Heat Input Ratio Research Articles

Combined effect of the magnetic field, orientation, and filling ratio on cylindrical pulsating heat pipe using distilled water and distilled water/Fe3O4 nanofluid

To investigate the effect of the magnetic field, a pulsating heat pipe was made in the shape of a cylinder and Fe3O4 nanoparticles (%0.1 wt) were used with the base fluid of distilled water as the working fluid. (Tetramethyl ammonium hydroxide) TMAH surfactant was used as a stabilizer. To investigate the effect of gravity on the performance of the pipe, the device was tested at different angles from zero to 90 degrees. In this research, the effect of different variables, including the type of working fluid (distilled water vs. nanofluid), filling ratio, slope, and amount of heat input to the evaporator (30–300 W), in two different states, once without the influence of the magnetic field and once again with the application of a magnetic field was investigated. The results of the tests showed that the performance of the device at 50 % filling ratio is better than 60 % filling ratio. The use of nanoparticles improved the performance of the device. Inclining the device increases the thermal resistance so that the device performs poorly in the horizontal mode in all modes except when it is under the influence of a magnetic field. The use of nanofluid as well as the application of a magnetic field makes the start-up time of the device decrease by 37 % and 30 %, respectively, compared to distilled water. The temperature of the start of fluctuations also decreases by 24 % and 32 %, respectively.

A Study on Gap Bridging Formation Conditions in Butt Root Pass Welding Using GTAW

GTA welding is a representative welding technique applied to root pass welding of piping. The pipe root pass welding significantly influences the determination of welding parameters owing to the root gap and step change occurring during installation. GTA welding has the advantage of being able to control current (A) and wire feeding speed (WFS) as independent variables; however, determining these variables is difficult. In this study, the change in the back bead height (Bbh) was observed by changing the root gap and WFS while the welding speed and welding current (A) were fixed. By fixing the welding speed and changing the welding current (A), root gap, and WFS, the gap bridging possible condition was expressed as a region. When the root gap changed from 0~1 mm and from 1~2 mm, the back bead height was greater than or equal to 0 mm. Possible welding current and WFS and the setting range of the welding heat input ratio (HIR) were presented.

Thermal performance improvement of a radial pulsating heat pipe with diverging channels by adopting Tesla valves at various heat fluxes

The thermal performance of a pulsating heat pipe (PHP) can be improved by increasing the flow circulation with the adoption of novel channel designs to minimize flow resistance. This study aimed to improve the thermal performance characteristics of a radial PHP with diverging channels by adopting Tesla valves. The effects of heat flux, condensation temperature, and heat transfer area ratio on the thermal resistance and heat transfer coefficient of the PHP with Tesla valves were measured under different heating and cooling conditions. In addition, the flow behaviors and pressure variations were analyzed for a short time frame. The PHP with Tesla valves exhibited a 17 %-lower thermal resistance than that without Tesla valves owing to the increased flow circulation with preferential movement in one direction. Furthermore, the heat transfer capability of the PHP with Tesla valves increased with increasing condensation temperature and heat transfer area ratio at the same heat flux. In addition, the optimal filling ratios were determined to be 70, 80, and 90 % for heat transfer area ratios of 0.13, 0.08, and 0.05, respectively. Finally, contour maps for the maximum temperature deviation were developed in terms of the heat flux, heat input, and heat transfer area ratio.

A Study on the Change of Wire Feeding Speed in GTA Welding (Ⅰ) - Changes in the Modes of Metal Transfer -

GTA welding (GTAW) is a representative welding technique employed for pipe root gap welding. Although this technique allows the control of the current and wire feeding speed as independent variables, it is difficult to determine these variables to ensure appropriate quality. In the pipe root gap welding task, the parameters of automated welding applications are difficult to determine due to gap and misalignment. Accordingly, this study was conducted to examine changes in the modes of metal transfer according to the welding current and wire feeding speed. In the various processes of GTAW, changes in volume transfer form yield certain advantages and disadvantages, necessitating appropriate tuning procedures to maintain a desired quality. Changes in heat input ratio (HIR), which relates to the welding heat input (HI) and wire feeding speed, were observed to predict modes of metal transfer. According to changes in welding current and wire feeding speed, metal transfer was expressed as an index, and a regression equation was formulated to predict the modes of metal transfer through said index.

