立式开式陈列柜风幕送风速度对其温度分布影响的实验研究

实验研究立式开式陈列柜风幕送风速度对其温度分布的影响。实验结果表明，降低其内风幕的送风速度或提高其外风幕的送风速度，均能使风幕向柜内侧偏移，减少冷风幕的外溢，提高风幕封闭敞口的能力，改善陈列柜的性能。     

减湿预冷器对冷藏陈列柜风幕性能的影响分析

本研究以中温立式多搁架冷藏陈列柜为研究对象，采用蒸发器分级的方法，第一级使用过热器作为减湿预冷器，第二级为蒸发器。使用减湿预冷器后，内层风幕风速下降趋势和风幕出口温度上升趋势明显平缓。试验表明减湿预冷器对外层风幕速度和温度的影响较小，可以提高陈列柜风幕封闭敞口能力，改善陈列柜性能。     

风幕特性对立式低温陈列柜运行性能影响的实验研究

风幕特性的好坏对敞开式制冷陈列柜性能影响很大.通过改变风幕的层数和各层风幕的送风速度,实验测试陈列柜运行期间柜内各层搁架上的瞬态温度值,来研究低温陈列柜内温度的变化和分布情况.研究表明,对于立式敞开式低温陈列柜采用三层风幕的结构是必要的,合理选配各层风幕的送风速度可使柜性能得到提高.     

Two- and three-dimensional CFD applied to vertical display cabinets simulation

A commercial CFD code has been employed to simulate the air flow pattern and the temperature distribution in a frozen food vertical display cabinet. At first the choice of solver parameters has been investigated in a 2D modelisation. 3D simulations have been then performed, and the effects of the cabinet length, of the warm air curtain and of longitudinal ambient air movement have been investigated. The results show that, in short cabinets, 3D secondary vortices at the side walls provide the most important mechanism for hot air entrainment. Comparison with experimental results shows that a 2D simulation is totally inadequate for such configurations, while 3D computations predict refrigeration power within engineering accuracy. Furthermore, the computed refrigerating power shows that even low room air velocity, due to its interaction with the end-wall vortices, has a significant impact on cabinet performance.     

Modified two-fluid model for air curtains in open vertical display cabinets

A modified two-fluid turbulence model is established to simulate the flow and heat transfer characteristics of air curtains in an open vertical display cabinet. The air exiting the back panel (AEBP), the inner air curtain and the outer air curtain are taken as the first fluid and described with the standard k− turbulence model (KE). The air outside the display cabinet is considered as the second fluid and calculated by the laminar model. Different from the existing two-fluid model, the mass transfer rate equation between the turbulent and the non-turbulent fluids is modified, and the face coefficient of honeycomb (the ratio of the effective area to the total area of honeycomb) is fetched with the volume fraction of air curtain in order to conveniently depict the blow characteristics of the honeycomb. The comparisons between the simulated temperatures and the experimental ones indicate that the modified two-fluid model (MTF) can give better agreement with the measurements than KE and two original two-fluid models (TF1 and TF2).     

敞开式陈列柜冷风幕的研究状况

本文介绍了敞开式食品陈列柜的冷风幕流动及换热机理和数值计算方面的研究状况 ,并分析了陈列柜冷风幕研究过程中存在的问题     

The use of CFD to improve the performance of a chilled multi-deck retail display cabinet

Maintaining food temperatures below critical values is the key to maximising the high quality display life of chilled foods. Studies were carried out to see if computational fluid dynamic (CFD) modelling could be used to rapidly identify the changes that would be required to an existing multi-deck display cabinet so that it would meet a higher test specification. Implementing the changes on a Pastorfrigor MV 200TP display cabinet reduced the average power consumption from 1.37 to 1.29 kW as well as significantly reducing the number of test packs which spent any time above 4 °C, from 12 to 1.     

Development of a design tool for display case evaporators

A model for simulating a fin-and-tube display case evaporator has been developed to serve as a design tool for improving performance in frosting conditions. It is capable of simulating cross-counterflow evaporators with multiple modules having completely different geometries. Quasi-steady heat and mass transfer calculations provide local values of all relevant variables, including heat and mass transfer coefficients, air and refrigerant-side pressure drops and fin and tube frost thicknesses. A multi-lump method enables the model to simulate both tube and fin frost thicknesses and surface temperatures. The results presented in this paper reflect interactions with the display case and its air curtains and predict local and overall effects of frost accumulation, to facilitate optimization of the larger display case system.     

