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A hollow fiber membrane-based semi-direct evaporative cooler (MSDEC) is proposed in this study to conduct a parametrical evaluation. The proposed direct evaporative cooling module is potentially considered as an effective strategy to eliminate the water droplet carryover issue without deteriorating the indoor air quality. A numerical model has been developed to obtain an in-depth understanding of the air treatment process. The model was compared with the experimental data to demonstrate its accuracy for predicting the air conditions in the membrane-based module. The heat and mass transfer performance of the module has been studied by employing the validated model. Simulation results indicated the capability of the proposed membrane-based module to cool and humidify the air. The performance of the membrane-based module has been studied by considering the impact of several key parameters including the inlet air velocity, the inlet air dry-bulb temperature, the inlet air relative humidity, the feed water velocity and the geometric dimensions. The wet-bulb effectiveness of the membrane-based module can be improved to 0.73 for an inlet air velocity of 0.5 m/s. The results were able to provide theoretical suggestions for the further optimized design and application of the hollow fiber membrane-based evaporative cooling module.

Introduction: Intraocular surgery has long been taboo in the management of eyes with retinoblastoma due to concern of extraocular spread that carries poor survivorship. Pars plana vitrectomy (PPV) and tumor endoresection has recently emerged in China as an effective surgical treatment to salvage eyes with tumor resistant to chemotherapy, the current standard of care. To investigate the safety and efficacy of this novel treatment, we studied survivorship, visual acuity, and eye salvage rate of retinoblastoma children/eyes treated with PPV. Methods: Outcomes were reviewed for 227 children (247 eyes) treated with PPV and endoresection for residual active tumor or recurrent tumor following chemotherapy at 29 Chinese centers between 2013 and 2014. Results: At 5 years following PPV, 14 patients died, 8 related to the eye that had PPV. The 5-year overall survival rate following PPV was 93.7% (95% CI: 90.4% to 97.0%). The 5-year PPV eye-related survival rate (PPVSR) was 96.3% (95% CI: 93.8% to 98.9%). Children with PPV for residual active tumor had better survival than those with PPV for recurrent tumor (5-year PPVSR 98.1% vs. 91.4%, P = .021). Children with 1 to 3 cycles of neoadjuvant chemotherapy (intra-arterial or systemic chemotherapy) prior to PPV had similar survival to children with ≥4 cycles of chemotherapy (98.2% vs. 93.7%, P = .093). Children with adjuvant systemic chemotherapy following PPV had 100% (95% CI: 93.5% to 100%) 5-year PPVSR, not significantly higher than those without adjuvant chemotherapy (100% vs. 94.8%, P = .102). Of 94 eyes with partial or no retinectomy and documented visual acuity, the post-PPV visual acuity was 20/20-20/60 (23, 24%); 20/7-20/160 (6, 6%); 20/17-20/400 (9, 10%); counting fingers, hand motion, or light perception vision (42, 45%); and no light perception (NLP) (14, 15%). Complete retinectomy was performed on 93 of 247 (37.7%) eyes that, as expected, had NLP. The 5-year eye salvage rate following PPV was 80.7% (95% CI: 75.5% to 85.9%). PPV for residual active tumor and recurrent tumor had similar eye salvage rate (82.0% vs. 76.8%, P = .372). Eyes with International Intraocular Retinoblastoma Classification (IIRC) A, B, or C staging had better salvage rate than eyes with IIRC D or E staging (100.0% vs. 78.1%, P = .005). Eyes that received 1 to 3 cycles and ≥4 cycles of neoadjuvant chemotherapy had similar salvage rate (81.4% vs. 79.8%, P = .796). Conclusion: We observed that PPV salvaged 80.7% of eyes with residual active tumor after primary chemotherapy or recurrent tumor after remission. The 5-year eye-specific survival was 96.3%, comparable to survivorship using other treatment modalities. More cycles of neoadjuvant chemotherapy did not improve survivorship or eye salvage rate. In this cohort, all children with adjuvant chemotherapy following PPV survived at 5 years. PPV may be a game changer to improve health outcomes of patients with retinoblastoma, with the potential to become the new standard of care. Citation Format: Junyang Zhao, Zhao Xun Feng, Qiyan Li, Songyi Wu, Liwen Jin, Brenda L. Gallie. Survivorship, vision, and eye salvage following pars plana vitrectomy for residual active or recurrent retinoblastoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B63.

Most existing studies of droplet freezing on cold solid surfaces focus on the use of different surface wettability and roughness which may be considered as passive methods. Here we report an active method using an applied magnetic field to control the deformation and freezing process of a sessile ferrofluid droplet on a cold surface. By changing the direction and magnitude of the magnetic field, we can elongate or squeeze the shape of ferrofluid droplets. Consequently, the droplet freezing time can be extended or shortened under the magnetic lift or squeezing conditions, respectively. Additionally, we use the modified Young-Laplace equation with consideration of an additional magnetic force effect to analyze the shape variation of a ferrofluid droplet with magnetic field, and also present a scaling analysis for the freezing time.

Direct evaporative cooling systems usually involve the process of spraying water, which may form the drift of water droplets. In addition, the use of circulating water can also lead to the growth of bacteria and molding on the surface of the packing material, affecting the indoor air quality. To address these issues, this paper intends to propose an evaporative cooling method incorporated with hollow fiber membranes. The selective permeation membrane technology allows the membrane module to isolate air from water, which selectively allows only water vapor to pass through, preventing the droplets from entraining bacteria into the air. A mathematical model has been developed to theoretically investigate the heat and moisture transfer between water and air in a hollow fiber membrane-based evaporative cooling module. The governing equations for the pre-cooling IEHX were established and then solved by employing the COMSOL Multiphysics platform. This study validated the model by comparing its outlet air dry bulb temperature and relative humidity against experimental data acquired from literature sources. The numerical model showed good agreement with the experimental findings with maximum discrepancy of 7.0%. The validated model was employed to investigate the influences of the inlet air velocity, inlet air dry-bulb temperature, inlet air relative humidity and geometric parameters on the cooling effect of the evaporative cooling module. Simulation results indicated that the outlet air temperature is greatly affected by the relative humidity of the inlet air under constant inlet air temperature conditions. A higher inlet air relative humidity will result in a higher outlet air dry bulb temperature. In addition, the cooling effectiveness was reduced for a higher inlet air velocity. The design of the hollow fiber membrane-based evaporative cooling module was optimized based on the simulation study.

