diff --git a/src/lagrangian/coalCombustion/submodels/surfaceReactionModel/COxidationIntrinsicRate/COxidationIntrinsicRate.C b/src/lagrangian/coalCombustion/submodels/surfaceReactionModel/COxidationIntrinsicRate/COxidationIntrinsicRate.C
index 1a260dac90e6e7fc3a49cc31cc891730095e1898..77435d66b48130a125332b23ad70a976a094c8e5 100644
--- a/src/lagrangian/coalCombustion/submodels/surfaceReactionModel/COxidationIntrinsicRate/COxidationIntrinsicRate.C
+++ b/src/lagrangian/coalCombustion/submodels/surfaceReactionModel/COxidationIntrinsicRate/COxidationIntrinsicRate.C
@@ -180,7 +180,7 @@ Foam::scalar Foam::COxidationIntrinsicRate<CloudType>::calculate
         max(0.5*d*sqrt(Sb_*rhop*Ag_*ki*ppO2/(De*rhoO2)), ROOTVSMALL);
 
     // Effectiveness factor []
-    const scalar eta = max(3.0*sqr(phi)*(phi/tanh(phi) - 1.0), 0.0);
+    const scalar eta = max(3.0/sqr(phi)*(phi/tanh(phi) - 1.0), 0.0);
 
     // Chemical rate [kmol/m2/s]
     const scalar R = eta*d/6.0*rhop*Ag_*ki;