Flow of lubricated granular material on an inclined plane

2025-05-06 0 0 559.69KB 21 页 10玖币

侵权投诉

Flow of lubricated granular material on an inclined

plane

Ravindra S. Ghodakea,c, Pankaj Doshib,∗

, Ashish V. Orpea,c,∗

aChemical Engineering and Process Development Division, CSIR-National Chemical

Laboratory, Pune 411008 India

bWorldwide Research and Development, Pﬁzer Products India Private Limited, Mumbai

400051 India

cAcademy of Scientiﬁc and Innovative Research (AcSIR), Ghaziabad 201002 India

Abstract

We have studied the gravity driven ﬂow of spherical shaped, millimetric sized

granular material coated with aspherical, micron-sized, near frictionless lubri-

cant particles. Experiments were performed on an inclined plane using two

diﬀerent sized particles for varying concentrations of the lubricant. The par-

ticle volumetric ﬂow rate exhibits a non-monotonic behavior with increasing

lubricant concentration. It shows an increase at smaller lubricant concentration

followed by a decrease at higher lubricant concentration. The lubricant parti-

cles adheres to the granular particle surface thereby reducing the inter-particle

friction. However, presence of lubricant particles at higher concentration damps

out inter-particle collision thereby reducing the inter-particle momentum trans-

fer. Non-monotonicity in the observed behavior is then conjectured to arise

due to competing eﬀects of inter-particle friction and inter-particle collision.

The present work and the overall observed behavior therein provides a simple

experimental system to characterise the eﬀects of added lubricant material in

pharmaceutical and other relevant industrial applications.

Keywords: granular, powder, lubrication, friction, inclined plane

∗Corresponding authors

Email addresses: pankaj.doshi@pfizer.com (Pankaj Doshi), av.orpe@ncl.res.in

(Ashish V. Orpe)

Preprint submitted to Powder Technology October 24, 2022

arXiv:2210.11758v1 [cond-mat.soft] 21 Oct 2022

1. Introduction

Can we simply alter the inter-particle interaction, a fundamental quantity

governing the overall behavior in a dry granular system? Doing so essentially

will require either some kind of chemistry to alter the particle surface or altering

the material itself. Both these methods will change the inter-particle friction

and collision characteristics thereby modifying the ﬂow. However, both the

methods pose restrictions in terms of material availability and limited scope

and ease in use of chemical treatment. Alternatively, DEM simulations allow

for studying dry granular systems by suitable tuning of inter-particle friction

and collisional properties [1, 2, 3]. But the technique still presents limitations

in terms of availability of experimental studies for a detailed comparison in spite

of several reported studies [4]

As it turns out, addition of plate-like particles (typically Magnesium Stearate

or MgSt) alters the inter-particle interactions in dry systems substantially [5].

This technique is used routinely in pharmaceutical industries handling granular

material in various forms. The primary aim is to reduce the friction in the com-

pression die during the process of tablet compaction. As an additional beneﬁt

the presence of MgSt also enhances the powder ﬂowability. Typically, the MgSt

powder is added in tiny quantities (weight ratio of O[10−2]). The individual

particles, about 10 micron sized, adhere to the large particles and are expected

to reduce the friction between them due to their own frictionless nature thereby

enhancing the ﬂowability. This ﬂowability, using MgSt as lubricant, has been

studied previously to a reasonable eﬀect [6, 7, 8, 9, 10, 11, 12]. However, all

these studies have primarily focused on characterising the optimality in terms

of lubricant concentration vis-a-vis ﬂow characteristics. One of them have also

focussed on studying the avalanching and angle of repose behavior of pharma-

ceutical powders in presence of various types of lubricants [10]. It was observed

that the addition of lubricant decreases the angle of repose and the time for

avalanching. The observed behavior was explained based on particle morphol-

ogy using scanning electron microscopy (SEM) imaging. On the other hand

usage of powder as a lubricant between two planar solid surfaces is very well

known within the domain of tribology and its merits and demerits with respect

to conventional liquid lubricants have been well documented [13]. However, the

carryover of the ﬂow [14, 15] and rheology [16] characteristics from these planar

surface studies to bulk ﬂow of lubricant-granular particles is not known.

Over here we attempt to connect the presence of lubricant particles, their

inﬂuence on the inter-particle interactions and eventually on the shear ﬂow

behavior in terms of ﬂow and concentration proﬁles using ﬂow visualization

techniques. Given that MgSt particles are soft in nature, their excessive presence

and eﬀectively higher coating on the larger particles can render the latter to be

soft, thereby inducing a higher loss of momentum during collisions. This may

eﬀectively nullify the advantage gained due to friction reducing properties of

the lubricant. We strive to understand these possible contrasting behaviors

in this work through detailed experimentation. To obtain the necessary shear

ﬂow, we have chosen chute (inclined plane) system, which is very well studied

in literature [4, 17, 1, 18, 2, 19, 20, 21] covering various ﬂow aspects and is,

moreover, simple in its handling and usage. The choice of the experimental

system is purely incidental and the purpose of this work is not to delve into

the details of inclined plane mechanics, but simply to create a shear ﬂow which

will allow for studying and understanding the lubricant inﬂuence on the ﬂow

behavior.

