Low-Temperature Circulating Constant Temperature Bath
The circulating low temperature constant temperature bath is an experimental device for precise temperature control. It is widely used in low temperature performance tests of fluids such as lubricating oil, hydraulic oil, fuel, coolant, and viscosity measurement experiments.
Equipment composition
| Component | Function |
|---|---|
| Cooling system (compressor + refrigerant) | Provide low temperature environment |
| Heating system (electric heater) | Precise temperature control |
| Circulation pump | Provides stable temperature uniformity |
| Constant temperature bath (with liquid level indicator) | Storage of experimental media, such as alcohol or coolant |
| Temperature controller (PID control) | Set and maintain target temperature with an accuracy of ±0.1°C |
| External loop interface | Can be connected to external experimental devices to provide stable low-temperature medium |
Main technical parameters
| Parameter | Typical range |
|---|---|
| Temperature range | -80°C ~ 100°C (depending on model) |
| Temperature stability | ±0.01°C ~ ±0.1°C |
| Refrigeration method | Mechanical refrigeration (compressors) |
| Circulation flow | 6-30 L/min (depending on model) |
| Tank capacity | 5-30L (depending on demand) |
| Applicable media | Ethanol, water/ethylene glycol, silicone oil, etc. |
Applicable standards and applications
(1) Lubricating oil low temperature test
- ASTM D97 / GB/T 510: Pour point determination
- ASTM D445 / GB/T 265: Determination of low temperature kinematic viscosity
- ASTM D5293 / GB/T 6538: CCS low temperature simulated viscosity determination
(2) Hydraulic oil & marine oil
- ISO 6743: Low temperature starting performance
- SH/T 0768: Determination of low temperature viscosity of hydraulic oil
(3) Other applications
- Low temperature engine coolant testing
- Refrigeration lubricant and coolant stability test
- Low temperature reactions in the chemical/pharmaceutical industry
Experimental procedures
Step 1: Preparation
✅ Select the appropriate medium (e.g. ethanol for -40°C, silicone oil for -80°C)
✅ Add liquid to the tank (make sure the liquid level is appropriate)
✅ Connect the external circulation interface (if necessary)
Step 2: Set the target temperature
✅ Set the temperature via PID controller (e.g. -40°C)
✅ Wait for the temperature to stabilize (usually 10-30 minutes)
✅ Observe the digital display to ensure that the temperature error is ≤ ±0.1°C
Step 3: Run the experiment
✅ Place the test sample in a thermostatic bath or connect it to an external circulation device
✅ Maintain the set temperature and perform low temperature testing
✅ Record experimental data, such as viscosity, fluidity, and freezing point
Step 4: Closing and Cleaning Up
✅ After the experiment is completed, warm up to room temperature to avoid refrigerant residue
✅ Replace or clean the coolant tank to prevent crystallization from blocking the circulation system
✅ Turn off the equipment and cut off the power
Purchase suggestions
✅ Temperature range: Does it meet -40°C, -60°C or -80°C?
✅ Accuracy requirement: ±0.1°C or ±0.01°C?
✅ Circulation flow: Is external circulation required (such as connecting a viscometer)?
✅ Tank capacity: 5L, 10L or 30L?
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Circulating cryostatic bath – application specific guide
The low temperature constant temperature bath is mainly used for testing the low temperature characteristics of fluids such as lubricating oil, hydraulic oil, fuel oil, etc. The following is a detailed experimental application guide, including equipment use, typical test methods and precautions.
Typical applications of low temperature constant temperature baths
| Application Scenario | Related standards | Objective |
|---|---|---|
| Lubricating oil pour point determination | ASTM D97 / GB/T 510 | Evaluating low temperature fluidity of oil |
| Kinematic viscosity determination (low temperature) | ASTM D445 / GB/T 265 | Measuring low temperature viscosity of oil |
| CCS Low Temperature Simulated Viscosity | ASTM D5293 / GB/T 6538 | Evaluating the cold-start performance of engine oils |
| Marine oil-water separation test | SH/T 0619 | Evaluating the Demulsibility of Marine Lubricants |
| Hydraulic oil low temperature starting performance | ISO 6743 / SH/T 0768 | Evaluating the flow properties of hydraulic oils at low temperatures |
| Low temperature fuel characteristics test | ASTM D2500（浊点）、ASTM D4539（冷滤点） | Evaluating fuel oil cold weather availability |
Specific experimental guidance
(1) Determination of low temperature pour point of lubricating oil (ASTM D97 / GB/T 510)
Purpose：
Pour Point refers to the lowest temperature at which lubricating oil can still flow during cooling. The lower the pour point, the better the fluidity of the oil in a cold environment.
Experimental Procedure：
- Sampling: Prepare 50mL of oil sample and pour it into the pour point test tube.
