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1.
A method for evaluating the heat and mass transfer characteristics in a reversibly used water cooling tower (RUWCT) for heat recovery 总被引:3,自引:0,他引:3
In sub-tropical regions, a standard water cooling tower may be reversibly used, as part of a desuperheater heat recovery system for service hot water heating, to extract free heat from ambient air in colder seasons when building cooling load is reduced. Chilled water is pumped into a reversibly used water cooling tower (RUWCT) where it is heated by warmer ambient moist air. This paper presents a method by which the heat and mass transfer characteristics in a counter-flow RUWCT can be evaluated. The method is developed by introducing to the Merkel's equation for standard water cooling towers the revisions that account for the differences in heat and mass transfer characteristics between a water cooling tower and a RUWCT. Field experimental results from a RUWCT installed in a sub-tropical region in China indicated that the method developed could be used to evaluate the thermal performance of a RUWCT with an acceptable accuracy. 相似文献
2.
E. Velasco Gmez F.J. Rey Martínez F. Varela Diez M.J. Molina Leyva R. Herrero Martín 《International Journal of Refrigeration》2005,28(5):654-662
Evaporative cooling is used in industrial and air conditioning processes to reduce temperature in different fluids. Direct evaporation systems can lead to environmental problems such as Legionnaire's disease, and indirect systems reduce system efficiency.This work presents the manufacture, test bed set up and trials carried out on a ceramic evaporative cooling system which acts as a semi-indirect cooler. Depending on air characteristics, it may act as a sensible or enthalpic exchanger. The water cooled in a cooling tower, using the return air coming from the conditioned room (22 °C and 50% comfort conditions) goes through the ceramic pipes, exchanging sensible and latent heat with a current of outdoor air.The use of this recovery system is mainly in climates with a high temperature and humidity such as tropical environments where the system yields a decrease in supply air humidity, using the cooling power of return air.The tests presented show the system behaviour for various supply air conditions. 相似文献
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This paper presents the results of a predictive two-dimensional mathematical model of an adsorption cooling machine consisting of a double consolidated adsorbent bed with internal heat recovery. The results of a base-case, taken as a reference, demonstrated that the COP of the double bed adsorption refrigeration cycle increases with respect to the single bed configuration. However, it was verified that, in order to maximize also the specific power of the machine, the adsorbent beds must have proper thermo-physical properties.Consequently, a sensitivity analysis was carried out, studying the influence of the main heat and mass transfer parameters on the performance of the machine. The results obtained allowed us to define the adsorbent bed design that maximizes its heat and mass transfer properties, as well as the most profitable heat recovery conditions. 相似文献
4.
成都华能电厂106.6 m钢筋砼冷却塔控制爆破拆除 总被引:1,自引:3,他引:1
介绍了1座高106.6 m、底部直径85.28 m的钢筋混凝土冷却塔的定向控制爆破拆除。针对冷却塔高度大、自重近9 000 t的特点,先采用预拆除方法将倾倒方向上一定高度的筒体由连续薄壁结构转变成独立薄壁柱体,然后只炸除人字立柱形成爆破切口,由此实现冷却塔的定向爆破拆除。根据薄壁立柱冲击溃屈的要求,确定了采用多段半秒延时起爆的设计原则,给出了相关的爆破参数。通过爆破过程中多方位的摄像观测和分析发现,应用半秒延时起爆技术逐渐对称地形成爆破切口,有利于冷却塔下坐前以及下坐过程中沿预定方向倾倒。 相似文献
5.
Absorption chiller crystallization control strategies for integrated cooling heating and power systems 总被引:1,自引:0,他引:1
The concept of an air-cooled absorption chiller system is attractive because the cooling tower and the associated installation and maintenance issues can be avoided. However, crystallization of the LiBr–H2O solution then becomes the main challenge in the operation of the chiller, since the air-cooled absorber tends to operate at a higher temperature and concentration level than the water-cooled absorber due to the relative heat transfer characteristics of the coolant. This leads to crystallization of the working fluid. The paper focuses on the crystallization issues and control strategies in LiBr–H2O air-cooled absorption chillers. As a result a novel application opportunity is proposed for the integration of absorption chillers into cooling, heating and power (CHP) systems. This new methodology allows for air cooler operation while avoiding crystallization. 相似文献
6.
