Wyniki wyszukiwania - BazTech

1

Thermal and visualisation study of the hfe7100 refrigerant condensation process

Bohdal Tadeusz, Sikora Małgorzata, Formela Karolina

Acta Mechanica et Automatica

|

2024

|

Vol. 18, no. 1

60--67

EN

Technological advances are contributing to the search for highly efficient energy designs, and increasing interest in compact heat exchangers. Indeed, small channel diameters determine large heat transfer coefficients and condition a significant heat transfer area about the overall volume of the heat exchanger, as well as a smaller amount of refrigerant flowing in the system. Nevertheless, the operat-ing stability and energy efficiency of compact heat exchangers are influenced by two-phase flow structures, which depend on thermal flow parameters. Knowledge of the structures formed during the condensation process is therefore essential for optimising the operation of re-frigeration and air-conditioning equipment. This article presents the results from experimental studies of the HFE7100 refrigerant, from the hydrofluorocarbon group, condensation process in mini-channels with hydraulic diameters dh = 2.0 mm, 1.2 mm, 0.8 mm and 0.5 mm. Thermal flow characteristics were determined, and the forming structures of two-phase flow were recorded. The results of visualisation were subjected to morphological image analysis, based on a special algorithm written in MATLAB software. The algorithm makes it possi-ble to determine the void fraction, which is necessary for calculating the vapour quality, as well as the area of vapour bubbles and their number, directionality and length along the x- and y-axes.

2

Performance investigation of hybrid photovoltaic thermal-heat with mini-channels for application in electric vehicles

Strąk Dariusz

Archiwum Motoryzacji

|

2023

|

Vol. 100, nr 2

5--30

EN

The first autonomous car was developed in the 1980s, but it wasn't until the early 2010s that the technology began to gain significant attention and investment. In 2010, Google began testing self-driving cars on public roads, and since then, many other companies have joined the race to develop fully autonomous vehicles. Hybrid PVT (Photovoltaic Thermal) heat exchangers cooled with mini-channels find application in autonomous vehicles as a solution that enables efficient cooling of the vehicle's electronics and batteries. The solution involves using photovoltaic panels to generate electricity and removing the heat produced during the process using mini-channels is removed by mini-channels. Hybrid PVT heat exchangers cooled with mini-channels can help maintain appropriate temperatures inside autonomous vehicles that generate large amounts of heat from electronic systems and sensors. The setup can improve the performance and reliability of autonomous systems, increase energy efficiency, and reduce energy demands. The experimental setup includes two parallel mini-channel systems separated by a smooth copper plate. The study aims to determine local heat-transfer coefficients, with a cooled solar cell efficiency range of 10% to 14% compared to other research. The cooled PV temperature range achieved was from 19.6 to 22.4 degrees Celsius, which is favorable for photovoltaic panels' operation under approximate light intensity for Poland's latitude. Heat-transfer from hot surfaces to cold fluids is analyzed during single-phase convection using two calculation methods: one-dimensional and numerical simulations using Simcenter STAR CCM+. Cooling photovoltaic modules is critical for the photovoltaic and autonomous vehicle systems sector, making this research significant both theoretically and practically. The research and methods presented in the article on mini-channel cooling of photovoltaic systems and autonomous vehicle systems are innovative at a global scale, and are crucial for further development of sustainable energy systems and reduction of greenhouse gas emissions.

3

Modeling the phenomena accompanying the condensation of environmentally friendly refrigerants in mini-channels

Kuczyński Waldemar

Archives of Thermodynamics

|

2023

|

Vol. 44, no 1

121--137

EN

This paper presents the results of an experimental study and mathematical modeling of the effect of dynamic instabilities on the condensation phase transformation of the refrigerants homogeneous R134a and its replacement in the form of isomers R1234yf and R1234ze and R404A or R507 and R448A in pipe mini-channels. In the case of homogeneous chlorofluorocarbons (CFCs), it is the 1234 isomers that are envisioned as substitutes for the withdrawn ones with high ozone depletion potential and global warming potential. For zeotropic and azeotropic mixtures, for example, these are R507 or R448A. The paper presents a dimensional analysis procedure based on the Buckingham Π theorem to develop a regression velocity model of pressure dynamic instabilities. The experimental part of the work was carried out with the use of tubular mini-channels with internal diameter 1.40–3.3 mm.

