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A van der Waals (vdW) heterostructure, can be used in efficient heat management, due to its promising anisotropic thermal transport feature, with high heat conductance in one direction and low conductance in the rest. A carbon nanotube (CNT) bundle, can be used as one of the most feasible vdW heterostructures in a wide range of nanoscale devices. However, detailed investigations of heat transport in CNT bundles are still lacking. In this paper, we study heat transport in different CNT bundles—homogeneous bundles consisting of the one CNT radius (curvature) and inhomogeneous bundles constructed from different CNTs with different curvatures. We also investigate the comparison between two possible thermostatting configurations: the two ends connected (TEC) case in which there is at least a direct covalently connected path between the hot and cold heat baths, and the one end connected (OEC) case in which the system can be divided at least into two parts, by a vdW interacting interface. Nonequilibrium molecular dynamics simulations have been carried out for a wide range of configurations and curvature differences. We find that, in homogeneous bundles, by increasing the number of outer CNTs, the heat conductance increases. In inhomogeneous bundles, the total heat flux shows dependence on the difference between the curvature of the core and outer CNTs. The less the difference between the curvature of the core and the outer CNTs, the more the thermal conductance in the system. By investigating the spectral heat conductance (SHC) in the system, we found that a larger curvature difference between the core and outer CNTs leads to a considerable decrease in the contribution of 0–10 THz phonons in the bundled zone. These results provide an insightful understanding of the heat transport mechanism in vdW nano-heterostructures, more important for designing nanoelectronic devices as well as systems in which asymmetry plays a significant role.

The heat generated in the process of light-curing may cause irreversible damage to the dental pulp. This study aimed to assess heat transfer in the process of irradiation of a dentin disc by using different modes of quartz-tungsten halogen (QTH) and light-emitting diode (LED) dental curing units. The surface temperature was measured by an infrared (IR) thermometer following light-curing with standard, ramp, boost, and bleaching modes of a QTH curing unit, and high, soft and pulse modes of a LED curing unit. Since the maximum temperature rise alone is not sufficient to study the thermal damage to the pulp tissue, we also assessed the temperature rise profile and heating rate, in addition to the maximum temperature rise in this study. The results showed that decreasing the duration of light-curing effectively decreased the risk of pulpal damage. Shorter radiation modes such as the 10 s standard mode, and the 10 s boost curing mode of the QTH curing unit and the 5 s high mode, and the 10 s pulse mode of the LED curing unit all had the lowest risk of thermal damage to the pulp.

The aim of the present work is to investigate the role of Al2O3/water nanofluid and the geometric parameters of flow in heat transfer, pressure drop and heat exchanger efficiency. By applying periodic conditions, the flow and heat transfer of Al2O3/water nanofluid inside a tube has been investigated at the presence of heat transfer enhancer and under the influence of constant wall temperature. The turbulent flow regime and Reynolds numbers are considered to be in the range of 2000–10,000. Computational fluid dynamics software has been applied to model the governing differential equations using baffles with heights of 2, 4 and 6 mm and pitchs p/d = 0.5, 1, 2 and nanofluid with volume fractions of 1 and 2. The results of numerical modeling show that using rectangular baffle inside the pipe increases heat transfer compared to a simple pipe. As can be seen, adding nanoparticles to the base fluid increases heat transfer and by increasing the volume percentage of the nanofluid, the Nusselt number and heat transfer also increase. Moreover, increasing the volume percentage of nanoparticles from 1 to 2% increases the thermal efficiency in the heat exchanger with and without baffle. As the Reynolds number increases, the heat efficiency coefficient of the baffleless heat exchanger decreases when the Reynolds number is more than 2000. However, in the heat exchanger with baffle, increasing the Reynolds number decreases the thermal efficiency initially and then, for the Reynolds number more than 3500, an increase in thermal efficiency is illustrated. The results of the present study can be used for cooling process and heat transfer in large-scale heat exchangers and integrated circuits.

Precise information regarding the thermal properties of human tooth structure such as its thermal conductivity and diffusivity can increase the accuracy of heat transfer modeling, which has recently gained popularity. Moreover, such information is highly important in the designing and production of dental materials. Since the thermal conductivity and diffusivity of human enamel and dentin can be temperature-dependent, the light flash method was used in the present study to measure the diffusivity of human enamel, sound dentin, and carious dentin. Also, data obtained by differential scanning calorimetry (DSC) were used to measure the specific heat, and then thermal conductivity was calculated. The results revealed that by an increase in temperature, the conductivity of enamel, sound, and carious dentin increased. The conductivity of enamel at 30, 40, and 50°C was 0.81, 1.20, and 1.53W/(m.K) , respectively. These values were 0.44, 0.91, and 1.15 W/(m.K) for sound dentin, and 0.78, 1.01, and 1.33 W/(m.K) for carious dentin, respectively.

