Search Results (198)

Evaporative cooling (EC) offers an energy-efficient alternative to direct expansion (DX) cooling but suffers from high water consumption. This limitation can be mitigated by pre-cooling incoming fresh air using cooler exhaust air via energy recovery. This study presents and optimizes a solar-driven EC system integrated with underfloor air distribution (UFAD) to enhance thermal comfort and minimize water use in a temporary office in Riyadh’s arid climate. A 3D CFD model was developed and validated against published data to simulate indoor airflow, providing data for thermal comfort evaluation using the predicted mean vote model in cases with and without energy recovery. A year-round hourly energy analysis revealed that the solar-driven EC-UFAD system reduces grid power consumption by 93.5% compared to DX-based UFAD under identical conditions. Energy recovery further cuts annual EC water usage by up to 31.3%. Operational costs decreased by 84% without recovery and 87% with recovery versus DX-UFAD. Full article

In a warming climate, rising temperature are expected to influence atmospheric humidity. This study examined the spatio-temporal dynamics of temperature (TEMP) and relative humidity (RH) across Equatorial Africa from 1980 to 2020. The analysis used RH data from European Centre of Medium-range Weather Forecasts Reanalysis v.5 (ERA5) reanalysis, TEMP and precipitation (PRE) from Climate Research Unit (CRU), and soil moisture (SM) and evapotranspiration (ET) from the Global Land Evaporation Amsterdam Model (GLEAM). In addition, four teleconnection indices were considered: El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO). This study used the Mann–Kendall test and Sen’s slope estimator to analyze trends, alongside multiple linear regression to investigate the relationships between TEMP, RH, and key climatic variables—namely evapotranspiration (ET), soil moisture (SM), and precipitation (PRE)—as well as large-scale teleconnection indices (e.g., IOD, ENSO, PDO, and NAO) on annual and seasonal scales. The key findings are as follows: (1) mean annual TEMP exceeding 30 °C and RH less than 30% were concentrated in arid regions of the Sahelian–Sudano belt in West Africa (WAF), Central Africa (CAF) and North East Africa (NEAF). Semi-arid regions in the Sahelian–Guinean belt recorded moderate TEMP (25–30 °C) and RH (30–60%), while the Guinean coastal belt and Congo Basin experienced cooler, more humid conditions (TEMP < 20 °C, RH (60–90%). (2) Trend analysis using Mann–Kendal and Sen slope estimator analysis revealed spatial heterogeneity, with increasing TEMP and deceasing RH trends varying by region and season. (3) The warming rate was higher in arid and semi-arid areas, with seasonal rates exceeding annual averages (0.18 °C decade⁻¹). Winter (0.27 °C decade⁻¹) and spring (0.20 °C decade⁻¹) exhibited the strongest warming, followed by autumn (0.18 °C decade⁻¹) and summer (0.10 °C decade⁻¹). (4) RH trends showed stronger seasonal decline compared to annual changes, with reduction ranging from 5 to 10% per decade in certain seasons, and about 2% per decade annually. (5) Pearson correlation analysis demonstrated a strong negative relationship between TEMP and RH with a correlation coefficient of r = − 0.60. (6) Significant associations were also observed between TEMP/RH and both climatic variables (ET, SM, PRE) and large scale-teleconnection indices (ENSO, IOD, PDO, NAO), indicating that surface conditions may reflect a combination of local response and remote climate influences. However, further analysis is needed to distinguish the extent to which local variability is independently driven versus being a response to large-scale forcing. Overall, this research highlights the physical mechanism linking TEMP and RH trends and their climatic drivers, offering insights into how these changes may impact different ecological and socio-economic sectors. Full article

Understanding morphological descriptions of plants documented by ancient peoples over 1000 years ago and identifying the species they described are critical for reconstructing the natural geographic distribution of plant taxa, tracking taxonomic variations, and inferring historical climate dynamics. Analyzing shifts in plant communities and climatic conditions during this period is essential to unravel the interplay among floristic composition, climate fluctuations, and anthropogenic impacts. However, research in this field remains limited, with greater emphasis placed on plant taxa from hundreds of millions of years ago. Investigations into flora and climate during the last two millennia are sparse, and pre-millennial climatic conditions remain poorly characterized. In this study, a historical text written 1475 years ago was analyzed to compile plant names and morphological features, followed by taxonomic identification. The research identified three gymnosperm species (one in Pinaceae, two in Cupressaceae), 1 Tamaricaceae species (dicotyledon), and 19 dicotyledon species. However, three plant groups could only be identified at the genus level. Using textual analysis and woody plant coexistence methods, the climate of 1475 years ago in western Henan Province, located in the middle-lower Yellow River basin in East Asia, was reconstructed. Results indicate that the mean temperature of the coldest month (MTCM) was approximately 1.3 °C higher than modern values. In comparison, the mean temperature of the warmest month (MTWM) and mean annual temperature (MAT) were lower than present-day levels. This suggests slightly cooler overall conditions with milder seasonal extremes in ancient Luoyang—a finding supported by contemporaneous studies. Furthermore, annual precipitation (AP), precipitation of the warmest quarter (PWQ), and precipitation of the coldest quarter (PCQ) in the Luoyang region 1475 years ago exceeded modern measurements, despite the area’s monsoonal climate. This suggests significantly higher atmospheric moisture content in ancient air masses compared to today. This study provides floristic and climatic baseline data for advancing our understanding of global climate variability at millennial scales. Full article

