Academic literature on the topic 'Triangular duct'

Earlier heat transfer studies with orthogonal rotation were conducted mostly on ducts of square cross section. This paper reports a different cross section, a triangular duct. Unlike a square cross section, the triangular shape provides more restriction to the formation of the secondary flows. Moreover, the studied orientation of the right triangular duct avoids formation of symmetric vortex structures in the crossflow plane. This paper presents turbulent heat transfer characteristics of a two-pass smooth-walled triangular duct. One pass is for radial outward flow and the other for radial inward flow. With rotation the radial outward and inward flow directions show different surface heat transfer characteristics. Like a square duct, differences between the trailing and the leading Nusselt number ratios for the triangular duct increase with rotation number. However, the rate of change of Nusselt number rations with rotation number varies for the two duct geometries. Standard k–ε model predictions for a radial outward flow situation show that the Nusselt number ratio variations with Reynolds number are not drastic for the same rotation number.

Included angles (?) have vital effect on the flow and heat transfer in cross-corrugated triangular ducts. The friction factor and Nusselt number were estimated at different Reynolds numbers from both experiments and simulations. Results show that the flow in the duck with ?=90 has the largest friction factor and Nusselt number. However, the included angle influences the flow and heat transfer in cross-corrugated triangular ducts in different ways. The field synergy principle was used to explore the mechanism of the different impacts of the included angle. Results show that the flow in the cross-corrugated triangular duct with ?=90o has the smallest domain averaged included angle (?m), which implies the best synergy performance. The results of the field synergy principle were also validated by analyzing the performance evaluation criterion and studying the velocity vector and temperature distributions.

Friction factors for fully developed flow in triangular ducts with fins of various height and width are investigated for Reynolds numbers ranging from 150 to 90,000. Two triangular ducts having apex angles of 60 and 38.8 deg are studied. Results are presented in the form of standard plots of friction factor as a function of Reynolds number. Friction factor values for the smooth triangular duct cases are in good agreement with the existing results. For the finned-duct cases, the fully developed axial velocity profiles in laminar flow are determined by solving the x-momentum equation iteratively by the Gauss–Seidel finite-difference technique. The theoretically determined friction factors for these cases are in good agreement with the experimental values of friction factors based on pressure drop measurements.

Background. The anatomical variability of bile ducts can leave surgeons in very difficult conditions.Ultrasonography, computed tomography, magnetic resonance imaging (MRCP) and endoscopic imaging methods are used in diagnosis. In addition to conservative approaches, endoscopic procedures and laparoscopic or open surgical interventions may be necessary for treatment. In this article, we present a case of aberrant bile duct in left triangular ligament (appendix fibrosa hepatis), which is rarely seen. Case. We report the case of a 67-year-old female patient who was operated on due to dumping syndrome symptoms and hiatal hernia. There was a drainage of bile from the left side of the liver which was placed under the cardioesophageal junction. MRCP found bile esophageal in the left triangular ligament of the liver. Aberrant bile ducts were found in the left triangular ligament and ligated. The patient was discharged on the 7th day after operation. Conclusion. The anatomical variability of bile ducts can leave surgeons in very difficult conditions. We recommend that the dissected left triangular ligament should be ligated for the aberrant bile duct, especially in female patient.

This study aims to determine the effect of the mold casting duct variations on shrinkage, porosity defects, density, hardness, and chemical composition of materials. The primary raw material uses melting secondary aluminium through a small-scale smelting furnace. Research study about three kinds of ducts: triangular duct, rectangular duct, and circular duct. The testing chemical composition uses an emission spectrometer. Research founds defects by comparing the dimensions of the original object with the specimen results of each duct variation. The density value calculates porosity defects. ASTM E10 standard Brinell test measures the hardness. Besides, ASTM E3 standard test quantifies the microstructure of the product. The highest average shrinkage is the triangular ducts at 3.68%. The least significant numbers of porosity were in rectangular ducts of 2.964 gr/ml. Higher the density value, the denser the material, and the more negligible the porosity. The density of the material affects the hardness material obtained from the results of the Brinell test. The hardness of the Brinell test brought that the rectangular duct with 102.5 BHN was the most enormous. In addition, the results showed that the chemical composition mainly contained mostly chemical elements (Al) 87.1% as the main chemical ingredient and (Si) 9.51%.