The most promising applications for standing-wave thermoacoustic cooling were investigated from the perspective of the ratio of coefficient of performance (COP) to the reversible COP or COPR. A design optimization program based on the thermoacoustic simulation program known as DELTAE was developed. The program was applied to two standing-wave thermoacoustic cooler configurations in order to determine the best possible COPRs for various temperature spans between hot-side and cold-side stack-end temperatures. It was found that the COPR of standing-wave thermoacoustic coolers increases with temperature span and reaches a maximum for temperature lifts around 80 °C. Analysis of the results and the losses clearly shows that the efficiency of these systems may be good for refrigeration, but not for air-conditioning and cryogenic cooling. The COPRs determined from measurements for various thermoacoustic coolers developed so far show similar trends, and generally support the optimization results. 相似文献
7.
The complex structure of the package systems currently used by the strawberry industry has prevented an efficient design of the forced-air cooling process. In this study, we investigated the mechanisms through which different design parameters affect the rate and uniformity of cooling, using a previously validated computational fluid dynamics model. The results indicated that the vent area has a significant effect on the cooling rate, but not on its uniformity. A design that reduces bypassing will not necessarily increase the cooling rate, because there is less bypass air to cool down the air exiting from each clamshell, so that the air entering the next clamshell becomes warmer. Periodic airflow reversal improves the rate and homogeneity of the cooling process. 相似文献
8.
对具有不同内部构件的超大型双曲冷却塔的内表面平均风压进行了CFD数值模拟。在计算流体动力学软件基础上进行二次开发,通过采用施加源项的方法,实现了对超大型冷却塔空塔及有十字挡板、填料及雨区阻力时的内表面平均风压分布的模拟;研究了冷却塔内部各主要构件对冷却塔内压的影响,得到了各工况下塔内外的绕流特性以及不同高度截面的内表面平均压力系数,并从机理上分析了内压曲线分布特性;研究结果与规范及试验结果吻合良好,指出了我国规范对内表面压力系数的取值不完善之处,得到了内压的建议取值,为超大型冷却塔的设计提供参考依据 相似文献
9.
This paper describes the final part of the detailed methodology for the thermal design of wet, counterflow and crossflow types of mechanical and natural draught cooling towers. This part includes the following design steps: the fill or packing, total packed height and the number of decks, water and air loading, pressure drop across the packing, natural draught tower, fan design for a mechanical draught cooling tower, blowdown and make-up water rate, water distribution systems and drift eliminators. Different empirical relations and assumptions are used in this part of the design procedure. 相似文献
10.
B. B. Saha S. Koyama T. Kashiwagi A. Akisawa K. C. Ng H. T. Chua 《International Journal of Refrigeration》2003,26(7):749-757
Over the past few decades there have been considerable efforts to use adsorption (solid/vapor) for cooling and heat pump applications, but intensified efforts were initiated only since the imposition of international restrictions on the production and utilization of CFCs and HCFCs. In this paper, a dual-mode silica gel–water adsorption chiller design is outlined along with the performance evaluation of the innovative chiller. This adsorption chiller utilizes effectively low-temperature solar or waste heat sources of temperature between 40 and 95 °C. Two operation modes are possible for the advanced chiller. The first operation mode will be to work as a highly efficient conventional chiller where the driving source temperature is between 60 and 95 °C. The second operation mode will be to work as an advanced three-stage adsorption chiller where the available driving source temperature is very low (between 40 and 60 °C). With this very low driving source temperature in combination with a coolant at 30 °C, no other cycle except an advanced adsorption cycle with staged regeneration will be operational. The drawback of this operational mode is its poor efficiency in terms of cooling capacity and COP. Simulation results show that the optimum COP values are obtained at driving source temperatures between 50 and 55 °C in three-stage mode, and between 80 and 85 °C in single-stage, multi-bed mode. 相似文献
11.
Kazuhiro Fukuyo Taichi Tanaami Haruko Ashida 《International Journal of Refrigeration》2003,26(2):249-255
The authors developed a new air-supply system for improving the thermal uniformity and the cooling rate inside a fresh food cabinet of a household refrigerator. For these purposes, we added a blower and jet slots to a conventional cooled air supply system. The jet slots circulate the air inside the cabinet at a higher velocity to optimize airflow velocity and its distribution. The jet stirs the air inside the cabinet and improves thermal uniformity, which resulted in half the temperature deviation in the cabinet as that of the conventional systems. The jet also improves the heat transfer on the surface of foods. We achieved a four times higher cooling rate with the new system than that with the conventional ones. In order to cut down the development period, we applied computational fluid dynamics to study air distribution inside the cabinet with the new system. We also derived the model of the cooling process by the jet using theoretical and empirical equations and applied it to decide the jet velocity for the rapid cooling. 相似文献
12.
