- Email: [email protected]
Harnessing the energy accompanying freezing
Energy Conversion and Management 52 (2011) 2241–2246
Contents lists available at ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Harnessing the energy accompanying freezing M. Akyurt ⇑, N. Türkmen Departments of Mechanical Engineering, King Abdulaziz University, Jeddah 21589, Saudi Arabia
a r t i c l e
i n f o
Article history: Received 3 March 2010 Received in revised form 25 November 2010 Accepted 13 December 2010
Keywords: Apparatus Burst Freeze Leak Maintenance Pressure
a b s t r a c t The progression of freezing of water inside a pipe is reviewed, with special emphasis on bursting. The process of pressure rise in confined bodies of water is discussed. The development of a method utilizing liquid carbon dioxide and liquid nitrogen, for the development of pressures inside closed containers is summarized. Then a novel method, utilizing mechanical refrigeration, is explained for the generation of high pressures. An experimental setup for the latter technique is described and results of experiments are summarized. A number of ways of utilizing the ice-pressurization technique are presented. Certain characteristics and advantages of ice-pressurization are enumerated as regards to burst and leak testing. It is noted that a number of other techniques such as shrink fitting, embossing and compaction of powders also seem to be particularly suitable. It is concluded that, with the advent of the portable and novel chilling apparatus, new vistas are approachable for undertaking maintenance operations in hospitals, power plants, nuclear facilities, and other systems that require uninterrupted operation. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Bursting of pipes due to freezing is common. Some pipeline accidents and aircraft stall cases are often attributed to freezing. It has been verified [1] that the commonly held view, that pipes burst when ice growth simply pushes against pipe walls, is not correct. Pipe bursting actually occurs when freezing temperatures give rise to a solid plug of concentric ice that forms inside a pipe such that this plug grows into a confined zone of water [2]. Fig. 1 depicts schematically temperatures and pressures in a water-filled pipe when the pipe is exposed to freezing temperatures [2]. Thus water first cools to freezing temperature (A to B), and then it is subcooled (B to C). Then sharp-cornered dendritic ice particles are formed (C to D), when temperatures go up to zero degrees. This is followed by a long period of isothermal solid-ice formation and growth (D to E). At E the entire cross sectional area of the pipe is frozen solid. Then the temperatures start to decline again. If the water in the pipe is confined, that means ice cannot grow anymore after point E. Hence pressures start rising, until at F the pipe bulges and then ruptures at G, ejecting part of the water, and releasing the pressure. Akyurt and associates [2] conducted a survey on ice energy applications to date. Among other applications, they found that crushed ice can be used to ‘‘clean’’ piping with bends. Thus Quarini
⇑ Corresponding author. Tel.: +966 2 6400000/68298; fax: +966 2 6952198. E-mail address: [email protected] (M. Akyurt). 0196-8904/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2010.12.016
[3] investigated the clean-in-place (CIP) capability of a crushed ice pigging system. The ‘pig’ consists of crushed ice in water with a freezing point depressant. The void fraction is carefully controlled so that the ice/water mix moves like a solid plug in free flow areas, but it is able flow like a fluid in constricted areas. The ice pig is able to flow in pipes with sharp bends, through orifice plates, through T’s and even in plate heat exchangers. The experimental work evaluating the ‘cleaning efficiency’ of this system indicated that the ice pig could easily and efficiently remove ‘soft’ fouling. The fouling materials tested included jam, fats, toothpaste, fine silt and sand in river water cooled heat exchangers. Zhkamukhov and Shokarov [4] presented calculations for predicting pressures inside closed enclosures during freezing. Habeebullah and associates [5] developed a prototype device for converting freezing energy into mechanical work. Fig. 2 shows the system they built. Akyurt and associates [6] described an ice-based technique they developed for burst testing of tubular elements. Consider to this end Fig. 3 [5,6] where donud-shaped cooling jackets (4) are placed near the two ends of a water-filled tube (1). When jackets (4) are cooled to temperatures that are below the freezing temperature of water, a part of the volume of water (5) that is located in the vicinity of the cooling jackets (4) is frozen solid. Thus the un-frozen body (3) of water is compressed as the ice at both frozen ends start growing. Fig. 4 [6] shows a ruptured tube that was ripped apart by ice pressurization. At both ends of the tube shown in Fig. 4 are liquid carbon dioxide cooled cooling jackets (not shown).
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M. Akyurt, N. Türkmen / Energy Conversion and Management 52 (2011) 2241–2246
Fig. 1. Temperatures and pressures during pipe bursting [2].
Fig. 5. The split formed at the central zone of the copper tube.
Fig. 6. Trace of the jet of water that was ejected during the splitting of another copper tube.
Fig. 2. Ice energy converter [5].
Fig. 3. The conceptual sketch for the use of freezing of water for internal iso-static pressurization.
Fig. 4. The split in the extruded aluminum tube and the shape of the ejected waterjet on the support board.
