Gas-Solids Mixing and Heat Transfer Studies in Incipiently Fluidized Beds of Nonuniform Cross-Sectional Area

1969 ◽  
Vol 8 (2) ◽  
pp. 232-240 ◽  
Author(s):  
K. J. Miller ◽  
R. M. Edwards
Keyword(s):  
Heat Transfer ◽  
Fluidized Beds ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Solids Mixing

scholarly journals Numerical Investigation of a two-inlet PVT air collector

2019 ◽  
Vol 136 ◽  
pp. 05014
Author(s):  
Zhangyang Kang ◽  
Zhaoyang Lu ◽  
Xin Deng ◽  
Qiongqiong Yao
Keyword(s):  
Heat Transfer ◽  
Single Channel ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Thermal Characteristics ◽  
Area Ratio ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Maximum Heat

A numerical study of heat and mass transfer characteristics of a two-inlet PV/T air collector is performed. The influence of thermal characteristics and efficiency is investigated as the area ratios of inlet and outlet of the single channel with two inlets are changed. The design of the two-inlet PV/T air collector can avoid the poor heat transfer conditions of the single inlet PV/T air collector and improve the total photo-thermal efficiency. When the inlet/outlet cross-sectional area ratio is reduced, the inlet air from the second inlet enhances the convection heat transfer in the second duct and the temperature distribution is more uniform. As the cross-sectional area of the second inlet increase, the maximum heat exchange amount of the two-inlet PV/T air collector occurs between the inlet and outlet cross-sectional area ratio L=0.645 and L=0.562.

Maximum Power From Fluid Flow: Results From the First and Second Laws of Thermodynamics

2012 ◽  
Author(s):  
German Amador Diaz ◽  
John Turizo Santos ◽  
Elkin Hernandez ◽  
Ricardo Vasquez Padilla ◽  
Lesme Corredor
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Power Output ◽  
Power Plants ◽  
Cross Sectional Area ◽  
Maximum Power ◽  
Sectional Area ◽  
Cross Sectional ◽  
Maximum Power Output ◽  
Piston Cylinder

The heat transfer principle of power maximization in power plants with heat transfer irreversibilities was cleverly extended by Bejan [1] to fluid flow, by obtaining that the energy conversion efficiency at maximum power is ηmax = 1/2(1 − P2/P1). This result is analog to the efficiency at maximum power for power plants, ηmax = 1 − (T2/T1)1/2 which was deduced by Curzon and Ahlborn [2]. In this paper, the analysis to obtain maximum power output delivered from a piston between two pressure reservoir across linear flow resistance is generalized by considering the piston cylinder friction, by obtaining relations of maximum power output and optimal speed of the piston in terms of first law efficiency. Expressions to relate the power output, cross sectional area of the chamber and first law efficiency, were deduced in order to evaluate the influence of the overall size constraints and fluid regime in the performance of the piston cylinder system. Flow in circular ducts and developed laminar flow between parallel plates, are considered to demonstrate that when two pressure reservoirs oriented in counterflow, with different and arbitrary cross sectional area, must have the same area in order to maximize the power output of the system. These results introduce some modifications to the results obtained by Bejan [1] and Chen [3]. This paper extends the Bejan and Chen’s work by estimating under turbulent regime the lost available work rate associated with the degree of irreversibilities caused by the flow resistances of the system. This analysis is equivalent to evaluate the irreversibilities in an endoirreversible Carnot heat engine model caused by the heat resistance loss between the engine and its surrounding heat reservoirs. This paper concludes with an application to illustrate the practical applications by estimating the lost available work of an actual steady-flow turbine and the layout pipes upstream and downstream of the same device.

scholarly journals Row Resolved Heat Transfer Variations in Pin-Fin Arrays Including Effects of Non-Uniform Arrays and Flow Convergence

1986 ◽  
Author(s):  
D. E. Metzger ◽  
W. B. Shepard ◽  
S. W. Haley
Keyword(s):  
Heat Transfer ◽  
Cross Sectional Area ◽  
Experimental Program ◽  
Internal Cooling ◽  
Sectional Area ◽  
Order Unity ◽  
Cross Sectional ◽  
Turbine Engine ◽  
Pin Fin ◽  
Pin Fin Arrays

