共查询到20条相似文献，搜索用时 15 毫秒
1.
AN ENTHALPY METHOD OF SOLVING PHASE CHANGE PROBLEMS BY COUPLING THE ENTHALPY AND THE MOVING BOUNDARY
Zeng xin Xin Mingdao 《保鲜与加工》1992,(3):62-67
A numerical enthalpy method is proposed for solving the multi-dimensional
phase change problem by coupling the enthalpy and the moving boundary. Its basic feature is to sepasate appearent and latent heat terms by transforming the standard enthalpy relation and to couple them into the latent heat term by introducing the idea of phase change rate between the axes and simultaneously to correct the heat flux of the inflowing/outflowing phase change control volume element , so that the accuracy of numerical solution is improved and the moving boundary can be accurately followed. 相似文献
2.
Differential scanning calorimetry(DSC) is a heat analysis method which studies matters' thermodynamic properties according the measured energy differential by temperature scanning under the control of linear temperature programme.Differential scanning calorimetry technique is used for the temperature and latent heat determination when some tissues in vitro such as pig muscle,fat,liver and beaf chang phase during the temperature rises.Then the latent heat and phase change temperature are derived.It is conclusion that the main influencing factors of latent heat and phase change temperature are water and fattiness in tissues;the more of water and the fewer of fattiness,the larger of latent heat and the boarder of the temperature area changing phase. 相似文献
3.
Zeng Xin Xin Mingdao Zhang Daming 《保鲜与加工》1992,(2):40-45
The one-dimensional heat transfer of microwave thawing in a food analogue material is experimentally studied. The results show that the phase change region is narrow and the latent heat is quickly released due to the effect of the microwave energy. Besides, in the rising section of the temperature after thawing. the internal heat source makes the temperature at the central point rise more quickly than that at other parts of the tested element. 相似文献
4.
A macroscopic and microscopic coupling mathematical model for solidification process of twin-roll thin strip is developed. In the model, the latent heat is treated by the enthalpy method, and the grid and node are divided by assumed streamline boundary. The heterogeneous nucleation and the columnar-equiaxed transform(CET)model are introduced, together with the revison of the dendrite growth dynamic model of KGT. With the help of solid fraction, the coupling of the macro/micro aspects is realized by using different grid-sizes and time-steps, macro and micro, together with the columnar dendrite front tracing. The columnar dendrite arm spacing and deflection angle calculated by proposed model are in agreement with the experimental ones. Therefore, the model is proved to be reliable, and it can be used to predict the effects of the processing parameters on the solidification structure of twin-roll thin strips. 相似文献
5.
On the core concepts that the distributing of temperature and solidified slab shell in mold are a stable process, a new method to calculate the temperature field in mold has been promoted. Consequently, a coupling model on fluid filed and temperature field in stable state has also been established. The concept of effective heat capacity is introduced to deal with the latent heat source term from phase transformation. During the programming for computation, the dynamic updating method is also applied to simulate the influence of solidification on physical properties. The resolution results of this model are analyzed and compared with the tested thickness of solidified shell from casting broke out slab, which demonstrates the correctness and applicability of this model to the practical continuous casting process. Additionally, the thickness distribution of solidified shell in slab mold are also studied in detail. 相似文献
6.
In this paper,a numerical simulation of the casting process for making the MMC.using the PEM, is studied.The convection of liquid metal and the release of latent heat of solidification are taken into account.The algorithm and program for axisymmetric casting model are developed to the problem of coupling between flow and heat transfer,as well as phase change.The variational curves of temperature,the position of flow front and the distrsbutions of volume fraction of solid metal in matrix and their variation with time are obtained.The influences of technological paarmeters to casting are discussed. 相似文献
7.
谷物呼吸热值测定研究 总被引：1，自引：0，他引：1
谷物呼吸热值测定是粮食通风散热课题的核心问题.本文利用气体分析仪和恒温水槽测定谷物呼吸对氧气的消耗量和二氧化碳的生成量,作者首次提出了同时考虑有氧呼吸和无氧呼吸两因素,对呼吸方程进行配平,从而由呼吸生成物与呼吸反应物之间生成??值之差来精确计算出呼吸热. 数据处理全过程由微机完成. 相似文献
8.
Based on the general thermodynamic theory,a mathematical model for thermodynamic parameters of hot-shot steam is derived,it includes the formula of specific enthalpy,specific volume,specific heat at constant pressure and specific entropy.The specific enthalpy formula of steam with a pressure range from 0 MPa to 90 MPa and the specific volume formula of steam with a pressure range from 0 MPa to 40 MPa within permission error of the International Steam Skeleton Tables in 1985,and that all the model with a temperature range from 273.15 K to 1 073.15 K.The model is applied to real-time simulation for supercritical fossil power unit and convenience in application of engineering. 相似文献
9.
