Coaxial Heat Exchanger Geometry for Reversible Evaporation and Condensation
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Solution Overview
Problem
Existing coaxial heat exchangers with axially parallel fins exhibit low heat transfer due to minimal turbulence, and they are not scalable or cost-effective for reversible operation as both an evaporator and a condenser.
Innovation Solution
A coaxial heat exchanger design featuring ribs on the inner tube and projections on the outer tube that form parallel channels, with optimized cross-sectional areas and angles to enhance turbulence and heat transfer, allowing for reversible operation and easy scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If axially parallel fins are used in coaxial heat exchangers, then pressure drop is reduced, but heat transfer is significantly impaired due to minimal turbulence
Solution Approach 1:
The patent replaces straight axially parallel fins with helically curved fins that wrap around the inner tube in a spiral pattern. This curvature creates turbulence in the fluid flow by continuously changing the flow direction, significantly improving heat transfer efficiency while maintaining acceptable pressure drop characteristics.
Solution Approach 2:
The helical fins create periodic disturbances in the fluid flow as the fluid moves through the heat exchanger. This periodic action generates controlled turbulence that enhances heat transfer by preventing boundary layer formation and improving fluid mixing, while the regular spacing maintains flow stability.
2Adaptability or versatility
If a coaxial heat exchanger is designed for reversible operation, then versatility is improved, but achieving equal thermal output in both modes increases design complexity
Solution Approach 1:
The heat exchanger is designed with symmetric thermal characteristics by matching the thermal output in both evaporation and condensation modes. The helical fin configuration and balanced channel design enable the same heat exchanger to function effectively as both an evaporator and a condenser, providing universal applicability without requiring separate units for each mode.
Solution Approach 2:
The patent optimizes geometric parameters such as fin pitch, fin height, and channel dimensions to achieve balanced thermal performance in both operating modes. By carefully selecting these parameters, the heat exchanger can deliver equal thermal output whether operating as an evaporator or condenser, simplifying the reversible operation design.
3Area of stationary object
If the flowable cross-sectional area between tubes is increased, then heat transfer area is improved, but the ratio to inner tube area becomes unbalanced affecting flow conditions
Solution Approach 1:
The patent systematically varies geometric parameters including the number of fins, fin height, fin pitch, and inner tube diameter to optimize the ratio between the flowable cross-sectional area and the inner tube cross-sectional area. This ensures adequate heat transfer area while maintaining proper flow velocity and pressure drop characteristics for efficient operation.
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 design achieves comparable thermal performance in both evaporation and condensation modes, with improved heat transfer and flexibility in capacity adjustment, while maintaining efficient flow conditions.
Implementation Method 1
axially parallel, smooth fins cause only slight turbulence of the medium flowing in the channels and therefore do not significantly improve heat transfer
Implementation Method 2
coaxial heat exchanger for reversible operation that is improved in terms of cost and performance
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a coaxial heat exchanger (1) for reversible operation, comprising an inner tube (2) with a tube axis (10), a tube wall (20), an outer surface (21) and an inner surface (22), wherein the inner tube (2) has a flowable cross-sectional area (A1) and wherein ribs (25) with a rib height (H1) are formed on the outer surface (21) of the inner tube (2), and comprising an outer tube (3) arranged coaxially to the inner tube (2) with a tube wall (30), an outer surface (31) and an inner surface (32), wherein projections (35) are formed on the inner surface (32) of the outer tube (3) which extend substantially radially from the tube wall (30) of the outer tube (3) and extend continuously parallel to the axis or helically along the inner surface (32) of the outer tube (3), wherein the projections (35) of the outer tube (3) are connected to the ribs (25) on the outside (21) of the inner tube (2) enclose an angle of at least 60° and are connected to these,wherein several parallel, flowable channels (4) are formed between the pipe wall (30) of the outer tube (3) and the tips (26) of the ribs (25) of the inner tube (2), each having a cross-sectional area (A2) measured transversely to the flow direction and a channel height (H2), wherein adjacent channels (4) are each separated from one another by a projection (35) of the outer tube (3), and wherein the ratio of the flowable cross-sectional area (A1) of the inner tube (2) to the sum of the cross-sectional areas (A2) of all channels (4) is at least 0.5 and at most 5. The invention further relates to a thermodynamic cycle with such a coaxial heat exchanger and a method for operating such a cycle.