Fluid Heat Transfer Rate Research Articles

Influence of periodicity on natural convection in a square porous cavity due to non-uniform heat under LTNE state

In this article, the influence of the local thermal non-equilibrium (LTNE) state on free convection in a square cavity filled with fluid-saturated porous medium is investigated numerically. The steady-state flow is induced due to sinusoidal heat distributed on the side walls of the cavity and insulated of the horizontal walls. The coupled flow governing equations are solved numerically by using the finite volume method (FVM) consisting of the SIMPLER (Semi-Implicit Method for Pressure Linked Equation Revised) Algorithm. The numerical simulations of temperature and stream-function contours are carried out for the non-Darcy model. The developed code is validated with existing numerical and present computed results for the case of a square enclosure associated with non-uniform heat source. Then, the present numerical results are analyzed over a range of physical parameters, like periodicity parameter ( N ≥ 1 ), interface heat transfer coefficient ( 10 − 2 ≤ H ≤ 10 2 ), porosity scaled thermal conductivity ratio ( 10 − 2 ≤ γ ≤ 10 2 ), with a fixed Rayleigh number ( Ra = 10 6 ), Darcy number ( Da = 10 − 4 ), Prandtl number (Pr = 0.71), and porosity ( ε = 0.8 ). To study the impacts of these key parameters on the fluid flow behavior and isotherm patterns of fluid as well as solid phase in the porous-square enclosure. From present numerical experiments that the structure of flow is controlled by multicellular structure with rotating clockwise and anticlockwise directions in the entire results. The flow dynamics are highly affected by the periodicity parameter (N) under LTNE circumstances. The characteristics of the local Nusselt number have the point of inflection and the maximum magnitude of it increases with N. The significant effect of H is found on the heat transfer rate of fluid phase but it is negligible on the heat transfer rate of solid phase. However, the influence of γ is found reverse in nature on the heat transfer rate of fluid as well as solid phase when as compared to the effect of H.

Analytical and numerical investigation for viscoelastic fluid with heat transfer analysis during rollover-web coating phenomena

Abstract The current study theoretically and computationally analyses the viscoelastic Sisko fluids during the non-isothermal rollover web phenomenon. The mathematical modeling produces a system of partial differential equations, which we further simplify into ordinary differential equations through appropriate transformations. We have formulated the problem based on the lubrication approximation theory. The solution has been obtained with the perturbation method, and the outcomes are found in mathematical, tabular, and graphical forms that highlight the influence of pertinent parameters on velocity profiles, pressure gradients, flow rates per unit width, Nusselt number, pressure profile, temperature distributions, and other significant engineering quantities. Further, A comparative analysis between analytic and numerical solutions, utilizing the middefer method in the Maple environment, demonstrates reasonable agreement. Also, we observe that the fluid parameter significantly influences both velocity and temperature profiles. Moreover, the determination of a separation point 2.5000, accompanied by the observation of a maximum coating thickness of 0.6960. The enhancement in fluid heat transfer rate is approximately 5% compared to non-Newtonian fluid parameter values, with potential for further improvement by increasing the non-Newtonian parameter values. This comprehensive investigation offers valuable insights for practical implementation and future scholarly endeavors, with zero-order findings showcasing enhanced precision.

Heat transfer analysis of Maxwell hybrid nanofluid with fractional Cattaneo heat flux

Hybrid nanofluids are widely used to improve the efficiency of a thermal system in many aspects of engineering and science. Therefore, the current work is design to investigate the heat transfer of Cu-Fe3O4 nanoparticles in water base Maxwell fluid flow over a cone, which is kept in a porous medium. Additionally, the fluid experiences magnetic field and thermal radiation effects. As a result, the impacts of volume fraction, porosity, magnetic field, and thermal radiation are properly taken into account. It is observed that increasing temperature time relaxation with constant temperature fractional derivative decreases the thermal gradient, whereas increasing temperature fractional derivative parameter with constant time relaxation increases the thermal gradient. Moreover, adding 1% Cu-Fe3O4 increases the heat transfer rate of the fluid up to 1.13% and 1.24% when Rd=0 and Rd=0.2, respectively. On the other hand, the heat transfer rate of Maxwell fluid decreases up to 0.5% in the presence of a magnetic field specifically considering M=2 without thermal radiation.

