Bottom Surface Temperature Research Articles

Ablation resistance and high-temperature insulation capacity of TiB2-B4C modified Al-coated carbon fibre/boron phenolic resin ceramizable composites

The inherent susceptibility to oxidation limits the application of carbon fibre/phenolic resin composites (CF/Ph) in the thermal protection of hypersonic vehicle engines. Herein, TiB2-B4C modified Al-coated carbon fibre/boron phenolic resin ceramizable composites were fabricated. The optimal ceramizable composite (T30C10) exhibited excellent ablation resistance and high-temperature insulation capacity at a linear ablation rate and bottom-surface temperature of -0.00768 mm/s and 129.8 °C, respectively. Oxygen consumption and inhibition, carbon fixation, and self-healing effects contributed to the excellent ablation resistance, and the effects of the Al coatings and carbothermal reduction reactions led to excellent high-temperature insulation capacities.

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.

Multi-objective parameter optimization design of tapered-type manifold/variable cross-section microchannel heat sink

Manifold microchannel heat sinks (MMCHS) have been widely used in the thermal management of high heat flux electronic devices. To improve the temperature uniformity of MMCHS and reduce the hot spot temperature, a tapered-type manifold/variable cross-section microchannel heat sink (TMVC-MCHS) is proposed in this study. Key parameters affecting the heat transfer performance of TMVC-MCHS were first investigated numerically. The results indicate that the width inclination ratio (αw,in) of the inlet manifold has a greater influence on the coolant flow distribution than the height inclination ratio (αh,in), with a ratio of more than 2.5. In addition, the microchannel inclination (β) and width ratio (ε) affect significantly the fluid flow and heat transfer. To further improve the cooling effect of the heat sink, this study adopted XGBoost and multi-objective genetic algorithm (NSGA-II) to optimize the structure. The maximum temperature of the substrate (Tmax) and the total pressure drop (ΔP) are the optimization objectives. Besides, the compromise solution (αw,in = 0.40, β = 0.63 and ε = 0.52) was determined by TOPSIS combined with the entropy weight method which was validated by the CFD method with an error margin of only 3 %. Finally, Compared to MMCHS, the temperature field distribution uniformity of TMVC-MCHS is significantly improved. The maximum bottom surface temperature is drastically reduced from 337.79 K to 320.01 K, and the temperature difference is reduced from 17.5 K to 3.5 K, at the cost of only a 3.5 kPa pressure rise. For inlet flow rates ranging from 1 m/s to 2.5 m/s, the TMVC-MCHS exhibits a hydrothermal performance factor (PEC) improvement of over 35 %, indicating superior comprehensive performance.

Investigation into the seamless construction for hundred-meter scale super-length raft structure based on magnesia expansive agent concrete

This research introduces an innovative construction method based on magnesia expansive agent concrete for the seamless construction of hundred-meter scale super-length raft structures, corroborated by the on-site test. The basic principle of this construction method is to use the pre compression stress generated by magnesia expansive agent to offset temperature and shrinkage stress. A temperature-strain monitoring system was employed to gather data, affirming the technique’s applicability and safety. Through the examination of temperature and strain dispersion trends in super-length raft structure, recommendations for the configuration of temperature-strain sensors have been put forth. Through the scrutiny of the temporal evolution pattern of temperature, the specific temporal and spatial coordinates that warrant particular vigilance during the surveillance of the raft’s inner-surface temperature difference were identified. Upon evaluating the correlation between strain dispersion and strain-temperature differential in the raft’s thickness dimension, a novel temperature control index (the bottom-surface temperature difference) was introduced. The threshold for this metric was established at 30°C, derived from empirical test outcomes conducted on-site. Furthermore, the critical regions for monitoring the bottom-surface temperature difference were specified.

