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Transient vehicle dynamics are deeply affected by the spatial distribution of tire temperature, heat generation, and heat dissipation capacity. However, the tire testing process involves numerous parameters, adding the complexity to monitoring the tire's thermal properties variation. To address this issue, this paper proposes a data-driven framework that combines the well-known Magic Formula with scaling factors and a long- and short-term memory (LSTM) neural network. The framework forecasts tire thermal properties and functionality under given conditions by learning from time-series data on tire operating conditions and mechanical characteristics. It predicts future spatially varying thermal properties of the tire, including temperatures, heat generation, and heat dissipation. This is achieved with a high degree of forecasting ability quantified by train size/test size ratios equaling 22 and 38% with an impressive Relative Root Mean Square Error (RRMSE) around 1−2%. Here, this framework is applied to quantify the impacts of various operating conditions, including vertical load, slip angle, and vehicle speed, on heat transfer for three crucial radial positions on the tire. Our results show that the vertical load is the primary influencing parameter among all operating conditions. The knowledge about transient tire dynamics will be advantageous to their performance optimization. [ABSTRACT FROM AUTHOR]

To understand the transient heat transfer characteristics of nanoporous aerogel insulating composites, solving the inverse heat transfer problem would be crucial for identifying the temperature-dependent thermal properties of composites. In this study, with constructed a forward model to numerically investigate the heat transfer in composites, a deep neural network (DNN) model and a particle swarm optimized deep neural network (PSO-DNN) model are conducted to rapidly estimate the effective temperature-dependent thermal conductivity of the desiccated and moist composites from the temperature response measurements. With the DNN model, the retrieved thermal conductivities for desiccated composites possess low deviation to experimental measurements (<3.2%) and constantly low errors (<5.2%) from 280 K to 1080 K. The precision of the DNN solver could be enhanced by adjusting the hyperparameters of the neural networks using PSO. The retrieved thermal conductivities possess low deviation from experiments (<2.5%) and low relative errors within 1.5%. Furthermore, the robustness of the PSO-DNN solver is discussed when commercial thermocouple measurement errors are considered, within retrieving the thermal properties of desiccated and moist aerogel composites. [ABSTRACT FROM AUTHOR]

The present experimental investigation incorporates the winglet twisted tapes as an insert to determine the thermal and hydraulic performance of a heat exchanger tube. The purpose of connecting the winglet to the twisted tape is to improve the heat transmission while minimizing the pressure loss by not disrupting the flow at the core portion. The thermal performance of a heat exchanger with turbulent promoters is assessed by varying geometric factors, such as the size of the promoters, Twist ratio ( y / W), Winglet pitch ratio ( P w / L T ), and Winglet height ratio ( h w / b w ). Experiments were carried out for Reynolds numbers (Re) ranging from 3,000 to 21,000. For a set of geometric parameters, the greatest thermohydraulic performance achieved was 1.58. Regression analysis is used to build a statistical association for Nusselt number N u and friction factor f , and the anticipated data obtained is of acceptable accuracy. The entropy generation is expressed in the form of entropy generation number and the Bejan number to fetch the dominance of thermal or friction entropy using winglet twisted tape. [ABSTRACT FROM AUTHOR]

Expanded polystyrene foams (EPS) are used as packaging materials and are often discarded by consumers after the goods are unpacked (WEPS). Most recycling centers do not accept them because their extremely low weight makes them uneconomic to transport. In the research described here, WEPS was collected from shipping containers and crushed in a blender into 2-4 mm spherical shapes that were used as a replacement for aggregates to make lightweight concretes (LWC) to build lightweight facilities. Eight types of concrete samples were prepared, with the WEPS replacing the natural aggregate at the levels of 0 to 85 percent by volume to study the effects of the WEPS on the properties of the LWC. The densities of the LWCs were less than that of those found from natural aggregate (NAG), as was expected (900–1700 kg/m3). The heat conductivity of the LWC samples was smaller than that of NAG when the composition of WEPS was below 50%. The 28-day compressive strengths of the LWC ranged from 11 MPa to 90 MPa, which satisfies the strength requirement of semi-structural LWC recommended by ASTM to be higher than 17 MPa. [ABSTRACT FROM AUTHOR]

The thermal properties of nanofluids are variable with working temperature and pressure and ignored by the existing empirical formula. In the present work, based on the application of nanofluids in pressurized water reactor (PWR) nuclear power plants, different concentrations of Al2O3/H2O nanofluids are prepared for measuring its thermal properties and then modifying empirical formulas at high temperature and high pressure (HTHP). In addition, the primary heat transfer process of PWR nuclear power plants is simulated by numerical method. The results show that, when volume fraction φ within 2.0%, the heat transfer performance of Al2O3 nanofluid increases with the increase of concentrations; however, it is on the contrary when the volume fraction of nanoparticles is larger than 2%. Comparing with water as the coolant, Al2O3 nanofluids with 2% volume fraction give the largest heat transfer enhancement of 103%. Therefore, Al2O3 nanofluids as the coolant can achieve the goals of heat transfer enhancement and safety limit improvement. [ABSTRACT FROM AUTHOR]

In the production of functional nonwovens with sustainable fibers, kapok, with unique qualities, becomes an excellent candidate for the production of thermal insulation textiles. However, the development of 100% raw kapok fiber structures is a challenge, since their mechanical resistance and interfiber cohesion is very low. In this work, the thermal behavior of new needle punched bi-layered nonwovens produced from 100% raw kapok fibers is studied. These innovative structures were obtained through dry heat-pressing of needle punched nonwovens, developed according to a novel method designed. The results obtained have shown that the heat-pressing conditions (temperature and number of cycles) affected the thermal properties of the nonwovens and the thermal performance profile of an insulating arrangement. The bi-layered nonwoven structures reinforced in one heat-pressing cycle at 100 °C showed the higher thermal resistance and the lower thermal conductivity and heat flux and led to the highest delay (decrement delay) of the heat transfer from the outside to the inside of the insulating assembly and vice-versa, acting as an effective thermal insulator. [ABSTRACT FROM AUTHOR]

