# CFD Analysis of Elements of an Adsorption Chiller with Desalination Function

^{*}

## Abstract

**:**

## 1. Introduction

^{2}/g; narrow porosity, 600–850 m

^{2}/g), thanks to which it is possible to adsorb a large amount of water vapor [2,4,5].

- Numerical modeling of the processes occurring in the evaporator, condenser, and bed of the adsorption chiller to understand better these processes;
- Analyzing the fields of temperature, pressure, and velocity;
- Indicating the locations with extremes of temperatures, pressures, and velocities;
- Determining the phenomena disrupting the operation of the main elements of the adsorption chiller;
- Determining potential changes in the structure of the main elements, which may improve the operating parameters of the individual elements of the chiller and increase its efficiency and reliability.

## 2. Materials and Methods

#### 2.1. Empirical Research

#### 2.2. Construction of Spatial Geometry and a Computational Grid

#### 2.2.1. Generation of a Computational Mesh

- The housing of the elements was simplified to the form of a cylinder, without sight glasses and measuring connectors.
- Irregularly shaped elements such as heating and cooling junction boxes in the evaporator and condenser were simplified to a cylinder form.
- For the sorption chamber, the structural elements supporting the bed were omitted, and the bed itself was simplified to the form of a cuboid.

- Orthogonal quality: its value is in the range <0,1>, where the value 1 means the highest possible quality.
- Skewness: its value is in the range <0,1>, with the value 0 being the highest possible quality.

#### 2.2.2. Boundary Conditions

- For the issues related to relatively low flow velocities (subsonic flow), flow solutions based on the pressure field (“pressure-based”) were used.
- It was assumed that the simulation would be carried out in the “transient” mode, which enables the observation of changes in parameters over time.
- The influence of gravity on the fluid elements was taken into account by appropriately defining the acceleration vector.
- Due to the inclusion of gravity in the model and the occurrence of mass interactions, the scheme of coupling the velocity and pressure fields (“coupled”) was applied.
- In the sorption chamber, reference conditions were defined in the entire domain as for sorption pressure of 1050 Pa and a temperature of 315.8 K, steam inlet at a temperature of 279.07 K, for desorption a pressure of 5250 Pa and a temperature of 301.98 K, and a steam outlet temperature of 312.82 K
- The sorption time was set at 100 s, and the desorption time 200 s
- Reference conditions for the evaporator was a pressure of 1050 Pa and a temperature of 279.09 K
- Evaporator water inlet temperature was 280.24 K, water outlet temperature was 280.29 K, and the steam outlet temperature was 279.09 K
- A second-order spatial discretization scheme was used for the governing equations (mass, momentum, and energy). However, for the dissipation of turbulence, a first-order scheme was used.
- Reference conditions for the condenser was a temperature of 301.98 K, and a pressure of 5250 Pa
- Steam inlet temperature to the condenser was 312.82 K, and the temperature of the cooling pipes was 292.82 K
- Condenser domain computation was set for a time equal to 500 s.

#### 2.2.3. Computational Methods

_{m}, p, $\stackrel{=}{\tau}$, $\rho \overline{g}$, $\overline{F}$, E, k

_{eff}, h

_{j}, ${\overline{J}}_{j}$, $\left({\stackrel{=}{\tau}}_{eff}\cdot \overline{v}\right)$, and S

_{h}stand for the density, time, velocity, source term, static pressure, stress tensor, gravitational body force, external mass forces acting on the fluid, energy, effective thermal conductivity coefficient, enthalpy of species j, diffusive flux of species j, viscous dissipation, and heat source, respectively.

