Selective Optical Sheet Material for Pool Covers
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Solution Overview
Problem
Existing pool covers either promote algae growth by allowing visible light or inhibit it but fail to optimize water heating due to inefficient heat transfer, and they often suffer from dimensional instability caused by heat absorption leading to shrinkage.
Innovation Solution
A sheet material with selective optical properties that transmits near-infrared radiation while blocking visible and mid-infrared radiation, comprising two layers: a mid-infrared absorbing upper layer and a visible light absorbing lower layer, made of low-density polyethylene with specific additives and glass microspheres, to optimize heat retention and prevent algae growth while minimizing shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the cover is transparent to allow solar radiation penetration for water heating, then water temperature increase is optimized, but algae growth is promoted due to visible light transmission
Solution Approach 1:
The patent applies local quality by creating different optical properties in different wavelength ranges within the same cover material. The cover selectively transmits near-infrared radiation (720-2500 nm) for water heating while blocking visible light (400-720 nm) to prevent algae growth, and blocks mid-infrared radiation for heat retention. This wavelength-specific selective transmission resolves the contradiction by treating different spectral regions differently.
Solution Approach 2:
The patent uses composite materials containing specific additives (such as carbon black, titanium dioxide, or other pigments) incorporated into the polymer matrix to achieve the selective optical properties. These composite materials enable differential transmission across the electromagnetic spectrum, allowing simultaneous optimization of heating and algae prevention functions.
2Object-affected harmful factors
If the cover is opaque to block visible light and prevent algae growth, then chemical costs are reduced, but water heating efficiency decreases due to inefficient heat transfer
Solution Approach 1:
The cover implements local quality by being opaque in the visible range (blocking algae growth) while maintaining high transmission in the near-infrared range (enabling water heating). This selective optical property allows the cover to appear opaque to the human eye while still allowing thermal radiation passage.
Solution Approach 2:
The patent employs color changes by incorporating pigments or additives that specifically absorb visible light wavelengths while remaining transparent to near-infrared radiation. This creates a material that appears colored or opaque in the visible spectrum but is transparent in the thermal infrared spectrum, simultaneously achieving algae prevention and heat transfer.
3Temperature
If the cover absorbs solar energy to heat water, then water temperature increases, but the cover material shrinks due to thermal expansion and stress relief
Solution Approach 1:
The patent addresses shrinkage by modifying the polymer material composition and thermal properties. This includes selecting polymers with appropriate thermal expansion coefficients, adding stabilizers and antioxidants to prevent degradation, and controlling the crystallinity and molecular weight of the polymer to maintain dimensional stability during thermal cycling while still allowing necessary heat absorption.
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 material effectively suppresses algae growth, enhances heat retention in the water, and reduces shrinkage by allowing near-infrared radiation to penetrate and heat to be conducted into the water, while maintaining low internal temperature to prevent cover shrinkage.
Implementation Method 1
selectively transmits electromagnetic radiation in the near-infrared region
Implementation Method 2
heat be conducted into the water
Implementation Method 3
additives for preventing transmission of radiation in the mid-infrared range
Implementation Method 4
additives for preventing the passage of specific bands of wavelengths of visible light which are required for growth of algae
Data Source
AI summary
Sheet material, for example for a swimming pool cover 12, comprises an upper layer 14 of mid-IR absorbing material and a lower layer 16, with bubbles 18, which absorbs visible light. The material passes at least 25% of radiation in the near-IR region, thus promoting heating of the water while suppressing growth of algae. Inorganic particles are used to block visible radiation and pigments are used to block mid-IR radiation.