Background: Effective pain management in children is essential, particularly when administering local anaesthesia. This study was undertaken to compare pain perception in children after application of pre-cooled and plain topical anaesthetic gel during local anaesthetic administration. Methods: A randomised, single-blinded controlled trial was conducted among 51 children between the ages of 6 and 12, visiting the paediatric clinic, Jazan (REC-45/10/1070). Children were allocated into one of the following three groups using a simple randomisation having a 1:1:1 allocation ratio into Group I (n = 17): Plain topical anaesthetic gel, Group II (n = 17): Pre-Cooled topical anaesthetic gel, and Group III (n = 17). An ice pack was applied for a period of 1 min at the injection site. The intensity of pain and the behaviour of the children were assessed using Face, Leg, Activity, Cry, Consolability (FLACC), the Modified Wong–Baker Scale (WBS) and the Frankel Behaviour Rating Scale (FBRS). Results: A significant difference in FBRS scores was observed during anaesthesia, with the highest median score [3 (3,3)] in the pre-cooled topical anaesthetic gel group (p value < 0.001). FLACC scores varied significantly among groups, with the ice pack group [3 (3, 3)] and [4 (4, 5)] showing the highest median score (p value < 0.001). WBS scores also differed significantly between groups (p value < 0.001) with a lower value in the pre-cooled topical gel group [0 (0, 0), 2 (0, 2)]. Conclusions: This study concluded that, the use of a pre-cooled topical anaesthetic gel before LA administration reduced the pain better than that of plain anaesthetic gel and ice pack application at the injection site during infiltration. Full article

Background and Objectives: Hyperthermia significantly limits endurance performance in hot environments. To enhance heat loss and optimize athletic performance, pre-cooling interventions can be employed to accelerate body cooling. Therefore, the aim of this study was to evaluate the effects of an internal pre-cooling intervention combined with external pre-cooling or hydrogen-rich water on endurance performance in the heat. Materials and Methods: In a double-blind crossover with counterbalanced trials, all participants underwent a shuttle run test after 30 min under the following conditions: (1) hydrogen-rich cold water ingestion (HRCW); (2) cold water ingestion and external pre-cooling (IEPC); and (3) cold-water ingestion (control). Maximal aerobic speed (MAS), number of shuttle run repetitions, dehydration, temperature, heart rate (HR), rate of perceived exertion (RPE), blood lactate, and feeling scale (FS) were measured during the 20 m shuttle run test. Results: Our results revealed a significant variation in dehydration, MAS, number of shuttle run repetitions, blood lactate, RPE, and FS (p = [0.001–0.036]); additionally, a significant group × time interaction was found for body temperature (p = 0.021). Post hoc tests revealed a significant change for MAS (HRCW: p < 0.001), number of shuttle run repetitions (HRCW: p < 0.001), dehydration (HRCW: p= 0.009; IEPC: p = 0.008), blood lactate (HRCW: p < 0.001; IEPC: p < 0.001), RPE (HRCW: p = 0.05; IEPC: p = 0.004), and FS (HRCW: p = 0.05; IEPC: p = 0.004), as well as a significant decrease in body temperature (IEPC: p < 0.001; HRCW: p = 0.028) compared to the control condition after the test. However, no significant differences were reported in HR among the different conditions. Conclusions: In conclusion, findings from this study suggest that ingesting hydrogen-rich cold water effectively mitigates the effects of heat stress, thereby improving endurance performance, enhancing mood, and reducing ratings of perceived exertion. Full article

