2 replies to this topic

[pratik]

Hello Folks,

 

For the current ongoing feasibility study project I have the following issues in calculating the flowrate of Hot water through Jacketed Pipe & Jacketed Vessel:

 

Jacketed Pipe:

1. I have a product which is highly viscous and need to maintain the temperature in the pipe to 52 deg C, below 45 deg C it becomes thicker and the pump is not designed for that viscosity. The product rate is 190 cu.m per hr, density 950 kg/m3, viscosity of 56 cP and thermal conductivity of 0.15 W/(m K). It was recommended to use Hot water jacketing around the pipe and maintain the temp to 52 C. The hot water is available at 65 deg C. The product pipe size is 200 NB
2. Approach 1: If I assume that the temp drop across the product is 1 deg C then I need to heat the product from 51 C to 52 C using hot water which has a delta T of 10 C and hence by simple heat balance across the product and the water gives me :

Mass of water (kg/hr) = 190*950*1.91*(52-51)/(4.18*(65-55)) = 8,248 kg/hr = 8.24 cu m per hr

But this seems to be on a very much higher side. Am I correct??

1. Approach 2: If I insulate the product pipe with rookwool, and using insulation thickness calculation method I arrive at a figure of 50 mm thickness, with a heat loss to the surrounding as 37.2 W/m of pipe. Surrounding atmosphere conditions Air at 0 deg C and velocity of 5 m/s.

And if consider zero thickness the heat loss to surrounding as 600 W/m of pipe. If then I use water to circulate around to absorb this much heat loss then the water required is 52 kg/hr.

 

Kindly advise which approach shall I follow in order to calculate the water required in jacketed pipe.

 

Jacketed Vessel:

1. I have a product which is highly viscous and need to maintain the temperature in 3 batch storage vessel, the vessel dia is 5 m and height is 10 m and volume is 200 cu.m each.

The required temp to be maintained in the vessel is 52 deg C, below 45 deg C it becomes thicker and the pump is not designed for that viscosity. Density 950 kg/m3, visocisity of 56 cP and thermal conductivity of 0.15 W/(m K). It was recommended to use Hot water jacketing around the vessel and maintain the temp to 52 C. The hot water is available at 65 deg C.

 

Kindly advise how to calculate the Hot water rate. There is no product rate as its a batch process the volume of the vessel is apprx the mass of the product.

 

Regards

Pratik

[Pilesar]

Why do you assume to have a temperature drop across the product pipe? Drawing a sketch might be helpful to your understanding when you see the heat transfer surfaces in diagram. For example, your Approach 2 describes product inside a pipe enclosed with rockwool and surrounded by air. It makes little sense to then jacket the air layer with water(?). You do not have heat transfer between the product and the air when the product pipe is completely enclosed with a water jacket. Instead, the heat lost to the air comes from the water. The question to answer is "How much water should flow to keep the water temperature above 52 C." As long as the water temperature is above the product temperature, there will be no heat lost from the product to the water.

[Pingue2008]

Pilesar,

 

something is not adding up in your calculations. I do not understand where you get your number.

please make an excel spreadsheet it will be easy to track where you are going wrong. I think the specific heat of your fluid is not given.

correct me if I am wrong.

1- your fluid can not be cooled under 45C. if this the case, a starting point for your product stream Q= (Heat capacity)*(Flow Rate)*(52C-45C)

2- Q=(heat capacity of hot H2O)*(Flow rate of Hot water)*(T-65C) at this point there are  two unknowns flow rate of hot water and the temperature T of the outlet of the hot fluid.

3- to solve you need a third equation Q=A*U*LogMeanTemp

Now you can solve two equation with two unknowns (U for your service can be in literatures) I guess you know the pipe length .

4- in my opinion the process should be as describe above but this time, the geometry of the tank should be taken into account.

 

Thank you,