A novel numerical method for steady-state thermal simulation based on loop-tree and HBRWG basis functions

Abstract

This article presents a novel numerical method for steady-state thermal simulation. This method firstly solves the heat flux efficiently by applying the loop-tree basis functions. Then, the temperature is obtained by finding solutions of the gradient equation. The half boundary Rao-Wilton-Glisson (HBRWG) basis functions are employed for handling arbitrary boundary conditions. In addition, the triangulation-based interpolation technique is utilized to interpolate temperature profile with obtained results in post-processing. Three examples with mixed boundary conditions are studied to validate the accuracy of proposed method for simulating steady-state thermal problems. Numerical results show that our method has a good accuracy and is well capable of handling arbitrary boundary conditions.     

Nonlinear analysis of dual-phase lag bio-heat model in living tissues induced by laser irradiation

Abstract

This paper provides a method for determining a numerical solution of the thermal damage of living tissues using a nonlinear dual phase lag model. Due to the nonlinearity of the basic equations, the finite element approach is adopted to solve such problems. The numerical outcomes obtained by the finite element technique are also compared with the existing experimental study to verify the accuracy of the numerical calculations. Based on the formulation of Arrhenius, the thermal damages to the tissues are estimated by the denatured protein range. Numerical results for temperatures are presented graphically. Also, the comparisons between the numerical outcomes and the existing experimental data show that the present mathematical models are effective tools to evaluate the bioheat transfer in a spherical living tissue.     

Novel approach of thermal modeling of partially dry–wet chilled water cooling coil under unit and nonunit Lewis number conditions

ABSTRACT

The main objective of this work is to present a new modeling approach of thermal performance and design of partially dry–wet cooling coils working under unit or nonunit Lewis number conditions. The innovative model is presented as a new simplified and practical correlation that interrelates the cooling coil effectiveness (ε) with its number of transfer unit, and vice versa. The simplified model was constructed on a basis of solving the heat and mass transfer equation “enthalpy potential method” simultaneously coupled with the thermodynamics equations. The validity of the new correlations was tested through predictions of its thermal performance. The output results of those correlations show satisfactory agreement with those obtained from the referenced data with deviation of less than 10%. The main feature of this novel correlation is its simplicity and easiness in calculation by knowing input Lewis number and some other key parameters. Also, the main benefit of this new model is to provide helpful guidelines for optimization of fully wet or partially dry–wet cooling coils’ performance and developing suitable control strategies to achieve higher thermal behavior of the cooling coil during its operation.     

Thermal performances of enhanced smooth and spiky twisted tapes for laminar and turbulent tubular flows

This experimental study investigates the heat transfer properties over developing and developed flow regimes, the pressure drop coefficients and the thermal performance factors (TPF) of tubular flows with the continuous and spiky twist tapes enhanced by perforated, jagged and notched winglets. The axial distributions of Nusselt number (Nu) and the mean Fanning friction factors (f) of the tubular flows at Reynolds numbers (Re) ranging from 500 to 40000 are comparatively examined for five different types of twisted tapes with three twist ratios (y) of 1.875, 2.186 and 2.815 for each type of twisted tapes. Through this comparative study, the favorable types of twisted tapes which generate the higher degrees of HTE impacts over the developing and developed flow regimes are respectively identified. These newly devised twist tapes enrich the varieties of passive heat transfer enhancement (HTE) devices, especially for retrofit applications. A set of selective Nu and f results illustrates the thermal characteristics of the enhanced tubular flows by these twisted tapes. The HTE and TPF properties for all the present types of twisted tapes are subsequently compared with those reported for other types of twisted tapes in the literature. Among these comparative groups, the present V-notched spiky twisted tape generally offers the highest HTE impacts with favorable TPF performances. Empirical correlations that evaluate the averaged Nu over the developing and developed flow regimes; as well as and tube-wise averaged f for the enhanced tubular flows fitted with all the present types of twisted tapes are generated.     

