Multi-Compartment Refrigeration Superheat Control Against Evaporator Flooding
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Solution Overview
Problem
Conventional multi-compartment transport refrigeration systems face complexity and instability due to shared evaporating temperatures across compartments, leading to potential flooding and dynamic power disturbances, particularly when cooling perishable and frozen products simultaneously.
Innovation Solution
A controller adjusts the superheat setpoint for each evaporator based on the return air temperatures of both compartments, preventing excessive refrigerant flow and reducing engine instability by calculating an adjusted superheat setpoint (SHadj = SHorg + (RATwarm - RATcold) to manage the difference in cooling demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common suction plenum is used to share evaporating temperature across compartments, then system complexity is reduced, but flooding and overfeeding of evaporators occurs
Solution Approach 1:
The patent divides the common suction plenum into separate suction plenums for each compartment (frozen compartment suction plenum and perishable compartment suction plenum). This segmentation allows independent control of refrigerant flow to each evaporator, preventing flooding while maintaining separate temperature control for each compartment type.
Solution Approach 2:
The patent introduces intermediary components including separate suction plenums, individual expansion valves for each compartment, and a control system that acts as a mediator to regulate refrigerant flow. These intermediaries enable precise control of refrigerant distribution to prevent evaporator flooding while maintaining system reliability.
2Adaptability or versatility
If fixed pulse width modulation is used to control liquid flow to higher temperature compartment, then simultaneous cooling capability is achieved, but engine instability and control instability occur
Solution Approach 1:
The patent replaces fixed pulse width modulation with a dynamic control system that continuously adjusts refrigerant flow based on real-time temperature sensors and compartment conditions. The control system dynamically modulates expansion valves and suction plenum configurations to maintain engine stability while enabling simultaneous cooling of multiple compartments at different temperatures.
Solution Approach 2:
The patent implements feedback control through temperature sensors in each compartment that continuously monitor conditions and feed information back to the control system. This feedback mechanism allows the system to adjust refrigerant flow and pulse width modulation in real-time, preventing engine instability while maintaining simultaneous cooling capability.
3Productivity
If expansion device opens to 100% due to high sensed superheat, then perishable compartment cooling demand is met, but evaporator flooding occurs
Solution Approach 1:
The patent applies local quality control by providing individual expansion valves for each compartment rather than a single shared expansion device. This allows the expansion valve in the perishable compartment to open to 100% when needed for rapid cooling without causing flooding in the frozen compartment evaporator, as each compartment's refrigerant flow is independently controlled.
Solution Approach 2:
By segmenting the refrigerant distribution system into separate suction plenums and expansion valve controls for each compartment, the patent enables the perishable compartment expansion device to operate at full capacity when needed without negatively impacting the frozen compartment evaporator, thus preventing flooding while meeting cooling demands.
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 stabilizes the system, reduces flooding risks, improves efficiency, and extends the life expectancy of expansion devices by minimizing pulsing and transient flooding, leading to better engine stability and reduced refrigerant saturation.
Implementation Method 1
a first evaporator having an first evaporator inlet coupled to the first evaporator expansion device and a first evaporator outlet coupled to the compressor inlet path, the first evaporator for cooling a first compartment of a container at a first temperature
Implementation Method 2
a compressor having a suction port and a discharge port
Implementation Method 3
a heat rejecting heat exchanger downstream of the compressor discharge port
Implementation Method 4
a controller for controlling the first evaporator expansion device in response to a first superheat setpoint and controlling the second evaporator expansion device in response to a second superheat setpoint, the controller adjusting the second superheat setpoint in response to the second temperature and the first temperature
Data Source
AI summary
A multi-compartment transport refrigeration system (10) includes a first evaporator (40) having an first evaporator inlet coupled to a first evaporator expansion device (140) and a first evaporator outlet coupled to a compressor inlet path, the first evaporator for cooling a first compartment of a container at a first temperature; a second evaporator (609 having a second evaporator inlet coupled to a second evaporator expansion device (160) and a second evaporator outlet coupled to the compressor inlet path, the second evaporator for cooling a second compartment of the container at a second temperature greater than the first temperature; and a controller (550) for controlling the first evaporator expansion device in response to a first superheat setpoint and controlling the second evaporator expansion device in response to a second superheat setpoint, the controller adjusting the second superheat setpoint in response to the second temperature and the first temperature.