A Study on the Change of Wire Feeding Speed in GTA Welding (Ⅱ) - Development of Weld Bead Shape Prediction Model -

Throughout the GTA welding (GTAW) process, bead width (Bw), bead height (Bh), penetration depth (Dp), and metal transfer modes change in accordance with welding current and wire feeding speed. Various processes employing GTAW include text marking welding systems that have bead width and bead height as the main management items, and some such processes require sufficiently complete penetration. It is judged that there will also be a metal transfer type advantageous for welding the first layer of the pipe root gap. Accordingly, a bead shape prediction model in GTAW has been proposed according to changes in welding current and wire feeding speed, wherein the bead shape change and metal transfer change interval are presented for the heat input ratio (HIR) change.

Experimental investigation on effect of external circulation system on preheating characteristics of pulverized coal

To explore whether self-preheating combustion systems ran steadily after loop seal failed, we comparatively investigated the influence of primary air ratio (λp) and extra heat input ratio (Cehi) on self-preheating of pulverized coal preheated in a 30 kW self-preheating burner with or without an external circulation (EC) system. For temperature distribution, lack of EC system greatly raised the temperature in the middle-lower part of the riser, and this temperature was more than 150 °C higher than that with the EC system. Moreover, extra heat input extended this influence throughout the riser. As λp and Cehi increased, the temperature in different positions always rose. For coal gas component and fuel component release, lack of EC system improved fuel composition conversion rates but reduced combustible gas yields. These two indexes increased simultaneously as λp and Cehi elevated properly, and there was an optimal λp with the EC system. Lack of EC system was inconducive to reducing particle size, improving specific surface area, promoting micro-pore generation on the surface and reducing graphitization extent, meaning the macrostructure and microstructure tended to be deteriorated in this condition. Nevertheless, the microstructure in this condition may be improved with extra heat input, and was even better than that with the EC system. The macrostructure and microstructure were improved as λp and Cehi increased properly, and there was an optimal λp with the EC system. The combustion reactivity of coal char was mainly influenced by the macrostructure, followed by the microstructure. Hence, absence of EC system tended to deteriorate it, and it was improved as λp and Cehi increased properly.

Characteristics of Laser-arc Hybrid Welding and the Effect of Heat Input Ratio on Welded Joint Performance

Characteristics of Laser-arc Hybrid Welding and the Effect of Heat Input Ratio on Welded Joint Performance

Penetration Estimation of GTAW with C-Type Filler by Net Heat Input Ratio

This study proposes a novel method to estimate the weld penetration in gas tungsten arc welding (GTAW) with filler metal. So far, there is no standard parameter available to accurately estimate penetration in GTAW with filler metal. Until now, the penetration could be estimated by heat input only in GTAW with and without filler metal. But in this study, it was revealed that the conventional heat input could not accurately estimate the penetration in GTAW with filler metal. Therefore, the new concept of net heat input ratio (NHIR), which is a ratio of net heat input to the bead cross-sectional area, was developed to accurately estimate the penetration in GTAW with filler metal. Using a C-type filler metal during GTAW, the NHIR was calculated for various welding conditions. The results showed that the NHIR was proportional to the welding current and voltage and inversely proportional to the welding speed and filler feed speed. Even though the NHIR was the same, the penetration increased as the welding current became higher. Four linear equations between NHIR and penetration were obtained from the experimental results for four levels of welding currents. By applying the concept of NHIR, the penetration could be estimated for any welding current.

Effect of Laser-Arc Heat Input Ratio on the Formation, Microstructure, and Properties of EH36 Steel with Laser-Metal Inert Gas Hybrid Welding

Effect of Laser-Arc Heat Input Ratio on the Formation, Microstructure, and Properties of EH36 Steel with Laser-Metal Inert Gas Hybrid Welding

Mechanisms of an innovative hybrid arc welding process in enhancing joint penetration and weld property control through resistive and induction heat

