Thermal performance evaluation of a solar air heater with and without thermal energy storage

This communication presents the experimental study and performance analysis of a solar air heater with and without phase change material (PCM) viz. paraffin wax and hytherm oil. There are three different arrangements viz. without PCM, with PCM and with hytherm oil to study the comparative performance of this experimental system. Inlet, outlet temperatures and radiation with respect to time have been recorded and found that the output temperature in case with thermal energy storage (TES) is higher than that of without TES, besides, the outlet temperature with paraffin wax is slightly greater than that of with hytherm oil. Also there is no energy gain in the evening in case of without TES but in case of with TES there is a heat gain for around 4 h in the evening which gives the backup for hot air for around four more hours which is the main advantage of this systems with TES. Based on the data, the efficiency of the system has been calculated and it is noted that the efficiency in the case of heat storage is higher than that of without TES, besides the efficiency in the case of the paraffin wax is slightly higher than that of the hytherm oil case.     

Experimental investigation on solar thermal air heater with a combination of roughness elements for heat transfer improvement

Journal of Thermal Analysis and Calorimetry - This work attempts to determine the influence of the integration of a combination of roughness elements on the heat dissipation and frictional losses...     

Effect of filler loading,geometry, dispersion and temperature on thermal conductivity of polymer nanocomposites

Using a unidirectional heat transfer apparatus, the roles of nanoparticle geometry, loading, dispersion and temperature on the thermal conductivity of polymer nanocomposites are investigated. The polymer nanocomposites (PNC) consist of epoxy matrices filled with silica nanopowder and carbon nanotubes, respectively, as well as poly (2-vinylpyridine) (P2VP) matrices loaded with silica nanoparticles. First, it is shown that thermal conductivity generally increases with nanofiller loading. These results are also reasonably described by the three phase Lewis-Nielsen or Halpin-Tsai analytical models. More importantly, it has been also demonstrated that the thermal conductivity of the polymer nanocomposites greatly depends on the dispersion state of the nanofillers. Furthermore, the effect of temperature on the thermal behavior of PNCs is briefly discussed. These results emphasize the important role of nanoparticles content and dispersion state on the thermal characteristics of polymer nanocomposites, which can be used to design composite materials with tunable thermal behavior.     

A study on the thermal conductivity of resilient materials

The floor system of apartments must have a certain level of floor impact sound performance (light-weight impact sound is 58 dB or less, heavy-weight impact sound is 50 dB or less), and comply with the building energy code to prevent energy loss in residential buildings in Korea. In this study, expanded polystyrene (EPS), expanded polypropylene (EPP), ethylene-vinyl acetate copolymer (EVA), polyethylene (PE) and urethane foam, which are widely used in Korea as resilient materials for floating floor system of apartments, were measured. Their thermal conductivity and apparent density were measured to analyze their thermal properties and their relation was analyzed by material. In case of resilient materials made of EPS and EPP, thermal conductivity tended to decrease as apparent density increased, whereas in case of resilient materials made of EVA and PE, as apparent density increased, thermal conductivity tended to increase as well.     

Exergetic performance evaluation of solar air heater having V-down perforated baffles on the absorber plate

Baffles serve as heat transfer augmentation features in solar air heaters; however, they increase pressure drop in flow channels. Perforated baffles are relatively good heat transfer augmentation features with superior performance over conventional smooth duct solar air heater and as a result find application in some solar air heaters. The exergy method is employed to in determining the roughness parameters, as second law-based exergy analysis is suitable for design of roughened solar air heaters. The exergetic efficiency of V down perforated baffled roughened duct solar air heater is studied analytically, and the results obtained compared with conventional system. Results indicate that high efficiency with optimum V down perforated baffle improves the heat absorption and dissipation potential of a solar air heater. Design plots are prepared to predict the optimum roughness parameter as a function of temperature rise parameter.     