4

Wpływ struktury przepływu na wymianę ciepła w procesie skraplania proekologicznych czynników chłodniczych w minikanałach

Sikora Małgorzata, Bohdal Tadeusz

Instal

|

2022

|

nr 5

20--26

PL

Podczas procesu skraplania w minikanałach następuje zmiana mechanizmów przenoszenia ciepła i masy wynikająca ze zmiany stopnia suchości x i stopnia zapełnienia φ, które wpływają na proces formowania się różnych struktur przepływu. Miarą efektywności energetycznej procesu jest współczynnik przejmowania ciepła α, który zależy od charakteru przepływu dwufazowego. W niniejszym artykule zaprezentowano wpływ formujących się struktur przepływu dwufazowego na proces wymiany ciepła podczas procesu skraplania czynników chłodniczych w poziomych minikanałach rurowych. Badania przeprowadzono dla trzech proekologicznych czynników niskociśnieniowych HFE7000, HFE7100, Novec649, o niskich wskaźnikach ODP i GWP. Proces skraplania zachodził w minikanałach rurowych o średnicy wewnętrznej dh = 2,0; 1,2; 0,8; 0,5 mm.

EN

During the condensation process in the mini-channels, the heat and mass transfer mechanisms change, resulting from the change in the vapor quality x and the void fraction φ, which in turn affect the process of formation of various flow structures. The measure of the energy efficiency of the process is the heat transfer coefficient α, which depends on the kind of the two-phase flow. This article presents the influence of the two-phase flow structures formed during the condensation process in horizontal pipe mini-channels on the heat transfer process. The research was carried out on three pro-ecological low-pressure refrigerants with low ODP and GWP coefficients, HFE7000, HFE7100, and Novec649. The condensation process took place in pipe mini-channels with an internal diameter of dh = 2.0; 1.2; 0.8; 0.5 mm

5

Thermal-FSI modeling of flow and heat transfer in a heat exchanger based on minichanels

Kornet S., Ziółkowski P., Jóźwik P., Ziółkowski P. J., Stajnke M., Badur J.

Journal of Power Technologies

|

2017

|

Vol. 97, nr 5

373--381

EN

In this paper selected numerical modelling problems for an advanced thermal-FSI ("Fluid Solid Interaction") mini-channel heat exchanger model are presented. Special attention is given to the heat transfer between the separated mediums for different mass flows. Similar modelling problems have also been discussed in the literature dedicated to numerical and theoretical modelling problems for typical heat exchangers [1, 2, 3]. Basic tests, including a comparison with experimental data, have been conducted using a Mini-channel Plate Heat Exchanger (MPHE). The MPHE was made out of two gasketed brazed plates with 40 mm long rectangular cross section channels (width - 1 mm, depth - 700 μm). The thermal-FSI analysis was applied for the heat exchanger model with one hot and one cold water flow passage through the mini-channels. Satisfactory agreement between the modelling results and the experimental data [4] was obtained.

6

Charakterystyka propagacji fali ciśnieniowej podczas procesu skraplania czynników chłodniczych R404A i R134a w minikanałach rurowych w warunkach periodycznych zakłóceń hydrodynamicznych

Kuczyński W., Denis A.

Chłodnictwo : organ Naczelnej Organizacji Technicznej

|

2016

|

R. 51, nr 12

18--26

PL

W procy podjęto próbą modelowania propagacji fali ciśnieniowej wywołanej niestabilnością hydrodynamiczną o charakterze periodycznym podczas procesu skraplania czynników chłodniczych R404A / R734a w minikanałach rurowych. W tym celu zastosowano jednorodny, dwupłytowy model oparty na równaniach bilansu: masy, padu. Model ten ujmuje złożoność przepływów wielofazowych. Wymianą ciepła pomiędzy fazami w procesie skraplania obliczono wykorzystując jednowymiarową postać równania Fouriera. Uwzględniono również zależność określającą międzyfazowe napięcia powierzchniowe przepływu w minikanałach.

EN

In the present paper, an attempt was undertaken to model the propagation of a pressure wave triggered off with hydrodynamic instabilities of a periodic nature in the condensation process of the R404A and R134a refrigerants in pipe mini-channels. A homogenous transient two-fluid model was used based on balance equations. The model presents the complexity of multi-phase flows, The heat exchange between the phases in the condensation process was calculated using the one-dimensional form of Fourier's equation. The dependence which defines the interfacial the drag forces for the flow in mini-channels was also taken into consideration. The results of the numerical calculations were verified with experimental investigations and satisfactory compliance was obtained.