Laboratory Water Bath Working Principle


When it comes to lab procedures, high precision and accuracy are expected while performing them. This is because even a slight change in the values may cause a drastic change in the end result. This is why various lab equipment and machinery have been introduced over time to reduce human error and make those procedures easier to perform. One such machine is the ‘Water Bath’ that allows the cooling or heating of the samples over a long period of time by using water to equally distribute the temperatures. It is used to culture the samples, and mix or incubate the samples where a particular constant temperature is required for the entire incubation period. Although most water baths have a digital and analogue interface to control the desired temperature, some water baths control their temperature by passing a current through a reader. A water bath is mainly used in situations where the sample needs to be heated below the boiling point. However, there is a lot more to learn about water baths and you can find all that information in this article.

What is a Laboratory Water Bath?

Water bath machine


A water bath machine is a laboratory equipment that is used to incubate samples at the desired temperature. It helps to keep the temperature constant throughout the incubation period. It is preferred to heat the samples in a water bath rather than heating directly because the water bath does not change the concentration of the constituents since there is no evaporation taking place. It also prevents ignition of the flammable compounds. The water bath is used in laboratories that perform incubation or general testing; therefore, it is commonly found in clinical and microbiology laboratories, university labs, environmental research labs, and even food technology labs for warming reagents, sample thawing, and corrosion tests.

A Brief History

In 1748, William Cullen demonstrated the first artificial refrigerator at UK’s Glasgow University. In 1851, John Gorrie introduced the first ice-making machine. Cooling of reactions and other lab samples became common using an Ice bath. In 1921, the primary centrifugal water chiller was patented by an inventor named Willis Carrier. Before this point, chillers used a reciprocating compressor to move the refrigerant through the system. The design of the centrifugal compressor was also finalized during this period.

In the 1930s, Glen and Ruth Morey invented the heating mantle, a reliable and non-flammable heating device with electric resistance wires woven into a fiberglass cloth sheath. The first heating mantle was sold in 1939, and the couple formed the Glas-Col Apparatus Company to manufacture their new product.

During the 1950s and 1960s, water baths became more advanced and offered a variety of new features along with new models. For instance, New Brunswick Scientists developed the G76 water bath shaker, which used a triple eccentric drive to achieve optimal shaking; it was also successful in maintaining the temperature within a controlled range. The company claims this iconic water bath, and the shaker is still being used in many labs worldwide.

In 1994, Yamato, a scientist, completed all the required improvements in its low-temperature/constant temperature incubator series. In 1999, Julabo who was another researcher working on the development of water baths released a series of water baths and shaking water baths that had facilities like splash-water protection to protect the user and samples during use. The same year, Julabo launched the Economy series of circulators featuring LED displays for increased energy efficiency and improved ease of use.

Between 2000 and 2006, Julabo introduced a variety of innovations to the domain of lab circulators, offering alternative ways to heat and cool down the laboratory processes. Thanks to all these advances, water baths and chillers could be controlled using circulators.

In 2010, Lab Armor introduced a new bead bath designed to function just with beads rather than water. This water (less) bath delivered temperature uniformly while eliminating the need for water, a well-known contaminant in the labs.

In 2011, PolyScience introduced its latest generation immersion circulator. This instrument minimized the reservoir space, providing more space for samples. In the same year, PolyScience also introduced circulating water baths designed. There were multiple new and innovative features including a swiveling control head that allowed viewing of the temperature display within a 180° viewing radius, and a corrosion and chemical resistant top plate.

Parts of a Laboratory Water Bath

  • Stainless steel Chamber: Inner and outer stainless steel chamber is easy to clean and benefits chemical and corrosion resistance. Its function is to hold the water and the samples along with a control interface. Stainless steel has high tensile strength and is a very durable material. It is very easy to clean and hence very low maintenance when it comes to cost as well.

  • Chamber Lid: The lid has a lot of important functions. It prevents contamination of the test samples from outside the environment. When the samples are incubated for longer periods, the growth of microbes can sometimes produce a foul smell, so the lid prevents the smell from spreading across the entire lab. It also helps in maintaining a controlled temperature, creating a barrier between outer and inner temperature. It also keeps the chamber watertight to prevent any leakage from happening.

  • Heating unit: In the lower part of the stainless steel chamber, there is a set of electrical resistances through which the heat is transferred to the water. There is also an external heating element that transfers the heat through thermal conduction. In most cases, the external heating element is covered by an insulating material to prevent any heat loss. The heat is generated through a Cu50 temperature sensor.
  • Thermometer: It gives the real-time reading of the temperature of the water bath, and hence helps to check if the required temperature is attained and maintained throughout the incubation period.

  • Thermostat: Keeps the temperature under check and keeps the temperature constant throughout the incubation period.

  • Outlet: It helps to drain the water out of the water bath.

  • Propeller/Motor: In a certain type of water bath like circulating water baths, a stirrer or propeller is installed to circulate the water so that the temperature is uniform. Some water baths also have magnetic shaking propellers.

  • Indicator light: An indicator light varies from model to model water bath. In the most basic designs, the indicator light is on when the water bath is heating, and it switches off after the desired temperature is attained, and the water bath maintains that temperature after that.

Water Bath

  • Temperature display unit: This is found in the digital water baths where the readings from the thermometer and the temperature from the thermostat reading are displayed on a digital interface.
  • Baffle plate: In a water bath, these plates ensure the maximum amount of contact between the water jacket and the combustion heat to keep the heat inside for as long as possible.

