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WBGT Meter

WBGT meter used in laboratory

1. What is WBGT meter?
    1.1 Working principle of WBGT meter
    1.2 Structure of WBGT meter
    1.3 Use of WBGT meter
2. Heat stress meter
    2.1 Heat hazard identification
3. Heat stress WBGT meter
4. How to buy WBGT meter?

What is WBGT meter?

A WBGT meter, which refers to a wet bulb globe temperature meter, is a thermometer in which the surface of the ball part (temperature pack) remains wet. One of the components of a dry and wet bulb hygrometer. It is usually wrapped on the surface of the ball with moistened gauze or cotton. The measured temperature is called the "wet bulb temperature".

Working principle of WBGT meter

WBGT meter is related to the humidity of the surrounding air, the lower the humidity, the stronger the evaporation of water on the wet bulb, the lower the wet bulb temperature, the greater the difference between dry and wet bulb temperature; conversely, the higher the humidity, the smaller the difference between dry and wet bulb temperature.

When the air is dry, wet bulb globe temperature meter gauze evaporates quickly and absorbs more heat, the difference between the two thermometers is relatively large. The larger the difference between the two thermometers, the drier the air. When the air is a lot of water vapor, wet bulb thermometer gauze evaporates slowly, absorbing less heat, the difference between the two thermometers is small. The smaller the difference between the two thermometers, then the more humid the air is.

Structure of WBGT meter

WBGT meter consists of two identical ordinary thermometers, one for measuring air temperature, called dry ball thermometer; the other in the ball with distilled water-soaked gauze wrapped, the lower end of the gauze immersed in distilled water, called wet ball thermometer. As the gauze-wrapped wet ball thermometer evaporates and absorbs heat after absorbing water so that the number is smaller than the dry ball thermometer. Wet balls of gauze often need to be replaced by new ones.

Use of WBGT meter

The ventilated dry and WBGT meter is composed of two mercury thermometers with high accuracy (scale of 0.1°C or 0.2°C). In the upper part of the thermometer is equipped with a small fan-driven electrically or mechanically (clockwork), through the conduit so that the airflow at a speed equal to or greater than 2.5 m / s through the thermometer's temperature package. The wet bulb globe temperature meter is equipped with a metal protective sleeve around it to prevent the influence of radiant heat on it. The gauze of the wet bulb thermometer should always be kept loose and have good water absorption when in use. It should be placed in the measurement place 15min in advance, and if used in windy conditions, people should be in the downwind direction to avoid affecting the measurement effect.

Heat stress meter

Heat stress meter is mainly used in the workplace, where it detects and classifies temperatures based on moisture content.

Heat hazard identification

Several factors can contribute to the risk of occupational heat stress for workers. These factors include the following.

a. Environmental conditions (e.g., temperature, humidity, sunlight, and wind speed), especially on consecutive days.

b. The presence of heat sources in the work area (e.g., hot tar stoves or fireplaces).

c. The level of physical activity, i.e., the workload that results in body heat production.

d. Use of clothing or protective equipment that will reduce the body's ability to dissipate heat.

e. Personal/personal risk factors.

Heat-related illness prevention begins with determining the presence of heat hazards in the workplace. Two types of heat sources increase the risk of heat-related illnesses.

a) Ambient heat is generated by a warm or hot environment.
b) Metabolic heat generated by the body is related to workload (physical activity).

WBGT meter contains three different thermometers, a dry bulb thermometer for measuring ambient air temperature, a natural wet bulb thermometer for measuring evaporative cooling possibilities, and a black bulb thermometer for measuring radiant heat.

WBGT monitors should be placed near the working location. For example, if the work is in direct sunlight, then the WBGT instrument should be in sunlight. The WBGT has important advantages over other environmental thermal measurements. A major advantage is that the WBGT takes into account all four major ambient thermal factors - temperature, humidity, radiant heat, and wind. In contrast, standard thermometers assess only one factor (air temperature). The heat index is another commonly used measure of heat stress. It is measured in the shade and combines air temperature and relative humidity to represent heat under resting conditions. The heat index does not take into account the effects of sunlight, wind, radiant heat sources, or workload. Air (dry bulb) temperature also ignores relative humidity. All of these factors affect the total heat stress experienced by the worker.

