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1
Content available Effect of nanofluid concentration on two-phase thermosyphon heat exchanger performance
100%
Cieśliński J. T.
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2016
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tom Vol. 37, no. 2
23--40
EN
An approach – relaying on application of nanofluid as a working fluid, to improve performance of the two-phase thermosyphon heat exchanger (TPTHEx) has been proposed. The prototype heat exchanger consists of two horizontal cylindrical vessels connected by two risers and a downcomer. Tube bundles placed in the lower and upper cylinders work as an evaporator and a condenser, respectively. Distilled water and nanofluid water-Al2O3 solution were used as working fluids. Nanoparticles were tested at the concentration of 0.01% and 0.1% by weight. A modified Peclet equation and Wilson method were used to estimate the overall heat transfer coefficient of the tested TPTHEx. The obtained results indicate better performance of the TPTHEx with nanofluids as working fluid compared to distilled water, independent of nanoparticle concentration tested. However, increase in nanoparticle concentration results in overall heat transfer coefficient decrease of the TPTHEx examined. It has been observed that, independent of nanoparticle concentration tested, decrease in operating pressure results in evaporation heat transfer coefficient increase.
2
Content available remote Measurements of gas and vapour bubble detachment frequency, diameter and rise velocity
63%
Szymczyk J. A. , Cieśliński J. T.
Transactions of the Institute of Fluid-Flow Machinery
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2001
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tom nr 109
69-85
EN
For single gas and vapour bubbles, the equivalent diameter, the rise velicity, and the frequency were measured on single artificial sites in distilled water. The air bubbles were emitted from glass nozzles with internal diameters of 0.3 mm, 0.6 mm, 0.9 mm and metallic orfice plates 2mm and 4 mm in diameter. Electrically heated needles have been employed to produce vapour bubbles. The needles made of brass and stainless steel were placed in glass tubes so a kind of pin fin were produced. The diameter of the pin fin at the base ranged from 0.27 mm to 0.78 mm and height from 0.48 to 4.8 mm. The experoments were conducted at atmospheric pressure. A technique based on Particle Image Velocimetry for measurement of bubble size and rise velocity has been developed and frequency of bubble departure was measured using a variable frequency stroboscope.
3
Content available remote Investigation of R 22 and R 134a flow boiling in enhanced tubes
63%
Cieśliński J. T. , Targański W.
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tom nr 112
21-36
EN
Results of heat transfer and pressure drop investigation during flow boiling of R.22 and R. 134a inside smooth tubes and selected enhanced tubes are presented. Corrugated and microfinned tubes served as enhanced tubes. The experiments have been conducted for average saturation temperature 0'C. Intel vapour quality was set to 0 and outlet quality: 0.7. Mass flux density varied from about 250 to 500 kg/(m2s). The experimental results have been compared with head transfer coefficients calculated from selected correlations. The test stand and experimental procedure are described. Higher average evaporation heat transfer coefficients and pressure drops for enhanced tubes have been observed. Refrigerant R.22 has an evident superiority over R. 134a for each tested type of tube.
4
Content available Pool boiling of nanofluids on rough and porous coated tubes: experimental and correlation
63%
Cieśliński J. T. , Kaczmarczyk T. Z.
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tom Vol. 35, no. 2
3--20
EN
The paper deals with pool boiling of water-Al2O3 and water-Cu nanofluids on rough and porous coated horizontal tubes. Commercially available stainless steel tubes having 10 mm outside diameter and 0.6 mm wall thickness were used to fabricate the test heater. The tube surface was roughed with emery paper 360 or polished with abrasive compound. Aluminium porous coatings of 0.15 mm thick with porosity of about 40% were produced by plasma spraying. The experiments were conducted under different absolute operating pressures, i.e., 200, 100, and 10 kPa. Nanoparticles were tested at the concentration of 0.01, 0.1, and 1% by weight. Ultrasonic vibration was used in order to stabilize the dispersion of the nanoparticles. It was observed that independent of operating pressure and roughness of the stainless steel tubes addition of even small amount of nanoparticles augments heat transfer in comparison to boiling of distilled water. Contrary to rough tubes boiling heat transfer coefficient of tested nanofluids on porous coated tubes was lower compared to that for distilled water while boiling on porous coated tubes. A correlation equation for prediction of the average heat transfer coefficient during boiling of nanofluids on smooth, rough and porous coated tubes is proposed. The correlation includes all tested variables in dimensionless form and is valid for low heat flux, i.e., below 100 kW/m2.
