Dimensional Transient Heat Transfer Research Articles

Numerical analysis of energy savings due to the use of PCM integrated in lightweight building walls

A new type of PCM layer integrated into an exterior building wall is to reduce the amplitude of the indoor temperature and maintaining the better thermal comfort for human beings. A numerical simulation has been carried out with and without integration of PCM in building walls. In this paper, the effect of different configuration of external building walls were studied and analyzed by the integration of PCM building walls. Using finite difference method, one dimensional transient heat transfer model was developed and solved. The indoor temperature was also analyzed for the summer and winter climatic conditions of Chennai city, India (13.1 Latitude and 79.9 Longitude) in the PCM and Non-PCM buildings. The building wall consists of clay brick with filled with PCM. The numerical simulation result shows that, PCM filled with clay brick wall improves the thermal inertia significantly. Location of PCM layer in the building wall is one of the important factors to reduce the heat gain in the building wall before it enters the room.

Optimum cure cycles of autoclave process for polymer matrix composites using genetic algorithm

Abstract Polymer matrix composites (Aluminium-polyester and carbon black-polyester) are used in diverse applications due to their easy adaptability in providing tailored mechanical properties. Their production process in autoclave curing results in long processing cycle, which invariably affects the quality negatively. Literatures are sparse on optimum production process parameters of polymer-matrix composites. The objective of this study was to determine optimum process parameters for the production of Aluminium-polyester and carbon black-polyester composites in autoclave oven. The process parameters (cure temperature, ultimate degree of cure and cure cycle) were first examined by experimentation according to ASTM D-790 as control by producing three set of samples of polyester-Aluminium and polyester-carbon black composites separately in 30, 20 and 10 % reinforcement composition. The optimization of the autoclave process was done by solving one dimensional transient heat transfer model coupled with cure kinetic model for the minimization of cure time as objective function subject to maximum and minimum allowable temperatures, as constraints using finite difference method and optimized by genetic algorithm. The results of the experimentation show that autoclave oven achieved cure temperatures of 90 and 75oC, ultimate degree of cure of 85.0 and 80.0% in 270 and 170 minutes for aluminium-polyester and carbon black-polyester, respectively. Autoclave optimum process parameters were able to achieve cure temperatures of 90 and 75 oC, ultimate degree of cure of 99.0 and 100.0% and also minimised the cure cycle to 30 and 23 minutes for aluminium-polyester and carbon black-polyester composites, respectively, compared to 270 and 170 minutes, respectively in the conventional control experiment. Optimum process parameters were obtained for different weight fractions of aluminium-polyester and carbon black-polyester composites and are useful for producing polymer composites with desirable microstructures and mechanical properties.

A Model for Predicting the Geometry of Crater on Grinding Wheel Surface Ablated with a Single Pulsed Laser

In this paper, a three dimensional transient heat transfer model for predicting the 3D geometry of crater and its cross sectional profile on grinding wheel surface ablated by a single pulsed Nd: YAG laser is covered. The model considers the heterogeneity of wheel structure, the variation of energy in a pulsed laser input to the wheel, heat transfer by conduction, convection, radiation and the thermo-physical and optical properties of bond and grit while predicting the temperature distribution in the irradiated region using COMSOL Multiphysics® 5.2 package. From this temperature distribution, the shape of crater was predicted. Crater depth predicted was validated with the published results confirming the suitability of this model for predicting the shape of crater in single pulsed laser ablation of wheel surface. Post modeling analysis gives insights of the process mechanism of laser dressing and the parameters affecting the crater geometry. Future scope and implementation of this model is discussed in detail.

A Study On Solidification Of Large Iron Casting In A Thin Water Cooled Copper Mould

The paper presents a one dimensional transient heat transfer model of casting to determine the temperature distribution as a function of time using FORTRAN software. Casting is considered to be semi-infinite. In the present work, the calculation of temperatures at any point within the casting is performed by calculating the error function. The solidification time and length of metal solidified at different times have also been determined. It can be concluded that this presented approach is computationally more efficient and faster.

Comparative study between dynamic transient and degree-hours methods to estimate heating and cooling loads of building's wall

In this paper, dynamic transient method and conventional degree-hours method (static) have been compared to estimate heating and cooling loads of building’s wall. All main wall surfaces of various orientations, i.e.South, West, East, North, and horizontal are considered in the climate of Tehran, Iran. In this study, a conventional wall structure, which is comprisedconcrete as main wall material, and EPS (expanded polystyrene), as insulation material, areused. The actual outdoor air temperature (used in dynamic method) was obtained by mean hourly measurementsrecorded in meteorological data over the period of 2006–12. Annual heating and cooling degree-hoursare calculated based on this recent weather data, and results are compared with the values reported in the national building regulations (topic 14). One dimensional transient heat transfer problem for multilayer walls has been solved to obtain temperature distribution within the wall. Annual heating and cooling load resulting from dynamic method have been compared with degree-hoursmethod; the results showed that there is a significant difference between these two estimations.

충전층을 이용한 암반공동 열에너지저장시스템의 열에너지 수지 분석

A packed bed thermal energy storage (TES) consisting of solid storage medium of rock or concrete through which the heat transfer fluid is circulated is considered as an attractive alternative for high temperature sensible heat storage, because of the economical viability and chemical stability of storage medium and the simplicity of operation. This study introduces the technologies of packed bed thermal energy storage, and presents a numerical model to analyze the thermal energy balance and the performance efficiency of the storage system. In this model, one dimensional transient heat transfer problem in the storage tank is solved using finite difference method, and temperature distribution in a storage tank and thermal energy loss from the tank wall can be calculated during the repeated thermal charging and discharging modes. In this study, a high temperature thermal energy storage connected with AA-CAES (advanced adiabatic compressed air energy storage) was modeled and analyzed for the temperature and the energy balance in the storage tank. Rock cavern type TES and above-ground type TES were both simulated and their results were compared in terms of the discharging efficiency and heat loss ratio.

