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The purpose of this study is to find the thermo-hydraulic performances of compact heat exchangers (CHE’s), which are strongly depending upon the prediction of performance of various types of heat transfer surfaces such as offset strip fins, wavy fins, rectangular fins, triangular fins, triangular and rectangular perforated fins in terms of Colburn “j” and Fanning friction “f” factors.

Numerical methods play a major role for analysis of compact plate-fin heat exchangers, which are cost-effective and fast. This paper presents the on-going research and work carried out earlier for single-phase steady-state heat transfer and pressure drop analysis on CHE passages and fins. An analysis of a cross-flow plate-fin compact heat exchanger, accounting for the individual effects of two-dimensional longitudinal heat conduction through the exchanger wall, inlet fluid flow maldistribution and inlet temperature non-uniformity are carried out using a Finite Element Method (FEM).

The performance deterioration of high-efficiency cross-flow plate-fin compact heat exchangers have been reviewed with the combined effects of wall longitudinal heat conduction and inlet fluid flow/temperature non-uniformity using a dedicated FEM analysis. It is found that the performance deterioration is quite significant in some typical applications due to the effects of wall longitudinal heat conduction and inlet fluid flow non-uniformity on cross-flow plate-fin heat exchangers. A Computational Fluid Dynamics (CFD) program FLUENT has been used to predict the design data in terms of “j” and “f” factors for plate-fin heat exchanger fins. The suitable design data are generated using CFD analysis covering the laminar, transition and turbulent flow regimes for various types of fins.

The correlations for the friction factor “f” and Colburn factor “j” have been found to be good. The correlations can be used by the heat exchanger designers and can reduce the number of tests and modification of the prototype to a minimum for similar applications and types of fins.

The effect of the tube wall heat conduction on the natural convection in a tilted long cylindrical envelope with constant, but different temperature of the two ends and an adiabatic outer surface was numerically investigated. The envelope is supposed to be a simplified model for the pulse tube in a pulse tube refrigerator when the pulse tube is positioned at different orientations. It is found that the cylindrical envelope lateral wall heat conduction can enhance the heat transfer from the hot end to the cold end, not only because of the increase in pure heat conduction in the wall, but more importantly, also the intensification of the natural convection within the enclosure. This enhancement is resulted from the big temperature difference between the tube wall and the adjacent fluid near the hot and cold ends. Adoption of low thermal conductivity tube can effectively reduce such additional heat transfers from hot to cold end, thus reducing the loss of cooling capacity for the pulse tube refrigerator.

The purpose of this paper is to predict the plate heat exchanger performance when axial conduction in plates and in flow channels are present and fluids' viscosities are temperature dependent.

The approach to achieve the objective of the paper is deriving the governing equations and developing a computer program based on finite differences to solve them. The governing equations become dimensionless defining reference values and then discretized using FTBCS and FTCS methods. To solve the governing equations, the flow channel is divided into small elements in axial direction. Physical properties are constant for each element, while viscosity changes from one element to another one.

The effect of axial conduction in plates as well as in flow channels on temperature distributions, are studied individually and simultaneously. The program is run under four different conditions, namely: no axial conduction, axial conduction in the plates and in the flow channels, axial conduction in the plates only, and axial conduction in the flow channels only.In all the above cases, temperature distributions are achieved and characteristic curves are plotted. The numerical results are validated by comparing them with those published in an established reference carried out ignoring the effect of axial conduction, using the same plate geometry and flow details.

This paper gives valuable information and offers practical help to plate heat exchanger design engineer in order to choose the proper material for the plates as well as the right service and product fluids.

MANY hold the view that the attainment of very high speeds of flight will be prohibited by the excessive skin temperatures involved, particularly in the vicinity of the wing leading edge, at least until that time when unforeseen advances in metallurgy, or in the application of ceramics, enable the extraordinary problems involved to be overcome. As an opinion it may for all one knows be justified by the event, but it seems (at least to the author) to exaggerate the facts, because it surely ignores the important role played by the conduction of heat along the skin in limiting the temperature. It is the intention of the present article to convert others to this way of thinking.

We first provide an overview of some predominant theoretical methods currently used for predicting thermal conductivity of thin dielectric films: the equation of radiative transfer, the temperature‐dependent thermal conductivity theories based on the Callaway model, and the molecular dynamics simulation. This overview also highlights temporal and spatial scale issues by looking at a unified theory that bridges physical issues presented in the Fourier and Cattaneo models. This newly developed unified theory is the so‐called C‐ and F‐processes constitutive model. This model introduces the notion of a new dimensionless heat conduction model number, which is the ratio of the thermal conductivity of the fast heat carrier F‐processes to the total thermal conductivity comprised of both the fast heat carriers F‐processes and the slow heat carriers C‐processes. Illustrative numerical examples for prediction of thermal conductivity in thin films are primarily presented.

