Plate Heat Exchanger Design for High Viscosity Fluids: Intricacies of Efficient Heat Transfer

Introduction

Plate heat exchangers are preferred in many industries due to their compact structure and high efficiency in heat transfer. However, when dealing with high viscosity fluids, standard plate heat exchanger designs can often fall short. In such applications, special design, material selection, and hydraulic optimization become critical.

In challenging process conditions frequently encountered in the food, chemical, petrochemical, and pharmaceutical sectors, the right selection and design of heat exchangers directly impact both process safety and energy efficiency.

1. What is High Viscosity and Why is it Important?

Viscosity is an internal resistance of a fluid and is generally defined as "resistance to flow." High viscosity fluids flow more slowly and require more energy.

During heating or cooling of such fluids, negative conditions such as laminar flow, limited mixing, and low heat transfer coefficient are observed.

2. Design Challenges and Key Approaches in Plate Heat Exchangers

Main problems encountered in high viscosity fluids are:

• Inadequate turbulence → low heat transfer
• High pressure drop → increased pump load
• Adhesion to plate surface → fouling, loss of efficiency
• Fluid remaining in "dead zones" in the exchanger → temperature difference, quality issues

Therefore, the following approaches should be implemented in design:

Use of Wide Gap Plates

• Increased distance between plates: 4 mm → 6–10 mm
• Suitable for solid particle or semi-solid substances
• Example: Free Flow, Wide Gap plate heat exchangers

Selection of Special Plate Patterns

• Use of low chevron angle plate pattern optimizing friction and turbulence
• Preference for 'wave' or 'corrugated' patterns rather than herringbone

Gradual Flow with Low Number of Plates

• Excess plates create high pressure drop. Instead, fewer but wider passages plates are preferred
• If necessary, dual or triple-stage structures are built to distribute temperature difference

Use of Horizontal Heat Exchanger

• In very viscous or sludgy fluids, drainage is facilitated by gravity
• In vertical types, flow can stop in some areas

Design Compatible with CIP (Clean-in-Place) for Process

• Dead zones in plate structure are minimized
• Gasket materials are selected compatible with CIP chemicals (EPDM, FKM, NBR variants)

3. How to Optimize Heat Transfer Performance in Plate Heat Exchangers?

Heat transfer coefficient decreases in high viscosity fluids due to the lack of turbulence or very limited turbulence. To improve this situation, the following measures should be taken:

4. Material and Gasket Selection in Plate Heat Exchangers

High viscosity fluids may often have aggressive chemical contents or high temperatures. Therefore, both plates and gaskets should be selected with suitable materials:

Plate Materials

• AISI 316L / 316Ti: Acidic environments and food applications
• Titanium: Salty water or chlorine-based fluids
• SMO 254: High chlorine and acid combinations

Gasket Materials

• EPDM: Hot water, steam, CIP chemicals
• NBR: Oil-based fluids (vegetable oil, grease)
• FKM/Viton: Chemical resistance, high temperature

5. Application Examples and Field Experiences in Plate Heat Exchangers

Food Industry (Tomato Paste, Molasses)

• Viscosity: 20,000–60,000 cP
• Solution Used: Wide-gap plate, horizontal installation
• Result: Heat transfer time decreased by 25%, cleaning time shortened by 40%

Petrochemical (Bitumen, Motor Oils)

• High temperature (120–180 °C)
• Solution Used: SMO plates, FKM gasket
• Result: Chemical resistance ensured, only 1 maintenance planned in 2 years

Cosmetic Production (Lotion, Cream)

• Delicate products: Fluid should not be altered
• Solution Used: Low plate count, multi-stage structure
• Result: Product temperature maintained with ±0.5 °C tolerance

6. Design Software and Simulation Tools for Plate Heat Exchangers

Selecting plate heat exchangers for high viscosity fluids manually is a challenging task today. Therefore, advanced thermal simulation and flow analysis software are utilized:

• Ekin PHE Selection Tool – special