Passive Heat Research Articles

Utility of Body Weight, Urine Color, and Thirst Perception (WUT) in Determining Hydration in Young Adults.

The primary aim of this study was to assess the efficacy of the weight, urine, thirst (WUT) framework in predicting dehydration after a body water manipulation protocol, while concurrently determining the individual and interactive contributions of the model components. The total study sample was 93 participants (female, n = 47), recruited from two institutions. Phase 1 involved collecting daily hydration measures from free-living participants (Study 1, 58 participants for 3 days; Study 2, 35 participants for 7 days). Phase 2 entailed a two-hour passive heating protocol, where participants from Study 2 were randomly assigned to one of three groups that manipulated total body water over 24-hours using passive heating and fluid restriction. During each Phase, participants provided urine samples, underwent body mass measurements, and completed questionnaires pertaining to thirst perception. Morning and 24-hour urine samples were assessed for color, osmolality, and specific gravity. Differences between intervention groups, based on the probability of hydration status, were examined (ANOVA) and ridge regression analysis assessed the relative importance of variables within the WUT model. The study revealed significant differences among the intervention groups for predicted probability of dehydration, as determined by changes in body mass (p = 0.001), urine color (p = 0.044), and thirst perception (p < 0.001). Binomial ridge regression indicated that change in body mass (58%) and thirst perception (26%) were the most influential predictors of dehydration. These data support use of an enhanced version of the WUT model, underscoring the significance of changes in body mass and thirst perception in the assessment of hydration status.

The effect of seasonal heat acclimatization on cool-seeking behaviour during passive heat stress in young adults.

Seasonal heat acclimatization is known to enhance autonomic thermoeffector responses, whereas the behavioural response following seasonal heat acclimatization remains unknown. We investigated whether seasonal heat acclimatization would alter autonomic and behavioural thermoregulatory responses. Sixteen healthy participants (eight males and eight females) underwent two trials involving 50 min of lower-leg passive heating (lower-leg submersion in 42°C water) with (Fan trial) and without (No fan trial) the voluntary use of a fan in a moderate thermal environment (27°C, 50% relative humidity) across winter and summer months. In Fan trials, participants were allowed to use a fan to maintain thermal comfort, but this was not allowed in the No fan trials. Cool-seeking behaviour was initiated at a lower change in rectal temperature [mean (SD): 0.21 (0.18)°C vs. 0.11 (0.13)°C, P=0.0327] and change in mean skin temperature [2.34 (0.56)°C vs. 1.81 (0.32)°C, P<0.0001], and cooling time was longer [16.46 (5.62) vs. 20.40 (4.87) min, P=0.0224] in summer compared with winter. However, thermal perception was not modified by season during lower-leg passive heating (all P>0.0864). Furthermore, rectal temperature was higher in summer (P=0.0433), whereas mean body temperature and skin temperature were not different (all P>0.0631) between the two seasons in Fan trials. In conclusion, seasonal heat acclimatization enhanced the cool-seeking behaviour from winter to summer.

Research on Operation Characteristics of Passive Containment Heat Removal System in Typical Accident Conditions

In order to verify the feasibility of the design of the third generation of nuclear power plant independently developed in China, this study investigated the operation characteristics of the passive containment heat removal system under five working conditions using the passive containment heat removal system general performance verification facility: the design conditions, low water level conditions, low pressure conditions in the containment, extreme accidents conditions and resistance increasing conditions are analyzed, and the thermal characteristics, power requirements and thermal parameters of the containment under different operating conditions are analyzed. The results show that the heat dissipation capacity of the passive containment heat removal system exceeds the design requirements under the design conditions. Under off-design low pressure conditions, the pressure in the system is significantly affected. The decrease in the cooling water tank’s water level not only did not adversely affect the operation of the system but instead led to a significant increase in the system’s heat dissipation power. In the case of extreme accidents, the system may initially stall, but a stable natural cycle can then be established. As the system resistance coefficient increases, the heat dissipation power of the passive containment heat removal system exhibits an approximate linear decreasing trend.

