**The 2nd International Conference on Advances in Mechanical Engineering**

Editors

**Muhammad Mahabat Khan Mohammad Javed Hyder Muhammad Irfan Manzar Masud**

MDPI • Basel • Beijing • Wuhan • Barcelona • Belgrade

*Editors* Muhammad Mahabat Khan Capital University of Science and Technology Pakistan Manzar Masud

Capital University of Science and Technology Pakistan

Mohammad Javed Hyder Capital University of Science and Technology Pakistan

Muhammad Irfan Capital University of Science and Technology Pakistan

*Editorial Office* MDPI St. Alban-Anlage 66 4052 Basel, Switzerland

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### **Contents**



Reprinted from: *Engineering Proceedings* **2022**, *23*, 17, doi:10.3390/engproc2022023017 ....... **99**


#### **Muhammad Hamza, Ahmad Ali, Saqlain Abbas and Zulkarnain Abbas**

Design and Airflow Analysis of 20 kW Horizontal AxisWind Turbine Blade Reprinted from: *Engineering Proceedings* **2022**, *23*, 11, doi:10.3390/engproc2022023011 ....... **157**


Reprinted from: *Engineering Proceedings* **2022**, *23*, 2, doi:10.3390/engproc2022023002 ....... **185**

### **About the Editors**

#### **Muhammad Mahabat Khan**

Muhammad Mahabat Khan (Dr.) is an Associate Professor and Head of the Mechanical Engineering Department at Capital University of Science and Technology (CUST), Islamabad, Pakistan. He obtained a Ph.D. degree in mechanical engineering with a specialization in Computation Fluid Dynamics from Ecole Centrale de Lyon, France. He served as an Advanced Development Engineer at the Systems Engineering division in Continental Automotive, France. He also worked as a Research Scholar in the Department of Mechanical Engineering, University of Leeds, UK. He has authored more than 30 WOS-indexed journal articles and serves as a reviewer for several international journals. His research interests include: CFD, engine sprays, heat-transfer augmentation, latent thermal energy storage systems, phase-change materials, fluidic oscillators, renewable energy, multi-phase flows, and turbulent flows.

#### **Mohammad Javed Hyder**

Mohammad Javed Hyder (Dr.) is a full professor at the Capital University of Science and Technology (CUST), Islamabad, Pakistan. His field of research focuses on renewable energy, Stirling engine design and development, mechanical system design, turbomachinery, nechanical behaviour of materials, and computational engineering. He has published around 30 articles in the journals and presented more than 35 research papers in the conferences. He has supervised 5 Doctoral theses and 175 Master's theses. He has organized various international conferences. He has teaching experience of about 40 years. He has taught more than 50 subjects in the field of mechanical engineering, material behaviour, computer science and engineering management to graduate and undergraduate students. He has vast experience in management as Dean of Faculty of Engineering, Head of Department of Mechanical Engineering, Head Department of Information and Public Relation and Director of Offices of Research, Innovation and Commercialization (ORICs).

#### **Muhammad Irfan**

Muhammad Irfan (Dr.) is an Assistant Professor of Mechanical Engineering at Capital University of Science and Technology (CUST), Islamabad. He obtained his PhD from Koc University Turkey, during which he worked on the development of a front-tracking multiphase phase change solver for the evaporation and combustion of fuel droplets. Chemkin package was integrated with the phase change solver to handle the chemical kinetics part. His current research interests include phase-change material-based energy-storage devices, performance enhancements of the photovoltaic panels, multiphase flows and ejector refrigeration system. He has published more than 10 articles in reputable international journals.

#### **Manzar Masud**

Manzar Masud is a lecturer at the Department of Mechanical Engineering, Capital University of Science and Technology (CUST), Islamabad, Pakistan. He received his BS degree in aerospace engineering from Institute of Space Technology, Pakistan and an MS degree in Mechanical Engineering from HITEC University, Pakistan. At present, he is a PhD candidate in the Department of Mechanical Engineering at the School of Mechanical and Manufacturing Engineering, National University of Science and Technology, Pakistan. His research interests include computational mechanics, the material characterization of composite materials, mechanical behavior of bio-hybrid composite materials and solid mechanics.

### **Preface to "The 2nd International Conference on Advances in Mechanical Engineering"**

International Conference on Advances in Mechanical Engineering (ICAME) is organized by the Mechanical Engineering Department of Capital University of Science & Technology (CUST), Islamabad, Pakistan. ICAME is an annual event and usually takes place in the last week of August. ICAME aims to attract engineers, scientists and research scholars from leading academic institutes and industry around the world to disseminate the latest research and innovations. ICAME also encourages participants to present novel ideas and sustainable solutions to tackle local and global engineering challenges. ICAME covers all the major areas of the Mechanical Engineering and Engineering Management.