The purpose of this paper is to analyze the effect of thermal conductivity on gas turbine blades, and to investigate the contribution of different rib configurations to the heat flux and the film cooling effectiveness.

The Renormalization Group (RNG) model with enhanced wall treatment was used for the turbulence modeling, and the SIMPLE algorithm was used to handle the pressure-velocity coupling.

A flame-shape distribution on the internal wall provides high heat flux compared to a hawk-shape distribution; the film cooling effectiveness on the external wall is enhanced for the lateral film cooling effectiveness by heat conduction and film cooling (convection); by comparing the square-rib and pin-rib configurations, the circular-rib configuration offers a higher film cooling effectiveness on the Aluminum wall.

In the present research, the combination of internal cooling and external cooling is used to predict cooling effectiveness on film-cooled flat plate; two kinds of different plate materials are used to obtain the influence of the thermal conductivity. The successful computational method should give guidelines for potential CFD users in engineering sciences.

The results of the paper are of engineering interest where film cooling and ribbed surfaces are applied. The successful computational method will also serve as guidelines for potential users of CFD in design as well as research and development work.

In the present research, the combination of internal cooling and external cooling is used to predict cooling effectiveness on film-cooled flat plate; two kinds of different plate materials are used to obtain the influence of the thermal conductivity.

The purpose of this paper is to frame a dual-phase-lag model using the fractional theory of thermoelasticity with relaxation time. The generalized Fourier law of heat conduction based upon Tzou model that includes temperature gradient, the thermal displacement and two different translations of heat flux vector and temperature gradient has been used to formulate the heat conduction model. The microstructural interactions and corresponding thermal changes have been studied due to the involvement of relaxation time and delay time translations. This results in achieving the finite speed of thermal wave. Classical coupled and generalized thermoelasticity theories are recovered by considering the various special cases for different order of fractional derivatives and two different translations under consideration.

The work presented in this manuscript proposes a dual-phase-lag mathematical model of a thick circular plate in a finite cylindrical domain subjected to axis-symmetric heat flux. The model has been designed in the context of fractional thermoelasticity by considering two successive terms in Taylor’s series expansion of fractional Fourier law of heat conduction in the two different translations of heat flux vector and temperature gradient. The analytical results have been obtained in Laplace transform domain by transforming the original problem into eigenvalue problem using Hankel and Laplace transforms. The numerical inversions of Laplace transforms have been achieved using the Gaver−Stehfast algorithm, and convergence criterion has been discussed. For illustrative purpose, the dual-phase-lag model proposed in this manuscript has been applied to a periodically varying heat source. The numerical results have been depicted graphically and compared with classical, fractional and generalized thermoelasticity for various fractional orders under consideration.

The microstructural interactions and corresponding thermal changes have been studied due to the involvement of relaxation time and delay time translations. This results in achieving the finite speed of thermal wave. Classical coupled and generalized thermoelasticity theories are recovered by considering the various special cases for different order of fractional derivatives and two different translations under consideration. This model has been applied to study the thermal effects in a thick circular plate subjected to a periodically varying heat source.

A dual-phase-lag model can effectively be incorporated to study the transient heat conduction problems for an exponentially decaying pulse boundary heat flux and/or for a short-pulse boundary heat flux in long solid tubes and cylinders. This model is also applicable to study the various effects of the thermal lag ratio and the shift time. These dual-phase-lag models are also practically applicable in the problems of modeling of nanoscale heat transport problems of semiconductor devices and accordingly semiconductors can be classified as per their ability of heat conduction.

To the authors’ knowledge, no one has discussed fractional thermoelastic dual-phase-lag problem associated with relaxation time in a finite cylindrical domain for a thick circular plate subjected to an axis-symmetric heat source. This is the latest and novel contribution to the field of thermal mechanics.

The study aims to highlight the behaviour of one-dimensional and two-dimensional fin models under the natural room conditions, considering the different values of dimensionless Biot number (Bi). The effect of convection and radiation on the heat transfer process has also been demonstrated using the meshless local Petrov–Galerkin (MLPG) approach.

It is true that MLPG method is time-consuming and expensive in terms of man-hours, as it is in the developing stage, but with the advent of computationally fast new-generation computers, there is a big possibility of the development of MLPG software, which will not only reduce the computational time and cost but also enhance the accuracy and precision in the results. Bi values of 0.01 and 0.10 have been taken for the experimental investigation of one-dimensional and two-dimensional rectangular fin models. The numerical simulation results obtained by the analytical method, benchmark numerical method and the MLPG method for both the models have been compared with that of the experimental investigation results for validation and found to be in good agreement. Performance of the fin has also been demonstrated.