Low costs (material, energy and time), high joint properties are the eternal pursuit of modern welding. In this paper, mechanisms of an innovative high frequency electric cooperated arc welding (HFAW) in enhancing welding productivity (joint penetration) and weld property control were comprehensively investigated. The process properties and weld mechanisms of this method were systematically compared with that of the traditional GMAW welding under typical process parameters. The results showed that 4.8 mm joint with an large aspect ratio of 4 was achieved by single pass HFAW at a high welding speed (15 mm/s) and a low welding heat input (reduced 1/3 than the traditional GMAW). The research on weld property control shows that the microstructure of weld zone and heat affected zone (HAZ) in the HFAW joint was much smaller than that in the GMAW joint under optimal parameters. The width of each zone in the HAZ, thermal cycle parameters such as elevated temperature holding time and cooling rate can be regulated independently by the high frequency electric heat input ratio. Such regulation is of great significance for high strength steel welding, which needs to control the welding thermal cycle process accurately. Combined with three-dimensional solid reconstruction of liquid filler metal, the mechanism of the HFAW in enhancing joint penetration was demonstrated. An interesting “self-tracking heating” of the high frequency current was found. The cutting-edge of the liquid metal was violently heated and more than half of the weld in thickness direction was achieved by a novel ultra-speed “interfacial tension driving penetrating” weld forming mechanism, which promises the HFAW high welding speed and large aspect ratio on the premise of satisfactory welding quality.

Multi-mode analysis and comparison of four different carbon dioxide-based combined cooling and power cycles for the distributed energy system

To meet the diversified demand of power and cooling for the distributed energy system, this paper proposes two combined cooling and power (CCP) systems combining the supercritical carbon dioxide cycles with a carbon dioxide ejector refrigeration cycle, which can switch between full power mode (Mode-P), combined cooling and power mode (Mode-PR), and full refrigeration mode (Mode-R) according to the energy demands of users. In the proposed CCP systems, the recompression cycle and modified dual-stage compression cycle are used to replace the regenerative cycle and basic dual-stage compression cycle in two reference systems respectively. The mathematical models of systems are established and verified. Detailed parametric analysis is conducted to investigate the effects of key parameters on the performances of proposed systems and reference systems. Moreover, the modified systems and reference systems are optimized and compared at three modes. Multi-mode analysis is also applied to study the ability of the four CCP systems to convert power into cooling. Finally, detailed exergy analysis and thermoeconomic analysis are performed for the optimal system. The results show that the modified systems can achieve higher exergy efficiency by recovering partial waste heat before the pre-cooler. Under the refrigeration condition (the evaporation temperature is 0 ℃), the exergy efficiencies of the modified single-stage compression (M−S) system are 13.71% and 14.08% higher than those of the reference system at Mode-P and Mode-R, respectively. The cooling capacities of the systems at Mode-PR and Mode-R are positively correlated with their power outputs at Mode-P. The M−S system has the best multi-mode performance owing to its highest exergy efficiency (64.01%) at Mode-P, minimal energy loss at Mode-PR, and the maximum cooling capacity to heat input ratio (1.714 at 0 ℃ and 0.964 at −20 ℃) at Mode-R. Under the freezing condition (the evaporation temperature is −20 ℃), the single-stage compression systems generally perform better than the dual-stage compression systems. During the process of switching from Mode-P to Mode-R, the total product unit cost of the M−S system increases from 12.24 $·GJ−1 to 44.74 $·GJ−1 under the refrigeration condition and from 12.24 $·GJ−1 to 38.15 $·GJ−1 under the freezing condition.

Development of fed friction-stir (FFS) process for dissimilar nanocomposite welding between AA2024 aluminum alloy and polycarbonate (PC)

In this research, a new fed friction-stir (FFS) technology was implemented for dissimilar nanocomposite joining between AA2024 aluminum alloy and polycarbonate (PC) polymer with a T-joint design. Alumina (Al2O3) nanoparticles in the form of paste were injected through the stir zone (SZ) during dissimilar mixing of aluminum and polymer using the FFS system to strengthen the polymer side. The effects of processing parameters on the soundness and characteristics of dissimilar weldments were examined in terms of rotational tool speed (w = 1400−2100 r/min), traverse velocity (v = 25−55 mm/min), and reinforcement powder feeding. Stiff competition was found between w and v on controlling the weld nugget formation and its property. Increasing w and heat input ratio showed a beneficial influence on the materials flow and intermixing. Meanwhile, increasing v revealed detrimental impact by affecting the alumina powder feeding rate into the SZ. According to experiments, to attain a sound and defect-free dissimilar nanocomposite joint with superior mechanical property, the central processing parameters were optimized in the moderate range as w = 1750 r/min and v = 35 mm/min. A maximum tensile strength of ∼36 MPa and maximum flexural strength of ∼74 MPa were noted. Hence, the maximum joining efficiency was determined by ∼53 % and 93 % ratios of PC as the weakest part of dissimilar weldment during tensile and bending tests, respectively, with a failure behavior across the SZ.

