Aspects of complexity of metal-fibrous microstructure for the construction of high-performance heat exchangers: thermal properties

The paper considers the application of metal – fibrous microstructures in the development of highly efficient heat exchangers. Such structures can be successfully used in air conditioning systems of modern planes or in heat pipes located in planes and spacecraft. Copper fibers of 50 mm diameter have been used to produce coatings of different volumetric porosity. The sintering process was used to produce the samples. Pool boiling heat transfer tests have been performed on the non – isothermal surfaces of the fin with distilled water and ethyl alcohol (99.8% purity) as boiling agents. A significant enhancement of heat transfer has been recorded with the use of the metal – fibrous microstructures in comparison to the smooth surface without any coating. The enhancement proved to vary considerably depending on the superheat value

Wymiana ciepła przy wrzeniu na powierzchniach chropowatych i z pokryciem mikrostrukturalnym

The paper presents the test results of pool boiling heat transfer on the rough surface and the surface covered with capillary – porous microstructure. The porous layer is made of copper fibers sintered in the reduction atmosphere. The volumetric porosity amounted to 68%, while its height 1 mm. Distilled water and ethyl alcohol were used as the working fluids. The experiments have been carried out under the atmospheric pressure. Enhancement of heat transfer in relation to the smooth reference surface has been recorded especially for the low range of superheats, which might be related to the density of active nucleation sites. Experimental results have been compared with selected models of boiling available in literature.Artykuł przedstawia wyniki badań wymiany ciepła przy wrzeniu na powierzchniach chropowatych i z porowatym pokryciem metalowo-włóknistym. Mikrostruktura porowata została wykonana z włókien miedzianych spiekanych w atmosferze redukcyjnej. Porowatość objętościowa wynosi 68%, a wysokość warstwy 1 mm. Badania prowadzono dla wody destylowanej i alkoholu etylowego jako cieczy wrzących pod ciśnieniem atmosferycznym. Zaobserwowano intensyfikację wymiany ciepła w porównaniu do powierzchni gładkiej, szczególnie w zakresie małych przegrzań, co może być związane z gęstością aktywnych centrów nukleacji. Wyniki badań eksperymentalnych porównano z wybranymi modelami wrzenia dla danych powierzchni

Studium przypadku komfortu cieplnego, oświetlenia i produktywności w dwóch salach dydaktycznych Politechniki Poznańskiej

The paper analyses subjective sensations of thermal comfort, lighting conditions and self-reported productivity of 51 students of Poznań Univeristy of Technology (Poland). The study took place in the spring and was based on the use of anonymous questionnaires with questions on thermal sensations, acceptability and preferences as well as the students’ assessment of their current productivity and lighting conditions. The test results indicate that the overwhelming majority was satisfied with thermal environment and lighting conditions in the rooms. Their general sensations were also largely positive, while self-reported productivity was generally assessed to be normal.Artykuł analizuje subiektywne odczucia komfortu cieplnego, warunków oświetleniowych oraz produktywności 51 studentów Politechniki Poznańskiej. Badanie odbyło się wiosną i opierało się na wykorzystaniu anonimowych kwestionariuszy z pytaniami o odczucia cieplne, akceptowalność i preferencje oraz ocenę przez studentów aktualnej produktywności i warunków oświetleniowych. Wyniki badań wskazują, że zdecydowana większość była zadowolona z warunków termicznych i oświetlenia w pomieszczeniach. Ich ogólne odczucia były również w dużej mierze pozytywne, podczas gdy produktywność została ogólnie oceniona jako normalna

Composite Heat Exchangers for Boiling Heat Transfer Enhancement

The paper deals with the development of high-performance composite heat exchangers made of different metals. The samples made of meshes and fine fibers have been sintered to the copper base in the reduction atmosphere to prevent oxidation. The test of boiling heat transfer performance have been carried out under ambient pressure with distilled water and ethyl alcohol as working agents. The obtained data indicates significant enhancement of heat flux of such composite heat exchangers in comparison to the smooth surface without any coating. The maximum heat flux for the microstructure covered heater has been several times higher than for the smooth surface. The enhancement has been observed to decrease as the temperature difference become higher.Artykuł dotyczy badań wysokowydajnych, kompozytowych wymienników ciepła wykonanych z różnych metali. Próbki wykonano poprzez spiekanie w atmosferze redukcyjnej (w celu uniknięcia utlenienia) warstw siatkowych i drobnych włókien metalu z podstawą miedzianą. Badania przeprowadzono pod ciśnieniem atmosferycznym dla dwóch cieczy roboczych tj. wody destylowanej i bezwodnego alkoholu etylowego. Uzyskane wyniki wskazują na znaczące możliwości zwiększenia wymienianych gęstości strumienia ciepła dla wymienników kompozytowych w porównaniu do powierzchni gładkiej bez pokrycia. Maksymalne wartości gęstości strumienia ciepła odbieranego z powierzchni z mikropokryciem nawet kilkakrotnie przewyższały te, odbierane z powierzchni gładkiej. Intensyfikacja wrzenia zmniejszała się jednak w miarę wzrostu przegrzania