典型草原区草地潜热通量特征 总被引：1，自引：1，他引：0
为研究局地小气候和草地生态系统变化提供依据。利用2010年6月1日—8月31日开路涡度相关系统和常规气象观测系统资料,分析锡林浩特典型草原区草地潜热通量变化特征及其与环境因子的关系。结果表明,6—8月总体能量平衡闭合很好,闭合度达83.9%。晴天闭合度为81.4%,阴天闭合度为95.0%,处于国内外同类观测闭合度范围的上等水平;潜热通量日变化呈单峰型二次曲线,日出后逐渐升高,中午左右达到峰值,然后逐渐降低,日落后趋于稳定。晴天和阴天的潜热通量日变化趋势相同,但阴天波动性较大,变幅大于晴天,且峰值滞后于晴天;潜热通量与净辐射、气温、地表温度、地表温度与气温差、呈极显著正相关,与相对湿度呈极显著负相关,而与水平风速的相关性相对较弱。其中,净辐射是最大的影响因素。 相似文献
10.
苏北地区日光温室能量分配动态研究 总被引：1，自引：1，他引：0
为了进一步提高日光温室保温性能,减轻温室内低温寡照灾害发生,以苏北（徐州）番茄日光温室为研究对象,利用采集的2010年12月-2011年4月温室小气候数据及番茄发育数据,根据日光温室小气候形成的物理过程与机理,系统研究了冬春季节不同天气类型及不同叶面积指数对温室能量分配的影响。结果表明：日光温室内潜热、显热随着室内总辐射量的改变而发生变化,阴天以显热消耗为主,潜热消耗量全天低于显热;晴天日光温室内用于作物蒸腾的能量显著多于阴天,阴天室内外贯流传热消耗的能量远远多于晴天;随着叶面积指数增大,到达地面的太阳辐射减少,地面升温慢,室内空气与地表的显热交换量减少,同时室内空气与墙体的显热交换增加。本研究结果可为温室的结构优化及冬春季节日光温室管理提供科学依据。 相似文献
11.
The conception of independent exergy evaluation of temperature and humidity control in HVAC systems is proposed with the corresponding evaluation indexes presented. This type of evaluation process is illustrated in an air conditioning system with primary return air from the view of thermodynamics. The results show that exergy efficiency of sensible heat is larger than that of latent heat. The reason lies in the fact that the destructions in reheat process and condensed water are very serious. It is concluded that the surface air cooler is not an energy saving equipment in respect of exergy utilization, and the regeneration of the supply air stream at the state of dew point would improve its exergy efficiency of latent heat. The analysis indicates that this independent exergy evaluation is benefit for the exergy evaluation for HVAC systems, and it provides effective resolutions. 相似文献
12.
淮河流域麦田湍流通量输送特征分析 总被引：1，自引：0，他引：1
利用淮河流域寿县国家气候观象台2007年11月至2008年5月的湍流通量观测资料,分析了该区域麦田湍流通量输送特征,结果表明：小麦各生育期净辐射通量、显热通量和潜热通量都存在明显的日变化;净辐射日变化最大值出现在成熟期;显热通量在中午温度最高时达到最大值,夜间显热通量多为负值;潜热通量峰值出现时间比净辐射通量峰值延迟1h左右;自拔节期开始,麦田潜热通量日平均值都大于50.0 ;三叶期和分蘖期,土壤热通量日平均值都为负值,其它时期为正值;H/Rn和LE/Rn均有明显的季节变化,且变化方向相反。 相似文献
13.
According to different construction ways and materials, three kinds of roof, that is ,passive evaporated roof with freedom water surface , water stored roof by means of pore material and hygroscopic roof,are introduced in this paper . Meanwhile the theory of heat insulation and energy efficiency on passive evaporation roofs and suitable weather and places to be used are also discussed .The results show that all kinds of passive evaporated roofs have high efficiency in heat insulation because of water's high specific heat and large quantity of absorbed latent heat,and that they can be adopted according to the practical local weather ,natural resource and economical development. 相似文献
14.
A theoretical model is developed for the dropwise condensation heat transfer on the horizontal circular surface with radial gradient surface energy based on the heat transfer model of individual condensate drop and the size distribution model of condensate drop on homogeneous condensation surface.The effect of variation of contact angle on the gradient surface on condensation heat transfer and condensate drop size distribution is taken account of in this model.The theoretical calculation method was obtained to predict the dropwise condensation heat transfer coefficient on the horizontal circular surface with radial gradient surface energy under various wall subcooled temperature,contact angle profile on wall surface,and working fluid.The effects of surface energy gradient,wall subcooled temperature,and thermophysical properties of condensate on the condensation heat transfer are discussed respectively.The calculation results show that the condensation heat transfer coefficient increases slightly with the increase of wall subcooled temperature.As latent heat and surface tension increasing,the condensation heat transfer coefficient increases.A larger surface energy gradient induces a larger condensation heat transfer coefficient. 相似文献
15.
