Constant Heat Input Research Articles

Active Vibration Avoidance Method for Variable Speed Welding in Robotic Friction Stir Welding Based on Constant Heat Input.

Robotic Friction Stir Welding (RFSW) technology integrates the advantages of friction stir welding and industrial robots, finding extensive applications and research in aerospace, shipbuilding, and new energy vehicles. However, the high-speed rotational process of friction stir welding combined with the low stiffness characteristics of serial industrial robots inevitably introduces vibrations during the welding process. This paper investigates the vibration patterns and impacts during the RFSW process and proposes an active vibration avoidance control method for variable speed welding based on constant heat input. This method utilizes a vibration feedback strategy that adjusts the spindle speed actively if the end-effector's vibration exceeds a threshold, thereby avoiding the modal frequencies of the robot at its current pose. Concurrently, it calculates and adjusts the welding speed of the robot according to the thermal equilibrium equation to maintain constant heat input. A simplified dynamic model of the RFSW robot was established, and the feasibility of this method was validated through simulation experiments. This study fills the gap in vibration analysis of RFSW and provides new insights into control strategies and process optimization for robotic friction stir welding.

Mechanical and micro-structural studies of pulsed and constant current TIG weldments of super duplex stainless steels and Austenitic stainless steels

Abstract In the present research work, the influence of heat input rates on microstructures, hot tensile properties, and weld surface hardness number of Super Duplex Stainless Steel 2507 super duplex steels and austenitic steels 316L plates were investigated. Pulsed current and constant current modes were used in Tungsten Inert Gas (TIG) welding to join the dissimilar metals using ER2205 as filler. Microstructural studies were revealed at different zones of pulsed and constant current TIG weldments using optical microscopy. The tensile test was conducted at two different temperature conditions (i.e., 27 and 350°C) to investigate the strength of dissimilar weldments. Hardness measurements were made on the weld surface along the transverse direction using Vicker’s hardness tester. The microstructures revealed the formation of inter-granular austenite at the fusion zone with grain boundaries with austenite structures. Due to the constant heat input, a significant microstructural development with high austenite fractions was observed in constant current (CC)-TIG weldment. In comparison to CC-TIG weldments (UTS at 27°C = 600 MPa UTS at 350°C = 456 MPa), higher tensile characteristics were noted in Pulsed Current (PC)-TIG weldments (UTS at 27°C = 695 MPa UTS at 350°C = 475 MPa). The UTS of PC-TIG weldment is improved by 15.8% when compared to CC-TIG weldment due to the controlled heat input rates. PC-TIG weldments exhibited improved hardness numbers in various zones with smaller HAZ widths than CC-TIG weldments.

Assessing the impact of CH[formula omitted]/H[formula omitted] blends on the thermodynamic performance of aero-derivative gas turbine CHP configurations

To attain a net zero-carbon emissions energy system, the grid needs dispatchable and flexible power production capable of responding to wind and solar energy variability. Hydrogen-fired gas turbines could play a role in meeting this requirement in the electricity grid; however, research and development are needed to assess the impact of the fuel change on these systems. This study aims to determine the effect of fuel switching on the cycle performance of a typical aero-derivative gas turbine, ranging from 25-35MW when combined with various steam-based bottoming cycles using Aspen Plus thermodynamic simulations. The gas turbine cycle’s efficiency and net output power increased by about 2.26% and 5.24%, respectively, when fueled with hydrogen for the constant TIT control strategy compared with the base case. The other two control strategies—constant TOT and heat input—are also positive. The performance of the combined heat and power configurations, expressed by the fuel charged to power, is better for almost all the hydrogen-fired cases compared with the methane case. This implies that using hydrogen as fuel in the gas turbine and duct-firing requires less fuel to produce heat and electricity. Although hydrogen integration into the overall system may pose challenges with auxiliary equipment, storage, supply, and combustion, hydrogen as fuel shows promise in improving the performance of gas turbine combined heat and power units.

