Nusselt Number Distributions Research Articles

Heat transfer and vibration response of a stationary cylinder and an elastic cylinder under mutual interference

Flow-induced vibration (FIV) of bluff bodies is an important safety-related issue in heat exchange equipment. The interaction of oscillation and heat exchange of two circular cylinders in staggered arrangement was numerically investigated. One cylinder (S-cyl.) is stationary and another cylinder (V-cyl.) undergoes FIV in the transverse flow direction. The influences of the spacing (S) and staggered angle (φ) of the two cylinders on the FIV response, near-wake structure, Nusselt number, and temperature distribution were studied. The results show that when the φ and S increase, the vortex pattern undergoes the following changes: double-row vortex street, 2S → S + P → 2S, three-row vortex street. As the staggered angle raises, the amplitude of V-cyl. firstly reduces to the lowest value, then increases and finally decreases. The maximum amplitude 0.79D is obtained when φ = 45° and S/D = 1.5 for the V-cyl. For the S-cyl., the local Nusselt number (NuL) generally peaks near the front stagnation point, and the main difference in the distribution of NuL can be observed around the back stagnation point. The averaged Nusselt number (NuA) of two cylinders rises as φ changes from 0° to 45° for S/D = 1.5. The maximum NuA increases by 54%. The change trends of NuA for the V-cly. with staggered angle are similar for S/D > 1.5.

THERMAL ANALYSIS OF LAMINAR WATER FLOW OVER A BACKWARD FACING CHANNEL WITH CARBON NANOPARTICLES

In the last few years, the thermo-hydraulic simulation of nanofluid flow bifurcation phenomena has become of great interest to researchers and a useful tool in many engineering applications. FVM has been employed in this article to numerically explore the laminar water flow over a backward facing channel with or without carbon nanoparticles (CN). The problem formulated in this paper has been solved by considering the effects of nanoparticle weight percentages (𝑤%), such as 0.00, 0.12, and 0.25 for different Reynolds number (𝑅𝑒). Nusselt number distribution (𝑁𝑢(𝑥)), coefficient of skin friction (𝐶𝑓), characteristics of pressure drop (Δ𝑝), velocity contours, static temperature, pumping power (𝑃𝑝) and thermal resistance factor (𝑅) have been investigated to know the behavior of thermo-hydraulic flow bifurcation phenomena. The present study shows that the surface temperature and coefficient of heat transfer can be reduced due to the effect of 𝑅𝑒 or w%. For different w%, it has been found that in the rise in the values of 𝑅𝑒 causes the increase of vortex length and as a result velocity gradient and Δ𝑝 arises. Furthermore, it has also been studied that the enhancement of 𝑅𝑒 causes the increaseof 𝑃𝑝 and Δ𝑝.

Intensification of heat transfer behind the backward-facing step using tabs

The influence of tab size and location on the flow structure, distribution of pressures on the surface, and heat transfer in the separation region behind the backward-facing step at Reynolds number Re = 4000 was experimentally investigated. The effect of tabs on the distribution of the local pressure and heat transfer coefficients in the longitudinal and transversal directions was studied. The presence of tabs significantly intensifies the heat transfer directly behind the separation point and brings the region of maximum heat transfer closer to the step. There is a strong uneven distribution of pressure coefficients and Nusselt numbers in the transverse direction due to the formation of vortical wake. The results of measurements are compared with the case of using two-dimensional obstacles in the form of solid ribs; the features of the development of the flow and heat transfer behind 3D tabs are analyzed. It is shown that the main difference in the installation of two-dimensional and three-dimensional obstacles is observed mainly in the immediate vicinity of the flow separation point at X/H < 6.

