Numerical Simulation of 3—D Temperature Distribution of the Flame Tube of the Combustion Chamber with Air Film COoling

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Temperature control of buildings by adobe wall design

The adobe house developed in the hot arid climate of the American Southwest has the virtue of being cool in the day and warm in the night. The adobe wall acts as a filter giving nearly a 12-hr phase lag in the outside temperature oscillation. However, on reaching the inside, the oscillation suffers a strong attenuation in amplitude. In a previous paper it was shown that if the resistivity of the wall could be varied in a certain way from outside to inside, thenthe attenuation would be considerably reduced. In this paper a formula is given for the minimum possible attenuation under given design restrictions. Then it is shown how to make an optimum wall by suitably proportioning two or three layers of different materials. Numerical illustrations are given.     

Thermal load levelling of heat flux through an insulated thermal storage water wall

This communication presents an investigation of the thickness distribution of a given total thickness of the insulation inside and outside a thermal storage water wall for acheiving the maximum load levelling of the heat flux entering through the wall. Analysis is based on the solution of the heat conduction equation for the temperature distribution in the insulated wall subjected to periodic solar radiation and atmospheric air on one side and in contact with room air at constant temperature (corresponding to air-conditioned rooms) on the other side. an explicit solution for a temperature distribution satisfying the apporpriate boundary conditions at the surface has been derived to obtaing a periodic heat flux through the storage water wall. It is found that for a given total thickness (cost) of insulation the thicknesses of outside and inside insulation must be equal for best load levelling. Moreover, more load levelling is achieved when the whole of the insulation is outside rather than inside the thermal storage water wall.     

不同外墙保温方式对墙体热工性能的影响及分析

通过对墙体的温度分布及内表面温度的分析和计算,对比分析了外保温与内保温两种外墙保温方式。研究表明外墙外保温方式在提高室内舒适度、减少墙体开裂、消除热桥影响及降低能耗等方面优于内保温方式。     

Prediction of protective banks in high temperature smelting furnaces by inverse heat transfer

An inverse phase change heat transfer method has been developed for predicting the time evolution of banks covering the surface of refractory brick walls inside high temperature smelting furnaces. The presence of these banks is indispensable as they serve as a protective barrier against the highly corrosive slag, thereby maintaining the structural integrity of the furnace and prolonging its active life. The numerical model rests on the conjugate gradient solution method with the adjoint equation. It predicts banks thickness and motion relying on the thermal conditions prevailing outside the furnace and temperature measurements taken at one location inside the brick wall. Simulations are carried out to examine the effect of different parameters on the predictive capabilities of the method. Results reveal that the method remains accurate in spite of the fact that the temperature measurements inside the wall are noisy and are taken at depth of few centimetres only. An example showing how the present inverse method can be used to warn on the imminent loss of the protective bank during the operation of a smelting furnace is then provided.     

扁管通道的轿车暖风器传热性能研究

对轿车暖风器的传热性能进行了数值模拟和实验研究,将数值模拟与试验结果相对比,验证了壁面温度选取的正确,为进一步的数值模拟研究打下了基础。依据实测数据,将管内外侧的对流换热系数从传热系数中分离出来,得到了管外换热关系无量纲准则式;对管内外的换热特性、阻力特性进行分析,指出了改善暖风器传热性能的方法,同时验证额定工况性能指标的合理性。     

Solar and thermal energy gain through windows in Jordan

Solar gain and thermal energy transfer through windows is studied for three different sites in Jordan using the TRNSYS computer program. Solar and thermal energy is calculated using the monthly average daily data for the above-mentioned three regions. Calculation of hourly radiation on a vertical plane is presented, and also the method of determination of the amount of radiation transmitted through the glazing layers is given. The effect of window orientation on the total solar gain is analysed. It is found that for all directions, solar gain is season-dependent, and this dependency varies from one direction to another. Calculations are carried out for two cases of glazing location: case 1, glazing flush with the outside of the wall; and case 2, glazing recessed by 15 cm from the outside wall, which represents a window with overhang and sidewalls. The number of glazing layers is taken as 1, 2 and 3 to observe the effect on solar gain as well as on the thermal energy exchange between the inside and outside of the building. During the calculations, the temperature of the inside is fixed at 22°C for the entire year. The results are tabulated to serve as a database for solar and thermal energy in Jordan.     

Mapping the thermal distribution within a silica preform tube using regenerated fibre Bragg gratings

The temperature profile of the reaction zone inside the silica substrate tube during thermal heating with a H₂/O₂ flame under conditions identical to those used in the fabrication of optical fibre preforms using a modified chemical vapour deposition lathe has been characterised with ultra-high temperature stable regenerated optical fibre Bragg gratings. Experimental and theoretical results indicate a significant drop in temperature – up to several hundred degrees – across the tube wall from outside to inside. These results are in contradiction with the broadly accepted assumption that there is no significant thermal gradient across the tube itself. An array of regenerated gratings demonstrates that optical fibre grating based sensing can achieve distributed ultra-high temperature mapping and monitoring in harsh environments.     

