Maximum Heat Transfer Enhancement Research Articles

Compelling Heat Transfer Augmentation of Laminar Natural Convection from Vertical Plates to Binary Gas Mixtures Formed with Light Helium and Selected Heavier Gases

The present study addresses a remarkable behavior of certain binary gas mixtures in connection to laminar natural convection along a heated vertical plate at constant temperature. The binary gas mixtures are formed with light helium (He) as the primary gas and selected heavier secondary gases. The heavier secondary gases are nitrogen (N2), oxygen (O2), xenon (Xe), carbon dioxide (CO2), methane (CH4), tetrafluoromethane (CF4) and sulfur hexafluoride (SF6). The central objective in the study is to investigate the attributes of the set of seven He‒based binary gas mixtures for heat transfer enhancement with respect to the heat transfer with helium (He) and air. From heat convection theory, four thermo‒physical properties: viscosity η, density ρ, thermal conductivity λ, and isobaric heat capacity Cp affect the thermo‒buoyant convection of fluids. In this study it became necessary to construct a particular correlation equation consigned to the set of seven He‒based binary gas mixtures, which operate in the Prandtl number closed sub‒interval [0.1, 1]. The heat transfer rate with the set of seven He‒based binary gas mixtures from the vertical plate involves four thermo‒physical properties: density ρmix, viscosity ηmix, thermal conductivity λmix, and isobaric heat capacity Cp, mix that vary with the molar gas composition w. A case study is performed to elucidate the unique characteristics of the modified convective heat transport that the set of seven He‒based binary gas mixtures brings forward as compared to the convective heat transport of He and air. It was found that the He+SF6 binary gas mixture renders an absolute maximum heat transfer enhancement rate that is 39 times higher than the heat transfer rate provided by He and 78 times higher than air.

Optimization and correlations development for heat transfer and fluid flow characteristics of ZnO/H2O-ethylene glycol-based nanofluid flow through an inclined ribbed square duct

One simple technique to improve the heat transfer rate is to roughen a square duct’s heated plate. This work is concerned with the heat transfer () and friction factor () of //ethylene glycol nanofluid flowing in ribbed square duct were optimized, and correlations have been developed. Design parameters include nanoparticle concentration (φ) 1–4%, relative angled rib pitch 2.18–3.25, relative angled rib height 0.10–0.25, flow attack angle of inclination rib and Reynolds number (Re) 4000–19,000. The response surface method (RSM) was utilized for optimization. Varying the roughness parameters improves the heat transfer performance of inclined ribbed, but it increases the pumping power of the square duct. RSM results indicated that the maximum heat transfer enhancement belongs to φ of 4%, of 2.50, of 0.20, and of 60°. In addition, a generalized quadratic correlation for Nu and f is constructed based on the analysis of variance, with percentage deviations of and respectively, in contrast to empirically obtained values of Nusselt number and friction factor.

Shape memory alloys enabled smart heat exchangers

Modern heat exchangers encounter the paradox between the high performance and low flow resistance while most of the tasks feature in wide operating conditions where great functional flexibility is required. In this paper, we propose to tackle the dilemma by integrating shape memory alloys into the design of heat exchangers, utilizing a two-way shape memory alloy (SMA) strip as the self-adjusting vortex generator (VG) for heat transfer enhancement. The SMA based vortex generators are trained with predetermined deformation according to the temperature of the working media. To be specific, at low temperature, the SMA strip is flat to reduce the flow resistance. While the temperature is high, the SMA strip is curved to form a rectangular wing vortex generator to enhance the heat transfer. This concept was firstly verified via the experimental study followed by detailed numerical investigation focusing on the mechanism explorations. The deformation characteristic was verified by water bath. With the increase of the temperature of fluid, the heat transfer is increased by 110 ∼ 125 %. On the other hand, the Darcy friction factor can be reduced by 74 ∼ 90 %, when the heat transfer demand decreases based on the concept proposed. The details of flow and heat transfer are given and analyzed by using numerical simulation. And the numerical results are in good agreement with the experimental ones with the relative error of 11 % ∼ 3 % (on heat transfer, Re=8004400) and the warping height ΔZ=4/5 hydraulic diameter (Dh)). The ratio of heat transfer and flow resistance are positively related to the warping height (ΔZ) of VG. Under six calculated Reynolds numbers (Re), the maximum heat transfer enhancement coefficient can be reached at Re = 400 and 800, respectively, with the values ranging from 1.18 ∼ 2.68 for different ΔZ. In the case that ΔZ equals to 4 / 5 hydraulic diameter (Dh), the best performance can be achieved with Re≤1600. If Re≤800, the design can always maintain better performance than the original flat channel, and the maximum performance evaluation criteria (PEC) achieved is 1.32. Based on our research, the smart heat exchanger is expected to satisfy the heat transfer requirements of specific variable working conditions in the future.