Evaluations on heat resistance of curtains with water film in a fire

Fire tests of fireproof and non-fireproof curtains were conducted to investigate the cooling performance of the proposed water film system. The experimental results showed that although commercial fireproof curtains without a water film system had good flame resistance, they had limited heat resistance. The maximum temperature on the unexposed surface of the tested commercial fireproof curtains without a water film system reached 693 °C, and the curtains failed in 30 min. In the cases of curtains with a water film system, the temperature of the unexposed surface was able to remain below 45 °C for the fireproof curtain and 55 °C for the non-fireproof curtain. The integrity of both curtains was conserved for the entire 60-min test duration. Using the proposed water film system, the heat resistance and fire integrity of curtains were greatly improved.     

环境送风式冷藏陈列柜的开发研究

为解决传统陈列柜功耗过大的问题,搭建了环境送风式陈列柜试验台。试验结果表明,与传统陈列柜比较,环境送风陈列柜可实现良好的节能特性。由于可引入室外冷空气,无需压缩机制冷,能节省大量的能耗。但此种供冷方式受到室外环境温度的限制。     

陈列柜蒸发器结霜对其风幕性能影响及融霜周期的实验研究

本文实验研究了陈列柜蒸发器结霜对其风幕送风速度的影响.实验结果表明蒸发器结霜大大降低风幕的送风速度.因此,蒸发器必须定期融霜.本文设定不同的融霜周期考察融霜周期、融霜时间和柜温回升三者之间的关系,为确定最佳的融霜周期提供实验性依据.     

Refrigerant flow instability as a means to predict the need for defrosting the evaporator in a retail display freezer cabinet

For refrigerated display cabinets to perform their function of keeping food cold, there must be free movement of air through the evaporator. The moisture in the ambient air entrained in the cabinet forms frost on the evaporator. It is traditional for heat to be applied to the evaporator at regular intervals to melt this frost. The frequency, typically 3–4 times per day, is enough to avoid the frost becoming excessive even in extreme conditions. For much of the time defrosting is not always necessary. A large portion of the energy used during a defrost is an overhead – heating and then cooling the metal and the food rather than melting the frost. The effect of this is examined in the paper along with the results from testing an algorithm that detects the need for a defrost from the pattern of refrigerant flow (or evaporator exit superheat). The algorithm allows the number of defrosts to be reduced without excessively raising the temperature of food stored in the cabinet. The reduction in energy and carbon dioxide emission were examined and were shown to be substantial.     

敞开式食品冷藏陈列柜耦合节能的试验研究

本文对环境温湿度对陈列柜及空调系统的影响进行了试验研究。从耦合节能的角度考虑,结合环境温湿度对陈列食品温度的影响,试验分析环境因素对陈列柜及空调系统能耗的影响情况。试验表明,当系统在环境温度23℃,相对湿度55%工况附近运行时,陈列柜及空调系统总能耗较小,陈列柜及空调系统可以达到较好的耦合节能效果。     

卧式陈列柜风幕的数值模拟

本文以卧式陈列柜为研究对象，在一些基本假设的基础上，建立了卧式陈列柜风幕及柜内空气流动和换热的二维数学模型；并运用SIMPLER算法编写程序进行了数值计算，计算过程中重点考虑了风幕送风速度和环境空气温度对风幕性能的影响。     

Numerical and experimental investigations on the use of mist flow process in refrigerated display cabinets

This study concerns the use of mist flow whereby fine water droplets are injected into the air curtain to improve the performance of Refrigerated Display Cabinets (RDCs). The deposition and evaporation of droplets on the surface of products partially compensate the radiative heat gained by the products by removing from it the amount of latent heat of the evaporated droplets.The experiments were carried out on an actual display cabinet. Numerical modelling was performed using Fluent Computational Fluid Dynamics (CFD) software. In two-phase flow, an Euler–Lagrange approach was adopted to predict the transport of droplets by the air curtain and their spatial distribution on the product surface of the RDC. An original numerical procedure was built in the CFD model in order to compute the deposited droplets while taking into account the evaporative flux of droplets on the product surface.The two-phase flow model was used to analyse the performance of the mist cooling process in terms of surface temperature decrease and the homogeneity of droplet deposition on the product surface of the RDC as a function of inlet droplet injection configurations.     

