Wall Temperature Research Articles

The Association Between The Physical Condition of the House and the Smoking Habits of Residents with the Incidence of Pneumonia In Children Under Five Years

Pneumonia is leading cause of death worldwide, with a prevalence of 44%, and is second leading cause of death among under-fives in Indonesia, at 15.5%. Pneumonia is caused by viruses and bacteria that are associated with physical conditions, air quality, and smoking habits in house. This study aimed to determine association between physical house conditions and smoking habits with incidence of pneumonia in children under five years in Cengkareng Health Center working area. This study was a case-control design analytic observational study. Population involved chindren under five aged 12-59 months with a sample of 43 cases and 43 controls calculated using Lemeshow’s formula, taken using purposive sampling technique. Independent variables included floor and wall types, ventilation, occupancy density, temperature, humidity, light intensity, PM10 and PM2.5 levels, and smoking habits. Dependent varariable are incident of pneumonia. Data were collected through observation, sanitarian kits, and questionnaires. Data were analyzed using chi-square and logistic regression with 95% CI and alpha 0.05. The results showed that PM2.5 levels (p=0.010, OR=3.290, 95% CI=1.323-8.181) and indoor smoking (p=0.044, OR=2.758, 95% CI=1.027-7.410) were most significant factors associated with pneumonia. This study recommends optimizing educational programs regarding PM2.5 exposure and smoking habits to improve healthy living practices and reduce risk of pneumonia

Computational fluid dynamics simulation of cryogenic vertical upflow boiling under Earth gravity

This study presents numerical simulations and their validation for flow boiling of liquid nitrogen (LN2) in a vertical upflow orientation, with a primary aim to understand the complex two-phase flow and heat transfer phenomena important to space applications. The computational fluid dynamics (CFD) model utilized the coupled level set volume of fluid (CLSVOF) method, incorporating additional source terms for bubble collision dispersion force and shear lift force in the momentum conservation equation to enhance simulation accuracy. The simulations were conducted for two mass velocities (G = 526 and 804 kg/m2s) and three different heat flux levels (approximately 10%, 30%, and 70% of critical heat flux (CHF) under Earth gravity. The model was validated against measured wall temperature data acquired from the authors’ previous experimental studies, demonstrating average deviations of less than 2.8 K across all operating conditions. The simulated two-phase flow contours illustrated various flow patterns, including bubbly, slug, churn, and annular. Both mass velocity and heat flux were observed to impact the onset of nucleate boiling (ONB), bubble nucleation, growth, and coalescence, and overall vapor structure. The simulations also offered insight into axial and radial void fraction and velocity profiles, revealing local flow acceleration trends synchronized with void fraction development. A comparison between predicted and measured bulk fluid temperature profiles showed excellent agreement, further validating the CFD model’s accuracy and practical usefulness for two-phase cryogenic flow boiling simulations in space applications.

Modeling the thermal and hydrodynamic performance of grooved wick flat heat pipes

A compact model is developed to predict the thermal and hydrodynamic performance of a flat heat pipe with a rectangular grooved wick. The present model relies on the analytical solution to the energy equation in the wall and an equivalent heat transfer coefficient predicted using a computationally efficient iterative method. This efficient iterative method can also provide a framework for modeling other grooved or porous wick heat pipes for which analytical or semi-analytical solutions to the wall conduction, fluid flow, and film equations exist. Compared to prior numerical tools, the present modeling approach is computationally efficient, making it compelling for use in parametric and optimization studies. Instead of numerically solving a set of coupled differential equations, the present model considers only analytical and semi-analytical solutions for evaporation and condensation heat transfer rates. The non-discretized nature of the present model allows computations on a typical workstation to be completed within seconds as opposed to the hours required for prevalent numerical tools. The present model accounts for varying liquid fill volumes, geometry, and interfacial properties, such as surface tension and contact angle. The present model closely agrees with published numerical and experimental results for wall temperatures and maximum heat transfer rates. Parametric studies, which vary wall thermal conductivity, water contact angle, and groove dimensions are conducted on a previously experimentally investigated heat pipe to demonstrate the present model’s capabilities. The present model found that the maximum heat transfer rate of the heat pipe can be enhanced by about 15 and 20% by varying its wetting angle and groove dimensions, respectively.

