# Influence of Phase Change Phenomena on the Performance of a Desiccant Dehumidification System

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Experimental Section

^{2}.

_{a}, U

_{a}, D

_{h}, and μ represent the density (kg/m

^{3}), velocity (m/s), hydraulic diameter (m), and dynamic viscosity of the air (kg/m.s), respectively.

- (1)
- Firstly, the desiccant material was heated by the hot air, which was provided by the air supply unit for the desorption phase. This process allowed the water vapor molecules, which were trapped in the desiccant material, to evaporate. Therefore, the desiccant material was regenerated and recovered the ability of moisture adsorption.
- (2)
- When the desiccant material reached the equilibrium, the process was switched into the adsorption process by using the air regulator. The desiccant material adsorbed the water vapor molecules. At the same time, in the interface of the desiccant material, the heat of adsorption was released.
- (3)
- Lastly, the process was repeated for three up to four cycles to obtain adequate data.

#### 2.2. Data Reduction Equations

#### 2.2.1. Dehumidification Index

_{in}is the humidity ratio of the inlet air (kg/kg), and X

_{out}is the humidity ratio of the outlet air (kg/kg), whereas ads and des indicate the adsorption and desorption processes. In the case of the desorption process, because the hot air brought about water vapor during the running of the system, the outlet humidity was thus higher than in the inlet, and the moisture removal became negative.

_{i}) was defined as:

#### 2.2.2. The Effect of Latent Heat on the Performance

_{ideal}is the ideal humidity ratio that is calculated by considering the isenthalpic line of the humidity ratio inlet of the adsorption process under the constant’s relative humidity of the regeneration inlet conditions (kg/kg). If the water content was dehumidified completely, the ideal humidity ratio would reach the zero value. This value can be considered for the optimization of the desiccant dehumidification system [36]. The differences between the humidity ratio inlet of the adsorption process and ideal humidity ratio were referred to as the maximum dehumidification capacity of the system.

_{lat}) was given by

_{sen}) was given by

_{lat}is the latent heat (W), Q

_{sen}is the sensible heat (W), Q

_{ads}is the average of enthalpy exchange in the adsorption process (W), Q

_{des}is the average of heat exchange in the desorption process (W), ṁ

_{a}is the air mass flow rate (kg/s), γ is latent heat of vaporization (kJ/s), c

_{p}is specific heat of the air at bulk temperature (kJ/kg·K), T

_{des,in}is air inlet temperature of the desorption process (K), and T

_{des,out}is the air outlet temperature of the desorption process (K).

#### 2.2.3. Uncertainty Analysis

_{s}is the saturation water vapor pressure.

_{i})

## 3. Results and Discussion

#### 3.1. Influence of Desorption Temperature on the Water Content Removal

#### 3.2. Influence of Desorption Temperature on Dehumidification Index

#### 3.3. The Effect of Latent Heat on the Performance of the System

#### 3.4. Energy Analysis

_{lat}), regenerating the material (Q

_{sen}), and circulating the air by using a fan (W

_{fan}). The total energy demand (E

_{t}) is given as

^{3}/s), pressure drop (Pa), and efficiency of the fan (%), respectively. The assumption of the efficiency of the fan was considered at the value of 70% [43]. Then, the electricity of the fan was found to be 0.15 kW. On the basis of the experimental results, the total energy demand was found in the value of 0.624 kWh. The calculation of the cost mainly depends on the supply price of electricity in each country. In the case of the standalone dehumidification system, the current system consumed less energy when compared to conventional air conditioning. However, the initial cost for the desiccant dehumidification system might be higher than the conventional one. The benefit can cover this drawback in that the energy-saving from the standalone dehumidification system is able to lower the operational cost of the system [44].

