Augmentation of Heat Transfer in Tubes by Use of Mesh and Brush Inserts

1974 ◽  
Vol 96 (2) ◽  
pp. 145-151 ◽  
Author(s):  
F. E. Megerlin ◽  
R. W. Murphy ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Mass Velocity ◽  
High Heat ◽  
Equal Mass ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Large Pressure ◽  
Empty Tube

This paper summarizes the results of a study to determine the heat transfer and pressure drop characteristics of two types of tube inserts developed specifically for augmenting heat transfer and accommodating high heat fluxes. The best performing mesh-insert tubes exhibited heat transfer coefficients nine times the coefficients with empty tubes while brush-insert tubes had coefficients averaging five times the empty tube values, both comparisons being made at equal mass velocity. Both inserts produced very large pressure drops. Subcooled boiling curves and burnout points are presented; burnout heat fluxes are two to three times the empty tube values at equal mass velocity. For single-phase conditions and for burnout, the mesh and brush tubes have favorable performance characteristics, based on pumping power, which suggest use of these inserts in certain special cooling systems.

Periodically Converging-Diverging Tubes and Their Turbulent Heat Transfer, Pressure Drop, Fluid Flow, and Enhancement Characteristics

1984 ◽  
Vol 106 (1) ◽  
pp. 55-63 ◽  
Author(s):  
P. Souza Mendes ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Surface Area ◽  
Equal Mass ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors

A comprehensive experimental study was performed to determine entrance region and fully developed heat transfer coefficients, pressure distributions and friction factors, and patterns of fluid flow in periodically converging and diverging tubes. The investigated tubes consisted of a succession of alternately converging and diverging conical sections (i.e., modules) placed end to end. Systematic variations were made in the Reynolds number, the taper angle of the converging and diverging modules, and the module aspect ratio. Flow visualizations were performed using the oil-lampblack technique. A performance analysis comparing periodic tubes and conventional straight tubes was made using the experimentally determined heat transfer coefficients and friction factors as input. For equal mass flow rate and equal transfer surface area, there are large enhancements of the heat transfer coefficient for periodic tubes, with accompanying large pressure drops. For equal pumping power and equal transfer surface area, enhancements in the 30–60 percent range were encountered. These findings indicate that periodic converging-diverging tubes possess favorable enhancement characteristics.

Numerical Investigation on the Effect of Transversal Septa on Forced Convection in Circular Tubes

2009 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Circular Tubes ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Conventional sources of energy have been depleting at an alarming rate, which makes future sustainable development of energy use very difficult. Thus, heat transfer enhancement technology plays an important role and it has been widely applied to many applications as in refrigeration, automotive, process industry, solar energy heater, etc. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. In this paper a numerical investigation is carried out on forced convection in circular tubes with septa heated by constant fluxes and characterized by different shapes. When gas flows in a tube, septa with one or more openings can be used as fins. Furthermore, when the openings are arranged to give a spiral motion around the cylinder axis wall-fluid contact area increases. As a consequence the presence of the septa may significantly augment pressure drops. The fluid is air and properties are function of temperature. Septa of the same material of the tube are introduced and several shapes and arrangements are analyzed as well as different Reynolds numbers, baffle spacings and heat fluxes applied on the external surface. The investigation is accomplished by means of the commercial code Fluent. A k-e turbulence model is used with enhanced wall treatment options. Results are presented in terms of temperature and velocity fields, local and average heat transfer coefficients, friction factors and pressure drops for different values of heat flux, Reynolds numbers and baffle spacings. The aim of this study is to find the shape and arrangement of septa such to give high heat transfer coefficients and low pressure drops.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

Numerical Investigation on Forced Convection in Circular Tubes With Septa

2008 ◽  
Author(s):  
D. Corrente ◽  
O. Manca ◽  
S. Nardini ◽  
D. Ricci ◽  
G. Masullo
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Forced Convection ◽  
High Heat ◽  
Ideal Gas ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Heating And Cooling ◽  
High Heat Transfer

Heat transfer in fluids is very important in many industrial heating and cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility to increase heat transfer with gas is to employ extended surfaces. When gas flows in a tube, septa with one or more openings can be used as fins. Furthermore, if the openings are arranged to give a spiral motion around the cylinder axis wall-fluid contact area increases. As a consequence the presence of the septa can significantly augment pressure drops. In this paper a numerical investigation is carried out on forced convection in circular isothermal tubes. The fluid is air and ideal gas model is employed. Septa are introduced and several shapes and arrangements are analyzed. The investigation is accomplished by means of the commercial code Fluent. A turbulence model is used. Results are presented in terms of temperature and velocity fields, local and average heat transfer coefficients and pressure drops. The aim of this study is to find the shape and arrangement of septa such to give high heat transfer coefficients and low pressure drops.

