Academic literature on the topic 'The enthalpy based heat transfer analysis (EBHT)'

A mathematic model of an enthalpy wheel has been developed to analyze its performance based on energy and mass balance and heat and mass transfer correlation in the enthalpy wheel. It is a one-dimensional transient model solved by the finite volume method. Both summer and winter conditions were studied to explore the impact on the performance of an enthalpy wheel from various design and operating conditions such as the wheel depth, process air face velocity, isotherm coefficient (C), and the maximum water content. The model result predicted that the total effectiveness of the enthalpy wheel is at range of 50∼75% at typical operation condition. The depth of wheel and the face velocity of process air play an important role in the performance of the enthalpy wheel, compared to the other studied parameters. The increase of the wheel depth from 0.15 meter to 0.3 meter can improve the total effectiveness of the enthalpy wheel from 53% and 58% to 72% and 69% in summer and winter. The increase of process air face velocity from 0.5 m/s to 1.5 m/s reduces the total effectiveness of the enthalpy wheel from 75% to 50%.

These days great effort is devoted to the study of turbocharging in order to minimize fuel consumption and pollutant emissions of turbocharged reciprocating engines. Among all the processes taking place in small automotive turbochargers, the heat transfer phenomenon is one of the least analysed in a systematic way. However turbocharger heat transfer phenomena are very important at low engine loads. An accurate prediction of gas temperatures at turbine and compressor outlet and fluid temperatures at the water and oil outlet ports is not possible without considering heat transfer phenomena in the turbocharger. In the present work a comprehensive study of these phenomena is presented, showing their relevance compared to gas enthalpy variations through the turbomachinery. The study provides an experimental methodology to consider the different heat fluxes in the turbocharger and modelling them by means of a lumped capacitance heat transfer model. The input data required for the model is obtained experimentally by a proper combination of both steady and transient tests. These tests are performed in different test benches, in which compressible fluids (gas) and incompressible fluids (oil) are used in a given sequence. The experimental data allows developing heat transfer correlations for the different turbocharger elements. These correlations take into account all the possible heat fluxes, discriminating between internal and external heat transfer. In order to analyse the relative importance of heat transfer phenomena in the predictability of the turbocharger performance and the different related variables; model results, in hot and cold conditions, have been compared with those provided by the standard technique, consisting on using look up maps of the turbocharger. The analysis of these results evidences the highly diabatic operative areas of the turbocharger and it provides clearly ground rules for using hot or cold maps. In addition, paper conclusions advise about using or not a heat transfer model, depending on the turbocharger variables and the operative conditions that one desires to predict.

A sample-based stochastic model is presented to investigate the effects of uncertainties of various input parameters, including laser fluence, laser pulse duration, thermal conductivity constants for electron, and electron-lattice coupling factor, on solid-liquid phase change of gold film under nano- to femtosecond laser irradiation. Rapid melting and resolidification of a free standing gold film subject to nano- to femtosecond laser are simulated using a two-temperature model incorporated with the interfacial tracking method. The interfacial velocity and temperature are obtained by solving the energy equation in terms of volumetric enthalpy for control volume. The convergence of variance (COV) is used to characterize the variability of the input parameters, and the interquartile range (IQR) is used to calculate the uncertainty of the output parameters. The IQR analysis shows that the laser fluence and the electron-lattice coupling factor have the strongest influences on the interfacial location, velocity, and temperatures.

In the present study, we initiate development of a non-iterative multiphase algorithm by enhancing the Pressure Implicit with Splitting of Operators (PISO) algorithm. The Gallium fusion problem, which is characterized by a solid-liquid phase front and natural convection effects, is employed as a test case for validation. The problem poses serious computational issues in form of a non-linear energy equation and a strong pressure-velocity-temperature coupling. The single-fluid modeling approach is adopted in conjunction with the enthalpy-based formulation for the temperature equation. The current algorithm computes the solution through a series of predictor-corrector steps with special treatment to achieve rapid convergence of the energy equation. The algorithm demonstrates an enhanced performance for the highly unsteady, chosen test problem. A reduced-order analysis of the simulated data is also performed by Proper Orthogonal Decomposition (POD). Specifically, impact of the constantly changing flow domain, and flow scales, on the POD implementation is highlighted.

