Radiation-selective absorber coating and absorber tube with radiation-selective absorber coating
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Solution Overview
Problem
Existing absorber coatings for parabolic trough collectors face challenges in maintaining high absorption and low emissivity at elevated temperatures, with adhesion issues and material diffusion affecting durability and performance.
Innovation Solution
A radiation-selective absorber coating is developed with a barrier layer of SiOx and an adhesion-improving layer of molybdenum, sandwiched between two barrier layers and an IR-reflecting silver layer, preventing substrate diffusion and enhancing adhesion, allowing operation up to 590°C with high absorption and low emissivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the operating temperature is increased to improve energy yield, then the absorption properties and reflection properties deteriorate due to aging and diffusion processes
Solution Approach 1:
A molybdenum adhesion-improving layer is introduced as an intermediary between the substrate and the IR-reflecting silver layer. This intermediate layer prevents direct contact and diffusion between the substrate and silver, while also improving adhesion. The barrier layers (SiOx and Al2O3) serve as additional intermediaries to prevent material diffusion at the interfaces, thereby maintaining optical properties at elevated temperatures up to 590°C.
2Reliability
If better IR reflective materials like copper or silver are used to improve reflection properties, then adhesion becomes insufficient and layer stability deteriorates
Solution Approach 1:
The molybdenum adhesion-improving layer serves as a mediator between the substrate and the silver IR-reflecting layer. Molybdenum provides both good adhesion to the substrate and compatibility with the silver layer, while the barrier layers (SiOx and Al2O3) further mediate to prevent diffusion and enhance interlayer adhesion, ensuring the stability of the silver layer at high temperatures.
Solution Approach 2:
The coating system employs a composite multi-layer structure combining different materials (substrate, SiOx barrier layer, molybdenum adhesion layer, silver IR-reflecting layer, Al2O3 barrier layer) to achieve properties that individual materials cannot provide alone. This composite approach optimizes both adhesion and reflection properties simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The coating achieves high solar absorption (≥95%) and low thermal emissivity (≤10%) stability over 1000 hours at elevated temperatures, improving energy yield and extending the service life of parabolic trough collectors, enabling more efficient and economical operation.
Implementation Method 1
the shielding of the layer reflecting in the IR range and the adhesion-improving layer from the substrate by a two-layer barrier effectively prevents this and thus increases the long-term temperature stability of the coating
Implementation Method 2
there is at least one between a barrier layer consisting of an SiO x compound, where x can assume the values 1 to 2, and a layer made of silver that reflects in the IR range adhesion-improving layer is arranged, which consists of molybdenum
Implementation Method 3
a layer made of silver that reflects in the IR range
Implementation Method 4
the coefficients of the degree of absorption α and the degree of emissivity ε, whereby a high degree of absorption (α ≥ 95%) and a low degree of emissivity (ε ≤ 10%) of the absorber coating are always sought
Implementation Method 5
a low degree of emissivity (ε ≤ 10%) of the absorber coating are always sought
Data Source
Figure 1
Figure 2
AI summary
The radiation-selective absorber coating (20) comprises a reflective layer that reflects in the infrared range, barrier layers (24a, 24b, 24c) arranged below the reflective layer, an absorption layer (22) arranged above the reflective layer, an antireflection layer (23) arranged above the absorption layer, and an adhesion-enhancing layer (25) arranged between the barrier layer and the reflective layer. The second of the two barrier layers consists of aluminum oxide compound (Al xO y), where x is 1 or 2 and y is 1, 2 or 3, and silicon oxide compound (SiO x), where x is 1-2. The radiation-selective absorber coating (20) comprises a reflective layer that reflects in the infrared range, barrier layers (24a, 24b, 24c) arranged below the reflective layer, an absorption layer (22) arranged above the reflective layer, an antireflection layer (23) arranged above the absorption layer, and an adhesion-enhancing layer (25) arranged between the barrier layer and the reflective layer. The second of the two barrier layers consists of aluminum oxide compound (Al xO y), where x is 1 or 2 and y is 1, 2 or 3, and silicon oxide compound (SiO x), where x is 1-2. The adhesion-enhancing layer has a thickness of 5-50 nm. The reflective layer has a thickness of 80-150 nm. Independent claims are included for: (1) an absorber tube for a parabolic trough collector; and (2) a method of operating a parabolic trough collector.