Decrease In Heat Transfer Rate Research Articles

Magnetic Field Effect on the Double Diffusive Natural Convection in Three-Dimensional Cavity Filled with Micropolar Nanofluid

This article presents a three-dimensional numerical investigation of heat and mass transfers and fluid flow in a cavity filled with an Al2O3/water micropolar fluid under uniform magnetic field. To solve the governing non-dimensional equations, Finite Volume Method (FVM) based on 3-D vorticity-vector potential formulation has been employed. The effects of various parameters such as buoyancy ratio (−2 ≤ N ≤ 0), Rayleigh number (103 ≤ Ra ≤ 105), Hartmann number (0≤ Ha≤ 60), nanoparticles volume fraction (0 ≤ φ ≤ 0.06) and micropolar material parameter (0≤ K≤ 5) on flow structure and on heat and mass transfers are presented. The results illustrate that for the micropolar nanofluid model, both heat and mass transfer rates and three-dimensional character of the flow are smaller when compared with the pure nanofluid model. It is also observed that increase and decrease in heat and mass transfer rates is experienced due to increase in Rayleigh number and Hartmann number, respectively. It is also noted that increase in vortex viscosity parameter reduces the average heat and mass transfer rates and is more evident when the magnetic field is imposed. Combined effects of magnetic field and nanoparticles volume fraction on heat and mass transfers are also explored.

MHD Free Convection and Entropy Generation in a Corrugated Cavity Filled with a Porous Medium Saturated with Nanofluids.

MHD free convection inside a triangular-wave-shaped corrugated porous cavity with Cu-water nanofluid is numerically studied with the finite element method. The influences of the Grashof number (), Hartmann number (), Darcy number () and solid volume fraction of the nanoparticle () on the convective flow features are examined. It is observed that increasing the Grashof number and Darcy number enhances the heat transfer, while the effect is opposite for the Hartmann number. As the corrugation frequency of the triangular wave increases, the local and averaged heat transfer rates decrease, which is more effective for higher values of Grashof and Darcy numbers. Normalized total entropy generation increases as the Darcy number and solid volume fraction of the nanoparticles increase and decreases as the Hartmann number increases both for flat and corrugated wall configurations.

Dual nature solution of water functionalized copper nanoparticles along a permeable shrinking cylinder: FDM approach

Present framework is established to deal the characteristics of axisymmetric mixed convection flow with heat transfer of water based copper (Cu-water) nanofluid along a porous shrinking cylinder with slip effects. The physical problem is modeled in the form of set of partial differential equations (PDEs) including conservation of mass, momentum and energy equations along with defined boundary conditions. Such PDEs are adapted to ordinary differential equations (ODEs) by utilizing similarity transformation technique. System of equations is emerged with the expressions of nanoparticle and based fluid. Numerical solution of governing ODEs is sought by using Finite Difference Method (FDM) against the range of several pertinent physical parameters. Base fluid (water) is analyzed in the presence of nanoparticles. The model encounters buoyancy opposing and assisting flow regions. Present study reveals that the solution in the assisting flow region is unique whereas multiple solutions exist in the opposing flow region. The results also indicate the existence of multiple solutions for certain amount of mass suction parameter. Moreover, increase in slip parameters and nanoparticle volume fraction enhances the range of suction parameter where the similarity solutions exist. It is further found that due to increase of nanoparticle volume fraction the skin friction increases whereas heat transfer rate decreases.