Experimental and numerical studies of detailed heat transfer and flow characteristics in the rib turbulated annulus of a double pipe heat exchanger

An enhancement in the overall heat transfer between the fluids in a Double pipe heat exchanger (DPHE) can be achieved through various active or passive techniques. The present study focuses on the passive heat transfer enhancement in the annular region of a DPHE by incorporating circular ribs on the outer surface of the inner pipe. The primary objective is to investigate the influence of the ribs on the local distribution of heat transfer and fluid flow in the annulus of the heat exchanger. The local Nusselt number (Nu) distribution was determined experimentally using a test section specially designed with a provision to measure the wall temperature distribution of the inner pipe with an IR thermal imaging camera. The pressure drop across the channels with the ribs was also measured in the experimental studies. Numerical studies are employed to gain insights into the flow characteristics in the annular region in the presence of ribs. Studies comprise various rib diameters (e/Dh = 0.08, 0.14), rib-to-rib pitches (P/e = 6, 12, 18), and Reynolds number values (Re = 5000, 7500, and 10000). The heat transfer behaviour from the experimental study is discussed based on the flow mechanism observed using numerical techniques. The flow separation and reattachment due to the rib and the induced recirculation zone cause large variations in the Nusselt number distribution between the ribs. The peak Nusselt number value between adjacent ribs is observed at the location of reattachment of the flow to the ribbed wall. Acquired data also shows that the flow and heat transfer characteristics differ significantly with changes in the P/e ratio. The rib configuration with e/Dh = 0.14 and P/e = 12 is identified as optimal, achieving a balanced improvement in heat transfer while showing a relatively lower pressure drop.

Interpretable machine learning-based prediction and analysis of supercritical fluid heat transfer characteristics at different boundary conditions

The study of the heat transfer characteristics of supercritical fluids is crucial for the safe and economical operation of supercritical energy systems. This study presents a new method to study the heat transfer characteristics of supercritical fluids, employing interpretable machine learning. Two back propagation neural network models are proposed for the prediction of heat transfer to supercritical fluid for the cases with given heat flux and given wall temperature, respectively. The particle swarm optimization algorithm was employed to search for the optimal hyperparameters, and the resulting accuracy was evaluated in comparison with that of the traditional empirical correlation and a number of machine learning models. Combining the SHAP interpretable algorithm with prediction models, the supercritical heat transfer mechanism is explored from the perspective of global and local prediction behaviors based on explainable models. The results demonstrate that the average error of two established neural network models on the test set is 0.47 % and 0.69 %. Furthermore, for vertical upward flow, the buoyancy and acceleration effects are of greater feature importance in heat transfer deterioration. They are the primary factors contributing to heat transfer deterioration behavior. The research method proposed in this study has certain reference significance for further study of the heat transfer characteristics of supercritical fluids.

Development of a transient analysis code for trans-critical simulation of SCWR

Supercritical water-cooled reactors (SCWR) experience pressure reductions below the critical point during a loss of coolant accident (LOCA). During the reactor depressurization, boiling crises may occur, leading to pressure fluctuations and significant increases in wall temperatures, posing a severe threat to the cladding. In this study, a one-dimensional transient analysis code has been developed to incorporate one-dimensional steady-state flow equations in the fluid domain and transient thermal conductivity equations in the solid domain. The code also includes a wall heat transfer model and a model for the velocity of the moving quench front to simulate transcritical depressurization transient processes. The simulation successfully predicts the typical experimental phenomena. It is reasonable to use the critical temperature as the demarcation point between the dry and wet conditions of the axial wall of the rod bundle under transcritical conditions. By combining the experimental data with the program calculations, the critical interface for the occurrence of boiling crisis under transcritical conditions is determined using mass flow rate, heat flow density and fluid temperature as inputs. The criterion for the occurrence of CHF under transcritical conditions is obtained, which provides a reference to the safety analysis of SCWRs.

