Conjugate Heat Transfer Analysis Research Articles

Experimental and Numerical Investigation of Effusion Cooling Performance Over Combustor Liner Flat Plate Model

ABSTRACTThis article presents a study of cooling performance of combustor liner of a gas turbine, using a flat plate model. The combustion process in gas turbine engines liberates very high temperature gases, which impacts the properties of the combustor liner. Hence, cooling of liner is important and is carried out by effusion cooling method. Experiments are carried out over a flat plate with staggered effusion holes. The hot mainstream air flows at a Reynolds number of 2.325 × 105, which indicates a turbulent flow. The coolant to mainstream density ratios of 1.3 and 1.5 is maintained by varying the blowing ratios ranging from 0.5 to 2.5. Test plate surface temperature measurements are recorded by an infrared camera and the overall cooling effectiveness in the flow direction is calculated. Numerical validation for conjugate heat transfer analysis is performed using ANSYS workbench and the temperature contours obtained are compared with infrared camera images. MATLAB program is used to obtain the effectiveness contours for experimental and computational fluid dynamics results. The effectiveness contours are found to be similar, showing the increase in effectiveness with the increase in blowing ratios. Density ratios comparison shows that with the increase in density ratio, the overall cooling effectiveness marginally decreases.

Investigation of Cooling Performances of a Non-Film-Cooled Turbine Vane Coated with a Thermal Barrier Coating Using Conjugate Heat Transfer

The aim of this paper is to numerically investigate cooling performances of a non-film-cooled turbine vane coated with a thermal barrier coating (TBC) at two turbulence intensities (Tu = 8.3% and 16.6%). Computational fluid dynamics (CFD) with conjugate heat transfer (CHT) analysis is used to predict the surface heat transfer coefficient, overall and TBC effectiveness, as well as internal and average temperatures under a condition of a NASA report provided by Hylton et al. [NASA CR-168015]. The following interesting phenomena are observed: (1) At each Tu, the TBC slightly dampens the heat transfer coefficient in general, and results in the quantitative increment of overall cooling effectiveness about 16–20%, but about 8% at the trailing edge (TE). (2) The protective ability of the TBC increases with Tu in many regions, that is, the leading edge (LE) and its neighborhoods on the suction side (SS), as well as the region from the LE to the front of the TE on the pressure side (PS), because the TBC causes the lower enhancement of the heat transfer coefficient in general at the higher Tu. (3) Considering the internal and average temperatures of the vane coated with two different TBCs, although the vane with the lower thermal conductivity protects more effectively, its role in the TE region reduces more significantly. (4) For both TBCs, the increment of Tu has a relatively small effect on the reduction of the average temperature of the vane.

Prediction of temperature distribution over cutting tool with alumina-MWCNT hybrid nanofluid using computational fluid dynamics (CFD) analysis

The accurate measurement of tool tip temperature in turning has been a challenging task for researchers. The present study covers the computational fluid dynamics (CFD) analysis of a single point carbide cutting tool dissipating heat and subjected to streams of nanofluid mist. This study is an attempt to numerically analyze the thermal behavior of the cutting tool having constant temperature heat source at its tip. To determine the optimized experimental value of nodal temperature, machining of AISI 304 steel has been carried out using alumina and alumina-MWCNT hybrid nanofluid mist with minimum quantity lubrication (MQL) system. Furthermore, the conjugate heat transfer (CHT) analysis has been performed to investigate the temperature distribution over the rake and flank face of carbide cutting insert. An overview of the mathematical model, complete geometry, and mesh generation of the carbide cutting tool is presented. Additionally, the CHT simulation results for the mist of alumina and alumina-MWCNT hybrid nanofluids were compared and validated successfully with the experimental data. The maximum variation of 5.79% has been observed between experimental and simulation data, which in turn proves the proposed conjugate heat transfer-based CFD model as an alternative approach to investigate the influence of cooling media on cutting tool under MQL technique.

Transient combined natural convection and radiation in a double space cavity with conducting walls

Two-dimensional numerical analysis of transient conjugate heat transfer in a double space gas filled enclosure with conducting solid walls has been carried out. This configuration can be found in cooling process of some electronic equipment in which the generated heat must be removed to avoid failure. Natural convection equations in the enclosures are solved in terms of the dimensionless stream function and vorticity using finite-difference technique. The discrete ordinates method (DOM) is used to solve the radiative transfer equation (RTE) in the filling gases which are considered to be absorbing, emitting and scattering. The effects of Rayleigh number and optical thickness of two radiating media in transient cooling process from the hot surface toward the cold one are investigated. The transient results show that when the optical thickness of the gas layer closed to the heat source is lower than the second layer, more heat penetrates into the enclosure which consequently leads to higher cooling performance and lower rates of thermal failure.

