Heating Mode Research Articles

Numerical Simulation of Microwave-Induced Cracking of Coal Containing Pyrite Powder Based on a Multi-Field Coupling Model

Microwave irradiation has become a potential technical method for coalbed degassing, which can effectively improve its permeability. A coupled electromagnetic—thermomechanical damage (ETMD) model was established to study the damage characteristics of coal containing pyrites. Under microwave irradiation, the temperature increase rate of pyrite was significantly higher compared to the coal matrix. The coal matrix was cracked by expansion stress in high-temperature spots. In the rotational heating mode, the coal matrix was easier to damage than under the static heating mode. The coal matrix damage efficiency was also related to the position of the sample under the static heating mode. Uniform centripetal pressure could inhibit coal matrix damage. Moreover, the pressure distribution affected the damage paths. Compared to no confining pressure, the percentage of areas damaged in coal was lower under low parallel pressure and higher under high parallel pressure.

Bioclimatic Zoning of the Pantanal

Human thermal perception, or thermal comfort, is a critical variable that directly influences the health, productivity, and well-being of populations. However, specific studies on thermal comfort in the Pantanal and its sub-regions are scarce. This study analyzes the distribution of thermal comfort classes in the Pantanal and its sub-regions using the Universal Thermal Climate Index (UTCI) for the period of 1979 to 2023. The main objective was to assess thermal discomfort in the region, identifying comfort classes and examining the influence of El Niño-Southern Oscillation (ENSO) events on this index. The analysis, based on reanalysis climatic data and statistical techniques, mapped the areas most susceptible to thermal stress. The central and southern regions of the Pantanal, such as Porto Murtinho, stood out as the most uncomfortable due to heat, while sub-regions in the north, such as Cáceres and Poconé, showed lower levels of thermal stress. Additionally, it was observed that the months of October and November present the highest UTCI values, indicating extreme thermal discomfort due to heat during the spring. Summer was identified as the most uncomfortable season in terms of heat, while winter showed moderate heat discomfort. The investigation of ENSO events revealed a tendency for greater thermal discomfort during La Niña years. It is concluded that there is a progressive increase in heat-related thermal discomfort in the Pantanal region, with a particularly pronounced trend in the spring.

Thermodynamics analyses on a novel CHP system integrated with multi-grade thermal energy storage

The high penetration level of intermittent renewable power necessitates the crucial requirement for combined heat and power systems to possess both high efficiency and flexibility. However, the heat-controlled operation modes of traditional combined heat and power systems impose limitations on their efficiency and flexibility. Therefore, it is of great significance to develop a heat-power decoupling technology that exhibits exceptional efficiency and flexibility. A novel combined heat and power system integrated with multi-grade thermal energy storage is proposed in this study. Thermodynamic analysis models of all operational conditions are developed, and the comprehensive characteristics of efficiency and operational flexibility for the proposed system are assessed by taking a 330 MW system as an example. Results show that the proposed system can decrease/increase 16.05 MW/30.96 MW power loads comparing with the reference system during the charging/discharging periods under the design condition. Energy efficiency of the proposed system can reach 49.40 %, which is improved by 1.66 percentage points. Exergy analysis reveals the exergy destruction order for the proposed system, and shows that the combustion and heat transfer in the boiler are the major process of exergy dissipation. Moreover, operation strategies of the proposed system during charging-discharging cycle are explored and formulated under off-design condition, suggesting that thermodynamic performances of the novel system under various conditions even extreme conditions exhibits exceptional properties. The maximum heat load of the proposed system can be improved by 46.78 % comparing with the reference system, and the maximum improvement of power load capacity during charging-discharging cycle is 14.58 percentage points. This study provides a promising approach for multi-grade thermal energy storage to improve the comprehensive characteristics of combined heat and power systems.

