Numerical Heat Transfer Investigation in a Solar Receiver Heat Exchanger Channel with Punched Elliptical-Winglet Vortex Generators

Thermal performance in a solar receiver heat exchanger (SRX) channel with punched elliptical-winglet vortex generator (P-EW) mounted on the absorber plate is numerically examined for Reynolds number (Re) ranging from 4000 to 24,000. In the present simulation, the P-EW characteristics included three ratios of winglet pitches (PR = 2.0, 1.5 and 1.0) including four sizes of the perforated-holes (nondimensional hole diameter, dR= 0.0, 0.25, 0.417 and 0.583) at one value of the attack angle (a =30°) and relative height (BR= 0.48). The computation reveals that employing P-EW generally yields considerably large friction factor (f) and Nusselt number (Nu) than the flat-plate channel alone. The use of smaller hole size causes the rise in Nu and f. It is noticeable that counter-spinning vortices pairs generated by the multiple P-EW can induce the impinging flow onto the absorber plate together with the air jet coming out of the hole, leading to the rise in the heat transfer rate greater than the smooth flat-plate channel. The highest thermal performance of about 1.9 was seen for the one with PR = 1.5 and dR = 0.417

Turbulent Heat Transfer and Pressure Loss in a Square-Duct Heat Exchanger with Inclined-Baffle Inserts

Thermal and friction loss characteristics in a square-duct heat exchanger fitted with inclined-baffles are experimentally examined. Air as the test fluid enters the test duct having a uniform surface heat-flux. The baffles are placed repeatedly on both sides of a rectangular centre-cleared tape/frame before diagonally inserting the baffled frame into the test duct to produce longitudinal vortex flows through the test section. Effects of five different relative baffle height or flow blockage ratios (b/H = BR = 0.1, 0.2, 0.3, 0.4 and 0.5) on heat transfer, pressure loss and thermal performance in the square duct are investigated for Reynolds number ranging from 4100 to 25,600. The relative baffle pitch or pitch ratio (P/H = PR) and baffle attack angle (a) are fixed at 3.0 and 30°, respectively. The experimental results reveal that the heat transfer and pressure drop in the form of respective Nusselt number (Nu) and friction factor (f) from using the baffle tend to increase with the rise of Reynolds number (Re) and BR. The maximum enhancement in Nu and f has been found to be 4.61 and 63.67 times above the smooth duct, respectively. The thermal enhancement factor (h) is maximum at BR = 0.3

การเพิ่มการถ่ายเทความร้อนในท่อที่มีการไหลแบบปั่นป่วนผ่านแผ่นปีกสามเหลี่ยมHeat Transfer Enhancement in Turbulent Tube Flow Through Delta-winglet Tapes