We experimentally show that for the same heat exchanger inventory allocation, a four-bed adsorption chiller delivers a 12% higher ultimate cooling capacity than its two-bed counterpart. In addition it delivers a significantly improved quality of instantaneous cooling than a two-bed chiller at the same cooling capacity. The COP-enhancing feature of a passive heat recovery scheme that does not involve additional pumping action or valves is experimentally proven. It improves the COPs of a two-bed chiller and a four-bed chiller by as much as 38 and 25%, respectively, without any effect on their cooling capacities. The highest COPs achieved with a two-bed and four-bed chillers are 0.46±0.02 and 0.45±0.02, respectively. These are measured at a hot-water inlet temperature of 85 °C, cooling-water inlet temperature of 29.4 °C and chilled-water inlet temperature of 12.2 °C. 相似文献
13.
Cooling rate and heat transfer characteristics of cooked meats using four different cooling systems of vacuum cooling, air blast cooling, water immersion cooling and slow air cooling were investigated. The experimental results show that only the vacuum cooling can achieve the requirement of cooling the cooked meats from about 74 to 10°C within 2.5 h. The vacuum cooling shows different heat transfer characteristics during the cooling process, as compared with other cooling methods. Vacuum cooling rate is controlled by the evaporation rate of water from the cooked meats, while the cooling rates of the other three cooling methods are governed by the thermal conductivity of the cooked meats. Therefore, it is impossible for air blast, water immersion and slow air cooling to obtain high cooling rates since these three methods are different only in the convective heat transfer from the surface of the cooked meat to the cooling medium. 相似文献
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A simulation model for a piston-cylinder type expansion device in which the linear motion of the piston is converted to the rotational motion of a crank via a connecting rod was developed for its use in a transcritical CO2 cycle. The model is based on lubrication theory with an assumption that the piston ring is a slippery bearing. This model has been used to verify the proper operation of the device in a prototype application and to identify the loss mechanisms of the device in the design stage. In addition, an analysis of the device has been conducted using this theoretical model for the device as installed in a prototype cycle as reported in a companion part I paper. 相似文献
18.
In order to get thermal flow field of direct air-cooled system, the hot water was supplied to the direct air-cooled condenser. The PIV experiments were carried out to get thermal flow field of a direct air-cooled system under different conditions in low velocity wind tunnel, at the same time, the recirculation ratio at cooling tower was measured, so the relationship between flow field characteristic and recirculation ratio of cooling tower can be discussed, from the results we can see that: the flow field configuration fore-and-aft cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed fore-and-aft cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle, the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration fore-and-aft cooling tower reasonably can decrease recirculation ratio under cooling tower, and heat dispel effect of ACC can also be improved. 相似文献
19.
A plate-type evaporator, working with natural refrigerant circulation, has been investigated both experimentally and theoretically. Motivated by the phase-out of ozone-depleting substances, HCFC22 was compared to HFC134a and two zeotropic refrigerant mixtures. The effect of different separator liquid levels, i.e. refrigerant flows, and its influence on heat transfer was also studied. The investigated plate-type evaporator consists of thirteen vertical flow channels and its size is 3.0 m × 0.5 m. The heat source for the evaporator is a falling water film on the outside of the plate. Experimental studies have been carried out using a test facility that enabled detailed measurements of heat transfer and pressure drop. Experiments were compared to results from a calculation method that simultaneously calculates heat transfer and pressure drop in a variable number of steps along the evaporator. The calculation method is based on a pressure drop correlation proposed by the VDI-Wärmeatlas and a heat transfer correlation for vertical tubes proposed by Steiner and Taborek. For different evaporator duties, heat transfer was over predicted by 12% for pure fluids by 15% for mixtures. Calculated pressure drops were well within ±5% of the measured values. Changes in heat transfer due to different flows were closely predicted by the proposed calculation method. 相似文献
20.
Jos Rui Camargo Carlos Daniel Ebinuma Jos Luz Silveira 《International Journal of Refrigeration》2005,28(7):2399
This paper presents the basic principles of the evaporative cooling process for human thermal comfort, the principles of operation for the direct evaporative cooling system and the mathematical development of the equations of thermal exchanges, allowing the determination of the effectiveness of saturation. It also presents the results of experimental tests in a direct evaporative cooler that take place in the Air Conditioning Laboratory at the University of Taubaté Mechanical Engineering Department, and the experimental results are used to determinate the convective heat transfer co-efficient and to compare with the mathematical model. 相似文献