Terms Of Heat Transfer Performance Research Articles

Investigation of the effects surface alteration via coatings on the condensation heat transfer and wettability

Background Heat exchangers are a critical component in organic Rankine cyclic (ORC) geothermal power plants as they represent more than 50% of the capital. In this study, the thermal performance of coatings devised for condensation heat exchangers have been studied. Methods For this purpose, a mock-up heat exchanger rig was designed and fabricated. The coatings used for the trials are of hydrophobic nature, in order to promote a change in the heat transfer mode from film-wise condensation to drop-wise condensation. The coatings for this study were developed by chemical vapour deposition and magnetron sputtering on aluminium substrates. The wettability and adhesion of the coatings was characterized before and after the tests. Statistical analysis was used to analyse the heat transfer related data. Results The results indicate that the silica based coating produced an improvement in the heat transfer performance indicators and the working fluid caused a deterioration of the wetting properties. However, even at the end of the tests, the coated samples performed better than the substrate material in terms of heat transfer performance. Conclusions The results of this research prove that shifting from film-wise condensation to drop-wise condensation is viable method to improve heat transfer efficacy. However, a one to one correlation could not be established with water contact angles measured in water or diiodomethane suggesting that wettability properties in ORC fluid could differ to established in these conventional fluids for contact angle measurements.

Experimental investigation of heat transfer performance in gas-atomized spray cooling

Spray cooling has substantial potential for wide application, given its unique characteristics, including high heat transfer coefficient, absence of contact thermal resistance, and the elimination of cooling hysteresis. In this study, a visualized experimental system featuring a gas-liquid two-phase cyclonic nozzle was constructed to study both the heat transfer and fluid morphology features pertaining to the wall. With the increase of wall superheat, a progressive transition across four distinct stages of heat transfer – liquid film, stream flow, droplet flow, and mist flow can be found. Of these, the droplet flow stage outperforms others in terms of heat transfer performance and is thus advocated as the preferred mode of application. In response to increasing spray pressure, the droplets generated on the wall during the droplet flow stage undergo a reduction in size, yet become more densely distributed. A notable increase in critical heat flux by 59.5 % is observed when spray pressure is elevated from 0.2 to 0.4 MPa. While raising the spray flow rate leaves the heat transfer performance during the liquid film stage largely unchanged, it effects a significant augmentation in critical heat flux. Our experimental results ultimately obtain the optimal operating parameters that facilitate the wall surface's retention in the droplet flow stage. These experimental results are poised to contribute meaningfully to the engineering practices associated with spray cooling applications.

Optimizing fin design for enhanced melting performance in latent heat thermal energy storage systems

The addition of fins to phase change material (PCM) in latent heat thermal energy storage (LHTES) systems is a widely employed technique to enhance thermal performance and significantly improve energy storage efficiency. This research focuses on a two-dimensional numerical model investigating heat transfer within a shell-and-tube structure of LHTES. Various combinations of fin number and fin height were explored to assess their influence on melting performance while maintaining the consistent fin volume. Subsequently, a topology optimization technique was developed to determine the most effective fin configuration. The optimized fins exhibited dendritic distributions and outperformed other fin designs in terms of heat transfer performance. The topology-optimized design resulted in a remarkable 74 % increase in melting performance compared to the structure without fins. Furthermore, we introduced a simplified model that takes into account manufacturing feasibility. We verified that a fin volume fraction of 6 % resulted in a significantly reduced melting time of 36 min, in stark contrast to the 249 min observed without fins.

