Chinaruk Thianpong

Thermal Performance Evaluation of Heat Exchanger Tubes Equipped with Coupling Twisted Tapes

The present work has been conducted to investigate the effect of coupling twisted tapes on heat transfer enhancement in a heat exchanger. The effects of (1) twisted tape orientation (co-coupling twisted tapes or counter-coupling twisted tapes), (2) width ratio, and (3) twist ratio were also examined. Results of coupling twisted tapes were also compared to those of a typical twisted tape. Experimental results showed that the use of counter-coupling twisted tapes resulted in higher heat transfer, friction loss, and thermal performance factor than that of co-coupling twisted tapes and typical twisted tapes. Thermal performance factor increased as twist ratio and Reynolds number decreased while width ratio increased.

Drying kinetic of peppercorns in a rectangular fluidized-bed with wavy surfaces

The paper presents the comparative study of drying peppercorns in a rectangular fluidized-bed and a rectangular fluidized-bed with wavy surfaces. This experimental work has been carried out in two different drying bed configurations: rectangular bed and rectangular bed with wavy surface (called “wavy surface bed”). The wavy surface bed is used to produce a stronger turbulence flow inside. For each run of both beds, inlet hot air at 80°C is used for drying peppercorns with initial moisture content at about 82.5% w.b. The inlet air velocity is adjusted to be 1.0Umf, 1.1Umf and 1.3Umf (Umf= minimum fluidization velocity of peppercorns) as desired. Drying time and weight of peppercorns are measured in 5 minute intervals for 120 minutes for each run. The experimental results show that in the rectangular bed, the peppercorns show low oscillating and it becomes dense bed. This causes low heat transfer rate between peppercorns and hot air leading to slower mass transfer of moisture in the peppercorns. In the wavy surface bed, the peppercorns has high fluctuations due to unsymmetrical flow in the bed creating a sustainable oscillating flow with stronger turbulence of hot air and it causes dilute bed, resulting in higher heat and mass transfer in peppercorns. Closer examination reveals that for a similar operating condition, the rectangular wavy surface bed performs better than the rectangular bed.

Thermal Performance in Circular Tube with Co/Counter-Twisted Tapes

Thiswork presents an experimental study on enhanced heat transfer and pressure loss characteristics in a tube having a uniform heat-fluxed wall by using small double and triple co-and counter-twisted tapes at two twist ratios, y/w=4 and 4.5. The investigation has been conducted for Reynolds number from 5300-20,000. The experimental results of the heat transfer and pressure drop are proposed in terms of Nusselt number and friction factor, respectively.The experimental results reveal thatthe maximum TEF for the triple counter-twisted tapesat smaller twist ratio isabout 1.26.

Performance Assessment in a Heat Exchanger Tube with Opposite/Parallel Wing Twisted Tapes

The thermohydraulic performance in a tube containing a modified twisted tape with alternate-axes and wing arrangements is reported. This work aims to investigate the effects of wing arrangements (opposite (O) and parallel (P) wings) at different wing shapes (triangle (Tri), rectangular (Rec), and trapezoidal (Tra) wings) and on the thermohydraulic performance characteristics. The obtained results show that wing twisted tapes with all wing shape arrangements (O-Tri/O-Rec/O-Tra/P-Tri/P-Rec/P-Tra) give superior thermohydraulic performance and heat transfer rate to the typical twisted tape. In addition, the tapes with opposite wing arrangement of O-Tra, O-Rec, and O-Tri give superior thermohydraulic performances to those with parallel wing arrangement of P-Tra, P-Rec, and P-Tri around 2.7%, 3.5%, and 3.2%, respectively.

