Closed wet cooling towers (CWCTs) are used widely because of their better water quality and smaller water consumption. However, the operating parameters shown in the technical documents are only for rated conditions in summer, not for any other conditions, especially in low air wet-bulb temperature areas such as those near 0°C. In addition, CWCTs often fail to achieve the designed cooling effect at low air wet-bulb temperatures. A experiment set of CWCT was built, and the performance of the CWCT at low air wet-bulb temperature near 0°C was investigated. The impact of the operating parameters (air flow rate, cooling water flow rate, and spray water flow rate) on the heat and mass transfer performance of the CWCT was measured and analyzed. The results show the cooling performance of the CWCT at an air wet-bulb temperature 0°C, 2°C, and 4°C is about 47%–63% of the rated operating condition; the optimal operating parameters of these conditions for the CWCT are just the same as those of the rated operating condition in summer. According to the experimental results, some operating advices are given. 闭式湿式冷却塔作为在民用、工业上广泛应用的冷却设备，具有水质好、水耗少的优点。经发现，冷却塔技术样本一般只提供冷却塔的夏季额定运行参数，并没有解释其他的气象条件特别是低湿球温度条件下冷却塔的性能。而在低湿球温度条件下，冷却塔的性能总是低于额定工况的设计性能的。鉴于在许多地区，如地中海沿岸、美国中南部和中国的长三角地区，一年中有较长的时间，湿球温度接近0℃，因此，本文开发出一组闭式湿塔模型，并通过一系列实验来研究在近0℃湿球温度条件下闭式湿式冷却塔的性能，同时也分析了冷却塔运行参数（风量、冷却水流量、喷淋水量）的改变对冷却塔性能的影响。研究发现，闭式湿塔在0℃, 2℃, 和 4℃湿球温度条件下的冷却性能分别约是同等运行参数条件夏季性能的47%~63%。而在低湿球温度条件下，闭式湿塔的最佳运行参数也恰好等同于夏季额定运行参数。另外，基于实验研究结果，提出了闭式湿塔在低湿球温度条件下的运行策略。

In this study, a modified ejector-expansion refrigeration cycle (MERC) is proposed for applications in small refrigeration units. A vapor bypass circuit is introduced into the standard ejector expansion refrigeration cycle (ERC) for increasing the ejector pressure lift ratio, thereby lowering the compressor pressure ratio in the MERC. A mathematical model has been established to evaluate the performances of MERC. Analysis results indicate that since a two phase vapor-liquid stream is used to drive the ejector in the MERC, a larger ejector pressure lift ratio can be achieved. Thus, the compressor pressure ratio decreases by 21.1% and the discharge temperature reduces from 93.6°C to 82.1°C at the evaporating temperature of -55°C when the vapor quality of two phase vapor-liquid stream increases from 0 to 0.2. In addition, the results show that the higher ejector component efficiencies are effective to reduce the compressor pressure ratio and the discharge temperature. Actually, the discharge temperature reduces from 91.4°C to 82.1°C with the ejector component efficiencies increasing from 0.75 to 0.85 at the two phase stream vapor quality of 0.2. Overall, the proposed cycle is found to be feasible in lower evaporating temperature cases.

An auto-cascade absorption refrigeration (ACAR) system could achieve a −60°C refrigeration temperature by low-grade heat. For an ACAR system, its performance is mainly affected by energy and mass coupling of the auto-cascade processes. A novel ACAR system with double-absorber was proposed to get higher- efficient refrigeration as low as ‒60°C in this context, which used R23-R134a-DMF (N,N-Dimethylformamide) as its working fluids. Theoretical calculation and analyses were conducted under different working conditions. From the calculated results, the new system gained a COP value 20% higher than that of an ACAR system with single-absorber under the same generating, condensing, absorbing and refrigerating temperatures. Compositions of a refrigerant mixture showed key influences on energy and mass coupling of the auto-cascade processes, and an optimal composition of the mixed refrigerants was obtained for the new ACAR system. In addition, it was clearly found that absorbing processes of the new system had great effects on energy and mass coupling of the auto-cascade processes. Based on the difference of absorbing characteristics among R23, R134a and DMF, the absorbing processes were intensified under the different absorbing pressures. As a result, an optimal matching pressure was obtained for the new ACAR system. Energy and mass coupling of the auto-cascade processes were further optimized, and the highest COP value was obtained. The theoretical analyses showed that performance of the innovative ACAR system could be superior to that of an ACAR system with single-absorber at a refrigeration temperature from ‒55°C to ‒60°C.

Stirling-type pulse tube cryocoolers (SPTCs) working at liquid-helium temperatures are appealing in space applications because of their promising advantages such as high reliability, compactness, etc. Worldwide efforts have been put in to develop SPTCs operating at liquid-helium temperatures especially with helium-4 as the working fluid. Staged structure is essential to reach such low temperatures. Generally, both the regenerator of the last section and the pulse tube together with the phase shifter are precooled by its upper stage or by external cold source to a low temperature of around 20 K. However, the precooling effects on the regenerator and the pulse tube are synthetic in previous studies, and their independent effects have not been studied clearly. In this manuscript, the precooling effects on the regenerator and on the pulse tube together with the phase shifter are tested independently on a unique-designed precooled SPTC. The tested precooling temperature is between 13.3 K and 22 K, and the no-load refrigeration temperature gets down to 3.6 K. Further analyses and numerical calculations have been carried out. It is found that the influence on the regenerator is remarkable, which is different from previous conclusions. It is also found that the precooling effects on the pulse tube are relatively weak because of the large pressure-induced enthalpy flow of a real gas working at the temperatures near to the critical point. Furthermore, the phase shifting capacity is analyzed with two cases and with both helium-4 and helium-3 as working fluids, and it keeps quite constant after optimizing the frequency and the precooling temperature for each case. The investigation on these independent effects will provide valid reference on the precooling mechanism study of SPTCs working down to liquid-helium temperatures.

Ejector refrigeration has the advantage of low capital cost, simple design, reliable operation, long lifespan and almost no maintenance. The only weakness is the low efficiency and its intolerance to deviations from design operation condition. R134a used in ejector refrigeration system gives better performance in comparison with many other environmental friendly refrigerants as the generation temperature is from 75°C to 80°C. The present work experimentally investigated the on-design and off-design performance of the ejector with fixed geometry using R134a as refrigerant, and cycle performance of the ejector refrigeration system. The experimental prototype was constructed and the effects of primary flow inlet pressure, secondary flow inlet pressure and ejector back pressure on ejector performance and cycle performance were investigated respectively. The operation conditions are: primary flow inlet pressure from 2.2 MPa to 3.25 MPa, secondary flow inlet pressure from 0.36 MPa to 0.51 MPa, ejector back pressure from 0.45 MPa to 0.67 MPa. Conclusions were drawn from the experimental results, and the experimental data can be used for validation of theoretical model for both critical and subcritical mode.