Thermal design and heat transfer optimisation of a liquid organic hydrogen carrier batch reactor for hydrogen storage

Liquid organic hydrogen carriers (LOHCs) are considered a promising hydrogen storage technology. Heat must be exchanged with an external medium, such as a heat transfer fluid, for the required chemical reactions to occur. Batch reactors are simple but useful solutions for small-scale storage applications, which can be modelled with a lumped-parameter approach, adequately reproducing their dynamic performance. For such reactors, power is consumed to circulate the external heat transfer fluid and stir the organic liquid inside the reactor, and heat transfer performance and power consumption are two key parameters in reactor optimisation. Therefore, with reference to the hydrogen release phase, this paper describes a procedure to optimise the reactor thermal design, based on a lumped-parameter model, in terms of heat transfer performance and minimum power consumption. Two batch reactors are analysed: a conventional jacketed reactor with agitation nozzles and a half-pipe coil reactor. Heat transfer performance is evaluated by introducing a newly defined dimensionless parameter, the Heat Transfer Ratio (HTR), whose value directly correlates to the heat rate required by the carrier's dehydrogenation reaction. The resulting model is a valid tool for adequately reproducing the hydrogen storage behaviour within dynamic models of complex and detailed energy systems.

Experimental study on the solidification and melting performances of magnetic NEPCMs composited with optimized filling metal foam in a uniform magnetic field

The present study experimentally investigates the magnetic nano-enhanced phase change material (NEPCM) filled with different strategies of metal foam in a uniform magnetic field for the solidification and melting processes. The thermochromic liquid crystals (TLC) technology is used to evaluate, compare and analyze the effects of magnetic field, partial filling (H = 0 h, 1/4h, 2/4h, 3/4h, 4/4h) and gradient porosity (positive and negative). The evolution of phase change interface, the temperature distributions and differences, solidification/melting rate, energy released/stored, and Nusselt number are comprehensively analyzed. The results show that the magnetic field inhibits convection but accelerates local heat transfer by the Kelvin force. As the porous filling height increases, the solidification rate and energy released increase firstly and then decrease. Comparing to pure PCM, the H = 3/4h case has the excellent solidification performance for 2.08 times increase and energy released for 40.22% improvement. The melting rate is advanced with the growth of filling height, but the energy storage capacity gradually decreases. In terms of heat transfer performance, the positive gradient porosity case owns best temperature uniformity and fastest phase change rate. Compared with pure PCM, its solidification rate and energy released are increased by 4.30 times and 36.7%, and melting time is reduced by 64.29%, but the energy stored is lost by 16.44%. As for the energy storage, the negative gradient porosity case can release and store more energy at the same time as maintaining high heat transfer performance.

Thermal Performance Investigation of Slotted Fin Minichannel Heat Sink for Microprocessor Cooling

Due to high heat flux generation inside microprocessors, water-cooled heat sinks have gained special attention. For the durability of the microprocessor, this generated flux should be effectively removed. The effective thermal management of high-processing devices is now becoming popular due to high heat flux generation. Heat removal plays a significant role in the longer operation and better performance of heat sinks. In this work, to tackle the heat generation issues, a slotted fin minichannel heat sink (SFMCHS) was investigated by modifying a conventional straight integral fin minichannel heat sink (SIFMCHS). SFMCHSs with fin spacings of 0.5 mm, 1 mm, and 1.5 mm were numerically studied. The numerical results were then compared with SIFMCHSs present in the literature. The base temperatures recorded for two slots per fin minichannel heat sink (SPFMCHS), with 0.5 mm, 1 mm, and 1.5 mm fin spacings, were 42.81 °C, 46.36 °C, and 48.86 °C, respectively, at 1 LPM. The reductions in base temperature achieved with two SPFMCHSs were 9.20%, 8.74%, and 7.39% for 0.5 mm, 1 mm, and 1.5 mm fin spacings, respectively, as compared to SIFMCHSs reported in the literature. The reductions in base temperature noted for three SPFMCHSs were 8.53%, 9.05%, and 5.95% for 0.5 mm, 1 mm, and 1.5 mm fin spacings, respectively, at 1 LPM, as compared to SIFMCHSs reported in the literature. In terms of heat transfer performance, the base temperature and thermal resistance of the 0.5 mm-spaced SPFMCHS is better compared to 1 mm and 1.5 mm fin spacings. The uniform temperature distribution at the base of the heat sink was observed in all cases solved in current work.