Nuplon: New synthetic polymers fully degradable in water

New crosslinked polyesters, which are fully degradable in the presence of water over several months in the environment, were synthesized by direct polyesterification of multi-hydroxylic alcohols (e.g., pentaerythritol or glycerol), multi-carboxylic acids (e.g., citric acid), and hydroxy acid compounds (e.g., lactic acid). The reaction produced a crosslinked matrix with mechanical properties of solid and useful degradability in the environment. This reaction can be performed with moderate heat (100–200 °C) and without requiring the aid of additional catalysts, inert gas, or vacuum. The crosslinked matrix can be thermoplastic or thermoset, depending on the extent of crosslinking, which is controlled by reaction time and temperature. The polyesters formed with various ratios of the monomers degrade in water in 12 h at 95 °C, 3 days at 70 °C, and about 3 months at 30 °C. These environmentally degradable alkyl polyesters include a range of mechanical strengths and elasticity, making them suitable for various applications. These environmentally degradable, synthetic polymers can replace current non-degradable polymers in various applications. These new polymers are named “Nuplons”.

Enhancing aerobic composting of food waste by adding hydrolytically active microorganisms

The biomass of native microorganisms in food waste (FW) suitable for accelerated composting is initially low and requires time for adaptation. Adding of efficient hydrolytic microorganisms should be able to enhance compost-specific microbial activity, adjust microbial community structure, and potentially hasten FW biodegradation. This study aimed to identify bacterial and fungal strains with growth characteristics suitable for accelerating FW composting. Over 7 weeks, FW was composted in a pilot-scale test, either inoculated at the start or on day 28 with three different mixtures of 10 autochthonous Bacillus and Penicillium spp. strains known for their high hydrolytic activity. The effects of inoculation were assessed by measuring the rate of carbon dioxide (CO2) and ammonia (NH3) production and also the increase in temperature due to spontaneous exothermic activity of the enhanced microbial population degrading FW. Inoculation with Bacillus spp., particularly B. amyloliquefaciens and B. subtilis, at the beginning of composting increased CO2 production nearly 3-fold while maintaining stable ammonia production and temperature. The high concentration of Bacillus relative to native FW microorganisms led to dominant fermentation processes even in the presence of oxygen, resulting in moderate heat release and elevated production of volatile organic compounds. Introducing Penicillium spp. at a later stage (day 28) increased CO2 production nearly 2-fold, along with higher NH3 levels and temperature. These findings highlight the significance of inoculation timing and microbial composition in regulating metabolic pathways during FW composting degradation, offering insights for designing effective microbial formulations for composting.

Diffusion characteristics of re-suspended PM2.5 within a radiant floor heating room under various ventilation modes

Few studies have revealed the effects of re-suspension of particulate matter deposited by radiant floor heating on indoor environments. The present study utilized Computational Fluid Dynamics (CFD) to investigate the impact of radiant floor heating and ventilation mode on indoor airflow patterns, as well as the dispersion and migration of re-suspended particulate matter, based on a turbulence model validated by an environmental test cabin. The Archimedes number (Ar) was employed to represent the strength of interaction between the thermal buoyancy force generated by floor radiation and the inertial force of the supply airflow. The results indicates that as Ar increases, the supply airflow exhibits a downward deflection, thereby forming a stable vortex below to prevent the diffusion of heat and re-suspended PM2.5 generated from the heated floor. As the Ar increases, the re-suspended PM2.5 deposited on the surrounding walls increased significantly, and the indoor PM2.5 concentration gradually decreased. When the Ar exceeds 6.03, the increase in Ar will no longer affect the indoor re-suspension PM2.5 diffusion, deposition characteristics, and removal efficiency. Therefore, it is recommended the critical Ar (Arcrit) of 6.03 for a radiant floor heating room under various ventilation modes, beyond which the indoor flow structure and distribution characteristics of re-suspended PM2.5 no longer change with increasing Ar. This study is helpful to further understand the diffusion and distribution characteristics of re-suspended particulates in floor heating and ventilation rooms, and provide technical reference for improving indoor air quality.