In this study, a RANS model of turbulent conjugate heat transfer has been developed, which is applicable across a range of different combination of fluid and solid thermal properties. This is achieved by focusing on the transport equations for the temperature variance and its dissipation rate across the solid walls which bound the flow region. In this investigation we make use of a wider range of DNS data reported by other researchers, to advance our understanding of the processes involved and to revise and extend the capabilities of the model of Craft et al [12] including a more physical fluid-solid interface condition on the dissipation of thermal fluctuations and a dependence of model coefficients on Prandtl number. The resulting model is shown to successfully reproduce the penetration of thermal fluctuations into solid regions, and their subsequent decay across the solid, for a wide range of fluid to solid thermal property ratios, and Prandtl numbers, thereby bringing a step change to RANS capabilities in turbulent conjugate heat transfer analysis. [ABSTRACT FROM AUTHOR]

The graphene-based additives containing polyethyleneimine (PEI) or hydroxyapatite (HAP) were synthesized and their effects on the flame retardancy, thermal, mechanical properties of polyvinyl alcohol (PVA) matrix were evaluated. Thermogravimetric analysis studies (TGA) and Scanning electron microscope (SEM) images were indicated that PEI and HAP have a strong influence on the fire behavior of the composites which might be explained by the forming of a uniform and compact char during combustion. The presence of nitrogen in PEI and phosphorus in HAP which are generated nonflammable gases and phosphoric radicals, respectively at combustion conditions could represent a significant role in the catalytic char residue formation, heat transfer limitation and then diminish or even stop the combustion reactions. The char yields of the 5 wt% PVA/GO-PEI nanocomposites were increased up to 22 folds without any significant change in mechanical properties; Moreover, the char yield of PVA/GO-HAP nanocomposites was more than pure PVA (24 folds) because of its thermal stability at high temperature. All these data demonstrated that not only did PVA/GO-PEI keep the mechanical properties nearly the same as in pure PVA but also improved flame retardancy. But, the PVA/GO-HAP has great potential as flame retardants between all obtained composites. [ABSTRACT FROM AUTHOR]

The bio-based materials have experienced in recent years a relevant evolution in construction and for many building applications. Despite the efforts to develop new solutions to achieve the objectives of numerical characterizations, a few researches in this area have been carried out using a heterogeneous wood-cement composite. This study is based on a constructive approach using the finite volume method in order to generate a numerical model capable of reproducing the equivalent transfer properties of a wood-cement composite. The challenge is to understand, design, and control this multiphase inhomogeneous structure and predict transfers and flows within the community in order to achieve an optimal functionality. Experimental measurements and microscopic characterization using X-ray microtomography were performed to compare and demonstrate the method validation. The comparative results demonstrate a less than 10% deviation between the measurements and the simulations of the equivalent thermal properties. Thus, thermal conductivity and permeability, under different medium configurations, were characterized. Therefore, it was observed that these properties depend strongly on the porosity and the pore distribution in the continuous phase. Moreover, these two parameters are highly dependent on cement percentages in the structure. [ABSTRACT FROM AUTHOR]

This paper studies the heat-shielding performance of a beetle forewing to explore how it has excellent thermal protective properties. With an experimental setup of a self-developed heating environment, the heat transfer characteristics of the beetle forewing were tested at 50°C under steady state conditions. Two types of the forewings are considered: cut wing and live wing. The heat transfer results show that the live forewing provides a good heat-shielding performance with the heat-shielding index stabilizing at around 22.1%, which is 60% higher than that of the cut wing. Based on scanning electron microscope images of the microstructure of the cross section of the beetle forewing, a simplified finite element analysis is performed to numerically calculate the heat transfer properties of the forewing. The numerical simulations reveal that the proposed structure of the forewing is good for the design of an effective thermal protection system. In addition, the uncertainty analysis is performed to evaluate the quality of experimental data. These results provide a foundational understanding of the heat transfer characteristics of beetle forewing, which will inspire a promising candidate for an actively cooled thermal protection systems. [ABSTRACT FROM AUTHOR]

The theoretical analysis of different concentrating photovoltaic and thermal systems (CPV/T) is presented in this paper; it allows to evaluate the cooling fluid temperature in different working conditions. In particular, two CPV/T systems with different optics, line-focus and point-focus, are studied and compared theoretically by means of a model developed in ANSYS-CFX able to evaluate the theoretical temperature values of the fluid that flows in the cooling circuit, designed with the Solidworks software. The comparison in terms of the thermal performances between the point-focus and line-focus configurations of a CPV/T system has been realized considering different working conditions. As model input the uniform cell temperature has been set to different values, included between 323 K and 363 K, or determined experimentally referring to the point-focus configuration. In particular, the outlet temperatures of the cooling fluid, the fluid and cells temperatures difference at the outlet section, the time necessary to reach a steady-state condition, the fluid temperature trend in different parts of the tube and along the circuit, have been evaluated. Moreover, the fluid temperature trend has been studied varying the fluid velocity, its mass flow rate, and the insulation thickness. Finally, the point-focus CPV/T system thermal performances have been also evaluated adopting some experimental measurements as input data; the fluid temperature trend has been tested under a variable cell temperature during different hours of a sunny and a cloudy day. [ABSTRACT FROM AUTHOR]

The determination of local convective heat transfer coefficients in microfluidics is a very hard task. Due to the small dimensions of channels and walls, the use of conventional measurement techniques is only partially suitable in microfluidics. For this reason, a strong effort has been made during the last decades in order to propose innovative techniques which use internal (to microdevices) sensors of reduced dimensions and/or external conventional sensors. In this paper a review of the main experimental techniques proposed for the determination of the local near-wall fluid temperature, the local wall temperature, and the local fluid bulk temperature will be given by putting in evidence for each technique's positive and negative aspects as well as their actual limitations with the aim to stimulate and address the research on this topic in the near future. The problems and the limitations existing nowadays for the accurate measurements of the local thermal properties of a convective microflow demonstrate that for the analysis of microconvection experimental data have to be always integrated by a numerical modeling of the observed system. [ABSTRACT FROM AUTHOR]

