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1

Effect of flow orientation in experimental studies on FC-770 boiling heat transfer in asymmetrically heated minichannels

Piasecka Magdalena, Strąk Kinga

Archives of Thermodynamics

|

2024

|

Vol. 45, no 2

29--39

EN

The article presents experimental results of boiling heat transfer during FC-770 flow in a group of five minichannels with a common heated wall. The flow orientation was changed from 0º to 180º, with a 15° increment. During the experiments, the temperature of its outer heated wall surface was measured by an infrared camera. At the same time, flow patterns were captured through the glass plate opposite the heated wall using a high-speed camera. The purpose of the calculations was to determine local heat transfer coefficients on the contact surface between the working fluid and the heated surface in the central minichannel, using a simplified 1D calculation method. The results in the form of dependences of the temperature of the heated wall and the heat transfer coefficient as a function of the distance from the channel inlet for various flow orientations were analysed. Furthermore, typical boiling curves and two-phase flow patterns were presented. The mean relative error of the heat transfer coefficient was determined for various flow orientation. The dependence of the void fraction as a function of heat flux was illustrated for various angles of minichannel inclination to the horizontal plane. It was observed that the void fraction increased with heat flux and with increasing angle of inclination of the minichannel to the horizontal plane.

2

Analiza modeli opisujących wrzenie w przepływie w kanałach konwencjonalnych

Jakubowska Blanka

Chłodnictwo : organ Naczelnej Organizacji Technicznej

|

2020

|

R. 55, nr 4

9--18

PL

W artykule przedstawiona została analiza wybranych korelacji pozwalających na wyznaczenie współczynników przejmowania ciepła podczas wrzenia w przepływie, które przeznaczone są dla kanałłów o średnicach konwencjonalnych. Przedstawiona w pracy analiza została wykonana na podstawie badań eksperymentalnych dostępnych w literaturze, które prowadzone były dla pełnego zakresu zmiany stopnia suchości oraz stosunkowo szerokiego zakresu zmiany prędkości masowej. Zebrana baza danych eksperymentalnych zawiera dziesięć czynników chłodniczych, takich jak: NH 3 , CO 2, R290, R600a, R1234yf, R134a, R245fa, R236fa, R152a oraz HFE7000. Zebraną i usystematyzowaną bazę danych eksperymentalnych porównano z dostępnymi w literaturze korelacjami opisującymi wrzenie w przepływie. W przedstawionych w pracy obliczeniach wykorzystanych zostało dziewięć modeli, tj. ogólną zależność Fanga i innych, Chena, Bertscha i innych, Shaha, Gungora i Wintertona, zmodyfikowaną korelację Gungora i Wintertona, Kima i Mudawara, Wojtana i innych oraz Lillo i innych.

EN

In the paper has been presented the analysis of selected correlations that allow the determination of heat transfer coefficients during flow boiling in conventional diameter channels. The analysis, which are presented, was carried out on the basis of experimental studies available in the literature, which were conducted for a full range of quality variation and a relatively wide range of mass velocity. The collected experimental database contains ten refrigerants such as: NH3, CO2, R290, R600a, R1234yf, R134a, R245fa, R236fa, R152a and HFE7000. The collected and systematized experimental database was compared with the correlations available in the literature, which modelling heat transfer during flow boiling. Nine models were used in the calculations presented in the paper, i.e. the general Fang et al. correlation, Chen, Bertsch et al., Shah, Gungor and Winterton, modified Gungor and Winterton, Kim and Mudawar, Wojtan et al. , and Lillo et al.

3

Subcooled flow boiling of a citric acid aqueous mixture

Abdolhossein Zadeh Mohammad Amin, Nakhjavani Shima

Archives of Thermodynamics

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2020

|

Vol. 41, no 1

193--217

EN

In the present research, an experimental investigation was conducted to assess the heat transfer coefficient of aqueous citric acid mixtures. The experimental facility provides conditions to assess the influence of various operating conditions such as the heat flux (0–190 kW/m2), mass flux (353–1059 kg/m2s) and the concentration of citric acid in water (10%–50% by volume) with a view to measure the subcooled flow boiling heat transfer coefficient of the mixture. The results showed that two main heat transfer mechanisms can be identified including the forced convective and nucleate boiling heat transfer. The onset point of nucleate boiling was also identified, which separates the forced convective heat transfer domain from the nucleate boiling region. The heat transfer coefficient was found to be higher in the nucleate boiling regime due to the presence of bubbles and their interaction. Also, the influence of heat flux on the heat transfer coefficient was more pronounced in the nucleate boiling heat transfer domain, which was also attributed to the increase in bubble size and rate of bubble formation. The obtained results were also compared with those theoretically obtained using the Chen type model and with some experimental data reported in the literature. Results were within a fair agreement of 22% against the Chen model and within 15% against the experimental data.