A Review on Heat Transfer Enhancement of Solar Air Heater Using Various Artificial Roughed Geometries

Solar air heater acts as one of the important components in utilization of solar energy. The air heater absorbs the irradiance and converts it into heat energy at the absorbing surface. The thermal energy is further use in heating flowing air through the duct. Solar air heaters are cost effective as well as simple in design. Solar air heater can be used in space heating, timber seasoning and agricultural drying. In spite of all these advantages the solar air heater has certain challenges such as the air has low heat transfer coefficient. The heat transfer rate from the heated absorber surface to the air is low. Hence in order to enhance the heat transfer coefficient the surface area either increases or the flow made to be turbulent. In order to do so the artificial roughened element must be incorporated on the heated surface. The use of artificial roughness is considered as an effective technique to enhance the heat transfer rate of fluid flowing through the duct of solar air heater. The heat transfer and friction characteristics of number of roughness geometries incorporated solar air heater have been investigated. In this paper an attempt has been made to review on element geometries used as artificial roughness in solar air heater in order to improve thermal and thermo hydraulic performance of solar air heater ducts.

Effects of temperature-dependent viscosity on natural convection in a porous cavity with a circular cylinder under local thermal non-equilibrium condition

In the present work, the influences of exponentially temperature-dependent viscosity on free convection in a porous cavity with a circular cylinder under local thermal non-equilibrium (LTNE) condition are investigated numerically via lattice Boltzmann (LB) method. To incorporate the LTNE effects, the temperature evolution equations are constructed by adding some unified source terms, which also preserve the parallel computation feature of the standard LB method. The effects of several physical parameters, including viscosity variation index (n), Rayleigh number (Ra), Darcy number (Da), ratio of fluid-to-solid thermal conductivity (λ) and inter-phase heat transfer coefficient (H) on flow and heat transfer characteristics are numerically studied. The numerical results show that as the LTNE parameters increase (i.e., H and λ), the solid heat transfer rate increases dramatically, while few changes are found for the heat transfer rate of fluid. Additionally, we find that for most given parameters, both the heat transfer rate of fluid and solid are generally decreased with the increase of n, while for relatively small values of H and λ, the heat transfer coefficient of solid phase depends little on the value of n. Further, the impacts of the porosity (ε) as well as the aspect ratio (Γ) are also considered.

A nanofluids and nanocoatings used for solar energy harvesting and heat transfer applications: A retrospective review analysis

It is known that harvesting the solar power is key issue in current scenario because of scarcity of non-renewable energy in future days to come. Hence the solar harvesting systems takes an important stand globally. Grabbing the solar energy is difficult task due to low thermal conductivity of fluids which are carrying heat and poor optical coatings of solar power devices. In order to enhance the heat transfer rate of fluids there should be an alternative, such alternative is nanofluid. Nanofluids are having nanoparticles suspended in base fluids stably. This paper critically reviewed and conveyed the up to date literature of usage of nanofluids and nanocoating’s in solar energy harvesting operating in low, medium and high temperature ranges for effectiveness in performance. Further solar energy conversion systems efficiencies can be raised by using the additives in base fluids termed as nanofluids and nano selective coatings for solar concentrators to improve optical performance.

Analysis of heat transfer characteristics with triangular cut twisted tape (TCTT) and circular cut twisted tape (CCTT) inserts

Abstract The paper represents the numerical investigation of heat transfer characteristics in a pipe provided with twisted tape inserts is analyzed. The heat transfer was analyzed in a swirling flow conditions using CFD simulation. A commercial CFD package was used for analyze twisted tape for circular tube fitted with triangular cut twisted tape and circular hole cut twisted tape inserts. The twisted tape system allows a significant increase of convective heat transfer coefficient by introducing the swirl flow motion. The swirl flow motion provides greater heat transfer rate extracted from the solid surface of the tube. The depth of cuts for triangular cut 5 mm and depth of hole cut 5 mm twisted tapes were used for simulation generation. In this paper CFD analysis was used for enhancement of heat transfer rate of fluid of laminar flow. The experimental investigation were conducted in double pipe heat exchanger and these value of plain twisted tape, triangular twisted tape and circular hole cit twisted tape were taken for used simulation analysis. The performance of heat transfer rate was enhanced 1.1–1.3 times compared that the plain twisted tape and circular cut twisted tape. The data obtained from the simulation correlations for triangular cut twisted tape and circular hole cut twisted tape; and these data were correlated with plain twisted tape.

