Wall Surface Temperature Research Articles

Mixed Bioconvection Flow Around a Vertical Thin Needle with Variable Surface Fluxes

This study investigates mixed convection flow over a vertical thin needle with variable surface heat, mass, and microbial flux, incorporating the influence of gyrotactic microorganisms. The governing partial differential equations are transformed into ordinary differential equations using appropriate similarity transformations and then solved numerically by employing MATLAB’s Bvp4c solver. The primary focus lies in examining the influence of various dimensionless parameters, including the mixed convection parameter, power-law index, buoyancy parameters, bioconvection parameters, and needle size parameters, on the velocity, temperature, concentration, and microbe profiles. The results indicate that these parameters significantly affect the surface (wall) temperature, fluid concentration, and motile microbe concentration, as well as the corresponding velocity, temperature, concentration, and microorganism profiles. The findings provide insights into the intricate dynamics of mixed convection flow with bioconvection and have potential applications in diverse fields such as biomedicine and engineering.

Spectral Heat Transfer Coefficient for Thermal Design Analysis—Part 1: Augmenting the Cooling Law for Non-Isothermal Wall

Abstract There are two major issues of interest in relation to Newton's law of cooling. The first is its applicability to flow bounded by a nonisothermal wall where the wall surface temperature is nonuniform. The second is the restriction by the basic linear assumption. In terms of the first issue, a general Green's function-based framework exists but its implementation as a working method has been lacking, attributable to the inherent locality of Green's function. Instead of setting up and solving the local–local influence and response, a new spectral heat transfer coefficient (SHTC) method takes a different avenue. It sets up and solves global-to-local temperature-heat flux influences for a small number of low order spectral modes of wall temperature disturbances. The SHTC approach covers a range of physically relevant and numerically resolvable length scales, which have been missing in the conventional cooling law. The present work is aimed at applying the SHTC methodology to turbine blade aerothermal analysis. Two aerothermal regimes are considered, respectively. In the first part (Part 1 of the two-part article), the SHTC approach is described and case-studied for a linear aerothermal regime where the flow energy equation behaves linearly and the corresponding temperature (thermal) field is passively dictated by the velocity (momentum) field. In the companion paper (Part II), the methodology will be extended to a nonlinear regime, where the temperature field will be actively interacting with (rather than passively influenced by) the velocity field.

Experimental analysis of the influence of PCM on the thermal behavior of lightweight buildings in different natural environments

Phase-change materials (PCM) can effectively improve the thermal performance of lightweight buildings, but their heat storage and release capacity are highly dependent on the heat exchange between the wall surface and the ambient environments. However, the current research mostly focuses on numerical simulation in a specific climate environment, and the effectiveness of PCM on the thermal regulation of lightweight buildings under a long-period natural environment is insufficient. Therefore, two experimental rooms (with and without PCM) of the same size were built and conducted in this paper to compare the changing rules of wall surface temperature, heat flux, and indoor temperature in different seasons without mechanical equipment. The results show that: (1) The effect of PCM on the thermal performance of lightweight buildings is highly correlated with seasons, and its contribution efficiency varies in different seasons; (2) The attenuation rate of the internal surface temperature in different seasons can be reduced by 18.08%–42.90 %, the delay time can be improved to 2.67–4 h compared with the reference wall; (3) PCM can effectively inhibit the fluctuation and rise of indoor temperature, which can reduce the maximum indoor temperature by 4.9–12.0 °C, increase the minimum temperature by 1.1–2.8 °C, and the thermal comfort hours added by 2–5 h; (4) Lightweight buildings incorporating PCM can saves 18.69 % and 49.63 % for the peak cooling in summer and transition seasons, and 15.9 % for the heating in winter. The research results can provide the theoretical basis and experimental support for the efficient application of PCM in lightweight buildings.

