Thermal and Mechanical Analyses of Compliant Thermoelectric Coils for Flexible and Bio-integrated Devices

2020 ◽  
pp. 1-12
Author(s):  
Kan Li ◽  
Lin Chen ◽  
Feng Zhu ◽  
Yonggang Huang
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Dissipation ◽  
Power Conversion ◽  
Thermoelectric Device ◽  
Coil Geometry ◽  
Integrated Devices ◽  
Analytical Approaches

Abstract Three-dimensional coil structures assembled by mechanically guided compressive buckling have shown potency on enabling efficient thermal impedance matching of thermoelectric devices at a small characteristic scale, which increases the efficiency of power conversion, and has the potential to supply electric power to flexible bio-integrated devices. The unconventional heat dissipation behavior at the side surfaces of the thin-film coil, which serves as a 'heat pump', is strongly dependent on the geometry and the material of the encapsulating dissipation layer (e.g., polyimide). The low heat transfer coefficient of the encapsulation layer, which may damp the heat transfer for a conventional thermoelectric device, usually limits the heat transfer efficiency. However, the unconventional geometry of the coil can take advantage of the low heat transfer coefficient to increase its hot-to-cold temperature difference, and this requires further thermal analysis of the coil in order to improve its power conversion efficiency. Another challenge for the coil is that the active thin-film thermoelectric materials employed (e.g., heavily doped Silicon) are usually very brittle, with the fracture strain less than 0.1% in general while the overall device may undergo large deformation (e.g., stretched 100%). Mechanic analysis is therefore necessary to avoid failure/fracture of the thermoelectric material. In this work, we study the effect of coil geometry on both thermal and mechanical behaviors by using numerical and analytical approaches, and optimize the coil geometry to improve the device performance, and to guide its design for future applications.

Theoretical Analysis of Thin Film Evaporation in the Wicks of Loop Heat Pipes

2021 ◽  
pp. 1-14
Author(s):  
Bingyao Lin ◽  
Nanxi Li ◽  
Shiyue Wang ◽  
Leren Tao ◽  
Guangming Xu ◽  
...  
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pore Size ◽  
Momentum Conservation ◽  
Loop Heat Pipes ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Quantity Of Heat

Abstract In this paper, a thin film evaporation model that includes expressions for energy, mass and momentum conservation was established through the augmented Young-Laplace model. Based on this model, the effects of pore size and superheating on heat transfer during thin film evaporation were analyzed. The influence of the wick diameter of the loop heat pipe (LHP) on the critical heat flux of the evaporator is analyzed theoretically. The results show that pore size and superheating mainly influence evaporation through changes in the length of the transition film and intrinsic meniscus. The contribution of the transition film area is mainly reflected in the heat transfer coefficient, and the contribution of the intrinsic meniscus area is mainly apparent in the quantity of heat that is transferred. When an LHP evaporator is operating in a state of surface evaporation, a higher heat transfer coefficient can be achieved using a smaller pore size.

Heat Transfer Coefficient Characterization for Large Aspect-Ratio Thin Films in Film-Riding Seals

2018 ◽  
Author(s):  
James A. Tallman ◽  
Rahul A. Bidkar
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Thin Films ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Test Data ◽  
Face Seal ◽  
Cfd Model ◽  
Low Leakage

Low-leakage film-riding seals are a key enabling technology for utility-scale supercritical carbon dioxide (sCO2) power cycles. Fluid film-riding rotor-stator seals (operating with sCO2 as the working fluid) are designed to track rotor movements and provide effective sealing by maintaining a tight operating clearance (of the order of several microns) from the spinning rotor. Thin film-riding seals generate viscous shear heat during high-speed operation, and the reliable operation of such thin-film seals depends critically on the designer’s ability to control the thermal deformations of the seal/rotor bearing face, which in turn are tied to the designer’s ability to understand and predict the heat transfer across the seal bearing face. In this paper, we develop a simple axisymmetric thermal-mechanical model of a typical face seal to highlight how the uncertainty in heat transfer coefficient (HTC) on the seal bearing face drives uncertainty in seal deformation predictions, especially when the HTCs are an order of magnitude lower than those predicted with duct-based Dittus-Boelter correlations. This uncertainty in seal bearing face HTCs drives the need for an experimental quantification of HTCs in high-aspect ratio thin films associated with low-leakage film-riding seals. In this paper, we describe a non-rotating experimental test rig designed for estimating the HTCs on the seal bearing face using a shim-heater technique along with IR-camera-based temperature measurements. The experimental set-up consists of a thin metal shim (representing the seal bearing face) forming one wall of a pressurized duct with geometric similarity to a typical thin film of a face seal. Pressurized airflow past the shim is used to simulate the flow field expected in a non-rotating seal. The HTC test data for a non-rotating film (as against the actual seal film with rotating fluid) are lower than the actual seal, and establish a lower bound on the HTCs. This is especially useful for bounding the seal deformation uncertainty, which is vulnerable to the HTCs in the low-HTC regime. We present representative test data that is non-dimensionalized using radial-flow-based Reynolds number and compare these HTC estimates both with the predictions of Dittus-Boelter type correlations, and with the predictions of a 3D computational fluid dynamics (CFD) model. The purpose of the CFD model is to develop a HTC prediction tool for such thin-film surfaces, and the test data are used for validating this predictive model.

