纳米氟碳涂层过冷却器动态制冰试验研究

针对过冷水动态制冰过程中过冷却器内易发生冰堵现象,采用纳米氟碳材料对过冷却器表面进行处理,并对纳米氟碳涂层过冷却器进行动态制冰试验研究及性能分析.研究结果表明:水在纳米氟碳涂层表面的接触角可高达163.01°,可有效抑制过冷却器结冰;对比无涂层过冷却器,在过冷水流速为1.95 m/s时,纳米氟碳涂层过冷却器出口过冷度降...     

过冷却器的介绍及Matlab程序设计

介绍过冷水动态制冰系统中关键部件--过冷却器(一种多管型套管式换热器).为了使纯水在一定流速下与一次制冷剂或二次制冷剂换热,并保证不会结冰而堵塞管道,提出了过冷却器的结构与性能要求.为了使其设计简单快速,减少工程设计人员的工作量,编制了过冷却器的计算机设计程序.最后得出换热器的设计要兼顾制造成本、运行费用以及性能要求,使换热器满足使用要求,达到优化目的.     

过冷却水制冰蓄冷性能的实验研究

利用过冷却水制冰蓄冷的关键设备是过冷却器，建立了过冷却器制冰蓄冷的实验装置。通过测定过冷却器进、出口两种流体的温度，整理绘制出正常状态下温度随时间的变化曲线。实验得出，当冷水温度为-1．5℃-1．7℃，流速在1．4-1．8m/s时，经管束喷出的水流会在碰撞后成冰，有利于制冰蓄冷，可得到较高的HPF值。     

平板过冷却器内结冰行为的实验研究

本文设计并搭建了一套过冷水动态制冰系统,开发了一种可视化平板过冷却器,通过实验研究流动和换热对过冷却器内结冰行为的影响,并基于经典成核理论与边界层理论对其作用机理进行解释。实验结果表明：平板过冷却器内存在两种典型结冰行为,结冰行为一表现为过冷却器内不结冰,系统可连续制取冰浆;结冰行为二表现为过冷却器内发生结冰,系统不能制取冰浆。载冷剂进口温度过低、制冰溶液流量过大或过小均会促进结冰行为二的出现,不利于系统制冰稳定性。发生结冰行为二时,相对距离d为0.15的壁面优先发生结冰,且该处壁面的温度总低于其余区域,因此优先发生结冰的局部条件是具有更低的壁面温度。     

纳米氟碳涂层抑制过冷却器冰堵的机理

冰浆由于良好的热物特性,在许多领域得到广泛的应用,其制取方式也成为关注的焦点。过冷水动态制冰是目前最有发展前途的制取冰浆方式之一,但其主要缺陷是过冷却器易发生冰堵。在此,基于水溶液结晶的机理,从影响过冷却器冰堵的因素出发,指出纳米氟碳表面改性材料可改善表面状况,有效抑制壁面结冰,减少制冰过程中的冰堵问题,提高整个系统的制冰效率,降低能耗。纳米氟碳涂层抑制过冷却器冰堵的机理对进一步深化和开发新一代防结冰技术有一定意义。     

水箱水温对CO2热泵热水器性能影响的实验研究

通过实验对比研究了循环加热和一次加热热水时,水箱水温对CO2热泵热水器性能的影响。循环加热工况时,随着水温的升高,压缩机的进、排气压力逐渐升高,功耗增加;气体冷却器的CO2进、出口温度升高,内侧CO2和外侧水的温差逐渐减小,换热量减小;CO2热泵系统的COP下降。一次加热工况时,进水温度一定,系统的各项运行参数稳定,COP基本保持不变。以水温度17℃为例,系统COP在3.5左右,远远高于循环加热的COP。实验结果表明水箱水温对系统的性能有一定影响。根据实验结果提出了水箱结构改进方案,使气冷器入口水温稳定在较低水平,可有效提高系统的性能。     

新型流态冰蒸发制冷循环及制冰量性能分析

介绍了蒸发过冷水制冰原理及系统流程,分析了相应的蒸发制冷循环,对单位质量(1k)干空气制冰量性能及影响因素进行了研究并建立了相关数学模型,计算结果显示,水的初始温度越高单位质量干空气制冰量越低,而单位质量干空气制冰量相同时水温越高对应的蒸发水量则越大,同时随着空气出口相对湿度增大,单位质量干空气制冰量也随之增加.另外,...     

具有较低最低不结冰温度的结冰基体的选择

选择具有较低最低不结冰温度(possible lowest unfrozen temperature,θPLU)的结冰基体对于提高过冷水动态制冰系统的制冰率和能量效率以及防止热泵蒸发器结霜具有重要意义.本文从异质形核理论和估算两相间界面能的Good-Girifalco极性理论出发,研究了具有较低θPLU的结冰基体的性质,提出了选择方法.选择了几种具有较低θPLU的结冰基体,测量了其θPLU值.所选择结冰基体的θPLU值比通常使用的不锈钢表面低3℃以上.     

