Heat Transfer in Bioprocessing

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Questions and Answers

What is a key aspect of heat transfer in a bioprocess plant?

It requires maintaining a constant temperature.

It includes heat exchange between hot and cold streams. (correct)

It eliminates the need for heat exchangers.

It only involves heating fluids.

What role does heat transfer play in batch sterilization of liquid medium?

To bring the temperature back to normal after heating. (correct)

To eliminate the need for cooling water.

To condense vapor for efficient heating.

To maintain a low temperature throughout the process.

Which method utilizes both fluids flowing in opposite directions?

Co-current heat exchanger

Fluid heater

Counter current heat exchanger (correct)

Vapor condenser

Which of the following best describes the resistances present in heat exchange through a solid wall?

Hot-fluid film resistance, wall resistance, and cold-fluid film resistance Signup and view all the answers

What is often necessary to manage in fermenters to ensure proper operation?

The removal of excess heat due to metabolic activity. Signup and view all the answers

Which type of heat exchanger would typically have both fluids moving in the same direction?

Co-current heat exchanger Signup and view all the answers

What is the unit of the heat transfer coefficient?

W.m-2K-1 Signup and view all the answers

Why is it important to control temperature in a bioreactor during operation?

To avoid excessive heat from metabolic activity. Signup and view all the answers

How is the overall resistance to heat transfer quantified in the context of a wall separating two fluids?

As a sum of the hot-fluid resistance, wall resistance, and cold-fluid resistance Signup and view all the answers

What is the equation used to express the rate of heat transfer through the wall?

Q = UA Signup and view all the answers

What equipment is commonly used for heat transfer in a chemical process industry?

Heat exchangers Signup and view all the answers

In the context of overall heat transfer, what does the symbol U represent?

Overall heat transfer coefficient Signup and view all the answers

What is one function of a heat exchanger?

To provide thermal contact for heat exchange. Signup and view all the answers

What is the principle behind Fourier's law of heat conduction?

The rate of heat flux is directly proportional to the temperature gradient Signup and view all the answers

In a steady state conduction scenario, how is heat flow characterized?

The rate of heat flow remains constant at each point in the wall Signup and view all the answers

What does the term 'Rw' represent in the context of heat transfer?

Overall heat transfer resistance Signup and view all the answers

How is the overall thermal resistance of a composite wall calculated?

Sum of individual resistances Signup and view all the answers

What is the formula used to determine the heating surface area in heat exchangers?

A = Q / (U * Tm) Signup and view all the answers

What is required to perform a proper design of a heat exchanger?

Initial and final temperatures for both fluids Signup and view all the answers

Which of the following statements regarding heat transfer mechanisms is correct?

Conduction occurs through solid walls during heat exchanges Signup and view all the answers

What does the log mean temperature difference (LMTD) help to calculate in heat exchangers?

The area required for proper heat exchange Signup and view all the answers

What is the heat exchanger area required to cool 55,000 lb/hr of light oil from 190°F to 140°F using cooling water?

1800 ft² Signup and view all the answers

What is the specific heat of the light oil used in the cooling process?

0.74 Btu/lb.°F Signup and view all the answers

What is the allowable heat increase of the cooling water in the given problem?

60°F Signup and view all the answers

If the cooling water flow rate is to be calculated, what would be the required mass flow rate of the cooling water necessary for the cooling process?

40,000 lb/hr Signup and view all the answers

What initial estimate is given for the Overall Heat Transfer Coefficient in the heat exchanger?

120 Btu/hr.ft².°F Signup and view all the answers

When liquids contact a solid surface in a heat exchanger, which layer is primarily responsible for heat transfer resistance?

Thermal boundary layer Signup and view all the answers

What diameter and length of tubes are considered in the design of the shell and tube heat exchanger?

3 inch diameter and 10 ft length Signup and view all the answers

During the convective heat transfer, which aspect of the fluid affects the rate of heat transfer significantly?

