As milk is a mix of various protiens, fats and minerals there is a range of properties. Generally for whole milk,
GS varies 1.03 - 1.04
Viscosity 4.28 CPoise@ 0C
2.12 CPoise@ 20C
Specific Heat 3.89 kJ/kg.K (Note there is an eutectic point around 20C where the specific heat increases due to a change in state for the fat content)
Thermal COnductivity 0.15 W/m.C
These figures have been collected over the years, I recomend you run some tests to determine actuals for your product and area. BTW where are you and what are you using the figures for?
Thanks Mark.
We are in Ontario, Canada and want to do some in-house testing of a milk processing concept that was presented to us for possible development.
Why is a shell&tube HX used, instead of a plate type? For liquid food processing especially in milk, the majority of heat exchangers is of a plate type.
As a higher heat transfer coefficient can be obtained, the are in general smaller and closer temperatures can be used/reached.
What is the HE used for?
In some jurisdictions milk handling equipment is required to be completely disassembled for cleaning periodically (daily in some cases) and PHE's meet that requirement. S&T's can't be cleaned in the same manner.
It is actually this cleaning that is the issue for our customer.
The higher heat transfer coefficient is secondary to the cost of the cleaning effort.
We are working on developing an "easily cleanable" S&T HX unit.
Why reinvent the wheel, an Australian Company have developed an efficient and CIP'able unit used widely in the dairy industry. I hope this does not bring down the wrath of the moderatord but Hipex are the company. They may be worth talking to.
With a corrugated tube you might create more turbulence than in standard shell & tube and therefore the cleaning effect will be higher. But still the turbulence in a plate heat exchanger will be much higher, therefore be easier to clean by CIP, and on top of that it can be easily disassembled for inspection.
Another advantage of a PHE is the fact that you can have them with double plates. This means that if a leakage in a plate occurs, you will notice this on the outside by small droplets, before contamination occurs.
Another thing you might need to consider, is the flowrate you need for CIP.In general this will be higher than the flowrate normally used. When using shell and tube, you will need more surface (lower HTC), use a larger fouling coefficient (which creates even more surface) due to less turbulence, need more CIP fluid (due to less turbulence). All of this might make a bigger pump necessary.
They are all shell & tube or Tube/Tube manufacture. APV and others also supply similar products. I have worked with Hipex and found them to be very good and supportive with their equipment. They have also assisted in development of H/X in dairy processes such as custard, yoghurt and other thick difficuly products.
DYV1973, the hipex tube/ube H/X units feature double seals with leak detection similar to a single plate PHE. The double plate PHE's will suffer with reduced performance. S&T and T/T heat exchangers have fewer seals compared to PHE's. There are many reasons to choose one over the other. Requirements of the process should determine the equipment selected. Shear sensitive products for example cannot always be handled in a PHE due to the higher turbulence and smaller flow paths.
@Mark
You are right that a PHE has more gaskets than a S&T, but for low viscosity products and food processes (which do not have that high pressure pulsations) this should not be a problem.
For shear sensitive and high viscosity products (like yoghurt), a tubular design will be a better solution, because you do not want turbulence and you want to maintain pressure losses as low as possible (otherwise pumps will need to force the product through, and you will have the shear problem there).
But the discussed application is milk....
The reduced HTC of a double plated PHE compared to single plated PHE is obvious, but if you want to have a design with leak detection on the heat transfer area you will always need double plates or pipes.
With a PHE you can have to plates (2x 0.35 mm) closely together, which will give you still a better HTC in general than a S&T.
I mentioned APV as they have a product range which includes all the described shell and tubes (multi-tube, tube in tube, corrugated tube), as well as scraped surfae HE and a complete range of PHE (single and double plated) for the dairy industry. And as they manufacture all the alternatives, they might be able to give a more unprejudiced advice than a company that manufactures only one of them (of course there are more Alfa Laval/Tetra or Gea).
