Closed-Cycle Cryogenic Engine With Water-Evaporation Heat Sink
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Solution Overview
Problem
Existing heat engines fail to efficiently harness ambient thermal energy for mechanical work due to limitations imposed by the Kelvin-Planck statement of the second law of thermodynamics, and prior cryogenic engines operate at low power densities or consume working fluids, making them impractical for widespread use.
Innovation Solution
A closed-cycle cryogenic engine design that uses hydrogen as a working fluid with a high specific heat and low critical temperature, remaining in a gaseous phase, and creates an artificial low-temperature heat sink by evaporating water to absorb heat of compression, allowing for isothermal recompression and repeated heat exchange with the ambient environment to generate mechanical work at high power densities without consuming the working fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If prior cryogenic engines are used to extract thermal energy from the environment, then mechanical work can be generated, but the power density is very low
Solution Approach 1:
The patent changes the operating parameters by using a working fluid with a critical temperature below ambient temperature (such as nitrogen, oxygen, or hydrogen) and operating the heat engine at temperatures above the fluid's critical temperature. This allows the fluid to remain in a supercritical or gaseous state throughout the cycle, enabling high-density energy extraction and high power density while maintaining continuous operation.
2Power
If liquefied gas is compressed to very high pressure to extract thermal energy, then mechanical work can be generated, but the working fluid is consumed and must be continuously replenished
Solution Approach 1:
The patent extracts only the thermal energy from the ambient environment through the working fluid, while the fluid itself remains in a closed循环 system. The working fluid is not consumed but continuously recycled through compression, expansion, and heat exchange processes, eliminating the need for continuous replenishment while maintaining high power output.
Solution Approach 2:
The patent implements a continuous closed-cycle operation where the working fluid continuously circulates through the heat engine system, absorbing thermal energy from the ambient environment, converting it to mechanical work, and returning to its initial state. This continuous cyclic operation ensures uninterrupted power generation without fluid consumption or depletion.
3Use of energy by moving object
If the second law of thermodynamics is strictly applied, then heat engines cannot operate with a single heat reservoir, but ambient thermal energy cannot be harnessed
Solution Approach 1:
The patent introduces a working fluid with critical temperature below ambient temperature as an intermediary between the ambient thermal energy (single heat reservoir) and the mechanical work output. This intermediary fluid enables heat absorption and conversion processes that effectively bridge the gap between the single-reservoir environment and the requirements for useful work extraction, circumventing the apparent contradiction with the second law.
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 engine achieves high power densities and efficient conversion of ambient heat into mechanical work, reducing environmental pollution and operational costs, as it operates indefinitely on water, a readily available and cost-free resource, while avoiding the limitations of traditional cryogenic engines.
Implementation Method 1
feeding it into a heat exchanger maintained in thermal contact with large amounts of flowing atmospheric air at ambient temperature where it is isobarically heated to ambient temperature
Implementation Method 2
The natural heat energy of the environment is extracted by isothermally compressing the gaseous working fluid at a sub-ambient temperature created by evaporating water
Implementation Method 3
isothermally compressing the gaseous working fluid at a sub-ambient temperature created by evaporating water to a pressure exceeding 500 Bar by absorbing the heat of compression
Implementation Method 4
fed into the first isentropic cryogenic expander of a large plurality of serially connected cryogenic expanders having very low pressure ratios that isentropically expands the compressed working fluid
Data Source
AI summary
A closed-cycle cryogenic engine includes a high specific heat working fluid remaining in a gaseous phase. The high temperature heat reservoir is the natural environment and the low temperature heat reservoir is created artificially by evaporating water. Isothermally compressing the working fluid at low temperature by absorbing compression heat by evaporating water extracts heat energy from the environment, converting it into net output. A plurality of serially connected isentropic expanders is interposed with a like plurality of re-heating stages. The temperature difference between the high and low temperature heat reservoirs is a few degrees, allowing expansion operation with low expansion ratios, enabling a large number of expanding and reheating steps Each engine cycle extracts natural heat energy from the environment, converting a large fraction into high density net output work. Very little water, the engine's only fuel, is consumed since evaporating water's latent heat is high.