Optimizing Heat Transfer in Pasteurization Systems: A Thermodynamics Question

[Jake Platt]

Hello,

For the purpose of developing a pasteurization system to kill food-borne pathogens, I am trying to devise a process to rapidly transfer heat from a hot-water (~220F because it is a brine solution not just water) delivery system to incoming food commodities (ambient temperature of 60-70F) in a large holding vessel.

Once the commodities are conveyed into the vessel, they are exposed to the hot water for about 3 minutes. The hot brine water is continuously pouring in at a constant temp (220F) and the products are slowly conveyed through the vessel to give the 3 minute residence time.

Now, the problem at hand is that the temperature of the water drops rapidly and the ambient temperature of the air and water within the vessel drop to around 120F. These temps are so low that the surface-level exposure of the food is not hot enough to effectuate a meaningful microbiological kill on contact with the water.

My question is what can I do to raise the air and water temps inside the vessel? I know I can raise the air pressure of the system to increase temps but that is a large complexity given the need to convey product in and out. Should I be watching relative humidity or some other factors? How can I increase the ambient temps inside the vessel by other means? The incoming commodities cannot be heated prior to arrival into the system.

Thank you.
Jake Platt

 

[Mech_Engineer]

Sounds to me like you have to increase the flow rate of the 220* water entering the tank. That, or possibly increase insulation on the tank and reduce the speed of the food passing through it.

Humidity alone will not account for the 100* drop in temperature you're seeing. You just aren't putting enough energy into the system right now to maintain a 220* temperature difference.

 

[DarioC]

Put a high output heating system on the tank itself to supply the additional energy required to keep the temperature up.
As in; build a fire under it.
DC

 

[dlgoff]

The hot brine water is continuously pouring in at a constant temp (220F) and the products are slowly conveyed through the vessel to give the 3 minute residence time.

So are you saying that the brine goes into the product?

If not, why not circulate the brine water through a heat exchanger (tubes) inside your vessel?

 

[russ_watters]

Is the vessel insulated?

 

[Jake Platt]

Thank you your your suggestions and questions.

The vessel is a large stainless steel perforated tumbler which is shrouded by stainless steel around it. It is uninsulated but I can try that. The perforations of the vessel allow the water to collected for recirculation. We can't put the water into a heat exchanger because it needs direct product contact for the microbial kill.