Heat transfer and friction characteristics of solar air heater duct having protruded roughness geometry on absorber plate

Protruded roughness geometry is generally considered to be simple, an innovative and economic technique for improving thermal performance of solar air heater. Experimental investigation has been carried to study the effect of different shapes, position, and height of protrusions on heat transfer and friction characteristics of solar air heater duct for the range of parameters. Correlations for Nusselt number and friction factor have been brought out from the experimental data which can be further used for evaluating performance of solar air heater having the considered roughness geometry.     

Effect of roughness elements on thermal and thermohydraulic performance of double pass solar air heater duct having discrete multi V-shaped and staggered rib roughness on both sides of the absorber plate

In this work, an experimental setup consisting of a double pass solar air heater duct provided with discrete multi V-shaped and staggered rib as artificial roughness on both sides of the absorber plate has been designed and fabricated. The parameters of interest investigated experimentally cover a wide range of Reynolds number (Re) from 2000 to 20000, relative staggered rib pitch (p’/p) from 0.2 to 0.8, relative staggered rib size (r/e) from 1 to 4, and relative roughness width (W/w) from 5 to 8. Experimental data related to heat transfer, pressure loss, and thermohydraulic performance has been determined. Substantial improvement has been obtained with some penalty of friction losses.     

Heat transfer and friction in rectangular solar air heater duct having spherical and inclined rib protrusions as roughness on absorber plate

In this work, an experimental investigation on heat and fluid flow characteristics of artificially roughened solar air heater duct has been carried out. The roughness and operating parameters covered a range of Reynolds number (Re) from 2000 to 20000, relative roughness pitch (P/e) from 15 to 30, relative rib length (r/g) from 0.4 to 1.0, and relative rib pitch (P_r/P) from 0.2 to 0.8. Other parameters, i.e., relative roughness height (e/D), angle of attack (α), and relative roughness gap are kept constant. Results show that the considerable enhancement in Nusselt number and Thermo-hydraulic performance has been obtained with an increase in friction factor using roughened surface.     

Heat transfer and friction factor characteristic of spherical and inclined teardrop dimple channel subjected to forced convection

An experimental and numerical investigation is performed in order to determine the outcome of dimple geometries on the heat transfer and friction factor in a dimple cooling channel subjected to turbulent flow. Two geometries taken into consideration are spherical and inclined teardrop. In order to have a better comparison between the two different dimple channel, the dimple depth, total wetted area of dimple, and dimple pitch have been kept constant. In case of spherical and inclined teardrop dimple channels, heat transfer augmentation, friction losses, and flow pattern have been obtained for a Reynolds Number range from 14,000 to 65,000. The investigation shows that the dimple geometry has a significant contribution to increasing the heat transfer augmentation and determining the flow pattern. The inclined teardrop dimple arrangement shows the maximum heat transfer that is 17% higher than the spherical dimple channel, whereas inclined teardrop dimple results in the rise of friction factor of about 5.93–16.14% times as compared to the spherical dimple within the specified Reynolds number. The inclined teardrop and spherical dimple channel show the heat transfer enhancement of 2.74 to 3.20 times and 2.38 to 2.68 times than that of smooth channels provided thermal boundary conditions and flow conditions are kept same. The numerical study has been performed, which provided a detailed insight into the flow structures and vortex formations in spherical and inclined teardrop dimple channel.     

Heat transfer and pressure drop measurements in channels roughened by variously shaped ribs on one wall

Heat transfer and pressure drop measurements were conducted to study the thermal-hydraulics in a square, round-edged channel roughened by ribs (e/D_h = 0.0638, p/e = 10) on one wall at Reynolds numbers ranging from 5.0 × 10⁴ to 2.5 × 10⁵. Three variously shaped ribs were investigated: Transverse ribs with square cross sections, transverse ribs, and upstream directed 60° V-shaped ribs with round-edged rib front and rear surfaces. Friction factors, Nusselt number ratios, roughness functions, and the thermal performance were presented. The highest heat transfer and best thermal performance is reached by the upstream directed V-shaped ribs.     

Experimental investigation of heat transfer and friction coefficient of the water/graphene oxide nanofluid in a pipe containing twisted tape inserts under air cross-flow

The water/graphene oxide nanofluid effect in a pipe equipped by twisted tape inserts under air cross-flow is investigated and the optimal tape geometry is determined. The range of internal and external Reynolds numbers are: 3800<Re_o<21500 and 550<Re_i<2000. Heat transfer and pressure drop increase by increasing Re and inserts width and heat transfer performance coefficient increased up to 1.4, indicating enhanced heat transfer compared to undesirable pressure drop. On the other hand, the heat transfer coefficient is 26% higher when compared with water in a plain tube. According to the results, this method is a good alternative in heat exchangers.     

Detailed heat transfer and friction factor characteristics in a rectangular duct with alternate solid and converging-slit ribs

Liquid crystal thermography and pressure drop measurements have been carried out to study the heat transfer and frictional characteristics in a rectangular duct with solid ribs (C1), converging slit-ribs (C2), and alternate solid-slit ribs (C3) mounted transversely on the bottom wall, where C2 carries a continuous converging-slit in the flow direction. Effect of rib configurations, and rib pitch to height ratios (6, 8, 10, and 12) has been investigated at Re of 9400, 26160, 42500, and 58850. Results show that converging-slit considerably enhances the heat transfer rate in the downstream vicinity, and help in obviating the local hot spot formation.

Abbreviations: LCT: Liquid crystal thermography; HTC: Heat transfer coefficient; LHI: Laser holographic interferometry; NST: Naphthalene sublimation technique; IR: Infrared; TPF: Thermo-hydraulic performance; PIV: Particle image velocimetry.     

An experimental study on convective heat transfer performance of steam and air flow in V-shaped rib roughened channels

An experimental study on heat transfer characteristics of steam and air flows in a V-shaped ribbed channels was conducted. The effects of Reynolds numbers and rib angles on heat transfer of steam and air were obtained. The area-averaged Nusselt numbers of steam flow at a Reynolds number of 12,000 were 13.9%, 20.6%, 27.1%, and 27.9% higher than those of air flow for rib angles of 90°, 75°, 60°, and 45°, respectively. The correlations for Nusselt number in terms of Reynolds number and rib angle for steam and air in V-shaped ribbed channels were developed.     

Evaluation of Nusselt number and effectiveness for a vertical shell-coiled tube heat exchanger with air bubble injection into shell side

Air bubble injection was employed to increase the heat transfer rate (Nusselt number) of a vertical shell and coiled tube heat exchanger in this article. Hot and cold water flowed into the coil side and shell side of heat exchanger, respectively, and air bubbles were injected inside the shell side of heat exchanger via a memorable method. Bubbles' vertical movement due to buoyancy forcing through the heat exchanger can enhance the heat transfer rate by mixing the thermal boundary layer, increasing the turbulence level of the fluid flow and increasing the shell-side fluid Reynolds number.