Solar Heat Exchanger CFD Simulation: Radiation and Thermal Performance Analysis

A comprehensive computational fluid dynamics investigation of a specialized solar heat exchanger design featuring an absorber plate, internal flow barriers, and dual-medium heat transfer. This simulation captures the complex interplay between solar radiation, conduction, and convection mechanisms to demonstrate the thermal performance characteristics of this renewable energy system.

Solar Heat Exchanger Design and Operating Principles

This simulation examines a specialized heat exchanger designed to capture and transfer solar thermal energy to a working fluid. The system incorporates an innovative dual-medium approach with an air gap and absorber plate to maximize solar energy capture and transfer to the water flow through strategic internal flow barriers.

System Configuration

• Primary Components:
  • Solar absorber plate exposed to radiation
  • Air gap between front plate and absorber
  • Water flow channel with internal flow barriers
  • Strategic internal walls for flow path extension
• Heat Transfer Pathway:
  • Solar radiation absorption at absorber plate
  • Air gap heating through radiation and convection
  • Conduction through absorber plate
  • Convective transfer to water flow

Geometric Specifications

• Flow Path Design: Extended water flow route via internal barriers
• Absorber Orientation: Positioned for maximum solar radiation capture
• Internal Barriers: Multiple rows of flow obstacles for extended fluid residence time
• Air Gap Configuration: Optimized spacing for thermal performance

Computational Approach and Radiation Modeling

Mesh Characteristics

• Grid Type: Unstructured mesh generated in ANSYS Meshing
• Cell Count: 304,200 elements
• Resolution Focus: Enhanced density near absorber plate and internal barriers
• Quality Parameters: Optimized for complex geometry with multiple domains

Radiation Modeling Strategy

• Primary Model: Discrete Ordinates (DO) radiation model
• Model Capabilities:
  • Handles scattering media
  • Accounts for semi-transparent boundaries
  • Manages specular surfaces
  • Supports wavelength-dependent transmission
• Solar Loading: Solar Ray Tracing model implementation
• Solar Parameters:
  • Direct solar radiation: 1150 W/m²
  • Diffuse solar radiation: 80 W/m²
  • Incidence angle: Perpendicular to absorber plane

Operating Conditions

• Water Flow: 4 m/s inlet velocity at 30°C
• Outlet Condition: Atmospheric pressure
• Air Gap: Natural convection and radiation heat transfer
• Thermal Boundaries: Solar radiation on absorber surface

Results and Performance Analysis

Thermal Characteristics

• Temperature Distribution: Visualization of thermal gradients throughout the system
• Heat Transfer Pathways: Identification of primary energy transfer routes
• Absorber Performance: Temperature profile across the solar collector surface
• Water Temperature Gain: Progressive heating along the extended flow path

Flow Behavior

• Velocity Patterns: Analysis of flow development around internal barriers
• Pressure Distribution: Characterization of pressure drop across the exchanger
• Recirculation Zones: Identification of potential thermal mixing regions
• Barrier Effectiveness: Assessment of flow path extension and residence time

Radiation Effects

• Absorption Patterns: Distribution of captured solar energy across absorber
• Air Gap Thermal Gradient: Temperature stratification in the front air layer
• Direct vs. Diffuse Contribution: Relative impact of radiation components
• Thermal Losses: Evaluation of energy not transferred to working fluid

Performance Metrics

• Overall Efficiency: Ratio of captured energy to incident solar radiation
• Temperature Rise: Quantification of water temperature increase
• Heat Transfer Rate: Total thermal energy transferred to water flow
• Pressure Drop: Hydraulic resistance through the extended flow path

Engineering Insights

• Design Optimization: Guidance for barrier placement and configuration
• Performance Enhancement: Strategies for improving solar absorption and transfer
• Operational Parameters: Effects of flow rate on thermal efficiency
• System Scalability: Considerations for larger implementation

This detailed CFD simulation provides valuable insights into the thermal-hydraulic behavior of this specialized solar heat exchanger design. The results demonstrate the effectiveness of combining strategic flow path extension with optimized solar absorption to achieve efficient thermal energy capture and transfer. The comprehensive radiation modeling approach ensures accurate representation of the complex heat transfer mechanisms involved in solar thermal systems, providing reliable guidance for design optimization and performance prediction in renewable energy applications.