Thermal Design Research Articles

Thermal Engineering of the Cryogenic Beam Position Monitors for the EIC Hadron Storage Ring

The Electron Ion Collider (EIC) Hadron Storage Ring (HSR) will reuse most of the existing superconducting magnets from the RHIC storage ring. However, the existing stripline beam position monitors (BPM) used for RHIC will not be compatible with the planned EIC hadron beam parameters that include higher intensity, shorter bunches, and some operational scenarios with large radial offsets of the beam in the vacuum chamber. To address these challenges, the existing RHIC stripline BPMs will be decommissioned, and a new BPM design using button pick-ups integrated in a new vacuum interconnect/bellows assembly will be installed adjacent to the decommissioned BPMs.A dedicated analysis of the new BPM housing and button pick-up design has been conducted to assess the thermal effects caused by heat conduction, beam induced resistive wall heating and the RF heating from the BPM signal propagation through the cryogenic cables. This paper reports on the thermal design and analysis results to quantify the heat transfer and temperature distribution that can be expected on the new HSR cryogenic BPM.

Research on high power and heat flux aerospace electronic products of integrated thermal conduction technology

In response to the increasing demand for enhanced computational capabilities within satellite systems, there has been a simultaneous rise in the heat flux density of onboard electronic components. The thermal output of these components has significantly increased compared to traditional satellite processing electronics, leading to a concurrent elevation in the heat flux density related to processing chips and the surfaces accommodating equipment installations. This paper establishes a model for conduction heat dissipation in aviation electronic products. The outlined calculation methodology facilitates a preliminary assessment of the system’s heat dissipation capacity. The article further examines the inherent heat dissipation capabilities in two commonly employed structural configurations. Additionally, it introduces an integrated design approach for structural heat dissipation, including experimental considerations and validation outcomes. The assessment methodologies and design principles detailed in this article are particularly relevant and applicable to the thermal design imperatives associated with high-power electronic products deployed for the extended operational durations typical of spacecraft.

Thermal design calculation method of the whole coil closed cooling tower with condensation inside the tube

In this paper, the heat exchange process of a closed cooling tower with condensation inside the tube is analyzed. Combined with the calculation method of a traditional closed cooling tower, the thermal model and mathematical model of the whole coil closed cooling tower with condensation inside the tube are established. The fourth-order Runge-Kutta (RK4) method is used to write a program to solve the differential equation. A case is calculated to solve the heat exchange area and spray water temperature. Its feasibility for design reference is verified.

Design and multi-criteria optimization and financial assessment of an innovative combined power plant and desalination process

Geothermal power generation programs are crucial due to their long-term sustainability and environmentally friendly characteristics, particularly for potential energy-based applications in the future. Innovative designs can yield improve efficien by mitigating irreversibility, resulting in enhanced power production. Hence, this study investigates an innovative cascade thermal design model that employs geothermal resources to enhance the efficiency and output of low-temperature power generation systems, specifically through the integration of organic flash and organic Rankine cycles. Additionally, this model introduces a novel cogeneration approach by incorporating a desalination unit based on humidification-dehumidification processes, aiming to concurrently produce electricity and fresh water. Employing a combination of thermodynamic analysis and financial assessment, the system's performance was simulated and optimized in MATLAB, using the Multi-Objective Particle Swarm Optimization (MOPSO) method. A sensitivity analysis preceded the optimization, leading to the development of three distinct optimization scenarios focused on balancing power and freshwater production, maximizing exergetic efficiency and net present value, and optimizing fixed capital investment for maximum financial viability. The results highlight the second scenario as particularly effective, achieving a power generation of 254.3 kW, an exergetic efficiency of 44.84 %, and a net present value of $405,099. Conversely, the third scenario offers the best balance between freshwater production capacity (0.504 kg/s), fixed capital investment ($820,822), and a payback period of 7.12 years. This research demonstrates the potential of integrating advanced thermal models with geothermal resources for sustainable and efficient energy and freshwater production, marking a significant step forward in the development of eco-friendly cogeneration systems.