Mesoscopic analysis of heatline and massline during double-diffusive MHD natural convection in an inclined cavity

Double-diffusive natural convection in an inclined cavity with the presence of magnetic field is studied numerically via heatline and massline approach. The governing equations are discretized using the Lattice Boltzmann Method (LBM). In this investigation, the controlling parameters involved are Rayleigh number (103 ≤ Ra ≤ 105), buoyancy ratio (−5 ≤ N ≤ 5), cavity inclination angle (0° ≤ Ø ≤ 180°), Lewis number (2 ≤ Le ≤ 10), Prandtl number (Pr = 5.0) and Hartmann number (0 ≤ Ha ≤ 50). The numerical results obtained by the effect of parameters mentioned above are reported as contours of streamlines, isotherms, isoconcentrations, heatlines, and masslines. The obtained results are compared with the existing literature to validate the coding. The heat and mass transfer rate decrease with increasing the magnetic field and increase with an increase in Rayleigh number. The impact of Ø is maximum for higher Ra and negligible for lower Ra (103). Increasing Le influences the mass transfer rate to increase and heat transfer to reduce for both opposing and aiding flow.

Wall Heat Transfer Analysis of Internal Combustion Engine with Free Piston Linear Motion

The manuscript should contain an abstract. The abstract should be self-contained and citation-free and should not exceed 200 words. The abstract should state the purpose, approach, results and conclusions of the work. The author should assume that the reader has some knowledge of the subject but has not read the paper. Thus, the abstract should be intelligible and complete in it-self (no numerical references); it should not cite figures, tables, or sections of the paper. The abstract should be written using third person instead of first person. Intensive researches are being carried out on the main power generator for free piston linear generator(FPLG) by both the academic and industrial research group due to its potential as a high fuel efficiency and low emission engine. The linear generator, which is a coil and a translator positioned to move linearly back and forth relative to each other. The study investigates the heat transfer data of internal combustion engine with free piston linear motion profile and compared with the conventional reciprocating engine for one cycle motion only. Engine simulation software GT-Power is employed which utilize the 1-D thermodynamic modeling. All parameters for both free-piston engine are set-up to be the same except for the piston motion profile and the injection timing. Both conventional and free piston engine models are built, simulation settings are set up, and simulations are launched in GT-ISE. Once simulation is done, results are viewed in GT-POST, the data collected was analysed and compared to investigate the dictinct effect of piston motion to heat transfer profile and data. The overall trend shows that free piston engine have a lower heat transfer rate throughout majority of the cycle. This finding agrees that due to less time of piston near top dead centre area, heat transfer losses to the wall per cycle are reduced. The heat transfer profile of the free piston also shown distinct feature compared to conventional with rapid increase and decrease of heat transfer rate, followed by a secondary peak of gradual decline of the profile.

Upshot of Chemical Species and Nonlinear Thermal Radiation on Oldroyd-B Nanofluid Flow Past a Bi-directional Stretched Surface with Heat Generation/Absorption in a Porous Media**Supported by the Korea Ministry of Trade, Industry and Energy, “Energy Technology Development Work in 2017”, Project No. 20172010105570

A three-dimensional mathematical model is developed to examine the flow of nonlinear thermal radiation Oldroyd-B nanofluid past a bidirectional linearly stretched surface in a porous medium. The flow is induced by temperature dependent thermal conductivity, chemical reaction and convective heat and mass conditions. Novel characteristics of Brownian motion and thermophoresis are accompanied by magnetohydrodynamic and heat generation/absorption. Self-similar transformations are employed to convert the system of nonlinear partial differential equations to a system of ordinary differential equations with high nonlinearity and are solved by strong analytic technique named as Homotopy Analysis method (HAM). Effects of varied arising parameters on involved distributions are reflected through graphical illustrations. From this study, it is perceived that strong magnetic field hinders the fluidʼs motion and leads to rise in temperature that eventually lowers heat transfer rate from the surface. Further, decrease in heat transfer rate is also observed for enhanced values of thermal radiation parameter. To validate our results, a comparison with already published paper in limiting case is also given and results are found in excellent oncurrence; hence reliable results are being presented.