The effect of radial flow injection on the heat transfer characteristics of a Taylor–Couette–Poiseuille flow in an annulus is numerically investigated using the SST k-ω turbulence model. Th...

In this study, a two-dimensional inverse algorithm is developed to determine the heat transfer coefficient distribution of a two-phase air–water bubbly jet impinging on a steel cylindrical thermal mass. All procedures of thermal mass heating and cooling are simulated by solving two-dimensional, transient heat conduction equations using finite difference method. Afterward, the nonlinear inverse heat conduction problem is implemented to directly predict the local convective heat transfer coefficient of the bubbly jet. The sum of squared differences between calculated and measured temperature data is the objective function. Conjugate gradient method is employed sequentially in every time step to optimize the objective function at four gas Reynolds numbers which represent four different two-phase jets. The inverse scheme is validated using exact temperature data without noise. Local heat transfer coefficients are then estimated by inverse technique at five data acquisition times and four initial temperatures of thermal mass in the presence of noise. Furthermore, the effects of uncertainties due to indefinite lateral boundary conditions, temperature dependency of thermal conductivity, and the non-uniformity of the initial temperature distribution are investigated. A satisfactory agreement between exact and estimated heat transfer coefficients is achieved. However, the results show a greater sensitivity to the highest value of initial temperature, the shortest data acquisition time, and the lowest gas Reynolds number allowing a better estimation of heat transfer distribution for the bubbly jet.

In this study, the synthetic jet position was optimized to obtain the maximum rate of heat transfer and the best state of temperature uniformity on a heated surface in micro-channels. Based on micro-channel length, several cases were simulated to investigate the effects of synthetic jet position on the heat transfer rate and temperature uniformity. After that, the synthetic jet position was optimized using the CFD results and the GMDH-MOGA optimization code. The obtained results show that the synthetic jet placement in all longitudinal positions of micro-channel increases the heat transfer rate, although the improvement of temperature uniformity of heated surface decreases at some positions as compared to the micro-channel without synthetic jet. The optimization results show that for obtaining the maximum value of heat transfer and the best state of temperature uniformity on the heated surface, the dimensionless longitudinal position of synthetic should be between 0.45 and 0.65. The maximum rate of heat transfer and the best state of temperature uniformity have been observed in the vicinity of lower and upper bounds of this range, respectively.

Finding a general optimum arrangement of the cross-flow staggered tube banks causes a significant decrease in using available energy resources due to their extensive use in industrial applications. This paper presents a numerical optimization study by generalized pattern search algorithm (GPSA) to investigate optimum longitudinal and transverse pitches of the staggered tube banks in turbulent flow regime. Symmetric and periodic boundary conditions are employed to simulate all the tube banks without considering the entire volume. Using these boundary conditions, the optimization process can be directly performed by simulating the flow and heat transfer through tube banks with a CFD code and the previous researchers' correlations are not employed in this process. The “goodness factor” which takes into consideration the effects of both heat transfer and pressure drop simultaneously in a proper order is used as the objective function. In the first part of the study, optimum pitches are calculated for specific inlet Reynolds and Prandtl numbers. Subsequently, the effect of both inlet Reynolds and Prandtl numbers are separately investigated on the optimum pitches in the turbulent regime. Results show that the optimum dimensionless longitudinal and transverse pitches of the staggered tube banks are independent of the inlet Reynolds and Prandtl numbers in the turbulent regime and equal to PL, opt ≅ 1 and PT, opt ≅ 1.3, respectively. As a result, a general compact arrangement for staggered tube banks is proposed that is applicable in practical applications due to its high efficiency and compactness.

In this study, a numerical algorithm is developed to determine the heat transfer coefficient distribution of mixed convection on a vertical plate with a two dimensional inverse method. Cooling procedures of hot plate include forced convection with buoyancy effect is simulated by solving two dimensional, transient heat conduction equation using finite difference method while the Grashof number is varied through natural convection in combination with forced convection resulting in a variation of the Richardson number from 0.1 to 1. The nonlinear inverse heat conduction problem is then implemented to directly predict the time-space-varying convective heat transfer coefficient of cooling in the mixed convection regime. The sum of squared differences between calculated and measured temperature data at thermocouples’ locations is the objective functional. The adjoint method is employed to optimize the functional using conjugate gradient method via the solutions of the direct, adjoint and sensitivity sub-problems in a whole time-domain optimization process. The inverse scheme is validated using exact temperature data without noise. Local heat transfer coefficients are then estimated by the adjoint method at four cooling strategies for ten minutes of data acquisition in the presence of noise with standard deviations of σ = 0.01 °C and σ = 0.1 °C. Although results are affected by noisy simulated temperatures, a satisfactory agreement between exact and estimated heat transfer coefficients is achieved. Furthermore, increasing data acquisition time to sixty minutes reveals that the inverse scheme is able to predict 1200 convective heat transfer coefficient components efficiently employing the rapidly convergent adjoint method.

