scholarly journals Convective Heat Transfer Enhancement through Laser-Etched Heat Sinks: Elliptic Scale-Roughened and Cones Patterns

Energies ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1360 ◽  
Author(s):  
Luigi Ventola ◽  
Matteo Fasano ◽  
Roberta Cappabianca ◽  
Luca Bergamasco ◽  
Francesca Clerici ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Exchangers ◽  
Heat Transfer Process ◽  
Heat Sinks ◽  
Turbulent Regime ◽  
Thermal Transmittance ◽  
Microstructured Surface ◽  
Surface Patterns

The efficient dissipation of localized heat flux by convection is a key request in several engineering applications, especially electronic ones. The recent advancements in manufacturing processes are unlocking the design and industrialization of heat exchangers with unprecedented geometric characteristics and, thus, performance. In this work, laser etching manufacturing technique is employed to develop metal surfaces with designed microstructured surface patterns. Such precise control of the solid-air interface (artificial roughness) allows to manufacture metal heat sinks with enhanced thermal transmittance with respect to traditional flat surfaces. Here, the thermal performance of these laser-etched devices is experimentally assessed by means of a wind tunnel in a fully turbulent regime. At the highest Reynolds number tested in the experiments ( R e L ≈ 16 , 500 ), elliptic scale-roughened surfaces show thermal transmittances improved by up to 81% with respect to heat sinks with flat surface. At similar testing conditions, cones patterns provide an enhancement in Nusselt number and thermal transmittance of up to 102% and 357%, respectively. The latter results are correlated with the main geometric and thermal fluid dynamics descriptors of the convective heat transfer process in order to achieve a predictive model of their performance. The experimental evidence shown in this work may encourage and guide a broader use of micro-patterned surfaces for enhancing convective heat transfer in heat exchangers.

Experimental Convective Heat Transfer With Nanofluids

2008 ◽  
Author(s):  
S. Kabelac ◽  
K. B. Anoop
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Turbulent Regime ◽  
Heat Transfer Characteristics ◽  
Forced Convective Heat Transfer ◽  
Transfer Characteristics

Nanofluids are colloidal suspensions with nano-sized particles (<100nm) dispersed in a base fluid. From literature it is seen that these fluids exhibit better heat transfer characteristics. In our present work, thermal conductivity and the forced convective heat transfer coefficient of an alumina-water nanofluid is investigated. Thermal conductivity is measured by a steady state method using a Guarded Hot Plate apparatus customized for liquids. Forced convective heat transfer characteristics are evaluated with help of a test loop under constant heat flux condition. Controlled experiments under turbulent flow regime are carried out using two particle concentrations (0.5vol% and 1vol %). Experimental results show that, thermal conductivity of nanofluids increases with concentration, but the heat transfer coefficient in the turbulent regime does not exhibit any remarkable increase above measurement uncertainty.

An Experimental Investigation of Convective Heat Transfer From Wire-On-Tube Heat Exchangers

1997 ◽  
Vol 119 (2) ◽  
pp. 348-356 ◽  
Author(s):  
J. L. Hoke ◽  
A. M. Clausing ◽  
T. D. Swofford
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Exchangers ◽  
Steel Wire ◽  
Convective Heat Transfer Coefficient ◽  
Wire Diameter ◽  
Forced Flow ◽  
Geometrical Parameters

An experimental investigation of the air-side convective heat transfer from wire-on-tube heat exchangers is described. The study is motivated by the desire to predict the performance, in a forced flow, of the steel wire-on-tube condensers used in most refrigerators. Previous investigations of wire-on-tube heat exchangers in a forced flow have not been reported in the literature. The many geometrical parameters (wire diameter, tube diameter, wire pitch, tube pitch, etc.), the complex conductive paths in the heat exchanger, and the importance of buoyant forces in a portion of the velocity regime of interest make the study a formidable one. A key to the successful correlation of the experimental results is a definition of the convective heat transfer coefficient, hw, that accounts for the temperature gradients in the wires as well as the vast difference in the two key characteristic lengths—the tube and wire diameters. Although this definition results in the need to solve a transcendental equation in order to obtain hw from the experimental data, the use of the resulting empirical correlation is straightforward. The complex influence of the mixed convection regime on the heat transfer from wire-on-tube heat exchangers is shown, as well as the effects of air velocity and the angle of attack. The study covers a velocity range of 0 to 2 m/s (the Reynolds number based on wire diameter extends to 200) and angles of attack varying from 0 deg (horizontal coils) to ±90 deg. Heat transfer data from seven different wire-on-tube heat exchangers are correlated so that 95 percent of the data below a Richardson number of 0.004, based on the wire diameter, lie within ±16.7 percent of the proposed correlation.