Curcuma and Scutellaria baicalensis extracts reduced thermoregulatory behavior in chickens subjected to moderate heat stress

Using phytogenic additives represents a new trend in the poultry feed industry because of purported beneficial impacts. There is limited information about the effects on chicken behavior, but based on new studies, some plant-based active compounds influence animal cognitive function. Therefore, the primary objective of this experiment was to investigate the impact of a feed additive consisting of a mixture of Curcuma and Scutellaria baicalensis on behaviors associated with exposure to heat stress in broiler chickens. Chickens before 21 days of age were kept in 12 littered floor boxes according to guidelines for Cobb 500 hybrid. The Cobb 500 chickens of both sexes were fed identical diets until they reached 21 days of age. From this point onward, the experimental group received in the diet a 0.1% supplement containing Curcuma and Scutellaria baicalensis extracts. The control group received a feed mixture without phytogenic additives. Both groups had six replicates, and each group comprised 75 chickens. The pens of experimental and control group were randomly selected. The experimental period spanned from 28 to 35 days of age, during which the chickens were subjected to mild constant heat stress (28°C). Ethological observations were conducted at 31, 32, and 33 days of age, divided into three observation periods at the beginning, middle, and end of the daylight period (18h) using the visual scan sampling method. After the experimental period at 35 days of age, chickens from both groups exhibited nearly identical live body weights and daily feed intake. However, the experimental group demonstrated significantly higher daily weight gain (P < 0.05). Thermoregulatory behaviors such as panting and wing spreading were suppressed (P < 0.05) in the experimental group, while there was a simultaneous increase in the number of chickens that were feeding (P < 0.05). Similarly, age significantly influenced behavioral patterns (P < 0.05), whereas time of the day only affected the number of chickens engaged in feeding (P < 0.05). In conclusion, the feed mixture enriched with Curcuma and Scutellaria baicalensis extracts exhibited performance-enhancing and behavior-changing effects, providing significant insights into the potential of this feed additive in improving performance and reducing thermoregulatory behavior manifestations within a flock under heat-stress conditions, thereby informing the poultry feed industry of a promising new development.

Thermodynamic performance analysis of retrofitting decommissioned coal-fired power plant by Carnot battery energy storage

Retrofitting decommissioned coal-fired power plants (CFPPs) to the Carnot battery (CB) with thermal energy storage (TES) could be an effective way to help the grid absorb more renewable energy. Towards the parameter matching problem in reconstructing the retired CFPP into CB, this paper proposes the feedwater temperature adjustment method and the steam parameter adjustment method to adjust the structure of the Rankine cycle. The results show that the feedwater temperature adjustment method and steam parameter adjustment method can improve the round-trip efficiency of power-to-heat (P2H) type schemes by 0.29 % to 0.95 % and 0.91 % to 0.97 %, respectively. As for CB constructed by heat pump (HP) form, the two methods can improve the round-trip efficiency by 0.09 % to 0.38 % and 0.95 % to 1.02 %, respectively. The sensitivity analysis shows that the feedwater temperature adjustment method is suitable for P2H type schemes and sensitive to variations in exhaust steam pressure. While the steam parameter adjustment method is sensitive to the heat absorption parameter on the heat source side of the matching process, a 1.36 % increase in efficiency can be achieved by regulating the thermodynamic parameters. Under combined heat and power mode, the energy utilization efficiency of CB can reach the maximum of 79.86 % (P2H) and 94.30 % (HP), respectively. At this point, two adjustment methods mentioned above can still be used to obtain efficiency gains close to the power generation model at different heat supply loads. The discounted CO2 reduction factors of different methods can reach about 0.38 t/MWh (P2H) and 0.46 t/MWh (HP) under different design conditions, respectively. This work would be expected to provide a detailed reference for the utilization of decommissioned CFPPs retrofitted to CB for renewable energy consumption.

Naturally circulated system under low to moderate heating condition with supercritical fluid: A comprehensive investigation of loop orientation and Ledinegg instability