In this paper, a series of works are conducted to study the effect of replacing natural gas burning heaters by a ground source heat pumps (GSHPs) to prevent natural gas freezing in the pressure reg...

A novel and practical transient-type technique named as “Jet Flush” is proposed for measuring temperature-dependent thermal conductivity of solid materials with low thermal conductivity. In order to estimate thermal conductivity of the sample, its surface is exposed to an impinging air jet flow with higher (or lower) temperature than the sample for a short period of time, while an infrared thermometer records the heated (or cooled) surface temperature history. A nonlinear 1D inverse heat conduction problem with constant convective heat transfer coefficient on the boundary condition is then employed for determining the temperature-dependent thermal conductivity using the measured temperatures. As a requirement for solving the inverse problem, the convective coefficient on the surface of the sample is measured in a separate experiment with the same flow condition using a standard sample. Sensitivity and error analyses are performed to discuss the effects of the estimation points (the temperatures in which the thermal conductivity is to be estimated), and the simplification assumption of constant convective heat transfer coefficient (with respect to time) on the solution of the inverse problem and the accuracy of the estimated results. In order to demonstrate the applicability of the proposed method, the thermal conductivities of three polymer-type materials (HDPE, PMMA and PA6) are measured over the temperature range of ~22–62 °C, and the results are found to be in good agreement with literature data. Moreover, the uncertainty analysis performed in this study showed that the accuracy of the proposed method can be better than 5% for an appreciable temperature range.

Knowledge about the thermal properties of human teeth is imperative for accurate understanding of heat transfer in dentistry. Despite the presence of specific heat in thermal conduction and heat transfer equations, and requiring this parameter for calculation of conductivity based on diffusivity, adequate attention has not been paid to experimental assessment of specific heat of the human enamel and dentin. Specific heat can be a temperature-dependent property. Thus, this study aimed to assess the specific heat of the human enamel, sound dentin, and carious dentin at 20 °C to 70 °C temperature (which is the realizable temperature range in dental procedures) using the differential scanning calorimetry (DSC). The results showed that the specific heat of the enamel, sound dentin and carious dentin increased with temperature rise. The specific heat of the enamel, sound dentin and carious dentin at 20 °C to 70 °C ranged from 709 J·kg−1·K−1 to 921 J·kg−1·K−1, 880 J·kg−1·K−1 to 1139 J·kg−1·K−1 and 951 J·kg−1·K−1 to 1311 J·kg−1·K−1, respectively.

Inverse boundary design problems in surface-to-surface radiation heat transfer occur when both the temperature and net heat flux are prescribed on some of the surfaces while neither is known on the remaining surfaces. The problem is to find the unknown surface temperatures required to produce the prescribed temperatures and net heat fluxes. This chapter presents a novel approach in which a transcendental function of position—in this case a Fourier cosine series—is used to represent the spatial distribution of the unknown fourth power of surface temperature. The problem then becomes one of the findings the Fourier coefficients and fundamental angular frequency that minimize the difference between the prescribed and calculated surface temperature distributions. The approach is shown to produce more accurate results than the classical optimization approach in a fraction of the execution time for the example of an industrial processing oven.

In this study, co-axial impinging jet was optimized in order to obtain uniform heat flux over an isothermal heated surface by determining four design variables including geometrical and flow variables. The governing equations were solved using the finite volume method for a laminar, incompressible, and axisymmetric flow. The solution of inverse design problem was achieved by minimizing the root mean square of the difference between the local Nusselt number and the uniform design Nusselt number. A combination of pattern search and gradient-based methods was used for optimization. Also a co-axial jet with a new geometry was presented to improve the objective function and two design variables were added to the four previous variables. Optimization was performed for two jet configurations under 15 different conditions. Heat flux uniformity was obtained by these two jets with acceptable errors less than 2% for the outer jet to the target surface diameter ratios of higher than 0.6. The proposed co-axial jet showed its superiority at the small diameter ratios (0.4 and 0.3) and it reduced the error significantly (about 50%) for design Nusselt numbers of 7 and 10.

