Wall Temperature Distribution Research Articles

Experimental Investigation of Post-Dryout Heat Transfer with R-134a at High Pressures

An experimental study of post-dryout (PDO) heat transfer in the coolant R-134a was performed in a vertical round tube with upward flow. Experiments were conducted at high pressures from 28.4 bars up to 39.8 bars, corresponding to a reduced pressure of 0.7 to 0.98, respectively. Mass flux was varied in the interval of 300 to 1500 kg/m2∙s, and overall equilibrium vapor quality was between −1.88 and 4.89. Depending on the settings of the experimental parameters, the heat flux was varied from around 11 to 100 kW/m2. The uniformly heated tube had an inside diameter of 10 mm and a heated length of 3000 mm. In total, more than 10 000 PDO data points were obtained. In the PDO region, the wall temperature distributions had similar behavior across the pressure range. At the occurrence of dryout, the wall temperature suddenly increased until it reached a peak. For higher mass flux, the wall temperature decreased after reaching the peak, followed by a second temperature increase with a lower slope. For lower mass flux, the wall temperature kept increasing after the dryout point. The temperature peak after the dryout point was smaller at higher pressure, while this effect was even stronger near the critical pressure. Likewise, the vapor quality corresponding to the first peak shifted to even lower values with increasing pressure. Furthermore, it was found that at increasing pressure and at increasing mass flux, the dryout location and the total temperature distribution shifted toward lower vapor qualities. In addition, several PDO correlations were assessed, and a new correlation for high-pressure conditions was developed and compared with the results of the existing ones.

Investigation of heat transfer characteristics and optimization design of platen superheaters in the furnace of a 350 MWe supercritical CFB boiler

With the scale-up of circulating fluidized bed (CFB) boilers, the size of the platen heating surface within the furnace increases. Deformation, crack, and tube explosion of the platen heating surface threaten the safe and stable operation of CFB boiler. Large wall temperature deviation and overtemperature of partial tubes of heating surfaces are two of main reasons resulting in above problems. To identify the causes of large wall temperature deviation and decrease them, the heat transfer characteristics and wall temperature distribution uniformity of platen superheaters in the furnace of a 350 MWe supercritical CFB boiler were studied by experimental tests, and the structure of the high temperature superheater was optimized by numerical simulation to improve the temperature distribution uniformity. The steam parameters and wall temperatures of the platen superheaters were measured at boiler loads of 50 % BMCR, 75 % BMCR, and 100 % BMCR. The heat transfer coefficient, heat flux, and wall temperature uniformity of the platen superheaters were analyzed. At 100 % BMCR boiler load, the average heat transfer coefficient and heat flux of the medium temperature superheater IIs were 165.5 W/(m2·°C) and 56 kW/m2, respectively; while those of the high temperature superheaters were 179.7 W/(m2·°C) and 53.2 kW/m2, respectively. The wall temperature distribution uniformity among six medium temperature superheater IIs or six high temperature superheaters was relative good, while the temperature distribution uniformity of a single platen superheater required improvement. An optimized structure of the high temperature superheater was obtained from eight structures by numerical simulation, achieving a steam temperature deviation of less than 8 °C at the boiler load of 100 % BMCR.

Numerical simulation of natural gas-ammonia combustion characteristics in a U-shaped radiant tube

NH3, recognized as a carbon-free fuel and a high-energy–density renewable hydrogen carrier, holds promise as a low-carbon alternative fuel. However, its direct combustion is often posed with challenges such as a limited ignition zone and high NOX emissions. To address this, the present paper proposes a strategy to blend more reactive hydrogen-containing fuels with ammonia to enhance combustion stability and concurrently reduce NOX emissions. This study developed numerical models for natural gas-ammonia combustion within a U-shaped radiant tube. The dynamic characteristics of combustion flame flow fields inside the radiation tube were investigated across various mixing ratios, analyzing the effects of nitrogen-containing fuel temperature on NOX generation and elucidating NOX generation patterns under different mixing ratios. The findings indicated that a 30 % NH3 blending ratio in the radiation tube yielded uniform wall temperature distribution along its length, minimal circumferential temperature variation, and an outlet NOX emission of only 20.3 ppm. Furthermore, Pearson correlation coefficient calculations revealed strong correlations between NH3 concentration (0.97), URT temperature (0.88), and NOX generation rate (0.88) within the U-type radiation tube combustion flame and NOX emission content.

