Estimation of heat flux and temperature distributions in a composite strip and homogeneous foundation

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent heat flux and temperature distributions for the system composed of a multi-layer composite strip and semi-infinite foundation, from the knowledge of temperature measurements taken within the strip. It is assumed that no prior information is available on the functional form of the unknown heat flux; hence the procedure is classified as the function estimation in inverse calculation. Results show that an excellent estimation on the time-dependent heat flux can be obtained for the test case considered in this study.     

Inverse problem of estimating time-dependent heat generation in a frictional heated strip and foundation

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent frictional heat generation for the tribosystem consisting of a semi-infinite foundation and a plane-parallel strip sliding over its surface, from the knowledge of temperature measurements taken within the foundation. It is assumed that no prior information is available on the functional form of the unknown heat generation; hence the procedure is classified as the function estimation in inverse calculation. Results show that an excellent estimation on the time-dependent heat generation can be obtained for the test case considered in this study. The current methodology can be applied to the prediction of heat generation in engineering problems involving sliding-contact elements.     

Estimation of Heat Flux and Thermal Stresses in Functionally Graded Hollow Circular Cylinders

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent heat flux at the inner surface of a functionally graded hollow circular cylinder from the knowledge of temperature measurements taken within the cylinder. Subsequently, the distributions of temperature and thermal stresses in the cylinder can be determined as well. It is assumed that no prior information is available on the functional form of the unknown heat flux; hence the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors in these measurements upon the precision of the estimated results is also considered. Results show that an excellent estimation on the time-dependent heat flux, temperature distributions, and thermal stresses can be obtained for the test case considered in this study.     

Numerical heat transfer analyses of a wavy-laminar falling film using moving curvilinear coordinates

In most processes using water film, surface instabilities can be found at the free surface. This work focuses on analyzing their influence on wall heat flux. This is a coupled phenomenon whose full solution would be computationally intensive, so a simplified method is developed. The interface of the film is predicted using an algorithm based on statistical data measurements and the velocity profile is supposed auto-similar to that of Nusselt. The problem is solved numerically using a moving mesh fitted to the shape of the interface. The subsequent statistical analysis highlighted the relative importance of height fluctuations on wall heat flux.     

Inverse Thermo-Mechanical Analysis of a Functionally Graded Fin

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent base heat flux of a functionally graded fin from the knowledge of temperature measurements taken within the fin. Subsequently, the distributions of temperature and thermal stresses in the fin can be determined as well. It is assumed that no prior information is available on the functional form of the unknown base heat flux; hence the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The influence of measurement errors and measurement location upon the precision of the estimated results is also investigated. Results show that an excellent estimation on the time-dependent base heat flux, temperature distributions, and thermal stresses can be obtained for the test case considered in this study.     

Estimation of thermal contact resistance and temperature distributions in the pad/disc tribosystem

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent thermal contact resistance for the tribosystem consisting of a semi-infinite foundation (disc) and a plane-parallel strip (pad) sliding over its surface, from the knowledge of temperature measurements taken within the foundation. Subsequently, the temperature distributions in the medium can be determined as well. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the measurement errors upon the precision of the estimated results is also considered. Results show that an excellent estimation on the time-dependent thermal contact resistance can be obtained for the test case considered in this study. The current methodology can be applied to the prediction of thermal contact resistance in engineering problems involving sliding-contact elements.     

Estimation of the time-dependent heat flux using the temperature distribution at a point by conjugate gradient method

In this paper, the conjugate gradient method coupled with adjoint problem is used in order to solve the inverse heat conduction problem and estimation of the time-dependent heat flux using the temperature distribution at a point. Also, the effects of noisy data and position of measured temperature on final solution are studied. The numerical solution of the governing equations is obtained by employing a finite-difference technique. For solving this problem the general coordinate method is used. We solve the inverse heat conduction problem of estimating the transient heat flux, applied on part of the boundary of an irregular region. The irregular region in the physical domain (r,z) is transformed into a rectangle in the computational domain (ξ,η). The present formulation is general and can be applied to the solution of boundary inverse heat conduction problems over any region that can be mapped into a rectangle. The obtained results for few selected examples show the good accuracy of the presented method. Also the solutions have good stability even if the input data includes noise and that the results are nearly independent of sensor position.     

Inverse estimation of boundary conditions on radiant enclosures by temperature measurement on a solid object

In this paper, we present an inverse analysis to estimate the thermal boundary conditions over a two-dimensional radiant enclosure from the knowledge of the measured temperatures for some points on a solid object within the enclosure. The conduction heat transfer in the solid object and the radiative heat transfer between the surface elements of the enclosure are formulated by the finite volume method and the net radiative method, respectively. The resultant set of nonlinear equations is solved by the Newton's method. The inverse problem for estimation of boundary conditions over the radiant enclosure is solved by the conjugate gradient method.     