载冷剂循环对间接式过冷水动态制冰性能的影响

为研究载冷剂循环系统对间接式过冷水制冰性能的影响,通过调整载冷剂泵频率分析不同载冷剂流量和泵耗功情况下的动态制冰系统效率。试验结果表明:载冷剂流量加大使制冷系统的蒸发温度得到提高,制冷效率小幅提升;载冷剂泵频率的增加虽会提高流量带来有益效果,但其产生的冷损失和能耗增加,使得冷量有效利用率和制冰效率大幅下降;为获得高制冰效率,建议维持蒸发温度在-5℃以上,且载冷剂泵能耗低于总能耗的35%。     

蒸发器出口过热度对汽车空调性能影响的实验研究

蒸发器出口过热度是制冷系统运行状态的一种特殊表征,为了研究在汽车空调中,蒸发器出口过热度对于蒸发器能力和系统影响的大小,本文在标准汽车空调实验台下实验,通过一种新型电子膨胀阀对蒸发器出口过热度进行控制,研究蒸发器出口过热度对于汽车空调性能、COP等参数的影响,研究结果表明,蒸发器能力随蒸发器出口过热度的减小而增大,在本文研究的系统中蒸发器的能力最多能被提升19.4%,系统COP随蒸发器出口过热度的减小先增大后减小,存在最大值,在本文研究的系统中系统COP最多能被提升17.8%。     

Performance of an HCFC22-based vapour absorption refrigeration system

A single-stage vapour absorption refrigeration system (VARS) is tested with monochlorodifluoromethane (HCF22) as refrigerant and different absorbents: dimethylether of tetraethylene glycol (DMETEG) and dimethyl acetamide (DMA). The influence of generator temperatures in the range 75–95°C, which represents low-grade heat sources, is studied. Cooling water temperatures were varied between 20 and 30°C. Two cases of cooling water flow paths are considered, i.e. water entering either absorber or condenser, which are connected in series. For HCFC22-DMETEG, COP values in the range 0.2–0.36 and evaporator temperatures between 0 and 10°C are obtained. For HCF22-DMA, COP values in the range 0.3–0.45 and evaporator temperatures between −10 and 10°C are obtained. It is observed that HCFC22-DMETEG can work at lower heat source temperatures than HCFC22-DMA. However, at the same operating conditions HCFC22-DMA is better from the viewpoints of circulation ratio and COP. Experiments also show that at low heat source temperature, cooling water temperature has strong influence on circulation ratio but does not affect COP significantly. Preferably, cooling water should first flow through the condenser and then through the absorber in order to achieve improved overall performance.     

Application of thermal battery in the ice storage air-conditioning system as a subcooler

This article experimentally investigates the thermal performance of a thermal battery used in the ice storage air-conditioning system as a subcooler. The thermal battery utilizes the superior heat transfer characteristics of two-phase closed thermosyphon and eliminates the drawbacks found in convectional energy storage systems. Experimental investigations are first conducted to study the thermal behavior of thermal battery under different charge temperatures (−5 °C to −9 °C) in which water is used as the energy storage material. This study also examines the thermal performance of the subcooled ice storage air conditioner under different cooling loads. Experimental data of temperature variation of water, ice fraction, refrigerant mass flow rate and coefficient of performance (COP) are obtained. The results show that supercooling phenomenon appears in the water and it can be ended when the charge temperature is lower than −6 °C. The system gives 28% more cooling capacity and 8% higher COP by the contribution of the thermal battery used as a subcooler.     

Thermodynamic limits to thermal regeneration in adsorption cooling cycles

Energy and exergy models for ideal adsorption cycles with isothermal beds and no mass recovery are developed to predict the limits to COP enhancement using thermal regeneration. The models are applied to compare the performance of zeolite–water and silica gel–water adsorbent–refrigerant pairs over a range of maximum bed temperatures. The thermodynamic consistencies of several alternate adsorption property assumptions are quantified. Differences in adsorption characteristics between zeolite–water and silica gel–water result in a significantly larger potential to enhance COP by implementing thermal regeneration for zeolite–water. Based on COP, the zeolite–water pair is preferred when both thermal regeneration and a high temperature thermal energy source (>150 °C) are used, while the silica gel–water pair is preferred when thermal regeneration is not used and/or a low temperature thermal energy source (<100 °C) is used.     

