Numerical Study on the Heat Transfer of Carbon Dioxide in Horizontal Straight Tubes under Supercritical Pressure

<div><p>Cooling heat transfer of supercritical CO₂ in horizontal straight tubes with wall is numerically investigated by using FLUENT. The results show that almost all models are able to present the trend of heat transfer qualitatively, and the stand <i>k</i>−<i>ε</i> with enhanced wall treatment model shows the best agreement with the experimental data, followed by LB low Re turbulence model. Then further studies are discussed on velocity, temperature and turbulence distributions. The parameters which are defined as the criterion of buoyancy effect on convection heat transfer are introduced to judge the condition of the fluid. The relationships among the inlet temperature, outlet temperature, the mass flow rate, the heat flux and the diameter are discussed and the difference between the cooling and heating of CO₂ are compared.</p></div

Development of wall temperature (Tw) and flow temperature (Tf) at 120kW/m².

<p>Development of wall temperature (Tw) and flow temperature (Tf) at 120kW/m².</p

Comparisons of heat transfer coefficient with wall and without wall at 33kW/m².

<p>Comparisons of heat transfer coefficient with wall and without wall at 33kW/m².</p

Development of wall temperature (Tw) and flow temperature (Tf) at different diameter.

<p>Development of wall temperature (Tw) and flow temperature (Tf) at different diameter.</p

Radial distributions of turbulence kinetic energy.

<p>Radial distributions of turbulence kinetic energy.</p

Comparisons of heat transfer coefficient at different inlet temperature with fluid temperature.

<p>Comparisons of heat transfer coefficient at different inlet temperature with fluid temperature.</p

Comparisons of calculated heat transfer coefficient using various turbulence models with the experimental data of Liu and He.

<p>(a)Stand k-ε +ewt, k-ω, RNG k-ε +ewt, SST; (b) Stand k-ε, RNG k-ε; (c) AB, LB, LS; and (d) YS, AKN, CHC.</p

The grid of horizontal straight tube.

<p>The grid of horizontal straight tube.</p

Comparisons of relevant parameters at d = 26mm.

<p>(a) h along the tube; (b) h with the fluid temperature; (c) Pr; (d) Re; (e) Gr; (f) Ri; (g) Gr/Re^2.7; (h) Kv.</p

Development of wall temperature (Tw) along the tube.

<p>Development of wall temperature (Tw) along the tube.</p