บทความนี้นำเสนออิทธิพลของการใส่แผ่นปีกสามเหลี่ยมในท่อภายใต้สภาวะฟลักซ์ความร้อนที่ผิวคงที่ต่อพฤติกรรมทางความร้อนและการต้านทานการไหล ในการทดลองแผ่นปีกสามเหลี่ยมทำมุมปะทะ (β) 45º ถูกใส่ภายในท่อโดยมีสัดส่วนความสูงปีกต่อเส้นผ่านศูนย์กลางท่อ 3 ค่า (b/D = 0.1, 0.15 และ 0.2) และสัดส่วนระยะพิตช์ปีกต่อเส้นผ่านศูนย์กลางท่อ 3 ค่า (P/D = 1, 2 และ 3) อากาศถูกใช้เป็นของไหลทดสอบซึ่งไหลผ่านท่อโดยแสดงในพจน์ของเลขเรย์โนลด์ในช่วง 4,200 ถึง 25,800 ผลการทดลองแสดงให้เห็นว่า การใส่แผ่นปีกสามเหลี่ยมสามารถเพิ่มค่าอัตราการถ่ายเทความร้อนได้ถึง 4.06 เท่า เมื่อเปรียบเทียบกับท่อเปล่าผิวเรียบ ขณะที่ตัวประกอบความเสียดทานมีค่าเพิ่มขึ้นถึง 31.63 เท่า เมื่อสัดส่วนความสูงปีกต่อเส้นผ่านศูนย์กลางท่อเพิ่มขึ้นส่งผลให้การถ่ายเทความร้อนและตัวประกอบความเสียดทานมีค่าเพิ่มขึ้น ขณะที่สัดส่วนระยะพิตช์ปีกต่อเส้นผ่านศูนย์กลางท่อเพิ่มขึ้นการถ่ายเทความร้อนและตัวประกอบความเสียดทานจะมีค่าลดลง ค่าสมรรถนะเชิงความร้อนของการใส่แผ่นปีกสามเหลี่ยมภายในท่อมีค่าอยู่ในช่วง 1.16–1.51 โดยมีค่าสูงสุดในกรณี b/D = 0.15 และ P/D = 1 นอกจากนี้สหสัมพันธ์ของเลขนัสเซิลท์ (Nu) และตัวประกอบความเสียดทาน (f ) ได้ถูกสร้างขึ้นเพื่อทำนายผลการทดลองThis article presents the influence of Delta-Winglet Tapes (DWT) placed in a uniform heat-fluxed tube on thermal and flow resistance characteristics. In the current experiment, the DWTs with inclination angle (β) of 45º are inserted into the tube with three winglet blockage ratios (b/D = 0.1, 0.15 and 0.2) and three relative winglet-pitches (P/D = 1, 2 and 3). Air as the test fluid flows through the tube for Reynolds number of about 4,200–25,800. The experimental results reveal that the DWT can considerably enhance the heat transfer rate up to 4.06 times above the smooth tube whereas the friction factor is up to 31.63 times. The increase in b/D leads to higher heat transfer and friction loss while the increment in P/D provides the reversing trend. The thermal enhancement factor of the DWT is in the range of 1.16–1.51 where its maximum regarded as the optimum point is at b/D = 0.15 and P/D = 1. Nusselt number (Nu) and friction factor (f ) correlations for the DWT are also determined

Numerical heat transfer in a solar air heater duct with punched delta-winglet vortex generators

The flow topology and thermohydraulic performance of a novel designed punched delta-winglet (P-DW) placed on the absorber of a solar air heater duct are numerically explored. The effects of geometrical parameters, namely, the relative winglet pitch, PR = 1–2 and the relative punched hole size, dR = 0–0.583 at a single value of blockage ratio, BR = 0.48 and attack angle, α = 30° on thermal characteristics are proposed for Reynolds number from 4000 to 24,000. Among several turbulence models, the simulation has shown that the realizable k–ε turbulence model is favorable with respect to measurements. For flow patterns, the P-DW produces several counter-spinning vortices helping induce the impinging jets onto the absorber surface whilst for thermal behaviors, the decline of PR and dR leads to the rise in the friction factor (f) and Nusselt number (Nu). The P-DW provides greater Nu and f than the plain flat plate by 17.1–78.21 and 3.92–5.9 times, respectively and gives the highest performance around 2.1. Further, the P-DW is modified by covering the punched hole partially with a circular flap, called the flapped delta-winglet (F-DW) and this F-DW yields the greatest performance around 2.16 higher than the P-DW about 2.9%

Heat release analysis and thermal efficiency of a single cylinder diesel dual fuel engine with gasoline port injection

Cleaner diesel engines have been successively developed to meet a compromised solution for issues concerning performance and emission regulation. Combustion and exhaust gas after-treatment technologies are exhaustively settled to resolve those problems. A key improvement of the emissions is diesel dual fuel combustion that increases operating range of the premixed combustion. The main aim of this work is to explore the heat release, fuel consumption, and thermal efficiency of a single cylinder diesel dual fuel engine. An intake port fuel injection of gasoline with the flow rates between 0 and 0.06 g/s was accomplished to form a premixed charge prior to induction into the combustion chamber and ignition by the main diesel fuel. The engine was operated on medium load at 1700 rpm without exhaust gas recirculation. An engine indicating system composed of a cylinder pressure transducer and a shaft encoder was used to investigate combustion characteristics based on the first law of thermodynamics. The combustion of higher gasoline pre-mixer increased heat release rates, shortened combustion duration, and increased maximum cylinder pressure than neat diesel combustion. Increasing gasoline proportion reduced the diesel fuel and total fuel consumptions. This enhanced the engine thermal efficiency over the diesel baseline combustion. Keywords: Combustion, Diesel, Dual fuel, Efficiency, Gasoline, Heat releas