Other examples of bursting of tubes by ice pressurization are shown in Figs. 5 and 6 [6]. Note that in each case the rupture occurs in the un-frozen part of the tube. It would be of interest to ascertain the pressures developed during the process of ice pressurization. Fig. 7 shows an arrangement for this purpose, where two freeze heads on a tube are cooled by liquid carbon dioxide. A crush-resistant sensor tube protruding through the upper freezing zone is used to measure pressures in the un-frozen middle zone. Typical pressures measured by the system are displayed in Fig. 8 for an aluminum tube and in Fig. 9 for a mild steel welded pipe. From Fig. 8 it is possible to tell that the tube starts to bulge at about 300 bar, the easing of pressures due to the enlarged volume, and then the rupture at the weakest point. In Fig. 9 the effect of bulging is noticeable at about 1000 bar, but pressures are not sufficient to cause a rupture. In all ice-pressurization work cited above, cooling jackets have been employed that are cooled either by liquid CO2 or by liquid nitrogen. Availability of these liquids calls for the ease of access to a gas liquefaction plant. The liquefied gases are then transported in insulated pressure cylinders to work areas to feed cooling jackets, where they are exchanged with fresh cylinders as they get used up. Admittedly this chain of events is not very convenient since there are repeated fees for cylinder filling, time losses during cylinder filling and transport, and labor and time requirements for cylinder handling operations during hookup to cooling setup or unhooking from it. The only exceptions to this dependence are what is reported from KAU by Turkmen and associates [7], Al-Aqel and associates [8] and Türkmen [9], where an innovative new system is introduced that does not depend on the availability of a gas liquefaction plant, and which does not involve pressure cylinders, transportation, and the costs and time losses associated with them. The new system seems to be practical, portable and economical while enabling the development of high pressures continuously in all
M. Akyurt, N. Türkmen / Energy Conversion and Management 52 (2011) 2241–2246
2243
Pressure - bars
Fig. 7. Schematic arrangement for the burst and leak testing of a tubular specimen [7].
350
2. Generation of high pressures
300 250
It is possible to generate mechanical work by using the volume expansion that takes place during the freezing of water. Eq. (1) expresses the work W done during the process as
200
W¼
pdV
ð1Þ
150
where p is the pressure in the system and dV is the change in volume. For a constant pressure process, the work equation simplifies to
100 50
W ¼ pDV
0 10
12
14
16
18
20
Time - min Fig. 8. Burst testing of 1.5 in. extruded aluminum tube [7].
1400
Pressure - bars
Z
1200
ð2Þ
Now, it may be recalled that when one liter of water freezes, its volume expands to about 1090 cubic cm, and if this expansion is prevented, enormous pressures, of up to about 2000 bar [4], can develop. Above 2000 bar, ice forms other than ice Ih appear, and ice contracts. Hence pressure build up does not occur during freezing in those regions. Consequently, an upper limit to pressure p is about 2000 bar. Thus, in accordance with Eq. (2), the upper limit of work that can be done under constant pressure conditions is
W up ¼ ð2000 barÞ ð90 cm3 Þ ¼ 18; 000 N m
1000 800
where Wup is the maximum possible work that can be done when one liter of water freezes. One would expect that the actual work that can be done would be noticeably less then Wup. The work expression of Eq. (1) can be alternatively expressed in term of force F and the incremental distance dx over which the force acts.
600 400 200 0 0
10
20
30
40
50
Time - min
W¼
Z
Fdx
ð3Þ
Fig. 9. Leak testing of seam-welded MS pipe (OD = 26.9, t = 2.6 mm) [7].
If the force is constant, then Eq. (3) simplifies t
W ¼ F Dx locations where electricity is available. The new system makes it possible to reach pressures in the vicinity of 2000 bar. In what follows, an overview is presented of the latest developments at KAU regarding ice pressurization. Also outlined are innovative vistas for ice pressurization applications in general as well as the possibilities laid open by the use of the new apparatus for ice pressurization that requires electricity only.
ð4Þ
where Dx is the distance traversed by F. Since the work expected from an ice energy conversion system may be mechanical in nature, one would expect the utility of Eq. (4). One immediate application may be that of a hydraulic actuator, where the high pressure fluid that results from freezing acts on a piston to displace a load or resistance by a distance Dx.