Thermodynamic behavior of high-power inductively coupled plasma quartz tube wall

High-power inductively coupled plasmas are commonly used in planetary entry simulations and are increasingly being used in electric propulsion applications. However, during the operation of the system, the walls of the quartz tube will crack and melt. Its thermodynamic behavior is key to ensuring the safe and reliable operation of the system, which is directly related to the distribution of thermal energy within the discharge volume. In this paper, the temperature and stress distribution of the quartz tube wall of an inductively coupled plasma generator at 27 kW–85 kW are described. A numerical simulation model was established to depict the interaction between the plasma and the quartz tube wall. In the field of experimental research, the temperature of the outer wall of the quartz tube was obtained by using a thermal imager, and a non-uniform B-spline difference method was proposed to fit the outer wall temperature of the quartz tube to eliminate the influence of the induction coil. It is found that the numerical simulation and experimental results show that the temperature is stable region, temperature rise area, temperature drop zone, and the high temperature region of the quartz tube wall is located in the coil area, and the high stress area is also located in this region. On this basis, the outer wall temperature and thermal stress of quartz tubes under different heat fluxes are studied. When the heat flux exceeds 18.6 kW/m2, the stresses in the coil area and downstream of the coil exceed the limit stress. Mechanical failures may occur in areas where the ultimate stresses are exceeded, and these results can provide theoretical data for the optimal design of high-power inductively coupled plasma generators.

Numerical investigation on the core thermal hydraulic behavior of pool-type sodium-cooled fast reactor (SFR)

A thorough understanding of the reactor core thermal hydraulic behavior is essential for the design and safety analysis of Sodium-cooled Fast Reactors (SFR). Due to the application of hexagonal subassembly, the core thermal hydraulic behavior is significantly affected by the flow field within the subassemblies, the inter-wrapper region and the hot pool. Analysis of the core thermal hydraulic behavior requires a model coupling the three regions mentioned above, which has been identified as one of the thermal hydraulic challenges in SFR. In the present study, a 3D model that covers the three regions was developed for the core of the China Experimental Fast Reactor (CEFR) with the Computational Fluid Dynamic (CFD) code, Fluent. The inter-wrapper region and the hot pool were modeled in detail, while the subassemblies were modeled with a special porous medium model. The core thermal hydraulics behavior under steady state was studied, more specifically, information for the flow field distribution at the core outlet, the inter-wrapper flow and the duct wall temperature distribution was obtained. Under steady state, liquid sodium in the inter-wrapper region is supplied by the inner region of the hot pool. And it enters the inter-wrapper region from the core outer region and returns back to the hot pool inner region from the core central region. The inter-wrapper flow is cooled by non-fuel subassemblies and heated up by fuel subassemblies. For non-fuel subassembly, the ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies could reaches 96%; for fuel subassemblies, the maximum ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies is 2.45%. Significant temperature gradients have been observed on the duct wall, with maximum values of 156.69 K/m in the vertical direction and 2,196.00 K/m in the circumferential direction. The largest temperature gradient appears on the duct of subassemblies adjacent to the transition region of fuel subassemblies and non-fuel subassemblies.