4

Pressure drop and temperature uniformity during flow boiling of refrigerant R245fa in microchannels

Sandler Stanisław, Zajączkowski Bartosz, Białko Bogusław

Zeszyty Energetyczne

|

2017

|

T. 4

1--12

EN

Cooling computer processors (CPUs) requires dissipating heat from small heat transfer areas. This results in high heat flux densities to be rejected from the microprocessor. Flow boiling in microchannels receives much attention as a potential solution for CPU cooling. It is characterized by high heat transfer coefficients and requires less working fluid inventory than air-based solutions. However, large pressure drop occurs during phase transition. Moreover, CPU cooling system should provide wall temperature uniformity of the cooled component. Heat transfer coefficient, pressure drop and microprocessor wall temperature depend on microchannel geometry, thermophysical properties of refrigerant, and saturation temperature at which the process is held. This paper focuses on studying pressure drop and temperature uniformity of 40 X 40 mm microchannel evaporator with R245fa as a working fluid. The analysed heat flux density is 80 kW/m2 and the vapor quality change along the heat exchanger is 0.2. The study covers saturation temperatures ranging from 30 to 70°С and microchannel diameters varying between 0.35 and 2 mm. Results of the analysis show that the heat transfer coefficient and wall temperature uniformity increase with increasing saturation temperature and decreasing hydraulic diameter. The maximum and minimum observed non-uniformities were 2.58 and 0.69 K, respectively. Decreasing hydraulic diameter increases pressure losses in the micro-evaporator. The observed pressure drop ranged from 38 to 3753 Pa. Saturation temperature has negligible impact on pressure drop.

5

Calculation method for flow boiling and flow condensation of R134a and R1234yf in conventional and small diameter channels

Mikielewicz D., Jakubowska B.

Polish Maritime Research

|

2017

|

S 1

141--148

EN

The paper presents the results of calculations performed using the authors’ model to predict the heat transfer coefficient during flow boiling for two refrigerants R134a and R1234yf. The experimental data from various past studies have been collected and the calculations have been conducted for the full range of quality variation and a wide range of mass velocity. The aim of the study was to test the sensitivity of the in-house flow boiling and flow condensation model. The importance of taking into account the surface tension as the parameter exhibiting its importance in case of the flow in minichannels, as well as the influence of the reduced pressure were analysed. The obtained numerical results show good consistency with those recorded in the experiments.

6

The application of Beck’s method combined with FEM and Trefftz functions to determine the heat transfer coefficient in a minichannel

Maciejewska B.

Journal of Theoretical and Applied Mechanics

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2017

|

Vol. 55 nr 1

103--116

EN

The aim of this study is to determine the heat transfer coefficient between the heated surface and the boiling fluid flowing in a minichannel on the basis of experimental data. The calculation model is based on Beck’s method coupled with the FEM and Trefftz functions. The Trefftz functions used in the Hermite interpolation are employed to construct the shape functions in the FEM. The unknown local values of the heat transfer coefficient at the foil- -fluid contact surface are calculated from Newton’s law. The temperature of the heated foil and the heat flux on the foil surface are determined by solving a two-dimensional inverse heat conduction problem. The study is focused on the identification of the heat transfer coefficients in the subcooled boiling region and the saturated nucleate boiling region. The results are compared with the data obtained through the one-dimensional method. The investigations also reveal how the smoothing of measurement data affects calculation results.

7

Determination of dryout localization using a five-equation model of annular flow for boiling in minichannels

Wajs J., Mikielewicz D.

