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1.
Cooling demand in the building sector is growing rapidly; thermal energy storage systems using phase change materials (PCM) can be a very useful way to improve the building thermal performance. This work shows the benefits of PCM when incorporated in wood fiber-polymer composite as floor cooling system using nano-encapsulated PCMs. The wood-plastic-NPCM composites were produced using compression molding process and its mechanical and thermal properties were investigated. Two dynamic simulators were employed to investigate synthesized composites thermal performance. Increasing NPCM content in WPC showed that the fluctuations of the simulator temperature was decreased while the heat fluxes through the floor was increased. The variations of ambient maximum temperature have little effect on the air temperature of the simulator with 40% PCM which indicates that the amount of PCM was enough for studied environmental condition. Field experiments were performed using two medium-scale test houses located on Tehran-Iran. It can be concluded that using NPCM helps to reduce heating and cooling demand. Moreover, the natural night ventilation by opening windows reduced the number of hours that the temperature is above 23°C from 499 h/year in case1 (without opening) to 255 h/year in case 2(with opening). This means that natural night ventilation could help reduce the overheating period to about 50% with the use of NPCM.  相似文献   

2.
Free cooling night ventilation is the process of storing the coolness in the night time and releasing this coolness in hot day time. In this paper, a numerical study was carried out to simulate and to find out the optimum design for plate type storage filled with phase change material (PCM) which is used in night ventilation systems. The effect of different parameters such as thickness of PCM-plates, inlet air temperature and air mass flow rates on melting front, cooling power, outlet temperature and thermal performance of heat exchanger was studied. The results showed that cooling power can be increased by increasing the mass flow rate. Also, the thickness of the plates in the storage device plays an important role in the thermal performance of the unit and has a linear relation with the melting process duration of PCM for considered configuration.  相似文献   

3.
提出一种基于太阳能热风供暖系统的多级相变通风吊顶新型供暖末端。建立多级相变太阳能通风吊顶传热数值模型,对比研究了单级、两级和三级相变太阳能通风吊顶的蓄放热特性,分析相变材料的长度配比、空气流速对供暖末端蓄放热性能的影响规律。研究结果表明,与采用单一相变材料的通风吊顶相比,多级相变太阳能通风吊顶在蓄放热过程中出口平均温度差异更小。相变蓄热级数为3时,通风吊顶的蓄、放热效率及相变材料利用率改善最大,分别为6.5%、7.9%和25.1%,各级相变材料长度的配比为1∶1∶1时,蓄、放热效率及相变材料利用率最佳,分别为51.0%、88.7%和93.9%。空气流速不宜大于1.6 m/s,在保证供暖效果的前提下可适当减小空气流速。  相似文献   

4.
基于湿空气热力学理论,以Flowmaster换热元件为基础,通过引入相变计算开发了考虑相变潜热的空冷器元件。经计算验证,所开发的元件计算结果与理论计算值吻合性较好,相同边界条件下,总换热量偏差和含湿量偏差均小于1%。分析表明:在高温、高湿环境条件下,湿空气会在空冷器中形成冷凝水,产生大量相变潜热,而Flowmaster换热元件模型由于未考虑相变因素,气侧出口温度计算结果偏低。采用所开发的相变空冷器元件模型可有效提高气侧出口温度计算的准确性,减小因相变带来的仿真误差。  相似文献   

5.
为利用太阳能获得稳定持续的高温空气工质,除了有效集热外,还需要解决因太阳辐射强度变化导致输出工质温度波动的问题。在性能优良的太阳能集热系统中采用蓄热技术是解决此问题的有效途径。根据给定的设计目标,研究将固-固相变蓄热材料季戊四醇应用到太阳能集热蓄热一体化的实验装置中。实验结果表明:按集热蓄热一体化思路设计的实验装置,集热单元能够输出最高温度超过220℃的高温空气,蓄热单元能够将高温空气的温度稳定在蓄热材料的相变温度附近。并且随着蓄热管级数的增加,空气出口温度稳定的时间就越长,为利用太阳能获得稳定持续的高温热媒工质奠定了基础。  相似文献   

