Efficient Heat Extraction Research Articles

Continuous-wave operation of vertically emitting ring interband cascade lasers at room temperature

We present vertical light emission in continuous-wave mode from an interband cascade laser (ICL) at a record temperature of up to 38 °C. These results pave the way toward a more efficient and compact integration of this technology in mobile spectroscopic applications. Our approach employs ring cavity ICLs that are mounted epi-side down for efficient heat extraction from the devices. The vertical single-mode emission relies on a metallized second-order distributed-feedback grating designed for an emission wavelength of 3.8 μm. A single lateral mode operation is favored by a narrow waveguide width of 4 μm. Optical output powers of more than 6 mW were measured at 20 °C for rings with a diameter of ∼800 μm. At this temperature, the threshold current-density amounted to 0.60 kA/cm2 and the device showed continuous current and temperature tuning rates of 0.06 nm/mA and 0.37 nm/K, respectively.

Numerical analysis of heat extraction efficiency in a multilateral-well enhanced geothermal system considering hydraulic fracture propagation and configuration

Studying the effects of physical-based hydraulic fracture configurations on heat extraction performance in a multi-lateral enhanced geothermal system (EGS) can provide meaningful suggestions for in-situ operations. In this work, we proposed a 3D thermal-hydro-mechanical (THM) coupled numerical model that is capable to simulate both hydraulic fracturing and heat extraction in dual porous and fracture medium. Using this model, the exploitation of deep geothermal energy in a multilateral-well EGS from creation and configuration of hydraulic fractures, to thermal extraction was simulated and comprehensively studied. Based on the results, the following conclusions were drawn: 1) configuration of fracture pattern in a multi-lateral well EGS was affected by in-situ geological conditions (e.g. in-situ stress state) and operation strategies (e.g. sequence of hydraulic fracturing operation, position of perforation for hydraulic fracturing etc.); 2) different fracture configurations lead to great differences in heat production. The final thermal power of the worst configuration was 5.55 MW, while that of the best configuration was approximately 7.25 MW in this study; 3) a zipper fracture configuration is advantageous for homogeneously heat reduction in the geothermal reservoir that is preferable for efficient heat extraction; 4) stress shadow induced by simultaneous hydraulic fracturing can be used to create a non-connected zipper fracture pattern that can improve the heat extraction performance in the fractures at the toe side.

Design and analysis of thermal hydraulic performance of compact heat exchanger for FDS-II auxiliary system

One key issue of a fusion power plant is the requirement of highly efficient heat extraction from the primary loop to ensure the safety and reliability. The Dual-coolant Lithium Lead (DLL) breeder blanket of the FDS-II with a compact heat exchanger (CHE) is one design option for the power extraction system, and the Lithium Lead eutectic (LiPb) and helium gas are used as the thermal fluids. In this work, the flat and corrugated plate structures with SiCf/SiC composites and ODS steel were designed for the comparison of thermal performance. The heat transfer rate of the SiCf/SiC was 11.4% higher as compared to the ODS steel and was chosen as a candidate structural material. According to the design parameters of the DLL, effectiveness and the overall heat transfer coefficient for the corrugated structure increased up to 19.8% and 25.06% at the LiPb velocity of 0.099 m/s and increased up to 26.2% and 33.03%, when the velocity of the LiPb decreased to 0.012 m/s. The Nusselt number for the LiPb and helium gas was calculated for the convective heat transfer. The numerical results agreed well with the correlations within a deviation of ̴ 2%. In addition, pressure drop of the corrugation structure increased but it can be neglected as compared to the increase in the thermal performance. The concept of CHE with the SiCf/SiC structure could be applied to the design of intermediate heat exchanger working in a fusion power plant.

72‐W vertical‐external‐cavity surface‐emitting laser with 1180‐nm emission for laser guide star adaptive optics

We report a high-power optically-pumped vertical-external-cavity surface-emitting laser emitting at around 1180 nm. The free-running laser produced 72 W of output power at a heatsink temperature of 0°C and 53 W near room temperature (20°C). The GaAs-based gain mirror was bonded to a 2-mm-thick diamond attached to a TEC-cooled copper mount in order to enable efficient heat extraction for high-power operation. Moreover, the spectrum of the laser was narrowed down to 0.06 nm by employing a combination of a birefringent filter and an etalon inside the cavity which yielded a maximum of 19 W at a heatsink temperature of 20°C. The demonstration opens a new perspective for the realisation of sodium laser guide star adaptive optics employing frequency doubling of 1180 nm radiation.

