The Experts below are selected from a list of 948 Experts worldwide ranked by ideXlab platform
Magdalena Piasecka - One of the best experts on this subject based on the ideXlab platform.
-
The heat transfer and instabilities results during the onset of flow boiling in Minichannels
'EDP Sciences', 2019Co-Authors: Beata Maciejewska, Magdalena Piasecka, Artur PiaseckiAbstract:The paper discusses the results of flow boiling heat transfer in Minichannels obtained on the basis of time-dependent experiments. The main interest of the work was to investigate the occurrence of the accompanying instabilities during the boiling incipience. The essential part of the experimental standwas a test section with two Minichannels, each of 1.7 mm depth. The heated element for FC–72flowing along the Minichannels was a thin foil. In the tested minichannel, the temperature of the outer surface of the foil was measured due to thermoelements. The onset of flow boiling in Minichannels was induced by increasing the heat flux supplied to the heater. The main aims of the investigation were to determine the heat transfer coefficient by means of the FEM with time—dependent Trefftz–type basis functions based on the Hermite interpolation and to recognize dynamic instabilities during boiling incipience. The results were illustrated as: the heat transfer coefficient, the mass flow rate and the inletpressure versustime and as boiling curves
-
Estimating uncertainty of temperature measurements for studies of flow boiling heat transfer in Minichannels
'EDP Sciences', 2019Co-Authors: Dariusz Michalski, Kinga Strąk, Magdalena PiaseckaAbstract:This paper presents the method of estimating the uncertainty of temperature measurements conducted using K-type thermocouples in the study of flow boiling heat transfer in Minichannels. During heat transfer experiments. the fluid temperature at the inlet and outlet of the minichannel is measured with thermocouples connected to a DaqLab 2005 data acquisition station. The major part of the experimental setup for calibration of temperature measurement included a calibrator of thermocouples. The thermocouples were manufactured by Czaki Thermo-Product. Poland. The temperatures recorded with the thermocouples were compared statistically while measuring the temperature of demineralised water at several characteristic points at liquid phase change or using the reference temperature known from the calibrator. The experimental error of the temperature measurement method was determined according to the principles of statistical analysis. Estimates of the mean value and the experimental standard deviation of the experimental error as well as the confidence interval for a single experimental error and the measurement accuracy were presented. The uncertainty of the difference in temperature was also calculate
-
the solution of a two dimensional inverse heat transfer problem using two methods the trefftz method and the beck method
International Journal of Numerical Methods for Heat & Fluid Flow, 2017Co-Authors: Beata Maciejewska, Kinga Strak, Magdalena PiaseckaAbstract:Purpose This paper aims to focus on flow boiling heat transfer in an asymmetrically heated minichannel. Two-dimensional inverse heat transfer problem was solved using the Trefftz and Beck methods. The primary purpose was to find an enhanced surface that could help intensify heat transfer. Design/methodology/approach The experimental set-up and methodology for FC-72 boiling heat transfer in two parallel vertical rectangular Minichannels with smooth or enhanced heated surfaces was presented. The heat transfer coefficient was calculated using the Trefftz and Beck methods. Findings The results confirm that considerable heat transfer enhancement takes place when selected enhanced heated surface is used in the minichannel flow boiling and that it depends on the type of surface enhancement. The analysis of the experimental data revealed that the values and distributions of the heat transfer coefficient obtained using the Beck and Trefftz methods were similar. Practical/implications Many studies have been recently devoted to flow boiling heat transfer in Minichannels because of the rapid development of high-performance integrated systems generating large amounts of heat. Highly efficient small-size cooling systems for new-generation compact devices are thus in great demand. Originality/value The present results are original and new in the study of cooling liquid boiling in Minichannels with enhanced heated surfaces that contribute to heat transfer enhancement. The paper allows the verification of state-of-the-art methods of solving the inverse problem by using empirical data from the experiment. The application of the Trefftz and Beck methods for finding a solution of the inverse heat transfer problem is promising.