Unsteady conjugated forced convective heat transfer in a duct with convection from the ambient

A numerical finite difference solution is found for the problem of unsteady, laminar, forced convection heat transfer in a parallel plate duct with finite thermal capacity walls which interact with an ambient medium outside the duct. Response functions are presented for the duct wall temperature, fluid bulk mean temperature, and inside wall surface heat flux as a function of position down the duct and time for a range of the parameters involved. Comparisons are made with the zero thermal capacity wall solution and with quasi-steady results.     

A two-region simulation model of vertical U-tube ground heat exchanger and its experimental verification

Heat transfer around vertical ground heat exchanger (GHE) is a common problem for the design and simulation of ground coupled heat pump (GCHP). In this paper, an updated two-region vertical U-tube GHE analytical model, which is fit for system dynamic simulation of GCHP, is proposed and developed. It divides the heat transfer region of GHE into two parts at the boundary of borehole wall, and the two regions are coupled by the temperature of borehole wall. Both steady and transient heat transfer method are used to analyze the heat transfer process inside and outside borehole, respectively. The transient borehole wall temperature is calculated for the soil region outside borehole by use of a variable heat flux cylindrical source model. As for the region inside borehole, considering the variation of fluid temperature along the borehole length and the heat interference between two adjacent legs of U-tube, a quasi-three dimensional steady-state heat transfer analytical model for the borehole is developed based on the element energy conservation. The implement process of the model used in the dynamic simulation of GCHPs is illuminated in detail and the application calculation example for it is also presented. The experimental validation on the model is performed in a solar-geothermal multifunctional heat pump experiment system with two vertical boreholes and each with a 30 m vertical 1 1/4 in nominal diameter HDPE single U-tube GHE, the results indicate that the calculated fluid outlet temperatures of GHE by the model are agreed well with the corresponding test data and the guess relative error is less than 6%.     

Numerical investigation of the heat and mass transfer in a vertical tube evaporator with the three-zone analysis

A numerical study for the flow, heat and mass transfer characteristics near the inflow region of the vertical evaporating tube with the films flowing down on both the inside and outside tube walls has been carried out. Condensation occurs along the outside wall and evaporation at the free surface of the inside film. The transport equations for momentum and energy are parabolized by the boundary-layer approximation and solved by using the marching technique. In this kind of numerical approach, the accurately predicting the early stage is really important because a small error at the previous step can produce the amplified big error at the next step. To accurately predict the flow at the inflow region of the vertical evaporating tube, the calculation domain of two film flow regions and tube wall is solved simultaneously. The interesting heat transfer characteristics revealed through this three-zone simulation, such as the evaporation delay and the temperature inflection at the very near inflow region are found and discussed along the discrepancy between the inner film inlet temperature and the saturation temperature. The case that the inner film comes in with the saturation temperature shows a good performance. The velocity and temperature fields as well as the amounts of the condensed and evaporated mass in both inner and outer films are predicted for the various conditions.     

A proposal for “correction values” for winter outdoor design temperatures

This study aims to find a correlation between winter outdoor design temperature (WDT) and mass of the building envelope. The daily variations of the inside surface temperatures and heat fluxes of the walls under various climatic conditions and different wall constructions have been calculated by a computer program based on the response factor technique, which uses variable outside air temperature and solar radiation and constant inside air temperature values as input climatic data. The analysis of the relation between mass of the walls and inside surface heat fluxes resulted with the correction values for winter design temperature (WDTCV) depending on the mass of the wall and on the direction of facades for different climatic zones.     

Experimental analysis and numerical modelling of inward solidification on a finned vertical tube for a latent heat storage unit

The enhancement of heat transfer in a thermal storage system consisting of a cylindrical vertical tube with internal longitudinal fin arrangement is discussed in this paper. This configuration that forms a V-shaped enclosure for the phase change material (PCM) gives maximum benefit to the fin arrangement. A theoretical model that also accounts for the circumferential heat flow through the tube wall is developed using enthalpy formulation and is employed in conjunction with the fully implicit finite difference method to solve the solidification in the convectively cooled vertical tube. A generalised enthalpy-temperature (H-T) relationship, developed by Date, is suitable for constant phase change temperature and this is modified in the present work to accommodate materials having either constant or a range of phase change temperatures. The numerical model is validated with experimental data. The instantaneous surface heat flux and the solidified fraction for different number of fins and tube radii, that are of interest for the design of latent heat thermal storage system consisting of an array of vertical cylindrical tubes containing PCM inside it, are also discussed in this article.     

Maximum thermal load levelling in a double hollow wall/roof

The effect of a metal sheet in the middle of a hollow concrete slab, on the thermal performance of the concrete slab has been studied; one face of the wall/roof is exposed to solar radiation and ambient air and the other is in contact with room air at constant temperature. the optimum distribution of inside and outside concrete thicknesses for maximum thermal load levelling has been obtained; it is seen that this is achived when the outer concrete thickness is as small as possbile. These result have also been compared with the results corresponding to single hollow and double hollow concrete slabs.     

