Optimisation of porous slab parameters for jet-impingement microchannel heat sink performance enhancement

Purpose Porous media can provide excellent performance in thermal energy transport applications. This study aims to optimise the square porous slabs (placed in the middle of the channel) parameters to enhance the cooling performance of the jet-impingement microchannel heat sink. Design/methodology/approach Three levels of each design parameters, i.e. porous slab side, porous slab height, type of material, permeability and quadratic drag factor, are studied; and an L27 orthogonal array is adopted to generate the design points in the specified design space. Optimum designs of the porous media slabs are achieved to minimise the maximum-wall temperature, thermal resistance and pressure drop and maximise the average heat transfer coefficient and figure of merit (FOM). Findings Results exhibited that the porous media material and permeability are the most, whereas drag factor is the least significant factors with respect to the overall performance of the heat sink. The optimum value of FOM for the proposed hybrid heat sink model belongs to the set of design variables, i.e. 0.4 mm slab side, 0.6 mm slab height, 5 × 10−11 m2 permeability, 0.21 drag factor and copper as substrate material. Originality/value This study proposes a novel design and a hybrid approach to investigate and optimise the hydrothermal performance of jet impingements on porous slabs inserted in the microchannels.

EVALUASI FAKTOR HAMBATAN SAMPING PADA PENENTUAN KAPASITAS JALAN STUDI KASUS: JALAN GATOT SUBROTO

Overcrowding often occurs in DKI Jakarta, especially on Jalan Gatot Subroto. This location is one of the biggest business centers in Jakarta. Roadside activities that impede traffic flow are called side friction. Side friction is an impact on traffic performance resulting from road segment activities. Highway capacity is also influential. That happens because the available highway capacity is no longer able to accommodate the increasing traffic flow. Therefore, research was conducted. To calculate the highway capacity, observations were made to see the number of vehicles. It takes the perception of side frictions using questionnaire data. Questionnaire data collected 100 respondents. So, the results show that section is in the VL (Very Low) side obstacle class, which occurs in the morning while the L (Low) side obstacle class occurs in the afternoon and evening. The results estimation of the side drag factor data shows that the volume is greater than the highway capacity. The correlation between observation data and questionnaire results vehicles parked or stopped on the side of the road and vehicles from roadside access have a sequential weight order, while pedestrians and non-motorized vehicles have non-sequential weights. Further research to expand the questionnaire and get more precise results. ABSTRAKKepadatan sering terjadi di DKI Jakarta khususnya di Jalan Gatot Subroto. Lokasi ini salah satu pusat bisnis terbesar di Jakarta. Aktivitas sisi jalan dapat menghambat arus lalu lintas disebut hambatan samping. Hambatan samping merupakan dampak terhadap kinerja lalu lintas yang dihasilkan dari aktivitas segmen jalan. Selain itu, kapasitas jalan juga berpengaruh. Hal ini terjadi karena kapasitas jalan yang tersedia sudah tidak mampu untuk menampung arus lalu lintas yang semakin tertambah kepadatannya. Oleh karena itu dilakukan penelitian. Untuk menghitung kapasitas jalan, dilakukan observasi untuk melihat jumlah kendaraan. Selain itu, dibutuhkan persepsi hambatan samping menggunakan data kuesioner. Data kuesioner terkumpul sebanyak 100 responden. Maka, hasil menunjukan ruas Jalan Gatot Subroto berada di kelas hambatan samping VL (Very Low) terjadi di waktu pagi hari sedangkan kelas hambatan samping L (Low) terjadi di waktu siang dan sore hari. Hasil dari estimasi faktor hambatan samping data menunjukan volume lebih besar daripada kapasitas jalan. Korelasi anatra data observasi dengan hasil kuesioner menunjukan bahwa kendaraan parkir atau berhenti di sisi jalan dan kendaraan dari akses sisi jalan memiliki urutan bobot yang berurutan sedangkan untuk pejalan kaki dan kendaraan tidak bermotor memiliki bobot yang tidak berurutan. Penelitian selanjutnya, diharapkan dapat memperluas kuesioner dan mendapatkan hasil yang lebih tepat.