Experimental study of thermal performance and pressure drop on a solar air heater with different orientations of arc-shape rib roughness

Journal of Thermal Analysis and Calorimetry - An exhaustive experimental investigation was carried out for the thermal performance of artificially roughened solar air heaters (SAHs) under the...     

Role of the Debye temperature in the lattice thermal conductivity of silicon

This paper is a theoretical study of the effect of the variation in the Debye temperature _D with temperature on the lattice thermal conductivity of Si in the temperature range 2–300 K. Expressions for the three-phonon scattering relaxation rates previously proposed by Shermaet al. are used here. The percentage changes in the lattice thermal conductivity due to the Debye temperature for the transverse and the longitudinal phonons are studied separately.

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Zusammenfassung Dieses Manuskript ist eine theoretische Untersuchung des Einflusses der Veränderung der Debey-Temperatur D mit der Temperatur auf die Gitterwärmeleitfähigkeit von Si im Temperaturbereich 2–300 K. Unlängst von Shermaet al. vorgeschlagene Ausdrücke für die drei Phononen-Streuungsrelaxations-Geschwindigkeiten fanden dabei Anwendung. Die prozentuelle Änderung der Gitterwärmeleitfähigkeit in Abhängigkeit von der Debey-Temperatur wurde für transversale als auch für longitudinale Phononen separat untersucht.

     

Effects of crosslinking and chain degradation on the thermal conductivity of polymers

Summary The thermal conductivity of the following polymers was measured in the temperature range from –170 to 140 °C: Two crosslinked polymers (irradiated PE and PMMA crosslinked with TAC) and two degradated polymers (heat-treated AN-MMA-copolymer and irradiated PMMA).In the temperature range fromT _g toT _m , the thermal conductivity of irradiated PE decreases with increasing temperature and with increasing dose up to 600 MRD. The observed decrease of the thermal conductivity is attributed to a decrease of crystallinity due to irradiation. At temperatures aboveT _m , the thermal conductivity increases with the radiation dose. This results from radiation induced crosslinking.For crosslinked PMMA, the thermal conductivity increases with increasing concentration of TAC.The thermal conductivity of heat-treated AN-MMA-copolymer seems to decrease with heating time. This is caused by a shift of the flat break atT _g to higher temperatures.For irradiated PMMA, the thermal conductivity decreases slightly with radiation doses greater than 100 MRD.

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Zusammenfassung Die Wärmeleitfähigkeit folgender Polymeren wurde im Temperaturbereich von –175 bis 140 °C gemessen: Zwei vernetzte Polymere (bestrahltes PÄ und mit TAC vernetztes PMMA) und zwei abgebaute Polymere (AN-MMA-Copolymer mit thermischer Vorbehandlung und bestrahltes PMMA).Im Temperaturbereich vonT _g bisT _m nimmt die Wärmeleitfähigkeit des bestrahlten PÄ mit wachsender Temperatur und mit zunehmender Bestrahlungsdosis bis 600 MRD ab. Dieser Abfall der Wärmeleitfähigkeit wird auf die Abnahme der Kristallinität infolge Bestrahlung zurückgeführt. Bei Temperaturen, oberhalbT _m steigt die Wärmeleitfähigkeit mit zunehmender Bestrahlungsdosis. Das ist auf die strahlungsinduzierte Vernetzung zurückzuführen.Bei vernetztem PMMA findet man mit zunehmender Konzentration von TAC eine Erhöhung der Wärmeleitfähigkeit und eine Verschiebung des flachen Knickes beiT _g nach höheren Temperaturen hin.Die Wärmeleitfähigkeit von AN-MMA-Copolymeren scheint mit zunehmender Temperzeit zu fallen. Das wird durch eine Verschiebung des flachen Knickes nach höheren Temperaturen verursacht.Bei bestrahltem PMMA zeigt die Wärmeleitfähigkeit einen kleinen Abfall mit Bestrahlungsdosen größer als 100 MRD.