In this research, an experimental evaluation is conducted on the hydrothermal behavior of water-based manganese ferrite nanofluid flowing in a metal foam tube. For this purpose, manganese ferrite nanoparticles are synthesized, and X-ray diffraction and scanning electron microscopy are implemented to specify the samples for determination of phase and size of nanoparticles. The effects of Reynolds number, Prandtl number, and presence of MnFe2O4 nanoparticles inside the water on the Nusselt number and friction factor have been studied. The experimental analysis shows that the increment of Reynolds number, Prandtl number, and nanoparticles concentration improve the heat transfer performance. The maximum of 19.1% and 10.5% increase in Nusselt number and friction factor have been achieved respectively by dispersion of 2 wt% manganese ferrite nanoparticles inside the deionized water at Reynolds number of 1,000. A hydrothermal index is proposed to consider the thermal and hydrodynamic characteristics of the nanofluid, and it is attained that the convection heat transfer improvement dominates the pressure drop in this work. According to the experimental results, the Nusselt number and friction factor of the nanofluid is modeled as a function of Reynolds number, Prandtl number, and nanoparticles concentration using artificial neural network with an acceptable precision. [ABSTRACT FROM AUTHOR]

Socks are prevented against wrinkle formation by preheat setting in greige form prior to wet processing. The current study is proposed to analyze the effect of socks presetting process on thermopysiological and wicking properties of comfort. In this analysis, main yarn linear density, plaiting yarn composition and number of needles are taken as variable on same machine setting. Sock samples were analyzed for comfort parameters (thermal conductivity, thermal resistivity, thermal absorptivity, thermal diffusivity, relative water vapor permeability (RWVP (%)), evaporation resistance (Ret), air permeability, vertical wicking, absorbency and color strength (K/S) value) after various processes (preheat setting, dyeing and postheat setting). The statistical analysis showed that preheat set process significantly affects vertical wicking, K/S value, absorbency, thermal conductivity, thermal resistivity and thermal diffusivity, respectively. While thermal absorptivity, air permeability, porosity, RWVP (%) and Ret couldn't show a significant impact. [ABSTRACT FROM AUTHOR]

Surimi-based products from lisa blanca (Mugil curema) were produced using different heating processes of steaming, boiling, frying, and baking. The cooking time, thermophysical properties, and overall acceptability of each product were determined. The specific heat (Cp) and density (ρ) of raw samples was determined by differential scanning calorimetry and by volume displacement with water, respectively. The temperature variation inside the surimi was measured by several thermocouples strategically placed. Experimental data of temperature and time were recorded and used to estimate thermal conductivity (k) and heat transfer coefficient (h) by nonlinear regression. A simulation of heat transfer was carried out by COMSOL Multiphysics 4.3 software. A sensory evaluation was performed with 100°C judges using a 9-point hedonic scale. The values of Cp and of raw surimi were 3768.56 ± 15.35 J/kg℃ and 1030 ± 15 kg/m3, respectively. The experimental cooking time of surimi was 120 and 65 min for the baking and boiling processes, respectively, and 50 min for steaming and frying processes. k and h were dependent on the thermal process used and could be used to calculate the process time of new products with different shapes and other operation conditions. The sensory evaluation of products indicated a good acceptance by consumers. [ABSTRACT FROM AUTHOR]

The thermal boundary resistances (TBRs) of twin boundaries occurring at three different atomic layers (Te1, Bi, and Te2) of bismuth telluride (Bi2Te3) are investigated in use of the non-equilibrium molecular dynamics (NEMD) simulation method. The simulation results show that among all, the Te1-twin boundaries bring about a lowest interfacial energy corresponding to a most stable system, which explains why this type of twin boundaries is mostly often observed in the laboratory; the Te2-twin boundaries on the other hand possess a largest interfacial energy, resulting in a least stable system. The order in magnitude of the TBRs associated with these three types of twin boundaries is Te2-twin > Bi-twin > Te1-twin. Moreover, the TBR associated with a pair of twin boundaries separated by a distance of 4 unit cell (UC) is found to be about twice as large as that of a single twin boundary of the same type. It implies that the mutual coupling, which causes an increase in TBRs, may be ignored and the effect of twin boundaries may be counted individually as long as the separation distance is larger than 4 UC. [ABSTRACT FROM AUTHOR]

Grout plays an important role in the heat-transfer performance of borehole heat exchangers. The current study developed a numerical model to investigate the effect of grout thermal conductivity and heat capacity on the heat-transfer performance of borehole heat exchangers. The “relative thermal conductivity” was defined to obtain the best matching relationship of thermal conductivity between grout and soil. The numerical model was validated through sandbox experiments. The results showed that, when the grout thermal conductivity and heat capacity were both varied by 47.00%, the effect of the grout thermal conductivity on the pipe wall temperature was 26.44% stronger than that of the grout heat capacity; whereas the effect of the grout heat capacity on the heat-transfer radius was 5.21% stronger than that of the thermal conductivity. As the same variation of the grout thermal conductivity, when the soil thermal conductivity change from 1.30 to 1.90 W/(m·K) (1.60 kcal/[m2 · h · °C]), the effect of the changing grout thermal conductivity on the heat-transfer performance decreased by 8.04%. The results also showed that the optimal relative thermal conductivity was 1.20-1.30. These results can serve as guidelines for selecting appropriate grouts for different geological conditions. [ABSTRACT FROM AUTHOR]

This study investigates the applicability of artificial neural networks (ANNs) as an efficient tool for the description of thermal conductivity of liquid alcohols for a broad range of temperatures. The proposed multilayer perceptron has 1 hidden layer with 43 neurons, determined according to the constructive approach. The model developed was trained and validated on the set of data gathered, showing that the accuracy of the ANN model is higher than that of other approaches proposed in the literature. The experimental or experimental and predicted thermal conductivity data of alcohols were taken from the database due to the ‘DIPPR Database’. The ability of the ANN method to reproduce the original data was tested for 26 alcohols in the liquid phase at reduced temperatures ranging from 0.30 to 0.90. The maximum absolute deviations between experimental and calculated thermal conductivity data points are generally less than 0.0110%, while the average absolute deviations are usually less than 0.0016%. This study shows that the model used is a good alternative to estimating thermal conductivity of alcohols with excellent precision. [ABSTRACT FROM AUTHOR]

