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Copy of The Effect of Mechanical Geometries on Cost and Thermal Performance of Shell and Tube Heat Exchanger

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abeer alfuqaha'a

on 15 May 2013

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Transcript of Copy of The Effect of Mechanical Geometries on Cost and Thermal Performance of Shell and Tube Heat Exchanger

The Effect of Mechanical Geometries on Cost and Thermal Performance of Shell and Tube Heat Exchangers Abstract Prepared by:


Abeer Y. Alfuqaha'a
Bayan M. Hmedat
Ghadeer M. Shana'ah
Heba T. Harb
Sarah O. Al-Majali
In this project the effects of baffle cut, pitch ratio, tube size, tube layout and the number of tube passes on the efficiency and the cost of shell and tube heat exchanger will be studied using Express Software .
We had run the software for three different cases . 
then were studied and analyzed the resulted figures to meet the objectives of our project .
As a result of our comparison, a strong relationship was found between the physical properties of both fluids in the Shell and Tube Sides and the mechanical geometry and thermal design.  Objectives 1- To investigate the effect of mechanical geometry on the thermal performance of Shell and tube heat exchangers:
 
- Baffle Cut
- Pitch Ratio
- Tube Layout
- Tube Size
- Number of Tube Passes 

2- To study the effect of physical properties on the behavior of heat exchanger. 

3- To minimize the cost of designing and operating the heat exchanger. 
What is the heat exchanger ? Applications and Uses - Power Plants
- Oil Refineries
- Manufacturing industries
- Nuclear Power Plants
- Food and Dairy Industries
- Refrigeration systems Shell and tube heat exchanger Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contains the fluid that must be either heated or cooled. 

The second fluid runs over the tubes that are being heated or cooled Shell and tube heat exchangers are typically used for high-pressure applications. 

It provides a comparatively large ratio of heat transfer area to volume and weight. 

Can be reasonably easily cleaned, and it’s components most subject to failure can be easily replaced. What are the main components of an STHE

providing the heat transfer surface between one fluid flowing inside the tube and the other fluid flowing across the outside of the tubes.

Channel Covers

The channel covers are round plates that bolt to the channel flanges and can be removed for tube inspection without disturbing the tube-side piping.
  
Tube Sheets

The tube sheet is usually a single round plate of metal that has been suitably drilled and grooved to take the tubes.  Shell side nozzles

The shell is simply the container for the shell-side fluid, and the nozzles are the inlet and exit ports.
 
Tube-side Channels and nozzles

Nozzles Tube-side channels simply control the flow of the tube-side fluid into and out of the tubes of the exchanger.
  Definitions Tube Pitch

Tube pitch is defined as the shortest distance between two adjacent tubes. 

Tube bundle

A set of tubes and may be composed of various tube configurations: plain, longitudinally finned, etc. Baffle cut

Is the ratio of the baffle window height to the shell inside diameter, it varies between15% to 45%of the shell inside diameter.   

Baffle spacing

Is the distance between baffles, optimal baffle spacing is between 40% to 60% of the shell diameter. 

Tube Layout Patterns

It refers to how tubes are positioned within the shell .There are four tube layout patterns such as :Triangular (30º),triangular (60º),square (90º),rotated square (45º). Industrial Case Studies Now we will discuss the behavior of three cases and the effect of changing the mechanical geometries on :
 
Predicted total cost.
Pressure drop in both shell side and tube side.
Clean O.H.T.C.

Our conclusions will be useful to optimize the best design of a shell and tube heat exchanger. Case study (1)

This case deals with stream of high viscosity, where the density in tube side (cold stream) =838.8 kg/m³,and in shell side (hot stream)= 951 kg/m³  

Case study (2)
 
This case deals with stream of low viscosity where the density in tube side =740 kg/m³ and in shell side =770 kg/m³ Case study (3) physical properties of case (2) such as:

- Density
- Specific heat capacity
- Thermal conductivity
- Viscosity
- wall thermal conductivity   And the same duty of case (1) such as:

- Flow rate
- Inlet temperature
- Outlet temperature
- Allowable pressure drop
- Fouling resistance
- Minimum velocity Total predicted cost vs. Baffle cut Total pressure drop in tube side vs. Baffle cut Total pressure drop in tube side vs. Baffle cut Effect of baffle cut change Observations and Conclusions 1- The mechanical geometries (Baffle Cut, Pitch Ratio, Tube Size, Number of Tube Passes, and Tube Layout), have clear effects on the thermal and hydraulic design (Overall Heat Transfer Coefficient, and the Total Pressure Drop in both Shell and Tube Sides) of Shell and Tube Heat Exchanger.  2- In both cases where light and heavy streams are applied, the total predicted cost, pressure drop and the overall heat transfer coefficient (O.H.T.C) decrease with an increasing in the tube size. However when examining the effect of the physical properties, the cost behavior converted from increasing to decreasing at a certain point. But pressure drop and O.H.T.C are slightly affected. 3- The predicted cost and overall heat transfer (O.H.T.C) are slightly affected when increasing the pitch ratio for both light and heavy streams cases and the total pressure drop in the tube side increases with the increase of pitch ratio. By changing the physical properties, the pressure drop and cost are slightly affected but there is no effect on the O.H.T.C. 5- In general, increasing the number of tube passes causes an increase in pressure drop, and cost of the heat exchanger. Whereas, O.H.T.C increases until it reaches the maximum, then drops with an increase in the tube passes. Change in the physical properties cause a slight effect on cost, pressure drop and O.H.T.C. But the optimum cost and pressure drop are achieved at the same number tube passes but differ for O.H.T.C. 6- When, increasing baffle cut, the predicted cost decreases for both cases of light and heavy streams, therefore, the baffle cut that gives a minimum cost which should be chosen. Tube side pressure drop and O.H.T.C increase as long as baffle cut increases. Changing the physical properties can cause slight effect on the cost, pressure drop in shell side and O.H.T.C parameters, and has no effect on the pressure drop in tube side. It is noticed that the pressure drop in shell side is only affected by baffle cut. The end Baffles

Increase the speed of shell fluid and intensify the turbulent level to improve the shell film coefficient of heat transfer; baffles are installed on the shell side.They also support the tubes for structural rigidity, thus prevent tube vibration and sagging. 4- With increasing layout, the predicted cost increases slightly also the total pressure drop in the tube side increases for heavy and light cases. The O.H.T.C has an optimum value at same layout = 90% for both heavy and light streams. The change in the physical properties streams has consistent behavior for cost, pressure drop and O.H.T.C above the 60 % layout. A heat exchanger is a device in which heat transfer occurs between two fluids at different temperatures separated by a solid wall.
  - Tubes
- Channel cover
- Tube sheet
- Shell side nozzles
- Tube side channel and nozzle
- Baffles
- Shell cover Tubes All thanks to our teachers who gave us great honest help, and specially our project supervisor. Express software that is used to study the effect of changing the mechanical geometries Clean O.H.T.C vs. baffle cut
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