Numerical Study on Thermal Hydraulic Performance of Supercritical LNG in Zigzag-Type Channel PCHEs
Abstract
:1. Introduction
2. Numerical Approach
2.1. Physical Model and Boundary Conditions
2.2. Thermo-Physical Properties of Supercritical LNG
2.3. Numerical Method and Grid Independence
2.4. Model Validation
3. Results and Discussion
3.1. Effect of Bend Angles of the Zigzag Channel
3.2. Effect of Mass Flux
3.3. Effect of Inlet Pressure
4. Conclusions
- (1)
- The local convection heat transfer coefficient rises and then falls along the streamwise direction, with the peak value appearing at the pseudo-critical temperature. The pressure drop also increases along the streamwise direction.
- (2)
- As the channel bend angle is increased, the local convection heat transfer coefficient and pressure drop rise, and so do the Nu and Euler numbers. The enhancement of heat transfer capability of supercritical LNG is mainly owed to increased turbulence. The increase of pressure drop is mainly due to the rising of velocity and the increase of flow resistance caused by the existence of vortices.
- (3)
- The local convective heat transfer coefficient and pressure drop increase significantly as the mass flux is increased due to the enhancement of turbulent flow. When the mass flux is increased by 2-fold, the local heat transfer coefficient rises by 1.4 times, and the pressure drop increases 3.3 times. The Nu increases as mass flux is increased. However, at the last third of the channel, Nu decreases as the mass flux is raised because of the decreased heat per unit volume absorbed by the LNG. This suggests that when the mass flux is raised, the heat transfer performance of the whole channel is better, but with the development of the fluid’s flow, the local heat transfer performance is reduced at the last third of the channel owing to the reduction of heat-absorbed capacity by the unit volume fluid.
- (4)
- The improvement of heat transfer performance with bend angle depends on the mass flux. The supercritical LNG has better heat transfer performance when the bend angle is less than 15° when the mass flux ranges from 207.2 kg/(m2·s) to 621.6 kg/(m2·s), and improves at bend angles of 10° and lower compared to 15° at mass fluxes above 414.4 kg/(m2·s).
- (5)
- Before the pseudo-critical temperature, the local convective heat transfer coefficient changes little with the inlet pressure, while it increases when the temperature surpasses pseudo-critical point. The pressure drop is reduced as the inlet pressure increases. Nu and EU decrease with increasing inlet pressure, while Nu/Eu reaches a maximum at 6.5 MPa. The results show that supercritical LNG has a better heat transfer performance in zigzag channel of PCHE at lower operating pressures.
Author Contributions
Funding
Conflicts of Interest
Nomenclature
T | Temperature (K) |
P | Pressure (Pa) |
L | length of channel (mm) |
Fanning factor | |
v | Velocity (m/s) |
Re | Reynolds number |
h | Convective heat transfer coefficient (W/(m2·K)) |
Nu | Nusselt number |
Eu | Euler number |
Cp | Specific heat (KJ/(kg·K)) |
Dh | hydraulic diameter (m) |
G | mass flux (kg/(m2·s)) |
∆P | pressure drop (Pa) |
pressure drop due to friction (Pa) | |
pressure drop due to acceleration (Pa) | |
τ | shear stress at the wall (Pa) |
Greek symbols | |
µ | viscosity (Pa·s) |
density (kg/m3) | |
λ | thermal conductivity (W/(m·K)) |
Subscript | |
w | Wall |
b | Bulk mean |
in | inlet |
out | outlet |
