Forced Convection Heat Transfer in Porous Structure: Effect of Morphology on Pressure Drop and Heat Transfer Coefficient

2021 ◽  
Author(s):  
Jiafei Zhao ◽  
Mingrui Sun ◽  
Lunxiang Zhang ◽  
Chengzhi Hu ◽  
Dawei Tang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Porous Structure ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Structure Effect ◽  
Convection Heat ◽  
Forced Convection Heat Transfer

Estimation of transient wall and flow temperature distributions in a circular duct using an inverse approach

2007 ◽  
Vol 221 (11) ◽  
pp. 1353-1361
Author(s):  
S D Masouros ◽  
K Mathioudakis
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient ◽  
Circular Duct ◽  
Inverse Approach ◽  
Forced Convection Heat Transfer

Inverse methods have become a useful tool for estimating parameters that cannot be measured or calculated directly in engineering applications. Parameters characterizing unsteady heat convection in circular duct flows are associated with numerous uncertainties. This fact renders the inverse approach appropriate for the determination of these parameters. An inverse problem for transient turbulent thermally developing and thermally developed forced-convection flow in a circular duct is formulated and discussed, and a simplified direct thermal model is presented. Parameters of the model are estimated by solving a minimization problem, using temperature data from the wall surface and/or the flow. A multivariable optimization algorithm is employed for this purpose. Furthermore, a model for the forced-convection heat-transfer coefficient is proposed and its effect on the results is discussed. The validity of the proposed method is assessed using data from two different circular duct flows. The method is shown to provide a good prediction capability in computationally demanding transient heat-data sequences of different duct flows, both in terms of duct and of flow characteristics. Results show that a hyperbolic axial distribution of the forced-convection heat-transfer coefficient in the developing region of the flow is essential for good adaptation of the method to the test data.

scholarly journals Forced Convection Nanofluid Heat Transfer as a Function of Distance in Microchannels

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3021
Author(s):  
Saeid Vafaei ◽  
Jonathan A. Yeager ◽  
Peter Daluga ◽  
Branden Scherer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Crystal Phase ◽  
Convection Heat ◽  
Effective Parameters ◽  
Forced Convection Heat Transfer ◽  
Base Liquid

As electronic devices become smaller and more powerful, the demand for micro-scale thermal management becomes necessary in achieving a more compact design. One way to do that is enhancing the forced convection heat transfer by adding nanoparticles into the base liquid. In this study, the nanofluid forced convection heat transfer coefficient was measured inside stainless-steel microchannels (ID = 210 μm) and heat transfer coefficient as a function of distance was measured to explore the effects of base liquid, crystal phase, nanoparticle material, and size on heat transfer coefficient. It was found that crystal phase, characteristics of nanoparticles, the thermal conductivity and viscosity of nanofluid can play a significant role on heat transfer coefficient. In addition, the effects of man-made and commercial TiO2 on heat transfer coefficient were investigated and it was found that man-made anatase TiO2 nanoparticles were more effective to enhance the heat transfer coefficient, for given conditions. This study also conducted a brief literature review on nanofluid forced convection heat transfer to investigate how nanofluid heat transfer coefficient as a function of distance would be affected by effective parameters such as base liquid, flow regime, concentration, and the characteristics of nanoparticles (material and size).

scholarly journals Determination of Heat Transfer Coefficient for the Air Forced Cooling Over a Flat Side of Coil

2019 ◽  
Vol 15 (1) ◽  
pp. 15-20 ◽  
Author(s):  
Payam Shams Ghahfarokhi ◽  
Ants Kallaste ◽  
Anouar Belahcen ◽  
Toomas Vaimann
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Analytical Results ◽  
Flat Side

AbstractThe paper deals with the analytical and experimental determination of the forced convection heat transfer coefficients over the flat coil module. In the analytical part, the forced convection coefficients at different wind speeds are calculated based on various known equations of the forced convection heat transfer coefficient with unheated starting length. The experimental part presents the description of the test: loading the coil with DC current and measurements of the coil temperatures with thermal sensors while it was inside a wind tunnel. Based on the measurement, the convection coefficients were determined. In the final part, the experimental and analytical results are compared. It is found that the accuracy of the analytical results is more precise in highly turbulent flows.

Forced Convection Heat Transfer of Nanofluids: A Review

2017 ◽  
Author(s):  
Aditya Kuchibhotla ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Specific Heat ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Convection Heat

Stable homogeneous colloidal suspensions of nanoparticles in a liquid solvents are termed as nanofluids. In this review the results for the forced convection heat transfer of nanofluids are gleaned from the literature reports. This study attempts to evaluate the experimental data in the literature for the efficacy of employing nanofluids as heat transfer fluids (HTF) and for Thermal Energy Storage (TES). The efficacy of nanofluids for improving the performance of compact heat exchangers were also explored. In addition to thermal conductivity and specific heat capacity the rheological behavior of nanofluids also play a significant role for various applications. The material properties of nanofluids are highly sensitive to small variations in synthesis protocols. Hence the scope of this review encompassed various sub-topics including: synthesis protocols for nanofluids, materials characterization, thermo-physical properties (thermal conductivity, viscosity, specific heat capacity), pressure drop and heat transfer coefficients under forced convection conditions. The measured values of heat transfer coefficient of the nanofluids varies with testing configuration i.e. flow regime, boundary condition and geometry. Furthermore, a review of the reported results on the effects of particle concentration, size, temperature is presented in this study. A brief discussion on the pros and cons of various models in the literature is also performed — especially pertaining to the reports on the anomalous enhancement in heat transfer coefficient of nanofluids. Furthermore, the experimental data in the literature indicate that the enhancement observed in heat transfer coefficient is incongruous compared to the level of thermal conductivity enhancement obtained in these studies. Plausible explanations for this incongruous behavior is explored in this review. A brief discussion on the applicability of conventional single phase convection correlations based on Newtonian rheological models for predicting the heat transfer characteristics of the nanofluids is also explored in this review (especially considering that nanofluids often display non-Newtonian rheology). Validity of various correlations reported in the literature that were developed from experiments, is also explored in this review. These comparisons were performed as a function of various parameters, such as, for the same mass flow rate, Reynolds number, mass averaged velocity and pumping power.