scholarly journals Experimental Investigation of Flow Condensation in Microgravity

2013 ◽  
Author(s):  
Hyoungsoon Lee ◽  
Ilchung Park ◽  
Christopher Konishi ◽  
Issam Mudawar ◽  
Rochelle I. May ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Condensation Heat Transfer ◽  
Interfacial Structure ◽  
Sensible Heat ◽  
Two Phase ◽  
The Heat Transfer Coefficient

Future manned missions to Mars are expected to greatly increase the space vehicle’s size, weight, and heat dissipation requirements. An effective means to reducing both size and weight is to replace single-phase thermal management systems with two-phase counterparts that capitalize upon both latent and sensible heat of the coolant rather than sensible heat alone. This shift is expected to yield orders of magnitude enhancements in flow boiling and condensation heat transfer coefficients. A major challenge to this shift is a lack of reliable tools for accurate prediction of two-phase pressure drop and heat transfer coefficient in reduced gravity. Developing such tools will require a sophisticated experimental facility to enable investigators to perform both flow boiling and condensation experiments in microgravity in pursuit of reliable databases. This study will discuss the development of the Flow Boiling and Condensation Experiment (FBCE) for the International Space Station (ISS), which was initiated in 2012 in collaboration between Purdue University and NASA Glenn Research Center. This facility was recently tested in parabolic flight to acquire condensation data for FC-72 in microgravity, aided by high-speed video analysis of interfacial structure of the condensation film. The condensation is achieved by rejecting heat to a counter flow of water, and experiments were performed at different mass velocities of FC-72 and water and different FC-72 inlet qualities. It is shown that the film flow varies from smooth-laminar to wavy-laminar and ultimately turbulent with increasing FC-72 mass velocity. The heat transfer coefficient is highest near the inlet of the condensation tube, where the film is thinnest, and decreases monotonically along the tube, except for high FC-72 mass velocities, where the heat transfer coefficient is enhanced downstream. This enhancement is attributed to both turbulence and increased interfacial waviness. One-ge correlations are shown to predict the average condensation heat transfer coefficient with varying degrees of success, and a recent correlation is identified for its superior predictive capability, evidenced by a mean absolute error of 21.7%.

Noninvasive Method to Measure Thermal Energy Flow Rate in a Pipe

2020 ◽  
Vol 13 (3) ◽  
Author(s):  
Mohammed A. Alanazi ◽  
Thomas E. Diller
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Energy ◽  
Thermal Contact ◽  
Heat Flux Sensor ◽  
Accurate Estimation ◽  
Fluid Temperature

Abstract A noninvasive, thermal energy flowrate sensor based on a combination of heat flux and temperature measurements is developed for measuring the volume flowrate and the fluid temperature in a pipe. The sensor is covered by a thin-film heater and clamped onto the outer surface of the pipe. Two types of thin-film thermocouple elements are compared to minimize the thermal contact resistance R″ between the thermocouple and the surface of the pipe. A thin, flexible thermopile heat flux sensor (PHFS) is mounted over the thermocouples. A one-dimensional transient thermal model is applied before and during activation of the external heater to provide estimates of the fluid heat transfer coefficient h. The results are correlated with the volume flowrate Q and the fluid temperature Twc. Several different parameter estimation codes are used to estimate the optimal parameters by using the minimum root-mean-square (rms) error between the analytical and experimental sensor temperature values. The experiments are completed over a range of volume flowrates—1.3 gallons/min to 14.5 gallons/min. Encouraging measurement results give good correlation, repeatability, and sensitivity between the heat transfer coefficient h and the volume flowrate Q with an accurate estimation of the fluid temperature Twc. The resulting noninvasive thermal energy flowrate sensor can be used to estimate the volume flowrate and the fluid temperature in a variety of applications.