2. Methodology

Experiments are performed on a chute inclined at an angle (θ) as shown in

ﬁg. 1. The system comprises two sections. The uppermost section of length

450 mm, width 50 mm and height 400 mm functions as a hopper ﬁlled with

granular material. The rest of the section, of length 1350 mm, width 50 mm

and height 200 mm, functions as a chute. The material from the hopper ﬂows

on to the chute through a gap of height 30 mm which can be opened or closed

using a manually operated gate. The side walls of the entire system are made

Figure 1: Schematic of the chute ﬂow system. (a) Side view exhibiting hopper, chute, collection

system and relevant dimensions. (b) Imaging of the ﬂow at one of the chute side wall (c)

Sample image captured using a high speed camera. See text for more details

out of stainless steel (SS316), except for a transparent acrylic window of length

600 mm and height 200 mm, located downstream (600 mm from chute end) for

imaging the ﬂow. The base of the chute (of width 50 mm) is made from glass

and is roughened by gluing glass beads of desired diameter (d) on it.

Nearly spherical glass beads (Jaygo Inc., USA) of diameter d= 2 and 3 mm,

with a polydispersity of 15% are used as granular material, while Magnesium

Stearate (MgSt) powder (Loba Chemie, India) is used as a lubricant material.

The individual particles of MgSt powder have plate-like structure, equivalent

sphere volume diameter of 10 µm with polydispersity of 10% and are nearly

frictionless with respect to each other. For each experiment, a pre-deﬁned, but

very tiny, quantity of MgSt powder was mixed with granular beads of either

size in a mixer. The mixer comprises an open plastic tank (diameter 185 mm

and height 100 mm) ﬁtted with an overhead stirrer. The mixing, for each

experiment, was carried out by rotating the stirrer at a speed of 30 revolutions

per minute (rpm) over a duration of 5 minutes. The glass beads were colored

using blue ink (Camlin Inc.) for ease in imaging and analysis. The MgSt powder,

white in color and slightly cohesive in nature, adheres itself to the surface of the

glass beads during the mixing process. The weight ratio of MgSt to glass beads

was varied between O(10−5) and O(10−3) across all experiments. For a given

weight ratio, the lubricant concentration was deﬁned cl=Ml/Ap, where Mlis

the total mass of lubricant, Ap=nπd2is the total surface area of particles, dis

particle diameter and nis the number of particles. The value of nis determined

as (6/πd3)(Mp/ρp), where Mpis total mass of particles, ρpis the particle density

(2.5g/cm3) and Mp/ρpis the total particle volume.

Given the tiny amounts of added MgSt powder and the small size of indi-

vidual particles, it was not possible to quantify the homogeneity of mixing as

well as any loss of MgSt powder in the mixing vessel. We, thus, resorted to

visual inspection, ensuring that the mixed material has whitish appearance and

no obvious traces were left on the mixer wall and stirrer surface. To ensure

consistency of the mixture, the mixing procedure, including mixing time and

speed, was maintained constant across all the experiments. The surface of par-

ticles after mixing with lubricant was imaged using FE-SEM (Field Emission

Scanning Electron Microscopy) to conﬁrm the altered texture and the adherence

of the lubricant. Figure 2 shows the images of 3 mm glass beads at two diﬀer-

ent magniﬁcations for three diﬀerent lubricant concentrations. A clean surface

is visible in ﬁg. 2b which gets progressively patchy with increasing lubricant

concentration as seen in ﬁg. 2d and f. Multiple layers of lubricant are visible

at the highest lubricant concentration. Similar surface texture variation is also

observed for 2 mm glass beads (not shown).

For every experiment, the chute hopper was ﬁlled upto 25% of its total

volume with the mixture of glass beads and MgSt while keeping the opening

closed. This ensured adequate supply of continuous feed to achieve steady ﬂow

for reasonable duration in the experiment. The gate was opened manually to

allow gravity induced ﬂow of material down the chute surface. Given that

our primary objective was to study the eﬀect of lubricant on the ﬂow and not

chute ﬂow mechanics, we kept all the operating parameters constant throughout,

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

10 玖币 0人已下载

立即下载

摘要：

FlowoflubricatedgranularmaterialonaninclinedplaneRavindraS.Ghodakea,c,PankajDoshib,,AshishV.Orpea,c,aChemicalEngineeringandProcessDevelopmentDivision,CSIR-NationalChemicalLaboratory,Pune411008IndiabWorldwideResearchandDevelopment,PzerProductsIndiaPrivateLimited,Mumbai400051IndiacAcademyofScienti...

展开>> 收起<<

Flow of lubricated granular material on an inclined plane.pdf

共21页,预览5页

还剩页未读，继续阅读

声明：本站为文档C2C交易模式，即用户上传的文档直接被用户下载，本站只是中间服务平台，本站所有文档下载所得的收益归上传人(含作者)所有。玖贝云文库仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私，请立即通知玖贝云文库，我们立即给予删除！

Flow of lubricated granular material on an inclined plane

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

热门标签

举报选择: