Value Of Thermal Enhancement Factor Research Articles

Hollow trapezoidal baffles in a rectangular channel: Thermal/hydraulic assessment with ANN numerical approach

In this study, thermal/hydraulic performance (THP) of a heated bottom surface channel, on which hollow straight, elliptic, and wavy top surface trapezoidal baffles are attached, have been investigated. Artificial neural network modeling (ANN) and 3D ANSYS numerical valuations are presented and validated using experimental data obtained by Sahin et al. (2019). Six parameters are studied: baffle height (H), baffle width (S), baffle length (L), corner angle (α), inclination angle (β), and Reynolds number (Re). This study is carried for both aligned and staggered baffles configuration. Air is considered to be the working fluid at a range of Reynolds number (5 × 103 ≤ Re ≤ 2.3 × 104). Backpropagation technique used to determine the optimal ANN size with the Bayesian regularization algorithm. Results show that the most effective parameters on THP are Re, α, and H. Based on the thermal hydraulic efficiency values, the optimum condition is obtained at α= 16°, β = 0°, and baffle dimensions of H = 20 mm, L = 25 mm, S = 26 mm. The average value of thermal enhancement factor (TEF) shows that the staggered arrangement is superior to aligned one for all baffle shapes at the optimum condition. The largest TEF is 1.2 which is captured for the case of the wavy top surface trapezoidal baffles in staggered arrangement at Re = 5000.

Enhancement of the turbulent convective heat transfer in channels through the baffling technique and oil/multiwalled carbon nanotube nanofluids

An attempt is made to improve the overall performances of channel heat exchangers. The techniques of baffles and nanofluids are combined to enhance the dynamic and thermal behaviors within the channel exchanger. Baffles under various attack angles are used as vortex generators. In addition, oil/multiwalled carbon nanotubes (MWCNT) is used as a working fluid. Both inclinations in the upstream and downstream directions were considered, referenced as Case A (UIB) and Case B (BIB), respectively. While the channel equipped with vertical baffles is referenced as Case C. The proposed models with combined techniques allowed a considerable enhancement in the overall efficiency. The comparison between the three cases revealed that the most significant value of thermal enhancement factor (TEF) of 5.634 was reached with vertical baffles (Case C) at the highest value of Reynolds number. When using inclined baffles, the 75° upstream attack angle (Case A) allowed the highest TEF of 4.814, compared with Case B.

Improvement of the performance of solar channels by using vortex generators and hydrogen fluid

An attempt is made to enhance the thermal hydrodynamic performance of a solar channel by using vortex generators including attached fins and detached bars. Hydrogen gas is used as a working fluid under turbulent flow conditions. The computational fluid dynamics method is used to achieve the investigations. Governing equations among fluid and solid sections are determined and solved by the computational finite volume method. The hydrodynamic characteristics, dynamic pressure, turbulent kinetic energy, turbulent viscosity, Nusselt number, skin friction, and the thermal enhancement factor (TEF) are investigated for a range of Reynolds number (Re) from 5000 to 20,000. The obtained results revealed that the TEF values are important (TEF > 1) for all Re values under investigation. The TEF values are between 1.2 and 3.5. An increase in the TEF values was observed with increased Reynolds number, where the maximum value of TEF of about 3.5 was achieved at Re = 20,000. At this value of Re, the normalized heat transfer value (Nu/Nu0) is the highest, while the normalized friction values (f/f0) are the lowest. This demonstrates the usefulness of the suggested vortex generators combined with the fluid (H2) for the successful thermal and dynamic performance within the smooth channels.

Combination of baffling technique and high-thermal conductivity fluids to enhance the overall performances of solar channels

In the present study, two-phase flow and forced-convection heat transfer of hydrogen gas (H2) in a solar finned and baffled channel heat exchanger (SFBCHE) is studied numerically. The effect of different obstacles in the channel is addressed. A H2 heat transfer fluid (HTF) having a high thermal conductivity with the baffling technique is implemented to enhance the overall performance of a solar channel. In the initial step, the results from the proposed numerical model were compared with the experimental data of a smooth channel, and then against data with a baffled channel. After checking the validity of our model, the same numerical approach was used for studying thermal-fluid characteristics of the channel with the new fluid. A hydrothermal analysis is presented for a range of Reynolds number (Re) from 5000 to 25,000. At the lowest Re = 5000, the thermal enhancement factor (TEF) is about 1.25. This value increases to 2.16, or 73.46%, when Re = 10,000. This increase in the TEF values continues as Re increases. The largest Re = 25,000 gives the highest TEF value, as it is about 4.18, which is 2.75 times greater than that given for the case of using the conventional gaseous fluid (air). Therefore, our proposed structure for the SFBCHE with high H2 HTF flow velocity leads to improve the values of dynamic pressure (Pd) and heat transfer (Nu), while reducing the skin friction (f) values, which increases the overall TEF of the channel. In addition, all performance values are greater than unity (or 1.00). This reflects the importance of the H2 HTF baffling and finning technique in improving the hydrodynamic thermal-energy performance of solar heat exchangers. The suggested model of SFBCHE filled with an H2 HTF having a high thermal conductivity allows a considerable enhancement in the overall thermal performances which can be employed in various thermal types of equipment, such as solar energy receivers, automotive radiators, and cooling in chemical industries.

