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Estudo do sistema duto-trocador de calor compacto para veículos de competição.; Study of duct-compact heat exchanger system for race cars.

Borsatti, Eugênio José
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/09/2010 PT
Relevância na Pesquisa
36.44%
Esse estudo procura integrar as áreas de termodinâmica, transferência de calor e aerodinâmica no desenvolvimento de veículos de alto desempenho. É proposta uma ferramenta computacional que auxilie a análise de alternativas de trocadores de calor compactos, parte integrante do sistema de arrefecimento veicular. O aplicativo desenvolvido, denominado TROCALC, tem dois modos de uso: para colaborar no projeto de um trocador de calor ou para avaliar o desempenho de um trocador existente. Estruturado por um conjunto de equações e parâmetros com base na metodologia de Kays e London (1984), no primeiro modo esse aplicativo fornece alternativas de trocadores a partir dos dados de rejeição de calor por parte do motor e dos valores de vazão e temperatura dos fluidos envolvidos. Para o modo de avaliação de desempenho, além dos dados de entrada já mencionados, é necessário o detalhamento da geometria de superfície do trocador para calcular a quantidade de calor que o radiador é capaz de remover do sistema e comparar com o valor de fluxo de calor rejeitado pelo motor. É adotado um estudo de caso que considerou um veículo de competição da Fórmula SAE para investigar a eficácia do aplicativo TROCALC na análise de desempenho e na definição de novas alternativas para o trocador de calor dedicado àquele automóvel. Foram realizados ensaios em laboratório com a medição de valores para a rejeição de calor...

Estudo teórico-experimental da transferência de calor e da perda de pressão em um dissipador de calor baseado em microcanais; A theoretical and experimental study on heat transfer and pressure drop in a heat sink based on microchannels

Nascimento, Francisco Júlio do
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/05/2012 PT
Relevância na Pesquisa
36.44%
A presente dissertação trata de um estudo teórico-experimental sobre escoamento monofásico e bifásico em um dissipador de calor baseado em microcanais. Este tipo de dissipador de calor tem sido usado para a intensificação da troca de calor em sistemas compactos e de alto desempenho. A intensificação da troca de calor promovida pelo escoamento em microcanais é acompanhada de um incremento na perda de pressão, portanto o estudo destes dois parâmetros é essencial para o entendimento dos fenômenos relacionados e fundamental para o desenvolvimento de ferramentas de projeto para dissipadores de calor baseados em microcanais. Inicialmente, um levantamento bibliográfico extenso sobre a ebulição convectiva em microcanais de reduzido diâmetro foi realizado. Este estudo da literatura trata de critérios de transição entre micro- e macro-escala, padrões de escoamento, métodos de previsão do coeficiente de transferência de calor e perda de pressão. Atenção específica foi dada a estudos de dissipadores de calor baseados em microcanais. Com base nesta análise da literatura, uma bancada experimental foi confeccionada para que dados experimentais de transferência de calor e perda de pressão pudessem ser levantados a partir de um dissipador de calor de microcanais. O dissipador de calor fabricado para este estudo é constituído de 50 microcanais retangulares dispostos paralelamente com 15 mm de comprimento...

Análise experimental dos efeitos do fluido e da orientação do escoamento no desempenho de dissipadores de calor baseados na ebulição convectiva em microcanais; Experimental evaluation of the effect of the fluid and the footprint orientation on the performance of a heat spreader based on flow boiling inside micro-scale channels