Study of a Novel 3D Façade Configuration and Its Impact on Energy Performance and Office Space Sustainability

This research paper examines how multi-angled façade systems improve and optimise energy performance compared to a flat façade and meet sustainability targets for lower energy use to align with UN SDGs 3, 11, 12, and 13. The multi-angled façade system does not tilt up and down. Instead, it employs two different window orientations on a vertical axis (left and right). The large portion orients more to the north to allow more daylight to penetrate inside the room, and the small part is oriented more to the south to provide passive solar heating. The investigations in this research paper were carried out using version 4.8 of the IDA ICE software, and the researchers evaluated the energy consumption, the energy action through the façade, and the building’s inside operative temperature. The results of this paper present the simulation findings for primary energy consumption in different scenarios. For example, the researchers explain that one can save 6.3 kWh/(m2·year) when using a multi-angled façade system compared to a flat façade. This is in addition to improving the thermal indoor climate that results from using the façades. The conclusions of the research show that the façade with multiple angles maximises using daylight and optimises solar power, thus avoiding overheating issues.

Experimental study on a novel self-driven multi-heat sinks system

This article presents a self-driven multi-heat sinks system suitable for cooling multiple heat sources simultaneously. This system can include one driving heat sink and multiple passive heat sinks. The porous medium inside the driving heat sink absorbs heat from its heat source, causing the working fluid to evaporate. The phase changing generating capillary force to drive the circulation of liquid throughout the system. The circulating working fluid flows through the fluid channels in the external passive heat sinks, carrying away the heat from the heat sources at each passive heat sink, thus simultaneously cooling multiple heat sources. This study primarily altered the connections between heat sinks, specifically connecting them in serial and parallel, forming systems with different structures. The operating characteristics of the two differently structured systems were studied through experiments. Results show that both systems effectively dissipate heat, maintaining stable operation at a maximum heat load of 100 W. By comparing the operating characteristics of each heat sink in different structures, it was found that the structure mainly affects the circulation resistance of the working fluid. In the serial system, the high circulation resistance leads to long startup times and high startup temperatures. In contrast, the parallel system effectively addresses these issues and, due to its lower internal circulation resistance, and reduces the operating temperature of the driving heat sink. The parallel system's startup time and temperature are 7% lower than the serial system, and its driving heat sink can handle an additional 10 W of heat load. However, due to the structural impact, each passive heat sink in the parallel system receives lower flow, resulting in higher operating temperatures for the passive heat sinks. Based on the research findings above, the article concludes by outlining the suitable operating conditions for different systems: series-connected and parallel-connected systems are respectively suitable for scenarios where the heat generation of multiple heat sources is similar and where it varies significantly.

Heat Attainment and Retention in Surfers with and without a Land-Based Warm-Up and Accompanying Passive Heat Retention.

Surfing is a growing, high-participation recreational and competitive activity. It is relatively unique, being performed on, in, and through water with a range of temperatures. In other sports, warm-up and heat retention have proved useful at augmenting performance and ameliorating injury risk. Little work has been carried out examining this in surfing. The purpose of this work was to measure thermal profiles in surfers with and without warm-up and passive heat retention, and secondarily to assess any potential influence on free surfing. A repeated measures pre- and post- design was adopted whereby participants surfed in an artificial wave pool following an active warm-up combined with passive heat retention (experimental condition) and after no warm-up (control). Core body temperature was measured both occasions. Our results showed increases in core body temperature were greater for the experimental condition versus control (p = 0.006), and a time effect exists (p < 0.001)-in particular, a warm-up effect in the water itself was shown in both groups, possibly due to further activity (e.g., paddling) and wetsuit properties. Finally, performance trended to being superior following warm-up. We conclude that body warmth in surfers may be facilitated by an active warm-up and passive heat retention. In free surfing, this is associated with a trend towards better performance; it may also reduce injury risk.