Two-phase active immersion cooling for vertically mounted electronics with interchip component-assisted bubble departure

To address growing heat dissipation demands in high-performance computing chips, there is a transition from conventional cooling methods to advanced two-phase immersion cooling techniques for electronics thermal management. Here, we present a numerical investigation into the fluid dynamics and heat transfer in two-phase immersion cooling systems with vertically mounted chips on a printed circuit board (PCB) with interchip components such as capacitors, switches, and inductors. Leveraging a combined phase tracking and volume of fluid model, we study how the physical layout and geometries of interchip components affect the flow paths of bubbles, bubble coalescence phenomena, vapor coverage on chip surfaces, and cooling rates of heated chips. In an optimal PCB topology, a maximum heat flux of 18 W/cm2 and a heat transfer coefficient of 9650 W/m2K are observed for dielectric hydrofluoroether (HFE) - 7100 at an excessive wall temperature of 20 K under a constant wall temperature boundary condition. The research offers insights into the electronic system design to achieve efficient cooling for high-performance computing applications, demonstrating the critical role of interchip components in heat transfer.

Analytical model development for vertical medium/deep ground heat exchangers with U-tube(s)

The U-shaped ground heat exchanger (UGHE) offers an effective solution for building heating and cooling purposes. In the practical applications of vertical UGHEs, the borehole wall temperature varies along the borehole depth due to the uneven initial ground temperature and transient heat transfer process. The assumption of a uniform temperature along the borehole wall in the existing quasi-3D model of UGHE causes a non-negligible error in the calculation of fluid temperature, especially for the cases of shallow-medium boreholes. Thus, two new analytical models are established to calculate the fluid temperatures for the single U-shaped GHE (1-UGHE) and double U-shaped GHE (2-UGHE), considering the depth-dependent borehole wall temperatures. The convolution theorem is employed to solve the mathematical problem of the nonlinear condition on the borehole wall, and the Laplace transformation is used for getting the final temperature expressions. The new analytical models are compared and verified by the on-site experiments. The results show that the two models exhibit promising prediction accuracies and similar variation trends in fluid temperatures. Then, parametrical and economical analyses for 1−/2- UGHEs have been carried out. Finally, the geographical thermal potentials of 1−/2- UGHEs across China have been comparatively investigated and the corresponding thermal map-based application potential recommendations have been given.

Thermal and hydrodynamic analysis inside a channel partially filled with porous material

AbstractIn this work, the transfer of heat and changes in fluid pressure within a rectangular channel fairly packed with porous material have been studied numerically for various Darcy numbers and dimensionless porous layers. The model was run with the following assumptions: laminar flow, forced convection, isotropic porous material, local thermodynamic equilibrium, constant wall temperature boundary condition, and no thermal dissipation. The study covers a broad range for the dimensionless porous layer, 0 ≤ hr < 1, and the Darcy number, 10−4 < Da < 10−2. The fully developed and developing flow over the channel is investigated in numerical study. It was observed that the inertia effect may be disregarded when Da < 10−4. The local dimensionless bulk temperature distribution, pressure drop, and velocity profiles were all shown to be impacted by the Darcy number and dimensionless porous layers, according to the numerical analysis results. The maximum heat transfer rate was attained when the ratio of the porous layer inside the channel was 0.8, and the pressure gradient was the highest. Partial packing of the channel with a porous material has two advantages: it increases the rate heat transmission rate and results in a much smaller pressure drop than a filled porous medium.

Determination of Local Heat Transfer Coefficients and Friction Factors at Variable Temperature and Velocity Boundary Conditions for Complex Flows

Transient conjugate heat transfer measurements under varying temperature and velocity inlet boundary conditions at incompressible flow conditions were performed for flat plate and ribbed channel geometries. Therefrom, local adiabatic wall temperatures and heat transfer coefficients were determined. The data were analyzed using typical heat transfer correlations, e.g., Nu=CRemPrn, determining the local distributions of C and m. It is shown that they are closely linked. A relationship lnC=A−mB is observed, with A and B as modeling parameters. They could be related to parameters in log-law or power-law representations for turbulent boundary layer flows. The parameter m is shown to have a close link to local pressure gradients and, therewith, near wall streamlines as well as friction factor distributions. A normalization of the C parameter allows one to derive a Reynolds analogy factor and, therefrom, local wall shear stresses.

