Transportation refrigeration system
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current transportation refrigeration units (TRUs) face inefficiencies at low load conditions, leading to frequent on/off cycles, reduced energy efficiency, and shortened component life, especially when powered by batteries, due to large temperature fluctuations and reduced battery work time.
Innovation Solution
A TRU system incorporating a damper assembly and routing assembly that directs air and refrigerant flows through pathways with pre-cooled phase change material (PCM), allowing for efficient cooling during high-load conditions and utilizing precooled PCM to maintain temperature during low-load conditions, reducing the need for compressor and condenser fan operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the TRU operates at low load conditions using conventional vapor compression cycle, then the cooling function is maintained, but the system frequently turns on and off leading to lower energy efficiency and larger temperature fluctuations
Solution Approach 1:
The PCM is pre-cooled during high-load conditions or when the TRU is off, storing thermal energy in advance. This preliminary cooling action allows the PCM to provide passive cooling during low-load conditions, eliminating the need for frequent compressor cycling and maintaining temperature stability without energy inefficiency.
Solution Approach 2:
The system utilizes the phase change properties of PCM (transition between solid and liquid states) to store and release thermal energy. During phase transition, the PCM absorbs or releases latent heat at constant temperature, providing stable thermal output during low-load conditions and reducing temperature fluctuations without requiring frequent system cycling.
2Productivity
If the TRU frequently cycles on and off at low load conditions, then the cooling demand is met, but component life is shortened and battery work time is reduced
Solution Approach 1:
The PCM provides continuous passive cooling action during low-load conditions without requiring the compressor to cycle on and off. This continuous thermal energy release from the PCM maintains cooling demand fulfillment while extending component life by reducing mechanical cycling and increasing battery work time by eliminating frequent compressor startup demands.
3Use of energy by moving object
If the TRU uses pre-cooled PCM during low-load conditions, then energy efficiency is improved and temperature fluctuations are reduced, but the system complexity increases with additional pathways and control mechanisms
Solution Approach 1:
The air pathway is segmented into a first pathway through the evaporator and a second pathway through the PCM coil element, allowing independent control of active and passive cooling modes. The refrigerant pathway is similarly segmented with first and second piping systems, enabling the system to route flows through different components based on load conditions without creating excessive complexity.
Solution Approach 2:
The PCM coil element serves multiple functions: it acts as a heat exchanger during high-load conditions and as a passive cooling source during low-load conditions. The damper assembly and routing assembly provide universal control capability for directing both air and refrigerant flows through appropriate pathways based on system demands, reducing the need for separate dedicated components for each mode.
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 solution reduces energy consumption, minimizes temperature fluctuations, and extends battery life by optimizing refrigeration cycles and component longevity, particularly in battery-powered systems.
Implementation Method 1
a coil element surrounded by phase change material (PCM) and disposed in the second pathway
Implementation Method 2
With the PCM pre-cooled, the damper and routing assemblies are controllable to respectively direct the air flows through the first pathway and the refrigerant through the evaporator when first conditions are met
Implementation Method 3
The cold mixture is then routed through the coil or tubes in an evaporator whereupon a fan circulates warm air in the enclosed space across the coil or tubes carrying the cold liquid and vapor refrigerant mixture. The warm air evaporates the liquid part and the circulating air is cooled
Implementation Method 4
The hot, compressed superheated vapor is then condensed within a condenser by air flowing across the coil or tubes of the condenser whereby heat is rejected from the system and carried away by the air
Implementation Method 5
the condensed refrigerant is routed as a saturated or subcooled liquid through an expansion valve where it undergoes an abrupt reduction in pressure resulting in an adiabatic flash evaporation of a part of the refrigerant and lowers the temperature of the liquid and vapor refrigerant mixture
Data Source
AI summary
A transportation refrigeration unit (TRU) system is provided and includes a damper assembly configured to direct air flows through first or second pathways and an evaporator disposed in the first pathway, a coil element surrounded by phase change material (PCM) and disposed in the second pathway and a routing assembly configured to direct refrigerant through the evaporator or the coil element. With the PCM pre-cooled, the damper and routing assemblies are controllable to respectively direct the air flows through the first pathway and the refrigerant through the evaporator when first conditions are met and to respectively direct the air flows through the second pathway when second conditions are met.