太阳能喷射式制冷系统性能的实验研究

对太阳能喷射式制冷系统进行了实验研究,采用电加热模拟太阳能辐射的方法,研究了冷凝器、发生器和蒸发器温度对制冷系统COP的影响,给出了太阳能喷射式制冷系统制冷能力与COP随时刻的变化关系。系统在80℃热源条件下,全天提供16℃的冷水,系统最大制冷量为0.43 kW。     

传统饮水机升级换代初探

正1我国传统饮水机现状本文所指的饮水机系采用加热内胆将桶装纯净水(或矿泉水)进行加热处理后供人们方便饮用的装置。这种饮水机虽然往往还派生出一些其他功能,如可以同时提供常温水、冰水等等,但其最显著的特点是采用内胆对水进行加热。该类饮水机的加热器功率一般在450W-550W。加热器的控制模式是:通过一个双金属片温度开关来控制加热器的通断,水温低于双金属片温度开关的闭合温度,就开始加温;水     

PLC控制的多温直饮饮水机设计

针对学校、车站、商场等公共场所广泛应用的即热式饮水机普遍存在加热功率大、沸水置凉热量浪费以及置凉等待时间长的现象,设计了一款基于PLC控制的多温直饮饮水机。该饮水机通过高效换热器利用沸水预热待加热冷水降低加热电量与加热时间,并且调节换热后温水与沸水的出水流量比,提供4种温度的饮用水,满足人们饮用开水、咖啡、泡茶、直饮温水的需求。     

一个新的吸收-喷射复合制冷循环

提出了一个新的吸收-喷射复合制冷循环.在新循环中,部分冷凝器出口的饱和液态制冷剂被冷剂泵加压到制冷剂在发生温度下对应的饱和压力,这股高压制冷剂液体在一个沸腾器里被加热成饱和高压蒸气后将预热器出口的过热制冷剂蒸气引射到冷凝压力.由于在新循环中发生压力可以比冷凝压力低,因此该系统可以利用较低品位的热量制取低温下的冷量.研究结果表明:新循环可以利用比传统两级吸收式制冷循环温度更低的热源,制取同一温度下的冷量.此外,在蒸发温度或发生温度较低时,新循环的COP比单效循环高得多;当发生温度或蒸发温度较高时,新循环和传统单效循环的COP相同.     

传统饮水机升级换代初探

<正>1我国传统饮水机现状本文所指的饮水机系采用加热内胆将桶装纯净水(或矿泉水)进行加热处理后供人们方便饮用的装置。这种饮水机虽然往往还派生出一些其他功能,如可以同时提供常温水、冰水等等,但其最显著的特点是采用内胆对水进行加热。该类饮水机的加热器功率一般在450W-550W。加热器的控制模式是:通过一个双金属片温度开关来控制加热器的通断,水温低于双金属片温度开关的闭合温度,就开始加温;水     

外部环境对冷板冷藏车制冷系统性能的影响

对冷板冷藏车中冷凝器建立了动态分布参数模型,并与蒸发器、压缩机及热力膨胀阀模型联立求解,得到了制冷系统运行的动态仿真解.分析了冷凝器迎面风速和进风温度对制冷系统运行的影响,结果表明:在一定冷凝器进风温度下,迎面风速的改变将对制冷量、制冷系数及充冷时问产生影响;冷凝器进风温度对制冷系统的制冷能力有一定影响,建议在环境温度...     

基于正交试验的间接式太阳能热水系统运行参数优化分析

太阳能热水系统相较于传统的热水系统更加节能环保，因而得到大规模的应用。本文就间接式太阳能热水系统中的温差控制条件、水箱容积和水箱内辅助加热器停止加热条件作为变量进行模拟分析，来探究总结不同条件对于系统能效的影响。本文采用TRNSYS软件建立间接式太阳能热水系统模型，经过对多组数据对比分析发现，温差控制器设置上限温度为5℃,下限温度为1℃时，能获得较高的水箱温度，并且几乎对系统能效没有影响；当改变水箱容积和辅助加热器停止加热温度时，系统能效和水箱温度成反比，通过设计正交试验，得出水箱容积2 m³、辅助加热器停止温度42℃为能够满足用户需求的最佳组合。针对间接式太阳能热水系统的优化，对于大型工程的资源节约和成本降低是十分必要的。     