- Precooling: Place the test tube in a -20°C low temperature constant temperature bath and keep it for 10 minutes.
- Cooling test:
- Every 3°C drop in temperature, tilt the test tube 45° to observe whether the oil flows.
- Until the oil stops flowing, it is the pour point (PP).
- Record the data and calculate the average value.
Typical Results：
| Oil | Pour point (°C) |
|---|---|
| 15W-40 Motor Oil | -27°C |
| ATF Transmission Fluid | -45°C |
| Hydraulic oil VG 32 | -39°C |
(2) Determination of low temperature kinematic viscosity of lubricating oil (ASTM D445 / GB/T 265)
Purpose:
Determine the viscosity (resistance to flow) of oil in low temperature environments. Common temperatures include -20°C, -30°C, and -40°C.
Experimental steps:
- Equipment preparation:
- Select a suitable capillary viscometer (Ubbelohde, countercurrent, etc.).
- Set the low temperature constant temperature bath temperature (e.g. -30°C).
- Oil sample pretreatment:
- Take 10-15mL sample and remove water and impurities.
- Leave in the low temperature bath for 15 minutes to reach the set temperature.
- Measure flow time:
- Let the oil sample flow in the capillary viscometer and use a stopwatch to record the outflow time (t).
- Calculate viscosity: ν=C×t Where:
- ν = kinematic viscosity (mm²/s)
- C = capillary viscometer constant
- t = test outflow time (seconds)
Typical results:
| Oil | -30°C Kinematic Viscosity (cSt) |
|---|---|
| 5W-30 Motor Oil | 3200 |
| ATF Transmission Fluid | 1200 |
| VG 46 hydraulic oil | 6500 |
(3) CCS low temperature simulated viscosity measurement (ASTM D5293 / GB/T 6538)
Purpose:
Determines the viscosity of engine oil at low temperature cold start, in mPa·s, which determines the engine’s starting ability in cold environments.
Experimental steps:
- Set temperature:
- For example: -30°C (5W level), -35°C (0W level).
- Load shear force:
- Apply shear force to simulate engine starting and measure the oil flow resistance (CCS viscosity).
- Result judgment:
- The lower the oil CCS viscosity, the easier it is to start.
Typical Standards：
| SAE Grade | CCS viscosity (mPa·s) | Test temperature (°C) |
|---|---|---|
| 0W-20 | ≤ 6200 | -35°C |
| 5W-30 | ≤ 6600 | -30°C |
| 10W-40 | ≤ 7000 | -25°C |
(4) Hydraulic oil low temperature starting performance test (ISO 6743 / SH/T 0768)
Purpose：
Determine the viscosity and fluidity of hydraulic oil in low temperature environment to ensure the normal operation of the hydraulic system in cold climate.
Experimental steps:
- Set temperature (e.g. -40°C) and stabilize for 30 minutes.
- Measures kinematic viscosity to determine whether hydraulic oil can flow at a set pressure.
- Result judgment:
- Low temperature viscosity ≤ 10,000 cSt ensures smooth pump priming.
- Excessively high low-temperature viscosity may cause difficulty in starting or damage the hydraulic system.
Typical hydraulic oil low temperature viscosity:
| Hydraulic oil | -30°C Kinematic Viscosity (cSt) |
|---|---|
| VG 32 | 5200 |
| VG 46 | 8500 |
| VG 68 | 12500 |
Precautions for using the low temperature constant temperature bath
✅ Tank selection: It is recommended to use ethanol or silicone oil below -40°C to prevent freezing.
✅ Temperature stability: Let stand for 15-30 minutes before testing to ensure uniform temperature.
✅ Oil sample treatment: Filter impurities to avoid contamination of the viscometer or test tube.
✅ Laboratory environment: Keep ventilation to avoid solvent volatilization.
Equipment selection suggestions
| Key Parameters | Recommended Configuration |
|---|---|
| Minimum temperature | -40°C / -60°C / -80°C |
| Temperature control accuracy | ±0.1°C / ±0.01°C |
| Tank capacity | 5L / 10L / 30L |
| Circulation flow | 6-30 L/min |
| External loop interface | Whether to support external connection |
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Specific ASTM, GB/T, SH/T standard methods, the following are several common low temperature test standards and their detailed processes:
Lubricating oil pour point test (ASTM D97 / GB/T 510)
1.1 Scope of application
Determine the lowest temperature at which the lubricating oil can still flow during the cooling process. It is suitable for engine oil, hydraulic oil, gear oil, transmission oil, etc.
1.2 Equipment requirements
✅ Low temperature constant temperature bath (e.g. -40°C, accuracy ±0.1°C)
✅ Pour point test tube (30mm diameter, 120mm height)
✅ Test thermometer (accuracy 0.5°C)
✅ Cooling medium (alcohol or low temperature silicone oil)
1.3 Test steps
- Sampling: Prepare 50mL of oil and pour it into a pour point test tube.
- Precooling: Place the test tube in a constant temperature bath at 0°C and let it stand for 30 minutes.
- Cooling process:
- Cool down every 3°C (e.g. -3°C → -6°C → -9°C…).
- After each cooling, tilt the test tube 45° and observe whether the oil flows.
- Final result:
- If the oil no longer flows at a certain temperature, raise the temperature by another 3°C and record this temperature as the pour point.
1.4 Result Example
| Oil | Pour point (°C) |
|---|---|
| 15W-40 Motor Oil | -27°C |
| ATF Transmission Fluid | -45°C |
| Hydraulic oil VG 32 | -39°C |
Kinematic viscosity test (ASTM D445 / GB/T 265)
2.1 Scope of application
Determine the viscosity of lubricating oil at different temperatures, suitable for hydraulic oil, gear oil, diesel, gasoline, coolant, etc.
2.2 Equipment requirements
✅ Ubbelohde or counter-flow capillary viscometer (inner diameter 0.4-2.0mm)
✅ Low temperature constant temperature bath (-40°C ~ 100°C, accuracy ±0.05°C)
✅ Stopwatch (accuracy 0.1s)
✅ Viscometer stand
2.3 Test steps
- Prepare oil sample: Take 10mL sample and filter to remove impurities.
- Capillary pretreatment:
- Wash the viscometer, dry it and place it in a constant temperature bath (-20°C, -30°C, -40°C).
- Measuring time:
- Pipette the oil to the mark and observe the time (seconds) required for the oil sample to flow through the scale line.
- Calculate viscosity: ν=C×t
- ν = kinematic viscosity (mm²/s)
- C = viscometer constant (provided)
- t = flow time (seconds)
2.4 Result Example
| Oil | -30°C Kinematic Viscosity (cSt) |
|---|---|
| 5W-30 Motor Oil | 3200 |
| ATF Transmission Fluid | 1200 |
| VG 46 hydraulic oil | 6500 |
CCS low temperature simulated viscosity test (ASTM D5293 / GB/T 6538)
3.1 Scope of application
Determine the viscosity of engine oil at low temperature cold start, suitable for 0W, 5W, 10W grade oil.
3.2 Equipment requirements
✅ CCS low temperature analog viscometer
✅ Low temperature cooling system (-35°C ~ -5°C, accuracy ±0.1°C)
✅ Viscosity measurement software
3.3 Test steps
- Set target temperature (e.g. -30°C).
- Apply shear force to simulate the oil flow resistance during engine cold start.
- Read CCS viscosity in mPa·s.
- Determine SAE viscosity grade.
3.4 Typical Results
| SAE Level | CCS viscosity (mPa·s) | Test temperature (°C) |
|---|---|---|
| 0W-20 | ≤ 6200 | -35°C |
| 5W-30 | ≤ 6600 | -30°C |
| 10W-40 | ≤ 7000 | -25°C |
Hydraulic oil low temperature starting performance test (ISO 6743 / SH/T 0768)
4.1 Scope of application
It is used to measure the viscosity and fluidity of hydraulic oil in low temperature environment. It is suitable for aviation hydraulic oil, engineering machinery oil, etc.
4.2 Equipment requirements
✅ Low temperature constant temperature bath (-50°C ~ 100°C, accuracy ±0.1°C)
✅ Hydraulic pump test bench
4.3 Test steps
- Set the target temperature (e.g. -40°C) and keep it constant for 30 minutes.
- Measure the kinematic viscosity to determine whether the hydraulic oil can flow at the set pressure.
- Record the data to determine the low temperature starting performance of the hydraulic oil.
4.4 Typical Results
| Hydraulic oil | -30°C Kinematic Viscosity (cSt) |
|---|---|
| VG 32 | 5200 |
| VG 46 | 8500 |
| VG 68 | 12500 |
Marine oil-water separation test (SH/T 0619)
5.1 Scope of application
Determine the water separation capacity of marine lubricating oil, suitable for diesel engine oil, hydraulic oil, etc.
5.2 Equipment requirements
✅ BF-100 Marine Oil-Water Separability Tester
✅ Constant Temperature Water Bath (54°C, Accuracy ±0.5°C)
✅ Standard Emulsification Reagent
5.3 Test steps
- Heat the oil sample to 54°C and stir for 5 minutes.
- Add the water phase and stir for 1 minute.
- Let stand and observe the separation (30min ~ 60min).
- Record the amount of separated water (mL) to determine the water separation property.
5.4 Result Example
| Oil | Separation time (min) | Separation rate (%) |
|---|---|---|
| Marine oil No. 40 | 20 | 98% |
| Marine oil No. 50 | 30 | 95% |
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