In the established model,
the cooling differences are considered between the surface of inner radius and that of
outer radius, and in the transverse direction of thin slab. And the conception for the
effective coefficient of spraying water in continuous casting is firstly put forward.
According to different casting speeds and different cooling zones, different time step
lengths are adopted. In this model the heat transfer differences are thought over among
vertical and curved zones, wide and narrow surfaces an well as angular zone of mould. The
method of the corrected equivalent specific heat is used to deal with latent heat. The
influence of forced convection is considered on heat transfer. Therefore, the model has
higher accuracy and is consistent with the practice. 相似文献
16.
For making the refrigeration system directly driven by low temperature waste flue gas heat more efficiently,an experimental research on the heat transfer of vertical in tube laminar falling film with different heat fluxes and different concentrations of lithium bromide solution is conducted.The outcome of falling film evaporation experiments show that the heat transfer coefficient increases with the decrease of inlet concentration of lithium bromide solution and significantly increases with the increase of heat flux.Based on multiple linear regression calculation of experimental data,an experimental correlation of falling film heat transfer coefficient is obtained.A falling film generator of lithium bromide absorption chiller is designed from the correlation,and the immersed generator whose heat load is equal to the falling film generator is designed.The comparison of the two generators on heat transfer coefficient,weight and volume of heat transfer components shows that the falling film generator has great advantages. 相似文献
17.
几种植被能量平衡的差异 总被引：4，自引：0，他引：4
根据１９８９年４－１０月的观测资料,分析了晋西黄土高原地区几种主要植被之间能量平衡的差异。结果表明,不同植被间反射率差异明显,在太阳总辐射差别不大的情况下,各下垫面得的净辐射差异显著,有效辐射的差异相对较小;不同植被之间土壤热通量（Ｑｓ）、显热通量（Ｈ）、潜热通量（ＬＥ）都存在一定的差异。在潜热通量的日间变化过程中,草地和刺槐林没有“午休”现象,而油松林和沙棘林有明显的“午休”现象。刺槐林的日平均 相似文献
18.
抗坏血酸/瓜尔豆胶复合作用对玉米淀粉回生特性的影响 总被引：1，自引：0，他引：1
抗坏血酸与瓜尔豆胶按照一定的比例混合后,与适量的玉米淀粉配制成淀粉水溶液。充分糊化后,放置不同时间,测定并分析淀粉溶液在回生过程中溶液透光率、脱水率、结晶度及焓变等相关参数的变化情况。研究结果表明,抗坏血酸和瓜尔豆胶按不同比例混合,对淀粉的回生具有不同程度的抑制作用。在相同条件下,二者配比为2∶1时抑制效果最好。 相似文献
19.
In order to enhance the heat transfer in the phase change heat storage device, a rectangular cavity filled with metal foam / paraffin wax is made. The melting heat storage experiment of foam metal / wax composite phase change material was carried out in the transverse wall temperature conditions. The temperature change curve is drawn according to different heating temperatures. Both the effects of natural convection in rectangular cavity on temperature distribution and the impact of heat transfer temperature difference on the thermal storage time are analyzed. The results show that the melting process of the paraffin in the body cavity is reinforced by the high thermal conductivity of copper foam. The remaining solid paraffin is accelerated to melt by the natural convection of the liquid paraffin formed near the heating surface; and the greater the heat transfer temperature difference is, the greater the natural convection is and the shorter the time for heat storage is. 相似文献
20.
Components of the energy and heat balances were examined in two maize hybrids grown at three different plant densities (40, 70 and 100 thousand plants per hectare). One of the hybrids was drought tolerant, while the other was bred for cultivation under irrigated conditions. An increase in plant density influenced not only the size of the leaf area, but also the distribution of the leaves at various plant heights. The extinction coefficient, which provides a quantification of radiation penetration, was higher in the irrigated treatments. By contrast to the other two treatments, the plant canopy in the thinly sown stands remained open throughout the vegetation period, and thus behaved quite differently to the closed stands, making it impossible to compare them. Smaller albedo values were recorded for the hybrid bred for irrigation and in thinly sown stands. The low plant density allowed more energy to reach the soil, from which it was reflected, making a considerable contribution to the final temperature in the stand. The latent heat, in keeping with the quantity of water transpired, was the greatest in the densely sown stands. There was little difference between the latent heat values of the normal and dense stands in either hybrid, indicating that they both had a similar sensitivity to increased stand density. If sufficient water is available it would appear that the stand density could be increased even for the drought-tolerant hybrid. 相似文献