Applied and Theoretical Aspects of Conjugate Heat Transfer Analysis: A Review

This paper documents all the important works in the field of conjugate heat transfer study. Theoretical and applied aspects of conjugate heat transfer analysis are reviewed and summarized to a great extent on the light of available literature in this field. Over the years, conjugate heat transfer analysis has been evolved as the most effective method of heat transfer study. In this approach the mutual effects of thermal conduction in the solid and convection in the fluid are considered in the analysis. Various analytical and computational studies are reported in this field. Comprehension of analytical as well as computational studies of this field will help the researchers and scientists who work in this area to progress in their research. That is the focus of this review. Early analytical studies related to conjugate heat transfer are reviewed and summarised in the first part of this paper. Background of theoretical studies is discussed briefly. More importance is given in summarising the computational studies in this field. Different coupling techniques proposed to date are presented in great detail. Important studies narrating the application of conjugate heat transfer analysis are also discussed under separate headings. Hence the present paper gives complete theoretical background of Conjugate heat transfer along with direction to its application envelope.

Numerical study of the optimum width of 2a diurnal double air-channel solar chimney

A conjugate heat transfer analysis of a double air channel solar chimney (SC-DC) aiming to determine the configuration that maximizes the mass flow rate of the system is presented. The design modifications consisted on two geometrical parameters: 1) the separation between the absorber wall and the glass covers that form the air channels (b), and 2) the height of the system (L). A code based on the Finite Volume Method was developed and a k-ω turbulence model was used to model air turbulence in the SC-DC. The code was validated and it showed a good agreement with experimental data reported in the literature. We found that the optimal configuration of the SC-DC under the considered conditions is L = 2 m and b = 0.125 m. The optimum L of the SC-DC is similar to the value reported for a conventional chimney, whereas the optimum b is smaller than the one of a conventional chimney. The optimal configuration of the SC-DC had a thermal efficiency of 38.5% and a mass flow rate of 0.1072 kg/s when it receives a beam solar radiation of 700 W/m2 and a diffuse solar radiation of 100 W/m2.

Polyhedral meshing in numerical analysis of conjugate heat transfer

Polyhedral meshing in numerical analysis of conjugate heat transfer

Polyhedral meshing in numerical analysis of conjugate heat transfer

Computational methods have been widely applied in conjugate heat transfer analysis. The very first and crucial step in such research is the meshing process which consists in dividing the analysed geometry into numerous small control volumes (cells). In Computational Fluid Dynamics (CFD) applications it is desirable to use the hexahedral cells as the resulting mesh is characterized by low numerical diffusion. Unfortunately generating such mesh can be a very time-consuming task and in case of complicated geometry - it may not be possible to generate cells of good quality. Therefore tetrahedral cells have been implemented into commercial pre-processors. Their advantage is the ease of its generation even in case of very complex geometry. On the other hand tetrahedrons cannot be stretched excessively without decreasing the mesh quality factor, so significantly larger number of cells has to be used in comparison to hexahedral mesh in order to achieve a reasonable accuracy. Moreover the numerical diffusion of tetrahedral elements is significantly higher. Therefore the polyhedral cells are proposed within the paper in order to combine the advantages of hexahedrons (low numerical diffusion resulting in accurate solution) and tetrahedrons (rapid semi-automatic generation) as well as to overcome the disadvantages of both the above mentioned mesh types. The major benefit of polyhedral mesh is that each individual cell has many neighbours, so gradients can be well approximated. Polyhedrons are also less sensitive to stretching than tetrahedrons which results in better mesh quality leading to improved numerical stability of the model. In addition, numerical diffusion is reduced due to mass exchange over numerous faces. This leads to a more accurate solution achieved with a lower cell count. Therefore detailed comparison of numerical modelling results concerning conjugate heat transfer using tetrahedral and polyhedral meshes is presented in the paper.

Analysis of heat transfer in a coated bed of an adsorption chiller

Adsorption chillers can be a promising part of sustainable development concept of the global economy due to the utilization of low grade thermal energy sources for cooling production. Therefore, research aiming at improving their performance i.e. Coefficient of Performance (COP) by optimizing the heat and mass transfer condition in the adsorption beds are crucial. Innovative modification of the sorbent layer structure are proposed in the paper in order to improve the heat transfer characteristics in the heat exchanger boundary layer. The analysis of desorption conditions in the parametric model of a coated adsorption bed construction is presented in the paper. The computational fluid dynamics with conjugate heat transfer analysis are used to determine the crucial input parameters for further analytical calculations. The heat transfer condition in novel coated design and a conventional fixed bed are compared in the paper. The developed computational model consisted of three subdomains representing heating water, heat exchanger material (copper) and sorbent (silica gel).