Leão, Hugo Leonardo Souza Lara
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 06/02/2014 PT
Relevância na Pesquisa
36.44%
A pesquisa realizada envolveu a avaliação experimental dos efeitos do fluido e da orientação do escoamento no desempenho de um dissipador de calor baseado na ebulição convectiva em microcanais. Estes dissipadores de calor são usados como uma nova aplicação para a refrigeração dos novos dispositivos eletrônicos que geram altas taxas de calor. Efetuou-se inicialmente uma extensa pesquisa bibliográfica sobre o escoamento monofásico e a ebulição convectiva em microcanais e em multi-microcanais através da qual levantou-se os principais métodos de previsão do coeficiente de transferência de calor e da perda de pressão. Então, utilizando o aparato experimental desenvolvido durante o mestrado de Do Nascimento (2012) avaliou-se a transferência de calor e perda de pressão de um dissipador de calor baseado em multi-microcanais paralelos. O dissipador de calor avaliado possui 50 microcanais retangulares dispostos paralelamente com 15 mm de comprimento, 100 µm de largura, 500 µm de altura e espaçados de 200 µm. Ensaios experimentais foram executados para o R245fa, fluido de baixa pressão utilizado em ciclos frigoríficos de baixa pressão, e R407C, fluido de alta pressão usado para conforto térmico, temperatura de saturação de 25 e 31°C...

Effects of heat stress on development, quality and survival of Bos indicus and Bos taurus embryos produced in vitro

Silva, C. F.; Sartorelli, E. S.; Castilho, A. C S; Satrapa, R. A.; Puelker, R. Z.; Razza, E. M.; Ticianelli, J. S.; Eduardo, H. P.; Loureiro, B.; Barros, C. M.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 351-357
ENG
Relevância na Pesquisa
36.44%
Heat stress is an important cause of poor development and low survival rates in bovine embryos. Experiments were conducted to test the hypothesis that Bos indicus embryos are more resistant to heat stress than are Bos taurus embryos. In experiment 1, Nelore and Jersey embryos from oocyte pick-up-derived oocytes were submitted to heat stress (96 hours post-insemination, 41 °C, 6 hours), developmental ratios were assessed at Day 7 (Day 0 = day of fertilization), and blastocysts were frozen for RNA extraction. Experiment 2 evaluated expression of COX2, CDX2, HSF1, and PLAC8 in previously frozen blastocysts. In experiment 3, Nellore and Angus embryos from oocyte pick-up-derived oocytes were submitted to heat stress (96 hours post-insemination, 41 °C, 12 hours) and transferred to recipients on Day 7. In experiment 4, embryos developed as in experiment 3 were fixed for Terminal deoxynucleotidyl transferase dUTP nick end labeling labeling and total cell counting. In experiment 1, heat stress decreased the percentage of Jersey oocytes that became blastocysts, but had no effect on Nellore embryos (34.6%, 25.0%, 39.5%, and 33.0% for Jersey control, Jersey heat-stressed, Nellore control, and Nellore heat-stressed oocytes, respectively; P < 0.05). In experiment 2...

Heat loss by the Earth, geothermal energy and geothermal heat pumps

Duque, Maria Rosa
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Aula
POR
Relevância na Pesquisa
36.47%
Heat loss by the Earth, geothermal energy and geothermal heat pumps Maria Rosa A. Duque (1) (1)Departamento de Física da Universidade de Évora, Rua Romão Ramalho 59, 7000-671 Évora Phone Number 351 266745372; E-mail: mrad@uevora.pt Geothermal energy is often labeled as renewable and sustainable. It is listed together with solar, wind and biomass as alternative energy options in governmental R& D programs. The temperature in the Earth’s interior increases with depth. This fact is responsible for the heat flow, from the interior to the surface. Heat loss through the Earth was calculated using heat flow density values obtained in continents and oceans. The result obtained [1] for the total heat loss is 46± 2 TW. Heat loss through continents is 14 TW. The direct use of geothermal energy dates back thousands of years when people began using hot springs for bathing and cooking. Today, geothermal energy can be used to generate electricity or directly in many applications. Worldwide direct utilizations of geothermal energy in 2005 was [2] 273372TJ/year, of which 32% were obtained through geothermal heat pumps. At this time, the equivalent annual savings in fuel oil amounts to 170 million barrels and 24 million tons in carbon emissions to the atmosphere. Since 2005...