Assessment of Thermal Performance of Non-Conventional Grooved Stepped Shoe Ribs by CFD Technique

In improvement of the thermal performance there is necessity of the heat transfer augmentation. Heat transfer enhancement can be achieved with enlarged or extended surface, impeded boundary level, augmentation in the turbulence etc. It is desired to keep the size of heat exchanger compact for better working conditions. In the proposed work, we made the Computational Fluid Dynamics (CFD) analysis of the non-conventional type of ribs. In this work the non-conventional Stepped grooved shoe shaped ribs were studied by changing its geometry parameters like rib height (15, 20,22mm), thickness of the rib (4, 5,10 mm), and the ratio between these entities. The numerical analysis was done to study change in rate of heat transfer and pressure drop. The effects of variation in staggered arrangements and truncation gap on thermal performance were also studied. It was observed that providing staggered arrangement with truncation gap of 20 mm gives the optimum value of thermal enhancement factor of 1.33.

Baffle orientation and geometry effects on turbulent heat transfer of a constant property incompressible fluid flow inside a rectangular channel

Purpose A computational fluid dynamics (CFD) analysis has been carried out on the aerodynamic and thermal behavior of an incompressible Newtonian fluid having a constant property and flowing turbulently through a two-dimensional horizontal high-performance heat transfer channel with a rectangular cross section. The top surface of the channel was kept at a constant temperature, while it was made sure to maintain the adiabatic condition of the bottom surface. Two obstacles, with different shapes, i.e. flat rectangular and V-shaped, were inserted into the channel; they were fixed to the top and bottom surfaces of the channel in a periodically staggered manner to force vortices to improve the mixing and consequently the heat transfer. The first fin-type obstacle is placed on the heated top channel surface, and the second baffle-type one is placed on the insulated bottom surface. Five different obstacle situations were considered in this study, which are referred as cases FF (flat fin and flat baffle), FVD (flat fin and V-downstream baffle), FVU (flat fin and V-upstream baffle), VVD (V-downstream fin and V-downstream baffle) and VVU (V-Upstream fin and V-upstream baffle). Design/methodology/approach The flow model is governed by Reynolds-averaged Navier–Stokes equations with the k-epsilon turbulence model and the energy equation. These governing equations are discretized by the finite volume method, in two dimensions, using the commercial CFD software FLUENT software with the Semi Implicit Method for Pressure Linked Equations (SIMPLE) algorithm for handling the pressure-velocity coupling. Air is the test fluid with the flow rate in terms of Reynolds numbers ranging from 12,000 to 32,000. Findings Important deformations and large recirculation regions were observed in the flow field. A vortex causes a rotary motion inside the flow field, which enhances the mixing by bringing the packets of fluid from the near-wall region of the channel to the bulk and the other way around. The largest value of the axial variations of the Nusselt number and skin friction coefficient is found in the region facing the baffle, while the smallest value is in the region near the fin, for all cases. The thermal enhancement factor (TEF) was also introduced and discussed to assess the performance of the channel for various obstacle situations. It is found that the TEF values are 1.273-1.368, 1.377-1.573, 1.444-1.833, 1.398-1.565 and 1.348-1.592 for FF, FVD, FVU, VVD and VVU respectively, depending on the Re values. In all cases, the TEF was found to be much larger than unity; its maximum value was around 1.833 for FVU at the highest Reynolds number. Therefore, the FVU may be considered as the best geometrical configuration when using the obstacles to improve the heat transfer efficiency inside the channel. Originality/value This study can be a real application in the field of shell-and-tube heat exchangers and flat plate solar air collectors.