Analysis and Characterization of the Weld Pool and Bead Geometry of Inconel 625 Super-TIG Welds

The welding market is changing globally, becoming eco-friendly, robotized and automated. The tungsten inert gas welding (TIG) process is indispensable in industries that require high-quality welds with the absence of spatter and fumes. However, the production rate of TIG welding is very low, which limits its many applications. The present study introduces a novel TIG welding method called super-TIG welding. Super-TIG welding is able to produce a high production rate of welds compared to other fusion welding methods. In super-TIG welding, the novel C-type filler is used, which is different from the conventional TIG welding of circular wire. The relations of the heat input ratio in super-TIG welding to weld pool length and weld bead geometry were measured using the Inconel 625 C-filler. Two types of deposition techniques were used for a bead-on-plate welds, such as stringer beads and oscillation beads. The weld pool and bead geometry measurements are found to be different between stringer beads and oscillation bead techniques. The length of the molten pool and bead size were higher for oscillation beads over the stringer beads. These changes were associated with the difference in heat transfer contact area and bead height.

Optimization of Welding Parameters for Small-Scale Resistance Spot Welding of Zirconium Alloys

This paper presents the results of optimization of parameters for resistance spot welding of parts made of E110 zirconium alloy with a thickness of 0.25 + 0.25 mm. Its purpose was to determine the influence of welding current profiles on nugget metal structure and mechanical properties of welds. The highest tensile strength comparable with base metal (380...440 MPa) was observed when the ratio of integral heat input to current pulse duration was about two. Formation of martensitic structure and coarsening of nugget metal was observed with larger ratios. A proper fusion zone was not formed with lower ratios. Annealing of welded joints at a pressure of ~ 10–4 Pa and a temperature of 580 °C for one hour was necessary to reduce residual stresses and transformation of metastable martensitic phase to a more stable state. This reduced microhardness of nugget metal by 30...35% and increased tensile strength of welds. It was also possible to increase tensile strength and reduce dispersion of its values by increasing duration of current down slope after formation of a nugget. An increase in duration from 1 to 14 ms caused rise in tensile strength by ~ 18% and dispersion of its values by ~ 3%.

A study on process development of super-TIG welding for 9% nickel steel with Alloy 625

The demands for liquefied natural gas and 9% nickel steel tanks for its storage have increased due to stricter regulations for ship emissions. In the present study, a super-TIG welding process was developed for the butt welding of 9% nickel steel by using Alloy 625 filler metal with a C-type cross-section. The mechanical properties of the welded specimens were compared with those of flux-cored arc welding, using Hastelloy and Alloy 600 filler metals in impact and tensile tests, while the structures were examined under an optical microscope. The newly developed super-TIG welding process was shown to have an effective heat input ratio, given that hot cracking does not occur.

A Study on Process Development of Deformation Reduction in TIG Overlay Welding

Overlay welding is a technique to obtain surface layer having a corrosion resistance or heat resistance. Because plant industry has developed, demand of overlay welding also increases. In the overlay welding, uninform heat cycle can cause a lot of welding deformation. Deformation of overlay welding has problems such as diminished dimensional accuracy and reduced product reliability. A lot of deformation is corrected in a number of ways. However, correction of deformation costs a lot of time and cost. Also correction of deformation requires skilled techniques. In addition, heat straightening produce a large amount of green-house gas and effect on global warming. In this study, the effect of welding process on the deformation was examined. The amount of deformation by the conventional TIG welding process and Super-TIG welding process was compared quantitatively. As a result, the amount of angular distortion was as follows: Conventional TIG > Super-TIG stringer bead > Super-TIG oscillation bead. It’s considered that the angular distortion by Super- TIG welding was small because heat input ratio of Super-TIG welding was low. Therefore, Super-TIG welding process has advantages in overlay welding because of low deformation and low dilution ratio. Key words: Angular distortion, TIG welding, Super-TIG welding, Overlay welding, Deformation, STS316L, Dilution ratio, Penetration

Effect of cold metal transfer and gas tungsten arc welding processes on the metallurgical and mechanical properties of Inconel® 625 weldings

