The focus of this study is to explore the thermodynamic characteristics of an intermediate heat-exchange cycle (IHEC) system in aero engines, employing experimental analysis. Using air, fuel, and ...intermediate working fluid (IWF) as working mediums, an IHEC system experimental platform incorporated two heat exchangers (HEX) was established. A theoretical analysis model for characteristics of the IHEC system was developed using the heat current method and a novel method for estimating the overall heat transfer coefficient (K). Deviations between experimental and simulation results for system equilibrium heat transfer rates and temperatures at each node of the IHEC system are within ±10%, and the maximum average relative deviation of the proposed method for estimating K is −7.93%. Detailed analyses have been conducted regarding the effects of fuel mass flow rate, IWF mass flow rate, air mass flow rate, and air inlet temperature on the system. Raising the fuel mass flow rate leads to reduced temperatures at each system node, while the system's equilibrium heat transfer rate initially increases and then stabilizes. Variations in IWF mass flow rate have complex impacts on the IHEC system, influenced by HEX design margins and heat transfer capacities. Tailored analyses are necessary based on specific circumstances.
•A theoretical analysis model for system-level characteristics of the IHEC system was developed.•A two-stage heat exchanger combined IHEC system experimental platform was established.•Different parameter's effects on systematic thermodynamic performance have been conducted.•The accuracy of the mathematical model was verified by experiments.
The ballast bed serves as the foundation of the ballasted track, and its performance is maintained through periodic ballast cleaning. Early detection of fouled ballast bed significantly reduces ...maintenance workload and capital investment. Some scholars have studied the feasibility of utilizing infrared thermography (IRT) for detecting fouled ballast bed (DBF) and have made some progress. Existing studies have predominantly employed simulated boxes to simulate the ballast bed. To better reflect real-world conditions, this study established two sections of ballast bed on a newly constructed line: one with clean ballast and the other fouled, with a volumetric fouling rate (VFR) of 27.6 % (FI ≈ 21.5 %). Moreover, this paper takes a pivotal step in exploring the thermodynamic transfer mechanisms within the ballast bed, the influences of meteorological factors on the detection effectiveness of IRT, and other detection indicators that could be used for DBF.
The results demonstrate that the different void fractions and composition substances of the clean and fouled ballast beds (CFB) contribute to their distinct thermodynamic properties. Furthermore, the high specific heat capacity of water exacerbates the thermodynamic property difference between the CFB. In terms of meteorological factors, both the solar radiation intensity (S) and air temperature (T) have a significant positive impact on the temperature of the ballasted structure (STT) and the temperature difference between the CFB (CF-S). Throughout the day, as the S and T increase, the ballast bed surface absorbs more solar heat than it loses, leading to an increase in its surface temperature. When it exceeds the soil temperature (S-S), heat is transferred downward. Since the poor heat conduction of the clean ballast bed, it has a higher surface temperature. As the S and T decrease, heat convection and conduction become dominant, leading to a decrease in the surface temperature of the ballast bed (BT-S). When the BT-S is lower than the S-S, heat is transferred upward, causing the surface temperature of the fouled ballast bed (F-S) to potentially exceed that of the clean ballast bed (C-S). Furthermore, the humidity (H) has a strong negative impact on the STT, while on sunny days following rain, it has a significantly positive impact on the CF-S. The effects of wind speed (W) on the STT and the CF-S are not prominently observed due to its low values during the experiment. Without considering rainfall, higher S and T, combined with reduced W, result in a greater CF-S and are more conducive to advancing fouling detection. Hence, the CF-S can reach up to about 3 °C on a sunny day and may even rise to about 5 °C after rainfall. Nonetheless, the CF-S is only around 0.71 °C on a cloudy day and 0.25 °C at night. Unexpectedly, there is a significant temperature difference between the sleeper and the ballast bed or the steel rail. These indicators could potentially be used for DBF on cloudy days. Overall, these findings demonstrate the feasibility of using IRT for DBF in the field, provding a broader theoretical support for its advancement and implementation.
•The feasibility of employing IRT to detect fouled ballast bed was confirmed through a field trial.•The thermodynamic transfer mechanism within the ballast bed was investigated on-site.•The impacts of different meteorological factors on the detection effectiveness of IRT were studied.•Other detection metrics that could be used to identify fouled ballast bed were investigated.
