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Improved Hydroentanglement Using Pulsed Elliptical Jets F98-C04

Michael S. Ellison, PI, Clemson University Bhuvenesh Goswami, co-PI, Clemson University Edward Vaughn, co-PI, Clemson University David A. Zumbrunnen, co-PI, Clemson University Krishna Guduru, Graduate Student, Clemson University Goal Statement The goal of this research is to increase the number and extent of entanglements in nonwoven fabrics produced with water jets while reducing water and energy expenditures to allow higher production rates and improved fabric properties.

Abstract Recent studies of impinging jet flows have shown that momentum exchange and heat transfer can be significantly improved if the jet flow is pulsed (Zumbrunnen, 1996). Moreover, when the jet holes are elliptical, jet free surfaces are formed into a helical structure. Upon pulsating the jet flow, the helical structure rotates and a strong twisting action can be imparted where the jet strikes a surface. The helical structure has greater definition in jets of very small diameter, such as those used in hydroentanglement systems, since surface tension forces are larger. Pulsations and elliptic free surfaces in impinging jet flows may thereby be an effective means of improving fiber entanglement. Pulsations might also be used to impart unique patterns in nonwoven fabrics since jet-to-jet interaction can be altered by changing pulsation frequency and magnitude. With this rationale, our objective is to perform controlled experiments where the effect of flow pulsations and jet hole shape on fiber entanglement is investigated. The extent of entanglements will be quantified for different pulsation frequencies and amplitudes and for circular jets and for elliptic jets. The entanglement performance of elliptic and standard circular holes will be compared.

Discussion The properties of fabrics produced by hydroentanglement processes depend directly on the extent of entanglements between separate caused by incident thin water jets. Means to increase the number and extent of the entanglements for a given water flow rate can reduce fluid and energy expenditures, improve fabric properties, and allow higher production rates. Reduced water consumption can also result in cost reductions in supporting equipment, such as in equipment needed to filter and recycle the jet fluid and vacuum and drying systems used in water extraction.

The process of hydroentanglement involves the reorientation of fiber segments both in-plane or out-of-plane of the fibrous mat. This is somewhat akin to what happens in needle punched fabrics although the orientation through the thickness of the fabric is relatively milder. Hydroentangled fabrics derive their integrity due to simple entanglement of the fiber segments. The degree of entanglement is affected by the process parameters (type of support screen, jet

National Center Annual Report: November 1999 F98-C04 1 F98-C04- Page 2 characteristics and conveyor belt speed) and the topographical and mechanical characteristics of constituent fibers. Fibers with low bending modulus entangle more easily than fibers with high bending modulus. Fabric strength is also directly proportional to fiber length, and a balance between fiber ends for more tie points or entangled areas. There is some general information available (US patent #3,485,706) on the general system design and the effect of jet pressure on the characteristics of fabrics. One study (M. Gandhi, MS Thesis, Clemson University, 1992) explores the effect of the level of energy (jet velocity and pressure) and fiber types ( and ) on the mechanical properties of fabrics. A recent search of the patent and open literature revealed no results of studies on pulsed and/or elliptical jets in hydroentanglement.

Advances have been made in recent years in the cooling, heating, and drying effectiveness of impinging jet flows. These advances include enhancing momentum and heat transport rates by inducing flow pulsations. When a jet is pulsed, instantaneous flow and heat transfer measurements with anemometry and heat flux microsensors have shown that mixing can occur much more rapidly (Mladin and Zumbrunnen, 1997). Elliptic jet holes have been shown in an ongoing heat transfer study at Clemson to produce jets with helical free surfaces. When pulsed, the free surfaces rotate and a twisting action in the jet arises that may be very effective in tangling fibers. Increased mixing has important implications to hydroentanglement technologies, since the extent of entanglements depends strongly on the motion of individual fibers and portions of fibers. Pulsating water jets may also allow control of pattern among fibers that may be altered through adjustment of pulse magnitude and frequency.

Apparatus Development To accomplish our experimental work, a new nozzle block (Figure 1) was designed and fabricated with elliptic shaped nozzles to impart pulsation and spirality to the water jet streams. The new elliptic nozzle block has the same jetting area as a conventional nozzle block with circular holes installed in a hydroentanglement system within our laboratory. As discussed above, this design may yield jets with helical free surfaces that may improve entanglement efficiency and thereby reduce energy consumption. Fabrics produced under identical conditions with both nozzle blocks will be compared. In order to produce pulsations, a separate pulsation system has been assembled and a photograph is shown in Figure 2. The pulsation system system receives water from a current pump used in the laboratory hydroentanglement system. The pulsation system consists principally of a motor-driven ball valve. Pulsation frequency is adjustable by varying the motor speed and also by re-arranging one of two drive belts among pulleys. The system provides for independent control of pulsation frequency, pulsation amplitude, and average impingement velocity by incorporating a flow partitioning network where pulsating flow and steady flow streams are combined according to valve settings. Pulsation frequency is measured electronically from a sensor detecting the valve rotations. The entire system is enclosed to prevent exposure to the drive belts and rotating parts.

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Figure 1. Schematic comparison of a circular orifice to an elliptic orifice both with convergent flow geometries to reduce pressure drop.

This study will be done taking into consideration the energy consumed to produce a pound of fabric. The energy consumed will be compared to the tensile strength of the fabric produced and also the weight of the fabric. The energy calculation methods of F.J.Evans (Du Pont Patent no: 3486168 DT, Dec 23 1969) will be used. Stroboscopic inspection will also be performed to allow examination of the periodic behavior in the incident jets in response to the pulsations. For example, the pulsating jet flows have been shown to promote periodic flow structures (Sheriff and Zumbrunnen, 1994). Such structures may affect entanglement mechanisms and, if understood, help identify optimal processing conditions.

Figure 2. Pulsating water system designed and assembled to supply water to the elliptic nozzle block.

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References Ghandi, M., 1992, MS Thesis, Clemson University, Clemson, South Carolina.

Mladin, E. C. and Zumbrunnen, D. A., 1997, “Local Convective Heat Transfer to Submerged Pulsating Jets,” International Journal of Heat and Mass Transfer, Vol. 40, pp. 3305-3321.

Sheriff, H. S. and Zumbrunnen, D. A., 1994, “Effect of Flow Pulsations on the Cooling Effectiveness of an Impinging Water Jet,” Journal of Heat Transfer, Vol. 116, pp. 886-895.

Zumbrunnen, D. A., 1996, “Convective Heat Transfer Modifications Due to Flow Pulsations in Impinging Jets,” in: Process, Enhanced, and Multiphase Heat Transfer, R. M. Manglik and A. D. Kraus, editors, Begell House, New York, pp. 307-318.

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