Analysis of conjugate Marangoni natural convection in a heating system with an open boundary flow

Marangoni natural convection involved in a heating system with an open boundary layer flow has been numerically analyzed in this article. An isoflux heater is placed below a steel pan (material: AISI 4340 steel) which is partially/fully filled with water to make this model more realistic. The surrounding of this pan has a two-dimensional air domain including a water-air interface. Hence, the air domain has three open boundaries within the computational domain. Conjugate natural convection heat transfer takes place from the solid pan to water and then air, whereas Marangoni convection is facilitated at the water-air interface. Two-dimensional, unsteady Navier-Stokes and energy equations are considered as the governing equations, and those are solved with the help of finite element method. Rayleigh number is varied in the range of laminar regime from 6 × 104 to 3 × 107 as the governing parameter under different water level conditions. Thermal and flow fields are visualized qualitatively, whereas quantitative distributions of average Nusselt numbers are taken for further analysis. Finally, the exergy of the system is inspected in terms of total entropy generation at individual flow domains. Here, overall heat transfer performance shows a strong dependency on the change of Rayleigh number.

Molecular Interaction and Magnetic Dipole Effects on Fully Developed Nanofluid Flowing via a Vertical Duct Applying Finite Volume Methodology

Interpreting the complex interaction of nanostructured fluid flow with a dipole in a duct, with peripherally uniform temperature distribution, is the main focus of the current work. This paper also sheds light on the changes in the Nusselt number, temperature profiles, and velocity distributions for the fully developed nanofluid flow in a vertical rectangular duct due to a dipole placed near a corner of the duct. A finite volume approach has been incorporated for the numerical study of the problem. It is interesting to note the unusually lower values of the Nusselt number for the higher values of the ratio Gr/Re. Due to the nanostructure in the fluid, an enhancement in the Nusselt number has been noted, which is strongly supported by the magnetic field caused by the dipole. However, as the duct shape is transformed from rectangular to square, the Nusselt number is reduced remarkably. Further, as the dipole is brought nearer to the duct corner, the Nusselt number increases significantly. On the other hand, the flow reversal in the middle of the duct has been noted at higher values of the ratio Gr/Re. The dipole is noted to have a low impact on the reversal flow as well as on the temperature distribution.

Heat transfer characteristics of jet impingement onto the concave surface of a cone

ABSTRACT Heat transfer coefficient measurements for jet impingement onto the concave surface of a cone with apex angles equal to 30° and 70° are reported in this study. Static pressure measurements along the cone surface are also reported which aid in explaining the results from the heat transfer measurements. The conical geometry finds application for the heating of aircraft gas turbine engine nose bullet region which could experience ice formation whenever aircraft operates at higher altitudes. The concave surface of the cone is heated by impinging hot air tapped from the compressor. The heat transfer coefficients, which are significantly different compared to flat surface impingement, and are scarcely available, are reported in this study. The influence of the jet axis coincident with the cone axis and impinging into apex region was studied first. The methodology where a thin stainless-steel foil is heated with a known heat flux by passing electric current through it and then measuring the detailed surface temperature using an infrared thermal camera, was used to compute the wall Nusselt distribution. The Nusselt number variation is presented as a function of nondimensional apex to nozzle spacing (L/D) and the nondimensional axis displacement (O/D). Three different diameter (D equal to 10 mm,14 mm and 20 mm) pipes were used for the concentric impingement case and the Nusselt number distribution was observed not depend on the injection diameter. The jet Reynolds number was varied between 25000 and 82000. The peak Nusselt number values are similar to those for flat plate impingement and do not occur at the cone apex, but at a nondimensional distance between 3.2 and 3.9 for 4.25 < L/D < 10.25 for the 30° cone. The peak Nusselt number values increase by almost 30% with decrease in the L/D from 10.2 to 3.0. Wall static pressure measurements indicated that the peak Nusselt number values occur in regions where the interaction between the incoming and outgoing streams is strongest – these regions occur at distances downstream from the stagnation region toward cone exit. The peak heat transfer coefficient location could not be obtained for the 70° cone, but the measured maximum values are higher by 30–50% compared to those for the 30° case. The jet is able to penetrate further toward the apex of the cone for 70° cone compared to 30° cone shifting the peak heat transfer locations closer to the apex for larger apex angle case. There is insignificant influence of jet diameter on Nusselt number variation for the three diameter values investigated in this study. The influence of displacing the jet axis by a distance equal to half the jet diameter in a direction perpendicular to the cone axis was also studied but detailed measurements were possible only for the 30° cone. Two semi-circular regions, one close to the impingement tube and the other away from the tube, displaying similar heat transfer coefficient behavior were observed. A peak in the Nusselt number occurs in each semi-circular region and the magnitude of the peaks are nearly same and they lie on either side of the peak location observed for the concentric impingement case when the flow geometric parameters are similar for the two cases. The measurements for the 70° cone exhibited all features of the 30° cone but the maximum values were higher by nearly 40% for this case.