Salt hydrate for application as secondary refrigerant in the air-conditioning system are selected based on the slurry forming according to the evaporator temperature 5°C–12°C. Research development of salt hydrate for application is done in three stages, namely; the study of the properties, flow, and heat transfer characteristics, also applications in air-conditioning systems. The study of the properties of the phase change materials is in the form of latent heat, freezing and melting temperature, thermal stability properties, viscosity, and rate of corrosion. The study of flow and heat transfer characteristics determine the effect of salt hydrates on the pressure drop and heat transfer in a heat exchanger. Studies on the application of the air-conditioning system is made to use a type of cooling room air-handling units and fan coil unit. The results of the researches for each of two stages are described in the discussion of the current article. The characteristics of salt hydrates from Na2HPO4and CaCl2are fitted to be applied as secondary refrigerant. This material has high latent heat value and matched phase change temperature, as well as a very low corrosion rate. This material also demonstrates excellent heat transfer performance, in which an increase as much as 18.62% for salt hydrate from calcium chloride and 13.9% for salt hydrate from disodium hydrogen phosphate. For its flow characteristics, there was a less significant increase on pressure drop for Na2HPO4. [ABSTRACT FROM PUBLISHER]

Black phosphorus (BP) is a layered direct bandgap semiconductor. Few-layer BP, an emergent and promising two-dimensional semiconductor, has attracted increasing interest for novel electronic, photonic, and energy conversion applications due to its unique tunable direct bandgap and anisotropic in-plane transport properties. Understanding the thermal transport properties is critical for thermal management of electronics and thermoelectric applications. In this review, we cover the thermal transport properties of single-layer, few-layer, and bulk BP from most recent theoretical and experimental work, with a particular focus on the anisotropic in-plane thermal conductivity. [ABSTRACT FROM AUTHOR]

Since 2010, hydro-fluoro-olefines have been experimentally studied during both boiling and condensation with the research productions continuously growing. At a glance, most of the data collected regards the two most available fluids, R1234yf and R1234ze(E), which were tested during two-phase flow both inside and outside smooth and microfin tubes or in brazed plate heat exchangers, as well on other different enhanced surfaces. A few data were obtained with noncommercially available hydro-fluoro-olefines, such as R1234ze(Z). In addition, relevant work has been dedicated to study the heat transfer capabilities of hydro-fluoro-carbon/hydro-fluoro-olefine mixtures. This article presents a critical review on the published research articles on in-tube two-phase heat transfer during boiling and condensation of hydro-fluoro-olefine refrigerants. In particular, a large database of experimental measurements was collected, reviewed, discussed, and then compared against common models to identify the most suitable for all the investigated two-phase heat transfer processes. [ABSTRACT FROM AUTHOR]

In order to enhance the thermal properties of turbine oil (TO), three different nanoparticles (CuO, Al2O3, and TiO2) are loaded into the TO. To measure the thermal performance of nanoparticle-based TO nanofluids at laminar flow and under constant heat flux boundary conditions, an experimental setup was applied. The obtained data clearly demonstrate the positive effect of all nanoparticles on the heat transfer rate of TO. As the most important factor, the heat transfer coefficient of the abovementioned two-phase systems is increased upon increasing both the volume concentration and the flow rate. An adaptive neuro-fuzzy inference system (ANFIS) is applied for modeling the effect of critical parameters on the heat transfer coefficient of nanoparticle-TO based nanofluids numerically. The results are compared with experimental ones for training and test data. The results suggest that the developed model is valid enough and promising for predicting the extant of the heat transfer coefficient.R2and MSE values for all data were 0.990208751 and 108.1150734, respectively. Based on the results, it is obvious that our proposed modeling by ANFIS is efficient and valid, which can be expanded for more general states. [ABSTRACT FROM AUTHOR]

This study investigates the performance of an adsorption chiller driven by thermal heat collected from solar collectors’ panels with heat storage. The heat is reserved in a storage tank and the reserved heat is used to drive the adsorption chiller. The investigation was carried on the climatic conditions of Dhaka, Bangladesh. Heat transfer fluid goes from the collectors to the adsorption cooling unit, then from the adsorption cooling unit to the storage tank. It is seen that heat storage is more effective than direct solar coupling; however, it requires more collectors, depending on the size of the storage tank. The analysis shows that cycle time is one of the most influential parameters for the solar-driven adsorption cooling system. It is seen that the size of the collector can be reduced if the proper cycle time is adjusted. The analysis also revealed that the system with 22 collectors (each of 2.415 m2) along with 1000 s cycle time provides better performance for the base run conditions. It is also seen that the solar-driven adsorption chiller with heat storage works well beyond the sunset time. [ABSTRACT FROM AUTHOR]

The objective of this study is to clarify physical mechanisms involved in the evaporation of small (a few microliters) sessile drops. We aim to understand the relation between local thermal information at the solid–liquid interface and overall evaporation. An infrared (IR) camera and a charge-coupled device (CCD) camera were used to determine the temperature and heat flux distribution at the solid–liquid interface and the profile of the evaporating drop, respectively. The temperature distribution at the solid–liquid interface was determined using a multilayer substrate consisting of a silicon wafer coated with a thin thermal insulator that is partially transparent to IR. The liquids used were water and FC-72. The evaporation rate of water drops was found to occur mostly at the contact line. However, the heat transfer distribution at the liquid–solid interface was relatively uniform, indicating the heat transferred from the wall must be transported within the drop to the contact line. The mechanisms by which this occurs have yet to be determined. In contrast, the evaporation rate of FC-72 drops where hydrothermal waves were present was found to be proportional to the liquid–vapor interface area rather than the circumference of the drop, indicating a more uniform distribution of evaporation. [ABSTRACT FROM AUTHOR]

For the development of industrial heat pump systems supplying a high-temperature heat source over 130°C, experiments were carried out on cooling heat transfer of supercritical pressure fluids flowing in a plate heat exchanger (PHE). Using two refrigerants of HFC134a and HCFC22 as the test fluids, heat transfer coefficient data were obtained at different pressure, flow rate, and heat load conditions. The heat transfer coefficient generally had a maximum in the vicinity of the pseudocritical point and showed seven- to ninefold values compared with tube flow. Based on the measurements, characteristics of cooling heat transfer of supercritical pressure fluids in the PHE were clarified and a correlation of heat transfer coefficient was developed. [ABSTRACT FROM AUTHOR]