Numerical study on heat restoration cycle performance of energy pile with backfilling PCM

The numerical analysis of energy pile backfilled with phase change material (PCM) was performed for the renewable geothermal energy utilization in building energy savings. Different operation modes and the melting temperature, latent heat, thermal conductivity of the PCMs within the energy piles were discussed to obtain the optimal parameters. Further, the restoration and heat transfer performance of energy piles were also analyzed for the prolonged operation. It was concluded that relatively higher latent heat and thermal conductivity were preferable to enhance the heat transfer rate per meter (Qm) of the PCM-backfilled energy pile. However, a relatively lower PCM latent heat may help to full utilization and restoration of PCMs during every cycle of cooling and heating when energy pile works. An ideal melting temperature of PCM is probably close to the initial soil temperature to achieve preferred restoration and heat transfer performance, rather than the inlet fluid temperature. In heating 12 h and cooling 12 h alternate mode, taking continuous operation as a reference, the Qm and the restoration rate of pile wall temperature of the PCM-backfilled energy pile were increased by 32.7 % and 52.5 % after operating 720 h.

Transition of the flow type in the supersonic cavity controlled by the wall temperature

The wall temperature of the high-speed aircraft increases quickly under hypersonic/supersonic incoming flow, which will cause a significant change in the flow structure. To study the transition of the flow type in the supersonic cavity controlled by the wall temperature, numerical simulations are conducted. The cavity length-to-depth ratio (L/D) is varied from 10 to 15, and the wall temperature ranges from 300 K to 1300 K. The results indicate that the type of cavity flow with an L/D ratio of 13 transforms from a closed cavity flow to a transitional cavity flow, when the temperature reaches approximately 775 K. And the transitional temperature rises with the elevated total temperature of the incoming flow. Furthermore, the mechanism of the cavity flow change with wall temperature could be the competition between the recirculation zone and the shear layer in the cavity. The rising pressure with higher wall temperature in the recirculation zone weakens the downward development of the cavity shear layer, preventing it from hitting the cavity floor. As a result, the mass exchange of cavity lip surface, pressure distribution, total pressure recovery coefficient, and heat transfer distribution in the supersonic cavity change dramatically. The critical wall temperature also affected by the sidewall effects and the inflow Mach number.

Effects of sinusoidal wall temperature on thermal dynamics and irreversibility around an inclined plate embedded in a square cavity

Abstract Effective thermal and flow control within complex geometries is essential for engineering applications. In this study, an in-depth examination of flow dynamics, entropy, and thermal regulation is undertaken within a square cavity featuring sinusoidal wall temperature. To introduce complexity, an inclined plate obstacle is strategically positioned within the cavity with an inclination angle of 45o, and the investigation spans three distinct scenarios: adiabatic, cold, and hot conditions. The initial physical model is developed by formulating a system of partial differential equations, which are then transformed into a dimensionless representation using relevant variables. Subsequently, the Galerkin method is employed for approximated analysis of the simplified fluid flow model, and the computational code is verified in tabular format. The embedded physical parameters are constrained to specific numerical values to ensure the convergence of the physical model in each scenario. The physical characteristics of isotherms, streamlines, Nusselt numbers, entropy, and Bejan numbers are investigated. Notably, the results demonstrate that the introduction of a cold inclined plate leads to peak values in generating the entropy and average heat transfer rates. When comparing the cold inclined plate to the heated inclined plate, an increase of approximately 20% in the average heat transfer rate and a 15% rise in the entropy generation rate was found for the cold inclined plate. Furthermore, the Bejan number showed a 10% decrease for the cold inclined plate compared to the heated inclined plate. Additionally, increasing the amplitude and wavenumber led to a rise in average heat transfer and entropy generation rates, with 25% and 30% increases, respectively.