The estimation of the underground rock-soil thermal conductivity from different depths is of great importance for the studies on the performance prediction and evaluation of geothermal utilization systems. Based on the authors’ previous work on the prediction of rock-soils with moderate porosities (0.2146 0.4764). The arrangement of different phases in the cubic cell element is introduced, and the thermal resistance for each part is theoretically derived to achieve the expression of the effective thermal conductivity. After verified by 74 experimentally measured and predicted results of rock-soil sample thermal conductivities in the existing work, the newly proposed method is validated to be successful to predict the rock-soil thermal conductivity with an average RMSE of 0.1289, which implies that the present model configured with two hemispheres and cylindrical water framework and based on the series-parallel resistance method provides an accurate prediction on the thermal conductivity of the rock-soils with different constituents and water contents at low or high porosity.

The thermal characteristics of lithium-ion battery affect significantly charging/discharging performance, cycle life and safety of electric vehicles (EVs) battery packs. In this study, a stagger-arranged battery pack consisting of three battery modules was developed to explore its transient thermal characteristics in charging/discharging process under the two cooling strategies, i.e., natural cooling and forced air cooling. The investigation of heat generation behavior of the battery with Li(NixCoyAlz)O2 cathode showed that the heat generation rate of the battery remains almost unchanged along the main discharging process, while a rapid increase in heat production is detected at the end of discharging. It was found that the maximum temperature and temperature difference in the battery pack subject to a moderate charging/discharging rate, e.g., 0.5 C, can be maintained within the desirable ranges by natural cooling. The forced air cooling strategy employing longitudinal airflow remarkably improves the battery’s transient thermal characteristics with achieving the depth of discharge (DOD) up to 84.2%, which is capable to prolong the battery pack’s cycle life to a large extent. Lastly, the appropriate air supply velocity of 0.8 m⋅s−1 is recommended for the proposed battery pack subject to a higher discharging rate, e.g., 1 C, from the viewpoint of cooling effectiveness.

BackgroundThe prevalence of ocular abnormalities of newborn in China has seldom been reported. To report the implementation of digital imaging in ocular screening of all newborns in multiple centres in China and to describe the abnormal findings of fundus examination, we did the cross-sectional study.MethodsFundus examinations were performed on newborns within the 42 days after birth using a RetCam wide-field digital imaging system. Digital images of the posterior pole, superior, nasal and temporal retinal fields of each participant were taken. All newborns were from eights centres across China from January 2009 to July 2017.ResultsA total of 199 851 newborns were included in the study. We detected 18 198 (9.11%) abnormal cases. The most frequent abnormality was severe retinal haemorrhage (RH) found in 12 810 cases (6.41%). The other anomalies included familial exudative vitreoretinopathy, retinopathy of prematurity, abnormal fundus pigmentation, subconjunctival haemorrhage, choroidal coloboma, idiopathic retinal venous tortuosity, exudative changes and other anomalies with uncertain identities.ConclusionThis large-scale study of newborn fundus examination showed a relatively high prevalence of ocular abnormalities. Hundreds of neonates with rare disorders that severely impair ocular health were also detected at an early age. The long-term impact of other anomalies including RHs on the ocular system should be investigated by a perspective study. Our study suggested that fundus examination of newborns can play a beneficial role in ocular health.

The natural convective heat transfer performance and thermo-fluidic characteristics of honeycombs with/without chimney extensions are numerically investigated. The present numerical simulations are validated by the purposely-designed experimental measurements on honeycombs with/without chimney. Good agreement between numerical simulation and experimental measurement is obtained. The influences of inclination angle and geometric parameters such as cell shape, streamwise and spanwise length are also numerically quantified. With the increment in inclination angle, the overall heat transfer rate decreases for the honeycombs with/without chimney. For honeycombs with the same void volume fraction but different cell shapes, there is little difference on the overall heat transfer rate. To enhance the natural convective heat transfer of honeycombs, these techniques including increasing the length of honeycomb in the streamwise/spanwise direction, increasing the thermal conductivity of hon-eycomb structure or adding a chimney extension may be helpful.

In this study, we explain the causes and effects of the geometrical impossible result encountered in the widely adopted tetrakaidecahedron model (Boomsma and Poulikakos, 2001; Dai et al., 2010) for the effective thermal conductivities (ETCs) of metal foam. The geometrical impossible result is successfully eliminated by accounting for the size variation of the node with porosity. The improved model provides predictions of ETCs that are more precise than available models. For aluminum foams (ks=218Wm-1K-1) using water and air as fluid media, the relative root-mean-square (RMS) deviation of the present predictions from the experimental data is about 5.3%; for the reticulated vitreous carbon (RVC) foams (ks=8.5Wm-1K-1), the relative RMS deviation is about 7.4%.

This paper reports both experimental and numerical studies of our proposed electrokinetic focusing technique. The technique utilizes a combined AC and DC field for enhancing Joule heating induced temperature gradient focusing (TGF) of sample solutes in a microfluidic device. Our experimental results show that introducing an AC field component can provide sufficient Joule heating to generate temperature gradient required for achieving TGF of sample solutes, while the electroosmotic flow is suppressed under the relatively high frequency of the AC electric field. Consequently, concentration enhancement of sample solutes is considerably increased by using the combined AC and DC electric field technique. A numerical model including a set of multi-physical governing equations is presented to describe the complex TGF of sample solutes under a combined AC and DC field, and a scaling analysis of the time scales of several transport processes is conducted to simplify the numerical model. The numerical predictions are found in reasonable agreement with the measured Joule heating induced temperature profiles and electrokinetic flow field but show less dispersive than the observed focusing band of sample solutes and slightly over-estimate the experimental concentration enhancement. Several factors such as mass dispersion and photobleaching effect can contribute to the discrepancies between the model predictions and the experimental results.