Effect of a Shield on Mixed Convection in a Rectangular Enclosure with Moving Cold Sidewalls and a Heat Source on the Bottom Wall

2010 ◽  
Vol 297-301 ◽  
pp. 584-589
Author(s):  
Ghanbar Ali Sheikhzadeh ◽  
S.H. Musavi ◽  
N. Sadoughi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Source ◽  
Transfer Coefficient ◽  
Heat Dissipation ◽  
Bottom Wall ◽  
Governing Equations ◽  
Thermal Shield ◽  
The Heat Transfer Coefficient ◽  
Specific Distance

In this work, the mixed convention of air inside a rectangular cavity with moving cold sidewalls is studied numerically. A constant flux heat source is attached to the bottom wall of the cavity. A thin thermal shield is located at a specific distance above the heat source. The governing equations are solved using appropriate numerical methods. A parametric study has been conducted and the effects of heat source length, its location and the shield distance from the source on the heat transfer have been investigated. The results show that the heat dissipation increases as the heat source and the shield are moved up to a certain distance towards either sidewall. However, moving them beyond this limiting distance results in the reduction of heat dissipation. It is shown that the presence of shield results in the reduction of the heat transfer coefficient. However, for the normalized distance of the shield from the heat source greater than , the shield’s effect on the reduction of the heat transfer coefficient is less than.

scholarly journals Heat Transfer between an Individual Carbon Nanotube and Gas Environment in a Wide Knudsen Number Regime

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Hai-Dong Wang ◽  
Jin-Hui Liu ◽  
Xing Zhang ◽  
Tian-Yi Li ◽  
Ru-Fan Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Carbon Nanotube ◽  
Transfer Coefficient ◽  
Heat Dissipation ◽  
Critical Diameter ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Efficient Prediction ◽  
Gas Environment

Applications of carbon nanotube (CNT) and graphene in thermal management have recently attracted significant attention. However, the lack of efficient prediction formula for heat transfer coefficient between nanomaterials and gas environment limits the further development of this technique. In this work, a kinetic model has been established to predict the heat transfer coefficient of an individual CNT in gas environment. The heat dissipation around the CNT is governed by molecular collisions, and outside the collision layer, the heat conduction is dominant. At nanoscales, the natural convection can be neglected. In order to describe the intermolecular collisions around the CNT quantitatively, a correction factor 1/24 is introduced and agrees well with the experimental observation. The prediction of the present model is in good agreement with our experimental results in free molecular regime. Further, a maximum heat transfer coefficient occurs at a critical diameter of several nanometers, providing guidelines on the practical design of CNT-based heat spreaders.

Heat Transfer Coefficient Between Flat Surface and Sand

2011 ◽  
Author(s):  
Matthew Golob ◽  
Sheldon Jeter ◽  
Dennis Sadowski
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Thermal Energy ◽  
Test Article ◽  
Article Surface ◽  
Thin Film Thermocouples ◽  
The Heat Transfer Coefficient

Thermal energy storage (TES) systems are of interest in solar thermal power applications as an effective means of retaining energy. One of the primary issues with this type system is the exchange of thermal energy coming off the power field. In a heat exchanger, the effective heat transfer coefficient between the exchange mediums plays a crucial factor in determining the sizing of the heat exchange unit. A concept utilizing sand as a cheap particulate thermal medium was recently proposed for an alternative thermal energy storage system. The overall system will be described in some detail; however, the primary focus of this research report will be to present the experimental results measuring the heat transfer coefficient between flowing sand and a representative heat exchanger surface. To measure the heat transfer coefficient a horizontal rotating drum is used to continuously deposit sand over a centrally positioned test article. The heat transfer coefficient in this case was calculated by taking the power input divided by the known area of the test article covered by the sand as well as the measured temperature difference between the article surface and sand temperature. Calibrated thin film thermocouples attached to the test article surface as well as thin film thermocouples suspended into the sand pooling in drum satisfy the needed temperature measurements. Then, by electrically heating a known area of the test article, a heat transfer coefficient between the sand and surface can be determined. Insulation of key end surfaces and errors such as heat leak due to air as well as measurement inaccuracies were also accounted for in the experimental setup and are included in the report’s error propagation analysis. The overall results compare heat transfer coefficients measurements for a range of different sands and sizes, as well as model comparisons with known literature on the subject.