Numerical investigations of corrugated tube and Fe3O4 nanoparticles on the mitigation effects of supercritical water heat transfer deterioration

When faced with high thermal loads, the dramatic variations in supercritical water (SCW) thermophysical properties can lead to heat transfer deterioration (HTD). Therefore, the present paper first proposes a new mechanism of HTD based on the pseudo boiling theory, and then numerically investigates the mitigation effects of nanoparticles and corrugations on the HTD. By the investigation of SCW in vertically upward smooth tube, the mechanism study illustrates that the pseudo film with the characteristics of low turbulence intensity and thermal conductivity induces the HTD, and the pseudo two-phase flow instability dominates the growth and dissipation of pseudo film. With the help of nanoparticles and corrugations, the wall temperature has a maximum decrease of 348 K, the wall temperature peak mitigation ratio was 33.5%, and the maximum heat transfer enhancement is 164%. Since the corrugations within the corrugated tube (CT) does not change the growth rate of pseudo film, "HTD cycles" occurs in the CT with large corrugation pitch and further deteriorates the overall heat transfer performance. By the inhibition of pseudo film growth and enhancement of gas-like SCW thermal conductivity, the coupling effect of nanoparticles and corrugations can effectively suppress the HTD as well as "HTD cycles".

ENHANCEMENT OF DUPUIT-DARCY THERMAL CONVECTION OF SWCNT-WATER NON-NEWTONIAN NANOFLUID SATURATED POROUS MEDIUM

The focus of this manuscript is to investigate numerically the free convection of a single-wall carbon nanotube-water non-Newtonian nanofluid saturating an inclined square porous medium, where the Dupuit-Darcy model is used for modeling the fluid flow inside the cavity along with the Carreau-Yasuda model for describing the apparent viscosity of the nanofluid. The top and bottom walls of the enclosure are kept adiabatic, whereas the others are differentially heated. The governing parameters for the problem are the Rayleigh number, nanotubes volume fraction, inertial effect parameter, the Carreau-Yasuda non-Newtonian parameters as well as the inclination angle of the cavity. The finite difference method is used to resolve the governing partial differential equations of the problem. The obtained results are presented through graphs, streamlines, isotherms, and apparent viscosity contours. In addition, a scale analysis is presented to show the maximum heat transfer enhancement recorded. As a matter of fact, the obtained momentum equation enables the analysis of the Newtonian and non-Newtonian behavior of the nanofluid along with the Darcy and the departure from Darcy situation. The findings show that the increase of the single-wall carbone nanotube (SWCNT) percentage significantly enhances the heat transfer even with the increase of the fluid viscosity. Furthermore, the increase of inertial effect parameter inhibits the flow inside the cavity and causes a decrease in the convection rate. In actual fact the power-law index parameter of the Carreau-Yasuda model has a significant effect on the fluid flow strength as well as the convection rate inside the enclosure, i.e., the more the shear thinning the fluid, the better is the rate of convection. The inclination angle of -30° presents better angle for maximum convection rate. An enhancement of 8% in convection rate is recorded for the case of the Newtonian behavior, while for the shear-thinning situation the enhancement reaches eight times of that recorded of Newtonian condition.

Numerical study of local heat transfer in tube bundle in pulsating flow

Forced pulsating flows enhance the heat transfer of various heat exchange equipment; however, such flows remain poorly understood. A numerical simulation was used to study how the position of a cylinder in a tube bundle affects the heat transfer during pulsating flow. The tubes of the tube bundle were arranged in an in-line order with the same relative pitch of 1.4. The Reynolds number and Prandtl number had constant values of 1500 and 4.03, respectively. The pulsating flow exhibits a reciprocating asymmetrical character. The pulsation amplitude related to the cylinder diameter was in the range from 0.1 to 0.4, and the pulsation frequency was in the range from 0.2 to 0.8 Hz. The numerical simulation results indicated that the heat transfer of the cylinder in the tube bundle was affected by the row number. With pulsating flow, the heat transfer of the cylinder in the first row had a minimum value, whereas the maximum heat transfer was observed in the last row. The effect of the position of the cylinder along the flow in the tube bundle decreases with increasing pulsation intensity. The maximum heat transfer enhancement of 51% was observed in the first row at a frequency of 0.8 Hz and amplitude of 0.4.

