Arkadiusz Ryfa

The heat transfer coefficient spatial distribution reconstruction by an inverse technique

This article presents a technique for obtaining the spatial distribution of the heat transfer coefficient (HTC) for an impingement heat exchange directly from transient temperature measurements. The HTC retrieval problem is formulated through the boundary temperature and the heat flux. That formulation makes it possible to utilize the superposition principle as the temperature field depends linearly on both the mentioned boundary conditions (BC). The unknown boundary temperature and heat flux are approximated by the set of trial functions chosen by the user. The key point is to utilize the definition of the convective BC in the objective function formulation. This fact allows us to take advantage of the fact that for the impingement heat exchange the HTC is constant in time. Such definition of the minimized function improves the stability of the solution in the presence of the measurement errors.

Application of the inverse analysis for boundary condition retrieval

The technique of solving linear steady-state and transient inverse problems aimed at retrieving an unknown heat transfer coefficient (HTC) is proposed. The idea is to approximate the temperature field by a linear combination of known auxiliary temperature fields. Each of these fields is evaluated by assuming that the unknown boundary temperature (heat flux) is described by a compact support, low-order trial function. The unknown coefficients of this linear combination are determined from the least square fit to the measured temperatures employing the modified Levenberg–Marquardt (LM) method. Once the boundary temperature and heat flux are retrieved, the HTC is determined from its definition. The auxiliary fields are evaluated using an arbitrary numerical or analytical technique. The sensitivity coefficients of the problem can readily be obtained by sampling the auxiliary fields at sensor locations. The values of the sensitivity coefficients used in the LM procedure need to be determined only once, before entering the iterative least squares procedure. Piecewise linear or stepwise functions were used to approximate the spatial and temporal variation of the retrieved heat flux and temperatures. The technique has been applied to reconstruct HTC for so-called time-to-arrival measurements technique with narrow band thermochromic liquid crystal used as temperature sensors. The idea behind this approach is to monitor the time at which a measuring point reaches a characteristic temperature. The developed technique has been used to retrieve the HTC for impingement cooling of the simplified piston of a car engine.

Simulations of the PC boiler equipped with complex swirling burners

Purpose – The purpose of this paper is to show possible approaches which can be used for modeling complex flow phenomena caused by swirl burners combined with simulating coal combustion process using air- and oxy-combustion technologies. Additionally, the response of exist boiler working parameter on changing the oxidizer composition from air to a mixture of the oxygen and recirculated flue gases is investigated. Moreover, the heat transfer in the superheaters section of the boiler was taken into account by modeling of the heat exchange process between continuum phase and three stages of the steam superheaters. Design/methodology/approach – An accurate solution of the flow field is required in order to predict combustion phenomena correctly for numerical simulations of the industrial pulverized coal (PC) boilers. Nevertheless, it is a very demanding task due to the complicated swirl burner construction and complex character of the flow. The presented simulations were performed using the discrete phase mod...

Direct and Inverse Methods for an Air Jet Impingement

The reconstruction of the distribution of the heat transfer coefficient (HTC) for the air jet impinging of a solid object is discussed. After an optimal turbulence model is selected, computational fluid dynamics is used to obtain detailed information about the HTC produced by a jet and to validate its invariability in time. Two inverse models of the temperature field in the solid impinged by the jet are derived as a linear combination of known, constant, or linear auxiliary fields. Simultaneous minimization of the discrepancies between the temperatures measured by an infrared camera and both inverse models produces the distribution of the HTC for various jets configurations.

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.

An experimental and numerical analysis of temperature and velocity field in PM BLDC motor

In this paper, a validated numerical model was introduced to determine the temperature and velocity fields outside the electric motor. The analysed object was a brushless permanent magnet motor (PM BLDC) having a rated power of 431 W with neodymium permanent magnets located on the rotor. The temperature and velocity measurements were conducted using thermocouples and constant-temperature anemometers. The numerical model covered the investigated motor and the same unit working as a generator and the air volume around them in order to improve the heat dissipation conditions. The numerical results show a satisfactory agreement with the values obtained during the measurements. Streszczenie. W pracy przedstawiono zwalidowany eksperymentalnie model numeryczny do wyznaczenia pola temperatury oraz predkości na obudowie oraz wokol bezszczotkowego silnika elektrycznego malej mocy. Pomiary temperatury i predkości przeprowadzono na stanowisku badawczym za pomocą termopar oraz anemometrow stalotemperaturowych i posluzyly one do walidacji modelu. Model numeryczny obejmowal silnik wraz z obciązającą go prądnicą oraz bryle powietrza wokol obu maszyn w celu dokladniejszego odwzorowania warunkow wymiany ciepla. Wyniki otrzymane z modelu numerycznego wykazaly satysfakcjonującą zgodnośc z wartościami otrzymanymi podczas pomiaru. Wyznaczania pola temperatury oraz predkości na obudowie oraz wokol bezszczotkowego silnika elektrycznego malej mocy

The Inverse Reconstruction of the Heat Transfer Coefficient for the Free Surface Water Jet

This article presents an application of inverse algorithm for reconstruction of heat transfer coefficient (HTC) for a water jet impinging a flat surface. Such an approach, allows for decoupling complex fluid flow from heat conduction in a solid impinged by jet. The approach starts with parameterization of a functional form of unknown boundary temperature and heat flux occurring at the fluid–solid interface. Later, Newtons law of cooling is used to force temporal invariability of HTC. Unknown coefficients of HTC distribution are determined from a least square fit between measured and computed temperatures. Temperatures entering the objective function are recorded by an infrared camera at the surface opposite to impinged one.