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With 8 figures and 3 tables

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To Professor Dr.K.-H. Hellwege on his sixtieth birthday     

Analytical investigation of exergetic performance on jet impingement solar air heater with multiple arc protrusion obstacles

Journal of Thermal Analysis and Calorimetry - In this present work, an exergetic efficiency of the solar air heater (SAH) with jet impingement on multiple arc protrusion roughened absorber plate is...     

Design of epoxide adhesive and sealing materials with high thermal conductivity

Epoxide adhesive materials of cold setting developed at OAO Kompozit are presented. It is shown that all the materials have low gas evolution and high thermal conductivity and provide products of aerospace engineering with the mode of thermal control.     

A semiclassical study of the thermal conductivity of low temperature liquids

The conventional classical energy current auto-correlation function has been extended into a quantum mechanical version and then approximated by the linearized semiclassical initial value representation approach. Comparison of the thermal conductivity to simulation results shows that about 15% quantum correction to the classical molecular dynamics results for liquid neon are quantitatively predicted. For liquid para-hydrogen the quantum effects are sufficiently large that the linearized semiclassical approach is only 20% accurate, while for both liquid He(4) and He(3) the thermal conductivity disagrees by a factor of 2, although exchange effects appear to play a minor role.     

Effects of preparation temperature on the conductivity of polypyrrole conducting polymer

An attempt has heen made to investigate the effect of temperature on the conductivity of polypyrrole conducting polymer films prepared by an electrochemical method in an aqueous medium using camphor sulfonate as the dopant. The polymer was grown from aqueous solutions employing a range of temperatures (l–60°C). It was found that with increase in temperature the conductivity decreased and the optimum temperature was found to be between 10 and 30°C. The results showthatthe polymer formed at low temperature has higher conductivity and is stronger than that formed at higher temperatures. Characterization by X-ray scattering shows that interlayer distance, d_Bragg (?), increases with increasing temperature. The morphology of the films formed was studied by using a scanning electron microscope (SEM). The changes in conductivity and physical appearance were interpreted as being due to compactness in the molecular packing and formation ofαβ linkages in the film.     

Effects of localised and global convection on thermal explosion in a parallel-plate geometry

During an exothermic reaction in a fluid, convection may ensue on a local scale and then develop to the scale of the entire vessel. In this work, we study the effects of both localised and global convection on thermal explosions occurring between parallel plates. Analytical relations are derived for the various transitions in regimes of convective and thermal behaviours. We show that these relations agree well with previous numerical work and with new simulations in the present investigation. We also determine analytically the time for onset of convection, as well as the temperature increase at that time, for stable and explosive systems. The effects of the Prandtl number of the fluid on the transitions between regimes are noted.     

Energetic,exergetic and enviro-economic analysis of parallel pass jet plate solar air heater with artificial roughness

Journal of Thermal Analysis and Calorimetry - In this work, the thermal performance of single-pass double-duct jet plate solar air heater with various designs of artificial roughness is analyzed by...     

Heat transfer and exergy analysis of solar air heater tube with helical corrugation and perforated circular disc inserts

Journal of Thermal Analysis and Calorimetry - The effects of perforated circular disc swirl generator on heat transfer (HT) and flow fields in a solar air heater helical corrugated tube have been...     

Effects of vapor‐phase‐formaldehyde treatments on thermal conductivity and diffusivity of ramie fibers in the range of low temperature

