# Performance Analysis of a Double Pass Solar Air Thermal Collector with Porous Media Using Lava Rock

^{1}

^{2}

^{*}

## Abstract

**:**

^{2}and 800 W/m

^{2}were 62% to 64%, respectively, with an optimum flow rate of 0.035 kg/s. The optimum porosity of about 89% was selected for the collector by considering the pressure drop and thermal efficiency. An optimal temperature output range between 41.7 °C and 48.3 °C could be achieved and was suitable for agricultural and food drying applications. Meanwhile, compared to conventional DPSAHs, the average percentage increase in the output temperature of the DPSAH with lava rock was found to be higher by 17.5%.

## 1. Introduction

## 2. Research Methodology

#### 2.1. Design Concept

- It has high porosity;
- It has a low density;
- It has high moisture absorption;
- It has a high heat capacity (capability to retain heat).

#### 2.2. Mathematical Model Using the Energy Balance Method

- The analysis is 1-dimensional;
- The heat capacity of glass, absorber plate, and back surface is negligible;
- Only the heat capacity of the porous material is considered in the transient analysis;
- The thermal resistance of the glass cover and the backplate are assumed to be negligible.

#### 2.3. Validation of the Mathematical Model

## 3. Results and Discussion

#### 3.1. Determination of the Optimum Mass Flow Rate

#### 3.2. Determination of the Optimum Porosity

#### 3.3. The Variation with the Time of the Day

#### 3.4. The Use of DPSAH with Lava Rock in Agricultural Drying

## 4. Conclusions

- With the use of lava rock, the optimum thermal efficiency for the DPSAH that can be achieved ranges from 62% to 64% at a mass flow rate of 0.035 kg/s and at irradiances between 500 W/m
^{2}and 800 W/m^{2}; - A porosity of 89% is the most suitable for considering the pressure drop and thermal efficiency trade-off;
- The optimal temperature output range between 41.7 °C and 48.3 °C can be utilized to dry food, resulting in better food quality;
- Compared to conventional double-pass solar air heaters (DPSAH), the overall temperature output of the DPSAH with lava rock is higher by approximately 17.5%;
- The use of lava rock significantly impacts heat storage and can maintain continuous heat when employed for solar drying under the Malaysian climate.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Nomenclature

${\mathrm{A}}_{\mathrm{c}}$ | Area of solar collector (${\mathrm{m}}^{2})$ |

${\mathrm{A}}_{\mathrm{pm}}$ | Area of porous (${\mathrm{m}}^{2})$ |

${\mathrm{A}}_{\mathrm{m}}$ | Wetted area (${\mathrm{m}}^{2})$ |

$\mathrm{C}$ | Specific heat capacity of fluid $\left(\mathrm{J}/\mathrm{kgK}\right)$ |

${\mathrm{C}}_{\mathrm{m}}$ | Specific heat capacity porous $\left(\mathrm{J}/\mathrm{kgK}\right)$ |

$\mathrm{d}$ | Collector depth $\left(\mathrm{m}\right)$ |

${\mathrm{D}}_{\mathrm{m}}$ | The equivalent diameter of packed bed $\left(\mathrm{m}\right)$ |

${\mathrm{D}}_{\mathrm{e}}$ | Characteristic length $\left(\mathrm{m}\right)$ |

${\mathrm{D}}_{\mathrm{h}}$ | Equivalent diameter $\left(\mathrm{m}\right)$ |

$\mathrm{f}$ | Friction factor |

$\mathrm{h}$ | Heat-transfer coefficient $\left(\mathrm{W}/{\mathrm{m}}^{2}\mathrm{K}\right)$ |

$\mathrm{I}$ | Irradiation $\left(\mathrm{W}/{\mathrm{m}}^{2}\right)$ |

$\mathrm{k}$ | Thermal conductivity $\left(\mathrm{W}/\mathrm{mK}\right)$ |

$\mathrm{L}$ | Length $\left(\mathrm{m}\right)$ |

$\mathrm{l}$ | Thickness $\left(\mathrm{m}\right)$ |

$\mathrm{\u1e41}$ | Mass flow rate $\left(\mathrm{kg}/\mathrm{s}\right)$ |

${\mathrm{M}}_{\mathrm{m}}$ | Mass of porous $\left({\mathrm{k}}_{\mathrm{g}}\right)$ |