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Inlet | Outlet | Left/Right Walls | Top/Bottom Walls | ||
---|---|---|---|---|---|
Pressure (MPa) | Temperature (K) | Mass flux (kg/m2·s) | Pressure outlet | Adiabatic | Constant heat flux (W/m2) |
10 | 121 | 207.2 | 7.5 × 104 |
Temperature Range (K) | Density |
---|---|
121–223 | ρ = −1.29548 × 10−6T4 + 7.459 × 10−4T3 − 0.16537T2 + 15.12763T − 2.45869 |
223–271 | ρ = −5.30962× 10−4T3 + 0.43352T2 − 119.03258T + 11,091.66885 |
271–385 | ρ = 1.32923 × 10−7T4 − 1.93454 × 10−4T3 + 0.10675T2 − 26.70158T + 2634.06161 |
Specific Heat | |
121–223 | = 0.00436T3 − 1.83425T2 + 263.05475T − 9567.33957 |
223–261 | = 0.06448T3 − 46.88971 × 103T2 + 11,278.86482T − 892,240.75366 |
261–385 | = −0.00111T3 + 1.18621T2 − 423.72673T + 53,206.50774 |
Thermal Conductivity | |
12–−235 | λ = 1.07039 × 10−8T3 − 4.35253 × 10−6T2 − 6.44568 × 10−4T + 0.30675 |
235–262 | λ = 7.96913 × 10−6T2 − 0.00432T + 0.62882 |
262–385 | λ = −6.69403 × 10−9T3 + 7.36829 × 10−6T2 − 0.00258 × 10−2T + 0.33402 |
Viscosity | |
121–218 | μ = −7.71822 × 10−11T3+ 4.71489 × 10−8T2 − 1.01809 × 10−5T + 8.02631 × 10−4 |
218–254 | μ = 6.9276 × 10−9T2 − 3.52808 × 10−6T + 4.64105 × 10−4 |
254–385 | μ = −2.07823 × 10−12T3 + 2.1834 × 10−9T2 − 7.43585 × 10−7T + 9.67009 × 10−5 |
σω1 | σω2 | κ | α1 | β* | |
---|---|---|---|---|---|
SST | 0.5 | 0.865 | 0.41 | 0.31 | 0.09 |
Case | Scale of Boundary Layer | Rows of Boundary Layer | Cells of Nodes | Heat Transfer Coefficient W/(m2·K) | Relative Error (%) |
---|---|---|---|---|---|
1 | 0.01 | 5 | 2,988,329 | 2678.57 | 3.4% |
2 | 0.01 | 8 | 3,589,947 | 2680.44 | 3.47% |
3 | 0.003 | 5 | 2,974,634 | 2678.32 | 3.4% |
4 | 0.03 | 5 | 2,697,546 | 2669.23 | 3.04% |
5 | 0.01 | 5 | 815,644 | 2590.42 | 0 |
6 | 1,962,788 | 2636.39 | 1.8% | ||
7 | 4,456,851 | 2680.62 | 3.48% |
Pressure (MPa) | Temperature Difference (K) | Relative Error (%) | Pressure Difference (Pa) | Relative Error (%) | ||
---|---|---|---|---|---|---|
Experiment | Simulation | Experiment | Simulation | |||
6.5 | 178.9 | 175.1 | 2.1 | 16,612.35 | 15,167.36 | 10.25 |
7 | 180.3 | 178 | 1.27 | 15,636.09 | 14,521.4 | 9.95 |
7.5 | 182.1 | 180.4 | 0.94 | 14,742.24 | 14,071.62 | 7.05 |
8 | 182.6 | 182.3 | 0.16 | 13,847.55 | 13,188.32 | 6.62 |
8.5 | 183.5 | 184 | 0.27 | 13,035.22 | 12,504.69 | 6.81 |
9 | 185.7 | 185.5 | 0.11 | 12,156.68 | 11,810.66 | 4.70 |
9.5 | 186.1 | 185.8 | 0.16 | 11,342.33 | 10,862.6 | 4.42 |
10 | 186.6 | 186.4 | 0.11 | 10,578.6 | 10,189.45 | 3.82 |
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Zhao, Z.; Zhou, Y.; Ma, X.; Chen, X.; Li, S.; Yang, S. Numerical Study on Thermal Hydraulic Performance of Supercritical LNG in Zigzag-Type Channel PCHEs. Energies 2019, 12, 548. https://doi.org/10.3390/en12030548
Zhao Z, Zhou Y, Ma X, Chen X, Li S, Yang S. Numerical Study on Thermal Hydraulic Performance of Supercritical LNG in Zigzag-Type Channel PCHEs. Energies. 2019; 12(3):548. https://doi.org/10.3390/en12030548
Chicago/Turabian StyleZhao, Zhongchao, Yimeng Zhou, Xiaolong Ma, Xudong Chen, Shilin Li, and Shan Yang. 2019. "Numerical Study on Thermal Hydraulic Performance of Supercritical LNG in Zigzag-Type Channel PCHEs" Energies 12, no. 3: 548. https://doi.org/10.3390/en12030548
APA StyleZhao, Z., Zhou, Y., Ma, X., Chen, X., Li, S., & Yang, S. (2019). Numerical Study on Thermal Hydraulic Performance of Supercritical LNG in Zigzag-Type Channel PCHEs. Energies, 12(3), 548. https://doi.org/10.3390/en12030548