In the present work, the thermal and exergy efficiency of the equilateral triangular duct solar air heater is analytically investigated and its performance is improved by attaching an inclined wire rib over the absorber surface. Using triangular ducts improves the operating flow conditions up to the Reynolds number of 35000. The thermal model of solar air heater is solved by using an iterative procedure by code developed in MATLAB. The analysis considers the roughness parameters that roughness pitch (P)-to-height (e) ratio (P/e) of 4 to 16, roughness height (e)-to-hydraulic diameter (Dh) ratio (e/Dh) of 0.021 to 0.043, and rib inclination angle (α) of 30 to 75°. While increasing the Reynolds number from 2000 to 35000, the inclined rib roughened triangular duct solar air heater thermal performance is increased and attains the maximum value of 83.61% and the effective thermal efficiency of 80.26%. The maximum exergy efficiency of 2.62% is obtained at the Reynolds number value of 1864. It improves the thermal performance by 14.2% as compared with the rectangular rib roughened triangular duct solar air heater. The optimum value of roughness parameters is P/e of 12, e/D of 0.042, and α of 75°. The air heater is useable to attain the temperature rise parameter ranges from 0.001 to 0.03 K·m2/W.

OBJECTIVE To characterize the structure of the parotid gland of the miniature pigs (minipig). METHODS Sialographic, anatomical, histological and ultrastructural studies of the parotid gland were performed on 11 minipigs. RESULTS Sialograms showed a long main duct and a triangular shaped gland. All branching ducts extended from the inferior-posterior margin of the main duct. No accessory glands were found. Typical serous acini were found microscopically and histochemically. CONCLUSION This study provides basic structural information on the parotid gland of the minipig.

An analytical investigation of three-dimensional mixed convection flow and heat transfer to power-law fluids in horizontal arbitrary cross-sectional ducts is undertaken. The continuity equation and parabolic forms of the energy and momentum equations in rectangular coordinates are transformed into new orthogonal coordinates with the boundaries of the duct coinciding with the coordinate surfaces. The transformed equations are solved by the finite difference technique. The fluid enters the duct with constant velocity and temperature profiles with the wall of the duct subjected to constant temperature. Local heat transfer coefficients and pressure drop for several values of Gr/Re and power-law index n are computed for the triangular, square, trapezoidal, pentagonal, and circular ducts. The buoyancy force is found to increase both the Nusselt number and the pressure drop.

Local breed cattle's liver, reddish-brown, occupies the right hypochondriac region with 35.2 ± 3.24 cm long and 5.5 ± 0.5 kg weight. Connected by left and right triangular ligaments; and falciform ligaments with the diaphragm, and hepatorenal ligament with the right kidney. While the coronary ligament encompassing the caudal vena cava divides into dorsal and ventral branches, enclosing the nuda region. The round ligament connects the umbilical fissure to the umbilicus. The lesser omentum on the liver's visceral surface connects the stomach and duodenum through hepatogastric and hepatoduodenal ligaments, respectively. The liver has, parietal and visceral surfaces; right, left, ventral, and dorsal borders; and left, right, caudate, and quadrate liver lobes that are not clearly separated, except for the caudate. The gallbladder has a dark green color and pear-shaped morphology, measures 16 ± 1.5 cm, and is located in a shallow cystic fossa. Consisting of the neck, forms an inverted funnel shape, body, and fundus. The diameters were 2 ± 0.3, 6 ± 1.2, and 4 ± 1.3 cm, respectively. The biliary tract consists of extrahepatic and intrahepatic ducts. The extrahepatic ducts have a left duct of 3 ± 0.5 cm and a right duct of 2 ± 0.25 cm. Converging to form a common hepatic duct 8 ± 0.5 cm. The cystic duct is 3± 0. cm, joins with the common hepatic duct ventrally. The intrahepatic ducts consisted of primary, secondary, tertiary, interlobular, intralobular, and intercalated ducts. The left hepatic duct received 9 ± 1 of dorsal primary ducts and 8 ± 2 ventral primary ducts. The right hepatic duct receives 4 ± 1 dorsal ducts and 2 ± 1 ventral ducts.