$\mathrm{N}\mathrm{u}$ | Nusselt number |

$\mathrm{r}$ | Prandtl number |

$\Delta \mathrm{P}$ | Pressure drops $\left(\mathrm{N}/{\mathrm{m}}^{2}\right)$ |

$\mathrm{Re}$ | Reynold number |

$\mathrm{T}$ | Temperature $(\xb0\mathrm{C})$ |

$\mathrm{U}$ | Loss coefficient $\left(\mathrm{W}/{\mathrm{m}}^{2}\mathrm{K}\right)$ |

$\mathrm{v}$ | Velocity $\left(\mathrm{m}/\mathrm{s}\right)$ |

$\mathrm{V}$ | Volume $\left({\mathrm{m}}^{3}\right)$ |

$\mathrm{W}$ | Collector width $\left(\mathrm{m}\right)$ |

Subscripts | |

$\mathrm{a}$ | Ambient |

$\mathrm{b}$ | Backplate |

$\mathrm{f}$ | Fluid |

$\mathrm{g}$ | Glass |

$\mathrm{i}$ | Inlet |

$\mathrm{m}$ | Porous media |

$\mathrm{o}$ | Outlet |

$\mathrm{p}$ | Plate |

$\mathrm{pm}$ | Porous media |

$\mathrm{r}$ | Radiation |

$\mathrm{s}$ | Sky |

$\mathrm{t}$ | Top |

$\mathrm{th}$ | Thermal |

$\mathrm{t}$ | Insulation |

$\mathrm{w}$ | Wind |

$1\text{}\mathrm{and}\text{}2$ | Refer to the first and second stream of fluid |

Greek | |

$\mathsf{\alpha}$ | Absorptivity |

$\mathsf{\epsilon}$ | Porosity |

$\mathsf{\eta}$ | Efficiency |

$\mathsf{\rho}$ | Density |

$\mathsf{\tau}$ | Transmissivity |

$\mathsf{\delta}$ | Thickness of porous |

$\mathsf{\mu}$ | Viscosity |

$\mathsf{\sigma}$ | Stefan’s Boltzmann constant |

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**Figure 1.**Schematic diagram of (

**a**) a single-pass and (

**b**) double-pass solar air heater with a packed bed [13].

**Figure 3.**(

**a**) Images of lava rock (Scoria type) ready for installation, (

**b**–

**d**) Scanning Electron Diffraction (SED) images of the lava rock (Scoria type) under different magnification showing the porosity of the rock.

**Figure 6.**The Variation in the temperature output against the change in the mass flow rate: a comparison between the study of El-Sebaii et al. [45] and our simulation.

**Figure 8.**(

**a**) Pressure drop against mass flow rate and (

**b**) variation in thermal efficiency against the mass flow rate with different porosity values.

**Figure 9.**Solar Irradiance I, ambient temperature T

_{a}, and air output temperature Tfo against the time of the day for the conventional double-pass solar air heater (DPSAH) and DPSAH with lava rock.

Author | Year | Type of Porous Material |
---|---|---|

Mahmood et al. [9] | 2015 | Wire mesh |

Roy et al. [14] | 2017 | Square shape steel wire mesh |

Ahmed and Mohammed [15] | 2017 | Glass Sphere |

Monem et al. [16] | 2019 | Black coated wire mesh |

Singh et al. [17] | 2019 | Ten successive wire mesh |

Author | Year | Type of Porous Material |
---|---|---|

Velmurugan and Kalaivanan [18] | 2015 | V-corrugated shaped wire mesh |

Dissa et al. [19] | 2016 | corrugated iron sheet and mesh of aluminum |

Singh and Dhiman [20] | 2016 | Wire mesh |

Singh and Dhiman [21] | 2018 | Wire mesh |

Hernández et al. [22] | 2019 | Porous matrix (in contact with absorber plate) |

Güler et al. [23] | 2020 | Iron wire mesh |

Singh [24] | 2020 | Serpentine wavy wire mesh |

Parameters | Numerical Values |
---|---|

The volume of lower channel, ${\mathrm{V}}_{1}$$\left({\mathrm{m}}^{3}\right)$ | 0.09 |

Ambient temperature, $\text{}{\mathrm{T}}_{\mathrm{a}}$$\text{}\left(\mathrm{K}\right)$ | 298.15 |

Inlet air temperature, $\text{}{\mathrm{T}}_{\mathrm{i}}$$\text{}\left(\mathrm{K}\right)$ | 300.15 |

