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International Journal of Technology (2017) 7: 1191-1196
ISSN 2086-9614
© IJTech 2017
PERFORMANCE OF ICE SLURRY GENERATOR WITH MECHANICAL
SCRAPER USING R-22 AND R-290
Fajri A. Rayhan1, Agus S. Pamitran1*
1
Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI
Depok, Depok 16424, Indonesia
(Received: January 2017 / Revised: May 2017 / Accepted: December 2017)
ABSTRACT
Ice slurry technology is highly favored to maintain the freshness of fish, as the cooling capacity
of ice slurry is higher than that of flaked ice, tubular ice, plate ice, and block ice. One important
part of an ice-slurry system is the ice generator. A mechanical scraper is the easiest type of iceslurry generator to fabricate, because mechanical scrapers use only one type of material, such as
stainless steel. The purpose of this research was to develop a prototype ice-slurry generator and
analyze its performance. To enable comparison of their performance, both the R-22 and R-290
refrigerants were used as the working fluids in the refrigeration system. The study observed the
time necessary to form ice and the scraper’s ability to scrape the ice on the inner surface of the
evaporator. The best system included faster ice-slurry generation and a durable generator that
did not freeze up. Four combinations of scraper RPM and pump RPM varied speeds from low
to high. The results showed that using R-290 refrigerant and lower RPM speeds for both the
scraper and the pump generated ice slurry in a shorter time.
Keywords: Ice slurry; Mechanical scraper; R-22; R-290; Sea water
1.
INTRODUCTION
The fishing industry is one of the largest assets possessed by maritime nations. Indonesia, as an
archipelagic nation, contains more than 18,000 islands and has about 81,000 km of coastline,
which, according to data from the Geospatial Information Agency, is the second-longest
coastline in the world, after Canada. Based on data from the Ministry of Fisheries Indonesia, the
nation had the potential to develop a fishing industry of up to 6.5 million tons in 2014 (KKP,
2014).
To support the fishing industry’s potential, technology to preserve the fish is necessary. There
are many types of fish preservation, one of which is ice-slurry technology, which has been the
subject of much research. Ice-slurry technology has many advantages: it can keep fish fresh for
six days without damaging the meat (Kitamurai et al., 2015), it provides high thermal density
storage, and it has a fast cooling rate. Ice slurry has advantages over traditional single-phase
fluids; however, applying ice slurry poses many challenges (Hernández et al., 2013).
An ice-slurry generator is a heat-exchange apparatus that produces ice slurry using various
types of solutions, and it works by using the basic principles of the refrigeration cycle.
Generally, there are many types of ice-slurry generators (Egolf & Kauffeld, 2005).
One that has been widely accepted over the last 20 years and that is currently used by many
*Corresponding author’s email: pamitran@eng.ui.ac.id, Tel. +62-21-7270032, Fax. +62-21-7270033
Permalink/DOI: https://doi.org/10.14716/ijtech.v8i7.686
1192
Performance of Ice Slurry Generator with Mechanical Scraper using R-22 and R-290
researchers is an ice-slurry generator that uses a mechanical scraper (Kauffeld et al., 2005).
Modifications to the various forms of this scraper have been made to increase the efficiency of
grinding the layer of ice that accumulates on the walls of the heat exchanger, thereby
optimizing the system’s operation.
The present study developed an ice-slurry generator that had a mechanical scraper. Sea water
was used as a solvent to generate the ice slurry (Melinder, 2010) because sea water is a natural
resource directly accessible to fishermen. The present study compared the performance of R290 and R-22 as working fluids for the refrigeration system.
2.
EXPERIMENTAL METHODS
2.1. Data Collection
Figure 1 shows the data-collection process. The generator was designed using type 316 stainless
steel. The system included a condensing unit, an electric motor, a magnetic pump, and an
inverter. After installation, the tools, including the digital thermometer, infrared thermometer,
and pressure gauge, were checked and caliberated.