NUMERICAL ALGORITHM FOR ESTIMATING TEMPERATURE-DEPENDENT THERMAL CONDUCTIVITY

Abstract

The hybrid scheme of the Laplace transform technique and the central difference approximation is applied to estimate the temperature-dependent thermal conductivity by utilizing temperature measurements inside the material at an arbitrary specified time. In the present study the functional form of the thermal conductivity is not known a priori. Thus, this problem can be regarded as the functional estimation in inverse calculation. The accuracy of the predicted results is examined from various illustrated cases using simulated exact and inexact temperature measurements obtained within the medium. Results show that a good estimation on the thermal conductivity can be obtained with any arbitrary initial guesses of the thermal conductivity. The advantage of the present method in the inverse analysis is that, for most types of boundary conditions, the relation between the thermal conductivity and temperature at any specified time can be determined without measuring the early temperature data.     

Heat Transfer and Fluid Flow Optimization of Titanium Dioxide–Water Nanofluids in a Turbulent Flow Regime

Abstract

In this study, the convection heat transfer and pressure drop of titanium dioxide–water nanofluids were modeled by applying the fuzzy C-means adaptive neuro-fuzzy inference system approach for a completely developed turbulent flow based on experimentally obtained training and test datasets. Two models were proposed based on the effective parameters; one model was developed for the Nusselt number considering the effects of the Reynolds number, Prandtl number, nanofluid volume concentration and average nanoparticle diameter. Another model was suggested for the pressure drop of the nanofluid as a function of the Reynolds number, nanofluid volume concentration, and average nanoparticle diameter. The results of these two proposed models were compared with experimental data as well as the existing correlations in the literature. The validity of the proposed models was benchmarked by statistical criteria. Moreover, a modified non-dominated sorting genetic algorithm multiobjective optimization technique was applied to obtain the optimum design points, and the final result was shown in a Pareto front.     

Prediction of CO2 Solubility in Oil and the Effects on the Oil Physical Properties

Abstract

CO₂ solubility in oil is a key parameter in CO₂ flooding process. It results in oil swelling, increased oil density, and decreased oil viscosity. Laboratory studies needed to cover a wider range of data, and are time consuming, costly, and may be not available or possible in many situations. On the other hand, although various models and correlations are useful in certain situations, they may are not be applicable in many situations.

In this study, a new genetic algorithm- (GA)-based technique has been used to develop more reliable correlations to predict CO₂ solubility, oil swelling factor (SF), CO₂-oil density, and viscosity of CO₂-oil mixtures. Based on the Darwinian theory, the GA technique mimics some of the natural process mechanisms. Furthermore, GA-based model correlations recognize all the major parameters that affect each physical property and also well address the effects of CO₂ liquefaction pressure.

Genetic algorithm-based correlations have been successfully validated with published experimental data. In addition, a comparison of these correlations has been made against widely used correlations in the literature. It has been noted that the GA-based correlations yield more accurate predictions with lower errors than all other correlations tested. Furthermore, unlike other correlations that are applicable to limited data ranges and conditions, GA-based correlations have been validated over a wider range of data.     

A Versatile Computer Simulation Model for Rotary Regenerative Heat Exchangers

A simulation technique for predicting the thermal performance of rotary regenerative heat exchangers, in particular those used for heating the intake air to power station boilers, has been developed and verified by means of site measurements. Various geometries of both rotating-hood and rotating-matrix types of air heaters can be accommodated in the simulation model, including packings of corrugated steel plates of various specified profiles and any given thicknesses and lengths in the flow direction. Rotational speed, leakage, blockage, and non-uniform inlet flow distribution may be taken into account as input variables. The heat transfer and pressure drop correlations for the various plates considered, which also form part of the input data, were determined experimentally using a single-blow transient test facility, constructed as part of this research program. The effect of erosion of the plates by fly ash particles carried in the outlet flue gas on heat transfer performance is also considered, and experimental results show that erosion has little effect on the thermal performance (up to the point that structural integrity is about to be compromised), but also that the pressure drop is reduced.     