Archives of Thermodynamics

|

2017

|

Vol. 38, no. 1

123--139

EN

Detailed studies have suggested that the critical heat flux in the form of dryout in minichannels occurs when the combined effects of entrainment, deposition, and evaporation of the film make the film flow rate go gradually and smoothly to zero. Most approaches so far used the mass balance equation for the liquid film with appropriate formulations for the rate of deposition and entrainment respectively. It must be acknowledged that any discrepancy in determination of deposition and entrainment rates, together with cross-correlations between them, leads to the loss of accuracy of model predictions. Conservation equations relating the primary parameters are established for the liquid film and vapor core. The model consists of three mass balance equations, for liquid in the film as well as two-phase core and the gas phase itself. These equations are supplemented by the corresponding momentum equations for liquid in the film and the two-phase core. Applicability of the model has been tested on some experimental data.

8

Prediction of flow boiling heat transfer coefficient for carbon dioxide in minichannels and conventional channels

Mikielewicz D., Jakubowska B.

Archives of Thermodynamics

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2016

|

Vol. 37, no. 2

89--106

EN

In the paper presented are the results of calculations using authors own model to predict heat transfer coefficient during flow boiling of carbon dioxide. The experimental data from various researches were collected. Calculations were conducted for a full range of quality variation and a wide range of mass velocity. The aim of the study was to test the sensitivity of the in-house model. The results show the importance of taking into account the surface tension as the parameter exhibiting its importance in case of the flow in minichannels as well as the influence of reduced pressure. The calculations were accomplished to test the sensitivity of the heat transfer model with respect to selection of the appropriate two-phase flow multiplier, which is one of the elements of the heat transfer model. For that purpose correlations due to Müller-Steinhagen and Heck as well as the one due to Friedel were considered. Obtained results show a good consistency with experimental results, however the selection of two-phase flow multiplier does not significantly influence the consistency of calculations.

9

Homotopy perturbation method combined with Trefftz method in numerical identification of liquid temperature in flow boiling

Hożejowska S.

Journal of Theoretical and Applied Mechanics

|

2015

|

Vol. 53 nr 4

969--980

EN

The paper is focused on numerical identification of 2D temperature fields in flow boiling of the liquid through a horizontal minichannel with a rectangular cross-section. The heat transfer process in the minichannel is described by a two-dimensional energy equation with the corresponding boundary conditions. Liquid temperature is determined using the homotopy perturbation method (HPM) with Trefftz functions for Laplace’a equation. The numerical solution to the energy equation found with the HPM is compared with the solution obtained for the simplified form of the energy equation. Considering that only the thermal sublayer is taken into account, both solutions give similar results.

10

Wyznaczanie współczynnika przejmowania ciepła podczas wrzenia w przepływie dwutlenku węgla

Mikielewicz D., Jakubowska B.

Chłodnictwo : organ Naczelnej Organizacji Technicznej

|

2015

|

R. 50, nr 1-2

28--34

PL

W pracy przedstawiono wyniki obliczeń uzyskane za pomocą własnego modelu półempirycznego dla wybranych danych eksperymentalnych dla wrzenia w przepływie dwutlenku węgla. Metoda obliczeniowa została zweryfikowana z danymi eksperymentalnymi Docoulombiera i innych (2011) oraz Mastrullo i innych (2009). Badania eksperymentalne dotyczą pełnego zakresu zmienności stopnia suchości oraz zakresu prędkości masowej G=2001200 kg/m2s. Rozwijany od lat w Katedrze Energetyki i Aparatury Przemysłowej Politechniki Gdańskiej model wrzenia w przepływie wykorzystuje do modelowania wymiany ciepła wyrażenie opisujące opory przepływu dwufazowego. W przedstawionych w pracy obliczeniach wykorzystano do tego celu dwa modele tj. Müllera-Steinhagena i Hecka oraz Friedela. W pracy pokazano również wpływ napięcia powierzchniowego na obliczenia oporów przepływu i wymiany ciepła oraz modyfikację naprężeń stycznych na granicy rozdziału faz.

EN

In the paper presented is the analysis of the results of calculations using a model to predict flow boiling of carbon dioxide. The model was verified with the experimental data due to Docoulombier et al. (2011) and Mastrullo et al. (2009). The experimental research was conducted for a full range of quality variation and a relatively wide range of mass velocity. The aim of present study was to test the sensitivity of development model of two-phase flow multiplier and the nonadiabatic effects. For that purpose two models have been analyzed namely due to Müller-Steinhagen and Heck correlation, Friedel correlation and introducing into the model the so called blowing parameter. Furthermore, in the paper shows the behavior of the heat transfer coefficient, when effect of bubbles generation is omitted and when the impact of flow resistance is omitted. In addition, the work shows the importance of taking into account in the calculation of the structure surface tension.