Eksperymentalne badanie komfortu cieplnego w budynkach uniwersyteckich na Słowacji

The paper discusses the issue of thermal comfort expressed by the students of the University of Žilina in anonymous questionnaires. The volunteers rated their thermal sensations, preferences as well as lighting conditions in the autumn season. The students were in favour of the prevailing thermal conditions - almost 88% of the volunteers expressed positive opinions about their environment. The comparison of the test results for a computer laboratory with the Fanger model calculation results was also made and indicated differences between the experimental data and values determined with the model.W artykule omówiono zagadnienie komfortu cieplnego studentów Uniwersytetu w Żylinie w oparciu o anonimowe ankiety. Ochotnicy oceniali swoje odczucia termiczne, preferencje oraz warunki oświetleniowe w okresie jesiennym. Studenci wyrazili się pozytywnie w zakresie panujących warunków termicznych - blisko 88% odpowiedzi. W pracy dokonano również porównania wyników badań w laboratorium komputerowym z wynikami obliczeń wg modelu Fangera i wykazano różnice między danymi eksperymentalnymi a wartościami wyznaczonymi modelem

Heat transfer enhancement in phase-change heat exchangers

The paper presents the results of boiling heat transfer enhancement due to the application of additional mesh on the heat exchanger surface. The copper mesh of porosity of 75% was sintered to the copper heater producing strong bonds between the elements. The results indicate a possibility of significant improvement of heat transfer conditions in comparison to the smooth surface. The heat flux was found to be almost six times higher for the same superheat if the mesh structure was applied. Distilled water and ethanol were the working fluids. The investigations were performed under atmospheric pressure

Preliminary results of thermal comfort analysis in selected buildings

The paper analyses thermal comfort in an intelligent building. Intelligent buildings are now widely seen both in Poland and abroad as a result of developments in engineering sciences. However, data on the thermal comfort provided in the buildings are limited. The research described in this paper was carried out in ENERGIS intelligent building of the Kielce University of Technology. The parameters measured included air temperature, relative air humidity, air flow rate and carbon dioxide concentration. Average radiation temperature was determined. The key element was the study of thermal sensation in occupants present at the time of the measurements. The studies were performed in classrooms during the class. The students completed a questionnaire at the beginning and end of the class. The persons present in the classrooms evaluated their thermal sensations using a seven-level thermal comfort scale. The questionnaire included such questions as the type of clothing and the degree of physical activity of the people sitting in the classroom. On the basis of the measurements of classroom microclimate parameters, PMV (Predicted Mean Vote) and PPD (Predicted Percentage Dissatisfied) indices were determined. The responses from the questionnaires provided actual average assessment of thermal sensation and actual percentage of dissatisfied people

Boiling heat transfer augmentation on surfaces covered with phosphor bronze meshes

The paper discusses the issue of boiling heat transfer augmentation on phosphor bronze wire mesh coatings during nucleate boiling heat transfer for distilled water and ethyl alcohol under ambient pressure. A significant enhancement of heat flux has been recorded for such treated surfaces in comparison to the smooth reference surface. The obtained results have been discussed and compared with models and correlations available in literature

Preliminary results of thermal comfort analysis in selected buildings

The paper analyses thermal comfort in an intelligent building. Intelligent buildings are now widely seen both in Poland and abroad as a result of developments in engineering sciences. However, data on the thermal comfort provided in the buildings are limited. The research described in this paper was carried out in ENERGIS intelligent building of the Kielce University of Technology. The parameters measured included air temperature, relative air humidity, air flow rate and carbon dioxide concentration. Average radiation temperature was determined. The key element was the study of thermal sensation in occupants present at the time of the measurements. The studies were performed in classrooms during the class. The students completed a questionnaire at the beginning and end of the class. The persons present in the classrooms evaluated their thermal sensations using a seven-level thermal comfort scale. The questionnaire included such questions as the type of clothing and the degree of physical activity of the people sitting in the classroom. On the basis of the measurements of classroom microclimate parameters, PMV (Predicted Mean Vote) and PPD (Predicted Percentage Dissatisfied) indices were determined. The responses from the questionnaires provided actual average assessment of thermal sensation and actual percentage of dissatisfied people

Distilled water and ethyl alcohol boiling heat transfer on selected meshed surfaces

The article deals with the problem of pool boiling heat transfer enhancement on metal wire mesh coatings made of copper and phosphor bronze at nucleate boiling of distilled water and high purity ethyl alcohol under ambient pressure. The tests have been performed on horizontal samples containing different microstructures produced with the sintering technology. The samples were attached to the heating block with soldering. As a result of the experiments, boiling curves were obtained, describing the relationship between the dissipated heat flux and the superheat values for each specimen. A considerable augmentation of heat flux has been recorded for the meshed surfaces in relation to the smooth reference surface without any coating. Generally, the highest enhancement was recorded for the low superheat values. The presented test results have been discussed and then compared with selected correlations available in literature for nucleate boiling heat transfer on microstructure coated surfaces