外界环境对热管式太阳能喷射制冷系统的影响

针对热管式太阳能制冷系统,分析了影响系统制冷性能的主要因素,并对喷射器内的压力和速度场进行了数值模拟.结果表明,热管式太阳能喷射制冷系统受太阳辐照强度、发生室温度、冷凝器温度和蒸发温度的影响;系统制冷性能系数随发生器内温度的升高而升高,随冷凝温度的升高而降低,随蒸发温度的升高而升高.     

流体冷却的节能新途径

一、前言 在传统制冷系统中,工质从压缩机出来后,进冷凝器冷凝,然后通过膨胀阀,再进蒸发器吸热制冷。 这种冷却工艺的缺点在于,制冷系统采用恒定的蒸发温度来吸热。如果采用螺杆双温机组分级降温,用一部分较低品位的中温冷量完成原料前段降温,将可大幅度提高产冷量和制冷系数,从而减少设备投资和运行费用。     

基于相变储能的半导体冰箱及热水系统性能分析

半导体制冷主要是帕尔帖效应在制冷方面的应用[1],根据半导体制冷的特点提出一种基于低品位热能驱动多功能半导体冰箱及相变蓄能热水系统。通过实验测量半导体冰箱热水循环系统中的温度和流量等参数。结果表明系统蓄热结束后,短时间内即可将水加热到40℃以上,同时为冰箱系统提供-3～-4℃的低温环境,仅1天即可节约4.92kWh的电量,实现能量高效利用。     

太阳能烟囱制冷系统的研究

通过分析制冷系统和太阳能烟囱热气流发电系统的技术和特点,提出了太阳能烟囱制冷系统.将太阳能烟囱系统与制冷系统相结合进行制冷,可实现制冷不用电.该系统由烟囱、集热棚、蓄热层、涡轮机、开启式制冷压缩机、冷凝器和变速器等组成.介绍了太阳能烟囱制冷系统的结构特点、工作原理以及系统相关参数的计算方法.分析结果表明,太阳能烟囱制冷系统结构简单,运行维护方便,制冷不用电,无污染,具有良好的环境效应,可根据环境温度改变压缩机运行转速调节供冷负荷,能有效解决热带及沙漠地区的供冷及供电问题.     

Application of evaporative cooling on the condenser of window-air-conditioner

Reduction of energy consumption is a major concern in the vapor compression refrigeration cycle especially in the area with very hot weather conditions (about 50 °C), where window-air-conditioners are usually used to cool homes. In this weather condition performance of air condenser window-air-conditioners decrease sharply and electrical power consumption increase considerably. These problems have activated the research programs in order to improve the performance of window-air-conditioners by enhancing heat transfer rate in the condenser. In this article, a new design with high commercialization potential for incorporating of evaporative cooling in the condenser of window-air-conditioner is introduced and experimentally investigated. A real air conditioner is used to test the innovation by putting two cooling pads in both sides of the air conditioner and injecting water on them in order to cool down the air before it passing over the condenser. The experimental results show that thermodynamic characteristics of new system are considerably improved and power consumption decreases by about 16% and the coefficient of performance increases by about 55%.     

A comparison of solar absorption system configurations

Solar thermal driven cooling systems for residential applications are a promising alternative to electric compression chillers, although its market introduction still represents a challenge, mainly due to the higher investment costs. The most common system configuration is an absorption chiller driven by a solar thermal system, backed up by a secondary heating source, normally a gas boiler. Heat storage in the primary (solar) circuit is mandatory to stabilize and extend the operation of the chiller, whereas a cold storage tank is not so common.This paper deals with the selection of the most suitable configuration for residential cooling systems with solar energy. In Spain, where cooling needs are usually higher than heating needs, the interest of a reversible heat pump as auxiliary system and a secondary cooling storage are analyzed.A complete TRNSYS model has been developed to compare a configuration with just hot storage (of typical capacity 40 L/m² of solar collector surface) and a configuration with both, hot and cool storages. The most suitable configuration is very sensible to the solar collector area. As the collector area increases, the advantages of a cool storage vanish. Increasing the collector area tends to increase the temperature of the hot storage, leading to higher thermal losses in both the collector and the tank. When the storage volume is concentrated in one tank, these effects are mitigated. The effect of other variables on the optimal configuration are also analyzed: collector efficiency curve, COP of the absorption chiller, storage size, and temperature set-points of the chillers.     