The absorption air-conditioning system is a low-power-consumption and low-noise system and is also good at balancing the electricity peak-valley system. It can be driven by low-grade energy, such as solar energy and industrial exhaust heat. The nanofluids, which possess the superior thermophysical properties, exhibit a great potential in enhancing heat and mass transfer. In this paper, nanofluids of H2O/LiBr with Fe3O4 nanoparticles were introduced into absorption air conditioning system. The effects of critical parameters, such as the flow rate of H2O/LiBr nanofluids, nanoparticle size and mass fraction, on the falling film absorption were investigated. The H2O/LiBr nanofluids with Fe3O4 nanoparticle mass fractions of 0.01 wt %, 0.05 wt % and 0.1 wt %, and nanoparticle sizes of 20 nm, 50 nm and 100 nm were tested. The results imply that the vapor absorption rate could be improved by adding the nanoparticles to H2O/LiBr solution. The smaller the nanoparticle size, the greater the enhancement of the heat and mass transfer. The absorption enhancement ratio increases sharply at first by increasing the nanoparticle mass fraction within a range of relatively low mass fraction and then exhibits a slow growing even reducing trends with increasing the mass fraction further. For Fe3O4 nanoparticle mass fraction of 0.05 wt % and nanoparticle size of 20 nm, the maximum mass transfer enhancement ratio is achieved about 2.28 at the flow rate of 100 L h−1. Meanwhile, a fitting formula of mass transfer enhancement ratio for Fe3O4 nanofluids has been improved.

As a relatively new type of functional material, porous graphite foam exhibits unique thermophysical properties. It possesses the advantages of low density, high specific surface area, and high bulk thermal conductivity and could be used as the core component of compact, lightweight, and efficient heat exchangers. Effective thermal conductivity serves one of the key thermophysical properties of foam-based heat exchangers. The complex three-dimensional topology and interstitial fluids significantly affect the heat conduction in the porous structure, reflecting a topologically based effective thermal conductivity. This paper presents a novel geometric model for representing the microstructure of graphite foams with simplifications and modifications made on the realistic pore structure, where the complex surfaces and tortuous ligaments were converted into a simplified geometry with cylindrical ligaments connected between cuboid nodes. The multiple-layer method was used to divide the proposed geometry into solvable areas, and the series–parallel relation was used to derive the analytical model for the effective thermal conductivity. To explore heat conduction mechanisms at the pore scale, direct numerical simulation was also conducted on the realistic geometric model. Achieving good agreement with experimental data, the simplified geometric model was validated. The numerically simulated conductivity followed the simplified model prediction that the two geometries are equivalent from thermal aspect. It validates further that the simplified model is capable of reflecting the internal microstructure of graphite foam, which would benefit the understandings of the thermophysical mechanisms of pore-scaled heat conduction and microstructures of graphite foam.

We present an analytical model capable of predicting permeability for isotropic and fully saturated micro-open-cell metal foam with surface modified by micro-rods (30–50 μm). The analytical model is based on the pore-scale volume-averaging approach and the assumption of piece-wise plane Poiseuille flow with the reconstructed three-dimensional cubic unit cell having cylindrical micro-rods synthesized on the cell walls. Both of the metal foam structure and the randomly distributed micro-rods are assumed to be periodic. The proposed model includes both the macroscopic and microscopic parameters that characterize the metal foam as well as the micro-roughness. The effects of micro-rod radius, height and interval on permeability and tortuosity are examined. To validate the present analytical model, experimental results are employed and good agreement is found. Results demonstrate that the micro-rods synthesized on the cell walls significantly decrease the permeability of the micro-foam. The increase in micro-rod radius/height or decrease in rod interval makes the metal foam surface rougher and thus decreases the foam permeability.

The radiant air conditioning system, possessing the characteristics of draft less and small temperature gradients in the occupied zone, is becoming increasingly attractive in recent years, due to its advantage of providing more comfortable indoor environment with low energy consumption against the conventional convective air conditioning system. In order to master the features of the radiant air conditioning system and improve its design process, the interrelation among the human thermal comfort and the heat exchange between human body and its surroundings subject to the radiant air conditioning system is investigated in this paper. Based on Fanger's thermal comfort model, the PMV (Predicted Mean Vote) is used to evaluate the human thermal comfort. To calculate the heat loss from human body, the human thermal balance and heat release characteristics under radiant cooling system are discussed in detail. The CFD model in terms of different cooling ceiling temperatures and air supply temperatures is simulated and analyzed by Airpak. The relationship between the heat loss from human body and thermal comfort is achieved based on the simplified formula for the heat loss and the PMV value obtained from numerical results. For human body under radiant air conditioning system, numerical results showed that the sensible heat loss from human body is approximately linear to the PMV under all simulated conditions. The simplified PMV model, directly from the respect of human heat balance instead of complicated environmental parameters, is finally proposed. Published version

A novel cylindrical oblique fin minichannel heat sink, in the form of an enveloping jacket, was proposed to be fitted over cylindrical heat sources. The presence of the oblique fins disrupts and reinitializes the boundary layer development at the leading edge of each fin. This results in a significant reduction of the boundary layer thickness and causes the flow to remain in the developing state. Experimental investigations were conducted to compare its heat transfer performance with conventional straight fin minichannel heat sink. The test pieces were fabricated from copper and measurements on the heat transfer characteristics were performed for Reynolds number ranging from 50 to 500. In addition, the effects of flow distribution were examined and it was found that cylindrical oblique fin structure eliminates the edge effect which is present in the planar oblique fin configuration. The uniform secondary flow generated by the cylindrical oblique fin structure improves fluid mixing and enhances heat transfer significantly. The experimental results showed that the average Nusselt number for the cylindrical oblique fin minichannel heat sink increases up to 75.6% and the total thermal resistance decreases up to 59.1% compared to the conventional straight fin heat sink. For a heat flux of 6.1 W/cm2 and Reynolds number of 300, the average surface temperature of cylindrical heat sink is reduced by 4.3 °C compared to conventional straight fin heat sink while the required pumping power remains comparable.