Influence of boundary effect on supersonic flows and non-equilibrium condensation in a Laval nozzle for natural gas dehydration

The natural gas extraction process is often accompanied by large amounts of water vapor, so natural gas dehydration is the first step in achieving natural gas utilization. Current work focuses on a clean technology that captures water vapor in natural gas through expansion refrigeration. Using water vapor as a medium, a mathematical model for predicting spontaneous condensation caused by non-equilibrium state is established and validated. The influence of boundary effect including surface roughness and wall temperature on supersonic flows and non-equilibrium condensation are studied. The surface roughness affects the energy and momentum exchange between the fluid in the main stream area and near the wall, and thus affects the Wilson point, boundary layer, and non-equilibrium condensation. When the roughness rises by 0.1 mm, the boundary layer thickness increases by 56.7%, and the radial nucleation range decreases by 11.4% from y=±5.27 mm to y=±4.67 mm. The influence of wall temperature on the central area in the nozzle is not significant, but it affects the presence of liquid phase. The radial scope of liquid-phase drops by 3.58% when the wall temperature increases by 100 K.

Spectral Heat Transfer Coefficient (SHTC) for Thermal Design Analysis - Part 2: Leveraging Diabatic Wall Conditioning for Nonlinear Regime

Abstract There are two main issues of interest in the context of Newton's law of cooling as applied to turbine aerothermal designs. First, in a linear aerothermal regime, how do we deal with a non-isothermal wall where the wall surface temperature is non-uniform? Secondly, what can we do if an aerothermal system becomes nonlinear, manifested by qualitatively large changes of the flow field affected by heat transfer? In Part 1, a new spectral heat transfer coefficient (SHTC) method has been introduced for blade thermal analysis subject to non-isothermal walls in a linear aerothermal regime. Part 2 is devoted to address the issue of nonlinearity when the temperature field actively interacts with the velocity field as in many practical aerothermal problems. It is noted that the conventional approach rests heavily on an adiabatic state, so much so that its working range becomes overly restrictive. To move away from the adiabatic state, we take advantage of smooth (‘differentiable’) heat flux-wall temperature relation afforded by strong solid diffusion. A local linearization can be utilized by decomposing a full thermal variable into a nonlinear base as the reference and a locally linear perturbation. This split enables us to directly compute a nonlinear base as well as to carry out a linearized scaling with the SHTC (HTC) on top of the selected nonlinear aerothermal base state. The results of several computational case studies clearly and consistently support the validity and effectiveness of the present approach and method implementation.

An Investigation of Globe Temperature in Street Canyons: A Scaled Model Study Implementing Cool Materials

The measurement of globe temperature (GT) is essential for investigating pedestrian thermal comfort in street canyons. The globe thermometer is the most common instrument used to measure GT; however, its application in scale models has not been thoroughly investigated to date. Therefore, this study explicitly investigates globe thermometer measurements in scale models and analyzes the need for customization of the globe thermometer for more reliable measurements. Scaling down with respect to the size of the globe thermometer and the effect of solar orientation/envelope materials are investigated in this study. The initial experiments were carried out in an outdoor setting using a typical street canyon model (scale 1:100) with an east-west street orientation. The results of the experiment are presented to compare a low solar reflectance street canyon (albedo of 0.4) and a high solar reflectance canyon (albedo of 0.6) in terms of surface temperatures, heat flux, and globe temperature. It is observed that although the wall and road surface temperatures are lower for the high solar reflectance canyon compared to those for the low solar reflectance canyon, the GT (measured at pedestrian height) is higher in a high reflectance canyon during the daytime, which could be due to the combined effect of direct radiation and short-wave reflection. However, for the hours after sunset, a reverse effect is observed, i.e., the GT becomes lower (up to 0.8 °C) in the case of a high reflectance canyon compared to that for the low reflectance canyon. Furthermore, the study emphasizes the impact of solar reflectance of canyon surfaces on GT values, due to the view factors that the globe thermometer on those surfaces.

