Techno-Societal 2018 pp 725-743 | Cite as

# Thermal Design and Performance Analysis of a Cross Flow Heat Exchanger Using Plain and Almond Dimple Tubes

## Abstract

Thermal performance analysis of a cross-flow heat exchanger using plain and almond dimple tubes has been investigated. Hot air and water are used as fluids on shell and tube side respectively. Reynolds Number is obtained in the range of 9000–30,000 by varying the mass flow rate of air on the shell side of cross-flow heat exchanger. The performance parameters such as overall heat transfer coefficient, water side heat duty, effectiveness, pressure drop are calculated for both the plain and dimple tubes. The dimpled tubes show heat transfer enhancement by 30% and more efficient heat recovery over plain tubes at the cost of small pressure drop penalty.

## Keywords

Cross flow heat exchange Dimple Heat transfer coefficient Pressure drop## Nomenclature

- B
Breadth of shell

*(s)*The effectiveness of the heat exchanger

*μ*Absolute viscosity

*ρ*Density

*A*Area available for heat transfer

*A*_{s}Actual shell side flow area

*A*_{t}Area of flow through each tube

*A*_{s1}Area of shell

*A*_{s2}Tube area blocking the flow on the shell side

*C*^{∗}Ratio of heat capacity

*C*_{L}Clearance between shell and tube

*C*_{max}Maximum heat capacity rate

*C*_{min}Minimum heat capacity rate

*c*_{ps}Specific heat capacity of air on the shell side

*c*_{pt}Specific heat capacity of water on the tube side

*d*_{i}Tube inner diameter

*d*_{o}Tube outer diameter

*D*_{ht}Hydraulic diameter on the tube side

*F*Factor for shell side heat transfer coefficient

*F*Friction factor

*tt*_{s}Gas mass velocity on the shell side

*H*Height of shell

*h*_{s}Heat transfer coefficient on the shell side

*h*_{t}Heat transfer coefficient on the tube side

*k*_{s}Thermal conductivity of air on the shell side

*k*_{t}Thermal conductivity of water on the tube side

*L*Tube length and Length of shell

*LMTD*Log Mean Temperature Difference

*m*_{s}Mass flow rate of air on the shell side

*m*_{t}Mass flow rate of water on the tube side

*N*_{d}Number of tube columns

*N*_{w}Number of tube rows

*N*_{us}Nusselt number on the shell side

*N*_{ut}Nusselt number on the tube side

*NTU*Number of Transfer Units.

*P*_{L}Longitudinal Pitch

*P*_{s}Pressure drop on the shell side

*P*_{T}Transverse Pitch

*P*_{ld}Dimensionless Longitudinal Pitch

*P*_{rs}Prandtl number on the shell side

*P*_{rt}Prandtl number on the tube side

*P*_{td}Dimensionless Transverse Pitch

*Q*Overall heat duty

*Q*_{s}Heat duty on the shell side

*Q*_{t}Heat duty on the tube side

*R*Capacity ratio

*R*_{es}Reynolds number on the shell side

*R*_{e}Reynolds number on the tube side

*S*Temperature ratio

*(s)*Tube thickness

*T*_{i}Air inlet temperature on the shell side

*t*_{i}Water inlet temperature on the tube side

*T*_{o}Air outlet temperature on the shell side

*t*_{o}Water outlet temperature on the tube side

*T*_{avg}Average (bulk) temperature on the shell side

_{Tavg}Average (bulk) temperature on the tube side

*U*Overall heat transfer coefficient

*V*_{s}Velocity of flow of air on the shell side

*V*_{t}Velocity of flow of water through the tube

*w*_{t}Mass flow rate through each tube

*F*_{t}Temperature difference correction factor

- C
Factor for tube side heat transfer coefficient

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