Advancing thermohydraulic performance of micro-grooved flat heat pipes through a combined numerical-experimental approach

A combined numerical-experimental model has been developed to predict the thermohydraulic characteristics of micro-grooved flat heat pipes (FHPs). This model uses a limited number of experimental data for calibration with two parameters, βexp,1 and βexp,2, which account for uncertainties in the accommodation coefficients used to determine evaporation and condensation mass fluxes. This calibration, which is a key feature of the developed model, addresses the uncertainties and challenges in determining these coefficients. Moreover, the model incorporates the effects of interfacial shear stress, axial wall conduction, heat transfer in the liquid block region, and the contact angle of the liquid–vapor interface. Furthermore, the evaporation mass flux from the curved liquid–vapor interface is calculated using a separate multiscale approach developed in two recent works for analyzing evaporation from the extended meniscus in microchannels, considering thin-film evaporation. The model demonstrates high accuracy in predicting the maximum heat transport capacity (Qmax) and wall temperature distribution across various input heat powers, with a maximum error of less than 0.5 % in wall temperature predictions, as validated against experimental data. The validated model is then used to explore a new micro-grooved wick structure featuring converging/diverging microchannels. In this structure, the channel width is constant and equal to Wf2 in the first half of the heat pipe, from the condenser end to the midpoint, and then it decreases or increases to Wf1 by the end of the evaporator section. Results indicate that a flat heat pipe with a converging micro-grooved wick structure (Wf1 = 200 µm and Wf2 = 160 µm) can enhance Qmax from 53 to 70 W, 70.8 to 91.8 W, and 91.2 to 116.5 W at working temperatures of 60 °C, 70 °C, and 80 °C, respectively. This means the new converging micro-grooved wick structure can boost flat heat pipe performance by more than 25 % compared to a flat heat pipe with a straight micro-grooved wick (Wf1 = Wf2 = 200 µm) without increasing the occupied space.

Experimental study on onset of nucleate boiling in wide-ranged parameters for narrow rectangular channels

The onset of nucleate boiling (ONB), which marks the emergence of nucleate boiling, is an important transition point in the boiling curve. For exploring the influence of geometric and thermodynamic parameters on ONB in rectangular narrow channels, a detailed experimental study is conducted to investigate ONB under wide range of parameters. The experimental parameters range is pressure of 0.1–5.5 MPa, mass flux of 200–2000 kg/m2s, inlet subcooling of 10–150 K. According to the experimental results, the location of ONB is identified based on the axial distribution of wall temperature, and the influence of various parameters on ONB in narrow rectangular channels is analyzed. It is found that heat flux, pressure, mass flux, and the gap size of the channel have a significant impact on ONB. By comparing the computed results of existing correlations, it is evident that there is a deviation, which can be attributed to the narrow range of experimental parameters in previous studies. Finally, a new ONB model is developed based on basic equations proposed by Hsu and the distribution of liquid temperature, taking into account the influence of mass flux and the enhanced heat transfer results from surrounding bubbles to correct the liquid temperature. The new correlation accurately describes the impact of each parameter and is in good agreement with the current experimental results.

Film hole layout optimization for multi-row film cooling plate in continuous parameter space under non-uniform inlet temperature distribution

Film cooling is an advanced external cooling technology for protecting gas turbine blades from excessive temperatures. To counteract non-uniform heat loads caused by hot streak and swirl effects at the combustion chamber outlet, fine design of film hole positions is necessary. However, the complexity due to the numerous film holes and their positional parameters presents challenges in the independent optimization of film hole positions in a continuous parameter space. This study proposed an optimization method grounded in the divide and conquer approach to address optimization for film hole layout. The film hole layout was decomposed into multiple single rows and optimized systematically by iteratively refining the single-row film hole layout along the streamwise direction using the expectation maximization algorithm. Optimized layouts for five different inlet temperature distributions were obtained using the proposed method and adiabatic wall temperature distributions were compared and analyzed for optimized and staggered layouts. Additionally, the cooling performance of the optimized layout was evaluated against the staggered layout under conjugate heat transfer conditions and the robustness of the optimized layout under various blowing ratios and peak temperature positions was tested. The results demonstrated that the proposed method can optimize the positions of 52 film holes within 0.3h, and it was generalized to various inlet temperature distributions. By enhancing lateral interactions among downstream film jets, the lifting effect of kidney vortex in the optimized layout was weakened, bringing the film jets closer to the wall and significantly increasing coolant coverage during streamwise development. Comparative analysis reveals the superior cooling performance of the optimized layout at the blowing ratio of 1.0, evidenced by a 15.1% reduction in total input heat transfer rate and a 12.3% enhancement in overall cooling efficiency relative to the staggered layout. Under conditions with blowing ratios ranging from 0.5 to 1.5 and peak temperature position deviations, the average wall temperature of the optimized layout consistently remained lower than the staggered layout, indicating the robustness of the optimized layout to variations in blowing ratio and hot streak position.