5
An approach to modelling nucleate pool boiling heat transfer from horizontal tubes at low heat flux density
63%
Cieśliński J. T. , Dominczak P. R.
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1999
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tom Z. 67
195--204
EN
An experiment on nucleate pool boiling heat transfer from horizontal cylinders to saturated, distilled water under atmospheric pressure is reported. Experiments of nucleate pool boiling were conducted using stainless steel tubes with OD: 8.15 mm and 18.04 mm and active length about 250 mm. In particular, measurements have been performed of inside circumferential temperature. Three component model of nucleate pool boiling outside horizontal tube has been proposed. The proposed mechanisms of heat transfer that have contribution in total heat flux are: free convection, evaporation to sliding bubbles and nucleate boiling.
6
Wrzenie mieszanin czynnika chłodniczego i oleju w rurach
63%
Cieśliński J. T. , Targański W.
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tom nr 11
401-405
PL
Przedstawiono wyniki badań współczynnika przejmowania ciepła i spadku ciśnienia podczas wrzenia czynników R 22, R 134a i R 407C oraz ich mieszanin z olejem w rurach gładkich. Opisano budowę stanowiska doświadczalnego wraz z procedurą badawczą. Podczas badań udział masowy oleju w mieszaninie z czynnikiem wynosił 1% i 5 %. Zaobserwowano negatywny wpływ obecności środka smarnego we wrzącym czynniku chłodniczym.
EN
The results of experimental investigations of the boiling heat transfer coefficient and the pressure drop during boiling of pure refrigerants R 22, R 134a and R 407C as well as the mixtures of these refrigerants with oil inside smooth tubes have been presented in the paper. The experimental stand as well as the test procedure have been described. The oil concentration in refrigerants was 1% up to 5% during experiments. The presence of oil caused the deterioration of boiling heat transfer.
7
Przejmowanie ciepła przy wrzeniu nanocieczy w dużej objętości. Część 3. Stan wiedzy
63%
Kaczmarczyk T. , Cieśliński J. T.
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tom nr 1
7--13
PL
Cykl artykułów poświęconych zagadnieniu przejmowania ciepła podczas wrzenia nanocieczy w dużej objętości. W części pierwszej tego cyklu („TCHK”, nr 11/2012) omówione zostały metody ich wytwarzania i bardziej szczegółowo właściwości termofizyczne, takie jak: współczynnik przewodzenia ciepła, lepkość, przewodność elektryczna, potencjał zeta, napięcie powierzchniowe i kąt zwilżania. W części drugiej („TCHK”, nr 12/2012) autorzy dokonali przeglądu publikowanych wyników nielicznych prac badawczych, dotyczących wrzenia nanocieczy na powierzchniach gładkich i chropowatych. W części trzeciej prezentujemy ciąg dalszy publikowanych w dostępnej literaturze wyników badań, tym razem dotyczących wrzenia nanocieczy na powierzchniach rozwiniętych.
EN
A series of articles on the issue of heat transfer during boiling nanofluids in high volume. In the first part of the cycle ("TCHK", No. 11/2012) discusses methods for their preparation, and more particularly thermophysical properties such as thermal conductivity, viscosity, conductivity, zeta potential, surface tension and contact angle. In the second part ("TCHK", No. 12/2012), the authors reviewed the published results of the few research works concerning the boiling nanofluids on smooth and rough surfaces. In the third part we present the continuation published in the open literature studies, this time on the point on the surface of nanofluids developed.
8
Simulation of temperature field in cylindrical boiling heating section
51%
Cieśliński J. T. , Kaczmarczyk T. Z. , Krasowski K.
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2007
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tom Vol. 12
59-64
EN
The present paper deals with inverse 3D heat conduction problem. Taking into account geometry and design of the heating scction temperature field of the cylindrical boiling section has been estimated. The finite element approach has been applied for solving the boundary problem.
9
Modelling of temperature field of flat boiling section with active single nucleation site
51%
Cieśliński J. T. , Jasiński R. , Polewski J.
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2007
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tom Vol. 12
65-73
EN
The main assumptions of selected models of boiling from single cavity are presented. The ability of the models to predict heat transfer rate is discussed on the basis of own experimental data. Numerical model has been developed in order to check the commonly accepted assumption that the area of influence of nucleation site is equal to twice of departure diameter of vapour bubble as well as gain more information about heating section design used in present study. The present numerical model deals with 2D axi-symmetrical, non-isotropic heat conduction boundary problem. The finite element approach has been applied for solving heat conduction differential equation with boundary conditions of first, second and third kind, simultaneously. Boundary condition of first second kind represents heat flux density connected with bubbles generated from single nucleation site.
