- Email: [email protected]
Characteristics of different pump types operating with ice slurry
International Journal of Refrigeration 28 (2005) 92–97 www.elsevier.com/locate/ijrefrig
Characteristics of different pump types operating with ice slurry B. Frei*, H. Huber Lucerne School of Engineering and Architecture (HTA Luzern), University of Applied Sciences of Central Switzerland, CH-6048 Horw, Switzerland Received 4 June 2003; received in revised form 11 March 2004; accepted 16 July 2004
Abstract The characteristics of three different principles of pumps—centrifugal, side-channel and screw—were investigated. For each type, the pump characteristics at three speeds of rotation and for four different ice fractions between 0 and 25% were determined. The pump total head, overall efficiency, and electrical power input in function of the volume flow rate were continuously measured. In the case of a centrifugal- or a side channel-pump, the measured pump characteristics with ice fractions between 0 and 15% were nearly of equal value. Marked differences were observed with ice fractions of 25%. In the case of a screw pump, characteristics and behaviour were different compared to the centrifugal and side channel-pump. For increasing ice fractions, the obtained values show a gradually altering behaviour. If the pressure and the speed of rotation are constant, the volume rate of flow increases with growing ice mass fraction. The overall efficiency is significantly lower without ice particles than with ice mass fractions of 5–25%. All tested pumps were running over hundreds or thousands of hours and were suitable for ice slurry applications. q 2004 Elsevier Ltd and IIR. All rights reserved. Keywords: Survey; Pump; Two-phase secondary refrigerant; Ice slurry; Performance
Pompes fonctionnant avec les coulis de glace: caracte´ristiques des divers types Mots cle´s: Enqueˆte; Pompe; Frigoporteur diphasique; Coulis de glace; Performance
1. Introduction As in other hydraulic energy transport systems, pumps were essential in ice slurry systems where ice particles were distributed between storage and cooling consumers. At present only few investigations on the behaviour of pumps
* Corresponding author. Tel.: C41-41-349-32-74; fax: C41-41349-39-34. E-mail address: [email protected] (B. Frei). 0140-7007/$35.00 q 2004 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2004.07.006
operating with ice slurry were carried out. Kauffeld et al. and Nørgaard et al. [1,2] presented studies concerning the use of single- and multi-stage centrifugal pumps. The fluid used in the mentioned studies was a mixture of water and propylene glycol at a volume fraction of 16%. Single- and multiple-stage centrifugal pumps have proved to work well with ice slurry at ice mass fractions up to 35%. Pump total head and efficiency decrease with increase in ice mass fraction. Power consumption increases with increase in ice mass fraction. The results can be explained with the change in viscosity and the presence of solid (ice) particles.
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
Nomenclature I M Q P P Dp r g f w h H
electric current (A) mass flow rate (kg sK1) volume flow rate (m3 sK1) power (W) pressure (Pa) pressure difference (Pa) density (kg mK3) gravity (m sK2) frequency (l/min) temperature (8C) overall efficiency pump total head (m)
The aim of the present study is to compare three principles of pumps operating with ice slurry. The selected principles were the following: centrifugal, side-channel and screw. The fluid used in the present study was a mixture of water and ethanol at a mass fraction of 9%. Due to the fact that the presented study was carried out in course of EUREKA Project FIFE, it was not possible to use the same fluid as reported by Kauffeld et al. and Nørgaard et al. [1,2].
2. Pump types investigated It was decided to investigate three pumps of three different principles with ice slurry containing 9 wt% ethanol and water. Commercially available pumps were chosen (see Fig. 1) operating in a range of volume flows between 1 and 2.5 m3/h. For a defined volume flow rate, the manufacturers decided which pump size should be built into the experimental device. In the case of the centrifugal principle,
93
a one-stage and a two-stage pump were chosen. Due to limited space in this paper only the results from the twostage centrifugal pump were presented. The results of the single-stage centrifugal pump are similar.
