冷库库门的非稳态RANS模型渗风研究

伴随冷库总量的快速增长,冷库的能耗问题已越来越受到关注。库门渗风作为冷库的一项占比很大的热负荷是冷库能耗研究的一个重点。本文采用非稳态RANS模型对库门渗风建立了动态模拟模型,利用对一座库高和门高之比为2∶1的冷库,在不同库内外温差和冷风机运行模式下,验证实测数据结果表明:所建模型预测的渗风量、测量点当地风速和温度的数值和变化趋势都与实验值有较好的吻合,在开门时间40 s内时,渗风量模拟误差在±10%以内。利用该模型对渗风的特性和机理进行了模拟分析,结果表明,受风机水平方向风场影响,风机开时库内温度均比风机关时低。库内外空气密度差较小,库内冷空气受重力的影响不大,因此渗风量随开门时间呈线性变化。     

２~８℃小型疫苗冷库热性能的实验及模拟

为研究2~8℃小型疫苗冷库内部温度场情况并优化热性能，本文以江苏省疾病预防控制中心一座20 m3疫苗冷库为研究对象，在不同工况下分别对其稳态温度场和库门呈30°或90°开启60s后的非稳态温度场进行实测，通过建立数学模型对冷库,结构进行了模拟优化，同时对冷库在测量时间段内和稳定运行时刻的制冷效果和冷库温度场均匀性等评价指标进行系统分析。结果表明:对于小型疫苗冷库，当长度L≥宽度W时，在L方向上布置两台制冷量适当的冷风机为最优布置方案，随着长宽比的降低，库内不均匀系数将更趋于理想状态，且当L＝W 时，疫苗冷库为最优结构；考虑开门影响，应规范疫苗箱摆放位置，库内疫苗箱距库门1.5ｍ范围内堆放高度建议不超过1.5ｍ整体堆放高度建议不超过1.8m。     

小型冷库风机动态模型的建立与数值模拟

为了揭示风机旋转气流对库内气流分布特性的影响,建立了风机及冷库的物理模型和数学模型,冷风机采用FAN模型,进行了数值模拟研究,得到不同运行工况下的速度流场和速度矢量分布,经分析得出各参量对流场的影响规律.     

空气渗透及其能耗的计算机动态仿真研究

本文在综合考虑影响渗风过程各主要因素的基础上建立一渗风简化模型并进行仿真，在对结果分析后认为，模型反映了渗风机理，体现了渗风量及其能耗的变化趋势且具有通用性，可供相关研究人员参考。     

空调送风参数对数据中心热环境的影响

选择合适的送风参数有利于机房IT设备的安全运行,提高冷量的利用率,还可以最大限度利用自然冷源,降低数据中心能耗。利用6SigmaRoom软件模拟不同送风参数下机柜进风温度分布以及0.2 m,0.8 m,1.6 m水平横截面温度分布,并分析送风参数改变对制冷能耗和风机能耗的影响。结果表明,回风温度为32℃时,送风温度从16℃提高到20℃,单台空调送风量从1.9 m3/s增加到2.5 m3/s,机房1.6 m截面处最高温度可从35℃降低到33℃,制冷能耗可减少2.73%。     

旋转气流及货物对冷库流场影响的研究

本文建立了小型装配式冷库的三维物理模型和紊流数学模型,采用fluent模拟技术和标准模型对库内吊顶式冷风机以及冷库进行数值模拟,分析冷风机的旋转气流以及货物摆放对库内流场的综合影响情况。     

土建冷库墙体保温的能耗分析

冷库围护结构的保温性能对冷库的运行能耗有很大影响。本文分析了土建冷库建筑围护中砌体、保温形式、保温材料、墙体表面材料对保温的影响,对土建冷库建筑的围护结构2种保温形式进行计算分析。结果表明采用外保温结构的冷库墙体保温性能更好,砌体的温度更低,蓄冷量大,能有效减小库内温度的波动;同时还减少了墙体的施工层数从而减少了施工周期和成本。     

低温冷库的温度要求与能效分级探讨

冷冻食品在低温冷库中贮藏是食品冷链中的重要环节,低温冷库的库温不均匀度、库温波动对货品品质有非常重要的影响。在保证正确的库温、合理的库内温度不均匀度和库温波动范围的前提下,对冷库能耗进行评价才有意义。制订低温冷库温度要求和对低温冷库的能效进行分级,将在规范低温冷库的设计和建设,提高冷库的货品品质,保证食品安全,降低冷库能耗,提高冷库的综合效益等方面发挥积极的作用。     

