2 replies to this topic

[Papps]

I recently carried out heat duty calculation for a couple of Heat Exchangers present in the process which are of Plate & Frame Heat Exchangers after the exchanger plates pack were replacement with new one's due to leakages.

 

From the calculations I have the below observations,

 

- Current flow rate through the heat exchanger is less than the design flow rate

- Current DT is almost double the times the design DT i.e Design DT is 8 deg C but attained DT is 15 deg C

15 deg C was intentional due to the process requirements.

- Confirmed that operating temperatures and pressure profile for the Hot & Cold side are within the design values.

- Calculated Heat Duty of the heat exchanger is less than the design heat duty. Heat duty was calculated based on the cold side flow rate which is known.

- Calculated Hot side flow rate based on the calculated heat duty as Qcold = QHot to verify if the Hot side medium flow rate is more than the design flow rate of hot side as DT is double the times of design DT but it was under the limit.

- Further, Calculated Overall Heat Transfer Coefficient with Heat Duty, LMTD, and Heat Transfer Area which was exceeding more than the design value.

 

What are the problems or negative implications which can be caused in the Heat Exchanger by operating the Heat Exchanger beyond the design Overall Heat Transfer Coefficient? 

 

Is the design Overall Heat Transfer Coefficient value used for the thermal design/manufacturing of the Heat Exchanger parts such that operation of the heat exchanger beyond design Overall Heat Transfer Coefficient value could cause thermal stress or fatigue or material degradation thereby reducing the potential life span of the heat exchanger ?

 

 

 

[Pilesar]

It is common and desirable for new heat exchangers to give results better than the required temperatures. Exchangers are designed to perform as required after they are fully fouled. The new exchanger has no fouling. Performance should decline with time as the exchanger surfaces become less new. There is no problem or negative implication with heat exchanger performance better than design unless it is regret for purchasing more exchanger than absolutely needed.

[Papps]

Thanks for responding to my query.

 

Apologies, I should have been more clearer in first instance. The calculation was for the old heat exchanger which was replaced with new one, calculation results are not for the new exchanger. I carried out calculation to see if there was any deviation from design values in terms of Heat Exchanger operation and found that only Overall Heat Exchanger Coefficient is exceeding design value.