Flow Structure and Heat Transfer of Jet Impingement on a Rib-Roughened Flat Plate

The jet impingement technique is an effective method to achieve a high heat transfer rate and is widely used in industry. Enhancing the heat transfer rate even minimally will improve the performance of many engineering systems and applications. In this numerical study, the convective heat transfer process between orthogonal air jet impingement on a smooth, horizontal surface and a roughened uniformly heated flat plate is studied. The roughness element takes the form of a circular rib of square cross-section positioned at different radii around the stagnation point. At each location, the effect of the roughness element on heat transfer rate was simulated for six different heights and the optimum rib location and rib dimension determined. The average Nusselt number has been evaluated within and beyond the stagnation region to better quantify the heat transfer advantages of ribbed surfaces over smooth surfaces. The results showed both flow and heat transfer features vary significantly with rib dimension and location on the heated surface. This variation in the streamwise direction included both augmentation and decrease in heat transfer rate when compared to the baseline no-rib case. The enhancement in normalized averaged Nusselt number obtained by placing the rib at the most optimum radial location R/D = 2 was 15.6% compared to the baseline case. It was also found that the maximum average Nusselt number for each location was achieved when the rib height was close to the corresponding boundary layer thickness of the smooth surface at the same rib position.

Change of flow structure and heat transfer performance of photosensitive micellar solutions with light irradiation

Heat transfer enhancement in the low Reynolds number condition is increasingly required with the perpetual attempt to integrate and miniaturize electronic devices. The authors have suggested the application of photo-rheological fluid, whose rheological properties change by external photic stimulus, to a coolant of small heat exchangers. High heat transfer state and low pressured drop state can be switched by light irradiation to the fluid according to the demand for heat transfer enhancement. This study investigated how the change of viscoelasticity of photosensitive micellar solutions by light irradiation relates to flow structure and heat transfer performance. Flow visualization and heat transfer measurement were conducted using an aqueous solution of surfactant and counterions (cetyl-trimethyl-ammonium bromide/sodium salicylate/ortho-methoxy cinnamic acid) with different light irradiation time in serpentine channels. The results showed that the decrease of the viscoelasticity with light irradiation caused the decrease in heat transfer rate and pressure drop. In the flow visualization, two types of secondary vortex, i.e., a single large-scaled vortex and a pair of counter-rotating vortices, were observed. As the light irradiation time increased, flow unsteadiness diminished, and the frequency in the appearance of a single vortex and fast flow near wall decreased. The decrease in heat transfer rate and pressure drop with light irradiation was ascribed to the deterioration of fluid mixing by flow unsteadiness, the reduction of momentum and thermal diffusion by the decrease in near-wall velocity gradient, and the decrease in the strength of a pair of vortices.

Stability analysis on the flow and heat transfer of nanofluid past a stretching/shrinking cylinder with suction effect

Abstract The steady boundary layer flow over a stretching/shrinking cylinder with suction effect is numerically studied. Using a similarity transformations, the governing partial differential equations are transformed into a set of nonlinear differential equations and have been solved numerically using a bvp4c code in Matlab software. The nanofluid model used is taking into account the effects of Brownian motion and thermophoresis. The influences of the governing parameters namely the curvature parameter γ, mass suction parameter S, Brownian motion parameter Nb and thermophoresis parameter Nt on the flow, heat and mass transfers characteristics are presented graphically. The numerical results obtained for the skin friction coefficient, local Nusselt number and local Sherwood number are thoroughly determined and presented graphically for several values of the governing parameters. From our investigation, it is found that the non-unique (dual) solutions exist for a certain range of mass suction parameter. It is observed that as curvature parameter increases, the skin friction coefficient and heat transfer rate decrease, meanwhile the mass transfer rates increase. Moreover, the stability analysis showed that the first solution is linearly stable, while the second solution is linearly unstable.

