Passive Heat Research Articles

Enhancing heat exchanger efficiency with novel perforated cone-shaped turbulators and nanofluids: a computational study

Abstract The present paper presents a numerical investigation of heat transfer in an exchanger fitted with a modified conical-shaped turbulator containing water/Fe2O3 nanofluid. The study aims to address the critical need for improved heat exchanger efficiency, a vital component in various industries, including the chemical, power generation, and food industries. The work focuses on achieving enhanced heat transfer performance within a smaller volume, a primary goal of modern technology and industrial processes. The innovation in this study lies in the design and analysis of a novel conical turbulator, which has not been explored extensively in the context of heat exchangers fitted with nanofluids. Unlike traditional methods, which often rely on active or semi-active means to enhance heat transfer, this research introduces a passive approach through the incorporation of turbulators. Specifically, the study investigates the use of perforated cone-shaped turbulators in conjunction with nanofluids to boost heat transfer performance. The research employs state-of-the-art computational fluid dynamics (CFD) models, allowing for a comprehensive evaluation of the turbulator’s performance across a wide range of Reynolds numbers (Re = 4000–20,000). It further examines the influence of various turbulator parameters, nanoparticle content, and geometry on heat transfer efficiency. Key findings indicate that the modified turbulator exhibits exceptional performance, increasing Nusselt numbers by 3.4–5.4 times and friction coefficients by 2.3–1.8 times compared to smooth pipes. Particularly noteworthy is the 92 % increase in the Nusselt number achieved with a mere 2 % increase in the Fe2O3 nanoparticle content. The present study introduces a novel passive heat transfer enhancement method using perforated cone-shaped turbulators and nanofluids, filling a significant gap in existing research. The innovative turbulator design and its substantial performance improvements offer promising prospects for achieving higher heat exchanger efficiency, making it a valuable contribution to thermal systems and heat transfer engineering.

Passive Mixing and Convective Heat Transfer Enhancement for Nanofluid Flow across Corrugated Base Microchannels

Vortex generators and pin fins are conventionally used to deliver fluid mixing and improved convective heat transfer. The increased pressure loss following a fractional increase in heat transfer, as well as the complex manufacturing design, leave room for improvement. The present work proposes a novel diverging–converging base corrugation model coupled with vortex generation using simple geometrical modifications across rectangular microchannels to ensure a superior performance. The Nusselt number, friction factor, and flow phenomenon were numerically studied across a Reynolds number range of 50–1000. The optimum cross-section of the microchannel-generating vortices was determined after thorough study, and base corrugation was further added to improve heat transfer. For the vortex–corrugation modeling, the heat transfer enhancement was verified in two optimized cases: (1) curved corrugated model, (2) interacting corrugated model. In the first case, an optimized curve generating Dean vortices was coupled with base corrugation. An overall increase in the Nusselt number of up to 32.69% and the thermal performance of “1.285 TPF” were observed at a high Reynolds number. The interacting channels with connecting bridges of varying width were found to generate vortices in the counter-flow configuration. The thermal performance of “1.25 TPF” was almost identical to the curved corrugated model; however, a major decrease in pressure, with a loss of 26.88%, was observed for this configuration.

Ag Nanoparticles-Coated Shish-Kebab Superstructure Film for Wearable Heater.

Passive and active wearable heaters have received widespread attention due to their efficient utilization of solar energy and all-weather heating capabilities, but the current challenges are their preparation processes being time-consuming and equipment expensive. Herein, a simple and facilitated preparation method for the multifunctional wearable heater was developed, which springs Ag nanoparticles on the shish-kebab superstructure film via deposited melanin-like polydopamine as the adhesive. The light absorption ability of the resultant wearable heater in the visible region can be significantly enhanced by the addition of polydopamine, realizing a highly efficient photothermal conversion ability. Accordingly, it can achieve rapid warming ability whether passive heating (up to 45 °C about 60 s at 100 mW/cm2) or active heating (up to 72 °C about 40 s at 0.6 V), compared to ordinary cotton fabric. In addition, it can realize a 6.3 °C temperature difference with Cotton, showing excellent heat preservation ability. This study demonstrates a simple and low-cost approach for the prepared shish-kebab superstructure-based wearable heaters.

