Heat Transfer In Configuration Research Articles

Experimental investigation on charging and discharging performance of finned shell and tube device containing pentaerythritol for low and medium temperature thermal energy storage

This work concerns the investigation of the charging and discharging performance of a finned shell and tube device that utilized for low and medium temperature thermal energy storage application. An experimental rig is built for evaluation in which a so-called solid–solid phase change material of pentaerythritol is used as energy storage substance and air is employed as heat transfer fluid. The PE has tested to have a melting temperature range of 185-205℃ and a latent heat of 290 kJ/kg. The study first examines the effect of fin number on the device thermal performance by considering configurations with 4, 6, 8, and 10 fins. Then the impact of fin height is evaluated where four different fin heights of 9 mm, 14 mm, 19 mm and 24 mm is investigated, and finally the influence of heat transfer fluid working condition is explored. The results indicate that the PE could be ideal PCM utilized in shell-tube typed thermal energy storage device. The enhancement of fin number and fin heigh can largely improve both the charging and discharging performance of the device. For a given air inlet pressure of 0.1 MPa, the device having fin number of 10 and fin height of 19 mm could be identified as the optimal configuration for heat transfer, and at such working conditions, the device achieves a charging efficiency of 91.49 % and a discharging efficiency of 86.4 %.

Heat transfer optimization for MH reactor using combined taguchi design and data-driven optimization method

Adding the heat transfer enhancement components into the MH reactor can improve the hydrogen absorption/desorption rate, but the vital indicators as the gravimetric and volumetric hydrogen storage density decrease at the same time, which is hardly considered in the published researches. In this study, a comprehensive hydrogen storage performance (CHSP) indicator for the MH reactor has been proposed considering the above contradiction, which can be applied to evaluate the comprehensive performance of the MH reactor and compare the reactor performances with different heat transfer configurations. Then, with the constraint of the CHSP, the heat transfer structure of the classical finned-tube MH reactor is optimized using a novel sieving optimization strategy which combines the Taguchi design and the data-driven optimization (ANN model + GA) to increase the optimization efficiency and the reliability of optimization solutions. The optimized results indicate that the optimal structural parameters of the finned-tube MH reactor are the diameter of heat exchange tube d of 5.13 mm, the fin thickness h of 0.28 mm, the fin radius r of 21.73 mm and the fin number N of 11, and the optimal CHSP is 0.547 mg/s.

Effect of twisted tapes and surface extensions in enhancing the condensation heat transfer of high-temperature saturated steam in a circumferential rectangular channel

This article numerically investigates the impact of twisted tapes and extended surfaces (fins) on enhancing high-temperature steam flow in a circumferential rectangular channel, akin to the external jacket cavity of a tyre cure press. The passive enhancement techniques for improving the mold warm-up time of the tyre curing process have received limited attention in previous studies, which have primarily focused on enhancing heat transfer in configurations and working conditions typical of heat exchanger applications. The objective of this article is to enhance the condensation heat and mass transfer rate by geometrically modifying the internal flow path of the circumferential rectangular channel, resembling an external jacket cavity of a tyre cure press, using twisted tapes and extended surfaces. Four configurations are simulated: i) conventional circumferential rectangular channel, ii) channel with twisted tapes, iii) channel with surface extension, and iv) channel with both twisted tapes and surface extension. The heat transfer performance of all the modified channel configurations derived from the simulation results is assessed in comparison to the conventional channel. The channel, featuring a design that includes five twisted tapes with a twist ratio of 8 and 54 extended surfaces, records a substantial 36.85% rise in heat flux along with a notable 24% increment in the condensation mass flux. The simulation results are validated using an in-house experimental study. The tyre cure press in the experimental setup is modified to align with the design proposed by the simulation results, and a warm-up study is conducted. The warm-up time for the modified mold to attain the desired temperature is reduced by 33%, with no accompanying increase in steam consumption, compared to the warm-up time for the conventional mold. This significant reduction in mold warm-up time holds immense potential in enhancing the productivity rate, an ongoing requirement of the automobile industry.