Forced Convection Heat Transfer for Helium Gas Under Exponentially Decreasing Flow Condition

2017 ◽  
Author(s):  
Qiusheng Liu ◽  
Li Wang ◽  
Makoto Shibahara ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Flow Rate ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Rate Condition ◽  
Initial Flow ◽  
Helium Gas

Knowledge of the heat transfer phenomenon during flow decay transient condition is important for the safety assessment of very high temperature reactor (VHTR) during the loss of coolant accident. In this study, transient heat transfer from a horizontal cylinder to helium gas under exponentially decreasing flow rate condition was experimentally studied. The experiment was performed by using a forced convection heat transfer test loop. A flow control value with its control system was used to realize the flow decay condition. Helium gas was used as coolant and platinum cylinder with 1 mm in diameter was used as the test heater. A uniform heat generation rate was added to the cylinder by a power source. The cylinder temperature was maintained at an initial value under a definite initial flow rate of the helium gas. Then, the mass flow rate of the helium gas starts to decrease exponentially with different time constants ranged from 4.3 s to 15.4 s. The initial flow velocity ranged from 10 m/s to 4 m/s. The surface temperature, heat flux, and heat transfer coefficient were measured during the flow decay transient process under wide experimental conditions such as initial flow rate, flow decay time constant. It was found that the temperature of the test heater shows rapid increase during this process, the increasing rate of the temperature is higher for a shorter time constant. The heat transfer coefficient versus time during the flow rate decreasing process was also obtained. The transient heat transfer process during exponentially decreasing flow rate condition was clarified based on the experimental data.

scholarly journals Effect of perforated concave delta winglet vortex generators on heat transfer augmentation of fluid flow inside a rectangular channel: An experimental study

2018 ◽  
Vol 204 ◽  
pp. 04015
Author(s):  
Syaiful ◽  
MSK Tony SU ◽  
Nazaruddin Sinaga ◽  
Retno Wulandari ◽  
Myung-whan Bae
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Vortex Generator ◽  
Longitudinal Vortex ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient ◽  
Delta Winglet

Compact heat exchanger with gas as a heat exchange medium is widely used in power plants, automotive, air conditioning, and others. However, the gas has a low thermal conductivity resulting in high thermal resistance causing a low rate of heat transfer. Therefore an improvement to the convection heat transfer coefficient is necessary. One way to enhance the convection heat transfer coefficient is to use a longitudinal vortex generator. However, the increase in convection heat transfer coefficient is followed by an increase in pressure drop. Therefore, this work aims to improve the convection heat transfer coefficient with a low pressure drop. To achieve this goal, experiments were carried out by perforating a longitudinal vortex generator with a diameter of 5 mm with variations in holes number one, two and three. Two types of longitudinal vortex generators are compared. The experimental results show that the convection heat transfer coefficient for the case of perforated concave delta winglet vortex generator is only decreased by 1% from that without a hole, while the pressure drop is decreased by 11.6%.

Numerical Simulation on Forced Convection Heat Transfer Performance and Pressure Drop of High Permeability Porous Media

2016 ◽  
Author(s):  
Shigeki Hirasawa ◽  
Tsuyoshi Kawanami ◽  
Katsuaki Shirai
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Air Flow ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Convection Heat

We studied the forced convection heat transfer performance and pressure drop of high permeability metal cellular porous media in air flow using a 3-dimensional thermofluid computation code. The temperature and velocity distributions in the air flow region, local heat transfer coefficient, and local heat flux on the surface of the porous media were numerically calculated for steady air flow by changing the parameters of the pore size and air velocity. The cellular porous media were modeled by pin array, cube geometry, and truncated octahedron geometry using thin wires. The diameter of the wires was 0.1 mm, and the pore per inch (PPI) was 5–50. The relations between the Nusselt number using the volumetric heat transfer coefficient and the Reynolds number were obtained from our calculation results, and we compared them with conventionally proposed experimental correlations. Also, the pressure drop calculation result was compared with conventionally proposed experimental correlations. The following results were obtained. The local heat transfer coefficient and local heat flux on the surface of porous media were small near the joint positions of the wires of the cellular porous media because of the thermal boundary layer. The volumetric heat transfer coefficient and pressure drop agreed with conventionally proposed experimental correlations within errors of twice the volumetric heat transfer coefficient and pressure drop. The relation between the heat transfer rate per unit volume and the heat transfer area per unit volume agreed with the convection heat transfer correlation for a tube bundle.

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