scholarly journals Model of Complex Heat Transfer in the Package of Rectangular Steel Sections

2020 ◽  
Vol 10 (24) ◽  
pp. 9044
Author(s):  
Rafał Wyczółkowski ◽  
Marek Gała ◽  
Vazgen Bagdasaryan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Resistance ◽  
Heat Radiation ◽  
Low Carbon ◽  
Contact Heat ◽  
Total Thermal Resistance ◽  
Model Calculations ◽  
Complex Heat Transfer ◽  
Steel Sections

During heat treatment of rectangular steel sections, a heated charge in the form of regularly arranged packages is placed in a furnace. The article presents a model of a complex heat transfer in such a package using the thermo-electric analogy. The model considers the following types of heat transfer: conduction in section walls, conduction and natural convection within gas, heat radiation between the walls of a section, as well as contact conduction between the adjacent sections. The results of our own experimental research were used for calculations of heat resistance applying to natural convection and contact conduction. We assumed that the material of sections was low-carbon steel and the gas was air. The result of the calculations of the presented model is total thermal resistance Rto. The calculations were performed for the temperature range 20–700 °C for four geometrical cases. Due to the variability of conditions for contact heat conduction, we assumed that total thermal resistance for a given charge is contained within a value range between Rto-min and Rto-max. We established that the value of Rto depends significantly on the section’s geometry. The larger the section sizes, the greater the changes of Rto. The minimal and maximal values of Rto for all packages were 0.0051 (m2·K)/W and 0.0238 (m2·K)/W, respectively. The correctness of model calculations was verified with the use of experimental data.

Combined Microstructure and Heat Transfer Modeling of Carbon Nanotube Thermal Interface Materials1

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Sridhar Sadasivam ◽  
Stephen L. Hodson ◽  
Matthew R. Maschmann ◽  
Timothy S. Fisher
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Finite Volume ◽  
Pressure Dependence ◽  
Matrix Material ◽  
Three Dimensional ◽  
Coarse Grain ◽  
Total Thermal Resistance ◽  
Thermal Interface ◽  
Cnt Arrays

A microstructure-sensitive thermomechanical simulation framework is developed to predict the mechanical and heat transfer properties of vertically aligned CNT (VACNT) arrays used as thermal interface materials (TIMs). The model addresses the gap between atomistic thermal transport simulations of individual CNTs (carbon nanotubes) and experimental measurements of thermal resistance of CNT arrays at mesoscopic length scales. Energy minimization is performed using a bead–spring coarse-grain model to obtain the microstructure of the CNT array as a function of the applied load. The microstructures obtained from the coarse-grain simulations are used as inputs to a finite volume solver that solves one-dimensional and three-dimensional Fourier heat conduction in the CNTs and filler matrix, respectively. Predictions from the finite volume solver are fitted to experimental data on the total thermal resistance of CNT arrays to obtain an individual CNT thermal conductivity of 12 W m−1 K−1 and CNT–substrate contact conductance of 7 × 107 W m−2 K−1. The results also indicate that the thermal resistance of the CNT array shows a weak dependence on the CNT–CNT contact resistance. Embedding the CNT array in wax is found to reduce the total thermal resistance of the array by almost 50%, and the pressure dependence of thermal resistance nearly vanishes when a matrix material is introduced. Detailed microstructural information such as the topology of CNT–substrate contacts and the pressure dependence of CNT–opposing substrate contact area are also reported.

Natural Convection on Both Sides of a Vertical Wall Separating Fluids at Different Temperatures

1980 ◽  
Vol 102 (4) ◽  
pp. 630-635 ◽  
Author(s):  
R. Anderson ◽  
A. Bejan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Resistance ◽  
Analytical Study ◽  
Vertical Wall ◽  
Conducting Wall ◽  
Different Temperatures ◽  
Laminar Natural Convection ◽  
Layer Flow ◽  
Two Sides

This paper describes an analytical study of laminar natural convection on both sides of a vertical conducting wall of finite height separating two semi-infinite fluid reservoirs of different temperatures. The countercurrent boundary layer flow formed on the two sides is illustrated via representative streamlines, temperature and heat flux distributions. The net heat transfer between reservoirs is reported for the general case in which the wall thermal resistance is not negligible relative to the overall reservoir-to-reservoir thermal resistance.