Performance Evaluation of R134a/DMF-Based Vapor Absorption Refrigeration System

This article describes an experimental investigation to measure performances of a vapor absorption refrigeration system of 1 ton of refrigeration capacity employing tetrafluoro ethane (R134a)/dimethyl formamide (DMF). Plate heat exchangers are used as system components for evaporator, condenser, absorber, generator, and solution heat exchanger. The bubble absorption principle is employed in the absorber. Hot water is used as a heat source to supply heat to the generator. Effects of operating parameters such as generator, condenser, and evaporator temperatures on system performance are investigated. System performance was compared with theoretically simulated performance. It was found that circulation ratio is lower at high generator and evaporator temperatures, whereas it is higher at higher condenser temperatures. The coefficient of performance is higher at high generator and evaporator temperatures, whereas it is lower at higher condenser temperatures. Experimental results indicate that with addition of a rectifier as well as improvement of vapor separation in the generator storage tank, the R134a/DMF-based vapor absorption refrigeration system with plate heat exchangers could be very competitive for applications ranging from –10°C to 10°C, with heat source temperature in the range of 80°C to 90°C and with cooling water as coolant for the absorber and condenser in a temperature range of 20°C to 35°C.     

Numerical simulation of underground seasonal cold energy storage for a 10 MW solar thermal power plant in north-western China using TRNSYS

This paper aims to explore an efficient, cost-effective, and water-saving seasonal cold energy storage technique based on borehole heat exchangers to cool the condenser water in a 10 MW solar thermal power plant. The proposed seasonal cooling mechanism is designed for the areas under typical weather conditions to utilize the low ambient temperature during the winter season and to store cold energy. The main objective of this paper is to utilize the storage unit in the peak summer months to cool the condenser water and to replace the dry cooling system. Using the simulation platform transient system simulation program (TRNSYS), the borehole thermal energy storage (BTES) system model has been developed and the dynamic capacity of the system in the charging and discharging mode of cold energy for one-year operation is studied. The typical meteorological year (TMY) data of Dunhuang, Gansu province, in north-western China, is utilized to determine the lowest ambient temperature and operation time of the system to store cold energy. The proposed seasonal cooling system is capable of enhancing the efficiency of a solar thermal power plant up to 1.54% and 2.74% in comparison with the water-cooled condenser system and air-cooled condenser system respectively. The techno-economic assessment of the proposed technique also supports its integration with the condenser unit in the solar thermal power plant. This technique has also a great potential to save the water in desert areas.     

Control of gas absorption in a geothermal steam direct contact condenser

The absorption of geothermal gases by the cooling water of a turbine exhaust steam condenser can be minimised by a combination of design and control technology. The condenser system should comprise the two stages of a condenser and gas cooler with parallel cooling water supply and hot water disposal systems. Each stage should operate countercurrently.The control system discussed allows the condenser to retain its traditional flexibility of improved vacuum in cool weather and yet maintains a distribution of heat loads between the condenser and gas cooler without the use of accurate heat balances.The design and control technology has been tested successfully on a pilot plant and resulted in a cooling water system that results in very low corrosion rates in moderate corrosion resistant materials.     