Influence of turbulence RANS models on heat transfer coefficients and stress distribution during thermal-FSI analysis of power turbine guide vane of helicopter turbine engine PZL-10W taking into account convergence of heat flux

In this work, we present thermal-FSI analysis of a power turbine guide vane of turbine helicopter engine PZL-10W. Firstly, CFD conjugate heat transfer analyses were carried out, then stress analyses were performed with boundary conditions obtained via CFD analyses. Influence of turbulence RANS models on heat transfer coefficients and stress distribution were investigated in detail. We used eddy-viscosity SST and γ - ReΘ SST transition models and two second closure: RSM and WJ-BSL-EARSM. In addition, effect of mass flow rate of rotor disc cooling fluid on stress distribution was examined. Moreover, we discuss heat flux convergence in vane on temperature and stress distribution. In order to model a material effort, the Burzynski parabolic model was implemented.

The Transient Conjugate Heat Transfer Analysis in Multi-zone of an Apartment House by using Crank-Nicolson Finite Difference Method (FDM)

Purpose: This study was conducted for the purpose of accurate energy analysis of apartment house which is composed of multi-zones such as a bedrooms, a livingroom, and a kitchen. Those of multi-zonal spaces have different indoor thermal environment requirements depending on space usage. For the analysis of this study was selected the 74 ㎡ type unit, which has the largest amount of supply in residential needs. The orientation of the apartment house unit was divided into the southeast and southwest directions, and the annual heating energy demand was calculated and compared. Method: A multi-zone heat transfer is done in dynamic and a very complex, such as conduction, convection, radiation and the solar radiation in a various building elements. In this paper, the Crank-Nicolson FDM scheme and the ISO 13790 algorithm were employed to analyze a complex and transient heat transfer in the multi-zone of apartment house. Result: The results of the analysis are as follows; the total amount of annual energy requirement for the apartment house unit which oriented in the southwest is 756 ㎾h. and equivalent to 10.2 ㎾h /㎡. When the required amount of primary energy was converted equivalent to electricity by unit floor area, it was 28.1 ㎾h /㎡. On the other hand, the total amount of annual energy requirement for a unit oriented in the southeast direction is 1,037 ㎾h and 14.0 ㎾h /㎡. The result of conversion (electricity) to primary energy is 38.5 ㎾h /㎡. This result indicates that the energy demand is about 27% higher than the southwest.

Numerical modeling of steady state errors for shielded thermocouples based on conjugate heat transfer analysis

In this paper, Conjugate Heat Transfer (CHT) numerical simulation method is implemented to estimate the different sources of steady state errors and their variation characteristics for a typical shielded thermocouple working at free-stream Mach numbers 0.2, 0.3, 0.4, 0.5 and 0.6. 1D physical models with high prediction accuracy and wide applicability, including velocity error model, conduction error model and radiation error model, are proposed. Based on the flow topologies in the shield tube and the Re-Cpb chart by Williamson, the Mach number of the flow around the thermocouple junction is modeled and then a velocity error model is proposed. Temperature deviations between the velocity error model and the CHT simulation results are less than 0.27 K. Considering the actual heat transfer process, a conduction error model is proposed by modeling the heat transfer of the shielded thermocouple as the heat transfer of two fins in series arrangement and propounding a semi-empirical method for predicting the average flow temperature around the shield tube. Temperature deviations between the conduction error model and the CHT simulation results are less than 1.32 K. As for radiation error modeling, the average temperature of the shield tube surface is reasonably estimated, and an equivalent method is introduced to explicitly solve the temperature of shield tube surface with high accuracy. Based on aforementioned parameters, a radiation error model is proposed by evaluating the convective, conductive and radiative heat transfer mechanisms prevalent in the thermocouple junction, shield, duct and flow. Temperature deviations between the radiation model and the CHT simulation results are less than 1.74 K; In order to vindicate the applicability of the proposed models, they are verified at free-stream Mach numbers of 0.1, 0.35 and 0.7. The results show that these models can be used to predict the shielded thermocouple’s steady state errors accurately in a wide Mach number region.

