Development of Thermal Switches Based on Shape Memory Alloy Actuators

2018 ◽  
Author(s):  
Immanuel Voigt ◽  
Welf-Guntram Drossel ◽  
Christoph Eppler ◽  
Kenny Pagel ◽  
André Bucht
Keyword(s):  
Heat Transfer ◽  
Machine Tool ◽  
Shape Memory ◽  
Smart Materials ◽  
Heat Fluxes ◽  
Conductive Heat ◽  
Additional Energy ◽  
Thermal Switch ◽  
Thermal Switches ◽  
The Impact

In machine tool engineering, the impact of thermal issues on machine precision and efficiency has been outlined in numerous studies. One of the major challenges is the energy-efficient distribution of heat within the machine structure. In order to control occurring heat fluxes without additional energy input into the machine tool, smart materials can be used for load-dependent adjustment of heat transfer characteristics. The present study illustrates the development and examination of heat transfer switch mechanisms using shape memory alloys. Experimental and numerical results demonstrate how different types of actuators can be used to enable an energy self-sufficient thermal switch function between heat source and heat sink. Different scenarios are considered and the combination of thermal switches with highly conductive heat-transfer devices and latent heat storages is evaluated.

scholarly journals CONVECTION IN MINERAL WOOL USED AS INSULATION FOR BUILDINGS

2013 ◽  
Vol 19 (2) ◽  
pp. 296-304 ◽  
Author(s):  
Vytautas Stankevičius ◽  
Valdas Paukštys ◽  
Raimondas Bliužius ◽  
Jolanta Šadauskienė ◽  
Zenonas Turskis ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Effects ◽  
Mineral Wool ◽  
Heat Fluxes ◽  
Conductive Heat ◽  
Climatic Chamber ◽  
Air Gaps ◽  
Pressure Fields ◽  
Air Movement ◽  
Modelling Methods

The paper considers the velocities of air movement in the ventilated air gaps of walls and focuses on pressure fields in both wall models arranged in a climatic chamber and exploited houses. The article investigates the influence of air movement on heat transfer through walls applying numerical modelling methods and conducting experiments in the climatic chamber. The thermal effects of air flows have been described with reference to the Nusselt number defined as the ratio of average convective and conductive heat fluxes and heat flux through still air

scholarly journals A Way to Visualise Heat Transfer in 3D Unsteady Flows

2009 ◽  
Author(s):  
M. F. M. Speetjens
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Motion ◽  
Unsteady Flows ◽  
Unsteady Motion ◽  
Heat Fluxes ◽  
Flow Visualisation ◽  
Conductive Heat ◽  
Steady Flows ◽  
Transfer Coefficients

Heat transfer in fluid flows traditionally is examined in terms of temperature field and heat-transfer coefficients. However, heat transfer may alternatively be considered as the transport of thermal energy by the total convective-conductive heat flux in a way analogous to the transport of fluid by the flow field. The paths followed by the total heat flux are the thermal counterpart to fluid trajectories and facilitate heat-transfer visualisation in a similar manner as flow visualisation. This has great potential for applications in which insight into the heat fluxes throughout the entire configuration is essential (e.g. cooling systems, heat exchangers). To date this concept has been restricted to 2D steady flows. The present study proposes its generalisation to 3D unsteady flows by representing heat transfer as the 3D unsteady motion of a virtual fluid subject to continuity. The heat-transfer visualisation is provided with a physical framework and demonstrated by way of representative examples. Furthermore, a fundamental analogy between fluid motion and heat transfer is addressed that may pave the way to future heat-transfer studies by well-established geometrical methods from laminar-mixing studies.