Experimental investigation of hydrogen enriched natural gas combustion with a focus on nitrogen oxide formation on a semi-industrial scale

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%.

Improving the performance of heat sinks through the integration of fins and the utilization of graphene-mixed latent heat energy storage

Effective thermal management is significant to ensure the safety of all operating systems. However, these systems demand innovative thermal management technology. A heat sink with improved thermal conductivity is one of the passive heat management techniques. This study focuses on enhancing thermal management in devices by evaluating the performance of a heat sink with and without fins integrated with high thermal conductivity graphene-incorporated phase change material. Paraffin wax with a melting temperature of 58 °C was used as the phase change material. The study examines how the addition of graphene nanoparticles improves heat transfer capacity and extends the heat sink's working duration. The findings revealed that the phase change material extends the heat sink's working duration while adding nanoparticles improves performance. The performance of the phase change material and mixture of the nanoparticles was examined using a finned heat sink under constant heat input. The heating and cooling cycle of the heat sink was examined. The performance of the heat sink with fins and nano PCM was increased by 30 % compared to the baseline heat sink at 15 W heat input. This performance was increased to 45 % when the heat input changed to 30 W. The results indicated that nanoparticles in the phase change material augment the heat sink's recovery time, irrespective of the influence of fins.

Hydrogen combustion in two-stage high-pressure gas turbine—thermal and flow simulations for performance comparison with fossil fuels

Hydrogen energy forms an attractive solution for reducing greenhouse gas emissions from gas turbine systems. Although hydrogen combustion has been widely studied for combustors, only a few studies have considered the combustion effect downstream of the combustor. This study conducted an integral simulation of the combustion and flow of a GE-E3 aero-engine under hydrogen fuel and compared its performance with that of representative fossil fuels such as Jet A in an aero-engine and methane in an industrial gas turbine. All simulations were conducted under a constant heat input at the combustor and turbine inlet temperatures. During combustion simulation, the HyChem mechanism was applied to evaluate the composition of the products in an equilibrium model. Specifically, Reynolds-averaged Navier–Stokes steady simulation of a two-stage high-pressure gas turbine was conducted using the calculated boundary condition from the combustion simulation and k − ω shear stress transport γ turbulence model. The results revealed the high velocity of the hydrogen combustion flue gas owing to its low density under a large pressure difference. Overall, the power output, thermal efficiency, and fuel consumption were improved by hydrogen combustion. The thermal and flow results of the simulation can be used to develop hydrogen gas turbines.

Experimental study on heat transfer and storage of a heating system coupled with solar flat heat pipe and phase change material unit

Using renewable energy, especially solar energy, is essential to achieve a low-carbon society. PCMs suffer from low thermal conductivity, which hinders the efficiency of phase change thermal storage systems. Heat pipes exhibit vastly superior thermal conductivity, making them a promising candidate for enhancing PCM-based systems. To solve the contradiction between building insulation and importing solar energy into buildings in winter, this study proposes a new building heating ceiling system consisting of a flat-plate heat pipe (FHP) coordinated with a phase change material (PCM), and establishes a platform for a heat stockpiling device integrating the FHP and PCM. This research investigates the impact of heating power and bending angle on the heat transfer efficiency of the heat pipe and phase change heat storage system. The experimental findings demonstrate a direct relationship between increasing heating power and the enhancement of the FHP's heat transfer efficiency. When the FHP is bent at a 5° angle and heating power is increased from 20 W to 80 W, to store heat energy into the PCM cavities, the effective thermal conductivity rises significantly, escalating from 7.26 × 104 W/(m·°C) to 15.1 × 104 W/(m·°C), marking a remarkable 108 % rise. Moreover, although increasing the bending angle leads to heightened effective thermal conductivity of the FHP under constant heat input, and the heat transfer in PCM cavities will be weakened within a bending angle of 15°, experimental results demonstrate that the melting time of PCM still decreases with the increase of bending angle; the heat transfer inertia of phase change materials is dominant.