Neutronic analysis of a heat-pipe cooled reactor

Heat-pipe cooled reactors belong to the group of nuclear reactors using heat pipes filled with liquid metals (such as sodium or potassium) to cool the core. Due to the passive heat removal system, there is no need to use closed loops with pumps, and the reactor can be operated with reduced operational requirements. Consequently, this system can be used in remote locations without access to an electrical grid, or it can be used for space applications.This paper deals with a neutronic study of the Special Purpose Reactor Design-B concept from the Idaho National Laboratory. Using Monte Carlo code Serpent 2 and ENDF/B VIII.0 library, a fixed-temperature model was created to calculate the safety characteristics of the system. This included reactivity coefficients, power distribution, neutron flux spectrum, and criticality safety. In a simplified depletion calculation, an effect of fuel depletion on safety systems was determined as well as a decay heat.

ANALYZING HEAT TRANSFER FLUIDS FOR IMPROVED SOLAR WATER HEATER PERFORMANCE

The First Chapter, discussed the Research background in the first section due to its potential to lower carbon emissions and energy costs, the use of solar water heaters for an environmentally friendly power alternative has increased. Also, it explained Current issues in that section Although rooftop water heater technology has advanced, choosing and optimizing heat transfer fluids (HTFs) continues to be a difficult task. The Second Chapterexplained first section is Passive solar water heating system in a passive solar water heating system uses the concept of radiation from the sun to heat water for domestic, commercial, or industrial usage without the use of active mechanical equipment like pumps or fans. It has also discussed Active solar water heating system as well as aspects affecting the performance of a solar water heater. Effective implementation of the Simulink model of the solar water heater has been adequately structured and interpreted. Additionally, proper implication over the entire work has been structured within this paper.

Low-field NMR with multilayer Halbach magnet and NMR selective excitation

This study introduces a low-field NMR spectrometer (LF-NMR) featuring a multilayer Halbach magnet supported by a combined mechanical and electrical shimming system. This setup offers improved field homogeneity and sensitivity compared to spectrometers relying on typical Halbach and dipole magnets. The multilayer Halbach magnet was designed and assembled using three nested cylindrical magnets, with an additional inner Halbach layer that can be rotated for mechanical shimming. The coils and shim-kernel of the electrical shimming system were constructed and coated with layers of zirconia, thermal epoxy, and silver-paste resin to facilitate passive heat dissipation and ensure mechanical and thermal stability. Furthermore, the 7-channel shim coils were divided into two parts connected in parallel, resulting in a reduction of joule heating temperatures from 96.2 to 32.6 °C. Without the shimming system, the Halbach magnet exhibits a field inhomogeneity of approximately 140 ppm over the sample volume. The probehead was designed to incorporate a solenoidal mini coil, integrated into a single planar board. This design choice aimed to enhance sensitivity, minimize B1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${B}_{1}$$\\end{document} inhomogeneity, and reduce impedance discrepancies, transmission loss, and signal reflections. Consequently, the resulting linewidth of water within a 3 mm length and 2.4 mm inner diameter sample volume was 4.5 Hz. To demonstrate the effectiveness of spectral editing in LF-NMR applications at 29.934 MHz, we selectively excited hydroxyl and/or methyl protons in neat acetic acid using optimal control pulses calculated through the Krotov algorithm.