Fluid Dynamics Numerical Assessment to Evaluate the Ice Formation Around the Pipeline

2019 ◽  
Author(s):  
Giuseppe Blasioli ◽  
Furio Marchesani
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Natural Convection ◽  
Thermal Resistance ◽  
Low Temperatures ◽  
Operating Conditions ◽  
Ice Formation ◽  
Convection Coefficient ◽  
Offshore Pipelines ◽  
Offshore Pipeline

Abstract In response to the UNCCC held in Paris in 2015 the need to reduce the global warming, due to CO2 release in atmosphere, led to a new business for the capture and storage of CO2 in dedicated deep water reservoir. In this sense the transport of the CO2 at low temperature, necessary to condensate the gas, through offshore pipeline is a commercial and technical valid strategy. One of the issues related to the transport of a condensate gas is the thermal exchange between the transport system, in this case offshore pipelines, and the environment. The gas is usually carried by ships in a liquid phase at very low temperatures, for example −30 °C in case of CO2. The fluid is introduced into the pipeline at the same temperature to not further consume energy for warming up. The design of the offshore pipeline subject to these operating conditions, very cold fluid internally and a water temperature slightly over 0°C at external side, can be affected by the ice formation around the pipe. The ice thickness formation is primarily governed by the external convection coefficient. For the offshore pipelines located in deep waters where the sea currents are negligible, only the natural convection phenomena can occur on the external surface of the pipeline. Considering steady state scenario the heat transfer from the internal fluid to the external environmental is governed by the thermal resistance of each component of the system like fluid, steel, anticorrosion coating, thermal insulation if any and external convection due to the seawater. The low temperatures of both seawater and ice formation, approximately at −2°C, allow to be close to the maximum value of the seawater density: usually this occurs at a slightly colder temperatures depending on salinity and water depth (for the fresh water the maximum is at 4°C). The natural convection is driven by the buoyancy effect due to fluid density variation with temperature: the scenario described above lead to minimizes these effects and consequently the heat transfer due to the natural convection (increasing the thermal resistance). Most of the correlations in literature are related to different temperature ranges, far away from this particular situation: a numerical investigation using computational fluid dynamics technique has been performed. The analysis is executed by means of commercial CFD software FLUENT: the model is based on a two dimensional grid of a pipe submerged in water. In this paper: • The state-of-the-art about the natural convection coefficient estimate for submerged cylinders proposed by different authors through Nusselt number assessment; • A description of the proposed numerical approach is given highlighting the different approaches based on the boundary layer behavior; • A typical application is shown.

Multi-Objective Optimization Design of Multi-Layer Rectangle Micro-Channel Heat Sink for Single-Phase Flow and Heat Transfer

2013 ◽  
Vol 709 ◽  
pp. 286-291 ◽  
Author(s):  
Li Feng Wang ◽  
Bao Dong Shao ◽  
He Ming Cheng
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Heat Sink ◽  
Optimization Design ◽  
High Heat ◽  
Micro Channel ◽  
Compact Structure ◽  
Total Thermal Resistance ◽  
High Heat Transfer

The purpose of this paper is to optimize the structural sizes of multi-layer rectangle micro-channel heat sink, which has been widely used to cool electronic chip for its high heat transfer coefficient and compact structure. Taking the thermal resistance and the pressure drop as goal functions, a binary-objective optimization model was proposed for the multi-layer rectangle micro-channel heat sink based on Sequential Quadratic Programming (SQP) method. The number of optimized micro-channel in width n1 and that in height n2 are 21 and 7, the width of optimized micro-channel Wc and fin Wf are 340 and 130μm, the height of optimized micro-channel Hc is 415μm, and the corresponding total thermal resistance of the whole micro-channel heat sink is 1.3354 °C/W. The corresponding pressure drop is about 1.3377 Pa. When the velocity of liquid is larger than 0.3 m/s, the effect of change of velocity of liquid on the thermal resistance and pressure drop can be neglected.

