Sizing Heat Exchangers for Slurry Service

Definition

Sizing heat exchangers for slurry service means estimating the heat transfer area needed when one or both fluids carry suspended solids. The fundamental equation is still A = Q / (U × ΔTₘ), but the inputs — especially U-value, fouling allowance, and velocity constraints — are harder to pin down than in clean-fluid service. Solids concentration, particle size distribution, settling behaviour, and abrasiveness all influence exchanger selection, geometry, and the confidence you can place in preliminary estimates.

Why it matters

Slurry services are among the most challenging applications in heat exchanger sizing. Solids can foul, erode, plug, or settle inside the exchanger, and the combination of these effects often rules out exchanger types or geometries that would work for clean fluids. Getting the preliminary sizing wrong — either too small or with the wrong exchanger type — leads to expensive redesign, premature failure, or chronic maintenance problems. A structured preliminary estimate helps identify which exchanger types are feasible, what area range to expect, and what questions to take to the vendor or specialist.

Formula

Units involved

• •A — heat transfer area in m² or ft²
• •Q — heat duty in kW, W, or BTU/h
• •U — overall heat transfer coefficient in W/(m²·K) or BTU/(h·ft²·°F)
• •ΔTₘ — log mean temperature difference in K, °C, or °F
• •F — LMTD correction factor (dimensionless)
• •Rd — fouling resistance in m²·K/W or h·ft²·°F/BTU
• •ṁ — mass flow rate in kg/s, kg/h, or lb/h
• •Cp — specific heat capacity in J/(kg·K) or BTU/(lb·°F)

Worked example

Common mistakes

• •Using clean-fluid U-values without reducing for slurry fouling and lower film coefficients — slurry U-values are typically 30–60% lower than equivalent clean-fluid values.
• •Ignoring minimum velocity requirements — solids can settle in horizontal tubes or low-velocity shell passes, causing plugging and hot spots.
• •Specifying tube-side flow without checking that tube diameter and velocity are compatible with the particle size — large particles or fibrous solids may require larger tubes or open-channel designs.
• •Applying standard fouling factors from TEMA tables for slurry service — slurry fouling is highly application-specific and often much higher than generic values.
• •Neglecting cleanability in the exchanger selection — some slurry services require exchangers that can be mechanically cleaned or chemically flushed.
• •Ignoring erosion at high velocities — there is a velocity window between settling (too low) and erosion (too high) that depends on solids hardness and concentration.

When to use the calculator

Use the Heat Duty Calculator for Q, the LMTD Calculator for ΔTₘ, and the Heat Exchanger Area Calculator to estimate A with design margin. Start with a conservative U-value (below clean-fluid ranges) and use the Fouling Factor Selector as a starting point — but note that slurry fouling is often higher than TEMA generic values. The Typical U-Values Reference and the Design Margin Reference provide additional context.

FAQ