Ionic liquid additives for use as an absorbent in absorption chillers
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Solution Overview
Problem
Conventional absorption chillers using lithium bromide (LiBr) as an absorbent face challenges due to its limited solubility and risk of crystallization, which can lead to system damage and require costly corrective actions, especially at higher concentrations and lower temperatures.
Innovation Solution
The addition of specific imidazolium bromide ionic liquids as additives to the lithium bromide-water working pair in absorption chillers expands the solubility range of the absorbent materials, reducing the crystallization risk and lowering the crystallization temperature, thereby enhancing the operational range of the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium bromide concentration is increased to improve absorption efficiency, then the absorbent's ability to absorb refrigerant vapor improves, but the risk of crystallization increases
Solution Approach 1:
An ionic liquid is introduced as an intermediary substance added to the lithium bromide absorbent. This intermediary modifies the absorbent's properties by lowering its crystallization temperature and adjusting its solubility characteristics, allowing the system to maintain high absorption efficiency while operating at lower concentrations to avoid crystallization
Solution Approach 2:
The crystallization temperature parameter of the absorbent is changed through the addition of ionic liquid. This parameter modification allows the absorbent to remain in liquid phase at lower temperatures and concentrations, expanding the safe operating range while maintaining absorption performance
2Productivity
If lithium bromide concentration is increased to enhance refrigerant absorption, then absorption performance improves, but system safety deteriorates due to potential crystallization damage
Solution Approach 1:
The ionic liquid acts as a safety mediator that modifies the absorbent's phase behavior. By lowering the crystallization temperature, it creates a safety buffer that prevents crystallization damage while allowing the system to operate at higher concentrations for improved absorption performance
Solution Approach 2:
The ionic liquid provides beforehand cushioning against crystallization by pre-modifying the absorbent's properties. This preventive measure ensures that even at high concentrations, the absorbent remains in liquid phase under normal operating conditions, cushioning the system against potential crystallization damage
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 use of imidazolium bromide ionic liquids as additives effectively suppresses the crystallization temperature of LiBr, expanding the working range of absorption chillers and preventing system damage, while maintaining the desired thermophysical properties and performance.
Implementation Method 1
The imidazolium bromide ionic liquid is used as an additive to lower the crystallization temperature of the absorbent
Implementation Method 2
The absorbent in the system should have a great tendency towards the refrigerant by dissolving it readily under the operating conditions of the system
Implementation Method 3
LiBr is a very efficient absorbent for water refrigerant due to its high hygroscopicity. LiBr, which as a pure salt has a melting temperature of 552°C, can absorb water to a high enough degree such that it becomes completely dissolved in the water it has absorbed
Implementation Method 4
The low pressure in the evaporator provides the benefit of evaporation of the refrigerant at lower temperatures, thereby making the system capable of producing a chilling effect at low temperatures
Implementation Method 5
Latent heat is consumed for the evaporation of the refrigerant, which provides a means of chilling
Implementation Method 6
an efficient absorbent is needed to thoroughly absorb the refrigerant vapor (which has been previously vaporized) by releasing latent heat to a cooling water stream and change it back into the liquid phase
Data Source
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AI summary
This invention relates to using an imidazolium bromide ionic liquid as an additive to lithium bromide in the absorbent for an absorption chiller. The imidazolium bromide ionic liquid is useful to increase the working region and to lower the risk of crystallization in an absorption chiller. The invention provides an absorption chiller comprising a mixture of a refrigerant and an absorbent, and the absorbent comprises lithium bromide and one or more imidazolium bromide ionic liquids.