Experiments are conducted to study the heat transfer and pressure drop characteristics in a triangular duct cooled by an array of tangential jets, simulating the leading-edge cooling circuit of a turbine blade. Coolant ejected from a high-pressure plenum through an array of orifices is aimed at the leading-edge apex and exits from the radial outlets. Three different outflow orientations, namely coincident with the entry flow, opposed to the entry flow, and both, are tested for various Reynolds numbers 12600⩽Re⩽42000. A transient liquid crystal technique is used to measure the detailed heat transfer coefficients on two walls forming the leading-edge apex. Flow rate across each jet hole and the crossflow development, which are closely related to the local heat transfer characteristics, are also measured. Results show that increasing Re increases the heat transfer on both walls. The outflow orientation affects significantly the local heat transfer characteristics through influencing the jet flow together with the crossflow in the triangular duct. The triangular duct with two openings is recommended since it has the highest wall-averaged heat transfer and the moderate loss coefficient among the three outflow orientations investigated. Correlations for wall-averaged Nusselt number and loss coefficient in the triangular duct have been developed by considering the Reynolds number for three different outflow orientations. [S0022-1481(00)01204-4]

An experimental investigation was performed to ascertain the nature of turbulence in a narrow apex angle isosceles triangular duct. The study involved the design and construction of a low noise, low turbulence wind tunnel that had an isosceles triangular test section with an apex angle of 11.5[degrees]. Experiments involved the measurement of velocity fluctuations using hot wire anemometry and wall pressure fluctuations using a condenser microphone. Measurement of the velocity fluctuations reconfirms the coexistence of laminar and turbulent regions at a given cross section for a range of Reynolds numbers. The laminar region is concentrated closer to the apex while the turbulent region is found closer to the base. The point of transition is a function of the Reynolds number and moves closer to the apex as the flow rate is increased. Moreover, it was found in this investigation that traditional scaling of the turbulent statistical quantities do not hold good in this geometry. Although velocity fluctuations showed distinctive flow regimes, no such distinction could be seen in the dynamic wall pressure data. The nature of the dynamic wall pressure was uniform throughout the entire cross section suggesting that wall pressure fluctuations, unlike the velocity fluctuations, are able to travel from the base to the apex, without being damped. This implies that the relationship between the velocity and the pressure fluctuations applicable in the other systems does not hold well in a narrow apex angle isosceles triangular duct. Further, the typical scaling relationships applied to wall pressure spectra of other geometries doesn't apply in this scenario and the ratio of the RMS pressure fluctuation to the mean shear is much higher compared to a flat plate or pipe flow situation.<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering;<br>Engineering and Computer Science<br>Mechanical Engineering PhD