Aerodynamic Investigation of Morphing Wing UAV with Adjustable Slotted Airfoil Configuration

Aviation has wide aspects to challenge and discover, the ability to land and take off at slow speed, sudden increase in drag for short runway landings. This paper puts forth the solution by the use of adjustable multi slots configuration of an airfoil. In this case, the slots extend from the wing leading edge to trailing edge. This causes change in the chord, thereby changing the camber of unsymmetrical airfoil. An investigation was made to determine and compare the aerodynamic characteristics of multi slotted adjustable airfoil with unmorphed unsymmetrical airfoil at varied speeds and Angle of Attack (AoA). There are three slots distanced equally along the airfoil. The extension of these slots increases the chord length by 10% of total chord. The slotted and unslotted airfoil profile are then studied using computational fluid dynamics of external flow over a body. The flow simulation is done at 10m/s, 20m/s, 30m/s, 40m/s and 50 m/s flow velocity and at 0, 3, 6, 9 ,12, 15 AoA. The results were obtained for each case and the values for base and slotted model were compared. It was found that lift of slotted model is slightly higher than base model at low flow velocity. It was also seen that the use of slots at high speed causes a large amount of drag. This increased drag factor can be used in UAV’s as spoilers during landing or for landing at shorter runways at lower speed, allowing a sudden decrease in aircraft speed and also to glide at a steeper angle over obstruction.

Case Study: Comparison of Swimsuits and Wetsuits Through Biomechanics and Energetics in Elite Female Open Water Swimmers

Aim: The authors investigated how the Arena Powerskin R-EVO Closed Back swimsuit and Arena Carbon Triwetsuit (full-sleeve wetsuit), both approved by the Fédération Internationale de Natation (FINA) regulations, affect biomechanics and energetics of 3 elite female open water (OW) swimmers at maximal and 4 submaximal swimming intensities. Methods: Three elite female OW swimmers (OW1 = 24 y, 1.64 m, 60 kg; OW2 = 23 y, 1.69 m, 65 kg; OW3 = 27 y, 1.63 m, 64.5 kg) were tested 1 week prior to a FINA/CNSG (China National Sports Group) Marathon Swim World Series event and 40 days before the 18th FINA World Championships 2019. Each OW swimmer completed 2 identical testing sessions, one with a swimsuit and other with a wetsuit, involving shoulder flexion power output assessed from medicine-ball throw, maximal performance and drag coefficient assessment, and an incremental intermittent swim test at 4 different relative intensities. Results: Estimated peak oxygen uptake was 4.4 L·min−1 for OW1, 5.6 L·min−1 for OW2, and 5.0 L·min−1 for OW3. Despite a distinct behavior observed on index of coordination for OW3, a null index of synchronization, increased stroke rate (mean difference = 2%–8%), reduced drag factor (minimum = −14%; maximum = −30%), lower energy cost (mean difference = −2% to −6%), and faster performance (mean difference = 2% to 3%) were observed with the wetsuit compared with swimsuit for all elite OW swimmers. Conclusion: The wetsuit enhances submaximal swimming performance, and this increase is dependent on the OW swimmer’s characteristics. The higher stroke rate and lower stroke length detected with wetsuit could be related to movement constraints imposed by the suit.

DETERMINATION OF THE BALLISTIC CHARACTERISTICS AND THE DAMAGING PROPERTIES OF SELF-MADE LOADING CARTRIDGES OF 7.62*39 CALIBER