Reliability and heat transfer performance of a miniature high-temperature thermosyphon-based thermal valve

Latent heat thermal energy storage systems have the advantages of near isothermal heat release and high energy density compared to sensible heat, generally resulting in higher power block efficiencies. Until now, there has been no highly effective and reliable method to passively extract that stored latent energy. Most modern attempts rely on external power supplied to a pump to move viscous heat transfer fluids from the phase change material (PCM) to the power block. In this work, the problem of latent heat dispatchability has been addressed with a redesigned thermosyphon geometry that can act as a “thermal valve” capable of passively and efficiently controlling the release of heat from a thermal reservoir. A bench-scale prototype with a stainless steel casing and sodium working fluid was designed and tested to be reliable for more than fifty “on/off” cycles at an operating temperature of 600 °C. The measured thermal resistances in the “on” and “off” states were 0.0395 K/W and 11.0 K/W respectively. This device demonstrated efficient, fast, reliable, and passive heat extraction from a PCM and may have application to other fields and industries using thermal processing.

Highly efficient heat extraction by double diamond heat-spreaders applied to a vertical external cavity surface-emitting laser

We compare the heat extraction efficiency for a standard Vertical External Cavity Surface-Emitting Laser and the distributed Bragg reflector (DBR)-free structure employing a single and double diamond heat-spreaders, respectively. Both heterostructures grown by Molecular Beam Epitaxy employ two identical active regions designed for emission at 980 nm. We show that the thermal resistance has been decreased 15 times when there is no DBR and heat is extracted from both side of active region. For DBR-free laser no thermal rollover of power conversion characteristic was observed in the range of considered input powers.

Geomechanical Characterization of a Host Rock for Enhanced Geothermal System in the North-German Basin

The North-German Basin offer at depth of approximately 5000 m sufficiently high temperatures for efficient and economic heat extraction by geothermal wells. The permeability of the carboniferous strata at that depth is very low so that conductive pathways have to be created by hydraulic fracturing. For some planned projects we conduct the characterization of the carboniferous strata as exposed in “analogous outcrops”. The geological setting for fracking is demanding, as the strata comprise strong sandstone, shale and weak coal seams. All necessary petrophysical properties will be collected by extended testing. The regional horst-and-graben system allows for mapping in outcrops and extrapolate the structural content towards the rock mass at depth.

Multifluid geo-energy systems: Using geologic CO2storage for geothermal energy production and grid-scale energy storage in sedimentary basins

We present an approach that uses the huge fluid and thermal storage capac­ity of the subsurface, together with geologic carbon dioxide (CO 2 ) ­storage, to harvest, store, and dispatch energy from subsurface (geothermal) and surface (solar, nuclear, fossil) thermal resources, as well as excess energy on electric grids. Captured CO 2 is injected into saline aquifers to store pressure, generate artesian flow of brine, and provide a supplemental working fluid for efficient heat extraction and power conversion. Concentric rings of injection and production wells create a hydraulic mound to store pressure, CO 2 , and thermal energy. This energy storage can take excess power from the grid and excess and/or waste thermal energy and dispatch that energy when it is demanded, and thus enable higher penetration of variable renewable energy technologies (e.g., wind and solar). CO 2 stored in the subsurface functions as a cushion gas to provide enormous pressure storage capacity and displace large quantities of brine, some of which can be treated for a variety of beneficial uses. Geo­thermal power and energy-storage applications may generate enough revenues to compensate for CO 2 capture costs. While our approach can use nitrogen (N 2 ), in addition to CO 2 , as a supplemental fluid, and store thermal energy, this study focuses on using CO 2 for geothermal energy production and grid-scale energy storage. We conduct a techno-economic assess­ment to determine the levelized cost of electricity using this approach to generate geothermal power. We present a reservoir pressure management strategy that diverts a small portion of the produced brine for beneficial consumptive use to reduce the pumping cost of fluid recirculation, while reducing the risk of seismicity, caprock fracture, and CO 2 leakage.