The optimization of roll-bond cold plate based on Taguchi-grey theory for server chips thermal management

The roll-bond cold plate, an economical and straightforward electronics liquid cooling approach, is highly promising to address the increasing electronics chip thermal management challenges. However, the roll-bond cold plate with staggered cellular flow channels, while having a sizable solid-liquid contact area and high heat dissipation potential, suffers from inadequate temperature uniformity and fluidity. This study addresses flow and temperature uniformity issues in current roll-bond cold plates by proposing a design—Direct Liquid Cooling Roll-Bond Plates (DLCRBP) tailored for high-performance server architectures. To investigate how regional combination, cellular diameter, and longitudinal spacing affect both thermal and flow performance, orthogonal experiments with diverse flow channel structures were conducted using the Taguchi-grey theory. COMSOL-based numerical simulation were used to analyze these experiment conditions. Multi-objective optimization, considering pressure drop, heat source temperature uniformity, and coolant temperature difference, was then performed using the grey correlation method. The optimized DLCRBP (A3B5C1) was fabricated, and its performance was compared with the staggered cellular DLCRBP (SCS), which is the control group without optimization, under various inlet flow velocities, heat source powers, and coolant inlet temperatures. Experimental comparisons illustrate that the optimized structure ensures outstanding temperature uniformity even at low inlet flow velocities. Specifically, at an inlet flow velocity of 0.2 m/s, the average and maximum temperature differences on the heat source's upper surface are 36.5 % and 75.3 % lower, respectively, compared to pre-optimization levels. Furthermore, A3B5C1's temperature uniformity improves with higher coolant inlet flow velocity and lower coolant inlet temperatures. At a coolant inlet flow velocity of 0.5 m/s or higher, A3B5C1 sustains the surface temperature of a 600 W chip below the thermal design's safe temperature of 77.8 °C, highlighting its enhanced performance.

Comparative investigation on the thermodynamic performance of coal-fired power plant integrating with the molten salt thermal storage system

One of the most critical challenges facing China is enhancing the operational flexibility of coal-fired power plants (CFPPs), given the increasing reliance on renewable energy for power generation. This study focuses on analyzing and comparing the molten salt thermal storage systems integrated in CFPP in consideration of peak-shaving capacity, equivalent round-trip efficiency, heat consumption rate, and exergy efficiency. Five charging schemes integrating thermal energy storage (TES), power to heat (P2H) and combination of TES and P2H are proposed and tested via their thermodynamic models. Results show that all five integrated molten salt thermal storage systems can enhance the peak shaving capability of the CFPP. When integrating P2H system, CFPP has the potential to achieve a zero-power output. Furthermore, comparing to the other four schemes, P2H-only integrating scheme has the highest equivalent round-trip efficiency of 36.23 % and the lowest heat consumption rate of 8288.87 kJ·(kW·h)−1. However, its exergy efficiency decreases to 36.51 % due to the electric heater experiencing the highest exergy loss of 132.56 MW, in contrast to the TES-coupled system which shows a higher exergy efficiency of 39.58 %. The P2H-only scheme boasts the largest investment of $33,353,100 and the longest repayment time, while also earning the highest compensation for peak shaving. This study provides a promising approach for molten salt thermal storage system designs in enhancing flexibility for CFPPs.

Tuning the Dynamic Thermal Parameters of Nanocarbon Ionanofluids: A Photopyroelectric Study

The present work delineates the tailoring of the thermal effusivity and diffusivity of the novel class of heat transfer fluids—ionanofluids—by the incorporation of nanocarbons like diesel soot (DS), camphor soot (CS), carbon nanotubes (CN), and graphene (GR). When the thermal diffusivity delivers information on the thermal energy propagation, the thermal effusivity concerns the energy exchange at the interface, enabling energy-efficient thermal system design. The nanocarbons are subjected to morphological characterisation by field emission scanning electron microscopy. Fourier-transform infrared and Raman spectroscopic analyses confirm functional groups and vibrational bands. The microcrystalline size and graphiticity are also understood from the Raman spectrum. Ionanofluids prepared by dispersing nanocarbons into an ionic liquid base 1-Butyl-3-methylimidazolium methyl sulfate (BMMS) are analysed by nondestructive photopyroelectric calorimetry (PPE). The PPE analysis of ionanofluids demonstrates that nanocarbons influence thermal parameters in the base fluid, with soot ionanofluids exhibiting increased thermal effusivity and diffusivity due to their various carbon allotropic composition. This study underscores the importance of selecting the appropriate carbon allotrope for tailoring ionanofluids’ thermal properties, providing insights into manipulating these properties for enhanced performance across various industrial applications.

