Bio Inspired Particle Enhanced Capillary Heat Exchanger

2008 ◽  
Author(s):  
Fatemeh Hassanipour ◽  
Jose´ Lage
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Exchange Process ◽  
Heat Fluxes ◽  
Measured Temperature ◽  
Lung Capillaries ◽  
The Heat Transfer Coefficient

This study proposes a new cooling concept using encapsulated phase-change material particles in mini-channels. This novel method is inspired by the gas exchange process in the lung capillaries. An important characteristic of capillary blood flow is that the red blood cells fit very snugly into the capillary opening. Hence, it is conjectured that using particles with diameter similar to the channel diameter, in a manner similar to red blood cells in lung capillaries, is likely to enhance the heat transfer coefficient, even under laminar flow. Preliminary tests are performed with encapsulated Octadecan paraffin (C18H38) in a low-conductivity thin melamine shell, flowing through a test module. The effect of flow rate on the heat transfer coefficient and also the effect of using particles on enhancement of Nusselt number has been measured. Temperature distribution on the chip has also been investigated under various particle concentrations, heat fluxes and Reynolds numbers.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Effect of Open Micro-Channels on External Condensation Heat Transfer

2016 ◽  
Author(s):  
Brandon Hulet ◽  
Andres Martinez ◽  
Melanie Derby ◽  
Amy Rachel Betz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Film Thickness ◽  
Transfer Coefficient ◽  
Heat Fluxes ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Micro Channels ◽  
Lower Heat ◽  
The Heat Transfer Coefficient

This research experimentally investigates the heat transfer performance of open-micro channels under filmwise condensation conditions. Filmwise condensation is an important factor in the design of steam condensers used in thermoelectric power generation, desalination, and other industrial applications. Filmwise condensation averages five times lower heat transfer coefficients than those present in dropwise condensation, and filmwise condensation is the dominant condensation regime in the steam condensers due to a lack of a durable dropwise condensation surface. Film thickness is also of concern because it is directly proportional to the condenser’s overall thermal resistance. This research focuses on optimizing the channel size to inhibit the creation of a water film and/or to reduce its overall thickness in order to maximize the heat transfer coefficient of the surface. Condensation heat transfer was measured in three square channels and a plane surface as a control. The sizes of the square fins were 0.25 mm; 0.5 mm; and 1 mm, and tests were done at a constant pressure of 6.2 kPa. At lower heat fluxes, the 0.25mm fins perform better, whereas at larger heat fluxes a smooth surface offers better performance. At lower heat fluxes, droplets are swept away by gravity before the channels are flooded. Whereas, at higher heat fluxes, the channels are flooded increasing the total film thickness, thereby reducing the heat transfer coefficient.

scholarly journals Deterioration in Heat Transfer to Fluids at Supercritical Pressure and High Heat Fluxes

1969 ◽  
Vol 91 (1) ◽  
pp. 27-36 ◽  
Author(s):  
B. S. Shiralkar ◽  
Peter Griffith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Heat ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Bulk Temperature ◽  
Operating Pressure ◽  
The Heat Transfer Coefficient

At slightly supercritical pressure and in the neighborhood of the pseudocritical temperature (which corresponds to the peak in the specific heat at the operating pressure), the heat transfer coefficient between fluid and tube wall is strongly dependent on the heat flux. For large heat fluxes, a marked deterioration takes place in the heat transfer coefficient in the region where the bulk temperature is below the pseudocritical temperature and the wall temperature above the pseudocritical temperature. Equations have been developed to predict the deterioration in heat transfer at high heat fluxes and the results compared with previously available results for steam. Experiments have been performed with carbon dioxide for additional comparison. Limits of safe operation for a supercritical pressure heat exchanger in terms of the allowable heat flux for a particular flow rate have been determined theoretically and experimentally.

Thermal Management of Time-Varying High Heat Flux Electronic Devices

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
T. David ◽  
D. Mendler ◽  
A. Mosyak ◽  
A. Bar-Cohen ◽  
G. Hetsroni
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Heat Fluxes ◽  
Vapor Quality ◽  
Flow Loop ◽  
Pin Fin ◽  
The Heat Transfer Coefficient