Figure 1 Schematic of methodology
Other components were also checked, including the electrical components; the copper pipes and
sea water pipes, which were leakage tested; and the vacuum system. Trials were conducted to
observe the effects of various combination of pump and motor RPM speeds on the following:
decreasing the temperature of 5 liters of sea water, the time necessary to form the ice slurry, the
density of the ice slurry, and the power required. The data obtained during the test were
processed and analyzed in graphical form.
2.2. Experimental Device and Ice-slurry System
The working principle of an ice-slurry generator is similar to that of a heat exchanger having a
concentric tube consisting of 2 tubes of different diameters but of the same height, one inside
the other. In the outer tube, refrigerant flows at a low pressure with a saturation phase, causing a
convection process that absorbs heat into the wall of the inner tube, necessitating that the wall
of the inner tube be cooled by a refrigerant. The material selected for both tubes was type 316
stainless steel, which can withstand the oxidative effects of corrosive solutions, such as sea
water, which has salinity of 30 parts per thousand. Figure 2 shows the design of the ice slurry’s
generator.
Continuous circulation of seawater in the generator will result in the build-up of ice on the wall
of the inner tube. The layer of ice significantly reduces the thermal conductivity of the inner
tube, because the ice has great heat resistance. If the ice is allowed to build up on the generator,
the flow of the solvent in the generator will slowed. Therefore, an additional apparatus is
needed to grind the ice off of the generator’s inner walls.
Rayhan & Pamitran
1193
Figure 2 Ice-slurry generator with two symmetric blades
A scraper is a shaft having blades that added to the generator to prevent ice from accumulating
on the wall of the inner tube and to maintain the homogeneity of the solution. The optimal
scraper design uses 2 symmetrical blades with a 2.5-mm clearance from the wall of the inner
tube (Lakhdar et al., 2005). To prevent sea water from leaking in at the top, the shaft’s leverage
used Teflon as gland packing. Teflon was used because it has the lowest coefficient of friction
of all solid materials. Hence, the rotation of the generator’s shaft had no significant frictional
resistance (Constantinou et al., 1990). A split condensing unit had 368 watts of power. The
system used a rotary compressor containing 2 helical screws that produced compressed air in
large quantities, because R-290 needs greater compression power than R-22. Pressure gauges
were located at 4 points: the inlet evaporator, inlet compressor, inlet condenser, and inlet
expansion valve). The system used a ball valve, which can be adjusted manually, as the
expansion valve. Figure 3 shows a schematic of the installed equipment.
Figure 3 Schematic of ice slurry system
A centrifugal-type magnetic pump is compatible with ice slurry and can be used for 1000 hours
without encountering problems (Frei & Huber, 2005). This system used a magnetic pump hat
had 45 watts of power and a flow rate of 40 liters/min. The magnetic pump is augmented by use
of an inverter to adjust the flow rate of the solution. An electric motor moved the generator’s
shaft, which was connected by a pulley and belt. The electric motor used had a power
1194
Performance of Ice Slurry Generator with Mechanical Scraper using R-22 and R-290
specification of 1 HP and 3 input phases. Like a magnetic pump, an electric motor uses an
inverter to adjust its rotation. The use of a refrigerant can affect the properties of ice slurry
(Kauffeld et al., 2010). The present study compared the performance of R-22 and R-290 as
refrigerants. Table 1 shows the properties of the two.
Table 1 Comparison of R-22 and R-290 (Wang & Wang, 2000)
Refrigerant
Name
Formula
Flash Point
Odor
Molar Mass
Melting Point
Boiling Point
GWP
ODP
3.
R-22
Chlorodifloromethane
CHClF2
Nonflammable
Sweetish
86.47 g/mol
−175.42 °C
−40.7 °C
1700
0.055
R-290
Propane
C3H8
Flammable
Odorless
44.1 g/mol
−187.7 °C
−42 °C
3
0
RESULTS AND DISCUSSION
Under ambient conditions, the temperature of sea water is 27oC. Because sea water is a fluid
that will turn into ice slurry, the present study applied it to the ice generator. The sea water’s
temperature decreased until it formed ice slurry at -2oC. The present study began recording
experimental data regarding sea water temperature at 15oC and continued until the sea water
formed ice slurry. The study also compared the results of using R-22 and R-290 in the
refrigeration system. To provide similar conditions for the two refrigerants, a low pressure (2
bar) was maintained for both refrigerants. In addition, the study varied the RPM speeds of both
the pump and motor from low to high to observe the influence of speed on decreasing the
temperature of the sea water. The pump’s impeller rotations were 1480, 1777, 2074, and 2371
RPMs. The scraper’s rotations were 486, 557, 646, and 737 RPMs. Figures 4 and 5 show the
values measured for the decreasing temperature of the sea water.
