediate heat exchanger, circulating pump and return pipe were reviewed. The state-of-the-art of existing mathematical models of radiation and evaporation characteristics of droplet layer from literatures were summarized. Furthermore, thermal designs of three LDR systems were completed. The weight and required planform area between the rectangular and triangular LDR systems were respectively compared and the evaporation models for calculating the mass loss were evaluated. Based on the review, some prospective studies of LDR system were put forward in this paper.

Thermal and Manufacturing Design Considerations for Silicon-Based Embedded Microchannel Three-Dimensional-Manifold Coolers (EMMC)—Part 3: Addressing Challenges in Laser Micromachining-Based Manufacturing of Three-Dimensional-Manifolded Microcooler Devices

Abstract Laser machining is an inexpensive and fast alternative to conventional microfabrication techniques and has the capability to produce complicated three-dimensional (3D), hierarchical structures. It is especially important while performing rapid prototyping and quick design studies of extreme heat flux cooling devices. One of the major issues plaguing the use of laser micromachining to manufacture commercially usable devices, is the formation of debris during cutting and the difficulty in removing these debris efficiently after the machining process. For silicon substrates, this debris can interfere with surrounding components and cause problems during bonding with other substrates by preventing uniform conformal contact. This study delves deep into the challenges faced and methods to overcome them during laser micromachining-based manufacturing of such complicated 3D-manifolded microcooler structures. Specifically, this work summarizes several postprocess techniques that can be employed for complete debris removal during etching of silicon samples using an Nd/YVO4 ultraviolet (UV) laser, detailing the advantages and drawbacks of each approach. A method that was found to be particularly promising to achieve very smooth surfaces with almost complete debris removal was the use of polydimethylsiloxane (PDMS) as a high-rigidity protective coating. In the process, a novel technique to strip PDMS from silicon surface was also developed. The result of this study is valuable to the microfabrication industry where smooth and clean substrate surfaces are highly desirable and it will significantly improve the process of using UV lasers to create microstructures for commercial applications as well as in a research environment.

Thermal and Manufacturing Design Considerations for Silicon-Based Embedded Microchannel-3D Manifold Coolers (EMMCs): Part 1—Experimental Study of Single-Phase Cooling Performance With R-245fa

Abstract High performance and economically viable cooling solutions must be developed to reduce weight and volume, allowing for a wide-spread utilization of hybrid electric vehicles. The traditional embedded microchannel cooling heat sinks suffer from high pressure drop due to small channel dimensions and long flow paths in two-dimensional (2D) plane. Utilizing direct “embedded cooling” strategy in combination with top access three-dimensional (3D) manifold strategy reduces the pressure drop by nearly an order of magnitude. In addition, it provides more temperature uniformity across large area chips and it is less prone to flow instability in two-phase boiling heat transfer. This study presents the experimental results for single-phase thermofluidic performance of an embedded silicon microchannel cold plate (CP) bonded to a 3D manifold for heat fluxes up to 300 W/cm2 using single-phase R-245fa. The heat exchanger consists of a 5 × 5 mm2 heated area with 25 parallel 75 × 150 μm2 microchannels, where the fluid is distributed by a 3D-manifold with four microconduits of 700 × 250 μm2. Heat is applied to the silicon heat sink using electrical Joule-heating in a metal serpentine bridge and the heated surface temperature is monitored in real-time by infrared (IR) camera and electrical resistance thermometry. The maximum and average temperatures of the chip, pressure drop, thermal resistance, and average heat transfer coefficient (HTC) are reported for flow rates of 0.1, 0.2. 0.3, and 0.37 L/min and heat fluxes from 25 to 300 W/cm2. The proposed embedded microchannels-3D manifold cooler, or EMMC, device is capable of removing 300 W/cm2 at maximum temperature 80 °C with pressure drop of less than 30 kPa, where the flow rate, inlet temperature, and pressures are 0.37 L/min, 25 °C and 350 kPa, respectively. The experimental uncertainties of the test results are estimated, and the uncertainties are the highest for heat fluxes < 50 W/cm2 due to difficulty in precisely measuring the fluid temperature at the inlet and outlet of the microcooler.

Thermal and Manufacturing Design Considerations for Silicon-Based Embedded Microchannel-Three-Dimensional Manifold Coolers—Part 2: Parametric Study of EMMCs for High Heat Flux (∼1 kW/cm2) Power Electronics Cooling

Abstract Thermal management of power electronics modules is one of the limiting factors in the peak power capability of the traction inverter system and overall efficiency of the e-drive. Liquid cooling using embedded microchannels with a three-dimensional (3D)-manifold cooler (EMMC) is a promising technology capable of removing heat fluxes of >1 kW/cm2 at tens of kPa pressure drop. In this work, we utilize computational fluid dynamics (CFD) simulations to conduct a parametric study of selected EMMC designs to improve the thermofluidic performance for a 5 mm × 5 mm heated area with the applied heat flux of 800 W/cm2 using single-phase water as working fluid at inlet temperature of 25 °C. We implemented strategies such as: (i) symmetric distribution of manifold inlet/outlet conduits, (ii) reducing the thickness of cold-plate (CP) substrate, and (iii) increasing fluid–solid interfacial area in CP microchannels, which resulted in a reduction in thermal resistance from 0.1 for baseline design to 0.04 cm2 K/W, while the pressure drop increased from 8 to 37 kPa.

Powering Milliwatts to Megawatts

Switched-mode power converters are used to interface equipments and consumer electronic devices over a wide range of power levels. The switch technology of any power converter is a signature of its power rating. The article discusses different power electronic switch technologies used in modern power supply implementation and evaluates their impact in the system design. From the design prospective, power loss is more important than efficiency. It can be established that as power level of converter goes up, it is indispensable to have higher efficiency due to thermal design considerations. A trend between the switching frequency and its efficiency with respect to the power rating of the converter has been inculcated in the article.

Thermal Design Considerations and Performance Evaluation of Cryogenic Tube in Tube Heat Exchangers

Heat exchangers are the most important equipment in refrigeration processes. Design and modeling of heat exchangers operating at low temperatures are different from other regular heat exchangers. This study includes two sections. In the first section, design and modeling considerations needed for evaluating the real thermal behavior of heat exchangers at low temperatures were discussed. These considerations are usually neglected by researchers who have modeled the heat exchanger at low temperatures. In the second section, a counter current helically coiled tube in tube heat exchanger operating in hydrogen liquefier was modeled and simulated considering notes discussed in the first section. The model was validated compared with the data presented by literature. The results showed the small positive effect of longitudinal heat conduction on hydrogen liquefaction. The heat in-leak into cold fluid resulted in higher cold fluid outlet temperature and higher hot fluid outlet temperature. Simulations showed that the heat in-leak into cold fluid leads to limit the overdesign for cryogenic heat exchangers. A comparison between models with considering different assumptions was presented and showed that the result may vary significantly based on the regarded assumptions.

Design considerations for an engine-integral reciprocating natural gas compressor

Abstract Conventionally, compressed natural gas (CNG) vehicles are refueled using a high-cost, centralized, and sparse network of CNG fueling stations that has primarily been developed for the use of fleet customers. An engine-integral reciprocating natural gas (NG) compressor has the capability to disrupt the incumbent CNG market by enabling the use of NG for personal transportation, fueled at home, from the preexisting low-pressure NG infrastructure, at low parts count, using conventional components, and therefore at low incremental costs. The principal objective of this paper is therefore to describe and analyze the dynamic and thermal design considerations for an automotive engine-integral reciprocating NG compressor. The purpose of this compressor is to pressurize storage tanks in NG vehicles from a low-pressure NG source by using one of the engine cylinders as a multi-stage reciprocating compressor. The engine-integral compressor is developed by making changes to a 5.9 l displacement diesel-cycle automotive engine. In this novel design and implementation, a small tank and its requisite valving are added to the engine as an intermediate gas storage system to enable a single compressor cylinder to perform two-stage compression. The resulting maximum pressure in the storage tank is 250 MPa, equivalent to the storage and delivery pressure of conventional CNG delivery systems. Dynamic simulation results show that the high cylinder pressures required for the compression process create reaction torques on the crankshaft, but do not generate abnormal rotational speed oscillations. Thermal simulation results show that the temperature of the storage tank and engine increases over the safety temperature of the natural gas storage system unless an active thermal management system is developed to cool the NG before it is admitted to the storage tanks.

Thermal Design Considerations for Raised Structures on Permafrost

AbstractWith advances in the ability to model complex geothermal conditions, the aspect of soil structure interaction as it relates to long-term changes in the geothermal regime can be considered. Traditional geothermal modeling relied on the so-called n-factor approach where the ground surface temperature was represented as the air temperature multiplied by some factor to account for ground surface effects. The application of surface energy balance formulations where the effects of the building including long wave radiation can be incorporated, allows for a more accurate representation of the geothermal regime under the structure. In considering the impact of climate warming on the performance of raised buildings in permafrost terrain, the use of a surface energy balance in the geothermal model is considered to be a more rigorous and technically preferable approach to addressing this problem. This paper addresses the use of a surface energy balance formulation in the geothermal analysis of raised buildin...

Magnetically Levitated Slice Motors

This paper provides a comprehensive overview of different concepts of magnetically levitated slice motors with ring-shaped rotors that differ in their construction and the way the bearing forces and drive torque are created. After a general classification of magnetic bearings and the description of the technical principle of the topologies, the design constraints for a fair topology comparison are specified. Mechanical, magnetic, electrical, and thermal design considerations are discussed and supported by 3-D finite-element method simulations. Four promising motor topologies are compared qualitatively and quantitatively by different criteria, such as acceleration behavior, compactness, bearing stability, and complexity of the control. The comparative evaluation is supported by performance measurements on laboratory prototypes.

Thermal Considerations for Meeting 20°C and Stringent Temperature Gradient Requirements of IXO SXT Mirror Modules

The Soft X-Ray Telescope (SXT) is an instrument on the International X-Ray Observatory (IXO). Its flight mirror assembly (FMA) has a single mirror configuration that includes a 3.3 m diameter and 0.93 m tall mirror assembly. It consists of 24 outer modules, 24 middle modules and 12 inner modules. Each module includes more than 200 mirror segments. There are a total of nearly 14,000 mirror segments. The operating temperature requirement of the SXT FMA is 20 C. The spatial temperature gradient requirement between the FMA modules is 1 C or smaller. The spatial temperature gradient requirement within a module is 0.5 C. This paper presents thermal design considerations to meet these stringent thermal requirements.

Technological investigations and efficiency analysis of a steam heat exchange condenser: conceptual design of a hybrid steam condenser

Most of the electricity being produced throughout the world today is from steam power plants. At the same time, many other competent means of gener-ating electricity have been developed viz. electricity from natural gas, MHD generators, biogas, solar cells, etc. But steam power plants will continue to be competent because of the use of water as the main working fluid which is abundantly available and is also reusable. The condenser remains among one of the key components of a steam power plant. The efficiency of a thermal power plant depends upon the efficiency of the condenser. In this paper, a the-oretical investigation about thermal analysis and design considerations of a steam condenser has been undertaken. A hybrid steam condenser using a higher surface area to diameter ratio of cooling a water tube has been analyzed. The use of a hybrid steam condenser enables higher efficiency of the steam power plant by lowering condenser steam pressure and increasing the vacuum inside the con-denser. The latent/sensible heat of steam is used to preheat the feed water supply to the boiler. A con-ceptual technological design aspect of a super vacu-um hybrid surface steam condenser has been theo-retically analyzed.

Thermal Considerations in Design of Vertically Integrated Si ∕ GaN ∕ SiC Multichip Modules

The thermal design of vertically integrated multichip modules (MCMs) based on high electron mobility transistor (HEMT) power amplifiers (PAs) on substrates with back-side heat-sink/antenna and Si modulators bonded to the common ground plane and PA chip using polydimethylsolixane (PDMS) is reported. The heat transfer in the integrated structure was estimated using finite element simulation for different PA power density, HEMT gate finger pitch, Si thickness, the presence or absence of the PDMS layer, and the thickness of dielectric isolation interlayers. The maximum temperature in the integrated antenna approach occurs near the gates of the HEMTs and hence the gate pitch has a strong effect on the temperature distribution. The presence of the PMDS has a major effect on the operating temperature of the PA and Si modulator, especially at high power densities, and also influences the temperature distribution within the MCM.

Thermal control and design considerations for a high-performance fluid warmer.

The process of warming liquids for intravenous infusion presents several technical challenges for the engineer: Typical liquid inlet temperatures can range from 5 degrees C to 20 degrees C, flow requirements can vary from essentially zero ("Keep Vein Open," or K.V.O.) to 30 L/h, and desired outlet temperature is fixed at a maximum threshold of 41 degrees C to minimize the risk of thermally mediated hemolysis. The primary challenge is developing a control technique that can tailor the energy introduced to the liquid in response to a randomly variable flow in order to achieve, but not exceed, a fixed temperature. The most difficult aspect of this challenge is preventing the transient infusate temperature from exceeding 43 degrees C, even when the power requirement varies by orders of magnitude, such as occurs when the flow suddenly decreases from maximum to zero. Many current-generation fluid warmers are optimized for operation at either low or high flow rates; we believed that it was possible to design an easy-to-use device that could achieve good performance across the entire range of flow rates. This article describes some of the methods that were used successfully to meet these challenges in the design of the Augustine Medical Ranger blood fluid warmer.