Fluid velocity Signup and view all the answers

Study Notes

Heat Transfer

Heat transfer is a key unit operation in chemical and bioprocess plants.
It involves the exchange of heat between a hot and a cold stream, not just the heating of fluids.
Understanding the rate of heat transfer allows for calculations of surface area and other conditions for the heat transfer system.
The text describes four types of heat exchangers based on fluid flow and phase change.
- Countercurrent heat exchanger: fluids flow in opposite directions without phase change.
- Cocurrent heat exchanger: fluids flow in the same direction without phase change.
- Fluid heater using condensing vapor: a fluid is heated by condensing vapor, like steam.
- Fluid cooler using a boiling liquid: a fluid is cooled by a boiling liquid.

Need for Heat Transfer

Two applications of heat transfer are crucial in bioreactor operations:
- Batch sterilization: heating and holding the fermenter vessel with the medium at a set temperature to sterilize it.
- Temperature control: removing heat generated by metabolic activity in fermenters to prevent excessive temperature rise. Most fermentations occur between 30°C and 37°C.

Mechanism of Heat Transfer

There are three main methods of heat transfer:
- Conduction: heat transfer through a solid wall.
- Convection: heat transfer within a bulk fluid, driven by mixing and turbulence.
- Radiation: heat transfer through electromagnetic radiation.

Conduction

Conduction is the primary method of heat transfer through a solid wall of a heat exchanger.
Fourier's Law is used to calculate the rate of conduction.
Fourier's Law states that the rate of heat flux is directly proportional to the temperature gradient.
The rate of heat flow (Q) is determined through Fourier's Law, where k is thermal conductivity, A is the area, and dT/dy is the temperature gradient.

Steady-State Conduction

When there is no accumulation or depletion of heat within the wall, it reaches steady-state.
The heat flow rate (Q) remains constant throughout the wall at steady state.
The Fourier's equation becomes Q = kAT/B, where B is the thickness of the wall.

Thermal Resistance in Series

For walls composed of multiple layers of different materials, each layer has its own thermal resistance.
The overall resistance (Rw) is the sum of individual resistances (R1, R2, R3).
The overall temperature drop is the sum of the temperature drop across each layer.

Design Equation for Heat Transfer

The design equation helps engineers design heat exchangers for specific purposes and heat duty (Q).
Q = UA * Tm, where U is the overall heat transfer coefficient, A is the heat transfer area, and Tm is the log mean temperature difference (LMTD).
The heat transfer area (A) can be calculated as A = Q/U * Tm.
LMTD is crucial for accurate design, representing the average temperature difference driving heat transfer.

Individual Heat Transfer Coefficient

There are three main resistances to heat transfer:
- Resistance due to the hot-fluid film at the wall
- Resistance due to the wall material
- Resistance due to the cold-fluid film at the wall
Heat transfer through each thermal boundary layer is given by Q = A * where h is the individual heat transfer coefficient.
Resistance to heat transfer on either side of the pipe is given by Rh = 1/hhA and Rc = 1/hcA.

Overall Heat Transfer Coefficient

The overall heat transfer coefficient (U) encapsulates the combined resistance to heat transfer through both fluids and the wall.
Q = UA * T, where T is the temperature difference between the bulk fluids.
Total resistance (RT) is the sum of all resistances: RT = Rh + Rw + RC.

Fouling Factor

Over time, deposits can form on heat transfer surfaces (fouling).
Fouling affects heat transfer efficiency, leading to a higher required area for the same heat duty.
The greater the fouling, the higher the overall heat transfer coefficient must be to maintain the same heat transfer performance.

Heat Transfer Equipment

The text provides information about the design and calculation of heat transfer areas in various types of heat exchangers.
Understanding the design equations and the LMTD is essential for designing effective heat exchangers.

Conclusion

This information highlights the importance of heat transfer in chemical and bioprocess industries.
Engineers can use this information to design and optimize heat exchangers for various applications.
The text also emphasizes the importance of understanding the different mechanisms of heat transfer and the factors that affect them.

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Description

This quiz explores the fundamental principles of heat transfer as it applies to chemical and bioprocess plants. Key concepts include different types of heat exchangers and their applications in operations such as batch sterilization. Test your knowledge on how heat exchange impacts system efficiency and design.