Measured streamwise (longitudinal) heat transfer variations, spanwise (transverse) averaged and resolved to single row spacings, are presented for large aspect ratio ducts containing staggered arrays of circular pin fins which span the entire duct height. A number of different array geometries have been investigated in an experimental program, including uniformly spaced arrays in constant cross sectional area ducts with streamwise row spacings over the range 1.5 to 5.0 pin diameters. Such arrays, with pin length-to-diameter ratio of order unity, are often used to enhance heat transfer in internal cooling passages of gas turbine engine airfoils. The effects of various length interruptions in the pin pattern and of abrapt changes in pin diameter are presented for constant cross sectional area ducts. In addition, results are presented for the effect of duct convergence, a common situation in the cooled turbine airfoil application. A concise summary of all the observed behavior is given, useful for predicting the performance of arbitrarily spaced pin fin arrays that may be specified to produce a particular cooling distribution. Predictions are compared with two final test, configurations which combine aspects of all of the effects investigated in the experimental program.

Optimization of Heat Transfer Rate in the Rectangular Microchannel of Different Aspect Ratios With Constant Cross Sectional Area

2008 ◽  
Author(s):  
F. Kowsary ◽  
N. Noroozi ◽  
M. Rezaei Barmi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Reynolds Numbers ◽  
Cross Sectional Area ◽  
Heat Sinks ◽  
Sectional Area ◽  
Cross Sectional ◽  
Aspect Ratios

The increased power dissipation and reduced dimensions of microelectronics devices have emphasized the need for highly efficient compact cooling technologies. Microchannel heat sinks are of particular interest due to the very high rates of heat transfer they enable in conjunction with greatly reduced heat sink length scales and coolant mass flow rate. Therefore, in the present work, optimization of laminar convective heat transfer in the microchannel heat sinks is investigated for uniform heat flux and different cross sectional areas of different aspect ratios. Three-dimensional numerical simulations of general form of energy equation were performed to predict Nusselt number in the laminar flow regime. Using these results, an optimum forced convective heat transfer coefficient was computed for several cross sectional areas and Reynolds numbers, utilizing the univariable search method. Different aspect ratios have different influences on Nusselt number in thermally developing and fully developed regions for different cross sectional areas and Reynolds numbers. There exists an optimum Nusselt number for each Reynolds number and cross sectional area by varying aspect ratio. Thus, optimized state is computed and related graphs are presented.

Enhanced Flow Boiling Heat Transfer Using Radial Microchannels

2016 ◽  
Author(s):  
Alyssa Recinella ◽  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Cross Sectional Area ◽  
Working Fluid ◽  
Transfer Performance ◽  
Sectional Area ◽  
Cross Sectional ◽  
Flow Rates ◽  
Flow Cross

Flow boiling has the ability to remove high heat fluxes while maintaining a low wall superheat. Various researchers have developed enhanced microchannel geometries to improve the heat transfer performance of the system. Recently, a number of new studies have used the increasing flow cross-sectional area concept to overcome flow instabilities and record high CHF. In this work, a new geometry is experimentally investigated utilizing a radial cross-section, which provides the increasing fluid flow cross-sectional area in the flow direction. The flow boiling performance is studied using radial microchannels and water as the working fluid. Four different flow rates ranging from 120–400 mL/min are studied for this new geometry. Heat transfer performance (boiling curve and heat transfer coefficient) and pressure drop characteristics are discussed for all flow rates. Furthermore, the work is supported by high speed visualization of the bubble dynamics. The boiling performance obtained is compared to the existing data in the literature.

Convective Heat Transfer and Contact Resistances Effects on Performance of Conventional and Composite Thermoelectric Devices

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
B. V. K. Reddy ◽  
Matthew Barry ◽  
John Li ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Conversion Efficiency ◽  
Power Output ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Transfer Coefficients ◽  
Cross Sectional ◽  
Heat Transfer Coefficients