Integrated Thermal Management System Concept With Combined Jet Plate, High Porosity Aluminum Foam, and Target Plate for Enhanced Heat Transfer

Abstract An experimental investigation was carried out on high porosity metal foams subjected to array jet impingement with an objective to develop enhanced heat transfer configurations. In this study, we propose an integrated thermal management system (TMS) aimed toward leveraging the conjugate heat transfer capabilities of target plate, metal foam, and the jet plate—all made from aluminum and assembled such that a proper contact between them can be established. Steady-state heat transfer experiments were carried out for 10 and 20 pores per inch (PPI) aluminum foams of 0.93 porosity. Both metal foams were 12.7-mm thick. The normalized jet-to-jet spacing was varied from 2 to 12 times the jet diameter, while the jet diameter was fixed. The ratio of the jet plate thickness and jet diameter (nozzle aspect ratio) was 6.35, which ensured proper development of jets inside the nozzles. Experiments were conducted over a wide range of Reynolds number (based on jet diameter) varied from 100 to 5000. The obtained convective heat transfer coefficient for different configuration was evaluated in context with pressure drop. The analysis of experimental results reveal that large open area ratio jets combined with high porosity metal foams provide highly efficient and high-performance cooling for the investigated range of Reynolds numbers.

Machine-assisted quantification of droplet boiling upon multiple solid materials

The intricate nature of droplet wetting and boiling on heated nano-/micro-structured surfaces has significant implications for practical applications. However, the multitude of factors influencing these liquid-vapor-solid interactions complicates the understanding of boiling behaviors across a wide range of operating conditions. In this study, we examined droplet impingement boiling over a large range of Weber numbers (We) on various surfaces, from smooth to nano-micro hierarchical ones, and from stationary to vibrated ones. The results indicate that the nano-micro hierarchical surface possesses the greatest heat transfer ability due to its superior superhydrophilicity, enhanced by nano-structures, and the vapor buffer effect caused by micro-structures. Additionally, vibration significantly improves boiling performance by 55.4%. However, contrary to previous findings, a higher We does not always enhance heat transfer performance due to a pronounced water hammer effect. We discovered that when the net pressure reaches a threshold value (∼ 90 kPa), a new phenomenon - jet flow - occurs, leading to a deterioration in heat transfer. Utilizing our database, we trained a machine learning framework to generate accurate droplet boiling data, providing a droplet boiling law that can extensively predict heat transfer performance. This paper proposes a fusion of physics and artificial intelligence to enhance our understanding and application of droplet boiling phenomena. Our findings are expected to contribute to the development of more efficient droplet-based boiling heat transfer devices and configurations across a wider range of industrial settings.

Evolution features and optimization of interface shape during CdZnTe crystal growth using Vertical Gradient Freeze (VGF) technique

The growth of CdZnTe crystal suffers from poor yield due to the low thermal conductivity, and a convex growth interface is usually essential to grow large-volume CdZnTe single crystal because it can lessen the adverse interactions between the growing crystal and crucible wall. The growth of 90 mm diameter CdZnTe crystal by VGF technique has been investigated using experimental and simulation methods. The influences of the growth parameters (such as temperature gradient and growth rate) and the heat transfer configurations on the growth interface shape have been inspected respectively by the unsteady simulation. The simulation results confirm that the interface shape exhibits the tendency to be “convex → flat → concave” due to the gradually deteriorated heat transfer environment with time during growth. In addition, a modified configuration has been designed and used in experiments based on the simulation results, with the aim of strengthening the conduction heat transfer of the center region of the configuration geometry. The modified configuration consists of the splicing tapered-contact quartz&graphite support with a shorter conical region and seed region, as well as the SiC holder. Experimental results demonstrate that the modified configuration would make the growth interface maintain a convex shape for a longer duration. The CdZnTe crystal grown by using the modified configuration possesses fewer grains compared with that using the initial configuration.