Heat transfer investigation of a 90° zigzag channel diffusion-bonded heat exchanger

Abstract Supercritical CO2 (S-CO2) Brayton cycle components are subject to high pressure and temperature conditions, which are intrinsic to the operation cycle. Among the equipment used for these applications, diffusion-bonded heat exchangers are receiving more attention to be used as pre-coolers on the cycle, due to their robustness and capability of operating at the demanded conditions. Currently, limited research focused on the influence of the pre-cooler’s cold-side fluid, water, on the thermal performance of the diffusion-bonded heat exchangers. In the present study, a novel zigzag channel for the diffusion-bonded heat exchangers with square cross-section was manufactured and experimentally investigated in a water-water configuration. During the experiments, the Reynolds number of the hot and the cold sides varied from 1529 to 8313 and from 1299 to 6618, respectively, covering laminar to turbulent flow regimes. A new heat transfer correlation is proposed based on dimensionless Reynolds and Prandtl numbers, covering a large Reynolds number range not yet experimentally investigated for the water. In the laminar regime, the current geometry increases the Nusselt number up to 4.1 times when compared to a straight channel. For the complete Reynolds number range evaluated, from 1299 to 8313, the average enhancement of a diffusion bonded heat exchanger with the proposed geometry compared to a straight channel one is of 2.2 times. Therefore, the current zigzag design proposed in this study provided a significant advantage in terms of heat transfer performance.

Analysis of Heat Transfer Performance in a Brayton Cycle Recuperator

Thermodynamic cycles are currently the most wanted means of converting nuclear power into available work due to the higher conversion efficiencies provided. Rankine cycles have been greatly applied for terrestrial reactors and nuclear submarines, while a lot of space projects have been using Brayton cycles for power conversion mainly due to mitigation in power-to-radiator area ratio. Regenerative Brayton cycles can present a considerable power conversion efficiency improvement when compared to the regular ones because of a reduction on the power demand from the hot heat exchanger of a cycle to achieve the same net output power. In this work, a cross-flow heat exchanger with He-Xe (40 g/mol) working fluid and Inconel 617 structural material used as the recuperator for the closed Brayton cycle of a nuclear reactor applicable for space systems is assessed in terms of heat transfer performance. The recuperator tubes are arranged in a staggered distribution around the exchanger axis. The matrix of tubes has a fixed count of 4 rows along the exchanger axis, while the number of tubes around the axis is variable, where the samples of 5, 7, 9, 12 and 16 are tested. The characteristic curves of heat transfer rate, effectiveness, convection coefficient and Colburn factor are built for each of the studied geometries in function of the Reynolds number. The obtained values for each of these parameters range between 1892.49 and 8493.21W (heat transfer rate), 0.165 and 0.325 (effectiveness), 60.3822 and 176.9682 W/m2K (cold side convection coefficient), 30.3276 and 104.3263 W/m2K (hot side convection coefficient), 0.0071 and 0.0109 (cold side Colburn factor), 0.0523 and 0.1370 (hot side Colburn factor).

Assessing advantages and disadvantages of macro- and micro-channel flow boiling for high-heat-flux thermal management using computational and theoretical/empirical methods

This study examines the advantages and disadvantages of micro- and macro-channel flow boiling for high-heat-flux cooling applications using both computational and theoretical/empirical methods. The computational simulations are conducted in ANSYS FLUENT using the Volume of Fluid (VOF) method along with the Lee phase change model, and accounting for both shear lift force and conjugate heat transfer along the channel walls. Computational results for both channel sizes are compared with theoretical/empirical results obtained using the Homogeneous Equilibrium Model (HEM) and Separated Flow Model (SFM), and both HEM and the Homogenous Frozen Model (HFM) are used to assess the potential for two-phase choking. The computational results show bubbles in micro-channels are highly confined and tend to grow longer in the flow direction. The two methods show good agreement in predicting wall temperatures. Overall, micro-channel heat sinks are shown to fare much better than macro-channels in terms of heat transfer performance, evidenced by both significantly higher heat transfer coefficients and lower wall temperatures, but this comes at the cost of significantly higher pressure drop and pumping power requirements. It is also shown micro-channels are prone to choking due to high two-phase Mach number.