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>Experiências foram realizadas para se determinar coeficientes de transferência de calor e fatores de atrito para escoamento em dutos cujas seções transversais têm a forma de triângulos isósceles. Dois dutos foram usados; um tinha um ângulo de vértice igual a 120 graus e o outro 60 graus. As experiências foram realizadas utilizando-se trocadores de calor de dutos triangulares. Os fluidos foram ar e água. Coeficientes médios de transferência de calor foram determinados através da medida dis coeficientes globais de transferência de calor dos trocadores. No caso do duto de 120 graus, as paredes dos triângulos isósceles eram lisas. Foram estudados escoamentos laminares e turbulentos. Para o duto de 60 graus, duas paredes pinadas. A finalidade dos pinos foi aumentar a área de troca de calor. Nesse caso (60 graus) apenas escoamento turbulento foi estudado. Para os dutos com paredes lisas, foi possível se obter a dependência dos coeficientes de troca de calor dos dutos com o número de Prandtl. Para se atingir condições totalmente desenvolvidas, os trocadores de calor, tinham um comprimento de entrada de aproximadamente 35 diâmetros hidráulicos. As condições de contorno térmicas consistiram de temperatura uniforme nas paredes iguais dos dutos, sendo a terceira parede isolada. Os dutos triangulares dos trocadores de calor consistiram de duas paredes metálicas e uma parede de material menos condutor. Os resultados são apresentados sob formas adimensionais. Números de Nusselt e fatores de atrito como funções dos números de Reynolds.<br>Experiments were performed to determine heat transfer coefficients and friction factors for flows in ducts whose cross sections have the shape of isosceles triangles. Two ducts were used; one with an apex angle equal to 120 degrees and the other 60 degrees. The experiments were performed by utilizing triangular duct heat exchangers. The fluids were air and water. Average heat transfer coefficients of the heat exchangers. In the case of the 120 degrees duct, the walls of the isosceles triangles were smooth. Laminar and turbulent flows were studied. For the 60 degrees duct, two situations were considered; one with smooth walls and the other with two pinned walls. The purpose of the pins was to increase the heat transfer area. In this case (60 degrees) only turbulent flow was studied. For the ducts with smooth walls, it was possible to obtain the dependence of the duct heat transfer coefficients with prandtl number. To attain the duct heat transfer coefficients with Prandtl number. To attain fully developed conditions, the heat exchangers had a starting length of approximately 35 hydraulic diameters. The thermal boundary conditions consisted of uniform temperature on the two equal walls of the duct, the third wall being insulated. The triangular ducts of the heat exchangers consisted of two metallic walls and of lesser conduction material. The results are presented in dimensionless forms. Nusselt numbers and friction factors as functions of Reynolds Numbers.

碩士<br>淡江大學<br>機械工程研究所<br>82<br>It has been known recently that significant heat transfer enhancement can be achieved using laminar non-newtonian flow in a non-circular duct. In the proposed study,one consider an aqueous solution of carbopol in triangular ducts where the flow is laminar,and is in the hydrodynamically developed but thermally developing region.The objective of the present study is to investigated the influence of heat transfer enhancement of the temperature dependence viscous and shear thinning effect. Two phase of the experimental work will be conducted. First, rheometer viscometer and capillary tube viscometer were used to measure the fluid viscousities in different shear rate range. Secondly,a small isosceles triangular duct test section made of Lexan will be install. Thermal boundary condition is upper wall heated other wall adiabatic, constant wall heat flux axially and constant temperature peripherally. Working fluid is different concentration of carbopol and water. The result of the viscometer experiment presented that the viscoity of the carbopol solution decreased with increasing temperature and shear rate. The experiment result of local Nusselt number for the carbopol solution show 60%~70% enhance over water.