The excessive use of fossil fuels could bring about a global environmental crisis. Transitioning from a carbon-based to a hydrogen-based economy is an important way to realize the low-carbon energy transition. The key to this economy transformation lies in the efficient utilization of hydrogen. Hydrogen liquefaction is an efficient technology for the transportation and storage of hydrogen, and the liquid hydrogen produced is also a direct feedstock for many important fields. Large-scale liquefaction of hydrogen has not been commercialized due to its high energy consumption (>10 kWh/kg_LH2) and low efficiency (<30%). However, conceptual designs for hydrogen liquefaction with a low energy consumption (about 6.4 kWh/kg_LH2) and high efficiency (>40%) are frequently reported in the existing literature. Therefore, in this paper, the production process of liquid hydrogen is reviewed from three aspects, which are hydrogen pre-cooling, hydrogen cryo-cooling, and ortho-para hydrogen (OPH) conversion. The focus is to summarize effective and realistic hydrogen liquefaction schemes in the existing studies to provide process guidance for the subsequent practical production of liquid hydrogen. The development of open and closed refrigeration cycles for hydrogen pre-cooling is reviewed following the lead of pre-coolant types. The implementation methods of structural optimization of different hydrogen cryo-cooling cycles are clarified and the performance improvements achieved are compared. Different modes of OPH conversion are presented and their realization in simulation and practical applications is summarized. Finally, subjective recommendations are given regarding the content of the review. Full article

Numerical simulation has become a pivotal tool for analyzing airflow dynamics and temperature patterns during the precooling of postharvest horticultural products stacked in vented package. In this study, a three-dimensional mathematical model for iceberg lettuces stacked symmetrically in plastic crate was developed. The influence of the physical model at different gap sizes on the simulation accuracy was studied by assessing wall drag coefficient, airflow distribution, and heat transfer efficiency. The results show a reasonable decrease in the drag coefficient with an increasing gap size to 6 mm in terms of airflow distribution inside the plastic crate; any further increase in gap size and the average airflow velocity in both windward and leeward sides decreases rapidly. Interestingly, the gap size exhibited a limited impact on heat transfer characteristics during the cooling process. Thus, 6 mm was found to be the optimal distance to ensure good accuracy in simulation results and reduce the complexity of grid division. The numerical model was verified by experimental data. Moreover, the validation confirms good consistency between the simulated predictions and experimental measurements. This study provides a theoretical basis for establishing a reliable numerical model for the precooling of agricultural produce stacked symmetrically in a vented package. Full article

The hydrogen fuel quality is critical to the efficiency and longevity of fuel cell electric vehicles (FCEVs), with ISO 14687:2019 grade D establishing stringent impurity limits. This study compared two different sampling techniques for assessing the hydrogen fuel quality, focusing on the National Physical Laboratory hydrogen direct sampling apparatus (NPL DirSAM) from a 35 MPa heavy-duty (HD) dispenser and qualitizer sampling from a 70 MPa light-duty (LD) nozzle, both of which were deployed on the same day at a local hydrogen refuelling station (HRS). The collected samples were analysed as per the ISO 14687:2019 contaminants using the NPL H₂-quality laboratory. The NPL DirSAM was able to sample an HD HRS, demonstrating the ability to realise such sampling on an HD nozzle. The comparison of the LD (H₂ Qualitizer sampling) and HD (NPL DirSAM) devices showed good agreement but significant variation, especially for sulphur compounds, non-methane hydrocarbons and carbon dioxide. These variations may be related to the HRS difference between the LD and HD devices (e.g., flow path, refuelling conditions and precooling for light duty versus no precooling for heavy duty). Further study of HD and LD H₂ fuel at HRSs is needed for a better understanding. Full article

This article proposes a mathematical model for experimental estimation of the volumetric heat capacity and thermal conductivity of flat samples, in particular samples cut from potato tubers. The method involved using two pairs of samples, each of which includes the test sample and a reference sample. The pairs of samples were pre-cooled in a refrigerator to a temperature that was 10 to 15 °C below room temperature. Then, the samples were removed from the refrigerator and placed in an air thermostat at ambient temperature, with one pair of samples additionally blown with a weak air flow. Using a thermal imager, the surface temperatures of the samples were recorded. The temperature measurement results were processed using the proposed mathematical models. The temperature measurement results of the reference samples were used to determine the Bi numbers characterizing the heat exchange conditions on the surfaces of the test samples. Taking into account the found Bi values, the volumetric heat capacity and thermal conductivity were calculated using the formulas described in the article. The article also presents a diagram of the measuring device and a method for processing experimental data using the results of experiments as an example, where potato samples were used as the test samples, and polymethyl methacrylate samples were used as the reference samples. The studies were conducted at an ambient air temperature of 20 to 24 °C and at a Bi < 0.3. The specific heat capacity of the potato samples was in the range of 2120–3795 J/(kg·K), and the thermal conductivity was in the range of 0.17–0.5 W/(m·K) with a moisture content of 10–60%. Full article