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2000
3. Portable cooling without liquified gases
1800 1600
Pressure (bar)
Turkmen and associates [7] developed a portable system for establishing ice blockages without the use of liquified carbon dioxide or nitrogen. Referring to Fig. 10, evaporator #1 of cooler #1 and condenser #2 of cooler #2 were immersed into two pools of liquid, which was initially water. Both tanks were provided with submersible pumps, each pumping the liquid in its tank into the other tank. Condenser #1 was cooled by ambient air, using the fan of the cooler. Evaporator #2, which was immersed into a pool of glycol, chilled the glycol that was circulated in the two heat exchangers of the freezing system. The latter tank was provided with exit and return ports for circulation of the glycol. Two thermostatic electrical heaters, visible at the left of the figure, were also provided for enhancing de-icing of the pressure pipe between experiments. Fig. 11 shows the actual chilling system during operation. The three tanks housing the evaporators #1 and #2 and the condenser #2 (Fig. 10) are visible with their styrofoam insulations. Al-Aqel and associates [8] conducted exhaustive testing on the new chilling device. Fig. 12 shows a typical sample from their findings, where it is observed that pressures in excess of 1800 bar were reached. The new system was further subjected to intensive testing by Türkmen [9]. Figs. 13 and 14 show the variation of pressures developed by essentially the same setup as that in Fig. 10. As it may be verified from the latter figure, the peak pressure of 2075 bar is achieved after about 150 min from the start of the experiment. It is to be noted that this is approximately the ultimate pressure that an ice-based system can be expected to develop, as predicted by Zhkamukhov and Shokarov [4]. What is significant about the experimental setup of Fig. 11 is its simplicity. It consists of two commercial air coolers connected in
1400 1200 1000 800 600 400 200 0
0
20
40
60
80
100
120
140
160
Time (min) Fig. 12. Variation of pressure with time (coolant entry at 21 °C) [8].
tandem. Using suitable liquid media, it is capable of cooling its output fluid to about 28 °C. When fed into cooling jackets, this results in the production of pressures of about 2000 bar. The highly economical setup of Fig. 11 can be readily sized for any freezing application. It can be promptly placed on wheels so that it becomes fully portable. Then ice blocks can be formed and high pressures can be developed continuously wherever and whenever this portable system is connected to electricity. The availability of a nearby gas liquefaction plant is no longer a prerequisite for ice pressurization. Consequently no pressure cylinders are needed for transporting liquefied gases, and no handling or transportation expenses involved. Cooling jackets can be serviced by connecting them to exit and return ports of the new transportable and friendly system.
Fig. 10. The chilling unit [7].
Fig. 11. The chilling system during operation [7].
M. Akyurt, N. Türkmen / Energy Conversion and Management 52 (2011) 2241–2246
250
Pressure (MPa)
200
150 Cooling Temperature
100
-27 ºC -25 ºC
50
0
-23 ºC
0
15
30
45
60
75
90
Time (min)
2245
tors, hospitals, hotels, and facilities which operate on a 24 h schedule. These facilities rely heavily on pipe isolation to establish a condition which allows for maintenance while remaining on line. With the current wide spread profusion of various plastics and composite materials for making pipes and other tubular shapes, the need has arisen to determine the physical characteristics of these newer tubes. This is especially true since the latter are essentially visco-elastic in nature, and hence their properties are time and temperature dependent. Testing of such thin-walled tubes for leaks and for bursting ordinarily requires an iso-static test pressure of about 400 bars and the availability of a costly jig. The same chore can be readily and cost effectively undertaken by resorting to pressurization by freezing. All one has to do is to setup an arrangement similar to that shown in Fig. 11 and to instrument it.
Fig. 13. Variation of pressures with time [9].
5. Salient features of leak and burst testing by ice pressurization One may summarize the salient features of leak- and burst testing by freezing as follows:
2500
Pressure (bar)
2000 1500 1000 500 0
0
20
40
60
80
100
120
140
160
Time (min) Fig. 14. Variation of pressure with time (coolant entry at 28 °C) [9].
It is believed that the novel and handy chilling apparatus [7–9] discussed here and shown in Fig. 11 opens new vistas in ice pressurization applications. This would imply leak- and burst testing as well as maintenance operations in hospitals, power plants, nuclear facilities, and other 24 h operational systems. 4. Exploring innovative vistas for ice pressurization applications One modern mode of application of freezing, aside from the commercial production of ice, and the freezing of foodstuffs, is in maintenance work. Engineers have been using ice plugs on piping to undertake maintenance chores without having to drain piping systems. Typically pipe diameters may be as large as 20 in. One such system [10] uses a bath of liquid nitrogen to establish and lock in place solid plugs of the fluid inside the pipe. Solid plugs effectively isolate work areas. It is reported that such plugs withstand pressures up to 8000 psig (550 bars) or 225,000 lbs (1000 kN) of axial force [10]. Kits are commercially available for rapidly forming an ice plug in static small-diameter water lines, 3/8–21/8 in. O.D., eliminating the need to drain down a system to make a repair. The coolant used for such kits is CO2. With the advent of the new system, it is plausible that the system of Fig. 11 can be engineered to replace liquid CO2 and N2 in this application. Considering costs of downtime, labor, and replacement fluids, pipe freezing is claimed to be substantially less costly, and in many cases it amounts to a small percentage of the expense of alternative maintenance procedures. Typical users of the technology include nuclear power plants, industrial companies, mechanical contrac-