Water flow boiling heat transfer and pressure drop in smooth, etched, and herringbone aluminum tubes

Designing next generation heat exchangers for efficient heat transfer and minimal material consumption is required for sustainable development of society. While several heat transfer augmentation techniques are available, extended surfaces have been the most widely adopted due to their relative ease of integration and high heat transfer enhancement. However, since extended surfaces are mainly applicable for soft metals, and require significant capital investment for manufacturing, we propose scalably fabricated microstructures as an alternative and scalable heat transfer augmentation technique. Our etching-based structures are cost-effective, scalable, and applicable to a wide array of metallic tubing. The conformal microstructures, which have length scales ranging between ∼ 1 to 12 μm, are introduced through chemical etching of internal tube walls using hydrochloric acid. To test the water flow boiling performance of our etched surfaces, experiments were conducted on 0.25-inch diameter aluminum tubes over a range of mass and heat fluxes spanning 200 kg/(m2·s) <G < 380 kg/(m2·s) and 60 kW/m2 <q″ < 125 kW/m2, respectively. Using deionized water as the working fluid, an enhancement of up to 104 % in the tube-averaged heat transfer coefficient with a concurrent increase of up to 65 % in pressure drop was observed. The increase in the heat transfer coefficient and pressure drop is attributed to the microstructures increasing the surface roughness and creating additional nucleation sites for bubble entrapment. When compared to commercially available finned herringbone tubes, we observed that for certain operating conditions, the enhancement in heat transfer due to use of microstructures in smooth tubes can exceed that of the enhancement observed using un-structured herringbone tubes. However, the pressure drop due to the increased surface area and fluid flow disruption of the chevron shaped herringbone fins always exceeded the etched aluminum round tube. This work provides insights and understanding related to how chemical etching and surface structuring can be utilized as an alternative passive heat transfer enhancement technique in flow boiling applications.

Experimental and numerical studies of detailed heat transfer and flow characteristics in the rib turbulated annulus of a double pipe heat exchanger

An enhancement in the overall heat transfer between the fluids in a Double pipe heat exchanger (DPHE) can be achieved through various active or passive techniques. The present study focuses on the passive heat transfer enhancement in the annular region of a DPHE by incorporating circular ribs on the outer surface of the inner pipe. The primary objective is to investigate the influence of the ribs on the local distribution of heat transfer and fluid flow in the annulus of the heat exchanger. The local Nusselt number (Nu) distribution was determined experimentally using a test section specially designed with a provision to measure the wall temperature distribution of the inner pipe with an IR thermal imaging camera. The pressure drop across the channels with the ribs was also measured in the experimental studies. Numerical studies are employed to gain insights into the flow characteristics in the annular region in the presence of ribs. Studies comprise various rib diameters (e/Dh = 0.08, 0.14), rib-to-rib pitches (P/e = 6, 12, 18), and Reynolds number values (Re = 5000, 7500, and 10000). The heat transfer behaviour from the experimental study is discussed based on the flow mechanism observed using numerical techniques. The flow separation and reattachment due to the rib and the induced recirculation zone cause large variations in the Nusselt number distribution between the ribs. The peak Nusselt number value between adjacent ribs is observed at the location of reattachment of the flow to the ribbed wall. Acquired data also shows that the flow and heat transfer characteristics differ significantly with changes in the P/e ratio. The rib configuration with e/Dh = 0.14 and P/e = 12 is identified as optimal, achieving a balanced improvement in heat transfer while showing a relatively lower pressure drop.

