Laundry dryer including a heat pump system
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Solution Overview
Problem
Current heat pump systems in laundry dryers rely on high-GWP refrigerants like HFCs, which contribute to global warming, and alternative flammable refrigerants like hydrocarbons face charge limitations due to safety concerns, affecting energy efficiency and drying performance.
Innovation Solution
The design of finned tube heat exchangers with specific configurations, including a central portion in contact with fins and end portions not in contact with fins, optimized for the refrigerant flow, allows for improved heat exchange efficiency and reduced refrigerant volume, using flammable hydrocarbons like propane or propylene with low GWP.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If flammable refrigerants like hydrocarbons are used to replace high-GWP refrigerants, then global warming impact is reduced, but safety concerns require charge limitations
Solution Approach 1:
The invention changes the physical parameters of the heat exchanger system by optimizing the surface area-to-volume ratio through specific geometric configurations (finned tubes with optimized fin spacing and tube dimensions). This allows achieving the required heat exchange capacity with reduced refrigerant charge, thereby resolving the contradiction between using flammable refrigerants and maintaining safety charge limits while still providing effective heat transfer performance
2Reliability
If refrigerant charge is reduced to meet safety regulations, then safety is improved, but heat exchange efficiency may deteriorate
Solution Approach 1:
The invention optimizes heat exchanger parameters including fin spacing, tube diameter, and surface area configuration to maximize heat transfer coefficient and surface area-to-volume ratio. These parameter changes enable efficient heat exchange with minimal refrigerant charge, thus maintaining safety while preventing deterioration of heat exchange efficiency
Solution Approach 2:
The invention employs composite heat exchanger structures combining tubes with finned surfaces, where the finned tube configuration creates a composite thermal transfer system that enhances heat exchange efficiency per unit volume of refrigerant, allowing reduced charge while maintaining effective heat transfer
3Loss of energy
If heat exchanger surface area is increased to improve heat exchange, then energy efficiency is improved, but refrigerant volume requirement increases
Solution Approach 1:
The invention changes the geometric parameters of the heat exchanger to optimize the surface area-to-volume ratio. By using finned tubes with specific fin spacing and tube dimensions, the system achieves high heat exchange efficiency with compact volume, thereby improving energy efficiency without proportionally increasing refrigerant volume requirements
Solution Approach 2:
The invention adds dimensional complexity to the heat exchanger design through finned tube structures, where fins extend in the radial dimension to increase heat transfer surface area without proportionally increasing the axial or radial footprint of the heat exchanger, thus achieving high energy efficiency with compact refrigerant volume
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 energy efficiency, reduces energy consumption, and minimizes the impact on global warming while adhering to safety regulations by optimizing the use of flammable refrigerants, achieving better drying performance and eco-friendliness.
Implementation Method 1
said first and/or second heat exchanger being apt to perform heat exchange between said refrigerant flowing in said refrigerant circuit and said process air
Implementation Method 2
a compressor to pressurize and circulate the refrigerant through the refrigerant circuit
Implementation Method 3
the process air stream is cooled down and dehumidified in an evaporator
Implementation Method 4
the process air stream is cooled down and dehumidified in an evaporator, heated up in a condenser
Data Source
Figure 1
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AI summary
The invention relates to a dryer (1) including ∘ A treating chamber (3) where items are introduced and treated with a process air flow; ∘ a heat pump system (30) having a refrigerant circuit in which a refrigerant can flow, said refrigerant circuit including a first heat exchanger (32) where the refrigerant is heated up, a second heat exchanger (31) where the refrigerant is cooled off, a compressor (33) to pressurize and circulate the refrigerant through the refrigerant circuit, and a pressure-lowering device; said first and/or second heat exchanger (32, 31) being apt to perform heat exchange between said refrigerant flowing in said refrigerant circuit and said process air; the refrigerant being a flammable refrigerant; ∘ wherein each of said first and second heat exchanger (32, 31): ▪ is a finned tube heat exchanger comprising a tube (40) having multiple sections (41) one above the other and a plurality of fins (50); ▪ is divided in three portions: a central portion (60) wherein said multiple sections (41) of the tube are in contact with said plurality of fins (50), and a first and second end portions (61, 62) where said tube (40) is not in contact with the plurality of fins (50); ∘ and wherein a ratio between a total external volume (TEV2) of all sections of the tube included in the central portion (60) in contact with the plurality of fins of the second heat exchanger (31) and a total external volume (TEV1) of all sections of the tube included in the central portion (60) in contact with the plurality of fins of the first heat exchanger (32) has a value lower than 0.95.