Low-temperature Heat Research Articles

Self-regulating heating and self-powered flexible fiber fabrics at low temperature

Self-regulating heating and self-powered flexibility are pivotal for future wearable devices. However, the low energy-conversion rate of wearable devices at low temperatures limits their application in plateaus and other environments. This study introduces an azopolymer with remarkable semicrystallinity and reversible photoinduced solid-liquid transition ability that is obtained through copolymerization of azobenzene (Azo) monomers and styrene. A composite of one such copolymer with an Azo: styrene molar ratio of 9:1 (copolymer is denoted as PAzo9:1-co-polystyrene (PS)) and nylon fabrics (NFs) is prepared (composite is denoted as PAzo9:1-co-PS@NF). PAzo9:1-co-PS@NF exhibits hydrophobicity and high wear resistance. Moreover, it shows good responsiveness (0.624 s−1) during isomerization under solid ultraviolet (UV) light (365 nm) with an energy density of 70.6 kJ kg−1. In addition, the open-circuit voltage, short-circuit current and quantity values of PAzo9:1-co-PS@NF exhibit small variations in a temperature range of -20 °C to 25 °C and remain at 170 V, 5 μA, and 62 nC, respectively. Notably, the involved NFs were cut and sewn into gloves to be worn on a human hand model. When the model was exposed to both UV radiation and friction, the temperature of the finger coated with PAzo9:1-co-PS was approximately 6.0°C higher than that of the other parts. Therefore, developing triboelectric nanogenerators based on the in situ photothermal cycles of Azo in wearable devices is important to develop low-temperature self-regulating heating and self-powered flexible devices for extreme environments.

Simulation analysis of low-temperature heat generation of power batteries based on the ECM model

Abstract When the power battery operates in low temperatures, it encounters challenges with charging and discharging, leading to a decline in battery performance, which can prevent electric vehicles from starting and reduce their driving range. To address this, the battery must possess the capability to adapt to both extremely high and low temperatures. This article employs ANSYS software to investigate the heat generation in batteries due to their own charging and discharging processes at different discharge rates under -20°C. When the battery is heated at a 1 C discharge rate for 20 minutes, its temperature rises by approximately 1.1°C; at 2 C, the temperature rises by about 5°C; and at 3 C, it rises by about 11°C. The greater the discharge rate is, the more heat is generated, resulting in a higher temperature rise. Furthermore, prolonged heating at a certain discharge rate can elevate the temperature to a level that is optimal for lithium-iron-phosphate batteries, ultimately reaching their optimal operating range. This research contributes to enabling lithium-ion power batteries to function normally in low-temperature environments, without compromising their lifespan. It is imperative to heat the interior of lithium-ion power batteries to ensure they can start normally after prolonged overnight parking, through preheating.

Effect of nanomaterials on the melting/freezing characteristics of phase-change material

A novel variant of composite phase-change material (PCM) was developed by incorporating 0.5 wt% aluminum oxide (Al2O3), silicon dioxide (SiO2), copper (II) oxide (CuO) and silver (Ag) nanomaterials into myristic acid. In this formulation, myristic acid served as the foundational material, while aluminum oxide, silicon dioxide, copper (II) oxide and silver were employed as supporting components. The morphology and crystalline structure of the nanomaterials were studied using field-emission scanning electron microscopy and X-ray diffraction analysis, respectively. The composite PCMs were fabricated using a two-step process. The phase-change properties of the composite PCMs were assessed using differential scanning calorimetry. The nanomaterials (0.5 wt% aluminum oxide, silicon dioxide, copper (II) oxide and silver) were suspended in myristic acid separately to investigate the heat-transfer performance of the composite PCMs during phase-change processes (melting and freezing). The results clearly indicated that the duration of the melting and freezing processes of the composite PCMs decreased compared with that of the pure PCM. Thus, the newly prepared composite PCMs are potential candidates for harvesting solar energy for low-temperature heating applications.