Demand response with PCM-based pipe-embedded wall in commercial buildings: Combined passive and active energy storage in envelopes

Demand response (DR) allows Heating Ventilation and Air Conditioning (HVAC) systems to reduce or shift their electricity consumption during peak periods through the global temperature adjustment strategy. Phase change materials (PCM) based walls are the effective energy storage facilities, storing energy in the pre-cooling period and releasing energy during DR event. However, the traditional configuration of PCM-based wall only allows the passive heat transfer between the walls and the indoor air, requiring a long time to complete the phase change process in the pre-cooling period. This paper presents a novel application of PCM-based pipe-embedded wall (PCM-based PE-wall) in building demand response, which combining active and passive heat transfer mechanism to enhance energy storage rates. The effect of PCM-based PE-walls on demand response is evaluated under two different pre-cooling modes: active pre-cooling only (Envelope-2A) and combined passive and active pre-cooling (Envelope-2B). The results show that the implementation of the PCM-based PE-wall can significantly enhance the overall heat transfer rate of the cooling storage in envelopes and thus improving the demand response performance. Compared to traditional PCM walls (Envelope-1), PCM-based PE-walls (Envelope-2B) could cause additional peak demand reductions of 15.78 % and additional energy reductions of 10.18 % during DR events.

Application of the passive turbocharger to PRHRS in integral PWR type SMR with an sCO2 power cycle

One of the potential design concepts for small modular reactor(SMR) is coupling an integral pressurized water reactor(IPWR) with a supercritical CO2(sCO2) power cycle to reduce the plant footprint. However, the passive safety systems of this SMR concept have not been well established compared to steam power cycle based SMRs. In this study, a passive turbocharger utilizing the unique characteristics of sCO2 is proposed as a way to improve the passive safety of sCO2 power cycle. This is the concept of installing a turbine-compressor set at the connection of passive residual heat removal system(PRHRS) to effectively remove the high level of residual heat in the early stages of an accident rather than relying only on natural circulation cooling. Based on the findings, it can be concluded that proposed sCO2 turbocharger concept has the potential to enhance performance of PRHRS and reduce the height of natural circulation loop leading to smaller volume.

Will global warming reduce the nutritional quality of wild blueberries?

Anthropogenic climate change may affect the nutritional quality of perennial crops. Wild blueberry is a perennial crop of cultural and economic importance and known for its health-promoting properties. Wild blueberry fields in Maine, USA are experiencing unprecedented warming, which may affect the quality and marketability of the fruit. We examined the biochemistry of wild blueberries grown under active open-top heating that elevated temperatures by 3.3 °C, passive open-top heating by 1.2 °C, and ambient conditions (control). We found that total soluble solids, fructose, total soluble sugars and total soluble protein decreased as temperatures increased. In contrast, anthocyanin, total flavonoid and phenolics were not affected. Additionally, warming weakened the correlation between sugars, total soluble solids, and other components. Our results suggest that future global warming may reduce the nutritional value and marketability of wild blueberries. Potential mitigation techniques will need to be developed for future production.

High-Fidelity Simulation of the Light-to-Dense Stratification Transient in the HiRJET Facility

Density stratification in a large enclosure is a crucial phenomenon to heat transfer and sustainable passive heat removal of a sodium fast reactor during reactivity transients. However, engineering turbulence models were identified to have unsatisfactory performance in predicting propagation of a stratified front. Yet, the scarcity of high-resolution data for stratification hampers the development of models. To explor e applications of leveraging direct numerical simulation (DNS) data to support turbulence model development, this work conducted DNS using NekRS to study a long stratification transient in the High-Resolution Jet (HiRJET) experimental facility. This work considers an experiment run where light fluid is injected into a tank containing a denser fluid with a relative density difference of 1.5%. Formation of the stratified layer is identified as impingement of the buoyant jet promoting mixing of the two fluids. Based on the transient statistics, transport of the concentration can be characterized by regions with dominating effects of turbulent mixing, buoyant dissipation, and molecular diffusion, respectively, as moving away from the elevation of jet impingement. Concentration near the stratified front also exhibits oscillation at Brunt-Väisälä frequency. Preliminary validation of the simulation showed encouraging agreement of the concentration distribution with the reference experiment.

