# CFD Simulation of Defogging Effectivity in Automotive Headlamp

^{*}

## Abstract

**:**

## 1. Introduction

- Sorption of plastic components—every plastic material is able to absorb a certain amount of ambient moisture, which may later be released when the thermal conditions change;
- Permeation of water vapor through housing and lens material—materials traditionally used for the headlamps are not completely impermeable to the water vapor;
- Moisture transferred via the venting system—the venting system serves to change the air inside the headlamps, which helps to reduce the amount of fogging by transporting in warmer air. This system may also bring in air with higher humidity, which can later lead to the undesirable fogging.

- Ventilation system with membranes—diffusive transfer of moisture from the headlamp. Pros: long-term solution, no dust ingress. Cons: reduces the airflow through the ventilation system.
- Anti-fog coating—prevents the formation of water droplets. Pros: works all the time. Cons: limited lifetime, does not remove moisture.
- Non-regenerable desiccant bags—absorb the moisture. Pros: simple solution, works all the time. Cons: limited lifetime.
- Fans—blow the waste heat from LEDs to other parts of the headlamp. Pros: long-term solution. Cons: works only when the vehicle is active, does not remove moisture.

## 2. Problem Description

## 3. Experiment on Fogging–Defogging Test Rig

## 4. Numerical Simulation Setup

^{−1}∙K

^{−1}and thermal conductivity defined by Equation (1):

^{−1}, the lowest air temperature was 4 °C, which has a kinematic viscosity of 1.36 × 10

^{6}m

^{2}∙s

^{−1}[11], and the height of the headlamp glass was 0.16 m. They Reynolds number could be calculated from Equation (2):

^{5}and in this case the Reynolds number was equal to 9.4 × 10

^{3}, and therefore a turbulence model was not accounted for because the considered flow was in the laminar regime.

#### Governing Equations

^{−1}, while the average velocity was 7 × 10

^{−4}m∙s

^{−1}. The right side shows air circulation inside the lamp during the defogging phase. In this cross section, the ventilation opening with the set pressure was at the top of the lamp. The maximum velocity was 0.18 m∙s

^{−1}and the average value was 0.02 m∙s

^{−1}.