ON A REFINED HEAT CONDUCTION THEORY FOR MICROPERIODIC LAYERED SOLIDS

Abstract

A refined averaged theory of a rigid heat conductor with a microperiodic structure is used to solve a one-dimensional initial boundary value problem of heat conduction in a periodically layered plate with a large number of homogeneous isotropic layers. In such a theory, the temperature θ = θ(x,t) (0 ≤ x ≤ L, t ≥ 0)is approximated by θ(x,t) = θ₀(x,t) + η(x)θ₁(x,t) where θ₀(x,t) is a temperature-corrector and η = η(x) is a prescribed microshape function; and the functions θ₀ = θ₀(x,t) and θ₁ = theta;₁(x,t) are to be found by solving an initial-boundary value problem described by a system of linear partial differential equations with averaged coefficients subject to suitable initial and boundary conditions. A uniqueness theorem for the averaged problem is proved and two closed-form solutions for a periodically layered semispace are obtained. One of the two solutions represents the temperature field in the layered semispace due to a sudden heating of the boundary plane, while the other stands for the temperature field in the layered semispace produced by laser surface heating. Numerical examples are included.     

Thermal buckling and postbuckling responses of geometrically imperfect FG porous beams based on physical neutral plane

Abstract

Considering the third-order shear deformation and physical neutral plane theories, thermal postbuckling analysis for functionally graded (FG) porous beam are performed in this research. The cases of shear deformable functionally graded materials (FGM) beams with initial deflection and uniformly distributed porosity are considered. Geometrically imperfect FG porous beams with two different types of immovable boundary conditions as clamped–rolling and clamped–clamped are analyzed. Thermomechanical nonhomogeneous material properties of the FG porous beam are assumed to be temperature and position dependent. FG porous beams are subjected to different types of thermal loads as heat conduction and uniform temperature rise. Heat conduction equation is solved analytically using the polynomial series solution for the one-dimensional condition. The governing equilibrium equations are obtained by applying the virtual displacement principle. Assuming von Kármán type of geometrical nonlinearity, equilibrium equations are nonlinear and are solved using an analytical method. A two-step perturbation technique is used to obtain the thermal buckling and postbuckling responses of FG porous beams. The numerical results are compared with the case of perfect FGM Timoshenko beams without porosity distribution based on the midplane formulation. Parametric studies of the perfect/imperfect FG porous beams for two types of thermal loading and boundary conditions are provided.     

Experimental study for the enhancement of heat transfer characteristics and development of thermal correlations of a roughened solar collector

The thermal performance of the flat plate solar collector is very low. The most beneficial and worthwhile method for increasing the thermal performance of a solar-powered air heater (SPAH) is to include a roughness element in the working zone of heat transfer that is located beneath the shear layer of the absorber surface. In this research work, efforts are made to enhance thermal performance and develop thermal correlations for the estimation of the Nusselt number and friction factor of a roughened SPAH. Experiments are performed for various ranges of flow, Reynolds numbers, and roughness parameters. The experimental technique of liquid crystal thermography is utilized to assess the dispersal of Nusselt number over the roughened surface for all roughness parameters. A maximum thermal performance enhancement index of 2.69 is obtained with the optimum value of the roughness parameter at a relative roughness pitch (RRP) of 9, a relative staggering distance (RSD) of 4, and a relative roughness length (RRL) of 6.15. Second, a mathematical correlation is developed using a regression model to estimate the Nusselt number and friction factor in terms of nondimensional roughness and flow parameters operated as RRP, RSD, RRL, and Re. The degree of discrepancy between the established the relationships and the findings from the experiment reveals incredibly satisfying results. Hence employing twisted V-ribs as an artificial roughness element no doubt increases the Nusselt number, and thermohydraulic performance enhancement index, but it also exerts less frictional power across the SPAH duct.     