The Present investigation has been carried out to study the performance of nano enhanced phase change material (NEPCM) based heat sink for thermal management of electronic components. Enthalpy based finite volume method is used for the analysis of phase change process in NEPCM. To enhance the thermal conductivity of phase change material (PCM), copper oxide nano particles of volume fractions 1%, 2.5% and 5% are added to PCM. A heat flux of 2500 W/m2 is taken as input to the heat sink. The thermal performance of the heat sink with PCM is compared with NEPCM for each volume fraction of nano particle for both finned and unfinned configurations. It is observed that the nano particle volume concentration plays a major role in removing the heat from the chip in case of unfinned heat sink configuration. However, for finned heat sink configuration, the volume concentration effect is not appreciable. In addition, the performance of NEPCM based finned heat sink is studied under cyclic loading in both natural and forced convection boundary conditions. It is observed that under forced convection the solidification time is reduced.

In the present study, the entire energy balance of a turbocharger is investigated applying an experimentally validated numerical approach with the intention of examining the heat transfer mechanism inside the turbo. The heat transfer results thus obtained are used amongst others to determine the diabatic effects on the turbine and compressor flow resulting in heat-transfer corrected performance maps. These maps are applied as matching data to 1D engine performance calculation and are utilized in the engine process simulation procedure with GT Power™. In detail, the numerical approach of the entire energy balance is based on a thermal network model (RC-resistance / capacity) where the 3D geometry of the turbocharger is subdivided into segments. These segments are defined as lumped mass elements of the thermal network. The entire energy balance of the modeled turbo is fulfilled by coupling the thermal network of the structure to the enthalpy flows of the turbine, compressor, oil circuit, and water coolant as well as the heat losses to ambient. The heat transfer between the structure and the enthalpy flows, respectively, is achieved by using heat transfer coefficients (HTC) performed in accordance with Nusselt-No. laws. Heat loss to ambient is expressed by natural convection and radiation. In general it would be possible to perform the energy balance of the turbo model in the steady state or transient regime. A time-governed finite volume calculation scheme is used for the solution algorithms. The code of the turbo heat transfer approach (THT) is written in Matlab™, something which facilitates flexible adjustments on the algorithm and good post-processing capabilities. Two routes are resorted to for validating the THT approach. Gas stand tests with instrumented turbochargers using thermocouples and pressure sensors are conducted in the first assignment for generating the essential experimental data. Segmentation of the 3D turbocharger geometry into discrete elements is accomplished in the second assignment by means of CAD technology and used for both, the setup of the THT thermal network model and in parallel for the generation of an AnsysCFX™ 3D CAE model. The same HTC thermal boundary conditions are applied to both models which is favorable in as far as it provides a one-to-one comparison of the heat flux and mean temperature in each segment of the two models, Matlab™ THT and CFX™. Ansys™ model heat flux and mean segment temperature results are validated by the measured experimental temperature data. The THT network model properties such as segment volume, areas, volume, and element distances are calibrated applying the results of the 3D CAD and CAE Ansys™ model. The results of the two numerical models are compared with each other, thus demonstrating the qualitative and quantitative level of agreement. The THT approach that has been developed is successfully applied to GT Power™ gasoline engine model. A thermal network model of that applied turbocharger was setup and validated by gas-stand and engine data obtained on an experimental basis with an instrumented turbo. Finally it was possible to demonstrate that the heat-transfer corrected turbocharger performance map data which was provided utilizing the THT model approach brings about a significant benefit to the determination process aimed at achieving a tailored turbocharger thermodynamic layout.