A numerical analysis for energy savings of different oriented and insulated walls in the cold climate of Turkey – Simulation-based study

Most of the energy expended in buildings is used for heating. Heating insulation of walls has been gaining much more interest in recent years not only because of the hazardous effects energy consumption on the environment, but also the high costs of energy sources. Therefore, the relationship between insulation thickness and orientation was investigated in this paper for in Elazığ (38.4°N), one of the cold regions in Turkey. One dimensional transient heat transfer problem of the walls with and without insulation was solved by using the explicit finite difference method. In the illustration model, hourly values of heat losses of mass and walls were calculated. The annual energy cost was calculated for walls. It was observed that energy consumption will decrease by 19–78%, depending on the insulation thickness. Payback periods based on insulation cost are 1.69–2.89 years.

Theoretical and experimental investigation of total equivalent temperature difference (TETD) values for building walls and flat roofs in Turkey

The aim of this study is to find time lag (TL), decrement factor (DF) and total equivalent temperature difference (TETD) values for multilayer walls and flat roofs of buildings using experimental and theoretical methods, and to compare the experimental results with theoretical ones. The TETD is a method for calculating cooling load due to heat gain from the walls or flat roofs, and it can be obtained using values of inside and outside air temperatures, solar radiation, TL and DF. The TL and DF depend on the highest and the lowest temperatures at the inner and outer surfaces of the walls or flat roofs, and the time periods involved in reaching these temperatures. Hence, two testing rooms each consisting of four multilayered walls and a flat roof, air conditioner, measuring elements are built to measure all required temperatures. The required temperatures, which are hourly inside and outside air temperatures, and surface temperatures of each structure layer, are measured in every minute during testing periods of the 2007 summer season of Gaziantep, Turkey. Hourly solar radiation values on the walls are computed using hourly measured solar radiation on a horizontal surface. The TL, DF and TETD values of eight different walls and two different flat roofs commonly used in Turkey are computed utilizing the measured temperature and solar radiation values. The computed values for the TL, DF and TETD are compared with theoretical results obtained numerically using periodic solution of one dimensional transient heat transfer problem for the same structures.

Coupled DQ–FE methods for two dimensional transient heat transfer analysis of functionally graded material

In this paper, a mixed finite element (FE) and differential quadrature (DQ) method as a simple, accurate and computationally efficient numerical tool for two dimensional transient heat transfer analysis of functionally graded materials (FGMs) is developed. The method benefits from the high accuracy, fast convergence behavior and low computational efforts of the DQ in conjunction with the advantages of the FE method in general geometry, loading and systematic boundary treatment. Also, the boundary conditions at the top and bottom surfaces of the domain can be implemented more precisely and in strong form. The temporal derivatives are discretized using an incremental DQ method (IDQM), whose numerical stability is not sensitive to time step size. The effects of non-uniform convective–radiative conditions on the boundaries are investigated. The accuracy of the proposed method is demonstrated by comparing its results with those available in the literature. It is shown that using few grid points, highly accurate results can be obtained.

炭素繊維強化熱可塑性樹脂複合材の抵抗スポット溶接による接合

Resistance spot welding concepts for fastening and attaching structural components made of CFRTP composite laminates are presented. Due to the presence of touching fibers, CFRTP laminates exhibit electrical conductivity in the direction transverse to fiber axes as well as in the fiber direction. Therefore, passing an electric current through two overlapping CFRTP laminates, which are sandwiched between upper and lower electrodes, Joule heat is generated in the region of current concentration to melt them together. When the current flow ceases, their contacting surfaces rapidly cool down and are joined together in one spot. One and three dimensional transient heat transfer analyses have been carried out to provide welding variables appropriate for the spot welding of CFRTP laminates. In the experiment, two pieces of CFRTP coupon specimen made of a commingled yarn prepreg are spot welded for various current and time combinations to investigate the effects of welding variables on the weld strength. Although the material properties of CFRTP composites which directly influence the weldability, —anisotropy, resistivity, thermal conductivity and melting temperature, etc. —are significantly different from those of metals, sound spot welds are produced by the present method.

Two dimensional transient heat transfer in He II

A comparison is presented of transient heat flow in He II as measured experimentally and as predicted by analysis based on the Gorter-Mellink equation. The geometry is that envisioned for the He II cooling of a SMES (superconducting magnetic energy storage) system, namely, an annular layer of He II in direct contact with one layer of a solenoid and extending the full height of the coil. A normal zone over a fraction of a turn provides for two-dimensional heat flow in the annular layer of the He II. The comparison is given for both adiabatic and isothermal boundary conditions at the end of the channel. Good agreement between the analysis and the experimental data is found, verifying the usefulness of the analysis for large-scale systems. In addition, discrepancies between the analysis and data provide insight into the stability process of the He II cooled superconductor. >

Modeling Residual Stresses And Damage InitiationIn Discontinuous Random Fiber SRIM Composites

Modeling Residual Stresses And Damage InitiationIn Discontinuous Random Fiber SRIM Composites