(a) The test setup required for pressurization is uncomplicated, requiring very little investment. There is no need for stainless steel air-assisted hydraulic cylinder setups that are commonly used for burst testing of pipes and tubes. (b) Sealing is extremely easy and effective. No special sealants are required. Ice will seal and sustain high pressures. (c) The process does not require specially designed end caps that are fitted with special bleeders and manifold fittings to connect the specimen pipes to the testing machine. Many geometries and thicknesses that would not permit the use of end caps and that are routinely fitted with special bleeders and manifold fittings can be tested readily by ice pressurization. (d) No special hydraulic/pneumatic power is required to generate high pressures. (e) Clamping is not required, and special threading and other measures are not needed. There is really little or no need to prepare specimens. (f) The thickness and strength of the tube material is of no consequence. The glass transition temperature of the material permitting, tubes made of any material can be tested. (g) No danger of a major explosion exists with ice pressurization. The practical consequence of these features is that ice pressurization allows the burst- and leak testing of practically all tubular materials that can be tested using classical testing techniques. Additionally, many thin tubular and non-tubular materials that are difficult to test using classical testing techniques can now be burst and leak tested by the new ice-based pressurization method. A further potential application for ice pressurization is for achieving shrink-fitted or interference-fitted assemblies of collars, bushings and sleeves at essentially ordinary temperatures. Utilizing an outer sleeve (6) as indicated in Fig. 3, the method would be applicable directly. The same technique can be used equally effectively when conditions preclude the use of conventional interference fitting techniques of heat treatment and/or axial pressing. An example of the latter case would be the inner cladding of the sleeve by a thin film of low-strength lining. It may be also pointed out that ice pressurization can be utilized for embossing of logos and other shapes on piping and other tubular surfaces, if a die is utilized in place of the sleeve of Fig. 3. It must
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be stressed here that it is not necessary for the tube (1) and die to be circular in cross section. Yet another prospective application of ice pressurization can be in compaction, including the compaction of powders into ferrous or nonferrous porous objects. Conventional techniques typically employ plungers for compaction, which result in Hertz-type nonuniform stress distributions under the die. The new method however, would eliminate non-homogeneities in the manufactured goods by applying on them truly iso-static pressures. 6. Conclusions Ice-based pressurization is elucidated to be easy to apply, undemanding in equipment requirements, versatile in applications and a safe technique for burst- and leak testing. It involves a simple test setup. It is convenient and cost effective. Little investment is needed for it, and there is little or no sample preparation. No clamping is needed. Thickness and strength of the specimen is of no concern. Sealing is extremely easy and effective. No special end caps are needed. In contrast to contemporary burst testing practices, no pneumatic or hydraulic power is needed. A further significant conclusion concerns the adhesive and shear strength of forces between the ice block and its container. These forces that hold the ice block secured and anchored to the wall of the container are so strong that forces due to pressures in excess of 2000 bar are not able to dislodge the ice blockage from the container, even in large-diameter pipes. The only precaution needed is that the designs must allow the removal of gases from the area being frozen before and during freezing. Utilizing the concept developed by Turkmen and associates [7], the ice pressurization assembly shown in Fig. 11 can be readily placed on wheels to become fully portable. Then pressures up to
about 2000 bar can be developed continuously wherever and whenever the system is connected to electricity. No nearby gas liquefaction plant is needed. Consequently no pressure cylinders are needed, and there are no handling or transportation expenses involved. Cooling jackets can be serviced by connecting them to exit and return ports of the new system. It is believed that the novel chilling apparatus [7–9] discussed here opens new vistas in ice pressurization applications, including leak- and burst testing as well as maintenance operations in hospitals, power plants, nuclear facilities, and other 24 h operational systems. References [1] Gordon JR. Prevention of bursting in water pipes. Research report no 96-1. Building Research Council, School of Architecture, University of Illinois at Urbana-Champaign; 1996. [2] Akyurt M, Zaki G, Habeebullah B. Freezing phenomena in ice–water systems. J Energy Convers Manage 2002;43:1773–89. [3] Quarini J. Pigging to reduce and remove fouling and to achieve clean-in-place. Appl Therm Eng 2002;22:747–53. [4] Zhkamukhov MK, Shokarov KhB. Calculation of stresses and strains developing in freezing of water in closed vessels. J Eng Phys Thermophys 2003;76(1):210–21. [5] Habeebullah B, Zaki G, Akyurt M. A prototype device for converting freezing energy into mechanical work. J Energy Convers Manage 2003;44:251–65. [6] Akyurt M, Aljawi ANA, Aldousari S. Development of an ice-based technique for burst testing of tubular elements. KAU J Eng Sci 2006;16(1):21–48. [7] Turkmen N, Akyurt M, Aljawi A. Investigation of pressures caused by ice blockage. In: Proceedings of the 7th Saudi conference of engineering, vol. 5, Riyadh; 26–28 November 2007. p. 185–97. [8] Al-Aqel MS, Najeeb A, Ahmed H. On applications of ice and a novel chilling apparatus. Unpublished BS project, Dept of Thermal Eng and Desal Technol, College of Engineering, KAU; 2009. [9] Türkmen N. Ice-based pressurization utilizing a novel chilling apparatus. Energy Convers Manage, submitted for publication. [10] http://www.bishopgroupservices.com/pipefreezing/index.html; 2010.