Workplace ambient heat should be measured in the field using a WBGT meter. The use of a heat index is a less desirable alternative. While local weather reports based on observatory weather data may be useful, the readings from these stations may not reflect the conditions at a particular work site. Thermal conditions at a job site can vary for a variety of reasons, from cloud cover and humidity to local heat sinks. The potential for error increases with the distance to the weather station.

In addition to possible distance-based errors, weather reports can be inaccurate if the job site has features that affect thermal conditions. These features include the following.

a. Indoor work. Weather forecasts do not measure conditions inside buildings.

b. Direct sunlight. The weather service measures temperatures and heat indices in the shade. Working in the sun may be hotter. Direct sunlight can increase the heat index by as much as 13.5°F (7.5°C).

c. Heat Source. Weather reports cannot account for the heat generated by fires, hot tar or other materials, heat-absorbing surfaces such as roads and roof surfaces, or heat-absorbing surfaces such as roads and roof surfaces.

d. Wind resistance. Some sites may be hotter than surrounding areas because structures impede airflow. Examples include trenches and bowl-shaped sports fields.

e. Reflective materials. Water, metal, or other materials that reflect sunlight at workers.

On sites with these characteristics, weather reports are unlikely to provide accurate estimates of ambient heat. Employers should use field measurements such as WBGT.

Heat stress WBGT meter

Wet bulb globe temperature refers to the adiabatic conditions, a large amount of water, and limited contact with wet air, the latent heat required for water evaporation comes entirely from the wet air temperature reduction of the sensible heat released when the air in the system reaches saturation and the system reaches thermal equilibrium when the system temperature. In layman's terms, the wet bulb temperature is the current environment only through the evaporation of water can reach the lowest temperature.

When measured correctly, the wet bulb temperature can be used instead of the thermodynamic wet bulb temperature in a wide range of engineering measurements.

The thermodynamic wet bulb temperature of wet air (adiabatic saturation temperature) refers to the temperature of wet air when it changes adiabatically to the saturated state and is usually measured with a wet bulb thermometer. However, theoretically and strictly speaking, the wet bulb temperature measured by a wet bulb thermometer is not the adiabatic saturation temperature of wet air, because the air around the wet bulb of the wet bulb thermometer is not saturated under adiabatic conditions (i.e., equal enthalpy), which is usually an enthalpy-increasing process.

Commonly used wet air charts or thermodynamic equations in the wet bulb temperature are referred to as the theoretical wet bulb temperature (adiabatic saturation temperature); it is in the adiabatic conditions of wet air and water to reach the equilibrium temperature after the exchange of heat and mass. Theoretical wet bulb temperature in practice is very difficult to determine, there is no direct formula, in practice, commonly used in the actual measured wet bulb temperature instead of theoretical wet bulb temperature, and the actual wet bulb thermometer is not in adiabatic condition. Therefore, the actual wet bulb temperature in addition to the wet air state, but also by the wind speed and the size of the wet ball diameter, and thus the actual wet bulb temperature is not the thermodynamic characteristics of wet air parameters. That is, it is not the theoretical wet bulb temperature (thermodynamic wet bulb temperature).

In drying, humidification, humidity reduction, and air conditioning calculations, the wet bulb temperature and adiabatic saturation temperature are often used as two parameters. These two temperatures are characterized by the nature and state of the wet air (hereinafter referred to as air), which is the air of two very important state parameters. They are conceptually different in nature, but there is a certain relationship between them. For the most commonly encountered in engineering water-air system, the two temperatures are approximately equal in value. For organic liquids (such as ethanol, benzene, and carbon tetrachloride) - air systems, the two are not equal, but the wet bulb temperature is higher than the adiabatic saturation temperature.

How to buy WBGT meter?

ANTITECK provide lab equipment, lab consumable, manufacturing equipment in life sciences sector.
If you are interested in our WBGT meter or have any questions, please write an e-mail to [email protected], we will reply to you as soon as possible.

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