Low-Temperature Heat Capacity of Zinc Tungstate Single Crystal

Low-Temperature Heat Capacity of Zinc Tungstate Single Crystal

Geospatial characterization of low-temperature heating and cooling demand in residential, commercial, manufacturing, agricultural, and data center sectors for potential geothermal applications in the United States

Thermal demand for heating and cooling has been predominantly supplied by fossil fuel combustion in the United States, although low-carbon alternatives are extensively available including geothermal, solar thermal, and waste heat. This study analyzed end-use energy consumption, fuel expenditure, and data center commissioned power data to geospatially characterize the U.S. low-temperature heating and cooling demand at the county level in residential, commercial, manufacturing, agricultural, and data center sectors and understand potential opportunities for geothermal applications. In the analysis, the regional-scale energy consumption data was incorporated with system efficiencies to address actual demand and was then disaggregated with weighting factors to the county level. The results indicated that total low-temperature heating and cooling demand is 16.7 EJ, combining heating demand of 10.8 EJ and cooling demand of 5.9 EJ. Overall, 59.9 % (10 EJ) of the low-temperature heating and cooling demand occurred in the residential sector. The heating and cooling demand visualized in maps represented that the geospatial distribution of heating and cooling demand in the residential and commercial sectors is governed by the number of housing units and climate zone designations, while heating and cooling demand in the manufacturing, agricultural, and data center sectors is dependent on the number and location of facilities. The results also demonstrated that geothermal heat pumps are broadly used in the residential and commercial sectors for heating and cooling in the U.S. Midwest, South, and Northeast regions but are limited in the West, implying great decarbonization potential in the future.

Evaluating building-level parameters for lower-temperature heating readiness: A sampling-based approach to addressing the heterogeneity of Dutch housing stock

The Dutch government aims to eliminate natural gas for residential heating in 1.5 million homes by 2030. One strategy is connecting existing dwellings to lower-temperature district heating (DH) systems, although these dwellings might require energy renovations. The heterogeneous dwelling stock causes varying renovation needs that complicate the energy transition. The present study addresses this issue by assessing the building-level parameters affecting the readiness of the Dutch terraced-intermediate and apartment types for lower-temperature heating (LTH) supplied by DH systems. A sampling-based approach was employed to capture variability within these dwelling types, addressing the limitations of archetype-based methods. The findings suggest a sample size of 1300 to represent the variations in these dwelling types. Parametric simulations and machine learning methods were used to identify significant building-level parameters for medium-temperature (MT: 70/50 °C) and low-temperature (LT: 55/35 °C) supply levels. These include heating setpoints (desired indoor temperature) and ventilation-related parameters (ventilation system type and air infiltration rate), followed by fabric-related parameters (roof, glazing, wall, ground, and door insulation) and geometric properties (orientation, compactness ratio, and window-to-wall ratio). Additionally, radiator oversizing also impacts LTH readiness. These results broadly apply to the studied dwelling types, although feature importance varies by supply temperature and dwelling type. The findings can guide stakeholders in assessing current conditions and prioritising renovation measures, aiding the development of targeted renovation solutions. Encompassing the representative variations within studied dwelling types enhances the robustness of the results. However, incorporating more refined data could improve the accuracy of the findings, better supporting the energy transition of these dwellings.

Effects of ammonia energy ratio and PODE injection timing on combustion and emissions in a PODE/ammonia RCCI engine

The application of ammonia as an alternative carbon-free fuel has attracted increasing attention. In this paper, the effects and mechanisms of ammonia energy ratio (AER) and polyoxymethylene dimethyl ethers (PODE) injection timing on the combustion and emissions characteristics of a PODE/ammonia RCCI engine are investigated by both experimental and numerical methods. Results show that increasing AER from 10% to 40% leads to the delayed low temperature heat release (LTHR) due to reduced OH radical generated by PODE and the competition between PODE and ammonia for OH radical consumption. The larger AER increases the indicated thermal efficiency (ITE) by lowering combustion temperature and reducing heat transfer losses at the cost of higher hydrocarbon (HC), carbon monoxide (CO), and unburned NH3 emissions. The reduction of fuel-based nitrogen oxide (NOx) emissions with a larger AER is attributed to the enhanced in-cylinder thermal denitrification reactions. The delayed start of injection (SOI) from −60 °CA ATDC to −45 °CA ATDC leads to the higher peak in-cylinder pressure and temperature, resulting in the larger heat transfer losses and lower ITE. The impact of retarding SOI on NOx is insignificant under the combined effect of more thermal NO formation, less fuel-based NO generation, and weakened denitrification reactions. Additionally, nitrous oxide (N2O) shows dominant effects on the total greenhouse gas (GHG) emissions, and increasing AER or advancing injection timing produces more GHG. Under low loads and low AERs, although the introduction of ammonia helps to improve ITE, more researches are required to further reduce exhaust emissions.

