Radiative Cooling Surface Passive Freezing Desalination
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Solution Overview
Problem
Conventional desalination methods, such as membrane-based and thermal evaporative processes, require significant energy inputs, which can be prohibitive as salinity increases and are limited by solar insolation in solar desalination.
Innovation Solution
The use of passive radiative cooling to freeze and desalinate salt water, where the outer space acts as a heat sink to absorb radiated heat, enabling passive freezing desalination with a radiative cooling surface that transfers heat from the water source to the atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional membrane-based desalination processes are used, then desalination can be achieved, but significant energy inputs are required which become prohibitive as salinity increases
Solution Approach 1:
The patent utilizes the phase transition of water from liquid to solid (freezing) to achieve desalination. When salt water freezes, pure ice crystals form while salt is excluded and concentrated in the remaining liquid, enabling separation without requiring energy-intensive membrane processes. The system leverages the natural phase change behavior of water at freezing temperatures to accomplish desalination.
Solution Approach 2:
The invention employs passive radiative cooling surfaces that automatically cool the salt water to freezing temperatures without requiring external energy input. The radiative cooling surfaces utilize the natural temperature difference between the Earth's surface and outer space to drive the freezing process, making the system self-sufficient and eliminating the need for energy-consuming cooling mechanisms.
2Use of energy by moving object
If solar desalination is used, then passive evaporative desalination can be achieved, but it is limited seasonally and geographically by solar insolation
Solution Approach 1:
The patent replaces solar-driven evaporative mechanisms with radiative cooling-driven freezing mechanisms. Instead of relying on solar radiation to heat and evaporate water, the system uses radiative cooling surfaces to passively cool and freeze water. This substitution enables desalination to occur independently of solar insolation, allowing operation during nighttime and in regions with limited sunlight.
Solution Approach 2:
The invention transitions from solar evaporative desalination (liquid to vapor phase change) to radiative cooling freezing desalination (liquid to solid phase change). This phase transition approach allows the system to operate passively without solar input, as the freezing process is driven by radiative heat loss to space rather than solar heating.
3Temperature
If radiative cooling surfaces with high emissivity are used, then passive freezing can be achieved, but system complexity increases
Solution Approach 1:
The patent modifies the emissivity parameter of the cooling surface to achieve effective radiative cooling. By selecting materials with high emissivity in the atmospheric transparency window (8-13 μm wavelength range), the system maximizes radiative heat loss to space. This parameter optimization enables passive freezing without requiring complex active cooling systems, maintaining simplicity while achieving the desired temperature reduction.
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
This method can recover at least 50% of fresh water from salt water and provides a complementary method to solar desalination, enabling 24-hour, year-round passive thermal desalination.
Implementation Method 1
Passive radiative cooling (PRC) is a passive process where objects under the sky spontaneously reflect sunlight and radiate heat into outer space through the long wavelength infrared (LWIR, 8-13 μm wavelength) transparency window of the atmosphere
Implementation Method 2
Passive radiative cooling (PRC) is a passive process where objects under the sky spontaneously reflect sunlight and radiate heat into outer space through the long wavelength infrared (LWIR, 8-13 μm wavelength) transparency window of the atmosphere. PRC has a net cooling effect that can be a sustainable way to cool buildings and outdoor structures
Implementation Method 3
The outer space can be used as a heat sink to absorb the radiated heat and enable passive freezing desalination through radiative cooling
Implementation Method 4
freezing the water source via radiative cooling to form ice and brine
Implementation Method 5
obtain desalinated water by thawing the ice, wherein the desalinated water has a salinity lower than the water source
Data Source
AI summary
Radiative cooling enabled passive freezing desalination processes are described. High salinity water can be desalinated via radiative cooling-driven freezing desalination. The passive freezing desalination processes can be a complementary method to solar desalination to enable 24-hour, year round passive thermal desalination.