The temperature and humidity uniformity of the constant temperature and humidity experimental chamber is the core guarantee for the accuracy of environmental reliability testing data (industry standards require temperature uniformity)The implementation logic is: ≤± 2 ℃, humidity uniformity ≤± 3% RHStructural design+fluid dynamics optimization+precise system collaborationTrinity, by eliminating the "temperature gradient" and "humidity gradient" inside the box, ensures that the temperature and humidity at each testing point are consistent. Below is a detailed breakdown of the guarantee mechanism for uniformity from three dimensions: core design, key technologies, and control strategies:

1、 Infrastructure Design: Eliminating Temperature and Humidity Differences from the Root

Structural design is a prerequisite for uniformity, and the core idea is The key design for achieving uniform diffusion of airflow, energy/water vapor includes:

1. Air ducts and circulation systems: the "uniformity skeleton" of forced convection

Air duct layout (core design)：

Mainstream adoption Double circulation air duct with "up and down return+left and right surround"Design an independent air duct interlayer on the inside of the box (left side)/Rear side), with air outlets arranged at the top (bar/porous design to ensure uniform air flow), and return air outlets arranged at the bottom/sides to form a closed loop;

avoid Single point air outlet ": The air outlet adopts a splitter plate design to divide the airflow into multiple uniform streams, covering various areas (including corners) inside the box, to prevent local airflow from directly hitting the sample and causing temperature differences;

Install a filter screen on the return air outlet to prevent dust from blocking the air duct, ensure smooth airflow, and avoid sample debris affecting circulation efficiency.

Fan and Wind Speed Control：

adopt Centrifugal fan (not axial fan)Generate a stable airflow with high static pressure and low wind speed (wind speed)0.5~1.5m/s）， It can ensure that the airflow covers the entire area without causing uneven temperature and humidity on the sample surface due to excessive wind speed (such as quickly removing water vapor from the sample surface);

Adjustable fan speed: The wind speed is adaptively adjusted according to the load inside the box (sample quantity, volume). When the load is high, the speed is increased to ensure airflow penetration, and when the load is low, the speed is reduced to avoid energy waste.

2. Box structure: reduce energy loss and local differences

Inner liner material and shape：

The inner liner adopts SUS304 stainless steel (mirror/brushed)Smooth surface and uniform thermal conductivity, avoiding local temperature and humidity differences caused by uneven thermal conductivity of the material;

The inner liner design is Rounded corner structure (no right angle dead corners)A right angle can easily form airflow eddies, leading to local accumulation of temperature and humidity. Rounded corners can guide smooth airflow circulation and eliminate blind spots.

Insulation and sealing design：

Box interlayer filling High density polyurethane high-pressure foam insulation layer (thermal conductivity)≤0.02W/(m ・K)）Reduce heat exchange between the box and the outside to avoid excessively low wall temperatures/Excessive temperature can cause local condensation or heating;

The box door adopts Double layer sealing strip (silicone)+Foam adhesiveTo prevent external air from seeping in (causing humidity fluctuations) and internal temperature and humidity leakage, the box door glass uses hollow laminated heating glass to avoid fogging and affecting observation, and the heating glass temperature is consistent with the temperature inside the box to prevent local cooling.

3. Layout of functional components: uniform diffusion of energy/water vapor

Heating tube: partitioned layout：

The heating tubes are not concentrated in a single position, but are dispersed and installed in the upper, middle, and lower areas of the air duct interlayer (such as the top)1 group, 2 groups in the middle, and 1 group at the bottom), ensure that the airflow absorbs heat evenly when passing through the air duct, and avoid local overheating;

The heating tube is made of stainless steel material, with no exposed resistance wires on the surface, to prevent high-temperature burning of the sample, and to achieve better heating uniformity.

Humidifier: Atomization/Uniform diffusion of steam：

The atomizing head of the ultrasonic humidifier is installed in the air duct (rather than directly atomizing inside the box): the water mist is evenly diffused into the box through the circulation of the airflow, avoiding local high humidity;

The steam outlet of the steam humidifier adopts a porous diversion design: the steam is divided into fine streams and mixed with the airflow to prevent local high temperature and high humidity (such as instantaneous high humidity near the steam outlet).

Evaporator: Full area coverage：

The evaporator adopts The "snake coil+fin" structure is installed at the front end of the air duct return air outlet, with a large contact area with the airflow, ensuring uniform cooling and dehumidification of the airflow passing through, and avoiding uneven condensation caused by rapid local cooling.

2、 Core technical means: optimizing the efficiency of airflow and temperature and humidity transfer

1. Optimization of airflow organization: simulation design of air ducts based on fluid mechanics

During the research and development phase, it will pass CFD (Computational Fluid Dynamics) simulation Simulate the airflow trajectory inside the box, optimize the shape of the air duct, the angle of the air outlet, and the position of the return air outlet to ensure that the airflow is formed inside the box Uniform turbulence "(rather than laminar or vortex flow):

Turbulent airflow can break the temperature and humidity stratification, allowing for rapid mixing between high and low temperature zones, high and low humidity zones, and eliminating gradients;

After simulation, actual testing will be conducted (arranged inside the box)Adjust the air duct parameters at 9-15 test points according to GB/T 2423 standard until the uniformity meets the standard.

