[TRNSYS-users] Parameter settings for Type 534

[Song Aoye]

Thank you for your suggestion.

In fact, it is because I don't quite understand the physical meaning of these parameters, and it is also difficult to find satisfactory answers on Google, so I misunderstood the meaning of Tube Length before, which led to the error in my setting.

I will try to find a real immersed heat exchanger to fix my model.




Aoye


-----Original Messages-----
From:"Jeff Thornton" <thornton at tess-inc.com>
Sent Time:2022-06-04 23:01:00 (Saturday)
To: "TRNSYS users mailing list at OneBuilding.org" <trnsys-users at lists.onebuilding.org>
Cc: "Song Aoye" <soymail at pku.edu.cn>
Subject: Re: [TRNSYS-users] Parameter settings for Type 534

From looking at your parameters, I’m guessing that this doesn’t represent a real heat exchanger that you’re trying to match as you specify a horizontal tube bank and then only have one tube - and it’s 30 meters long.  So unless your tank is 30 meters long this probably isn’t right.  


So you’d like more heat transfer - so that means either more HX surface area or lower heat transfer resistance (or a bigger temperature difference but it sounds like you’re comfortable with those conditions).  The pipes are copper and the Nusselt number parameters are pretty good (could go higher on the multiplier (maybe up to 1) and slightly higher on the exponent (maybe up to 0.3)) so your best bet is to add more tubes, make the tubes bigger, etc.  


Like many questions asked here, the answer is usually along the line of “What would you do in real life to fix it”.  Always start there as almost all TRNSYS models are based on the physics of the real equipment.


Jeff 


Sent from my iPhone

On Jun 4, 2022, at 8:41 AM, Song Aoye via TRNSYS-users <trnsys-users at lists.onebuilding.org> wrote:



Dear All,




Does anyone know how to set up the immersed heat exchanger so that its heat transfer capacity can be increased?

My current setting is:

Exchanger type        horizontal tube bank
Fluid        20% Ethylene Glycol solution
Multiplier for Natural Convection Correlation        0.6
Exponent for Rayleigh Number        0.25
Geometry Factor        1
Geometry Factor Exponent        0
Tube lnner Diameter        0.098 m
Tube Outer Diameter        0.105 m
wall Conductivity        1440 kJ/h m K
Tube Length        30 m
Number of Tubes        1
Header volume        0.0226 m3
Cross Sectional Area        0.0075 m2


This setting will make it difficult for the cold energy of the fluid in the exchanger to be transferred to the water tank. 

When the temperature difference between the fluid in the exchanger and the water outside is 5 °C, the temperature of the fluid flowing into the exchanger will only increase by 0.13 °C after it flows out. 

So how should I change the above parameters to make the heat transfer ability of this exchanger stronger?

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