Out of the two stability characteristics i.e. static and dynamics, static instability has hardly been explored in such systems due to mathematical complexity and absence of explicit boundary conditions. Present numerical investigation deals with the 1D numerical framework analyzing the steady-state and static instability of the loop under different loop orientation i.e., horizontal heater horizontal cooler (HHHC), vertical heater horizontal cooler (VHHC), horizontal heater vertical cooler (HHVC) and vertical heater vertical cooler (VHVC). The range of heating power considered is applicable in the low to moderate heating condition such as in solar heater and electronic chip cooling. Due to uneven generation of buoyancy and friction throughout the flow path, occurrence of FiHTD is also dependent on it, with best and worst thermalhydraulic characteristics for HHHC and VHVC respectively. For every condition, the appearance of static instability was found to be within the heating power limit. For T∞ = 295 K it spanned over 1050 W for HHHC orientated loop which got decreased by 9.5%, 23.8% and 65.7% for VHHC, HHVC and VHVC respectively. Under the condition of increased of T∞ = 300 K the same was found within the limit of 575 W and got decreased by 13%, 21.7% and 64.3% for cases mentioned above insequential manner. Stability maps drawn using well known non-dimensional numbers holds a good qualitative behavior of static instability. Dynamic instability is well explored for HHHC combination has throughly done previously by various authors and hence, has not been considered here. The authors believe that dynamic instability will not be much more prominant due to predefined flow direction and can be explored as a future work.

Development and demonstration of a BISON–Griffin modeling framework for the design of targeted TRISO transient experiments in the Transient Reactor Test Facility

Uranium oxycarbide (UCO)-bearing tri-structural isotropic (TRISO) particle fuels are expected to be used in numerous U.S. commercial reactor applications within the next decade. In this work, we reviewed historical particle fuel transient experiments to identify gaps in TRISO fuel performance transient testing. A BISON–Griffin modeling framework was then developed to conduct preliminary TRISO transient analyses and begin to address these gaps. The framework was demonstrated using limiting-case transient conditions from a prototypic high-temperature gas-cooled reactor (HTGR). It was then applied to develop a matrix of experiments that could be performed in the Transient Reactor Test Facility (TREAT) to (1) evaluate UCO-fueled particle performance at moderate and high heat rates, (2) assess whether historical testing involving UO2-fueled particles is applicable to modern UCO-fueled particles, (3) deconvolute the impacts of temperature and heat rate on particle transient response, and (4) collect the data needed for fuel performance model validation and/or further development.

A proteomics–bioinformatics approach to assess the molecular and physicochemical properties of brewer's spent grain protein concentrates: Effect of alkali-heat treatment

Brewer's spent grain (BSG) can serve as an attractive protein source due to its low cost and excellent nutritional and functional attributes. Alterations induced by protein extraction process in the BSG protein molecules can affect their functionality and nutritive value. This study investigated the effects of moderate heating during alkaline extraction on the molecular-physicochemical properties of BSG proteins. To this end, BSG protein concentrates were extracted at either room temperature or 50 °C, followed by proteomics and bioinformatics analyses. It was observed that the sample extracted at 50 °C contained proteins with a higher molecular weight, longer length, and enhanced stability relative to the sample extracted at room temperature. The content of acidic proteins showed a 14 % increase due to extraction at 50 °C. A simultaneous decrease in the content of both highly hydrophilic and highly hydrophobic proteins occurred in the sample extracted at 50 °C, while increasing the content of mildly hydrophilic proteins by approximately 25 %. This sample also contained a higher content of essential amino acids. Moreover, the content of proteins with a very high extinction coefficient (>50000 M−1cm−1) increased by 26 % due to extraction at 50 °C. Overall, these findings demonstrate that moderate heating during alkaline extraction can modulate the physicochemical and molecular properties of BSG proteins, providing insights into tailoring their functionality for specific industrial applications.

Performance and optimal design parameters of tunnel lining CHEs under typical design conditions