Performance review of a novel combined thermoelectric power generation and water desalination system

A novel combined thermoelectric power generation and water desalination system is described with a system schematic. The proposed system utilises low grade thermal energy to heat thermoelectric generators for power generation and water desalination. A theoretical analysis presents the governing equations to estimate the systems performance characteristics combined with experimental validation. Experimental set-up consists of an electric heat source, thermoelectric modules, heat pipes, a heat sink and an evaporator vessel. Four heat pipes are embedded in a heat spreader block to passively cool the bottom side of the thermoelectric cells. The condenser of these four heat pipes is immersed in a pool of saline water stored in an evaporation vessel which is maintained at sub-atmospheric pressure. The liquid to vapour phase change cooling method achieve low saturation temperature and offers a high heat transfer coefficient for the cooling of the thermoelectric generators. At the same time this method utilises the low temperature heat extracted from the cold side of the thermoelectric generator for water desalination. It was observed that at low saturation temperatures greater heat flux could be supplied to the thermoelectric generators with less heat losses to the atmosphere.     

Thermal behavior of lithium batteries used in electric vehicles using phase change materials

Electric vehicles equipped with lithium-ion batteries face a huge challenge, and the fact that battery life is very much affected by the temperature conditions of their operating environment, the heat reduces battery life cycle and time and increases the likelihood of thermal degradation and explosion. This problem has forced engineers to cool the battery. The methods used to cool the battery includes a cool water method (passing water or a dielectric fluid from the battery pack), cooling air (blowing air into the battery compartment by the fan), using a refrigeration system (such as cooling screens), and the use of phase-change material (PCM). In this research after reviewing and referring to valid authorities, it was found that PCMs are superior to all three other cooling systems because the air-conditioning system is not very desirable due to the high-temperature gradient between the battery cells. Also, cooling and refrigeration systems with refrigerant gases will also cost a very high cost on the electric car. The results of the studies showed that the cooling the battery using the PCM creates a similar temperature profile between the batteries in the battery pack, the temperature gradient is much smaller than the air cooler and cool water, and the final cost will be much lower. Also, it performs more efficiently in high-speed road dynamics and increases the battery life of an electric car or electric hybrid.     

Transcritical CO2 refrigerator and sub‐critical R134a refrigerator: A comparison of the experimental results

This paper describes experiments comparing a commercial available R134a refrigeration plant subjected to a cold store and a prototype R744 (carbon dioxide) system working as a classical ‘split‐systems’ to cool air in residential applications in a transcritical cycle. Both plants are able to develope a refrigeration power equal to 3000 W. The R744 system utilizes aluminium heat exchangers, a semi‐hermetic compressor, a back‐pressure valve and a thermostatic expansion valve. The R134a refrigeration plant operates using a semi‐hermetic reciprocating compressor, an air condenser followed by a liquid receiver, a manifold with two expansion valves, a thermostatic one and a manual one mounted in parallel, and an air cooling evaporator inside the cold store. System performances are compared for two evaporation temperatures varying the temperature of the external air running over the gas‐cooler and over the condenser. The refrigeration load in the cold store is simulated by means of some electrical resistances, whereas the air evaporator of the R744 plant is placed in a very large ambient. The results of the comparison are discussed in terms of temperature of the refrigerants at the compressor discharge line, of refrigerants mass flow rate and of coefficient of performance (COP). The performances measured in terms of COPs show a decrease with respect to the R134a plant working at the same external and internal conditions. Further improvements regarding the components of the cycle are necessary to use in a large‐scale ‘split‐systems’ working with the carbon dioxide. Copyright © 2009 John Wiley & Sons, Ltd.     

冷热组合型超市系统的设计与经济性分析

设计了冷热组合型超市系统,利用CO2跨临界循环对空间夏季供冷和冬季供热,采用R290/CO2复叠式制冷循环对食品冷冻冷藏,同时回收CO2跨临界循环高温气体散发的热量和R290/CO2复叠式制冷循环R290高温循环气体的冷凝热,实现夏季空间供冷、食品制冷的同时供应生活热水,冬季空间供暖、食品制冷的同时供应生活热水,及春秋季节食品制冷同时供应生活热水。并与供冷、供暖、食品制冷和供应生活热水分别进行的常规R404A超市系统的能效相比较,得出冷热组合型超市系统的能耗大大降低,能效明显增加,不仅节约能源,而且保护环境,是很有发展前景的绿色环保系统。