3. Experimental device and test procedure The experimental device is a part of a larger test unit (see Figs. 2 and 3) located at the Pru¨fstelle HLK of HTA Luzern. Frei and Egolf [3] reported that a time-dependent behaviour of ice slurry was observed in some of their experiments using the mentioned test unit. Special attention was paid to this subject in the subsequent experiments. In a preparatory procedure, the generation and accumulation of ice particles up to the predefined ice mass fraction was obtained. After attaining the desired ice mass fraction, measured by Coriolis massflow meters, the ice generator was shut-off by the control system. The ice slurry was homogeneously mixed by a three-cone-mixer in the storage [4]. For each pump type, the characteristics at three speeds of rotation and four different ice fractions between 0 and 25% were determined, in accordance with the standard CEN/TC 197 [5]. The pump total head, the overall efficiency, and the electrical power input in function of the volume flow rate were continuously measured during the test procedure. With Coriolis massflow meters, the mass flow, density, and temperature were continuously measured. The pressure difference over the pump and the absolute pressure at the inlet of the pump were measured by piezoelectric pressure transmitters. Measurement uncertainty for the pressure and the volume flow rate was G0.3%. The relative uncertainty for the overall efficiency, caused by the measurement equipment, was G1%. Fig. 4 shows the screw pump mounted into the
Fig. 1. Centrifugal, side-channel, and screw pump (from left to right).
94
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
Fig. 2. Schematic layout of the test unit located at the Pru¨fstelle HLK of HTA Luzern.
experimental device. The connecting pipes are shown without insulation.
4. Results and discussion 4.1. Pump total head Kauffeld et al. and Nørgaard et al. [1,2] reported that a commercially available centrifugal pump showed an altered behaviour for increasing ice fraction. Similar observations were made in our experiments. In Fig. 5 the measured values for the pump total head are displayed. For ice mass fractions between 0 and 15%, no significant differences were observed. At an ice mass fraction of 25%, the pump total head was lower compared to the values at 0 or even 15%. This can be explained by the significantly higher viscosity at this ice mass fraction. For a commercially available side-channel pump, the values for pump total head for ice mass fractions between 0 and 15% were within the range of measurement uncertainty. Markedly lower values for pump total head were measured for an ice mass fraction of 25%. This observation can be explained—as mentioned
Fig. 3. Schematic layout of the experimental device.
Fig. 4. Screw pump mounted into the experimental device (without insulation).
before—by the significantly higher viscosity at 25% ice mass fraction. The slope of the curve characteristic of a sidechannel pump was of higher value than the slope of a centrifugal pump. Finally the pump total head of a commercially available screw pump was determined. For a given flow rate, the total head of the pump increased by increasing the ice mass fraction. The results without ice particles differed significantly from those with ice particles. This can be explained by the fact that the pump was especially designed for ice slurry. The distance between the three spindles was extended. In those cases where a screw pump is used it should be insured that the ice mass fraction is not lower than 5%. This should be considered in the layout of an ice slurry plant. 4.2. Electrical power input The chosen centrifugal pump was equipped with a builtin frequency converter. Therefore, the electrical power input measurements carried out with a three-phase high precision power analyser include the power consumption of the frequency converter (Fig. 6). For the side channel- and the screw pump, however, the used frequency converter Danfoss VLT 5002 was taken from laboratory equipment. Therefore, the measured electrical power input did not include the power input of the frequency converter. If the ice mass fraction does not exceed 15%, measurements from the centrifugal pump are almost unchanged. At an ice mass fraction of 25% higher values were obtained. The values for the electrical power input increased with increasing volume flow rate. Scatter of individual measuring points of the sidechannel pump varied within the range of measurement
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
Fig. 5. Pump total head for centrifugal, side-channel and screw pump (from top to bottom).
95
Fig. 6. Electrical power input for centrifugal, side-channel and screw pump (from top to bottom).
4.3. Overall efficiency uncertainty. The ice mass fraction, even for values of 25% had no observable influence. The values for the electrical power input increased with decreasing volume rate of flow. Measurements of the screw pump showed an increased slope of the obtained curves with increasing ice mass fractions. A considerable difference in the behaviour was observed in the case of the occurrence of ice particles. Even for low ice mass fractions, i.e. 5%, a significant increase of the slope was observable. Again the reason lies in the construction principle of this pump.
The overall efficiency was calculated as displayed in Eq. (1), where the volume flow rate Q (m3 sK1), pump total head H (m), density r (kg mK3), and electrical power input Pel (W) were measured: hZ
QHrg Pel
(1)
Corresponding to Fig. 7 overall efficiencies showed differences depending on which pump type was in use. A dependence on ice mass fraction was also observable. The
96
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
Fig. 7. Overall efficiency for centrifugal, side channel and screw pump (from top to bottom).
centrifugal and the side-channel pump show comparable characteristics. In the case of the side-channel pump, an optimum exists for the investigated flow range. In contrast the screw pump indicates that the overall efficiency is positively influenced by the viscosity. For this type, increased ice mass fraction, i.e. a higher viscosity value means an increased value of the overall efficiency. For the centrifugal pump with ice mass fractions of 0– 15%, the overall efficiency was nearly of equal value. At 25% ice mass fraction there was a significant reduction of the quality of the performance characteristics. For the side-channel pump with ice mass fractions of 5– 15%, the differences vary within the range of measurement
uncertainty. With an ice fraction of 25%, the overall efficiency was significantly lower. For the screw pump, the overall efficiency was significantly lower without ice particles than with ice mass fractions of 5–25%.