The second International Conference on Advances in Mechanical Engineering (ICAME-22) was held on August 25, 2022. ICAME-22 published 36 articles after a strict peer review process. More than 100 registered participants attended the conference from industry and academia. Five International keynote speakers joined the conference virtually, namely Prof. Alexey Burluka, Northumbria University; Prof. Amir Farooq, King Abdullah University of Science and Technology; Prof. Neyara Radwan, Suez Canal University; Prof. Lei Yue, Guangzhou University; Prof. Sam Yu, Vice President Tinbowah Investment China. The Conference proceedings were published as a Special Edition of Engineering Proceeding, Volume 23, 2022.

**Muhammad Mahabat Khan, Mohammad Javed Hyder, Muhammad Irfan, and Manzar Masud** *Editors*

### *Editorial* **Statement of Peer Review †**

### **Muhammad Mahabat Khan , Mohammad Javed Hyder \* , Muhammad Irfan and Manzar Masud**

Department of Mechanical Engineering, Capital University of Science and Technology (CUST), Islamabad 44000, Pakistan


In submitting conference proceedings to *Engineering Proceedings*, the volume editors of the proceedings certify to the publisher that all papers published in this volume have been subjected to peer review administered by the volume editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal.


**Citation:** Khan, M.M.; Hyder, M.J.; Irfan, M.; Masud, M. Statement of Peer Review. *Eng. Proc.* **2022**, *23*, 37. https://doi.org/10.3390/ engproc2022023037

Published: 11 October 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

### *Proceeding Paper* **Study of Steam Jet Condensation for CD Spray Nozzle Exhausting into Quiescent Water †**

**Haseeb Afzal 1,\* , Ajmal Shah 2, Abdul Quddus <sup>1</sup> , Noman Arif Khan <sup>1</sup> , Shumail Hassan <sup>1</sup> , Muhammad Khawar Ayub <sup>3</sup> and Mazhar Iqbal <sup>1</sup>**


**Abstract:** Direct contact condensation (DCC) has achieved a well-known significance because of exceptional reasons such as efficient heat and mass transfer characteristics. The current experimental investigation involves considering the steam cavity shape characteristics with varying steam pressure, when the saturated steam is condensed into the one-phase water atmosphere using a convergingdiverging (CD) nozzle. The results indicate the four different shapes of steam jet (oscillatory, conical, ellipsoidal and double expansion–contraction). It is observed that the penetration length and the maximum expansion ratio increase with the increase in steam saturated pressure and are found in the range of 1.8–2.8 and 1–1.13, respectively. Furthermore, the current results for jet length are compared with previously developed jet length predicting models which are found to be in good agreement.

**Keywords:** converging diverging nozzle; direct contact condensation; multiphase flows; steam cavity length; steam cavity shape

#### **1. Introduction**

DCC occurs when the vapors are brought directly in contact with the cold liquid [1]. Kerney et al. [2] studied steam plume length whose correlation was developed as a function of subcooled water temperature, steam mass velocity and nozzle cavity diameter. Kerney's model was later modified by Weimer et al. [3] using turbulent entrainment and variable density theories. The calculations for chugging, oscillatory and stratified flows were executed by Aya et al. [4].

Later on, Chun et al. [5] presented the qualitative regime map of the saturated steam using both vertical and horizontal nozzles with the help of a total of 346 experiments. Kim et al. [6] attempted to measure the dimensionless length and expansion ratios of steam cavity for various steam conditions. Due to the unavailability of DCC involving supersonic steam jet, Wu et al. [7] presented the jet shape of the submerged supersonic nozzle. Shah et al. [8] examined the DCC of steam discharging into the liquid water atmosphere using the lab scale model of steam jet pump.

The current research aims to study steam plume parameters such as plume shape, dimensionless penetration length and maximum expansion ratio when the saturated steam is exhausted into the quiescent water tank via DCC. The outcomes would be significant in safe and economic design of DCC based equipment as well as in the validation of CFD results.

**Citation:** Afzal, H.; Shah, A.; Quddus, A.; Khan, N.A.; Hassan, S.; Ayub, M.K.; Iqbal, M. Study of Steam Jet Condensation for CD Spray Nozzle Exhausting into Quiescent Water. *Eng. Proc.* **2022**, *23*, 6. https:// doi.org/10.3390/engproc2022023006

Academic Editors: Mahabat Khan, M. Javed Hyder, Muhammad Irfan and Manzar Masud

Published: 20 September 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **2. Materials and Methods**

The experimental setup utilized in the current research is shown in Figure 1. This setup consists of electric boiler, surge tank, water tank, CD nozzle, instrumentation, valves, mobile measuring probe and high-speed camera. The steam generator, which is most crucial component of the setup, is used to supply saturated steam with the quality of ~99% having a peak value of operating pressure of 8 bar. The steam is injected horizontally via the CD nozzle. A rectangular water tank with dimensions of 1.2 m × 1 m × 1 m is used for the water storage. The captured images are processed using MATLAB to calculate the jet parameters. The operating and geometric conditions of the present experimental investigation are given in Table 1.