Inconel® 625 weld metal has lower mechanical properties than its corresponding annealed base metal due to the precipitation of brittle phases during solidification. To control the precipitation of these phases, a reduction in heat input and amount of iron and silicon in the weld metal and an increase in the cooling rate are proposed. Cold metal transfer (CMT)–gas metal arc welding (GMAW) is a process that digitally controls filler metal transfer to the weld, which reduces the heat input and dilution ratio. In this work, weldments of 2-mm-thick Alloy 625 sheets were prepared using CMT and gas tungsten arc welding (GTAW) process to compare the mechanical properties (tensile and stress-controlled fatigue life tests) of the welded joints. An increment in the tensile properties and fatigue life of CMT welds was found when compared with the GTAW welds. Microstructure characterization, grain size in the heat-affected zone, phase content in the weld metal, secondary arm spacing, and Vickers hardness measurements were performed to establish the causes of the observed differences. This result was a consequence of the lower dilution of the base metal and amount of particles in the weld metal produced by a lower heat input supplied by CMT.

Adaptive Resistance Spot Welding Process that Reduces the Shunting Effect for Automotive High-Strength Steels

Although short-pitch resistance spot welding (RSW) significantly increases vehicle body strength, its application has been limited because of the associated shunting effect. In this study, a reference-based adaptive RSW process intended to minimize the shunting effect was proposed, and a related RSW system that controls welding current and power was developed to implement the adaptive method. The proposed RSW method compensates for the heat input loss caused by the shunting effect based on the estimated weld pitch and reference data obtained under suitable welding conditions. An exponential model was developed using a unique indicator (i.e., the ratio of the adaptive welding heat input to the reference welding heat input until the reference welding power curve peak) to estimate the weld pitch. A logistic growth model was next developed based on the relationship of the nugget diameter, heat input, and weld pitch to estimate the heat input compensation. A unique strategy using power control with a modified reference power curve was applied to supply the calculated heat input compensation. The experimental results intended to validate the proposed adaptive RSW process indicated that the proposed process effectively reduced the shunting effect and produced an improved nugget shape relative to the conventional RSW process.

Combined effects of MIG and TIG arcs on weld appearance and interface properties in Al/steel double-sided butt welding-brazing

AA5052 aluminum alloy and Q235 low-carbon steel of 3.0mm thickness were butt joined without groove. The combined effects of the MIG-TIG double-sided arc on the weld appearance and interface properties were investigated in three aspects: weld appearance, interfacial properties and joint tensile strength. Form efficiency was defined to evaluate the quality of the weld appearance. The strength of the whole joint and the brazed interface were examined in the tensile tests of joints with and without excess weld metal, respectively. The weld appearance can be well characterized by the form efficiency. The form efficiency is found to be most sensitive to TIG current. Sensibility of the form efficiency to MIG voltage and welding speed is relatively low, indicating that the TIG arc at the back of the weld is the key factor for the double-sided weld appearance. Double-sided weld appearance can be achieved at a maximum welding speed of 2.2cm/s because a part of welding energy is input by TIG arc directly to the back weld. The interfacial properties of the joints are closely tied to the heat input ratio of MIG and TIG. Proper input ratio (1.35–1.64) leads to uniform deformation of the base metals and suppresses the initiation of the cracks in interfacial IMC layer. The differences between the interfacial strength and the whole joint strength indicate that the optimum weld appearance with desirable excess weld metal provides extra 20MPa strength for the whole joint. Benefitting from combined effects of the best weld appearance and toughest interfacial IMC layer, the highest tensile strength of the joint exceeds 70% the tensile strength of 5052 alloy.

Influence of heat input and radius to pipe thickness ratio on the residual stresses in circumferential arc welded pipes of API X46 steels

The present work aims to study residual stresses caused by circumferentially welding of two similar API X46 steel pipes by means of finite element modeling. Considering the metallurgical phase transformations and through thermal-mechanical uncoupled analysis, the 3D modeling was carried out by SYSWELD software. Materialistic thermal and mechanical properties of all phases were defined in terms of temperature as well as phase transformation properties. Residual stress was measured through hole-drilling method. The obtained results were used to verify the finite element model. By means of full factorial experiment designing method, effects of heat input and radius to pipe thickness ratio on maximum values of hoop and axial residual stresses were investigated. The effect of each factor was studied in 3 levels and by 9 experiments. Results of statistical analysis revealed that increase in heat input and radius-thickness ratio would lead to higher values of maximum hoop and axial residual stresses. However, interactions of high level of heat input and a low level of radius-thickness ratio increased inter-pass temperature and consequently caused a sudden raise in maximum values of residual stresses.