Improving Microstructural Homogeneity of Investment‐Cast Single‐Crystalline Ni‐Base Superalloys by Using Fluidized Carbon Bed Cooling

One impeding factor for faster solidification in typical investment casting processes is the limited heat removal capability. This study compares the classical Bridgman technique and the fluidized carbon bed cooling (FCBC) casting method. In particular, the influence of the thermal design is investigated in terms of microstructural and compositional homogeneity in single‐crystalline CMSX‐4. These investment casting processes mainly differ in the baffle type used to insulate the hot and cold zones inside of the casting vessel. While the Bridgman process is based on radiation cooling, the FCBC casting process relies on a dynamic baffle made of expanded graphite that is buoyant on fluidized bed of glassy carbon beads. Such a dynamic insulation layer can adapt to the cross‐sectional variation of ceramic shell molds and provide a better thermal insulation, which results in more uniform solidification conditions. This enables a reduction in the primary dendrite arm spacing by up to 26%, an increase in the homogeneity of the microstructure and composition, as well as a reduction in overall porosity and mean pore size of 41%.

An improved methodology for thermal calculation and design optimization of a thermosiphon waste heat boiler for CCPP

The study is dedicated to enhancing design and computational methodologies for thermosiphon waste heat boilers (WHB) within combined cycle power plants (CCPP). The optimized WHB design and an improved thermal calculation approach are shown. The efficiency of the proposed WHB has been improved by optimizing the area and arrangement of the surface. The novel method incorporates considerations for the internal thermal resistance within thermosyphons and the graded velocity of natural circulation within the evaporation circuit. To refine the calculation method, empirical and experimental data concerning internal temperature gradient in thermosiphon functioning within a heat load spectrum of up to 17 kW/m2, were used. Important findings include three categories. Firstly, increasing the number of sections will slightly increase capital costs and decrease WHB gas temperature, which could be neglected by the unification of thermosiphon sections. Secondly, by applying this modified methodology to a power plant facility featuring a 6700 kW gas turbine engine (GTE), notable adjustments in thermal power were realized, amounting to 157 kW (approximately 6 %), along with corresponding electrical power adjustments of 149 kW (approximately 2 %). Third, the new method is limited to a GTE power of up to 10 MW due to the experimental data used for validation.

The Challenge of Integrating Seismic and Energy Retrofitting of Buildings: An Opportunity for Sustainable Materials?

Recent earthquakes and escalating energy demands are exposing building stock deficiencies, particularly in terms of seismic resilience and energy efficiency. Many aged constructions do not fulfil current regulations both in terms of seismic and thermal design principles, thus requiring suitable retrofitting solutions. Integrated approaches for concurrent seismic and energy renovation have emerged as promising strategies in recent years, offering holistic solutions that optimize interventions and maximize benefits. While these combined methods hold significant potential for practical applications, there remain opportunities for further research to enhance their advantages. Furthermore, addressing climate concerns requires concentrated effort within the construction sector, where synergetic refurbishments can serve a dual purpose by reducing emissions and promoting the use of more sustainable materials. This study discusses strategies proposed in the literature for integrated retrofitting, considering their environmental impact, both in terms of energy performance and embodied carbon. The overview shows the innovation potential for the development of materials and systems combining acceptable performance with eco-friendly attributes. Yet, their application in integrated retrofitting systems, either as structural components or insulators, is still limited, underscoring the need for continued investigation and advancement. This paper concludes with recommendations to inspire further research and advancements in this critical field.