10
Content available remote Performance of the PEM fuel cell module. Part 2. Effect of excess ratio and stack temperature
51%
Cieśliński J. T. , Kaczmarczyk T. , Dawidowicz B.
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tom Vol. 97, nr 3
246--251
EN
The paper describes a fuel cell based system performance under different thermal conditions. The system could be fed with bottled hydrogen or with very high purity hydrogen obtained from reforming of methanol. The system is based on two fuel cell units (1.2 kW each, produced by Ballard Power Systems Inc. and called Nexa), DC/DC converter, DC/AC inverter, microprocessor control unit, load unit, bottled hydrogen supply system and a set of measurement instruments. In this study steady-state operation of the PEM fuel cell system at different values of air excess ratio and different stack temperature was investigated. The load of the system was provided with the aid of a set of resistors. The results obtained show that the net power of the system does not depend on the air excess ratio within the range of O2 from 1.9 to 5.0. The polarization curves of the fuel cell module showed that the fuel cell performance was improved with increased stack temperature within the range of 30°C to 65°C. It was established that the total efficiency of the tested system depends on the hydrogen source and is higher when using bottled hydrogen of about 30% and 16%, for minimum and maximum load, respectively.
11
Content available Heat transfer in plate heat exchanger channels: Experimental validation of selected correlation equations
51%
Cieśliński J. T. , Fiuk A. , Typiński K. , Siemieńczuk B.
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tom Vol. 37, no. 3
19--29
EN
This study is focused on experimental investigation of selected type of brazed plate heat exchanger (PHEx). The Wilson plot approach was applied in order to estimate heat transfer coefficients for the PHEx passages. The main aim of the paper was to experimentally check ability of several correlations published in the literature to predict heat transfer coefficients by comparison experimentally obtained data with appropriate predictions. The results obtained revealed that Hausen and Dittus-Boelter correlations underestimated heat transfer coefficient for the tested PHEx by an order of magnitude. The Aspen Plate code overestimated heat transfer coefficient by about 50%, while Muley-Manglik correlation overestimated it from 1% to 25%, dependent on the value of Reynolds number and hot or cold liquid side.
12
Content available Measurement of temperature-dependent viscosity and thermal conductivity of alumina and titania thermal oil nanofluids
51%
Cieśliński J. T. , Ronewicz K. , Smoleń S.
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2015
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tom Vol. 36, no. 4
35--47
EN
In this study the results of simultaneous measurements of dynamic viscosity, thermal conductivity, electrical conductivity and pH of two nanofluids, i.e., thermal oil/Al2O3 and thermal oil/TiO2 are presented. Thermal oil is selected as a base liquid because of possible application in ORC systems as an intermediate heating agent. Nanoparticles were tested at the concentration of 0.1%, 1%, and 5% by weight within temperature range from 20°C to 60°C. Measurement devices were carefully calibrated by comparison obtained results for pure base liquid (thermal oil) with manufacturer’s data. The results obtained for tested nanofluids were compared with predictions made by use of existing models for liquid/solid particles mixtures.
13
Content available remote Experimental investigation of free convection of glycol-Al2O3 nanofluid from horizontal tube
51%
Cieśliński J. T. , Smoleń S. , Sawicka D.
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tom z. 88 [293], nr 4
315--322
EN
Nanofluids are considered to be a new generation of coolants, both in single- and two phase systems. Furthermore, nanofluids or nanocomposites may be used as a media in thermal energy storage (TES) in such systems as sensible heat storage (SHS) and phase change materials (PCM). In the SHS systems the dominating mechanism of the heat transfer is natural convection. However, in the literature only a few investigations of free convection of nanofluids have been discussed. This paper presents preliminary results of the experimental investigation of natural convection heat transfer of glycol-Al2O3 nanofluid from horizontal tube.
PL
Nanociecze uważane są za nową generację czynników chłodzących w układach jednofazowych oraz dwufazowych. Ponadto, nanociecze i nanokomponenty mogą być użyte jako środki magazynowania energii cieplnej (TES) w takich systemach jak SHS czy PCM. W systemach wykorzystujących ciepło jawne dominującym sposobem wymiany ciepła jest konwekcja swobodna. Mimo tego, jak dotąd, przeprowadzono niewiele badań eksperymentalnych i numerycznych dotyczących zjawiska konwekcji swobodnej nanocieczy. W pracy zaprezentowano wstępne wyniki badań eksperymentalnych wymiany ciepła podczas konwekcji swobodnej nanocieczy glikol-Al2O3 na poziomej rurce.
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