Evaporation Heat Transfer Tube Step-Like Structure
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Solution Overview
Problem
Existing evaporation heat transfer tubes face challenges in enhancing heat exchange performance, particularly at lower temperature differences, where nucleate boiling is less efficient due to limited nucleation sites and surface optimization.
Innovation Solution
The evaporation heat transfer tube features a step-like structure on its outer surface, with sharp corners and flanges that intersect with the inter-fin grooves, increasing nucleation sites and reducing condensate film thickness, combined with internal threads to enhance heat exchange coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional machining methods are used to form fins and inter-fin grooves on the tube surface, then the heat transfer area is increased, but the nucleation sites are insufficient and the boiling heat transfer coefficient remains low
Solution Approach 1:
The patent applies porous materials by forming a porous layer on the outer surface of the tube through sintering metal particles. This porous structure provides numerous nucleation sites for bubble formation during boiling, significantly enhancing the boiling heat transfer coefficient while maintaining adequate heat transfer area.
Solution Approach 2:
The patent applies local quality by creating distinct regions with different functions: the porous layer provides nucleation sites, while the fin structures provide heat transfer area. The inter-fin grooves are specifically designed to accommodate the porous material and concentrate refrigerant, creating localized zones of enhanced boiling activity.
2Loss of energy
If the temperature difference in heat transfer is reduced to improve energy efficiency, then energy consumption is decreased, but the nucleate boiling efficiency drops due to insufficient nucleation sites
Solution Approach 1:
The porous layer formed by sintered metal particles provides abundant nucleation sites that enable effective nucleate boiling even at small temperature differences. The porous structure captures and holds refrigerant, ensuring continuous boiling activity without requiring large temperature gradients.
Solution Approach 2:
The patent applies preliminary action by pre-forming the porous structure and inter-fin grooves during manufacturing, which prepares the surface to immediately provide nucleation sites when refrigerant flows through. This pre-prepared nucleation infrastructure enables efficient boiling to occur at lower temperature differences without requiring operational adjustments.
3Quantity of substance
If the inter-fin grooves are made completely sealed to retain refrigerant, then the refrigerant retention is improved, but the heat exchange efficiency through the grooves is reduced
Solution Approach 1:
The inter-fin grooves are filled with porous material that has controlled porosity, allowing it to retain refrigerant through capillary action while still permitting heat transfer. The porous structure holds the refrigerant in place for continuous boiling, yet maintains thermal conductivity for efficient heat exchange between the refrigerant and tube wall.
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 design significantly increases the boiling heat transfer coefficient by over 25% at lower temperature differences, improving heat exchange efficiency and suitability for large-scale applications.
Implementation Method 1
The main mechanism is to utilize the nucleate boiling theory of the flooded evaporation. Machining is carried out to form the fins, knurlings, plain rollings on the outer surface of tube main body 5 and to form porous structures or inter-fin grooves 2 on the outer surface of the tube main body 5, thus providing nucleation sites of nucleate boiling to reinforce the evaporation heat exchange.
Implementation Method 2
This design significantly increases the boiling heat transfer coefficient by over 25% at lower temperature differences, improving heat exchange efficiency and suitability for large-scale applications.
Implementation Method 3
Flooded evaporators have been widely applied in chillers for refrigeration and air conditioning. Most of them are shell-and-tube heat exchangers wherein the refrigerant exchanges heat by phase change outside of the tube and the cooling medium or coolant (e.g. water) exchanges heat by flowing inside of the tube.
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to an evaporation heat transfer tube, which comprises a tube main body and a step-like structure; outer fins are arranged at intervals on the outer surface of the tube main body and an inter-fin groove is formed between two adjacent outer fins; the step-like structure respectively abuts against the bottom plane and one of the side walls of the inter-fin groove. The step-like structure comprises a first surface, a second surface and at least one flange formed by the intersection of the two surfaces, wherein the first and the second surface are intersected respectively with the side wall and the bottom plane. Preferably, the first surface and the side wall are intersected to form a sharp corner; the second surface and the bottom plane are intersected to form a sharp corner, the radius of curvature is 0 to 0.01 mm, the angle formed by the first surface and the side wall is less than or equal to 90 degree, or the angle formed by the second surface and the bottom plane is less than or equal to 90 degree. The height Hr of the step-like structure and the height H of the inter-fin groove meet the following relation: Hr/H is greater than or equal to 0.2. The present invention is ingeniously designed and concisely structured and it remarkably enhances the boiling coefficient between the outer surface and the liquid outside the tube, and it reinforces the heat transfer in boiling and is suitable for large-scale application.