11

Funkcje Trefftza w wyznaczaniu dwuwymiarowych pól temperatury przy wrzeniu w przepływie

Hożejowska S.

Logistyka

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2014

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nr 6

4545-4554

PL

W pracy przedstawiono dwuwymiarowy model opisujący proces wymiany ciepła przy przepływie wrzącego czynnika chłodniczego przez asymetrycznie ogrzewany minikanał o przekroju prostokąta. W każdym z trzech obszarów modułu testowego: szklanej szybie, folii grzejnej i cieczy, proces wymiany ciepła opisany został przez inne równanie różniczkowe wraz z odpowiednim układem warunków brzegowych. Rozwiązanie tych równań prowadzi do rozwiązania potrójnego sprzężonego zagadnienia wymiany ciepła składającego się z jednego zagadnienia prostego (w szklanej szybie) oraz dwóch zagadnień odwrotnych (w folii grzejnej i wrzącej cieczy). Do wyznaczenia dwuwymiarowych rozkładów temperatury szklanej szyby, folii grzejnej i cieczy zastosowano metodę Trefftza. Wyliczając aproksymaty temperatury szklanej przegrody i folii grzejnej wykorzystano funkcje Trefftza dla równania Laplace’a. W celu obliczenia aproksymaty temperatury cieczy zastosowano funkcje Trefftza dla równania zachowania energii zależne od profilu prędkości cieczy. W modelu przyjęto trzy typy prędkości cieczy: stały, dachowy i paraboliczny. Obliczenia wykonane dla rozwiniętego przepływu pęcherzykowego oraz pęcherzykowo- korkowego dały zbieżne wyniki.

EN

The paper presented two-dimensional mathematical model describing heat transfer in flow boiling in an asymmetrically heated rectangular minichannel. In each of the three domains of the test section: the glass pane, the heating foil and the liquid, the heat transfer process has been described by different differential equations with appropriate boundary conditions. The solution of these equations leads to the solution of a threefold conjugated heat transfer problem consisting of a direct problem (in the glass pane) and two inverse problems (in the heating foil and boiling liquid). Trefftz method was used to determine two-dimensional temperature distributions in the glass pane, in the heating foil and in the liquid. The Trefftz functions for Laplace’s equation were applied to compute temperature distribution of both the glass pane and the heating foil. To calculate the temperature of the liquid Trefftz functions satisfying the energy equation and depending on the velocity profile of the liquid were used. The presented model involved three types of liquid velocity: solid, roof and parabolic. The calculations performed for bubbly and bubbly – slug flows gave similar results.

12

Prediction of flow boiling heat transfer data for R134a, R600a and R290 in minichannels

Mikielewicz D., Jakubowska B.

Archives of Thermodynamics

|

2014

|

Vol. 35, no. 4

97--114

EN

In the paper presented is the analysis of the results of calculations using a model to predict flow boiling of refrigerants such as R134a, R600a and R290. The latter two fluids were not used in the development of the model semiempirical correction. For that reason the model was verified with present experimental data. The experimental research was conducted for a full range of quality variation and a relatively wide range of mass velocity. The aim of the present study was also to test the sensitivity of developed model to a selection of the model of two-phase flow multiplier and the nonadiabatic effects. For that purpose two models have been analysed namely the one due to Müller-Steinhagen and Heck, and Friedel. In addition, the work shows the importance of taking surface tension into account in the calculation of the flow structure.

13

Adjustment calculus and Trefftz functions applied to local heat transfer coefficient determination in a minichannel

Grysa K., Hożejowska S., Maciejewska B.

Journal of Theoretical and Applied Mechanics

|

2012

|

Vol. 50 nr 4

1087-1096

EN

The paper presents results of numerical calculations conducted in order to define the heat transfer coefficient in flow boiling in a vertical minichannel with one side made of a heating foil with liquid crystals. During the experiment, we measured the local temperature of the foil, inlet and outlet liquid temperature and pressure, current and voltage drop of the electric power supplied to the heater. Local measurements of foil temperature were approximated with a linear combination of the Trefftz functions. The known temperature measurement errors allowed application of the adjustment calculus. The foil temperature distribution was determined by the FEM combined with the Trefftz functions. Local heat transfer coefficients between the foil and the boiling fluid were calculated from the third-kind condition.