Heat transfer and flow structure characteristics of film-cooled leading edge model with sweeping and normal jets

The heat transfer and flow structure characteristics of a film-cooled leading edge model with sweeping and normal jets were numerically investigated using the conjugate heat transfer method. The leading edge model is a simplified obtuse body model that has three rows of traditional cylindrical film holes, each with three holes inclined at 25° with respect to the surface and three angles oriented at 0° and ± 30° with respect to the axial direction. A normal jet has one row of cylindrical impingement nozzles, and a sweeping jet has only one fluidic oscillator. Three blowing ratios (M = 1.05, 2.07, and 4.11) and three temperature ratios (TR = 0.5, 0.625, and 0.75) are considered in the study. The shear stress transport k–ω turbulence model and an extremely fine structured grid were validated and applied to all simulations. The results indicate that the total pressure loss coefficient and heat transfer performance increase internally and externally, respectively, with the blowing ratio. However, they are insensitive to the temperature ratio in all cooling configurations. The sweeping jet and film (SJF) composite cooling exhibits 1.6162, 2.1195, and 2.1766 times the total pressure loss coefficient of the normal jet and film composite cooling when the blowing ratio increases from 1.05 to 4.11. However, the SJF offers the advantages of uniform Nusselt number distribution on the impinging surface and high overall cooling effectiveness on the external surface.

Impact of inclination on the thermal performance of shell and tube latent heat storage system under simultaneous charging and discharging: Numerical investigation

In this paper, the impact of inclination on the thermal performance of latent heat storage system (LHSS) based cylindrical shell and tube heat exchanger is investigated. During the simultaneous charging and discharging (SCD) process, a visualized numerical simulation is carried out to demonstrate the melting process of phase change material (PCM). The SCD technique for the LHSS comprises charging of PCM from one side while discharging from the other. To investigate the performance of the LHSS, a transient numerical model based on the enthalpy-porosity method is used. The distribution of temperature, melt fraction, energy stored, and average Nusselt number are analyzed to study the effect of natural convection on the performance of LHSS with inclination angles viz. 90° (vertical) 60°, 30° and 0° (horizontal). Results illustrate that better thermal performance is provided by the horizontal (0°) configuration. The effect of natural convection on the PCM under the SCD melting process has differed with the angle of inclination. The position of cold heat transfer fluid (HTF) showed a considerable influence on the process of melting. With the decrease of inclination angle from 90° to 0°; there is an increase in melt fraction by 38.02 %. The maximum energy stored (231 kJ) obtained at the horizontal (0°) configuration is 26.2 % higher than the vertical position. Also, the steady-state condition is observed earlier in the horizontal position. Further, the flow behavior of PCM with inclination is also illustrated.