Numerical Simulation of Heat Transfer Performance of a Dimpled Tubular Heat Exchanger

The processing of dimple on the outer wall of tube will produce corresponding protrusion dimple on the inner wall. The turbulent flow and heat transfer performance of a tubular heat exchanger containing a dimpled inner tube is studied numerically. The results show that the main reason for the enhancement of heat transfer ability of the dimple is the flow vortex in the concave dimple and the shock to the wall induced by the protrusion dimple. Compared with the smooth wall of the tube, the maximum enhancement of heat transfer was 1.94 times in concave dimple and 2.74 times in protrusion dimple. By comparing the heat transfer performance, flow resistance, and comprehensive heat transfer factor of the tube and shell of different sizes of exchange heat pipe, it is determined that the combination of inner and outer wall dimple size of 10–15 mm is a structure with better comprehensive heat transfer performance.

Electrohydrodynamic (EHD) effects on condensation heat transfer of R-11 on circular and elliptical cylinders: An experimental study

In the current experimental research, electrohydrodynamic (EHD) assisted condensation heat transfer of R-11 on a horizontal cylinder is studied for two different cases of circular and elliptical cross sections. Experiments are carried out for different various tilting angles of the elliptical cylinder. Furthermore, effects the involving parameters such as electric voltage, electrode-cylinder distance, and imposed evaporative heat flux are investigated. A separate set of complementary experiments is also conducted to visualize the EHD influence on instability of the condensate liquid surface. The electric field effects are shown to start at a specific voltage depending on the electrode-cylinder distance. Passing the onset of EHD initiation point, slight increase of the condensation heat transfer at low voltages is followed by a significant rise at elevated voltages until the electric discharge takes place. It is shown that increasing the electrode-cylinder distance causes the reduction of the heat transfer rate due to the weakened electric field. However, it delays the electric discharge and thus extends the maximum possible heat transfer enhancement. Results also indicate that the condensation heat transfer on the elliptical cylinder inversely depends on the angle between the minor diameter and horizontal direction. The elliptical cylinder generally facilitates the separation and falling of the condensate film thus leads to a maximum of 24% higher heat transfer enhancement compared to the circular cylinder. Moreover, visual observations of the condensation process reveal that thinning and disturbance of the liquid condensate film change of the film to pseudo-dropwise condensation are the two main possible mechanisms responsible for the heat transfer enhancement under the applied electric field. The maximum heat transfer enhancement values of 3.17 and 3.36 are obtained at electrode voltage of V = 24 kV, for circular and elliptical cylinders respectively.

Heat transfer and flow characteristic of a flat confined loop thermosyphon with ternary hybrid nanofluids for electronic devices cooling

The purpose of this study is to explore the feasibility of the application of ternary hybrid nanofluids in heat pipes and the effect mechanism of nanofluids on the operation performance of flat confined loop thermosiphon (FCLTS), which are also the novelty of this study. Al2O3:Cu:TiO2 ternary hybrid nanofluids with different mixing ratios and concentrations were prepared. The synergistic effect of thermal conductivity enhancement was analyzed to obtain the ternary hybrid nanofluids with the optimal mixing ratio of 4:2:4. Thermal performance of a FCLTS with Al2O3:Cu:TiO2 nanofluids was investigated. This study focused on the effect of nanofluid concentrations, heat loads and inclination angles. This study revealed a unique phenomenon that nanofluids could be cleverly attached to the upper heated surface of evaporator, i.e., above the liquid level, improving the wettability of the upper surface. The optimal inclination angle was 90° due to the gravity-assisted effect. In the coupling of assistance and resistance, the optimal concentration was 0.3 vol%. The lowest thermal resistance of 0.09 K/W and maximum heat transfer enhancement efficiency of 22.5 % were observed for nanofluids with concentration of 0.3 vol% at a heat load of 80 W and inclination angle of 90°. Compared with miniature loop heat pipe with single nanofluids or binary hybrid nanofluids in the literature, ternary hybrid nanofluids exhibit favorable heat transfer enhancement for FCLTS at lower cost. The research provides theoretical basis and technical support for heat pipe design.