An Innovative Heating Solution for Sustainable Agriculture: A Feasibility Study on the Integration of Phase Change Materials as Passive Heating Elements

In this study, we investigate an innovative option for the ecological management of agricultural land. The focus is on the use of phase change materials (PCMs) for passive temperature regulation in greenhouses and fruit crop fields in order to reduce yield losses due to unforeseen late frost events. The use of PCMs represents a novel approach to enhancing crop growth and extending growing seasons without relying on conventional energy-intensive methods, providing a stable microclimate that can protect plants from cold stress. This passive regulation of temperature helps to reduce the need for fossil fuel-based heating systems, thereby lowering greenhouse gas emissions and operational costs. The application of PCMs in agricultural settings is particularly innovative as it leverages naturally occurring temperature variations to create a self-sustaining, low-maintenance solution that aligns with the principles of sustainable farming. This approach not only improves energy efficiency but also contributes to the resilience of agricultural practices in the face of climate variability. This study focuses on the possible use of PCMs in passive heating modules for the protection of potted plants in greenhouses. Various PCMs such as paraffin, beeswax, and shea butter were tested. Experiments were then conducted, using one kind of paraffin-based PCM, in a specially designed module. In addition, an FEM simulation model (CFD) was built and tested. The model was used to perform detailed analyses of the heat transfer efficiency, fluid dynamics, and overall performance of the modules. The model can also be used for optimization purposes (e.g., efficiency improvements).

Enhanced multifunctional sensing in human motion with speed-controlled coaxial wet-spun hollow MWCNT-TPU/TPU smart fibers

In the field of personal health management and athletic performance optimization, the demand for multi-parameter human signal monitoring devices is rapidly increasing. Currently, flexible sensors produced through wet spinning techniques face challenges of simplistic structure and functionality, as well as difficulty in balancing strength and sensitivity. In-depth research is needed to develop high-performance wet spinning techniques, which will lay the foundation for commercial smart garments capable of unobtrusively monitoring human motion in the future. This study innovatively employs specialized slurry formulations and spinning speed controls to utilize the timing differences in fiber precipitation and the affinity among similar materials. Through the coaxial wet spinning process, it enables the continuous, large-scale manufacturing of hollow core–shell fibers, MT/T-S5, which feature a dense inner layer and a porous outer conductive layer. This special structure endows the fibers with high strength, high signal stability, and capabilities for both active and passive heating. These fibers achieve a maximum gauge factor (GF) 65.2 in stretch sensing applications and can detect pressures as low as 0.1 N. The MT/T-S5 smart fibers can sense human joint movements, and through connection with an Arduino microcontroller, they can control a robotic hand and perform independent and real-time motion detection of five fingers to distinguish gestures. This research not only provides a new type of fiber material for the development of future smart textiles but also reveals a formation mechanism for hollow core–shell fibers in the field of wet spinning. This discovery can offer valuable inspiration for fiber structural design in future research.

Towards Climate, Bioclimatism, and Building Performance—A Characterization of the Brazilian Territory from 2008 to 2022

Representative weather data are fundamental to characterizing a place and determining ideal design approaches. This is particularly important for large countries like Brazil, whose extension and geographical position contribute to defining diverse climatic conditions along the territory. In this context, this study intends to characterize the Brazilian territory based on a 15-year weather record (2008–2022), providing a climatic assessment based on a climatic and bioclimatic profile for the whole country. The climate analysis was focused on temperature, humidity, precipitation, and solar radiation, followed by a bioclimatic analysis guided by the Givoni chart and the natural ventilation potential assessment. In both situations, the results were analyzed using three resolutions: country-level, administrative division, and bioclimatic zones. This study also identified representative locations for the Brazilian bioclimatic zones for a building-centered analysis based on the thermal and energy performance of a single-family house with different envelope configurations. The results proved that most Brazilian territories increased above 0.4 °C in the dry bulb temperature and reduced relative humidity. The precipitation had the highest reduction, reaching more than 50% for some locations. The warmer and drier conditions impacted also the Köppen–Geiger classification, with an increase in the number of Semi-Arid and Arid locations. The bioclimatic study showed that ventilation is the primary strategy for the Brazilian territory, as confirmed by the natural ventilation potential results, followed by passive heating strategies during the year’s coldest months. Finally, building performance simulation underlined that, in colder climates, indoor thermal comfort conditions and air-conditioning demands are less affected by solar absorptance for constructions with low U-values, while in warmer climates, low solar absorptance with intermediary U-values is recommended.