Tese de doutoramento em Engenharia Mecânica, no ramo de Aerodinâmica Industrial e Engenharia do Vento, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra<br>The transport of soil particles by wind is of enormous relevance in a wide range of events from those related to agriculture (e.g., seed transport) to the formation and modification of the landscape. A classic example is sand dunes, which can be formed, moved, or entirely eroded due to aeolian processes. Still, aeolian transport of particles may cause serious damage in transportation, communications and severe environmental problems, such as the degradation of air quality due to dispersion of pollutants from stockpiles. The wind exposure will lead to the particles movement through several mechanisms, such as, suspension, creeping, saltation, and saltation bombardment. Consequently, the free surface will change over time due to entrainment and deposition phenomena. The main objective of this study is assessing the airflow characteristics over and around granular material complex three-dimensional piles when subjected to the wind erosion and its influence in the behavior of the free surface, as well as, in the sand emission rate. A literature review was made over the main subjects of interest to the present work, from the basics, such as granular material and aeolian transport mechanisms, to the key magnitudes involved in the wind erosion phenomena. Studies performed to calculate the dust emission from stockpiles are presented and reviewed along with the widely applied methodology from United States Environmental Protection Agency (USEPA). This methodology estimates the emission of particles from stockpiles only during specific erosion events, such as bursts, when in reality emissions occur in many other occasions. The present work offers the possibility of conducting the determination of emissions from stockpiles along time; this approach makes viable to follow the time-dependent evolution of the free surface enhancing in this way the accuracy of the predictions. Therefore, studies that are related to free surface progress are also reviewed. The present work has a significant experimental component, and the thesis describes in considerable detail the experimental apparatus and procedures, including wind tunnel, granular material, tested pile configurations and performed tests – in particular, erosion and shear stress (with Irwin probes) measurements. In addition, the use of Computational Fluid Dynamics (CFD) plays an important role in the present study; therefore, for completeness, key concepts related to CFD are included in this thesis along with a brief survey of studies that employ CFD methodology to evaluate aeolian erosion. The present CFD studies were conducted by using an open source CFD code – OpenFOAM (OF). The motivation for the selection of OF, as the CFD tool, is related to its wide acceptance in the scientific community; moreover, its application to the prediction and study of wind erosion is an original contribution to this field of research. Full description of the numerical model and its implementation are given along with the methodology used in the model validation. Two different pile configurations were studied - a two-dimensional triangular pile and a three-dimensional oblong pile. The increasing geometrical complexity of the piles allowed gaining gradual experience with the procedures and methodologies involved. The experimental and numerical studies for these cases and their results are analyzed and discussed. In what concerns the oblong piles, the numerical results are correlated with the registered free surface deformation of the piles and compared against other study available in the literature, in which oil film visualization tests were conducted and a different CFD tool was used. Considering that the model validation is partly performed against experimental results, particular attention was given to their accuracy. For the triangular piles, the comparison is primarily against the wall shear stress results obtained using the Irwin probes, which were built and calibrated for this work. The study of these probes was extensive and it led to an innovative and significant contribution to this field of research, which justifies an integrated, but autonomous Part B of this thesis. Due to the versatility of experimental apparatus built to assist the calibration of the Irwin probes, a more in-depth study was also carried out on the flow through rectangular ducts with a constant and variable cross-section. Finally, the main findings resulting from the present work are summed up and some recommendations for future work are given.