Cooling of Heated Blocks with Triangular Guide Protrusions Simulating Printed Circuit Boards

There is no study that investigates triangular guide protrusions including their systematical geometrical changes together with the effects of channel height in the open literature in the context of the authors’ knowledge. Moreover, the number of laminar studies is less than turbulent studies, whereas low velocity or natural convection cases are still important, especially for small devices in small PCB passages. The objective of this study is to investigate numerically the effects of triangular guide protrusions for the enhancement of heat transfer from the blocks’ simulated electronic components in laminar flow conditions. Two-dimensional, incompressible, steady, and laminar flow analysis was performed to predict fluid flow and heat transfer characteristics for three heated blocks in a PCB (printed circuit board) passage with triangular guide protrusions mounted on the upper wall. The Galerkin finite element method of weighted residuals was used to discretize conservation equations. The effects of the channel expansion ratio and inlet velocity were investigated for five geometrical cases. If the size of the protrusions is increased, the existence of protrusions starts to affect the flow patterns on the lower wall. The size of the last protrusion controls the flow structure downstream of the last block. On the upper wall, after the last protrusion, a recirculation is formed and the length of the recirculation increases with an increasing Re number. Moreover, the reattachment length of recirculation after the last block increases with an increasing Reynolds number for a fixed expansion ratio. Expansion ratio and inflow conditions caused by blocks and protrusions have a great influence on the formation of secondary recirculation in addition to the Reynolds number. Heat transfer increases with increasing sizes of upper triangular protrusions. Maximum overall heat transfer enhancement is provided as 47.7% with the geometry of the maximum sized protrusions for the channel height of 3 h. In the case of 4 h, the maximum overall heat transfer enhancement is 24.21%. These enhancements in heat transfer that can be encountered in PCB cooling applications may help the PCB cooling designers.

Enhancement of Heat Transfer Performance of a Heat Pipe by Using Calcium Magnesium Carbonate-Ethylene Glycol/Water Nanofluid with Sodium Dodecylbenzene Sulfonate

In this paper, the effect of using CaMg(CO3)2/Ethylene Glycol-water (50:50%) as a working fluid on the thermal performance of thermosyphon heat pipe was experimentally studied. Nanofluid was prepared by two-step method using 2% concentration of CaMg(CO3)2 nanoparticle and 0.05% surfactant (Sodium dodecylbenzene sulfonate). For the experimental set-up, a straight copper pipe of one-meter length was used. The inner diameter of the pipe is 13 mm, and the outer diameter is 15 mm. Experiments were conducted at three different cooling water mass flow rates (5, 7.5, and 10 g/s) and different heating powers (200, 300, 400 W) to test heat pipe performance. It was observed that the CaMg(CO3)2 nanofluid reduced the average wall temperature of the heat pipe according to the base fluid. Furthermore, the efficiency and thermal resistance of the heat pipe were investigated separately for EG/water and CaMg(CO3)2 nanofluid. The maximum heat transfer enhancement was obtained as 9.55% under 400 W heating power and 10 g/s cooling water mass flow rate conditions and the maximum improvement in thermal resistance was observed as 21% at 200 W and 10 g/s cooling mass flow rate. Viscosity and specific heat of base fluid and CaMg(CO3)2 nanofluid were also determined and compared to each other.

Preheating Effects on Compression Ignition Engine Through Waste Heat Recovery Using THNF-Based Radiator Coolant: An Experimental Study

