Zbigniew Bulinski

A comparison of heterogenous and homogenous models of two-phase transonic compressible CO2 flow through a heat pump ejector

This paper presents mathematical model of a two-phase transonic flow occurring in a CO2 ejector which replaces a throttling valve typically used in heat pump systems. It combines functions of the expander and compressor and it recovers the expansion energy lost by a throttling valve in the classical heat pump cycle. Two modelling approaches were applied for this problem, namely a heterogenous and homogenous. In the heterogenous model an additional differential transport equation for the mass fraction of the gas phase is solved. The evaporation and condensation process in this model is described with use of the Rayleigh-Plesset equation. In the homogenous model, phases are traced based on the thermodynamic parameters. Hence the heterogenous model is capable to predict non-equilibrium conditions. Results obtained with both models were compared with the experimental measurements.

Inverse thermal problems in computational modelling of the paper vacuum drying process

In this article, a mathematical model of the vacuum paper drying process was developed utilizing Fluent, a commercial Computational Fluid Dynamic software. Paper is treated as a porous medium, which is in thermodynamic equilibrium with humid air. Water distribution within paper is resolved by solving a so-called lumped diffusion equation. A developed model requires numerous experimental data and unknown/uncertain parameters. The latter ones are subjects of inverse thermal analysis. This analysis is based on the Levenberg–Marquardt method.

A validated numerical model of heat and mass transfer in a PM BLDC electric motor

In the paper, a validated numerical model describing heat transfer and air flow phenomena in a PM BLDC motor is presented. Validation was performed using the results of multiple velocity and temperature measurements. The air velocity was measured by constant temperature anemometers (CTA) and using Laser Doppler Anemometry (LDA) outside and inside the motor casing, respectively. The temperature measurements were conducted involving over 40 thermocouples located on the stator winding, internal and external casing walls and in the surrounding air. The numerical and experimental results were in a satisfactory agreement.

CFD simulations of transport phenomena during transcritical flow of real fluid (CO2) within ejector

Purpose – The purpose of this paper is to overview successful approaches to the computational simulation of real fluid (R744 – carbon dioxide (CO2)) flow within an ejector is presented. Important issues such as the ejector geometry and its optimisation, the adapted equations of state and the proposed models of the process, fluid parameters, etc., are examined and critically discussed. Whenever possible, the discussed models are experimentally validated. In the conclusion, some trends in future research are pointed out. Design/methodology/approach – Flow within CO2 ejector is generally transcritical and compressible. Models existing in the literature are shortly described and critically compared. Whenever possible, those models were validated against the experimental data. In a model validation process, the primary and secondary mass flow rates as well as the pressures at the selected points in the mixing section and diffuser were compared, showing a satisfactory agreement between experimental and computat...

Retrieving of the initial moisture field in porous material based on temperature measurements during drying

In this article, a simultaneous initial inverse problem and parameter estimation inverse problem in context of the vacuum paper drying process is presented. In this problem an evaporation constant and initial distribution of the water content are retrieved indirectly based on the temperature measurements at selected sampling points during vacuum phase of the process. As such, a problem is ill-posed and two different Tikhonov-type regularization techniques are proposed. The L-curve method was used to establish the value of the regularization parameter for both techniques. Results obtained with both regularization techniques are compared.

Mathematical Modelling of Two‐Phase Transonic Compressible CO2 Flow Through Heat Pump Ejector

In this paper mathematical modelling of a two‐phase flow occurring in an ejector which replaces a throttling valve typically used in a heat pump cycle is numerically considered. The geometry of the model is three dimensional taking one cross‐sectional symmetry plane into account. In such model different discretizations were generated to study an influence of the rapidly changing quantities on the system operation. The density variations are defined using real gas model i.e. Redlich‐Kwong for CO2 and REFPROP databases were employed. Both models produced similar character of the results. In addition, it was observed that the effects of wall roughness value defined as in planned experiments in such high speed systems can be neglected.

Estimation of the non-linear diffusion coefficient with Marcov Chain Monte Carlo method based on the integral information

Purpose This paper aims to present development and application of the Bayesian inverse approach for retrieving parameters of non-linear diffusion coefficient based on the integral information. Design/methodology/approach The Bayes formula was used to construct posterior distribution of the unknown parameters of non-linear diffusion coefficient. The resulting aposteriori distribution of sought parameters was integrated using Markov Chain Monte Carlo method to obtain expected values of estimated diffusivity parameters as well as their confidence intervals. Unsteady non-linear diffusion equation was discretised with the Global Radial Basis Function Collocation method and solved in time using Crank–Nicholson technique. Findings A number of manufactured analytical solutions of the non-linear diffusion problem was used to verify accuracy of the developed inverse approach. Reasonably good agreement, even for highly correlated parameters, was obtained. Therefore, the technique was used to compute concentration dependent diffusion coefficient of water in paper. Originality/value An original inverse technique, which couples efficiently meshless solution of the diffusion problem with the Bayesian inverse methodology, is presented in the paper. This methodology was extensively verified and applied to the real-life problem.

Numerical analysis and experimental validation of the free surface flow and heat transfer in electrical transformers moulding processes

Purpose – The purpose of this paper is to present a numerical and mathematical model of a moulding process of a dry electrical transformer. Moreover, the calculated results are reported and compared with experimental measurements.Design/methodology/approach – An experimental rig, for carrying out and monitoring a moulding process, has been designed and built. Two experiments were preformed. First was an isothermal experiment in which an analog liquid was used. The second experiment was a non‐isothermal one in which an epoxy resin was used. For the rig geometry, the numerical mesh, with the use of the commercial code Gambit, was built. All necessary physical properties, including viscosity, surface tension and contact angle of fluids used in the experiments were measured.Findings – The Euler approach for modelling multiphase flow with a free surface is addressed in the presented work. Comparison of the computational results with measurements on the designed experimental rig revealed good agreement. Compari...