**Figure 1.** DCC experimental facility.

**Table 1.** Operating conditions.


#### **3. Results and Discussion**

#### *3.1. Influence of Steam Saturated Pressure on the Jet Shapes*

The alteration of steam cavity shapes with the steam saturated pressure at the constant temperature of 35 ◦C is shown in Figure 2. At the low pressures of 1.5 bar and 2 bar, (a) and (b) show the unstable steam jet shapes and oscillations take place at the steam water interface. This phenomenon is called condensation oscillations. At the pressures of 2.5 bar and 3 bar, the shape of steam plume is found to be conical as shown in (c) and (d). This type of shape is formed if the pressure at the exit of the nozzle is kept below the atmospheric pressure, hence resulting in the compression of plume.

However, as the pressure is further increased, an ellipsoidal shape was observed as shown in (e) and (f). The formation of this type of shape is associated with the theory of expansion and contraction. If the pressure is increased further to 4.5 bar, the plume manifests a double expansion–contraction shape which is shown in (g). The formation of this shape is associated with the fact that as the pressure elevates further at the constant temperature, momentum is imparted along with the transfer of thermal energy to the water.

**Figure 2.** Steam pressure effect on jet shapes at 35 ◦C: (**a**) 1.5, (**b**) 2, (**c**) 2.5, (**d**) 3, (**e**) 3.5, (**f**) 4, (**g**) 4.5.

#### *3.2. Influence of Steam Saturated Pressure on the Dimensionless Penetration Length*

The variation of penetration length with the steam pressure at a temperature of 35 ◦C is shown as the black line in Figure 3. The parameter is taken in the dimensionless form by dividing the penetration length over the nozzle exit diameter. It is clear from the trend that as the steam pressure is increased, the dimensionless penetration length goes on increasing. This variation is obvious because at higher steam pressure, higher momentum is imparted, and the input content of heat energy also rises. The values of dimensionless penetration were found in the range of 1.8–2.8 which is in well accordance with the range of previous researchers at the low temperatures.

**Figure 3.** Comparison of Current Experimental Results with the Predicted Data.

The dimensionless penetration length is also predicted using the various correlations given in the literature for the comparison purposes. Overall, all the correlations determined the much reasonable agreement lying within the −30% and +5% as a whole with the absolute average deviation of 10.2%. The inflection point is observed in the current data because of the variation of shape from ellipsoidal to double-expansion contraction.

#### *3.3. Influence of Steam Saturated Pressure on the Expansion Ratio*

It has been found that as the saturated steam pressure increases, the maximum expansion ratio also increases. The reason behind the increasing trend of maximum expansion ratio with the steam pressure can be explained on the basis of higher momentum transfer which expands the steam in the radial direction. At the low pressures, the maximum expansion ratio was simply 1 because of the convergent shape; however, it increases as the plume becomes ellipsoidal at higher pressures. It was found to be maximum at the maximum pressure of 4.5 bar where the double expansion–contraction shape was found. The maximum expansion ratio was obtained in the range of 1–1.133 which is in accordance with the previous studies at lower temperatures.

The following are some of the major conclusions obtained after the current investigation:


**Author Contributions:** Conceptualization, H.A., A.Q. and A.S.; methodology, H.A. and M.I.; software, H.A., A.Q. and N.A.K.; validation, H.A. and N.A.K.; formal analysis, H.A. and S.H.; investigation, H.A. and M.I.; data curation, M.K.A. and S.H.; writing—original draft preparation, H.A.; writing—review and editing, H.A. and M.I.; supervision, M.I.; project administration, H.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors acknowledge financial, technical, and administrative support provided by Pakistan Institute of Engineering and Applied Sciences for the present study.

**Conflicts of Interest:** The authors declare no conflict of interest.


### *Proceeding Paper* **Experimental Study on Steam Cavity Characteristics for Swirled Flow Nozzle Exhausting into Quiescent Water †**

**Abdul Quddus 1,\* , Ajmal Shah 2, Kamran Rasheed Qureshi 1, Muhammad Khawar Ayub 3, Mazhar Iqbal 1, Noman Arif Khan 1, Haseeb Afzal <sup>1</sup> and Shumail Hassan <sup>1</sup>**


**Abstract:** The steam–water direct contact condensation (DCC) process is commonly observed in various industries due to its fast heat and mass exchange characteristics. This study investigates steam plume characteristics by experimentally condensing the steam jet issuing from a swirled flow spray nozzle into stagnant subcooled water. On the basis of high-speed imaging, the effects of subcooled water temperatures on the cavity shape, its length, and maximum expansion ratio were explored. The existence of three distinct cavity shapes (ellipsoidal, double expansion–contraction and divergent) were identified. The dimensionless steam cavity penetration length and maximum expansion ratio were found to be in the range of 6.28–11.5 and 1.71–3.06, respectively. The results indicate that with the rise in water temperature, plume length and maximum expansion ratio increase.