Droplet microfluidic systems have attracted a large amount of research due to their numerous applications in biomedical micro-devices and drug discovery/delivery platforms. One of the most important problems in such systems is to investigate deformation, coalescence, and breakup of droplets within the channel. The present study demonstrates numerical simulation of a falling droplet subject to gravitational force in a channel with embedded rectangular obstacles. The lattice Boltzmann method incorporated using He–Chen–Zhang method for two phase flow is employed. Two rectangular obstacles with inverse aspect ratios are introduced to investigate the mechanism of breakup and deformation of the droplet. The influence of gravity magnitude, viscosity and surface tension on the deformation rate of droplet for two different aspect ratios of the obstacle is studied. It is observed that increasing the gravity force, decreasing the viscosity or surface tension increase droplet deformation rate resulting in more stretched filaments and so breakup occurs in a shorter time.

In this paper, a cylindrical swirl chamber, which can be used on the leading edge of a turbine blade is numerically modeled to investigate the effects of multiple slots at each section of the swirl chamber. The RANS equations are solved using four different turbulence models, and it was found that the SST k − ω model, resulted in the reasonable agreement with the experimental data. Two different chamber types, i.e., swirl chamber (SC) and double swirl chamber (DSC), are considered to be modeled with five different inlet configurations. In all configurations, rectangular inlet slots are located at the beginning and middle sections of the swirl chamber, but the number and direction of inlet slots will change in each configuration. SC and DSC configurations are compared using two different scenarios, where the width of both chamber types are identical in the first scenario and the hydraulic diameters are assumed to be identical in the next one. It is concluded that the comparison according to the identical width is more reasonable in the case of gas turbine blades. Results for the same Reynolds number and coolant mass flow rate confirm that the multiple inlets at each section with proper direction creates stronger vortices, which enhances the Nusselt number by 33% as compared to the base inlet configuration.

In this research paper, a novel Heating, Ventilation, and Air Conditioning (HVAC) system is proposed to mitigate the unfavorable effects of conventional HVAC systems on the Electric Vehicle (EV) range. The HVAC system is composed of a heat pump (HP) system with an additional phase change material (PCM) heat exchanger, which is a shell and tube heat exchanger and is parallel to the external heat exchanger of the heat pump cycle. This heat exchanger is designed to function as both condenser and evaporator in the cycle temporarily. The n-hexadecane is selected as the PCM in the shell, and R134a is the refrigerant in the tubes. The specific melting point of PCM in the comfort zone range leads to diminishing the compressor's power consumption and consequently the whole system. A copper foam is used to enhance the low thermal conductivity of the PCM. The enthalpy-porosity technique with the Volume Averaged Method (VAM) for modeling of the PCM-copper foam is applied for Computational Fluid Dynamics (CFD) analysis of the PCM's melting and solidification cycles in ANSYS Fluent software, and the results are obtained for modeling the heat exchanger in the heat pump cycle. A comprehensive thermal model is developed for the vehicle's cabin to improve the accuracy of the results. Nissan Leaf is modeled as the selected EV at different weather temperatures in the range of −5 °C to 50 °C with the Urban Dynamometer Driving Schedule (UDDS) driving cycle in Simcenter Amesim software. The results show that the proposed system increases the vehicle range by 19% and 11% compared with the conventional heat pump systems at the weather temperatures of 10 °C and 0 °C, respectively. Moreover, the energy consumption of various components in the cold start and hot start are compared and the results are interpreted.

In this paper, the feasibility of a solar absorption refrigeration system to be powered by a latent heat storage (LHS) unit is investigated for a representative building. A single effect absorption chiller, utilizing Li-Br and water as working fluids is thermodynamically simulated. Then, the simulation of the latent heat storage unit is performed by applying finite difference method and the results were validated by the researches in the literature. Then, the geometry of a phase change material (PCM) based LHS system was optimized using multi-objective Genetic Algorithm for simultaneously minimizing the charging time, and maximizing the discharging time. Since the paper considers conflicting objectives, a Pareto front is presented that can be used for obtaining the optimum geometry according to the environmental conditions and working hours of the absorption system. As an illustrative example, the designed heat storage system was shown to be able to drive the 72 kW generator of an absorption system, for at least 10 h of operation in the discharging mode with the absence of sunlight. Therefore, it is possible to run absorption chillers under low-load operation conditions using the solar energy if the appropriate storage unit, such as what is introduced here, is used.