Investigation of Surface Roughness for Inconel 625 using Wire Electric Discharge Machining

Due to the increase in the demand of materials with good surface finish and complex shapes, conventional machining processes became out of date. This directed to the increasing demand of non-conventional machining processes. This research work is focuses on the optimization of Surface Roughness (SR) using Wire Electrical Discharge Machining (WEDM) method on Inconel 625 super alloy material. The diffused wire tool electrode (plain and cryo-treated) is used for experimental work. Taguchi’s L18 (21*35) orthogonal array’s has been used to design for experimental run. The machining parameters selected for optimization are tool electrode, current (Ip), pulse on time (Ton), pulse off time (Toff), wire feed (Wf) and wire tension (Wt). Rectangular slits has been fabricated, which are useful for many industrial application like increase the heat transfer rate of fluids, micro-channels, micro-fins etc. Design of Experiment (DoE) optimization technique is used to find the most significant factor.

A thermal non-equilibrium model for 3D double diffusive convection of power-law fluids with chemical reaction in the porous medium

The article reports a numerical study of the double-diffusive natural convection of power-law fluids in a porous cubic cavity with chemical reaction under the local thermal non-equilibrium (LTNE) state and submitted to horizontal temperature and concentration gradients. The complete governing equations, in which the generalized non-Darcy model is employed as momentum equation and a two-temperature model that represents temperature fields of the fluid and solid phases separately is used for energy equation, are solved by the compact high order finite volume method. Special attentions are given to detecting the effects of the porosity modified conductivity ratio (γ), the inter-phase heat transfer coefficient (H), the chemical reaction parameter (λ), the Dufour parameter (Du), the Soret parameter (Sr) and the Lewis number (Le) on the fluid flow as well as on rates of heat and mass transfer. Our simulations show that the heat transfer rate of solid increases, while the heat transfer rate of fluid and mass transfer rate keep constants, as the LTNE parameters (i.e., γ and H) increase. For any relatively large value of γ and H, the almost thermal equilibrium state is achieved due to the similar thermal distribution of fluid and solid phases. On the contrary, the chemical reaction parameter has significant influence on mass transfer than on heat transfer under the LTNE conditions. In addition, the heat and mass transfer enhance with the increment of the Soret and Dufour parameters. Augmentation of Lewis number enhances mass transfer but reduces heat transfer. Apart from that, our numerical tests show the flow field is influenced appreciably by the presence of the power-law index (n), Darcy number (Da) and porous thermal Rayleigh number (Ra).

Natural convection in square cavity filled with ferrofluid saturated porous medium in the presence of uniform magnetic field

This article contains numerical results for free convection through square enclosure enclosing ferrofluid saturated porous medium when uniform magnetic field is applied upon the flow along x-axis. Heat is provided through bottom wall and a square blockage placed near left or right bottom corner of enclosure as a heat source. Left and right vertical boundaries of the cavity are considered insulated while upper wall is taken cold. The problem is modelled in terms of system of nonlinear partial differential equations. Finite element method has been adopted to compute numerical simulations of mathematical problem for wide range of pertinent flow parameters including Rayleigh number, Hartman number, Darcy number and Prandtl number.Analysis of results reveals that the strength of streamline circulation is an increasing function of Darcy and Prandtl number where convection heat transfer is dominant for large values of these parameters whereas increase in Hartman number has opposite effects on isotherms and streamline circulations. Thermal conductivity and hence local heat transfer rate of fluid gets increased when ferroparticles are introduced in the fluid. Average Nusselt number increases with increase in Darcy and Rayleigh numbers while it is decreases when Hartman number is increased.