**Keywords:** multiphase flow; plume cavity; swirl flow; direct contact condensation; fluid dynamics

#### **1. Introduction**

The phenomenon of steam-water DCC of steam has become of paramount interest in the industrial sector due to the high exchange rate of heat and mass at the interface [1]. Its typical applications in industry includes direct mixing heaters, thermal degasification systems, steam injectors, and nuclear reactor safety systems [2–4].

In the published literature, scholars mainly give stress to the study of steam jet characteristics including steam cavity shapes, cavity length, temperature profiles, heat exchange rate, and condensation oscillations [1,5,6]. Recently, researchers have considered the steam cavity shape as a key parameter during submerged jet condensing with water. It is also strongly linked with the above said research areas [4–8]. Additionally, it provides guidelines in the design and functionality of the DCC based systems [4,7]. Hence, the topic of the steam jet characteristics have become attractive in the field of DCC.

Previously published literature indicates that steam cavity characteristics depend upon the operating and geometric conditions [6–8]. Kerney's study [8] was the first a predicting model for steam cavity axial size was formulated. Weimer et al. [9] modified Karney's model by including phasic densities effect.

Shah et al. [7] pointed out that the steam cavity shape is dependent on nozzle geometric parameters. Zhang and his group [10] studied the steam jet features for double hole nozzle under stable flow conditions. Quddus et al. [11,12] studied the steam jet features from the beveled steam spray nozzles. They also developed a predicting model for steam jet length by including the effects of nozzle exit bevel angle. In their study, they explored the physics of the jet shapes for various beveled nozzles.

**Citation:** Quddus, A.; Shah, A.; Qureshi, K.R.; Ayub, M.K.; Iqbal, M.; Khan, N.A.; Afzal, H.; Hassan, S. Experimental Study on Steam Cavity Characteristics for Swirled Flow Nozzle Exhausting into Quiescent Water. *Eng. Proc.* **2022**, *23*, 28. https://doi.org/10.3390/ engproc2022023028

Academic Editors: Mahabat Khan, Muhammad Javed Hyder, Muhammad Irfan and Manzar Masud

Published: 22 September 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

The purpose of the present work is to investigate the characteristics of steam cavity shapes for swirled flow spray nozzles discharging into stagnant water. A high speed imaging technique was used for capturing the steam cavity shapes. The present findings are believed to be helpful for gaining more insight into steam-water DCC systems and understanding the associated problems.

#### **2. Experimental Setup and Methodology**

The details of the experimental facility and methodology are the same as presented in our previous work [11,12]. The only difference is the type of steam nozzle used. Here, as mentioned earlier, a steam swirled flow spray nozzle has been used which is shown in Figure 1.

**Figure 1.** (**a**) Section view of steam swirled flow spray nozzle. (**b**) Fabricated nozzle.

#### **3. Results and Discussion**

#### *3.1. Effect on Steam Cavity Shape*

This section presents the variation in cavity shapes under the action of the changing tank water temperature for steam issuing from a swirled flow spray nozzle exhausting into stagnant water at constant steam pressure, *Ps =* 500 KPa.

Figure 2a–e illustrates the steam cavity shape observed at various water temperatures i.e., Tw = 30, 40, 50, 60, and 70 ◦C, respectively. From this figure, it can be seen that at Tw = 30 ◦C, the ellipsoidal cavity shape exists as shown in Figure 2a. The formation of such a cavity shape can be explained by the steam jet becoming under expanded at elevated steam pressures. From expansion-contraction theory, such cavities are expanded as the steam is ejected out from the nozzle at the exit location. When Tw = 50 and 60 ◦C, condensation capabilities of cooling medium decrease. To dissipate the extra input of steam thermal energy, additional expansion of the plume occurs by increasing the surface area of the cavity. The cavity is again compressed by nearby water which is at relatively high pressure. The plume thus becomes inflexed which finally condenses to ambient water conditions. Consequently, the double expansion–contraction shaped cavity is formulated, as presented in Figure 2b,c. When Tw = 60 and 70 ◦C, there is continuous expansion in the cavity which transforms the shape of the plume into a divergent jet as illustrated in Figure 2d,e. For such shapes, the losses for heat exchange capabilities become large due to escaping of steam bubbles which carry the heat with them.