Polycarbonate composites for material extrusion-based additive manufacturing of thermally conductive objects

Enhanced thermally conductive polymer composites can be used in many engineering applications where either the physicochemical properties of plastics or the processing properties of plastics are required. Rapid prototyping is currently being addressed for a number of applications that require good heat transfer properties. Such applications include various types of heat exchangers containing coolant/heating fluid as well as passive heat sinks for standard heat removal from various types of heat-generating products. The present work is focused on the research of thermally conductive composites for printing such structures using additive manufacturing (AM), namely material extrusion. In this study, a number of parameters of the composites were investigated that affect the final properties of the printed structures; these include the TC (Thermal Conductivity), mechanical properties, and printability of the composites, depending on the composition, but also the printing direction. The composites studied were made up of a matrix of PC (Polycarbonate) and a mixture of different thermally conductive fillers, specifically, h-BN (Hexagonal Boron Nitride), EG (Expanded Graphite), PCFs (Pitch-based Carbon Fibers) and Al (Aluminum Particles). Different types of thermally conductive composites were studied, from binary to ternary combinations of fillers. One of the best-performing composites was achieved for the combination of all four types of filler, where thermal conductivity along the printing direction was achieved for the PC matrix with 30 wt% of the mixture of all fillers. Up to 1.56 W m−1 K−1 was achieved, which is 5-fold higher than for neat PC. Although these composites have approximately half the tensile strength only, the hardness is similar to that of the neat PC. The behavior of fillers was observed by SEM analysis. Al, EG, and PCFs behave predictably. Unusual behavior was observed in the case of PC only with h-BN, where the filler migration from the matrix to the voids between the non-fused printing paths occurred, likely caused by a larger amount of dispersion component of the overall surface energy of h-BN. Such phenomena could be used in the optimized form in the future so that segregated thermally conductive structures could be created using material extrusion-based AM and allow even higher thermal conductivity of final structures.

Exploring the Implementation Path of Passive Heat-Protection Design Heritage in Lingnan Buildings

To achieve indoor thermal comfort via natural ventilation, traditional buildings in South China’s Lingnan region have evolved distinct features tailored to the hot and humid climate conditions, involving site planning, function layout, and construction techniques. This study delves into the influences of these features on aspects such as sun-shading, ventilation, and heat insulation. By analyzing over ten Lingnan buildings in both the traditional and modern forms, several representative standardized models have been developed. Through a hybrid approach of combining qualitative and quantitative methodologies, including simulations, quantifications, and comparisons, several passive heat-protection measures commonly employed in Lingnan buildings were examined and evaluated. The effectiveness of shading, ventilation, and heat insulation in both traditional and modern buildings was assessed, resulting in the compilation of design principles for passive heat protection in buildings located in similar climatic zones. Key findings include (1) Shading: traditional methods reduce sunlight by 54.55%, while modern buildings enhance shading by applying new materials; (2) ventilation: traditional design achieves an outdoor wind speed of 1.5 m/s, improving thermal comfort, while modern Lingnan buildings optimize these principles; (3) insulation: traditional techniques maintain indoor temperatures below 26.0 °C, and modern buildings introduce innovation solutions for improved thermal insulation. In summary, traditional Lingnan design effectively addresses the challenges of the hot and humid climate by employing passive strategies for thermal comfort. Modern Lingnan buildings, in turn, preserve these principles while introducing innovative approaches.

Event Sequence Based Fault Tree Analysis to Evaluate Minimal Combination of Event Sequences Leading to the Reactor Core Damage

Probabilistic safety assessment has been widely used to evaluate nuclear power plant safety systems. It couples fault tree (FT) analysis and event tree (ET) analysis. FT analysis is to develop failure scenarios, to quantify the failure probability and to identify critical components. ET analysis is to develop event sequences (ESs) leading to reactor core damage and quantify core damage frequency. Currently, there is no approach in probabilistic safety assessment that can be used to identify minimal combinations of safety system failures leading to reactor core damage. This study proposes an event sequence based fault tree analysis, which integrates FT model with ET model. The ET model is to identify the ESs leading to the reactor core damage. Meanwhile, the FT model is to identify minimal combinations of those ESs found in the ET model. The motivation of this study is on how to identify critical safety systems in nuclear power plants to mitigate disturbances caused by a group of postulated initiating events to avoid core damage. To confirm the feasibility and the applicability of the proposed approach, the performance of the AP1000 passive core cooling system is evaluated. It is found that if in-containment refueling water storage tank, automatic depressurization system - full, accumulator, core make-up tank, and passive residual heat removal work properly, the reactor core will intact. These results confirmed that the proposed approach can be applicable to identify minimal combinations of safety systems to keep the reactor core intact.