Heat insulation and thermal insulation method of passive low energy consumption residential building exterior envelope structure based on BIM

With the improvement of economic level, a continuous rise in building energy consumption brings about serious environmental problems. Therefore, this study proposes a passive energy-consuming residential building envelope thermal insulation and heat preservation method based on building information modeling technology for building energy consumption increasing and envelope structure's performance improving. Firstly, it is a study on the passive low-energy residential building envelope's thermal insulation materials and architecture, and secondly, it is a study on the improvement of the thermal insulation and heat preservation performance of the passive low-energy residential building envelope on the foundation of building information modeling. These experimental results show that in the residential building, the indoor temperature averages around 27.8 °C, of which the highest indoor ambient temperature is found at 21 o'clock, with a temperature value of 28.4 °C, which reduces 2.1 °C when comparing with the indoor temperature under the traditional residential building. Under the exterior wall construction utilizing this technology, the temperature change of the indoor environment is smoother, which satisfies people's requirements for the indoor living environment. At the same time, the area parameters of the ventilation area of the building and the area of the envelope obtained after the analysis of BIM technology have a significant effect on the cooling of the interior. This method reduces the use of resources and lays a good foundation for the further development of building informatization, which is significant in realizing the informatization developing in construction.

Numerical investigations on the performance of coupled NCL based passive heat removal system of an IPHWR

Passive heat removal systems (PHRS) are indispensable additional safety features in nuclear reactors to deal with station blackout (SBO) conditions. These systems are based on coupled natural circulation loops (C-NCL) connected in series configuration. Further, these system's design, operating conditions, working fluid, heat removal capacity, etc., are specific to the reactor type. In the present work, the operational performance of such first of a kind PHRS of 700 MWe Indian pressurized heavy water reactor (IPHWR) is investigated. For this purpose, a coupled two-phase NCL code is developed, validated and employed. This PHRS consists of two NCLs connected in HHVC-VHVC (horizontal heater and vertical cooler - vertical heater and vertical cooler) configuration. In this study, initially, the full power reactor thermal-hydraulic conditions are established, subsequently, the performance of the PHRS under SBO is investigated. The analyses demonstrated that the system is adequate to effectively eradicate the decay heat by establishing single and two-phase natural circulation (NC) flows of ∼4.5 % and ∼5.6 % of rated conditions in primary and secondary transport loops, respectively. The maximum PHRS capability is predicted to be ∼72 MWth which is more than 3 % of full power. The transients of flow, pressure, energy transfer and heat sink thermal conditions are analyzed when the system changes from forced to NC. Further, the influence of system conditions such as loop diameter, loop height, sink volume, sink temperature and heat exchanger area on PHRS performance was predicted and the changes in system parameters were analyzed. The vital parameters influencing the PHRS performance are identified based on sensitivity analyses. This investigation provides significant insight into the flow and heat transfer characteristics of two-phase and coupled NCLs in the PHRS.

