Roman Duda

In the paper the method of automatic control of the two stage hybrid sorption-compression refrigeration system for different ambient conditions is presented. The main advantages of the system are its environmental friendly working fluids and waste or renewable low temperature heat source utilization. The control algorithm is designed for operation in four seasons’ conditions. During cold seasons the heat from the second stage condenser, as waste heat, may be used to increase the temperature of the heat pump source. The system is composed of dependent subsystems with individual controls, however it is controlled by the computer program as master control. The issues related to the optimization of operation of the refrigeration system, taking into account the maximum usage of available renewable or waste heat sources, are discussed in the paper.

The aim of this work is to calculate the effective area of a compressor recirculation valve. Analytical solution and numerical modeling for compressible flow through a valve will be presented. Critical parameters of flow will be determined. Numerical modeling will be performed using ANSYS FLUENT. The results of the numerical solution will be compared with the analytical solutions.

The aim of this paper is the presentation of the method for thermal conductivity measurement and numerical modeling of temperature distribution in apparatus for measuring the thermal conductivity. Experimental studies will be carried out in transient state until the steady state heat conduction in apparatus is achieved. The calculated and measured temperature distribution will be compared. The time to steady state in apparatus for different samples will be estimated based on numerical and experimental results. The influence of the contact resistance between the sample and the measuring device will be analyzed.

In the flow of mathematical ideas from the West to Central-Eastern Europe one can distinguish several typical forms: 1) foreign mathematicians, invited to cultivate mathematics upon new ground (e.g. Euler in Russia); 2) domestic mathematicians who completed their studies abroad and continued research after returning home (e.g. W. Buniakowski or M. Ostrogradski in Russia); 3) domestic mathematicians who dared developing new directions, thus initiating original schools of mathematics (e.g. N. N. Lusin in Russia). A separate phenomenon was a startling discovery of non-euclidean geometry (N. N. Lobatchevsky in Russia, J. Bolyai in Hungary).

Since medieval times mathematics was being developed mainly in Central and Western Europe but in the 19th century it greatly expanded both to the United States and to some countries of Central-Eastern Europe. This expansion, accompanied by the rapid growth of mathematics as a whole, has recently become an object of interest and investigation. The interest, however, reflects the Western viewpoint, cf. [17], with the bibliography covering Germany, Spain, Italy, France, Moscow. The aim of this paper is to outline the history of emerging national mathematical research communities in Russia, Poland, Bohemia, Lithuania and some other countries of Central-Eastern Europe.

The requirements for environmentally friendly refrigerants promote the application of both CO2 and water as working fluids. Both solutions have disadvantages resulting from the high temperature limit for CO2 and the low temperature limit for water. This can be avoided by the application of the hybrid adsorption-compression system, where water is the working fluid in the adsorption cycle which is used to cool down the CO2 compression cycle condenser. The adsorption process is powered with a low-temperature renewable heat source such as solar collectors or waste heat sources. This solution has been developed by the authors of this paper and has not been reported in any other literature source. The different ambient conditions over the course of the year require specially designed controlprocedures and the automation system. The algorithm has to control positive and negative heat sources operation, valve actions, pumps, fans and compressor operation. In the control algorithm, the ambient temperature and solar conditions or other waste heat sources have to be introduced as control parameters, optimised to achieve maximum efficiency of the whole system. The refrigeration effect as a parameter has to be considered both for the refrigeration capacity as well as the CO2 evaporation temperature.