A thermal non-equilibrium approach on double-diffusive natural convection in a square porous-medium cavity

In this manuscript the influence of local thermal non-equilibrium state on double-diffusive natural convection in a square cavity filled with fluid-saturated porous medium has been addressed numerically. The two dimensional steady state flow is induced due to maintenance of constant temperature and concentration on the vertical walls and insulation of both horizontal walls of the cavity. Non-Darcy (Darcy–Brinkman–Forchheimer) model has been taken and the complete governing equations are solved by standard SIMPLER algorithm. A comparative study of the effect of the presence of Brinkman term in the momentum equation showed that results under the Darcy model are very close to those for the non-Darcy Brinkman model for relatively low permeable medium (e.g., in this study Da=10-4). From our experiments it has been found that the impact of Lewis number (Le) on the average heat transfer rate of fluid (Nuf) and solid (Nus) as well as on the thermal distribution of fluid and solid is not straightforward. It depends on the buoyancy ratio (N) and the value of inter-phase heat transfer coefficient (H). However, Le increases the average mass transfer rate (Sh). Also, for each Le there exist a point in the domain of N where Nuf is minimum. Similar points also exist for Nus and Sh. In general, these points are different and depend on the LTNE state parameters, except at Le=1. For any relatively large value of H, when almost thermal equilibrium state is achieved, the point at which Nuf and Nus are minimum is same due to similar thermal distribution of fluid and solid. Also, it has been found that, for the buoyancy aided flow (N>0), the increase in H up to a threshold value (H0) decreases Sh as well as Nuf but increases Nus. The H0 is found to be a decreasing function of the porosity scaled thermal conductivity ratio (γ) of fluid and solid phases. Overall, the impact of LTNE state on the heat transfer rate and thermal distribution is significant but it is negligible on the mass transfer rate and solute distribution.

Effect of Buoyancy Ratio on Non-Darcy Mixed Convection in a Vertical Channel: A Thermal Non-equilibrium Approach

This article presents a numerical study of the doublediffusive mixed convection in a vertical channel filled with porous medium by using non-equilibrium model. The flow is assumed fully developed, uni-directional and steady state. The controlling parameters are thermal Rayleigh number (RaT ), Darcy number (Da), Forchheimer number (F), buoyancy ratio (N), inter phase heat transfer coefficient (H), and porosity scaled thermal conductivity ratio (γ). The Brinkman-extended non-Darcy model is considered. The governing equations are solved by spectral collocation method. The main emphasize is given on flow profiles as well as heat and solute transfer rates, when two diffusive components in terms of buoyancy ratio are in favor (against) of each other and solid matrix and fluid are thermally non-equilibrium. The results show that, for aiding flow (RaT = 1000), the heat transfer rate of fluid (Nuf ) increases upto a certain value of H, beyond that decreases smoothly and converges to a constant, whereas in case of opposing flow (RaT = -1000), the result is same for N = 0 and 1. The variation of Nuf in (N, Nuf )-plane shows sinusoidal pattern for RaT = -1000. For both cases (aiding and opposing) the flow destabilize on increasing N by inviting point of inflection or flow separation on the velocity profile. Overall, the buoyancy force have significant impact on the non-Darcy mixed convection under LTNE conditions. Keywords—buoyancy ratio, mixed convection, non-Darcy model, thermal non-equilibrium

A thermal non-equilibrium perspective on mixed convection in a vertical channel

This paper addresses the influence of thermal non-equilibrium state on fully developed mixed convection in a vertical channel filled with porous medium. The non-Darcy-Brinkman-Forchheimer extended model has been considered. The governing equations are solved numerically by spectral collocation method and analytically for a special case (form drag equal to zero). The governing parameters for this problem are Rayleigh number (Ra), Darcy number (Da), Forchheimer number (F), inter-phase heat transfer coefficient (H), and porosity-scaled thermal conductivity ratio (γ). Special attention is given to understand the effect of thermal non-equilibrium parameters: H and γ on the rates of heat transfer and fluid flow profiles, for both buoyancy assisted as well as opposed cases. A comprehensive investigation indicates that, in case of buoyancy assisted flow, for each Ra considered in this study and when γ ≤ 1, there exists a minimum value Ho of H such that the heat transfer rate of fluid (Nuf) at the wall is an increasing function in [0, Ho]. Furthermore, as H is varied beyond Ho, Nuf decreases. Initially the decay of Nuf is fast, but later on it becomes smooth and slow. Similar results are also observed in buoyancy opposed case for very small values of γ. Variation of velocity profile as a function of γ indicates that change in velocity profile is sudden and abrupt. For H > 6, when γ = 0.01, Da = 10−2, |Ra| = 103 and F = 102, flow separation and point of inflection are completely died out from the profile. Overall, for both the cases, on increasing H makes the flow profile smooth (stabilizes the flow) and recovers the system equivalent to equilibrium state, whereas, γ destabilizes the flow by inviting point of inflection or flow separation on the velocity profile.

