Liquid-to-liquid heat exchangers
A liquid-to-liquid heat exchanger is a device used to transfer heat from one liquid to another, usually by passing the two fluids close to each other but separated by a barrier. They are commonly used to make production more energy efficient.
In this article, we will explore the different types of liquid-to-liquid heat exchangers, plus applications and design considerations.
Some typical applications of liquid-to-liquid heat exchangers are industrial processes such as oil refining and chemical manufacturing, as well as heating and cooling systems for buildings, power plants, and other facilities.
Process heating and cooling
If you work in chemical processing, food and beverage processing, or HVAC, your process likely includes water, glycol, or oil. A liquid-to-liquid heat exchanger may be the right solution to heat or cool these liquids to dissipate unwanted heat from the process.
Pasteurisation involves heating milk to a temperature that kills bacteria. When pasteurisation is complete, the heat in the treated milk can be recovered through a liquid-to-liquid heat exchanger to preheat the cold milk and save energy. You can read more about how heat exchanges are used in milk processing in this handbook from Tetra Pak.
Heat recovery from waste
Many industries, including chemical manufacturing and electric power plants, produce high-temperature wastewater as a by-product. The heat in that liquid can be recovered and used in various ways (preheating the feed stream, for example) using a liquid-to-liquid heat exchanger. This cuts energy consumption, costs and environmental damage.
Types of liquid-to-liquid heat exchangers
Several types of liquid-to-liquid heat exchangers are available, each with unique features and benefits. Here are some of the most common types of heat exchangers:
Shell and tube heat exchangers
Shell and tube heat exchangers are the most commonly used liquid-to-liquid heat exchangers. They consist of a series of tubes inside a cylindrical shell where one fluid flows through the tubes inside the shell while the second fluid of a different temperature flows around the outside of the tubes. This allows conduction between the materials, cooling one and heating the other as temperatures try to equalise.
Shell and tube heat exchangers are suitable for high-pressure and high-temperature applications. This makes them versatile and widely used solutions for heat transfer in many industries, including chemical processing, power generation, and oil and gas refining.
Spiral heat exchangers
A spiral heat exchanger is a circular unit containing two concentric spiral flow channels, one for each fluid. One fluid enters the unit’s centre and flows towards the periphery, and the other enters the unit at the periphery and moves towards the centre.
These heat exchange types are best suited for high-viscosity fluids and high-fouling applications. They also are low maintenance and have low operating costs.
Double tube heat exchangers
Double tube heat exchangers resemble shell and tube designs but with the addition of a tube inside the nest. It provides a leak path in the event of a tube failure, avoiding costly contamination and production losses.
Liquid-to-liquid heat exchanger design considerations
When designing a liquid-to-liquid heat exchanger, several factors must be considered, such as the type of fluids used, flow rates, temperature, pressure, fouling, corrosion and maintenance requirements.
In liquid-to-liquid heat exchangers, the properties of the two fluids, such as density, viscosity, thermal conductivity and specific heat, play an important role in the design. All these properties affect the heat transfer rate, pressure drop and overall efficiency of the heat exchanger.
The flow rate of the two fluids will determine the heat transfer rate and the pressure drop across the heat exchanger. Therefore, it is essential to ensure that the heat exchanger design is compatible with the mechanical characteristics of the system.
Temperature and pressure
The two fluids’ temperature and pressure impact the heat exchanger’s design. That makes selecting materials that can withstand operating conditions essential to ensure the design meets the required safety standards.
Fouling and corrosion
Fouling and corrosion are significant factors that can impact the heat transfer rate and the lifespan of the heat exchanger. When designing a heat exchanger, it is vital to select materials resistant to fouling and corrosion where possible and incorporate sufficient material.
These heat exchangers can be designed with high surface area, counter-flow configurations, and optimised flow paths to increase energy efficiency. The energy efficiency of a specific liquid-to-liquid heat exchanger depends on factors such as its design, size, materials, and operating conditions.
When designing these heat exchangers, a manufacturer should make cleaning and maintenance easier to reduce the risk of contamination. Sterling TT certainly does. It’s important you follow proper maintenance and cleaning procedures to ensure the heat exchanger operates safely and effectively.
Benefits of heat exchangers
As with all heat exchangers, liquid-to-liquid heat exchangers can hugely benefit your industrial and commercial applications.
Liquid-to-liquid heat exchangers efficiently transfer heat between the fluids and can help maintain the desired temperature while reducing the energy needed.
Liquid-to-liquid heat exchangers can be used for various applications and can handle different types of liquids and operating conditions. They can be made from a range of materials, including metals, plastics, and ceramics, allowing them to be used in environments where corrosion or other chemical reactions may occur.
Reduce contamination risks
Liquid-to-liquid heat exchangers can help to reduce the risk of contamination in industrial processes or other applications where purity is critical because they prevent direct contact between the fluids being heated or cooled.
Sterling TT designs bespoke heat exchangers
At Sterling TT, we have over 100 years of experience designing and manufacturing heat exchangers for various industries. So, if you’re looking for specialist heat exchange equipment, we are your expert.
Get in touch today, and an experienced member of our team will be in contact with you.