Contents lists available at ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Harnessing the energy accompanying freezing M. Akyurt ⇑, N. Türkmen Departments of Mechanical Engineering, King Abdulaziz University, Jeddah 21589, Saudi Arabia
a r t i c l e
i n f o
Article history: Received 3 March 2010 Received in revised form 25 November 2010 Accepted 13 December 2010
Keywords: Apparatus Burst Freeze Leak Maintenance Pressure
a b s t r a c t The progression of freezing of water inside a pipe is reviewed, with special emphasis on bursting. The process of pressure rise in confined bodies of water is discussed. The development of a method utilizing liquid carbon dioxide and liquid nitrogen, for the development of pressures inside closed containers is summarized. Then a novel method, utilizing mechanical refrigeration, is explained for the generation of high pressures. An experimental setup for the latter technique is described and results of experiments are summarized. A number of ways of utilizing the ice-pressurization technique are presented. Certain characteristics and advantages of ice-pressurization are enumerated as regards to burst and leak testing. It is noted that a number of other techniques such as shrink fitting, embossing and compaction of powders also seem to be particularly suitable. It is concluded that, with the advent of the portable and novel chilling apparatus, new vistas are approachable for undertaking maintenance operations in hospitals, power plants, nuclear facilities, and other systems that require uninterrupted operation. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Bursting of pipes due to freezing is common. Some pipeline accidents and aircraft stall cases are often attributed to freezing. It has been verified [1] that the commonly held view, that pipes burst when ice growth simply pushes against pipe walls, is not correct. Pipe bursting actually occurs when freezing temperatures give rise to a solid plug of concentric ice that forms inside a pipe such that this plug grows into a confined zone of water [2]. Fig. 1 depicts schematically temperatures and pressures in a water-filled pipe when the pipe is exposed to freezing temperatures [2]. Thus water first cools to freezing temperature (A to B), and then it is subcooled (B to C). Then sharp-cornered dendritic ice particles are formed (C to D), when temperatures go up to zero degrees. This is followed by a long period of isothermal solid-ice formation and growth (D to E). At E the entire cross sectional area of the pipe is frozen solid. Then the temperatures start to decline again. If the water in the pipe is confined, that means ice cannot grow anymore after point E. Hence pressures start rising, until at F the pipe bulges and then ruptures at G, ejecting part of the water, and releasing the pressure. Akyurt and associates [2] conducted a survey on ice energy applications to date. Among other applications, they found that crushed ice can be used to ‘‘clean’’ piping with bends. Thus Quarini
⇑ Corresponding author. Tel.: +966 2 6400000/68298; fax: +966 2 6952198. E-mail address: [email protected] (M. Akyurt). 0196-8904/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2010.12.016
[3] investigated the clean-in-place (CIP) capability of a crushed ice pigging system. The ‘pig’ consists of crushed ice in water with a freezing point depressant. The void fraction is carefully controlled so that the ice/water mix moves like a solid plug in free flow areas, but it is able flow like a fluid in constricted areas. The ice pig is able to flow in pipes with sharp bends, through orifice plates, through T’s and even in plate heat exchangers. The experimental work evaluating the ‘cleaning efficiency’ of this system indicated that the ice pig could easily and efficiently remove ‘soft’ fouling. The fouling materials tested included jam, fats, toothpaste, fine silt and sand in river water cooled heat exchangers. Zhkamukhov and Shokarov [4] presented calculations for predicting pressures inside closed enclosures during freezing. Habeebullah and associates [5] developed a prototype device for converting freezing energy into mechanical work. Fig. 2 shows the system they built. Akyurt and associates [6] described an ice-based technique they developed for burst testing of tubular elements. Consider to this end Fig. 3 [5,6] where donud-shaped cooling jackets (4) are placed near the two ends of a water-filled tube (1). When jackets (4) are cooled to temperatures that are below the freezing temperature of water, a part of the volume of water (5) that is located in the vicinity of the cooling jackets (4) is frozen solid. Thus the un-frozen body (3) of water is compressed as the ice at both frozen ends start growing. Fig. 4 [6] shows a ruptured tube that was ripped apart by ice pressurization. At both ends of the tube shown in Fig. 4 are liquid carbon dioxide cooled cooling jackets (not shown).
2242
M. Akyurt, N. Türkmen / Energy Conversion and Management 52 (2011) 2241–2246
Fig. 1. Temperatures and pressures during pipe bursting [2].
Fig. 5. The split formed at the central zone of the copper tube.
Fig. 6. Trace of the jet of water that was ejected during the splitting of another copper tube.