Effects of the swirl number, Reynolds number and nozzle-to-plate distance on impingement heat transfer from swirling jets

This paper reports on a parametric study of the impingement heat transfer from swirling jets issuing from a circular nozzle. The swirl velocity component is imparted to the flow via a tangential entry into a recirculation chamber located upstream of the nozzle; the degree of swirl is varied by changing the angle of the channels leading to the chamber with respect to the radial direction. The effects of the dimensionless impingement distance (H/D=1, 2, 3, 4, 6, 8, 10, 12, 14 with D being the nozzle diameter), the swirl number (S=0, 0.078, 0.22, 0.37, 0.54) and the Reynolds number (Re=20,800, 31,100, 41,500) on the spatial distribution of the heat transfer are investigated by means of infrared thermography and the heated thin foil sensor. The present results show that the swirl number and the impingement distance significantly influence the structure of the heat transfer distribution, while the Reynolds number affects essentially the magnitude. Four distinct ranges with different behaviours can be identified by distinguishing between weakly or non swirling jets (0≤S≤0.22) and moderately swirling jets (0.37≤S≤0.54) and between short and long impingement distances (1≤H/D≤4 and 6≤H/D≤14 respectively). A comparative assessment of the performance of the swirling jets is carried out by focusing on the area-averaged Nusselt number distributions. It is found that in the range of short impingement distances and over relatively small target areas an enhancement of the heat transfer rates can be obtained at a small extent by adding a weak swirl with no detrimental effect on the uniformity of the distribution and at a larger extent by a moderate swirl with a deterioration of the uniformity. For long impingement distances no enhancement is observed, although swirl yields a significant reduction of the non-uniformity. Finally, correlation laws of the area-averaged Nusselt number as a function of the control parameters are derived in the four regimes identified.

Combined effects of particle shape, incident angle and porosity on momentum and heat transfer between spheroids and fluids

• PR-DNS is used to study momentum and heat transfer of porous spheroids under laminar flow . • Effects of particle shape , incident angle, porosity and Reynolds number are quantified. • Novel correlations of Cd and Nu for porous spheroids under laminar flow are established. Particle-resolved direct numerical simulations are carried out to investigate the distribution of drag coefficient ( Cd ) and average Nusselt number ( Nu ) of a porous spheroid in a fluid under different Reynolds number (20≤ Re ≤200), particle shape (aspect ratio, 0.5≤ Ar ≤2.5), incident angle (0°≤ θ ≤90°) and porosity (0.57≤ ε ≤0.94). Through the analysis on the numerical simulation results from 525 study cases, it is found that Cd increases first and then decreases with the increase of Ar for prolate spheroids and this trend is opposite for oblate spheroids. For both prolate and oblate spheroids, it is found that Nu decreases first and then increases with the increase of Ar. Under higher Reynolds number (100≤ Re ≤200), the effect of ε on Cd and Nu is noticeable. On the contrary, the effect of ε is almost negligible at low Reynolds number (20≤ Re <100). Numerical results also show that when Ar <1, Cd decreases considerably and Nu decreases slightly with the increase of θ , and this variation trend is opposite when Ar >1. Finally, based on the numerical database, new predictive correlations of Cd and Nu for irregular porous particles in a fluid are established and the accuracy is assured by comparing the prediction results and the numerical data. These correlations can be used to improve the macroscopic multiphase models such as two-fluid model and coupled computational fluid dynamics and discrete element method.

Modeling of heat transfer in a narrow rectangular channel with partial swelling blockage