Covalently Bonded Graphene–Carbon Nanotube Hybrid for High‐Performance Thermal Interfaces

The remarkable thermal properties of graphene and carbon nanotubes (CNTs) have been the subject of intensive investigations for the thermal management of integrated circuits. However, the small contact area of CNTs and the large anisotropic heat conduction of graphene have hindered their applications as effective thermal interface materials (TIMs). Here, a covalently bonded graphene–CNT (G‐CNT) hybrid is presented that multiplies the axial heat transfer capability of individual CNTs through their parallel arrangement, while at the same time it provides a large contact area for efficient heat extraction. Through computer simulations, it is demonstrated that the G‐CNT outperforms few‐layer graphene by more than 2 orders of magnitude for the c‐axis heat transfer, while its thermal resistance is 3 orders of magnitude lower than the state‐of‐the‐art TIMs. We show that heat can be removed from the G‐CNT by immersing it in a liquid. The heat transfer characteristics of G‐CNT suggest that it has the potential to revolutionize the design of high‐performance TIMs.

Laboratory and Numerical Studies of Heat Extraction from Hot Porous Media by Means of Supercritical $$\hbox {CO}_{2}$$ CO 2

The use of $$\hbox {CO}_{2}$$ as a heat transfer fluid has been proposed as an alternative to water in enhanced geothermal systems (EGS) and in $$\hbox {CO}_{2}$$ -plume geothermal systems (CPG). Numerical simulations have shown that under expected EGS operating conditions, $$\hbox {CO}_{2}$$ would achieve more efficient heat extraction performance compared to water, especially at sites with low geothermal temperatures and low subsurface heat flow rates. With increased interest in carbon capture and sequestration (CCS), the possibility of combining geothermal energy production with carbon sequestration is actively being explored. Simulations have shown that $$\hbox {CO}_{2}$$ -based geothermal energy production could substantially offset the cost of CCS. Since numerical models are critical for the planning and operation of geothermal systems that employ $$\hbox {CO}_{2}$$ as the working fluid, it is important to validate the results of the current numerical tools against real- world experimental data. In a set of laboratory experiments, we have investigated heat extraction by flowing dry supercritical $$\hbox {CO}_{2}$$ through a heated porous medium in a laboratory pressure vessel and have compared experimental results with a numerical model using TOUGH2 with the ECO2N module. In addition, experiments were performed using (1) $$\hbox {CO}_{2}$$ and (2) water as the working fluids under similar operating conditions in order to compare the heat transfer behavior and the overall heat extraction rates. Our laboratory apparatus is capable of operating at temperatures up to 200 $$^{\circ }\hbox {C}$$ , pressures up to 34.5 MPa, and flow rates up to 400 ml/min. The experimental system was designed such that measurements and controls at the boundaries could be readily modeled using TOUGH2. We have made estimates of the density and the effective thermal conductivity of our saturated porous media, and have found that both properties change significantly during the course of experiments. The large changes in $$\hbox {CO}_{2}$$ density, due to decreasing system temperatures, can result in fluid accumulation in the system that may have significant impacts on geothermal reservoir management. The large changes in thermal conductivity as a function of temperature are of concern because the TOUGH2 code does not update the thermal conductivity of the system during the course of a simulation. Our data can be used by geologic reservoir modelers to ensure that their models accurately capture the heat extraction behavior of $$\hbox {CO}_{2}$$ to aid in the further investigations of EGS, CPG, and CCS.

New design aspects of cooling scheme for SST-1 plasma facing components

PFC of SST-1 comprising of baffles, divertors and passive stabilizers have been designed and fabricated for a maximum heat load up to 1.0MW/m2. In operational condition, SST-1 divertors and passive stabilizers are expected to operate with a heat load of 0.6 and 0.25MW/m2, respectively. During plasma operation, the heat loads on PFC are required to be removed promptly and efficiently. Thereby the design of an efficient cooling scheme becomes extremely important for an efficient operation of PFC. PFCs are also baked up to 350°C in order to remove absorbed moistures and other gases.3D thermal analysis of PFC using ANSYS has been carried out to ensure its thermal stability. The cooling parameters have been calculated according to average incident flux on divertors and passive stabilizers. Engineering design demonstrated the required mass flow rate and velocity for cooling water in each sub-connection are optimized to be 0.43kg/s and 5.5m/s for efficient heat extraction under steady state heat load. Maximum temperature which PFC could be maintained is 355°C and is well within threshold limits of material property degradation. The header distribution, modeled using AFT fathom, resulted for required parameters within maximum 5% of deviation.