In the thermal radiation analysis via Monte Carlo method, the ray tracing algorithm often consumes a significant fraction of CPU time. As such, an efficient grid traversal algorithm can considerably affect the performance of the Monte Carlo method. This paper presents a new grid traversal acceleration algorithm by merging adjacent small empty voxels in a preprocessing step due to the fact that larger empty space, named “macro-voxel”, allows for traversing a ray over a large distance at a smaller cost. The proposed algorithm is validated theoretically, and the results are examined for a gray box with diffuse surfaces. Timing results of the new algorithm are compared with the USD method in a typical 3D radiation furnace with concave geometry and the speedup ratio of both the macro-voxel algorithm and the USD method with respect to direct method are calculated for an optimal grid of voxels. For the considered geometry, the macro-voxel algorithm is found to be clearly superior to the USD even if the size of the problem is large and the geometry is not convex.

Heat transfer from a pulsating laminar impingement slot jet on a flat surface was investigated numerically and experimentally. Inlet velocity was considered sinusoidal velocity and square wave velo...

In this article, a new hybrid method based on the combination of the genetic algorithm (GA) and artificial neural network (ANN) is developed to optimize the design of three-dimensional (3-D) radiant furnaces. A 3-D irregular shape design body (DB) heated inside a 3-D radiant furnace is considered as a case study. The uniform thermal conditions on the DB surfaces are obtained by minimizing an objective function. An ANN is developed to predict the objective function value which is trained through the data produced by applying the Monte Carlo method. The trained ANN is used in conjunction with the GA to find the optimal design variables. The results show that the computational time using the GA-ANN approach is significantly less than that of the conventional method. It is concluded that the integration of the ANN with GA is an efficient technique for optimization of the radiant furnaces.

The modeling of radiative heat transfer in complex radiant enclosures is a particularly challenging subject. This simulation is often best treated by calculating distribution factors through the Monte Carlo method. In order to enhance performance of the Monte Carlo method, efficient algorithms to find location of emission and direction of emission in the original Monte Carlo method are implemented. Next, the best ray tracing algorithm is introduced by comparing timing results of the USD, the BSP, the Simplex and the VVA acceleration ray tracing algorithms to make it numerically efficient as possible. Also, the constrained maximum likelihood estimation is used to enhance accuracy of the Monte Carlo by smoothing inherent random errors in the estimated distribution factors to simultaneously satisfy both of the reciprocity and summation rules. Accuracy of the Monte Carlo method is tested for a classical problem, namely a 3D box, with diffuse gray walls. For efficiency study, the optimized Monte Carlo method is then tested for two real radiative enclosures with convex and concave geometries. All ray tracing algorithms are found to result in computational gains, with respect to direct calculations that do not employ any acceleration technique. In the considered test cases, the VVA and the USD algorithms are found to be clearly superior to the BSP and the Simplex algorithms, particularly for concave geometries that have some obstructions within the computational domain.

An experimental study on pulsating impingement semi-confined slot jet has been performed. The effect of pulsations frequency was examined for various Reynolds numbers and Nozzle to plate distances. Convective heat transfer coefficient is estimated using the measured temperatures in the target plate and conjugate gradient method with adjoint equation. Heat transfer coefficient in Re 3000), heat transfer coefficient is affected by the pulsation from particular frequency. In this study, the threshold Strouhal number (St) is 0.11. No significant heat transfer enhancement was obtained for St

The numerical solution of the heat equation is a particularly challenging subject in complex, practical applications such as functionally graded materials for which analytical solution is not available or hardly attainable. The Monte Carlo method is a powerful technique with some advantages compared to the conventional methods and is often used when all else fail. In this paper, we introduce the Finite Volume Monte Carlo (FVMC) method for solving 3D steady-state heat equation where, instead of using the usual finite difference scheme for discretization of the heat equation, the finite volume scheme is used. The FVMC method is tested for three problems to assess the robustness of the method, first one in a simple geometry for validation and evaluation of the predictive performance, the second one in a complex geometry with unstructured mesh and the last one in a problem with a variable heat source and different kinds of boundary conditions. Comparisons were made to the analytical solution in the first test case, whereas for the remaining test cases, the CFD methods were utilized in the absence of the analytical solutions. It was observed that the FVMC temperature distribution agrees perfectly with analytical and CFD solutions in all problems. Despite expecting computational accuracy to improve by increasing total number of particles in the FVMC method, a very good accuracy was obtained for all considered problems after a small number of walks, and the calculated relative root-mean-square errors were below 1%.

In this paper for the first time, the Levenberg-Marquardt (LM) algorithm assisted by a fuzzy method is presented to solve an inverse heat transfer problem. Given the importance of the damping factor in the consistency and efficiency of the LM algorithm in solving ill-posed problems, a new method based on fuzzy logic theory is used to adjust the value of the damping factor during the solution iteration step. In order to investigate the convergence speed, stability and robustness of the fuzzy LM algorithm, a one-dimensional heat transfer problem is solved using three different experimental heat fluxes including quadratic polynomial, cubic polynomial, and sine function, and the results are compared with classical LM algorithm. According to the results, the speed and the convergence stability of the solution of an inverse problem for different noisy temperatures are significantly improved by combining fuzzy logic with classical LM algorithm. Also, the new method robustness is comparable with the LM algorithm.

