Performance analysis of screw compressors – numerical simulation and experimental verification

This article describes a theoretical model and computer program for calculating the pressure–volume ( PV ) diagram and the efficiency of an oil-injected screw compressor. The proposed model considers the mass and energy conservation laws, the heat transfer between air and oil, the leakages through various paths, and the discharges of air and oil. The proposed program, which uses seven empirical constants to account for the difference between the flow and the heat-transfer rates in the screw compressor and those estimated by available correlations, solves for the efficiency and the pressure curve of the compressed air. A systematic methodology for the determination of the seven empirical constants is presented in this article. Optimization is carried out to determine the seven empirical constants. With the empirical constants, which are determined with four sets of experiments, the maximum difference between the calculated and measured results in the training process, the verification process and the total process is 2.0 per cent for the volumetric and isentropic efficiencies and 5 per cent for the pressure curve. In the discharge process, the pressure in the compression chamber is noted to be affected by the area of the outlet port and the pressure in the neighbouring chambers.

Download Full-text

Heat transfer to a moving wire immersed in a gas fluidized bed furnace

10.32920/ryerson.14668305 ◽

2021 ◽

Author(s):

Antonio Tannas

Keyword(s):

Heat Transfer ◽

Fluidized Bed ◽

Steel Wire ◽

Transfer Rates ◽

New Correlation ◽

Bed Temperature ◽

Molten Lead ◽

The Difference ◽

Considerable Work ◽

Work Done

In order to replace hazardous molten lead baths in the heat treatment of carbon steel wire with environmentally friendly fluidized bed furnaces a better understanding is needed of their heat transfer rates. There has been considerable work done in examining heat transfer rates to large cylinders immersed in fluidized beds, and some on wire sized ones as well, but all previous studies have been conducted on static cylinders. In order to gain a deeper understanding of heat transfer rates to a moving wire immersed in a fluidized bed furnace an apparatus has been constructed to move a wire through a fluidized bed. The heat transfer rates were calculated using the difference in inlet and outlet temperatures, wire speed and the bed temperature. As predicted, correlations for static wire were found to under-predict heat transfer rates at higher wire speeds, so a new correlation was developed by modifying an existing one.

Download Full-text

Effects of the Heat Transfer at the Side Walls on Natural Convection in Cavities

Journal of Heat Transfer ◽

10.1115/1.2910387 ◽

1990 ◽

Vol 112 (2) ◽

pp. 370-378 ◽

Cited By ~ 28

Author(s):

Y. Le Peutrec ◽

G. Lauriat

Keyword(s):

Heat Transfer ◽

Natural Convection ◽

Numerical Solutions ◽

Three Dimensional ◽

Thermal Conductance ◽

Fluid Flows ◽

Heat Losses ◽

Transfer Rates ◽

Side Walls ◽

The Difference

Numerical solutions are obtained for fluid flows and heat transfer rates for three-dimensional natural convection in rectangular enclosures. The effects of heat losses at the conducting side walls are investigated. The problem is related to the design of cavities suitable for visualizing the flow field. The computations cover Rayleigh numbers from 103 to 107 and the thermal conductance of side walls ranging from adiabatic to commonly used glazed walls. The effect of the difference between the ambient temperature and the average temperature of the two isothermal walls is discussed for both air and water-filled enclosures. The results reported in the paper allow quantitative evaluations of the effects of heat losses to the surroundings, which are important considerations in the design of a test cell.

Download Full-text

Numerical and Experimental Research in Heat Transfer to Screw Compressor Rotors

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44255 ◽

2011 ◽

Cited By ~ 1

Author(s):

Nikola Stosic ◽

Ian K. Smith ◽

Ahmed Kovacevic

Keyword(s):

Heat Transfer ◽

Cross Section ◽

Screw Compressor ◽

Relative Significance ◽

Axial Coordinate ◽

Transfer Rates ◽

Design Changes ◽

Liquid Injection ◽

Lower Temperature ◽

Flow Study

Due to fast rotation of screw compressor rotors, temperature is uniform in a cross section and temperature field is a function of the axial coordinate only. The rotors in one cross section the rotors are simultaneously heated by hot gas on one side while cooled at another side by cold gas. As a result of identification of the main modes of heat transfer both in the rotors and between the rotors and their surroundings and the relative significance of each, a novel procedure is suggested to cool the rotors by injection of minute quantities of a volatile fluid. By this means the compressed gas should attain higher temperatures without rotor distortion. To confirm these concepts and quantify both the heat transfer rates and the rate of liquid injection required for rotor cooling, both a one dimensional flow study and a more complex 3-D numerical analysis were performed, the latter with the aid of a CFD code. The results indicated that the rotors could be maintained at a far lower temperature than that of the discharged gas by flash evaporative cooling, as a result of injecting a fractional percentage by mass of a volatile fluid. This was confirmed by experiment. This technique may be used to operate dry compressors at substantially higher pressure ratios than are currently possible in such machines. It is also shown that only minor design changes are needed to implement it.