Hydrogen or coal-derivative syngas turbines promise increased efficiency with exceptionally low NOx emissions compared to the natural gas based turbines. To reach this goal, turbine inlet temperature (TIT) will need to be elevated to a level exceeding 1700°C [1, 2]. The thermal load induced by such a temperature increase alone will lead to immense challenges in maintaining material integrity of turbine components. In addition, as working fluid in the gas path will primarily be steam, possibly mixed with carbon oxides, the aero-thermal characteristic in a hydrogen turbine is expected to be far different from that of air/nitrogen enriched gas stream in a gas turbine. For instance, steam has distinctly higher density and specific heat in comparison to a mixture of air and combustion gases as they are expanded in a conventional gas turbine. Even if the temperature limits remain about the same, the expansion in a hydrogen turbine will have to proceed with a greater enthalpy drop and therefore requires a larger number of stages. This also implies that the flow areas may need to be expanded and blade span to be enlarged. Meanwhile, a greater number of stages and hot surfaces need to be protected. This also suggests that current cooling technology available for modern day gas turbines has to be significantly improved. The ultimate goal of the present study is to systematically investigate critical issues concerning cooling technology as it is applicable to oxy-fuel and hydrogen turbine systems, and the main scope is to develop viable means to estimate the thermal load on the turbine “gas side”, that is eventually to be removed from the “coolant side”, and to comparatively quantify the implication of external heat load and potential thermal barrier coating (TBC) degradation on the component durability and lifing. The analysis is based on two well-tested commercial codes, FLUENT and ANSYS.

Aiming in the direction of designing more efficient aero engines, various concepts have been developed in recent years, among which is the concept of an intercooled and recuperative aero engine. Particularly in the area of recuperation, MTU Aero Engines has been driving research activities in the last decade. This concept is based on the use of a system of heat exchangers mounted inside the hot-gas exhaust nozzle (recuperator). Through the operation of the system of heat exchangers, the heat from the exhaust gas, downstream the LP turbine of the jet engine is driven back to the combustion chamber. Thus, the preheated air enters the engine combustion chamber with increased enthalpy, providing improved combustion and by consequence, increased fuel economy and low-level emissions. If additionally an intercooler is placed between the compressor stages of the aero engine, the compressed air is then cooled by the intercooler thus, less compression work is required to reach the compressor target pressure. In this paper an overall assessment of the system is presented with particular focus on the recuperative system and the heat exchangers mounted into the aero engine’s exhaust nozzle. The herein presented results were based on the combined use of CFD computations, experimental measurements and thermodynamic cycle analysis. They focus on the effects of total pressure losses and heat exchanger efficiency on the aero engine performance especially the engine’s overall efficiency and the specific fuel consumption. More specifically, two different hot-gas exhaust nozzle configurations incorporating modifications in the system of heat exchangers are examined. The results show that significant improvements can be achieved in overall efficiency and specific fuel consumption hence contributing into the reduction of CO2 and NOx emissions. The design of a more sophisticated recuperation system can lead to further improvements in the aero engine efficiency in the reduction of fuel consumption. This work is part of the European funded research program LEMCOTEC (Low Emissions Core engine Technologies).

A mathematic model, which can be used to predict the evaporation and fluid flow in thin film region, is developed based on momentum and energy conservations and the augmented Young-Laplace equation in this paper. In the model the variations of the enthalpy and kinetics energy of the thin-film along the evaporating region are considered. By theoretical analysis, we have obtained the governing equation for thin film profile. The fluid flow and phase-change heat transfer in an evaporating extended meniscus are numerically studied. The differences between the model considering momentum conservation only and including both momentum and energy conservations are compared. It is found that the maximum heat flux of the thin-film evaporation by using two mathematical models obtained has no change, but when considering the momentum and energy conservations the total heat transfer rate unit width along the thin-film evaporation region is greater than that of only including momentum equation.

The present paper describes the application of computational fluid-dynamics (CFD) for the analysis of the melting process in a single vertical shell-and-tube heat exchanger. The computations are based on a 2D axial-symmetric model that takes in account the phase change phenomenon by means of the enthalpy method. The numerical studies aimed at clarifying the importance of the different heat transfer mechanisms with a particular focus on natural convection demonstrating its fundamental importance on the phase change process by enhancing the heat transfer between HTF and solid PCM. the paper discusses the effect of two different common performance enhancement techniques: dispersion of high conductive nano-particles in the PCM and the introduction of radial fins. An extensive thermo-fluid dynamic study has been undertaken exploring the effect on the thermal performance enhancement of particle volume fraction and fins. The analysis shows that in comparison to the standard design, the performances of the LHTS unit in terms of charging time could be improved by up to 40 % for nano-particle enhancement. When fins are considered charging time can be reduced to one-third of its original value. Significant improvements are also achieved during the solidification process: discharge time is reduced of 33% with fins enhancement.