Fig. 2. Ice energy converter [5].
Fig. 3. The conceptual sketch for the use of freezing of water for internal iso-static pressurization.
Fig. 4. The split in the extruded aluminum tube and the shape of the ejected waterjet on the support board.
Other examples of bursting of tubes by ice pressurization are shown in Figs. 5 and 6 [6]. Note that in each case the rupture occurs in the un-frozen part of the tube. It would be of interest to ascertain the pressures developed during the process of ice pressurization. Fig. 7 shows an arrangement for this purpose, where two freeze heads on a tube are cooled by liquid carbon dioxide. A crush-resistant sensor tube protruding through the upper freezing zone is used to measure pressures in the un-frozen middle zone. Typical pressures measured by the system are displayed in Fig. 8 for an aluminum tube and in Fig. 9 for a mild steel welded pipe. From Fig. 8 it is possible to tell that the tube starts to bulge at about 300 bar, the easing of pressures due to the enlarged volume, and then the rupture at the weakest point. In Fig. 9 the effect of bulging is noticeable at about 1000 bar, but pressures are not sufficient to cause a rupture. In all ice-pressurization work cited above, cooling jackets have been employed that are cooled either by liquid CO2 or by liquid nitrogen. Availability of these liquids calls for the ease of access to a gas liquefaction plant. The liquefied gases are then transported in insulated pressure cylinders to work areas to feed cooling jackets, where they are exchanged with fresh cylinders as they get used up. Admittedly this chain of events is not very convenient since there are repeated fees for cylinder filling, time losses during cylinder filling and transport, and labor and time requirements for cylinder handling operations during hookup to cooling setup or unhooking from it. The only exceptions to this dependence are what is reported from KAU by Turkmen and associates [7], Al-Aqel and associates [8] and Türkmen [9], where an innovative new system is introduced that does not depend on the availability of a gas liquefaction plant, and which does not involve pressure cylinders, transportation, and the costs and time losses associated with them. The new system seems to be practical, portable and economical while enabling the development of high pressures continuously in all
M. Akyurt, N. Türkmen / Energy Conversion and Management 52 (2011) 2241–2246
2243
Pressure - bars
Fig. 7. Schematic arrangement for the burst and leak testing of a tubular specimen [7].
350
2. Generation of high pressures
300 250
It is possible to generate mechanical work by using the volume expansion that takes place during the freezing of water. Eq. (1) expresses the work W done during the process as
200
W¼
pdV
ð1Þ
150
where p is the pressure in the system and dV is the change in volume. For a constant pressure process, the work equation simplifies to
100 50
W ¼ pDV
0 10
12
14
16
18
20
Time - min Fig. 8. Burst testing of 1.5 in. extruded aluminum tube [7].
1400
Pressure - bars
Z
1200
ð2Þ
Now, it may be recalled that when one liter of water freezes, its volume expands to about 1090 cubic cm, and if this expansion is prevented, enormous pressures, of up to about 2000 bar [4], can develop. Above 2000 bar, ice forms other than ice Ih appear, and ice contracts. Hence pressure build up does not occur during freezing in those regions. Consequently, an upper limit to pressure p is about 2000 bar. Thus, in accordance with Eq. (2), the upper limit of work that can be done under constant pressure conditions is
W up ¼ ð2000 barÞ ð90 cm3 Þ ¼ 18; 000 N m
1000 800
where Wup is the maximum possible work that can be done when one liter of water freezes. One would expect that the actual work that can be done would be noticeably less then Wup. The work expression of Eq. (1) can be alternatively expressed in term of force F and the incremental distance dx over which the force acts.
600 400 200 0 0
10
20
30
40
50
Time - min
W¼
Z
Fdx
ð3Þ
Fig. 9. Leak testing of seam-welded MS pipe (OD = 26.9, t = 2.6 mm) [7].
If the force is constant, then Eq. (3) simplifies t
W ¼ F Dx locations where electricity is available. The new system makes it possible to reach pressures in the vicinity of 2000 bar. In what follows, an overview is presented of the latest developments at KAU regarding ice pressurization. Also outlined are innovative vistas for ice pressurization applications in general as well as the possibilities laid open by the use of the new apparatus for ice pressurization that requires electricity only.
ð4Þ
where Dx is the distance traversed by F. Since the work expected from an ice energy conversion system may be mechanical in nature, one would expect the utility of Eq. (4). One immediate application may be that of a hydraulic actuator, where the high pressure fluid that results from freezing acts on a piston to displace a load or resistance by a distance Dx.