High potency of application on an open direct-contact thermal storage using humid air

To reuse low-temperature wasted heat as a thermal resource for high temperature, a direct-contact adsorption thermal storage was focused using humid air and zeolite 13X particles as the working fluid and adsorbent, respectively. Only a few previous studies have chosen the working fluid in gaseous form because it is unavailable for latent heat in generating heat sources. Recovering waste heat in humid air to generate hotter steam is unique and becomes an originality of our present work. The time required to regenerate zeolite particles and the maximum temperature of the generated steam were investigated assuming a warm-up device for a vehicle. The time required to regenerate zeolite was investigated by changing the dew point, temperature, and superficial velocity of the inlet humid air. It was mainly affected by the temperature of the inlet air. The absorbent was regenerated within 30 min when the humid air preheated to 200 °C was supplied. On the other hand, the maximum steam temperature was investigated by changing the superficial velocity and temperature of saturated inlet humid air. As one of the significant and novel finding in this work, the steam of >200 °C was obtained as a high-temperature heat source even with saturated humid air unavailable latent heat. Moreover, as theoretical knowledge, it was revealed that the maximum temperature of the heat source can be estimated by the relationship between the heat balance on the packed bed and adsorption equilibrium.

Crystal Growth, Structure, and Diverse Magnetic Behaviors in Frustrated Triangular Lattice REBO3 (RE = Tb-Yb).

Triangular lattice (TL) materials are a rich playground for investigating exotic quantum spin states and related applications in quantum computing and quantum information. Millimeter-level single crystals of REBO3 (RE = Tb-Yb) with a nearly perfect RE-based TL have been successfully grown via a high-temperature flux method and structurally characterized via single-crystal X-ray diffraction. These 113-type materials crystallize in a monoclinic crystal system with a C2/c space group. Anisotropic magnetism and dominant antiferromagnetic interactions are found for the above materials based on DC magnetic susceptibility measurements. The comprehensive low-temperature specific heat data of REBO3 (RE = Tb-Tm) are characterized on single crystals for the first time, which exhibit diverse magnetic behaviors. Specifically, two weak-field-induced transitions could be found in the case of DyBO3 based on the specific heat measurements. Our results suggest that REBO3 (RE = Tb-Yb) is a TL magnetic system for investigating potential quantum magnetism.

Design and Implementation of a Non-Destructive AC Heating System for Lithium-Ion Battery Modules

The electrification of transportation is experiencing rapid development. Electric bicycles (e-bikes) are commonly employed as convenient modes of transportation. Thanks to the advantages of long life and high energy density, lithium-ion batteries (LIBs) are widely used in e-bikes. In certain business models, e-bikes can utilize rental LIBs, which are centrally managed at charging stations. The low-temperature charging and discharging performance of the LIB system poses a significant challenge during usage. Among various heating methods, alternating current (AC) heating has garnered attention due to its high efficiency and has been applied to quickly warm up the LIB system. To address this issue, an AC heating model was established to determine the appropriate frequency and magnitude of the current, and a prototype AC heating system for the LIB modules used in e-bikes was designed. A full-bridge topology system model was established, and an experimental platform was constructed to test the effectiveness of the proposed AC heating topology and thermoelectric model under different AC heating frequencies and currents. The results show that the proposed AC heating system can heat an 18650 battery module within 20 min. Under an ambient temperature of −20 °C, using a 10 A, a 100 Hz excitation current achieves a heating rate of 1.3 °C per minute, with minimum power losses. The prototype also has a fast response time of only 70 ms. Finally, the strategies of LIB heating and insulation are proposed for the scenario of a battery swapping station. This research holds great significance in resolving the problem of low-temperature heating for e-bikes in cold regions.