The thermal characteristics of a laboratory pin-fin microchannel heat sink were empirically obtained for heat flux, q″, in the range of 30–170 W/cm2, mass flux, m, in the range of 230–380 kg/m2 s, and an exit vapor quality, xout, from 0.2 to 0.75. Refrigerant R 134a (HFC-134a) was chosen as the working fluid. The heat sink was a pin-fin microchannel module installed in open flow loop. Deviation from the measured average temperatures was 1.5 °C at q = 30 W/cm2, and 2.0 °C at q = 170 W/cm2. These results indicate that use of pin-fin microchannel heat sink enables keeping an electronic device near uniform temperature under steady state and transient conditions. The heat transfer coefficient varied significantly with refrigerant quality and showed a peak at an exit vapor quality of 0.55 in all the experiments. At relatively low heat fluxes and vapor qualities, the heat transfer coefficient increased with vapor quality. At high heat fluxes and vapor qualities, the heat transfer coefficient decreased with vapor quality. A noteworthy feature of the present data is the larger magnitude of the transient heat transfer coefficients compared to values obtained under steady state conditions. The results of transient boiling were compared with those for steady state conditions. In contrast to the more common techniques, the low cost technique, based on open flow loop was developed to promote cooling using micropin fin sinks. Results of this experimental study may be used for designing the cooling high power laser and rocket-born electronic devices.

The Effect of Swirl, Inlet Conditions, Flow Direction, and Tube Diameter on the Heat Transfer to Fluids at Supercritical Pressure

1970 ◽  
Vol 92 (3) ◽  
pp. 465-471 ◽  
Author(s):  
B. Shiralkar ◽  
P. Griffith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Tube Diameter ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

An investigation has been made of the factors governing the heat transfer coefficient to supercritical pressure fluids, particularly at high heat fluxes. The deterioration in heat transfer to supercritical carbon dioxide has been experimentally studied with reference to the operating conditions of mass velocity and heat flux, tube diameter, orientation, tape induced swirl, inlet temperature, and pressure. A detailed comparison has been made with the apparently contradictory results of other investigators, and operating regions, in which the heat transfer coefficient behaves differently, have been defined. The terms used to describe these regions are the Reynolds number, a heat-flux parameter, and a free-convection parameter.

scholarly journals Experimental Study of Nucleate Boiling of Flammable, Environmentally Friendly Refrigerants

Energies ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 160 ◽  
Author(s):  
Bartosz Gil ◽  
Beata Fijałkowska
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
New Correlation ◽  
Boiling Process ◽  
The Heat Transfer Coefficient

This paper investigates the nucleate boiling process of dimethyl ether and selected hydrocarbons. The main goal of this study is to measure the heat transfer coefficients of RE170, R600a, and R601, and to compare them with R134a. The experiments were carried out for heat fluxes up to 70 kW/m2. Experimental results have shown a typical trend that the heat transfer coefficient of flammable refrigerants increases as the heat flux increases. Among the tested fluids, the highest values of heat transfer coefficient were obtained for RE170. Available correlations describing this coefficient showed a deviation of up to 93%, as compared to the data obtained. The new correlation was developed by regression analysis taking into account dimensionless variables affecting the boiling process.

Numerical Simulation of Supercritical Water Heat Transfer in the Vertically Heated Tube

2013 ◽  
Author(s):  
Feng Wang ◽  
Bo Cui ◽  
Shijun Zhang ◽  
Xue Qin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbulence Model ◽  
Mesh Size ◽  
High Heat ◽  
Heat Fluxes ◽  
Symmetric Model ◽  
Heated Tube ◽  
The Heat Transfer Coefficient

The heat transfer of water in a vertically heated tube at 24.52 MPa is numerically simulated by computational fluid dynamics software of FLUENT. The IAPWS-IF97 formulation is applied to obtain the water properties, which vary substantially at supercritical condition. The two-dimensional axi-symmetric model using RNG k-ε turbulence model with enhanced wall treatment gives fine prediction of wall temperature and heat transfer coefficient. The mesh size near the wall adapted smaller when at high heat fluxes for the accuracy of computed results. The wall heat fluxes were set to be 233, 698, 930 and 1100 kW/m2 to match the simulation with experiment performed by Yamagata. It is found that k-ε turbulence model with enhanced wall treatment can give outstanding prediction of heat transfer enhancement and heat transfer deterioration. The heat transfer coefficient value reaches a maximum near the pseudocritical point and it decreases with increase of heat flux.