Experimental and numerical investigation of the influence of varying micro-channel width on flow and heat transfer uniformity

This study integrates experimental and numerical methods to investigate the heat transfer and flow characteristics of microchannel heat sinks with varying width distributions. Water is used as the working fluid and laminar flow model is applied for simulation. Specifically, ten different width distribution structures were designed, including uniform-width configurations and nine non-uniform-width structures (I to IX) with progressively refined intermediate channel widths. Numerical simulations were employed to analyze the flow and heat transfer behaviors, and experimental validations were conducted on both the uniform-width structure and structures II, IV, V, VI, and IX. Results indicate that in uniform-width channel structures, the pressure drop and mass flow rate in intermediate channels exceed those in side channels, resulting in uneven temperature distribution at the base. Conversely, refining the intermediate channel widths under constant total width promotes more uniform flow and wall temperature distributions. A Performance Evaluation Criterion for Non-uniform Channels (PECNC) was introduced to identify the optimal structure. Ultimately, structure VI, characterized by continuously refined intermediate widths, emerged as the optimal design for achieving uniform temperature distribution. A mathematical expression for calculating the optimal microchannel width distribution conducive to uniform temperature distribution was also established.

Experimental Study on Temperatures of Water Walls in a 1000 MW Ultra-Supercritical Boiler under the Condition of Flexible Peak Regulation

To meet the Chinese government’s energy-saving and emission-reduction policies, flexible peak regulation is necessary for traditional coal-fired boilers. Flexible peaking leads to large changes in boiler load, which affects the safety of the boiler water wall. In this paper, a 1000 MW ultra-supercritical unit was tracked for three years, and effective data were selected to study the temperature characteristics of the water wall under flexible peak regulation. The results show that the lower the load, the greater the temperature fluctuation of the water wall. The temperature distribution of the spiral water wall is more uniform. The position of the temperature valley value of the rear spiral water wall was found, and the load of more even temperature distribution was also found. The temperature change of the front vertical water wall was the most complex of all the water walls. The 643.9 MW load case showed different behavior to the temperature distribution of the water wall. The side water walls were heated evenly under the different loads. The characteristics of the temperature distribution of the side vertical water wall were found through statistical analysis. The fitting equation for the change rule of the temperature is presented. The higher the load, the better the equations. Finally, this paper gives some advice on how to avoid temperature deviation in the water wall, and the detailed research highlights the safe running of water walls.

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.

Lab-based scale measurements of internal storage of crude oil tank based on non-contact infrared thermography technique

Non-contact sludge measurement methods for storage tanks can address the challenge of measuring the volume of sedimented sludge during long-term storage. While infrared thermography technology can address the issue of liquid level detection, its measurement accuracy for the undulating interface of sludge is insufficient. This study designed and constructed experimental setups for measuring sludge in storage tanks. In this study, infrared images taken by an infrared camera were used to record the temperature distribution of the outer wall of the storage tank. The threshold segmentation method is used to determine the accurate sludge boundary line in image processing. Finally, the Three-Dimensional Tank Residue Recovery Algorithm (3D-TRRA) was applied to fit the 3D distribution of the sludge and calculate accurate sludge volumes. The results indicate that the best segmentation is achieved with a threshold of 170. The measurement error for sludge volume is less than 5%. Accurate visual positioning and recognition of sludge are achieved.