Statistical Modelling of Bubble Nucleation and Heat Transfer Using Interface Tracking in TransAT CMFD Code

2010 ◽  
Author(s):  
Chidambaram Narayanan ◽  
Siju Thomas ◽  
Djamel Lakehal
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Statistical Modelling ◽  
Nucleate Boiling ◽  
High Heat ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Conductive Heat Transfer ◽  
Transfer Model ◽  
Conductive Heat

This paper presents results of numerical simulations of various processes that demonstrate phase change heat transfer at high heat fluxes using the level-set method. The model used for the purpose has been first validated for the growth of an evaporating bubble in infinite medium, and fim boiling in 2D and 3D. It has then been applied to simulate the nucleation and departure of a single bubble from a solid body subject to conductive heat transfer. Unlike our previous investigations where phase change induced evaporation rate was incorporated like a sub-grid scale heat transfer model applied to the triple contact line, the present work reports simulations with direct phase change modelling by integrating energy fluxes at the interface. The effect of the conductive heat transfer in the solid from which the bubble departs is also taken into account. Comparison with visual images suggests that accounting for conjugate heat transfer is important to capturing micro-hydrodynamics in nucleate boiling, at least qualitatively.

scholarly journals Conjugate Effect on the Thermal Characteristics of Air Impinging Jet

CFD Letters ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 25-35
Author(s):  
Ghassan Nasif ◽  
Yasser El-Okda
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat ◽  
Thermal Characteristics ◽  
Heat Fluxes ◽  
Conductive Heat ◽  
Stagnation Region ◽  
Jet Cooling ◽  
Air Jet ◽  
Finite Volume Approach

A computational fluid dynamics (CFD) investigation to determine the conjugate heat transfer (CHT) effect on the stagnation and local thermal characteristics due to an impinging process has been carried out in this study using STAR-CCM+ - Siemens PLM commercial code. The transient Navier-Stokes’s equations are numerically solved using a finite volume approach with k-ω SST eddy viscosity as the turbulence model. A fully developed circular air jet with different Reynolds numbers, impinging vertically onto a heated flat disc with different metals, thicknesses, and boundary heat fluxes are employed in the current study to examine the thermal characteristics and provide an enhanced picture for the convection mechanism that used in jet cooling technology. It is found that the thermal characteristics are influenced by the thermal conductivity and thickness of the target upon using air as a cooling jet. The CHT process enhances the local convective heat transfer at the fluid-solid interface due to the variation in transverse and axial conductive heat transfer inside the metal up to a certain redial extent from the stagnation region compared to the process with no CHT. The extent of the radial enhancement depends on the thermal conductivity of the metal. For a given thermal conductivity, the CHT process acts to increase the temperature and convective heat flux of the stagnation region as the metal thickness increases.

scholarly journals The Simultaneous Analysis of Droplets’ Impacts and Heat Transfer during Water Spray Cooling Using a Transparent Heater

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2730
Author(s):  
Vladimir Serdyukov ◽  
Nikolay Miskiv ◽  
Anton Surtaev
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Spray Cooling ◽  
Capillary Waves ◽  
Heat Fluxes ◽  
Small Scale ◽  
Unsteady Temperature ◽  
The Impact

This paper demonstrates the advantages and prospects of transparent design of the heating surface for the simultaneous study of the hydrodynamic and thermal characteristics of spray cooling. It was shown that the high-speed recording from the reverse side of such heater allows to identify individual droplets before their impact on the forming liquid film, which makes it possible to measure their sizes with high spatial resolution. In addition, such format enables one to estimate the number of droplets falling onto the impact surface and to study the features of the interface evolution during the droplets’ impacts. In particular, the experiments showed various possible scenarios for this interaction, such as the formation of small-scale capillary waves during impacts of small droplets, as well as the appearance of “craters” and splashing crowns in the case of large ones. Moreover, the unsteady temperature field during spray cooling in regimes without boiling was investigated using high-speed infrared thermography. Based on the obtained data, the intensity of heat transfer during spray cooling for various liquid flow rates and heat fluxes was analyzed. It was shown that, for the studied regimes, the heat transfer coefficient weakly depends on the heat flux density and is primarily determined by the flow rate. In addition, the comparison of the processes of spray cooling and nucleate boiling was made, and an analogy was shown in the mechanisms that determine their intensity of heat transfer.

scholarly journals A Preliminary 1D-3D Analysis of the Darmstadt Research Engine Under Motored Condition

