Conjugated Heat Transfer in Heat Spreaders With Micro-Channels

2013 ◽  
Author(s):  
Diego C. Knupp ◽  
Renato M. Cotta ◽  
Carolina P. Naveira Cotta
Keyword(s):  
Heat Transfer ◽  
Integral Transform ◽  
Convection Heat Transfer ◽  
Variable Coefficients ◽  
Hot Water ◽  
Single Domain ◽  
Normal Operation ◽  
Heat Spreader ◽  
Micro Channels ◽  
Micro Systems

This work is aimed at the experimental verification of a recently proposed single domain formulation of conjugated conduction-convection heat transfer problems, which are often of relevance in thermal micro-systems analysis. The single domain formulation simultaneously models the heat transfer phenomena at both the fluid streams and the channels walls by making use of coefficients represented as space variable functions with abrupt transitions occurring at the fluid-wall interfaces. The Generalized Integral Transform Technique (GITT) is then employed in the hybrid numerical-analytical solution of the resulting convection-diffusion problem with variable coefficients. The considered experimental investigation involves the determination of the temperature distribution over a heat spreader made of a nanocomposite plate with a longitudinally molded single micro-channel that exchanges heat with the plate by flowing hot water at an adjustable mass flow rate. The infrared thermography technique is employed to analyze the response of the heat spreader surface, aiming at the analysis of micro-systems that provide a thermal response from either their normal operation or due to a promoted stimulus for characterization purposes.

Conjugated Convection-Conduction Analysis in Microchannels With Axial Diffusion Effects and a Single Domain Formulation

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Diego C. Knupp ◽  
Carolina P. Naveira-Cotta ◽  
Renato M. Cotta
Keyword(s):  
Heat Transfer ◽  
Eigenvalue Problem ◽  
Integral Transform ◽  
Convection Heat Transfer ◽  
Solution Procedure ◽  
Variable Coefficients ◽  
Single Domain ◽  
Axial Diffusion ◽  
Diffusion Effects ◽  
Transfer Problems

An extension of a recently proposed single domain formulation of conjugated conduction–convection heat transfer problems is presented, taking into account the axial diffusion effects at both the walls and fluid regions, which are often of relevance in microchannels flows. The single domain formulation simultaneously models the heat transfer phenomena at both the fluid stream and the channel walls, by making use of coefficients represented as space variable functions, with abrupt transitions occurring at the fluid-wall interface. The generalized integral transform technique (GITT) is then employed in the hybrid numerical–analytical solution of the resulting convection–diffusion problem with variable coefficients. With axial diffusion included in the formulation, a nonclassical eigenvalue problem may be preferred in the solution procedure, which is itself handled with the GITT. To allow for critical comparisons against the results obtained by means of this alternative solution path, we have also proposed a more direct solution involving a pseudotransient term, but with the aid of a classical Sturm-Liouville eigenvalue problem. The fully converged results confirm the adequacy of this single domain approach in handling conjugated heat transfer problems in microchannels, when axial diffusion effects must be accounted for.

Conjugated Heat Transfer in Micro-Channels With a Single Domain Formulation and Integral Transforms

2012 ◽  
Author(s):  
Diego C. Knupp ◽  
Carolina P. Naveira Cotta ◽  
Renato M. Cotta
Keyword(s):  
Heat Transfer ◽  
Analytical Solution ◽  
Eigenvalue Problem ◽  
Space Variable ◽  
Variable Coefficients ◽  
Single Domain ◽  
Axial Conduction ◽  
Micro Channels ◽  
Conjugated Heat Transfer ◽  
Transfer Problems

The present work is an extension of a novel methodology recently proposed by the authors for the analytical solution of conjugated heat transfer problems in channel flow, here taking into account the axial diffusion effects which are often of relevance in micro-channels. This methodology is based on a single domain formulation, which is proposed for modeling the heat transfer phenomena at both the fluid stream and the channel walls regions. By making use of coefficients represented as space variable functions, with abrupt transitions occurring at the fluid-wall interface, the mathematical model is fed with the information concerning the transition of the two domains, unifying the model into a single domain formulation with space variable coefficients. The Generalized Integral Transform Technique (GITT) is then employed in the hybrid numerical-analytical solution of the resulting convection-diffusion problem with variable coefficients. When the axial conduction term is included into the formulation, a non-classical eigenvalue problem must be employed in the solution procedure, which is itself handled with the GITT. In order to covalidate the results obtained by means of this solution path, we have also proposed an alternative solution, including a pseudo-transient term, with the aid of a classical Sturm-Liouville eigenvalue problem. The remarkable results demonstrate the feasibility of this single domain approach in handling conjugated heat transfer problems in micro-channels, as well as when fluid axial conduction cannot be neglected.