In plate-fuel-assembly reactor cores, owing to the cladding swelling caused by irradiation damage under high burnup conditions, narrow rectangular channels may be partially blocked. The partial blockage will alter the flow channel shape and affect the heat transfer characteristics. Thus, it is important to focus on the flow and heat transfer characteristics under partial blockage conditions. Accordingly, in this study, the heat transfer at the entrance region of a narrow rectangular channel with protrusions is numerically investigated. Further, variations in the local Nusselt number and fluid field distribution are studied. Results reveal that the protrusions lead to a wake effect that influences the local heat transfer in the blockage region and wake zones. At the upwind face of the protrusions, the local heat transfer increases to a crest value over the hydraulic diameter. A low-speed recirculation region is also formed over a short distance at the intermediate leeward face of the protrusion, resulting in local deterioration of the heat transfer. Moreover, in the wake zone, heat transfer is enhanced owing to the disturbance of the flow streams with different velocities. The effects of the blockage ratio, number, and interval of protrusions on the local heat transfer are also analyzed. This augmentation of the heat transfer decreases with an increase in the Reynolds number, whereas it increases with the height ratio of the protrusions. Additionally, a multiple regression analysis method is employed to analyze the numerical simulation data. Based on these numerical investigations, dimensionless correlations are proposed to estimate the local Nusselt number for rectangular channels with and without partial swelling blockages. The predicted results are in good agreement with the experimental data and reference correlations. For Eqs. (20) and (22), the major points are located within the relative deviation limit of ± 15%, while for Eq. (21), all the data points fall within the relative deviation limit of ± 20%. Comparison results indicate that the correlations can be used to understand the heat transfer upstream and downstream of partial blockages. Furthermore, numerical investigations and qualitative analyses of the effect of spare protrusions on the local heat transfer in the wake area are performed. These spare protrusions lead to local heat transfer deterioration in the wake zone; notably, the spacing between these protrusions does not have a significant influence on the augmentation of the heat transfer downstream.

Simulation of flow structure and heat transfer of sweeping jet and film composite cooling on a flat plate

Numerical simulation was performed to investigate the heat transfer characteristics of sweeping jet and film cooling along with the representative flow characteristics on a flat plate. The SST k-ω turbulence model was employed for a fluidic oscillator with 20 cylindrical film holes at four different nozzle Reynolds numbers and four different inclination angles. Time-resolved flow field and time-averaged heat transfer analyses considering the thermal convection and conduction by the coupling of fluid and solid domains are presented. The results show that the total pressure loss coefficient of the sweeping jet is larger than that of the normal jet, especially when the nozzle Reynolds numbers are relatively higher. In all cases, the Nusselt number and overall cooling effectiveness monotonically increased with the increase in the nozzle Reynolds numbers and decrease in inclination angle. However, the Nusselt number distribution on the impinging surface is insensitive to the inclination angle of the film holes. Compared with the normal jet and film composite cooling, sweeping jet and film composite cooling (SJF) has a more spatially uniform heat removal rate, and the area-averaged Nusselt number and overall cooling effectiveness are higher. Therefore, the SJF is preferred to improve the utilization rate of the coolant and to make the distribution of the flat wall heat transfer more uniform. However, the impinging distance of the fluidic oscillator should be further optimized to improve the impingement cooling effectiveness and the total pressure loss coefficient.

Computational Analysis of MHD Nonlinear Radiation Casson Hybrid Nanofluid Flow at Vertical Stretching Sheet

The stagnation point flow of unsteady compressible Casson hybrid nanofluid flow over a vertical stretching sheet was analyzed. The comparative study of Yamada Ota, Tiwari Das, and Xue hybrid nanofluid models was performed. The Lorentz force was applied normal to flow directions. The effect of nonlinear radiation was studied. We considered the SWCNT (signal wall carbon nanotube) and MWCNT (multi-wall carbon nanotube) with base liquid (water). Under the flow suppositions, a mathematical model was settled by means of boundary layer approximations in terms of partial differential equations. The suitable transformation was developed by using the lie symmetry method. Partial differential equations were transformed into ordinary differential equations by suitable transformations. The dimensionless system was elucidated through a numerical technique named bvp4c. The impacts of pertinent flow parameters on skin friction, Nusselt number, and temperature and velocity distributions were depicted through tabular form as well as graphical form. In this study, the Yamada Ota model achieved a higher heat transfer rate compared to the Tiwari Das and Xue hybrid nanofluid models. The skin friction (CfxRe−1/2) increased and temperature gradient (NuxRe−1/2) declined due to the increment of solid nanoparticle concentration (ϕ2). Physically, skin friction increased because the higher values of the solid nanoparticles increased resistance to the fluid motion.