Conjugate Heat Transfer Analysis of Thermal Management of a Li-Ion Battery Pack

Thermal management of Li-ion battery packs is a critical technological challenge that directly impacts safety and performance. Removal of heat generated in individual Li-ion cells into the ambient is a considerably complicated problem involving multiple heat transfer modes. This paper develops an iterative analytical technique to model conjugate heat transfer in coolant-based thermal management of a Li-ion battery pack. Solutions for the governing energy conservation equations for thermal conduction and convection are derived and coupled with each other in an iterative fashion to determine the final temperature distribution. The analytical model is used to investigate the dependence of the temperature field on various geometrical and material parameters. This work shows that the coolant flowrate required for effective cooling can be reduced significantly by improving the thermal conductivity of individual Li-ion cells. Further, this work helps understand key thermal–electrochemical trade-offs in the design of thermal management for Li-ion battery packs, such as the trade-off between temperature rise and energy storage density in the battery pack.

Local field synergy analysis of conjugate heat transfer for different plane fin configurations

The aim of the present study is to achieve conjugate heat transfer enhancement in a finned heat exchanger by only modifying the isotherms distribution in the fins. A three-dimensional numerical study of a flat plate and its geometric variants is therefore carried out for a steady incompressible laminar flow. The results are analyzed by carrying out an extensive analysis of the local field synergy which shows the effect of local velocity and local temperature gradient vectors on the heat transfer process. Depending upon the magnitudes of the field synergy parameters, in general, it is found that the local heat transfer coefficient is in accordance with the field synergy principle for the regions in the thermal boundary layer very close to the heated surface. Gain in thermal performance is obtained due to orientation of the velocity and the temperature gradient vectors in the same direction near the upstream fin modification as well as due to the enhancement of the modulus of the inner product of velocity and temperature gradient. For one of the tested configurations, the results show an increase of 7% of PEC associated with about 14.4% less aluminum material used.

Topology optimization of fluid flow channel in cold plate for active phased array antenna

This article presents a topology optimization method for the design of the fluid flow channel of cold plate, aiming to solve the problem of heat dissipation for power devices in active phased array antenna (APAA). The density-based topology optimization method is used in the topology optimization design of flow path, in which the conjugate heat transfer analysis is performed. In the numerical experiment, we use the central plane of the cold plate to make a two-dimensional topology optimization, and then the result of two-dimensional topology optimization was used to build the three-dimensional flow channel of cold plate. The results of simulation show that the optimized flow channel has a better ability of heat dissipation compared with the traditional S style flow channel, which provides important reference for engineering application.

Conjugate thermal creep flow in a thin microchannel

In the present work, we analyze asymptotically and numerically the conjugate heat transfer between a rarified gas flow and the lower wall of a thin horizontal microchannel. The laminar motion of the gas is originated only by the thermal creep or transpiration effect on the lower wall of the microchannel. It is well known the need to impose, in general, a variable temperature regime at the lower wall to induce the transpiration effect. Usually, it can be reached by setting a linear temperature profile as a boundary condition. However, in our case, we prefer to avoid this simplification taking into account that in practical applications, the temperature profile at the lower wall can be unknown. This case can occur, for instance, in a heat sink or a similar device with a well defined heat dissipation rate. Under this physical configuration, we can assume then that the bottom or external face of this heat sink with finite thermal conductivity is exposed to a uniform heat flux. On the other hand, the upper wall of the microchannel is subjected to a prescribed condition. The above conditions are sufficient to consider the simultaneous or conjugate heat transfer analysis of the heat conduction equation for the heat sink and the mass, momentum and energy equations for the gaseous-phase. Resulting governing equations are written in dimensionless form, assuming that the Reynolds number associated with the characteristic velocity of the thermal creep and the aspect ratio of the microchannel, are both very small. The velocity and temperature profiles for the gas phase and the temperature profiles for the solid wall are predicted as functions of the involved dimensionless parameters and the main results confirm that the phenomenon of conjugate thermal creep exists whenever the temperature of the lower wall varies linearly or nonlinearly.