A nano-sheet graphene-based enhanced thermal radiation composite for passive heat dissipation from vehicle batteries

In response to thermal runaway (TR) of electric vehicles, recent attention has been focused on mitigation strategies such as efficient heat dredging in battery thermal management. Thermal management with particular focus on battery cooling has been becoming increasingly significant. TR usually happened when an electric vehicle is unpowered and charged. In this state, traditional active battery cooling schemes are disabled, which can easily lead to dangerous incidents due to loss of cooling ability, and advanced passive cooling strategies are therefore gaining importance. Herein, we developed an enhanced thermal radiation material, consisting of ∼1 ​μm thick multilayered nano-sheet graphene film coated upon the heat dissipation surface, thereby enhancing thermal radiation in the nanoscale. The surface was characterized on the nanoscale, and tested in a battery-cooling scenario. We found that the graphene-based coating's spectral emissivity is between 91 ​% and 95 ​% in the mid-infrared region, and thermal experiments consequently illustrated that graphene-based radiative cooling yielded up to 15.1 ​% temperature reduction when compared to the uncoated analogue. Using the novel graphene surface to augment a heat pipe, the temperature reduction can be further enlarged to 25.6 ​%. The new material may contribute to transportation safety, global warming mitigation and carbon neutralization.

Combined passive enhancement techniques improve the thermal performance of latent heat storage system: A design anomaly?

Poor heat transfer rate due to low thermal conductivity of phase change material limits the wide application of latent heat storage (LHS) systems. Thermal performance enhancement techniques can be potential methods to address this major limitation of LHS systems. In this context, the present numerical study examines the individual and cumulative impact of two passive heat transfer enhancement techniques (the orientation of the domain and position of the heat transfer fluid (HTF) tube) on the thermal performance of the latent heat storage (LHS) system consisting of high-temperature (HT) phase change medium (PCM). The individual effect of orientation decreases the charging duration of θ = 0° (horizontal configuration) by 10.5 %, 15 %, and 19.04 % than θ = 30°, θ = 60° and θ = 90° (vertical configuration), respectively. However, the discharging duration remains unchanged for all inclinations (11.5–12 h). The individual effect of eccentricity decreases the charging duration of horizontal (θ = 0⁰, ey = −5 mm,-10 mm,-20 mm) system by 6.25 %,12.8 %, and 18.75 % than concentric horizontal (θ = 0°, ex = ey = 0) system. Moreover, the combined effect of orientation and eccentricity (θ = 0⁰,ey = −5 mm,-10 mm,-20 mm) reduces charging duration by 28.75 %, 33.33 %, and 38.1 % than vertical concentric domain (θ = 90°, ex = ey = 0), respectively. However, eccentricity in vertically upward and downward directions increases the discharging duration compared to the concentric domain. Hence, the combined effect results in a design anomaly for HT-LHS system. The charging and discharging performances are observed to be predominantly sensitive to the Rayleigh number than the Reynolds number.

Exposure to passive heat and cold stress differentially modulates cerebrovascular-CO2 responsiveness.