Heat and Mass Transfer of Micropolar-Casson Nanofluid over Vertical Variable Stretching Riga Sheet

In this analysis, we considered a comparative study of micropolar Casson nanofluid flow on a vertical nonlinear Riga stretching sheet. Effects of thermal and velocity slip are considered under thermophoresis and Brownian motions. Select nonlinear PDEs transformed into nonlinear coupled ODEs using the set of suitable transformations. The nonlinear coupled ODEs are solved through a numerical technique along with the Runge–Kutta 4th-order scheme. The impacts of pertinent flow parameters on skin friction, Nusselt number, temperature, and velocity distributions are depicted through tabular and graphical form. Brownian motion and the magnitude of the Sherwood number have opposite performances; likewise, the Nusselt number and Brownian motion also have opposite performances. The Sherwood number and Nusselt number succeeded with higher values. The increment of the Casson fluid parameter declined with fluid velocity, which shows that thickness is reduced due to the increment of the Casson fluid parameter. Fluid velocity distribution curves show increasing behavior due to increments of the micropolar parameter.

Improving a rotating steel milling tool cooling by an air jet impingement flow

Turbulent jets impacting flat or curved surfaces have been the subject of several research reports in the literature over the past decades, and it is all about the improvement of localized heat and/or mass transfer in part of a system, to achieve this goal, it is necessary to understand the dynamic behavior of the fluid and its effect on local heat and/or mass transfer. The aim of our work is the numerical investigation of a steel milling tool cooling driven in rotation, emitting a heat flux caused by machining a surface, using an impacting cold air jet; Although the technology of cooling the machining tools exists by using liquid jets, it signaled that it is less economical and efficient then using the impinging air jet. The milling tool is cooled using forced convection produced by the air jet at different Reynolds numbers, this phenomenon is governed by the equations of conservation of mass, momentum, and energy. We adopted a mathematical model based on the finite volume method; the calculation code was validated using experimental results available in the literature. We obtained our results by varying the Reynolds number between 12,000 and 26,000 values for an impact distance ratio h/D = 4, and two configurations: one nozzle and two nozzles. Our results showed that when using two cold air jet inlets to cool the milling tool, the distribution of the Nusselt number on the surface is enhanced compared to the one nozzle case, mainly because of the two impact points of the jet on the surface. We also note that increasing the Reynolds number has a significant influence on the distribution of the averaged Nusselt number.

Laminar natural convection in a 2-D pentagonal house with sloping roof heated by constant heat flux

Natural convection in a pentagonal house with a protruding cooler for summer is numerically investigated. The sloping roof is subjected to constant heat flux, and the cooler maintains at a uniform cold temperature. The remaining walls of the house are insulated. Local multi-quadratic radial basis function (LMQRBF) method is applied in solution of Navier–Stokes equations in stream function-vorticity form. The working fluid in the house is air with Pr = 0.71. The effects of Rayleigh number (103 ≤ Ra ≤ 106), heat flux of the roof (0.1 ≤ q ≤ 2.0), and the cooler’s vertical position (0.65 ≤ H/L ≤ 0.85) are explored. Streamlines, isotherms, velocity profiles, and the distribution of Nusselt number are displayed. Numerical results indicate that for the top and right wall of the cooler, the heat transfer is stronger than that for the bottom wall. It reveals that all the governing parameters efficiently impact the generation and evolution of the secondary and tertiary vortex in the gable roof. It is also observed that the variation of average Nusselt number on the right wall with Rayleigh number is under the combined influence of the heat flux and the cooler’s vertical position.

The effect of plate motion on heat transfer enhancement using turbulent offset jet flow: A conjugate approach

The present research is focused on computational analysis of conjugate heat transfer behavior of a turbulent offset jet flow over a moving flat plate in a quiescent environment. The plate of definite thickness and conductivity is subjected to isothermal condition at the plate bottom surface. The computation is carried out with a low-Reynolds number (LRN) turbulence model proposed by Yang and Shih which involves integration to wall (ITW) approach to capture the thin viscous sub-layer region within the boundary layer. The variation of offset ratio (ranging as 3, 7 and 11) and plate velocity (Up = 0 − 2) plays quite a major role in the distribution of interface temperature and Nusselt number. The conduction heat flow rate in solid depends upon the plate thickness ratio (S) which is varied as 0.5 − 1.5 and the conductivity ratio (K) ranging as 500 − 2000. The variation of average Nusselt number gives evidence of better cooling rate for smaller offset ratios and higher plate to jet velocity ratio.