Translation-rotation coupling and heat transfer in orientationally-disordered phase of CCl4

Open Physics ◽  
2006 ◽  
Vol 4 (2) ◽  
Author(s):  
Oleg Pursky ◽  
Vyacheslav Konstantinov
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Free Path ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Mobility Edge ◽  
Total Thermal Resistance ◽  
Disordered Phase ◽  
Diffusive Modes

AbstractThe isochoric thermal conductivity of an orientationally-disordered phase of CCl4 is analysed within a model in which heat is transferred by phonons and above the phonon mobility edge by ”diffusive” modes migrating randomly from site to site. The mobility edge ω0 is found from the condition that the phonon mean-free path cannot become smaller than half the phonon wavelength. The contributions of phonon-phonon, one-, and two-phonon scattering to the total thermal resistance of solid CCl4 are calcualted under the assumption that the different scattering mechanisms contribute additively. An increase in the isochoric thermal conductivity with temperature is explained by suppression of phonon scattering at rotational excitations due to a decrease in correlation in the rotation of neighbouring molecules.

scholarly journals Experimental tests for the occurence of convective heat transfer within the bed of rectangular steel profiles

2012 ◽  
Vol 33 (3) ◽  
pp. 84-95
Author(s):  
Rafał Wyczółkowski ◽  
Dorota Musiał
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Natural Convection ◽  
Heat Exchange ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Experimental Tests ◽  
Steel Sections

Abstract The paper describes tests intended to examine the occurrence of natural convection within the space occupied by 40×20 mm rectangular steel sections. Within these tests the bed of four layers of section was heated by the electric palate heater. Depending on the manner in which the heater was positioned, the tests were divided into two series. In the case of heating from above, the heat flowing through the bed is transferred only by conduction and radiation. When heating the bed from below, in addition to conduction and radiation, also a convective heat transfer will occur. Should this be the case, it will result in the intensification of the heat exchange. The results of measurements carried out have not demonstrated that the occurrence of any possible natural convection would influence the development of a temperature field in this type of charge.

Contact heat exchange in conjunction with metal surfaces which have deviations in form or waviness

2015 ◽  
Vol 5 (4) ◽  
pp. 234-241
Author(s):  
Ерин ◽  
Oleg Erin ◽  
Кондратенко ◽  
Irina Kondratenko ◽  
Попов ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Metal Surfaces ◽  
Calculated Data ◽  
Contact Thermal Resistance ◽  
Contact Heat ◽  
Mechanical Loads ◽  
Physical Experiments ◽  
Contact Heat Exchange ◽  
Constituent Elements

In the design of thermally stressed units in the sectors of mechanical engineering, aviation, aerospace, energetics it is often necessary to have information about the formation of the contact thermal resistance resulting from the discrete nature of parts metal surfaces contacting. While passing through the section zones of heat flows the temperature gradient increases, thus reducing the heat transfer capability of the contact junction and leads to thermal expansion of the constituent elements of the systems, relative shifts and warpages. The process of heat transfer through the zone of contact between metal surfaces having deviation of shapes in the form of nonflatness or waviness under conditions suitable to small mechanical loads is considered. The model of formation of the contact thermal resistance (CTR), in case of double contraction of the heat flow of channel and contact mаcrospots, caused by nonflatness or waviness, and then to microspots caused by roughness. Subject to the provisions of the theory of mechanical contacting of solids theoretical curves is derived describing the contact thermal resistance for compounds with surfaces having microdeviation or waviness operating in the regime of small mechanical loads. The results of physical experiments give satisfactory agreement with the calculated data. It was established that the presence of nonflatness or waviness on the contact surfaces increases CTR significantly as compared with rough surfaces. Increase of CTR is explained by the increase of wave height or equivalent nonflatness

Heat Transfer Characteristics and Cooling Performance of Microchannel Heat Sinks With Nanofluids

2009 ◽  
Author(s):  
Chien-Hsin Chen ◽  
Chang-Yi Ding
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Thermal Resistance ◽  
Inertial Force ◽  
Fluid Phase ◽  
Inertial Effect ◽  
Microchannel Heat Sink ◽  
Heat Transfer Characteristics ◽  
Total Thermal Resistance ◽  
Cooling Performance