The effect of different laser head angles and shielding gas supply systems to maximize the depth of penetration by minimizing the plasma shielding effect in fiber laser welding of 3-mm thick NiTinol sheet

Bead-on-plate laser welding of 3 mm thick NiTinol sheet was tried with the help of 2.3 kW Yb:Fiber laser. It was found that the laser power was insufficient to get the full penetration with narrow weld-bead by varying the scan speed when shielding gas was provided from the side of the bead and the laser head was kept perpendicular to the plate. It was observed that when gas was supplied from the top of the plate and moving with the laser head, fully penetrated bead was obtained at much lesser value of heat input (P/v) because of the reduction of length of plasma plume. It was also detected that with increase in rotation of laser head angle the depth of penetration and laser bead width decreases because of the increase in laser spot area, reduction of laser intensity and increase in length of plasma plume. The increase in length of plasma plume increased the plasma shielding effect and reduced the absorptivity of the laser in the NiTinol sheet. According to the study, the maximum depth of penetration at a constant laser heat input was obtained for minimum value of plasma plume length and maximum value of laser intensity.

Flow and heat transfer characteristics of natural convection in hydrothermal reactor with segmented heating

Hydrothermal reactor is very suitable to utilize low-grade heat especially concentrated solar energy. However, the heat flux generated by solar heating is usually non-uniform, which affects the natural convection inside the reactor. In this work, natural convection of near critical water in cylindrical hydrothermal reactor is investigated by numerical simulation. With constant total heat input into the cylinder, the sidewall is divided into two halves with different heat flux density. The effect of heating schemes and physical properties on flow structure, temperature distribution, fluid motion and wall heat transfer are analyzed. It is found that natural convection is dominated by a large vortex with high velocity when heat flux ratio is lower than 1, and is dominated by two independent weak vortices when heat flux ratio is higher than 1. In addition, the former case has more uniform vertical temperature distribution, stronger fluid flow and weaker wall heat transfer, while the latter case is in the opposite. When the temperature approaches the pseudocritical point, the flow structure remains qualitatively unchanged, but wall heat transfer is enhanced and fluid motion is generally weakened. The change of heat flux ratio significantly regulates fluid motion but slightly affects wall heat transfer. Besides, the regulating effect of heat flux ratio is weakened in near critical region.

Heat transfer from a constant heat source to the plate surface: An analytical solution

This paper proposes an analytical solution to the thermoelasticity problem for a plate heated by a source with a constant heat input on one surface. Numerous comparisons were made between the results obtained on the basis of the analytical solution and the numerical one. When comparing the analytical and numerical solutions, it was shown that the advantage of the analytical solution is that it makes it possible to determine the greatest stress values over the entire heating time range, while using the numerical method it is necessary to perform a large number of calculations at fixed time values. However, the finite-element method allows for determining stresses in areas of the plate that are far from its centre, where the analytical solution proves to be unfair. Key words: , , , .

Design, 3E scrutiny, and multi-criteria optimization of a trigeneration plant centered on geothermal and solar energy, using PTC and flash binary cycle

A hybrid solar-geothermal power plant for electricity, heating, and cooling is provided in this paper. A flash-binary geothermal cycle, parabolic trough solar collectors, auxiliary heater, single effect LiBr-water absorption chiller, and heat exchangers are all part of the planned integrated power plant. The plant provides steady electrical power as well as the necessary heating and cooling for the yeast industry. The solar-geothermal power plant's energetic and exergetic efficiencies for the proposed system under steady-state conditions with constant irradiation are 10.78 percent and 23.1 percent, respectively. The auxiliary heater is found to function in 85 percent of the year due to the inability of solar energy to increase the fluid temperature to the necessary amount throughout several periods of the year. The impacts of different performance factors on the system's exergetic efficiency and overall cost rate are also evaluated using parametric analysis. It was discovered that parameters such as the flash separator's inlet pressure and temperature, the pinch point temperature difference in the heat recovery steam generator (HRSG), and the geofluid outlet temperature in the heat exchanger 1 (HX1) have a significant impact on the system's exergetic efficiency and total cost rate. Furthermore, the effect of variations in sunbeam irradiance on assessment parameters is examined. In constant heat input to the cycle, increasing beam irradiance results in increased total exergy efficiency and a lower overall cost rate of the system. By raising the sunbeam irradiance, the proportion of the auxiliary heater in the plant's energy supply and the mass flow rate of the fuel would be reduced. Also, the optimization findings show that the exergy efficiency of 33.8 percent might be attained under ideal operating circumstances.