## 3. Results and Discussion

#### 3.1. Results of Numerical Calculations

#### 3.2. Simulation Results for the Sorption Chamber

#### 3.2.1. Sorption Process

#### 3.2.2. Desorption Process

#### 3.3. Simulation Results for the Evaporator

#### 3.4. Simulation Results for the Condenser

#### 3.5. Validation of Simulation

## 4. Conclusions

- Changing the tube banks in the evaporator from an in-line arrangement to a staggered arrangement while simultaneously maintaining the same heat transfer surface area. This change can improve the cooling capacity of the evaporator and provide a more uniform temperature distribution;
- Using a turbulator inside the tubes in the evaporator, as the heat transfer rate is significantly greater for turbulent flow compared to laminar flow.
- Changing the arrangement of the tubes in the condenser, as the temperature distribution in the condenser is non-uniform. Another arrangement of the tubes could provide more uniform temperature distribution, which could result in a faster vapor condensation and thus a more efficient performance of the entire device;
- Reducing the length of the water vapor supply pipe or using a jet diffusion cone or a straight baffle at the stream outlet should be considered. The proposed solutions will lower the velocity of water vapor and improve its dispersion. As a result, the force acting on the sorbent will be reduced;
- Using a distribution manifold that distributes the vapor uniformly over the entire surface of the bed, which will accelerate the sorption. As shown in Figure 10, the water vapor diffusion in the bed is not uniform, which lengthens the adsorption time and decreases the overall efficiency of the adsorption chiller.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Scheme of the adsorption chiller with desalination test bench at the Center of Energy AGH [6,29]. 1—condenser; 2—distillate tank; 3—adsorbent bed; 4—brine tank; 5—evaporator; 6—deaerator; TT01—temperature in the evaporator; TT04—hot water inlet temperature; TT05—hot water outlet temperature; TT06—chilled water inlet temperature; TT07—chilled water outlet temperature; TT11—temperature in Bed 1; TT12—temperature in Bed 2; TT13—temperature in Bed 3; TT18—temperature in the condenser; PT04—pressure in the evaporator; PT07—pressure in Bed 1; PT06—pressure in Bed 2; PT05—pressure in Bed 3; PT10—pressure in the condenser; FT01—hot water flow; FT03—chilled water flow.

**Figure 2.**Temperature changes over time. 1—heating water inlet to the beds; 2—heating water outlet from the beds; 3—chilled water outlet from the evaporator; 4—cooling water outlet from the condenser; 5—heat exchanger in the first bed; 6—heat exchanger in the second bed; 7—free space of the first bed; 8—free space of the second bed; 9—cooling water outlet from the beds; 10—free space of the evaporator; 11—free space of the condenser.

**Figure 8.**Cross-Section K1 for the sorption: (

**a**) temperature distribution; (

**b**) pressure distribution; (

**c**) velocity distribution.

**Figure 16.**Comparison of the results of simulation and experimental studies—pressure over time for the sorption process.

**Figure 17.**Comparison of the results of simulation and experimental studies—pressure over time for the desorption process.

**Figure 18.**Comparison of the results of simulation and experimental studies—temperature over time for the sorption process.

**Figure 19.**Comparison of the results of simulation and experimental studies—temperature over time for the desorption process.

Evaporator | ||

Cooling capacity | 1.50 | kW |

Chilled water inlet temperature | 32 | °C |

Chilled water outlet temperature | 30 | °C |

Chilled water mass flow rate | 0.184 | kg/s |

Condenser | ||

Capacity | 2.00 | kW |

Cooling water inlet temperature | 30 | °C |

Cooling water outlet temperature | 32 | °C |

Cooling water mass flow rate | 0.25 | kg/s |

Daily distillate production | 40 | kg |

Beds | ||

Required cooling capacity (adsorption) | 2.90 | kW |

Required heating capacity (desorption) | 2.90 | kW |

Cooling water mass flow rate | 0.25 | kg/s |

Heating water mass flow rate | 0.25 | kg/s |

Cooling water inlet temperature | 30 | °C |

Heating water inlet temperature | 85 | °C |

Cooling Capacity | ||

Chilled Water: inlet/outlet temperature; mass flow rate: 32/30 °C; 0.184 kg/s | 1.50 | kW |

Chilled Water: inlet/outlet temperature; mass flow rate: 16/11 °C; 0.0523 kg/s | 1.32 | kW |

Chilled Water: inlet/outlet temperature; mass flow rate: 12/7 °C; 0.0523 kg/s | 1.10 | kW |

Temperature | Sensor | Range | Uncertainty |

Heating water inlet to the beds Heating water outlet from the beds Free surface of the beds Inside the heat exchanger in the beds Cooling water outlet from the beds Cooling water outlet from the condenser Chilled water outlet from the evaporator Free space of the evaporator Free space of the condenser | Pt-1000 | From −80 °C to 150 °C | ±0.1 °C |

Pressure | Sensor | Range | Uncertainty |

Condenser Evaporator Beds | Pressure transducer | From 0 to 99 kPa | ±0.5% |

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**MDPI and ACS Style**

Sztekler, K.; Siwek, T.; Kalawa, W.; Lis, L.; Mika, L.; Radomska, E.; Nowak, W.
CFD Analysis of Elements of an Adsorption Chiller with Desalination Function. *Energies* **2021**, *14*, 7804.
https://doi.org/10.3390/en14227804

**AMA Style**

Sztekler K, Siwek T, Kalawa W, Lis L, Mika L, Radomska E, Nowak W.
CFD Analysis of Elements of an Adsorption Chiller with Desalination Function. *Energies*. 2021; 14(22):7804.
https://doi.org/10.3390/en14227804

**Chicago/Turabian Style**

Sztekler, Karol, Tomasz Siwek, Wojciech Kalawa, Lukasz Lis, Lukasz Mika, Ewelina Radomska, and Wojciech Nowak.
2021. "CFD Analysis of Elements of an Adsorption Chiller with Desalination Function" *Energies* 14, no. 22: 7804.
https://doi.org/10.3390/en14227804