## 5. Results Comparison

#### 5.1. Comparison of Results C1—1 mL of Evaporated Water

#### 5.2. Comparison of Results C1.5—1.5 mL of Evaporated Water

#### 5.3. Comparison of Results C2—2 mL of Evaporated Water

## 6. Conclusions

## 7. Patents

## Author Contributions

## Funding

## Conflicts of Interest

## Nomenclature

$k$ | Thermal conductivity (W∙m^{−1}∙K^{−1}) |

$T$ | Temperature (K) |

$L$ | Characteristic length (m) |

$v$ | Velocity (m∙s^{−1}) |

$\nu $ | Kinematic viscosity (m^{2}∙s^{−1}) |

$Q$ | Mass flow (kg∙s^{−1}) |

$m$ | Mass (kg) |

$t$ | Time (s) |

$\rho $ | Density (kg∙m^{−3}) |

$h$ | Height (m) |

${\mathit{\Nabla}}_{s}$ | Surface gradient operator (1) |

$\overline{V}$ | Mean velocity (m∙s^{−1}) |

$\dot{m}$ | Mass flow rate (kg∙s^{−1}) |

$P$ | Pressure (Pa) |

$\dot{q}$ | Heat flux (J∙m^{−2}∙s^{−1}) |

$L\left({T}_{s}\right)$ | Latent heat (J∙kg^{−1}) |

$g$ | Gravitational acceleration (m∙s^{−2}) |

$\beta $ | Volumetric expansion coefficient (°C^{−1}) |

$\mathsf{\Theta}$ | Temperature difference (°C) |

$\alpha $ | Thermal diffusivity (m^{2}∙s^{−1}) |

${t}_{def}$ | Defogging time (s) |

${V}_{w}$ | Amount of evaporated water (m^{3}) |

## References

- Kouloh, H.; Geissler, U.; Weber, D.; Mueller, A. Active Moisture Removal Puts Headlamp Condensation Protection on a New Level. In SIA VISION 2018; Technical Paper; Société des ingénieurs de l’automobile: Paris, France, 2018; pp. 103–109. [Google Scholar]
- Tseng, K.-W.; Chen, T.-H.; Chen, S.-J.; Su, Y.-D.; Wang, H.-C.; Feng, S.-W.; Ye, Z.; Tu, K.-H. Laser Headlamp with a Tunable Light Field. Energies
**2019**, 12, 707. [Google Scholar] [CrossRef] - Sun, Y.S.; Emery, A.F. Effects of wall conduction, internal heat sources and an internal baffle on natural convection heat transfer in a rectangular enclosure. Int. J. Heat Mass Transf.
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**2003**, 40, 83–89. [Google Scholar] [CrossRef] - Groce, G.; D’Agaro, P.; Mattiello, F.; De Angelis, A. A Numerical Procedure for Defogging Process Simulation in Automotive Industry. In Proceedings of the International Conference on Heat and Mass Transfer, Corfu, Greece, 17–19 August 2004; pp. 17–19. [Google Scholar]
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**2007**, 221, 1241–1250. [Google Scholar] [CrossRef] - Moore, W.I.; Powers, C.R. Temperature Predictions for Automotive Headlamps Using a Coupled Specular Radiation and Natural Convection Model; SAE Technical Paper; SAE International: Warrendale, PA, USA, 1999. [Google Scholar] [CrossRef]
- Singh, R.; Kuzhikkali, R.; Shet, N.; Natarajan, S.; Kizhedath, G.; Arumugam, M. Automotive LED Headlamp Defogging: Experimental and Numerical Investigation; SAE Technical Paper; SAE International: Warrendale, PA, USA, 2016. [Google Scholar] [CrossRef]
- Deponti, A.; Damiani, F.; Brugati, L.; Bucchieri, L.; Zattoni, S. Modelling of condensate formation and disposal inside an automotive headlamp. In Proceedings of the 4th European Automotive Simulation Conference, Munich, Germany, 6–7 July 2009. [Google Scholar]
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**Figure 1.**Schematic of the test rig (1: pressurized air; 2: regulators; 3: humidifier; 4: headlamp; 5: camera).

**Figure 2.**Testing rig used for fogging/defogging (1: pressurized air; 2: regulators; 3: humidifier; 4: headlamp).

**Figure 4.**Geometric model used for the numerical simulations. (

**left**) Position of the humidifier; (

**right**) positions of the vent holes (1−4: inlets; 5: outlet).

**Figure 5.**Cross section of the domain. (

**left**) simulation of fogging (preparative stage); (

**right**) simulation of defogging (evaluated stage).

**Figure 8.**Velocity distribution inside the headlamp in case C2—cross section through the humidifier. (

**left**) Simulation of fogging (preparative stage—20 min since the beginning of humidification); (

**right**) simulation of defogging (evaluated stage—30 min since the beginning of defogging).

**Figure 10.**Temperature and relative humidity (RH) of the ambient air and inside the headlamp and the temperature of the front glass during the C1 defogging phase.

**Figure 12.**Temperature and relative humidity of the ambient air, air inside the headlamp, and temperature of the front glass during the C1.5 defogging phase.

**Figure 14.**Temperature and relative humidity of the ambient air and inside the headlamp and temperature of the front glass during the C2 defogging phase.