Study on the Coupling of Air-Source Heat Pumps (ASHPs) and Passive Heating in Cold Regions

Air-source heat pumps (ASHPs), as an active device, are widely used in building heating and cooling processes. However, in severe cold regions, they face reduced heating efficiency and frosting problems in winter. This paper proposes a new heating solution by coupling an ASHP with passive heating systems. It combines an ASHP with passive sunrooms and heat storage systems for heating. Through software simulations and mathematical modeling, the new scheme is compared and analyzed against traditional ASHP solutions to explore the performance of this scheme in rural houses in severe cold regions of China during winter. According to simulation and calculation analysis, on the coldest day of winter, the coupling scheme can provide approximately 99.41 kWh of heat to the indoors, which exceeds the 86.67 kWh required to maintain an indoor temperature of 20 °C. The system’s power consumption is 36.96 kWh, which is 66.88% lower than that of traditional heat pump heating. The study shows that the coupling system of an ASHP and passive heating has a good heating effect in severe cold regions. For the situation of insufficient solar energy at night, the design of phase-change materials and heat storage media can meet heating needs throughout the day.

Effects of sodium bicarbonate ingestion on ventilatory and cerebrovascular responses in resting heated humans.

Hyperthermia stimulates ventilation in humans. This hyperthermia-induced hyperventilation may be mediated by the activation of peripheral chemoreceptors implicated in the regulation of respiration in reaction to various chemical stimuli, including reductions in arterial pH. Here, we investigated the hypothesis that during passive heating at rest, the increases in arterial pH achieved with sodium bicarbonate ingestion, which could attenuate peripheral chemoreceptors activity, mitigate hyperthermia-induced hyperventilation. We also assessed that the effect of sodium bicarbonate ingestion on cerebral blood flow responses, which are associated with hyperthermia-induced hyperventilation. Twelve healthy men ingested a sodium bicarbonate (0.3 g/kg body weight) or sodium chloride (0.208 g/kg). One hundred minutes after the ingestion, the participants were passively heated using hot-water immersion (42°C) combined with a water-perfused suit. Increases in esophageal temperature (an index of core temperature) and minute ventilation (VE) during the heating were similar in the two trials. Moreover, when VE is expressed as a function of esophageal temperature, there were no between-trial differences in the core temperature threshold for hyperventilation (37.9 ± 0.3 vs. 38.0 ± 0.4°C, P = 0.338), and sensitivity of hyperthermia-induced hyperventilation as assessed by the slope of the core temperature-VE relation (13.7 ± 14.9 vs. 15.8 ± 15.6 L/min/°C, P = 0.748). Furthermore, middle cerebral artery mean blood velocity (an index of cerebral blood flow) decreased similarly with heating duration in both trials. These results suggest that sodium bicarbonate ingestion does not mitigate hyperthermia-induced hyperventilation and the reductions in cerebral blood flow index in resting heated humans.

Enhancing heat exchanger performance with perforated/non‐perforated flow modulators generating continuous/discontinuous swirl flow: A comprehensive review

AbstractHeat exchangers are crucial in transferring heat and finding applications across various industries. Numerous strategies have been devised to improve and optimize the heat transfer process within these systems. Among these, passive methods have garnered significant attention for their ability to operate without external power consumption. This article examines the recent experimental and computational studies conducted by researchers since 2018 on passive enhancement techniques, especially twisted tape, wire coil, swirl flow generator, and others, to boost the thermal efficiency of heat exchangers and aid designers in adopting passive augmentation methods for compact heat exchangers. Recently, researchers' new class of flow maldistribution devices, referred to as swirl flow devices, has gained attention; which enhances convective heat transfer by introducing swirl into the main flow and disrupting the boundary layer at the tube surface through alterations in surface geometry. Twisted tape inserts are devices that demonstrate better performance in laminar flow compared to turbulent flow. Conversely, other passive techniques like ribs, conical nozzles, and conical rings are generally more effective in turbulent flow than laminar flow. A recent research trend is the utilization of nanofluids in combination with other passive heat transfer enhancement techniques like turbulators, ribs, and twisted tape inserts in heat exchangers, which can reduce exergy losses and improve overall convective heat transfer coefficient and effectiveness of heat exchanger.