Chilled Surface Research Articles

Enhanced antibacterial photodynamic therapy with Qu/Ce6@ZIF-8 nanoplatform for Staphylococcus aureus control in food preservation

Antimicrobial Photodynamic Therapy (aPDT) effectively combats Staphylococcus aureus (S. aureus) infections and mitigates antibiotic resistance. However, the application of aPDT is constrained by challenges related to photosensitizers, such as poor water solubility, a tendency to aggregate, and low bioavailability. In response, we have developed a nanoplatform using ZIF-8 nanocomposites. Through in-situ synthesis, we incorporated the chlorin e6 (Ce6) into the ZIF-8 matrix based on competitive coordination strategy, significantly enhancing its photocatalytic activity. The bioactivity of quercetin (Qu), through competitive inhibition of Sortase A (SrtA), enhances bacterial cell membrane permeability, thereby boosting the efficacy of the Qu/Ce6@ZIF-8 nanoparticles. This dual antibacterial strategy markedly suppresses S. aureus growth (MIC = 150 μg/mL). Moreover, we have engineered a polycaprolactone (PCL) composite film embedding these nanoparticles, which, under red light irradiation, substantially inhibits S. aureus proliferation on chilled chicken surfaces, thus extending shelf life to eight days. This innovative approach offers a promising strategy for antimicrobial food preservation, employing a multifunctional nano-antibacterial platform.

Observations and simulations for phase separation process of immiscible Fe50Sn50 alloy droplets placed on a chilling surface

Liquid phase separation and microstructure evolution mechanisms of immiscible Fe50Sn50 alloy droplets placed on a chilling surface have been investigated by both arc melting experiments and lattice-Boltzmann simulations. The pattern selection of phase-separated morphologies strongly depended on the sample diameter. With the reduction in sample size, phase separation time was shortened, two-layer macrosegregation morphologies first transformed into intermediate phase-separated morphologies and finally changed into a homogeneously dispersed microstructure. The farther away from the sample bottom the longer the phase separation time and the larger the Sn-rich phase. A heat transfer equation was proposed to analyze the temperature field characteristics of Fe50Sn50 alloy droplets placed on the surface of a water-cooled copper mold. Theoretical analyses revealed that the sample gradually cooled from the bottom to the top of the sample. There existed a relatively high temperature gradient of several hundred Kelvins per millimeter between the top and the bottom of the arc melted sample, which induced the occurrence of an extremely intense Marangoni convection. The smaller the sample size the larger the temperature gradient and the greater deviation-degree of Fe-rich zone in two-layer macrosegregation structure from the bottom of the sample. The simulated two-layer phase-separated morphology agreed well with the experimental observations. Numerical simulations demonstrated that the effect of Marangoni convection on the phase separation was significantly stronger than the Stokes motion, and Fe-rich globules with a larger density tended to move upward to form a Fe-rich zone deviating from the bottom of the sample.

An Experimental Study of Frost Formation on Chilled Surfaces with Hydrophobic Coatings

An Experimental Study of Frost Formation on Chilled Surfaces with Hydrophobic Coatings

Impact of ventilation system type on indoor thermal environment and human thermal comfort in a ceiling cooling room

A ceiling cooling (CC) system integrated with a mechanical ventilation system is an advanced HVAC system for the modern office building with glass curtain wall. In this paper, considering the influence of heat transfer of external envelope, the indoor thermal environment and human thermal comfort were objectively measured and subjectively evaluated in a CC room with mixing ventilation (MV) or underfloor air distribution (UFAD). Indoor physical parameters and human skin temperatures were measured as the chilled ceiling surface temperature and supply air temperature were 17.1-17.6? and 22.2-22.6?. Simultaneously, 16 subjects (8 males and 8 females) were selected to subjectively evaluate the thermal environment. The results showed that the difference between mean radiant temperature and air temperature in the occupied zone was 0.8? with CC + MV and 1.2? with CC +UFAD, and the indoor air velocity was 0.17 m/s with CC + MV and 0.13 m/s with CC + UFAD. In addition, the calculated and measured thermal sensation votes with CC + MV were all slightly less than those with CC + UFAD. Therefore, ventilation system type had a slight impact on the indoor thermal envi?ronment and human thermal comfort in the CC room.