Manufacturing Influence on the Delamination Fracture Behavior of the T800H/3900-2 Carbon Fiber Reinforced Polymer Composites

‘Torayca’ T800H/3900-2 is the first material qualified on Boeing Material Specification (BMS 8-276) which utilizes the thermoplastic-particulate interlayer toughening technology. Two manufacturing processes, the autoclave process and the fast heating rated Quickstep™ process, were employed to cure this material. The Quickstep process is a unique composite production technology which utilizes the fast heat transfer rate of fluid to heat and cure polymer composite components. The manufacturing influence on the mode I delamination fracture toughness of laminates was investigated by performing double cantilever beam tests. The composite specimens fabricated by two processes exhibited dissimilar delamination resistance curves (R-curves) under mode I loading. The initial value of fracture toughness G IC–INIT was 564 J/m2 for the autoclave specimens and 527 J/m2 for the Quickstep specimens. However, the average propagation fracture toughness G IC–PROP was 783 J/m2 for the Quickstep specimens, which was 2.6 times of that for the autoclave specimens. The mechanism of fracture occurred during delamination was studied under scanning electron microscope (SEM). Three types of fracture were observed: the interlayer fracture, the interface fracture, and the intralaminar fracture. These three types of fracture played different roles in affecting the delamination resistance curves during the crack growth. More fiber bridging was found in the process of delamination for the Quickstep specimens. Better fiber/matrix adhesion was found in the Quickstep specimens by conducting indentation-debond tests.

Integrated microthermoelectric cooler for microfluidic channels

Precise fluid temperature control in microfluidic channels is a requirement for many lab-on-a-chip and microreactor devices, especially in biotechnology where most processes are highly temperature sensitive. We demonstrate the concept of a microthermoelectric cooler integrated into a microfluidic channel in order to give rapid and localised fluid cooling. The key aspect of this concept is the use of a second imbedded microfluidic channel that is used as a miniature heat sink. An analytical thermal model has been derived that couples thermoelectric effects with fluid heat-transfer rates from both the hot and cold connections. Using this model, the effect on cooling performance of varying the thermal resistance between the hot and cold connections and the fluid has been quantified, as well as the effect of substrate thermal conductivity. If the substrate thermal conductivity is too high, heat leakage renders the thermoelectric cooler ineffective. The optimum electrical current for cooling has been shown to be a function of the thermal resistance of the heat sink. For thermoelectric coolers there is competition between temperature reduction and cooling power. Using this fact, based on the final fluid temperature required, we have calculated the maximum flow rate that will achieve this. Finally, a prototype integrated microthermoelectric cooler has been fabricated and tested.

Flow visualization and heat transfer experiments in fluid-superposed packed beds heated from below

Flow visualization and heat transfer experiments are reported for buoyancy-induced flow in a cylindrical cavity filled with a fluid-superposed packed bed and heated from below. An immersion method is used to measure the refractive index of acrylic spheres, which is then matched with that of the silicon fluid. This allows visualization of interesting flow interactions between the porous bed and overlying fluid. Flow channels through large voids produce highly asymmetric and complicated flow structures, and the number of convective rolls depends on the porous layer height η. The heat transfer rate increases with the Rayleigh number Ra ∗, but the dependence on the particle size γ and the porous bed height is very complex. The average Nusselt number generally increases with the solid-bead diameter, but there may exist some values of η for which the heat transfer rate for a smaller particle size in higher than that for a larger value of γ. Also, the Nusselt number first decreases from the fluid heat transfer rates with an increase in porous matrix height η and reaches a minimum at η min. Any further increase in porous layer height beyond η min augments the heat transfer rate, and the Nusselt number curves show peaks at η min < η ≤1.