Heat Transfer Analysis of Microgrooved Evaporator and Condenser Surfaces Utilized in a High Heat Flux Two-Phase Flow Loop

2007 ◽  
Author(s):  
Edvin Cetegen ◽  
Thomas Baummer ◽  
Serguei Dessiatoun ◽  
Michael Ohadi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Heat ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Microgrooved Surface

This paper investigates the heat transfer and pressure drop analysis of micro grooved surfaces utilized in evaporators and condensers of a two-phase flow cooling loop. These devices utilize the vapor-liquid phase change to transfer large amounts of heat, and they offer substantially higher heat flux performance with lower pumping power than most liquid cooling technologies. Microgrooved surfaces, combined with force-fed evaporation and condensation technology discussed in this paper yield high heat transfer coefficients with low pressure drops. Our most recent results, aiming to test the limits of the technology, demonstrated dissipation of almost 1kW/cm2 from silicon electronics using HFE 7100 as the working fluid. In a compact two phase system, the heat generated by the electronic components can be absorbed by microgrooved evaporators and rejected through the microgrooved surface condensers to liquid cooled slots with high heat transfer coefficients and low pressure drops on the refrigerant side. In the case of air-cooling, the same microgrooved surface heat exchanger can reject heat with a heat transfer coefficient of 3847 W/cm2 and a pressure drop of 4156 Pa. These heat transfer processes have the added capability of being combined and used together in a self-contained system cooled either by liquid or air.

Cavitation Enhanced Heat Transfer in Microchannels

2006 ◽  
Vol 128 (12) ◽  
pp. 1293-1301 ◽  
Author(s):  
Brandon Schneider ◽  
Ali Koşar ◽  
Chih-Jung Kuo ◽  
Chandan Mishra ◽  
Gregory S. Cole ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Fluxes ◽  
Hydrodynamic Cavitation ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation ◽  
Supercavitating Flow ◽  
Hydraulic Conditions ◽  
The Heat Transfer Coefficient

Heat transfer has been investigated in the presence of hydrodynamic cavitation instigated by 20-μm wide inlet micro-orifices entrenched inside 227-μm hydraulic diameter microchannels. Average surface temperatures, heat transfer coefficients, and pressure drops have been obtained over effective heat fluxes ranging from 39 to 558W∕cm2 at mass flux of 1814kg∕m2s under noncavitating and three cavitating conditions. Significant heat transfer enhancement has been recorded during supercavitating flow conditions in comparison to noncavitating flows with minimal pressure drop penalty. Once supercavitating conditions were reached, no apparent heat transfer augmentation was detected with the reduction of the cavitation index. Visualization of the flow morphology and the heat transfer coefficient characteristics aided in the evaluation of the dominant heat transfer mechanism under various thermal-hydraulic conditions.

Numerical Analysis on the Effects of Transversal Ribs on Forced Convection in Channels

2009 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci ◽  
S. Tamburrino
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Forced Convection ◽  
High Heat ◽  
Constant Heat Flux ◽  
Wall Turbulence ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Heat transfer in fluids is very important in many industrial heating and cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. When a fluid flows in a channel, transversal ribs can be used as fins and break the laminar sublayer creating local wall turbulence. However, as a consequence the presence of the ribs can significantly augment pressure drops. In this paper a numerical investigation is carried out on forced convection in channels heated by a constant heat flux. Also conductive effects are taken into account. The fluid is air and properties are assumed as function of temperature. Ribs of the same material of the channel walls are introduced and several arrangements are analyzed. The investigation is accomplished by means of the commercial code Fluent. A turbulence model is used. Results are presented in terms of temperature and velocity fields, average heat transfer coefficients, friction factor profiles and pressure drops. The aim of this study is to find arrangement of ribs such to give high heat transfer coefficients and low pressure drops. The maximum Nusselt number and friction factor have been detected for dimensionless pitches equal, respectively, to 12 and 10.

