# Vanishing heat conductivity limit for the 2D Cahn-Hilliard-Boussinesq system

Zaihong Jiang1* and Jishan Fan2

### Author affiliations

1 Department of Mathematics, Zhejiang Normal University, Jinhua 321004, People's Republic of China

2 Department of Applied Mathematics, Nanjing Forestry University, Nanjing 210037, People's Republic of China

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Boundary Value Problems 2011, 2011:54  doi:10.1186/1687-2770-2011-54

 Received: 18 October 2011 Accepted: 22 December 2011 Published: 22 December 2011

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### Abstract

This article studies the vanishing heat conductivity limit for the 2D Cahn-Hilliard-boussinesq system in a bounded domain with non-slip boundary condition. The result has been proved globally in time.

2010 MSC: 35Q30; 76D03; 76D05; 76D07.

##### Keywords:
Cahn-Hilliard-Boussinesq; inviscid limit; non-slip boundary condition

### 1 Introduction

Let Ω ⊆ ℝ2 be a bounded, simply connected domain with smooth boundary ∂Ω, and n is the unit outward normal vector to ∂Ω. We consider the following Cahn-Hilliard-Boussinesq system in Ω × (0, ∞) [1]:

(1.1)

(1.2)

(1.3)

(1.4)

(1.5)

(1.6)

(1.7)

where u, π, θ and ϕ denote unknown velocity field, pressure scalar, temperature of the fluid and the order parameter, respectively. ε > 0 is the heat conductivity coefficient and e2 : = (0, 1)t. μ is a chemical potential and is the double well potential.

When ϕ = 0, (1.1), (1.2) and (1.3) is the well-known Boussinesq system. In [2] Zhou and Fan proved a regularity criterion for the 3D Boussinesq system with partial viscosity. Later, in [3] Zhou and Fan studied the Cauchy problem of certain Boussinesq-α equations in n dimensions with n = 2 or 3. We establish regularity for the solution under . Here denotes the homogeneous Besov space. Chae [4] studied the vanishing viscosity limit ε → 0 when Ω = ℝ2. The aim of this article is to prove a similar result. We will prove that

Theorem 1.1. Let , ϕ0 H4, div u0 = 0 in Ω and on ∂Ω. Then, there exists a positive constant C independent of ε such that

(1.8)

for any T > 0, which implies

(1.9)

Here, (u, θ, ϕ) is the solution of the problem (1.1)-(1.7) with ε = 0.

#### 2 Proof of Theorem 1.1

Since (1.9) follows easily from (1.8) by the Aubin-Lions compactness principle, we only need to prove the a priori estimates (1.8). From now on, we will drop the subscript ε and throughout this section C will be a constant independent of ε.

First, by the maximum principle, it follows from (1.2), (1.3), and (1.6) that

(2.1)

Testing (1.3) by θ, using (1.2) and (1.6), we see that

whence

(2.2)

Testing (1.1) and (1.4) by u and μ, respectively, using (1.2), (1.6), (2.1), and summing up the result, we find that

which gives

(2.3)

(2.4)

(2.5)

Testing (1.4) by ϕ, using (1.2), (1.5) and (1.6), we infer that

(2.6)

We will use the following Gagliardo-Nirenberg inequality:

(2.7)

It follows from (2.6), (2.7), (2.5), (2.3) and (1.5) that

(2.8)

which yields

(2.9)

(2.10)

(2.11)

Testing (1.4) by Δ2ϕ, using (1.5), (2.4), (2.3), (2.10) and (2.11), we derive

which implies

(2.12)

Testing (1.1) by -Δu + ∇π, using (1.2), (1.6), (2.12), (2.1) and (2.4), we reach

which yields

(2.13)

Here, we have used the Gagliardo-Nirenberg inequalities:

and the H2-theory of the Stokes system:

(2.14)

Similarly to (2.13), we have

(2.15)

(1.1), (1.2), (1.6) and (1.7) can be rewritten as

Using (2.12), (2.1), (2.13), and the regularity theory of Stokes system, we have

(2.16)

for any 2 < p < ∞.

(2.16) gives

(2.17)

It follows from (1.3) and (1.6) that

(2.18)

Applying Δ to (1.3), testing by Δθ, using (1.2), (1.6), (2.16), (2.17) and (2.18), we obtain

which implies

(2.19)

It follows from (1.3), (1.6), (2.19) and (2.13) that

(2.20)

Taking ∂t to (1.4) and (1.5), testing by ∂tϕ, using (1.2), (1.6), (2.12), and (2.15), we have

which gives

(2.21)

By the regularity theory of elliptic equation, it follows from (1.4), (1.5), (1.6), (2.21), (2.13) and (2.12) that

(2.22)

Taking ∂t to (1.1), testing by ∂tu, using (1.2), (1.6), (2.17), (2.22), (2.21) and (1.5), we conclude that

which implies

(2.23)

Using (2.23), (2.22), (2.1), (2.13), (1.1), (1.2), (1.6) and the H2-theory of the Stokes system, we arrive at

This completes the proof.

### Competing interests

The authors declare that they have no competing interests.

### Authors' contributions

All authors read and approved the final manuscript.

### Acknowledgements

This study was supported by the NSFC (No. 11171154) and NSFC (Grant No. 11101376).

### References

1. Boyer, Franck: Mathematical study of multi-phase flow under shear through order parameter formulation. Asymptot Anal. 20, 175–212 (1999)

2. Fan, Jishan, Zhou, Yong: A note on regularity criterion for the 3D Boussinesq system with partial viscosity. Appl Math Lett. 22, 802–805 (2009). Publisher Full Text

3. Zhou, Yong, Fan, Jishan: On the Cauchy problems for certain Boussinesq-α equations. Proc R Soc Edinburgh Sect A. 140, 319–327 (2010). Publisher Full Text

4. Chae, Dongho: Global regularity for the 2D Boussinesq equations with partial viscosity terms. Adv Math. 203, 497–513 (2006). Publisher Full Text