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采用敞口型、温室型、温室-集热型3种干燥装置,研究了污泥在不同太阳辐射强度下的含水率变化,结果显示,太阳能干燥污泥的传热机理主要是太阳微波辐射及空气对流换热,干燥过程存在初始、增速、恒速、降速4个区别明显的阶段,并且空气流速对干燥过程的影响权重大于空气温度。当平均太阳辐射强度大于620W/m2时,能在180 min内将污泥的含水率降到38%以下;大于900 W/m2时,含水率能在120 min内降至38%。研究使用Logarithmic模型,建立了仅含太阳辐射强度S、干燥时间τ两种变量的干燥特性方程,简化了污泥干燥一般规律的预测计算。模型计算结果和实验值吻合较好,误差小于3.9%。 相似文献
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盘管腔式集热器可为太阳能布雷顿循环提供高温空气,也能直接用于工业生产,应用前景广阔。聚焦能流的腔内分布是影响盘管温度梯度和出口空气温度的主要因素,为优化盘管腔式集热器结构,合理分布聚焦能流,对不同结构(高度,腔体直径,管径和盘旋形状)的盘管式空气集热器进行了建模及模拟。模拟过程耦合了光学模型和传热模型,采用蒙特卡洛模型获得腔内能流分布,并将其作为边界条件加载到三维CFD(Computaional Fluid Dynamics,CFD)传热模型中,进而获得集热管内空气的温度场分布,为结构优化提供重要参考。 相似文献
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针对一种太阳能烟囱模型中的自然通风进行研究,选择k-ε方程建立模型,利用计算流体力学(CFD)软件对不同集热板倾角和烟囱高度的4个模型内空气温度和流速进行数值模拟,以更直观地研究模型内空气各个位置的状态,分析系统内的传热和流动,找出最优结构。综合温度和速度分布图,经济性和干燥效果的考虑,集热板倾角15,烟囱高度为0.41m的太阳能烟囱模型为最优结构。 相似文献
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我国太阳能干燥器应用 总被引:4,自引:0,他引:4
我国各地试验的各种太阳能干燥装置有多种形式,大体上可分为:温室型、集热器型、集热器与温室结合型、整体式和抛物面聚光型等。下面分别介绍这几种类型干燥装置的结构、特性、用途和干燥效果,以及一些应用实例。1温室型太阳能干燥器温室型干燥器的结构与栽培农作物的温室相似,温室即为干燥室,待干物料置于温室内,直接吸收太阳辐射,温室内的空气被加热升温,物料脱去水分,达到干燥的目的。温室型干燥器一般都设有排风装置,排去含湿量大的空气,加快物料的干燥周期。由于这种干燥器结构简单,造价低廉,在山西、河北、北京、广东等… 相似文献
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Himanshu Dehra 《Solar Energy》2009,83(11):1933-1942
A two dimensional thermal network model is proposed to predict the temperature distribution for a section of photovoltaic solar wall installed in an outdoor room laboratory in Concordia University, Montréal, Canada. The photovoltaic solar wall is constructed with a pair of glass coated photovoltaic modules and a polystyrene filled plywood board as back panel. The active solar ventilation through a photovoltaic solar wall is achieved with an exhaust fan fixed in the outdoor room laboratory. The steady state thermal network nodal equations are developed for conjugate heat exchange and heat transport for a section of a photovoltaic solar wall. The matrix solution procedure is adopted for formulation of conductance and heat source matrices for obtaining numerical solution of one dimensional heat conduction and heat transport equations by performing two dimensional thermal network analyses. The temperature distribution is predicted by the model with measurement data obtained from the section of a photovoltaic solar wall. The effect of conduction heat flow and multi-node radiation heat exchange between composite surfaces is useful for predicting a ventilation rate through a solar ventilation system. 相似文献
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涡轮薄层污泥干化是涉及导热、对流传热与传质、高速旋流相耦合的复杂过程,掌握污泥的耦合干化机理与规律、确定干化设备核心参数,是该技术成功应用的关键。本文用机理分析方法构建涡轮薄层干化过程传热、传质的数学模型,基于该模型对污泥干化过程开展数值模拟,揭示涡轮薄层干化过程单一气相和气固两相流的速度、温度和含水率的分布规律,探究涡轮薄层干化的关键技术及参数。设计开发涡轮薄层污泥干化系统并开展实验研究。结果表明:干化机内部的桨叶阵列设计能够实现物料的顺利运输,桨叶末端是干化机内混合传热效果最佳位置,最优桨叶安装角度为45°,出口污泥含水率可降至20%。 相似文献
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不同环境条件下土壤温度日变化的计算模拟 总被引:16,自引:2,他引:16
应用多孔介质中传热传质的数学模型,对夏天和冬天,环境风速分别为4m/s和1m/s以及环境相对湿度分别为35%和85%这3种情况下高为500mm,半径为250mm的圆柱土壤床中温度的日变化进行了比较。根据数值模拟的结果绘出土壤中不同深度处温度的日变化曲线表明:(1)土壤中各点的温度随气温和土壤表面获得的辐射能的周期性变化而呈周期性变化;(2)随着深度的增加,土壤温度受气温和太阳辐射的影内变小,温度变化的滞后效应越来越明显;(3)在夏天,一天的大部分时间土壤表层的温度高于深层的温度,冬天则恰恰相反;(4)风速对土壤表层的温度影内较大。风速越大,土壤温度降低得越多;(5)干燥气候下,由于土壤水分的蒸发制冷作用,一天中土壤各点的温度低于湿润气候下相应各点的温度,土壤表层尤为明显。 相似文献
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《Energy》2004,29(2):211-224
This paper presents the thin layer convective solar drying and mathematical modeling of prickly pear peel. For these purposes, an indirect forced convection solar dryer consisting of a solar air collector, an auxiliary heater, a circulation fan and a drying cabinet is used for drying experiments. Moreover, the prickly pear peel is sufficiently dried in the ranges of 32 to 36 °C of ambient air temperature, 50 to 60 °C of drying air temperature, 23 to 34% of relative humidity, 0.0277 to 0.0833 m3/s of drying air flow rate and 200 to 950 W/m2 of daily solar radiation. The experimental drying curves show only a falling drying rate period. The main factor in controlling the drying rate was found to be the drying air temperature. The drying rate equation is determined empirically from the characteristic drying curve.Also, the experimental drying curves obtained were fitted to a number of mathematical models. The Midilli–Kucuk drying model was found to satisfactorily describe the solar drying curves of prickly pear peel with a correlation coefficient (r) of 0.9998 and chi-square (χ2) of 4.6572 10−5. 相似文献