A novel cylindrical oblique fin minichannel heat sink was proposed and studied for cooling heat source with cylindrical surfaces. To optimize and analyze the heat transfer performance of the heat sink, a similarity analysis and parametric study on the geometric dimensions of the heat sink were performed. Three dimensional conjugated heat transfer simulation using CFD (Computational Fluid Dynamics) approach was used to analyze the laminar convective heat transfer and apparent friction characteristics for 43 different cylindrical heat sinks with varied geometric dimensions. The studies were performed by varying the oblique angle from 20° to 45°, secondary channel gap from 1 mm to 5 mm and Reynolds number from 200 to 900. In this paper, the flow distribution was also investigated and reported, as the secondary channel gap, oblique angle and Reynolds number were varied. Based on the 259 numerical data points, multiple correlations for the average Nusselt number and the apparent friction constant were formulated, verified and presented. The average deviation for the approximation of average Nusselt number is from −5.8% to 7.0% while it is from −5.1% to 7.1% for the apparent friction constant. These correlations can be used for further studies such as performance prediction or geometrical optimization.

The development of electric vehicles (EVs) demands for complementary technologies in battery thermal management. To achieve fast charging/discharging capacity, liquid cooling is an effective means of maintaining temperature of a battery in operation within a narrow optimal range. In conventional straight channels, convective heat transfer deteriorates along the axial direction with the development of the hydrodynamic boundary layer, resulting in elevated maximum temperature and significant temperature gradient in the fully developed region. This is a serious problem as temperature uniformity is of utmost importance to the performance and lifespan of a Li–ion battery. In this research, a simple configuration of oblique cuts across the straight fins of a conventional straight channel design was developed, to enhance the performance of the conventional channel with minimal pressure penalty. These oblique cuts across the straight fins form an oblique fin array. The designed liquid cold plate (LCP) contains these simple oblique fins with optimized angle and width. This segmentation of the continuous fin into oblique sections leads to the re-initialization of boundary layers, providing a solution to the elevated temperatures caused by a thick boundary layer in the fully developed region. Experimental results show that heat transfer coefficients of oblique minichannel are higher than those of conventional straight minichannel. The oblique LCP is able to maintain the battery surface average temperature below 50 °C for a heat load of 1240 W at a flow rate lower than 0.9 l/min. This implies that a proper designed minichannel cold plate could be a promising solution for EV battery thermal management.

The relationship between lithium-ion battery performance and operating temperature is of significance in designing battery thermal management system (BTMS). In this study, two different thermal conditions, namely constant temperature condition and near-adiabatic condition are established to explore charging/discharging characteristics and heat generation behaviors of the lithium-ion battery with Li(NixCoyAlz)O2 cathode. The objective of creating near-adiabatic condition is to discover the effect of the heat generated by battery itself on charging/discharging characteristics. The experimental results show that the battery charging characteristics are nearly independent on the charging temperature ranged from 20 °C to 40 °C, while the battery charging/discharging performance degrade dramatically for the battery temperature lower than 20 °C. Although the heat generated by battery itself may accelerate battery degradation during cycling due to the adverse effect of excessive temperature, however it improves the discharging performance in a suitable temperature range. This implies that a battery pack may have an excellent discharging performance without BTMS intervention at a moderate discharging rate (e.g., 0.5 C). The irreversible heat could be regarded as the sole heat source term to simplify the battery thermal model due to negligible thermal effect caused by the small amount of reversible heat when the battery is discharged at higher discharging rates.

A counter-flow regenerative indirect evaporative heat exchanger (RIEHX) was introduced and investigated. This paper aims to conduct an experimental study for the RIEHX to investigate the cooling performance under different operating conditions. The experimental prototype was able to adjust the inlet air flow rate and temperature. The thermal performance of the RIEHX was tested with variable inlet conditions. The experimental results have demonstrated that the supply air can be effectively cooled along the product air flow passages by transferring heat to the wet side of the RIEHX due to water evaporation. Under a constant inlet air velocity, the product air with a higher inlet temperature can obtain a larger temperature reduction. In addition, a lower air flow rate may enhance the cooling effect due to the increased contact duration between the air streams. The proposed system is able to improve the cooling effectiveness of the conventional plate-type indirect evaporative cooler.

As the most commonly used power battery in electric vehicles, lithium-ion battery is sensitive to the operation temperature. The performance and lifespan of lithium-ion battery are strongly dependent on its working temperature. Various thermal management systems have been developed to maintain batteries’ operating temperature within an appropriate range. A properly designed thermal management system relies upon the understanding of battery’s heat-generation characteristics and the temperature effect on its discharging performance. In this research, an experimental investigation is carried out to study the electro-thermal characteristics of the commercial prismatic ternary lithium-ion battery under three thermal conditions. Constant temperature condition is built to explore the effect of the operating temperature, while near-adiabatic condition and natural-convection condition are employed to study the heat-generation characteristics of lithium-ion battery. The results show that the effect of operating temperature on discharge performance becomes more pronounced as the discharge rate increases. It is found that the surface temperature decreases when the battery discharges at small rates within the capacity ranged from 17Ah to 27Ah, demonstrating that the reversible heat makes up a large proportion of battery heat generation.

Heat transfer rate in curve channel decreases with channel curvature since the secondary flow turns weak with the decrease of centrifugal force. In this paper, the periodical wave wall structure is introduced into curve channel for improving heat transfer rate in the curve channel with small curvature. The channel radius is not constant anymore but varies periodically based on a cosinoidal function. Three-dimensional numerical investigation was carried out to explore the flow and heat transfer characteristics in the curve-wave channel, and the effects of wave frequency and average curvature on the heat transfer performance were analysed. The results show that the heat transfer rate in curve channel can be improve up to 95.50% due to the periodical wave wall structure, while the friction factor increases by 53.94%. The effect of periodical wave wall structure gets obvious with the increase of Re. Heat transfer in curve-wave channel can be further enhanced by increasing wave frequency of channel wall. In addition, the effect of wave wall structure on heat transfer is dependent on the overall curvature of curve-wave channel and stronger for larger-curvature curve-wave channel. The performance factors of all the curve-wave channels are almost above 1, indicating that this structure can be used as an economic passive heat transfer enhancement method.