Numerical analysis of tapered wick configurations in cylindrical heat pipes

Heat pipes are essential devices in thermal engineering due to their ability to transport heat with remarkable efficiency. They are crucial for heat distribution and control in a variety of applications, such as aircraft systems and electronics cooling. This paper presents a numerical analysis on the performance characteristics of a cylindrical heat pipe featuring a novel tapered wick geometry. A two-dimensional numerical model incorporating non-Darcian liquid transport is formulated and solved at steady state. To investigate the effect of the tapered wick geometry, major characteristics such as axial distribution of vapor pressure, liquid pressure and wall temperature are evaluated and analyzed. Based on the direction of taper, three configurations viz., THPE (Tapering wick heat pipe from evaporator end), THPC (Tapering wick heat pipe from condenser end) and THPA (Tapering wick heat pipe at adiabatic center) are studied. A novel non-dimensional parameter termed as Temperature Pressure Index (TPI) is proposed to signify the extent to which an HP can reduce its evaporator temperature relative to increase in pressure drop. Initially a parametric study is performed. Results showed a superior performance of THPE and THPC designs over THPA in terms of output parameters. The numerical findings demonstrate that when compared to a uniform wick heat pipe, both the THPE and THPC configurations exhibit a notable enhancement of 58 % in effective thermal conductivity under a maximum load of 455 W. Further, by conducting a variance-based (Sobol) sensitivity analysis, the THPC design is found to be marginally better as compared to THPE. Finally, the BOBYQA optimization algorithm is employed to find optimum taper angle for THPC design that maximizes the output parameters. The optimum taper angle of the wick is found to be 0.0372° for minimum average evaporator temperature in the present case. For this optimized THPC design, a reduction in average evaporator temperature of 6.51 K is obtained compared to uniform wick heat pipe. Additionally, the obtained TPI value is about 1.86 times than that of a uniform wick heat pipe.

Spatiotemporal Surface Temperature Measurements Resolving Flame-Wall Interactions of Lean H2-Air and CH4-Air Flames Using Phosphor Thermometry

AbstractSpatiotemporal wall temperature (Twall) distributions resulting from flame-wall interactions of lean H2-air and CH4-air flames are measured using phosphor thermometry. Such measurements are important to understand transient heat transfer and wall heat flux associated with various flame features. This is particularly true for hydrogen, which can exhibit a range of unique flame features associated with combustion instabilities. Experiments are performed within a two-wall passage, in an optically accessible chamber. The phosphor ScVO4:Bi3+ is used to measure Twall in a 22 × 22 mm2 region with 180 µm/pixel resolution and repetition rate of 1 kHz. Chemiluminescence imaging is combined with phosphor thermometry to correlate the spatiotemporal dynamics of the flame with the heat signatures imposed on the wall. Measurements are performed for lean H2-air flames with equivalence ratio Φ = 0.56 and compared to CH4-air flames with Φ = 1. Twall signatures for H2-air Φ = 0.56 exhibit alternating high and low-temperature vertical streaks associated with finger-like flame structures, while CH4-air flames exhibit larger scale wrinkling with identifiable crest/cusp regions that exhibit higher/lower wall temperatures, respectively. The underlying differences in flame morphology and Twall distributions observed between the CH4-air and lean H2-air mixtures are attributed to the differences in their Lewis number (CH4-air Φ = 1: Le = 0.94; H2-air Φ = 0.56: Le = 0.39). Findings are presented at two different passage spacings to study the increased wall heat loss with larger surface-area-to-volume ratios. Additional experiments are conducted for H2-air mixtures with Φ = 0.45, where flame propagation was slower and was more suitable to resolve the wall heat signatures associated with thermodiffusive instabilities. These unstable flame features impose similar wall heat fluxes as flames with 2–3 times greater flame power. In this study, these flame instabilities occur within a small space/time domain, but demonstrate the capability to impose appreciable heat fluxes on surfaces.

