Performance Optimization of Mechanical Vapor Compression Desalination System Using a Water-Injected Twin-Screw Compressor

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Yousif Alkhulaifi ◽  
Esmail M. A. Mokheimer ◽  
Jihad H. AlSadah
Keyword(s):  
Heat Transfer ◽  
Performance Optimization ◽  
System Performance ◽  
Seawater Temperature ◽  
Injection Pressure ◽  
Screw Compressor ◽  
Vapor Compression ◽  
Compression Process ◽  
Twin Screw ◽  
Brine Salinity

In this study, the thermal and operational characteristics of a 400 m3/day mechanical vapor compression desalination (MVCD) system that uses a water-injected twin-screw compressor have been studied and presented. A mathematical model of the MVCD system has been developed including mass and energy conservation equations, heat transfer equations, as well as thermophysical correlations. The effects of the MVCD system design and operation parameters on the system performance are analyzed and discussed. The effect of different boiling-point elevation correlations on the specific area is investigated. The brine and distillate preheaters' areas are studied as a function of inlet seawater temperature. The effect of the injection pressure on system performance is studied. Results show that the optimal injection point is close to the beginning of the compression process. Using this optimum injection pressure, the reduction in power consumption was found to be about 7.3% for high compression ratios. The effects of the brine and feed salinity on system performance are also analyzed. It is found that the specific heat transfer area strongly depends on the brine salinity, especially at temperature differences less than 6 °C. It increases by 44% and 32% at a temperature difference of 4 and 6 °C, respectively. The compressor inlet volume flowrate increases by 9% when the brine salinity increases from 50,000 to 150,000 ppm at all brine boiling temperatures considered. The feed-to-distillate ratio increases rapidly with rising feed salinity, while it decreases with rising brine salinity.

Development of a water-injected twin-screw compressor for mechanical vapor compression desalination systems

2016 ◽  
Vol 95 ◽  
pp. 125-135 ◽  
Author(s):  
Jiubing Shen ◽  
Ziwen Xing ◽  
Kai Zhang ◽  
Zhilong He ◽  
Xiaolin Wang
Keyword(s):  
Screw Compressor ◽  
Vapor Compression ◽  
Twin Screw

Theoretical and experimental research on the performance of twin screw compressor using R513A as R134a replacement

2020 ◽  
pp. 095440892095114
Author(s):  
Zhiping Zhang ◽  
Ying Wang ◽  
Xiaokun Wu ◽  
Xi Pan ◽  
Ziwen Xing
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Pressure Ratio ◽  
Volumetric Efficiency ◽  
Screw Compressor ◽  
Test Results ◽  
Lubricant Oil ◽  
Twin Screw ◽  
The Cost ◽  
Significant Attention

The refrigerant R513A receives significant attention as an alternative to R134a used in water chiller, due to its lower global warming potential. However, whether R513A can directly and efficiently take the place of R134a in the twin screw compressor has not been verified. In this paper, a thermodynamic model is applied to compare the performance of R513A and R134a in a twin screw compressor. The leakage process and heat transfer between refrigerant and lubricant oil are taken into account. With this model, the volumetric efficiency and adiabatic efficiency are simulated and p- V indicator diagram is presented. Simulated results show that R513A is the refrigerant with low temperature lift, low pressure ratio but high pressure difference. Experimentally, the test compressor originally designed for R134a is used to compare the performance of R134a and R513A. Test results show that the differences of volumetric efficiency and adiabatic efficiency between R134a and R513A are very small and acceptable. The COP of R513A is only a little bit lower than that of R134a. Hence, taking the cost of replacing equipment and GWP into account, R513A can directly take the place of R134a in the twin screw compressor.

The twin helical screw compressor Part 2: A mathematical model of the working process

1998 ◽  
Vol 212 (5) ◽  
pp. 369-380 ◽  
Author(s):  
J S Fleming ◽  
Y Tang ◽  
G Cook
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Geometric Model ◽  
Measured Data ◽  
Screw Compressor ◽  
Gas Oil ◽  
Working Process ◽  
Compression Process ◽  
Rotor Angle ◽  
Current Accuracy

Part 1 of this paper describes the physical characteristics, applications and analytical procedures currently relevant to the twin helical screw compressor. Part 2, presented here, describes a mathematical model of the working process of the machine. Use is made of a geometric model developed by Tang [2] which describes all the essential features as functions of the male rotor angle of rotation. The following effects are taken into account: internal leakage through six paths, gas—oil heat transfer, injected liquid refrigerant flashing in the compression cavity, dissolved refrigerant flashing from the oil injected into the compression cavity, dissolved refrigerant flashing in the end casings from oil supplied to the bearings and the draining of flashed refrigerant gas from the end casings to the low-pressure regions of the main casing. Internal friction at the principal rubbing surfaces is taken to cause heating of the oil and is modelled by making use of extensive measured data and manufacturers’ information. The hotter oil influences the compression process via a changed gas—oil heat transfer rate. The gas-oil heat transfer coefficient and the internal leakage coefficients are determined from measured data for mid-range conditions and applied over a range of conditions. The model output is compared with measured data; its current accuracy and possible improvement are commented upon.

Prediction of Heat Transfer and Visualisation of Temperature Field in Screw Compressors

2014 ◽  
Author(s):  
S. Rane ◽  
N. Stosic ◽  
A. Dhunput
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Three Dimensional ◽  
Power Input ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Screw Compressor ◽  
Compression Process ◽  
Machine Parts ◽  
Compressor Power

The heat transfer within a screw compressor is not considered to affect its performance significantly, because thermal energy dissipation represents less than 1% of the compressor power input. However, it can influence the machine reliability because heat transfer, resulting from the compression process, creates a non-uniform three dimensional temperature field leading to local distortions which may be larger than the clearances between the machine parts. This phenomenon is widely known and special control procedures are required to allow for start-up and shut down as well as for steady running operation without seizing. However, these are normally derived only from test data and may result in larger internal clearances than are really necessary, thereby reducing the optimum performance. This paper describes a method for calculating the heat transferred during screw compressor processes, more precisely and hence how to obtain the temperature fields within the screw machine parts, which are needed to establish the size of the necessary clearances to maintain safe operating conditions.

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