Josip Župan

The sorption of sulfamethazine on soil samples: Isotherms and error analysis

In this paper, batch sorption of sulfamethazine on eight soil samples (six from Croatia and two from Bosnia and Hercegovina) with different organic matter contents ranging from 1.52 to 12.8% was investigated. The effects of various parameters such as agitation time, initial concentration, and ionic strength on the sulfamethazine sorption were studied. The experimental data were analysed using a one-parameter model, Linear isotherm, and two two-parameter models, the Freundlich and Dubinin-Radushkevich isotherms. The goodness of fit was measured using the linear regression and the determination coefficient (R(2)) value. Also, the equilibrium data of the two-parameter models were analysed using the residual root mean square error (RMSE), the sum of squares of errors (ERRSQ), and a composite fractional error function (HYBRID). Non-linear regression has better characteristics for analysing experimental data. The obtained sorption coefficients Kd (from 0.25 to 8.10 mL/g) and the Freundlich sorption coefficients KF (from 1.16 to 7.99 (μg/g)(mL/μg)(1/n)) exhibited quite low values, which indicated that sulfamethazine is weakly adsorbed on the evaluated soils, is highly mobile, and has a great potential to penetrate and pollute the ground water. The Dubinin-Radushkevich isotherm was used to estimate the apparent free energy of sorption.

The effect of TiO2 nanoparticles on fluid quenching characteristics

AbstractNanofluids are colloidal suspensions of nanoparticles in base fluids. Some of the particles used in recent research are metal oxide and carbide particles, such as SiC, CuO, Al2O3 and TiO2, graphite and carbon nanotubes and particles. Quenching in such colloids results in better cooling abilities, higher impact toughness and smaller dimension changes of steels, compared with pure quenching media. In this investigation, nanofluids with TiO2 powders of 50 nm average particle size were investigated. Base fluids of primary interest were deionised (DI) water, some commercial quenching oils and polyalkylene glycol water solution of various polymer concentrations, 5–30 vol.-%. The investigated fluids were prepared with the addition of the same TiO2 powder with different concentrations, from extremely low, 10 mg nanopowder per litre to 1 g L−1. The cooling characteristics of these colloids were compared with the results of base fluids, but also with the results of previous measurements carried out on the f...

Systematic analysis of cooling curves for liquid quenchants

This investigation suggests and describes a systematic approach to the analysis of liquid quenchant characteristics using a standard ISO Inconel alloy probe. A new systematic mathematical model for the cooling curve analysis has been developed. The model allows for a more precise determination of quenching parameters and links certain parameters with a mathematical model for microstructure prediction and properties of quenched workpieces. Besides the usual technological parameters (cooling rate at 700°C, maximum cooling rate, cooling time from 800 to 500°C, cooling rate at 300°C, quenching intensity H), the heat transfer coefficient is determined using the following methods: the lumped heat capacity method, the Kobasko method and the inverse heat transfer method according to ‘SQIntegra’ software. The results of the heat transfer coefficient calculation according to the aforementioned methods are compared and verified with the ISO Inconel alloy probe cooling curve analysis for quenching in water, industria...

Effect of composition on oil quenchant performance

AbstractQuenching is the most common method of hardening metals and involves continuous cooling from a given austenitising temperature to achieve full transformation into a martensitic structure. The cooling rate depends mainly on the thermal characteristics of the metal, the section thickness of the workpieces and the heat removal properties of the quenching medium. Oils, when used as quenching media contain a base oil and different types of additives according to the application requirements. As the base oil, it is possible to use mineral, synthetic and natural oils, either separately or in combination. Mineral base oils are widely used because of their advantages in stability in comparison with natural oils, or lower price in comparison with synthetic oils. There are numerous additives available for use but, besides functional properties, the environmental and safety requirements have to be considered in their selection, e.g. barium additives must be replaced with less harmful compounds. Additionally, ...

A Prediction of Quenching Parameters Using Inverse Analysis

The cooling curves of still water and of water-based polymer quenchant polyalkylene glycol (PAG) were recorded with the ISO Inconel 600 probe with 12.5 diameter and 60 mm length equipped with a type K thermocouple inserted into the probes geometric center. The research included recording of cooling curves for still water in temperature range from 20 to 60°C, as well as quenching experiments with water based polymer solutions with concentration from 10 to 30 vol. % of PAG. The possibility of a new cooling curve determination method for any given water temperature based on interpolation model and experimental data for cooling curves at three different water temperatures was tested. Surface temperature, heat flux density, and heat transfer coefficient (HTC) were estimated based on the recorded cooling curve at the center of the ISO Inconel 600 probe using the solutions of inverse heat conduction problem (IHCP). The results of the inverse heat transfer analysis of the ISO Inconel 600 probe cooling in water and water based polymer solutions were compared to the results of the commercial software ivf SQintegra ver4.0 for the same cooling experiments. The proposed inverse determination of HTC can be used for the specification of boundary conditions in numerical simulations of quenching axisymmetric work pieces with similar dimensions to the ISO Inconel 600 probe.

