Composite Closure Bars for Plate Fin Heat Exchangers

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Solution Overview

Problem

In plate fin heat exchangers, the rapid thermal expansion of closure bars due to high velocity hot air and the high thermal expansion coefficient of materials like aluminum can cause physical damage to components, such as crushing of heat transfer fins, due to restrained expansion.

Innovation Solution

The use of an inner core with a lower coefficient of thermal expansion, such as titanium, surrounded by an outer cladding with a higher coefficient of thermal expansion, like aluminum, reduces the overall thermal expansion properties of the closure bars, preventing damage and facilitating attachment to other components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If closure bars are formed of aluminum with high heat transfer coefficient, then heat transfer efficiency is improved, but thermal expansion causes physical damage to components

Engineering Contradiction:

Improveheat transfer efficiencyVSAvoidcomponent integrity

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The closure bar employs a composite structure with an aluminum outer cladding for high heat transfer coefficient and an inner core made of low thermal expansion material (such as Invar or titanium) to minimize thermal expansion. This composite design allows the closure bar to maintain excellent thermal conductivity while resisting dimensional changes under thermal stress, thereby preventing damage to heat transfer fins and other components.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

Different portions of the closure bar are made of different materials with different properties. The outer cladding is aluminum for heat transfer, while the inner core is a low expansion material for dimensional stability. This local differentiation of material properties allows each region of the closure bar to fulfill its specific function optimally.

Inventive Principle:

Principle #3Local quality

2Productivity

If high velocity hot air flows over closure bars, then heat transfer is enhanced, but rapid thermal expansion occurs causing component damage

Engineering Contradiction:

Improveheat transfer rateVSAvoidthermal expansion damage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The composite closure bar structure with aluminum cladding and low expansion inner core enables the bar to withstand rapid heating from high velocity hot air flow. The aluminum cladding conducts heat efficiently while the inner core restrains thermal expansion, preventing the harmful effects of rapid dimensional changes even under intense thermal conditions.

Inventive Principle:

Principle #40Composite materials

3Stability of the object's composition

If corners of heat exchanger restrain overall expansion, then structural stability is maintained, but stress concentration causes physical damage to core components

Engineering Contradiction:

Improvestructural stabilityVSAvoidstress concentration

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The solution extracts the problematic thermal expansion characteristic from the closure bar by using an inner core material with very low thermal expansion coefficient. This removes the source of stress concentration that would otherwise be restrained by the heat exchanger corners, while maintaining the necessary structural stability for proper functioning.

Inventive Principle:

Principle #2Taking out (Extraction)

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 configuration enhances the reliability and longevity of plate fin heat exchanger components by minimizing stress and physical damage from thermal expansion, ensuring efficient heat transfer and maintaining structural integrity.

Implementation Method 1

a combination of a high velocity of hot air at the inlet and a relatively high coefficient of thermal expansion of aluminum can cause rapid physical expansion of the closure bars

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

Heat is transferred between the hot and cool air via the heat transfer sheets that separate the layers

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 3

The heat transfer fins increase turbulence and a surface area that is exposed to the airflow, thereby enhancing heat transfer between the layers

Methodology Applied

Scientific EffectTurbulence: Turbulence

Data Source

PatentUS9777970B2Reduced thermal expansion closure bars for a heat exchanger

Publication Date: 2017.10.03 HAMILTON SUNDSTRAND CORP

AI summary

A plate fin heat exchanger is configured to receive hot flow from a hot source and cool flow from a cool source. The plate fin heat exchanger includes a plurality of plates arranged in parallel to define a plurality of flow passages there between, and a set of closure bars arranged at a first side of the plurality of plates to seal a first set of the flow passages against ingress of the hot flow, thereby directing the hot flow into a second set of the flow passages. Each respective closure bar includes an inner core formed of a first material having a first coefficient of thermal expansion and an outer cladding arranged about the inner core, the outer cladding formed of a second material having a second coefficient of thermal expansion. The first coefficient of thermal expansion is less than the second coefficient of thermal expansion.