-
calculations of flow boiling heat transfer in a minichannel based on liquid crystal and infrared thermography data
Heat Transfer Engineering, 2017Co-Authors: Magdalena Piasecka, Kinga Strąk, Beata MaciejewskaAbstract:ABSTRACTThis paper analyzes results concerning flow boiling heat transfer in two parallel, asymmetrically heated vertical Minichannels. The heating element for FC-72 Fluorinert flowing in the Minichannels was a thin foil with an enhanced surface on the side in contact with the fluid. In one minichannel, changes in the temperature on the smooth side of the foil were monitored using liquid crystal thermography. Changes in the temperature on the outer surface of the glass in one minichannel and on the foil in the other minichannel were observed using infrared thermography. The heat transfer coefficient at the foil–fluid interface was calculated on the basis of one- and two-dimensional heat transfer models. In the two-dimensional method, the distribution of temperature on the enhanced side of the foil was determined by solving the inverse heat conduction problem. The governing equations were solved using the finite-element method combined with the Trefftz functions used as shape functions. The temperature mea...
-
comparison of two surface temperature measurement using thermocouples and infrared camera
EPJ Web of Conferences, 2017Co-Authors: Dariusz Michalski, Kinga Strąk, Magdalena PiaseckaAbstract:This paper compares two methods applied to measure surface temperatures at an experimental setup designed to analyse flow boiling heat transfer. The temperature measurements were performed in two parallel rectangular Minichannels, both 1.7 mm deep, 16 mm wide and 180 mm long. The heating element for the fluid flowing in each minichannel was a thin foil made of Haynes-230. The two measurement methods employed to determine the surface temperature of the foil were: the contact method, which involved mounting thermocouples at several points in one minichannel, and the contactless method to study the other minichannel, where the results were provided with an infrared camera. Calculations were necessary to compare the temperature results. Two sets of measurement data obtained for different values of the heat flux were analysed using the basic statistical methods, the method error and the method accuracy. The experimental error and the method accuracy were taken into account. The comparative analysis showed that although the values and distributions of the surface temperatures obtained with the two methods were similar but both methods had certain limitations.
Luisa Rossetto - One of the best experts on this subject based on the ideXlab platform.
-
KEYNOTE PAPER UPDATE ON CONDENSATION HEAT TRANSFER AND PRESSURE DROP INSIDE Minichannels
2020Co-Authors: Alberto Cavallini, Marko Matkovič, Luca Doretti, Luisa RossettoAbstract:ABSTRACT The present paper reviews published experimental work focusing on condensation flow regimes, heat transfer and pressure drop in Minichannels. New experimental data are available with high pressure (R410A), medium (R134a) and low pressure (R236ea) refrigerants in Minichannels of different cross section geometry and with hydraulic diameters ranging from 0.4 to 3 mm. Because of the influence of flow regimes on heat transfer and pressure drop, a literature review is presented to discuss flow regimes transitions. The available experimental frictional pressure gradients and heat transfer coefficients are compared with semi empirical and theoretical models developed for conventional channels and with models specifically created for Minichannels. Starting from the results of the comparison between experimental data and models, the paper will discuss and evaluate the opportunity for a new heat transfer model for condensation in Minichannels; the new model attempts to take into account the effect of the entrainment rate of droplets from the liquid film
-
Experimental study on condensation heat transfer inside a single circular minichannel
International journal of heat and mass transfer, 2017Co-Authors: Marko Matkovič, Alberto Cavallini, Davide Del Col, Luisa RossettoAbstract:The measurement of the condensation heat transfer coefficient inside micro- and Minichannels is still somewhat elusive due to the difficult task of getting accurate values of the heat transfer coefficients during the condensation process, particularly when studied within single Minichannels. The present paper reports local heat transfer coefficients obtained from the measurement of the local heat flux and the direct measurement of the saturation and wall temperatures during condensation of R134a and R32 within asingle circular 0.96 mm diameter minichannel. Except for the lowest mass velocity, the test results do not show significant discrepancy from the trendsexpected for macroscale tubes.