Optimization for the temperature range of radiator for preventing draught risk of cold window

High surface temperature of radiator can provide thermal plume with enough momentum intensity and thus counteracts the downdraft caused by window. Meanwhile, it is necessary to avoid causing indoor temperature to exceed upper limit of thermal comfort zone. In this paper, influence of heat transfer coefficients of window and exterior wall, outdoor temperature, and average surface temperature of radiator on operative temperature (Top) and temperature difference between indoor air and window (Td) was investigated. Based on response surface method, single factor and interaction effects for the four influencing factors on Top and Td were analyzed. A framework optimizing average surface temperature of radiator for preventing draught risk of window was established. When the heat transfer coefficient of window was around 1.4 W/m2·°C and satisfied related energy-conservation standard, cold draught could be eliminated without causing indoor environment overheating. Based on the optimized temperature range, the supply water temperature was controlled, and seasonal performance using the variable temperature strategy was investigated based on TRNSYS simulation. With the variable water temperature control strategy, the output hourly indoor air temperature was within the comfortable range. In the whole heating season, hours that did not meet cold draught requirement occupied 77.22 %, as the heat transfer coefficients of window dis-satisfied the energy-saving design standard. As meeting the design standard, the proportion decreased to 12.97 %. Utilizing the optimized temperature interval can prevent discomfort caused by cold draught to the greatest extent. This study is conducive to improving thermal environment with the convective–heating system and may lead to the reduction of energy consumption for heating.

Computational analysis of turbulent flow characteristics in nanofluids containing 1-D and 2-D carbon nanomaterials: grid optimization and performance evaluation

1D and 2D carbon nanomaterials such as multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) were investigated numerically. The thermophysical properties of water and nanofluids using MWCNTs in different outer diameters (ODs) and GNPs in different surface areas (SSA) were measured at an inlet temperature of 303.15 K and 0.1wt.%. The 3D geometry was solved under a fully developed turbulent flow of 6000 ≤ Re ≤ 16,000 using the model of k-ω SST via (ANSYS FLUENT 2022R2) software. Four numerical networks, Polyhedra, Polyhexacore, Hexacore, and Tetrahedral, were optimized. Moreover, seven parameters were discussed, namely wall surface temperature (Tw), heat transfer coefficient (htc), average Nusselt number (Nuavg), friction factor (f), pressure drop (ΔP), and total thermal performance index (PIth). Polyhexacore was the main grid over Polyhedra, Hexacore, and Tetrahedral with the average error (Dittus-Boelter: 2.754%, Gnielinski: 2.343%, Blasius: 1.441%, and Petukhov: 0.640%). Heat transfer increased by 18.38% with GNPs-300, 22.05% with GNPs-500, 23.25% with GNPs-750, 13.63% with CNT < 8 nm, and 11.42% with CNT 20–30 nm, relative to H2O at Re = 16,000. Pressure drop increased by about 42.01% with GNPs-300, 45.16% with GNPs-500, 44.84% with GNPs-750, 36.72% with CNT < 8 nm, and 34.39% with CNT 20-30 nm.

A Simplified Evaluation Framework for Adaptation Measures to Urban Heat Islands

Adaptation measures to urban heat islands are classified into the following three categories: measures to reduce solar radiation incident on the human body, measures to control and cool ground and wall surface temperature, and measures to control and cool the air and human body temperature. Case studies are conducted to evaluate the effects of the implementation of a cool water circulation sunshade and to examine the adverse effects of cool pavements on the human thermal environment, in addition to the effects of mist sprays on the human body. The effect of the sunshade, watering road, and mist spray, which are typical adaptation measures to urban heat islands, on the human thermal environment was estimated using Wet Bulb Globe Temperature (WBGT) as an indicator for heat stroke prevention and Standard New Effective Temperature (SET*) as an indicator for thermal comfort assessment. The effect of solar radiation shielding on improving the human thermal environment was the most significant, with a large decrease in the amount of solar radiation absorbed by the human body, resulting in a large decrease in SET* and WBGT of 2.7 °C and 1.0 °C, respectively, on fine summer days.