Numerical investigation of the effects of fin shape, antifreeze and nanoparticles on the performance of compact finned-tube heat exchangers for automobile radiator

In this paper, heat transfer and pressure drop of air in the radiator of an internal combustion engine automobile were investigated. First, three types of fins including louvered, triangular vortex generator and rectangular vortex generator were modeled and their performance were compared with a plain fin. Effects of adding antifreeze in volume ratios of 40, 50 and 60% on the performance of louvered and rectangular vortex generator fins were investigated. Finally, the effects of adding copper oxide and aluminum oxide nanoparticles on the heat transfer improvement of louvered and rectangular vortex generator fins were simulated. The results demonstrated that louvered fin had the highest heat transfer rate compared to the other fins and improved it up to 24.6% in comparison with plain fin; however, its air side pressure drop increased 67.7%. Adding antifreeze resulted in a decrease in heat transfer rate. For example, heat transfer rate decreased for louvered and rectangular vortex generator fins at 60% vol. antifreeze, 12.9 and 11.8% compared to pure water, respectively. Also, adding copper oxide and aluminum oxide nanoparticles improved heat transfer rate and compensated harmful effects of antifreeze and it increased heat transfer rate in comparison with pure water.

Study on ammonia/water hybrid absorption/compression heat pump cycle to produce high temperature process water

The objectives of this paper are to analyze the heat transfer characteristics during the ammonia water absorption process for the hybrid absorption/compression heat pump system application. The hybrid absorption/compression heat pump cycle aims at obtaining the high temperature process water. The parametric analysis on the effects of each key parameter, which are system high-pressure, ammonia weak solution concentration, ammonia weak solution and vapor flow rates is carried out. It is found that the increases in the high pressure and ammonia weak solution flow rate have positive effects on the absorber heat transfer rate, whereas the increase in the weak solution concentration does negative effect. It is also found that the weak solution concentration acts as the most important parameter to obtain the high temperature process water. As the weak solution concentration increases, the absorber heat transfer rate decreases, but the system COP tends to increase. It is concluded that the concentration of the weak solution should be maintained at approximately 0.40–0.45, the flow rate of the weak solution be lower than 0.03 kg/s, and the high-pressure be higher than 1700 kPa to obtain process water of higher than 80 °C.

Entransy analysis on boiler air pre-heater with multi-stage LHS unit

Boiler air pre-heater with multi-stage LHS unit is investigated with entransy analysis. Optimum melting temperature match is derived. It is concluded that optimum melting temperature decreases alongside flow direction of flue gas. Optimum melting temperature at inlet increases with stage number, while that at outlet decreases. Temperature difference of PCMs in two nearby portions is the same but decreases with stage number. Entransy dissipation in LHS unit is compared with that in LHS unit. It is concluded that normalized entransy dissipation is not always reduced in LHS unit in the whole period, due to the decrease of heat transfer rate in SHS unit. However, entransy dissipation is always reduced in LHS unit, except single-stage unit, when heat storage amount is constrained. Reduction degree increases with stage number. Therefore, air pre-heater with multi-stage LHS unit is favored for recovery of waste heat in flue gas and improvement of boiler efficiency.

Effects of particles deposition on thermal performance of a convective-radiative heat sink porous fin of an electronic component

The advent of high-power electronic system components and slim margin errors require the proper understanding of particle deposition characteristics and its effects on the thermal performance of electronic heat sinks of electronic devices. In this work, we investigate the effects of particle deposition on the thermal performance of convective-radiative porous fin heat sink of an electronic component using Chebyshev spectral collocation method. The numerical solutions from the developed thermal models are also used to study the influence of thermal conductivity, porosity, convection, and radiation parameter on the temperature distribution and overall fin efficiency. The analysis establishes that presence of particles or thermal fouling on the surface of the fin increases the temperature distribution and temperature uniformity of the fin whilst decreasing the heat transfer rate from the fin. The study also establishes that decrease in heat transfer rate from the fin is due to the particle deposition on the fin, which depends on the particle size, particle density and cooling air flow rate. Moreover, the fin efficiency decreases with an increasing value of the fouled Biot, Darcy and radiation numbers, and thermo-geometric parameter. The study further shows that the efficiency of the fouled porous fin is always greater than the efficiency of the clean porous fin. The analysis established that the result of Chebyshev spectral collocation method is in good agreement with that of the convectional numerical method using Runge-Kutta coupled with shooting method.