Optimization of microchannel-based cooling systems

Abstract

In this article, microchannel systems for cooling applications such as in the thermal management of electronic equipment are investigated and optimized. Numerical simulations are carried out to study the conjugate heat transfer and flow behavior. The numerical model has been validated by comparing with analytical results. Two sets of design variables are evaluated: (Set I) Incoming flow rate and the number of channels and (Set II) Incoming flow rate and heat flux input. Response surfaces are used to represent the thermal and fluid behavior in the microchannel systems. Based on the polynomial response surface (PRS) modeling results, a multi-objective optimization problem is formulated to reduce both pumping power and thermal resistance. Two major practical concerns, hot-spot temperature and pressure difference, serve as optimization constraints. With varying weights on the two conflicting objectives, Pareto frontiers are obtained. It is also shown that an optimal configuration exists under pressure and temperature constraints. This study provides a feasible design domain and optimal solutions for microchannel-based cooling systems. The optimization process can also be applied to different applications of similar thermal systems.     

Neural-Network-Assisted Optimization of Rectangular Channels with Intersecting Ribs for Enhanced Thermal Performance

Abstract

Optimization of rectangular cooling channels with intersecting ribs was performed to determine optimal rib configurations for thermal performance enhancement using Reynolds averaged Navier-stokes equations at Reynolds number of 10,000. The study aims to achieve two-fold objectives: (1) to maximize the thermal performance in three different rectangular channels with aspect ratios equal to 1, 2, and 4, respectively at a fixed hydraulic diameter and (2) analyze the trend in optimum design variables with change in aspect ratio. Angle of attack, position of the intersecting rib relative to channel center-line, and height of rib were selected as design variables for optimization. The objective function viz. thermal efficiency was formulated using radial basis neural network and particle swam optimization was used to determine the optimal point. The thermal performance of the channel was found to be sensitive to the chosen design variables, and strongly governed by rib-induced secondary motion. As a result of optimization, the optimal design showed an enhancement of 14.4, 12.8, and 16.2% in overall thermal efficiency for channels with aspect ratios 1, 2, and 4, respectively. Finally, to achieve maximum thermal efficiency, shift in optimum design variables was observed with change in aspect ratios of rectangular channels.     

Thermoelastic analysis of laminated composite and sandwich shells considering the effects of transverse shear and normal deformations

Abstract

In the present study, thermoelastic analysis of laminated composite and sandwich shells (cylindrical/spherical) is presented using fifth-order shear and normal deformation theory. The significant characteristic of the present theory is that it includes the effects of both transverse shear and normal deformations. The mathematical formulation uses the principle of virtual work to derive the variationally consistent governing equations and traction free boundary conditions. To obtain the static solution, these governing equations are solved by employing Navier’s solution technique. The shell is subjected to a mechanical/thermal load sinusoidally distributed over the top surface of the shell. The thermal load linearly varies across the thickness of the shell. The present results are compared with other higher-order models and 3D elasticity solution wherever possible. Thermal stresses presented in this study will act as a benchmark for the future work.     

Thermoelastic Analysis of an Annulus Using the Green-Naghdi Model

ABSTRACT

The linear theory of thermoelasticity of Green-Naghdi (GN) types II and III for homogeneous and isotropic materials are employed to study the thermal and mechanical waves in an annulus domain. The disturbances are generated by sudden application of temperature to the boundary. The nondimensional form of the governing equations are solved utilizing the Laplace transform method. Locally transversal linearization (LTL) technique, and a numerical inverse Laplace transform method are used to obtain the temperature, displacement, and stress fields in the physical time domain. The thermomechanical wave propagation and reflection from the boundary are investigated and the influence of the damping parameter on temperature, displacement, and stress fields in the Green-Naghdi type III is discussed.     

