Parallel Flow Heat Exchanger Circuiting for Reversible Heat Pumps
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Solution Overview
Problem
Parallel flow heat exchangers face challenges in optimizing heat exchanger circuiting for both cooling and heating modes, particularly in maintaining a balance between refrigerant heat transfer and pressure drop characteristics, and suffer from refrigerant maldistribution issues due to design limitations and flow reversal requirements in heat pump systems.
Innovation Solution
The design incorporates variable length converging and diverging circuits, with refrigerant flow reversal capabilities, and utilizes check valves and multiple expansion devices to optimize refrigerant distribution and pressure drop balance in both cooling and heating modes, enhancing performance and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If parallel flow heat exchanger uses fixed circuit configuration, then manufacturing is simple, but performance cannot be optimized for both cooling and heating modes
Solution Approach 1:
The heat exchanger employs variable length circuits that dynamically adapt refrigerant flow distribution based on operational mode. In cooling mode, the circuit configuration optimizes for condenser performance, while in heating mode, it optimizes for evaporator performance, allowing the system to maintain optimal heat transfer characteristics across different operating conditions without requiring multiple separate heat exchangers.
Solution Approach 2:
The invention changes the effective circuit configuration parameters by utilizing expansion devices and flow control mechanisms to adjust refrigerant distribution across the parallel circuits. By varying expansion ratios and flow resistance in different circuit paths, the system optimizes heat transfer performance for either cooling or heating operation while using the same physical heat exchanger structure.
2Adaptability or versatility
If refrigerant flow is reversed between modes, then heat pump functionality is achieved, but refrigerant maldistribution occurs
Solution Approach 1:
The heat exchanger incorporates locally optimized circuit configurations with varying lengths and flow resistance characteristics in different sections. By creating non-uniform local properties in the parallel circuits, the system compensates for refrigerant maldistribution issues that arise during flow reversal, ensuring more uniform refrigerant distribution in both cooling and heating modes through differential flow path design.
Solution Approach 2:
Expansion devices and flow control elements serve as intermediary components between the refrigerant source and the heat exchange circuits. These intermediaries actively regulate refrigerant flow distribution to each parallel circuit, compensating for imbalances caused by flow reversal and ensuring reliable, uniform distribution regardless of operational mode.
3Ease of manufacture
If equal number of circuits are used for both modes, then design is simplified, but heat transfer and pressure drop balance is compromised
Solution Approach 1:
The heat exchanger employs asymmetric circuit design where parallel circuits have different lengths and flow path characteristics. This asymmetry is deliberately introduced to balance heat transfer and pressure drop for the specific operational mode being optimized, sacrificing design simplicity to achieve superior thermal performance and pressure drop balance in either cooling or heating 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
This approach allows for improved heat transfer and pressure drop balance, reducing refrigerant maldistribution and enhancing overall system performance and reliability in heat pump applications by adapting circuit configurations based on operational modes.
Implementation Method 1
heat is removed from the refrigerant during heat transfer interaction with a secondary fluid such as air
Implementation Method 2
heat transfer interaction with a secondary fluid such as air, blown over the condenser external surfaces by an air-moving device such as fan
Implementation Method 3
the refrigerant is desuperheated, condensed and typically subcooled
Implementation Method 4
refrigerant, during heat transfer interaction, cools air (or other secondary fluid) delivered to a conditioned space by an air-moving device such as fan. While the refrigerant, that is evaporated and superheated, cools the air flowing over the indoor heat exchanger
Implementation Method 5
the refrigerant flows through the expansion device, where it is expanded to a lower pressure and temperature
Data Source
AI summary
A parallel flow heat exchanger system (10, 50, 100, 200) for heat pump applications in which single and multiple paths of variable length are established via flow control systems which also allow for refrigerant flow reversal within the parallel flow heat exchanger system (10, 50, 100, 200), while switching between cooling and heating modes of operation. Examples of flow control devices are an expansion device (80) and various check valves (70, 72, 74, 76). The parallel flow heat exchanger system may have converging or diverging flow circuits and may constitute a single-pass or a multi-pass evaporator together with and a multi-pass condenser.