This paper presents a highly effective desiccant rotor that can be regenerated at a temperature between 20 and 30°C, corresponding to return air exhausted from conditioned spaces. The desiccant rotor consists of a honeycomb structure, which is coated with organic polymer desiccant materials. For a specific operating condition, the desiccant rotor functions as a rotary total heat exchanger. Desiccant rotors with thickness of 0.2 m and more lead to both higher dehumidification and temperature efficiencies compared to conventional total rotary heat exchangers in different states of the inlet process and regeneration airflows. Both the dehumidification and temperature efficiencies achieve 100% at a thickness of 0.4 m, and at rotational speeds between 100 and 300 rph. Dehumidification, together with cooling, is very effective. For the desiccant rotor with a thickness of 0.4 m, the humidity change of the process air corresponds closely to isothermal dehumidification. In terms of the dehumidification and cooling functions, the performance of the desiccant rotor with thickness of 0.2 m and more is very advantageous compared to conventional desiccant rotors and rotary total heat exchangers. [ABSTRACT FROM AUTHOR]

This paper concerns the further testing of a new double calorimeter. We earlier reported initial development of the calorimeter and thereafter inferred rates coefficients for adsorption of moisture under a “large pressure jump.” (The test materials were silica gel type A and water.) The paper presents a further check on the calorimeter by demonstrating that measured desorption and adsorption rates were compatible. A disappointing aspect was an unintended near step change in condenser pressure at the start of the experiment. The condenser design was deficient, and better drainage is needed in the future to maintain vapor in immediate contact with cold surfaces. Notwithstanding the lower than intended pressure driving force, the heat addition to the silica gel was measurable, following an exponential pattern against time with regression coefficient better than 99%. The rate coefficients that fitted each data set were broadly in line with coefficients reported for adsorption (within the limits of experimental error). [ABSTRACT FROM AUTHOR]

The commercial success of sorption refrigeration and heat pump systems depends on a good heat and mass transfer in the adsorbent bed, which allows higher coefficients of performance and greater specific heating or cooling power that reduce capital costs. In this study the thermal conductivity and thermal contact resistance of vibrated and compressed granular active carbon and binary mixtures of active carbon are investigated using two types of conductivity measurements: a steady-state measurement between flat plates and a transient hot tube measurement. With these results is possible to draw conclusions on how the wall geometry, particle size distribution, and bulk density affect the overall thermal performance. Results show that using binary mixtures of grains and powder gives results superior to those of either grains or powder alone. The conductivity of the binary mixtures increases roughly linearly with bulk density and the 2/3 grain mixture achieves the highest densities. The method used to achieve compaction (vibration or compression) did not seem to affect the result. Thermal contact resistances reduce with increasing density but do vary with the mixture ratio, also appearing to be best with a 2/3 grain–1/3 powder mixture. [ABSTRACT FROM AUTHOR]

Thermal energy storage is critical for reducing the discrepancy between energy supply and energy demand, as well as for improving the efficiency of solar thermal energy systems. Among the different types of thermal energy storage, phase-change materials (PCM) thermal energy storage has gained significant attention recently because of its high energy density per unit mass/volume at nearly constant temperature. This study experimentally investigates the using of a triplex tube heat exchanger (TTHX) with PCM in the middle tube as the thermal energy storage to power a liquid desiccant air-conditioning system. Four longitudinal fins were welded to each of the inner and middle tubes as a heat transfer enhancement in the TTHX to improve the thermal performance of the thermal energy storage. The average temperature of the PCM during the melting process in the TTHX with and without fins was compared. The PCM temperature gradients in the angular direction were analyzed to study the effect of the natural convection in the melting process of the thermal storage. The energy storage efficiency of the TTHX was determined. Results indicated that there was a considerable enhancement in the melting rate by using fins in the TTHX thermal storage. The PCM melting time is reduced to 86% by increasing of the inlet heat transfer fluid. The average heat storage efficiency calculated from experimental data for all the PCMs is 71.8%, meaning that 28.2% of the heat actually was lost. [ABSTRACT FROM AUTHOR]

This article presents the design and the heat transfer study in a novel adsorbent bed with compound parabolic concentrator (CPC) for solar adsorption chillers. The objectives of the study were to investigate the heat transfer in the adsorbent bed experimentally, and to verify the fins layout through finite-element analysis (FEA) simulation. CPCs with different concentration ratios were experimentally tested and an appropriate design of CPC was selected for a prototype. The prototype was designed with the objective of improving the heat and mass transfer ability of the adsorbent bed. Fins were placed in the transverse direction under the receiver area of each CPC. Spaces were provided from three sides of the adsorbent for easy movement of the refrigerant. FEA software was used to study the effect of the fins layout and fins pitch. The experimental results showed that the heat was efficiently transferring up to the end and extended parts of the bed. Simulation results indicated that the present strategy of placing the fins in a transverse direction gives uniform heat distribution compared to a fins layout with fins placed in a longitudinal direction. The proposed design scheme will be helpful to improve the system performance by increasing the heat and mass transfer ability of an adsorbent bed. [ABSTRACT FROM AUTHOR]

For the development of a high-performance heat exchanger using small channels or minichannels for air-conditioning systems, it is necessary to clarify the characteristics of vapor‐liquid two-phase flow and heat transfer of refrigerants in small-diameter tubes. In this keynote paper, the related research works that have already been performed by the author and coworkers are introduced. Based on the observations and experiments of R410A flowing in small-diameter circular and noncircular tubes with hydraulic diameter of about 1 mm, the characteristics of vapor‐liquid two-phase flow pattern and boiling heat transfer were clarified. In low quality or mass flux and low heat flux condition, in which the flow was mainly slug, the “liquid film conduction evaporation” heat transfer peculiar to small-diameter tubes prevailed and exhibited considerably good heat transfer compared to nucleate boiling and forced convection evaporation heat transfer. The effects of the tube cross-sectional shape and flow direction on the heat transfer primarily appeared in the region of the “liquid film conduction evaporation” heat transfer. A new heat transfer correlation considering all of three contributions has been developed for small circular tubes. [ABSTRACT FROM AUTHOR]