Could FA-PG-SPIONs act as a hyperthermia sensitizing agent? An in vitro study

The therapeutic effect of polyglycerol coated iron oxide nanoparticles (PG-SPIONs, non-targeted nanoparticles) and folic acid-conjugated polyglycerol coated iron oxide nanoparticles (FA-PG-SPIONs, targeted nanoparticles) in combination with hyperthermia on viability of HeLa cells was investigated. It was observed that coated and uncoated SPIONs have spherical shapes with an average diameter of 17.9 ± 2.85 nm and 5.4 ± 0.75 nm, respectively. The penetration rate for cells treated with targeted nanoparticles was shown to be more than that of non-targeted nanoparticles. Moreover, it was revealed that the treatment of cells with ≥ 50 µg/ml FA-PG-SPIONs in combination with hyperthermia induced cytotoxicity in comparison to control cells. The results also showed that increasing the concentrations of targeted nanoparticles (FA-PG-SPIONs) and heating time would increase the value of thermal enhancement factor (TEF). In contrast, TEF values were not increased with increasing heating time and concentrations of non-targeted nanoparticles (PG-SPIONs). On the other hand, TEF values were increased with increasing concentrations and heating time so that the maximum TEF value was obtained at the highest concentration (FA-PG-SPION, 200 µg/ml) as well as the longest heating duration (60 min). Thus, it is concluded that FA-PG-SPIONs with concentrations ≥ 100 µg/ml could be introduced and used as hyperthermia sensitizing agents leading to enhanced cancer therapy efficiency.

Numerical investigation of fully developed periodic turbulent flow in a square channel fitted with 45° in-line V-baffle turbulators pointing upstream

This paper presents numerical simulation of periodic fully developed turbulent flow and thermal characteristics in a square channel fitted with V-baffles using air as the working fluid at Re ranging from 5000 to 25000. V-baffles with an angle of attack of 45° pointing upstream are mounted in both lower and upper walls with an in-line arrangement. Effect of various baffle blockage ratios (BR=0.2, 0.4 and 0.6) and baffles pitch ratios (PR=0.5,1 and 1.5) on flow behavior and heat transfer are investigated. The results show that the V-baffle induces four counter-rotating vortices, and their core centers appear to spirally move close to each other along the baffle cavity which leads to induce better flow mixing between the core and wall flow regions. Also, V-baffle pointing upstream causes high impinging regions on the channel walls leads to higher Nusselt number rates in jet impinging areas. Higher BR and/or lower PR result in an increase in Nusselt number. Thermal enhancement factor tends to increase as BR decreases. The BR=0.2 give value of thermal enhancement factor=0.78 at the lower Re=5000. Also, lower value of PR (PR=0.5) leads to higher enhancement factor.

Numerical investigation of heat transfer and pressure drop of in-line array of heated obstacles cooled by jet impingement in cross-flow

A computational study of cooling in-line array of heated obstacles simulating electronic components by jet impingement in cross-flow (JICF) has been investigated using RNG k-ε turbulence model. The jet position has been changed to impinge each obstacle consecutively at different jet-to-channel Reynolds number ratios, Rej/Rec=1, 2, and 4. The main flow structure, the static pressure, local and average Nusselt numbers as well as the thermal enhancement factor have been investigated.The results show that there is a significant variation between the flow structures around an obstacle when subjected to JICF or CF. The friction factor for JICF is greater than that for cross-flow only (CF) by 88% at the first jet position and Rej/Rec=4. The irregular distribution of local Nusselt number (Nu) on the impinged obstacle is moderated by increasing the Reynolds number ratios. Increasing Reynolds number ratio increases the average Nusselt number (Nu‾) of the downstream obstacles and decreases it for the upstream obstacles. The increment of Nu‾ for whole array for JICF than CF is about 26% at JP3 and Rej/Rec=4. Moreover, the highest value of thermal enhancement factor is attained at JP3 and it equals 12% for Rej/Rec=4.

Enhanced DNA Damages of Human Prostate Cancer Cells Induced by Radiofrequency Capacitive Hyperthermia Pre- and Post X-rays: 6 MV versus 15 MV.