In practice of forensic medicine and forensic ballistics there are quite often the cases of different types ofgunshot wounds infliction by atypical damaging elements which were used in illegal independent loading of cartridges to the rifle weapon. The purpose of the researches being performed - studying on a concrete example from criminalistics practice of damaging properties of 7.62 mm rifle bullets of type FMJBT (Full Metal Jacketed Boat Tail) which were used for loading by self-made way cartridges of 7.62 * 39 caliber. Originally, during natural tests in the conditions of a ballistic track the ballistic characteristics of the shot bullets and the value of their ballistic coefficient were established. At the following stage of researches the losses of kinetic energy of rifle bullets on punching blocks of ballistic plasticine with the thickness of 100-140 mm were determined. As a result of tests the character of formation of the damage channel in the thickness of biological tissues simulator is established at the stable and unstable movement of the bullets in the visco elastic medium. Besides, during the researches the values of the parameters necessary for calculations ofpenetration depth of the bullets into a fabric of biological object depending on their speed at the moment of hit in the target, were determined. In particular it was established that at unstable movement of an investigated bullet in thickness of the simulator the value of boundary speed amounts 138.1 m/s, and the value of the medium drag factor - 1.782. Using estimated values offlight speed of the bullets in the trajectory the values of depth wound channels in biological tissues were calculated and the conclusion was drawn on the guaranteed causing of penetrating wounds in all established distances of shooting. Thus, use of the methodfor estimation of damaging properties of investigated bullets, the criterion of which is the length of the wound channel and its boundary value was obviously demonstrated.

KAJIAN NILAI KOEFISIEN HAMBAT PADA SALURAN TERBUKA

Open channel flow is the natural phenomenon that research by hydraulic engineer. Roughness of thechannel is the drag factor of the flow and the value depend on the roughness caracteristics. Chezy coefficient is the coefficient of flow equation determining velocity at the channel. The value of the chezy coefficient is depend of flow caracteristics and roughness of the channel. Research target conducted to learn the value of the chezy coefficient and drag coefficient at the open channel flow with the cylindrical roughness and determine the parameter having an effect on and also relation usher the parameter. The result of cylindrical will be application to the flow with the resistance grow on mangrove. This research used 6 vertical bar model by 6 variation of density to 2 vertical bar diameter. Simulation model the vertical bar conducted by 4 variation of discharge the stream range from 0,00825 until 0,01374 m3/s and 5 variation of stream deepness by turning around back door ( tail gate). Scale model 1 : 10 used to support the measurement correctness beside consideration of equipments limitation. Research data analysis use the way of comparison between theoretical with the research to yield the relation of non dimensionaless. Result of this research indicate that ever greater of density, depth flow and diameter of cylindrical hence yielded chezy coefficient smaller that mean drag flow is greater. Chezy coefficient yielded range 3,82 – 10,579 m1/2/s with the density range 0,498 – 6,883 while drag coefficient value result of average 0,95. Average velocity for cylindrical roughness can be determine with the equation of Chezy

Relation between Maximal Anaerobic Power Output and Tests on Rowing Ergometer

SummaryAim of this study was to compare relation between maximal anaerobic power output and 2,000 m test on rowing ergometer and relation between 6,000 m test and 2,000 m on rowing ergometer. It can be assumed that 2,000 m performance on rowing ergometer will significantly correlate with maximal anaerobic power output and 6,000 m performance. A group of 9 welltrained rowers (age: 18.3 years ± 2.8 years, sport age: 4.9 years ± 3.7 years, weight: 78.9 kg ± 12.2 kg, height: 182.3 cm ± 7.6 cm) performed three tests in 1 week to determine maximal anaerobic power, 6,000 m and 2,000 m performance on Concept 2 model D rowing ergometer. A value of simple maximal stroke out of 10-second all-out test with drag factor set to 200 was taken as a measure of maximal anaerobic power. Drag factor for 6,000 m and 2,000 m test was set individually. Average power during these tests was record. Research showed that both maximal anaerobic power and 6,000 m test correlated with 2,000 m test on rowing ergometer significantly (rmap= 0.93 p < 0.01, r6k= 0.95 p < 0.01). Maximal anaerobic power and 6,000 m tests seem to be good predictors for 2,000 m score on rowing ergometer. However, maximal anaerobic power test can be used to monitor rowing performance during specific training cycle instead of longer and more demanding 6,000 m test.