夏季冷热联供模式下的燃气机热泵机组性能分析

本文建立了一套以R134a为制冷剂工质、以天然气为一次能源驱动开启式压缩机做功的燃气机热泵系统,研究了当蒸发器进水温度为12～22℃,室外环境温度为24.2～35.6℃,发动机转速为1 400～2 000 r/min,夏季冷热联供模式时,空气源燃气机热泵(GEHP)机组的性能。结果表明:发动机转速和蒸发器进水温度的变化对系统性能的影响大于室外环境温度变化的影响。随着发动机转速由1 400 r/min增至2 000 r/min,系统COP_1、COP_2、PER_1、PER_2分别减小了15.5%、9.9%、18.8%、13.5%。在工况范围内,机组冷水出水温度可达6.7～19.3℃,热水出水温度可达40.7～61.7℃,考虑余热回收情况下系统PER_2可达1.14～1.45。     

Theoretical and experimental study on characteristics of a novel silica gel–water chiller under the conditions of variable heat source temperature

In this paper, a transient model of a silica gel–water adsorption chiller, which is developed in Shanghai Jiao Tong University (SJTU), is developed in order to simulate the evaporating, condensing, and adsorption temperature. Furthermore, this model is verified by a series of experiments. The theoretical studies and experimental data show that the coefficient of performance (COP) is influenced significantly by the variation rates of the heat source temperatures. The results also show that when this chiller is driven by solar energy, a buffer tank should be adopted in the system in order to get better performance when solar insolation is low, and should not be utilized when solar insolation is high, otherwise low COP will be gotten for the reason of the consumption of high electric energy.     

Experimental study on a continuous adsorption water chiller with novel design

A newly developed adsorption water chiller is introduced and tested. In the new adsorption refrigeration system, there are no refrigerant valves, the problem of mass transfer resistance resulting in pressure drop along refrigerant passage in conventional systems when methanol or water is used as refrigerant can be absolutely solved. Silica-gel–water is used as working pair and mass recovery-like process is adopted in order to use low temperature heat source ranging from 70 to 85 °C effectively. The experiment results demonstrate that the chiller (26.4 kg silica-gel in each adsorber) has a cooling capacity of 2–7.3 kW and COP ranging 0.2–0.42 according to different evaporating temperatures. Based on the experimental tests of the first prototype, the second prototype is designed and tested; the experimental data demonstrate that the chiller performance has been greatly improved, with a heat source temperature of 80 °C, a COP over 0.5 and cooling capacity of 9 kW has been achieved at evaporating temperature of 13 °C.     

臭氧处理冷水机组循环冷却水的节能试验研究

从目前循环冷却水系统中普遍存在的结垢问题入手,引出臭氧水处理法,它是一种环保、安全、高效的水处理方法。臭氧在处理循环冷却水时能起到杀菌、缓蚀、阻垢及脱垢的作用。简要阐述臭氧处理循环冷却水的阻垢及脱垢原理,分析污垢对冷水机组性能的影响。臭氧处理冷水机组循环冷却水的试验表明,臭氧水处理方法能够显著提高冷水机组的COP。     

空气源热泵热水器系统性能分析

为了预测空气源热泵热水器的运行性能,提高系统稳定性和降低能耗,建立空气源热泵热水器系统仿真模型,在焓差实验室对一台水箱容积为150L的一体式空气源热泵热水器样机进行变工况实验以验证模型的准确性,利用所建立的模型研究蒸发器入口空气流速及制冷剂质量流量对机组性能的影响。结果表明:系统制热量和COP都随环境温度的升高而不断增大;系统制热量随蒸发器入口空气流速的增大而呈增大趋势,在达到某值后,系统制热量变化趋于稳定;系统COP随制冷剂质量流量的不断增加呈先增大后减小的趋势,即制冷剂质量流量存在最佳值使得热泵性能系数最高。     

Performance of double effect absorption compression cycles for air-conditioning using methanol–TEGDME and TFE–TEGDME systems as working pairs: Performances de cycles à compression absorption à double effet pour le conditionnement d'air utilisant les couples méthanol–TEGDME ou TFE–TEGDME

The organic working pairs trifluoroethanol (TFE)–tetraethyleneglycol dimethyether (TEGDME or E181) and methanol–TEGDME have some advantages over classical water–LiBr and ammonia water working pairs in absorption cycles. One of the most important features is the wide working range caused by the absence of crystallization, the low freezing temperatures of the refrigerants and the thermal stability of the mixtures at high temperatures.The performance of a double effect absorption cycle for these organic mixtures can be improved if a compression stage is introduced between the evaporator and the absorber. The coefficient of performance (COP) and primary energy ratio (PER) values in the cooling mode are significantly increased over a wide working range: the cycle can work with temperature lifts of 50ºC at 5ºC in the evaporator or it can also be powered by low grade heat. For these conditions COP and PER values are higher than 1.0 and 0.7 respectively, and the power supplied to the compressor represents up to 15% of the thermal energy supplied to the generator. As it is possible to work at high temperatures lifts, the absorber and condenser can be air cooled.