Study the thermal management of Li-ion batteries using looped heat pipes with different nanofluids

The production of electric vehicles and their accessories is grooming day by day in the automotive industry. The heart of these electric vehicles is the power source, which is known as batteries. The capacity and performance of such batteries demand a high rating, due to the customer's need and improved vehicle features. Unfortunately, the batteries are facing thermal failures caused by the poor thermal management approach. Li-ion batteries are the most familiar ones which have a very high energy density compared to others. But, these batteries lead to the breakdown of ions and lithium plating because of the fluctuation in temperature distribution and fast charging characteristics. The temperature distribution varies with respect to loading and application. However, this process is accompanied by thermal runaway, which may result in the fatal destruction of batteries. To overcome such issues, the present work selected looped heat pipes (LHP) as a device to transfer the excessive temperature on batteries using nanofluids. Water, Ethylene glycol and acetone were selected as working fluids along with graphene oxide (GO) Nanoparticles. The experiment is conducted for a constant heat input of 30W and various filling ratios (20%, 35%, 50%, 65%). Stability, thermal conductivity, thermal resistance and temperature distributions are discussed. The experiment results are validated with Computational fluid dynamics.

Towards a Uniform Welding Quality: A Novel Weaving Welding Control Algorithm Based on Constant Heat Input.

The weaving welding process is a key method used to improve the welding quality in multi-layer and multi-pass welding processes using robots. However, the heat-input fluctuation in the weaving welding process restricts its development. In this paper, we developed a novel weaving welding control algorithm to maintain a constant weld heat input through velocity adaptive planning. First, the heat consumption during the weaving welding was modeled to describe the influence of weaving parameters on the weld heat input. Then, based on the obtained relationship between the weld heat input and the weaving parameters, a velocity-adaptive trajectory planning strategy was proposed by leveraging the transformation matrix derived from the relationship between the workpiece and the robot co-ordinate systems. The simulation and experimental results show that the proposed strategy can compensate for the weaving parameters to maintain a constant heat input based on heat consumption and improve the quality of the robotic multi-layer and multi-pass welding process.

The Effect of Heat Source Path on Thermal Evolution during Electro-Gas Welding of Thick Steel Plates.

In recent years, the shipbuilding industry has experienced a growing demand for tighter control and higher strength requirements in thick steel plate welding. Electro-gas welding (EGW) is a high heat input welding method, widely used to improve the welding efficiency of thick plates. Modelling the EGW process of thick steel plates has been challenging due to difficulties in accurately depicting the heat source path movement. An EGW experiment on 30 mm thickness E36 steel plates was conducted in this study. A semi-ellipsoid heat source model was implemented, and its movement was mathematically expressed using linear, sinusoidal, or oscillate-stop paths. The geometry of welding joints, process variables, and steel composition are taken from industrial scale experiments. The resulting thermal evolutions across all heat source-path approaches were verified against experimental observations. Practical industrial recommendations are provided and discussed in terms of the fusion quality for E36 steel plates with a heat input of 157 kJ/cm. It was found that the oscillate-stop heat path predicts thermal profile more accurately than the sinusoidal function and linear heat path for EGW welding of 30 mm thickness and above. The linear heat path approach is recommended for E36 steel plate thickness up to 20 mm, whereas maximum thickness up to 30 mm is appropriate for sinusoidal path, and maximum thickness up to 35 mm is appropriate for oscillate-stop path in EGW welding, assuming constant heat input.