The performance of Π shaped conventional and composite thermoelectric devices (TEDs) applied to waste heat recovery by taking the Fourier heat conduction, Joule heating, and the Peltier and Thomson effects in TE materials is investigated using analytical solutions. The TE legs built with semiconductor materials bonded onto a highly conductive interconnector material in a segmented fashion is treated as the composite TED, whereas the legs merely made from semiconductors is treated as the conventional TED. The top and bottom surfaces of TEDs are subjected to convective heat transfer conditions while the remaining surfaces exposed to ambient are kept adiabatic. The effects of contact resistances, convective heat transfer coefficients, and TE leg heights L on TEDs' performance are studied. An increase in electrical and/or thermal contact resistance and a decrease in heat transfer coefficients are resulted in a decrease in power output P0 and conversion efficiency η. Depending on the contact resistances and convective heat transfer loads, the optimum L where a maximum Po occurs is obtained typically in the range of 1–4 mm. For TE leg size greater than optimum L and TED operating under higher convective heat transfer conditions, the composite design exhibited better power output and lower conversion efficiency compared to conventional design. The effects of interconnector lengths and cross-sectional area on the composite TED's characteristics are also investigated. An increase in a length and a decrease in a cross-sectional area of the interconnector decreases the composite TED's performance. However, based on the increase of the interconnector's electrical resistance in relation to the device's total internal resistance, the composite TED exhibited both negligible and significant change behavior in P0.

Fully Developed Flow and Heat Transfer in Ducts Having Streamwise-Periodic Variations of Cross-Sectional Area

1977 ◽  
Vol 99 (2) ◽  
pp. 180-186 ◽  
Author(s):  
S. V. Patankar ◽  
C. H. Liu ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Flow Field ◽  
Cross Sectional Area ◽  
Bulk Temperature ◽  
Sectional Area ◽  
Cross Sectional ◽  
Reduced Pressure ◽  
Fully Developed Flow ◽  
Flow And Heat Transfer

The concepts of fully developed flow and heat transfer have been generalized to accommodate ducts whose cross-sectional area varies periodically in the streamwise direction. The identification of the periodicity characteristics of the velocity components and of a reduced pressure function enables the flow field analysis to be confined to a single isolated module, without involvement with the entrance region problem. A similar modular analysis can be made for the temperature field, but the periodicity conditions are of a different nature depending on the thermal boundary conditions. For uniform wall temperature, profiles of similar shape recur periodically. On the other band, for prescribed wall heat flux which is the same for all modules, the temperature field itself is periodic provided that a linear term related to the bulk temperature change is subtracted. The concepts and solution procedure for the periodic fully developed regime were applied to a heat exchanger configuration consisting of successive ranks of isothermal plate segments placed transverse to the mainflow direction. The computed laminar flow field was found to be characterized by strong blockage effects and massive recirculation zones. The fully developed Nusselt numbers are much higher than those for conventional laminar duct flows and show a marked dependence on the Reynolds number.

Heat Transfer and Pressure Loss in a Two-Pass, Rectangular Channel Featuring a Reduced Cross-Sectional Area After the 180- Degree Tip Turn with Different Turning Vane Configurations

2021 ◽  
pp. 1-44
Author(s):  
Sulaiman Alsaleem ◽  
Lesley Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Cross Section ◽  
Pressure Loss ◽  
Guide Vane ◽  
Circular Cross Section ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Number Range

Abstract Serpentine, multi-pass cooling passages, are used in cooling advanced gas turbine blades. In open literature, most internal cooling studies use a fixed cross-sectional area for multi-pass channels. Studies that use varying aspect ratio channels, along with a guide vane to direct the flow with turning, are scarce. Therefore, this study investigates the effect of using different guide vane designs on both detailed heat transfer distribution and pressure loss in a multi-pass channel with an aspect ratio of (4:1) in the entry passage and (2:1) in the second passage downstream of the vane (s). The first vane configuration is one solid-vane with a semi-circular cross-section connecting the two flow passages. The second configuration has three broken-vanes with a quarter-circular cross-section; two broken vanes are located downstream in the first passage, and one broken vane is upstream in the second passage. Detailed heat transfer distributions were obtained on all surfaces within the flow passages by using a transient liquid crystal method. Results show that including the semi-circular vane in the turning region enhanced the overall heat transfer by around 29% with a reduction in pressure loss by around 20%. Moreover, results show the quarter-circular vane design provides higher overall averaged heat transfer enhancement than the semi-circular vane design by around 9% with penalty of higher pressure drop by 6%, which yields higher thermal performance by 7%, over a Reynolds number range from 15,000 to 45,000.

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