Heat loss by the Earth, geothermal energy and geothermal Heat pumps

Duque, Maria Rosa
Fonte: 4th International Congress on Energy and Environment Engineering and Management Publicador: 4th International Congress on Energy and Environment Engineering and Management
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
36.46%
Geothermal energy is often labeled as renewable and sustainable. It is listed together with solar, wind and biomass as alternative energy options in governmental R& D programs. The temperature in the Earth’s interior increases with depth. This fact is responsible for the heat flow, from the interior to the surface. Heat loss through the Earth was calculated using heat flow density values obtained in continents and oceans. The result obtained [1] for the total heat loss is 46± 2 TW. Heat loss through continents is 14 TW. The direct use of geothermal energy dates back thousands of years when people began using hot springs for bathing and cooking. Today, geothermal energy can be used to generate electricity or directly in many applications. Worldwide direct utilizations of geothermal energy in 2005 was [2] 273372TJ/year, of which 32% were obtained through geothermal heat pumps. At this time, the equivalent annual savings in fuel oil amounts to 170 million barrels and 24 million tons in carbon emissions to the atmosphere. Since 2005, the use of geothermal heat pumps has been wide in both residential and commercial buildings, due to the attractive advantages of high efficiency and environmental friendliness. Geothermal heat pumps are similar to ordinary heat pumps...

Modernization of the District Heating Systems in Ukraine : Heat Metering and Consumption-Based Billing

Semikolenova, Yadviga; Pierce, Lauren; Hankinson, Denzel
Fonte: Washington, DC: World Bank Publicador: Washington, DC: World Bank
EN_US
Relevância na Pesquisa
36.47%
District heating (DH) plays a critical role in meeting basic heating needs in Ukraine, but the sector faces serious challenges that must be resolved to avoid collapse. For DH companies, the primary concern is financial sustainability. Companies lack the revenue to invest adequately in DH networks leading to lower quality of service and higher operating costs. For customers, the primary concern is quality of service and affordability. Artificially low prices have resulted in the continued deterioration of DH supply assets (and gas supply assets) resulting in lower heat supply quality. Low DH prices have provided little incentive for investment in energy efficiency. As a result, Ukraine is one of the highest energy intensive countries in the world. Ukraine, together with other Former Soviet Union countries, did not follow the path chosen by their neighbors to modernize their DH sectors. Many countries of Eastern Europe enacted critical reforms in the 1990s to address problems related to affordability, quality of service, and financial sustainability similar to those now facing Ukraine. Evidence from these countries suggests that these challenges currently facing Ukraine, while difficult, are far from insurmountable. This study situates heat metering and consumption-based billing in the context of the various DH sector reforms needed in Ukraine. It builds on the work of previous studies including the recommendations of the 2010 Energy Sector Management Assistance Program (ESMAP)-funded study...

Tubular and Sector Heat Pipes with Interconnected Branches for Gas Turbine and/or Compressor Cooling

Reding, Brian D., II
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
36.47%
Designing turbines for either aerospace or power production is a daunting task for any heat transfer scientist or engineer. Turbine designers are continuously pursuing better ways to convert the stored chemical energy in the fuel into useful work with maximum efficiency. Based on thermodynamic principles, one way to improve thermal efficiency is to increase the turbine inlet pressure and temperature. Generally, the inlet temperature may exceed the capabilities of standard materials for safe and long-life operation of the turbine. Next generation propulsion systems, whether for new supersonic transport or for improving existing aviation transport, will require more aggressive cooling system for many hot-gas-path components of the turbine. Heat pipe technology offers a possible cooling technique for the structures exposed to the high heat fluxes. Hence, the objective of this dissertation is to develop new radially rotating heat pipe systems that integrate multiple rotating miniature heat pipes with a common reservoir for a more effective and practical solution to turbine or compressor cooling. In this dissertation, two radially rotating miniature heat pipes and two sector heat pipes are analyzed and studied by utilizing suitable fluid flow and heat transfer modeling along with experimental tests. Analytical solutions for the film thickness and the lengthwise vapor temperature distribution for a single heat pipe are derived. Experimental tests on single radially rotating miniature heat pipes and sector heat pipes are undertaken with different important parameters and the manner in which these parameters affect heat pipe operation. Analytical and experimental studies have proven that the radially rotating miniature heat pipes have an incredibly high effective thermal conductance and an enormous heat transfer capability. Concurrently...