5. Conclusions In the present study, three different principles of commercially available pumps are investigated. All tested pumps are suitable for ice slurry operation and cause no problems during running periods of thousands of hours.
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
The tested single- and two-stage centrifugal pump have proved to work well with ice slurry up to 25% ice mass fraction. Modified rotors and houses will certainly improve the performance characteristic. Compared to side channeland screw pumps the centrifugal pumps are less expensive and therefore of great interest. Above 25% ice mass fraction side-channel or screw pumps are recommended. Other construction principles, e.g. lobe rotor and progressing cavity pumps could be an additional option especially for higher ice mass fractions than 30%. An important first step in that case is to contact a pump manufacturer or distributor to discuss each individual application towards a cost-effective, efficient and practical solution.
[2]
[3]
[4]
[5]
References [1] M. Kauffeld, et al., Experience with ice slurry, Proceedings of
97
the First Workshop on Ice Slurries of the International Institute of Refrigeration, Yverdon-les-Bains, Switzerland, 1999 p. 42– 73. E. Nørgaard, et al., Performance of components of ice slurry systems: pumps, plate heat exchanger, fittings, Proceedings of the Third Workshop on Ice Slurries of the International Institute of Refrigeration, Horw/Lucerne, Switzerland, 2001 p. 129–36. B. Frei, P.W. Egolf, Viscometry applied to the Bingham substance ice slurry, Proceedings of the Second Workshop on Ice Slurries of the International Institute of Refrigeration, Paris, 2000 p. 48–60. P.W. Egolf, B. Frei, The continuous-properties model for melting and freezing applied to fine-crystalline ice slurries, Proceedings of the First Workshop on Ice Slurries of the International Institute of Refrigeration; Yverdon-les-Bains, Switzerland, 1999 p. 25–40. Circulation pumps for heating and service water installations; 1992. CEN/TC 197/SC4/WG1.
Characteristics of different pump types operating with ice slurry B. Frei*, H. Huber Lucerne School of Engineering and Architecture (HTA Luzern), University of Applied Sciences of Central Switzerland, CH-6048 Horw, Switzerland Received 4 June 2003; received in revised form 11 March 2004; accepted 16 July 2004
Abstract The characteristics of three different principles of pumps—centrifugal, side-channel and screw—were investigated. For each type, the pump characteristics at three speeds of rotation and for four different ice fractions between 0 and 25% were determined. The pump total head, overall efficiency, and electrical power input in function of the volume flow rate were continuously measured. In the case of a centrifugal- or a side channel-pump, the measured pump characteristics with ice fractions between 0 and 15% were nearly of equal value. Marked differences were observed with ice fractions of 25%. In the case of a screw pump, characteristics and behaviour were different compared to the centrifugal and side channel-pump. For increasing ice fractions, the obtained values show a gradually altering behaviour. If the pressure and the speed of rotation are constant, the volume rate of flow increases with growing ice mass fraction. The overall efficiency is significantly lower without ice particles than with ice mass fractions of 5–25%. All tested pumps were running over hundreds or thousands of hours and were suitable for ice slurry applications. q 2004 Elsevier Ltd and IIR. All rights reserved. Keywords: Survey; Pump; Two-phase secondary refrigerant; Ice slurry; Performance
Pompes fonctionnant avec les coulis de glace: caracte´ristiques des divers types Mots cle´s: Enqueˆte; Pompe; Frigoporteur diphasique; Coulis de glace; Performance
1. Introduction As in other hydraulic energy transport systems, pumps were essential in ice slurry systems where ice particles were distributed between storage and cooling consumers. At present only few investigations on the behaviour of pumps
* Corresponding author. Tel.: C41-41-349-32-74; fax: C41-41349-39-34. E-mail address: [email protected] (B. Frei). 0140-7007/$35.00 q 2004 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2004.07.006
operating with ice slurry were carried out. Kauffeld et al. and Nørgaard et al. [1,2] presented studies concerning the use of single- and multi-stage centrifugal pumps. The fluid used in the mentioned studies was a mixture of water and propylene glycol at a volume fraction of 16%. Single- and multiple-stage centrifugal pumps have proved to work well with ice slurry at ice mass fractions up to 35%. Pump total head and efficiency decrease with increase in ice mass fraction. Power consumption increases with increase in ice mass fraction. The results can be explained with the change in viscosity and the presence of solid (ice) particles.
