Sutapat Kwankaomeng

Thermal performance enhancement in solar air heater channel with periodically V-shaped baffles

The research paper presents a study on thermal performance enhancement in a rectangular channel heat exchanger mounted with periodically V-shaped baffles. The channel has an aspect ratio (width to height ratio), AR=10 and height, H=30 mm while baffle characteristics are the baffle to channel height ratio, e/H=0.2, 0.3 and 0.4; the baffle pitch to channel height ratio, PR=P/H=2 and 2.67; the attack angle (α) of 30° relative to the flow direction. The experiment has been conducted by varying air flow velocity in order to adjust Reynolds number range from 5000 to 25,000. The upper wall of the channel is uniformly heated as a constant heat flux while the rests are covered with thermal insulations to reduce heat loss to surroundings. The effects of the baffles on Nusselt number and friction factor have been examined. The overall performance of tested baffled channel is evaluated to obtain the degree of heat transfer enhancement and friction factor induced by baffles with respect to the smooth channel under similar flow conditions.

Thermal characteristics in square channel with 45° staggered baffle inserts

The paper presents a study of heat transfer in a heat exchanger channel inserted with staggered inclined baffles. The channel has a square section with uniform wall heat flux conditions. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 4000 to 25,000. The inclined baffles with an axial pitch equal to three times of channel height and with the attack angle of 45° are mounted in tandem and staggered arrangement on the lower and upper walls of the test channel. Effects of four baffle-to-channel height ratios (e/H = 0.1, 0.2, 0.3 and 0.4) on heat transfer in terms of Nusselt number and pressure loss in the form of friction factor are experimentally investigated. The experimental result shows that the insertion of staggered inclined baffles with the e/H=0.4 provides higher heat transfer and friction factor values than others. This is caused by higher baffle-to-channel height ratios of using e/H = 0.4 interrupting the flow and diverting its direction thus promoting high levels of mixing over others.

Laminar periodic flow and heat transfer in square channel with 30° inclined baffles

A numerical investigation has been carried out to study laminar flow and heat transfer characteristics in a three-dimensional isothermal wall square-channel with 30° staggered angled-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 100 to 1200. To generate a pair of streamwise counter-rotating vortex (P-vortex) flows through the tested channel, the baffles (like rectangular winglet) with the attack angle of 30° are mounted in tandem and staggered arrangement on both upper and lower walls of the test channel. Effects of different baffle heights at a single pitch ratio (PR=3) on heat transfer and pressure loss in the channel are studied. It is found that P-vortex flows created by the 30° baffle exist and help to induce impinging jets on a side wall and the upper and lower wall leading to drastic increase in heat transfer rate over the test channel. In addition, the increase in the baffle height results in the rise of Nusselt number and friction factor values. The computational results reveal that the optimum thermal enhancement factor of the baffle is about 2.9 at height of 0.15 times of the channel height.

Investigation and Development of Modified Ross Yoke Mechanism on Alpha-Parallel-Cylinder Stirling Engine

This paper presents the redesign and modification of a Ross yoke mechanism driving an alpha Stirling engine with parallel cylinder arrangement. Engine sealing is a crucial factor affecting engine operation, power, and maintenance. Friction and lateral force acting on piston seals induce major wear and finally lead to leakage and losses in both power and operating cost. To reduce these problems, linear reciprocating and balancing motion of both piston and connecting rod are preferred. Mechanical inversion is introduced to invert general motion of connecting rod to rectilinear translation. The original Ross yoke part is altered from pin joints to slot pin joints allowing piston rod to be driven straight. Length of the slot groove was adjusted and optimized. Motion of the modified Ross yoke was investigated theoretically and experimentally. Both analytical model and prototype have the same operating conditions and swept volume of 25 cm3. The ambient air was used as the working gas which was heated by LPG at flow rate of 0.6 kg/h and cooled by water. The maximum speed of 977 rpm was attained. Recorded maximum power and torque were 0.549 W at 486 rpm and 0.014 Nm at 260 rpm, respectively. The modified Ross yoke Stirling engine has operated smoothly when its piston rods were redesigned to slide linearly.

Thermal Characteristics in a Tube Fitted with Inclined Vortex Rings

The paper presents an experimental study on the heat transfer, pressure loss and thermal performance characteristics in a round tube fitted repeatedly with inclined vortex ring (VR) under a uniform wall heat flux. Periodically VRs are inserted into the tube with a view to generating vortex flows that assist to increase the heat transfer rate of the tube. The airflow rate in terms of Reynolds number is ranging from 5000 to 25,000. Measurements are carried out for the VR with a single blockage ratio, BR= e/D = 0.1 and an attack angle, α = 20o, at fourVR pitch ratios, PR= P/D = 0.5, 1.0, 1.5 and 2.0. The variations of heat transfer and pressure loss are presented in the form of mean Nusselt number and friction factor respectively. The experimental results show that the use of the VRs leads to the considerable increase in heat transfer and friction factor values in comparison with the smooth tube. The VRs at PR = 0.5 provides the highest heat transfer and friction factor.