Preparation and Characterization of Rutile Titania Nanofluids Stabilized in Different Surfactants Base Fluids

Background: Improvement of conventional heat transfer fluids for achieving higher energy efficiencies in thermal equipment is a key parameter to conserve energy in industries. The heat transfer fluids such as water, oil and ethylene glycol greatly suffer low heat transfer performance in industrial processes. There is a need to develop new types of heat transfer fluids that are more effective in terms of heat transfer performance. Nanofluids enhance thermal conductivity and improve the thermal performance of heat transfer systems. Methods: New titania nanofluid samples consisting of 0.0625 to 1% TiO2 nanoparticles were prepared and characterized. The method of preparation was based on prior precipitation of TiO2 from an ammoniacal solution of pH 9 and calcination at 900°C. Solubilization, homogenization and stabilization of the of the nanoparticles were performed by sonication in the presence of sodium dodecyl sulfate (SDS) anionic surfactant and cetyltrimethylammonium bromide (CTAB) cationic surfactant. Results: This treatment was also utilized to increase the stability and improve the thermal properties of the fluid. Conclusion: Several characterization techniques including measurements of hydrodynamic size distribution, zeta potential, transmission electron microscopy (TEM), viscosity, density, specific heat, thermal conductivity, and sedimentation photo capturing were used to measure and confirm the stability and sedimentation rate of the prepared nanofluids.

Improved Thermophysical Properties and Energy Efficiency of Aqueous Ionic Liquid/MXene Nanofluid in a Hybrid PV/T Solar System.

In recent years, solar energy technologies have developed an emerging edge. The incessant research to develop a power source alternative to fossil fuel because of its scarcity and detrimental effects on the environment is the main driving force. In addition, nanofluids have gained immense interest as superior heat transfer fluid in solar technologies for the last decades. In this research, a binary solution of ionic liquid (IL) + water based ionanofluids is formulated successfully with two dimensional MXene (Ti3C2) nano additives at three distinct concentrations of 0.05, 0.10, and 0.20 wt % and the optimum concentration is used to check the performance of a hybrid solar PV/T system. The layered structure of MXene and high absorbance of prepared nanofluids have been perceived by SEM and UV–vis respectively. Rheometer and DSC are used to assess the viscosity and heat capacity respectively while transient hot wire technique is engaged for thermal conductivity measurement. A maximum improvement of 47% in thermal conductivity is observed for 0.20 wt % loading of MXene. Furthermore, the viscosity is found to rise insignificantly with addition of Ti3C2 by different concentrations. Conversely, viscosity decreases substantially as the temperature increases from 20 °C to 60 °C. However, based on their thermophysical properties, 0.20 wt % is found to be the optimum concentration. A comparative analysis in terms of heat transfer performance with three different nanofluids in PV/T system shows that, IL+ water/MXene ionanofluid exhibits highest thermal, electrical, and overall heat transfer efficiency compared to water/alumina, palm oil/MXene, and water alone. Maximum electrical efficiency and thermal efficiency are recorded as 13.95% and 81.15% respectively using IL + water/MXene, besides that, heat transfer coefficients are also noticed to increase by 12.6% and 2% when compared to water/alumina and palm oil/MXene respectively. In conclusion, it can be demonstrated that MXene dispersed ionanofluid might be great a prospect in the field of heat transfer applications since they can augment the heat transfer rate considerably which improves system efficiency.