Multi-objective optimization of a hybrid nanofluid jet impinging on a microchannel heat sink with semi-airfoil ribs based on field synergy principle

With the increasing power density of electronic devices, improving the cooling performance of their heat sinks is an important aspect of heat transfer enhancement research. A novel jet impinging microchannel heat sink with semi-airfoil ribs (JIMCHS-SAR) is proposed. Hybrid Cu-Al2O3/H2O nanofluid is adopted as the coolant. Using the field synergy principle, the flow and heat-transfer characteristics of the hybrid nanofluid impinging on the JIMCHS-SAR are investigated by both single-factor analysis and multi-objective optimization. The effects of jet Reynolds number and hybrid nanoparticle concentration on the optimized JIMCHS-SAR are also evaluated. The results show that a bilateral symmetrical arrangement of the semi-airfoil ribs provides the best thermal resistance and the smallest field synergy angle. Using the optimal structural parameters of the JIMCHS-SAR obtained from multi-objective optimization can significantly improve its overall performance. The thermal resistance and pump power of the optimal JIMCHS-SAR are 1.080 K/W and 0.387 W, respectively. The maximum temperature of the JIMCHS-SAR bottom surface is 8.1 K less than that for a jet impingement microchannel flat plate heat sink. As Reynolds number increases from 6000 to 14,000 and hybrid nanofluid volume fraction increases from 0 to 2.0 %, the thermal resistance decreases from 1.185 K/W to 0.908 K/W, a decrease of 23.4 %, while the pump power increases from 0.22 W to 2.1 W, a nearly 10-fold increase.

Investigation and Analysis of the Influence of Environmental Factors on the Temperature Distribution of Thin-Walled Concrete

The temperature field of thin-walled concrete is susceptible to the influence of the external environment, which may endanger the safety of its operation in projects. Therefore, it is essential for construction designers to conduct a full cycle experiment to clarify the influence of various environmental factors on thin-walled concrete temperature. In this paper, based on a long-term outdoor measurement experiment, the mean temperature and gradient temperature were both statistically analyzed seasonally, and two extreme gradient temperature patterns were identified and summarized. In addition, random forest regression was introduced to conduct a sensitivity analysis. It was found that the air temperature controlled the mean temperature and that solar radiation was the dominant factor affecting the gradient temperature, while the effect of wind speed was overall negligible. In addition, correlations between the concrete’s temperature and environmental factors were analyzed. It was concluded that the concrete’s mean temperature was positively and linearly correlated with the air temperature, while the minimum gradient temperature for the bottom shadow surface and maximum gradient temperature for the top shadow surface, respectively, had negative and positive linear correlations with the average solar radiation.

Numerical study and performance analyses of counter flow minichannel heat sink with slots on ribs

Various minichannel heat sinks are developed to cope with the increasing demand for thermal dissipation of electronic equipment. However, with the rapid development of microelectronics technology, temperature uniformity has gradually become a thorny problem needing more attention. Counter flow minichannel heat sinks with slots on ribs (CSF) were designed to enhance heat transfer and improve temperature uniformity. A 3D conjugated heat transfer model was developed in laminar flow regime, water has been selected as the working fluid, the constant heat flux was applied on the bottom surface of minichannel heat sinks. The counter flow minichannel heat sinks with slots on ribs not only possess higher heat transfer capacity, but also have better temperature uniformity. The average Nusselt number maximum increases to 2.01 times and the maximum temperature of bottom surface reduces 14.6 K for counter flow minichannel heat sink with five slots on ribs (CSF5) compared with parallel flow minichannel heat sink at Reynolds numberRe = 904. The temperature standard deviation of bottom surface maximum reduces 4.3 K for CSF3 minichannel heat sink atRe = 904. The effect mechanism of setting slots on ribs on the performance of counter flow minichannel heat sink was analyzed, it can be attributed to (i) interrupting and re-developing thermal boundary layer, and (ii) heat transfer between adjacent channels in which working fluid flows in opposite directions. Due to more uniform temperature of bottom surface and better heat transfer performance, the novel minichannel heat sink has potential application for thermal dissipation of electronic equipment.