Download Full-text

Heat-Transfer Enhancement Incorporating Fin-Like Structures Inside Droplet on Hydrophobic Surface

Journal of Heat Transfer ◽

10.1115/1.4042771 ◽

2019 ◽

Vol 141 (4) ◽

Cited By ~ 1

Author(s):

Abdullah Al-Sharafi ◽

Bekir S. Yilbas ◽

Abdullah Al-Zahrani

Keyword(s):

Heat Transfer ◽

Hydrophobic Surface ◽

Surface Characteristics ◽

Bond Number ◽

Temperature Fields ◽

Experimental Conditions ◽

Transfer Rates ◽

Temperature Heat ◽

The Difference ◽

Source Flow

Enhancement of droplet heat transfer on a hydrophobic surface is examined via introducing the fin-like structures inside the droplet without altering the wetting state of the surface. A solution crystallization of polycarbonate surface is carried out and the functionalized silica particles are deposited onto the crystallized surface to create the hydrophobic surface characteristics. The ferrous particles (Fe2O3) are locally spread onto the hydrophobic surface and, later, manipulated by an external magneto-static force generating various configurations of fin-like structures inside the droplet. The droplet with fin-like structures is heated from the hydrophobic surface through introducing a constant temperature heat source. Flow and temperature fields inside the droplet are simulated in line with the experimental conditions. It is found that changing the configuration of the fin-like structures in the droplet modifies significantly the flow and temperature fields inside the droplet. The Bond number remains less than unity for all configurations of the fin-like structures while demonstrating the importance of the Marangoni current over the buoyancy current in the flow field. The presence of the fin-like structures lowers the difference between the fluid bulk and the minimum temperatures inside the droplet and improves considerably the heat transfer rates and the Nusselt number.

Download Full-text

Natural Convection Heat Transfer Through Inclined Longitudinal Slots

Journal of Heat Transfer ◽

10.1115/1.3246758 ◽

1984 ◽

Vol 106 (4) ◽

pp. 824-829 ◽

Cited By ~ 22

Author(s):

J. G. Symons ◽

M. K. Peck

Keyword(s):

Heat Transfer ◽

Natural Convection ◽

Aspect Ratio ◽

Convective Flow ◽

Convection Heat Transfer ◽

Flow Measurements ◽

Transfer Rates ◽

Isothermal Surface ◽

Aspect Ratios ◽

The Difference

The convective rates of heat transfer through inclined longitudinal slots is studied for the case where heat is transferred from a lower heated isothermal surface, through the slots, to an upper cooled isothermal surface. Experimental data are given for longitudinal slots having aspect ratios from 6–12, slot heights of 25–60 mm, inclinations from horizontal to vertical, and Ra < 107. Data are also given for a transverse slot of aspect ratio 6, for inclinations from horizontal to vertical, and Ra < 107. It is shown that convective heat transfer rates are essentially independent of slot orientation for inclinations up to 15 deg from the horizontal, but longitudinal slots are more effective in suppressing natural convection than transverse slots with the same aspect ratio, for inclinations from 24 to 75 deg from the horizontal. The difference in heat transfer rates for longitudinal and transverse slots inclined between 24 and 75 deg from the horizontal are shown to be due to different convective flows occurring in each slot. The heat flow measurements are supported by convective flow visualization experiments which demonstrate the modes of convective flow within slots.

Download Full-text

Heat transfer to a moving wire immersed in a gas fluidized bed furnace

10.32920/ryerson.14668305.v1 ◽

2021 ◽

Author(s):

Antonio Tannas

Keyword(s):

Heat Transfer ◽

Fluidized Bed ◽

Steel Wire ◽

Transfer Rates ◽

New Correlation ◽

Bed Temperature ◽

Molten Lead ◽

The Difference ◽

Considerable Work ◽

Work Done

Download Full-text

Use of a Shroud and Baffle to Improve Natural Convection to Immersed Heat Exchangers

Journal of Solar Energy Engineering ◽

10.1115/1.4005089 ◽

2011 ◽

Vol 134 (1) ◽

Cited By ~ 9

Author(s):

Sandra K. S. Boetcher ◽

F. A. Kulacki ◽

Jane H. Davidson

Keyword(s):

Heat Transfer ◽

Heat Exchanger ◽

High Performance ◽

Discharge Process ◽

Thermal Systems ◽

Transfer Rates ◽

Water Storage Tank ◽

Flow Control Devices ◽

Commercial Applications ◽

Thermal Stores

Optimizing heat transfer during the charge and discharge of thermal stores is crucial for high performance of solar thermal systems for domestic and commercial applications. This study models a sensible water storage tank for which discharge is accomplished using a heat exchanger immersed in the storage fluid. The heat exchanger is a two-dimensional isothermal cylinder in an adiabatic enclosure with no initial stratification. An adiabatic shroud and baffle whose geometry is parametrically varied is placed around and below the cylinder. Transient numerical simulations of the discharge process are obtained for 105 < RaD < 107, and estimates of the time needed to discharge a given fraction of the initial stored energy are obtained. We find that a short baffle is least effective in increasing heat transfer rates. The performance benefit is greatest early in the transient discharge period when the buoyant flow in the store is strongest. As with all flow control devices, the benefit decreases as energy is extracted from the tank and the temperature difference driving the flow decreases. The use of a shroud increases the transient Nusselt number by as much as twentyfold.

Download Full-text