2. Temperature and humidity compensation technology: dynamically correcting local differences

temperature compensation：

Some models are installed in key areas inside the box, such as corners and the bottom layer of the sample rack Auxiliary temperature sensorReal time monitoring of local temperature, if it is found that the temperature in a certain area is too low (such as the corners being lower than the center)At 1.5 ℃, the controller will fine tune the power of the heating tube in the corresponding area (such as starting the auxiliary heating near the corner) and dynamically compensate for the temperature difference.

humidity compensation：

The humidity sensor adopts Multi point collection+average calculation ": Some models are equipped with 2-3 humidity sensors (top, middle, bottom) inside the box, and the controller takes the average value as the real-time humidity to avoid adjustment errors caused by local humidity deviation of a single sensor;

Low humidity scene（≤ 20% RH) is used rotary dehumidification+Secondary humidificationBefore entering the box, the dry airflow after rotary dehumidification will pass through A "humidifier" (with a small amount of water vapor replenishment) is used to avoid local humidity being too low (such as 10% RH at one point inside the box and 15% RH at another point), ensuring consistent humidity throughout the box.

3. Sample rack design: reduce airflow obstruction

Sample rack adopts Hollow grid structure (instead of solid board): Grid aperture≥10mm， The airflow can penetrate the sample rack to avoid the sample rack blocking the airflow and causing uneven temperature and humidity of the lower samples;

Adjustable height of sample rack: convenient to adjust the spacing according to the sample size, ensuring reserved space between samples and between samples and the box wallA gap of ≥ 5cm (required by industry standards) should be avoided to prevent sample aggregation and hinder airflow.

3、 Precise control strategy: dynamic balance of temperature and humidity differences

1. PID adaptive regulation: to avoid the decrease in uniformity caused by temperature and humidity fluctuations

The controller adopts PID+Fuzzy Control AlgorithmNot only does it regulate the overall temperature and humidity, but it also dynamically optimizes parameters based on the temperature and humidity distribution inside the box:

When significant temperature and humidity fluctuations are detected in a certain area inside the box (such as stable center temperature and corner fluctuations) ± 1 ℃), the controller will reduce the adjustment rate (such as changing the heating power from "rapid heating" to "slow heating"), to avoid the overall temperature and humidity oscillation driving the expansion of local differences;

Using different temperature and humidity rangesPID parameters (such as smoother PID parameters in high temperature and high humidity areas, and more sensitive parameters in low temperature and low humidity areas) ensure uniformity and stability under various operating conditions.

2. System collaborative control: synchronous linkage of heating/cooling/humidification/dehumidification

Temperature and humidity regulation is not carried out independently, but Synchronized linkage "to avoid uniformity disruption caused by a single system working:

For example, during humidification, the controller will synchronously activate the heating tube (low power) to compensate for the heat absorbed by water vapor evaporation (evaporation heat absorption will cause local temperature drop), avoiding Humidification and simultaneous cooling lead to temperature and humidity gradients;

During dehumidification, the controller will synchronously reduce the heating power to avoid local low temperatures caused by refrigeration dehumidification, which may affect humidity uniformity (temperature affects relative humidity, and at the same moisture content, low temperature leads to high relative humidity).

3. Load adaptive adjustment: dynamically adjust according to sample characteristics

The experimental chamber will automatically recognize the sample load (determined by current and temperature change rate):

If the sample is High thermal conductivity materials (such as metal parts) have fast heat transfer and are prone to local temperature unevenness. The controller will increase the fan speed, enhance airflow circulation, and reduce the heating/cooling power adjustment rate;

If the sample is High moisture absorbing materials (such as textiles) quickly absorb water vapor during humidification, resulting in low local humidity. The controller will extend the humidification time, increase the atomization amount, and maintain high airflow speed to ensure rapid diffusion of water vapor.

4、 Factory calibration and standard compliance: ensuring uniformity meets standards

1. Uniformity testing and calibration before leaving the factory

Manufacturer according to GB/T 2423.1-2008、ISO 60068-2-1:2007 Arrange according to standards inside the boxNine test points (3 x 3 matrix, 3 points each at the top, middle, and bottom) were tested under no-load and rated load conditions

Temperature uniformity: the maximum difference between the temperature at each test point and the average temperature≤±2℃；

Humidity uniformity: maximum difference between humidity at each testing point and the average humidity≤±3% RH；

If the standard is not met, the air duct and heating tube will be adjusted/Humidifier position and PID parameters until they meet the standards.

2. Regular calibration and maintenance: maintain long-term uniformity

During the use of the equipment, it is necessary to regularly (such as annually)Perform uniformity calibration once (CNAS certification agency can be commissioned):

Clean the air duct, filter screen, and evaporator fins (to avoid dust accumulation affecting airflow);

Check whether the heating tube, humidifier, and fan are working properly (such as whether the heating tube is locally damaged and whether the fan speed has decreased);

retestUniformity of 9 points, adjust controller parameters if necessary.

summary

The guarantee logic for the uniformity of temperature and humidity in the constant temperature and humidity experimental chamber is:with With "uniform airflow circulation" as the core, dead corners and gradients are eliminated through structural design (air duct, box, component layout), transmission efficiency is optimized through technical means (CFD simulation, multi-point compensation), and differences are dynamically corrected through control strategies (PID adaptive, system collaboration), ultimately achieving consistent temperature and humidity throughout the box.

The key points can be summarized as follows:

Air duct design is the foundation (uniform convection);

Component layout is key (heating)/Uniform distribution of humidification/cooling;

The control algorithm is the core (dynamic compensation, collaborative adjustment);

Calibration and maintenance are guarantees (factory testing)+Regular calibration).

This mechanism ensures that the experimental chamber can meet industry standard requirements under different loads and temperature and humidity conditions, providing accurate and reproducible environmental simulation basis for product reliability testing.