Objective This study aimed to determine the effect of 13.56 MHz radiofrequency (RF) capacitive hyperthermia (HT) on radiosensivity of human prostate cancer cells pre and post X-ray radiation treatment (RT). Materials and Methods In this experimental study, the human prostate cancer cell line DU145 was cultured as 300 µm diameter spheroids. We divided the spheroids into group I: control, group II: HT at 43˚C for 30 minutes (HT), group III: 4 Gy irradiation with 6 MV X-ray [RT (6 MV)], group IV: 4 Gy irradiation with 15 MV X-ray [RT (15 MV)], group V: HT+RT (6 MV), group VI: HT+RT (15 MV), group VII: RT (6 MV)+HT, and group VIII: RT (15 MV)+HT. The alkaline comet assay was used to assess DNA damages in terms of tail moment (TM). Thermal enhancement factor (TEF) was obtained for the different treatment combinations. Results Mean TM increased with increasing photon energy. Group II had significantly greater TM compared to group I. Groups III and IV also had significantly higher TM compared to group I. Significant differences in TM existed between groups V, VII, and III (P<0.05). We observed significant differences in TM between groups VI, VIII, and IV. TEF values demonstrated that enhanced response to radiation was more pronounced in group V compared to the other combined treatments. ConclusionOur results suggest that HT applied before RT leads to higher radiosensivity compared to after RT. HT at 43˚C for 30 minutes added to 6 MV X-ray causes higher enhancement of radiation compared to 15 MV X-ray.

Forchheimer forced convection in a rectangular channel partially filled with aluminum foam

In this paper, heat transfer and pressure drop were investigated by placing open-cell aluminum foam in different ratios according to the channel volume in a hydrodynamically fully developed rectangular channel. Aluminum foams were placed inside the channel in the thermally developing flow region in four different ways; filling the channel completely, convex, concave or triangular against the flow. Air was used as working fluid. The experiments were performed over a wide range of the Reynolds number (968<ReDh<29,624) based on the channel equivalent diameter. The aluminum foam was used in the experiments having two different pore densities (10 and 20 pores per inch, PPI). Empirical equations were derived from the results obtained from the experiments in both laminar and turbulent channel flow regimes. The experiments for heat transfer and pressure drop applications in the porous medium led to original and useful findings; namely, while obtaining the highest value of heat transfer in the channel fully filled with aluminum foam according to the Reynolds number and pore density, the pressure drop and also the pump power increased substantially. This was defined as the thermal enhancement factor (TEF). The value of TEF for 20PPI was greater than 10PPI for both laminar and turbulent flow at a fully filled state. In contrast, the value of the TEF and heat transfer capability (HTC) was always higher for 10PPI when the channel is partially filled with aluminum foam.

A CFD (computational fluid dynamics) based heat transfer and fluid flow analysis of a solar air heater provided with circular transverse wire rib roughness on the absorber plate

This article presents the study of heat transfer and fluid flow processes in an artificially roughened solar air heater by using computational fluid dynamics (CFD). The effects of small diameter of transverse wire rib roughness on heat transfer and fluid flow have been investigated. The Reynolds number, relative roughness pitch (P/e) and relative roughness height (e/D) are chosen as design variables. A two-dimensional CFD simulation is performed using the ANSYS FLUENT 12.1 code. The Renormalization-group (RNG) k–ε model is selected as the most appropriate one. Results are validated by comparing with available experimental results. It is apparent that the turbulence created by small diameter of transverse wire ribs result in greater increase in heat transfer over the duct. However, the use of artificial roughness results in higher friction losses. The present CFD investigation clearly demonstrates that the average Nusselt number and average friction factor increase with increase in the relative roughness height while giving opposite trend with increase in relative roughness pitch. The condition for optimum performance has been determined in term of thermal enhancement factor. A maximum value of thermal enhancement factor has been found to be 1.65 for the range of parameters investigated.

Heat transfer and pressure drop in a channel with multiple 60° V-baffles

The research work has been conducted to assess turbulent forced convection heat transfer and friction loss behaviors for airflow through a channel fitted with a multiple 60° V-baffle turbulator. Measurements have been carried out for the channel of aspect ratio, AR = 10 and height, H = 30 mm with three different baffle blockage ratios, ( e/ H = 0.10, 0.20 and 0.30) and three baffle pitch spacing ratios, (PR = P / H = 1, 2 and 3) while the transverse pitch of the V-baffle is set to 2H and kept constant. The air flow rate is in terms of Reynolds numbers based on the inlet hydraulic diameter of the test channel ranging from 5000 to 25,000. The experimental results show that the V-baffle provides the drastic increase in Nusselt number, friction factor and thermal enhancement factor values over the smooth wall channel due to better flow mixing from the formation of secondary flows induced by vortex flows generated by the V-baffle. In addition, substantial increases in Nusselt number and friction factor values are found for the rise in blockage ratio and/or for the decrease in pitch ratio values. Assessing thermal performance of the V-baffled channel, the use of the V-baffle with PR = 1 and e/ H = 0.10 leads to maximum thermal enhancement factor of about 1.87 at lower Reynolds number.