High water use plants influence green roof substrate temperatures and their insulative benefits

Green roofs are amongst the solutions employed to deliver sustainable buildings in cities. Their vegetation and substrate layers can reduce the heat transfer through the roof, thus potentially reducing energy used for building cooling and heating. However, little research has investigated the insulative properties of drought-tolerant plants which also have high water use. These plants have been found to improve runoff retention by removing larger volumes of water from the substrate through higher transpiration rates than succulents. This planting strategy may also enhance green roof cooling performance due to their greater evapotranspiration rates.In this study, the thermal performance of three drought-tolerant species with high water use — Lomandra longifolia, Dianella admixta, and Stypandra glauca — was evaluated and compared with a commonly used succulent species (Sedum pachyphyllum) and a bare unplanted module.L. longifolia had the best insulative performance during the entire investigated period, reducing green roof substrate surface temperature up to 1.86 °C compared to succulent S. pachyphyllum. In summer, the mixture reduced heat gain to a greater extent than monoculture plantings of all species except L. longifolia. Summer measurements also suggest that plants with high leaf area index (LAI) and higher albedo should be selected to reduce surface temperatures. High evapotranspiration rates of high water use L. longifolia led to greatest reduction of bottom surface temperatures during a heatwave when decreasing its water content from 18.5% to 2.9%. Results obtained using an analytical hierarchical partitioning technique indicated air temperature had the most significant impact on temperatures at both the surface of the planting substrate and the bottom of each green roof unit, accounting for 48% to 58% of the variation.

Three-dimensional semi-analytical solutions of arbitrary functionally graded piezoelectric doubly curved shell panel under thermo-electric load

In this article, a methodological approach for the three-dimensional (3D) static behavior of functionally graded (FG) thermo-electro-elastic doubly curved shells subjected to a thermal and electrical load is presented. A coupling procedure based on the state space, a multilayered Runge-Kutta and transfer matrix methods is elaborated for numerical solution of the 3D thermo-electro-elastic governing equations. In the thickness direction, recursive relationships using a propagator matrix are elaborated allowing to handle arbitrary functionally graded effects. A global transfer matrix is formulated permitting to investigate the effects of various types of bottom and top surface temperature loads and heat flux. Some benchmark tests are presented to validate the presented approach and to analyze the influence of the material-property gradient index, the curvature radius ratio, the span-to-thickness ratio, the temperature, normal heat flux, and the electric voltage on the mechanic, electric, and thermal variables of doubly curved shells.

ANALYSIS OF AN ASYMMETRIC TRUNCATED CONCAVE PARABOLIC FIN

An asymmetric truncated concave parabolic fin is analyzed using a two-dimensional analytical method. In this analysis, the variation in the ratio of the top surface temperature to the bottom surface temperature along the fin length is presented. Heat loss from each surface and that from the fin are shown as a function of the convection characteristic number and the fin base height. The ratios of heat loss from each surface to that from the fin are given as a function of the actual fin length. The relationship between the convection characteristic number and the fin base height, as well as that between the actual fin length and the fin base height, are presented for equal amounts of heat loss. One of the results shows that the effect of fin base height variation on heat loss from the fin bottom surface and on heat loss from the fin tip surface is negligible when the actual fin length is fixed.

Experimental study on the heat transfer performance of loop heat pipe with different particle morphology and wettability of porous wick