Numerical assessment of hydrothermal and entropy generation characteristics of graphene quantum dots nanofluid in a microchannel heat sink incorporating secondary channels and ribs

Efficient heat dissipation from electronic chips is essential for enhancing their performance and longevity. Significant progress has been achieved through the introduction of nanofluids and microchannel heat sinks. However, there is still a need for nanofluids that demonstrate exceptional thermal properties and stability. Graphene quantum dots nanofluid, an innovative carbon-based coolant with zero-dimensional nanostructures, presents promising features such as excellent chemical stability, surfactant-free preparation, superior thermal properties, and minimal impact on rheological characteristics. This study explores, for the first time, the hydrothermal behavior and entropy generation of graphene quantum dots nanofluid in a microchannel heat sink comprising secondary flow channels and ribs. To this end, a three-dimensional conjugate heat transfer model is built using ANSYS Fluent software, and the governing equations are solved using the finite volume method. The simulations are carried out considering temperature-dependent thermophysical properties under different concentrations ranging from 0 to 0.5 % and Reynolds numbers ranging from 100 to 500. The results reveal that the maximum bottom wall surface temperature decreases by 5.88 K, while the heat transfer coefficient improves by 24.9 % compared to the base fluid. Moreover, the total entropy generation reduces by 14.7 %. On the other hand, the pressure drop increases by 43 %. Overall, the highest increment in Performance Evaluation Criteria is 10.8 % at a Reynolds number of 100 and a concentration of 0.5 %, making this particular condition suitable for practical applications.

Functional ventilation building envelope integrated photovoltaic modules and phrase change material in subtropical climate: An in-depth numerical investigation

Most of existing solar ventilation envelope systems adopt a single structure including a glass cover a massive wall, which possesses the drawbacks of low thermal efficiency and poor stability. In recent decades, auxiliary power generation devices, led by photovoltaic (PV), have made epochal achievements in integrated building applications, while the superior thermal regulation capability of thermal storage materials, represented by phrase change materials (PCM), has further helped to improve the thermal environment of buildings, and the above two technologies have demonstrated great energy conservation potential. In order to explore the application and synergistic effect of the above two energy-conservation technologies in passive ventilation envelopes, a novel functional ventilation building envelope (FVBE) integrated with PV panel and PCM is proposed in this paper. A comprehensive exploration of the influence of various key parameters on the thermal performance of the FVBE-PV/PCM system. The electrical and thermal performance of the system is explored based on different seasonal climates. Specifically, effects of thickness as well as the melting temperature of PCM and the air channel width has been provided in this study. Taking the inner wall surface temperature (Tinner_wall), equivalent indoor load (Qload) and electrical efficiency (ηe) as evaluation indexes, the thermal efficiency, electrical performance and the coupling mechanism was assessed. Specifically, the coupling mechanism between the thermal performance and electrical performance of the FVBE-PV/PCM system was analyzed from the perspective of combined heat and power, revealing the functional characteristics of the system. Meanwhile, the article conducted a comparative study on the thermal and electrical performance of a typical building integrated PV (BIPV), FVBE-PV system FVBE-PV/PCM system. In particular, energy and exergy analysis is carried out to characterize the energy utilization of the FVBE-PV/PCM system in different structural systems. The research found that increasing the thickness of both the PCM and air channel leads to lower indoor temperature and heat flux, with different optimal phase transition temperatures for summer and winter. Although the FVBE-PV system exhibited a maximum 3.12 % reduction in power generation efficiency compared to the BIPV system due to increased PV temperature caused by air layer insulation, incorporating PCM can reduce exergy losses by an average of 31.731 % to mitigate this drawback and improve energy efficiency. Additionally, the analysis revealed varying coupling correlations between thermal performance and power generation based on two key parameters. This study could contribute to the functional improvement of the building envelope and simultaneous indoor thermal regulation.

