Lovrenc Novak

HEAT TRANSFER EVALUATION METHOD IN COMPLEX ROTATING ENVIRONMENTS EMPLOYING IR THERMOGRAPHY AND CFD

This article presents a measuring method for determination of convective heat transfer in rotating environments. The method is used to obtain temperature and Nusselt number distributions on optically accessible objects inside real operating environments, without the need for implementation of complex surface heat flux measurements. Temperature maps of the observed surfaces are acquired non-intrusively by infrared (IR) thermography, whereas heat flux data is computed numerically by computational fluid dynamics (CFD) tools. The method was employed on a rotating hollow blade, heated internally by secondary air flow. Experimental and numerical results for the observed blade side are compared in terms of surface temperature 2D distributions. Temperature distributions are further statistically evaluated and show good agreement, which is the basic precondition for combining experimental and numerical data by the method. Results are presented in terms of combined experimental-numerical Nusselt number shown as two-dimensional distribution on the blade pressure side.

Influence of drum inlet air conditions on drying process in a domestic tumble dryer

Abstract This study examines how the inlet air temperature, relative humidity, and flow rate influence the textile drying process in an open cycle tumble dryer. An experimental setup was prepared by connecting a domestic tumble dryer to an external system for controlled heating, humidification, and transport of air. Experiments were conducted by drying cotton textiles (8 kg dry mass) at different air inlet conditions. On the basis of measured data, correlations for determination of the total drying time, the moisture evaporation rate during the constant drying rate, and the area-mass transfer coefficient were developed. The process in the drum was modeled by using an established moisture evaporation model, based on sorption isotherms. A commonly used and a recently reported sorption isotherm for cotton were used with the model. Agreement between calculated and measured drying curves was better in case of the commonly used sorption isotherm, but final moisture content was better predicted by the recently reported sorption isotherm.

Numerical Modeling of Heat Transfer and Flow Phenomena in an Axial Rotating Rotor Cascade

This paper presents a study of heat transfer in a rotating axial rotor. The study was done on the basis of computational fluid dynamics simulations and validated with an infrared thermocamera experimental setup. The influence of full turbulence vs. Menters boundary layer method was studied in terms of heat transfer and flow phenomena. Additionally it was found out that a thin paint layer has a major influence on heat transfer phenomena and acts as insulation. For comparison of numerical results with experimental, a model of the actual rotor was established. Results were found to be in good agreement, so the effect of rotation on heat transfer was studied. Results are presented in terms of Nusselt number distribution and an empirical model of heat transfer.

Modeling of heat pump tumble dryer energy consumption and drying time

Abstract The use of heat pump tumble dryers is nowadays more common because they offer huge energy savings compared to conventional tumble dryers. Earlier studies made on conventional tumble dryers have shown that parameters such as heater power, fan speed, drum speed, weight and initial moisture content of textiles and air leakage have a huge impact on the energy efficiency and drying time. In the present study, a modified commercial heat pump tumble dryer was evaluated for energy consumption and drying time by changing operating parameters including fan speed, drum speed, and mass load. The total energy consumption and drying time were measured and corrected for the initial and final moisture content in the textiles. The experimental results based on 27 drying tests were evaluated to develop linear regression models for energy consumption and drying time, which show a good agreement with the experimental data. The results show that a large mass load, a high drum speed, and a low fan speed give the highest energy efficiency, i.e. the lowest energy consumption per kg of drying load. Larger loads extend the length of the drying cycle while higher fan and drum speeds result in shorter drying time.