Jet entrainment rate in air curtain of open refrigerated display cases

Experimental and computational methods are used to address those parameters that have significant effects on the amount of entrained (warm) air in an open refrigerated display case. These parameters are identified, quantified, and the rate of entrainment is expressed as a function of these parameters. It is found that the turbulence intensity, the shape of the mean velocity profile at the discharge air grill, and the Reynolds number are mainly responsible for the amount of entrained air in a display case. It is also concluded that lower Reynolds numbers will reduce the amount of the entrained air in the display case, however, the trade off will be higher temperature of the food products on shelves. Digital particle image velocimetry (DPIV) was used to map the entire mean velocity flowfield and the turbulence intensity. The laser doppler velocimetry technique was also used to verify the mean velocity and turbulence intensity measurements made by DPIV. The results indicated an excellent agreement between both methods. Parametric studies for the rate of entrainment of the outside air into the display case were performed using a computational fluid dynamics tool. The results indicate that lowering the Reynolds number of the air curtain reduces the entrainment rate. However, sufficiently high momentum should still exist to enforce the integrity of the air curtain structure.     

The impact of geometric structure and flow arrangement on the performance of CO2 evaporators in multi-deck medium temperature display cabinets

The CO₂ refrigerant is widely applied in retail refrigeration systems to replace HFC fluids such as R404A, but its system performance requires further improvement. One feasible method would be to pinpoint the matching components of the system, in particular its evaporator coils. This paper focuses on the potential optimization of the CO₂ evaporator design in an existing multi-deck medium temperature display cabinet charged previously with R404A refrigerant. To achieve this target, a display cabinet model with an integrated CFD and detailed evaporator sub models was utilized. This model could readily imitate the actual cabinet performance under varied operating conditions and component designs. Various design options of the CO₂ cabinet evaporator were considered and their impacts on the cabinet performances were predicted by the integrated model. Ultimately, the optimized designs of CO₂ cabinet evaporator coil geometries and refrigerant side operating parameters have been attained.     

陈列柜风幕的数值研究及其影响因素分析

本文根据流体力学和数值传热学的基本方程，建立了陈列柜风幕及柜内空气流动和换热的二维数学模型；并采用湍流模型和SIMPLER算法进行了数值计算。文中重点分析了风幕送风速度、环境空气温度和送回风口尺寸三个因素对风幕性能的影响。本文的研究结果为陈列柜的优化设计和实验研究提供了依据。     

Experimental study on the heat and mass transfer characteristics in a refrigerated truck

An experimental study on the heat and mass transfer characteristics in the body of a refrigerated truck for cases without an air curtain, with a fan air curtain and with a plastic strip curtain have been carried out. The variations in temperature and relative humidity inside the stationary truck during a short duration after the door is opened are the present focus. The average air temperature inside is found to increase to 14, 7 and 8°C from an initial temperature of −10°C, for cases without an air curtain, with a fan air curtain and with a plastic strip curtain, respectively, within 2 min after the door is opened. It is found that using an air curtain can have energy savings up to 40 and 11%, respectively, compared to the cases without an air curtain and using plastic strip curtain. Comparison between the experiment and numerical results also shows reasonable agreement in terms of average temperature inside the body.     

陈列柜摆放位置对荔枝货架期品质的影响

目的研究不同销售方式及摆放位置对货架期荔枝果实品质变化的影响,为荔枝果实货架期保鲜和销售货架设计提供一定的参考。方法在敞开式陈列柜和常温货架上,以盒装的"怀枝"荔枝果实为实验材料,开展荔枝果实贮藏试验,研究货架期72h内荔枝果实分别放置在冷藏陈列柜不同位置和常温货架上品质的变化情况。结果在货架期内,冷藏陈列柜第4层和常温货架贮藏荔枝的果实褐变指数高于其他陈列位置,好果率低于其他陈列位置;冷藏陈列柜第4层的荔枝果实质量损失率的上升速率最快,72 h后上升至11.01%,其果皮色差a*值最小;第3层荔枝果实的质量损失率上升得最缓慢,其果皮色差a*值最大;常温货架荔枝的果皮色差L*值最大,其果肉的可溶性固形物含量和硬度最低;不同销售方式及摆放位置对荔枝果肉可滴定酸含量的变化影响不显著。结论在冷藏陈列柜中、上部摆放位置贮藏能相对更好地保证荔枝果实的销售品质,冷藏陈列柜的结构优化及其对温湿度场分布特性的影响将会是今后的研究方向。