Field experiment examining condensation reduction methods based on underground parking lot types

ABSTRACT In this study, condensation reduction methods with high field applicability to various types of underground parking lots in apartment buildings were selected and tested. The selected methods included floor-insulating drainage plates, induction fans with heating wires, and an automatic control ventilation system based on indoor and outdoor temperatures and humidity. The effectiveness of these methods was evaluated via real-world field experiments. The results indicated that while the insulating drainage plates initially blocked the cold, their long-term effectiveness matched that of normal drainage plates (difference 0.1°C). The induction fan with a heating wire showed average increases of 0.8°C and 2.7°C in wall surface temperature after one and three months, compared to normal induction fans. The absolute humidity of the automatic control ventilation decreased by 1.8 g/kg after 10 h of operation during rainy weather, whereas the manual control ventilation system increased by 0.6 g/kg under the same conditions. This study offers insights into the most effective application of these methods for various parking lot configurations.

Influence of blowing ratio on double-wall cooling characteristics under the condition of high-temperature flue gas

Double-wall cooling has been extensively investigated due to its exceptional cooling performance. However, most previous studies on the cooling characteristics of double-wall geometry have been conducted under non-reacting conditions, neglecting the influence of high-temperature flue gas radiation. In this paper, an experiment investigation was carried out to evaluate the impact of blowing ratio &lt;italic&gt;M&lt;/italic&gt; and coolant-to-gas temperature ratio on the cooling characteristics of effusion/impingement cooling at reacting flow conditions. The experiments were performed at atmospheric pressure with flame temperatures of 1,800 and 1,900 K respectively. Flue gas temperature was measured by S-type thermocouples, while an infrared camera and N-type thermocouples were employed for the gas-side wall surface temperature distribution measurements. The results demonstrate that the laterally averaged cooling effectiveness of the effusion/impingement cooling system increases with the increase of &lt;italic&gt;M&lt;/italic&gt;. However, beyond a blowing ratio of 5.1, further increments in &lt;italic&gt;M&lt;/italic&gt; do not significantly affect the cooling effectiveness. Moreover, it is observed that the laterally averaged cooling effectiveness gradually improves along the flow direction but at a reduced rate. Additionally, no significant changes in cooling effectiveness are observed after &lt;italic&gt;X&lt;/italic&gt;/&lt;italic&gt;D&lt;/italic&gt; &gt; 50. Furthermore, when considering a blowing ratio of 4, higher coolant temperatures result in higher cooling effectiveness compared to lower coolant temperatures.

Numerical study of the effect of helical fuel rod geometry on single-phase flow and heat transfer characteristics

Helical fuel is a promising nuclear fuel proposed to improve the core power density and safety margin. In this study, the effect of helical fuel rod geometry on single-phase flow and heat transfer characteristics in helical fuel annuli has been investigated. The volumetric energy source is applied to the fuel pin, and coupled walls are used at the coolant-cladding and cladding-fuel interfaces. The numerical method with SST k-ω turbulence model has been validated with the results of bare annulus. The flow field, fuel central temperature, friction factor, and the circumferential distribution of swirl intensity, heat flux and wall temperature are obtained based on the numerical simulation. The increase in R2/R1 will result in broadening transverse flow region, reducing the gradient of surface heat flux and wall temperature, lowering the maximum wall temperature, but increasing the fuel central temperature and has no significant effect on the friction resistance. The decrease of helical pitch increases the swirl intensity and friction factor, but worsens the heat transfer at the blade roots.

EXPLORING THE IMPACT OF GEOMETRIC PARAMETERS ON HEAT TRANSFER AND FLUID FLOW CHARACTERISTICS IN CROSS-TRIANGULAR GROOVED CHANNELS: A COMPUTATIONAL STUDY