高温水源工况下带冷却塔预冷的制冷机房控制策略研究

为了降低高温工况下的水源制冷机房能耗,本文提出了对高温水源水先进行冷却塔预冷的运行策略.通过在TRNSYS软件上建立制冷机房模拟平台,对预冷控制方式和常规控制方式下的制冷机房总能耗进行比较研究.结果表明:当水源温度高于一定值时,先对高温冷却水先进行预冷,可有效降低制冷机房总功率,实现节能;通过比较不同水温下和不同变频风机风量下的制冷机房能耗,确定了预冷的转换点温度、预冷终温取值和最佳风量值.     

地铁可调通风型站台门过渡季节自然通风性能测试

可调通风型站台门是一种区别于传统结构的新型的屏蔽门,门上装有可开启和调节角度的风阀,空调季运行时关闭风阀,车站和隧道空气不相通,过渡季节时开启风阀利用活塞风对车站进行自然通风。目前针对该新型屏蔽门实际的通风性能数据缺乏,因此对设置可调通风型站台门的地铁车站在过渡季节的通风性能进行了测试,测试参数包括对通过可调通风型站台门的风量、地铁车站出入口风量以及车站的CO2浓度和温度。测试分析表明,依靠列车活塞效应引起的通风量能够满足过渡季节车站风量的设计要求,因此过渡季节可以关闭车站风机,减少风机能耗。     

An experimental investigation of the single-sided infiltration through doorways of the cold store

The frequent infiltration through doorways accounts for a very large proportion of the total heat load of cold stores. Understanding the influence factors, along with wider range of experiments, clearly supports the accurate prediction and cuts down the infiltration. This paper provides a series of experimental investigations on the infiltration under different conditions. The experiments take factors of various door opening sizes, temperature differences and on/off of the cooling fans into account. It is observed that the infiltration flow rate stays steady while the indoor temperatures of the local probes change vigorously. The infiltration air volume changes linearly with the door open time, whether the cooling fans are turned on or off. Moreover, the air mixture effect related to the cooling fans can counteract the infiltration process.     

Weight loss from lamb carcasses in frozen storage: influence of environmental factors

Tests were conducted to measure the influence of various environmental factors on the rate of weight loss of frozen lamb carcasses in single-storey cold stores. Weight loss was mainly affected by relative humidity, which is most cases depended primarily on the temperature difference between the store floor and the air. Other factors such as air temperature, coil split, temperature fluctuations, air velocity, store volume and coil area had minor effects or no observable effect within the range of parameters covered by these tests (although a store with an exceptionally low coil area/store volume did have a high desiccation rate, which was attributable to the continuous running of the evaporator fans). The observed rate of weight loss is satisfactorily correlated with environmental factors by a previously developed theory.     

24-hour cooling of a building by a PCM-integrated adsorption system

This study presents a theoretical investigation into integration of phase change materials (PCMs) with an adsorption cooling system in order to provide 24-hour air conditioning. A latent heat storage unit containing PCM is used to store solar energy during the daytime, and at nighttime the conserved thermal energy and an auxiliary heater drive the adsorption chiller. The system adopts a cooling channel to reduce the air temperature. The air flow to the channel is provided by use of fans and at different fresh air ratios (FR). Room temperature and the room's maximum cooling demand for which thermal comfort can be achieved are estimated. In addition, the effects of different parameters on room temperature and solar fraction are studied. It is indicated that an optimum ACH value exists for which the room temperature is the lowest. Also, rise of ACH and FR decrease solar fraction and increase auxiliary energy consumption. It is found that when ACH = 4 and FR = 20%, daily solar fraction is 0.76 and 217 MJ of auxiliary energy is required during the 24 hours. Under this condition, thermal comfort is achieved for a maximum cooling demand of 4000 W during the 24 hours.     

Thermosyphon-assisted cooling system for refrigeration applications

Residential refrigeration is one of the largest contributors to home appliance energy consumption in the U.S. This energy use is nearly doubled if commercial refrigeration is included. By using cold outside temperatures for cooling, however, energy savings can be realized. In this work, a thermosyphon-assisted cooling system for a household refrigerator is presented. A single finned copper-tube thermosyphon with methanol as the working fluid is used. An environmental chamber that can reproduce outside ambient temperatures to −5 °C is located above the refrigerator. Results are presented for different outside temperatures, fan speeds, and filling ratios in the thermosyphon. The electricity use for both the original equipment refrigeration and the thermosyphon system is reported. The interior temperature is found to vary depending on the number of fans that are used to blow air over the thermosyphon evaporator in the refrigerated space. This can be used to produce localized micro-climates within the refrigerated space for further energy savings.     

