Single-circuit refrigerator
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Solution Overview
Problem
Existing single-circuit refrigeration devices with two temperature zones struggle to regulate pressure differences between evaporators effectively, leading to inefficient cooling capacity distribution and temperature fluctuations.
Innovation Solution
Incorporating a series connection of an expansion valve and capillary, with a controllable expansion valve adjusting the flow conductance to create a variable pressure drop between evaporators, and using a heat exchanger to preheat refrigerant vapor before the first evaporator, allowing for partial evaporation and reducing noisy throughput fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a capillary is used to connect evaporators in series, then the pressure difference between evaporators is determined by compressor throughput, but the regulation of pressure difference is insufficient and evaporation temperatures cannot be precisely controlled
Solution Approach 1:
The throttle device is segmented into two independent parts: a capillary (first throttle section) and an expansion valve (second throttle section). The capillary provides a fixed pressure drop that prevents refrigerant vapor from reaching the expansion valve, while the expansion valve independently regulates the pressure difference between evaporators. This segmentation allows precise evaporation temperature control without excessive complexity.
Solution Approach 2:
The capillary acts as an intermediary element between the condenser and the expansion valve. It creates a fixed pressure drop that ensures refrigerant arrives at the expansion valve in liquid form, preventing vapor lock and enabling the expansion valve to precisely control the pressure difference and evaporation temperature in the first evaporator.
2Temperature
If evaporators are connected without flow resistance between them, then pressures are approximately the same, but the temperature difference between evaporators and warmer zones becomes excessively large
Solution Approach 1:
The expansion valve provides dynamic control of the pressure difference between evaporators. By adjusting the valve opening, the system can optimize the pressure difference to match varying cooling demands in different zones, enabling flexible and efficient cooling capacity distribution rather than a fixed temperature distribution.
3Stress or pressure
If the expansion valve is solely responsible for pressure drop, then pressure regulation is flexible, but refrigerant vapor may reach the valve causing noisy fluctuations
Solution Approach 1:
The capillary performs a preliminary pressure drop before the refrigerant reaches the expansion valve. This preliminary action ensures that refrigerant arrives at the expansion valve as liquid, preventing vapor from reaching the valve and causing noisy fluctuations. The capillary's fixed pressure drop is established in advance to protect the expansion valve's operation.
Solution Approach 2:
The function of creating pressure drop is extracted from the expansion valve and divided between two elements: the capillary handles the preliminary pressure drop to prevent vapor arrival, while the expansion valve handles the regulated pressure drop for temperature control. This extraction of functions eliminates the harmful effect of vapor reaching the expansion valve.
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 enables precise regulation of pressure differences and cooling capacity distribution between evaporators, improving energy efficiency by avoiding start-stop losses and temperature fluctuations, while maintaining overall cooling capacity and preventing noisy mass flow oscillations.
Implementation Method 1
When the refrigerant vapor reaches the downstream section of the suction line, it is already preheated by the second heat exchanger to a temperature that is at most slightly below the evaporation temperature in the first evaporator.
Implementation Method 2
Because the expansion valve is connected in series with the capillary, the pressure drop is made up of a fixed contribution from the capillary and a variable contribution from the expansion valve.
Implementation Method 3
the flow resistance of the capillary is constant; therefore, when the compressor is running, the difference in pressure between the evaporators and thus also the difference in their evaporation temperatures is determined by the throughput of the compressor
Implementation Method 4
A cooling of the refrigerant in the first throttle section to a temperature below the evaporation temperature of the first evaporator can thus be ruled out. Partial evaporation of the refrigerant in the first throttling section thus remains possible
Data Source
Figure 1~2
Figure 3~5
AI summary
In the refrigerant circuit of a single-circuit refrigerator, the following are connected in series one after another between a pressure port (2) and an intake port (3) of a compressor (1): a condenser (5), a first throttle section (6), a first evaporator (8) for cooling a first temperature zone (16) of the single-circuit refrigerator, a second throttle section (9), a second evaporator (10) for cooling a second temperature zone (17) of the single circuit refrigerator, and an intake line (11). A downstream section (13) of the intake line (11) is connected with the first throttle section (6) to a first heat exchanger (15), and an upstream section (12) of the intake line (11) is connected with the second throttle section (9) to a second heat exchanger (14).