Particle morphology and wettability of porous wick affect the movement and distribution of the working fluid in wicks, which further affects the phase change heat transfer. So the heat transfer performance will be significantly different for loop heat pipe (LHP) with different porous wicks. To study the effects of particle morphology and wettability of porous wick on the heat transfer performance of LHP from the perspective of phase separation, four types of porous wicks were fabricated and applied in LHP. Porous wicks were sintered with spherical and dendritic particle copper powder, respectively. Superhydrophilic wicks can be obtained by H2O2 oxidation. The results showed that capillary performance of dendritic particle wick was better than that of spherical particle wick. At t = 470 s, the climbing height of distilled water in the hydrophilic dendritic and spherical particle wicks were 19.8 and 18.1 cm, respectively. Compared with hydrophilic wick, superhydrophilic wick has a maximum 2.0 cm enhancement in climbing height at present experiments. The particle morphology of porous wicks had great effects on the heat transfer performance of LHPs. For LHPs with spherical or dendritic particle wick before H2O2 oxidation, their operating temperatures were 73.5 and 68.9 °C under θ = 90°, Q = 220 W situation. The latter has a lower operating temperature. For LHP with superhydrophilic dendritic particle wick, it had the best heat transfer performance among four kinds of LHP. The minimum thermal resistance can reach 0.07 K/W at Q = 300 W. Two diffusion modes of liquid in porous wicks were found in the visualization experiment, the distribution of the working fluid in dendritic particle wick was more uniform than that of spherical particle wick, which can explain well that the temperature of evaporator bottom surface is more uniform for LHP with dendritic particle wick. These results have a good guiding role for the preparation of high-performance LHP.

Experimental study of solar PV/T panel to increase the energy conversion efficiency by air cooling

An increase in the operating temperature of photovoltaic (PV) panels caused by high levels of solar irradiation can affect the efficiency and lifespan of PV panels. In this study experimental analysis to investigate the reduction in the operating temperature of PV panels with an air-cooling system. The proposed experimental setup was designed and attached to the back of the PV panel. In this paper, the experimental study of solar PV penal with and without bottom air cooling system to reduce the operating temperature of photovoltaic panel is presented. The experimental investigation of solar PV panel was conducted with different mass flow rate of air. The influence of mass flow rate of air on the heat transfer from a PV panel and the circulating ambient air was investigated. The results showed a substantial decrease in the operating temperature of the PV panel and an increase in its electrical performance. The average PV penal temperature is reduced to 9 °C. The mass flow rate of air was 0.08 kg/sec, average maximum bottom surface temperatures with and without air cooling are 45.60 0C and 50.24 0C.As a consequence of decreasing its temperature, there is increased in the electrical energy conversion efficiency of the PV penal from 7 to 12.6%. Therefore, the use of air cooling system could provide a potential solution to prevent PV panels from overheating.

NATURAL CONVECTION HEAT TRANSFER IN AN ENCLOSURE FILLED WITH Fe3O4 FERROFLUID UNDER STATIC MAGNETIC FIELD: EXPERIMENTAL INVESTIGATION AND COMPUTATIONAL FLUID DYNAMICS MODELING

This survey presents experimental and CFD studies on natural convection heat transfer of Fe3O4 ferrofluid in the presence of a static magnetic field (SMF). Natural heat transfer from the bottom surface of a rectangular enclosure with constant temperature to the cold liquid was investigated. The magnetic field's intensity is controlled by adjusting magnet distance from the upper surface of the enclosure (d=8-22 mm). The concentration of dispersed nanoparticles (ϕ) is another key parameter that had to be considered. On the other hand, the heat received from the bottom is controlled by adjusting temperature of bottom surface (Ts) between 36 and 46oC. The experimental design software (Box-Behnken method) is employed to evaluate the effects of the considered variables on the amount of heat transferred. After the experiments, the prediction Box-Behnken models based on ferrofluid bulk temperature (Tb), and Nusselt number (Nu) are acquired in terms of variables. Assigning to various criteria, the Box-Behnken models are highly accurate. The results show that increasing the nanoparticle concentration positively affects heat transfer while moving the magnet away from the system reduced this consequence. The Box-Behnken method introduced the optimal conditions for each model to achieve maximum response. For each model, the optimum values of the predicted responses are: Tb= 43.56 ℃ , and Nu= 1288.98 at ϕ=1% wt. All values obtained for the answers under optimal conditions are only 0.1%-0.3% different from the predicted values, which indicates the high validity of the models. In addition, CFD results for Tb confirmed the experimental data with maximum relative error of 7.68%.