Motion of Williamson Fluid over an Upper Horizontal Surface of a Paraboloid of Revolution due to Partial Slip and Buoyancy: Boundary Layer Analysis

In this article, the motion of a non-Newtonian visco-inelastic fluid over an object that is neither a cone/wedge nor horizontal/vertical is presented. It is assumed that partial slip and buoyancy induces the flow of Williamson fluid over this kind of object herein referred to as an upper horizontal surface of a paraboloid of revolution. Considering the relationship between the thicknesses of the object and velocity index; the relevance of partial slip at the leading edge is significant and illustrated in this article. The governing equation which models the flow is non-dimensionalized and parameterized. The corresponding dimensionless equations are solved numerically using shooting technique along with fourth order Runge-Kutta integration scheme. Due to the presence of partial slip and thermal jump, increase in horizontal velocity at the wall is ascertained. The decrease in local heat transfer rate is ascertained within large interval next to the surface of a paraboloid of revolution in the absence of partial slip and thermal jump. A significant decrease in temperature distribution near the surface of an upper horizontal surface of a paraboloid of revolution is guaranteed with an increase in thermal buoyancy parameter in the presence of thermal jump.

A numerical investigation on the heat and fluid flow of various nanofluids on a stretching sheet

AbstractFollowing the necessity of investigating fluid flow and heat transfer in the stretching sheet problem and effect of nanofluids on them, performance of various nanofluids were investigated in the present study. Three base fluids (deionized water, ethylene glycol, and engine oil) in combination with 18 nanoparticles (metals and their oxides) were investigated. While experimental methods are preferable, a mathematical model was developed and solved by applying differential quadrature method due to lack of such experimental data. With the results obtained in the real dimensions, the error caused by the cancellation of the viscosity effect due to the dimensionless variables was omitted. Effects of magnetic field and volume fraction of nanoparticle on the fluid flow and heat transfer characteristics were investigated. Highest heat transfer rate as well as small amounts of shear stress was obtained for deionized water–Al and deionized water–Mg nanofluids. Increasing volume fraction of nanoparticle was observed to increase both heat transfer and shear stress rates, while presence of a magnetic field caused an increase in shear stress and decrease in heat transfer rate.

Three-dimensional transient numerical study on latent heat thermal storage for waste heat recovery from a low temperature gas flow

We propose a latent heat thermal storage (LHTS) system to recover the waste thermal energy from a low temperature gas flow. Paraffin wax is selected as the phase change materials (PCMs) for energy storage. To analyze the performance of LHTS during the heat recovery process, a numerical tool is developed. The time-dependent mathematical model is built in fully three-dimensional (3D) on the basis of the incompressible Navier-Stokes equations. The multi-physical fields including the laminar flow, heat transfer and phase change process are simulated simultaneously across the Air-Aluminum-PCM domains. Natural convection effect is considered and evaluated when the solid PCM melts to the liquid state. The heat transfer characteristics and mechanisms with phase change evolving are performed by the 3D simulations. Compared with the two-dimensional model, the 3D modeling provides more accurate phase change evolution in space. In a duration of 4-h waste heat recovery process, about 2239kJ thermal energy is collected by the LHTS units, and 52.48% of them is stored in the latent heat form with only an 8°C temperature rise. By comparing with the experimental results, a good agreement is observed on the evolution of temperature and heat transfer rate. Parametric studies on the flow rate and heater power input have also been conducted. When the flow rate increases by varying the fan speed from 25, 30 to 45 RPM under a fixed power input of 2kW, the melting rate of PCMs becomes slower as the heat transfer rate decreases; while increasing the heater power under a fixed fan speed input can be helpful for the PCM melting. The presented 3D numerical model manages to predict the performance of the LHTS units for the waste heat recovery.