In this study, the impact of geometric parameters of rectangular baffles with varying location angles and heights is investigated on the heat transfer and fluid flow characteristics of cross-triangular grooved channels. Computational methods are employed to explore these effects, utilizing the Ansys-Fluent program to solve the Navier-Stokes and energy equations, incorporating the k-ε turbulence model for numerical simulations. The inlet temperature of the air, serving as the working fluid, is set at 293 K, while the wall surface temperature of the lower triangular grooved channel remains fixed at 373 K. Rectangular baffles are tested with angles of 30°, 60°, and 90°, and heights of 0.25H, 0.5H, and 0.75H, respectively. The numerical results show good agreement with a 3.53% deviation compared to existing empirical data in the literature. The obtained findings are presented in terms of mean Nusselt (Num) number, fluid temperature, and Performance Evaluation Criterion (PEC) number variations taking into consideration of pressure drop for each rectangular baffle angle and height. Additionally, contour distributions of temperature and velocity are evaluated for different Reynolds numbers (Re) and arrangements of rectangular baffles. It has been determined that the Nu number value increases by 197.56% at a 90° angle and 0.75H height, compared to the 0.25H baffle height at Re=6000. Furthermore, at Re=1000, the PEC number is 84.50% higher with a baffle height of 0.25H and a baffle angle of 30° compared to the condition with a 90° angle.

Hygrothermal Performance of the Hemp Concrete Building Envelope

The search for environmentally friendly and low-carbon-footprint construction materials continues progressively. Researchers are now interested in innovative materials that connect with the principles of sustainable construction, and materials such as hemp concrete prove to be promising. This article presents the results of a study that aimed to evaluate the hygrothermal performance of hemp concrete integrated into the building envelope using the hygrothermal tool WUFI Pro 6.2. The simulation model was compared and verified with existing models before its utilization for this study. The results of this verification were in good agreement, which gave us more confidence in its application for further parametric studies of building envelopes in hot climate zones. Three wall systems were simulated: (i) a wall system with hemp concrete, (ii) a compressed earth block wall, and (iii) a cement block wall. The most important variables used in the simulations were the hygrothermal properties of the materials or wall components and the incident solar radiation. The simulation results showed that hemp concrete has good thermal performance and temperature and humidity regulation capabilities of the building envelope. The interior surface temperatures of the hemp concrete walls were between 22.1 °C and 24.6 °C compared to the compressed earth block and cement block walls, where the surface temperatures were between 22.0 °C and 27 °C and between 21.2 °C and 28.7 °C, respectively, and between 23 °C and 45 °C for the exterior temperatures. These values remain the same with the increase in exterior temperatures for hemp concrete walls. In conclusion, hemp concrete could be a great alternative material for use in construction for hot climate zones.

Estimation of Piston Surface Temperature During Engine Transient Operation for Emissions Reduction

Abstract Piston surface temperature is an important factor in the reduction of harmful emissions in modern gasoline direct injection (GDI) engines. In transient operation, the piston surface temperature can change rapidly, increasing the risk of fuel puddling. The prediction of the piston surface temperature can provide the means to significantly improve multiple-pulse fuel injection control strategies through the avoidance of fuel puddling. It could also be used to intelligently control the piston cooling jet (PCJ), which is common in modern engines. Considerable research has been undertaken to identify generalized engine heat transfer correlations and to predict piston and cylinder wall surface temperatures during operation. Most of these correlations require in-cylinder combustion pressure as an input, as well as the identification of numerous model parameters. These requirements render such an approach impractical. In this study, the authors have developed a thermodynamic model of piston surface temperature based on the global energy balance (GEB) methodology, which includes the effect of PCJ activation. The advantages are a simple structure and no requirement for in-cylinder pressure data, and only limited experimental tests are needed for model parameter identification. Moreover, the proposed model works well during engine transient operation, with maximum average error of 6.68% during rapid transients. A detailed identification procedure is given. This and the model performance have been demonstrated using experimental piston crown surface temperature data from a prototype 1-liter 3-cylinder turbocharged GDI engine, operated in both engine steady-state and transient conditions with an oil jet used for piston cooling turned both on and off.