This study presents a preliminary analysis of an innovative system that combines indoor air conditioning with water recovery and storage. The device integrates Peltier cells with a horizontal Earth-to-Air Heat Exchanger (EAHX), exploiting the ground stable temperature to enhance cooling and promote condensation. Warm, humid air is pre-cooled via the geothermal pipe, then split by a fan into two streams: one passes over the cold side of the Peltier cells for cooling and dehumidification, while the other flows over the hot side and heats up. The two airstreams are then mixed in a water storage tank, which also serves as a thermal mixing chamber to regulate the final air temperature. The analysis investigates the influence of soil thermal conditions on condensation within the horizontal pipe and the resulting cooling effect in indoor spaces. A hybrid simulation approach was adopted, coupling a 3D model implemented in COMSOL Multiphysics^® with a 1D analytical model. Boundary conditions and meteorological data were based on the Typical Meteorological Year (TMY) for Palermo. Two scenarios were considered. In Case A, during the hours when air conditioning is not operating (between 11 p.m. and 9 a.m.), air is circulated in the exchanger to pre-cool the ground and the air leaving the exchanger is rejected into the environment. In Case B, the no air is not circulated in the heat exchanger during non-conditioning periods. Results from the June–August period show that the EAHXs reduced the average outdoor air temperature from 27.81 °C to 25.45 °C, with relative humidity rising from 58.2% to 66.66%, while maintaining nearly constant specific humidity. The system exchanged average powers of 102 W (Case A) and 96 W (Case B), corresponding to energy removals of 225 kWh and 212 kWh, respectively. Case A, which included nighttime soil pre-cooling, showed a 6% increase in efficiency. Condensation water production values range from around 0.005 g/s with one Peltier cell to almost 0.5 g/s with seven Peltier cells. As the number of Peltier cells increases, the cooling effect becomes more pronounced, reducing the output temperature considerably. This solution is scalable and well-suited for implementation in developing countries, where it can be efficiently powered by stand-alone photovoltaic systems. Full article

Hydrogen (H₂) liquefaction is an energy-intensive process, and improving its efficiency is critical for large-scale deployment in H₂ infrastructure. Industrial waste heat recovery contributes to energy savings and environmental improvements in liquid H₂ processes. This study proposes a comparative framework for industrial waste heat recovery in H₂ liquefaction systems by examining three recovery cycles, including an ammonia–water absorption refrigeration (ABR) unit, a diffusion absorption refrigeration (DAR) process, and a combined organic Rankine/Kalina plant. All scenarios incorporate 2 MW of industrial waste heat to improve precooling and reduce the external power demand. The simulations were conducted using Aspen HYSYS (V10) in combination with an m-file code in MATLAB (R2022b) programming to model each configuration under consistent operating conditions. Detailed energy and exergy analyses are performed to assess performance. Among the three scenarios, the ORC/Kalina-based system achieves the lowest specific power consumption (4.306 kWh/kg LH₂) and the highest exergy efficiency in the precooling unit (70.84%), making it the most energy-efficient solution. Although the DAR-based system shows slightly lower performance, the ABR-based system achieves the highest exergy efficiency of 52.47%, despite its reduced energy efficiency. By comparing three innovative configurations using the same industrial waste heat input, this work provides a valuable tool for selecting the most suitable design based on either energy performance or thermodynamic efficiency. The proposed methodology can serve as a foundation for future system optimization and scale-up. Full article

“Foam container + ice pack” is a common packaging form for e-commerce logistics of litchis. However, there are numerous factors affecting the temperature variation under this logistics mode, making it difficult to control the packaging temperature and litchi quality during the e-commerce logistics process. In order to explore the impact of the packaging scheme on the packaging environment temperature and the quality variation in litchis during the “foam container + ice pack” logistics process, this paper takes the number of ice packs, the terminal pre-cooling temperature of litchis, the weight of litchis, and whether to use aluminum foil insulating film as variable factors to study the impact rules of these factors on the EPS (Expanded Polystyrene) foam container environment temperature, the total number of fruit pericarp, and the marketable fruit rate. The experimental results show the following trends: the terminal pre-cooling temperature has a significant impact on the daily average temperature of the fruit layer; the packaging environment temperature of the 15 °C pre-cooling group on the first day and the second day is 5.00 °C and 2.78 °C higher than that of the 5 °C pre-cooling experimental group, respectively. Moreover, under this treatment, the growth rate of fruit pericarp fungi is relatively fast, which could reach 3.87 Lg (CFU/g) on the second day. Increasing the amount of litchis could maintain a lower temperature environment, but it will cause the relative conductivity increasing 4.12% compared with the groups with no weight increasing. Increasing the number of ice packs could significantly reduce the decline rate of fruit soluble solids in the first two days. The research results of this paper are expected to provide a certain reference for the quality assurance logistics and the formulation of long-distance transportation strategies for perishable agricultural products. Full article

