What are the considerations while designing a Plate and Frame Heat Exchanger?

Question

I need to use for viscous fluids.

Answer 1

I would suggest against a Plate & Frame HE. Although they have high heat transfer area and co-efficients, they are not suitable for viscous fluids or fluids that contain suspended matter. You should realize that the clearance between the plates is about 3 mm. Imagine the problems suspended matter would cause. You have a very high transfer area in lower floor space, but the fabrication costs and skills required are very high. Most Plate HE are constructed of SS, I don't know the MOC you plan to use, but SS would burn a hole in your pocket. Also Plate HE are known to cause leakage problems. Computing the numbers of plates is a function of the HT area required to achieve the desired change in temperature. These HE however have the advantage that if you ever need to increase the HT area, all you have to do is add a few plates. The number of plates is dependent on HT area required

Q = U * A * LMTD

Here, U = Overall HT co-effecient

A = Total HT area

LMTD = Log mean temperature difference

To calculate U, you need to know the inside and outside HT co-efficients too.

Plate HE are suitable for lower flow rates and heat sensitive substances. Also if you need high turbulence, than you have to fabricate corrugated plates, which will further add to fabrication costs. The number of plates required is dependent on the flow rate, so if your business is small, your requirements may be lower too. Plate HE are popular for lower pressure drops. Also in a corrugated Plate HE, the pressure drops can be higher than a non-corrugated ones.

Design optimizations can be achieved by conducting an extensive study of your requirements. Dimensions of the plates depend on your flow rate. Remember that a corrugated plate HE will offer higher HT area but pressure drops and pumping costs will be higher too. Moreover, hey are difficult to clean and maintain. I would suggest that you go for a non-corrugated one, that will save you the fabrication, pumping and maintenance costs, but at the expense of HT area. HT area will not be a major concern if you have sufficient floor space.

You have a lot of parameters to consider. Flow rate, temperature difference required, heat load, the other fluid you plan to use to exchnage heat, the plate MOC. Also remember that Plate HE are prone to leaking and make sure you use the proper gaskets. Remember that good gaskets are the key to efficient operation here because they will prevent leakages and also the pressure drops. Operating pressure will determine the thickness, and eventually the cost of the plates. At the end of all, the fabrication, operation and maintenance costs should be considered to arrive at a suitable design.

Answer 2

*Pl. read below:

"Plate heat exchanger.(THERMAL PROCESSING & HEAT TRANSFER)

* Ideal for viscous fluids

* Increased pressure performance

* Wide-gap cross section

T20S wide-gap plate heat exchanger with a plate channel construction is ideal for use with process fluids that would normally clog other types of heat exchangers. Heat exchanger is designed to handle fluids which are highly viscous or contain large amounts of fibers and coarse particles. With a wide-gap cross-section of 11mm, heat exchanger will handle duties that involve fluids too viscous for conventional plate heat exchangers or shell-and-tube heat exchangers. These include sugar mills, distilleries, textile industries and others. It offers the conventional plate heat exchanger benefit of heat transfer coefficients two to three times those of shell-and-tube heat exchangers. Alfa Laval Inc. "

*Spiral plate heat exchangers have a niche in some industrial heat transfer applications due to their

• compact geometry (up to 70 m2/m3)

• good temperature control facilitated by nearly ideal countercurrent flow

• improved laminar heat transfer from low L/D values

• increased turbulent heat transfer from centrifugal force enhanced convection

• good performance for slurries as well as viscous and fouling fluids.

*The heat transfer method takes into account near wall convection effects, which could be significant for highly viscous fluids commonly used in spiral plate heat exchangers. A factor not currently accounted for in any model is the effect of spacer studs in pressure drop and heat transfer predictions. Spacer studs are usually present in spiral plate heat exchangers to maintain channel spacing during fabrication and pressure flexation during operation. These studs are believed to prevent true laminar flow by promoting turbulence. Future models should be further enhanced by explicitly accounting for the effect of various spacer stud patterns.

*Pl. click on:

http://www.genemco.com/catalog/pdf/CA39p...

http://geoheat.oit.edu/pdf/tp54.pdf

*If you really want to design phe for viscous fluid,please have a book:

Fundamentals of Heat Exchanger Design

Ramesh K. Shah, Dusan P. Sekulic

ISBN: 978-0-471-32171-2

Hardcover

976 pages

August 2003

Wiley List Price:  US $185.00

Answer 3

surface area, desired heat loss / retention