HEAT TRANSFER & HEAT EXCHANGERS CHBE 446 – Group5 Stephan Donfack Benjamin Harbor Nguyen Huynh Cyndi Mbaguim

AGENDA  Concept and Mechanism  Heat Transfer Equations  Design  Material Selection  Conclusion

CONCEPT Definition Discipline of thermal engineering that involves the generation, use, conversion, and exchange of thermal energy and heat between physical systems. The driving force of heat transfer is as result of temperature gradient between two regions. During heat transfer, thermal energy always moves in the same direction: HOT COLD

Mechanism for Heat Transfer Three types of energy transfer : -Conduction: Transfer of heat within a substance by molecular interaction. -Convection: During macroscopic flow, energy associated with fluid is carried to another region of space. -Radiation: Heat transferred through wave energy (electromagnetic waves)

Q hot Q cold ThTh T i,wall T o,wall TcTc Region I : Hot Liquid- Solid Convection NEWTON’S LAW OF CCOLING Region II : Conduction Across Copper Wall FOURIER’S LAW Region III: Solid – Cold Liquid Convection NEWTON’S LAW OF CCOLING THERMAL BOUNDARY LAYER Energy moves from hot fluid to a surface by convection, through the wall by conduction, and then by convection from the surface to the cold fluid.

PROJECT FLOWSHEET

HEAT EXCHANGERS in INDUSTRY Commonly used throughout the chemical process industries as a means of heating and cooling process in product streams. Common industry utilization: Space heating Refrigeration Air conditioning Power plants Petrochemical plants Petroleum refineries Natural gas processing Sewage treatment

TYPES of HEAT EXCHANGERS Double-pipe Shell and tube Plate and frame Spiral Pipe coil

CONFIGURATIONS IN HEAT EXCHANGERS Co-current flowCounter-current flow Double tube – Single Pass Heat Exchanger

TEMPERATURE PROFILE

HEAT TRANSFER EQUATION IN HEAT EXCHANGERS

Log Mean Temperature Difference (LMTD) CO-CURRENT CONFIGURATION COUNTER CURRENT CONFIGURATION

Heat Duty (Q) ASSUMPTIONS - Steady State - No phase changes - Negligible heat loss - Constant overall heat transfer

Overall Heat Transfer Coef (U) X w : wall thickness K m : thermal conductivity of wall h i, h o : individual convective heat transfer coef coefficients in & out of tube Di, D o: Inner & outer diameter

DIMENSIONLESS ANALYSIS TO CHARACTERIZE H.E h = convective H.T coef K = conductive H.T coef µ = dynamic viscosity ρ = density C p = heat capacity ν = mean velocity D & L = Length scale parameters

ESTIMATED U  Overall Heat Transfer Coefficient can be estimated for different fluids as well as the type of heat exchanger system involved (Shell & Tube).  Frequently used sources: o Perry’s Handbook o ChemE Design Textbook o Aspen Tech Software…

Area (Sizing)

HEAT EXCHANGERS IN GAS SWEETENING Simplified schematic of gas sweetening process

HEAT EXCHANGER DESIGN The main heat exchanger called rich/lean amine interchanger. It requires:  Good heat recovery  the thermal length of heat exchanger is a key feature.  To minimize the fouling tendencies: high pressure drop (above 70 kPa) to keep shear stress high (50Pa)

GASKET MATERIAL SELECTION Normal ethylene propylene diene monomer (EPDM): used in amine systems due to its inherent resistance to H 2 S and CO 2. Disadvantage: suffers degradation from hydrocarbons or other fluids on an increasing severity based on the degree of the non-polar nature of the fluid Plate with EPDM gasket

CONT’d EPDM XH is a combination of EPDM and other rubber resins creating an extra hard EPDM rubber, developed for applications with hydrocarbon exposure. Other rubber materials: Aflas gaskets can be used for amine duties, but not longer lifetime and increase capital investment and replacement cost.

SHELL & PLATE HEAT EXCHANGER Using a shell and plate heat exchanger as a reboiler allows a small temperature difference between the hot and cold sides-> prevent amine from overheated and degradation A shell and plate heat exchanger followed by a separator vessel is recommended for condenser. A typical shell and plate heat exchanger

CONCLUSION Select the fit for purpose heat exchanger will improve the performance of the amine plant, reduce investment costs and overall costs of ownership. Selecting the right gasket plate will increase the efficiency while maintenance costs and intervals can be reduced. Shell and plate heat exchangers are more commonly used than shell and tube heat exchangers.

REFERENCE Middleman, Stanley. An Introduction to Mass and Heat Transfer, Principles of Analysis and Design.Wiley, Dec McCabe, Smith, and Harriott. Unit Operations of Chemical Engineering Treat.pdf Treat.pdf