The effective thermal conductivities (ETCs) of porous electrodes in electrolyte are of rather significance for determining the thermal conductivity of Li-ion battery which is an important factor in designing battery thermal management system and predicting battery thermal behaviour. In this study, the representative Li-ion battery consisting of a Li(NiCoMn)O2 positive electrode and a graphite negative electrode was chosen to explore the ETCs of porous electrodes. The effects of ETCs of porous electrodes on the Li-ion battery’s thermal conductivity were firstly discussed, and the ETCs were analysed based on its internal configuration and basic assumptions. Most importantly, the ETCs bounds of porous electrodes were acquired using basic thermal conductivity models and the limits of ETCs were obtained based on Maxwell 2 model combined with volume fractions of electrolyte. The results show that the ETCs of porous electrodes in electrolyte are obviously lower than the thermal conductivities of active materials, namely Li(NiCoMn)O2 and graphite. In addition, the ETCs of porous electrodes are not constant but variable values caused by the variation of volume fractions of electrolyte in porous electrodes which indicates that the volume fractions of electrolyte should be considered for accurately estimate the thermal conductivity of commercial Li-ion battery.

Thermal energy storage has attracted more and more attentions due mainly to its ability of peak load shifting. Shell-and-tube configuration is a typical heat exchanger for thermal energy storage. T ...

Concentric pipe heat exchangers have been utilized extensively in practical project, such as petroleum, chemical, geothermal energy utilization and other fields. The study of annular flow between vertical concentric pipes is dominated by boiling heat transfer, while the study of forced convection heat transfer for single-phase flow is scarce. In this paper, an experimental investigation is carried out to study of the flow and heat transfer characteristics of the annular flow between vertical concentric pipes. The annular in a vertical concentric pipe heat exchanger with 25mm ring gap is tested with different volume flow rates and different constant heat flow densities. The results show that the Nusselt number of annular flow between vertical concentric pipes increases with Reynolds number. The local convective heat transfer coefficients reduce with the distance from the top to the bottom, which lead to a gradually increased trend in the fluid temperature along the flow direction. Based on the experimental data, an empirical equation of the Nusselt number is obtained to evaluate the overall heat transfer performance of vertically concentric pipe heat exchangers.

Understanding the dynamics in the deposition of water droplets onto solid surfaces is of importance from both fundamental and practical viewpoints. While the deposition of a water droplet onto a heated surface is extensively studied, the characteristics of depositing a droplet onto a cold surface and the phenomena leading to such behavior remain elusive. Here we report the formation of a triple condensate halo observed during the deposition of a water droplet onto a cold surface, due to the interplay between droplet impact dynamics and vapor diffusion. Two subsequent condensation stages occur during the droplet spreading and cooling processes, engendering this unique condensate halo with three distinctive bands. We further proposed a scaling model to interpret the size of each band, and the model is validated by the experiments of droplets with different impact velocity and varying substrate temperature. Our experimental and theoretical investigation of the droplet impact dynamics and the associated condensation unravels the mass and heat transfer among droplet, vapor and substrate, offer a new sight for designing of heat exchange devices.

Compared with traditional air-conditioning systems which aim at maintaining the designed indoor air temperature and humidity, radiant panels are capable to improve the human thermal comfort through the direct radiant heat transfer with occupants. Based on the Fanger's thermal comfort model, the simplified PMV (Predicted Mean Vote) model and calculation equation of cooling load are established. This paper analyzes the relationship between the human thermal comfort and indoor sensible cooling load, and explores the design and operation methods of indoor parameters. The model room with typical boundary conditions in the hot-summer and cold-winter zone of China is simulated and analyzed by Airpak. The widely accepted PMV and PPD (Predicted Percentage of Dissatisfied) indices are adopted to evaluate the indoor human thermal comfort. The parameters including the radiant surface temperature, the air supply temperature, the relative humidity and the ratio of the radiant surface areas are researched. The optimum indoor parameters in typical summer conditions are finally obtained, it is expected to provide a relevant reference for the design and operation methods subject to the radiant panel combined with fresh air system.

A novel cylindrical oblique fin minichannel heat sink was proposed to fit over cylindrical heat sources in the form of an enveloping jacket. The periodic cylindrical oblique fin causes the hydrodynamic boundary layer development to be reinitialized at the leading edge of the next downstream fin. This decreases the average thermal boundary layer thickness, enhances the heat transfer performance and yields negligible pressure drop penalty due to combined effect of thermal boundary layer re-development and flow mixing. Its cooling effectiveness is compared with conventional straight fin minichannel heat sinks through experimental and numerical approach for the Reynolds number ranged from 50 to 500. The results showed that the averaged Nusselt number, Nu ave for the cylindrical oblique-cut fin minichannel heat sink increases up to 75.6% and the total thermal resistance decreases up to 59.1% when compared with the conventional straight fin minichannel heat sink. It is also found firstly that a flow recirculation zone will form at larger Reynolds number in the secondary channel however this recirculation is insignificant in the present low Reynolds number study. Heat transfer enhancement ( E Nu ) and pressure drop penalty ( E f ) show that a significant improvement of the cylindrical oblique fin minichannel over conventional straight fin minichannel overall.

Two phase microgap heat sink has a large potential to minimize the drawbacks associated with two phase microchannel heat sink, especially flow instabilities, flow reversal and lateral variation of flow and wall temperature between channels. This new concept of the two-phase microgap heat sink is very promising due to its high heat transfer rate and ease of fabrication. However, comparison of the performance of microgap heat sink (heat transfer, pressure drop and instability characteristics) with some conventional heat sink has not been investigated extensively. In this study, experiments have been conducted to investigate the heat transfer and pressure drop characteristics of deionized water (DI) in microgap heat sink and compare these experimental results with similar data obtained for microchannel heat sink. These studies are carried out with the inlet DI water temperatures 86 °C at different mass fluxes ranging from 400 to 1000 kg/m2 s, for effective heat flux 0–85 W/cm2. High speed flow visualizations are conducted simultaneously along with experiments to illustrate the bubble characteristics in the microchannel and microgap heat sink. Experimental result shows that microgap heat sink performs better at high heat flux and low mass flux due to confined slug and annular boiling dominance and consequent delay of dryout phase. So, this microgap technology is promising and an effective method to dissipate very high heat fluxes in compact space with a smaller rate of coolant flow. Moreover, pressure drop is higher in microchannel than microgap heat sink at all the heat fluxes. In addition, encouraging results have been obtained using microgap as it can potentially mitigate local hotspot, reduce flow instabilities, flow reversal and maintain uniform wall temperatures over the heated surface.