2020 ◽  
Vol 197 ◽  
pp. 06006
Author(s):  
Clara Iacovano ◽  
Fabio Berni ◽  
Alessio Barbato ◽  
Stefano Fontanesi
Keyword(s):  
Heat Transfer ◽  
Compression Ratio ◽  
Ad Hoc ◽  
Slight Modification ◽  
3D Models ◽  
Research Unit ◽  
Heat Fluxes ◽  
3D Analysis ◽  
Cfd Models ◽  
The Impact

In the present paper, 1D and 3D CFD models of the Darmstadt research engine undergo a preliminary validation against the available experimental dataset at motored condition. The Darmstadt engine is a single-cylinder optical research unit and the chosen operating point is characterized by a revving speed equal to 800 rpm with intake temperature and pressure of 24 °C and 0.95 bar, respectively. Experimental data are available from the TU Darmstadt engine research group. Several aspects of the engine are analyzed, such as crevice modeling, blow-by, heat transfer and compression ratio, with the aim to minimize numerical uncertainties. On the one hand, a GT-Power model of the engine is used to investigate the impact of blow-by and crevices modeling during compression and expansion strokes. Moreover, it provides boundary conditions for the following 3D CFD simulations. On the other hand, the latter, carried out in a RANS framework with both highand low-Reynolds wall treatments, allow a deeper investigation of the boundary layer phenomena and, thus, of the gas-to-wall heat transfer. A detailed modeling of the crevice, along with an ad hoc tuning of both blow-by and heat fluxes lead to a remarkable improvement of the results. However, in order to adequately match the experimental mean in-cylinder pressure, a slight modification of the compression ratio from the nominal value is accounted for, based on the uncertainty which usually characterizes such geometrical parameter. The present preliminary study aims at providing reliable numerical setups for 1D and 3D models to be adopted in future detailed investigations on the Darmstadt research engine.

scholarly journals Modeling the conjugate problem of heat transfer at hot jet impingement onto a cooled surface

2021 ◽  
Vol 2119 (1) ◽  
pp. 012157
Author(s):  
V V Lukashov ◽  
V S Naumkin
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Flat Plate ◽  
Gas Flow ◽  
Jet Impingement ◽  
Conjugate Problem ◽  
Heat Fluxes ◽  
The Other ◽  
Local Maxima ◽  
The Impact

Abstract The paper solves the problem of thermal conductivity inside a flat plate under the impact of a hot jet of nitrogen impinging from one side and cooled by a gas flow from the other side. In this formulation of the problem, there may be local maxima and minima of the temperature inside the plate, caused by an uneven distribution of heat fluxes along the plate.

scholarly journals OPTIMIZATION OF NICKEL CONTENT ON SOME PROPERTIES OF (NITI) SHAPE MEMORY ALLOY

2020 ◽  
Vol 1 (01) ◽  
pp. 40-47
Author(s):  
Aissa Bouaissi ◽  
Nabaa S Radhi ◽  
Karrar F. Morad ◽  
Mohammad H. Hafiz ◽  
Alaa Abdulhasan Atiyah
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Smart Materials ◽  
Shape Recovery ◽  
Fatigue Behavior ◽  
Nickel Content ◽  
Functionally Graded ◽  
Niti Shape Memory Alloy ◽  
Shape Effect ◽  
The Impact

Shape Memory Alloys (SMAs) are one of the most hopeful smart materials, especially, Nickel–Titanium (NiTi or Nitinol). These alloys are great and desirable due to their excellent reliability and behavior among all the commercially available alloys. In addition, strain recovery, (Ni–Ti) is granulated for a wide variety of medical uses because of its favorite properties such as fatigue behavior, corrosion resistance and biocompatibility. This paper explores the creation and the characterization of functionally graded (NiTi) materials. This work demonstrations the impact of Nickel contains changes on the characteristics of NiTi shape memory alloy, in order to obtain the suitable addition of Nickel contain, which gives the optimal balance between hardness, start and finish martensitic point, shape recovery and shape effect of alloys properties. These materials are prepared to obtain suddenly or gradually microstructure or composition differences inside the structure of one piece of material, the specimens made by powder metallurgy process and the influence of every layer of composite by; micro-hardness, transformation temperature DSC and shape effect. The hardness value and shape recovery decrease with increase nickel content. superior shape memory effect (SME) and shape recovery (SR) properties (i.e., 8.747, 10.270 for SMA-FGM1 SMA-FGM2 respectively, and SR is 1.735, 2.977 for SMA-FGM1 SMA-FGM2) respectively.  