The effects of turbulence structures on the air-side performance of compact tube-fin heat exchangers.

Allison, Colin Bidden
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2006
Relevância na Pesquisa
36.47%
Energy is an essential and critical commodity and our reliance on it has fuelled much of the debate and interest in society and academia alike. Environmental concerns, depleted energy resources and higher energy prices are the main factors that drive this interest. Energy efficiency is one of the main avenues to preserve and better utilize this valuable commodity. The energy exchange by employment of heat exchangers is extensive and tube-fin heat exchangers are widely used in industrial and commercial applications. Smarter designs could not only improve energy efficiency but may also save on material costs. Although mass production and improved manufacturing techniques have reduced manufacturing costs, tube fin heat exchangers have not evolved greatly to take advantage of these improvements. There has been a large range of fin surface enhancements proposed, such as waffled fins or louvres and while limited improvements in capacity have been achieved, this is generally accomplished at a much larger pressure drop penalty. Numerous studies have been performed in order to examine the potential of various surface enhancement geometries on an ad hoc basis. These presumably operate on the basis of enhanced convection due to increased turbulence levels. However very few of these studies examine the actual nature of turbulence that is responsible for convection enhancement. A series of experiments and numerical studies have been conducted to quantify the effect of the turbulence vortex characteristics on the air side heat convection of a tube-fin heat exchanger. Homogeneous...

Extreme heat arrangements in South Australia: an assessment of trigger temperatures

Williams, S.; Nitschke, M.; Tucker, G.; Bi, P.
Fonte: Australian Health Promotion Association Publicador: Australian Health Promotion Association
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
36.44%
ISSUE ADDRESSED: The high mortality and morbidity associated with the 2009 heat wave across South Eastern Australia highlighted the need for effective heat-related health promotion and preventive strategies. The adverse health effects of extreme heat are largely preventable, and heat-related health promotion can advise the public about the dangers of hot weather and how to reduce health risks. The South Australian State Emergency Service has outlined a co-ordinated response system in their Extreme Heat Arrangements for South Australia. This paper evaluates the health impacts at the temperature trigger levels incorporated in this plan. METHODS: Heat events in Adelaide between 1994 and 2009 were compared in terms of heat duration, heat intensity and their impact on mortality and ambulance call-outs.The health impacts for events meeting specific temperature triggers were estimated. RESULTS: Individual heat events varied in terms of estimated excess mortality and ambulance call-outs. Increased mortality was associated with heat events of 3 or more consecutive days with maximum temperature (T(max)) > or = 43 degrees C or average daily temperature (ADT) > or = 34 degrees C, while ambulance call-outs increased significantly at lower T(max) levels.The two events reaching the temperature triggers for an extreme heat warning were associated with a 44% (95% CI 26-63%) increase in mortality. CONCLUSIONS: The results support the temperature trigger for an extreme heat warning within the Extreme Heat Arrangements for Adelaide...

Heat waves and climate change: applying the health belief model to identify predictors of risk perception and adaptive behaviours in Adelaide, Australia

