Comparing Water (R718) to Other Refrigerants

2006 ◽  
Author(s):  
Amir A. Kharazi ◽  
Norbert Mu¨ller
Keyword(s):  
High Pressure ◽  
Water Vapor ◽  
State Of The Art ◽  
Pressure Ratio ◽  
Cooling Capacity ◽  
Specific Work ◽  
High Pressure Ratio ◽  
Current State ◽  
Two Factors ◽  
Volumetric Cooling

Even though water (R718) is one of the oldest refrigerants, state of the art technology is required to use water as a refrigerant in compression refrigeration plants with turbo compressors. To compare water (R718) to other refrigerants, a code is developed in which all refrigerants can be compared in a single p-h, T-s, or p-T diagram. Using the code, the COP isolines of water (R718) and any refrigerant can be generated in a graph to determine which refrigerant has a better COP for a certain evaporation temperature and temperature lift. In regard to using water (R718) as a refrigerant, some specific features complicate its application in refrigeration plants with turbo compressors. Because the cycle works at very low pressure, the volumetric cooling capacity of water vapor is very low. Hence, huge volume flows have to be compressed with relatively high pressure ratios. Therefore, the use of water (R718) as a refrigerant, compared to classical refrigerants, such as R134a or R12, requires approximately 200 times the volume flow, and about twice the pressure ratio for the same applications. Because of the thermodynamic properties of water vapor, this high pressure ratio requires approximately a two to four times higher compressor tip speed, depending on the impeller design; while the speed of sound is approximately 2.5 times higher. Reynolds numbers are about 300 times lower and the specific work transmission per unit of mass has to be around 15 times higher. Two factors are introduced to compare the irreversibilities of R718 and other refrigerants and the main source of irrevercibility in R718 cycle is identified. Finally, the current state-of-the-art R718 is reviewed.

The Development of Centrifugal Compressor Impeller

2008 ◽  
Author(s):  
C. Xu ◽  
R. S. Amano
Keyword(s):  
Centrifugal Compressor ◽  
State Of The Art ◽  
Pressure Ratio ◽  
Structure Design ◽  
Centrifugal Compressors ◽  
Rotating Speed ◽  
Operating Range ◽  
High Pressure Ratio ◽  
Current State ◽  
Compressor Impeller

Impeller is one of the key components of industrial centrifugal compressors and turbochargers. Aerodynamic and structure designs of the impeller are critical to the success of the whole compressor stages. The requirements for efficiency and operating range of industrial centrifugal compressors and turbochargers have been increased dramatically compared with the situation in the past. The efficiency of newly developed low-pressure ratio centrifugal compressor has reached the possible level of the machine. However, the efficiency level of intermediate and high-pressure ratio machine still have gap between the current state-of-the-art and possible level. The challenge for centrifugal compressor design is to keep the efficiency level at state-of-the-art and increase the compressor operating range. Increase of the compressor operating range without sacrificing compressor peak efficiency is difficult to achieve. The product globalization requires one product design, which can be used in all locations. In some counties, due to the technology differences, electricity frequencies variations could be 10%. Turbocharger compressors work at different rotational speeds for majority of the time. The compressor impeller rotating speeds change in certain range. The impeller rotating speed variation makes the impeller structure design more challenging. In this study, a full-3D impeller was designed to optimize impeller aerodynamic performance and structure characteristics.

Effects of Reynolds number on the performance of a high pressure-ratio turbocharger compressor

2013 ◽  
Vol 56 (6) ◽  
pp. 1361-1369 ◽  
Author(s):  
XinQian Zheng ◽  
Yun Lin ◽  
BinLin Gan ◽  
WeiLin Zhuge ◽  
YangJun Zhang
Keyword(s):  
Reynolds Number ◽  
High Pressure ◽  
Pressure Ratio ◽  
High Pressure Ratio

Effect of Recirculation Device With Counter Swirl Vane on Performance of High Pressure Ratio Centrifugal Compressor

2011 ◽  
Author(s):  
Hideaki Tamaki
Keyword(s):  
High Pressure ◽  
Mach Number ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Negative Slope ◽  
Tip Leakage Flow ◽  
Recirculation Flow ◽  
Operating Range ◽  
High Pressure Ratio

Centrifugal compressors used for turbochargers need to achieve a wide operating range. The author has developed a high pressure ratio centrifugal compressor with pressure ratio 5.7 for a marine use turbocharger. In order to enhance operating range, two different types of recirculation devices were applied. One is a conventional recirculation device. The other is a new one. The conventional recirculation device consists of an upstream slot, bleed slot and the annular cavity which connects both slots. The new recirculation device has vanes installed in the cavity. These vanes were designed to provide recirculation flow with negative preswirl at the impeller inlet, a swirl counterwise to the impeller rotational direction. The benefits of the application of both of the recirculation devices were ensured. The new device in particular, shifted surge line to a lower flow rate compared to the conventional device. This paper discusses how the new recirculation device affects the flow field in the above transonic centrifugal compressor by using steady 3-D calculations. Since the conventional recirculation device injects the flow with positive preswirl at the impeller inlet, the major difference between the conventional and new recirculation device is the direction of preswirl that the recirculation flow brings to the impeller inlet. This study focuses on two effects which preswirl of the recirculation flow will generate. (1) Additional work transfer from impeller to fluid. (2) Increase or decrease of relative Mach number. Negative preswirl increases work transfer from the impeller to fluid as the flow rate reduces. It increases negative slope on pressure ratio characteristics. Hence the recirculation flow with negative preswirl will contribute to stability of the compressor. Negative preswirl also increases the relative Mach number at the impeller inlet. It moves shock downstream compared to the conventional recirculation device. It leads to the suppression of the extension of blockage due to the interaction of shock with tip leakage flow.

scholarly journals The Design and Evaluation of a High Pressure Ratio Radial Turbine

1992 ◽  
Author(s):  
K. R. Pullen ◽  
N. C. Baines ◽  
S. H. Hill
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Pressure Ratio ◽  
Performance Measurements ◽  
Turbine Engine ◽  
High Pressure Ratio ◽  
Turbine Efficiency ◽  
Wide Range ◽  
Dimensional Parameters ◽  
Very High

A single stage, high speed, high pressure ratio radial inflow turbine was designed for a single shaft gas turbine engine in the 200 kW power range. A model turbine has been tested in a cold rig facility with correct simulation of the important non-dimensional parameters. Performance measurements over a wide range of operation were made, together with extensive volute and exhaust traverses, so that gas velocities and incidence and deviation angles could be deduced. The turbine efficiency was lower than expected at all but the lowest speed. The rotor incidence and exit swirl angles, as obtained from the rig test data, were very similar to the design assumptions. However, evidence was found of a region of separation in the nozzle vane passages, presumably caused by a very high curvature in the endwall just upstream of the vane leading edges. The effects of such a separation are shown to be consistent with the observed performance.

Stability Improvement of a High-Pressure Ratio Centrifugal Compressor by Flow Injection

2020 ◽  
Vol 33 (6) ◽  
pp. 04020072
Author(s):  
Wenchao Zhang ◽  
Xiao He ◽  
Baotong Wang ◽  
Zhenzhong Sun ◽  
Xinqian Zheng
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Flow Injection ◽  
Pressure Ratio ◽  
High Pressure Ratio
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