In achieving a regularized solution of inverse heat conduction problems (IHCPs), Tikhonov Regularization works based on adding either a zeroth-, a first-, or a second-order term to the sum of squared errors function. In other words, considering combinations of these terms are not often considered. This work investigates employing standard optimization techniques in order to obtain optimal regularization parameters when combinations of these three regularization terms are used. Five different heat pulses are used as test cases: step, triangular, quadratic, quartic, and half-sine. The criterion used to find the optimal value for the regularization parameters is sum of the squares of deviations between the estimated heat flux and the exact heat flux pulse. A hybrid method which utilizes both the Genetic Algorithm and the Pattern Search is used for the optimization through functions defined in MATLAB software. Moreover, a general case containing all five heat flux test cases is considered in finding the optimal combination of three versions of Tikhonov method. All separate and general optimal combined models are used in estimating five pulse heat flux functions, and for each case, the RMS errors are calculated to give an insight toward the combined Tikhonov regularization technique. The proposed approach is also used to recover the surface heat flux using measured temperature data from an experiment. Some discussion about the Morozov discrepancy principle for this application is considered at the end.

This paper presents the optimal design of a hybrid liquid desiccant-regenerative evaporative air conditioner. A hybrid air conditioner was proposed which comprises a liquid-to-air membrane energy exchanger (LAMEE) as a desiccant dehumidifier and a regenerative heat and mass exchanger (RHMX) as an evaporative cooler. The air conditions across the LAMEE and the RHMX were achieved by two heat and mass transfer sub-models, and validation of the sub-models was conducted by comparison of the simulation results against the published experimental measurements. Intake air flow rate, LAMEE-to-total length ratio and working-to-intake air flow ratio are regarded as design variables. The simplified conjugate gradient method (SCGM) was employed as an optimization scheme to find the optimum set of design variables, which maximizes the room cooling capacity (RCC) of the proposed hybrid air conditioner. The influences of different design and operating conditions on the optimal RCC and the optimum set of design variables were studied.

The purpose of this paper is to present experimental applications of the inverse heat transfer methods (conjugate gradient method and sequential method). Three experiments are designed to estimate the heat ux and the heat transfer coe cients. In the third experiment, convective heat transfer coe cient is estimated directly and indirectly. In direct estimation, the conjugate gradient method with adjoint equation is used. The results show that inverse heat transfer methods are able to estimate the desired parameters with good accuracy in experimental state when mathematical model and boundary condition are correct and appropriate with experimental model.

Recently, increasing heat transfer rate of heat exchangers and reducing their size without experiencing a significant increase in flow resistance has been the main focus of several studies. Through the course of these studies, a wide range of active and passive methods have been implemented. Among these methods, changing the geometry of the heat exchanger tubes has received an increasing attention due to its simplicity and cost-effectiveness. In this study, a new geometry called the alternating flattened tube is introduced and its performance against other widely used tubes is evaluated. To compare the heat transfer, pressure drop, and compactness of the tubes simultaneously, a parameter called tube performance enhancement ratio is introduced. Both experimental and numerical results show that the alternating flattened tube has a better performance enhancement ratio compared to the previously studied tubes and can be an advantageous alternative for the conventional circular tubes.

This paper provides a novel and efficient approach for the simulation-based multi-criteria optimization of the building energy performance. In the current investigation, a multi-objective non-dominated sorting genetic algorithm (NSGA-II) is coupled with EnergyPlus building energy simulation program to obtain optimal solutions leads to increase the building energy performance. The main aim of this work is to explore the effect of some architectural parameters, including the building orientation, the window size and the overhang specifications on the building energy consumption in four major climatic regions of Iran, e.g. cold, mild, warm-dry, and warm-humid. In the optimization section, mono-criterion and bi-criteria optimization analyses of the annual cooling and lighting building energy demands are studied with the purpose of understanding the interactions between these objective functions. The results point out that the bi-criteria optimization of the test case model brings down the annual cooling energy consumption 55.8–76.4% in various climates. However, the annual lighting electricity demand increases 1–4.8%. As a result, the final optimum configuration leads to 23.8–42.2% decrease in the annual total building energy consumption. The results depict that the climate and the appropriate selection of the architectural parameters are very important and critical in reducing the building energy consumption. The proposed optimization methodology is a powerful and useful tool to achieve this goal and to facilitate decision-making in early phases of a building design in order to enhance its energy efficiency.