2244
M. Akyurt, N. Türkmen / Energy Conversion and Management 52 (2011) 2241–2246
2000
3. Portable cooling without liquified gases
1800 1600
Pressure (bar)
Turkmen and associates [7] developed a portable system for establishing ice blockages without the use of liquified carbon dioxide or nitrogen. Referring to Fig. 10, evaporator #1 of cooler #1 and condenser #2 of cooler #2 were immersed into two pools of liquid, which was initially water. Both tanks were provided with submersible pumps, each pumping the liquid in its tank into the other tank. Condenser #1 was cooled by ambient air, using the fan of the cooler. Evaporator #2, which was immersed into a pool of glycol, chilled the glycol that was circulated in the two heat exchangers of the freezing system. The latter tank was provided with exit and return ports for circulation of the glycol. Two thermostatic electrical heaters, visible at the left of the figure, were also provided for enhancing de-icing of the pressure pipe between experiments. Fig. 11 shows the actual chilling system during operation. The three tanks housing the evaporators #1 and #2 and the condenser #2 (Fig. 10) are visible with their styrofoam insulations. Al-Aqel and associates [8] conducted exhaustive testing on the new chilling device. Fig. 12 shows a typical sample from their findings, where it is observed that pressures in excess of 1800 bar were reached. The new system was further subjected to intensive testing by Türkmen [9]. Figs. 13 and 14 show the variation of pressures developed by essentially the same setup as that in Fig. 10. As it may be verified from the latter figure, the peak pressure of 2075 bar is achieved after about 150 min from the start of the experiment. It is to be noted that this is approximately the ultimate pressure that an ice-based system can be expected to develop, as predicted by Zhkamukhov and Shokarov [4]. What is significant about the experimental setup of Fig. 11 is its simplicity. It consists of two commercial air coolers connected in
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tandem. Using suitable liquid media, it is capable of cooling its output fluid to about 28 °C. When fed into cooling jackets, this results in the production of pressures of about 2000 bar. The highly economical setup of Fig. 11 can be readily sized for any freezing application. It can be promptly placed on wheels so that it becomes fully portable. Then ice blocks can be formed and high pressures can be developed continuously wherever and whenever this portable system is connected to electricity. The availability of a nearby gas liquefaction plant is no longer a prerequisite for ice pressurization. Consequently no pressure cylinders are needed for transporting liquefied gases, and no handling or transportation expenses involved. Cooling jackets can be serviced by connecting them to exit and return ports of the new transportable and friendly system.
Fig. 10. The chilling unit [7].
Fig. 11. The chilling system during operation [7].
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tors, hospitals, hotels, and facilities which operate on a 24 h schedule. These facilities rely heavily on pipe isolation to establish a condition which allows for maintenance while remaining on line. With the current wide spread profusion of various plastics and composite materials for making pipes and other tubular shapes, the need has arisen to determine the physical characteristics of these newer tubes. This is especially true since the latter are essentially visco-elastic in nature, and hence their properties are time and temperature dependent. Testing of such thin-walled tubes for leaks and for bursting ordinarily requires an iso-static test pressure of about 400 bars and the availability of a costly jig. The same chore can be readily and cost effectively undertaken by resorting to pressurization by freezing. All one has to do is to setup an arrangement similar to that shown in Fig. 11 and to instrument it.
Fig. 13. Variation of pressures with time [9].
5. Salient features of leak and burst testing by ice pressurization One may summarize the salient features of leak- and burst testing by freezing as follows:
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It is believed that the novel and handy chilling apparatus [7–9] discussed here and shown in Fig. 11 opens new vistas in ice pressurization applications. This would imply leak- and burst testing as well as maintenance operations in hospitals, power plants, nuclear facilities, and other 24 h operational systems. 4. Exploring innovative vistas for ice pressurization applications One modern mode of application of freezing, aside from the commercial production of ice, and the freezing of foodstuffs, is in maintenance work. Engineers have been using ice plugs on piping to undertake maintenance chores without having to drain piping systems. Typically pipe diameters may be as large as 20 in. One such system [10] uses a bath of liquid nitrogen to establish and lock in place solid plugs of the fluid inside the pipe. Solid plugs effectively isolate work areas. It is reported that such plugs withstand pressures up to 8000 psig (550 bars) or 225,000 lbs (1000 kN) of axial force [10]. Kits are commercially available for rapidly forming an ice plug in static small-diameter water lines, 3/8–21/8 in. O.D., eliminating the need to drain down a system to make a repair. The coolant used for such kits is CO2. With the advent of the new system, it is plausible that the system of Fig. 11 can be engineered to replace liquid CO2 and N2 in this application. Considering costs of downtime, labor, and replacement fluids, pipe freezing is claimed to be substantially less costly, and in many cases it amounts to a small percentage of the expense of alternative maintenance procedures. Typical users of the technology include nuclear power plants, industrial companies, mechanical contrac-