Heat and cold stress influence cerebral blood flow (CBF) regulatory factors (e.g., arterial CO2 partial pressure). However, it is unclear whether the CBF response to a CO2 stimulus (i.e., cerebrovascular-CO2 responsiveness) is maintained under different thermal conditions. This study aimed to compare cerebrovascular-CO2 responsiveness between normothermia, passive heat, and cold stress conditions. Sixteen participants (8 females; 25 ± 7 yr) completed two experimental sessions (randomized) comprising normothermic and either passive heat or cold stress conditions. Middle and posterior cerebral artery velocity (MCAv, PCAv) were measured during rest, hypercapnia (5% CO2 inhalation), and hypocapnia (voluntary hyperventilation to an end-tidal CO2 of 30 mmHg). The linear slope of the cerebral blood velocity (CBv) response to changing end-tidal CO2 was calculated to measure cerebrovascular-CO2 responsiveness, and cerebrovascular conductance (CVC) was used to examine responsiveness independent of blood pressure. CBv-CVC-CO2 responsiveness to hypocapnia was greater during heat stress compared with cold stress (MCA: +0.05 ± 0.08 cm/s/mmHg/mmHg, P = 0.04; PCA: +0.02 ± 0.02 cm/s/mmHg/mmHg, P = 0.002). CBv-CO2 responsiveness to hypercapnia decreased during heat stress (MCA: -0.67 ± 0.89 cm/s/mmHg, P = 0.02; PCA: -0.64 ± 0.62 cm/s/mmHg; P = 0.01) and increased during cold stress (MCA: +0.98 ± 1.33 cm/s/mmHg, P = 0.03; PCA: +1.00 ± 0.82 cm/s/mmHg; P = 0.01) compared with normothermia. However, CBv-CVC-CO2 responsiveness to hypercapnia was not different between thermal conditions (P > 0.08). Overall, passive heat, but not cold, stress challenges the maintenance of cerebral perfusion. A greater cerebrovascular responsiveness to hypocapnia during heat stress likely reduces an already impaired cerebrovascular reserve capacity and may contribute to adverse events (e.g., syncope).NEW & NOTEWORTHY This study demonstrates that thermoregulatory-driven perfusion pressure changes, from either cold or heat stress, impact cerebrovascular responsiveness to hypercapnia. Compared with cold stress, heat stress poses a greater challenge to the maintenance of cerebral perfusion during hypocapnia, challenging cerebrovascular reserve capacity while increasing cerebrovascular-CO2 responsiveness. This likely exacerbates cerebral hypoperfusion during heat stress since hyperthermia-induced hyperventilation results in hypocapnia. No regional differences in middle and posterior cerebral artery responsiveness were found with thermal stress.

Thermal and energy efficiency study of passive heating and cooling systems in Morocco's cold desert climate

This research aims to showcase the imperative of integrating passive cooling and heating techniques within buildings to effectively decrease energy consumption. To accomplish this objective, numerical simulations were conducted on a representative double-walled brick building in two cold desert climates using TRNSYS software. The simulations were performed to compare and evaluate the thermal and energy performance of two distinct passive techniques, one for cooling the reflective roof and the other for heating the Trombe wall (TW). The findings demonstrate that employing a reflective roof building with an air gap significantly reduces indoor temperatures by 3 °C during the hottest weekdays of summer, as compared to the reference building, across the two studied Moroccan climates. Moreover, this approach decreases the demand for cooling energy by an impressive 69–78 %. Similarly, the passive heating technique proves highly effective during winter, reducing energy requirements by 26–30 % while increasing indoor temperatures by over 2.9 °C. Combining both techniques proves to be the most efficient solution, resulting in a 37.87 % reduction in total annual energy consumption for cooling and heating in Er-Rachidia and a 30 % reduction in Ifran. These results strongly support the suggestion that Moroccan thermal regulations should incentivize the adoption of passive cooling and heating systems, particularly in cold desert climates.

Thermal storage characteristics of microencapsulated phase change material coatings in low-energy rural prefabricated building walls