Numerical modeling of alkali metal heat pipes

Heat pipe cooled reactors passively transfer heat from the core to the energy conversion system through alkali metal heat pipes. Further studies of the heat transfer characteristics of alkali metal heat pipes are needed to develop heat pipe cooled reactors. This work used a two-dimensional heat and mass transfer model of an alkali metal heat pipe. The flow field was validated against CFD predictions which showed that the model has less than 10 % errors in the velocity distribution and less than 5 % errors in the pressure distribution. A comparison of the predictions with experimental data in the literature indicated that the predicted wall temperature error was within 30 °C. This model was then used to analyze four factors that affect heat transfer in sodium heat pipes. The simulations show that higher heat fluxes shorten the startup time by approximately 70 % but significantly increase the operating temperature. The heat flux distribution significantly affects the evaporator temperature distribution. The heat transfer boundary condition on the condenser’s outer surface mainly affects the operating temperature and startup time. Increasing the heat pipe length-to-diameter ratio with a fixed heat flux increases the operating temperature with the increase proportional to the heat flux. This model provides accurate simulations of sodium heat pipes for various heat transfer boundary conditions. The simulations provide a reference for the selection of working conditions for heat pipe operation instability experiments.

Modeling & experimental studies on enhancement of H2S conversion using catalytic membrane reactor for hydrogen production

Abstract Acidic gases such as H2S and CO2 are generated in the refineries during coal gasification. These pollutant gases need to be treated before releasing to the atmosphere. Conventionally, H2S gas is treated by Claus process in which H2S is converted to elemental S and H2O, in presence of O2 at ∼1,200 K. In the present energy scenarios, hydrogen has got importance as a source of clean fuel for industrial application. The H2S generated in the refineries can be a potential precursor of hydrogen. If this hydrogen can be obtained by thermal decomposition of H2S, that can increase the overall economic value of the H2S containing streams and the produced hydrogen can be used for hydrocracking and hydro-treating in refineries, as well as to synthesize value-added products for chemical industries. However, H2S thermal decomposition is an endothermic and equilibrium limited reaction (equilibrium conversion is only ∼15 % at 1,000 K), requiring a very high temperature (∼1,500 K) to achieve even a conversion of greater than 40 %. Packed Bed Catalytic Membrane Reactor (PBCMR) for thermal decomposition of H2S can be a potential technology augmentation and process intensification to increase this equilibrium conversion. In this work, modeling and experimental studies of H2S thermal decomposition using in-house designed & developed PBCMR have been carried out. The modeling studies were validated with experimental data. Clay-alumina ceramic tubular membrane (L: 250 mm; OD: 12 mm; thickness: 2 mm) was fabricated using extrusion process having an average membrane pore size of ∼1 μm and with a porosity of ∼20 %. Pt (2 %) coated alumina extrudes were used as catalyst to accelerate the reaction kinetics. Experimental studies showed that H2S to hydrogen conversion of ∼90 % is achieved using PBCMR at ∼1,523 K, compared to only ∼40 % conversion in a conventional packed bed tubular reactor (without membrane). Modelling studies were carried out to study the influence of operating parameters such as, reactor wall temperature, feed temperature, pressure and feed velocity. Studies showed that reactor wall temperature is having the most dominant effect on H2S conversion, which is confirmed by experimental findings. The studies offer useful insights into the application of PBCMR technology for management of waste gas stream containing H2S and recovery of hydrogen.