**Figure 2.** Steam cavity shape observed at P*s*= 500 kPa and at T*w* = (**a**) 30 ◦C, (**b**) 40 ◦C, (**c**) 50 ◦C, (**d**) 60 ◦C, and (**e**) 70 ◦C.

#### *3.2. Effect on Steam Cavity Length*

Figure 3a describes the effects of liquid phase temperature on steam cavity length at constant steam pressure, i.e., 500 kPa. The plume length was measured at five water temperatures, i.e., Tw = 30, 40, 50, 60 and 70 ◦C. From the findings, it can be concluded that with the decrease in degree of subcooling of water, the steam cavity length prolongs in axial dimensions. This fact can be explained as follows: as the degree of subcooling of water decreases, its temperature rises, and its corresponding condensing capability is reduced. The heat transfer area of the cavity is increased to thermally balance the input heat. Consequently, the penetration length of the steam jet increases.

**Figure 3.** Effect of tank water temperature on (**a**) cavity dimensionless length, and (**b**) maximum expan-sion ratio.

#### *3.3. Effect on Steam Cavity Maximum Expansion Ratio*

Figure 3b shows the variation of the steam jet maximum expansion ratio with water temperature at constant steam pressure Ps = 500 kPa. The maximum expansion ratio has been calculated at various degrees of subcooling of water by changing water temperature (i.e., Tw = 30, 40, 50, 60 and 70 ◦C). It was observed that with the decrease in degree of subcooling, the steam jet maximum expansion ratio increases. This can be explained by the condensation capacity of the water reducing with increase in water temperature. Moreover, the area across which the jet exchanges its heat with the liquid phase is increased to thermally balance the heat. The increase in area is both from the axial and radial growth of the jet. Consequently, the radial growth of the cavity diameter increases the maximum expansion ratio.

#### **4. Conclusions**

In the current study, a steam jet from a swirled flow spray nozzle was condensed experimentally into stagnant subcooled water. A high speed imaging technique was utilized to explore the steam cavity characteristics. The effect of water temperature (range, 30–70 ◦C) on cavity parameters at steam inlet pressure 500 kPa was studied. The following main conclusions were obtained.


**Author Contributions:** A.Q.: Conceptualization, methodology, validation, investigation, data curation, original draft preparation; A.S.: Conceptualization, writing—review and editing, supervision, project administration; K.R.Q.: investigation, supervision, project administration. M.K.A.: formal analysis, data curation, software; M.I.: investigation, project administration; N.A.K.: formal analysis, data curation; H.A.: formal analysis, data curation; S.H.: formal analysis, data curation. All authors have read and agreed to the published version of the manuscript.

**Funding:** The project was funded by Higher Education Commission of Pakistan under HEC indigenous PhD fellowship scheme (417-47877-2EG4-042).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data may be available on request.

**Acknowledgments:** The authors acknowledge the financial assistance from the Higher Education Commission, Pakistan for this work.

**Conflicts of Interest:** The authors declare no conflict of interest.


### *Proceeding Paper* **Numerical Investigation of Different Configurations of Pin Fin Heat Sinks with and without PCM †**

**Hamza Fayyaz \* , Abid Hussain and Talal Bin Irshad**

† Presented at the 2nd International Conference on Advances in Mechanical Engineering (ICAME-22), Islamabad, Pakistan, 25 August 2022.

**Abstract:** The miniaturization of electronic components leads to poor heat dissipation, performance, and reliability of the devices. To optimize heat transfer from electrical components, pin fins are the best choice due to their high thermal conductivity. Different configurations of square and triangular pin fins for heat transfer characteristics were numerically investigated in this study. Threedimensional numerical simulations were carried out for two different configurations with heat fluxes of 0.82 kW/m2 subjected to the base of the heat sink. The heat transfer coefficients among the numerical simulation study and experimentation results provided a good correlation. To evaluate the overall performance, it was indicated from both numerical and experimental results that the maximum square pin fin configuration reduced the base temperature by up to 17.7% and 19%, respectively. In comparison to other configurations, the square pin fin performed better because of its increased surface area.

**Keywords:** numerical simulation; electronic devices; pin fin heat sink; heat transfer coefficient

**Citation:** Fayyaz, H.; Hussain, A.; Irshad, T.B. Numerical Investigation of Different Configurations of Pin Fin Heat Sinks with and without PCM. *Eng. Proc.* **2022**, *23*, 22. https:// doi.org/10.3390/engproc2022023022

Academic Editors: Mahabat Khan, M. Javed Hyder, Muhammad Irfan and Manzar Masud

Published: 21 September 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **1. Introduction**

Recent advancements in electronics have led to an exponential rise in the temperature and heat transfer rates, which are affected due to their smaller sizes [1]. The main purpose of heat sinks is to cool electrical equipment. Pin- and plate-finned heat sinks are the two key forms that increase thermal performance. [2]. There are wide range of heat sink design geometries, although the most common pin fin designs are square, triangular, circular, and elliptic shapes. The performance of heat sink is significantly impacted by increasing the number and thickness of fins [3]. Phase change materials alter their phases by absorbing a huge amount of heat during melting, and releasing it during solidification [4]. Numerous studies have been already performed on PCM conductivity, and to overcome this problem, researchers tend to add fin geometries, composites metal, and ultrafine particles in addition to PCM [5].