Effects of supply Diffuser Shape on Air Age and Human Comfort in an Office with Displacement Ventilation and Chilled Ceiling System in Hot and Dry climate

In recent years, the need to provide a clean environment in enclosed places has drawn increasing levels of attention due to the spread of epidemics and viruses across the world. Chilled ceilings with displacement ventilation represent promising technology. The combined ventilation system has not yet been used in Iraqi buildings, then it’s a good starting point for study the performance of this system in Iraq-Hilla city climate (hot and dry climate). An office room with a combined ventilation system was simulated using AIRPAK software. Indoor air age, air temperature distribution, CO2 concentration and thermal efficiency were estimated numerically. During the simulation process, the effects of two different supply diffuser shapes (one way rectangular diffuser and semicircle diffuser) were compared to investigated the effect of supply diffuser shape on air age and thermal environment in hot and dry climate (passed on peak summer temperatures in Hilla city). Three tests were performed for each case based on changing the load treated by the chilled ceiling as (25%, 50% and 80%) respect to total cooling load and represented (26, 53, 85W/m2) respectively based on floor area. The temperature of chilled ceiling surface varied as (21.5, 19 and 16°C) and the air supply temperature similarly varied (19, 22, and 24.5 °C) respectively at constant air flowrate of (0.045m3/s). The results of the tests found that the effect of diffuser shape on the local age of air decreased with height, the maximum difference between two cases at the 0.1m level was about 49s while at 2.25m level it was only about 11s. The air exchange efficiency for the CC/DV system using a semicircle diffuser in the predetermined office space was higher by an average of 8.5% as compared with a similar system using a rectangular diffuser; this differential reduced about 3% at each increase in portion of cooling load treated by the chilled ceiling, however.

Differences in temperature measurement by commercial room temperature sensors: Effects of room cooling system, loads, sensor type and position

Thermostats control the heating, ventilation and air-conditioning (HVAC) system of a building based on the temperature they measure. Integration with communication network technologies allows wireless sensors to be used as the temperature sensing component of an HVAC system, increasing the flexibility in the selection and positioning of sensors. This study compared the temperature measuring performance of nine wireless and two conventional wired temperature sensors against reference air and globe temperature sensors in a climate chamber with a two-person office setup. The influence of sensor position, room cooling system (all-air or radiant with ventilation) and cooling load (33, 61 W/m2) was studied.Sensors placed at the same position had a measurement difference of up to 1.8 K, and assumptions about the type of temperature a sensor measures (air or globe) had the largest impact on the deviation from the reference temperatures. As opposed to common assumptions, conventional wired temperature sensors measured closer to globe temperature sensors and could be a possible indicator for the operative temperature. When the load settings were high, measurements in radiant system cases had smaller deviations from the reference sensors compared with all-air systems, due to the chilled surface compensating for the radiation from the loads.

Image and Ray Tracing Analysis of a Parabolic Dish Collector to Achieve High Flux on a Solar Volumetric Reactor

The need to achieve a uniform distribution of concentrated solar flux in the photovoltaic, thermal or any other receivers is a common problem; therefore, the optical characterization of the concentration system is necessary to determinate the physical characteristics of the receptors. In this work, a parabolic dish concentrator of 1.65x1.65 m2, developed by research from the University of Arizona, is optically characterized under normal operating conditions, also known as environmental conditions that refer to non-controlled conditions as solar radiation, environmental temperature and wind velocity that could affect slightly, by thermal and mechanical efforts, the distribution profiles of the concentrated solar radiation. The set used for the evaluation consisted of the parabolic mirror and Chilled Lambertian Flat Surface installed in the focal point on the optical axis of the mirror. The evaluation was divided into two parts: a theoretical part that consist on using ray tracing simulation and an experimental part that corresponds to image analysis. The used methodology in this work has been stablish in many researches, so this is a reliable method. The global optical error was 2.3 mrad under normal operating conditions.

Influence of sensible cooling load on indoor air distribution in an office room with ceiling cooling and mixing ventilation

A mixing ventilation system integrated with a ceiling cooling system is a potential advanced heating, ventilation and air conditioning system for modern office buildings with a high sensible cooling load. This paper presents an evaluation of the effect of sensible cooling load on the indoor air distribution in a typical office room with mixing ventilation and ceiling cooling. The vertical distributions of indoor air temperature, air velocity and contaminant (CO2) concentration were evaluated by the vertical air temperature difference, turbulence intensity and contaminant removal effectiveness. The results showed that when the chilled ceiling surface temperature was increased from 15.0°C to 23.0°C and supply air temperature was decreased from 22.0°C to 19.0°C, the average vertical air temperature difference, turbulence intensity and contaminant removal effectiveness were 0.2°C–0.3°C, 27%–32% and 0.53–0.81 as both internal and external sensible cooling loads were 41.5 W/m2. Moreover, these evaluation indices varied slightly as the external sensible cooling load was increased from 41.5 W/m2 to 69.5 W/m2, whereas they varied greatly as the internal sensible cooling load was increased from 41.5 W/m2 to 69.5 W/m2. Hence, the external sensible cooling load could slightly affect the indoor air distribution, whereas the internal sensible cooling load could clearly affect the indoor air distribution in an office room with mixing ventilation and ceiling cooling.