Solution of inverse heat conduction problem using the lattice Boltzmann method

In this paper the D2Q9 lattice Boltzmann method (LBM) was utilized for the solution of a two-dimensional inverse heat conduction (IHCP) problem. The accuracy of the LBM results was validated against those obtained from prevalent numerical methods using a common benchmark problem. The conjugate gradient method was used in order to estimate the heat flux test case. A complete error analysis was performed. As the LBM is attuned to parallel computations, its use is recommended in conjugation with IHCP solution methods.     

Simultaneous measurement of local film thickness and temperature distribution in wavy liquid films using a luminescence technique

Heat transfer in falling liquid film systems is enhanced by waviness. Comprehension of the underlying kinetic phenomena requires experimental data of the temperature field with high spatiotemporal resolution. Therefore a non-invasive measuring method based on luminescence indicators is developed. It is used to determine the temperature distribution and the local film thickness simultaneously. First results are presented for the temperature distribution measurement in a laminar-wavy water film with a liquid side Reynolds number of 126 flowing down a heated plane with an inclination angle of 2°. The measured temperature distributions are used to calculate the local heat transfer coefficient and the convective heat flux perpendicular to the wall for different points in the development of a solitary wave.     

Study of transition from laminar to turbulent boundary layer on a tilted flat plate using heat transfer measurements

The boundary layer transition over a flat tilted plate has been studied by means of heat transfer measurements.Aheat flux sensor has been developed,in order to measure the efficiency of convective heat transfer for varioustypes of surfaces or flows.Its operation at constant temperature allows direct and fast measurements of heat flux.The present paper reports the development of the sensor and presents its application to the study of transition in aboundary layer depending on the angle of incidence of the external flow.An exponential relationship betweencritical Reynolds number and pressure gradient parameter has been found.     

An iterative regularization method in estimating the transient heat-transfer rate on the surface of the insulation layer of a double circular pipe

In this study, a conjugate gradient method based inverse algorithm is applied to estimate the unknown space- and time-dependent heat-transfer rate on the surface of the insulation layer of a double circular pipe heat exchanger using temperature measurements. It is assumed that no prior information is available on the functional form of the unknown heat-transfer rate; hence the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The accuracy of the inverse analysis is examined by using simulated exact and inexact temperature measurements. Results show that an excellent estimation on the space- and time-dependent heat-transfer rate can be obtained for the test case considered in this study.     

Inverse Radiation Problem of Boundary Incident Radiation Heat Flux in Semitransparent Planar Slab with Semitransparent Boundaries

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An inverse problem of parameter estimation for heat and mass transfer in capillary porous media

This work deals with the solution of an inverse problem of parameter estimation involving heat and mass transfer in capillary porous media, as described by the dimensionless linear Luikov’s equations. The physical problem under picture involves the drying of a moist porous one-dimensional medium. The main objective of this paper is to simultaneously estimate the dimensionless parameters appearing in the formulation of the physical problem by using transient temperature and moisture content measurements taken inside the medium. The inverse problem is solved by using the Levenberg-Marquardt method of minimization of the least-squares norm with simulated measurements.     

Study of the steady and transient temperature field and heat flow in the combustion chamber components of a medium speed diesel engine using finite element analyses

The present work describes the development of a model for the calculation of the temperature field and heat flow in the combustion chamber components of internal combustion piston engines, which occur both under steady and transient engine operating conditions. Two and three-dimensional finite-element analyses were implemented for the representation of the complex geometry metal components (piston, liner and cylinder head). The model is applied for the piston and liner of a medium speed diesel engine, for which relevant experimental data exist in the literature. Special care is given for accurately specifying the thermal boundary conditions (temperatures and heat transfer coefficients). Gas side boundary conditions are calculated using a thermodynamic cycle simulation code, including spatial variation of the gas side heat transfer coefficient. Coolant sides (water on the external liner surface and oil on the piston undercrown surface) boundary conditions are calculated using correlations pertaining to real engine conditions. Also an effort is made to model the piston-ring belt-liner complex thermal paths using equivalent thermal circuits. A satisfactory degree of agreement is found between theoretical predictions and experimental measurements, revealing that the finite-element methods presented are successful in formulating this kind of problem, giving accurate results with reasonable computational cost. The utilization of the model reveals very clearly the essential role of engine operating transients (sudden changes in speed and/or load) in the generation of sharp temperature excursions in the metal components until a new steady state is reached. The phenomenon should be taken into account for correct engine design and safe operation (i.e. the avoidance of high local stresses).     

Numerical and experimental analysis of chemical dehydration, heat and mass transfers in a concrete hollow cylinder submitted to high temperatures

This paper presents a thermo-hydro-chemical model for concrete at high temperatures. Non-linear phenomena, heat and mass transfers, evolution of the phases constituting the porous medium are taken into account in a full three phases coupled analysis. The proposed model does not take into account mechanical aspects, i.e. the solid skeleton is considered as rigid. An experimental set-up and a numerical simulation are also presented. A hollow cylinder has been heated up to 523.15 K (250 °C) on the internal side and submitted to gas pressure/temperature measurements. A numerical simulation of the cylinder has been performed, showing a good correlation with the experimental observations.