Investigation on the Multiple Jet Impingement Heat Transfer Using Al2O3-Water Nanofluid

2013 ◽  
Author(s):  
Caner Senkal ◽  
Shuichi Torii
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Heat Dissipation ◽  
Jet Impingement ◽  
High Heat ◽  
Experimental Results ◽  
Transfer Enhancement ◽  
Particle Volume

In recent years, increasing demands for high performance electronic devices give rise to a necessity to remove enormous amount of heat fluxes from small areas. Uniform temperature distribution and sufficient heat transfer dissipation are crucial issues for proper operation of electronic components. To cope up with thermal management of high heat dissipation devices, an efficient cooling method is required. Jet impingement cooling is one of those promising candidates which can handle heat dissipation in an effective way due to its superior heat transfer rates. In this paper, Al2O3 nanofluid heat transfer characteristics are investigated experimentally. Particle diameter of 31nm Al2O3 is taken into consideration in experiments. Impingement surface (surface area:780mm2) were made from oxygen-free copper to simulate high heat flux dissipating electronic component. The experimental results show that the suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid.. Nanofluids with particle volume fractions up to 4% can provide significant heat transfer enhancement, on the other hand, it has been found that high volume fractions (higher then 6%), is not appropriate for heat transfer enhancement under the free jet array configuration. Within the range of parameters considered in this study, experimental results indicated that maximum heat transfer coefficient can be obtained for the intermediate jet to heated target distance (around five times of jet diameter) and closely spaced jets (S/D = 3) for the particle volume fraction 2%. Closely spaced jets are particularly suitable for the electronics cooling applications with regards to provide temperature uniformity on the heated surface.

Heat Dissipation Beyond 1 kW/cm2 With Low Pressure Drop and High Heat Transfer Coefficient for Flow Boiling Using Open Microchannels With Tapered Manifold

2016 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Low Pressure ◽  
High Heat ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient

Heat dissipation beyond 1 kW/cm2 accompanied with high heat transfer coefficient and low pressure drop using water has been a long-standing goal in the flow boiling research directed toward electronic cooling application. In the present work, three approaches are combined to reach this goal: (a) a microchannel with a manifold to increase critical heat flux (CHF) and heat transfer coefficient (HTC), (b) a tapered manifold to reduce the pressure drop, and (c) high flow rates for further enhancing CHF from liquid inertia forces. A CHF of 1.07 kW/cm2 was achieved with a heat transfer coefficient of 295 kW/m2°C with a pressure drop of 30 kPa. Effect of flow rate on CHF and HTC is investigated. High speed visualization to understand the underlying bubble dynamics responsible for low pressure drop and high CHF is also presented.

scholarly journals The Effect of Circular Perforation on a V-Corrugated Fin Performance under Natural Convection

2018 ◽  
Vol 24 (7) ◽  
pp. 19
Author(s):  
Maha Ali Hussein
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Heat Sink ◽  
Heat Dissipation ◽  
Past Research

An experimental investigation has been made to study the influence of using v-corrugated aluminum fin on heat transfer coefficient and heat dissipation in a heat sink. The geometry of fin is changed to investigate their performance. 27 circular perforations with 1 cm diameter were made. The holes designed into two ways, inline arrangement and staggered in the corrugated edges arrangement. The experiments were done in enclosure space under natural convection. Three different voltages supplied to the heat sink to study their effects on the fins performance. All the studied cases are compared with v-corrugated smooth solid fin. Each experiment was repeated two times to reduce the error and the data recorded after reaching the steady state conditions. The results showed that the v-corrugated fin dissipate heat twice and triple times than flat plate mentioned in past research with the same dimension. Also, the inline perforated fin gave higher enhancement percentage than solid one by 15, 32 and 36% for 110, 150 and 200 V voltages supplied. Finally, the staggered perforation arrangement gave the higher enhancement percentage with 22, 42 and 45% for the same voltages supply.  

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