ABSTRACT Prefabricated buildings in rural areas of China waste a large amount of energy due to poor thermal insulation. Phase change materials (PCMs) are able to stabilize room temperature by latent heat absorption and release during the phase change process. This study incorporated PCMs in the form of microcapsules into the interior wall coatings of prefabricated buildings, and by taking advantage of PCMs’ energy storage capacity, the thermal storage characteristics of PCM-coated bricks were investigated. The results show that microencapsulated phase change material(MPCM) coatings for prefabricated walls exhibit excellent thermal stability properties and effectively reduce the heat flux of prefabricated walls, with coatings having a MPCM mass fraction of 15% and a thickness of 5 mm providing the highest overall benefits. By fitting the numerical simulation results with experimental data, a novel multifunctional passive solar phase change heat collection and storage wall system was developed. This study innovatively combines energy storage materials with interior wall coatings in prefabricated walls of modular buildings investigating how it enhances the thermal stability of the external insulation walls and effectively reduces the reliance on heating equipment for auxiliary heating in rural residences. This essay aims to provide feasible recommendations for optimizing the dual-stage energy-saving and carbon reduction goals in both the construction and operation of rural areas.

Preliminary design of the suppressive containment system based on HPR1000

The current HPR1000 has a high construction cost and weak economic competitiveness due to its complex system and large containment. This study proposes a conceptual design of an advanced containment system based on HPR1000, which aims at reducing the construction cost of nuclear power plants without reducing their safety. In the design, the In-containment Refueling Water Storage Tank (IRWST) and spray system were discarded, and the space of the double containment vessel was used to create an annular cavity pool (ACP). The transient pressurization in the containment caused in the early stages of the accident can be quickly suppressed by ACP instead of the traditional large-volume suppression concept. And due to the significant condensation of steam within the ACP water, the transportation of air into the ACP results in a reduction in the air mass fraction in the vicinity of the passive containment heat removal system (PCHR) located within the containment structure. This phenomenon subsequently leads to an enhancement in heat transfer performance. In addition, ACP also serves as the water source for the safety injection system, the reactor cavity water injection system, and the core replacement system. Compared with HPR1000, the system of the preliminary design has been greatly simplified, and the size of the containment vessel has been reduced by nearly 47%. The simulation of the large-break loss-of-coolant accident (LBLOCA) scenario has been conducted to examine the response of the containment system, specifically focusing on the performance of the safety injection system and suppression system. The results show that the integrity of the containment and core was ensured throughout the accident, and there was a safety margin.

Primary and Secondary Organic Aerosol Formation from Asphalt Pavements.

Asphalt is ubiquitous across cities and a source of organic compounds spanning a wide range of volatility and may be an overlooked source of urban organic aerosols. The emission rate and composition depend strongly on temperature, but emissions have been observed at both application temperatures and surface temperatures during warm sunny days. Here we report primary organic aerosol (POA) emissions and secondary organic aerosol (SOA) production from asphalt. We reheated real-world asphalt samples to application-relevant temperatures (∼130 °C) and typical summertime road-surface temperatures (∼55 °C) and then flushed the emitted vapors into an environmental oxidation chamber containing ammonium sulfate seed particles. SOA was then formed following the photo-oxidation of emissions under high-NOx conditions typical of urban atmospheres. We find that POA only forms at application temperature as it does not require further oxidation, whereas SOA forms under both conditions; with the resulting POA and SOA both being semi-volatile. While total OA formation rates were substantially greater under the limited time spent under application conditions, SOA formation from passive asphalt heating presents a potential long-term source, as heating continues for the lifetime of the road surface. This suggests that persistent asphalt solar heating is likely a considerable and continued source of summertime SOA in urban environments.

Innovative experimental approach for the dynamic Multi-Variable investigation of Pulsating heat Pipes