Figure 4 Graphs of sea water degradation temperature with 1480 RPM for pump and 468 RPM for
motor (left) and 1777 RPM for pump and 557 RPM for motor (right)
Overall, the results of the data showed that the higher the RPM speed of the scraper, the longer
it took to generate ice. Although this higher speed required a longer time to generate ice, it
helped maintain the performance of the scraper, preventing its sudden cessation. In addition,
Rayhan & Pamitran
1195
when the scraper speed was higher, the process of transferring heat to the evaporator was more
even, and a higher speed enabled the scraper to continue grinding the ice layer that built up on
the inner walls of the evaporator.
The data regarding the R-22 refrigerant indicated that a sudden cessation of the scraper could be
caused by the accumulation of ice in the generator. When R-22 was used as the refrigerant, the
ice slurry was generated the fastest when the speeds of both the pump and scraper were higher,
2371 RPM and 737 RPM, respectively. At these speeds, it took 18 minutes for ice slurry to be
generated from sea water that had an initial temperature of 15℃.
In contrast, when R-290 was used as the refrigerant, the scraper was kept rotating with no
sudden cessations, and the ice slurry was generated the fastest when the speeds of both the
pump and the scraper were slower, 1480 RPM and 468 RPM, respectively. At these speeds, it
only took 13 minutes to form ice slurry.
Regarding the efficiency of the two refrigerants, when R-22 was used as the refrigerant, all five
liters of sea water could not be converted into ice slurry, and only a small volume of ice slurry
was generated. In contrast, when R-290 was used as the refrigerant, all five liters of sea water
were converted into ice slurry, demonstrating the superior ability of the R-290 refrigerant to
absorb heat from the sea water.
Figure 5 Graph of temperature decrease in sea water at 2074 RPM speed for pump and 646 RPM speed
for motor (left) and at 2371 RPM speed for pump and 737 RPM speed for motor (right)
1800
Density of Ice Slurry (Kg/m^3)
1600
1690
1570
1400
1200
1300
1200
1000
800
600
400
200
0
Pump : 1480 RPM Pump : 1777 RPM Pump : 2074 RPM Pump : 2371RPM
Scraper : 468 RPM Scraper : 557 RPM Scraper : 646 RPM Scraper : 737 RPM
Figure 6 Effects of pump and scraper RPM speeds on ice-slurry density
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Performance of Ice Slurry Generator with Mechanical Scraper using R-22 and R-290
In addition, the data showed that the higher the RPM speed of the pump, the faster the
temperature of the sea water decreased. This can be explained by the fact that the higher pump
speed increased circulation of the sea water in the evaporator, causing the heat from the water to
be absorbed more quickly. In contrast, faster RPM speeds of both the pump and the scraper
resulted in less dense ice slurries, as shown in Figure 6.
4.
CONCLUSION
The present study investigated the performance of an ice-slurry generator having a mechanical
scraper. The results showed that a higher scraper speed and a constant pump speed took longer
to produce ice slurry than did a lower scraper speed but had the advantage of maintaining
scraper performance without sudden cessations. In contrast, a higher pump speed and a constant
scraper speed decreased the temperature of sea water more quickly. In addition, the results
indicated that R-290 was a more efficient refrigerant than R-22, efficiently lowering the
temperature of more sea water, enabling ice scraping, and avoiding generator freezing.
5.
ACKNOWLEDGEMENT
This study was funded by a grant from Fundamental RISTEKDIKTI, Number :
2566/UN2.R3.1/HKP05.00/2017
6.
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