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建立步进式加热炉内流动、燃烧和传热的数学模型.炉内流场的模拟采用κ-ε双方程模型,辐射换热计算采用P-1辐射模型,气相燃烧采用Species Transport模型,流场计算采用Simpler算法.采用上述模型与算法得到了炉内详细合理的温度、速度和浓度分布,并对其中影响板坯加热的温度场进行了试验验证. 相似文献
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Simulation of a localized heating system for broiler brooding to improve energy performance 下载免费PDF全文
The aim of this work is to evaluate the performance of an innovative localized solar‐assisted pen heating system for brooding using a 3D computational simulation model of the heated space. The warm air‐curtained pen ensures acceptable temperature, air velocity, relative humidity, and air quality that meet the ventilation and heat requirements for a typical pen of 100 chicks as recommended by the American Society of Heating Refrigeration and Air Conditioning Engineers and American Society of Agricultural and Biological Engineers. The supply flow characteristics and the simulated velocity and temperature field of the curtained region were determined such that they meet the ventilation requirements and comfort criteria. Results show that air supplied at 40°C is capable of delivering the desired microenvironment at bird level while the heat input to the unit is 685 W when outdoor temperature is ?5°C. The system's energy performance was then analyzed using a prototype of 16 pens. The energy consumption of the new heating scheme consumed one third of the energy required by conventional non‐localized system. Moreover, integrating the new design with a solar system utilizing parabolic concentrators provided 72% of the power load from solar energy during a winter flock operation and 100% during other seasons. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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This paper presents a three-dimensional analysis for thermal comfort and contaminant removal in a hospital operating room. The room model includes a patient lying on an operating table, four surgical staff members standing around, and surgical lights above the patient. Cold clean air is supplied to the room through high sidewall grilles and exhausted through low sidewall grilles on the opposite wall. Steady-state heat and mass transfer in the room are simulated by employing computational fluid dynamics modeling approach. Solutions of the distribution of airflow velocity, temperature, relative humidity, and contaminant concentration are presented and discussed. The simulation results show a good agreement with experimental data from the literature. The predicted mean vote (PMV) is calculated for assessing thermal comfort of the occupants. The contaminant removal effectiveness (CRE) and the mean contaminant concentration in the breathing zone are used to assess the ventilation performance of the room. Effects of horizontal locations of supply and exhaust grilles on thermal comfort and contaminant removal are explored. Regression models for thermal comfort and contaminant removal as functions of these locations are built for design optimization. It is found that an overall better performance can be achieved by placing the supply grilles closer to the vertical centerline of the wall while the location of the exhaust grilles is somewhat insignificant. 相似文献
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搭建热泵干燥实验台,研究干燥室内不同热风温度、循环风速和排湿时间对菊花干燥特性的影响,并感官评定成品品质。结果表明:热风温度越高、循环风速越大或排湿时间越长,含水率越低,热风温度对含水率的影响最为明显;热风温度越高或循环风速越大,干燥初始相对湿度越大,干燥到一定时间相对湿度反而越小,转折时间点均约为10h,干燥全过程排湿时间越长,相对湿度越小;热风温度、循环风速对干燥速率与对相对湿度的影响呈现相同的规律,转折时间点分别为15和17h;热风温度越高、循环风速越大或排湿时间越长,干燥周期越短。任何一种参数过高均会影响成品品质,需综合调控这三个参数才能得到最佳干燥品质。 相似文献
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针对一个采用置换通风系统的典型办公室,建立了物理模型及数学模型,采用 κ-ε湍流模型结合壁面函数法对空调室内的湍流流动进行描述,采用有限客积法对控制方程进行离散,利用AirPak软件对不同工况下室内温度场、速度场进行了模拟计算,分析了送风温度、送风速度、送风口位置等因素对室内气流组织的影响。 相似文献