CVFEM for influence of external magnetic source on Fe3O4-H2O nanofluid behavior in a permeable cavity considering shape effect

This research is made to show the impact of external magnetic source on Fe3O4 – water nanofluid treatment in a permeable cavity. Shape factor effect on nanofluid properties are taken into account. Final equations are derived by means of vorticity stream function formulation. Control volume based finite element method is employed for solving final formulae. Figures are depicted for various values of radiation parameter, Darcy number, Fe3O4 –water volume fraction, Rayleigh number and Hartmann number. Results reveal that selecting Platelet shaped nanoparticles results the highest heat transfer rate. Nanofluid velocity and heat transfer rate decrease with augment of Hartmann number.

Local heat transfer distribution on a flat plate impinged by a swirling jet generated by a twisted tape

An experimental investigation is conducted to study the local heat transfer distribution on a flat surface normally impinged by a swirling air jet. Twisted tapes of twist ratios equal to 2, 3.2, 4.5 and 7.5 (corresponding swirl numbers S = 0.79, 0.49, 0.35, 0.21) are inserted in a circular tube to generate swirling effect. Experiments are carried out for Reynolds number varying from 500 to 3000 for jet to plate spacing varying from 1 to 4. The local heat transfer characteristics are estimated using thermal images obtained by thermal infrared imaging technique. The jet flow profile on the target plate is evaluated by the flow visualisation carried out using lamp black technique. The heat transfer rate is found to initially increase with the increase in twist ratio (or decrease in swirl number) from 2 to 4.5 and thereafter it reduces with the increase in the twist ratio from 4.5 to 7.5. The heat transfer rate is maximum for a twist ratio of 4.5 and minimum for a twist ratio of 7.5. The jet to plate spacing also shows strong influence on the heat transfer rate. With the increase in jet to plate spacing, the heat transfer rate decreases. The maximum heat transfer rate is obtained at z/d = 1 for the different twist ratios and Reynolds number.

Effect of viscous dissipation and suction/injection on MHD nanofluid flow over a wedge with porous medium and slip

The purpose of present study is to identify the effects of viscous dissipation and suction/injection on MHD flow of a nanofluid past a wedge with convective surface in the appearance of slip flow and porous medium. The basic non-linear PDEs of flow and energy are altered into a set of non-linear ODEs using auxiliary similarity transformations. The system of equations together with coupled boundary conditions have been solved numerically by applying Runge-Kutta-Fehlberg procedure via shooting scheme. The influence of relevant parameters on non-dimensional velocity and temperature profiles are depicted graphically and investigated in detail. The results elucidate that as enhance in the Eckert number, the skin friction coefficient increases, while heat transfer rate decreases. The outcomes also specify that thermal boundary layer thickness declines with an increase in suction parameter. Moreover, it is accelerated with augment in injection parameter. The results are analogized with the study published earlier and it creates a fine concord.

Numerical study of natural convection heat transfer in a heat exchanger filled with nanofluids

Natural convection of nanofluids around several pairs of hot and cold cylinders in an adiabatic enclosure is investigated numerically. Hot and cold cylinders are maintained at the different constant temperatures (Th > Tc) while the walls of the enclosure are thermally insulated. A parametric study is undertaken to explore the effects of the pertinent parameters, such as; Rayleigh number, size and type of the nanoparticles, shape of the enclosure, orientation and number of the hot and cold cylinders on the fluid flow and heat transfer characteristic. The simulations show that at low Ra, by changing shape of the enclosure from square to triangular one, the heat transfer rate decreases. It is also found that at each Ra, there is an optimum volume fraction of nanoparticles (ϕopt) where the heat transfer rate within the enclosure has a maximum value. Moreover, the results of this study showed by altering orientation of the hot and cold cylinders from horizontal to vertical mode, the heat transfer rate enhances. Finally, the results indicated that, by decreasing the size of the nanoparticles, the heat transfer rate and optimal particle loading (ϕopt) enhances.