Thermo-fluidic analysis of microchannel heat sink with inline/staggered square/elliptical fins

The present study reports the thermo-fluidic behavior of a microchannel heat sink employed over a heat source dissipating a heat flux of 50 W/cm2. The microchannel heat sink is embedded with elliptical and square fins varied from 11 × 3 (11 fins per row with a total of 3 rows) to 79 × 3 fins and 100 μm to 300 μm height to obtain the optimum configuration for maximum heat transfer and minimum frictional loss. Fluid flow is considered in the laminar range of Re varying from 100 to 400. The problem is solved numerically using a Finite Volume Method based multigrid solver of ANSYS Fluent. The aim of the present study is to investigate the shape effect of square fin (α = 0), square fin (α = 45) and elliptical fins on the heat transfer from the heater surface and frictional loss. This is achieved by keeping the correctional area and the surface the same for all types of fins. It is found that the heater surface temperature monotonously decreases with the number of fins for a fin height more than 200 μm. When different fin shapes are compared, no remarkable difference in the heater surface temperature is observed; however, elliptical fins are marginally more effective for a greater number of fins than the square fin with α = 0 followed by α = 45. Increasing the fin height results in augmenting the heat transfer for all cases. When different arrangements are compared, staggered fins result in slightly better heat transfer than the inline fins except 11 × 3 and 79 × 3 fins. As far as friction factor is concerned, elliptical fins with staggered arrangement provide the least frictional resistance.

Parameter estimation of thermal response test: A Bayesian inference using Markov chain Monte Carlo - Metropolis Hastings (MCMC-MH) approach

To understand and model the thermal response of a body engulfed in fire, the knowledge of the geometrical and thermo-physical properties is necessary. In this work, simultaneous estimation of parameters of convective heat transfer coefficient (h) and configuration factor (F) of a thermal response test is accomplished with reported fire experiments. The measurements of these parameters in a fire environment is complex. Sometimes it demands numerical simulations and semi-empirical modelling. Therefore, a Bayesian driven Markov Chain Monte Carlo Metropolis-Hastings (MCMC-MH) approach is applied as an alternative to estimate the unknown parameters h and F simultaneously. The priors for h and F are generated using the offline Bayesian method. The generated priors are given as means of the Gaussian distribution and parameters are estimated simultaneously by generating the samples dynamically. The uncertainty of the estimates is reported in the form of their standard deviations. Moreover, the validation of the estimated parameters is performed. It is observed that the simulated temperature distribution with estimated parameters is in good agreement with the measured temperature distribution as their deviation lies at less than 1%. The efficacy of the output of the Bayesian inference framework is also reported.

Identification of Impulse Responses in Heat Transfer: Parameterization, Doses, Partial Time Moments

Convolutive models, linking a local or average temperature to a thermal excitation in transient regime are as good as analytical or numerical solutions of the heat equation and of its associated boundary conditions, provided that the corresponding equations are linear with coefficients that do not depend on time, but with possible dependence on the space dimensions. These convolutive models are based on an impulse response function which can be identified, using measurements of input and output signals, together with some kind of regularization because of the ill-posed character of this inverse problem. Here, another exploratory approach is tested. It is based i) on a parameterization of the three functions involved by projection onto a Dirac comb basis to get a vector/matrix form of the convolution model derived in terms of doses, ii) on an alternate model based on an exact analytical relationship between the time moments of these functions and iii) on the different ways to use this last model in an inversion procedure using the parsimony principle. This is applied to a heat transfer configuration of one-dimensional heat diffusion in a slab, where conclusions and perspectives are drawn for this type of dosal-moment model.

Thermal performance of nanofluids in elliptical zigzag tube: a numerical approach

This work was aimed at evaluating the thermal performance of nanofluids in an elliptical zigzag tube. The particle diameter and volume fraction of nanofluids were quantitatively investigated using two passive heat transfer configurations. The governing equations of mass, momentum, and energy of nanofluids containing ZnO and SiO2 in water at volume fractions of 1–4%, nanoparticle diameters of 15, 35, and 55 nm, and Reynolds number ranging from 400 to 2000 were solved using ANSYS. The results generally indicate that the Nusselt number and heat transfer coefficient increased with increasing volume fraction as Reynolds number increases. SiO2 exhibits a better thermal performance than ZnO, wherein a 4% volume fraction of 15 nm nanoparticle renders a greater heat transfer coefficient of 1149 W/m2·K at Reynolds number = 2000. The heat transfer is essentially improved at smaller particle diameter and higher volume fraction. The zigzag curvature displays an important attribute to enhance the heat transfer over the straight tube, although the skin friction coefficient increases with an increasing angle at 45°.