Thermal conduction in polycrystalline or amorphous transparent conductive oxide films

With the widespread utilization of transparent conductive oxides (TCO) in various electronic devices, it is beneficial to revisit the fundamentals of heat conduction to formulate a comprehensive physical understanding for thermal properties of TCOs with the aim of improving the thermal design of electronic devices. For degenerate polycrystalline TCO films, both free electrons and phonons act as heat carriers, where free electron contribution can be calculated based on the Wiedemann-Franz law.Interestingly, the phonon thermal conductivity remains almost constant for degenerated polycrystalline TCO films with different dopant concentrations, suggesting the existence of dopant-induced minimum phonon thermal conductivity. For degenerate amorphous TCO film, free electrons act as heat carriers along the conduction path formed by the orbital overlap of cations, which also obey the Wiedemann-Franz law. Moreover, the atomic vibration contribution to thermal conductivity almost keeps unchanged for amorphous TCO films deposited under different conditions, indicating the existence of a minimum thermal conductivity caused by the scattering of vibrational mode due to structural randomness appeared in the bond angle. We anticipate that these fundamental understanding can provide a guide for the discovery of TCO materials with optimized thermal properties.

Thermal design of operating parameter for reliable AlSi7Mg selective laser melting

Gas turbines require high power density for applications like aircraft and future mobility. Increasing operating temperature, particularly turbine inlet temperature, boosts performance. However, conventional cooling methods limit this increase. Selective laser melting (SLM) offers a promising avenue for realizing advanced cooling configurations beyond conventional fabrication techniques. However, unexpected defects in the final product can occur, making pre-fabrication quality estimation difficult. This necessitates thermal analysis during SLM and design guidelines for suitable fabrication. This study investigates the thermal design guidelines for AlSi7Mg alloy using SLM for high-heat-flux applications. Simulations explored melt pool size dependence on operating parameters like laser power and scan speed. Comparisons with experimental results revealed diverse heat transfer modes under different operating conditions. Finally, a normalized enthalpy factor, integrating operating parameters like scan speed and laser power, was proposed for thermal design in SLM processes for high-heat-flux applications.

Observation of parity-time symmetry in diffusive systems.

Phase modulation has scarcely been mentioned in diffusive physical systems because the diffusion process does not carry the momentum like waves. Recently, non-Hermitian physics provides a unique perspective for understanding diffusion and shows prospects in thermal phase regulation, exemplified by the discovery of anti-parity-time (APT) symmetry in diffusive systems. However, precise control of thermal phase remains elusive hitherto and can hardly be realized, due to the phase oscillations. Here we construct the PT-symmetric diffusive systems to achieve the complete suppression of thermal phase oscillation. The real coupling of diffusive fields is readily established through a strong convective background, and the decay-rate detuning is enabled by thermal metamaterial design. We observe the phase transition of PT symmetry breaking with the symmetry-determined amplitude and phase regulation of coupled temperature fields. Our work shows the existence of PT symmetry in dissipative energy exchanges and provides unique approaches for harnessing the mass transfer of particles, wave dynamics in strongly scattering systems, and thermal conduction.

Three-dimensional fluid-thermal–mechanical coupling numerical modeling of elastocaloric cooler for electronic chip

The rapid progress in electronic component integration poses formidable challenges to electronic circuit thermal design. The elastocaloric cooling system is a promising solution to address the escalating need for efficient small-scale cooling and temperature control. This study aims to develop an electronic chip cooler based on the elastocaloric effect of shape memory alloys. To more accurately capture the spatial temperature distribution and the intricate fluid flow mixing process of the cooling system, we developed a novel three-dimensional elastocaloric cooling numerical model, also addressing the limitations of existing numerical models in accuracy and applicability. Three cases were designed and evaluated, varying in flow rate, cycle frequency, and strain rate. We propose a criterion for determining the optimal cycle frequency under fixed flow and strain rate: during system stabilization, the frequency that minimizes the disparity between the cooling start line and the cooling end line. The results reveal that the optimal cycle frequency is 1/2.6 Hz at a flow rate of 0.5 L/min and a strain rate of 0.45 s−1. Compared to conventional approaches, our custom-designed elastocaloric cooler results in an additional reduction of 16 K in the chip's maximum temperature. This system achieves a specific cooling power of 6.69 W/g and a coefficient of performance of 1.55.