Solidification Characteristics and Segregation Behavior of Cu-15Ni-8Sn Alloy

The solidification characteristics and segregation behavior of Cu-15Ni-8Sn alloy were systematically investigated in the present study. The solidification characteristics were revealed with the assistance of a solidification quenching experiment, DTA analysis and Scheil simulation. The solidification microstructure of Cu-15Ni-8Sn alloy was characterized by SEM, and the results indicated that the as-cast microstructure of Cu-15Ni-8Sn alloy mainly consists of Sn-depleted α-Cu(Ni,Sn) matrix, Sn-rich γ phase and lamellar (α + γ) structure. It has been demonstrated that the solidification process begins with the nucleation and growth of primary Sn-depleted α1 phase ($$ L \to \alpha_{1} $$ at 1114 °C) and terminates with the divorced eutectic reaction ($$ L_{2} \to \alpha_{2} + \gamma $$ at 868 °C). During the subsequent cooling process, the discontinuous precipitation ($$ \alpha_{2} \to \alpha_{1} + \gamma $$) takes place in the temperature range from about 700 °C to 600 °C. In addition, the macrosegregation behavior of Sn in Cu-15Ni-8Sn alloy was investigated by adopting vertical unidirectional solidification and measuring the cooling curves at different positions. The results indicated that an inverse macrosegregation of Sn solute exists in the as-prepared ingot, which mainly segregates at the chill surface of the alloy ingot. Namely, the Sn content is higher than 8 wt pct at the chill surface and about 8 wt pct inside the ingot for Cu-15Ni-8Sn alloy.

How ice bridges the gap.

When supercooled dew droplets form on a chilled surface, the subsequent freezing process is driven by a fascinating phenomenon of propagating inter-droplet ice bridges. Here, we explore the range of conditions under which an individual ice dendrite can successfully bridge the gap from a frozen droplet to its nearest liquid neighbor. Ranging the droplet sizes from 1 μm-10 mm, we find that the criterion for ice bridging is purely geometric and independent of temperature, ambient humidity, and surface wettability. We model the growth of individual ice bridges as well as the global speed of percolating fronts sweeping across large droplet populations. We also give a dynamical law for dry zone formation when ice fails to bridge the gap.

Impact of chilled ceiling on indoor air distribution in a room with mixing ventilation

A mixing ventilation (MV) system integrated with a chilled ceiling (CC) cooling system will be a potential advanced heating, ventilation and air conditioning (HVAC) system in the modern buildings. This paper presented an experimental study concerning the effect of CC on the indoor air distribution with MV when the internal and external sensible cooling loads changed. The vertical distributions of indoor air temperature, air velocity and contaminant (CO2) concentration were evaluated by the vertical air temperature difference, turbulence intensity and contaminant removal effectiveness, respectively. The results showed that when chilled ceiling surface temperature ranged from 17.0 °C to 26.0 °C, the average vertical air temperature difference, turbulence intensity and contaminant removal effectiveness were 0.2 °C–0.4 °C, 30%–36% and 0.6–0.84 when both internal and external sensible cooling loads were 41.5 W/m2. Moreover, the ranges of these evaluation indices varied slightly when the internal or external sensible cooling load increased from 41.5 W/m2 to 69.5 W/m2. Hence, the chilled ceiling had a slight impact on the indoor air distribution in a room with mixing ventilation. It is interestingly found that the small vertical air temperature difference coincided with the large turbulence intensity and contaminant removal effectiveness with different internal or external cooling loads.