Cross-helix corrugation: The optimal geometry for effective food thermal processing

In the present paper, an innovative and effective heat transfer enhancement technique for food processing, cross-helix profile wall corrugation, is proposed and tested. In the food industry, the two most promising corrugation profiles are the transversal and single-helix ones because they both satisfy hygienic design principles. Among the available wall corrugation techniques, transversal corrugation allows for the highest heat transfer performance, and the spirally corrugated tubes guarantee the easiest manufacturing. For this reason, single-helix corrugated tubes are the most commonly employed in heat exchangers for food processing. The cross-helix profile presented in this work represents an intermediate solution between transversal and single-helix corrugation aimed at combining their positive aspects.One of the main goals of the current research is to identify an optimal geometry that maximises the heat transfer performance by limiting the pressure drop augmentation for this specific engineering application (i.e., food thermal processing). For this purpose, the effect of the geometrical parameters of the corrugation profile is investigated by varying two of the most influent quantities in terms of heat transfer performance and pressure drop: corrugation depth and corrugation pitch. Six pipes characterised by different cross-helix corrugations are tested. Their performance is evaluated by studying the forced convective heat transfer in the Reynolds and Prandtl numbers ranges (50–14,000 and 5–150, respectively), using ethylene glycol, water and a mixture of the two as the working fluids.The outcomes show that corrugation depth plays a crucial role in enhancing the heat transfer performance of the tested pipes. An optimal geometry is established, and correlations to describe its thermal and fluid flow behaviours are proposed. This optimal geometry shows superior performance to that of the most widely adopted types of corrugation. For the low/intermediate Reynolds number range (i.e., 200–2000), the efficiency of the proposed cross-helix profile is up to three times greater than that of the single helix and is also greater than that of transversally corrugated tubes. These outcomes make cross-helix a recommended option to be used in the design of optimised heat exchangers.Because the studied geometry is expressly developed for food industry application, a set of measurements is also performed in which apricot juice is adopted as the working fluid. The findings confirm the efficiency of the proposed correlations with non-Newtonian fluid foods and enable them to be extended to a wide range of real food industrial applications.

A Review of Phase Change Materials for the Thermal Management and Isothermalisation of Lithium-Ion Cells

Abstract Li-Ion batteries will play an important role in reaching emission targets by sustaining the further integration of renewable energy technologies and Electric Vehicles (EVs) in society. Their performance however is quite sensitive to temperature, leading to capacity fade, acceleration of ageing effect and possible thermal runaway. A Thermal Management System (TMS) should maintain a battery at an operating temperature within an optimal range and maximise temperature uniformity, i.e. approaching an isothermal condition. Many studies have experimentally investigated the electrical performance of Li-Ion batteries under controlled environmental temperatures. Notably however, these controlled conditions do not impose a uniform temperature or a controlled rate of cooling, as a TMS would. From a review of the relevant literature a ratio of the heat generation to the power production is proposed, i.e. quantifying an equivalent electro-chemical efficiency to advance research in this technological area and as additional TMS design metric. Overall, there is enough evidence that 25–30 °C is the best temperature range to minimise the ageing effect while 25–40 °C is typically reported as the general Li-Ion cells operating range. No specific temperature is identified to optimise the cycle electro-chemical efficiency and minimise the ageing effect. Therefore, a TMS should keep Li-Ion batteries within a specific temperature range according to the need for either higher electro-chemical efficiencies (i.e. higher powers and lower heat generation rates) or higher operating life. There are four main thermal management approaches of Li-Ion batteries: air-cooling, liquid-cooling, boiling and Phase Change Materials (PCM). Air cooling is preferred for safety reasons but is less efficient as the rate of heat transfer achievable is relatively low. Forced air cooling can effectively keep the temperature at a preferred level but fails to guarantee a uniform temperature. Liquid cooling is better in terms of heat transfer performance, but it is less safe and can still result in significant thermal gradients within the pack. Boiling effectively keeps Li-Ion cells temperature constant and uniform but can be quite complex to operate and control. Phase Change Materials (PCMs) as a passive cooling approach are proposed as an effective and low-cost isothermalisation technique. However, when Li-Ion batteries are operated under extreme conditions (high ambient temperature, high discharge rates), PCM are not able to recover all latent energy potential during solidification and this leads to possible thermal runaway. Overall, it is clear that no TMS alone is holistically better than others and the choice between air cooling, liquid cooling, boiling and latent heat PCM systems is entirely linked to the specific combination of temperatures, heat rates, cells capacity and geometry. Active PCM systems however, mainly a combination of liquid cooling and passive PCM, show promising results towards an ideal isothermal condition. Also, they introduce the potential to store the thermal energy and use it as needed, converting a Li-Ion cell from an Electrical Energy Storage System (EESS) to a Combined Heat and Power (CHP) system.

