Refrigeration System for Frozen Centrifuges

The core value of a refrigerated centrifuge lies not only in “centrifugation” itself, but even more so in its precise temperature control—allowing it to maintain sample temperatures at -20℃ or even -40℃ while spinning at high speed, thereby preventing biological samples (such as proteins and cell lysates) from becoming inactivated during the centrifugation process.

This refrigeration system can be described as a “refrigerator-air conditioner combo” within a centrifuge. Below, we’ll break down its operating principle and key technologies from five different perspectives.

I. The Four Core Components of a Refrigeration System
1. Compressor (heart)
Function: Compress the refrigerant gas, raising its temperature and pressure.
Type:
Reciprocating compressor: A commonly used traditional model with low cost but high noise levels (similar to a household refrigerator).
Scroll compressors: Standard equipment in high-end models, offering quiet operation, high efficiency, and long service life (e.g., Thermo’s Multifuge series).
2. Condenser (radiator)
Principle: The high-temperature, high-pressure gaseous refrigerant releases heat here and condenses into a liquid.
Design:
Air-cooled: Uses a fan to forcibly dissipate heat (commonly adopted in most models).
Water-cooled: Used when the laboratory has a circulating water system, offering higher cooling efficiency (e.g., Beckman Coulter’s Avanti J-26XP).
3. Evaporator (refrigeration core)
Location: Directly encloses the centrifugal chamber.
Workflow: The liquid refrigerant evaporates here, absorbing heat and “drawing away” the heat from the centrifugal chamber.
4. Expansion valve (flow control)
Function: Regulates the refrigerant flow and controls the evaporator temperature (similar to a throttling valve in a faucet).

II. Working Process of the Refrigeration System (Illustrated Explanation)
Compression and Heating: The compressor compresses the low-temperature, low-pressure gaseous refrigerant (such as R134a) into a high-temperature, high-pressure gas.
Condensation and heat release: High-temperature gas flows through the condenser, releases heat, and then transforms into a medium-temperature, high-pressure liquid.
Throttling and pressure reduction: The liquid passes through an expansion valve, causing a sudden drop in pressure and partial vaporization.
Evaporation absorbs heat: The low-temperature, low-pressure liquid/gas mixture refrigerant absorbs heat in the evaporator, thereby achieving cooling.
Cycle restart: After absorbing heat, the refrigerant returns to the compressor and begins the next cycle.
Key indicators:
Cooling rate: High-end models can reduce the centrifuge chamber temperature from 25℃ to 4℃ within 5 minutes (e.g., Eppendorf 5430R).
Temperature control accuracy: ±1℃ (standard) vs. ±0.1℃ (research-grade model).

III. Two Types of Refrigeration Systems for Frozen Centrifuges

IV. Common Faults in Refrigeration Systems and Self-Help Guidelines
1. Refrigeration failure (the centrifugal chamber fails to cool down)
Possible causes:
Refrigerant leak (oil stains on the piping) → Requires professional leak detection and recharge.
Condenser fouling and poor heat dissipation → Clean the fins with compressed air.
Compressor seized → Replace the compressor (cost ≈ 30% of the equipment price).
2. Large temperature fluctuations
Self-check steps:
Check whether the seal strip on the centrifuge chamber door is aged (leaking cold air).
Confirm whether the sample size is too small (at least 50% of the rotor capacity).
Avoid frequent power on/off cycles (the compressor’s start-up interval should be greater than 3 minutes).
3. Frosting/Icing
Precautions:
After centrifugation, wipe dry any moisture inside the chamber.
Run the “defrost mode” before a prolonged shutdown (if this function is available).

V. A Checklist for Avoiding Pitfalls When Purchasing and Using
1. Select a refrigeration solution based on your needs.
-20℃ Conventional Experiment: Select a dual-compressor model (primary/backup switching, preventing unexpected shutdowns).
4℃ precise temperature control: Semiconductor cooling is quieter (suitable for sensitive environments such as cell culture rooms).
2. Calculate the consumables costs clearly.
The annual maintenance cost for a compressor-based refrigeration unit is approximately 5,000 yuan (refrigerant + labor).
Although semiconductor cooling requires no maintenance, it cools slowly (and the temperature may rebound when operating at high speed).
3. The safety red line must not be crossed.
Prohibit idling the refrigeration system: Running the refrigeration system without samples placed inside will cause the evaporator to freeze and get damaged.
Over-temperature differential startup is strictly prohibited: If the room temperature is 30℃ and you forcibly set the temperature to -20℃, the compressor will be overloaded.

VI. Cutting-Edge Technologies: The Future of Refrigeration Systems
Magnetic Levitation Compressor: Oil-free lubrication, with a 50% longer service life (Hitachi Industrial Machinery’s latest patent).
CO₂ Eco-Friendly Refrigerant: An alternative to Freon, reducing the greenhouse effect (EU mandatory standard).
AI temperature control algorithm: Automatically adjusts cooling power based on rotational speed (reducing energy consumption by 30%).