Abstract The present paper focuses on the thermohydraulic performance of a car radiator using Al2O3, CuO, and TiO2 nanoparticles disseminated in an equal fraction in the range of 0.06–0.12% called Ternary hybrid nanofluid (THNF), in water-based fluid, operated at coolant flowrate (CFR) range of 3–8 lpm and fan air velocity of 0.25–1.25 m/s). Moreover, a detailed accentuation has been given on the extensive nanofluid characterization mainly thermophysical properties and its stability, to justify nanofluid durability for the long run (scanning electron microscope, Zeta potential). Performance evaluation criteria (PEC) and friction factors were analyzed to evaluate the penalty in pressure drop for the heat transfer enhancement achieved. The experimental analysis revealed a maximum heat transfer enhancement in the coolant of 14.2% at CFR of 6lpm using 0.12% vol. fraction of THNF. The PEC value found within the limit of 1.0045–1.098 indicates a remarkable heat transfer enhancement on nanoparticle addition. Concurrently fuel elevated temperature improved thermal efficiency by 13.6% at 0.25 m/s of frontal air velocity during a maximum fuel-saving of 14.28% at 50% load on the engine. Hence, the preheating of fuel through the radiator waste heat improves the thermal efficiency, lowers the brake-specific fuel consumption, and saves fuel consumption successfully.

Combined effect of electric field and nanofluid on bubble behaviors and heat transfer in flow boiling of minichannels

In this work, electric field and nanofluid are coupled to enhance flow boiling heat transfer in minichannel. Pin electrodes are adopted to create non-uniform electric field. The effects of nanoparticle mass concentration, surfactant type and mass concentration under electric field on nanofluid flow boiling heat transfer are studied. Image analysis technique is used to quantify boiling bubble behaviors. The results demonstrate that without electric field, bubbles for nanofluid flow boiling are smaller and more discrete than R141b. Under electric field, bubble size reduces and the number of bubbles increases, which reveals synergy effect of electric field and nanofluid on bubble behaviors is effective. Besides, electric forces mitigate bubble coalescence and delay transition from bubbly to slug flow. Maximum heat transfer coefficient of nanofluid is 80% higher than R141b. Under electric field, boiling heat transfer of nanofluid modified by anionic surfactant (SDBS) is better than cationic (CTAB) and nonionic (Span80) surfactant. • Electric field and nanofluid were devised to enhance flow boiling of minichannel. • Bubble behaviors and flow pattern transition in nanofluid flow boiling under electric field was discussed. • Synergy effects of electric field and nanofluids on enhancing flow boiling heat transfer was discussed. • Maximum heat transfer enhancement ratio of 1.8 for nanofluid and electric field is obtained.

Computational Investigation on the Thermal and Flow Characteristics of a Turbulent Dual Jet Impinging on a Heated Moving Surface

Abstract The present investigation explores the dynamic effects of wall motion on the turbulent flow and thermal characteristics of a dual jet. The effects of variation in Reynolds number (Re) and offset ratio (OR) on different heat transfer and flow characteristics of turbulent dual jet have also been elucidated. The Reynolds number of flow and offset ratio are considered in the range Re=10000−25000 and OR=5−13, respectively. The wall to jet velocity ratio (Uw) is varied in the range of 0−2 at an interval of 0.5. The detailed study of heat transfer from moving impingement wall has been done by considering either the isoflux or the isothermal boundary condition on the heated wall. The motion of the wall strongly affects the thermal behavior and several flow characteristics of the dual jet. The nature of the velocity profile in the vector diagram changes from parabolic to linear in the far-field region due to the motion of the wall. The dual jet flow exhibits different patterns of self-similar profiles for different values of velocity ratio. The value of maximum longitudinal velocity (Umax) at a given axial position increases with the increase in impingement wall velocity. The exhaustive parametric study of dual jet flow over a moving wall reveals the fact that the process of heat transfer from heated moving wall to fluid is more intense for the higher value of Reynolds number and offset ratio, and for isoflux boundary condition. For the moving wall case, the maximum enhancement in heat transfer with reference to the stationary wall has been found to be 45.31%.

Graphene-coated sintered porous copper surfaces for boiling heat transfer enhancement