Numerical study on drag and heat flux reduction induced by a counterflowing jet for rarefied hypersonic flow over a blunt body

This paper focuses on the drag and heat flux reduction induced by a counterflowing jet located on the leading edge of the blunt body head in rarefied hypersonic flows using the direct simulation Monte Carlo method. Flow structures in the flowfield, such as detached shock wave, Mach disk, contact surface, jet layer, and recompression shock wave, are all weakened gradually with the increase in the freestream altitude, and they eventually disappear at the altitude of 90 km. The increase in the jet pressure provides a great drag reduction by up to 53% when it increases from 800 to 1600 Pa, but the proportion of drag on the blunt body head to the total drag is only affected slightly by the jet pressure. A noteworthy finding is that further increasing jet pressure almost have no effect on heat flux variation when it is larger than 1200 Pa. On the whole, jet temperature has a quite weak influence on both flow structures and drag, while heat flux on the blunt body head is closely related to jet temperature. The results suggest that jet temperature should vary with that of blunt body surface, and moreover, the optimal jet temperature should be moderately lower than the wall surface temperature. In addition, increasing freestream altitude can provide excellent performance of drag reduction, but it causes non-monotonic variation of heat flux. In view of this, it is worth noting that heat flux on the blunt body head actually increases with altitude when the blunt body is in a severely rarefied atmospheric environment, such as the altitude H &amp;gt; 70 km.

Thermal performance of an active casing pipe macro-encapsulated PCM wall for space cooling and heating of residential building in hot summer and cold winter region in China

Phase change material (PCM) wall is expected to match the building type and its climate region effectively. In order to meet the space cooling and heating of residential buildings in hot summer and cold winter regions in China, a new active casing pipe macro-encapsulated PCM wall is proposed, in which the cold storage and heat storage PCMs are sealed between the inner pipe and outer pipe with no leakage. To obtain the optimal structure parameters and better thermal performance of the PCM wall, the mathematical model of the PCM wall is established and validated by experiment, and the effects of PCM filling pattern, structural parameter of casing pipe, water temperature in inner pipe and indoor setting temperature are simulated and analyzed. The results show that the optimal PCM filling pattern is to fill the cold storage PCM and heat storage PCM in the gap between the inner pipe and outer pipe separately; the optimal PCM filling thickness is 13 mm; the optimal structural parameters are inner pipe diameter of 20 mm and casing pipe centre spacing of 61 mm. The water temperature in the inner pipe and PCM energy storage/release time reasonably match the indoor setting temperature. Under the optimal operating conditions, the average PCM wall surface temperatures of 20.5 and 26.8 ℃ and the PCM wall surface heat fluxes of 45.9 and 57.2 W/m2 can be obtained in summer and winter conditions, respectively. The research provides an optimized casing pipe macro-encapsulated PCM wall system that can reliably and efficiently meet both the space heating and cooling demands of residential buildings in hot summer and cold winter regions in China.

Effects of tree density variations on outdoor heritage conservation: Numerical study of an ancient brick city wall with four orientations

Trees possess the potential to safeguard outdoor cultural heritage through the regulation of microclimates in their surroundings. The Leaf Area Index (LAI), a collective measure of the foliar portion within vegetation structure, reflects the regulatory ability of trees. In this study, numerical simulations were performed to compare the hygrothermal conditions of the Nanjing City Wall facing four orientations under the influence of evergreen trees with four LAI values, while also assessing the potential risks of salt weathering and algal growth. The results were as follows: 1) under the protective canopy of trees with identical LAI, the west and east walls experienced the highest temperature fluctuations, followed by the south and north sides. Wall surface temperature fluctuation was negatively correlated with LAI; 2) except for LAI = 1.5, the north wall had the least water content fluctuation under equivalent LAI levels. Water content fluctuation generally exhibited a decreasing trend with rising LAI; 3) at the same LAI level, the south wall presented the highest risk of salt weathering (including efflorescence and subflorescence), whereas the north wall faced the lowest risk. The risk of salt weathering decreased with an increase in LAI; 4) When shielded by trees with identical LAI, the north wall exhibited the greatest risk of algal growth, while the east wall faced least the risk. Higher LAI values were associated with an increased risk of algal growth on the wall surface. These results could provide a theoretical basis for large outdoor immovable heritage conservation and plant management around heritage sites.