山东省果蔬冷库技术状况剖析

根据对山东果蔬冷库问卷调查的反馈,对80份有效问卷进行统计分析。发现山东果蔬冷库的技术水平偏低,仅5％的冷库采用自动控制,基本采用活塞式压缩机。制冷系统的管理十分薄弱,50％左右的冷库缺乏专业人员。有1／4的问卷没有反馈全年的电费和用电量。对于相同库容量的冷库,全年电耗差别可达3倍以上,反映出山东果蔬冷库的节能有巨大的潜力。     

梯级送风对冷藏车厢内温度场的影响分析

合理的厢内温度场是保证冷藏车运输货物品质、节能降耗的关键因素之一。为提高厢内温度场的均匀性,本文提出了单温区冷藏车的梯级送风模式。无梯级送风时,冷风在车厢内形成整体环流,流动方向较为集中,不利于整体降温;有梯级送风时,车厢顶部增加了风机,冷风速度得以提高,且流动方向更加分散,有利于提高整体降温速度和温度场均匀性。建立了冷藏车厢的仿真模型,利用CFD研究梯级送风对空仓时冷藏车厢内温度场的影响,并进行了实验验证。以射流区平均温度、车厢内整体平均温度、温度场不均匀系数和温度极差作为评价指标,对实验中采集到的温度数据进行对比分析。结果表明：梯级送风模式能够有效降低冷藏车厢内的射流区平均温度、整体平均温度、温度场不均匀系数,减小温度极差,提高降温速度;在射流区,梯级送风的影响最为显著,该处的降温幅度和降温速度都有明显优化;在车厢尾部近地面的拐角处,梯级送风的降温效果虽不明显,但降温速度明显加快。     

冷库门门洞净空尺寸对节能的影响

冷库门是冷库的配套设施之一,是操作人员和货物进出以及库内库外冷热空气交换的重要通道。本文通过对冷库门开启过程中的冷量损失和电机耗功的分析,提出最佳冷库门门洞的净空尺寸的计算方法,以达到节能的目的。     

直接蒸发冷却通风降温系统在兰州地铁的应用分析

对兰州地铁提出假设模型,针对兰州地区地铁对室内温湿度的要求,分别计算送风状态点、直接蒸发冷却效率、风量等。利用兰州地区的逐时气象参数,计算开启直接蒸发冷却系统的时间及其在夏季空调系统运行时间的占比,并对采用直接蒸发冷却系统和传统机械制冷闭式空调系统2种方案的能耗与经济性进行对比分析。结果表明,兰州地铁非常适合采用直接蒸发冷却通风降温系统,其开启时间占夏季空调运行总时间的41%,运行能耗约为机械制冷的1/2。     

Steady state CFD modeling of airflow, heat transfer and moisture loss in a commercial potato cold store

Storage loss beyond permissible limit is one of the most important problems in Indian potato cold stores, which has been hindering further growth of this industry. The losses in the stored potatoes have a direct relation to the intricate coupled transport phenomena of heat, mass and momentum transfer therein. Therefore, airflow, heat transfer and moisture loss was investigated in a potato cold store of commercial scale under steady state condition using the computational fluid dynamics technique. The developed CFD model was a two-dimensional simplification of the cold store. Heat and mass transfer at the cooling coils were not modeled, instead temperature and relative humidity in the air space were specified based on measured values. The model was validated in a commercial scale cold store and was found to be capable of predicting the air velocity as well as product temperature with an average accuracy of 19.5% and 0.5 °C, respectively and also the simulated average total moisture loss was found to be only 0.61% water (w.b.) higher than the experimental one for a storage period of 6 months. The main deficiencies of the airflow pattern which resulted in wide variations in temperature and moisture loss within the stored commodity can be investigated. The model located the probable zones of hot and cold spots, excessive product dehydration and moisture condensation within the storage facility, which might lead to qualitative and quantitative deterioration in stored product. This modeling tool could very well be applied to incorporate necessary design improvements with a view to improve the airflow distribution and heat transfer in order to limit the storage losses within the permissible limit.