The AIAS group studying Energetic Methods for Experimental Analysis, MEAS, is performing round robin experimental tests for the rapid determination of fatigue limit on steels by different ...thermographic techniques. This work is part of the project and describes the experimental activity performed at Politecnico di Milano, based on stepwise cyclic tests. Thermograms are processed in terms of: 1) amplitude of the first order harmonic, in-phase with respect to the loading signal; 2) amplitude of the second harmonic, out-of-phase; 3) slope of the thermal signal with respect to the number of cycles. These values typically show bilinear trends, allowing to define a breakup point and a corresponding stress which is the thermographic estimation of the fatigue limit. The paper presents and discusses the results of tests with different stress ratios, i.e. fully reversed cycling with R=-1 and tensile-tensile cycling with R=0.1.
Proper design of the receiver is vital to maximize the performance of solar parabolic dish concentrator. In this paper, an experimental study on the thermal performance of the conical cavity receiver ...with different aspect ratios for solar parabolic dish concentrator is presented. The receivers of aspect ratio 0.8, 1.0 and 1.2 are constructed for a given cone angle and tested in bright sunny days with average beam radiation above 600 W/m2. The energy efficiency, exergy efficiency and overall heat loss factor of the receivers were evaluated and compared. As expected, the receiver surface temperature got reduced with increase in aspect ratio. However the thermal performance is observed to decrease. The receiver with aspect ratio of 0.8 shown highest performance among all the receivers tested. It is revealed that reduction in receiver surface temperature alone is not adequate to improve the thermal performance, the surface area is also an influencing factor. Hence the aspect ratio of the receiver has a significant impact on the thermal performance and should be carefully chosen while designing the receiver. The results presented in this work are useful for further optimization of the receiver design.
•Cavity receiver with different aspect ratios are developed for dish concentrator.•Energy and exergy analyses were carried out experimentally.•Results show that aspect ratio has a significant impact on the receiver performance.
•A hull girder ultimate strength verification is made based on experimental results and the dimensional theory.•The result of the ultimate strength test of three box girders, is used to evaluate the ...ultimate strength.•The analysis maintains the first-order similarity between the model and real structures.
The objective of this work is to perform a hull girder ultimate strength verification according to the Class Society rules based on experimental results and the dimensional theory. The results of the ultimate strength test of three box girders, that may represent the behaviour of a mid-ship section of a ship, deteriorated in a real corrosive seawater environment representing different levels of corrosion degradation of ageing ship structures, is used to evaluate the ultimate strength. The analysis is based on a structural model, used in the experimental test, which maintains the first-order similarity between the model and real structures. The present analysis may be used to validate the global ultimate strength of ship hull structures in the phase of the new structural design or during the service life and to calibrate the new developed codes.
The experimental and computational analyses of a 500 m deep coaxial borehole heat exchanger system for geothermal power generation are studied in this paper. The experiments are carried out on a high ...temperature resourced well with an average thermal gradient of 0.38 °C/m. The experiment lasts 456 h, and the findings are described in terms of fluid inlet and outlet temperatures, subsurface temperature distribution profiles over time, and flowrate. The in-situ ground temperature distribution profile is measured using Distributed Temperature Sensing System for different hours of the experiment. A detailed, three-dimensional, unsteady-state, finite volume-based computational model has been developed, which solves conjugate fluid-flow and heat transfer phenomena. The simulation outcomes are compared to the results of the experiments. With validated numerical model, to determine the circle of influence, temperature profile of the ground is observed at various radial distances from the borehole. A parametric study is performed by varying inlet temperature of the fluid, mass flow rate, and the thermal conductivity of the ground. The numerical model developed also predicts the temperature recovery behavior of the ground. The results indicate that the average output thermal power for 456 h from the geothermal system ranges from 172 kW to 262 kW based on operating condition chosen and the total thermal energy generated changes between 82 MWh and 194 MWh from a single borehole. After the extraction is terminated, around 86% of the initial ground temperature is restored after 456 h.
•Field-test experiment was performed for 456 h in a fresh drilled well.•3D conjugate numerical model was developed and validated.•Parametric study was performed for different operating conditions.•Sensitivity analysis was conducted to study the degree of influence.•Temperature recovery period was predicted with the developed numerical model.