6.
Phase change materials absorb a large amount of energy as latent heat at a constant phase transition temperature and are thus used for passive heat storage and temperature control, example applications include electronics, and storage of perishable items. Encapsulated phase change materials incorporated into gypsum wallboards of buildings may be suitable for absorbing solar energy directly, reducing temperature rise. Improvement in human comfort is to be expected due to a decrease in the frequency and magnitude of internal air temperature swings, maintaining the temperature closer to the desired set temperature passively for a long period of time.This paper summarises the results of a detailed theoretical investigation and analysis of thermal energy storage and temperature control achieved using passive building construction elements incorporating phase change materials. The predictions detail the effects of using various quantities of different PCM materials with phase change temperatures of 28 and 43 °C incorporated into a selection of wall constructions for selected ambient conditions of temperature and insolation. From this parametric study, optimum arrangements are proposed.  相似文献   

7.
Latent heat thermal energy storage systems can be used to recover the rejected heat from air conditioning systems, which can be used to generate low-temperature hot water. It decreases not only the consumption of primary energy for heating domestic hot water but also the calefaction to the surroundings due to the rejection of heat from air conditioning systems. A recovery system using phase change materials (PCMs) to store the rejected (sensible and condensation) heat from air conditioning system has been developed and studied, making up the shortage of other sensible heat storage system. Also, PCMs compliant for heat recovery of air conditioning system should be developed. Technical grade paraffin wax has been discussed in this paper in order to develop a paraffin wax based PCM for the recovery of rejected heat from air conditioning systems. The thermal properties of technical grade paraffin wax and the mixtures of paraffin wax with lauric acid and with liquid paraffin (paraffin oil) are investigated and discussed, including volume expansion during the phase change process, the freezing point and the heat of fusion.  相似文献   

8.
A parametric analysis is conducted for space cooling systems based on cold water flowing, during the night, within regularly arranged pipes embedded in a layer of phase change material (PCM), located among the structural layers of the ceiling. The introduced PCM layer in conjunction with night cooling add to the usual ceiling cooling systems offers the advantages of low energy consumption, high cool storage capacity, operation under reduced night electricity price, smoothing of electricity consumption by eliminating daily peak loads, improved thermal comfort and elimination of ceiling dripping. Our parametric analysis is based on a transient three‐dimensional finite‐difference solution of the related heat‐transfer problem for various values of all the main system parameters. PCM phase change process is simulated by using the effective thermal capacity function, which is determined experimentally for PCM suitable for air‐conditioning applications. Our tests showed that the main parameters of the system are pipe spacing, PCM layer thickness, pipe depth within the ceiling, cooling water inlet temperature, night cooling duration and PCM properties (thermal conductivity, phase change heat and ends of phase change temperature range). The effect of all the above parameters is analysed and suggestions are made for selecting the proper combinations of their values in order to obtain the lowest energy consumption in conjunction with the highest level of thermal comfort. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

9.
This paper presents the results of a comprehensive numerical study on the thermal performance of an air based phase change thermal storage unit (TSU) for space heating. The unit is designed for integration into space heating and cooling systems. The unit consists of a number of one dimensional phase change material (PCM) slabs contained in a rectangular duct where air passes between the slabs. The numerical analysis was based on an experimentally validated model. A parametric study has been carried out including the study on the effects of charge and discharge temperature differences, air mass flow rate, slab thicknesses, air gaps and slab dimensions on the air outlet temperatures and heat transfer rates of the thermal storage unit. The paper introduces and discusses quantities called charge and discharge temperature differences which play an important role in the melting and freezing processes.  相似文献   

10.
热管式吸热器单元热管传热的数值模拟分析   总被引:1,自引:1,他引:1  
热管式吸热器的热性能分析对吸热器设计有着重要意义,但由于其相变过程与热管传热的耦合作用十分复杂,至今仍是很少有人深入研究的领域。本文基于焓法建立单元热管耦合传热的物理和数学模型,模拟计算了热管壁温、蓄热容器壁温、循环工质出口温度及相变材料熔化率等参数,并与基本型吸热器进行比较,验证了热管吸热器明显改善了温度分布的均匀性和相变材料的熔化率。  相似文献   