Aluminum alloy hot stamping technology has quickly become a research hotspot for many scholars due to its ability to solve key challenges such as poor formability, large rebound, and low dimensional accuracy of aluminum alloy sheets at room temperature. This work systematically reviews the progress of Hot-Forming-Quenching (HFQ^®) technology and its optimization processes. The effects of key forming parameters are summarized, including temperature, forming rate, friction, and crimping force on the forming properties of aluminum alloys. Additionally, an ontological model of thermal deformation behavior and damage evolution during hot forming is analyzed. A multifactorial strength prediction model, integrating grain size and reinforcement mechanisms, is highlighted for its ability to accurately predict post-forming yield strength. To address the limitations of HFQ^®, optimization methods for solid solution and aging heat-treatment stages are categorized and evaluated, along with their advantages and disadvantages. Furthermore, the latest advancements in two innovative hot stamping processes (Low-Temperature Hot Form and Quench (LT-HFQ^®) and pre-hardened hot forming (PHF)) are reviewed. LT-HFQ^® improves formability by pre-cooling the sheet while maintaining solution treatment, while PHF utilizes pre-hardened aluminum alloys, enabling brief heating, forming, and quenching to significantly reduce cycle time while ensuring component strength. Finally, by summarizing current technological progress and challenges, future directions for aluminum alloy hot stamping are outlined, including advancements in forming processes, material modeling, and optimization through multidisciplinary collaboration and artificial intelligence to drive further innovation. Full article

Heating, Ventilation, and Air Conditioning (HVAC) systems primarily consist of pre-cooling air handling units (PAUs), air handling units (AHUs), and air ducts. Existing HVAC control methods, such as Proportional–Integral–Derivative (PID) control or Model Predictive Control (MPC), face limitations in understanding high-level information, handling rare events, and optimizing control decisions. Therefore, to address the various challenges in temperature and humidity control, a more sophisticated control approach is required to make high-level decisions and coordinate the operation of HVAC components. This paper utilizes Large Language Models (LLMs) as a core component for interpreting complex operational scenarios and making high-level decisions. A chain-of-thought mechanism is designed to enable comprehensive reasoning through LLMs, and an algorithm is developed to convert LLM decisions into executable HVAC control commands. This approach leverages adaptive guidance through parameter matrices to seamlessly integrate LLMs with underlying MPC controllers. Simulated experimental results demonstrate that the improved control strategy, optimized through LLM-enhanced Model Predictive Control (MPC), significantly enhances the energy efficiency and stability of HVAC system control. During the summer conditions, energy consumption is reduced by 33.3% compared to the on–off control strategy and by 6.7% relative to the conventional low-level MPC strategy. Additionally, during the system startup phase, energy consumption is slightly reduced by approximately 17.1% compared to the on–off control strategy. Moreover, the proposed method achieves superior temperature stability, with the mean squared error (MSE) reduced by approximately 35% compared to MPC and by 45% relative to on–off control. Full article

Seasonal freeze–thaw irrigation areas face challenges of soil salinization and water scarcity, requiring a deep understanding of soil freeze–thaw dynamics under the interaction between irrigation and groundwater. An in situ lysimeter experiment was conducted in the winters of 2020–2021 and 2023–2024 to investigate the effects of autumn irrigation (AI) timing (late AI conducted in late November and icing AI conducted in early December) and quota (0, 35, 135, 270 mm) on soil water, heat, and salt transport under varying groundwater levels in the Hetao Irrigation District, Northwest China. Results showed that AI had a strong short-term effect on the groundwater depth and there was a significant negative correlation between groundwater depth and air temperature on a monthly scale. The quota and air temperature during AI were the key factors in utilizing the “refrigerator effect”—where irrigation water pre-cooled by frozen layer accelerates soil freezing—to regulate soil water and salt transport under freeze–thaw cycles. The drastic reduction in AI water consumption lowered the groundwater level, highlighting air temperature as the dominant driver of soil dynamics. Thus, icing AI with low quota (35 mm) can optimize water use (water saving of 77% compared to the traditional quota of 150 mm) while maintaining soil moisture (an increase of 17.4% in water storage) and salinity control (a decrease of 41.6% in salt storage) in the root zone (0–40 cm) through the “refrigerator effect”, demonstrating its potential for sustainable irrigation in water-scarce cold regions. Full article