The rapid increase of heat flux in high performance electronic devices has necessitated the development of high capacity thermal management techniques that can support extremely high heat transfer rates. Flow boiling in microgap is very promising for this purpose due to its high heat transfer rate and ease of fabrication. However, the effects of microgap dimension on heat transfer and pressure drop characteristics along with flow visualization have not been investigated extensively. This paper focuses on flow boiling experiments of deionized water in silicon microgap heat sink for ten different microgap dimensions from a range of 80 μm–1000 μm to determine the most effective and efficient range of microgap dimensions based on heat transfer and pressure drop performance. High speed flow visualization is conducted simultaneously along with experiments to illustrate the bubble characteristics in the boiling flow in microgap. The results of this study show that confinement in flow boiling occurs for microgap sizes 500 μm and below and confined slug/annular flow is the main dominant regime whereas physical confinement does not occur for microgap sizes 700 μm and above and bubbly flow is the dominant flow regime. The microgap is ineffective below 100 μm as partial dryout strikes very early and the wall temperature is much higher for a fixed heat flux as microgap size increases above 500 μm. In addition, results show that pressure drop and pressure fluctuation decrease with the increases of gap size whereas wall temperature and wall temperature fluctuation increase with the increases of gap size. A strong dependence of heat transfer coefficient on microgap sizes is observed for microgap sizes 500 μm and below. However, the heat transfer coefficient is independent of microgap size for microgap sizes 700 μm and above.

As a new type of functional material, porous graphite foam exhibits unique thermal physical properties and geometric characteristics in heat transfer applications. It has the advantages of low density, high specific surface area, high porosity and high bulk thermal conductivity, which can be used as the core component of small, lightweight, compact and efficient heat sinks. Effective thermal conductivity serves one of the key thermophysical properties for foam-cored heat sinks. The complex three-dimensional topology and interstitial fluids significantly affect the heat conduction through such kind of porous structures, reflecting a topologically based effective thermal conductivity. This paper presents a novel geometric model for representing the microstructure of graphite foams, with simplifications and modifications made on the actual pore structure of graphite foam. For calculation simplicity, we convert the realized geometry consisting of complex surfaces and tortuous ligaments into a simplified geometry with circular ligaments joined at cuboid nodes, on the basis of the volume equivalency rule. The multiple-layer method is used to divide the proposed geometry into solvable areas and the series-parallel relations are used to derive the analytical model for effective thermal conductivity. To physically explore the heat conduction mechanisms at pore scale, direction numerical simulations were conducted on the reconstructed geometric model. Achieving good agreement with experimental data, the present analytical model (based on the simplified geometry) is validated. Further, the numerically simulated conductivities follow the model prediction, favoring thermally that the two geometries are equal. The present geometry model is more realized and capable of reflecting the internal microstructure of graphite foam, which will benefit the understandings for the thermo-physical mechanisms of pore-scaled heat conduction and micro structures of graphite foam.Copyright © 2016 by ASME

This paper presents an experimental study of the pool boiling phenomena and performance of porous graphite foam evaporators of different structures and thermophysical properties. Two dielectric liquids viz. FC-72 and HFE-7000 were used as working fluids. Block and fin evaporators of different fin-to-block-surface-area ratios (AR) were designed to study the role of the internal pore structure of graphite foams in a compact air-cooled thermosyphon under saturated pool boiling condition for high heat flux electronics cooling applications. The wall temperatures were measured and the boiling heat transfer coefficients were calculated to analyze the boiling performance. It was found that both fin structures with AR = 3.70 and 2.73 result in reduced boiling heat transfer performances and higher wall temperatures. The experimental results show that the boiling heat transfer coefficients of the block structures are about 1.2–1.6 times higher than those of the fin structures. The total internal surface area to volume ratio (β) and the total exposed areas (AT) of the graphite foams were calculated in this study. The results show that the values of β and AT of the block structures are much higher than the fin structures for both tested “Pocofoam” 61% porosity and “Kfoam” 78% porosity evaporators which resulted in higher boiling heat transfer coefficient and lower wall temperature of the block structures. A visualization study shows that more bubbles were generated from the block structures compared to the fin structures due to the larger number of nucleation sites from the block structures. It was also found that use of FC-72 resulted in better boiling heat transfer performance compared to HFE-7000.

Two-phase microgap channel cooling concept has been recently proposed for cooling the heat sources directly in application of electronic devices thermal management. This concept is relatively new and more research should be carried out systematically to investigate the size effects of microgap channel on heat transfer and pressure drop mechanisms. In this study, local flow boiling phenomenon in different microgap sizes has been investigated experimentally. Experiments are performed in silicon based microgap heat sink having microgap of depth 190 μm, 285 μm and 381 μm, using deionized water with inlet temperature of 86 °C. The effects of mass flux and heat flux on heat transfer coefficient and pressure drop characteristics are examined by using three different mass fluxes 420 kg/m2 s, 690 kg/m2 s and 970 kg/m2 s and effective heat flux varying from 0 to 110 W/cm2. An array of integrated micro-temperature sensors are used in this study to obtain the local temperatures and subsequently local heat transfer coefficients are determined. Apart from these experimental investigations, simultaneous high speed visualizations are conducted to observe and explore the mechanism of flow boiling in microgap channel. The results of this study show that flow boiling heat transfer coefficient is dependent on gap size, and the lower the gap size, higher the heat transfer coefficient. Moreover, it has been observed that confined slug and annular boiling are the dominant heat transfer mechanisms in microgap channels after the onset of nucleate boiling. Hence, local heat transfer coefficient increases significantly because of thin film evaporation during confined boiling at high heat flux. This study also evaluates the effectiveness of microgap cooling technology, to eliminate temperature gradient and hotspots.

Many forms of electronic equipment such as battery packs and telecom equipment must be stored in harsh outdoor environment. It is essential that these facilities be protected from a wide range of ambient temperatures and solar radiation. Temperature extremes greatly reduce lead-acid based battery performance and shorten battery life. Therefore, it is important to maintain the cabinet temperature within the optimal values between 20 °C and 30 °C to ensure battery stability and to extend battery lifespan. To this end, cabinet enclosures with proper thermal management have been developed to house such electronic equipment in a highly weather tight manner, especially for battery cabinet. In this paper, the flow field and temperature distribution inside an outdoor cabinet are studied experimentally and numerically. The battery cabinets house 24 batteries in two configurations namely, two-layer configuration and six-layer configuration respectively. The cabinet walls are maintained at a constant temperature by a refrigeration system. The cabinet's ability to protect the batteries from an ambient temperature as high as 50 °C is studied. An experimental facility is developed to measure the battery surface temperatures and to validate the numerical simulations. The differences between the experimental and computational fluid dynamic (CFD) results are within 5%.