Case Studies Editor's Note:We at theJournal of Heat Transfer Engineering (HTE)are happy to announce the introduction of a new section entitled “Case Studies.” The first case study was published in vol. 37(3–4). This is the second case study in the series. We are asking authors to contribute their practical experiences in the form of real-world case studies.  The goal is to disseminate practical information especially to young engineers who are stepping into the real world. The format of such articles will be a full-length paper or a short brief.  It does not have to entail a typical research-type paper format with details about measurement accuracies, references, and so on.  The article could have a brief introduction with the problem description, remedy, lessons learned, and recommendations.  The review process will be simple and less involved than with typical research papers.  The goal is not to discredit a person or a company but to share experiences.  We all make mistakes; however, we also find solutions, and it is the solution part that is rewarding and that should be shared for the betterment of the society. Zahid Ayub HTECase Studies Editor [ABSTRACT FROM AUTHOR]

In this study, experiments were performed to examine characteristics of flow boiling heat transfer and pressure drop of a low global warming potential refrigerant R32 flowing in a horizontal copper circular tube with 1.0 mm inside diameter for the development of a high-performance heat exchanger using small-diameter tubes or minichannels for air conditioning systems. Axially local heat transfer coefficients were measured in the range of mass fluxes from 30 to 400 kg/(m2·s), qualities from 0.05 to 1.0, and heat fluxes from 2 to 24 kW/m2at the saturation temperature of 10°C. Pressure drops were also measured in the rage of mass fluxes from 30 to 400 kg/(m2·s) and qualities from 0.05 to 0.9 at the saturation temperature of 10°C under adiabatic condition. In addition, two-phase flow patterns were observed through a sight glass fixed at the tube exit with a digital camera. The characteristics of boiling heat transfer and pressure drop were clarified based on the measurements and the comparison with data of R410A obtained previously. Also, measured heat transfer coefficients were compared with two existing correlations. [ABSTRACT FROM AUTHOR]

A series of field tests of hybrid desiccant cooling systems was conducted during July and August 2012. The temperature and humidity of supply and return air and power and heat consumption were monitored, and data were transferred in real time through the internet. The performance of the cooling system (i.e., cooling capacity and the coefficient of performance [COP]) was evaluated from measured data and variations with regard to outdoor conditions were analyzed. The cooling capacity decreased with an increase of outdoor temperature, while it increased as outdoor humidity increased. The COP also increased with an increase in outdoor humidity. However, the dependence of the COP on outdoor temperature was rather weak. [ABSTRACT FROM AUTHOR]

This study investigated the cycle optimization of four-bed, silica gel–water adsorption with reheat cycle, where the desorber (upper bed) and adsorber (lower bed) always interact with the condenser and evaporator, to exploit a low heat-source temperature. In a previous study, the performance of a reheat cycle with chilled water outlet temperature fixed at 9°C was observed without considering the cycle optimization. Maintaining a constant chilled water outlet temperature is also of equal importance to improve the conversion efficiency so that maximum cooling capacity can be derived. In this paper, a simulation model of reheat adsorption cycles is developed to analyze the optimization of the cycle time, including adsorption/desorption time, mass recovery time, and preheating/precooling time, with chilled water outlet temperature fixed. The reheat working principle is also introduced. The proposed cycle is compared with the four-bed versison without reheat cycle in terms of coefficient of performance (COP) and cooling capacity. The result shows that the performance of a reheat cycle is superior to that of four-bed version without reheat, especially for low heat-source temperature. For low heat-source temperature (55–65°C) both COP and cooling capacity of the reheat cycle with optimization were raised significantly compared to the high heat-source temperature (70–80°C). [ABSTRACT FROM AUTHOR]

Several mathematical models are available for estimation of effective thermal conductivity of nonreactive packed beds. Keeping in view the salient differences between metal hydride beds in which chemisorption of hydrogen takes place and conventional nonreactive packed beds, modified models are proposed here to predict the effective thermal conductivity. Variation in properties such as solid thermal conductivity and porosity during hydrogen absorption and desorption processes are incorporated. These extended models have been applied to simulate the effective thermal conductivity of the MmNi4.5Al0.5hydride bed and are compared with the experimental results. Applicability of the extended models for estimation of the effective thermal conductivity at different operating conditions such as pressure, temperature, and hydrogen concentration is discussed. [ABSTRACT FROM AUTHOR]

The effective use of marine biomass has recently been identified as a feasible method of renewable energy production. Therefore, to facilitate the effective use of algae biomass, it is essential to develop techniques for the mass production of algal cultures. It is also important to develop artificial culture techniques that are not affected by natural phenomena such as weather. This study utilized a newly developed culture technology that uses seawater with high concentrations of dissolved CO2(CO2seawater). The experiments in this study were conducted to test the effects of CO2seawater on algal growth. In addition to experimental conditions that were previously investigated in industrial algae farming scenarios, it is also necessary to consider the effects of new parameters associated with increased CO2concentrations. The following four conditions were experimentally investigated: (1) the tolerance of algae to changes in pH, (2) the effect of CO2seawater on long-term culture growth, (3) the effect of continuous culture experiments, and (4) the effect of water flow rate on cultured algae. The results in terms of having excelled especially indicate that a 1-month long-term algae culture period in seawater with CO2concentration of 1.0% led to growth that was approximately 4.5 times faster than growth in seawater without the CO2additive. Furthermore, the results also provided useful information regarding the proper flow rate needed to enhance algal growth. [ABSTRACT FROM AUTHOR]

A numerical investigation is carried out to understand the effect of natural convection, surface thermal radiation, and wall thermal conduction on the heat transfer from a plate heat source located at the bottom of a three-dimensional rectangular enclosure. The distributions of convective, radiative, and total Nusselt numbers and the average Nusselt number at the surface of the heat source are obtained for the ranges of parameters of 1 × 102 ≤ Ra ≤ 1 × 106, 0 ≤ ϵ ≤ 1, 1 ≤ kr ≤ 15, and 0.5 ≤ AR ≤ 1.5. The increase of thermal radiation restrains the convective heat transfer, but increases the total heat transfer and the overall heat transfer uniformity. Useful correlations have been developed for the average and the standard deviation of the Nusselt numbers at the heat source. [ABSTRACT FROM AUTHOR]