Energy efficient thermal management at low Reynolds number with air-ferrofluid Taylor bubble flows

Existing thermal management strategies for mini-/micro scale electronic devices have already reached their limits in several applications, necessitating development of innovative heat transfer methods. In this context, a novel heat transfer configuration involving convective heat transfer of two-phase air-ferrofluid Taylor bubble flow in a square mini channel at low Reynolds number (Re between 70 and 150) is investigated. Presence of a magnetic field enhances local heat transfer while the pressure drop penalty is not high. Experimental results confirm significant augmentation of heat transfer coefficient, of the order of ~88% to ~95% depending on the flow Re. The augmentation strategy is particularly attractive for low Re flows, typically encountered in mini-/micro systems, where the induced magnetic forces will be able to dominate the flow inertia. Potential advantages of air-ferrofluid Taylor flows subjected to a magnetic field for heat transfer augmentation is exemplified through this study.

Conceptual design of a copper-bonded steam generator for SFR and the development of its thermal-hydraulic analyzing code

The Korea Atomic Energy Research Institute (KAERI) studied the sodium-water reaction (SWR) minimized steam generator for the safety of the sodium-cooled fast reactor (SFR), and selected the copper bonded steam generator (CBSG) as the optimal concept. This paper introduces the conceptual design of the CBSG and the development of the CBSG sizing analyzer (CBSGSA). The CBSG consists of multiple heat transfer modules with a crossflow heat transfer configuration where sodium flows horizontally and water flows vertically. The heat transfer modules are stacked along a vertical direction to achieve the targeted large heat transfer capacity. The CBSGSA code was developed for the thermal-hydraulic analysis of the CBSG in a multi-pass crossflow heat transfer configuration. Finally, we conducted a preliminary sizing and rating analysis of the CBSG for the trans-uranium (TRU) core system using the CBSGSA code proposed by KAERI.

Analysis and optimization of the electrohydrodynamic (EHD) flow with a wire-to-two-cylinder configuration for convective heat transfer

Electrohydrodynamic (EHD) flow is a promising field, especially for gas pumping applications. The EHD flow could be produced by the formation of non-thermal plasma (NTP) on a surface with high curvature. In this study, an analytical model was employed, and the experiment was carried out with the configuration of a wire and two cylinders in an open space. The Townsend relation between electric signals was checked for the stable generation of corona discharge, and the empirical equation was employed to verify the relation between parameters, such as current, voltage, and momentum. In this process, the momentum of EHD flow can be expressed as a function of the design variables, so that the characteristics of the NTP pump can be estimated. The efficiency of the system could be determined from the experimental results. The optimal point obtained from the electrical and hydraulic characteristics showed an efficiency of 2.6%, which was 2 times larger than that of the NTP pump reported in previous works. Heat transfer experiments were also carried out for the cooling effect of EHD flow as a pump using a heat plate with constant heat flux, which was placed parallel to the cylinder electrodes. For various cylinder electrode heights and voltages, the heat plate was cooled by the EHD flow, and the temperature was measured using thermocouples. The cooling performance of the EHD flow was evaluated by comparison with the heat transfer coefficient of natural convection. The heat transfer coefficient and Nusselt number were calculated, and their correlation could be obtained. Additionally, an infrared thermal camera was used for spatial reduction, and the global temperature of the overall heat plate could be obtained.

