Liquid Line Subcooling for Fast Pull-Down Vehicle Refrigerators
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Solution Overview
Problem
Conventional vapor cycle refrigeration systems in vehicles, such as aircraft, face challenges in quickly reducing the temperature of food and beverage compartments from ambient to refrigerated temperatures without increasing the size and weight of the refrigeration units, which is necessary for efficient initial cooling without the need for oversized components.
Innovation Solution
Incorporating a thermoelectric device (TED) sub-cooler into the refrigeration system, which works in conjunction with the vapor cycle system to enhance cooling capacity by sub-cooling the refrigerant, allowing for faster temperature reduction without significantly increasing the system's size or weight, and controlling the TED sub-cooler based on temperature thresholds to optimize energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the components of the vapor cycle system are made larger and heavier to increase cooling capacity, then the temperature can be pulled down more quickly, but the size and weight of the refrigeration unit increases
Solution Approach 1:
The refrigeration system is segmented into two distinct cooling subsystems: a vapor cycle system for steady-state cooling and a thermoelectric device (TED) subsystem for rapid initial cooling. This segmentation allows each subsystem to be optimized for its specific function, with the TED providing high-power pulse cooling without requiring the entire vapor cycle system to be oversized.
Solution Approach 2:
The thermoelectric device performs preliminary cooling action during the initial transient phase when the compartment temperature needs to be pulled down rapidly. By handling the initial high heat load with the TED, the system prepares the compartment for subsequent steady-state maintenance by the vapor cycle system, avoiding the need for oversized components throughout.
2Productivity
If the components of the vapor cycle system are made larger and heavier to increase cooling capacity, then the temperature can be pulled down more quickly, but the space occupied by the refrigeration unit increases
Solution Approach 1:
The refrigeration system is segmented into two distinct cooling subsystems: a vapor cycle system for steady-state cooling and a thermoelectric device (TED) subsystem for rapid initial cooling. This segmentation allows each subsystem to be optimized for its specific function, with the TED providing high-power pulse cooling without requiring the entire vapor cycle system to be oversized.
Solution Approach 2:
The thermoelectric device performs preliminary cooling action during the initial transient phase when the compartment temperature needs to be pulled down rapidly. By handling the initial high heat load with the TED, the system prepares the compartment for subsequent steady-state maintenance by the vapor cycle system, avoiding the need for oversized components throughout.
3Measurement precision
If the TED sub-cooler is operated continuously to maintain set temperature, then temperature control precision is improved, but energy consumption increases
Solution Approach 1:
The control system dynamically adjusts the operation of the TED sub-cooler based on real-time temperature measurements. The TED is activated when the compartment temperature approaches the setpoint threshold and deactivated when the temperature is maintained within the desired range, creating a dynamic on-off control pattern that maintains precision while minimizing energy consumption.
Solution Approach 2:
The system employs feedback control by continuously monitoring the compartment temperature and using this information to control the TED sub-cooler operation. When the temperature sensor detects that the temperature has reached or exceeded the threshold, the controller activates the TED; when the temperature is maintained within the maintenance range, the TED is deactivated, ensuring precise control with minimal energy use.
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 integration of the TED sub-cooler increases the cooling capacity of the refrigeration system, enabling quicker temperature reduction during initial cooling phases while maintaining efficiency during steady-state operation, thus reducing the need for oversized components and minimizing fuel costs by keeping the system lightweight and compact.
Implementation Method 1
a thermoelectric device (TED) sub-cooler... controlling the TED sub-cooler when the temperature is greater or equal to the preset threshold
Data Source
AI summary
A vapor cycle refrigeration system includes a thermoelectric device (TED) as a sub-cooler to sub-cool liquid refrigerant exiting a condenser to increase cooling capacity of an evaporator and pull down temperature within a refrigerated compartment quickly. The TED sub-cooler is turned off after initial temperature pull down and is not operated during steady state operation for maintenance of the compartment temperature.