Impact of chilled ceiling in a high sensible cooling load room with underfloor air distribution

The use of an underfloor air distribution (UFAD) system integrated with a chilled ceiling (CC) cooling system can provide a potentially advanced heating, ventilation, and air conditioning (HVAC) system with high sensible cooling loads in modern office buildings. In this paper, an experimental study of the impact of CC in a room with a high sensible cooling load with UFAD was performed when the chilled ceiling surface temperature increased from 17.0 to 26.0 °C. The vertical distributions of indoor air temperature, air velocity, and pollutant (CO2) concentration were measured and evaluated by the vertical air temperature difference (VATD), turbulence intensity (TI), and contaminant removal effectiveness (CRE), respectively. The results showed that the average VATD, TI, and CRE were 0.1–0.9 °C, 4–40%, and 0.85–1.19, respectively, when the internal and external sensible cooling loads equal 41.5W/m2. These evaluation indices varied clearly when the internal sensible cooling load increased from 41.5 to 69.5W/m2, whereas they were almost the same when the external sensible cooling load increased from 41.5 to 69.5W/m2. The minimum CRE and air diffusion performance index (ADPI) coincided with the maximum heat removal effectiveness (HRE) under a constant cooling load condition. The results suggest that it is better to balance the energy consumption as well as indoor air quality and thermal comfort in a room with UFAD + CC.

Numerical Modeling of Heat and Specie Transfer in a Diffusion Dominated Continuum Model of Binary-Alloy Castings

A numerical modeling of diffusion-controlled heat and specie transfer using a source base method to determine evolution of liquid/solid fraction from energy equation both for constant densities in the phases and variable densities as a function of temperature and concentration was developed to predict macro-solute redistribution in binary alloy system. From the results, it is observed that there was a solute depleted zone near the chill surface and that, the source base method can be effectively implemented without the need for setting a large arbitrary value in determining the derivative of liquid fraction-temperature function . The cooling curve and the liquid volume fraction versus temperature profile shows a smooth transition from fully liquid to mushy zone and then to fully solid state, hence, adequate handling of the jump discontinuity was ensured. The liquid fraction-temperature relation outlined in this work is suitable for tracking the liquid/solid interface.

Falling water ice affinity purification of ice-binding proteins

Ice-binding proteins (IBPs) permit their hosts to thrive in the presence of ice. The ability of IBPs to control ice growth makes them potential additives in industries ranging from food storage and cryopreservation to anti-icing systems. For IBPs to be used in commercial applications, however, methods are needed to produce sufficient quantities of high-quality proteins. Here, we describe a new method for IBP purification, termed falling water ice affinity purification (FWIP). The method is based on the affinity of IBPs for ice and does not require molecular tags. A crude IBP solution is allowed to flow over a chilled vertical surface of a commercial ice machine. The temperature of the surface is lowered gradually until ice crystals are produced, to which the IBPs bind but other solutes do not. We found that a maximum of 35 mg of IBP was incorporated in 1 kg of ice. Two rounds of FWIP resulted in >95% purity. An ice machine that produces 60 kg of ice per day can be used to purify one gram of IBP per day. In combination with efficient concentration of the protein solution by tangential flow filtration the FWIP method is suitable for the purification of grams of IBPs for research purposes and applications.

Piezoelectric MEMS resonant dew point meters

This work presents a new class of dew point meters using Thin-film Piezoelectric-on-Silicon (TPoS) resonators. The proposed approach utilizes microelectromechanical resonant balances coupled with a cooling element in which a standard chilled surface technique is used to deposit layers of moisture on the resonator surface. Reducing the temperature causes the resonance frequency of the resonator to increase due to its negative temperature coefficient of frequency (TCF). However, when the temperature of the cooled resonator reaches the dew point (DP) of the surrounding environment, a thin layer of frost starts to form on the resonator surface causing an abrupt negative shift in the resonant frequency due to mass-loading. Therefore, the resonance frequency will be at its maximum value when the dew or frost starts to form i.e., at DP. A custommade setup which includes a MEMS dew point sensor head, a dew point generator and a measurement/control/data collection interface is assembled to enable automated measurements. Using the proposed setup, dew points as low as -41 °C i.e., a dry air containing 145 ppmv H2O, are measured with a standard deviation of 0.1 °C. Long-term reliability and accuracy of the sensors presented here are investigated by conducting 35,000 cycles of uninterrupted measurements. The long-term stability, precision, and durability of the presented dew point meters make them suitable solutions for a wide variety of industrial applications.