Pulsating Heat Pipes (PHP) are passive two-phase heat transfer devices characterized by a simple structure and high heat transfer capabilities. Despite this, their large-scale application is still hindered by the actual unpredictability of their dynamic behavior during the startup and the thermal crisis. An innovative experimental apparatus is designed to systematically investigate the above-mentioned phenomena. It consists in a square loop made of four borosilicate transparent glass tubes joined at corners by means of brass connectors. The external tube surface is coated with several transparent Indium Tin Oxide heaters. The device is used to topologically reproduce 5, 7, and 11 evaporator/condenser sections PHPs with a 2 mm inner diameter tube, filled with pure ethanol and tested in horizontal position. First a steady-state characterization is performed. The condenser temperature is varied from 10 °C to 40 °C; the input power goes from 10 W to 40 W. Results show that both the increase of number of evaporator sections and condenser temperature enhance the PHP performance in terms of equivalent thermal resistance. Then, the effect of the condenser temperature on the initial liquid phase distribution is analyzed. It is observed that at low condenser temperatures (10 °C, 20 °C), the liquid phase tends to gather in the condenser sections rather than the evaporator sections and it is arranged in short liquid plugs; conversely, for high condenser temperatures (30 °C, 40 °C), the amount of liquid phase in evaporators is higher and it is arranged in long liquid plugs. Finally, the transient behavior is studied in terms of startup time. It is observed that the parameter influencing most the startup time is the initial fluid distribution; the startup time increases with the increase of evaporator sections volume occupied by liquid phase and with the length of liquid plugs; on the other hand, the startup time decreases with the increase of number of menisci in the evaporator sections.

Study on impact of photovoltaic power tracking modes on photovoltaic-photothermal performance of PV-PCM-Trombe wall system

Due to the lack of research on the impact of photovoltaic (PV) power tracking methods on the performance of Building-Integrated Photovoltaic-Thermal (BIPV/T) systems, this study comparatively analyzes the photovoltaic-photothermal performance of the PV-PCM-Trombe Wall system operating in Pulse Width Modulation (PWM) and Maximum Power Point Tracking (MPPT) modes during winter passive heating conditions. Additionally, the study investigates the influence of these modes on the thermal characteristics of buildings. The results indicate that the MPPT strategy achieved a PV efficiency of 15.50 %, while the PWM strategy resulted in a significant reduction to 12.72 % (a decrease of 2.78 % compared to MPPT). Importantly, both strategies effectively utilized solar energy for passive space heating without noticeable differences in photothermal performance. Furthermore, the study observed that the upper part of the PCM plate reached higher peak temperatures earlier in the vertical dimension. Experiment A exhibited peak temperatures ranging from 33.57 °C to 34.76 °C, while Experiment B had a wider range of 27.99 °C to 36.10 °C. Minimal temperature variations were observed across the PCM plate in the thickness direction, measuring only 0.60 °C in Experiment A and 0.70 °C in Experiment B. These research findings provide valuable insights into the roles and impacts of different PV power tracking strategies in PV-PCM-Trombe wall systems.

Numerical simulations on the thermal performance of ventilated walls with passive solar heating and latent heat storage in winter

Numerical simulations on the thermal performance of ventilated walls with passive solar heating and latent heat storage in winter

A COMPREHENSIVE REVIEW STUDY ON HEAT TRANSFER IMPROVEMENT TECHNIQUES WITHIN TWISTED TUBES

Heat transfer equipment has been used in many different domestic and industrial applications. There has been a concentrated effort to create a heat exchanger design that will reduce energy requirements while saving materials and other costs. Increasing the effective heat transfer surface area or creating turbulence are two common ways to improve heat transfer and hence lower thermal resistance. The thermal Performance Factor is the ratio of the difference in heat transfer rate to the difference in friction factor and serves as a metric to assess the efficiency of heat transfer enhancement technologies. Different types of twisted tubes are used in many heat transfer improvement devices. geometrical parameters of the twisted tube encompassing the aspect ratio, twist ratio, twist direction, twist length, etc. impact the heat transfer. For Instance, oval pipes with unequal twist pitches have a thermal performance factor (1.75) and equal twist pitches have a thermal performance factor (1.98). furthermore, the thermal performance factor of the twisted tube with oval dimples is equal to 1.19 compared with the twisted tube without dimples. The thermal performance factor of the twisted tube with oval dimples is equal to 1.38 compared with the straight tube, with another improvement to the twisted tube that improves the heat transfer properties by disrupting the thermal boundary layer and destabilizing it. This paper presents a comprehensive investigation of passive heat transfer devices (twisted tubes) and their relative merits in a myriad of commercial applications.