The subway source heat pump system (SSHPS) incorporating a tunnel lining capillary heat exchanger (CHE) is an efficient technology for mitigating thermal degradation in subway tunnels while fully harnessing geothermal energy for heating and cooling purposes. Although extensive research has been conducted on the performance of tunnel lining heat exchangers, a practical engineering design method is still lacking. The objective of this study is to analyze the heat transfer characteristics of tunnel lining CHEs under typical design conditions and subsequently determine the optimal design conditions based on the analysis results. A numerical model of tunnel lining CHEs was developed using ANSYS, based on a demonstration project of SSHPS in Qingdao. Subsequently, the heat transfer performance of CHEs under various design parameters was simulated and analyzed. Finally, a statistical analysis was conducted to examine the impact of different factors on the heat transfer performance of CHEs. The analysis results indicate that the tunnel air temperature has the most significant influence, followed by the CHE inlet temperature parameter and the length of CHE laying pipe. The impact of the CHE inlet flow velocity is minimal. It is recommended that, during the design stage of a CHE heat exchanger, priority should be given to controlling the tunnel air temperature, optimizing the CHE inlet temperature and pipe length, and setting a minimum possible CHE inlet flow velocity. The optimal combination of design parameters for the tunnel lining CHEs were determined as follows: under the cooling mode, a tunnel air temperature of 23 °C, a CHE design inlet temperature of 39 °C, a laying pipe length of 6 m, and an inlet flow velocity of 0.08 m/s; under the heating mode, a tunnel air temperature of 20 °C, a design inlet temperature of 4 °C, a laying pipe length of 6 m, and an identical flow velocity of 0.08 m/s. This study can serve as a valuable reference for tunnel lining CHE design in practical engineering.

Effect of heat stress during the early lactation period on milk quality traits and reproductive performance of Holstein cows in the western region of Algeria

This study aimed to determine the influence of heat stress during the during early lactation period on milk quality traits and reproductive performance of Holstein cows. Reproduction and milk production records of cows, as well as meteorological data between October 2022 and November 2023, from a 10 commercial dairy herd (n = 228 cows), were used to determine the relationship between heat stress during the early lactation period and reproductive efficiency and milk quality traits. THI was divided into &lt; 70 (no heat stress, n=85), 70–80 (moderate heat stress, n=78), and &gt; 80 (severe heat stress, n= 65). The reproductive result was poor with an average of CFSI (105 ± 35.3 days), CCI (123 ± 38.8 days), NSPC (1.7) and conception rate at first service 53.8%. All CFSI and CCI was highest (P &lt; 0.05) for cows experiencing moderate or severe heat stress during the early lactation period and lowest for cows not undergoing heat stress during the early lactation period. Conception rate at first service of cows decreased (P &lt; 0.05) with increasing hyperthermia during the dry period (63.3%, 50.8%, and 43.5% for THI &lt; 70, 70–80, and &gt; 80, respectively). Cows not experiencing heat stress during the early lactation period required a mean ± SD of 1, 4 ± 0, 7 services per conception compared with 2, 1 ± 0,8 (P &lt; 0.05) for cows subjected to THI &gt; 80 during the early lactation period. Overall, heat stress conditions lowered significantly (P &lt; 0.05) the quality of milk, with fat, protein and lactose content being greatly reduced. In conclusion, Heat stress had a negative impact on the performance of Prim Holsteins dairy cows in the western region of Algeria. The results indicated a need for more research on the relationship between the effect of heat stress and animal characteristics. This study calls for the implementation of mitigation strategies in heat-stressed herds due to the substantial decrease in productivity. This genotype x environment interaction studies deserve to be continued.

Testing of a multi-energy complementary absorption heat pump prototype for combined cooling and heating with large temperature range from − 20 to 90 °C

In the process of carbon neutrality, the comprehensive utilization of clean and renewable energy, including solar, geothermal and biomass, is a potential solution to the low-carbon cooling and heating in distributed areas with weak power grids, such as countryside and suburban. In this paper, an absorption heat pump with multi-energy complementary was built to provide combined cooling and heating. Solar energy was collected through an evacuated tube collector using heat conduction oil, and a gas boiler was adopted to further heat the oil and balance the solar thermal fluctuations. Heat collected in the oil circulation was used to drive an ammonia-water absorption heat pump. A control strategy was proposed to achieve stable energy supply under different weather condition, and efficient operation in wide temperature zone. Environmental test of the prototype was performed in Jinan. The results showed that the prototype ran stably to provide 5-15 kW cooling at −20 to 10 °C, and 20-35 kW heating at 40 to 90 °C, with solar thermal ratio of 20–35 % in different weather conditions, and the renewable energy ratio in heating mode could exceed 55 % through further recovery of ambient heat. Furthermore, the COP for cooling reached 0.30–0.43 at −20 °C cold supply, and 0.70–0.78 at 7 °C cold supply, with cooling water temperatures varied from 30 to 20 °C; and the COP of heating reached 1.40–1.90 at 45 °C heat supply, and 1.35–1.56 at 80 °C heat supply, with evaporation temperature varied from −15 to 20 °C. Results demonstrated that the proposed prototype has significant energy and carbon reduction potential, and is a solution for combined cooling and heating in distributed areas.