PL

Przedstawiono wyniki obliczeń numerycznych przeprowadzonych w celu określenia współczynnika przejmowania ciepła przy przepływie wrzącej cieczy w pionowym minikanale, którego jedna ściana wykonana jest z folii grzewczej pokrytej ciekłymi kryształami. Podczas eksperymentu mierzono: lokalną temperaturę folii, temperaturę cieczy na wlocie i wylocie z minikanału, ciśnienie cieczy w minikanale oraz spadek natężenia i napięcia prądu stałego dostarczanej do folii grzewczej. Lokalne pomiary temperatury folii aproksymowano kombinacją liniową funkcji Trefftza. Znane błędy pomiaru temperatury pozwoliły na stosowanie rachunku wyrównawczego. Rozkład temperatury folii został określony przy zastosowaniu MES w powiązaniu z funkcjami Trefftza. Lokalne współczynniki wymiany ciepła pomiędzy folią i wrzącym płynem zostały wyliczone z warunku trzeciego rodzaju.

14

An investigation into the influence of different parameters on the onset of boiling in minichannels

Piasecka M.

Archives of Thermodynamics

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2012

|

Vol. 33, no. 4

67-90

EN

The paper presents experimental studies on boiling heat transfer in rectangular minichannels. The investigations focus on the transition from single phase forced convection to nucleate boiling, i.e., in the zone of boiling incipience. The experiment has been carried out with FC-72, R-123 and R-11 at the Reynolds number below 4700, corresponding to mass flow rate range 95-710 kg/(m s). The main part of the test section is a minichannel of pre-set depth from 0.7 to 2 mm and width (20, 40 and 60 mm), with different spatial orientations from vertical to horizontal and 30% inclination angle adjustment. The objective of the paper includes the impact of selected parameters (liquid flow velocity, pressure and inlet liquid subcooling, channel dimensions and spatial orientation) on the boiling incipience in minichannels. The investigations are intended to develop a correlation for the calculations of the Nusselt number under the conditions of boiling incipience in the minichannel as a function of changeable parameters.

15

Experimental and theoretical study of dryout in annular flow in small diameter channels

Mikielewicz D., Gliński M., Wajs J.

Archives of Thermodynamics

|

2011

|

Vol. 32, no. 1

89-109

EN

In the paper the experimental analysis of dryout in small diameter channels is presented. The investigations were carried out in vertical pipes of internal diameter equal to 1.15 mm and 2.3 mm. Low-boiling point fluids such as SES36 and R123 were examined. The modern experimental techniques were applied to record liquid film dryout on the wall, among the others the infrared camera. On the basis of experimental data an empirical correlation for predictions of critical heat flux was proposed. It shows a good agreement with experimental data within the error band of 30%. Additionally, a unique approach to liquid film dryout modeling in annular flow was presented. It led to the development of the three-equation model based on consideration of liquid mass balance in the film, a two-phase mixture in the core and gas. The results of experimental validation of the model exhibit improvement in comparison to other models from literature.

16

Koncepcja stanowiska do badania wrzenia w przepływie przez minikanał z grzejnikiem porowatym

Piasecka M.

Logistyka

|

2010

|

nr 6

PL

Celem artykułu jest przedstawienie koncepcji nowego stanowiska do badania wrzenia w minikanale, którego jedną ze ścian stanowi jednostronnie porowata folia grzejna. Omówiono podstawowy układ przepływowy stanowiska oraz układ akwizycji danych pomiarowych i obrazów kolorowych realizowany na stanowisku badawczym. Przedstawiono moduł pomiarowy wraz z właściwościami materiałowymi jego elementów: tj. korpusu z tworzywa sztucznego oraz folii grzejnej. Cienka folia grzejna o grubości ok. 0,1 mm wykonana jest ze stopu Haynes-230. W module pomiarowym stanowi ona jedną ze ścian minikanału jako grzejnik porowaty. Wprowadzenie do układu grzejnika porowatego winno zintensyfikować wymianę ciepła, co jest celem planowanych badań.