Development of a Cure Model for Unsaturated Polyester Resin Systems Based on Processing Conditions.

Unsaturated polyester resin (UPR) systems are extensively used in composite materials for applications in the transportation, marine, and infrastructure sectors. There are continually evolving formulations of UPRs that need to be evaluated and optimized for processing. Differential Scanning Calorimetry (DSC) provides valuable insight into the non-isothermal and isothermal behavior of UPRs within a prescribed temperature range. In the present work, non-isothermal DSC tests were carried out between temperatures of 0.0 °C and 250 °C, through different heating and cooling ramp rates. The isothermal DSC tests were carried out between 0.0 and 170 °C. The instantaneous rate of cure of the tested temperatures were measured. The application of an autocatalytic model in a calculator was used to simulate curing behaviors under different processing conditions. As the temperature increased from 10 °C up to 170 °C, the rate of cure reduced, and the heat of reaction increased. The simulated cure behavior from the DSC data showed that the degree of cure (α) maximum value of 71.25% was achieved at the highest heating temperature of 85 °C. For the low heating temperature, i.e., 5 °C, the maximum degree of cure (α) did not exceed 12% because there was not enough heat to activate the catalyst to crosslink further.

Kinetics of Water Adsorption in Metal-Organic Framework(MOF-303) for Adsorption Cooling Application

Adsorption cooling systems (ACS) powered by low-temperature heat offer an energy-efficient and environmentally friendly alternative to traditional vapor-compression systems. The effectiveness of ACS is significantly influenced by the alignment of the adsorbent properties with the operating conditions of the cycle. Metal-Organic Frameworks (MOFs) are considered the next generation of water harvesting and ACS. Many MOFs are synthesized and tested for water harvesting systems, one of these MOFs is MOF-303 which was reported to have very rapid water sorption dynamics under atmospheric conditions. However, MOF-303 has never been tested under the same conditions as ACS (under vacuum). In this study, the isotherms and kinetics of water adsorption on MOF-303, as an efficient adsorbent of water vapor, is experimentally investigated for the ACS using the linear driving force model. The diffusion coefficients across a wide range of relative pressures under two different temperatures were estimated. The study compares the adsorption process of MOF-303 with traditional silica gel (SG) in the context of diffusion kinetics relevant to ACS. Based on the output and at a constant temperature of 25 °C and across all relative pressure ranges, MOF-303 exhibited an average increase of approximately eight times in diffusion kinetics compared to SG. Specifically, within the relative pressure range of 10–30 %, which is optimal for ACS, MOF-303 demonstrated a seven-fold increase in diffusion kinetics over SG. The diffusion values for SG display a clear upward trend with increasing temperature. In contrast, the diffusion values for MOF-303 are subject to fluctuations with temperature changes under investigation. Notably, the isotherm for MOF-303 shows an inflection point at relative pressures between 10–15 %, causing a significant reduction in diffusion at these specific relative pressures compared to other relative pressure values. The findings in this study highlight the potential use of MOF-303 as a highly efficient water adsorbent for the ACS which will enable scientists and engineers to develop sustainable low-grade energy systems.