Conjugate heat transfer measurements with single-phase and water flow boiling in a single-side heated monoblock flow channel

Optimized and robust designs of one-side heated plasma-facing components and other heat flux removal components are dependent on conjugate heat transfer. In the present case, the conjugate heat transfer involved measuring the local distributions of the inside wall temperature and heat flux in a single-side heated monoblock flow channel with: (1) peripheral (radial and circumferential) heat transfer; and, (2) coupled internal turbulent, forced convective single-phase flow and flow boiling. For the first time, multi-dimensional boiling curves have been measured for a single-side heated monoblock flow channel. Using a thermal hydraulic diameter as the characteristic dimension in select correlations for the highest mass velocity (3.2 Mg/m² s), good agreement was obtained. At lower mass velocities, only the single-phase correlations agreed better with the data for the averaged net incident heat flux vs the inside channel wall temperature. Hence, additional correlation development and adaptation are needed for single-side heated monoblocks with peripheral heat transfer.     

Influence of moving heat source on skin tissue in the context of two-temperature memory-dependent heat transport law

Abstract

Modeling and understanding heat transport and temperature variations within biological tissues and body organs are key issues in medical thermal therapeutic applications, such as hyperthermia cancer treatment. In the present analysis, the bioheat equation is studied in the context of memory responses. The heat transport equation for this problem involving the memory-dependent derivative (MDD) on a slipping interval in the context of three-phase (3P) lag model under two-temperature theory is formulated and is then used to study the thermal damage within the skin tissue during the thermal therapy. Laplace transform technique is implemented to solve the governing equations. The influences of the MDD and moving heat source velocity on the temperature of skin tissues are precisely investigated. The numerical inversion of the Laplace transform is carried out using Zakian method. The numerical outcomes of temperatures are represented graphically. Excellent predictive capability is demonstrated for identification of an appropriate procedure to select different kernel functions to reach effective heating in hyperthermia treatment. Significant effect of thermal therapy is reported due to the effect of delay time and the velocity of moving heat source as well.     

Thermal-shock problem for a hollow cylinder via a multi-dual-phase-lag theory

Abstract

An exact solution of a thermal shock for a circular cylinder is presented. A refined multi-dual-phase-lag generalized thermoelasticity model is proposed. The application of initial conditions without using Laplace transform is effected. The exact solutions of main physical fields are obtained analytically in the radial direction using the normal mode technique. For the case where the mechanical and thermal loads are applied on the inner and outer surfaces of the cylinder. Numerical results for the distributions of radial displacement, temperature, radial, hoop, and axial stresses are illustrated graphically. Extensive results are tabulated to show the accuracy of the present model. The results will also be used as benchmarks for forthcoming comparisons with other investigations. The results indicate that the effects of internal and external pressures and time are very pronounced.     

Thermal Decomposition Behaviors of Lignite by Pyrolysis-FTIR

An in situ pyrolysis reactor combined with the Fourier transformation infrared spectrometer (PFTIR) technique is employed to study the coal structure and its thermal decomposition behaviors. The interface of pyroprobe with FTIR was designed delicately to ensure the path of the laser beam in FTIR was just 3 mm above the coal sample, so any detection information of products from coal pyrolysis would be acquired previous to the secondary reaction. The PFTIR technique can be adopted to determine the activation energy of coal pyrolysis. Lignite coal has been used to evaluate this new method. The thermal decomposition behaviors of functional groups from lignite pyrolysis coincide with the first-order reaction.     

Expressions for absorptance of the cover plates with/without an absorbing surface

Expressions are obtained for calculating the fraction of insolation absorbed by each plate of a cover system for solar thermal devices having n non-identical plates in the presence/absence of an absorbing surface below the cover system. The average angle of incidence, averaged over 277 clear days of 1974, is obtained for the absorbing surface and for a cover system having one, two or three plates.