# Development of an In-House Code for Dry Tower of Heat Transfer Analysis in Hydrogen Purification System

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## Abstract

**:**

## 1. Introduction

_{2}/CO/CO

_{2}/CH

_{4}/H

_{2}) using a one column VPSA process with AC5-KS. A heat and mass transfer model with porous media adsorption was used to predict the performance of the VPSA process, and the simulation results closely matched experimental data. The model was utilized to analyze the effects of the P/F ratio and adsorption time in the VPSA unit. The model assessed the effects of the P/F ratio and adsorption time, revealing that increasing the P/F ratio and decreasing the feeding time led to higher hydrogen purity but lower recovery. Ye et al. [14] investigated that a PSA cycle model was implemented on the Aspen Adsorption platform to simulate the PSA process for a ternary component gas mixture (H

_{2}/CO

_{2}/CO) using a Cu-BTC adsorbent bed. Increasing adsorption pressure improved hydrogen purity but reduced recovery while extending adsorption time and lowering product flow rate increased recovery but decreased purity. Sakas et al. [15] developed a simulation model for optimizing cost and energy efficiency in an alkaline water electrolysis plant. They used MATLAB functions and Simulink to solve the energy and mass balances of the 3 MW, 16 bar plant. A TSA type dryer was used for moisture adsorption, achieving a minimum threshold moisture content through condensation drying at an ambient temperature of 25–30 °C. The thermal model accurately predicted the real-world scenario with 98.7% accuracy.

## 2. PEM System and Development of Program Code

#### 2.1. Understanding of the PEM System

#### 2.2. Development of Program Code (In-House Code)

- Hydrogen is considered an ideal gas;
- The temperature gradient in the radial direction is disregarded;
- The fluid flow within the drying tower exhibits axial dispersion flow characteristics;
- Structural factors in the drying tower, including diameter, cross-sectional area, and porosity, are assumed to be uniform;
- The axial heat transfer of the body occurs exclusively through conduction;
- The axial heat transfer of the adsorbent occurs exclusively through conduction;
- Heat transfer between the body and the adsorbent occurs exclusively through convection;
- Heat transfer between the adsorbent and hydrogen occurs exclusively through convection.

_{2}, respectively. The temperature of each component was calculated using Equations (1)–(3).

_{p}is the specific heat capacity of the material. R

_{w}and R

_{a}are thermal conduction resistances of dryer tower wall and adsorbent, and calculated using

_{w}

_{,}and k

_{a}are the thermal conductivity of the material, and A is the cross-sectional area of heat transfer through the interface.

_{2}pressure should be provided as the gauge pressure in units of the bar, and the H

_{2}flow rate should be specified as the mass flow rate in units of kg/h. For the dimensions of the drying tower, please enter the inlet and outlet diameter, and length, as well as the density, specific heat, and thermal conductivity of the tower material. Regarding alumina and the adsorbent, please provide the diameter, filled length, specific heat, thermal conductivity, porosity, and initial temperature.

_{p}), and convective heat transfer coefficient (h) is crucial for the energy balance equation of hydrogen. In this study, these parameters were derived using REFPROP 9.0, provided by the National Institute of Standards and Technology (NIST), with the final function formulas presented in Equations (6)–(9) [19].

_{2}was analyzed at velocities of 2 m/s, 8 m/s, and 16 m/s using the commercially available computer analysis code ANSYS FLUENT. A mathematical relationship between the convective heat transfer coefficient (h) and velocity (V) was derived and implemented as a subroutine in the in-house code. Equations (10) and (11) represent the functional formulas for the convective heat transfer coefficients of alumina and adsorbent, respectively.

## 3. Results and Discussion

^{3}to 3850 kg/m

^{3}. In the figure, 780_TA and 3850_TA represent the temperature histories of densities of 780 kg/m

^{3}and 3850 kg/m

^{3}, respectively, over time, while 780_AL and 3850_AL signify the temperature histories of Alumina with densities of 780 kg/m

^{3}and 3850 kg/m

^{3}, respectively. As observed in Figure 6, the slope of the temperature history concerning time change increases steeply with decreasing density.

_{2}increased in both Case 1 (Figure 9a) and Case 2 (Figure 9b). After supplying the cooling fluid, we observed a temperature jump in both the adsorbent and H

_{2}phases. As a result, when the cooling fluid is supplied to the dryer, the convective heat transfer coefficient rises in accordance with an increase in flow rate. The adsorbent and H

_{2}absorb more heat from the body than during the On-Off Cycle process, leading to a temperature increase. After that, the adsorbent and H

_{2}are immediately cooled. The convective heat transfer coefficient has a significant effect on the internal temperature during the dryer’s regeneration process.

_{2}increased rapidly from 187.1 °C to 203.7 °C when the cooling flow was introduced. In contrast, the analysis result showed a temperature range of 196.4 °C (4.97%) to 212.7 °C (4.42%), resulting in a difference of approximately 10 °C from the experimental results. During the heating process, it was observed that the temperature values measured in the experiment were consistently 6 °C to 10 °C lower than the values obtained through analysis. This discrepancy can be attributed to heat loss occurring during the transfer of heat from the actual heat jacket (heat source) to the dryer tower. Upon completion of the regeneration heating, the actual cooling time of the dryer tower was approximately 5300 s, whereas the calculated result showed approximately 4600 s. This discrepancy arises from differences between the cooling flow input values considered in the analysis and the fluctuations in temperature and flow rate of the gas supplied for cooling in the actual system.

## 4. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 3.**Layout for dry tower composition and heat transfer analysis (

**a**,

**b**) and scheme of heat transfer of dryer tower, adsorbent, and H

_{2}(

**c**–

**e**).

**Figure 6.**Temperature calculation results over time when Alumina and adsorbent densities are 780 kg/m

^{3}and 3850 kg/m

^{3}.

**Figure 9.**Numerical results of the regeneration process of (

**a**) case 1 (1000 W) and (

**b**) case 2 (2000 W).

**Figure 10.**Regeneration process of experimental and numerical results (case 2) for the (

**a**) heater and (

**b**) adsorbent.

Division | Case 1 | Case 2 |
---|---|---|

Total Time for Calculation | 1400 s | 710 s |

Time Interval of On-Off Cycle | 150 s | 150 s |

No. of On-Off Cycle | 10 | 10 |

Supplied Heat at On-Off Cycle | 170 W | 190 W |

Cooling Flow | 7.8 kg/h | 7.8 kg/h |

Pi Factor2 for Convection Coeff. | 1 | 1 |

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**MDPI and ACS Style**

Kwon, S.; Eom, S.; Yang, J.-S.; Choi, G.
Development of an In-House Code for Dry Tower of Heat Transfer Analysis in Hydrogen Purification System. *Energies* **2023**, *16*, 5090.
https://doi.org/10.3390/en16135090

**AMA Style**

Kwon S, Eom S, Yang J-S, Choi G.
Development of an In-House Code for Dry Tower of Heat Transfer Analysis in Hydrogen Purification System. *Energies*. 2023; 16(13):5090.
https://doi.org/10.3390/en16135090

**Chicago/Turabian Style**

Kwon, Sooin, Seongyong Eom, Jang-Sik Yang, and Gyungmin Choi.
2023. "Development of an In-House Code for Dry Tower of Heat Transfer Analysis in Hydrogen Purification System" *Energies* 16, no. 13: 5090.
https://doi.org/10.3390/en16135090