Water Bath Machine Working Principle

The water bath machine is fitted with a temperature sensor that transfers the reading of the water temperature to the resistance value. This value is then amplified and compared by an integrated amplifier. The output is based on the control signal that controls the average heat power for the electric heating tube as a result of which a constant temperature is maintained within the chamber of the water bath.

How to operate a Laboratory Water Bath?

  1. Firstly, make sure that the platform and the surrounding areas are clean and dry to avoid unwanted contamination. Switch ‘ON’ the main power supply of the water heater.
  2. Pour the water into the water bath container and ensure that the heating unit is properly in contact with the water. Do not overfill the water and use only purified water to fill the container.
  3. Place the containers or the samples to be incubated. In order to heat the containers, their level should be between 4 and 5 cm from the top edge of the tank.
  4. In most of the water baths, a glowing Red light indicates that the mains is “ON,” and a glowing yellow light indicates that the heater is “ON”, but it may vary from model to model.
  5. Set the control temperature on the thermostat and place the thermometer if it is not preinstalled in the control panel. The thermostat acts as a safety control that cuts off the power supply if the selected temperature is exceeded. This way, the temperature sensor will maintain this set temperature for the entire duration of the incubation.
  6. After using the bath, take out the samples very carefully, and do not forget to switch off the main power supply.

Types of Laboratory Water Bath Machine

There are two main types of water bath machines:

Circulating water baths

The circulating water baths are the ones that have magnetic or electric propellers at the bottom of the stainless steel container. They are mainly used for cases where temperature uniformity is absolutely necessary and critical. Some examples are enzymatic and serological cases. The circulating water baths further have 3 different variations, regular circular bath, recirculating water bath, and refrigerating circular water bath. The regular ones are most commonly used for heating or cooling the samples rapidly and efficiently. The recirculating one can be used for drying, concentration, distillation, and impregnation of chemical reagents and drugs, including biological products. The refrigerated circulating bath is also widely popular especially to meet the needs of applications that require refrigeration with circulation. The refrigerated circulating baths can reach up to -30°C temperature.

Non-circulating water baths

These can be categorized into Shaking Water Baths and Digital Water Baths.

Shaking Water Baths: Shaking water baths are ideal for situations where the samples have to be moved constantly. For example, in microbiological experiments, where the constant shaking allows the cell cultures to grow properly as they get a constant mix with the air due to shaking. The control for shaking can be enabled or disabled anytime manually. They also come with adjustable shaking frequencies and a user-friendly keypad for control.

Digital Water Baths: The analog water bath has been modified into a digital water bath these days. It is a digitally controlled unit that maintains a particular temperature, usually, temperatures in a range of 32ºC to 80ºC, and is used to soften a variety of wax or compound materials.

Advantages of a Laboratory Water Bath

  1. For determining the melting point of an object, the other heating methods like heating the object on an alcohol flame would lead to a sudden rise in temperature, and hence, the melting point cannot be determined. With the help of a water bath that allows controlled heating, the melting point can be easily determined.
  2. It can be useful in cases where the substance to be heated is flammable, and sudden heat would destroy the composition of the sample completely.
  3. Incubation of cell cultures and other microbes that require a warm and moist environment is done through the water bath.
  4. It can help in the initiation of certain chemical reactions.
  5. It is used for melting waxes and some other compound materials.
  6. Some of the insoluble substances are rendered soluble after heating them in the water bath at a particular temperature.
  7. They provide a large space for multiple samples to be heated, cooled, or incubated together.
  8. Water in the water bath helps to transfer the heat to the samples more quickly and uniformly, and hence, helps to achieve precise results since there is equal distribution of heat.

Limitations of the Laboratory Water Bath

  1. The water needs regular changing and cannot be reused.
  2. Water is a major source of contamination in the labs because warm water when exposed to the environment can harbor unwanted microbial growths.
  3. Sometimes the vessels start tipping, so they are not always stable.

The above-mentioned limitations can be avoided or minimized by proper maintenance of the device.

Maintenance of the Laboratory Water Bath

  1. The type of water used to fill up the stainless steel container plays a huge role. Distilled or deionized water is preferred over tap water because the latter can lead to build-up over time due to minerals present in it.
  2. Never heat the water bath above the flash point and avoid using the water bath at all in case of samples that have a tendency to ignite instantly upon exposure to oxygen.
  3. Use a clean cloth while drying and cleaning the container and make sure to clean the lid as well.
  4. Heat the bath to 90-92 degrees C for half an hour, one per week, to decontaminate the container.
  5. Do not keep stagnant water in the container for a long period of time. Drain it immediately after the incubation procedure is completed.
  6. Avoid using bleaches and high chlorine contents to clean.
  7. Do not keep the power ON unnecessarily.

Safety Features of the Laboratory Water Bath

  1. Temperature control feature: The temperature control feature does not allow the water bath to heat excessively and especially not above the set temperature. If the machine starts to heat up excessively, the temperature control feature cuts off the electricity supply automatically.
  2. Shaking controller: In shaking type of water baths, the controller can be found on the machine where you can switch the shaker on or off by your choice.
  3. Speed controller: This is only present in some of the shaking and circulating types of water baths where the speed can be increased or decreased manually.
Tanu Neb
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