Thermal comfort is one of the most important components of comfort which shows physiological, psychological, and physical harmony between human body and environment. The heat and moisture transfer capacity of fabric from skin to environment affects the thermal comfort of garments. The transfer capacity depends on the characteristic features of raw materials and fabric structural properties. In this study, it is aimed to determine the advantages of knitted fabric types, taking into account the environmental condition and activity level by measuring the thermal comfort properties such as air permeability, wicking, moisture management, thermal and water vapor resistances. Two knitted structures composed of tuck and float combinations and six raw materials were chosen for the fabrics produced. According to the measurement results, the polyester and cotton/Coolmax fabrics with float stitches have had good liquid moisture transport properties. Besides, high air permeability and low water vapor resistance have been obtained in viscose and Tencel LF fabrics with tuck stitches. On the basis of the results obtained in this investigation, and taking into consideration thermal behavior of human body, four women’s and five men’s T-shirts are designed. These T-shirt designs may be helpful for further approaches on the optimization of thermal comfort for sports activities in hot environment. [ABSTRACT FROM PUBLISHER]

In this research, super absorbent materials were incorporated into the internal layer of the firefighters’ protective clothing with the aim of increasing absorption of sweat to improve the thermo-physiological comfort properties. The performance properties were evaluated following the standard test methods (ISO 6942:2002 and ISO 9151: 1995(E)) and the thermo-physiological comfort-related properties were evaluated by measuring the transport properties such as air permeability, water sorption and evaporation, thermal resistance and water vapour resistance of the fabric assemblies with super absorbent materials. The results indicated that it is possible to improve the comfort properties of the protective clothing by the incorporation of super absorbent materials into the internal layer. The use of super absorbent materials is likely to help in the absorption of sweat in higher amount and keeping the skin and internal microclimate dry, which in turn improves the comfort level. The performance properties of all the combinations satisfied the requirements for firefighter’s clothing as mentioned in AS/NZS 4967-2009. [ABSTRACT FROM PUBLISHER]

In Korea, the Very High Temperature Gas-Cooled Reactor (VHTR) PMR200 is being developed in the Nuclear Hydrogen Development and Demonstration project. Its core consists of hexagonal prism-shaped graphite blocks for the fuel and reflector, and each hexagonal fuel block contains 108 cylindrical coolant holes and 210 fuel compacts. Because of these holes and fuels, the heat transfer in lateral directions in the fuel blocks becomes very complicated. Especially in accident situations when forced convection is lost, the majority of the afterheat flows in the radial direction by conduction across the large number of coolant holes. Moreover, radiation heat transfer is supposed to be added to the radial heat transfer modes owing to the high temperature of the VHTR core. Because of these complexities in radial heat transfer, reliable modeling for effective thermal conductivity (ETC) is required in order to analyze the reactor core thermal behavior using lumped-parameter codes, which are often used to evaluate the integrity of nuclear fuel embedded in the graphite block. In this study, the ETC model adopted in the GAMMA+ code was introduced, and the adequacy of the model was assessed by the commercial computational fluid dynamics (CFD) code CFX-13. The results of the CFD analysis were consistent with, the ETC model in general even if a slight disagreement was shown for the case of high temperature. From these analyses, it could be concluded that the ETC model adopted in the GAMMA+ code is an adequate model for the analysis of the PMR200 reactor core. Moreover, it was found that the effect of fuel gap can cause an overprediction of the ETC if the fuel compact thermal conductivity is larger than the applicable range of the model. [ABSTRACT FROM AUTHOR]

The thermal characteristics of the phase change process due to three different configurations of the solution domain are studied using n-octadecene as a phase change material (PCM). The configurations include the PCM only, aluminum foam filled with the PCM, and aluminum mesh in the presence of the PCM. The time taken for the complete melting of the PCM is predicted for each configuration. In the analysis, the amount of PCM is kept the same for all configurations, and the amount of aluminum material is kept constant in the aluminum foam and the aluminum mesh configurations. The performance characteristics are the dimensionless temperature ratio ((Tmax − Tb)/(Tmax − Tin), where Tmaxis the maximum temperature, Tbis the bulk temperature, and Tinis the initial temperature), the minimum liquid fraction, the ratio of the cumulative energy stored during phase change over the total energy input to the storage system, and the total molten mass over the total mass of the PCM in each configuration. An experiment is conducted to verify the predictions of the numerical simulations for the aluminum foam. It is found that the experimental findings of the molten states of the PCM in the aluminum foam agree well with their counterparts predicted from the simulations. Aluminum mesh in the presence of the PCM significantly shortens the time required for complete melting in the thermal storage system. [ABSTRACT FROM AUTHOR]

Finite element simulations were carried out to analyze entropy generation during mixed convection inside square enclosures with an isothermally hot bottom wall, adiabatic top wall, and isothermally cold side walls (case 1) or linearly heated side walls (case 2), or linearly heated left wall with isothermally cold right wall (case 3) forPr = 0.015–7.2,Re = 1–100, andGr = 103–105. Local entropy maps are studied in detail, and the dominance of thermal (Sθ,l) and frictional (Sψ,l) irreversibility is studied using Bejan number maps. In addition, variation in total entropy generation (Stotal), average Bejan number (Beav), and average Nusselt number at the bottom wallwithGrare analyzed to correlate irreversibility and the overall heat transfer rate of the system or process. It is found that, forPr = 0.015 and 7.2,Re = 100 may be the optimal level for higher convective heat transport with minimum entropy generation in all the cases forGr = 103–105. [ABSTRACT FROM AUTHOR]

The thermal properties of polyester/polyethylene non-woven blankets of varying thicknesses impregnated with aerogel were studied and compared. The SEM images were also taken to study the physical configuration of the aerogel-based fibrous webs. Specific thermal properties like conductivity, resistance and effusivity were measured using C-Therm TCi thermal conductivity analyzer. One major objective was to understand the potential of a newly fabricated equipment to study the thermal properties of non-woven textile fabrics treated with aerogel at sub-zero temperatures. Thermal conductivity was calculated using the empirical relation in Fourier’s law. The relationship between the thermal conductivity and thermal resistance of the samples was studied at various environmental temperatures (which was set in the climatic temperature system between (+25°C and −25°C). The newly fabricated equipment was found to be suitable for thermal measurements at sub-zero temperatures. The results were statistically analysed and compared. It was found that fabric thickness and density have a significant effect on the thermal properties and permeability of the aerogel-treated non-woven fabrics. The results also showed that the selected polyester and polyethylene non-woven fabrics were suitable for usage as thermal insulators during construction of buildings and for insulation of oil and gas pipelines. [ABSTRACT FROM PUBLISHER]