A Method of the Inverse Evaluation for Heat Transfer Coefficient between Al-Cu Alloys and Cooling Water

2011 ◽  
Vol 189-193 ◽  
pp. 2294-2299
Author(s):  
Zhong Lin Hou ◽  
Ting Li ◽  
Jun Qiao ◽  
Sheng Li Li
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling Water ◽  
Transfer Model ◽  
Inductive Heating ◽  
Measured Temperature ◽  
Cu Alloys ◽  
The Heat Transfer Coefficient ◽  
Peak Value

The heat transfer coefficient between the alloys and cooling water is affected by a lot of factors and hard to measure, a new method was investigated with a self-designed system ultilizing SP-15 high-frequency inductive heating unit. Based on measured temperature curves and Fourier heat transfer model, quantitative correlation between heat transfer coefficient and temperature was obtained by inverse algorithm method of iterative simulation and automatic optimization. The results showed that in submerged water-cooling process, the heat transfer coefficient reached to a peak value at the beginning and then decreased with increasing temperature. A decrease of cooling water temperature increased the peak value of the heat transfer coefficient, but did not change temperature range of the peak value from 200°C to 225°C . The heat transfer coefficient was mainly dependent of interfacial temperature between the Al-Cu alloys and the cooling water.The temperatures range from 200°C to 225°C gave the highest heat flux transfer.

Heat Transfer Mechanisms of Propane Boiling on Horizontal Steel Tubes With Smooth and Enhanced Surfaces

2010 ◽  
Author(s):  
A. Luke ◽  
Bjo¨rn C. F. Mu¨ller
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Mild Steel ◽  
Transfer Coefficient ◽  
Steel Surface ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Mild Steel Surface ◽  
The Heat Transfer Coefficient

The trend towards a better understanding of the fundamentals of nucleate boiling in re-entrant cavities is supported by the variation of the heating surface’s characteristics and the identification of parameters influencing the heat transfer at enhanced tubes. The optimized surface of enhanced evaporator tubes supports the bubble formation by providing stable nucleation sites, which are cavities that trapped the necessary amount of vapor to generate the next bubble. The optimal size of the cavities for bubble formation depends on various thermodynamic properties of the fluid and the wall material. The knowledge of these physical mechanisms is important for the further optimization. The influence of micro- and macrostructures on the overall heat transfer coefficient is investigated with the refrigerant R134a and the hydrocarbon propane (R290) boiling in a wide range of reduced pressures (p* = ps/pc = 0.03 to 0.5) and heat fluxes (0.05 to 100 kW/m2). The measurements are carried out using a standard apparatus and a horizontally positioned, electrically heated surface with various wall materials. Two different materials — copper and mild steel — with the same surface preparation by polishing are investigated. Furthermore, heat transfer measurements are carried out on a plain mild steel tube and on an industrially manufactured surface of the GEWA-PB type. The polished surfaces demonstrate a deterministic microstructure, the roughness parameters depends strongly on the measurement direction. The heat transfer coefficient as function of the heat flux of the polished copper tube can be described by the correlation of the VDI Heat Atlas, while the mild steel surface differ from former investigations due to the deep re-entrant cavities remaining from the drawn surface. The onset of boiling is nearly the same of both materials because of these cavities on the mild steel surface. As presented in the recent years, the heat transfer of nucleate boiling at tubes with subsurface channels can be divided into different domains, each influenced by different parameters like wettability, the product of vapor density and evaporation enthalpy. The identification of parameters influencing the bubble formation is done by heat transfer measurements, high-speed-video recording and photographic documentation. The experimental results of this work are compared to results of the polished surfaces. The heat transfer coefficient increases drastically for the enhanced tube, especially for beginning nucleation. The same α-q-relationship as on plain tubes is observed for higher pressures and heat fluxes but for three times higher values of the heat transfer coefficient α.

Measurement of the Heat Transfer Coefficient for Mercury Flowing in a Narrow Channel

2002 ◽  
Vol 124 (6) ◽  
pp. 1034-1038 ◽  
Author(s):  
J. M. Crye ◽  
A. E. Ruggles ◽  
W. D. Pointer ◽  
D. K. Felde ◽  
P. A. Jallouk ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cross Section ◽  
Narrow Channel ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
The Heat Transfer Coefficient

The heat transfer coefficient is inferred from measurements for mercury flowing in a channel of cross-section 2 mm×40 mm with flow velocities from 1 m/s to 4 m/s and heat fluxes from 192 kW/m2 to 1.14 MW/m2. Mercury bulk temperatures vary from 67°C to 143°C. Inferred heat transfer coefficients agree with open literature tube data when compared on a Nusselt versus. Peclet number plot, with Nusselt numbers examined from 8 to 17 and Peclet numbers examined from 790 to 3070.

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