Comparison of Maximum Heat Transfer Rate of Thin Vapor Chambers with Different Wicks under Multiple Heat Sources and Sinks

In this paper, we present a new analytical model to investigate the maximum heat transfer rate of a thin vapor chamber (TVC) with multiple heat sources and sinks. The model can specifically consider different heat flux conditions for each heat source. Both capillary limitations and allowable maximum temperature constraints were employed to determine the maximum heat transfer rate. The liquid and vapor pressure distributions within the TVC were analytically derived using the Brinkman-extended Darcy equation and the Hagen–Poiseuille equation, respectively. Additionally, the theoretical wall temperature distribution was calculated based on the 3D energy equation, considering different heat flux conditions for multiple heat sources with a weighting factor. Our results demonstrate that the heat flux conditions applied to the heat sources significantly impact the internal flow pattern of the TVC. These changes in flow patterns influence the pressure distributions of the liquid and vapor, thereby affecting the maximum heat transfer rate. Furthermore, the effects of wick parameters on the maximum heat transfer rate under various heat flux conditions were examined.

Study on heat transfer characteristics and enhancement mechanism of supercritical carbon dioxide in adaptive channels

Supercritical CO2 power cycles have promising applications in many fields, the heat transfer of supercritical CO2 is critical to the efficiency and safe operation of cycle system. The adaptive channel was previously proposed by our group to improve heat transfer of supercritical CO2, the performance of heat exchanger with adaptive channel was experimentally studied. Whereas the effect of adaptive channel on heat transfer deterioration of supercritical CO2 and the mechanism remain unclear. In this study, the effect of adaptive channel on heat transfer deterioration of supercritical CO2 and the mechanism are analyzed numerically based on a single channel, the effect of structure on heat transfer is analyzed through the maximum wall temperature and average heat transfer coefficient under the same length and heat transfer area. The results reveal adaptive channel is effective at alleviating heat transfer deterioration with no local peak in wall temperature distribution. The channel variation length of adaptive channel need to be increased from 0.4 to 0.8 with the aggravation of heat transfer deterioration in order to eliminate local wall temperature peak. For the heat transfer deterioration conditions, the maximum wall temperature lowers first and then increases as channel variation length increases, there is a length that makes the maximum wall temperature lowest, which is lowered by more than 40 °C compared with straight channel. The average heat transfer coefficient can be increased by 1.1 ∼ 1.5 times as channel variation length increases. For the no heat transfer deterioration conditions, the maximum wall temperature increases about 30 °C whereas average heat transfer coefficient can be increased by 58 %∼76 % with channel variation length increasing. The mechanism of adaptive channel alleviating heat transfer deterioration is as follows: the fluid velocity always presents an inverted U-shaped distribution along the radial direction in adaptive channel, the radial density difference is less and buoyancy effects heat transfer weakly. The turbulent kinetic energy is kept at high, so the heat near the wall is transferred to the main flow timely.

Impact of impinging jet ventilation on thermal comfort and aerosol transmission: A numerical investigation in a densely-occupied classroom with solar effect

Urgent demands for ensuring safe and healthy spaces for children have been raised due to the post-COVID-19 pandemic. This study numerically modelled a densely populated classroom with 40 students and one teacher across two layouts with different relative vent positions to assess the effectiveness of an emerging ventilation scheme, impinging jet ventilation (IJV), in balancing thermal comfort and controlling indoor transmission. The effect of solar radiation was carefully analysed. Cough-induced contaminants were expelled from the infectious teacher and were traced by the Eulerian-Lagrangian approach. The exposure risk of students was further assessed via the inhalation index (ID) based on the spatial characteristics of the released particles. The thermal comfort was evaluated by the Fanger model. The results demonstrated that IJV with Layout 2 (teacher at the supply inlet and exhaust side) was found more optimal in counterbalancing the occupants’ thermal comfort and indoor transmission control. This layout not only aligned better with ASHRAE standards for thermal comfort, showing a reduced vertical thermal gradient but also lowered student exposure risk by 18.9%–135.2%. With solar radiation, heat absorbed by the windows led to non-uniform wall temperature distributions, causing the air near the windows to also exhibit a non-uniform profile. This interaction with the cooler air from the IJV system was found to facilitate contaminant dispersion. This resulted in a 10.3% to 26% increase in students’ average exposure risk compared to those without solar radiation cases. This study aimed to investigate the practical applications of IJV system for densely-occupied classrooms.