11.
An ideal naturally ventilated building model that allows a theoretical study of the effect of thermal mass associating with the non-linear coupling between the airflow rate and the indoor air temperature is proposed. When the ventilation rate is constant, both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system and the dimensionless convective heat transfer number. When the ventilation rate is a function of indoor and outdoor air temperature difference, the thermal mass number and the convective heat transfer air change parameter are suggested. The new thermal mass number measures the capacity of heat storage, rather than the amount of thermal mass. The analyses and numerical results show that the non-linearity of the system does neither change the periodic behaviour of the system, nor the behaviour of phase shift of the indoor air temperature when a periodic outdoor air temperature profile is considered. The maximum indoor air temperature phase shift induced by the direct outdoor air supply without control is 6 h.  相似文献   

12.
组合相变材料换热管吸热器性能的数值分析   总被引:2,自引:1,他引:2  
吸热器是空间太阳能热动力发电系统关键部件之一。传统吸热器采用单一熔点的相变材料。该文提出了由不同溶点的相变材料组成的组合PCM换热管吸热器模型,计算了换热管最大温度、工质出口温度、各容器PCM熔化率、换热管总PCM熔化率等结果。并与单一PCM换热管吸热器进行了比较分析,说明了采用组合PCM换热管可以很好的提高吸热器的性能,对于减少工质温度波动、减少吸热器质量有重要的意义。计算结果可以较好的指导吸热器的设计。  相似文献   

13.
The main objective of this study is to predict air temperature and humidity at the outlet of a wire-on-tube type heat exchanger using neural networks. For this purpose, initially the heat exchanger was coupled to a refrigeration unit and placed in a wind tunnel. Afterwards, its performance was tested under various experimental conditions. We measured nine input parameters, namely, temperature and humidity of the air entering the coil, air velocity, frost weight, the temperature at the coil surface, mass flow rate of the heat transfer fluid and its temperatures at the inlet and outlet of the coil along with ambient temperature. Additionally, we measured temperature and humidity of the air leaving the coil as the output parameters. Then, a feed-forward neural network based on backpropagation algorithm was developed to model the thermal performance of the coil. The artificial neural network (ANN) was trained using the experimental data to predict the air conditions at the outlet of the coil. The predicted values are found to be in good agreement with the actual values from the experiments with mean relative errors less than 1% for outlet air temperature and 2% for outlet humidity. This demonstrates that the neural network presented can help the manufacturer predict the performance of cooling coils in air-conditioning systems under various operating conditions.  相似文献   

14.
针对果蔬预冷设备应用场合,提出并设计了一套以冰浆作为载冷介质的湿冷热湿交换器,并搭建单体性能测试台架,以出风温度和相对湿度为指标,通过改变填料类型(金属、纸质填料)、载冷介质种类(冰浆、冷水)和喷淋流量进行了性能实验研究。结果表明:实验工况下,金属填料的换热性能较纸质填料好;以冰浆作为载冷介质相比以冷水的情况,可以获得更低的出风温度,但出风相对湿度也有所降低;随着进风干球温度的降低,出风温度明显降低,而出风相对湿度变化并不明显;在一定范围内,提高载冷介质的喷淋流量,有利于湿冷热湿交换器出风温度的降低和出风相对湿度的升高;低浓度的冰浆可以在湿冷热湿交换器中稳定运行,且降温效果较冷水湿冷热湿交换器更加明显,虽然相对湿度略有下降但仍然可保持在90%左右,适用于果蔬预冷和保鲜。  相似文献   