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
Nomenclature I M Q P P Dp r g f w h H
electric current (A) mass flow rate (kg sK1) volume flow rate (m3 sK1) power (W) pressure (Pa) pressure difference (Pa) density (kg mK3) gravity (m sK2) frequency (l/min) temperature (8C) overall efficiency pump total head (m)
The aim of the present study is to compare three principles of pumps operating with ice slurry. The selected principles were the following: centrifugal, side-channel and screw. The fluid used in the present study was a mixture of water and ethanol at a mass fraction of 9%. Due to the fact that the presented study was carried out in course of EUREKA Project FIFE, it was not possible to use the same fluid as reported by Kauffeld et al. and Nørgaard et al. [1,2].
2. Pump types investigated It was decided to investigate three pumps of three different principles with ice slurry containing 9 wt% ethanol and water. Commercially available pumps were chosen (see Fig. 1) operating in a range of volume flows between 1 and 2.5 m3/h. For a defined volume flow rate, the manufacturers decided which pump size should be built into the experimental device. In the case of the centrifugal principle,
93
a one-stage and a two-stage pump were chosen. Due to limited space in this paper only the results from the twostage centrifugal pump were presented. The results of the single-stage centrifugal pump are similar.
3. Experimental device and test procedure The experimental device is a part of a larger test unit (see Figs. 2 and 3) located at the Pru¨fstelle HLK of HTA Luzern. Frei and Egolf [3] reported that a time-dependent behaviour of ice slurry was observed in some of their experiments using the mentioned test unit. Special attention was paid to this subject in the subsequent experiments. In a preparatory procedure, the generation and accumulation of ice particles up to the predefined ice mass fraction was obtained. After attaining the desired ice mass fraction, measured by Coriolis massflow meters, the ice generator was shut-off by the control system. The ice slurry was homogeneously mixed by a three-cone-mixer in the storage [4]. For each pump type, the characteristics at three speeds of rotation and four different ice fractions between 0 and 25% were determined, in accordance with the standard CEN/TC 197 [5]. The pump total head, the overall efficiency, and the electrical power input in function of the volume flow rate were continuously measured during the test procedure. With Coriolis massflow meters, the mass flow, density, and temperature were continuously measured. The pressure difference over the pump and the absolute pressure at the inlet of the pump were measured by piezoelectric pressure transmitters. Measurement uncertainty for the pressure and the volume flow rate was G0.3%. The relative uncertainty for the overall efficiency, caused by the measurement equipment, was G1%. Fig. 4 shows the screw pump mounted into the
Fig. 1. Centrifugal, side-channel, and screw pump (from left to right).
94
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
Fig. 2. Schematic layout of the test unit located at the Pru¨fstelle HLK of HTA Luzern.
experimental device. The connecting pipes are shown without insulation.
4. Results and discussion 4.1. Pump total head Kauffeld et al. and Nørgaard et al. [1,2] reported that a commercially available centrifugal pump showed an altered behaviour for increasing ice fraction. Similar observations were made in our experiments. In Fig. 5 the measured values for the pump total head are displayed. For ice mass fractions between 0 and 15%, no significant differences were observed. At an ice mass fraction of 25%, the pump total head was lower compared to the values at 0 or even 15%. This can be explained by the significantly higher viscosity at this ice mass fraction. For a commercially available side-channel pump, the values for pump total head for ice mass fractions between 0 and 15% were within the range of measurement uncertainty. Markedly lower values for pump total head were measured for an ice mass fraction of 25%. This observation can be explained—as mentioned
Fig. 3. Schematic layout of the experimental device.
