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Manesty: Medicine Manufacture with STAR-Pro/E
Alex Read, CD-adapco
Barry Lyon and George Smith, Manesty

In recent years, questions have been raised about how current manufacturing methods in the pharmaceutical industry can be improved. One of the catalysts for this discussion was a directive from the US Government’s Food and Drug Administration on innovative manufacturing and quality assurance. The directive challenged the pharmaceutical industry to enhance the understanding of their process, to improve manufacturing efficiency, and to investigate the adoption of techniques that are routinely used in other industries.

 

 

One such technique is Computational Fluid Dynamics (CFD). CFD is the simulation of flow and thermal behavior. It can be used to analyze anything from flow around or through objects, through to chemical reacting flows, phase change and heat transfer.

In other industries (such as automotive and food) CFD has now become an integral part of the product design and manufacturing process; almost every component on a modern automobile is designed with the aid of CFD. Manesty traditionally has had a strong ethos of technical excellence, which means that they are always seeking to leverage technology to improve the performance of their products for end user companies. This article details how they have adopted CFD technology and successfully deployed it within their design process. This has enabled their expert engineers to understand and correct problems early in the design cycle, thereby considerably reducing product development costs at the same time as improving product performance.

Tablet coating
Manesty supply the pharmaceutical industry with tablet compression and coating equipment of which spray guns are an integral part of the process. Coating improves the appearance of tablets, makes them easier to swallow, modifies drug release, masks taste, and gives environmental protection.

The coating process consists of a number of complex fluid dynamic phenomena. Coating fluid and air pass through chambers within the spray gun; the coating fluid is then atomized at the spray gun nozzle; a further two side-jets (known as “fan air”) are directed into the side of the main jet to control its shape. As the droplets are transmitted between the nozzle and the tablets, further droplet break-up and coalescence occurs and moisture is lost from the droplets by evaporation due to the airflow in the coating chamber. On contact with the tablet surface the droplets stick, splash and spread before drying to form the film coating. This continuous coating process is carried out over a moving bed of tablets until a uniform coating is applied to each of the tablets. Any problems during this process can have a detrimental effect on the end product: “logo bridging”, edge chipping and splitting, color variation, orange peel effect, picking, twinning and surface roughness are common descriptions of coating problems.


When they occur, fixing these problems can be a lengthy and expensive process. Traditionally a trial-and-error approach is adopted, varying the spray gun settings or design. Manesty decided that it would be more cost-effective to invest in gaining a deeper insight into this process early in the design cycle, thereby improving product performance and significantly reducing total costs.

Bearding
A common problem with spray guns is an effect known as “bearding”. This is when deposits of coating fluid form on the nozzle surface. In severe cases, these eposits can be enough to block the nozzle.

Early experimental tests on one of Manesty’s new spray gun models, revealed that bearding had occurred. Rather than undertake a potentially lengthy and costly trial-and-error exercise to resolve the problem, Manesty deployed CFD in order to understand and resolve the issue.

STAR-Pro/E Gateway
Although Manesty possessed significant in-house expertise with CAD tools (primarily Pro/E), they were new to CFD. Consequently, an incremental approach to the simulation was adopted using CD-adapco’s STAR-Pro/E Gateway.

The benefits of STAR-Pro/E Gateway are numerous. First, the user operates within the Pro/ENGINEER environment, so the learning curve for engineers new to CFD is significantly reduced. Second, 3D-CAD tools are significantly better at handling/creating/modifying geometry than dedicated CFD tools: that is after all, what they’re designed for. With this kind of CAD-embedded solution, the CFD model is directly associated with the CAD model, so when the design is modified in Pro/E the CFD model is also automatically updated. Finally, STAR-Pro/E Gateway is based on the technology of STAR-CD and so the user has full access to the capabilities of STAR-CD. An issue commonly found with less comprehensive “upfront” solutions is that the user quickly outgrows the limited capabilities of these tools. With STARPro/ E Gateway, models are entirely compatible with STAR-CD, so after Manesty had completed the cold flow analyses, they were able to progress to running compressible flow, multiphase spray analyses in STAR-CD.


       Fig:01
       Shows velocity magnitude plots through two sections close
       to the spray gun nozzle.

 

     Fig:02
     Shows pressure contours close to the spray gun nozzle. 


The analysis
Using STAR-Pro/E Gateway the geometry was created and meshed, and boundary conditions were applied within Pro/ENGINEER. Calculations on an initial design were run and the results analyzed. Figure 2 shows that there are large areas of low pressure (seen in blue) close to the nozzle surface: the scales have been limited to accentuate these regions. Droplets of coating fluid are entrained into these “dead zone” or areas of recirculation, and deposit on the nozzle. Manesty’s expert engineers were then able to make some quick design alterations within Pro/E in an attempt to resolve this issue. Once the geometry had been modified, they simply had to click one button to obtain updated flow results and to identify a new design, where the low-pressure regions had been moved away from nozzle surface.

Buoyed by their success, Manesty’s engineers quickly progressed onto more advanced simulations. These fall into two categories: multiphase and thermal.

One of the key design parameters for the sprays guns is the shape of the spray. As mentioned earlier, side-jets (fan air) are used to alter the shape of the jet. Without these the jet would be a hollow cone, with them it forms an elliptical shape. Manesty wanted to understand whether they could reproduce this effect using CFD – thereby enabling them to run detailed studies on how to obtain an optimized spray shape. The next step for their multiphase project is to analyze the film as it forms.

The thermal analyses concentrated on the cabinets in which the spray guns sit. These rotate the tablets, moving them into position to be sprayed and then rotating them while they dry. Air is blown through the cabinet to dry the tablets. The analysis involved understanding the flow through the cabinet, and to see whether it would be sufficient to influence the flow in the vicinity of the spray guns.

Conclusion
The pharmaceutical industry has identified that by adopting technology commonly used in other industries it can enhance process understanding, and improve manufacturing efficiency. An example is Manesty, who have successfully adopted the use of CFD, a tool commonly used in other industries, within their design cycle. As a result of this investment, design problems discovered early in the development cycle were investigated, understood and resolved: reducing overall development costs while improving product quality.

 

 

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