Numerical thermal control design for applicability to a large-scale high-capacity lithium-ion energy storage system subjected to forced cooling

Overheating and non-uniform temperature distributions within the energy storage system (ESS) often reduce the electric capacity and cycle lifespan of lithium-ion batteries. In this numerical work, the thermal design inside the battery cabinet is explored. The battery cabinet has seven-level configurations with the suction fans located on the top of the ESS to efficiently realize heat dissipation. First, the numerical modeling is validated by the available experimental data, and the discrepancy in the maximum temperature increase between the experimental and computational results is found to be 3.2% or 0.64 K. Then, the optimum airflow rates of the fans are determined, where the single-cell model is also compared with the model of seven-level modules (i.e., 1/3ESS cabinet). Finally, the airflow channel widths, air gaps between the battery modules, as well as the air gaps between the 7th level module and the fans are examined. It is indicated for the precise model of 1/3ESS cabinet that: i) The maximum temperature rise of 4.63 K, and the maximum temperature variation of 2.14 K from cell to cell & the temperature uniformity of 2.82 K from module to module are all controlled with the requirements of operating temperature < 313.15 K, and temperature differences < 5.0 K, respectively; ii) The airflow channel width of 3.0 mm and the air gap of 10 mm between two adjacent modules & air gap of 20 mm between 7th level module and six parallel-fans are designed, and the ESS cabinet can increase the batteries of one level caused by the saved inside space.

Moisture absorption and desorption characteristics and prediction model analysis of building thermal insulation materials

Understanding the isothermal moisture absorption and desorption characteristics of building thermal insulation materials and how they affect thermal conductivity, is curial for accurate building thermal design and energy-saving calculation. In this paper, five types of building thermal insulation materials are selected for investigation. First, the variation trend of the equilibrium mass moisture content of materials in different moisture absorption and desorption stages is studied employing the saturated salt solution method and the constant temperature and humidity box method, and the effect of temperature on the moisture absorption and desorption processes is evaluated. Additionally, the applicable model of the material in the moisture absorption and desorption process is obtained through a fitting analysis of the experimental data. Finally, the influence of the material’s moisture absorption and desorption characteristics on the thermal conductivity is analyzed using the transient thermal conductivity test method. The results highlight that there is a need to consider the moisture absorption and desorption processes to accurately determine the wet material thermal conductivity, and the hysteresis effect of the material in the moisture absorption and desorption processes is directly related to its microstructure and the relative humidity at the initial moisture desorption. At a temperature of 25 oC, the autoclaved aerated concrete exhibits its highest hysteresis rate of thermal conductivity during the moisture desorption process of third stage, reaching 13.2%.

Data-driven dimensional analysis of critical heat flux in subcooled vertical flow: A two-stage machine learning approach

This study presents a novel two-stage machine learning algorithm that identifies dominant dimensionless numbers for critical heat flux (CHF) prediction, circumventing the limitations of traditional dimensional analysis by integrating the Buckingham Pi theorem with advanced computational methods, including the active subspace method and machine learning. When applied to extensive datasets, including 1438 data points from subcooled departure from nucleate boiling (DNB) conditions and validated against a non-overlapping 24,284-point lookup table dataset, our algorithm effectively discerns and validates the dimensionless numbers critical to the CHF phenomena. Notably, it identifies a significant negative correlation between a newly discovered dominant dimensionless number and the boiling number Bochf = q″w,chf / (G hfg), and introduces a new simplified scaling law for water under earth's gravitational conditions, outperforming existing models with substantial predictive accuracy. This scaling law and the identified dimensionless numbers, derived from an initial dataset of 1438 data points, exhibit exceptional generalization capabilities when validated against a significantly larger dataset of 24,284 points. These findings also emphasize the nonlinear effects of inlet quality on the boiling number Bochf. The contribution of this research lies in its potential to deepen the understanding of CHF based on data-driven fashion, with the potential to enhance thermal management and design optimization across various applications.

Thermal design of insulation on the outside of the cavity for a Trombe wall with phase change materials

A Trombe wall with a phase change material (TW-PCM) is a practical and low-carbon passive solar heating method. However, the heat efficiency is not high due to the large amount of heat loss at night. Insulation on the outside of the cavity is a suitable solution, but the design method has not been obtained, which hinders the realization of zero energy buildings. In the present study, we analyzed the thermal performance of a TW-PCM with insulation on the outside of the cavity at nighttime to develop the design approach. A mathematical model was established and validated based on experiments. This model was used to analyze the heat efficiency in different outdoor climates for a TW-PCM with insulation on the outside of the cavity. As well, the solar heating fraction (SHF) was analyzed. The results indicated that insulation on the outside of the cavity could significantly improve the thermal performance due to the reduced heat loss during the nighttime. The recommended additional thermal resistance due to the insulation on the outside of the cavity was negatively correlated with the average outdoor air temperature in January based on the analysis of various climates in China. The thermal resistance of the closed air cavity, formed by the TW-PCM and the insulation component, at the same wall emissivity was similar under the recommended additional thermal resistance in different outdoor climates. The SHF was improved significantly for the TW-PCM buildings with insulation on the outside of the cavity and it had a linear relationship with the solar heating load ratio (SLR).

Analysis of NePCM melting flow inside a trapezoidal enclosure with hot cylinders: Effects of hot cylinders configuration and slope angle

Hot cylinders within the cavity can find diverse thermal applications, ranging from electronic devices and heat exchangers to solar systems, nuclear reactors, and the thermal design of passive cooling systems. Consequently, considering the use of phase change materials (PCM) close to hot cylinders emerges as a viable method for both cooling and storing thermal energy. In this work, two hot cylinders are arranged vertically and horizontally in the nano-enhanced phase change material (NePCM) trapezoidal enclosure with varying angles. The novelty of the current study lies in the fact that no prior research has explored the impact of hot cylinders arrangement on the melting process of a NePCM within a trapezoidal cavity, considering various inclination angles. The fixed grid, adaptive mesh refinement, and enthalpy-porosity method are used to model the melting flow. The numerical results indicate that the trapezoidal enclosure with vertically arranged hot cylinders exhibits better thermal performance than the other configuration. It is also found that the full melting time for both arrangements is minimum when the angle of the trapezoidal enclosure is γ=+40°. The reduction in full melting times for the vertical and horizontal arrangements of this angle are 25.3% and 29.6%, respectively, compared to the trapezoidal enclosure with γ=0.0°. Moreover, the NePCM with the graphite nanoplatelets (GNPs) of φ=1.0% has the shortest melting time for 0.0%≤φ≤3.0%. As future research, further exploration into the complexities of non-Newtonian NePCM flow can be pursued. Additionally, there is potential to explore modifying the cylinders' geometry into elliptical forms, encompassing a range of aspect ratios.

Enhancing Mechanical Properties of Carbon–Silicon Steel through Two‐Stage Quenching and Partitioning with Bainitic Transformation: Ultimate Tensile Strength of 1875 MPa and Total Elongation of 8.03%

To achieve the desired microstructural properties, the ongoing development and innovation in new structural steels require novel thermal processing. This study aims to improve the mechanical properties of a commercial spring carbon–silicon steel by tailoring its microstructure through a process involving quenching and partitioning (Q&amp;P) followed by bainitic transformation. A two‐stage Q&amp;P process is proposed to generate a nanoscale dispersion of stable retained austenite and carbides within the tempered martensite and bainite microstructure. The resulting tensile properties demonstrate a yield strength of 1280 MPa, an ultimate tensile strength of 1875 MPa, and a total elongation of 8.03%. These values surpass those of conventional spring 9254 steel, highlighting the effectiveness of the thermal treatment design. Microstructure analysis reveals the presence of tempered martensite, bainite sheaves, nanoscale carbides, and aggregates of retained austenite. Moreover, the resulting body‐centered cubic matrix exhibits minimal lattice tetragonality of ≈1.0051, coupled with stable retained austenite featuring a carbon concentration of ≈3.42 ± 0.5 wt%, resulting in outstanding strength–ductility properties. These findings indicate that the proposed two‐stage Q&amp;P process, followed by bainitic transformation, significantly enhances the mechanical properties of carbon–silicon steels, making it a promising candidate for high‐performance spring applications.