<br>O transporte de partículas do solo pelo vento é de enorme relevância numa ampla gama de eventos, desde os relacionados com a agricultura (por exemplo, o transporte de sementes) até a formação e modificação da paisagem. Um exemplo clássico são as dunas de areia, que se podem formar, mover ou erodir totalmente devido a processos eólicos. Por outro lado, o transporte de partículas pode provocar sérios danos no sector dos transportes, comunicações e graves problemas ambientais, como a degradação da qualidade do ar devido à dispersão de poluentes provenientes de pilhas de armazenamento. A exposição ao vento pode levar ao movimento das partículas através de vários mecanismos, tais como, suspensão, arrastamento, saltação e bombardeamento das partículas em saltação. Consequentemente, a superfície livre irá mudar ao longo do tempo devido aos fenómenos de arrastamento e deposição. O objetivo principal deste estudo é investigar as características do fluxo de ar sobre e ao redor de pilhas tridimensionais (3D) complexas de material granular quando sujeitas à erosão do vento e avaliar a sua influência no comportamento da superfície livre, bem como na taxa de emissão. Uma revisão bibliográfica foi feita sobre os principais temas de interesse para o presente trabalho, desde o básico, como material granular e mecanismos de transporte eólicos, até às grandezas chave envolvidas nos fenómenos de erosão do vento. Estudos realizados para calcular a emissão de poeira de pilhas de armazenamento são apresentados e revistos juntamente com a metodologia, amplamente aplicada, da Agência de Proteção Ambiental dos Estados Unidos (United States Environmental Protection Agency - USEPA). Esta metodologia estima as emissões de partículas a partir de pilhas de armazenamento apenas durante eventos de erosão específicos, tais como rajadas, quando as emissões na realidade ocorrem em muitas outras ocasiões. O presente trabalho oferece a possibilidade de realizar a determinação de emissões de pilhas de armazenamento ao longo do tempo; esta abordagem torna viável seguir a evolução dependente do tempo da superfície livre, aumentando assim a precisão das previsões. Portanto, estudos relacionados com a evolução da superfície livre são também revistos. O presente trabalho tem uma componente experimental significativa, e a tese descreve em considerável detalhe a montagem experimental e os procedimentos, incluindo o túnel de vento, material granular, as configurações de pilhas testadas e os testes executadas – em particular, testes de erosão e de medição da tensão de atrito (com sondas Irwin). Adicionalmente, o uso da Dinâmica de Fluidos Computacional (em inglês: Computational Fluid Dynamics — CFD) desempenha um papel importante no presente estudo, assim sendo, para completar, conceitos chave relacionados a CFD estão incluídos nesta tese, juntamente com uma breve pesquisa de estudos que empregam a metodologia CFD para avaliar a erosão eólica. Os presentes estudos CFD foram realizados usando um software CFD de código aberto - OpenFOAM (OF). A motivação para a seleção do OF, como ferramenta CFD, está relacionada com a sua ampla aceitação na comunidade científica; e além disso, a sua aplicação na previsão e estudo da erosão eólica é uma contribuição original para este campo de pesquisa. A descrição completa do modelo numérico e da sua implementação são dadas juntamente com a metodologia utilizada na validação do modelo. Foram estudadas duas configurações de pilha diferentes - uma pilha triangular bidimensional (2D) e uma pilha tridimensional (3D) oblonga. A crescente complexidade geométrica das pilhas permitiu ganhar experiência de forma gradual com os procedimentos e metodologias envolvidos no estudo. Os estudos experimentais e numéricos para estes casos, bem como os seus resultados, são analisados e discutidos No que diz respeito às pilhas oblongas, os resultados numéricos são correlacionados com a deformação de superfície livre das pilhas e comparados com outro estudo disponível na literatura, no qual foram realizados testes de visualização de filmes de óleo e utilizada uma ferramenta CFD diferente. Considerando que a validação do modelo é parcialmente realizada através da comparação dados experimentais; especial atenção foi dada à sua precisão. Para as pilhas triangulares, a comparação é feita, principalmente, com resultados da tensão de atrito da parede medidos através das sondas Irwin, as quais foram construídas e calibradas para este trabalho. O estudo efetuado com estas sondas foi extenso e contribuiu de forma inovadora e significativa para esta área de pesquisa, o que justifica uma Parte B integrada, mas autónoma desta tese. Devido à versatilidade da montagem experimental construída para auxiliar a calibração das sondas Irwin, um estudo mais aprofundado foi também realizado sobre escoamentos em condutas retangulares com seção transversal constante e variável. Finalmente, as principais conclusões que resultam do presente trabalho são resumidas e sugerem-se algumas recomendações para o trabalho futuro.