Effect of Waveform Channel on the Cooling Performance of Hybrid Microchannel

To improve comprehensive hydrothermal performance of microfluidic cooling, a new type of hybrid microchannel is proposed. In this paper, turbulent flow and heat transfer characteristics of rectangular cross section straight hybrid microchannel, trapezoidal cross section straight hybrid microchannel, and trapezoidal cross section waveform hybrid microchannel (TWHM) are compared numerically by a realizable turbulence model under different pump power and heat flux. The results show that TWHM has a greater pressure drop at the same Reynolds number but has the best heat dissipation performance at the same pump power, in which temperature difference can be reduced up to 55.01%. The effect of arc height and chord length on the cooling performance of TWHM is also studied. As increases or decreases under the same pump power, the friction factor increases, while the total thermal resistance and bottom surface temperature difference decrease gradually. The cooling performance of channels becomes closer as the pump power increases. In addition, with the same cross-sectional area, the cooling performance of the waveform hybrid microchannel can be further improved by optimizing cross-sectional shape . The best cooling performance can be obtained at .

Hydrothermal performance of single and hybrid nanofluids in Left-Right and Up-Down wavy microchannels using two-phase mixture approach

The aim of this study is to explore the hydrothermal attributes of three types of nanofluid containing the silver nanoparticles, aluminum oxide nanoparticles, and hybrid silver–aluminum oxide nanoparticles in two different types of microchannel, namely Left-Right and Up-Down wavy microchannels. The multi-phase mixture model is utilized to numerically simulate the flow at constant pumping powers. The results unmask that the secondary flow formed due to the wavy structure is more severe for the Left-Right wavy microchannel compared to the Up-Down one. Also, a maximum 330% enhancement in the convective heat transfer coefficient was observed for the Up-Down wavy microchannel working with the silver nanofluid, while the same value for the Left-Right one was 200%. Although the impact of using the nanofluids is more dominant for the Up-Down wavy microchannel, the Left-Right one exhibited better cooling performance in terms of the Nusselt number. It was observed that utilizing the nanofluids has minor impact on improving the bottom surface temperature uniformity for the Left-Right wavy microchannel, while for the Up-Down one this effect is more dominant. Lower amounts of thermal resistance were obtained in the case of using the nanofluids for both wavy structures, with more impact on the Up-Down one.

Performance evaluation of thermally insulated building integrated photovoltaic roof

In this paper, the thermal performance of insulated BIPV roofs is studied compared to non-insulated BIPV roofs. The BIPV roof prototype is designed, developed, and experimentally evaluated for composite climatic conditions in the summer season. A surface temperature of PV module and different insulation Polyurethane foam, Rockwool, and Expanded Polystyrene were observed.It was seen that the PUF insulated BIPV roof has a decrement factor of 0.24 and a time lag of 1 h. The average bottom surface temperature of the insulated BIPV roofs is found between 37.4°C to 39°C.while, non-insulated BIPV has the average temperature of 46 °C. Further, heat gain and percentage heat reduction with respect to non-insulated BIPV roof are calculated. Also, the average Discomfort index ranged between 26 and 29 for all the cases of insulated BIPV roof. The study reveals that the thermal feasibility of the insulated BIPV roof is acceptable.

Optimization and Re-Design of Integrated Thermal Protection Systems Considering Thermo-Mechanical Performance

Integrated thermal protection system (ITPS) is regarded as one of the most promising thermal protection concepts with both thermal insulation and load-bearing capacities. However, the traditional layout of webs could inevitably lead to thermal short effects and high risk of buckling failure of the ITPS. A topological optimization method for the unit cell of the ITPS was established to minimize the equivalent thermal conductivity and elastic strain energy with the constraint of maintaining structural efficiency. The ITPS was re-designed consulting the optimized cell configuration. In order to control the buckling-mode shape and the associated buckling load of the ITPS, the new design was further optimized, subjected to the total weight of the initial design. Detailed finite element models were established to validate the structural responses. By contrast, the optimized design presents lower bottom surface temperature and better thermal buckling characteristics, performing a better balance between thermal insulation and load-bearing constraints.