Distributed Thermal Response Multi-Source Modeling to Evaluate Heterogeneous Subsurface Properties.

A thorough assessment of thermal properties in heterogeneous subsurface is necessary in design of low-temperature borehole heat exchangers (BHEs). A distributed thermal response test (DTRT), which combines distributed temperature sensing (DTS) with a conventional thermal response test (TRT), was conducted in a U-bend geothermal loop installed in an open borehole at the University of Illinois at Urbana-Champaign to estimate thermal properties by analyzing the thermal response of different geologic materials while applying a constant heat input rate. Fiber-optic cables in the DTRT were deployed both inside the U-bend geothermal loop and in the center of the borehole to improve the accuracy of calculated heat-loss rates and borehole temperature profile measurements. To assess the subsurface thermal conductivity during the heating phase of the DTRT, a single-source model and a multi-source model, both based on the infinite line source method, were developed using the borehole temperature data and temperatures inside and along the outside of the loop, separately. The two models returned similar thermal conductivity values. The multi-source modeling has the advantage of predicting the thermal conductivity of heterogeneous geologic materials from borehole temperature profiles during the DTRT heating phase. In addition, based on the distributed thermal conductivity measured in the borehole, estimates were made for both radial thermal impacts and the rate of heat loss in the BHE.

Turbulent Flow in Forced Convection Heat Transfer - Numerical Validation

Forced convective heat transfer of airflow through circular pipe with constant heat input and different free stream velocities is numerically validated. The significance of the present work is that the suction flow has been employed in the forced convection set up domain kept in the wind tunnel. From first law of thermodynamics and applying the energy balance equation, experimental heat transfer coefficient is determined. Further correlations are used to validate the experimental results. Although correlations provide reasonable estimates from the point of feasibility and accuracy, computational methods are used to estimate the convective heat transfer coefficient. Hence in this paper experimental, theoretical and computational analysis is carried out. The results reveal that the numerical validation is an effective tool from the point of feasibility and accuracy to determine the convective heat transfer coefficient.

Fluid flow analysis in a closed loop pulsating heat pipe-simulation study

Thermal Management is needed very much in modern day electronics as there is complexity in the systems leading to rapid thermal management requirement. Cooling technology is the main solution for reducing heat dissipation rates. Pulsating heat pipe which consists of an heated section evaporator, cooling section condenser and an adiabatic section is one of the promising two phase heat transfer devices in the present day scenario. In the present paper a simulation study model has been modelled to analyze the distribution of fluid flow in the pipe and also the temperature variation from evaporator to condenser. A multi turn Closed loop Pulsating pipe operating with different working fluids at different fill ratios has been selected. The design consists of copper capillary tube of 2 mm and 3 mm inner and outer diameters respectively and a length of 264 mm. The liquid slugs and vapor bubbles will be observed along with the temperatures in the evaporator and condenser sections of CLPHP working with base fluids viz… water, methanol and ethanol at volume fill ratios of 50%, 60% and 75%. with a constant heat Input of 60 W. The performance parameter thermal resistance has been calculated from the difference of average temperatures for a given heat input. The temperature, thermal resistance and fill ratio graphs are drawn for comparative study of CLPHP working at different conditions for working fluids considered.

Comparative Study of Rankine Cycle Power Generation using Water and Organic Fluids in Saturated and Superheated States

The Rankine cycle is an electricity generation system that uses water or organic fluids as high-grade or low-grade heat sources, respectively. In this paper, we present the results of our study of Rankine-cycle power generation in which we compared water and organic fluids (toluene and n-nonane) as working fluids in saturated and superheated states. We analyzed the energy and exergy of the Rankine cycle in a saturated vapor state at 300 °C and superheated states at 400 °C and 500 °C (the pressure remained the same as that at 300 °C), and assumed a constant heat input for all states. In the energy analysis, we determined the mass flow rate, heat rejection, work input of the pump, work generated by the turbine, net work output, and thermal efficiency. In the exergy analysis, we determined the exergy input, exergy loss, exergy destruction at the pump and the turbine, and the exergetic efficiency. The results show that water, categorized as a wet fluid, obtains a better performance with respect to both analyses in saturated and superheated states than toluene and n-nonane, which are categorized as isentropic and dry fluids, respectively. The water realizes a higher performance in the superheated than in the saturated state, whereas the performances of toluene and n-nonane are poorer in the superheated than in the saturated state.