Flow boiling experiments were conducted in straight and expanding microchannels with similar dimensions and operating conditions. Deionized water was used as the coolant. The test vehicles were made from copper with a footprint area of 25 mm × 25 mm. Microchannels having nominal width of 300 μm and a nominal aspect ratio of 4 were formed by wire cut Electro Discharge Machining process. The measured surface roughness (Ra) was about 2.0 μm. To facilitate easier comparison with the straight microchannels and also to simplify the method of fabrication, the expanding channels were formed with the removal of fins at selected location from the straight microchannel design, instead of using a diverging channel. Tests were performed on both the microchannels over a range of mass fluxes, heat fluxes and an inlet temperature of 90 °C. It was observed that the two-phase pressure drop across the expanding microchannel heat sink was significantly lower as compared to its straight counterpart. The pressure drop and wall temperature fluctuations were seen reduced in the expanding microchannel heat sink. It was also noted that the expanding microchannel heat sink had a better heat transfer performance than the straight microchannel heat sink, under similar operating conditions. This phenomenon in expanding microchannel heat sink, which was observed in spite of it having a lower convective heat transfer area, is explained based on its improved flow boiling stability that reduces the pressure drop oscillations, temperature oscillations and hence partial dry out.

This paper presents an investigation of heat transfer enhancement using highly conductive graphite foam as porous insert in a pool boiling evaporator. Graphite foams of different bulk thermal conductivities and pore sizes were investigated with phase change coolants FC-72 and HFE-7000 and compared with a copper block in a designed thermosyphon. The heater wall temperature, superheat and thermal resistances were obtained to evaluate the boiling performance. Associated with the analysis of various boiling regimes, nondimensional parameters including the Capillary, Grashof and Bond numbers were used to analyze the bubble formation from the porous insert. The experimental results show that the boiling thermal resistances of the system with a graphite foam insert are about 2 and 3 times lower than those of the copper block immersed in FC-72 and HFE-7000, respectively. The nondimensional analysis showed that the bubbles from the small pore diameter graphite foam have to overcome a large surface tension force before departure, although the foam possesses high thermal conductivity. This implies that a balanced relation between thermal conductivity and pore diameter could maximize the enhancement on pool boiling heat transfer. The current thermosyphon with a porous insert can allow a heat flux of 112 W/cm 2 to be removed with a maximum heater temperature of 90 °C.

This paper presents the results of an experimental study of heat transfer in a pool boiling evaporator with porous insert. Different types of graphite foams were tested with the phase change coolant FC-72 in a designed thermosyphon. Comparisons between the graphite foams and a solid copper block show that the porous structure enhances pool boiling significantly. The boiling thermal resistance of the tested graphite foams was found to be about 2 times lower than that of the copper block. The bubble formation recorded by a high speed camera indicates that boiling from a graphite foam is more vigorous than from a copper block. The designed thermosyphon with graphite foam insert can remove heat fluxes of up to 112 W/cm2 with the maximum heater temperature maintained below 100°C.

Fluid flow with phase change heat transfer in a three-dimensional porous channel with asymmetrically heating from one side is numerically studied in this paper. The “modified” Kirchhoff method is used to deal with the spatial discontinuity in the thermal diffusion coefficient in the energy equation. The velocity and temperature fields, as well as the liquid saturation field on the heated section of the wall with different Peclet and Rayleigh numbers are investigated. The results show that the liquid flow bypasses the two-phase zone, while the vapor flows primarily to the interface between the sub-cooled liquid zone and the two-phase zone. An increase in the Peclet number decreases the two-phase region while an increase in the Rayleigh number helps to spread the heat to a larger region of the domain. The distribution of the liquid saturation on the heated section of the wall indicates that the minimum liquid saturation increases with the increase of both the Peclet and Rayleigh numbers.

The transient behavior of two-phase flow and heat transfer in a channel filled with porous media was numerically studied in this paper. Based on the two-phase mixture model, numerical solutions were obtained using the Finite-Volume Method (FVM). Two methods to treat the discontinuous diffusion coefficient in the energy equation, i.e. the harmonic mean method and the “modified” Kirchhoff method were compared. It was found that the “modified” Kirchhoff method was better in dealing with the rapid change in the diffusion coefficient. Three different cases, with discrete heat flux applied at (1) the upper wall, (2) lower wall and (3) both the upper and lower walls were studied. The velocity and temperature fields for these cases were discussed. The results show that the liquid and vapor flow fields, as well as the temperature and liquid saturation fields have distinctly different features with the change in heating location. An analysis of the vapor volume fraction indicates that the largest amount of vapor with the highest vapor generation rate was for the case in which the heat flux is applied from the lower wall.

Fluid flow and heat transfer characteristics in a channel with staggered porous blocks were numerically studied in this paper. The Navier–Stokes and Brinkman–Forchheimer equations were used to model the fluid flow in the open and porous regions, respectively. Coupling of the pressure and velocity fields was resolved using the SIMPLER algorithm. The local thermal equilibrium model was adopted in the energy equation to evaluate the solid and fluid temperatures. The effect of Darcy number, Reynolds number, porous block height and width on the velocity field were studied. In addition, the effects of the above parameters as well as the thermal conductivity ratio between the porous blocks and the fluid on the local heat transfer were analyzed. The pressure drops across the channel for different cases were discussed. The results show that the flow behavior and its associated local heat transfer are sensitive to the variation of the above parameters. It is predicted by the present study that an increase in the thermal conductivity ratio between the porous blocks and the fluid results in significant enhancement of heat transfer at the locations of the porous blocks.