Experimental investigation of the melting heat transfer of phase change material-based heat sinks under mechanical agitation with a no-delay-start strategy

Phase change materials (PCMs) are commonly used for the thermal management of electronic devices, but their low thermal conductivity limits their suitability for higher heat fluxes and shorter heat storage/release durations. Existing studies on heat transfer enhancement have focused mainly on conduction and lack consideration of convection. Therefore, melting experiments on n-docosane under mechanical agitation (0–1600 RPM) were carried out. A no-delay-start strategy of agitation was achieved by submerging the paddle with the addition of water (200 and 400 mL). As the rotation speed (n) increases, the heating wall temperature (Tw) generally decreases, especially at 0–400 RPM. For 200 mL, Tw decreases by 31.2 °C from 0 to 1600 RPM at 3600 s; for 400 mL, the decrease is 29.2 °C at 5400 s. The temperature difference between the heating wall and PCM decreases remarkably under agitation, reaching only 2.7 and 1.7 °C for 200 and 400 mL, respectively, at 1600 RPM and 6300 s. The temperature field uniformity is also improved by agitation. In addition, with increasing n, the complete melting time (tc) generally decreases, while the holding time (thold) basically increases. Under agitation, the Tw values for 200 and 400 mL are generally lower than that for 0 mL, indicating that the no-delay-start strategy is feasible and advantageous. At n ≥ 800 RPM, Tw for 200 mL is greater than that for 400 mL throughout the entire melting process, while at n < 800 RPM, this trend occurs only during the solid-phase heat conduction stage. The effects of both the rotation speed and water volume depend on the combined function of the intensity of the PCM-water interface and the heat storage capacity of water. Even when the heat flux increases from 8.5 to 25.4 kW/m2, the thold can still be extended under agitation. The power consumption (Qc) of agitation increases with rotation speed, decreases with water volume, and exhibits less sensitivity to heat flux. It reaches a maximum value of 10 W at 1600 RPM. Considering factors such as Tw, thold and Qc, the optimal configuration is determined to be a water volume of 400 mL and a rotation speed of 1600 RPM. This study demonstrated that convection enhancement of PCMs with a no-delay-start strategy effectively addresses the thermal management challenges of electronic devices.

Experimental investigation of the cooling effect of topology-optimized structure on photovoltaic wall

Nowadays, photovoltaic walls have been widely used, which will generate heat behind the PV panel and cause overheating, making the lower efficiency of the PV panel and higher temperature of the exterior wall. Topology optimization structures have been explored in many fields for heat dissipation, but few are applied in heat dissipation of the PV wall systems. The purpose of this paper is to experimentally investigate the effect of topological optimized structure of the copper sheet on electricity generation efficiency of the PV panel and cooling effect of the exterior wall. The topology optimization method is used to numerically find the optimal geometric configuration of high thermal conductivity material of copper sheet on the back of the photovoltaic panel. And the topology-optimized copper sheet is fabricated by 3D printing and experimented with four different cases. The experimental results show that under natural convection, compared with the reference photovoltaic wall, the largest reduction of temperature of the photovoltaic panel (ΔTpv) and the largest output power increment rate (ΔE/E) of the photovoltaic wall with topology-optimized copper in the 5 test days are 2.7℃and 1.30 % respectively, and the largest reduction of temperature of the exterior wall (ΔTw) is 1.6℃. Under forced convection, the temperature reduction (ΔTpv) and the increment of output power (ΔE) of the photovoltaic panel and the temperature reduction of the exterior wall (ΔTw) increase significantly under wind speed of 1 m/s compared with natural convection. But when the wind speed is increased from 1.5 m/s to 2 m/s, the increment is less obvious. Therefore, the optimal wind speed in the air gap of the photovoltaic wall with topology-optimized copper is 1 ∼ 1.5 m/s. At last, based on the results of our previous study, the optimal-constructed photovoltaic wall in hot summer and cold winter area is discussed. The results of this research can provide some technical guidance for engineering application of the photovoltaic panel integrated with walls in similar climate regions.

