Refrigerator Door Frame Composite Structure for Thermal Breaks
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Solution Overview
Problem
Existing refrigerated display case door frames face challenges with insufficient thermal insulation, leading to exterior condensation and structural issues due to high thermal conductivity and coefficient of thermal expansion (CTE), which results in increased energy consumption for anti-sweat heaters and potential cracking from thermal shrinkage.
Innovation Solution
A thermally efficient door frame design featuring an aluminum/PVC/aluminum sandwich structure with PVC foam insulation and compliant adhesive or acrylic tape, where PVC middle plastic sections are thermally welded and not adhered to each other, providing a thermal break and structural integrity while minimizing thermal shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If aluminum or fiberglass materials are used for door frames, then structural strength and low CTE are achieved, but thermal insulation is insufficient leading to exterior condensation
Solution Approach 1:
The patent employs a composite door frame structure consisting of an inner aluminum member providing structural strength and low CTE, an outer PVC member providing superior thermal insulation, and foam rubber inserts filling the interface between members. This composite construction combines the advantageous properties of different materials to simultaneously achieve structural integrity and thermal efficiency, preventing exterior condensation while maintaining frame strength.
2Loss of energy
If rigid PVC is used for door frames, then thermal resistance is superior, but high CTE causes significant thermal shrinkage leading to cracking
Solution Approach 1:
The patent creates a composite structure where rigid PVC provides thermal resistance while an inner aluminum member absorbs thermal expansion and contraction stresses. The aluminum's low CTE compensates for the PVC's high CTE, preventing cracking during thermal cycles while the PVC maintains superior thermal resistance.
Solution Approach 2:
The patent incorporates foam rubber inserts at the interface between the aluminum and PVC members. This flexible material accommodates differential thermal expansion and contraction between the two rigid members, allowing the structure to expand and contract without generating cracking stresses, thus maintaining stability during temperature variations.
3Strength
If aluminum jambs are welded to header and sill members, then structural joint strength is achieved, but thermal infiltration increases at joint locations
Solution Approach 1:
The patent replaces metal-to-metal welded joints with a composite joint system where foam rubber inserts are placed between the aluminum jambs and the header/sill members. This foam rubber barrier interrupts the thermal conduction path at the joint locations, significantly reducing thermal infiltration while the foam's adhesive properties maintain joint strength without requiring welding.
4Ease of manufacture
If molded plastic brackets are used to screw frame together, then ease of assembly is improved, but thermal conductivity at bracket locations creates cold spots and condensation
Solution Approach 1:
The patent eliminates the need for separate molded plastic brackets by integrating the joining function into the foam rubber inserts themselves. The foam material provides both mechanical attachment capability and thermal insulation, creating a thermally broken joint that avoids the cold spots and condensation issues associated with conductive plastic brackets while maintaining ease of assembly.
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 solution significantly reduces energy consumption for anti-sweat heaters and prevents cracking by maintaining structural integrity and enhancing thermal insulation, ensuring effective condensation prevention and durability.
Implementation Method 1
the thermal insulation of this construction is insufficient for the exterior to stay above the ambient dewpoint
Implementation Method 2
PVC middle plastic sections are thermally welded and not adhered to each other, providing a thermal break and structural integrity
Data Source
AI summary
A door frame for a refrigerator display case that includes an inner metal member, an outer metal member, and first and second single plastic modules sandwiched between the inner and outer metal members. The inner and outer metal members and first and second plastic modules cooperate to define first and second door openings. The first and second single plastic modules each include a jamb middle plastic section, a header middle plastic section, a sill middle plastic section and a mullion middle plastic section. The first and second single plastic modules are adhered to the inner metal member and the outer metal member, and the first mullion plastic section and the second mullion plastic section are not adhered to one another.