-
Two-phase frictional pressure gradient of R236ea, R134a and R410A inside multi-port mini-channels
Experimental thermal and fluid science, 2016Co-Authors: Marko Matkovič, Alberto Cavallini, Luca Doretti, Luisa Rossetto, Davide Del Col, Claudio ZilioAbstract:In the present paper the pressure drop characteristics of a 1.4 mm hydraulic diameter multiport minichannel tube during adiabatic two-phase flow of HFC refrigerants are discussed. The tube consists of eleven parallel rectangular cross section channels. Although much experimental research has been devoted to investigate the pressure drop characteristics of R134a inside multiport Minichannels in the last years, very little information is available on different refrigerants, such as R236ea (low pressure) and R410A (high pressure), whose behaviour is different from R134a. The experimental runs are carried out at mass velocities ranging from 200 to 1400 kg/(m2 s), depending on the refrigerant under test, at constant value of vapour quality. The frictional pressure gradient is obtained from the saturation temperature drop measurement. The results presented here cover a wide range of the reduced pressure, from 0.1 up to 0.5. The experimental frictional pressure drop data is compared against models available in the literature for prediction of frictional pressure gradient in channels. The comparison of calculated to experimental values shows that the R134a frictional pressure gradient in the multiport minichannel test tube can be fairly well predicted by available correlations, but not satisfactory agreement is found for R236ea data and evenworse in the case of R410A data.
-
Condensation heat transfer and pressure gradient inside multiport Minichannels
Heat transfer engineering, 2016Co-Authors: Marko Matkovič, Alberto Cavallini, Luca Doretti, Luisa Rossetto, Davide Del Col, Claudio ZilioAbstract:In this paper, the experimental heat transfer coefficients measured during condensation of R134a and R41 DA inside multiport Minichannels are presented. The frictional pressure gradient was also measured during adiabatic two-phase flow. The need for experimental research on condensation inside multiport Minichannels comes from the wide use of those channels in automotive air-conditioners. The perspective for the adoption of similar channels in the residential air conditioning applications also cals for experimental research on new high pressure refrigerants, such as R41OA. Experimental data are corripared against models to show the accuracy of the models in the prediction of heat transfer coefficients and pressure drop inside Minichannels.
-
heat transfer and pressure drop of natural refrigerants in Minichannels low charge equipment
International Journal of Refrigeration-revue Internationale Du Froid, 2013Co-Authors: Alberto Cavallini, Luisa RossettoAbstract:The paper presents a comprehensive overview of the most recent research works on heat transfer (and pressure drop) with natural refrigerants in Minichannels, aimed at proper design of heat transfer equipment. About boiling heat transfer, experimental HT results are mainly fitted by empirical correlations referring to the common mechanisms used in more conventional geometries (nucleate and convective boiling); evaporation heat transfer through thin liquid film around vapor plugs is at times considered. About shear dominated condensation heat transfer, suggested design tools again mostly refer to the extension of the semi-empirical correlations earlier established for conventional geometries. For CO2, heat transfer at supercritical conditions, such as in a gas cooler, is also treated. Finally the concept of the Penalty Factor is applied to shear condensation in Minichannels to establish the heat transfer performance of the different working fluids, the superior effectiveness of minitubes over macrotubes, and the optimization of minichannel condensers.
Alberto Cavallini - One of the best experts on this subject based on the ideXlab platform.
-
KEYNOTE PAPER UPDATE ON CONDENSATION HEAT TRANSFER AND PRESSURE DROP INSIDE Minichannels
2020Co-Authors: Alberto Cavallini, Marko Matkovič, Luca Doretti, Luisa RossettoAbstract:ABSTRACT The present paper reviews published experimental work focusing on condensation flow regimes, heat transfer and pressure drop in Minichannels. New experimental data are available with high pressure (R410A), medium (R134a) and low pressure (R236ea) refrigerants in Minichannels of different cross section geometry and with hydraulic diameters ranging from 0.4 to 3 mm. Because of the influence of flow regimes on heat transfer and pressure drop, a literature review is presented to discuss flow regimes transitions. The available experimental frictional pressure gradients and heat transfer coefficients are compared with semi empirical and theoretical models developed for conventional channels and with models specifically created for Minichannels. Starting from the results of the comparison between experimental data and models, the paper will discuss and evaluate the opportunity for a new heat transfer model for condensation in Minichannels; the new model attempts to take into account the effect of the entrainment rate of droplets from the liquid film
-
Experimental study on condensation heat transfer inside a single circular minichannel
International journal of heat and mass transfer, 2017Co-Authors: Marko Matkovič, Alberto Cavallini, Davide Del Col, Luisa RossettoAbstract:The measurement of the condensation heat transfer coefficient inside micro- and Minichannels is still somewhat elusive due to the difficult task of getting accurate values of the heat transfer coefficients during the condensation process, particularly when studied within single Minichannels. The present paper reports local heat transfer coefficients obtained from the measurement of the local heat flux and the direct measurement of the saturation and wall temperatures during condensation of R134a and R32 within asingle circular 0.96 mm diameter minichannel. Except for the lowest mass velocity, the test results do not show significant discrepancy from the trendsexpected for macroscale tubes.