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Nomenclature

A | adsorption potential (kJ/kg) |

c_{p} | specific heat capacity (J/kg·K) |

c_{p,b} | specific heat capacity of the bed (kJ/kg·K) |

d | moisture removal capacity (kg/kg) |

D_{h} | hydraulic diameter of the air channel (m) |

D_{i} | dehumidification index (kg/kg) |

E | adsorption characteristics parameter (kJ/kg) |

E_{t} | total energy demand (W) |

h | channel height (air layer) |

H | desiccant block height (m) |

k_{d} | thermal conductivity of sorbent (W/m·K) |

L | desiccant block length (m) |

LHR | latent heat ratio |

n | fitting constant |

p | fin spacing (m) |

P | partial pressure (kPa) |

P_{o} | saturation pressure (kPa) |

Q_{ads} | average of enthalpy exchange in adsorption process (W) |

Q_{des} | average of heat exchange in the desorption process (W) |

Q_{lat} | latent heat transfer (W) |

Q_{sen} | sensible heat transfer (W) |

r | radius of the adsorption particle (m) |

R | specific gas constant for water (kJ/kg·K) |

t | dehumidification time (s) |

T | temperature (K) |

Re | Reynolds number |

RH | relative humidity (%) |

U_{a} | air velocity (m/s) |

w | desiccant block width (m) |

${\dot{V}}_{a}$, | volume flow rate (m^{3}/s) |

W | equilibrium adsorption uptake (kg/kg) |

W_{fan} | electricity for fan (W) |

W_{o} | maximum adsorption capacity (kg/kg) |

X | humidity ratio (kg/kg) |

X_{ideal} | ideal humidity ratio of air stream at the outlet of dehumidification system (kg/kg) |

∆H | heat of adsorption (kJ/kg) |

Greek symbol | |

ε | latent heat effectiveness |

ε_{fan} | efficiency of the fan (%) |

δ | sorbent thickness (m) |

γ | latent heat of vaporization (kJ/s) |

μ | dynamic viscosity of the air (kg/m.s) |

ρ_{a} | air density (kg/m^{3}) |

ρ_{b} | bed density (kg/m^{3}) |

ϕ | porosity |

Subscript | |

ads | adsorption |

des | desorption |

in | inlet |

out | outlet |

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**Figure 1.**(

**a**) The photograph [9]; (

**b**) schematic diagram of the desiccant dehumidification system; (

**c**) structure of the polymer desiccant block.

**Figure 3.**Water content removal during adsorption/desorption processes for different desorption temperatures.

**Figure 5.**Latent heat effect on the performance of the system under various desorption temperatures.

**Table 1.**Parameters of polymer honeycomb desiccant structure [9].

Parameter | Symbol | Value | Unit |
---|---|---|---|

Width | w | 0.2 | m |

Length | L | 0.2 | m |

Height | H | 0.2 | m |

Thickness of sorbent | δ | 3 × 10^{−4} | m |

Channel height (air layer) | h | 1.7 × 10^{−3} | m |

Fin spacing | p | 3.6 × 10^{−3} | m |

Heat of adsorption | ΔH | 2500 | kJ/kg |

Density | ρ_{b} | 1500 | kg/m^{3} |

Specific heat capacity of the bed | c_{p,b} | 805 | kJ/kg·K |

Thermal conductivity of sorbent | k_{d} | 0.33 | W/m·K |

Porosity | ϕ | 0.9 | - |

Radius of the adsorbent particle | r | 1.29 × 10^{−6} | m |

**Table 2.**Experimental conditions of the desiccant dehumidification system. T

_{in}: Temperature inlet, X

_{in}: Humidity ratio inlet, RH

_{in}: Relative humidity inlet, U

_{a}: air velocity, Re: Reynolds number.

Process | Parameters | ||||
---|---|---|---|---|---|

T_{in} (K) | X_{in} (g/kg) | RH_{in} (%) | U_{a} (m/s) | Re | |

Desorption | 308 | 12.2 | 35.23 | 0.16 | 447.6 |

318 | 11.5 | 20.19 | 0.16 | 526.6 | |

328 | 13.7 | 15.5 | 0.16 | 593.7 | |

338 | 13.8 | 9.10 | 0.15 | 701.9 | |

345 | 13.5 | 6.63 | 0.15 | 712.7 | |

Adsorption | 293 | 9.2 | 60.25 | 0.16 | 304.4 |

Parameter | Symbol | Value |
---|---|---|

Humidity ratio | X | 2.37% |

Dehumidification index | D_{i} | 4.61% |

Latent effectiveness | ε | 4.8% |

Latent heat ratio | LHR | 5.31% |

Reynolds number | Re | 3.72% |

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**MDPI and ACS Style**

Yaningsih, I.; Wijayanta, A.T.; Thu, K.; Miyazaki, T.
Influence of Phase Change Phenomena on the Performance of a Desiccant Dehumidification System. *Appl. Sci.* **2020**, *10*, 868.
https://doi.org/10.3390/app10030868

**AMA Style**

Yaningsih I, Wijayanta AT, Thu K, Miyazaki T.
Influence of Phase Change Phenomena on the Performance of a Desiccant Dehumidification System. *Applied Sciences*. 2020; 10(3):868.
https://doi.org/10.3390/app10030868

**Chicago/Turabian Style**

Yaningsih, Indri, Agung Tri Wijayanta, Kyaw Thu, and Takahiko Miyazaki.
2020. "Influence of Phase Change Phenomena on the Performance of a Desiccant Dehumidification System" *Applied Sciences* 10, no. 3: 868.
https://doi.org/10.3390/app10030868