When beginning pharmaceutical production, you want to ensure your processes are safe and economical while maintaining consistent performance and quality standards over time. The heat exchanger that you choose plays a crucial role in maintaining reliability and efficiency in your processes. But with plate-and-frame, shell-and-tube and welded plate options amongst several others, you might find yourself asking: which heat exchanger is more efficient for the specific applications that I need?
What is a heat exchanger?
To begin with, a heat exchanger is an energy exchange system used in a number of industries including manufacturing, HVAC, and food and beverage. It may be used to manage electrical waste heat in many industries, but in pharma, the most effective heat exchanger is necessary to ensure the integrity of the fine chemical processes that are employed to create pharmaceutical products.
Choosing the right heat exchanger is one of the most important decisions you will make while setting up or replacing a system. Your decision will play an integral role in ensuring hygiene, safety, consistency and production economy. Developing the next big drug or vaccine requires cutting-edge technology, and finding the most effective heat exchanger for your specific purposes will make all the difference to your process’ quality and efficiency.
Where are heat exchangers used?
Heat exchangers have uses across industries. From industrial and sanitary applications in biodiesel and paint industries, dairy and worts cooling amongst other F&B applications to pharmaceutical applications in Water-for-Injection (WFI), Purified Water (PW) and other processes, heat exchangers serve a vast variety of purposes. And naturally, the design and characteristics of heat exchangers will differ for each application.
Factors to consider in selecting a heat exchanger: effectiveness vs efficiency, geometry & application
There is a significant amount of diversity in the geometry of heat exchangers: shell and tube, welded plates, plate and gasket, spiral or scraped surface heat exchangers. So to help you choose the ideal, most effective heat exchanger, for the application of your choice, there are some important factors to consider.
Depending on the application and project for which the heat exchanger is being used, you would have to consider the thermal properties of the fluid on both the product and service side: density, specific heat capacity, viscosity and conductivity, and their variation at the different temperatures they may encounter within the working range. It would also be useful to have data on process flow rate, inlet and outlet temperatures, inlet pressure and physical properties of the products.
In deciding which type of heat exchanger is more efficient than the others available in the market, from the standpoint of design and materials, you would have to consider another set of criteria as well, picking the ones which are most critical to your operation. The most effective heat exchanger, for instance, may not meet the sanitary standards for your project. Or the most easily available materials may not have enough corrosion-resistance for your specific purposes.
Given your priorities, here are the factors to consider:
- Thermal efficiency – In case of a tubular heat exchanger, the thermal conductivity of the tube material is most important. While copper and copper/nickel are the most conductive based on thermal modelling comparisons using HTRI software, carbon steel and stainless steel amongst other higher alloys are also comparable. Corrugating can also enhance thermal performance (more on this later).
- Corrosion resistance – For low to moderate corrosion resistance, stainless steel is a go-to choice for heat exchangers, whereas for extreme corrosion resistance, titanium, zirconium and tantalum can be considered.
- Cleanability – Ease of maintenance and hygiene should be top priorities in pharmaceutical manufacturing, so the materials chosen in your heat exchanger should be able to tolerate your mechanical, chemical or ultrasonic cleaning regimen. In sanitary markets including F&B and pharma, product contact surfaces must be cleanable stainless steel or a higher alloy in order to comply with strict FDA, ASME BPE and 3-A Sanitary Standard guidelines, so you will want to avoid carbon steel and copper.
- Durability – Corrosion is not a problem to contend with when it comes to stainless and higher alloys. Using higher alloys means thinner, lighter materials which do not require painting as protection against corrosion. Therefore, these are always a better choice when selecting the most effective heat exchanger. This not only ensures long-term durability, but also decreases maintenance cost and time.
Tubular or plate heat exchangers: which type of heat exchanger is more efficient?
When it comes to narrowing down on a heat exchanger by comparing heat exchanger effectiveness vs efficiency for your particular application, plate-and-frame or plate heat exchangers (PHE) have the advantages of lower cost, withstanding high turbulence, easy cleanability, and high heat regeneration. However, with their relatively low operating temperatures, high maintenance cost due to the gaskets, and inability to handle products of high viscosity, they are not necessarily the ideal heat exchanger for pharma applications.
Tubular heat exchangers, on the other hand, are more traditionally used and have a number of superior features as compared to other products in the category. Tubular heat exchangers are completely welded, so there is almost no need for spare parts, greatly reducing maintenance costs. Due to the absence of gaskets, they have a high working pressure and a high working temperature. Not only can they process particulate and fibre products, but they also allow for easy inspection and disassembly and are easy to enlarge due to modular designs. Most importantly for pharma, tubular heat exchangers with double tube sheets offer high security in aseptic processes, preventing cross-contamination in the event of a leakage.
Selecting the most effective heat exchanger: advantages of corrugation
As mentioned earlier, corrugation is used to improve the thermal efficiency of heat exchangers. A corrugated tube is essentially a pipe with a helical groove obtained from a plain tube via cold forming. To optimise heat transfer and performance, the number of starts and the angles of the helix can be modified – all without altering the mechanical properties of the original tube.
Based on corrugation angle, depth and pitch, a corrugated tube may be soft, hard or dimpled – each serving a slightly different purpose. While hard corrugation helps the process achieve a very high improvement of heat transfer coefficient, soft corrugation demonstrates a lower pressure drop.
One of the main advantages of corrugation is the increased fluid turbulence that it achieves, even at a low velocity. Corrugation also helps with homogenous thermal treatment due to enhanced mixing capability, lower fouling due to the self-cleaning effect created by the higher turbulence, longer running times and shorter residence times due to their higher response to CIP.
Heat exchanger effectiveness vs efficiency
Ultimately, while choosing which type of heat exchanger is more efficient, you must also consider heat exchanger effectiveness vs efficiency. The key to enhanced efficiency of corrugated tube heat exchangers lies in its design of tubes with minimal boundary layer resistance. There is more than one style of tube corrugation – it could be intermittent spot indentation or continuous spiral indentation. The latter continuous disturbance of the boundary wall of the tube side fluid enhances turbulence levels, thereby increasing the overall rate at which heat is transferred, given the tube side fluid has a higher resistance to heat flow.
Ultimately, considering the high sanitary standards required in pharma production, tubular heat exchangers are the ideal choice for their high security in aseptic processes, high temperature tolerance and easy inspection due to their modular design.