Low thermal resistance GaN-on-diamond transistors characterized by three-dimensional Raman thermography mapping

In order to achieve ultra-high radio frequency output power densities in GaN-based transistors new thermal management solutions must be developed for efficient heat extraction, including the use of high thermal conductivity substrates. Integration of GaN devices with the highest thermal conductivity material available, diamond, instead of the standard GaN-on-SiC, can lead to a substantial reduction in device thermal resistance. Current GaN-on-diamond transistors are shown to result in a 40% reduction in peak channel temperature when benchmarked against equivalent GaN-on-SiC transistors, with the potential for even further reductions through optimization. In order to understand the contribution of substrate and GaN/substrate interface to the device thermal resistance, a 3D Raman thermography mapping and modelling approach has been developed. The GaN/diamond interface thermal resistance is found to have the largest contribution to the thermal resistance of current GaN-on-diamond devices.

Conceptual Design of Experimental Helium Cooling Loop for Indian TBM R&D Experiments

This paper deals with the conceptual design of Experimental Helium Cooling Loop (EHCL) for Indian Test Blanket Module (TBM) and its related thermal hydraulic experiments. Indian TBM team is developing Lead Lithium cooled Ceramic Breeder (INLLCB) TBM to be tested in ITER. The TBM box structure is cooled by high pressure (8 MPa) and high temperature (300-500C) helium gas. The first wall of TBM made of complex channel geometry having several parallel channels carrying helium gas for efficient heat extraction. Several mock-ups of these channels need to be tested before finalizing the TBM first wall design and fabrication. Besides the individual testing of such mock-ups of breeding blanket, the testing of Pb-Li to helium heat exchanger, the operational experience of helium loop and understanding of the behavior of high pressure and high temperature system components are very essential for final development of Helium Cooling System for LLCB TBM in ITER. The main requirements and characteristics of the EHCL and its conceptual design are presented in this paper. Keywords—DEMO, EHCL, ITER, LLCB TBM.

Integrating CO2 Storage with Geothermal Resources for Dispatchable Renewable Electricity

We present an approach that uses the huge fluid and thermal storage capacity of the subsurface, together with geologic CO2 storage, to harvest, store, and dispatch energy from subsurface (geothermal) and surface (solar, nuclear, fossil) thermal resources, as well as energy from electrical grids. Captured CO2 is injected into saline aquifers to store pressure, generate artesian flow of brine, and provide an additional working fluid for efficient heat extraction and power conversion. Concentric rings of injection and production wells are used to create a hydraulic divide to store pressure, CO2, and thermal energy. Such storage can take excess power from the grid and excess/waste thermal energy, and dispatch that energy when it is demanded, enabling increased penetration of variable renewables. Stored CO2 functions as a cushion gas to provide enormous pressure-storage capacity and displaces large quantities of brine, which can be desalinated and/or treated for a variety of beneficial uses. Geothermal power and energy-storage applications may generate enough revenues to justify CO2 capture costs.

Improved thermal management for GaN power electronics: Silver diamond composite packages

A novel packaging solution for GaN power electronics for efficient heat extraction in high power devices is presented. The benefits of using silver diamond composites as base plate in packages for GaN power bars are demonstrated. Micro-Raman thermography measurements were carried out to probe the device temperature for devices mounted on different base plates, silver diamond composites and standard CuW, at a range of operating power levels. A significant improvement in terms of thermal management, achieving a reduction in GaN power electronics temperature by up to a factor of two, was obtained when using silver diamond composites base plates with respect to the existing packaging technologies such as of CuW. Bare silver diamond and Cu-plated silver diamond base plates were compared. The influence of die attach to the base plates on thermal performance of GaN power electronics is also discussed. Finite element thermal model was built to correlate to the experiments, and good agreement was achieved.

Experimental Trials of the Thin Shell Casting (TSC) Technology for Directional Solidification

In this paper a novel directional solidification process - Thin Shell Casting (TSC) is presented. According to this new technology a thin shell mould mounted to a chill is dipped through the floating baffle into the melt bath. By pulling up the shell mould, a directional solidification can be performed in a downward direction. Due to the use of extremely thin shell moulds and the application of gas cooling, an efficient heat extraction can be achieved in comparison to the conventional and modified Bridgman techniques. In the experiments with Cu- and Al-alloys, not only directional solidification (DS), but also single crystal (SC) growth can be successfully performed. This confirms the feasibility of the new technology, which will be further applied to the production of SC components of superalloys.