Numerical investigations for optimizing a novel micro-channel sink with perforated baffles and perforated walls

A novel micro-channel sink with perforated baffles and perforated walls (MSPBPW) is proposed to ameliorate the bottom surface temperature of the heat sink. Firstly, the performance the MSPBPW are numerically studied. L1 represents the width of the rectangular hole on the baffle, and L2 represents the distance between the channel wall perforation and the center of the hole on the baffle. The results show that the heat transfer ability of MSPBPW with pressure drop penalty can be significantly improved, and the thermal performance evaluation criterion (PEC) value is always greater than unity. The substrate maximum temperature can be reduced by 17.8 K when introducing perforated baffles and punching holes on the channel walls into the conventional heat sink. Secondly, the effects of the width of the rectangular hole (L1) and the distance (L2) between the channel wall perforation and the center of the hole on the baffle on the cooling capacity of the MSPBPW are discussed numerically. Finally, the best parameters are achieved by single-objective optimization according to genetic algorithms. At the same Reynolds number (Re), both the Nusselt number and the friction coefficient decrease with the increase of L1, while those increase with the increase of L2. The data of the single-objective optimization are consistent with CFD results.

Modelling dry-weather temperature profiles in urban stormwater management ponds

One of the unintended consequences of urban stormwater quality management wet ponds is the thermal enrichment of the shallow pond water during the summer months. The outflow from thermally enriched ponds can degrade the cold and cool water aquatic habitat in urban streams. An accurate model of the pond temperature profile is needed to assess the pond effluent thermal load. However, most models developed for this purpose are process-based and not simple to use, requiring a lengthy monitoring dataset to calibrate. This paper introduces a new design/assessment tool to predict the hourly water temperatures in these ponds at different depths during the summer season dry-weather warming periods and the diurnal cycles. We compiled monitoring data from five ponds in the Greater Toronto Area from 2013 − 2016 to evaluate the ponds' thermal impact on the receiving cold water streams. Using these datasets, we developed a new equation that allows for separating the active upper portion and stable lower portion of the pond. This ensures the focus is on the active upper part, where the majority of the heat transfer within the pond occurs and exhibits diurnal temperature fluctuations. We also used machine-learning tools to develop accurate equations for the bottom temperature and surface temperature, as well as, key equation parameters that characterize the thermal profiles. The developed thermal profile equation allows for the simple determination of other key thermal metrics such as average temperature, energy stored, thermocline location, which may be used as inputs to model wet weather flow conditions and pond outflow temperature. The results show that the proposed machine-learning model is acceptably accurate and capable, according to the low mean absolute percentage error (MAPE) and coefficient of determination (R2) values of 5% and 0.965, respectively, for temperature prediction for all depths. This work provides a building block for the overall objective to develop a new, easy to use, wet weather explicit equation for predicting the outlet temperature from stormwater management wet ponds since it establishes the initial thermal condition before the storm hits.

Fabrication of cooling asphalt pavement by novel material and its thermodynamics model

It is an important research field to restrict the extreme temperature of pavement by using the robust thermal performance of phase change materials. In this study, diatomite, expanded perlite, and stearic acid were chosen to prepare compound phase change materials (CPCMs) for the fabrication of novel cooling asphalt pavement. The microtopography and characteristics of CPCMs were described by scanning electronic micro-scopy, Fourier transform infrared spectroscopy and X-ray diffraction. The thermal performance and stability were confirmed by thermogravimetric analysis and differential scanning calorimetry. The cooling asphalt pavement was evaluated by pavement performance and thermal performance test. Finally, the heat transfer simulation of the cooling asphalt pavement and the conventional asphalt pavement were established by the finite element method. CPCMs with diatomite as carrier still feature superior chemical and thermal stability after 100 cycles. The upper and bottom surface temperatures of the asphalt pavement can be reduced by 10.90 °C and 5.03 °C, respectively. The temperature gradient at each stage showed that the addition of CPCMs helps to restrict the extreme temperature of the pavement, and has the potential to restrict the temperature extremities in pavement and the effect of urban heat island.