Thermoelastic Models of Continua

Axially symmetric thermal stresses in an elastic pipe weakened by two cylindrical cracks are provided. The surfaces of the cracks are assumed to be thermally insulated. The outer surface of the pipe is heated to maintain a constant temperature T _d , and the inner surface of the pipe is cooled to maintain a constant temperature T _b . As a first step, the boundary conditions related to the temperature field are reduced to dual integral equations using the Fourier transform technique. To satisfy the boundary conditions outside the cracks, the temperature difference at the crack surfaces is expanded into a series of functions that diminish to zero outside the cracks. The unknown coefficients in the series are determined by the Schmidt method so as to satisfy the thermal insulation inside the cracks. Next, the boundary conditions related to the stress field are reduced to dual integral equations. To solve the equations, the differences in the displacements at the crack surfaces are again expanded in a series of functions that diminish to zero outside the cracks. The Schmidt method is also used to solve the unknown coefficients in the series so as to satisfy the stress-free conditions inside the cracks. The stress intensity factors are defined and calculated numerically for several configurations of the pipe.     

Effect of phase change material on passive thermal heating of a greenhouse

In this study, a periodic analysis of a greenhouse with combination of phase change material (PCM) and insulation as a north wall has been developed for thermal heating. The thermal model is based on Fourier analysis. Effect of distribution of PCM thickness on plant and room air temperature has been studied in detail. The plant and room air temperature have been evaluated with and without north wall. Numerical computations have been carried out for a typical winter day of New Delhi. On the basis of numerical results, it is inferred that (i) there is a significant effect of PCM north wall and heat capacity of plant temperature during off‐sunshine hour due to storage effect and (ii) the rate of heat flux inside greenhouse from north wall is maximum for least thickness of PCM. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of Blocked Core-Tube Diameter on Heat Transfer Performance of Internally Longitudinal Finned Tubes

Three-dimensional turbulent flow and heat transfer in an internally finned tube with a blocked core-tube have been numerically studied by the realizable k ? ε turbulence model with the wall-function method. The numerical method is validated by comparing the calculated results with experimental data. The range of ratio of blocked core-tube outside diameter to outer-tube inside diameter (d ₀/D _i ) is from 0.25 to 0.75. The computational results demonstrated that there exists an optimal ratio of (d ₀/D _i ) under both identical mass flow rate and identical pressure drop. The optimal ratio of (d ₀/D _i ), which is reduced with the increase of mass flow rate, is approximately 0.5 to 0.625 at given mass flow rate for both constant wall temperature and uniform wall heat flux. The optimal ratio of (d ₀/D _i ) at a given pressure drop is from 0.44 to 0.50, which is also slightly reduced with the increase of pressure drop. Furthermore, the optimal ratio of (d ₀/D _i ) is not sensitive to the number of cross-section wavy fins of an internally longitudinal finned tube, in the range of a fin wave number of 15–25.     

高温过热器壁温测试及计算

过热器超温爆管是造成火电机组非计划停机的重要原因之一。为全面掌握过热器壁温状况,在410t/h超高压锅炉上实时采集了炉内壁温及炉外壁温的变化情况。在考虑炉膛出口三维烟温,烟速分布的情况下,建立了过热器炉内壁温分布的计算模型,编写了基于MATLAB语言的三维可视化计算程序。可通过此程序计算得到对流过热器各个管排各部位管壁温度分布,并以图形的方式显示烟温、烟速、及过热器管壁温度的立体分布,将理论计算结果与试验进行了比较,符合较好。     

高层节能住宅外墙外保温施工浅谈

阐述了高层建筑外墙外保温的发展方向简况,介绍了一种全新的外墙外保温体系－将钢丝网聚苯板放置于外墙外板内侧墙体浇注混凝土时一次成型的外保温墙体,阐述了保温板、墙体热工性能、施工工艺以及防止抹灰裂缝措施等方面的情况．     

Experimental study on flame height and temperature profile of buoyant window spill plume from an under-ventilated compartment fire

Fire experiments were carried out in a scale model, consisting of an 0.8 m cubic fire compartment with six window like geometries and an attached 3 m (wide) × 5 m (high) façade wall. A propane porous gas burner with controlled fuel supply rate was the fire source. Gas temperature profiles were measured inside the compartment and near the façade wall. The outside spill flame heights were recorded by a CCD Digital camera. Temperature and flame heights are correlated with heat release rate and the window geometry using physically non-dimensional analysis. The steady gas temperatures inside the compartment are determined by an overall energy balance between the heat release rate inside the compartment and the wall conduction and opening radiation heat losses using an effective overall heat loss coefficient. Flame heights on the façade are non-dimensionally correlated by the excess fuel heat release rate outside the enclosure and a characteristic length scale for the window. These results agree with previous results in the literature. Vertical gas temperatures near the façade wall outside the enclosure are non-dimensionally correlated with the total convective heat flow rate above the flames and the same characteristic window length scale as the flame height, with the additional necessary determination of a virtual origin of the convective flow above the flame. These results and correlations are new and a significant improvement over previous results in the literature.