This study focuses on the numerical model investigation of various arrangements of (square and triangular) pin fin heat sinks with and without PCM. Numerical simulations using COMSOL Multiphysics 5.5 with various parameters were studied on finned heat sinks. Variables such as heat transfer rate, base temperature reduction, and the maximum temperature of all configurations were analyzed.

#### **2. Numerical Methodology and Materials**

In this study, a fin model for thermal performance characteristics is presented. The model was generated in AutoCAD software and imported into COMSOL Multiphysics 5.5. Aluminum grade 2024 was selected for both configurations. Two arrangements of pin fin configurations (square and triangular) were studied in this research (Figure 1). The base plate of the pin fin configurations had a surface area of 114 × 114 mm2, and the thickness

Department of Mechanical Engineering, University of Engineering and Technology Taxila, Punjab 47050, Pakistan **\*** Correspondence: hamza.fayyaz@students.uettaxila.edu.pk

of the base plate was 4 mm. There were 72 fins in total, which were extruded up to 25 mm above the base plate (Table 1).

**Figure 1.** Pin fin heat sinks: (**a**) square; (**b**) triangular.

**Table 1.** Heat sink geometric properties.


#### **3. Experimental Setup**

A comparison between heating and cooling of heat sink was conducted by employing different arrangements of pin fin heat sinks, i.e., square and triangular, with and without PCM. A power level of 10 W was used for this experiment and the heat sink discharged in the same way it charged, with the sidewalls and base insulated to enable heat flow in only one direction—from top to bottom—for thermal analysis. The experimental setup and exploded view of the heat sink assembly for this study are shown in Figures 2 and 3. Subsequently, the temperature contours of heat sink at different intervals of time are presented in Figure 4.

**Figure 2.** Experimental setup.

**Figure 3.** Exploded view of the assembly.

**Figure 4.** Temperature contours of a heat sink assembly at different intervals.

#### **4. Results and Discussion**

This study consisted of two phases: fins without PCM, and fins with PCM. The first set of simulations, performed for fins without PCM, and the second set of simulations, performed for fins with PCM, for both configurations, are shown in Figure 5.

**Figure 5.** Simulation of square and triangular pin fins with and without PCM.

The reductions in base temperature are clearly seen by the in addition of PCM. Both configurations yielded the best results and maximum reduction in the base temperature of 17.7% with the square configuration, whereas the triangular configuration reduced the base temperature by up to 17.1%.

An experimental comparison of both configurations, with and without PCM, is shown in Figure 6. The maximum temperature reductions by square and triangular pin fins are 19% and 16%, respectively.

**Figure 6.** Experimental results of square and triangular pin fins.

#### *Validation*

Simulation results were compared with experimental data to validate the model shown in Figure 7. The observed error range was 2% for the pin fin with PCM and 3% for the pin fin without PCM, which was calculated using the formula: [Percentage error = Numerical Value—Experimental Value/Numerical Value], which was negligible. Overall, the numerical results showed the best results with the experimental data, indicating that the model was logical.

**Figure 7.** Validation of simulation results with experimental data.

#### **5. Conclusions**

This study focused on the reduction in base temperature in electronic applications. Numerical analyses of square and triangular pin fins provided the same results as the experimental data. The results concluded that adding PCM into the square configuration reduced the temperature by up to 17.7% as compared with a pin fin without PCM. The maximum peak temperature of the square pin fin without PCM was 62.1 ◦C, whereas the maximum peak temperature with PCM in the same configuration was 51.2 ◦C. The experimental results of the square configuration showed a maximum base temperature reduction of up to 19%. The present numerical simulation results of COMSOL Multiphysics were validated with an experimental model with the same pattern. Overall, the square configuration demonstrated better results for temperature reduction, due to the difference in surface area.

**Author Contributions:** H.F.: Conceptualization, methodology, validation, formal analysis, investigation, resources, data curation, writing—original draft preparation, T.B.I.: software, A.H.: writing review and editing, supervision. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.