-
Two-phase frictional pressure gradient of R236ea, R134a and R410A inside multi-port mini-channels
Experimental thermal and fluid science, 2016Co-Authors: Marko Matkovič, Alberto Cavallini, Luca Doretti, Luisa Rossetto, Davide Del Col, Claudio ZilioAbstract:In the present paper the pressure drop characteristics of a 1.4 mm hydraulic diameter multiport minichannel tube during adiabatic two-phase flow of HFC refrigerants are discussed. The tube consists of eleven parallel rectangular cross section channels. Although much experimental research has been devoted to investigate the pressure drop characteristics of R134a inside multiport Minichannels in the last years, very little information is available on different refrigerants, such as R236ea (low pressure) and R410A (high pressure), whose behaviour is different from R134a. The experimental runs are carried out at mass velocities ranging from 200 to 1400 kg/(m2 s), depending on the refrigerant under test, at constant value of vapour quality. The frictional pressure gradient is obtained from the saturation temperature drop measurement. The results presented here cover a wide range of the reduced pressure, from 0.1 up to 0.5. The experimental frictional pressure drop data is compared against models available in the literature for prediction of frictional pressure gradient in channels. The comparison of calculated to experimental values shows that the R134a frictional pressure gradient in the multiport minichannel test tube can be fairly well predicted by available correlations, but not satisfactory agreement is found for R236ea data and evenworse in the case of R410A data.
-
Condensation heat transfer and pressure gradient inside multiport Minichannels
Heat transfer engineering, 2016Co-Authors: Marko Matkovič, Alberto Cavallini, Luca Doretti, Luisa Rossetto, Davide Del Col, Claudio ZilioAbstract:In this paper, the experimental heat transfer coefficients measured during condensation of R134a and R41 DA inside multiport Minichannels are presented. The frictional pressure gradient was also measured during adiabatic two-phase flow. The need for experimental research on condensation inside multiport Minichannels comes from the wide use of those channels in automotive air-conditioners. The perspective for the adoption of similar channels in the residential air conditioning applications also cals for experimental research on new high pressure refrigerants, such as R41OA. Experimental data are corripared against models to show the accuracy of the models in the prediction of heat transfer coefficients and pressure drop inside Minichannels.
-
heat transfer and pressure drop of natural refrigerants in Minichannels low charge equipment
International Journal of Refrigeration-revue Internationale Du Froid, 2013Co-Authors: Alberto Cavallini, Luisa RossettoAbstract:The paper presents a comprehensive overview of the most recent research works on heat transfer (and pressure drop) with natural refrigerants in Minichannels, aimed at proper design of heat transfer equipment. About boiling heat transfer, experimental HT results are mainly fitted by empirical correlations referring to the common mechanisms used in more conventional geometries (nucleate and convective boiling); evaporation heat transfer through thin liquid film around vapor plugs is at times considered. About shear dominated condensation heat transfer, suggested design tools again mostly refer to the extension of the semi-empirical correlations earlier established for conventional geometries. For CO2, heat transfer at supercritical conditions, such as in a gas cooler, is also treated. Finally the concept of the Penalty Factor is applied to shear condensation in Minichannels to establish the heat transfer performance of the different working fluids, the superior effectiveness of minitubes over macrotubes, and the optimization of minichannel condensers.
Shigeru Koyama - One of the best experts on this subject based on the ideXlab platform.