Evaluation of Passive Anti-Fouling Technology Applied to CO2 Heat Pump Water Heaters

2014 ◽  
Author(s):  
Portia Murray ◽  
Stephen J. Harrison ◽  
Ben Stinson
Keyword(s):  
Heat Transfer ◽  
Water Supply ◽  
Heat Pump ◽  
Hot Water ◽  
Normal Operation ◽  
Mineral Deposits ◽  
Reverse Direction ◽  
Water Tank ◽  
Flow Rates ◽  
Water Heaters

Heat pump water heaters are increasing in popularity due to their increased energy efficiency and low environmental impact. This paper describes the experimental testing of a transcritical CO2 heat pump water heater at Queen’s University. A modified 4.5 kW Eco-Cute unit was studied. It sourced heat from a constant temperature water supply and rejected the heat to a 273 litre hot water tank through a gas-cooler. The high temperatures that occur in the gas-cooler of this unit make it ideally suited for natural convection, (i.e., thermosyphon) circulation on the potable water side. This has the potential to reduce pumping power, simplify system operation and design, and increase thermal stratification in the hot water storage tank. This configuration, however, is susceptible to the accumulation of sediments, scale and mineral deposits (i.e., fouling) in geographic regions where high mineral deposits may be present in the water supply. To counteract fouling in these cases, a passive back-flushing system was proposed to prevent the accumulation of deposits on the heat transfer surfaces of the gas-cooler. As hot water is drawn from the system, the cold “mains” supply water is directed through the gas-cooler in the reverse direction of normal operation, scouring the heat transfer surfaces and dissolving deposits of inverse-soluble salts which are a major contributor to fouling on hot heat transfer surfaces. The gas-cooler used was a specially designed unit that, although offering high performance in a compact unit, may be susceptible to the fouling and blockage of the heat transfer passages when used at thermosyphon flow rates. Experiments were conducted to evaluate the effects of the back-flush operation on heat pump performance (i.e., COP) and operation. These were conducted under controlled laboratory conditions, at a range of draw flow rates and temperatures, and are summarized in this paper.

scholarly journals An Experimental Investigation on Heat Transfer Characteristics of Air and CO2 in Microtubes

2011 ◽  
Author(s):  
Chia-Wei Chen ◽  
Ting-Yu Lin ◽  
Chien-Yuh Yang ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Performance ◽  
Convection Heat Transfer ◽  
Transfer Performance ◽  
Gaseous Flow ◽  
Compressibility Effect ◽  
Micro Channels ◽  
Significant Difference ◽  
Laminar And Turbulent Flow

Several researches dealing with the single-phase forced convection heat transfer inside micro channels have been published in the past decades. The performance of liquid flow has been proved that agree with the conventional correlations very well (Yang and Lin [2007]). However, owing to the low heat transfer coefficient of gaseous flow, it is more difficult to eliminate the effects of thermal shunt and heat loss than water flow while measuring its heat transfer performance. This study provides an experimental investigation on forced convective heat transfer performance of air and gaseous carbon dioxide flowing through two microtube with inner diameter of 920 μm. A non-contacted liquid crystal thermography (LCT) temperature measurement method that proposed by Lin and Yang [2007] was used in this study to measure the surface temperature of microtube. The test results show that the conventional heat transfer correlations for laminar and turbulent flow can be well applied for predicting the fully developed heat transfer performance in microtubes while taking account of the compressibility effect of high pressure gaseous flow in micro tubes. There is no significant difference between CO2 and air in both heat transfer and friction.

Effects of Baffle Width on Heat Transfer to an Immersed Coil Heat Exchanger: Experimental Optimization

2019 ◽  
Author(s):  
Julia Haltiwanger Nicodemus ◽  
Xiaoqi Huang ◽  
Emily Dentinger ◽  
Kyle Petitt ◽  
Joshua H. Smith
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Convection Heat Transfer ◽  
Hot Water ◽  
Outlet Temperature ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Water Storage Tank ◽  
Coil Heat Exchanger

Abstract In this work, we investigate the effects of the width of an annular baffle region on natural convection heat transfer to an immersed, coiled heat exchanger in an otherwise quiescent sensible hot water storage tank. In experiments, the coiled heat exchanger sits in an annular region created by the tank wall and a straight, cylindrical baffle. The width of this baffle region is 1.5, 2, 3, or 4 times the heat exchanger diameter, These experiments are compared to each other and to corresponding control experiments with no baffle. In general, all baffles create considerable benefits over their respective control experiments, consistent with past studies. The considered metrics of heat transfer rate, fraction of energy discharged from the tank, and heat exchanger outlet temperature show that heat transfer is improved slightly by narrowing the baffle region. For example, relative to their respective controls, the energy extracted from the tank after 30 min of discharge in the 1.5D, 2D, 3D and 4D experiments is 23.2%, 20.8%, 18.1%, and 14.7% higher, respectively. This improvement in natural convection heat transfer as the baffle region narrows is attributed to the increasing thermal stratification observed in experiments with increasingly narrow baffle regions.

Feasibility Study of Effective Cooling Through Microchannel Heat Sink (MCHS) and Nanofluid Applications

2018 ◽  
Author(s):  
Darryl Jennings ◽  
Sonya Smith
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Forced Convection ◽  
Analytical Model ◽  
Heat Sink ◽  
Convection Heat Transfer ◽  
Microchannel Heat Sink ◽  
Convection Heat ◽  
Ansys Fluent ◽  
Micro Channels

The goal of this research is to present an analytical model of nanostructures and study the effects of their geometry on the performance of micro channels. The pressure drop experienced by micro channels is of interest as it presents a limit on forced convection heat transfer. This work will demonstrate how the presence of nanostructures alleviates pressure drop and results in enhanced cooling capabilities. Multiple transient analyses were performed in ANSYS FLUENT to ascertain performance characteristics of microchannels without the presence of hydrophobic nanostructures. The results were compared to the analytical model developed in this study.

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