Direct metal deposition (DMD) of H13 tool steel on copper alloy substrate: Evaluation of mechanical properties

H13 tool steel powder was clad on copper alloy substrate both directly and using 41C stainless steel (high Ni steel) powder as a buffer layer by direct metal deposition (DMD). Cu–steel bimetallic die casting and injection molding tools are of high interest for reduction of cycle time by efficient heat extraction due to high thermal conductivity of copper. The mechanical properties of these bimetallic structures were investigated in terms of bond strength, impact energy and fracture toughness. The bond interfaces of these claddings showed porous and crack free transition regions. The bond strength was higher in the directly clad H13 tool steel compared to the H13 tool steel clad with 41C stainless steel as buffer layer. The fracture morphology in tensile test specimens showed ductile dimple fracture. Presence of necking just below the interface depicted the softening of substrate in heat affected zone (HAZ) during cladding. The Charpy impact energy is little higher in the 41C stainless steel buffered specimens compared to the directly clad H13 tool steel specimens but the fracture toughness results showed reduction of fracture toughness in the 41C stainless steel buffered specimens due to the low strength in the tensile test. However the fracture toughness value was in the ductile region for both deposits.

Development of Shaping Textured YBaCuO Superconductors

Using a combination of standard ceramic processing and an infiltration technique, single-grain superconductor foams and with multiple holes of YBa 2 Cu 3 O y (Y123) have been produced. The process, involving negligible shrinkage, results in an improved microstructure with a uniform distribution of submicron Y 2 Ba 1 Cu 1 O 5 (Y211) inclusions in the Y123 matrix. The foam or artificially patterned holes structure could be highly favorable for good oxygenation, better cooling and consequently for an efficient heat extraction from the superconducting element in view to overcome the typical hot-spot phenomena commonly observed in superconducting fault current limiters. In this work, the processing conditions and the magneto-transport measurements of these foams are reported. The investigations reveal the superconducting properties to be similar to those of bulk melt processed materials. The magnetic hysteresis vs. field measurements show a high anisotropy of the critical current density in good agreement with the microstructural observations. The advantages of the infiltration growth process and of the novel porous superconductor (Y123) ceramic are discussed.

Scaling theory for steady-state plastic flows in amorphous solids

Strongly correlated amorphous solids are a class of glass formers whose interparticle potential admits an approximate inverse power-law form in a relevant range of interparticle distances. We study the steady-state plastic flow of such systems, first in the athermal quasistatic limit and second at finite temperatures and strain rates. In all cases we demonstrate the usefulness of scaling concepts to reduce the data to universal scaling functions where the scaling exponents are determined a priori from the interparticle potential. In particular we show that the steady plastic flow at finite temperatures with efficient heat extraction is uniquely characterized by two scaled variables; equivalently, the steady-state displays an equation of state that relates one scaled variable to the other two. We discuss the range of applicability of the scaling theory, and the connection to density scaling in supercooled liquid dynamics. We explain that the description of transient states calls for additional state variables whose identity is still far from obvious.

Improved thermal management of GaN/sapphire light-emitting diodes embedded in reflective heat spreaders

Using maskless lithography and electroforming techniques, we have demonstrated an enhanced performance of GaN/sapphire light-emitting diode (LED) embedded in a reflective copper heat spreader. The chip size and dominant wavelength of the blue emitter used in this research is 1×1 mm2 and 455 nm, respectively. The cup-shaped LED heat sink is electroformed on sapphire directly using the spin-coated photoresist coated with the Au/Cr/Ag mirror as a mold and dicing into the embedded LED with a Cu base dimension of 3×3 mm2, which effectively enhances the heat dissipation down to the metal frame and reaps the light flux generated from the side emission. With the aid of a reflective heat spreader, the encapsulated LED sample driven at 1 A yields the light output power of 700 mW and around 2.7-times increase in the wall-plug efficiency compared to that of the conventional GaN/sapphire LED. Infrared thermal images confirm the GaN/sapphire LED with more efficient heat extraction and better temperature uniformity. These results exhibit an alternative solution to thermal management of high power LED-on-sapphire samples besides the laser lift-off technique.