Membrane Indirect Evaporative Cooler for Single-Stage Dehumidification
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Solution Overview
Problem
Conventional evaporative coolers are inefficient in providing adequate cooling and dehumidification, especially in humid climates, and require high maintenance, which limits their adoption in commercial and residential applications due to increased operating and maintenance costs.
Innovation Solution
An indirect evaporative cooler with a mass/heat transfer assembly using alternating stacks of permeable membrane layers and separation walls, where coolant and liquid desiccant flows are alternated to facilitate simultaneous dehumidification and evaporative cooling, allowing air to be cooled and dehumidified in a single stage without direct contact, reducing system size and maintenance needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional evaporative coolers are used, then cooling is provided through simple water evaporation, but adequate cooling and dehumidification cannot be achieved, especially in humid climates
Solution Approach 1:
A hydrophobic membrane is introduced as an intermediary between the liquid desiccant and the air stream. The membrane allows water vapor to pass through while blocking liquid desiccant, enabling dehumidification without direct contact between the desiccant and air, thus preventing carryover while maintaining cooling effectiveness in humid climates
Solution Approach 2:
The invention changes the physical state and properties of the working fluid from simple water to liquid desiccant solutions with varying concentrations. By adjusting the desiccant concentration and using a hydrophobic membrane, the system achieves effective dehumidification and cooling performance across different climate conditions, including humid environments where conventional evaporative coolers fail
2Loss of substance
If liquid desiccant is used for dehumidification, then dehumidification is achieved, but liquid desiccant may be expelled with the conditioned air causing carryover
Solution Approach 1:
The hydrophobic membrane serves as a selective barrier that permits water vapor transmission for dehumidification while rejecting liquid desiccant molecules. This intermediary structure enables the system to achieve effective dehumidification without the harmful side effect of liquid desiccant carryover into the conditioned air stream
Solution Approach 2:
A thin hydrophobic membrane film is used to separate the liquid desiccant from the air stream. The membrane's hydrophobic properties prevent liquid penetration while allowing vapor transmission, thus eliminating carryover issues associated with conventional liquid desiccant systems that use direct contact or wicking methods
3Device complexity
If conventional evaporative coolers are used, then system complexity is reduced, but maintenance requirements increase due to mineral deposits and pad cleaning
Solution Approach 1:
The hydrophobic membrane acts as a protective intermediary that prevents liquid desiccant from contacting and depositing on the air-facing surfaces. This eliminates the mineral deposit buildup that occurs in conventional evaporative coolers, significantly reducing maintenance requirements for pad cleaning and system repairs
Solution Approach 2:
The use of a thin hydrophobic membrane film creates a non-porous barrier that prevents liquid accumulation and mineral deposition on evaporative surfaces. This film structure eliminates the need for regular pad cleaning and replacement, reducing maintenance efforts while maintaining system complexity at an acceptable level
4Temperature
If direct evaporative cooling is used, then cooling is achieved through water evaporation, but the outlet air has high relative humidity reducing comfort and causing condensation
Solution Approach 1:
The invention changes the working fluid from pure water to liquid desiccant solutions, which have different hygroscopic properties. By adjusting the desiccant concentration and using a hydrophobic membrane, the system achieves both cooling and dehumidification, producing outlet air with lower relative humidity that improves comfort and prevents condensation while maintaining the evaporative cooling effect
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 solution achieves high energy transfer rates, reduces system costs, eliminates liquid desiccant carryover, and allows for the use of less expensive desiccants, providing effective cooling and dehumidification while minimizing maintenance requirements.
Implementation Method 1
The membrane is permeable to water molecules in a vapor state
Implementation Method 2
water molecules are transferred through the membrane to the liquid desiccant
Implementation Method 3
water molecules are transferred through the membrane to the liquid desiccant
Implementation Method 4
The wall is formed from a material that is impermeable to the liquid but that allows heat to be transferred from the air to the liquid
Implementation Method 5
evaporation of water in air to provide cooling
Implementation Method 6
using the latent heat of evaporation to create cool moist air
Data Source
AI summary
An indirect evaporative cooler for cooling inlet supply air from a first temperature to a second, lower temperature using a stream of liquid coolant and a stream of exhaust or purge air. The cooler includes a first flow channel for inlet supply air and a second flow channel adjacent the first for exhaust air. The first and second flow channels are defined in part by sheets of a membrane permeable to water vapor such that mass is transferred as a vapor through the membrane from the inlet supply air to a contained liquid desiccant for dehumidification and also to the exhaust air as heat is transferred from the inlet supply air to the liquid coolant. A separation wall divides the liquid desiccant and the coolant but allows heat to be transferred from the supply air to the coolant which releases water vapor to the counter or cross flowing exhaust air.