Pleomorphic calcifications are categorized among calcifications with suspicious morphology: amorphous, coarse heterogeneous, fine linear or fine-linear branching, and fine pleomorphic calcifications. Unlike amorphous calcifications, pleomorphic calcifications are more conspicuous, with discernible shapes that appear predominantly irregular, and are variable in size and configuration. A segmental distribution, seen as a triangular shape with its apex centered at the nipple, is especially suspicious for ductal carcinoma in situ (DCIS) or multifocal breast cancer, as its pattern of calcium deposition suggests involvement of a duct system within the breast. This chapter, appearing in the section on calcifications, reviews the key clinical and imaging features, imaging protocols, differential diagnoses, and management recommendations for pleomorphic calcifications. Topics discussed include characteristic morphology and distribution of pleomorphic calcifications, BI-RADS assessments, core needle biopsy, and radiological–pathological correlation.

The thematic focus of this yearbook is concerned with the various relations of „art“ and „technology“. It seeks to interrogate and reflect their conceptual filiations, their complementarities and mutual stimulations, and contrasts and tensions. The very notion of the „work“ challenges us to explode or triangulate the dichotomy of art and technology. This connects to further problems in and for the philosophy of technology, such as the relation of arts and crafts, the question of Kitsch or camp in art and technology, or the role of play as a basic modality of artful technical production. Finally, of course, comes design, packaging, marketing and the aesthetic effects of works. With contributions by Katrin Becker, Rainer Becker, Andreas Beinsteiner, Hans Blumenberg, Johanna Dombois, Daniel Martin Feige, Nico Formanek, Petra Gehring, Sebastian Hallensleben, Andreas Hauschke, Dawid Kasprowicz, Viet Anh Nguyen Duc, Regina Oehler, Anika Reineke, Dirk Rustemeyer, Bernhard Siebert, Larissa Ullmann, Claudia Wiesemann, Ryan Mitchell Wittingslow and Konstanze Wolter.

This study presents a comparative numerical solution of a conjugate-transient three-dimensional heat and mass transfer problem between a solid desiccant (silica gel) and a humid transient-laminar air stream in ducts with different cross sectional geometries: square, circular, and triangular. The problem is solved by using a finite control-volume method, and validated relative to available experimental data. The effects of the u velocity gradient normal to the wall (∂u/∂y) and the pressure drop (Δp) on the heat and mass transport for the three ducts are investigated. In duct flows, the results show that the average (∂u/∂y) for the triangular duct is 6.6% and 19.6% larger than that in the circular and square ducts, respectively; therefore, the triangular duct provides the largest convective heat and mass transport, and absorbs 11% and 42% more water than the circular and square ducts, respectively. At the same time, the average pressure drop for the triangular duct is 69% and 73.5% larger than the one for the square and circular ducts, respectively, which would result in higher fan power consumption. Using a figure of merit (Wr) that is a ratio of the required fan work to the dehumidification attained, the circular duct was found to be the best and the triangular the worst among the three geometries compared.

Earlier heat transfer studies with orthogonal rotation were conducted mostly on ducts of square cross-section. This paper reports a different cross-section, a triangular duct. Unlike a square cross-section, the triangular shape provides more restriction to the formation of the secondary flows. Moreover, the studied orientation of the right triangular duct avoids formation of symmetric vortex structures in the cross flow plane. This paper presents turbulent heat transfer characteristics of a two-pass smooth walled triangular duct. One pass is for radial outward flow and the other for radial inward flow. With rotation the radial outward and inward flow directions show different surface heat transfer characteristics. Like a square duct, differences between the trailing and the leading Nusselt number ratios for the triangular duct increase with rotation number. However, the rate of change of Nusselt number ratios with rotation number varies for the two duct geometries. Standard k-ε model predictions for a radial outward flow situation show that the Nusselt number ratio variations with Reynolds number are not drastic for the same rotation number.

Microchannel are at the fore front of today’s cooling technologies. They are widely being considered for cooling of electronic devices and in micro heat exchanger systems due to their ease of manufacture. One issue which arises in the use of microchannels is related to the small length scale of the channel or channel cross-section. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in microchannels of various cross-section having finite volume for laminar flow conditions. Solutions are presented for 10 different channel cross sections, namely parallel plate channel, circular duct, rectangular channel, elliptical duct, polygonal ducts, equilateral triangular duct, isosceles triangular duct, right triangular duct, rhombic duct and trapezoidal duct. The model is only a function of Prandtl number and geometrical parameters of the cross-section, i.e., area and perimeter. This solution is performed with two exact and approximate methods. Finally, in addition to comparison and discussion about these two methods, validation of the relationship is provided using results from the open literature.

Experimental investigations have been reported on steady state natural convection from the outer surface of vertical triangular cross section ducts in air. Three ducts have been used with equilateral side length of 0.044, 0.06 and 0.08 m. The ducts are heated using internal constant heat flux heating elements. The temperatures along the vertical surface and the peripheral directions of the duct wall are measured. Axial (perimeter averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition to turbulent regimes of natural convection heat transfer. Axial (perimeter averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for laminar and transition regime using the vertical axial distance as a characteristic length. Critical values of the modified Rayleigh numbers are obtained for transition to turbulent. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers for all ducts. The local axial (perimeter averaged) heat transfer coefficients are observed to decrease in the laminar region and increase in the transition region. Laminar regimes are obtained at the lower half of the ducts and its chance to appear decreases as the heat flux increases.