15.
Lightweight envelopes are widely used in modern buildings but they lack sufficient thermal capacity for passive solar utilization. An attractive solution to increase the building thermal capacity is to incorporate phase change material (PCM) into the building envelope. In this paper, a simplified theoretical model is established to optimize an interior PCM for energy storage in a lightweight passive solar room. Analytical equations are presented to calculate the optimal phase change temperature and the total amount of latent heat capacity and to estimate the benefit of the interior PCM for energy storage. Further, as an example, the analytical optimization is applied to the interior PCM panels in a direct-gain room with realistic outdoor climatic conditions of Beijing. The analytical results agree well with the numerical results. The analytical results show that: (1) the optimal phase change temperature depends on the average indoor air temperature and the radiation absorbed by the PCM panels; (2) the interior PCM has little effect on average indoor air temperature; and (3) the amplitude of the indoor air temperature fluctuation depends on the product of surface heat transfer coefficient hin and area A of the PCM panels in a lightweight passive solar room.  相似文献   

16.
The drying needs of agricultural, industrial process heat requirements and for space heating, solar energy is one of the prime sources which is renewable and pollution free. As the solar energy is inconsistent and nature dependent, more often there is a mismatch between the solar thermal energy availability and requirement. This drawback could be addressed to an extent with the help of thermal energy storage systems combined with solar air heaters. This review article focuses on solar air heaters with integrated and separate thermal energy storage systems as well as greenhouses with thermal storage units. A comprehensive study was carried out in solar thermal storage units consisting of sensible heat storage materials and latent heat storage materials. As the phase change heat storage materials offer many advantages over the sensible heat storage materials, the researchers are more interested in this system. The charging and discharging characteristics of thermal storage materials with various operational parameters have been reported. All the possible solar air heater applications with storage units have also been discussed.  相似文献   

17.
非共晶相变材料应用于太阳能吸热蓄热器的数值分析   总被引:1,自引:0,他引:1  
通过计算分析发现对于目前的吸热蓄热器结构,采用相变发生在一个温度区间的非共晶熔盐混合物作为相变材料可以较好的提高吸热蓄热器的整体性能。主要表现在明显地提高相变材料的利用率、减小换热管工质出口温度波动、减小容器表面最大温度及容器表面温度变化,经过合理的设计还可以减小整体系统的质量。分析结果可以作为吸热器设计的参考。  相似文献   

18.
A novel form‐stable phase change wallboard (PCW) was prepared for low‐temperature latent heat thermal energy storage by incorporating eutectic mixture of capric acid and stearic acid and gypsum wallboard. Thermal properties of form‐stable PCW were measured by DSC analysis. The form‐stable PCW has good thermal reliability with respect to the changes in its thermal properties after accelerated thermal cycling. Thermal performance test indicated that the use of such a type of PCW can decrease indoor air temperature fluctuation due to absorption of heat by the eutectic phase change material. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

19.
对高温相变材料铝硅合金的相变温度和潜热进行了分析测定,研究了其热稳定性,并对此类相变材料与金属容器的相容性进行了实验研究。实验结果表明,相变材料AlSi12相变温度适中而潜热大,可作为蓄热介质来储存太阳能;温度对AlSi12与不锈钢材料之间的扩散渗透影响显著。  相似文献   

20.
Phase change materials (PCMs) have found considerable applications in large air conditioning schemes. PCMs were primarily used to introduce capacitance within a system, which enabled them to take into account the fluctuations in the daily cooling load. However, this technology has been developed recently and integrated into the refrigeration system directly to save energy and for better control. This has been achieved through lowering the temperature of the sub-cooled refrigerant and stabilizing the superheat. A prototype demonstrating this novel use of PCMs in refrigeration systems has been developed and tested. Results show that by lowering the temperature of the sub-cooled refrigerant, up to 8% energy savings can be achieved in the UK climate conditions. By using the PCM heat exchanger as a pre-condenser in a refrigeration system, the system’s COP can be improved by 6%. The benefit achieved by reducing the superheat is somewhat offset by its extra pressure drop, although simulation work has showed elsewhere [F. Wang, The passive use of phase change materials in refrigeration system, Ph.D. thesis, London South Bank University, 2003] that the COP can be improved by 4% using a low pressure drop PCM heat exchanger in any climate zone.  相似文献   

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