This study examined the characteristics of heat and water transfer in structurally modified urban soils. To satisfy our goals, we measured the temperature and moisture content of anthropogenic soils to a depth of 50 cm. Field observations was carried out for three sets (each of two pedons) of soils in the Tokyo Metropolitan area. Each pedon had the same turf coverage but different profile modifications in the green areas. Soil temperature, soil moisture, and precipitation data were collected during the summer (July–Sept) and winter (Oct–Feb) every 10 min. From the results, we calculated the thermal diffusivity and thermal conductivity in each pedon. Soil temperature showed a clear daily variation down to 30 cm depth. Temperature transmission to deeper layers was faster in pedon having stronger soil compaction and more artificial fragments than in pedons with weaker soil compaction and fewer concrete fragments. This finding suggests that strongly compacted soil has a relatively high thermal conductivity, and easily transfers heat to deeper soil. In pedons composed of soft, organic-rich, and clay-rich soil, water retention impedes the increase in soil temperature during daytime, whereas nighttime cooling is prevented by the lower heat transmission due to the larger porosity. Throughout the observations, the water content ranged from 0.1 to 0.45 m3 m−3. The thermal diffusivity was obtained as 1.2–5.0 × 10−3 cm2 s−1in pedons without artifacts, but was higher (2.5–7.3 × 10−3 cm2 s−1) in all pedons containing larger volumes of concrete artifacts. Although the directions of heat flow by time within the profiles having lithological disturbance was not much different with that of natural soils, the observation data revealed that heat flow per time differed by structural properties of the profiles. Furthermore, thermal properties such as thermal diffusivity and thermal conductivity of the soils characterized with lithological disturbance were significantly higher than those of natural soils and it was notable that they were not influenced by either volume fraction of water or air in the soil. The fact suggested that the anthropogenic soils containing a large amount of modifiers and concrete artifacts have small capacity of water retention due to specific macro pores. Artificial materials and compaction regulate the drainage and water retention of the soil, although the water transfer behavior in the studied pedons could be rather complicated. [ABSTRACT FROM PUBLISHER]

Analytical solutions of the problem of heat conductivity in heating thin plates with moving axisymmetric heat sources with different radial distributions are presented. The solutions can be used for efficient calculations of the characteristics of the temperature field. [ABSTRACT FROM PUBLISHER]

Automobile engine coolant liquids are commonly used for efficient heat transfer from the engine to the surroundings. In this work we have investigated the thermal diffusivity of various commonly available engine coolants in Indian automobile market. We have used single beam laser induced thermal lens technique for the measurements. Engine coolants are generally available in concentrated solution form and are recommended to use at specified dilution. We have investigated the samples in the entire recommended concentration range for the use in radiators. While some of the brands show an enhanced thermal diffusivity compared to pure water, others show slight decrease in thermal diffusivity. [ABSTRACT FROM PUBLISHER]

Thermo-physiological properties of fabrics intended for next to skin applications, apparel, and functional wear are related to the heat and moisture transmission properties. A gammet of fiber, yarn, and fabric variables affect the thermal and moisture management properties and hence contribute to the overall comfort and state of well-being of the wearer. In this study, the effect of loop length and filament fineness on the thermo-physiological properties of polyester-cotton single jersey plated fabrics has been reported. The thermo-physiological properties were correlated with structural parameters of knit structures such as fabric tightness factor, thickness, porosity, stitch density, and loop length. Fabrics knitted with longer loop length (slack constructions) showed higher thermal resistance and would be perceived warmer on initial skin contact owing to lower value of thermal absorptivity, were permeable to air and moisture vapor transmission, had higher water evaporation percentage however water absorbency and transplanar wicking was lower. Fabrics knitted with finer filaments showed higher value of thermal resistance, lower value of thermal absorptivity, and were less permeable to air and moisture vapor transmission. The water absorbency and transplanar wicking increased and water evaporation percentage decreased as the filament fineness increased. General linear model was used to obtain prediction models in the form of equations at varying levels of loop length and filament fineness. A high value of coefficient of determination between predicted and experimental values validated the model. Pearson correlation coefficient was deduced to establish pair-wise association among the different thermo-physiological properties. Air permeability was observed to be positively related to moisture vapor transmission rate and water evaporation percentage as suggested by high values of pearson correlation coefficients. [ABSTRACT FROM PUBLISHER]

Sodium-to-air heat exchangers (AHX) are used in fast breeder reactors for removal of decay heat generated in the core after a reactor shutdown. The AHX is an important component of the safety-grade decay heat removal system in a fast reactor. Decay heat removal critically depends on the performance of the AHX, which is essentially a cross-flow heat exchanger with liquid sodium flowing on the tube side and air flowing across finned tubes in the cross-flow mode. In this paper, a three-dimensional numerical study is carried out to investigate the flow and heat transfer characteristics when air flows over a representative bank of finned tubes in an AHX. The computational model has been validated against published experimental benchmarks. Based on parametric studies, appropriate correlations for the Nusselt number and fin effectiveness are derived. A computationally efficient porous body model is then developed and an integrated thermal hydraulics study of AHX is carried out using the derived heat transfer correlation. The numerical predictions of the porous body model are compared with the results of an experimental AHX tested at the Indira Gandhi Centre for Atomic Research; Kalpakkam, India. A good agreement between the results is seen. [ABSTRACT FROM PUBLISHER]

Accurate simulation of the cooling characteristics of newly paved asphalt concrete (AC) layers is of particular significance due to its potential use in efficient planning and scheduling of paving works. This study builds on principles of thermodynamics and heat transfer to develop a finite element framework that simulates the actual cooling of newly paved AC layers. For a given set of climatic conditions, such as wind, solar flux and air temperature, the presented model incorporates the effects of conduction, convection and radiation to predict the cooling rates of the pavement. The model is first validated using data acquired from laboratory and field set-ups. Then, the model is used to assess the effect of critical parameters such as layer thickness, time of paving, and material properties on asphalt cooling rates and their impact on paving operations. [ABSTRACT FROM AUTHOR]