This paper presents a numerical study on the heat transfer characteristics and cooling performance of a microchannel heat sink with water-γAl2O3 nanofluids having different nanoparticle volume fraction. In view of the small dimensions of the microstructures, the microchannel heat sink is modeled as a fluid-saturated porous medium in the simulation. The Forchheimer-Brinkman-extended Darcy equation is used to describe the fluid flow and the two-equation model with thermal dispersion is utilized for heat transfer. Typical results for the temperature distributions of the fin and fluid phase are presented for various values of the inertial force parameter. It is found that the fin temperature distribution is practically not sensitive to the inertial effect, while the fluid temperature distribution and the total thermal resistance change significantly due to the inertial force effect. In general, the effect of fluid inertia is to reduce the total thermal resistance and the temperature difference between the fin and the fluid phase. The total thermal resistances obtained from the present model with inertial effect match well with the available experimental results, whereas the thermal resistance is overestimated as the inertial effect is neglected.

Numerical Analysis on Natural Convection Heat Transfer of a Heat Sink with Cylindrical Pin Fin

2014 ◽  
Vol 695 ◽  
pp. 398-402
Author(s):  
Yap Zi Qin ◽  
Amer Nordin Darus ◽  
Nor Azwadi Che Sidik
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Thermal Resistance ◽  
Thermal Management ◽  
Heat Sink ◽  
Information Age ◽  
Convection Heat Transfer ◽  
Pin Fin ◽  
Technology Advancement ◽  
Optimum Porosity

As technology advancement progressed in this information age or commonly known as digital age, thermal management has equally improved to keep up with demands from the electronic sector. Hence, heat sink study has become more and more prominent. Natural convection holds advantages since it is maintenance free and has zero power consumption. The purpose of this research is to study the heat transfer performance of heat sink with parametric variations of number and height of pin fin at temperature 308K, 323K, 338K, 353K and 368K. In addition, effect of porosity ranges from 0.524 to 0.960 on thermal resistance was investigated as well. Study found that heat transfer coefficient increases as temperature difference between heat sink and ambient increases. Thermal resistance decreases when porosity increases until it reaches the minimum and subsequently increases. The optimum porosity shown in this study is around 88%.

Comprehensive Reduction of Thermal Resistance in Air Cooled Condensers

2015 ◽  
Author(s):  
Ahmad Saleh ◽  
Jayanta Kapat
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Transfer Process ◽  
Cooling System ◽  
Ambient Air ◽  
Heat Transfer Process ◽  
Air Cooling ◽  
Total Thermal Resistance ◽  
Fin Efficiency

Restriction on water consumption is becoming an increasing problem for the power generation industry. As an alternative both to once-through cooling and to surface condenser/wet-cooling tower combination, utility companies and equipment manufacturers are considering, and even implementing, air-cooled condenser (ACC). However, the industry is quite reluctant to switch over to ACC for three important reasons: (a) lower power output, (b) higher capital cost, and (c) larger physical foot-print, all because of the same reason — it is not as efficient to transfer heat from condensing steam to air as it is to transfer to water. In other words, overall thermal resistance from condensing steam to the ambient air is significantly higher than to cooling water. To get a clear and full understanding of the heat transfer process occur in air-cooling condenser, Detailed mathematical equations were derived to model the heat transfer process through the fined-tubes of the ACC. The total thermal resistance model was analyzed and investigated to identify the design components with highest affect in the process. The paper proposes a viable cooling system based on novel heat pipe technology which addresses these problems. This technology employs boiling as the means to store and transfer heat energy. A detailed mathematical set of equations was derived to model the heat pipe thermal resistance. A comparison of the heat transfer performances of the ACC technology and the proposed method is presented. The proposed cooling system suggests a solution for each of the three components of the thermal resistance, the super-hydrophobic coating of the steam ducts internal surfaces increased the condensing heat transfer rate by an order of magnitude, the proposed design of the heat pipes improved the external heat transfer, and the installation mechanism improves the fin efficiency by eliminating the contact resistance between steam duct and the heat pipe.

Sign in / Sign up

Export Citation Format

Share Document