Investigation on heat transfer and flow-induced vibration of three cylinders in equilateral triangle arrangement

Flow-induced vibration (FIV) and heat transfer of three circular cylinders were numerically investigated in the reduced velocity range of 3 ≤ U⁎ ≤ 15. To obtain the vibration and heat transfer characters, the influence of FIV and Richardson number (0 ≤ Ri ≤ 1) on the heat transfer performance are studied. It's found that the rise of Ri can lead to the suppression of FIV and narrow the reduced velocity (U⁎) range of lock-in. The amplitude and lift coefficient of two downstream cylinders are higher than that of 1st cylinder (upstream one) for most of U⁎. The FIV can significantly enhance the heat transfer of 2nd and 3rd cylinders (downstream cylinders), the highest increments of averaged Nusselt number are 9.74% (2nd cylinder) and 9.78% (3rd cylinder), which can be obtained when Ri = 0.5 and U⁎ = 5. Meanwhile, the distribution of local Nusselt number shows that the heat transfer mainly occurs at the upstream side of each oscillator. The heat transfer characteristics on the surface of each cylinder are closely influenced by the thickness of thermal boundary, which determines the gradient of temperature around cylinders.

Numerical investigation of conjugate heat transfer to a turbulent dual offset jet

The present study considers a computational model to simulate conjugate heat transfer to a turbulent dual offset jet from a heated wall having a finite thickness and subjected to a constant wall temperature. To capture the effects of turbulence on the flow and heat transfer, the Reynolds Averaged Navier–Stokes equations (RANS) with the standard k−ε turbulence model have been employed. The convection equation in the flow regime is solved together with the conduction equation in the solid medium iteratively. For the purpose of the analysis, four parameters, namely, the Reynolds number (Re), the thermal conductivity ratio of the solid material and the fluid, the solid wall thickness, and the fluid Prandtl number (Pr), are varied within suitable ranges. The flow field solution exhibits two recirculation zones; the first one is enclosed by the two jets and the other is formed underneath the lower jet. Conjugate heat transfer to the dual offset jet flow is analysed through the distribution of temperature, heat flux, and Nusselt number, at the interface between the fluid and solid regions. Results indicate that the non-dimensional temperature and heat flux profiles along the fluid–solid interface depend on all four parameters. In contrast, the distribution of the Nusselt number along the fluid–solid interface depends only on the Reynolds number and the Prandtl number. Increasing either of them leads to an overall increase in the interface Nusselt number. A correlation for the average Nusselt number along the interface is presented as a function of Re and Pr.

Heat Transfer Due to Annular Jets Impinging on a Moving Surface

Abstract This work investigates flow and heat transfer under an array of annular jets impinging on a heated moving surface. Numerical solutions of the full Navier–Stokes equation were attempted with a highly refined mesh. This study reports results for Reynolds numbers up to 500. In the surface movement direction, a periodic element from a jet-bank configuration was chosen, and the nondimensional surface velocity was considered from zero (i.e., a stationary plate) to two times the jet velocity. The impact of annular jet impingement over a moving surface on flow and heat transfer characteristics, including the development of the flow field, velocity profiles, skin friction coefficient and topology of skin friction lines, and local as well as surface averaged Nusselt number distribution are presented. It is observed that both the flow field and thermal performance are strongly affected by the surface motion. Heat transfer from the surface initially increases with the increasing surface motion, and after attainment of the highest value, heat transfer reduces with a further increase in surface velocity. However, higher surface velocity leads to higher uniformity in heat transfer, which may be beneficial for situations demanding uniformity in heat transfer.