Current Investigations at Quenching Research Centre

Quenching Research Centre (QRC) was established at the beginning of 2010 through the financial support for excellence of the Ministry of Science Education and Sport, of the Republic of Croatia. The main investigation and research possibilities and potentials of the QRC are: quenching in liquids or in a salt bath and cooling by high pressure gases. As a result of long term research, the Temperature Gradient System has been designed, together with a unique cylindrical probe of 50 mm diameter by 200 mm instrumented with three thermocouples. Another device used at the Centre was the IVFSmartQuench® system according to ISO 9950, using a quenching device with agitation according to the ASTM D6482 standard. That equipment is used to investigate liquid quenchants and process parameters, including development of new quenchants: water, oil, and polymer based nanofluids, agitated by ultrasonic vibrations as a novel technology. QRC is also equipped with unique high pressure gas quenching facilities, providing the hardware for controllable heat extraction. The aim of using that equipment is to develop the method for measuring hardenability of high-alloyed steels when they are gas quenched and where a Jominy test is not applicable. QRC is also one of the initiators and an active participant in the project Global database on cooling intensities of liquid quenchants, which is coordinated and conducted by International Federation for Heat Treatment and Surface Engineering (IFHTSE).

Application of Ultrasound Stirring for Quenching in a Liquid Medium

This paper investigates an application of ultrasonic stirring in water and oil-immersion quenching of a medium carbon steel sample. By developing a pressure acoustic simulation, the distribution of ultrasound pressure and acceleration in quenching media was predicted. By using the standard temperature probe of Inconel 600, the cooling curves of water and quench oil were recorded with and without ultrasound agitation. Using the same conditions, a quenching of the steel cylinders made for carbon steel C45 was performed. The experimental results have shown a significant impact of ultrasound agitation on cooling curve parameters, sample distortions, and surface hardness distribution and its hardenability.

Modeling of Dimensional Changes and Residual Stresses After Transformation-Free Cooling

Predicting thermal distortions and residual stresses after steel heat treatment is a complex task in which the solution involves the use of a number of process parameters and nonlinear variation of steel properties. Former investigations in transformation-free cooling processes of long cylindrical work pieces in a gas nozzle field showed a typical behavior of the dimensional changes which indicated the possibility of introducing dimensionless numbers to predict thermal distortions. It was found that the changes in the dimensions of cylinders correlate well with only a few dimensionless numbers which are defined as function of shape and dimensions of components, its initial temperature, temperature of the quenching media, heat transfer coefficient, heat conductivity, heat capacity, density, thermal expansion coefficient, Youngs modulus, Poissons ratio, yield strength, and strain hardening behavior. For a systematic investigation of impacts on dimensional changes and residual stresses after transformation-free cooling, a representative group of 28 austenitic stainless steels was selected from literature. Their properties were statistically analyzed and three representative combinations of steel properties have been selected. The numerical simulations were carried out by use of the commercial finite element (FE) program SYSWELD 2005 with the aim to predict residual stresses and change of dimensions of a long cylinder made of austenitic stainless steel after gas cooling from the high temperature down to room temperature. The FE results were analyzed with the nonlinear regression methods and with genetic programming methods. From these analyses, two dimensionless mathematical models were proposed, one for prediction of thermal distortions and the other for prediction of equivalent residual stresses. The proposed dimensionless regression models allow the portability of the calculation results to similar cooling conditions (temperature independent heat transfer) for a transformation-free cooling of long cylinders made from any austenitic steel selected from the considered representative group of steels.

Cooling Characteristics of Water Based Nanofluids With Agitation

A series of quenching experiments was performed according to the ISO 9950, ASTM 6200-01, and ASTM D6482-06 standards. Water based nanofluids with 0.01, 0.1, and 0.2 g/L TiO2 were prepared using a two-step method and ultrasonic homogenization. The nanofluids were tested to see the possibility of their application as high temperature heat transfer fluids. Nanoparticles used in this series of experiments were 50 nm in diameter. All of the cooling curves were recorded and analyzed using the ivf SmartQuench system. The first set of experiments was conducted under still conditions according to the ISO 9950 standard. Pure water and nanofluids were investigated. The addition of nanoparticles showed an effect on the full film phase duration, an increase in the maximum cooling rate, and a change in transition temperature. A second series of quenching experiments was conducted according to ASTM D 6482-06. For this purpose, a quenching bath with agitation was built at the QRC. Three levels of agitation were tested: one according to the standard, 1000 rpm, one below, and one above the specified speed. Experiments with pure water and all three nanofluids were conducted and cooling curves recorded. The cooling curves were analyzed using software ivf SQintegra ver4.0. The effects of agitation and nanoparticles contents on cooling characteristics were compared.