Fig. 4. Screw pump mounted into the experimental device (without insulation).
before—by the significantly higher viscosity at 25% ice mass fraction. The slope of the curve characteristic of a sidechannel pump was of higher value than the slope of a centrifugal pump. Finally the pump total head of a commercially available screw pump was determined. For a given flow rate, the total head of the pump increased by increasing the ice mass fraction. The results without ice particles differed significantly from those with ice particles. This can be explained by the fact that the pump was especially designed for ice slurry. The distance between the three spindles was extended. In those cases where a screw pump is used it should be insured that the ice mass fraction is not lower than 5%. This should be considered in the layout of an ice slurry plant. 4.2. Electrical power input The chosen centrifugal pump was equipped with a builtin frequency converter. Therefore, the electrical power input measurements carried out with a three-phase high precision power analyser include the power consumption of the frequency converter (Fig. 6). For the side channel- and the screw pump, however, the used frequency converter Danfoss VLT 5002 was taken from laboratory equipment. Therefore, the measured electrical power input did not include the power input of the frequency converter. If the ice mass fraction does not exceed 15%, measurements from the centrifugal pump are almost unchanged. At an ice mass fraction of 25% higher values were obtained. The values for the electrical power input increased with increasing volume flow rate. Scatter of individual measuring points of the sidechannel pump varied within the range of measurement
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
Fig. 5. Pump total head for centrifugal, side-channel and screw pump (from top to bottom).
95
Fig. 6. Electrical power input for centrifugal, side-channel and screw pump (from top to bottom).
4.3. Overall efficiency uncertainty. The ice mass fraction, even for values of 25% had no observable influence. The values for the electrical power input increased with decreasing volume rate of flow. Measurements of the screw pump showed an increased slope of the obtained curves with increasing ice mass fractions. A considerable difference in the behaviour was observed in the case of the occurrence of ice particles. Even for low ice mass fractions, i.e. 5%, a significant increase of the slope was observable. Again the reason lies in the construction principle of this pump.
The overall efficiency was calculated as displayed in Eq. (1), where the volume flow rate Q (m3 sK1), pump total head H (m), density r (kg mK3), and electrical power input Pel (W) were measured: hZ
QHrg Pel
(1)
Corresponding to Fig. 7 overall efficiencies showed differences depending on which pump type was in use. A dependence on ice mass fraction was also observable. The
96
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
Fig. 7. Overall efficiency for centrifugal, side channel and screw pump (from top to bottom).
centrifugal and the side-channel pump show comparable characteristics. In the case of the side-channel pump, an optimum exists for the investigated flow range. In contrast the screw pump indicates that the overall efficiency is positively influenced by the viscosity. For this type, increased ice mass fraction, i.e. a higher viscosity value means an increased value of the overall efficiency. For the centrifugal pump with ice mass fractions of 0– 15%, the overall efficiency was nearly of equal value. At 25% ice mass fraction there was a significant reduction of the quality of the performance characteristics. For the side-channel pump with ice mass fractions of 5– 15%, the differences vary within the range of measurement
uncertainty. With an ice fraction of 25%, the overall efficiency was significantly lower. For the screw pump, the overall efficiency was significantly lower without ice particles than with ice mass fractions of 5–25%.
5. Conclusions In the present study, three different principles of commercially available pumps are investigated. All tested pumps are suitable for ice slurry operation and cause no problems during running periods of thousands of hours.
B. Frei, H. Huber / International Journal of Refrigeration 28 (2005) 92–97
The tested single- and two-stage centrifugal pump have proved to work well with ice slurry up to 25% ice mass fraction. Modified rotors and houses will certainly improve the performance characteristic. Compared to side channeland screw pumps the centrifugal pumps are less expensive and therefore of great interest. Above 25% ice mass fraction side-channel or screw pumps are recommended. Other construction principles, e.g. lobe rotor and progressing cavity pumps could be an additional option especially for higher ice mass fractions than 30%. An important first step in that case is to contact a pump manufacturer or distributor to discuss each individual application towards a cost-effective, efficient and practical solution.
[2]
[3]
[4]
[5]
References [1] M. Kauffeld, et al., Experience with ice slurry, Proceedings of
97
the First Workshop on Ice Slurries of the International Institute of Refrigeration, Yverdon-les-Bains, Switzerland, 1999 p. 42– 73. E. Nørgaard, et al., Performance of components of ice slurry systems: pumps, plate heat exchanger, fittings, Proceedings of the Third Workshop on Ice Slurries of the International Institute of Refrigeration, Horw/Lucerne, Switzerland, 2001 p. 129–36. B. Frei, P.W. Egolf, Viscometry applied to the Bingham substance ice slurry, Proceedings of the Second Workshop on Ice Slurries of the International Institute of Refrigeration, Paris, 2000 p. 48–60. P.W. Egolf, B. Frei, The continuous-properties model for melting and freezing applied to fine-crystalline ice slurries, Proceedings of the First Workshop on Ice Slurries of the International Institute of Refrigeration; Yverdon-les-Bains, Switzerland, 1999 p. 25–40. Circulation pumps for heating and service water installations; 1992. CEN/TC 197/SC4/WG1.