M. Reza Malayeri

Influence of Injected Projectiles on the Induction Period of Crystallization Fouling

Projectiles of various shapes and hardness are increasingly used in process industries to mitigate fouling in tubular heat exchangers. It is a common practice to inject the projectiles at the early stage of fouling, though laboratory results are quite scarce in the open literature to assess whether this is an appropriate operating procedure. The present work aims at investigating the influence of injected projectiles on the induction period of CaSO4 crystallization fouling. Fouling experiments have been performed in a plain heated tube. The projectiles were of spherical shape with diameter of 20.2 mm, that is, 1% bigger than the inner diameter of the heated tube, and were injected at various intervals. It has been observed that overall the attempted projectile reduced the induction period and thus expedited the fouling process. The asymptotic behavior of crystallization fouling is also approached more quickly but much less so than that of no injection. The induction period increased linearly with the flow velocity in case of no injection, while it was independent of the flow velocity when the projectile was injected as long as the injection rate was kept constant. Increasing the injection rate decreased the induction period and started the fouling process earlier. This is because the propulsion of projectiles induces air bubbles into the heat exchanger tube, which would in turn promote fouling to occur more quickly, and thus shorter induction periods are expected. Therefore, it is highly recommended to inject projectiles only after the induction period, to make use of the fouling-free operation during the induction period.

Model-Based Performance of Turbulence Induced Structures in Exhaust Gas Recirculation (EGR) Coolers

Exhaust gas recirculation (EGR) coolers can profoundly reduce hazardous NOx emissions from diesel engines. Nevertheless, the formation of deposits on EGR surfaces causes design uncertainty and maintenance problems. The present study underlines how changing the EGR surface structure for the same inlet velocity can result in substantial increase in shear stress, which otherwise would be needed for an effective deposit suppression. Various structures have been developed, then studied numerically using computational fluid dynamics. The results have been compared with a baseline flat plate rectangular EGR cooler. The numerical findings show that shear stress is increased from 150 to 350% while the overall pressure drop is always below 550 mbar. The geometrical modifications also cause a minor reduction of up to 7% in effective heat transfer area of EGR.

Mitigation of Crystallization Fouling in a Single Heated Tube Using Projectiles of Different Sizes and Hardness

Fouling of heat exchangers is a prevalent operating drawback in many process industries. Efficient chemical inhibitors have predominantly been used for many years to combat deposit formation. Nevertheless, new stringent environmental legislations limit their utilization. On-line mitigation techniques, such as propulsion of projectiles at different injection rates, can also be utilized, which can, in turn, minimize the need for chemical inhibitors. Nevertheless, the experimental data are scarce and nonconclusive. In this experimental study, two spherical-type projectiles of different sizes and hardness have been used to clean the inner surface of a single heated tube that was subjected to the deposition of calcium sulfate. Projectiles were then introduced at different injection rate of every 2, 5, 10, 15, and 30 min. The experimental results show that (i) the projectiles would expedite initial nucleation of crystals even if they are soft and easy to propel inside the tube; (ii) fouling can only be mitigated if the projectiles exert a shear force such that the corresponding removal rate is greater than the net rate of the deposition; and finally (iii) harder projectiles with larger surface contact area are more efficient in cleaning the surface compared to those that are softer.

Propensity of Soot Deposition in a Rectangular Exhaust Gas Recirculation Cooler Using Kalman Filter

The detection of fouling in exhaust gas recirculation (EGR) coolers of diesel engines should be fast and accurate. This would facilitate deciding an effective strategy to combat fouling and to prolong the lifetime of EGR coolers. In the present study, the propensity of soot deposition in a rectangular EGR cooler is modeled using Kalman filters. Noises, coherent feature of many deposition processes which can be resulted from measurement sensors such as thermocouples or incidental deposit flake-off, are also considered in the model. The Kalman filter minimizes the estimation error covariance by considering the measurement and process noise covariance matrices while it can simultaneously handle the noisy data. The results are characterized with measurement process noise covariance. The relation between these two defines the smoothness and shape of the estimated trend of fouling resistance. Comparisons of the experimental data and the resultant model confirmed the usefulness of the applied method for various operating conditions of an EGR cooler prone to particulate deposition of soot particles. The paper proceeds with the impact of such models in monitoring fouling and taking an appropriate mitigation approach in diesel engines.

10th International Conference on Heat Exchanger Fouling and Cleaning—2013 Budapest, Hungary

The heat exchanger fouling and cleaning community is confronted with new challenges that have not been foreseen in the past and with old problems that are increasingly getting worse. For example, the automotive industry utilizes more heat exchangers to meet efficiency and emission standards by reducing NOx through exhaust gas recirculation (EGR) coolers. While theoretically very effective, this technique has been severely hindered by rapid formation of various types of deposit on the cooler surfaces. Along the same lines, oil refineries nowadays have to cope with heavier crude oils or densified residuals with higher risk of fouling from sources that until recently have not been economical to process. World population growth, particularly in arid areas, demands more potable water, which is mainly produced from seawater, which in thermal desalination units is prone to the chronic formation of deposits. Numerous studies have shown that heat exchanger fouling may be responsible for 1–2.5% of global CO2 emissions. Cost penalties due to fouling, for example, for additional fuel, down-time, overdesign, cleaning chemicals, and so on, have been estimated as about 0.25% of the gross domestic product (GDP) of industrialized nations.

Hans Müller-Steinhagen: Up, Up and Away—A Global Career in Research, Education, Management, and Leadership

Address correspondence to Dr. M. Reza Malayeri, Institute of Thermodynamics and Thermal Engineering, University of Stuttgart, Pfaffenwaldring 6, D-70550, Stuttgart, Germany. E-mail: m.malayeri@itw.uni-stuttgart.de Outstanding scientific status can only be achieved through natural talent in combination with exceptional dedication and determination. Professor DEng, Dr.-Ing habil, Dr. h.c. Hans Müller-Steinhagen is a sterling example of such a unique personality. It gives us, as Guest Editors to this special issue of Heat Transfer Engineering, great pleasure to write this editorial to honour him, on the occasion of his 60th birthday on February 22, 2014. This is the celebration of a sharp-minded researcher, an avid writer, a savvy conference organizer, a highly successful manager and research leader as well as a dedicated, caring teacher and supervisor. He rose through the world of academia in an astounding and creative way that can serve as an inspiration to many young academics and graduate students. Hans Müller-Steinhagen—or affectionately Hans as he is known to many of his colleagues, associates, students and friends was born in Karlsruhe, Germany. After graduating with a Diploma of Engineering (the German equivalent of an MSc) from the University of Karlsruhe in 1980, he investigated the flow boiling of cryogenic liquids in the same University under the supervision of Professor Ernst-Ulrich Schlünder, to obtain his first doctoral degree in 1984. Feeling the need to ‘stretch his legs’, he then started a career that took him around the globe and established him as a global player with numerous international collaborative ventures.