• The effect of sintered porous copper structure thickness on pool boiling heat transfer was investigated. • The additional contribution of graphene coating to further HTC enhancement was presented. • Increased wetted area and nucleation sites enhanced heat transfer on sintered porous surfaces. • Liquid supply mechanism and thermal conductivity with graphene coatings further enhanced heat transfer. • Effective heat dissipation underneath bubbles and prevention of hot spots are possible with Graphene coatings. Phase change heat transfer via pool boiling is an effective and low-cost method for applications such as electronics cooling and noticeably depends on bubble dynamics behavior. Porous copper surfaces provide a larger heat transfer area and more nucleation sites at the liquid-surface interface and improve heat transfer compared to bare copper surfaces. In addition, the capability of copper foams in surface replenishment and capillary wicking prevents surface dry-out at elevated heat fluxes. Graphene has recently attracted increasing attention in thermal management applications due to its exceptional thermal and mechanical properties. This study focuses on the effects of foam thickness (i.e., 0.5 mm, 1 mm, 1.5 mm, and 2 mm) and graphene-coating on pool boiling heat transfer on sintered porous surfaces by combining the porous structure with graphene coating. According to the obtained results, thinner samples (i.e., 0.5 mm and 1 mm) exhibited a better performance due to their lower vapor resistance and efficient liquid supply compared to thicker samples (i.e., 1.5 mm and 2 mm). The optimum surface configuration depends on the operating condition. Graphene-coating affects bubble dynamics and leads to further enhancement in boiling heat transfer by increasing the thermal conductivity and wicking rate. The maximum heat transfer enhancement was recorded for the thickness of 0.5 mm on graphene-coated sintered porous copper surfaces as 161% compared to the bare copper surface, while the maximum enhancement with graphene coating was 24% relative to the porous copper surface of the same thickness. Thus, the contribution of graphene coating on sintered porous copper surfaces to further boiling heat transfer enhancement was proven in this study.

The developing flow characteristics of water - ethylene glycol mixture based Fe3O4 nanofluids in eccentric annular ducts in low temperature applications

• The effect of nanofluids’ lower viscosity values on heat transfer was investigated. • Annular flow propagation of water-ethylene glycol based Fe 3 O 4 nanofluid was studied. • Maximum heat transfer enhancement was obtained for highest concentration. • Addition of the nanoparticles resulted in delay to reach steady-state conditions. • The performance evaluation criteria, pressure drop and exergy analysis were studied. Natural circulation loops with double pipe heat exchangers at heating and cooling ends have a potential to be used in the refrigeration systems as an alternative to suction line heat exchangers. The heat transfer capability of such natural circulation loops depends on the geometrical parameters as well as thermophysical properties of the working fluid. This study aims to investigate the effect of water-ethylene glycol mixture based Fe 3 O 4 nanofluids (0.01, 0.05 and 0.1 vol.%) on the annular flow propagation and heat transfer in the annuli of double pipe heat exchanger at low pressure side of the refrigeration cycle. In addition to increased non-dimensional velocity values due to the lower viscosity and higher non-dimensional temperature values with expanded temperature gradient, improved heat transfer by nanofluids shows that they can be used as secondary heat transfer fluids at low-pressure side in refrigeration systems. Although the maximum transferred (13.6% improvement compared to base fluid) heat observed for the highest concentration, the nanofluids with smallest concentration has the minimum pressure drop value (25% reduction compared to base fluid) and the highest performance evaluation criteria (PEC) value (PEC = 1.08) with tiny increase in exergy destruction (1.45% compared to base fluid).

Numerical Analysis for Augmentation of Thermal Performance of Single-Phase Flow in Microchannel Heat Sink of Different Sizes with or without Micro-Inserts

With the development of miniaturized and enormous heat density generating novel technologies, the microchannel heat sink is rapidly establishing itself in modern cooling fields. Enhancement of heat transfer performance of microchannels is done by incorporating improved design structure, changing working fluids and flow conditions, using different materials for fabrication, etc. Coupling of two parameters influencing heat transfer performance of microchannels is in a nascent age, and complex coupling of heat transfer influencing parameters of microchannel sinks has not been clearly understood yet. This study provides the thermal-fluid flow features–fluid flow characteristics and heat transfer characteristics- of single-phase flow in microchannel of different sizes with or without microinserts by the use of computational fluid dynamics. The numerical simulation is performed by employing distilled water with thermophysical properties that depends on temperature for the Reynolds number range of 56–2242. The effect of microinserts on characteristics of fluid flow and heat transfer is analyzed. The results of numerical analysis show that heat transfer performance in microchannel with microinserts is enhanced effectively, however resistance in fluid flow is increased simultaneously. The 0.5 mm microchannel with microinserts shows the best performance of heat transfer characteristics with enhancement of 1–9% in the Reynolds number range of 56–2242 with simultaneous maximum increase in pressure drop by 14.5%. It’s overall performance, evaluated by thermal performance factor, is found to be best among all cases of three different channel sizes with and without microinserts. The maximum enhancement of heat transfer is found to be in case of 0.5 mm channel size with microinserts by a factor of 1.09. The maximum pressure drop is increased is found to be by factor of 2.28 in case of 2 mm channel size with microinserts.