Heat transfer modeling within the microclimate between 3D human body and clothing: effects of ventilation openings and fire intensity

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Miao Tian ◽  
Jun Li
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Temperature Distribution ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Human Body ◽  
Thermal Environment ◽  
Heat Transfer Process ◽  
Fire Intensity ◽  
Content Type

PurposeThe purpose of this study is to determine the effect of ventilation openings and fire intensity on heat transfer and fluid flow within the microclimate between 3D human body and clothing.Design/methodology/approachOn account of interaction effects of fire and ventilation openings on heat transfer process, a 3D transient computational fluid dynamics model considering the real shape of human body and clothing was developed. The model was validated by comparing heat flux history and distribution with experimental results. Heat transfer modes and fluid flow were investigated under three levels of fire intensity for the microclimate with ventilation openings and closures.FindingsTemperature distribution on skin surface with open microclimate was heavily depended on the heat transfer through ventilation openings. Higher temperature for the clothing with confined microclimate was affected by the position and direction of flames injection. The presence of openings contributed to the greater velocity at forearms, shanks and around neck, which enhanced the convective heat transfer within microclimate. Thermal radiation was the dominant heat transfer mode within the microclimate for garment with closures. On the contrary, convective heat transfer within microclimate for clothing with openings cannot be neglected.Practical implicationsThe findings provided fundamental supports for the ease and pattern design of the improved thermal protective systems, so as to realize the optimal thermal insulation of the microclimate on the garment level in the future.Originality/valueThe outcomes broaden the insights of results obtained from the mesoscale models. Different high skin temperature distribution and heat transfer modes caused by thermal environment and clothing structure provide basis for advanced thermal protective clothing design.

Comparative thermal power efficiency of methods to improve convective heat transfer in heat exchangers

1991 ◽  
Vol 27 (12) ◽  
pp. 681-683
Author(s):  
G. Sh. Polishchuk ◽  
V. M. Gurovich ◽  
Ya. S. Teplitskii ◽  
O. A. Vartevanyan
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Exchangers ◽  
Power Efficiency ◽  
Thermal Power

Numerical Investigation of Convective Heat Transfer to Supercritical Hydrogen in a Straight Tube

2017 ◽  
Author(s):  
Yu Ji ◽  
Lei Shi ◽  
Jun Sun
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Specific Impulse ◽  
Local Heat Transfer ◽  
Heat Transfer Process ◽  
Subcritical State ◽  
High Heat Flux ◽  
Straight Tube ◽  
Heat Transfer Deterioration

Hydrogen is adopted as coolant for regenerative cooling nozzle and reactor reflector in nuclear thermal propulsion (NTP), which may be a promising technology for human space exploration in the near future due to its large thrust and high specific impulse. During the cooling processes, the hydrogen experiences the transition from subcritical state to supercritical state, which influences the heat transfer severely. This paper is intended to study the characteristic of convective heat transfer to supercritical hydrogen in a straight tube under high heat flux through numerical simulation, which is a common phenomenon in NTP operation. The thermophysical properties and transport properties including the equation of state, specific heat capacity, viscosity and thermal conductivity of hydrogen are evaluated firstly by compared with the data from National Institute of Standards and Technology (NIST). Then, the flow and heat transfer process is investigated using Reynolds Averaged Naiver-Stokes (RANS) model, and the approach is validated by the successfully predicted behavior called local heat transfer deterioration. Moreover, the mechanism of heat transfer deterioration is analyzed briefly according to the detailed information of flow field. This work herein contributes to the further NTP design and research.

Sign in / Sign up

Export Citation Format

Share Document