Investigations of refrigerant condensation in pipe minichannels are very challenging and complicated issue. Due to the multitude of influences very important is mathematical and computer modeling. Its allows for performing calculations for many different refrigerants under different flow conditions. A large number of experimental results published in the literature allows for experimental verification of correctness of the models. In this work is presented a mathematical model for calculation of flow resistance during condensation of refrigerants in the pipe minichannel. The model was developed in environment based on conservation equations. The results of calculations were verified by authors own experimental investigations results.
The objective of this work is to present an energy analysis of different absorption refrigerating systems operating with diverse refrigerants. Also is applied the method of experimental design to optimize configurations proposed by the absorption pairs used and the operating conditions. Both acceptable coefficient of performance and low operating generator temperature are scrutinised. Therefore, a computer program is developed. An investigation of the thermodynamic properties is presented. Results show the coefficient of performance evolution versus respectively the evaporator temperature, temperature of condensation and generator temperature. A particular interest is devoted to the intermediate pressure effect on the performance of different systems. In order to better converge in the selection of the configuration and the refrigerant, which can ensure a high coefficient of performance associated to relatively low operating generator temperature the plan of experiments has been developed, taking in account all parameters influencing the system performance and the function of operating temperature. Results show that the refrigerating machine containing a compressor between the evaporator and the absorber has a coefficient of performance quite acceptable and that it can work at low generator temperature for about 60 ◦C and using the NH3/LiNO3 as refrigerant.
Analysis of the state of-the-art in research of refrigerant condensation in miniature heat exchangers, so-called multiports, was made. Results of refrigerant R407C condensation in a mini condenser made in the form of two bundles of tubular minichannels from stainless steel with an inside diameter 0.64 mm and length 100 mm have been presented. Two exchangers consisted of four minichannels and 8 minichannels have been investigated. The values of average heat transfer coefficient and frictional pressure drops throughout the condensation process were designated. The impact of the vapor quality of refrigerant and the mass flux density on the intensity of heat transfer and flow resistance were illustrated. A comparative analysis of test results for various refrigerants in both mini heat exchangers were made.
The purpose of this article was to discuss the use of adsorption chillers for waste heat recovery. The introduction discusses the need to undertake broader measures for the effective management of waste heat in the industry and discusses the benefits and technical problems related to heat recovery in industrial plants. In addition, heat sources for adsorption chillers and their application examples were described. The principle of operation of adsorption chillers is explained in the next chapter. Heat sources for adsorption chillers are indicated and their application examples are described. The above considerations have allowed the benefits and technical obstacles related to the use of adsorption chillers to be highlighted. The currently used adsorbents and adsorbates are discussed later in the article. The main part of the paper discusses the use of adsorption chillers for waste heat management in the glassworks. The calculations assumed the natural gas demand of 20.1 million m3 per year and the electricity demand of 20,000 MWh/year. As a result of conducted calculations, a 231 kW adsorption chiller, ensuring the annual cold production of 2,021 MWh, was selected. The economic analysis of the proposed solution has shown that the investment in the adsorption chiller supplied with waste heat from the heat recovery system will bring significant economic benefits after 10 years from its implementation, even with total investment costs of PLN 1,900,000. However, it was noted that in order to obtain satisfactory economic results the production must meet the demand while the cost of building a heat recovery system shall not exceed PLN 1 million.
Performance assessment of ejector-expansion vapor compression refrigeration system with eco-friendly R134a alternative refrigerants (R152a, R1234yf, R600a, R600, R290, R161, R32, and propylene) is presented for air-conditioning application. Ejector has been modeled by considering experimental data based correlations of component efficiencies to take care of all irreversibilities. Ejector area ratio has been optimized based on maximum coefficient of performance (COP) for typical air-conditioner operating temperatures. Selected refrigerants have been compared based on area ratio, pressure lift ratio, entrainment ratio, COP, COP improvement and volumetric cooling capacity. Effects of normal boiling point and critical point on the performances have been studied as well. Using ejector as an expansion device, maximum improvement in COP is noted in R1234yf (10.1%), which reduces the COP deviation with R134a (4.5% less in basic cycle and 2.5% less in ejector cycle). Hence, R1234yf seems to be best alternative for ejector expansion system due to its mild flammability and comparable volumetric capacity and cooling COP. refrigerant R161 is superior to R134a in terms of both COP and volumetric cooling capacity, although may be restricted for low capacity application due to its flammability.
Słowa kluczowe
Zgodnie z dyrektywą Komisji Europejskiej numer 842/2006 (a później 517/2014) od stycznia 2017 roku zakazano stosowania czynników chłodniczych we wszystkich nowych urządzeniach klimatyzacji samochodowej, dla których wskaźnik GWP, charakteryzujący potencjał tworzenia globalnego ocieplenia, wynosi więcej niż 150. Z tego względu, stosowany powszechnie czynnik R-134a zostaje stopniowo wycofywany z użytkowania. Zaczęto poszukiwania alternatywnego czynnika, który spełni wszystkie wymogi. Według międzynarodowych zaleceń, czynnik powinien posiadać przede wszystkim właściwości przyjazne środowisku oraz powinien być bezpieczny w eksploatacji, nie stanowiąc zagrożenia dla życia ludzkiego. W artykule porównano dwie alternatywne substancje, które w większym lub mniejszym stopniu mogą być zamiennikami czynnika R-134a w układach klimatyzacji pojazdów. Są to syntetycznie otrzymywany czynnik oznaczony symbolem R-1234yf z grupy HFO oraz występujący w środowisku naturalnym dwutlenek węgla CO2 o symbolu R-744. W pracy opisano ich budowę chemiczną, właściwości fizyczne oraz termodynamiczne. Zestawiono publikacje naukowe, uwzględniające wyniki badań doświadczalnych wydajności, osiąganych przez układy chłodnicze, w których stosowano porównywane czynniki. Dokonano opisu metodyki badawczej, scharakteryzowano wykorzystane narzędzia oraz przedstawiono najważniejsze, z punktu widzenia autorów artykułu, wyniki badań. Alternatywne czynniki poddano również analizie środowiskowej. Sprawdzono ich wpływ na degradację warstwy ozonowej oraz scharakteryzowano wskaźnik potencjału tworzenia globalnego ocieplenia. Ponadto przeanalizowano kwestie bezpieczeństwa, zgodnie z obowiązującym normami, pod względem palności, toksyczności, klasyfikując poszczególne czynniki do odpowiednich grup bezpieczeństwa. Omówiono negatywne działania czynników na ludzki organizm, podczas eksploatacji urządzeń napełnionych ocenianymi czynnikami oraz ich awarii. Dokonano krótkiego porównania ekonomicznego, analizując obecne ceny czynników i usług serwisowych.
The purpose of this research is to substantiate a technical solution for improving the working conditions for the thermal factor in the extraction of oil by the thermoshaft method using the mine refrigeration technology. The review of manufacturers and technical characteristics of refrigeration technology in Russia, CIS countries and Western Europe was conducted. It was shown that the use of a water cooling machine in the mine air conditioning system will reduce the air temperature in the oil production gallery to the required values and will allow to abandon the long-term construction of a surface stationary refrigeration station. Normalization of the thermal regime reduces the costs of benefits and compensation for work in harmful labor conditions and improves the quality of service of production wells by operators. The practical significance is that the proposed project for the introduction of air conditioning has a high level of profitability, and its payoff will occur in the second year of operation.