Simulation study on heat and mass transfer characteristics within tubular moving bed heat exchangers

In the field of waste heat recovery, tubular moving bed heat exchangers (MBHEs) hold great promise as equipment capable of effectively handling large-sized granular materials with high temperature. To further clarify the heat and mass transfer characteristics within tubular MBHEs, this study firstly conducted detailed investigations on the contributions of different heat transfer mechanisms. The result shows that heat radiation (∼45 %) and gas film heat conduction (∼42 %) control the heat transfer processes involving tube walls, with an inlet particle temperature of 600 °C, tube wall temperature of 50 °C, and particle descent velocity of 2 mm/s. These contributions can be influenced by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. Additionally, for a specific particle, its heat transfer state is highly depended on where it is located. Subsequently, the time-varying and space-varying characteristics of the heat transfer processes involving tube walls are studied. The results suggest that the time-varying and space-varying characteristics are inherent in tubular MBHEs due to the difficulty to achieve complete stability. Meanwhile, temporal fluctuations intensify with an increase in the inlet particle temperature, a decrease in wall temperature, or an increase in particle descent velocity. The result of power spectral density (PSD) indicates that the heat transfer processes exhibit a degree of chaotic behavior due to the nonlinear property of sub-models, as well as the randomness in particle feeding and contacts. The space-varying characteristic is mainly determined by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. This characteristic can be observed in both the axial and circumferential directions, with the circumferential variation being more pronounced than the axial variation. Furthermore, a double-tube MBHE, a topic that has received scant attention in previous research, is investigated in comparison to a single-tube MBHE to explore the differences in heat and mass transfer between the two configurations. It indicates that under the same boundary conditions, there are differences in heat transfer results, which are attributed to the interactions between two vertically arranged tubes. These interactions are reflected in the reconstruction of particle flow patterns and the effect altering the temperature distribution for the particles or fluid surrounding the tubes. The obtained results provide valuable insights into the mass and heat transfer behaviors of particles and fluids within tubular MBHEs, laying a foundation for advancing the development of efficient tubular MBHEs.

Investigation on the heat transfer estimation of subcooled liquid hydrogen for transportation applications using intelligent technique

Hydrogen, as a sustainable fuel for transportation sector as well as some other heavy industries, should be stored or transferred in liquid phase. To prevent the evaporation of hydrogen in the tanks and the consequent hazards, it is common to lower its temperature below the saturation point known as subcooling of the fluid. When the subcooled liquid hydrogen flows through pipes with higher wall temperatures, the hydrogen can evaporate and flow boiling occurs, resulting in a complex heat transfer behavior of the fluid. In this study, we propose an advanced intelligent model based on the Cascade Forward Neural Network (CFNN) to predict Heat Transfer Coefficient (HTC) of subcooled liquid hydrogen under various flow conditions. Our model leverages on a dataset that is nearly twice the size of the largest previously used in the literature, significantly enhancing its generalization, reliability, and accuracy. The proposed CFNN model incorporates 19 input features, including crucial dimensionless parameters, orientation and thermodynamic condition of the fluid, and characteristics of the pipe that hydrogen flow through to accurately estimate HTC in unseen fluid conditions. The results demonstrate that the proposed model achieves an R-squared value of 0.9978, substantially outperforming the best empirical methods, which have an R-squared value of only 0.8058 for the same testing data. This innovative approach provides a highly accurate and reliable tool for predicting HTC, offering significant improvements over conventional methods and contributing valuable insights for real-world applications in the energy and transportation sectors.

Numerical study on combustion and energy efficiency characteristics of thermophotovoltaic-thermoelectric two-stage utilization system filled with porous media

Addressing the issues of low energy conversion efficiency and unstable combustion at the micro-scale resulting from significant energy loss in micro-energy systems, this paper proposes a two-stage utilization system integrating thermo-photovoltaic-thermoelectric technology filled with porous media. The research explored the impact of the placement, thickness, and porosity of porous media on both combustion and energy efficiency within a two-stage utilization system. Performance evaluation indexes such as temperature distribution, pressure drop loss, output power, and efficiency revealed the combustion characteristics of porous media at the micro-scale. The results indicate that the mean outer wall temperature of MTPV increases by 174.3 K as the porous media transitioned from a partially filled to a fully filled state. After comprehensive consideration of various factors, the optimal layout parameter for porous media is determined to be a two-stage uniform filling of porous media (SS304 with a porosity of 0.86 and a thickness of 14 mm). Consequently, the two-stage combustion system achieves an output power of 14.88 W and an energy conversion efficiency of 7.33 %.