00/01944 Thermal modeling and design considerations of lithium-ion batteries

00/01944 Thermal modeling and design considerations of lithium-ion batteries

Thermal modeling and design considerations of lithium-ion batteries

Abstract A simplified one-dimensional thermal mathematical model with lumped parameters was used to simulate temperature profiles inside lithium-ion cells. The model makes use of heat-generation parameters established experimentally for the Sony (US18650) cell. The simulation results showed good agreement with temperature measurements at C/2, C/3, and C/6 discharge rates, while some deviation was noticed for the C/1 discharge rate. The model was used to simulate temperature profiles under different operating conditions and cooling rates for scaled-up cylindrical lithium-ion cells of 10 and 100 A h capacity. Results showed a strong effect of the cooling rate on cell temperature for all discharge rates. A significant temperature gradient inside the cell was found only at higher cooling rates, where the Biot number is expected to be >0.1. At lower cooling rates, the cell behaves as a lumped system with uniform temperature. To establish the limits of temperature allowable in scale-up by the simplified model, commercial lithium-ion cells at different open circuit potentials were tested inside an accelerated rate calorimeter (ARC) to determine the onset-of-thermal-runaway (OTR) temperatures. Sony (US18650) cells at 4.06, 3.0, and 2.8 V open circuit voltage (OCV) were tested and their measured OTR temperatures were found to be 104, 109, and 144°C, respectively. A sharp drop in the OCV, indicating internal short circuit, was noticed at temperatures close to the melting point of the separator material for all open circuit voltages.

Electrical, thermal and optomechanical packaging of large 2D optoelectronic device arrays for free-space optical interconnects

Innovative approaches to the design of a high-performance package module accommodating a array of surface-active devices indium bump bonded to a VLSI chip are presented. Electrical, thermal and optomechanical design considerations are discussed and experimental performance results of a prototype implementation are described. The package module supports 139 impedance-controlled signal connections as well as active temperature stabilization of the optoelectronic VLSI chip. The package module is compact, simple to assemble, alignment-tolerant and can be passively inserted into a free-space optical system with no need for further adjustments.

A thermal analysis of a sub-surface, vertical flow constructed wetland

Since November of 1991, an experimental constructed wetland has successfully treated municipal sewage effluent on a year round basis in a cool climate. The sub-surface, vertically pulsed flow system is located at a latitude of approximately 43 degrees, 15 minutes north latitude in south-central Canada. The 5 metre long by 5 metre wide by 1.2 metre deep constructed wetland cells were designed to operate through extended freezing periods via a number of specific features. The most important features being the allowance of thatch accumulation atop the system, ice accretion within the upper cell strata both acting as insulating layers, and the transfer of thermal energy to the system from warmer deep soils. The cells were hydraulically loaded below this frozen layer of granular matrix six times a day. A dense three dimensional array of thermocouples was planted within the first of the three constructed wetland cells in a series to allow for the assessment of thermal data at a high level of temporal and spatial resolution. Thermal data were sampled every five minutes and averaged and stored every hour over a two year period (1994 and 1995). The data were reviewed statistically to determine the operating envelope experienced at the Niagara-On-The-Lake experimental constructed wetland site. A detailed review of winter thermal data was made to provide parameters for the use of the HEATFLOW density-dependent ground water flow and thermal energy transport numerical model (Molson and Frind, 1995). The use of this coupled Darcy flux, thermal transport model has allowed for a better understanding of the importance of various thermal design considerations, and has allowed for the undertaking of sensitivity analyses for design assessment and optimization. The sensitivity analyses indicate that the retention of deep soil heat and top insulation from plant thatch are the most important thermal features. It is likely that this technology can be used in areas colder than Niagara-On-The-Lake.

A thermal analysis of a sub-surface, vertical flow constructed wetland

Since November of 1991, an experimental constructed wetland has successfully treated municipal sewage effluent on a year round basis in a cool climate. The sub-surface, vertically pulsed flow system is located at a latitude of approximately 43 degrees, 15 minutes north latitude in south-central Canada. The 5 metre long by 5 metre wide by 1.2 metre deep constructed wetland cells were designed to operate through extended freezing periods via a number of specific features. The most important features being the allowance of thatch accumulation atop the system, ice accretion within the upper cell strata both acting as insulating layers, and the transfer of thermal energy to the system from warmer deep soils. The cells were hydraulically loaded below this frozen layer of granular matrix six times a day. A dense three dimensional array of thermocouples was planted within the first of the three constructed wetland cells in a series to allow for the assessment of thermal data at a high level of temporal and spatial resolution. Thermal data were sampled every five minutes and averaged and stored every hour over a two year period (1994 and 1995). The data were reviewed statistically to determine the operating envelope experienced at the Niagara-on-The-Lake experimental constructed wetland site. A detailed review of winter thermal data was made to provide parameters for the use of the HEATFLOW density-dependent ground water flow and thermal energy transport numerical model (Molson and Frind, 1995). The use of this coupled Darcy flux, thermal transport model has allowed for a better understanding of the importance of various thermal design considerations, and has allowed for the undertaking of sensitivity analyses for design assessment and optimization. The sensitivity analyses indicate that the retention of deep soil heat and top insulation from plant thatch are the most important thermal features. It is likely that this technology can be used in areas colder than Niagara-On-The-Lake.