Computational Conjugate Heat Transfer Analysis of a Hybrid Electric Vehicle Inverter

ABSTRACTA physics-based computational simulation of the heat transfer characteristics of an insulated gate bipolar transistor (IGBT) developmental inverter is reported. The simulation considers the fluid/thermal multiphysics interactions via a conjugate heat transfer analysis. The fluid phase includes air and liquid coolant; the solid phase, where the heat is conducted, includes various solid materials. Numerical solutions of the heat conduction and convection phenomena in and around the IGBT modules and the inverter, built as a three-dimensional computational model, are sought for by using parallel computing. Comparisons with the available experimental data show a satisfactory agreement of the inverter temperature at three power levels under two different coolant flow rates. Detailed examination of the flow field reveals that the design features of the rectangular coolant flow chamber in the heat sink and the small clearance between the tips of the pin fin and the walls lead to an evenly distributed coolant flow around most of the pin fins. The temperature distributions of the pin fins depend highly on their locations relative to the IGBT modules. The findings from the current study can be useful in future efforts to optimize the thermal performance of IGBT inverters.

Numerical analysis of transient conjugate heat transfer and thermal stress distribution in geothermal drilling with high-pressure liquid nitrogen jet

This paper presents a numerical analysis of heat transfer and thermal stress in bottomhole rocks during geothermal drilling with high-pressure liquid nitrogen jet. The simulation is conducted by a three-dimensional model in transient state. The conjugate heat transfer method is employed to compute heat transfer between solid and liquid. The thermo-physical properties of liquid nitrogen and rocks are considered in detail. The results indicate that high velocity and turbulence kinetic energy of liquid nitrogen jet at impingement surface enhance heat transfer efficiency between cryogenic fluid and hot rock. Huge tensile stress is generated adjacent to the solid-liquid interface, which is favorable for rock breaking on bottomhole. The primitive rock temperature has a significant impact on maximal stress value. A set of experiments is conducted to validate the effects of thermal stresses on rock breakage. The thermal stresses diminish significantly under laboratory conditions without effective constraint on rock boundaries. In our experiments, the coal rather than other types of rock, was selected as working specimen due to its well-developed natural cracks and small tensile strength. Our results would shed light on the geothermal drilling with high-pressure nitrogen jet.

Film Cooling Performances at Different Turbulence Intensities Using Conjugate Heat Transfer Analysis

This study presents a numerical investigation of cooling performances of a modified vane of the film-cooled vane reported by Timko (NASA CR-168289) at different mainstream turbulence intensities (Tus). A 3D conjugate heat transfer (CHT) analysis with SST k-ω turbulence model in FLUENT V.15 is used. Three different mechanisms in CHT analysis, i.e. fluid flow, heat convection between solid surfaces and flowing fluid in an external mainstream and internal cooling passages, and heat conduction within the vane structure, are simultaneously considered. Numerical results are conducted in terms of overall cooling effectiveness at Tu=3.3, 10, and 20%. Comparison between overall cooling effectiveness and film effectiveness under adiabatic assumption is discussed at the three Tus, also. The findings of this research indicate the following phenomena: 1) overall cooling effectiveness decreases with Tu, and this effect on the pressure side (PS) is stronger than that on the suction side (SS) in general. 2) By comparison with adiabatic film effectiveness, the level of overall cooling effectiveness in most regions is higher and more uniform than that of adiabatic film effectiveness for all three Tus. 3) In the leading edge (LE), when Tu increases, near the exits of film holes overall cooling effectiveness deteriorates, but adiabatic film effectiveness improves. Furthermore, a large area with relatively low overall cooling effectiveness is able to move with Tu in the LE region.

HALE 무인기의 태양전지 열특성에 관한 해석적 연구

본 연구에서는 수치해석을 통해 장기체공 무인기(HALE UAV)에 사용되는 태양전지에 대해 유동 및 열전달 해석을 수행하였다. 무인기가 운용되는 성층권에서는 강한 태양복사에너지가 유입되며, 자연대류에 의한 열전달이 감소하고 주위 유동에 의한 강제대류의 지배를 받는다. 이러한 환경에서의 태양전지 온도범위를 예측하기 위해 주익에 부착되어 있는 태양전지모듈을 대상으로 복합열전달 해석을 수행하였으며, 성층권 환경에서 시간에 따른 태양복사에너지, 비행속도, 밀도, 온도 등의 외기환경이 태양전지의 온도분포와 열전달 특성에 미치는 영향을 분석하였다. In this study, a numerical analysis is made of the fluid flow and heat transfer characteristics in the solar arrays of HALE (High Altitude Lond Endurance) UAV. In the stratosphere where UAV operates, high level solar radiation is induced, heat transfer decreases due to natural convection and forced convection is dominated by ambient flow. In order to predict the solar array temperature range in this environment condition, the conjugate heat transfer analysis was carried out for the solar arrays on the main wing. The investigation focused on the temperature distribution of solar array and heat transfer characteristics according to influence of solar energy, flight condition as vehicle speed, air density, temperature.