(a) The test setup required for pressurization is uncomplicated, requiring very little investment. There is no need for stainless steel air-assisted hydraulic cylinder setups that are commonly used for burst testing of pipes and tubes. (b) Sealing is extremely easy and effective. No special sealants are required. Ice will seal and sustain high pressures. (c) The process does not require specially designed end caps that are fitted with special bleeders and manifold fittings to connect the specimen pipes to the testing machine. Many geometries and thicknesses that would not permit the use of end caps and that are routinely fitted with special bleeders and manifold fittings can be tested readily by ice pressurization. (d) No special hydraulic/pneumatic power is required to generate high pressures. (e) Clamping is not required, and special threading and other measures are not needed. There is really little or no need to prepare specimens. (f) The thickness and strength of the tube material is of no consequence. The glass transition temperature of the material permitting, tubes made of any material can be tested. (g) No danger of a major explosion exists with ice pressurization. The practical consequence of these features is that ice pressurization allows the burst- and leak testing of practically all tubular materials that can be tested using classical testing techniques. Additionally, many thin tubular and non-tubular materials that are difficult to test using classical testing techniques can now be burst and leak tested by the new ice-based pressurization method. A further potential application for ice pressurization is for achieving shrink-fitted or interference-fitted assemblies of collars, bushings and sleeves at essentially ordinary temperatures. Utilizing an outer sleeve (6) as indicated in Fig. 3, the method would be applicable directly. The same technique can be used equally effectively when conditions preclude the use of conventional interference fitting techniques of heat treatment and/or axial pressing. An example of the latter case would be the inner cladding of the sleeve by a thin film of low-strength lining. It may be also pointed out that ice pressurization can be utilized for embossing of logos and other shapes on piping and other tubular surfaces, if a die is utilized in place of the sleeve of Fig. 3. It must
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be stressed here that it is not necessary for the tube (1) and die to be circular in cross section. Yet another prospective application of ice pressurization can be in compaction, including the compaction of powders into ferrous or nonferrous porous objects. Conventional techniques typically employ plungers for compaction, which result in Hertz-type nonuniform stress distributions under the die. The new method however, would eliminate non-homogeneities in the manufactured goods by applying on them truly iso-static pressures. 6. Conclusions Ice-based pressurization is elucidated to be easy to apply, undemanding in equipment requirements, versatile in applications and a safe technique for burst- and leak testing. It involves a simple test setup. It is convenient and cost effective. Little investment is needed for it, and there is little or no sample preparation. No clamping is needed. Thickness and strength of the specimen is of no concern. Sealing is extremely easy and effective. No special end caps are needed. In contrast to contemporary burst testing practices, no pneumatic or hydraulic power is needed. A further significant conclusion concerns the adhesive and shear strength of forces between the ice block and its container. These forces that hold the ice block secured and anchored to the wall of the container are so strong that forces due to pressures in excess of 2000 bar are not able to dislodge the ice blockage from the container, even in large-diameter pipes. The only precaution needed is that the designs must allow the removal of gases from the area being frozen before and during freezing. Utilizing the concept developed by Turkmen and associates [7], the ice pressurization assembly shown in Fig. 11 can be readily placed on wheels to become fully portable. Then pressures up to
about 2000 bar can be developed continuously wherever and whenever the system is connected to electricity. No nearby gas liquefaction plant is needed. Consequently no pressure cylinders are needed, and there are no handling or transportation expenses involved. Cooling jackets can be serviced by connecting them to exit and return ports of the new system. It is believed that the novel chilling apparatus [7–9] discussed here opens new vistas in ice pressurization applications, including leak- and burst testing as well as maintenance operations in hospitals, power plants, nuclear facilities, and other 24 h operational systems. References [1] Gordon JR. Prevention of bursting in water pipes. Research report no 96-1. Building Research Council, School of Architecture, University of Illinois at Urbana-Champaign; 1996. [2] Akyurt M, Zaki G, Habeebullah B. Freezing phenomena in ice–water systems. J Energy Convers Manage 2002;43:1773–89. [3] Quarini J. Pigging to reduce and remove fouling and to achieve clean-in-place. Appl Therm Eng 2002;22:747–53. [4] Zhkamukhov MK, Shokarov KhB. Calculation of stresses and strains developing in freezing of water in closed vessels. J Eng Phys Thermophys 2003;76(1):210–21. [5] Habeebullah B, Zaki G, Akyurt M. A prototype device for converting freezing energy into mechanical work. J Energy Convers Manage 2003;44:251–65. [6] Akyurt M, Aljawi ANA, Aldousari S. Development of an ice-based technique for burst testing of tubular elements. KAU J Eng Sci 2006;16(1):21–48. [7] Turkmen N, Akyurt M, Aljawi A. Investigation of pressures caused by ice blockage. In: Proceedings of the 7th Saudi conference of engineering, vol. 5, Riyadh; 26–28 November 2007. p. 185–97. [8] Al-Aqel MS, Najeeb A, Ahmed H. On applications of ice and a novel chilling apparatus. Unpublished BS project, Dept of Thermal Eng and Desal Technol, College of Engineering, KAU; 2009. [9] Türkmen N. Ice-based pressurization utilizing a novel chilling apparatus. Energy Convers Manage, submitted for publication. [10] http://www.bishopgroupservices.com/pipefreezing/index.html; 2010.