What is meant by kLa?

kLa = kL × a. Where kLa is the mass transfer coefficient from the gas to liquid phase, given in sec‑1. kL = liquid side mass transfer coefficient (resistance in gas side film can be neglected) a = bubble surface (available for diffusion)

What is the significance of kLa?

A constant kLa ensures equal oxygen transfer independent of physical differences between each scale. kLa is influenced by factors such as bioreactor geometry, gas flow, superficial gas velocity, impeller type and speed, and power input for mixing per unit reaction volume.

What is mean by kLa in fermentation?

For aerobic fermentation, oxygen supply is one of the key limiting factors for microbial growth and product formation, thus volumetric oxygen transfer coefficient (kLa) is generally used as a scale-up criterion [25,26]. kLa plays an important role in the design, scale-up and economy of the fermentation process.

What is mass transfer coefficient kLa?

The kLa (Volumetric Mass Transfer Coefficient) and the OTR (Oxygen Transfer Rate) detail how efficient oxygen is transferred from the gas bubbles into the bioreactor medium, i.e. how much oxygen is available for the cultivated biomass.

What does KLA depend on?

The values of kLa are affected by many factors, such as geometrical and operating characteristics of the reactor (type of impeller, the geometry of the bioreactor, the agitation speed and the air flow rate), media composition and properties, concentration and microorganism’s morphology and biocatalyst’s properties [3].

Which method is better for KLA determination?

Some investigators are of the opinion that oxygen balance over the whole system is the best method for evaluation of KLa in fermenters, because no assumption need be made on the effects of cell, surface active agents, viscosity, and forth.

What does kLa depend on?

Which method is better for kLa determination?

What do you mean by NA in mass transfer?

NA is the molar mass transfer of A across the boundary (moles /(area time)), cA∞ is molar concentration of A (moles / volume) in the bulk of the system far away from the boundary (surface), and cAS is the molar concentration of A right at the boundary but still on the same side as the bulk of the system. Page 11.

Does temperature affect kLa?

The results show that the temperature plays an important role on mass transfer phenomena as kLa increases as temperature is increased. However, temperature does not have, significantly, influence on the solids effect on kLa.

Which method is better for KLa determination and why?

What does the KLA tell you about the oxygen transfer in your?

The k L a actually consists of two coefficients: Mass transfer coefficient k L: describes the transport of oxygen and gas into the liquid phase a: Gas-liquid exchange area per unit of liquid volume Since it is difficult to measure the k L and a value separately, they are combined into one parameter.

How is the KLA related to the concentration gradient?

In this relation, the volumetric oxygen transfer coefficient, K L a, has the units of m mol, of O 2 /ml. h. unit concentration gradient. Using the proper concentration units, K L a has the unit of reciprocal of time (i.e., time -1 ).

How is the KLA measured in a bioreactor?

There are different chemical, biological and physical methods that measure the k L a in bioreactors. However, one has become the standard as it is easy to use and provides accurate measurements. With the “static gassing-out” method, an oxygen sensor is installed in the bioreactor to measure the dissolved oxygen concentration in the medium.

Is the KL of oxygen equal to the local coefficient?

However, because the solubility of oxygen in water is very low and the vast majority of mass-transfer resistance is on the liquid side of the interface, the overall mass transfer coefficient can be assumed to be equal to the local coefficient ( KL = kL ).