Combustion of hydrogen-enriched natural gas is a valuable short-term strategy for reducing CO2 emissions from high temperature industrial heating. This paper presents several experiments on ...combustion characteristics and the formation of nitrogen oxides. The experiments included hydrogen contents up to 100% and fuel heat inputs up to 75 kW. Water-cooled lances were used to influence the furnace temperature. The analysis includes the distribution of furnace temperatures, the composition of flue gas, the cooling capacity of the lances under steady-state operating conditions, and OH*-chemiluminescence imaging of the near burner region. The presented results demonstrate the dependence of furnace conditions and NOX formation on various factors, such as different air inlet fluxes, furnace temperature, and fuel composition, for constant heat inputs. Efficiency increased by up to 5.5% and significant changes in flame shaped along with a maximum increase in NOX emissions when comparing natural gas to hydrogen was measured at 167%.
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•Combustion of hydrogen-enriched natural gas with 0 to 100% H2•Experimental analysis of an industrial burner in a steady state, false air-free furnace.•Converged measurements for temperature, flue gas composition and cooling heat fluxes.•Dependence of NOX in mg/kWh on flame shape, temperature, fuel blend and air ratio.•Imaging of self-emitted OH*-chemiluminescence from turbulent jet flames.
•Pool boiling experiments were conducted to study the effect of pitch, width, and depth of parallel channels in bi-conductive surfaces.•The optimal channel pitch reduced the bubble departure diameter ...by about 21%.•Increasing the channel width up to the optimum value can cause thermal concentration and enhance heat transfer at low heat fluxes.•The highest value of HTC with 58% improvement was achieved in the lowest value of the channel depth.
Since pool boiling is widely used in many modern industries, the need to improve it has led to the development of new methods. One of the new methods studied much less so far, is creating bi-conductive surfaces. In our study, in three separate series, the effect of pitch, width, and depth of low-conductive channels are investigated. Copper samples were grooved by wire electrical discharge machining (WEDM) and filled with a mixture of epoxy and hydrophilic silica aerogel. Pool boiling experiments were conducted with deionized water at atmospheric pressure. In addition, the samples' images were obtained by scanning electron microscopy (SEM), and visualization of bubble formation was provided by a high-speed camera. According to the results, sample 4 with 2.5 mm channel pitch, 0.5 mm width, and 0.3 mm depth reached a heat flux of 103.9 W/cm2 and heat transfer coefficient (HTC) of 7.6 W/cm2 K. This shows 62 % and 58 % improvement respectively, compared to the plain surface. Channel pitch best selection resulted in 21 % reduction in bubble departure diameter. Increasing the channel width to an optimal value of 1.5 mm leads to thermal concentration and improving HTC up to 146 % in low heat fluxes. In depth variation series, the lowest value of 0.3 mm led to the best performance in improving heat transfer. The present study provides a good understanding of dimensional characteristics' impact of low-conductive channels on pool boiling heat transfer.
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Increasing energy need and running out of fossil-based fuels direct us to renewable energy resources. Although hydrogen is not an energy source by itself, it is an energy carrier with a high specific ...heat capacity. As it is used as fuel in unitized regenerative PEM fuel cells, water is separated in electrolyzer mode and stored by producing hydrogen when there is no need for energy. In this study, performance tests on the unitized regenerative PEM electrolyzer/fuel cell were carried out and numerical modelling has been performed. The validity of the developed model was confirmed by the results of the experimental study. Before starting the performance tests, the cell's leakproofness tests were carried out, and the appropriate torque force was optimized, reducing the contact resistance that causes performance loss. The material selection of the cell components and corrosion-resistant materials that can operate in both electrolyzer and fuel cell modes were preferred.
In this study, 0.019 slpm of hydrogen and 0.0095 slpm of oxygen gas is produced in the electrolyzer mode, while a power density of 0.353 W/cm2 is obtained in the fuel cell mode at 80 °C, from a unitized regenerative PEM fuel cell with a 5 cm2 active area, whose cell elements are combined with a 3 Nm clamping torque by using 12 bolts.
•Three dimensional two phase flow modelling of regenerative PEM FC was performed.•Working parameters of unitized regenerative PEM fuel cell were optimized.•The developed model was verified by comparing the experimental and numerical results.•An increase in cell performance was achieved for both modes.
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