scholarly journals Thin Film Evaporation Using Nanoporous Membranes for Enhanced Heat Transfer

2012 ◽  
Author(s):  
Rong Xiao ◽  
Shalabh C. Maroo ◽  
Evelyn N. Wang
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Thermal Management ◽  
High Heat ◽  
Heat Fluxes ◽  
Nanoporous Membranes ◽  
Transfer Coefficients ◽  
Thin Film Evaporation ◽  
Heat Transfer Coefficients ◽  
Film Evaporation

Recent advancements in integrated circuits demand the development of novel thermal management schemes that can dissipate ultra-high heat fluxes with high heat transfer coefficients. Previous study demonstrated the potential of thin film evaporation on micro/nanostructured surfaces [1–11]. Theoretical calculations indicate that heat transfer coefficients on the order of 106 W/m2K and heat fluxes of 105 W/cm2 can be achievable with water [1, 5–6]. However, in previous experimental setup, the coolant has to propagate across the surface which limits the increase in heat flux and the heat transfer coefficient, while adding complexity to the system design. This work aims to decouple the propagation of the coolant from the evaporation process through a novel experimental configuration. Thin nanoporous membranes of 13 mm diameter were used where a metal layer was deposited on the top surface to serve as a resistance heater. Liquid was supplied from the bottom of the membrane, driven through the nanopores by capillary force, and evaporated from the top surface. Heat transfer coefficient over 104 W/m2K was obtained with isopropyl alcohol (IPA) as the coolant, which is only two orders of magnitude smaller than the theoretical limit. This work offers insights into optimal experimental designs towards achieving kinetic limits of heat transfer for thin film evaporation based thermal management solutions.

A Numerical Investigation on Nanofluids Forced Convection in Channels With Transverse Ribs

2010 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Forced Convection ◽  
High Heat ◽  
Constant Heat Flux ◽  
Wall Turbulence ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Heat transfer enhancement technologies are adopted in several applications as heat exchangers for refrigeration, automotives, process industry, solar heaters. A possibility for increasing the convective heat transfer in a fluid is to employ rough surfaces or adopting additives. When a fluid flows in a channel, ribs break the laminar sub-layer and create local wall turbulence due to flow separation and reattachment between consecutive ribs, which reduce thermal resistance and greatly augment the heat transfer. This behaviour overcomes the effect linked to the increased heat transfer area due to the ribs. However, higher friction losses are expected. In this paper a numerical investigation is carried out on forced convection with nanofluids (water-Al2O3) in a ribbed channel with a constant heat flux applied on the external walls. Properties of fluid are considered constant and a single phase model is employed. Flow regime is turbulent; in fact, Reynolds numbers ranging from 20000 to 60000 are considered. Furthermore, different shapes, such as square, rectangular, triangular ones, and different dimensionless heights and pitches of elements are analyzed. Moreover, two volume particle concentrations are investigated. Results are presented in terms of temperature and velocity fields, average heat transfer coefficients and pressure drop profiles. The aim of this study is to find arrangement of ribs such to give high heat transfer coefficients and low pressure drops in presence of nanofluids.

Heat Transfer During Forced Convection Boiling of R-12 Under Swirl Flow

1986 ◽  
Vol 108 (3) ◽  
pp. 567-573 ◽  
Author(s):  
K. N. Agrawal ◽  
H. K. Varma ◽  
S. Lal
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Swirl Flow ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation ◽  
Twisted Tapes ◽  
Flow Heat

This work is an experimental investigation of heat transfer augmentation in a horizontal R-12 evaporator, continuing an earlier study [1] by the authors on swirl flow pressure drops. Twisted tapes were used to create swirl motion during the flow boiling inside an evaporator tube of 10 mm i.d. Average heat transfer coefficients have been determined for 60 runs corresponding to three heat fluxes, five mass velocities, and four twist ratios. Swirl flow heat transfer coefficients have been found, in general, to be greater than the corresponding plain flow values, but the degree of enhancement varies depending on the test conditions and the twist ratio of the inserted tape. An empirical correlation which predicts the average swirl flow heat transfer coefficients within ± 30 percent of the experimentally observed values has been successfully developed.

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