Microwave pyrolysis of Choerospondias axillaris seeds with their derived biochar for comprehensive utilization of the biomass

Lignocellulosic biomass is a promising resource for producing biofuels with improved properties and has been extensively utilized in microwave pyrolysis. This study explores the use of Choerospondias axillaris seeds for bio-oil production, with the derived biochar serving as both a microwave absorber and in-situ catalyst. The research characterized the biochar including SEM, BET, NH3-TPD, FTIR, etc, and investigated the impact of different heating modes and types of microwave absorbers on the composition and distribution of pyrolysis products. The results demonstrated that the biochar exhibits excellent microwave absorption properties and catalytic performance. The biochar exhibits a dielectric loss tangent of 0.23 and a specific surface area of 154.54 m2·g−1, characterized by a rich hollow porous structure and surface functional groups. It contains metal elements such as Na, K, and Ca, along with Lewis acid sites, making it an excellent microwave absorption catalyst. Furthermore, the study investigated the effects of microwave power and pyrolysis temperature, revealing that optimal conditions of 700 W and 500 °C result in a fast heating rate of 77.7 °C·min−1, a bio-oil yield of 34.5 wt%, and an aromatics relative content of 61.0 %. The stability of the biochar as a microwave absorption catalyst was evaluated through a reuse study, demonstrating its relatively excellent warming characteristics and product distribution even after five cycles. In summary, this paper proposed an innovative method that employs the derived biochar to enhance biomass pyrolysis, thereby achieving the comprehensive and high-value utilization of Choerospondias axillaris seeds and providing a viable pathway for their sustainable development.

Analysis of OLED glass substrate heated by heating tube array based on multiple optimization algorithms

The temperature uniformity of OLED glass substrate during heat treatment is a key factor affecting the quality of its imaging display. This paper constructs the heating process model of OLED glass substrate based on heating tube array according to the actual scene, studies the thermal characteristics of OLED glass substrate, and then optimizes the temperature uniformity of glass substrate under isometric heating mode based on genetic algorithm, particle swarm optimization algorithm and simulated annealing algorithm. Compared with the initial solution of the algorithm, the optimization rates of the three algorithms respectively reach 75.5%, 86.4% and 98.3%, and the temperature differences are reduced to 3.82℃, 1.44℃ and 0.30℃. Finally, an experimental platform is built to verify the optimization results of different algorithms. The absolute errors are 0.58℃, 1.46℃, 1.30℃ respectively, all lower than 1.5℃, which is within the allowable range of process requirements. It is proved that the proposed optimization algorithm control mode can reduce the heating temperature difference of glass substrate to the ideal level based on the heating device with low cost and simple structure. This scheme provides some reference for the formulation of temperature distribution solution in heat pipe heating technology.

Pulse-Driven MEMS NO2 Sensors Based on Hierarchical In2O3 Nanostructures for Sensitive and Ultra-Low Power Detection.

As the mainstream type of gas sensors, metal oxide semiconductor (MOS) gas sensors have garnered widespread attention due to their high sensitivity, fast response time, broad detection spectrum, long lifetime, low cost, and simple structure. However, the high power consumption due to the high operating temperature limits its application in some application scenarios such as mobile and wearable devices. At the same time, highly sensitive and low-power gas sensors are becoming more necessary and indispensable in response to the growth of the environmental problems and development of miniaturized sensing technologies. In this work, hierarchical indium oxide (In2O3) sensing materials were designed and the pulse-driven microelectromechanical system (MEMS) gas sensors were also fabricated. The hierarchical In2O3 assembled with the mass of nanosheets possess abundant accessible active sites. In addition, compared with the traditional direct current (DC) heating mode, the pulse-driven MEMS sensor appears to have the higher sensitivity for the detection of low-concentrations of nitrogen dioxide (NO2). The limit of detection (LOD) is as low as 100 ppb. It is worth mentioning that the average power consumption of the sensor is as low as 0.075 mW which is one three-hundredth of that in the DC heating mode. The enhanced sensing performances are attributed to loose and porous structures and the reducing desorption of the target gas driven by pulse heating. The combination of morphology design and pulse-driven strategy makes the MEMS sensors highly attractive for portable equipment and wearable devices.