Forced convection heat transfer in a channel with different configurations of graphite foams is experimentally and numerically studied in this paper. The physical properties of graphite foams such as the porosity, pore diameter, density, permeability and Forchheimer coefficient are determined experimentally. The local temperatures at the surface of the heat source and the pressure drops across different configurations of graphite foams are measured. In the numerical simulations, the Navier–Stokes and Brinkman–Forchheimer equations are used to model the fluid flow in the open and porous regions, respectively. The local thermal non-equilibrium model is adopted in the energy equations to evaluate the solid and fluid temperatures. Comparisons are made between the experimental and simulation results. The results showed that the solid block foam has the best heat transfer performance at the expense of high pressure drop. However, the proposed configurations can achieve relatively good enhancement of heat transfer at moderate pressure drop.

This paper reports experimental results for forced convection heat transfer in microcellular graphite foams of high thermal conductivity. The graphite foam heat sinks were fabricated into different structures and compared with conventional aluminum heat sinks of the same configurations. The results show that better heat transfer performance is obtained by graphite foam heat sinks as compared to the solid aluminum heat sinks of different configurations. An analysis of the structure effect of graphite foams on convective heat transfer indicates that the better performance of graphite foams is due to its internal porous structure. The advantage of isotropic thermal properties of graphite foams combined with open cell structure lends itself to novel designs in electronic cooling applications.

Open-cell metal foams are often used in heat exchangers and absorption equipment because they exhibit large specific surface area and present tortuous coolant flow paths. However, published research works on the characteristics of fluid flow in metal foams are relatively scarce, especially for the flow oscillation condition. The present experimental investigation attempts to uncover the behavior of steady and oscillating flows through metal foams with a tetrakaidecahedron structure. In the experiments, steady flow was supplied by an auto-balance compressor and flow oscillation was provided by an oscillating flow generator. The pressure drop and velocity were measured by the differential pressure transducer and hot-wire sensor, respectively. The friction factor of steady flow in metal foam channel was analyzed through the permeability and inertia coefficient of the porous medium. The results show that flow resistance in the metal foams increases with increasing form coefficient and decreasing permeability. The empirical equation obtained by the present study indicates that the maximum friction factor of oscillating flow through the tested aluminum foams with specific structure is governed by the hydraulic ligament diameter-based kinetic Reynolds number and the dimensionless flow amplitude.

This paper reports the results of an experimental investigation on the heat transfer performance of metal foam as a heat sink subjected to oscillating flow. The measured pressure drops, velocities, and surface temperatures of oscillating flow through aluminum 40 PPI foam are presented in detail. The calculated cycle-averaged local temperatures and Nusselt numbers for different kinetic Reynolds numbers were analyzed. The variation of total heat transfer rate with a kinetic Reynolds number suggests that oscillating flow at relative low frequency has a substantial effect on heat transfer enhancement in a metal foam heat sink. A comparison of the length-averaged Nusselt numbers between oscillating and steady flows indicates that higher heat transfer rates can be obtained in metal foams subjected to oscillating flow. The relation between pumping power and total heat transfer rates for the oscillating flow cooling system was also analyzed with a view to designing a novel heat sink using metal foam. The results show that high heat transfer performance of metal foam heat sinks subject to oscillating flow can be obtained with moderate pumping power

An experimental study was performed to investigate the characteristics of oscillating flow through a channel filled with open-cell metal foam with a fully inter-connected pore structure. Detailed experimental data of oscillating flow pressure drops and velocities for a wide range of oscillatory frequency and the maximum flow displacement were presented. A correlation equation for the maximum friction factor of metal foams subject to oscillating flow was obtained and compared with the results for channels inserted with wire-screens obtained by other investigators. The results showed that oscillating flow characteristics in an open-cell metal foam are governed by a hydraulic ligament diameter based kinetic Reynolds number Reω(Dh) and the dimensionless flow displacement amplitude ADh. The effects of kinetic Reynolds number on the variations of pressure drop and flow velocity in metal foam are more significant than that of the dimensionless flow displacement amplitude. The maximum friction factor of oscillating flow in open-cell metal foams is much smaller than that of oscillating flow in wire-screens for large flow displacement amplitudes.

Many forms of electronic equipment, of necessity, must be located in an outdoor environment. Such equipment in typical form may be battery packs or telecom-equipment. It is essential that these facilities be protected from a wide range of ambient temperatures and solar radiation. To this end, cabinet enclosures with proper thermal management have been developed to house such electronic equipment in a highly weather tight manner, especially for battery cabinet. Often the batteries are of a lead-acid construction which is known to be adversely affected by temperature extremes in terms of battery performance and life. Therefore, it is important to maintain the cabinet temperature ideally for ensuring battery stability and extending battery lifespan. In this paper, physical and mathematical models are established to investigate the flow field and temperature distribution inside an outdoor cabinet, which contains 24 batteries with two configurations of two-layer and six-layer respectively. The cabinet walls are maintained at a constant temperature by a refrigeration system and the ambient temperature is up to 50 °C according to the practical situation. The flow field and temperature distribution are analyzed with and without consideration of solar radiation. An experimental facility is then developed to measure the battery surface temperatures and to validate the numerical simulation. The differences between the CFD and experimental results are within 2%, which confirms the CFD model.

Due to the characteristics of large surface area-to-volume ratio and inter-connected ligament structure, open-cell metal foams are promising materials for enhancing heat transfer in forced convection and have been researched for thermal applications in thermal management systems, air-cooled condensers and compact heat sinks for power electronics. However, the tortuous complex flow path inside metal foams leads to relatively higher pressure drop, which requires larger system pumping power. Hence, it is important to study the heat transfer performance of metal foam compared to its flow resistance characteristics. Detailed experimental study of forced convection subjected to constant heat flux in metal foams is conducted in the present paper. The objective of the investigation is to compare the heat transfer performance and hydraulic characteristics of aluminum foams with different pore densities. The tested aluminium foam samples are of 50.0mm (L) × 25.0mm (W) × 12.0mm (H) in geometric dimensions and pore densities are of 5ppi, 10ppi and 40ppi, respectively. Experiments are performed in forced convective heat transfer using deionized water as the cooling fluid. To minimize the heat loss, the test section is built adiabatically with Teflon and polycarbonate materials. The inlet flow velocity, the temperature distribution on the heating surface and the pressure drop across the metal form are measured. Based on the analysis of experimental data, it is found that convective heat transfer performance in high ppi foam is higher than that in low ppi foam, while the pressure drop shows the opposite trend for a given flow rate.