### *Proceeding Paper* **Acoustic Response of Fully Passive Airfoil under Gust †**

**Muhammad Arqam , Kashif Ayaz, Muhammad Ebrahem and Shehryar Manzoor \***

Department of Mechanical Engineering, University of Engineering and Technology, Taxila 47070, Pakistan

**\*** Correspondence: m.shehryar@uettaxila.edu.pk

† Presented at the 2nd International Conference on Advances in Mechanical Engineering (ICAME-22), Islamabad, Pakistan, 25 August 2022.

**Abstract:** Acoustic response from a freely responding symmetric airfoil subjected to gust is investigated in a two-dimensional numerical environment. Gust model is superimposed on the inlet velocity up till the critical flutter velocity. Second order transient formulation, *k* − *ω* turbulence model and dynamic meshing technique were adopted. By employing the Ffowcs Williams and Hawkings (FW-H) acoustic methodology, the acoustic signature generated by the airfoil for the range of velocities (0.85 ≤ *U*/*Uc* ≤ 1 near the critical flutter velocity is quantified over a range of acoustic receivers in the surrounding of the airfoil. Sound pressure levels (SPLs) are determined, and directionalities have been studied. It is revealed that the distribution of sound pressure level at the exciting frequency is affected by the gust profile. Scales of these sound pressure levels, however, relied on the Reynolds number and the dynamics of the system.

**Keywords:** gust response; flow noise; aeroacoustics; fully passive airfoil

**Citation:** Arqam, M.; Ayaz, K.; Ebrahem, M.; Manzoor, S. Acoustic Response of Fully Passive Airfoil under Gust. *Eng. Proc.* **2022**, *23*, 36. https://doi.org/10.3390/ engproc2022023036

Academic Editors: Mahabat Khan, M. Javed Hyder, Muhammad Irfan and Manzar Masud

Published: 27 September 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **1. Introduction**

The interior noise and airframe noise have been explored extensively in the recent past. There is an ever-increasing urgency to mitigate the influence of aerospace productions on the environment with the European commission calling for noise reduction [1], which has resulted in the development of systems capable of meeting noise certification needs.

The flow of fluid over stiffened structures is known to yield sound, as well as disturbs and sustains vibrations in the structure. When a body moves in a nonuniform fluid flow, the contact between the body and the unsteady fluid harvests pressure fluctuations on the body surface resulting in the noise propagated to the far-field. This investigation has numerous applications in the design and mitigation of microaerial vehicles (MAVs) as well as aircraft structural noise.

Métivier et al. [2] performed a series of investigations experimentally on an unrestricted pitching wing (chord length = 0.156 m) at Reynolds numbers of 5.104–1.105 and revealed that the airfoil became unstable, exhibiting limit-cycle oscillations. Wind tunnel studies using a pitching and plunging airfoil in the previous Reynolds number range have also been performed [3]. The consequence of laminar separation on the flapping airfoil has been considered experimentally and numerically by [2,4]. These research studies confirm that the separation of the boundary layer in the laminar region at the trailing edge is accountable for pitching oscillations.

#### **2. Governing Equations**

The current effort utilised the two-dimensional unsteady Reynolds averaged Navier– Stokes (URANS) methodology improved with a transitional turbulent solver for the flow calculations (*k* − *ω* Shear Stress Transport). Moreover, the Ffowcs Williams and Hawkings's (FW-H) method was employed for the aeroacoustics calculations. The model was selected as it was not computationally expensive and was apt for predicting the tonal noise from the flow and the interface of the flow with nonpermeable contours.

#### *2.1. Aeroelastic Model*

An airfoil able to move in pitching and heaving degrees of freedom is placed on a pivot point passing through the pitching axis (*z*) (Figure 1). The equations of motion [5] for such an airfoil can be given as (Equations (1) and (2)):

$$F = m\_h \ddot{y} + D\_h \dot{y} + k\_h y + S(\dot{\theta}^2 \sin \theta - \ddot{\theta} \cos \theta) \tag{1}$$

$$M = I\_{\theta}\ddot{\theta} + D\_{\theta}\dot{\theta} + k\_{\theta}\theta - S\ddot{y}\cos\theta \tag{2}$$

where *mh* is the heaving mass (kg), *D* is the damping (kg s−<sup>1</sup> and kg m2 s−<sup>1</sup> rad−<sup>1</sup> for pitching and heaving, respectively) and *k* is the stiffness coefficient (Nm-1 and Nm.rad−<sup>1</sup> for pitching and heaving, respectively). *I<sup>θ</sup>* (kg m2) is the moment of inertia around the angular axis. The subscripts *h* and *θ* denote heaving and pitching. Plugging *S* = *mpx<sup>θ</sup>* (where *mp* is the pitching mass (kg) and *x<sup>θ</sup>* the centre of gravity location (m)), an inertial coupling exists in both degrees of freedom.

**Figure 1.** Basic representation of an inflexible, elastically mounted, symmetrical airfoil through figurative illustration of main parameters.