-
evaporation heat transfer and pressure drop characteristics of r32 inside a multiport tube with microfins
International Journal of Air-conditioning and Refrigeration, 2018Co-Authors: Daisuke Jige, Shogo Kikuchi, Hikaru Eda, Norihiro Inoue, Shigeru KoyamaAbstract:This study investigated the evaporation heat transfer and pressure drop characteristics of R32 in a horizontal multiport tube consisting of rectangular Minichannels with straight microfins. The hea...
-
Two-phase flow characteristics of R32 in horizontal multiport Minichannels: Flow visualization and development of flow regime map
International Journal of Refrigeration, 2018Co-Authors: Daisuke Jige, Shogo Kikuchi, Hikaru Eda, Norihiro Inoue, Shigeru KoyamaAbstract:Abstract The two-phase flow characteristics of R32 were experimentally investigated for horizontal multiport rectangular Minichannels with hydraulic diameters of 0.5 and 1.0 mm. The two-phase flow was observed using a high-speed camera, with a mass velocity range of 30–400 kgm−2s−1 at a saturation temperature of 15 °C. The effects of mass velocity, quality, and channel size on the two-phase flow were clarified. The observed two-phase flow was classified into intermittent, transition, and annular flow regimes. The intermittent flow regime was observed at a lower quality region. The quality of transition from intermittent to transition flow regimes decreased with increasing mass velocity and channel size. Previously proposed flow regime maps could not predict the two-phase flow regime in multiport rectangular Minichannels with sufficient accuracy. Thus, a new prediction method of flow regimes for multiport Minichannels, considering channel size, was developed.
-
condensation of refrigerants in a multiport tube with rectangular Minichannels
International Journal of Refrigeration-revue Internationale Du Froid, 2016Co-Authors: Daisuke Jige, Norihiro Inoue, Shigeru KoyamaAbstract:Abstract This study investigated the condensation heat transfer and pressure drop characteristics of refrigerants R134a, R32, R1234ze(E), and R410A in a horizontal multiport tube with rectangular Minichannels, in the mass velocity range of 100–400 kg m−2 s−1 and saturation temperature set at 40 and 60 °C. The effect of mass velocity, vapor quality, saturation temperature, refrigerant properties, and hydraulic diameter of rectangular channels on condensation characteristics is clarified. A new correlation is proposed for predicting the frictional pressure drop for condensation flow in Minichannels. A heat transfer model for condensation heat transfer in rectangular Minichannels is developed considering the flow patterns and effects of vapor shear stress and surface tension. Then, based on this model, a new heat transfer correlation is proposed. The proposed correlations successfully predict the experimental frictional pressure drop and heat transfer coefficients of the test refrigerants in horizontal rectangular Minichannels.
Davide Del Col - One of the best experts on this subject based on the ideXlab platform.
-
Effects of geometry and fluid properties during condensation in Minichannels: experiments and simulations
Heat and Mass Transfer, 2019Co-Authors: Paolo Toninelli, Stefano Bortolin, Marco Azzolin, Davide Del ColAbstract:The present paper aims at investigating the condensation process inside Minichannels, at low mass fluxes, where bigger discrepancies from conventional channels can be expected. At high mass flux, the condensation in Minichannels is expected to be shear stress dominated. Therefore, models originally developed for conventional channels could still do a good job in predicting the heat transfer coefficient. When the mass flow rate decreases, the condensation process in Minichannels starts to display differences with the same process in macro-channels. With the purpose of investigating condensation at these operating conditions, new experimental data are here reported and compared with data already published in the literature. In particular, heat transfer coefficients have been measured during R134a and R1234ze(E) condensation inside circular and square cross section Minichannels at mass flux ranging between 65 and 200 kg m^−2 s^−1. These new data are compared with those of R32, R717, R290, R152a to show the effect of channel shape and fluid properties and to assess the applicability of correlations developed for macroscale condensation. For this purpose, a new criterion based on the Weber number is presented to decide when the macroscale condensation correlation can be applied. The present experimental data are also compared against three-dimensional Volume of Fluid (VOF) simulations of condensation in Minichannels with circular and square cross section. This comparison allows to get an insight into the process and evaluate the main heat transfer mechanisms.