Heat Transfer Enhancement in a Double Pipe Heat Exchanger by Insertion of Propeller-Type Swirl Generators

This paper describes an experimental study of turbulent convective heat transfer and flow friction characteristics in a double tube heat exchanger equipped with propellers (2 blade-type). The propellers are used as the decaying swirl generators in the inner tube. The experiments were performed using the propellers with four different interval lengths (l = 1D, 2D, 3D and 4D where D is diameter of the inner tube), for the Reynolds number ranging from 5000 to 32,000, using water with temperature of 27°C and 70°C as cold and hot working fluids, respectively. The data of the tube equipped with the propellers are reported together with those of the plain tube, for comparison. The obtained results demonstrate that the heat transfer rate in term of Nusselt number (Nu) and friction factor (f) in the tube with propellers are higher than those in the plain tube at the similar operating conditions. This is due to the chaotic mixing and efficient interruption of thermal boundary layer caused by the propellers. In addition, the Nusselt number and friction factor in the tube fitted with the propellers increase as the interval length decreases. Depending on Reynolds number and interval length, Nusselt numbers and friction factors in the tube fitted with the propellers are augmented to 1.95 to 2.3 times and 5.8 to 13.2 times of those in the plain tube. In addition, the correlations of the Nusselt number (Nu) and the friction factor (f) for tube fitted with the propellers are reported and the performance evaluation to access the real benefits of using the turbulators is also determined.Copyright

Simulation of Turbulent Heat Transfer in a Tube Fitted with Twisted Tape Placed Separately from the Tube Walls

The effects of loose-fit twisted tape (LFT) on the heat transfer rate, friction factor, fluid phenomena and thermal performance of a tube under constant wall temperature are examined. It is observed that apart from the rise of Reynolds number, the reduction of the clearance ratio (c/D) leads to an increase in the heat transfer and pressure loss. According to the numerical results, the heat transfer and friction factor in the tubes with loose-fit twisted tape (LFT) for the smallest clearance ratio of c/D = 0.05 are higher those other clearance ratios. In addition, the thermal performances of clearance ratio c/D = 0.05 are found to be higher than those other clearance ratios (c/D) for all Reynolds numbers examined.

Laminar Convection Heat Transfer in Square Channel Fitted Diagonally with 45° V-Discrete Baffles

This work presents a numerical investigation of laminar periodic flow and heat transfer in a constant heat flux-surfaced square-channel fitted diagonally with 45° V-discrete baffles. The computations are based on the finite volume method, and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 200 to 1,200. Effects of different blockage ratios (BR=b/H), BR in range from 0.05-0.2 with pitch ratio of 1.0 on heat transfer and pressure loss in the channel are studied. It is apparent that vortex flows created by the 45° diagonal V-discrete baffle exist and help to induce impinging flows on wall leading to drastic increase in heat transfer rate over the smooth channel. In addition, the increase in the BR results in the rise of Nusselt number and friction factor values. The computational results reveal that the optimum thermal enhancement factor of the 45° V-discrete baffle is about 2.24 at BR=0.2.

Influences of twisted-tape with parallel rectangular-wing on thermal performance of a heat exchanger

The present paper reports heat transfer enhancement and friction factor characteristics in the tubes inserted with rectangular-winged twisted-tapes (TT-RWs). The wing-depth ratio (d/W) was varied from 0.1 to 0.3 while the tape-twist ratio was kept constant at y/W = 4.0. The experiments were conducted under uniform heat flux condition for Reynolds number between 5500 and 20,200 (based on the inner diameter, D), using water as the working fluid. The tubes with typical twisted tape (TT) and twisted tape with alternate-axis (TA) as well as a plain tube were also tested for assessment. The obtained results demonstrate that the utilization of the tubes with TT-RWs leads to the increases of both Nusselt number and friction compared to those from the uses of the tubes with TT, TA and the plain tube. In addition, Nusselt number increases as a wing-depth ratio of the twisted tape increases. The improvement of Nusselt number is directly related to the superior destruction of the boundary layer which is responsible by the stronger swirl flow and turbulence intensity. According to the results, the TT-RW with d/W = 0.3 yields the highest Nusselt number which is around 100% higher than that of the plain tube, corresponding to the thermal performance factor of 1.36 at constant pumping power.