The experimental and numerical investigations have been conducted for one-dimensional and two-dimensional linear and nonlinear fin models of rectangular shape. MLPG is used as a potential numerical method. Effect of radiation is also, implemented successfully. Results are found to be in good agreement with analytical solution, when one-dimensional steady problem is solved; however, two-dimensional results obtained by the MLPG method are compared with that of the finite element method and found that the proposed method is as accurate as the established method. It is also found that for higher Bi, the one-dimensional model is not appropriate, as it does not demonstrate the appreciated error; hence, a two-dimensional model is required to predict the performance of a fin. Radiative fin illustrates more heat transfer than the pure convective fin. The performance parameters show that as the Bi increases, the performance of fin decreases because of high thermal resistance.

Though, best of the efforts have been put to showcase the behaviour of one-dimensional and two-dimensional fins under nonlinear conditions, at different Bi values, yet lot more is to be demonstrated. Nonlinearity, in the present paper, is exhibited by using the thermal and material properties as the function of temperature, but can be further demonstrated with their dependency on the area. Additionally, this paper can be made more elaborative by extending the research for transient problems, with different fin profiles. Natural convection model is adopted in the present study but it can also be studied by using forced convection model.

Fins are the most commonly used medium to enhance heat transfer from a hot primary surface. Heat transfer in its natural condition is nonlinear and hence been demonstrated. The outcome is practically viable, as it is applicable at large to the broad areas like automobile, aerospace and electronic and electrical devices.

As per the literature survey, lot of work has been done on fins using different numerical methods; but to the best of authors’ knowledge, this study is first in the area of nonlinear heat transfer of fins using dimensionless Bi by the truly meshfree MLPG method.

Heat exchangers working in cryogenic temperature ranges are strongly affected by heat ingression from the ambient. This paper aims to investigate the effect of ambient heat-in-leak on the performance of a three-fluid cross-flow cryogenic heat exchanger.

The governing equations are derived for a three-fluid cross-flow cryogenic heat exchanger based on the conservation of energy principle. For given fluid inlet temperatures, the governing equations are solved using the finite element method to obtain exit temperatures of the three-fluid exchanger. The performance of the heat exchanger is determined using effectiveness-number of transfer units (e-NTU) method. In the present analysis, the amount of ambient heat-in-leak to the heat exchanger is accounted by two parameters H_t and H_b. The variation of the heat exchanger effectiveness due to ambient heat-in-leak is analyzed for various non-dimensional parameters defined to study the heat exchanger performance.

The effect of ambient heat in leak to the heat exchanger from the surrounding is to increase the dimensionless exit mean temperature of all three fluids. An increase in heat in leak parameter (H_t = H_b) value from 0 to 0.1 reduces hot fluid effectiveness by 32 per cent for an NTU value of 10.

The effect of heat-in-leak on a three-fluid cross-flow cryogenic heat exchanger is significant, but so far, no investigations are carried out. The results establish the efficacy of the method and throw light on important considerations involved in the design of such heat exchangers.

In this paper, temperature distribution and fin efficiency in a moving porous fin have been discussed. The heat transfer equation is formulated by using Darcy's model. Heat transfer coefficient and thermal conductivity vary with temperature. The surface emissivity of the fin varies with temperature as well as with wavelength. Thermal conductivity is taken as a linear and quadratic form of temperature. The entire analysis of the paper is presented in non-dimensional form.

In this study, a new mathematical model is investigated. The novelty of this model is surface emissivity which is considered temperature and wavelength dependent. Another interesting point is the addition of porous material. The Legendre wavelet collocation method has been used to solve the nonlinear heat transfer equation. Numerical simulations are carried out in MATLAB software.

An attempt has been made to discuss temperature distribution in the presence of porosity and wavelength-temperature-dependent surface emissivity. The effect of various parameters on temperature has been discussed, including thermal conductivity, emissivity, convection-radiation, Peclet number, sink temperature, exponent “n” and porosity. Fin efficiency is also calculated for some parameters. According to the study, heat transfer rate increases with higher radiation-convection, emissivity, wavelength and porosity parameters.

The numerical results are carried out by using the Legendre wavelet collocation method, which has been compared with exact results in a particular case and found to be in good agreement. The percent error is calculated to find the error between the current method and the exact result. A comparison of the obtained results with the previous data is presented to validate the numerical results.