Solar air collectors are primarily classified into two main categories based on the design of their absorber plates and the path of the airflow.
Classification of Solar Air Collectors
Solar air heaters, or collectors, are broadly categorized by how the air interacts with the absorber plate, which is the component that absorbs solar radiation. This fundamental difference in design dictates their operational characteristics and applications.
Based on the provided classification, the two main types are:
1. Nonporous Absorber Type
This category includes solar air collectors where the air stream does not flow through the absorber plate itself. Instead, the air flows in channels or ducts located either above, below, or both above and below the solid, nonporous absorber plate. Heat is transferred from the heated absorber plate to the air as it passes by.
Characteristics:
- Airflow: Air circulates externally to the absorber plate.
- Absorber Design: Typically a solid, flat, or corrugated metal sheet.
- Heat Transfer: Convective heat transfer occurs as air moves along the heated surface of the absorber.
- Examples: Most common flat-plate solar air collectors, often used for space heating or drying applications.
2. Porous Absorber Type
In contrast, solar air collectors with a porous absorber design allow the air stream to flow directly through the absorber plate. The absorber is made of a material with numerous small openings or a matrix-like structure, enabling air to pass through and absorb heat more directly from the entire volume of the heated material.
Characteristics:
- Airflow: Air permeates and flows through the absorber material.
- Absorber Design: Can be screens, metal wool, rock beds, or other permeable materials.
- Heat Transfer: Enhanced heat transfer due to a larger surface area for contact between air and the heated absorber material.
- Examples: Transpired collectors, rock-bed storage systems, or specialized high-efficiency collectors.
Summary Table: Solar Air Collector Classification
| Classification Type | Absorber Characteristics | Airflow Path | Key Feature |
|---|---|---|---|
| Nonporous Absorber | Solid plate, not permeable to air. | Air flows above and/or below the absorber plate. | Air does not flow through the absorber. |
| Porous Absorber | Material with openings, permeable to air. | Air flows through the absorber plate. | Air does flow through the absorber. |
This classification is fundamental to understanding the design and operational principles of various solar air heating systems, guiding their selection for specific thermal energy applications.