Model | Settings |
---|---|

Energy | On |

Viscous | Laminar |

Species | Species transport |

EWF | On |

Variable | Scheme |
---|---|

Gradient | Least squares cell-based |

Pressure | Standard |

Momentum | Second-order upwind |

H_{2}O | Second-order upwind |

Energy | Second-order upwind |

Transient formulation | Second-order implicit |

IC (Initial Conditions) | Setting | C1 | C1.5 | C2 |
---|---|---|---|---|

Glass temperature (°C) | Set according to the experiment | 20.3 | 23.2 | 24.4 |

Internal temperature (°C) | Set according to the experiment | 22.1 | 21.9 | 22.5 |

Internal humidity (%) | Set according to the experiment | 55.2 | 61.5 | 61.2 |

Case | Evaporation Time (mm:ss) | Mass Flow Rate (×10^{−6} kg∙s) |
---|---|---|

C1 | 15:00 | 1.11 |

C1.5 | 22:30 | 1.11 |

C2 | 20:00 | 1.67 |

BC (Boundary Conditions) | Setting | C1 | C1.5 | C2 |
---|---|---|---|---|

Ambient air temperature (°C) | Set according to the experiment | 23.1 | 21.0 | 27.0 |

Ambient air humidity (%) | Set according to the experiment | 38.9 | 29.4 | 41.1 |

Ventilation opening 1 (Pa) | Pressure inlet, 60 Pa | 60 | 60 | 60 |

Ventilation opening 2 (Pa) | Pressure inlet, 60 Pa | 60 | 60 | 60 |

Ventilation opening 3 (Pa) | Pressure inlet, 60 Pa | 60 | 60 | 60 |

Ventilation opening 4 (Pa) | Pressure inlet, 60 Pa | 60 | 60 | 60 |

Ventilation opening 5 | Pressure outlet | - | - | - |

Heat transfer coefficient on the glass surface | Calculated according to Equation (9) | 4.3 | 4.2 | 4.4 |

50% Defogged (h:mm:ss) | 80% Defogged (h:mm:ss) | |
---|---|---|

Experiment | 0:26:00 | 0:48:00 |

Simulation | 0:21:14 | 0:47:10 |

Offset | 0:04:46 | 0:00:50 |

Experiment | Simulation |
---|---|

Beginning of defogging | |

12 min from the beginning of defogging | |

24 min from the beginning of defogging | |

36 min from the beginning of defogging | |

1 h from the beginning of defogging | |

End of defogging | |

50% Defogged (h:mm:ss) | 80% Defogged (h:mm:ss) | |
---|---|---|

Experiment | 0:31:00 | 1:08:00 |

Simulation | 0:30:00 | 1:06:00 |

Offset | 0:01:00 | 0:02:00 |

Experiment | Simulation |
---|---|

Beginning of defogging | |

28 min from the beginning of defogging | |

44 min from the beginning of defogging | |

1 h and 8 min from the beginning of defogging | |

1 h and 36 min from the beginning of defogging | |

End of defogging | |

50% Defogged (h:mm:ss) | 80% Defogged (h:mm:ss) | |
---|---|---|

Experiment | 0:41:00 | 1:24:00 |

Simulation | 0:35:33 | 1:18:34 |

Offset | 0:05:27 | 0:05:34 |

Experiment | Simulation |
---|---|

Beginning of defogging | |

28 min from the beginning of defogging | |

44 min from the beginning of defogging | |

1 h and 8 min from the beginning of defogging | |

1 h and 36 min from the beginning of defogging | |

End of defogging | |

C1 | C1.5 | C2 | |
---|---|---|---|

Amount of evaporated water (mL) | 1 | 1.5 | 2 |

Total defogging time (h:mm) | 1:27 | 2:10 | 2:53 |

Ambient temperature (°C) | 23.1 | 21.0 | 27.0 |

Ambient humidity (%) | 38.9 | 29.5 | 41.1 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Guzej, M.; Zachar, M.
CFD Simulation of Defogging Effectivity in Automotive Headlamp. *Energies* **2019**, *12*, 2609.
https://doi.org/10.3390/en12132609

**AMA Style**

Guzej M, Zachar M.
CFD Simulation of Defogging Effectivity in Automotive Headlamp. *Energies*. 2019; 12(13):2609.
https://doi.org/10.3390/en12132609

**Chicago/Turabian Style**

Guzej, Michal, and Martin Zachar.
2019. "CFD Simulation of Defogging Effectivity in Automotive Headlamp" *Energies* 12, no. 13: 2609.
https://doi.org/10.3390/en12132609