Metallurgical characterization of melt-spun ribbons of U-5.4 wt%Nb alloy

The microstructures and micro-mechanical properties of the melt-spun ribbons of U-5.4 wt%Nb alloy were characterized using optical microscopy, scanning electron microscopy, X-ray diffraction and nanoindentation. Observed variations in microstructures and properties are related to the changes in ribbon thicknesses and cooling rates. The microstructures of the melt-spun ribbon consist of fine-scale columnar grains (∼1 μm) adjacent to the chill surface and coarse cellular grains in the remainder of the ribbon. In addition, the formation of inclusions in the ribbon is suppressed kinetically due to the high cooling rate during melt spinning. Compared with the water-quenched specimen prepared by traditional gravity casting and solution heat treatment, the elastic modulus values of the U-5.4 wt%Nb alloy were examined to vary with grain size and exhibited diverse energy dissipation capacities.

Chilling effect on hardness and microstructural behavior of grey iron

The presentation in this paper briefs the experimental results obtained for evaluating the hardness and comparing with its microstructural pattern. Mild steel chills (MSC) are used to check the chilling effect. The results show that chill position influences the hardness of cast iron. Increase in hardness is observed by placing MSC at different locations. Specimens were prepared for microstructural examination using scanning electron microscope (SEM). Microstructure analysis was also carried out to evaluate the graphite morphology and carbide content using material plus and imageJ analyzer. Longer graphite flakes fare found in normally manufactured grey cast iron (GCI) without using MSC. Low size graphite’s and formation of carbides in the form of needles are seen near the chilled end surface. Effect of MSC position on hardness is studied and analyzed using image analyzers.

Experimental investigation and data-driven regression models for performance characterization of single and multiple passive chilled beam systems

The performance of passive chilled beams is characterized in this study to understand their physical behavior when applied in real indoor environments. Two full-scale experimental studies were conducted to map the performance of passive chilled beams in two different experimental settings: (i) single passive chilled beam testing in a controlled laboratory environment and (ii) multiple passive chilled beams testing in a real open plan office setting. The experimental results were then used to develop regression models for predicting the total cooling capacity and chilled surface temperature of single and multiple passive chilled beams, as a function of water flow rate, water supply temperature, air temperature above the chilled beam and area-weighted uncooled surface temperature in the space. The developed models showed good agreement with experimental results and can be used in building energy modeling tools for system simulation using passive chilled beams. Finally, it was found that the conventional method of predicting the total cooling capacity of a passive chilled beam from individual beam laboratory tests or manufacturers’ catalogs may significantly underestimate the system performance in multi-unit configurations. These differences could influence optimal system sizing and commissioning and should be considered in future studies.

Effect of cerium addition on casting/chill interfacial heat flux and casting surface profile during solidification of Al-14%Si alloy

In the present investigation, Al-14 wt. % Si alloy was solidified against copper, brass and cast iron chills, to study the effect of Ce melt treatment on casting/chill interfacial heat flux transients and casting surface profile. The heat flux across the casting/chill interface was estimated using inverse modelling technique. On addition of 1.5% Ce, the peak heat flux increased by about 38%, 42% and 43% for copper, brass and cast iron chills respectively. The effect of Ce addition on casting surface texture was analyzed using a surface profilometer. The surface profile of the casting and the chill surfaces clearly indicated the formation of an air gap at the periphery of the casting. The arithmetic average value of the profile departure from the mean line (Ra) and arithmetical mean of the absolute departures of the waviness profile from the centre line (Wa) were found to decrease on Ce addition. The interfacial gap width formed for the unmodified and Ce treated casting surfaces at the periphery were found to be about 35µm and 13µm respectively. The enhancement in heat transfer on addition of Ce addition was attributed to the lowering of the surface tension of the liquid melt. The gap width at the interface was used to determine the variation of heat transfer coefficient (HTC) across the chill surface after the formation of stable solid shell. It was found that the HTC decreased along the radial direction for copper and brass chills and increased along radial direction for cast iron chills.

Controlling condensation and frost growth with chemical micropatterns.

In-plane frost growth on chilled hydrophobic surfaces is an inter-droplet phenomenon, where frozen droplets harvest water from neighboring supercooled liquid droplets to grow ice bridges that propagate across the surface in a chain reaction. To date, no surface has been able to passively prevent the in-plane growth of ice bridges across the population of supercooled condensate. Here, we demonstrate that when the separation between adjacent nucleation sites for supercooled condensate is properly controlled with chemical micropatterns prior to freezing, inter-droplet ice bridging can be slowed and even halted entirely. Since the edge-to-edge separation between adjacent supercooled droplets decreases with growth time, deliberately triggering an early freezing event to minimize the size of nascent condensation was also necessary. These findings reveal that inter-droplet frost growth can be passively suppressed by designing surfaces to spatially control nucleation sites and by temporally controlling the onset of freezing events.