#### *2.2. Oncoming Gust Shape*

The gust shape presented in this work comprises two components [5], i.e., vertical and horizontal. The horizontal and vertical components (Equations (3) and (4)) were modelled by using the symmetric Gaussian distribution function:

$$
\mu = a \times e^{\left[-\left(\frac{x-d}{n}\right)^2\right]} \tag{3}
$$

$$w = -a\_0 \times e^{\left[-\left(\frac{x-d\_0}{n\_0}\right)^2\right]} + a\_1 \times e^{\left[-\left(\frac{x-d\_1}{n\_1}\right)^2\right]} \tag{4}$$

where *d* (*m*) denotes the centroid position, *a* (*m*) denotes the amplitude and *n* (*sec*) denotes the time throughout which the components have a value above 50% of their peak amplitude, i.e., full duration at half maximum.

#### **3. Numerical Procedure**

The flow solution was performed on a numerical set of 143,416 structured cells consisting of NACA 0015 airfoil with a chord length of 0.12 m. The domain size was equal to 160*c*.

For the URANS solution, the pressure-based solver was utilised with the SIMPLE algorithm. The gust model was overlapped on the inlet velocity up till the critical flutter velocity. Numerical simulations for the velocity range of (0.85 ≤ *U*/*Uc* ≤ 1) near the critical flutter velocity were performed (where *Uc* is critical velocity).

Acoustic data were acquired for 20,000 time steps along with a time step size duration of 10−<sup>5</sup> s after the URANS model achieved steady state. The pressure was noted by the placement of acoustic receivers as described in the literature [6].

#### *Model Validation*

In order to validate the model, the coefficients of lift, drag and sound pressure levels were compared (Table 1) with those stated by experimental [7] and numerical setups [8,9]. Lastly, the sound pressure level in the one-third octave bands (SPL1/3) were established and further related with the validation cases along with the mesh convergence study (Figure 2). The current model replicated the position of the main tone (~1.6 kHz) and sound pressure level (75 dB), which was in perfect harmony with the published data [7,10,11].

**Table 1.** Comparison of time averaged aerodynamic coefficients.


**Figure 2.** One-third octave band SPL showing SBES, URANS and experimental comparison for M2 along with mesh convergence study.

#### **4. Results and Discussion**

A fast Fourier transform (FFT) method was employed to determine the frequencies from the acoustic pressure signals. Here, the role of velocity (*U*/*UC*), and the excitation frequency was investigated for the production of aerodynamic noise.

#### *Production of Sound Waves*

The current numerical simulations were performed for *Re* = 80, 000–120, 000 while varying *U*/*Uc* from 0.85 to 1. Figure 3 depicts a magnified schematic at *U* = 0.85*Uc* for one of the 38 receivers at the circle (x = 5c). The forcing frequency (10.54 Hz) and its even harmonic (21.08 Hz) has a significant role in the production of the flow noise as the oncoming gust influences these signals for the lift and drag. This tendency is palpably seen for all receivers.

**Figure 3.** Frequency configuration of SPL about the flapping hydrofoil at one of the receiver locations in the middle circle.

An evaluation for the SPL for microphones positioned at the circles (x = 5c, 8c) is shown in Figure 4. The setting where the incoming velocity is equal to the critical velocity represents the highest perturbations in the flow media in terms of frequency and oscillation amplitude. With a growing (*U*/*UC*), the SPL increases for the excitation frequencies. While traveling away from the airfoil, the amplitudes of SPL decrease.

**Figure 4.** Polar plots showing the spread of SPL: the row expresses data for *<sup>U</sup> Uc* = 1; columns 1 and 2 characterize measurements at the middle (x = 5c) and outer circles (x = 8c), respectively.

#### **5. Conclusions**

In this research work, the acoustic response of a passively moving airfoil subjected to a specific gust profile for a range of flow velocities was investigated numerically. The dependency of the sound pressure level magnitude on various parameters was explored. The flow velocity was one of the significant factors to control the change in the sound pressure level magnitudes. For the whole range of velocities (*U*/*UC*), the sound pressure levels depicted the tonal noise on the excitation frequencies. The oscillation frequencies were a function of the force coefficients, which were basically reliant on the gust shape. The oscillation frequencies governed the whole spectrum of sound pressure levels. This aspect was the crux of this study and can be the pioneer phase to control the sound levels at will in real-world applications.

**Author Contributions:** Conceptualization, M.A. and K.A.; methodology, M.A. and S.M.; software, M.A. and K.A.; validation, M.A. and K.A.; formal analysis, M.E. and M.A.; investigation, M.A. and M.E.; data curation, M.A.; writing—original draft preparation, S.M.; writing—review and editing, M.A. and M.E.; supervision, M.E.; project administration, S.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