Computational study of rib shape and configuration for heat transfer and fluid flow characteristics of microchannel heat sinks with fan-shaped cavities

Cavities and ribs are usually utilized in the design of microchannel heat sink systems, and their combination may lead to the optimum overall performance. However, it remains unclear how different combination methods contribute to the performance and efficiency of the systems. Computational fluid dynamics simulations were conducted to identify the optimum rib shape and configuration for the systems with fan-shaped cavities. The ribs are rectangular, diamond, hexagonal, or elliptic in cross-section. The effects of rib shape, dimensions, and configuration are investigated, and the optimum comprehensive performance was determined. The results indicated that the shape, dimensions, and configuration of ribs are important factors that affect performance and heat transfer efficiency. The shape and position of ribs must be optimized to minimize pressure drop while maximizing heat removal efficiency. The shape of ribs can be an important factor in obtaining high efficiency of heat removal while limiting the pressure drop across the channels. When the ribs are rectangular in shape, the maximum pressure drop occurs but the maximum relative Nusselt number is achieved. The maximum comprehensive performance factor is achieved when the ribs are elliptic in shape and the Reynolds number is highest. Further improvement in performance can be achieved by choosing particular rib dimensions and configuration. In order to provide appropriate benefit to such a microchannel heat sink system without inducing additional pressure drop that reduces the performance of the system, it is desirable to properly shape and position the ribs relative to the cooling flow and the cavities in a way that takes best advantage of the benefits provided by the combination of cavities and ribs. The effect of trailing edge vortexes on heat transfer performance is significant. A maximum comprehensive performance factor of 1.96 is achieved when the Reynolds number of the laminar flow is 460.

Process Intensification through Directly Coupled Autothermal Operation of Chemical Reactors

Summary Autothermal operation of a chemical reactor involves coupling exothermic and endothermic chemical reactions for the purpose of thermal management without resorting to external energy sinks or sources. Often this is accomplished through regenerative or recuperative heat exchange between spatially or temporally separated exothermic and endothermic reactions. However, it is also possible to directly couple these reactions simultaneously within the same reactor volume, eliminating the heat-transfer bottleneck that characterizes much of chemical manufacture. It is not widely recognized that directly coupled autothermal operation allows dramatic process intensification. This perspective defines autothermal operation and contrasts it with conventional heat transfer for thermal management of chemical processes. The intensification and cost savings that can be achieved are quantified, and the implications to modular chemical process intensification are presented. Guidelines are proposed for designing directly coupled autothermal processes. Diverse examples are presented. Several challenges to expanding the field are critically discussed.

Dimensionless formulation and similarity to assess the main phenomena of heat and mass transfer in building porous material

Within the environmental context, several tools based on simulations have been proposed to analyze the physical phenomena of heat and mass transfer in porous materials. However, it is still an open challenge to propose tools that do not require to perform computations to catch the dominant processes. Thus, this article proposes to explore advantages of using a dimensionless analysis by scaling the governing equations of heat and mass transfer. Proposed methodology introduces dimensionless numbers and their nonlinear distortions. The relevant investigation enables to enhance the preponderant phenomena to (i) compare different categories of materials, (ii) evaluate the competition between heat and mass transfer for each material or (iii) describe the transfer in multi-layered wall configurations. It also permits to define hygrothermal kinetic, geometric and dynamic similarities among different physical materials. Equivalent systems can be characterized in the framework of experimental or wall designs. Three cases are presented for similarity studies in terms of (i) equivalent material length, (ii) time of heat and mass transfer and (iii) experimental configurations. All these advantages are illustrated in the given article considering 49 building materials separated in 7 categories.

Nanoparticles and metal foams for heat transfer enhancement of phase change materials: A comparative experimental study

This paper presents an experimental work addressing the low thermal conductivity of phase change materials (PCMs), which is a major challenge associated with PCMs, when used as thermal energy storage solutions. This study experimentally compares the effectiveness of using copper oxide nanoparticles and copper metal foams, together and separately, for improving the performance of a selected PCM (RT44HC) during melting and solidification processes and for different heat transfer configurations. Four samples of pure PCM (as the base case), PCM-nanoparticle, PCM-metal foam, and PCM-nanoparticle-metal foam were tested. Two types of melting experiments were conducted: at constant temperature and with constant heat flux heat sources. The solidification experiments were conducted with a constant temperature heat sink. The results of the experiments showed that, compared to the base case of pure PCM, the heat transfer rate inside the PCM-nanoparticle, PCM-metal foam, and PCM-nanoparticle-metal foam composites increased by, respectively, about 13%, 17%, and 24% during melting with constant temperature heat source, about 24%, 26%, and 65% during solidification with constant temperature heat source, and about 7%, 11%, and 12% during melting with constant heat flux heat source. This study also shed light on some other challenges associated with using PCM as well as the role and the practicality of applying above-mentioned thermal techniques in addressing them.

