Latest Published PapersNovember 29, 2017
We have a substantial collection of published papers available to registered members, with detailed information about various aspects of heat exchangers.
Here below is information about the latest published papers, made available during the second half of 2017.
These are available via the Knowledge Base (You need to login first to get access)
PP90 – Use of hiTRAN tube side enhancement in revamps to improve operability and efficiency
Peter Drögemüller and Peter Ellerby (CALGAVIN)
Over the past decades various innovations in the design of heat exchangers have been major driving forces in the improvement of thermal process efficiency. hiTRAN thermal systems is an example of one of those technologies. The enhancement technique is applied on the tube side of tubular heat exchangers and can play a vital role in boosting the performance of this equipment. It is of special interest in revamp situations since it can be installed in situ during operational shut down. The technology can be used most efficiently in tubular single and two-phase heat exchangers were poor tube side heat transfer is the limiting factor. Poor performance can be found in exchangers operating under laminar and transitional flow conditions.
Here hiTRAN technology can offer up to 8 times higher tube side heat transfer for the same pressure drop compared to the empty tube design. This increased performance can be used in different ways. Often increased throughput is the highest priority. But reduced or increased outlet temperatures or lower temperature driving forces between the fluids can be of equal value for the plant operator to apply this technology. Apart from the clear economic benefits, the use of this technology offers also operational benefits. Examples of this are suppression of waxing problems in aircooler operation or the suppression of flow instabilities in thermosiphon reboilers. The paper explains the basic concept how and when to apply this technology in single and two phase applications. Real case studies are presented, which show in detail the benefits when using hiTRAN technology in retrofit scenarios.
PP91 – Computational Fluid Dynamics investigation of air cooled heat exchangers
William Osley, Peter Drögemüller and Peter Ellerby (CALGAVIN) and Ian Gibbard (Progressive Thermal Engineering)
Cooling of process streams is a standard operation in many industries, and where possible water cooling is the most cost effective solution. However, in areas where water supply is limited Air Cooled Heat Exchangers (ACHE’s) are often the only alternative. The overall coefficient is limited by the air side heat transfer. To improve this coefficient the air flow should be evenly distributed and at as high velocity as possible over the whole bundle. The limits are set by the fan power consumption and the generated noise level. The required fan power forms a significant part of running costs. In order to keep these costs as low as possible knowledge concerning the flow distributions within the bundle can be important.
Fluid bypass within the tube-side can be of similar importance. In design calculations, an equal fluid flow velocity per tube is typically assumed from the total inlet mass flow. However, if some of the fluid bypasses the tube bundle due to poor header design lower than expected fluid velocities in the tubes will be found, leading to underperforming ACHE’s, since heat transfer and fouling behaviour are influenced by the fluid velocity.
In this paper, Computational Fluid Dynamics (CFD) techniques will be used to investigate the tube side and air side flow of ACHE’s. CFD has been found to be a powerful tool to investigate how fluid flows through a defined geometry. The main focus will be on finding areas of fluid maldistribution within the air side and the effect of bypass on the tube-side of ACHE’s.
PP92 – Values and benefits of improving the performance of existing heat exchangers used in the hydrocarbon processing industries
Peter Drögemüller and Martin Gough
The selection of equipment type, design, and geometry specification in the field of heat exchangers may be considered to be quite a simple task, using relatively accurate performance predictions based on well proven methodologies. In reality and for many cases this concept of assumed accuracy can be far from the truth. Limitations include the inherent in-accuracy of the fundamental data available, anomalies in predicting specific fluid flow dynamics, effects of wall friction causing fluid maldistribution, 2-Phase flow instabilities together with transient and unstable temperature gradients.
A further and significant level of uncertainty is the unpredictable impact of fouling. This all leads to the need for design engineers to make significant and ‘subjective allowances’ based on ‘experience’ to meet the level of commercial confidence required to fulfil the technical contract. It follows from the above that often heat exchangers do not meet performance requirements at the beginning or fail to maintain performance level over time. These often critical processing limitations become substantial challenges to plant engineers.
An area of fundamental and applied research together with associated product development that has growing success to meet these multi-variable design and performance challenges is discussed in this paper. The paper includes: The contribution and benefits provided by the use of CFD in determining boundary layer effects and combating fluid mal-distribution. The value of selecting the appropriate wall shear rate to reduce the effects of fouling. It explains the application of enhancement techniques to significantly improve the performance of tubular exchangers. Presentation of a refinery case study, demonstrating plant improvement energy recovery and associated improved plant economics.