An experimental study has been performed to measure local heat transfer coefficients and static well pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right-triangular ducts of the same altitude and different apex angles of β = 30 deg (Duct A), 45 deg (Duct B) and 60 deg (Duct C) are tested for various jet Reynolds numbers (3000≦Rej≦12600) and jet spacings (s/d = 3.0 and 6.0). Results show that an increase in Rej increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Rej, the Duct C has the highest wall-averaged heat transfer because of the highest jet center velocity as well as the smallest jet inclined angle. Moreover, the distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.

Heat transfer from arrays of circular and non-circular ducts subject to finite volume and constant pressure drop constraints is examined. It is shown that the optimal duct dimension is independent of the array structure and hence represents an optimal construction element. Solutions are presented for the optimal duct dimensions and maximum heat transfer per unit volume for the parallel plate channel, rectangular channel, elliptic duct, circular duct, polygonal ducts, and triangular ducts. Approximate analytical results show that the optimal shape is the isosceles right triangle and square duct due to their ability to provide the most efficient packing in a fixed volume. Whereas a more exact analysis reveals that the parallel plate channel array is in fact the superior system. An approximate relationship is developed which is very nearly a universal solution for any duct shape in terms of the Bejan number and duct aspect ratio. Finally, validation of the relationships is provided using exact results from the open literature.

Detailed heat transfer coefficient distributions and pressure drop have been obtained for high aspect ratio (AR = Width/Height = 12.5) ducts with triangular trench enhancement features oriented normal to the coolant flow direction. Numerical and experimental approaches analyze the performance of triangular trenches for six geometrically identical ducts branching from a common plenum. The numerical approach is based on a Reynolds Averaged Navier Stokes (RANS) turbulence model with an unstructured mesh. A transient liquid crystal (TLC) technique is used to experimentally calculate Nu on the ducts surfaces. Reynolds number (Re = 7080, 14800, and 22400, with respect to the duct hydraulic diameter are explored. As Computational Fluid Dynamics (CFD) and TLC results are both detailed, qualitative and quantitative comparisons are made. Experimental results show the closest and furthest ducts from the entrance of the plenum are considerably affected, as recirculation zones develop which partially choke the inlet the respective ducts. Results from the experiments are compared to CFD predictions from Duct 4. In addition, the experimental data are recalculated with the maximum bias in TLC temperature to indicate an improved matching between CFD and experimental methods to demonstrate that CFD captures the wall heat transfer coefficient trends similar to experimental results. The triangular trenches enhance heat transfer in the ducts two-fold compared to smooth wall Dittus-Boelter Nusselt number correlation for flow in tubes.

Experiments have been carried out to investigate the convective heat transfer characteristics from triangular folded fin heat sinks in a suction-type fan duct. The dimension of the triangular folded fin heat sinks is 62 mm in height with a 12 mm thick base plate, 292 mm in width, and 447 mm in length. The inlet flow velocity is varied in the range of 0.6–5.3 m/s. Thermal performance of triangular folded fin heat sinks is evaluated in terms of thermal resistance of heat sinks according to flow velocity and fan power. The results obtained show that the present triangular folded-fin heat sink shows a higher thermal performance compared to a conventional extruded plate-fin heat sink. Especially, a perforated slit folded-fin heat sink displays a lower thermal resistance. As the number of slit fabricated on the perforated folded fins increases, thermal performance is more pronounced.

This study presents an analysis of forced convection in a porous triangular channel. The flow is laminar, fully developed and assumed to have constant properties. The porous channel has an isotropic matrix and the boundary conditions are fixed with constant temperature. In this paper, accurate analytical solutions are presented to determine the effects of apex angle and porous media properties on the velocity and temperature distribution in a triangular channel along with the friction factor fRe, and Nusselt number NuT. The presentaion includes numerical features of the exact series solution using Brinkman’s model. Numerical results for dimensionless average temperature and velocity are presented for various porosities, permeabilities and apex angles.