Utilization of the Planar Laser-Induced Fluorescence Technique (PLIF) to Measure Temperature Fields in a Gas-Stirred Ladle

A 1/17th water physical model of a 200-ton steel ladle furnace with a single gas injection was used to simulate bath heating using a single burner to mimic the heat flux due to electric arcs in the industrial steel ladle. Two phases were considered, using water to simulate the molten steel and air to simulate the argon injection at a flow rate of 1.54 NL min−1. The planar Laser-Induced Fluorescence (PLIF) technique was for the first time experimentally implemented to measure temperature fields in a longitudinal plane of the gas-stirred ladle model. PLIF employs a laser source of 532-nm wavelength to light water seeded with rhodamine B, which emits fluorescence depending on its temperature, after a complex calibration is made. Next, the fluorescence is captured by a camera with a 550-nm wavelength filter. The PLIF measurements were validated by local thermocouple measurements at five different locations in the measurement plane. Temperature fields measured by PLIF are in good agreement with those obtained locally by thermocouples, so the PLIF technique can be used to measure temperature fields with the advantage of getting a complete temperature contour field, in contrast to point values of temperatures with thermocouples. Experiments were carried out to study the thermal mixing for two common tuyere positions, i.e., axisymmetric and eccentric (mid-radius) positions. Results on the injection mode show that axisymmetric gas injection is a more efficient heat transfer configuration between the burner and the liquid phase than is the symmetric injection mode for the particular heating configuration studied in this work.

Study of a Hybrid of Pulsating Heat Pipe and Distributed Jet Array

Pulsating heat pipes (PHPs) are effective devices for transferring a large amount of heat. For the existing PHP design, the U-turn geometry makes it difficult to use on small heat spots, which are very common in electronic cooling and many high heat flux applications. Additionally, the pipe flow in PHPs is not an optimum form for convective heat transfer. So far little research has attempted to resolve these issues. In this study, a hybrid design is introduced incorporating the characteristics of the PHP for its passive operation and the distributed jet array for its efficient convection. Based on the proposed structure, test articles are fabricated and experimentally studied. The design is proved successful. The heat transfer performance is evaluated by parametric studies and compared with the closed-loop PHPs. The flow visualization results are analyzed with different operational stages, flow patterns, and dimensionless numbers. The investigation concludes that the proposed design not only provides a new configuration for passive oscillatory heat transfer but also offers enhanced performance and applicability over the existing PHPs.

Fully developed turbulent convection of Lead Bismuth Eutectic in the elementary cell of the NACIE-UP Fuel Pin Bundle

One of the requirements for achieving high levels of safety in fourth generation nuclear power plants, is that core thermal-hydraulics can be simulated numerically at a good level of accuracy. To this aim, detailed validation of turbulent heat transfer models needs to be carried out and discussed, in relevant flow and heat transfer configurations, and for low Prandtl-number fluids.The focus of this research is the turbulent, fully developed convection in a heated rod bundle with a triangular arrangement, and a pitch-to-diameter ratio P/D=1.4. Statistics derived from a set of Direct Numerical Simulations (DNS) at the moderate Reynolds number of Re=8290 are compared to Reynolds Averaged Navier-Stokes (RANS) solutions where the closure is provided by the two-equation model SST k-ω and by the Reynolds-Stress Model. Comparisons are drawn for forced flow and in mixed convection conditions (Ri≈0.25). Global quantities extracted from experiments performed in very similar conditions are also compared against the numerical results. Profiles of the turbulent Prandtl number about the unit flow cell are also displayed and discussed.This work clarifies through detailed comparison that if, on the one hand, only the Reynolds-Stress model is able to reasonably capture important flow features like secondary flow components, on the other hand also the SST k-ω two-equation model considered is acceptably accurate in predicting the integral quantities of interest.