In this paper, an inverse boundary design problem of combined natural convection-radiation considering specular reflectivity and participating media is solved. The aim of this paper is to find the strength of heaters in a step-like enclosure to produce the desired temperature and heat flux distribution on the design surface. The finite volume method for transition flow (which causes a faster convergence) is used as the direct solver of the energy and momentum equations. The SIMPLE algorithm is utilized to satisfy pressure–velocity coupling in order to solve the free convection heat transfer. Also, the backward Monte Carlo method is employed in order to be able to compute the distribution factors and carry out the radiant exchange calculations. Finally, the goal function which is defined on the basis of square root error is minimized by means of a conjugate gradients method. The effects of variation of specularity ratio for specular surfaces are investigated to compare the results for diffuse and specular surfaces in the enclosure considering radiation and free convection. The effects of variation of range of parameters such as the Rayleigh number, temperature ratio, radiation conduction parameter and the specularity ratio on the relative root mean square and heat flux are investigated and results are compared. The results demonstrate the efficiency and the accuracy of the proposed method.

This article presents the optimal design of a regenerative heat and mass exchanger (RHMX) for indirect evaporative cooling. The room cooling capacity which is the product of the supply air mass flow rate, specific heat of the supply air and the difference between the supply air temperature and the comfort temperature, was considered as a criterion to evaluate the cooling performance of the RHMX. The air conditions throughout the RHMX were obtained by a heat and mass transfer model. The model was validated by comparing the modeled results with the existing experimental data. The simplified conjugate gradient method was used as an optimizer to obtain the optimal performance, and to adjust the design variables, i.e. product air flow rate and working-to-product air flow ratio. The effects of the exchanger’s parameters as well as the inlet air condition on the performance of the optimized RHMX and on the values of the design variables were discussed. It was concluded that the working-to-product air flow ratio is around 0.4 under various climatic and design conditions. Moreover, the channel length and the channel height should be selected between 0.4–0.6 m and 0.004–0.006 m, respectively, to have a high RCC with an acceptable fan power.

This paper proposes an efficient methodology for the simulation-based multi-objective optimization problems, which addresses important limitations for the optimization of the building energy performance. In this work, a mono- and multi-objective particle swarm optimization (MOPSO) algorithm is coupled with EnergyPlus building energy simulation software to find a set of non-dominated solutions to enhance the building energy performance. To evaluate the capability and effectiveness of the approach, the developed method is applied to a single room model, and the effect of building architectural parameters including, the building orientation, the shading overhang specifications, the window size, and the glazing and the wall material properties on the building energy consumption are studied in four major climatic regions of Iran. In the optimization section, mono-criterion and multi-criteria optimization analyses of the annual cooling, heating, and lighting electricity consumption are examined to understand interactions between the objective functions and to minimize the annual total building energy demand. The achieved optimum solutions from the multi-objective optimization process are also reported as Pareto optimal fronts. Finally, the result of multi-criteria minimization is compared with the mono-criterion ones. The results of the triple-objective optimization problem point out that for our typical model, the annual cooling electricity decreases about 19.8–33.3%; while the annual heating and lighting ones increase 1.7–4.8% and 0.5–2.6%, respectively, in comparison to the baseline model for four diverse climatic regions of Iran. In addition, the optimum design leads to 1.6–11.3% diminution of the total annual building electricity demand. The proposed optimization method shows a powerful and useful tool that can save time while searching for the optimal solutions with conflicting objective functions; therefore facilitate decision making in early phases of a building design in order to enhance its energy efficiency.

Inverse identification of the radiative properties of a two-component media based on multi-phase approach (MPA) formulation of the radiative transfer phenomenon is investigated. Packed bed of semitransparent spheres under a normal collimated laser beam is considered as the geometry of the mentioned problem. Discrete normal directional reflectance and transmittance of the packed bed is used as input data to the identification procedure. The sensitivity of these two parameters to radiative properties of the medium is studied first, followed by the inverse parameter estimation. The discrete ordinates method is used to solve the direct problem while interior trust region (ITRA) algorithm is utilized in the identification process. Results indicate the ability of the presented procedure to estimate the desired radiative properties of the medium within an acceptable error margin. Moreover, the effect of uncertainty of the normal directional reflectance and transmittance data on the accuracy of the estimated parameters is assessed.