To understand the influence to thermal conductivity by bridging in the polymer fibers, the thermal conductivity, and thermal diffusivity of ramie fiber and those bridged by formaldehyde (HCHO) using vapor‐phase method (VP‐HCHO treatment) were investigated in the lower temperature range. The thermal conductivities of ramie fiber with and without VP‐HCHO treatments decreased with decreasing temperature. Thermal diffusivities of ramie fiber with and without VP‐HCHO treatments were almost constant in the temperature range of 250–50 K, and increased by decreasing temperature below 50 K. Thermal conductivity and thermal diffusivity of ramie fiber decreased by VP‐HCHO treatment. The crystallinities and orientation angles of ramie fibers with and without VP‐HCHO treatment were measured using solid state NMR and X‐ray diffraction. These were almost independent of VP‐HCHO treatment. Although tensile modulus decreased slightly by VP‐HCHO treatment, the decrease could not explain the decrease in thermal conductivity and diffusivity with decreasing sound velocity. The decrease of the thermal diffusivity and thermal conductivity by VP‐HCHO treatment suggested the possibility of the reduction of the mean free path of phonon by HCHO in VP‐HCHO treated ramie fiber. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2754–2766, 2005     

Pyrolysis-gas chromatography with linearly programmed temperature packed and open tubular columns. the thermal degradation of polyolefins

Summary The advantages of the use of programmed temperature open tubular columns for the separation of the pyrolysis products of polymers is again demonstrated, using polyethylene samples. It is also shown that the combination of pyrolysis-gas chromatography with subsequent hydrogenation of the thermal breakdown products using open tubular columns for separation can successfully be used in the identification of the unsaturated components formed during pyrolysis.Based on the obtained results, the schematic of the thermal breakdown mechanism of polyethylene could be established.It is further proved that the investigation of the Chromatographic pyrolysis pattern permits an evaluation regarding the degree of branching in the original polyethylene molecules.

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Zusammenfassung Die Anwendung von linear-temperaturprogrammierten Capillarsäulen zur Auftrennung von Pyrolyseprodukten wird am Beispiel der Pyrolyse von verschiedenen Polyäthylenproben beschrieben. Es wird ferner gezeigt, da\ die Methode der hydrierenden Pyrolyse-Gaschromatographie ebenfalls in Verbindung mit Capillarsäulen mÖglich ist und zur Identifizierung von bei der Pyrolyse entstandenen ungesättigten Verbindungen verwendet werden kann.Auf Grund der gewonnenen Ergebnisse konnte ein Schema fÜr den thermischen Abbaumechanismus des Polyäthylens aufgestellt werden.Weiterhin ist es mÖglich, im Pyrolyse-Chromatogramm unterschiedliche Verzweigungsgrade von Polyäthylenen zu unterscheiden.

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Dedicated to Professor Dr. Dr. h. c. Stefan Goldschmidt on the occasion of his 75th birthday.

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This paper is part of the work carried out by K. H. Kaiser at the Technikum fÜr Chemie und Physik Dr. GrÜbler, Isny/Allgäu, for his chemical engineering degree.

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Part I: Cieplinski, E. W., and co-workers.     

Experimental determination of thermal conductivity and viscosity of different nanofluids and its effect on a hybrid solar collector

In this research, three different volume concentrations (??=?0.05, 0.1 and 0.2%) of Al₂O₃/water, CuO/water and Al₂O₃–CuO/water (50:50) nanofluids are prepared by adopting a two-step nanofluid preparation method. Al₂O₃ and CuO nanoparticles with the average diameter of 50 nm and 27 nm were dispersed in distilled water. The thermal conductivity and viscosity of prepared nanofluids are measured for different temperatures by using KD2 Pro thermal property analyzed and Brookfield viscometer, respectively. The effects of nanofluids on the thermal, electrical and overall efficiency of photovoltaic thermal (PVT) solar collector are also studied. The experimental results revealed that the thermal conductivity and viscosity increase with the increase in percentage volume concentration and viscosity decreases with the increase in temperature. Furthermore, the obtained maximum thermal and electrical efficiencies of a PVT solar collector for 0.2% volume concentration of hybrid nanofluids are 82% and 15%, respectively, at peak solar radiation. The highest overall efficiency of a PVT collector with .2% volume concentration of hybrid nanofluid was 97% at peak solar radiation. Results recommend that nanofluids can be used as a heat transfer in PVT solar collector.