., A.; Bi, P.; Williams, S.; Grant, J.; Walker, I.; Augoustinos, M.
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
36.44%
Heat waves are considered a health risk and they are likely to increase in frequency, intensity and duration as a consequence of climate change. The effects of heat waves on human health could be reduced if individuals recognise the risks and adopt healthy behaviours during a heat wave. The purpose of this study was to determine the predictors of risk perception using a heat wave scenario and identify the constructs of the health belief model that could predict adaptive behaviours during a heat wave. A cross-sectional study was conducted during the summer of 2012 among a sample of persons aged between 30 to 69 years in Adelaide. Participants’ perceptions were assessed using the health belief model as a conceptual frame. Their knowledge about heat waves and adaptive behaviours during heat waves was also assessed. Logistic regression analyses were performed to determine the predictors of risk perception to a heat wave scenario and adaptive behaviours during a heat wave. Of the 267 participants, about half (50.9%) had a high risk perception to heat waves while 82.8% had good adaptive behaviours during a heat wave. Multivariate models found that age was a significant predictor of risk perception. In addition, participants who were married (OR = 0.21; 95% CI...

Extreme heat and workers’ health in South Australia: association, perceptions, and adaptations in the workplace.

Xiang, Jianjun
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
36.48%
Background: Occupational heat exposure may lead to adverse health effects and contribute to work-related injury, illness or even death. With the predicted increase in the frequency and intensity of extremely hot weather in South Australia, workplace heat exposure is presenting a growing challenge to workers’ health and safety. This thesis aims to examine the effects of workplace heat exposure on workers’ health and safety in Adelaide, South Australia, to investigate perceptions of risks associated with workplace heat exposure, and to provide scientific evidence for the development of heat necessary heat prevention and adaptation strategies particularly in a warming climate. Methods: This study can be broadly divided into two parts. The first part is the analyses of workers’ compensation claim data and weather data, obtained from the SafeWork South Australia and the Bureau of Meteorology, respectively for 2001-2010. Time-series analysis approach was used to quantify the effects of heat exposure on workers’ health and safety. Heat-related claims were identified according to the Type of Occurrence Classification System coding information and text-based diagnosis-related descriptions. Case-crossover analytic approach was undertaken to estimate the risk of occupational heat illnesses during heatwaves. The second part of this study comprises two cross-sectional questionnaire surveys to investigate how workers and occupational hygienists perceive the risk of workplace heat exposure and health impact. Results: Analyses of workers’ compensation claim data Generally...

Physiological studies on the response of wheat to short-term heat stress during reproductive development.

Talukder, A.S.M. Hasim Morshed
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
36.48%
In Mediterranean environments, cereal crops are often exposed to short periods of elevated temperatures in spring when crops are approaching flowering and grain filling. Most studies on heat stress have focused on crop responses to extended periods of high temperature under controlled environment (CE) conditions possibly due to difficulties in applying heat stress in the field. It is possible wheat may respond quite differently to heat stress imposed under field and CE conditions. Therefore, experiments were designed to develop a methodology to apply heat treatments in the field. Studies were also undertaken to compare the response of wheat genotypes to a single-day heat stress event in the field and CE conditions. Wheat genotypes were exposed to heat stress for a single-day at two different stages, near flowering or green anther stage (H1), and early grain set or 7-10 days after anthesis (DAA) (H2) in 2009 and 2010. Heat treatment was applied in the field in a portable purpose-built heat chamber in which the temperature was steadily increased to a maximum of 35°C, which was maintained for 3 hours before being allowed to steadily decrease to the ambient temperature, like a typical natural spring heat event. Similar to the field studies...

Extreme heat and occupational heat illnesses in South Australia, 2001-2010

Xiang, J.; Hansen, A.; Pisaniello, D.; Bi, P.
Fonte: BMJ Publicador: BMJ
Tipo: Artigo de Revista Científica
Publicado em //2015 EN
Relevância na Pesquisa
36.44%
Objectives This study aims to examine the epidemiological characteristics of occupational heat illnesses in South Australia, to quantify the association between ambient temperature and occupational heat illnesses, and to investigate the impact of heatwaves on occupational heat illnesses. Methods Workers ’ compensation claims data and weather data were obtained from SafeWork South Australia and the Bureau of Meteorology, respectively, for 2001 – 2010. Time series analysis with generalised estimation equation models and linear spline functions was used to quantify the temperature – heat illness claims association. A case-crossover design was applied to investigate the impact of heatwaves on occupational heat illnesses. Results There were 306 heat illness claims during the study period, with an incidence rate of 4.5 per 100 000 employees. The overall risk of occupational heat illness was positively associated with maximum temperature (T max ), especially when T max was over the threshold of 35.5°C. One degree increase of T max was associated with a 12.7% (incidence rate ratio 1.127, 95% CI 1.067 to 1.190) increase of occupational heat illness claims. During heatwave periods, the risk of occupational heat illness was about 4 – 7 times higher than that of non- heatwave periods. Conclusions There is a need to develop or re fi ne current heat-related regulations and guidelines to minimise the risk of occupational heat illnesses in vulnerable workers in a warming climate.; Jianjun Xiang...