EN

The article aims to present a concept of a new experimental stand for boiling flow in a minichannel in which one of the walls is a single-sided porous heating foil. The stand's basic flow system has been discussed, together with an acquisition system for measurement data and colour images as realised at the experimental stand. The article presents the test section and materials properties of its elements, i.e. the plastic body and the heating foil. The thin heating foil, ca. 0.1 mm thick, is made of the Haynes-230 alloy. In the test section, it constitutes one of the minnichannel walls as a porous heater. The introduction of a porous heater into the stand ought to intensify heat transfer which is the objective of the planned experiment.

17

Współczynnik przejmowania ciepła przy wrzeniu w minikanale : badania doświadczalne i metody obliczeniowe z wykorzystaniem funkcji Trefftza

Piasecka M., Hożejowska S., Maciejewska B.

Inżynieria i Aparatura Chemiczna

|

2010

|

Nr 2

95-96

PL

Przedstawiono metody wyznaczania współczynnika przejmowania ciepła przy wrzeniu w przepływie płynu chłodniczego w minikanale. Zastosowana technika termografli ciekłokrystalicznej pozwala określić wystąpienie inicjacji wrzenia. Zagadnienie rozwiązywane jest za pomocą funkcji Trefftza, którymi aproksymuje się nieznane temperatury. Ponadto funkcje Trefftza służą do tworzenia funkcji bazowych w metodzie elementów skończonych (MEST). Porównano wyniki otrzymane przy wykorzystaniu obu metod. Słowa kluczowe: wymiana ciepła, minikanał, wrzenie w przepływie, termo-grafia ciekłokrystaliczna, funkcje Trefftza, MES

EN

The paper presents methods for the determination of heat transfer coefficient in cooling liquid flow boiling in a minichannel. The applied technique of liquid crystal thermography enables the determination of boiling incipience. To solve this problem, Trefftz functions are used to approximate unknown temperatures. Moreover, Trefftz functions are employed to obtain base functions in the finite element method (FEM). The results obtained using of both methods were compared.

18

Dryout in annular flow - theoretical analysis

Mikielewicz D., Wajs J., Gliński M., Zrooga A.

Archives of Thermodynamics

|

2009

|

Vol. 30, no. 2

77-90

EN

In the paper a two-equation model of mass balance of liquid in the film and in the core for calculation of dryout at high vapour quality is modified from the earlier version presented by Sedler and Mikielewicz [1]. Additionally, the mass balance equation for the liquid film contains a modified evaporation term. Modified is the heat flux density applied in evaporation of liquid film which now is variable within film thickness. The solution of such equations requires prior knowledge of rates of deposition and entrainment. The theoretical determination of there quantities involves serious difficulties. The relations for determination of deposition and entrainment rate are taken therefore from Okawa et al. [3], The results of calculations are validated against experimental data of Sedler and Mikielewicz [1], showing a satisfactory consistency.

19

A study of flow boiling heat transfer in minichannels

Mikielewicz D., Klugmann M.

Archives of Thermodynamics

|

2008

|

Vol. 29, no. 2

73-84

EN

In the paper presented has been a study into flow boiling of R123 in a small diameter tube of 2.3 mm. The experiments have been accomplished for a wide range of variation of quality, mass flow rate and heat fluxes, i.e. x = 0.01 - 0.9, G = 650 - 3000 kg/m[^2]s and q = 40 - 80 kW/m[^2], respectively. The saturation temperature ranged from 30-70 [degrees]C.

20

Horizontal flow boiling of R22, R134a and their mixtures with oil in smooth and enhanced tubes

Cieśliński J., Targański W.

Archives of Thermodynamics

|

2007

|

Vol. 28, no. 2

19-40

EN

The experimental stand and procedure for flow boiling investigations are described. Experimental data for pure R 22, R134a and their mixtures with oil in two smooth tubes and two enhanced tubes are also presented. The performance benefits of the micro-fin tube and corrugated tube are quantified and discussed. During tests inlet vapour quality was set 0[plus-minus]0,05 and outlet quality 0,7[plus-mines]0,01. Mass flux density varied from about 250 to 500 kg/m[^2]s. The experiments have been conducted for average saturation temperature 0[degrees]C. The ability of selected models to predict the boiling heat transfer coefficient is evaluated by comparison with the experimental data obtained in smooth tubes for pure R 22 and R134a.