Research Papers: Alternative Energy Sources

Damping Pressure Pulsations in a Wave-Powered Desalination System

[+] Author and Article Information
Brandon J. Hopkins, Nikhil Padhye

Department of Mechanical Engineering,
Cambridge, MA 02139

Alison Greenlee, James Torres, Levon Thomas, Dean M. Ljubicic, Mortiz P. Kassner

Department of Mechanical Engineering,
Cambridge, MA 02139

Alexander H. Slocum

Department of Mechanical Engineering,
Cambridge, MA 02139
e-mail: npdhye,slocum@mit.edu

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received October 18, 2012; final manuscript received January 17, 2014; published online April 9, 2014. Editor: Hameed Metghalchi.

J. Energy Resour. Technol 136(2), 021205 (Apr 09, 2014) (9 pages) Paper No: JERT-12-1244; doi: 10.1115/1.4026635 History: Received October 18, 2012; Revised January 17, 2014

Wave-driven reverse osmosis desalination systems can be a cost-effective option for providing a safe and reliable source of drinking water for large coastal communities. Such systems usually require the stabilization of pulsating pressures for desalination purposes. The key challenge is to convert a fluctuating pressure flow into a constant pressure flow. To address this task, stub-filters, accumulators, and radially elastic-pipes are considered for smoothing the pressure fluctuations in the flow. An analytical model for fluidic capacitance of accumulators and elastic pipes are derived and verified. Commercially available accumulators in combination with essentially rigid (and low cost) piping are found to be a cost-effective solution for this application, and a model for selecting accumulators with the required fluidic-capacitance for the intended system is thus presented.

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Fig. 1

Schematic of resolute marine energy [10] wave-powered desalination system. The paddle, driven by ocean waves, powers a pump that sucks water from a beach well and pushes it toward a reverse osmosis membrane. The pressure pulsations in the beach well water are stabilized by a pressure damping device.

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Fig. 2

(a) Stub-filters, (b) elastic pipe, and (c) accumulators

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Fig. 3

Bladder accumulator

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Fig. 4

Different shapes tested for pipe

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Fig. 5

Material and flow cross-sections in the pipe

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Fig. 6

(a) Cylindrical pipe with uniform stress field. (b) Triangular pipe with non-uniform stress field and stress concentration at the corners on the inner side.

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Fig. 7

(a) Square pipe with nonuniform stress field and stress concentration at the corner on the inner side. (b) Elliptical pipe with nonuniform stress field and higher stress levels on the major axis.

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Fig. 8

Spherical capacitive elements

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Fig. 9

Circuit diagram for input-output model. Iin is the incoming pulsating flow and Iout is the flow to the resistor. Pch is the line charge pressure and is only present if an accumulator is used. RRP is the resistance of the RO membrane and C is the capacitance of the fluidic capacitive element.

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Fig. 10

Assembled experimental setup

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Fig. 11

Flowchart for experimental setup

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Fig. 12

(a) Flow at the inlet and after accumulator. Average pressure substracted from presented values. (b) Comparison of % ripple based on prediction experiments. Factor of 2 Fit is the predicted value multiplied by a factor of 2.

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Fig. 13

Cost comparison of different shapes at varying internal pressure

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Fig. 14

Cost of ownership of spheres and accumulators over the course of time

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Fig. 15

Capacitance from a pipe

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Fig. 16

Stress generation in a circular pipe under internal pressure

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Fig. 17

(a) Triangular cross-section, (b) uniformly loaded beam, and (c) pinned-pinned end-conditions




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