A thermal efficiency analysis of a Gas Tungsten Arch Welding process using a temperature moving sensor

AISI 316 stainless steel (SS316) is an attractive material for industrial applications. Welding of this alloy can lead to severe distortion that often results in dimensional inaccuracies. With the help of specially designed fixture and clamping mandrels, tungsten inert gas (TIG) welding on SS316 pipes is employed to investigate the effect of liquid nitrogen on the circumferential distortion, weld penetration and delta-ferrite distribution in different welding zones. The experimental results reveal that the presence of trailing heat sink in TIG welded butt joint has almost zero distortion at a distance of 30 mm from the weld centerline and 64% decrement in residual circumferential distortion at the center of the weld bead. A metallurgical microscope is used to find the weld penetration, (fusion zone) FZ and (heat affected zone) HAZ. The results illustrate that increase in current and the presence of intensive cooling media yield deeper penetration in TIG welding. Liquid nitrogen (LN2) also constricts the FZ and HAZ. Instead of evaluating delta-ferrite contents using the ferrite number technique, a MATLAB® code for image processing is developed to evaluate the delta-ferrite distribution in the different regions of a single-pass weldment. Delta-ferrite contents are maximum in the presence of intensive cooling media near HAZ and increase with an increase in the current value. Hence, TIG welding with LN2 as trailing heat sink is the most suitable scheme to weld industrial pipes owing to its higher weld penetration, higher delta-ferrite contents and minimum circumferential distortion.

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Influence of liquid nitrogen on residual circumferential distortion, weld penetration and delta-ferrite distribution in clamped tungsten inert gas welded butt joint of 316 stainless steel

This work presents a global model to determine the time dependent thermal efficiency in a GTAW process. With the purpose of estimating the amount of heat delivered by the GTAW torch, a previously developed homemade C++ code was improved. The new model proposes the heat flux estimation through the Golden Section optimization with Temperature Moving Sensor technique. An innovative methodology based on Time Traveling concept is proposed to regularize the Golden Section technique. In order to test the capacity of the model to adapt to a range of conditions, a set of lab-controlled experiments were performed under different welding conditions based on a Robust Project matrix (Taguchi). The objective function was determined based on to the fourth power between the experimental and the calculated values. Moreover, the work also presents an analysis of the cooling rate of the process by convection and radiation. An empirical correlation based on the local Nusselt number for flat plates was used to estimate the local heat transfer coefficient. The proposed model proved to be a first-class method to determine the thermal efficiency in a welding process.

A thermal efficiency analisys of gtaw process in stainless steel

Abstract In this paper, the Jaya algorithm is coupled with the traditional conjugate gradient method (CGM) for solving the inverse heat transfer problem. The coupling of two algorithms is termed as enhanced conjugate gradient method (ECGM). Two different applications have been considered to determine the accuracy and stability of ECGM. First, the algorithm is applied in a steady-state two-dimensional laminar flow through a duct for the boundary heat flux estimation. The accuracy of estimation has been compared with traditional CGM by calculating the root mean square (RMS) error. The ECGM algorithm (RMS =0.142 kW/m2) is found to be more accurate than conventional CGM (RMS = 0.198 kW/m2). ECGM is then applied to determine the peripheral variation of heat flux at the fluid-solid interface of a tube at a section downstream to the T-junction. The experimental temperature readings at the outer periphery of the tube required in the inverse algorithm are simulated by solving the direct heat conduction problem. Here, the heat flux at the fluid-solid interface is obtained by solving the governing equations of the turbulent flow by using commercial computational fluid dynamics software. ECGM is found to be a stable and accurate inverse heat transfer algorithm.

Enhanced Conjugate Gradient Method for Heat Flux Estimation in Laminar and T-Junction Turbulent Mixing Flow

Film transfer coefficient is one of the most challenging variables to measure in experimental heat transfer. This happens because such a variable depends on too many others. Examples include type of media (gas or liquid), body geometry, fluid flow, thermal conductivity, and many more thermodynamic properties. In chapter proposes an estimation strategy for the film transfer coefficient by solving an inverse heat transfer problem via the Cuckoo Search global optimization algorithm. The designs were achieved through the entropy generation minimization criterion, also powered by Cuckoo Search, employing several specifications (material, working fluid and heat power). Obtained results show great estimations for signal-to-noise ratios above 30 dB, which can be reached with virtually any modern temperature sensors.

Assessing Film Coefficients of Microchannel Heat Sinks via Cuckoo Search Algorithm

Welding induces distortions and stresses in welded structures. A heat sink trailing the weld arc is one among the methods used to reduce the stresses and distortions. Researchers have made use of cooling agents like atomized water and liquid nitrogen (LN2) jet as trailing heat sinks. As the inclusion of a heat sink alters the temperature distribution, estimation of heat removal due to cooling jet is a prerequisite for the study of the effects of the heat sink on stresses and distortions. Analytical methods for the estimation of heat transfer parameters are complicated due to nonuniform cooling by the impinging jet, boiling heat transfer of cooling jet, stray fluid particles on the work-piece surface, and the sharp localized temperature gradient on the work piece due to weld heat input. Therefore, an inverse heat transfer (IHT) method is adapted to estimate the heat transfer parameters due to heat sink. Experiments were conducted using automated tungsten inert gas welding apparatus on a low-carbon steel wo...

Nagalla Siva Prasad

Papers

Comparative Study of Heat Transfer Parameter Estimation Using Inverse Heat Transfer Models of a Trailing Liquid Nitrogen Jet in Welding