-
Experimental study on condensation heat transfer inside a single circular minichannel
International journal of heat and mass transfer, 2017Co-Authors: Marko Matkovič, Alberto Cavallini, Davide Del Col, Luisa RossettoAbstract:The measurement of the condensation heat transfer coefficient inside micro- and Minichannels is still somewhat elusive due to the difficult task of getting accurate values of the heat transfer coefficients during the condensation process, particularly when studied within single Minichannels. The present paper reports local heat transfer coefficients obtained from the measurement of the local heat flux and the direct measurement of the saturation and wall temperatures during condensation of R134a and R32 within asingle circular 0.96 mm diameter minichannel. Except for the lowest mass velocity, the test results do not show significant discrepancy from the trendsexpected for macroscale tubes.
-
Two-phase frictional pressure gradient of R236ea, R134a and R410A inside multi-port mini-channels
Experimental thermal and fluid science, 2016Co-Authors: Marko Matkovič, Alberto Cavallini, Luca Doretti, Luisa Rossetto, Davide Del Col, Claudio ZilioAbstract:In the present paper the pressure drop characteristics of a 1.4 mm hydraulic diameter multiport minichannel tube during adiabatic two-phase flow of HFC refrigerants are discussed. The tube consists of eleven parallel rectangular cross section channels. Although much experimental research has been devoted to investigate the pressure drop characteristics of R134a inside multiport Minichannels in the last years, very little information is available on different refrigerants, such as R236ea (low pressure) and R410A (high pressure), whose behaviour is different from R134a. The experimental runs are carried out at mass velocities ranging from 200 to 1400 kg/(m2 s), depending on the refrigerant under test, at constant value of vapour quality. The frictional pressure gradient is obtained from the saturation temperature drop measurement. The results presented here cover a wide range of the reduced pressure, from 0.1 up to 0.5. The experimental frictional pressure drop data is compared against models available in the literature for prediction of frictional pressure gradient in channels. The comparison of calculated to experimental values shows that the R134a frictional pressure gradient in the multiport minichannel test tube can be fairly well predicted by available correlations, but not satisfactory agreement is found for R236ea data and evenworse in the case of R410A data.
-
Condensation heat transfer and pressure gradient inside multiport Minichannels
Heat transfer engineering, 2016Co-Authors: Marko Matkovič, Alberto Cavallini, Luca Doretti, Luisa Rossetto, Davide Del Col, Claudio ZilioAbstract:In this paper, the experimental heat transfer coefficients measured during condensation of R134a and R41 DA inside multiport Minichannels are presented. The frictional pressure gradient was also measured during adiabatic two-phase flow. The need for experimental research on condensation inside multiport Minichannels comes from the wide use of those channels in automotive air-conditioners. The perspective for the adoption of similar channels in the residential air conditioning applications also cals for experimental research on new high pressure refrigerants, such as R41OA. Experimental data are corripared against models to show the accuracy of the models in the prediction of heat transfer coefficients and pressure drop inside Minichannels.
-
comprehensive experimental investigation of two phase heat transfer and pressure drop with propane in a minichannel
International Journal of Refrigeration-revue Internationale Du Froid, 2014Co-Authors: Davide Del Col, Matteo Bortolato, Stefano BortolinAbstract:Abstract The use of hydrocarbons as natural refrigerants inside small diameter channels allows charge minimization and therefore it may be an interesting option in the refrigerating and heat pump technology. The aim of the present experimental work is to fully characterize the thermal performance of propane (R290) in Minichannels by measuring frictional pressure drop, condensation and flow boiling heat transfer coefficients inside a circular cross section horizontal minichannel with an internal diameter of 0.96 mm and a rough inner surface. Measurements of frictional pressure drop during adiabatic two-phase flow have been performed at mass velocity ranging between 200 and 800 kg m−2 s−1. Local heat transfer coefficients have been measured during condensation and during flow boiling in the mass velocity range from 100 to 1000 kg m−2 s−1. The present database, including frictional pressure gradient, condensation and vaporization heat transfer coefficients, is compared against predicting correlations available in the open literature.