Comprehensive theoretical framework for the analysis of microgap thermionic energy conversion under constant heat inputs

We present a comprehensive model to fully characterize the behavior of thermionic energy conversion devices subject to constant heat flux inputs. Thermionic energy converters (TECs) have recently gained enormous attention mainly due to technological advances enabling the fabrication of converters with micro/nanometer interelectrode gaps. The reduced gap appeared to solve the long-lasting issue of negative space-charge build-up within TECs. However, the decrease in gap distance leads to the appearance of new physics in the energy interactions between the two electrodes, such as the image-charge effect and near-field thermal radiation. The intertwined energy exchange mechanisms require a deeper look and a systematic approach for accurately modeling the performance of TECs in the micro/nanoscales, especially in practical applications where the device is exposed to external energy sources such as concentrated solar power. We conducted a steady-state energy balance analysis to calculate the operating temperatures of the electrodes by considering constant heat flux inputs (such as concentrated solar energy) to the emitter and various cooling rates of the collector. The potential barrier profile within the interelectrode gap, the net current density, and the power output are subsequently calculated for a TEC with electrodes made of tungsten with and without electron reflection. The optimal values of the gap distance are also reported for various input scenarios revealing considerable deviation from the previously reported ones. An overall efficiency of 38.3% with a power output of 19.2 kW/m2 can be reached for a TEC with perfectly absorbing electrodes at the gap distance of 6μm operating under a heat flux input of 50 kW/m2 and convective heat transfer coefficient of 500 W/m2K. We believe that the present work provides an unabridged framework for the rigorous analysis of thermionic power generation with (sub) micrometer interelectrode distances and offers substantial insight into the design and characterization of TECs.

Development and experimental investigation of a novel solar-powered cooling system

The development of novel and improvement of existing technologies for utilising solar thermal energy for cooling purposes traditionally attracts increased attention in both industry and academia. This work presents the development of a novel cooling system with a simple design and direct utilisation of solar thermal energy. The cooling system combines a liquid piston engine and cooling machine and is driven by an evacuated tube solar collector. A prototype of such the system was designed, built and tested in laboratory conditions using a solar radiation simulator. Variations in pressures, temperatures, and the fluid piston oscillation amplitudes in the system during its operation were recorded, and the indicated power of the engine and cooling capacity of the system were determined for a range of operation and design parameters. For the heat input range of 700–900 W and the constant temperature of the cooling water equal to 26.0 °C, the engine indicated power and cooling capacity of the system varied in the range of 70.0–88.0 and 51.0–61.0 W. The corresponding indicated efficiency of the engine and cooling system were in the range of 10.0–9.7 and 7.2–6.7%. The temperature in the cooling chamber was registered in the range of 20.0–18.2 °C at an ambient temperature of 24.0 °C. The COP of the cooling machine decreased from 0.71 to 0.69. The system performance improved in tests with a constant heat input (700 W) and reducing cooling water temperature. For cooling water temperature reduction from 26.0 to 18.0 °C, the engine indicated power and cooling capacity of the system varied in the range of 70.0–111.9 and 51.0–72.0 W. The corresponding indicated efficiency of the engine and cooling system were in the range of 10.0–16.0 and 7.2–10.3%. The COP of the cooling machine decreased from 0.71 to 0.64. The temperature in the cooling chamber was registered in the range of 20.0–14.4 °C at an ambient temperature of 24.0 °C. Experimental results obtained using the system's initial design demonstrate that the engine has efficiency comparable to low-temperature steam and Organic Rankine Cycle turbines. The Coefficient of Performance of the system is similar to that of single-stage absorption chillers.