An experimental validation study of a numerical modeling approach to predicting post-consolidation dimensions of thermoplastic composites

Consolidation is an important step in the processing of thermoplastic unidirectional (UD) tapes, as it creates a bond between individual tapes to form a semi-finished sheet: The tape stack is first heated and then cooled, both while being subjected to pressure. If the material is in a soft or even molten state and its flow unrestricted, this compression can result in squeeze flow, the direction of which is determined by the fibers of the tapes. Extensive squeeze flow not only results in significant changes in part geometry to the point where it may fail to meet design and application specifications but can also lead to severe distortion and residual stresses. To address this, we developed a model that, given the process parameters and fiber orientation, predicts the effects of squeeze flow. Based on experimental data on UD polycarbonate tapes with 44% carbon fibers by volume consolidated at various process settings, this paper presents the validation of the model for industrial application. We found that at low heating temperatures, where the matrix viscosity is too high and prevents the material from flowing, the simulation results deviated markedly from the experimental data. With these temperatures excluded, however, the overall deviation of the model was 8.7% for thickness change and 5.3% for area change.

Effects of Low-Temperature Heat Treatment on Mong Hsu Rubies

Effects of Low-Temperature Heat Treatment on Mong Hsu Rubies

Numerical analysis of the Maxwell-Cattaneo-Vernotte nonlinear model

In the literature, one can find numerous modifications of Fourier’s law, the first of which is the Maxwell–Cattaneo–Vernotte heat equation. Although this model has been known for decades and successfully used to model low-temperature damped heat wave propagation, its nonlinear properties are rarely investigated. This paper aims to present the functional relationship between the transport coefficients and the consequences of their temperature dependence, particularly focusing on thermal conductivity. These are the consequences of the second law of thermodynamics. Furthermore, we introduce a particular implicit numerical scheme in order to solve such nonlinear heat equations reliably, free from artificial numerical errors. We investigate the scheme’s stability, dissipation, and dispersion attributes. We demonstrate the effect of temperature-dependent thermal conductivity on two different initial-boundary value problems, including time-dependent boundaries and heterogeneous initial conditions, for which we discuss the nontrivial constraints following irreversible thermodynamics.

Flexible Thermoelectric Electrode with a New Nitrogen-Modified MXene/SWCNT Layered Structure for Efficient Low-Grade Thermal Energy Collection.

Confronting the global challenge of energy efficiency in the backdrop of environmental concerns, the innovation of a flexible thermoelectric electrode marks a significant stride forward, especially in the realm of low-temperature heat recovery. This investigation unveils a pioneering electrode material, a nitrogen-doped SWCNT/MXene bilayer thin film, which was meticulously engineered for thermoelectric systems. Surpassing the conventional Pt electrode with inherent inflexibility and prohibitive cost, our proposed electrode showcases excellent ductility alongside commendable thermoelectric properties. Our electrodes demonstrate significant advancement, achieving a thermopower output of 14.11 μW·cm-2 with the Seebeck coefficient escalating to 1.61 mV·K-1 even at a modest temperature differential of 40 °C. The results mark a substantial 32% enhancement in thermoelectric performance compared to the power output at 10.69 μW·cm-2 for a Pt electrode under similar conditions. This remarkable improvement underscores the superior efficiency and potential of our electrodes for practical thermoelectric application, offering a viable and cost-effective alternative to traditional Pt-based solutions. This innovation not only positions itself as a formidable contender to Pt electrodes but also signals a new dawn for efficient thermoelectric energy harvesting, underscored by the material's scalability and ready availability.

Preparation of Soft Magnetic Composite Using Cold Sintering Technique

Soft magnetic composites are powder metal products under development as an alternative to 2D laminates in electric motor applications. The 3D design of SMCs offers greater energy efficiency but poses a challenge to maintain adequate strength properties required for application. Soft magnetic composites are fabricated through compaction and heat treatment of iron particles coated with insulated coating to form a dense compact. The soft magnetic properties of the compact are affected by the properties of the iron powder, density of compact as well as the efficacy of forming uniform thin insulating coating at the particle boundary. Additionally, the strength of the compact is also affected by the nature of the insulating boundary at the particle interfaces. We report a low temperature process that involves cold sintering phenomenon to densify and strengthen soft magnetic composites. Iron powders have been modified using a co-precipitation method that forms a hydrated copper/iron oxalate coating on individual iron particles. Warm compaction of the modified iron powders at 100°C resulted in a highly dense soft magnetic composite which demonstrated ~ 3x improvement in strength. The compacts can be further heat treated in air at higher temperatures to form high strength oxide coating iron based soft magnetic composites. Results of the AC and DC magnetic measurements of fabricated cold sintered toroid compacts made as a function of heat treatment temperature reveal that DC permeability increased with heat treatment temperature. Analysis of AC core loss data showed that hysteresis power losses dominated the performance at lower heat treatment temperatures (< 300°C) beyond which dynamic core losses significantly increased.