Numerical modelling and performance maps of a printed circuit heat exchanger for use as recuperator in supercritical CO2 power cycles

In heat to power systems with CO2 as working fluid in the supercritical state (sCO2), heat exchangers account for nearly 80% of the capital expenditure. Therefore, improved design, materials and manufacturing methodologies are required to enable the economic feasibility of the sCO2 technology. In this study, a comparison of different modelling methodologies for Printed Circuit Heat Exchangers (PCHE) is proposed to identify strengths and weaknesses of both the approaches. The elementary heat transfer unit of a PCHE recuperator for sCO2 applications is firstly modelled using 1D and 3D CFD methodologies respectively; implemented in GT-SUITE and ANSYS FLUENT software. After the comparison in terms of heat transfer performance and pressure drops, the 1D approach is used to model a 630kW PCHE recuperator. The PCHE model calibration on the design point, followed by its validation against off-design operating points provided by the manufacturer, eventually enabled to broaden the simulation spectrum and retrieve performance maps of the device. The CFD models comparison shows a good agreement between temperature profiles. However, the local heat transfer coefficient, modelled in the 1D approach through the Dittus-Boelter correlation, experiences a +10% offset on the hot side and a -20% on the cold one with respect to the 3D CFD calculations. Besides, the performance maps of the full scale PCHE recuperator show that the maximum temperature of the hot stream impose a greater influence than the maximum pressure of the cold one in terms of overall heat transfer coefficient. Nonetheless, both these operating parameters contribute to affect the heat exchanger effectiveness.

Magneto-hydrodynamic natural convection of CuO-water nanofluid in complex shaped enclosure considering various nanoparticle shapes

PurposeThe purpose of this study is to peruse natural convection in a CuO-water nanofluid-filled complex-shaped enclosure under the influence of a uniform magnetic field by using control volume finite element method.Design/methodology/approachGoverning equations formulated in dimensionless stream function, vorticity and temperature variables using the single-phase nanofluid model with the Koo–Kleinstreuer–Li correlation for the effective dynamic viscosity and the effective thermal conductivity have been solved numerically by control volume finite element method.FindingsEffects of various pertinent parameters such as Rayleigh number, Hartmann number, volume fraction of nanofluid and shape factor of nanoparticle on the convective heat transfer characteristics are analysed. It was observed that local and average heat transfer rates increase for higher value of Rayleigh number and lower value of Hartmann number. Among various nanoparticle shapes, platelets were found to be best in terms of heat transfer performance. The amount of average Nusselt number reductions was found to be different when nanofluids with different solid particle volume fractions were considered due to thermal and electrical conductivity enhancement of fluid with nanoparticle addition.Originality/valueA comprehensive study of the natural convection in a CuO-water nanofluid-filled complex-shaped enclosure under the influence of a uniform magnetic field by using control volume finite element method is addressed.

Comparison of thermal performances of water-filled, SiC nanofluid-filled and SiC nanoparticles-coated heat pipes

In the present study, thermal performances of water-filled and 0.01 and 0.1vol% SiC/water nanofluids-filled heat pipes with a screen mesh wick and water-filled heat pipe with a SiC nanoparticles-coated screen mesh wick were compared in order to investigate the effects of nanoparticles depositions on inner surface structures of heat pipes. The wall temperatures of the SiC nanoparticles-coated heat pipe were found to be higher than those of an uncoated heat pipe while the thermal performance for the heat pipe using a SiC/water nanofluid was not enhanced compared to the heat pipe using water as a working fluid. Also, the heat pipes containing SiC/water nanofluids and SiC-coated wick showed slight increases in evaporator thermal resistances, but minute changes in condenser thermal resistances compared to the water-filled heat pipe. Moreover, the overall thermal resistances of the heat pipes with the SiC/water nanofluids and SiC-coated wick were similar with those of the heat pipe charged with water. In terms of heat transfer performance, the boiling heat transfer of the evaporator zone is explained by changes of the number of activated nucleation sites due to nanoparticle deposition on the wick structure, whereas heat transfer characteristics of the adiabatic and condenser zones are attributed to the liquid film layer which is formed on the wick structure by capillary wicking and is considerable as additional thermal resistance. The SEM images for wicks of heat pipes with nanoparticles-coated layers support the thermal performance characteristics of three types of heat pipes investigated in the study.