Influence of the Building’s Thermal Insulation on Intermittent Heating Mode Efficiency

Abstract The results of mathematical modeling of a building’s thermal insulation influence on the efficiency of intermittent heating mode are presented. This work aim is to assess the influence of thermal insulation on the efficiency of using the intermittent heating mode for the educational building of the Odessa National Polytechnic University’s Heat Engineering Laboratory. The paper analyzes the factors related to improving the efficiency of the programmed heat supply mode. Modeling of the operating modes for heat supply system operated in intermittent heating mode is carried out. There was performed the mathematical modeling of the heating system operation modes for the most unfavorable climatic conditions at low outdoor temperatures, with respective system efficiency indicators obtaining. The potential of energy saving level for administrative, educational, and office buildings depending on the thickness of thermal insulation of external and internal walls is studied. Recommendations have been elaborated for the use of buildings thermal insulation to improve the efficiency of intermittent heating.

Thermal performance of concentrically arranged two interconnected single-loop pulsating heat pipes

Pulsating heat pipes (PHPs) have garnered significant attention due to their complex thermo-hydrodynamic behavior and their broad applicability in heat transfer. This study focuses on enhancing the two-phase flow startup characteristics of PHPs under concentrated heat loads. A novel concentric-loop PHP configuration was investigated, consisting of two single-turn loops arranged concentrically. The heat pipe has an interconnection between the loops, with the heater positioned on the opposite side to utilize both heating and flow-path asymmetry. The performance was evaluated using pure water as the working fluid, with varying filling ratios, heat loads, and inclination angles. The setup was fabricated with the pure copper capillary tube loops with bend radii of 10 mm and 16 mm, an adiabatic section length of 165 mm, and a condenser section length of 40 mm. The condenser was cooled using a fluid at 20 °C with a flow rate of 20 kg/h. Thermal performance was assessed through measured temperature and thermal resistance under transient conditions. The results showed successful startup at a minimal heat load of 5 W, with the evaporator reaching a lower temperature of 40 °C, leading to a rapid temperature drop and early establishment of a pseudo-steady state. The evaporator was capable of handling a heat flux of up to 22.5 W/cm² in vertical bottom heat mode with a 70% filling ratio. These findings suggest that this new PHP configuration is highly effective for versatile heat transfer applications, including thermal energy storage, power electronics, and electronic systems.

Single-Loop Triple-Diameter Pulsating Heat Pipes at Reduced Heat Input: A CFD Study on Inner Diameter Optimization

The geometric configuration, particularly the inner tube diameter, plays a significant role in the thermal performance of pulsating heat pipes (PHPs). Previous experimental research has demonstrated that single-loop triple-diameter PHPs (TD-PHPs) outperform single-loop single-diameter PHPs (SD-PHPs) and dual-diameter PHPs (DD-PHPs) in terms of thermal performance under moderate heating input powers ranging from 25 W to 75 W. However, a reduction in heat input from 75 W to 25 W leads to a diminished impact of TD-PHPs on the thermal performance. Therefore, to improve the overall performance of TD-PHPs, this study used two-dimensional transient computational fluid dynamics simulations to identify the optimal inner tube diameters for TD-PHPs at a low heat input by evaluating the thermal resistance of five TD-PHPs with various inner diameters. The findings reveal that the TD-PHP configuration exhibits minimum thermal resistance, with inner diameters of 4.5 mm for the upper arch (the condenser section), 4.0 mm for the wide branch, and 2.5 mm for the narrow branch, primarily due to its full circulation flow pattern. Furthermore, the overall heat transfer performance of the optimal TD-PHP was compared with that of an SD-PHP at low heat inputs (10 and 18 W), indicating that although the optimal TD-PHP shows lower thermal resistance, it does not significantly affect the start-up time.