A novel micro-combustor with dual-inlets hedging and center opening for enhancing comprehensive performance of micro thermophotovoltaic system

Micro-combustor outer wall temperature uniformity is a critical bottleneck in the widespread application of micro thermophotovoltaic system. In this study, we proposed a novel micro-combustor with dual-inlets hedging and center opening structure to improve the wall temperature distribution and achieve a stable and high-energy of micro thermophotovoltaic system output, and we applied the overall performance evaluation criteria to evaluate the performance of micro thermophotovoltaic system comprehensively. Initially, we conducted a comparative analysis among the traditional micro-combustor, the single rectangular center opening, and the double rectangular center opening micro-combustor. The findings indicate that the double rectangular center opening micro-combustor exhibits superior comprehensive thermal performance, showcasing a mean outer wall temperature and temperature standard deviation of 1362.05 K and 32.77 K, bringing better temperature uniformity. Then, the center opening distance of the double rectangular center opening micro-combustor was optimized from 0.5 mm to 3.0 mm, the results reveal that the double rectangular center opening micro-combustor with a distance of 2.5 mm possesses the best comprehensive performance, specifically, temperature standard deviation and overall performance evaluation criteria values of 23.17 K and 4.882. Ultimately, the effect of inlet velocity on the thermal performance was investigated, revealing that an increase in inlet velocity stimulates the output energy, but concurrently diminishing the energy conversion efficiency, leading to a reduction in overall thermal performance. This study introduces a novel concept for designing micro-combustor structures for promoting overall performance of micro thermophotovoltaic systems.

In-flight anti-icing simulation of electrothermal ice protection systems with inhomogeneous thermal boundary condition

Conventional anti-icing computational solvers calculate the convective heat transfer coefficient using a homogeneous thermal boundary condition, assuming a constant temperature across the surface. However, this approach can lead to inaccuracies in regions with significant temperature variations. To address this limitation, the present study proposes a novel approach that utilizes an inhomogeneous thermal boundary condition, which updates the convective heat transfer coefficient based on the transient wall temperature distribution. We developed a unified finite volume framework that efficiently integrates various in-house solvers, including a compressible Navier-Stokes-Fourier (NSF) airflow solver, a Eulerian droplet impingement solver, a PDE-based ice solver, and a multilayer heat conduction solver. Thermal interaction between the different solvers was modeled using the conjugate heat transfer method. The effects of updating airflow on anti-icing results were investigated by comparing the results obtained by coupled and decoupled solvers. While the decoupled solver computes airflow once and remains unchanged, the coupled solver updates the airflow during the anti-icing simulation. Our findings show that the decoupled solver has the highest deviations from the coupled solver in evaporative anti-icing regimes, where dry regions form within the protection limits. Using coupled solvers in designing ice protection systems in evaporative regimes improves temperature prediction accuracy, enabling designers to reduce safety factors and save energy.

A conjugate heat transfer investigation of outer-wall cooling performance in double-wall vane pressure side

Double wall cooling has significant potential for high-pressure turbine vane cooling technology. Geometric parameters of the double-wall vane play a crucial role in determining the cooling performance. This paper presents a double-wall cooling model with five outer wall thicknesses and three injection angles, using the curvature of the actual pressure side of the engine as a reference. The overall cooling effectiveness is investigated over the range of blowing ratio from 0.5 to 2.5. Results indicate that, at injection angles of 20° and 30°, an outer-wall thickness of 1.5D f maximizes the combined benefits of film cooling and thermal conductivity in solid domains. At an injection angle of 40°, the blowing ratio becomes a determining factor in selecting the optimal outer wall thickness. Additionally, a reasonable arrangement of pin fins promotes a more uniform outer wall temperature distribution. A thinner outer wall at higher blowing ratios provides optimum overall cooling effectiveness.