Heat transport modeling in shallow aquifers. The role of thermal dispersion in aquifers and heat conduction into confining layers; Simulation des Wärmetransports in oberflächennahen Aquiferen. Die Rolle der thermischen Dispersion in Aquiferen und von Wärmekonduktion in Aquitarden

Molina Giraldo, Nelson Alejandro
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
36.45%
Heat transfer by conduction through the fluid and solid phase and advection through the moving water mainly determine the heat transport in the subsurface. Additionally, heat transfer by thermal dispersion occurs due to differential advection at the pore-scale and heterogeneities of the permeability field at macroscopic scales. Compare to solute diffusion coefficients, heat diffusion coefficients are normally higher. This difference has led to dissimilar ways of treating the processes and the boundary conditions in heat and contaminant transport simulations. In particular, effects of hydrodynamic dispersion in aquifers and diffusion through the confining layers. Most conceptualizations of heat transport in the underground neglect these processes and the error introduced is not often evaluated. Hence, in the present study, an analytical and numerical modeling study is carried out to evaluate the effect of such simplifications on heat transport simulations. Two practical applications of heat transport in the subsurface are used to tackle these problems: Low-enthalpy geothermal systems and natural temperature variations as hydrogeological tracer. A concise discussion of the effect of thermal dispersion on the simulation of temperature plumes in aquifers that evolve from vertical ground source heat pump systems is presented. Results indicate that the effect of thermal dispersion on the temperature plume distribution around a borehole heat exchanger can be neglected if thermal dispersion depends only on the Peclet number. On the other hand...

China : Development of National Heat Pricing and Billing Policy

Meyer, Anke Sofia; Kalkum, Bernd
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research :: ESMAP Paper; Publications & Research
ENGLISH; EN_US
Relevância na Pesquisa
36.49%
Market-based reforms in China's urban centralized heating sector are essential to addressing the perpetual inefficiency of a sector built on welfare based principles. The reform of heat pricing and billing is a crucial part of overall heat reform, since it will commodity heat and thus create economic incentives to provide and use heat much more efficiently. Heat pricing and billing reform requires substantial changes in four interrelated areas: (i) transfer of heat payment responsibility from work units to consumers, a change from invisible to visible heat subsidies and an improved targeted subsidy system; (ii) determination of an economically efficient and equitable heat pricing system; (iii) promotion of heat metering, consumer control of heat consumption and consumption based billing; and (iv) improvement of the system of heat price administration.

Optimization of the heat pumping capacity of a thermoelectric heat pump

Heavner, David A.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
36.45%
A steady state model of a thermoelectric heat pump fitted with pin fin heat exchange surfaces is developed from the equations governing the operation of a thermoelectric device and pressure drop/ heat transfer correlations for staggered tube banks in cross flow. The model computes current draw, heat pumped at the cold side, heat rejected at the hot side, hot and cold side exhaust temperatures, and hot and cold side pin base temperatures when given the following parameters: ambient temperature, thermoelectric geometry factor, number of thermocouple junctions, input voltage, pin diameter, pin height, transverse pin stagger, longitudinal pin stagger, contact resistance between the thermoelectric modules and the heat ex change surfaces, and fan performance curves for the hot and cold sides. Results of a FIDAP numerical model of a 4 row heated pin system are presented and compared to the heat transfer and pressure drop correlations chosen for use in the model. Nine tests were run with a working thermoelectric heat pump unit under various air flow and voltage input to collect data for the purpose of comparison with the model. Using empirically determined contact resistance values, the model predicted Qc (heat pumped from the cold side) values that agreed with experiment within about 10%...