Heat Transfer Enhancement in Microchannels Incorporating Slanted Grooves

2008 ◽  
Author(s):  
Poh-Seng Lee ◽  
Chiang-Juay Teo
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Direction ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Fluid Temperature ◽  
Additional Energy ◽  
Pressure Drops ◽  
Microchannel Heat Sinks ◽  
Significant Temperature

The ever-increasing density, speed, and power consumption of microelectronics has led to a rapid increase in the heat fluxes which need to be dissipated in order to ensure their stable and reliable operation. The shrinking dimensions of electronics devices, in parallel, have imposed severe space constraints on the volume available for the cooling solution, defining the need for innovative and highly effective compact cooling techniques. Microchannel heat sinks have the potential to satisfy these requirements. However, significant temperature variations across the chip persist for conventional single-pass parallel flow microchannel heat sinks since the heat transfer performance deteriorates in the flow direction in microchannels as the boundary layers thicken and the coolant heats up. To accommodate higher heat fluxes, enhanced microchannel designs are needed. The present work presents an idea to enhance the single-phase convective heat transfer in microchannels. The proposed technique is passive, and does not require additional energy to be expended to enhance the heat transfer. The idea incorporates the generation of a spanwise or secondary flow to enhance mixing and hence decrease fluid temperature gradients across the microchannel. Slanted grooves can be created on the microchannel wall to induce the flow to twist and rotate thus introducing an additional component to the otherwise laminar flow in the microchannel. Numerical results are presented to demonstrate the effectiveness of such an enhanced microchannel heat sink. The heat transfer was found to increase by up to 12% without incurring substantial additional pressure drops.

Lumped Capacitance and 3D CFD Conjugate Heat Transfer Modelling of an Automotive Turbocharger

2015 ◽  
Author(s):  
R. Burke ◽  
C. Copeland ◽  
T. Duda ◽  
M. A. Reyes-Belmonte
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Weak Link ◽  
Three Dimensional ◽  
Sensitivity Study ◽  
Heat Fluxes ◽  
Strategy Development ◽  
Inlet Temperature ◽  
Compression Process ◽  
The Impact

One dimensional wave-action engine models have become an essential tool within engine development including stages of component selection, understanding system interactions and control strategy development. Simple turbocharger models are seen as a weak link in the accuracy of these simulation tools and advanced models have been proposed to account for phenomena including heat transfer. In order to run within a full engine code, these models are necessarily simple in structure yet are required to describe a highly complex 3D problem. This paper aims to assess the validity of one of the key assumptions in simple heat transfer models, namely, that the heat transfer between the compressor casing and intake air occurs only after the compression process. Initially a sensitivity study was conducted on a simple lumped capacity thermal model of a turbocharger. A new partition parameter was introduced αA, which divides the internal wetted area of the compressor housing into pre and post compression. The sensitivity of heat fluxes to αA was quantified with respect to the sensitivity to turbine inlet temperature (TIT). At low speeds, the TIT was the dominant effect on compressor efficiency whereas at high speed αA had a similar influence to TIT. However, modelling of the conduction within the compressor housing using an additional thermal resistance caused changes in heat flows of less than 10%. Three dimensional CFD analysis was undertaken using a number of cases approximating different values of αA. It was seen that when considering a case similar to αA=0, meaning that heat transfer on the compressor side is considered to occur only after the compression process, significant temperature could build up in the impeller area of the compressor housing, indicating the importance of the pre-compression heat path. The 3D simulation was used to estimate a realistic value for αA which was suggested to be between 0.15 and 0.3. Using a value of this magnitude in the lumped capacitance model showed that at low speed there would be less than 1% point effect on apparent efficiency which would be negligible compared to the 8% point seen as a result of TIT. In contrast, at high speeds, the impact of αA was similar to that of TIT, both leading to approximately 1% point apparent efficiency error.

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