Mass Flow rate, $\text{}$$\text{}(\mathrm{kg}/\mathrm{s})$ | 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065 |

Solar Irradiance, $\text{}$$\text{}\mathrm{W}/{\mathrm{m}}^{2}$ | 500, 600, 700, 800 |

The transmittance of glass, $\text{}{\mathsf{\tau}}_{\mathrm{g}}$ | 0.80 |

Absorption of glass, $\text{}{\mathsf{\alpha}}_{\mathrm{g}}$ | 0.05 |

Absorption of the plate, $\text{}{\mathsf{\alpha}}_{\mathrm{p}}$ | 0.95 |

An emissivity of glass,$\text{}{\mathsf{\epsilon}}_{\mathrm{g}}$ (Low emissivity coated glass) | 0.35 |

An emissivity of the absorber plate, $\text{}{\mathsf{\epsilon}}_{\mathrm{p}}$ | 0.9 |

An emissivity of the bottom plate, $\text{}{\mathsf{\epsilon}}_{\mathrm{b}}$ | 0.86 |

An emissivity of porous material, $\text{}{\mathsf{\epsilon}}_{\mathrm{pm}}$ | 0.93 |

Sigma, $\text{}\mathsf{\sigma}$ | 5.670 × 10^{−8} |

Thermal conductivity of insulation, $\text{}\frac{\mathrm{W}}{{\mathrm{m}}^{2}}$ | 0.038 |

Thermal conductivity of porous,$\text{}\frac{\mathrm{W}}{{\mathrm{m}}^{2}}$ [28] | 1.56 |

Specific heat capacity of porous,$\text{}\frac{\mathrm{J}}{\mathrm{kgK}}$ [28] | 1200 |

The density of porous material,$\text{}{\mathsf{\rho}}_{\mathrm{m}}$ [28] | 2600 |

Wind velocity, $\text{}{\mathrm{V}}_{\mathrm{w}}$$,\text{}\mathrm{m}/\mathrm{s}$ | 1 |

Parameter | ${\mathrm{T}}_{\mathrm{f}\mathrm{o}}$ |
---|---|

RMSPD | 6.08% |

MAPE | 5.46% |

Ref. | Sample | Temperature | Remark |
---|---|---|---|

[52] | Marine fish | 45–50 °C | Products made at temperatures ranging from 45 °C to 50 °C were outstanding in taste, color, and texture. |

[53] | Mint leaves | 40–50 °C | $\mathrm{Mass}\text{}\mathrm{flow}\text{}\mathrm{rate}\text{}\mathrm{is}\text{}\mathrm{set}\text{}\mathrm{up}\text{}\mathrm{between}\text{}0.01\text{}\mathrm{kg}/\mathrm{s}$$\text{}\mathrm{to}\text{}0.05\text{}\mathrm{kg}/\mathrm{s}$. |

[54] | Apple slices | 20–50 °C | The thickness of the slice should be taken into account. |

[55] | Cassava | 40–50 °C | Temperatures higher than 80 °C may reduce the quality of the crop. |

[56] | Unsalted and Salted catfish | 50 °C | Drying for 8 h is recommended. |

[57] | Red chili | 28–55 °C | Maximum moisture content can be reduced to 10% within 33 h, maintaining an average drying temperature of about 44 °C. |

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## Share and Cite

**MDPI and ACS Style**

Ismail, A.F.; Abd Hamid, A.S.; Ibrahim, A.; Jarimi, H.; Sopian, K. Performance Analysis of a Double Pass Solar Air Thermal Collector with Porous Media Using Lava Rock. *Energies* **2022**, *15*, 905.
https://doi.org/10.3390/en15030905

**AMA Style**

Ismail AF, Abd Hamid AS, Ibrahim A, Jarimi H, Sopian K. Performance Analysis of a Double Pass Solar Air Thermal Collector with Porous Media Using Lava Rock. *Energies*. 2022; 15(3):905.
https://doi.org/10.3390/en15030905

**Chicago/Turabian Style**

Ismail, Amar Fahmi, Ag Sufiyan Abd Hamid, Adnan Ibrahim, Hasila Jarimi, and Kamaruzzaman Sopian. 2022. "Performance Analysis of a Double Pass Solar Air Thermal Collector with Porous Media Using Lava Rock" *Energies* 15, no. 3: 905.
https://doi.org/10.3390/en15030905