Simulating the Effects of Ammonia Crossover and Alternative Ligands in Thermally Regenerative Flow Batteries

There is a significant amount of low-temperature heat (< 100 °C) available globally from various sources such as geothermal energy, industrial processes, and thermal power plants. Electrochemical and membrane-based methods for harnessing this heat are becoming of greater interest due to their ability to utilize the low temperature energy sources and because they can be sized modularly to fit the power, energy, and spatial requirements of the application. The all-aqueous thermally regenerative ammonia battery (Cuaq-TRAB) is a leading technology in the waste heat to electrical power production space due to recent results showing operational power densities of 25 mW cm-2 with an estimated thermal energy efficiency of 7%, outperforming most technologies in this space. Previous research on the Cuaq-TRAB has shown that the battery suffers from the crossover of ammonia through the membrane which adversely impacts battery performance.To investigate these impacts, we developed a simple numerical model that simulates discharge curves using one fitting parameter to account for parasitic crossover instead of modeling species transport through the membrane. The model was able to replicate experimental data from Cuaq-TRABs with different membrane materials and for multiple applied current densities with < 5% error for average power and energy capacity. Results showed that there is a 20% loss in Cuaq-TRAB energy capacity due to ammonia crossover when compared to a discharge with no parasitic crossover losses. The model was then extended to demonstrate the impact of different changes to the electrolyte chemistry on the resultant power and energy capacities for Cuaq-TRABs. Using this model, we estimate that if chloride was the ligand for the positive electrolyte instead of bromide, it would decrease the power and energy capacity of the battery by 30%. However, considering that an economic analysis showed that chloride is 80% cheaper than bromide, it may be beneficial to consider the use of chloride ligands in this technology despite its worse electrochemical performance.

Dynamic simulation of a combined solar system including phase change material storage and its experimental validation

Thermal energy storage is a key issue in efficient energy system applications, especially in renewable energies. In this respect, phase change materials (PCM) have attracted interest as an active solution for efficient energy management, particularly in the building sector. This paper presents a modelling of a PCM thermal battery in solar system assisted by heat pump. The storage stores the heat produced by unglazed solar panels (Batisol®) and releases it into a heat pump. Then this heat is sent to two other PCM storages. In this way, the low-temperature heating and domestic hot water needs of a commercial building in winter are met. The storage consists of a block of PCM contained between two plates of heat transfer fluid. It acts as a plate heat exchanger that can be charged and discharged simultaneously. The objective of the study is to dynamically simulate the thermal behaviour of this storage for different hot inlet temperature profiles. A rectangular profile is used to validate the model using experimental results. Then, a solar system assisted by heat pump and three PCM storages is dynamically simulated. This 2D model would be useful to validate a simpler model for optimising the operational parameters of the system.

Non-Fermi-liquid behavior consistent with a preasymptotic disorder-tuned ferromagnetic quantum critical point in the heavy fermion system CeTi1−xVxGe3

An investigation of the thermodynamic and electrical transport properties of the isoelectronic chemical substitution series CeTi1−xVxGe3 (CTVG) single crystals is reported. As x increases, the ferromagnetic (FM) transition temperature is suppressed, reaching absolute zero at the critical concentration x=0.4, where a non-Fermi-liquid low-temperature specific heat and electrical resistivity, as well as the hyperscaling of specific heat and magnetization, are found. Our study suggests the presence of an FM quantum critical point (QCP) in CTVG. The obtained critical exponents indicate that CTVG falls in the preasymptotic region of the disorder-tuned FM QCP predicted by the Belitz-Kirkpatrick-Vojta theory. Published by the American Physical Society 2024