Experimental Study of Entropy Generation of Nanofluid Flow in Minichannel

This study investigates the effects of ZnO, , and particles in the water-based fluid on entropy generation minimization in a minichannel heat exchanger. Distilled water has been chosen as the base fluid for nanoparticle volume concentration of 0.5% under the laminar and turbulent regime, steady-state flow, and the constant wall temperature. Dynamic viscosity, thermal conductivity, heat transfer, pressure drop, and total entropy generation rates of nanofluids have been experimentally analyzed in the minichannel (stainless steel), which has an inner diameter of and length of 20 cm, at the constant wall temperature (283 K). The nanofluid mixtures have been studied at different flow rates (from 10 to 50 ml/min) at the constant inlet (323 K) and constant channel wall temperature (283 K). The thermal performance, the pressure drop, and total entropy generation rates of the fluids have been compared for three different types of nanofluids. Maximum heat transfer enhancement of 16.04% was obtained using water-based . Results have shown that three nanofluids have less dimensionless entropy generation than pure water. In addition, compared to pure water with these three nanofluids, the minimum value of the total entropy generation has been obtained for with 5.54%.

Enhanced heat transfer mechanism and flow topology of a channel contained with semi-circular hinged V-shaped baffles

The current work presents a numerical analysis of heat transfer mechanism and flow topology of channels with V-shaped baffles (VB) and semi-circular hinged V-shaped baffles (SH-VB). The vital purpose of applying SH-VB roughened channels is to induce combined vortex and impinging jets flows and reduce the pressure drop in the channel as compared to the use of VB. The effects of geometric parameters: pitch ratios (PR = 0.5, 1.0, 1.5 and 2.0), blockage ratios (BR = 0.1, 0.15 and 0.2), semi-circular hinge angles (β = 5°, 10° and 15°) were studied in the turbulent region (3000 ≤ Re ≤ 19,000). The study was performed at constant aspect ratio (AR) of 10.0 and V-baffle attack angle of α = 45°. The numerical results showed that the decrease of PR and increase of BR resulted in an increase of heat transfer enhancement and pressure drop. The maximum heat transfer enhancement of 5.57 times over the smooth rectangular channel was found at PR = 0.5, BR = 0.2, β = 10°, and Re = 3000. The numerical results also indicated that SH-VB gave higher heat transfer and thermal enhancement factors (TEF) and lower pressure losses than VB. SH-VB provided higher Nu/Nu0, lower f/f0 and higher TEF than VB by around 1.73–8.98%, 5.41–26.84% and 4.51–15.22%, respectively depending on Re, BR, PR and β. The optimum parameters of SH-VB which gave the maximum TEF at 2.6, were BR = 0.10, PR = 0.5 and β = 10° at Re = 3000.

Heat transfer intensification by EHD conduction pumping for electronic cooling applications

Liquid based cooling has become a new prospect in the thermal management of electronic devices. This work numerically investigates the potential of EHD conduction pumping to remove heat from a high density flux heat source, as commonly encountered in electronic cooling applications. A 2-D horizontal plate configuration with a heated patch releasing uniform heat flux has been considered. EHD conduction flow of dielectric fluid generated by the space charge developed due to the Onsager effect has been considered. The coupled set of governing equations are incorporated into the finite-volume framework of OpenFOAM®. The numerical implementation in OpenFOAM® is validated against experimental and numerical benchmark results. Present results exhibit good agreement with the benchmark solutions. Combined interaction of natural convective flow and EHD conduction pumping induced flow is studied. The effects of Rayleigh number and electric Reynolds number are investigated. The flow morphology of thermal convection is altered by the EHD conduction pumping flow. Flow strength is intensified and lead to heat transfer augmentation. Lower temperature distribution and higher mean Nusselt numbers are observed along the heated patch. The heat transfer intensification obtained by EHD conduction pumping is more prominent at lower Rayleigh numbers and higher electric Reynolds numbers. A maximum heat transfer enhancement of up to 31.2% is obtained for the configuration and parameters considered in this study.