Experimental study of pool boiling heat transfer enhancement over microchanneled surfaces

Cooke, Dwight
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
36.45%
Pool boiling is of interest in heat transfer applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is still not comparable to the cooling ability provided by enhanced microchannels operating under single-phase conditions. This investigation focuses on the bubble dynamics and heat transfer on plain and structured microchanneled surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism through the use of a high speed camera. In a preliminary study, silicon chips have been tested in the nucleate boiling regime, and beneficial microchannel geometries have been identified. It is determined that heat transfer enhancement occurs because of (i) an increase in surface area and (ii) an improvement in the heat transfer mechanism through the channels functioning as liquid conduits for three side heating. The range for channel size in which the greatest enhancement occurs has been identified as being 200 - 400 µm width and 300 - 500 µm depth. The second study has been investigated with copper chips, with improvements to the test setup for accurate measurement of surface temperature. Ten chips...

Role of heat pipes in improving the hydrogen charging rate in a metal hydride storage tank

Liu, Yuzhu
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
36.45%
Prasad, Ajay K.; Advani, Suresh G.; Metal hydrides can store hydrogen at high volumetric efficiencies. As the process of charging hydrogen into a metal powder to form its hydride is exothermic, the heat released must be removed quickly to maintain a rapid charging rate. An effective heat removal method is to incorporate a heat exchanger such as a heat pipe within the metal hydride bed. In this paper, we describe a two-dimensional axi-symmetric study to predict the transient heat and mass transfer in a cylindrical metal hydride tank embedded with one or more heat pipes. Results from a parametric study of hydrogen storage efficiency are presented as a function of storage tank size, water jacket temperature and its convective heat transfer coefficient, and heat pipe radius and its convective heat transfer coefficient. The effect of enhancing the thermal conductivity of the metal hydride by adding aluminum foam is also investigated. The study reveals that the cooling water jacket temperature and the heat pipe's heat transfer coefficient are most influential in determining the heat removal rate. The addition of aluminum foam reduces the filling time as expected. For larger tanks, more than one heat pipe is necessary for rapid charging. It was found that using more heat pipes of smaller radii is better than using fewer heat pipes with larger radii. The optimal distribution of multiple heat pipes was also determined and it is shown that their relative position within the tank scales with the tank size.; University of Delaware...

Exergy-based ecological optimization for an endoreversible variable-temperature heat reservoir air heat pump cycle

Bi,Yuehong; Chen,Lingen; Sun,Fengrui
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2009 EN
Relevância na Pesquisa
36.45%
An ecological performance analysis and optimization based on the exergetic analysis is carried out in this paper for an endoreversible air heat pump cycle with variable-temperature heat reservoirs. An exergy-based ecological optimization criterion, which consists of maximizing a function representing the best compromise between the exergy output rate and exergy loss rate (entropy generation rate and environment temperature product) of the heat pump cycle, is taken as the objective function. The analytical relation of the exergy-based ecological function is derived. The effects of pressure ratio, the effectiveness of the heat exchangers, the inlet temperature ratio of the heat reservoirs and the ratio of hot-side heat reservoir inlet temperature to ambiént temperature on ecological function are analyzed. The cycle performance optimizations are performed by searching the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for fixed total heat exchanger inventory and the optimum heat capacity rate matching between the working fluid and the heat reservoirs, respectively. The influences of some design parameters, including heat exchanger inventory and heat capacity rate of the working fluid on the optimal performance of the endoreversible air heat pump are provided by numerical examples. The results show that the exergy-based ecological optimization is an important and effective criterion for the evaluation of air heat pumps.