Characterization of a mini-channel heat exchanger for a heat pump system

In this paper a mini-channel aluminum heat exchanger used in a reversible heat pump is presented. Mini-channel finned heat exchangers are getting more and more interest for refrigeration systems, especially when compactness and low refrigerant charge are desired. Purpose of this paper was to characterize the mini-channel heat exchanger used as evaporator in terms of heat transfer performance and to study the refrigerant distribution in the manifold. The heat exchanger characterization was performed experimentally by means of a test rig built up for this purpose. It is composed of an air-to-air heat pump, air channels for the external and internal air circulation arranged in a closed loop, measurement sensors and an acquisition system. The overall heat transfer capacity was assessed. Moreover, in order to characterize the flow field of the refrigerant in the manifold of the heat exchanger, a numerical investigation of the fluid flow by means of CFD was performed. It was meant to evaluate the goodness of the present design and to identify possible solutions for the future improvement of the manifold design.

Experimental research of heat transfer performance on natural draft counter flow wet cooling tower under cross-wind conditions

The experiment in terms of heat transfer performance of natural draft counter-flow wet cooling is done for cases with cross-wind conditions. The variation of circulating-water temperature difference ( Δ T ) and cooling coefficient of efficiency ( η ) with cross-wind velocity, circulating water inlet temperature and flow rate, are shown under cross-wind conditions, compared with cases without wind. According to experimental results, it is found that Δ T and η are influenced by the cross-wind, and Δ T and η can decrease mostly by 6% and 5%, respectively. When the critical Fr l number is less than 0.174, Δ T and η decrease with increasing cross-wind velocity, however, when it is greater than 0.174, Δ T and η increase with increasing cross-wind velocity. In addition, based on the data regression analysis, the correlation between Δ T, η and parameters, such as circulating-water inlet temperature and flow rate, is derived for cases with windless conditions. Furthermore, its correspondence is given out for cases with cross-wind conditions.

4548258 Method and means for inhibiting corrosion in a heat pipe: John A Nelson, Joan D Banks assigned to Whirlpool Corporation

In the present study, thermal performances of water-filled and 0.01 and 0.1 vol% SiC/water nanofluids-filled heat pipes with a screen mesh wick and water-filled heat pipe with a SiC nanoparticles-coated screen mesh wick were compared in order to investigate the effects of nanoparticles depositions on inner surface structures of heat pipes. The wall temperatures of the SiC nanoparticles-coated heat pipe were found to be higher than those of an uncoated heat pipe while the thermal performance for the heat pipe using a SiC/water nanofluid was not enhanced compared to the heat pipe using water as a working fluid. Also, the heat pipes containing SiC/water nanofluids and SiC-coated wick showed slight increases in evaporator thermal resistances, but minute changes in condenser thermal resistances compared to the water-filled heat pipe. Moreover, the overall thermal resistances of the heat pipes with the SiC/water nanofluids and SiC-coated wick were similar with those of the heat pipe charged with water. In terms of heat transfer performance, the boiling heat transfer of the evaporator zone is explained by changes of the number of activated nucleation sites due to nanoparticle deposition on the wick structure, whereas heat transfer characteristics of the adiabatic and condenser zones are attributed to the liquid film layer which is formed on the wick structure by capillary wicking and is considerable as additional thermal resistance. The SEM images for wicks of heat pipes with nanoparticles-coated layers support the thermal performance characteristics of three types of heat pipes investigated in the study.