Heat transfer occurs frequently in numerous dental treatment procedures. In almost all of the related experimental studies, use of infrared camera for temperature measurement, is becoming more and more popular, considering the many advantages of this technique. This technique has been employed in some recent studies as a non-invasive method for disease diagnosis. However, use of the infrared camera for temperature measurements requires knowledge of the emissivity of the target surface. The present in vitro study aims to determine the emissivity of enamel and dentin. The emissivity of enamel was found to be 0.96 ± 0.01 in the temperature range of 20–40 °C and 0.97 ± 0.01 in the temperature range of 40–60 °C. The emissivity of dentin was found to be 0.92 ± 0.01 at 20–40 °C and 0.93 ± 0.01 at 40–60 °C. The difference in the emissivity of enamel and dentin can be attributed to their different composition and constituents, structure and surface quality.

In this study, we calculated the temperature profile for a nanoscopic Poiseuille flow system via two methods. The first method involved employing the tools of Molecular dynamics (MD) simulation, and the second method involved solving Navier’s equation analytically while the rates of fluid dynamic viscosity and thermal conductivity were calculated through MD. We used a temperature jump model as the boundary condition required for the latter method, which was also calculated through MD. We repeated the calculations for various amounts of wall temperature and fluid-wall interaction strength, and we observed a satisfactory agreement between the results of the two methods.

The multiphase approach (MPA) is used to analyze the radiation in a semi-infinite heterogeneous medium which is exposed to a normal and collimated laser beam. The directional reflectance, R(θ), has been calculated under various types of boundary condition and scattering phase functions. The main target is to compare the influences of the two limiting cases for boundary conditions, i.e., diffuse and specular, on the normal-directional reflectance of the medium, thermal heat flux, and directional-spatial distribution of the radiation intensity. It is found that the effect of scattering phase functions on the R(θ) depends on the type of boundary condition.

The convective heat transfer coefficients resulting from a slot jet on a plane surface have been estimated by using the real measured temperatures in the plate and inverse method. In this study, the inverse method used the conjugate gradient method with an adjoint equation. Distributions of the local heat transfer coefficient on the impingement surface were determined for various Re and H/Dh. It was found the heat transfer coefficients generally tended to decrease with increasing separation distance and to increase with an increase in Reynolds number. This presented method is able to estimate the variation of the local Nusselt number with time.

In this study, an optimization methodology is presented to obtain the uniform thermal conditions over the design body (DB) surfaces. The DB has an asymmetrical and irregular shape that is placed inside a 3-D radiant enclosure equipped with heaters on its top wall. The Monte Carlo ray tracing (MCRT) method and genetic algorithm (GA) are employed to find the optimal temperatures of the heaters and the best location of the DB inside the enclosure. The radiative heat transfer problem is solved on the basis of the MCRT method to calculate heat fluxes on the DB surfaces. The GA is used to minimize the objective function defined based on the calculated and desired heat fluxes. The results indicate that thermal conditions on the DB surfaces are greatly influenced by the location of the DB and temperatures of the heaters. It is concluded that the introduced method is very capable of achieving the uniform thermal conditions on the DB surfaces by finding the optimal values for temperatures of the heaters and the bes...

In this study, an inverse algorithm based on the Artificial Neural Networks and the Sequential Function Specification method was successfully applied for estimation of the heat flux absorbed by the locomotive brake disc. The three dimensional direct problem involving turbulent, unsteady and conjugate heat transfer boundary condition is numerically solved for known values of 47 different heat fluxes, and temperature histories of 18 different locations inside the brake disc were obtained. The braking process is experimentally simulated and the experimental data are used to verify the simulation results. Then 39 simulated heat fluxes are utilized to train the ANN and 8 remaining are used to test it. Results showed the ability of the ANN in accurate heat flux estimation. Furthermore, the consequence of changing the number and the locations of temperature sensors on the accuracy of the estimated results has been considered. Finally, the effect of noise on the exact temperature on the heat flux estimation has been investigated.

In recent years, many research works focused on improving and reducing the cost of solar collectors. This paper focuses upon the development of an efficient modeling and optimization of solar collector. The approach adopted in modeling utilizes a parabolic trough collector absorber tube with non-uniform heat flux, fully developed mixed convection flow and Al2O3/synthetic oil as a base fluid. Optimization of thermal analysis in a solar trough collector using nanofluid is non-convex, non-linear and computationally intensive process. In order to overcome these difficulties, a hybrid optimization method involving GA (genetic algorithm) and SQP (sequential quadratic programming) is introduced in the optimization process. The optimization problem used in this study involves maximization of a non-dimensional correlation consisting of Nusselt number and pressure drop with Reynolds and Richardson number which are used as design constraints. The methodology implemented within an integrated environment involving Matlab, Gambit and Fluent. The results obtained show that heat transfer enhancement has a direct relationship with the nanoparticle concentration ratio whereas it has inverse relationship with the operational temperature. In addition, the results show that the proposed methodology provides an effective way of solving thermal analysis in a solar parabolic trough collectors based on simulation models.