Chilled Air Research Articles

Tool Life and Surface Roughness of FCD 700 Ductile Cast Iron when Dry Turning Using Carbide Tool

Machining is one of the most important processes in producing automotive component such as difficult-to-cut FCD700 cast iron grade. Efforts are continuously made to improve the machining technique for the benefit of human and environment. This paper presents an environmental friendly when turning FCD700 cast iron using carbide tool in the absent of coolant. The turning process was carried out in three medium of dry conditions i.e. without air, chilled air and normal air. The turning parameters studied were cutting speed (100-300 m/min), feed rate (0.1-0.4 mm/rev), and depth of cut (0.2-2.0 mm). Result shows that the average surface roughness (Ra) was greatly affected by the feed rate and the effect of depth of cut was negligible. Low Ra value was produced when using high cutting speed, especially at medium air temperature of 10 deg C. Whereas when turning at high depth of cut and high feed rate, the tool life was shorten drastically. In addition, the cutting speed was significantly affecting the tool life. The tool life was found to be inversely proportional with the cutting speed. The longest tool life was obtained at cutting speed of 100 m/min, feed rate of 0.15 mm/rev, depth of cut of 0.2 mm and temperature of -2 deg C. Generally, chilled air at temperature of -2deg C will increase the tool life, but the Ra obtained was deteriorated when compared at higher temperature of chilled air and without air cutting environment. Therefore, these findings can be used a guide depending on the preference of the user, either to obtain a better tool life or Ra value.

Heat transfer enhancement in cool-thermal discharge systems from ice melting with time–velocity variations

A mathematical model for the cool-thermal discharge systems which produce chilled air by melting ice to supply on-peak daytime air-conditioning needs under time-velocity variations and external recycle was developed. The model resolves the moving liquid–solid interface problem with the integral boundary-layer analysis method. For specified target of the outlet air temperature, time variation of the air velocity can be theoretically predicted for the given ambient air inlet temperature functions. The heat transfer efficiency can be improved by employing the external recycle design under the expense of power consumption. The analysis indicates that the recycle effect is more significant for the case with higher outlet air temperature target. Besides, optimal reflux ratio exists for the analyzed system.

Genotype × environment interactions for chilling tolerance of rice recombinant inbred lines under different low temperature environments

Chilling injury is one of the major environmental stresses in rice cultivation in high-latitude and high-altitude regions. In this study, we cultivated a set of recombinant inbred lines (RILs) derived from Milyang 23 ( indica)/Tong 88-7 ( japonica) crosses in Kunming (high-altitude location), Yanji (high-latitude location), Chuncheon (cold water irrigation), and Suwon (normal) to evaluate the genotype × environment (G × E) interactions for chilling tolerance. RILs were the most severely damaged under the natural chilling air temperatures in Kunming. Significant G × E interactions in all measured agronomic traits were detected, and thus, the additive main effects and multiplicative interaction (AMMI) statistical model was applied to dissect the G × E interactions. The biplots of grand mean and IPCA1 (interaction principal component axes) of chilling-related traits accounted for most of the total treatment sums of squares. The IPCA scores of spikelet fertility and phenotypic acceptability were relatively smaller in Chuncheon than in Yanji and Kunming, implying that the screening for chilling tolerance with cold water irrigation in Chuncheon was more stable, whereas the Yanji and Kunming plantings were more sensitive to G × E interactions for chilling tolerance. These results demonstrate that multi-locational screening should be the best strategy for developing widely adaptable chilling-tolerant varieties in rice.

A review of cryogenic cooling in high speed machining (HSM) of mold and die steels

Metal cutting generates heat which influences the quality of a finished product, the force needed in cutting as well as limiting the life of the cutting tool. There are various attempts by researchers all over the world to understand the mechanism and theory behind the temperature built-up during machining in order to achieve optimized machining procedure and best workpiece results. Theories are developed, experiments conducted as well as models and simulations proposed. The latest attempt in metal cutting cooling is through the use of chilled air, cryogenic cooling. A Ranque-Hilsch vortex tube (RHVT), a device with no moving parts, is used for this low-cost refrigeration purpose. Backgrounds of RHVT, various studies conducted on it, its performance and applications are discussed for the high speed metal cutting cooling application for mold and die steels. Option for future research is proposed. Key words: High speed machining, end milling, cryogenic cooling, vortex tube, mold and die.

에어컨 임펠러의 파손 거동에 관한 실험 및 수치적 연구

An air conditioner impeller has been used to suck the warm air and to blow the chilled air by the centrifugal force induced from the rotation of it. To check the possibility of the fracture due to resonance, both numerical and experimental approach was carried out. For the structural analysis, the commercial code ANSYS based on the Finite Element Method was employed. The possibility of the fracture is the resonance between the natural frequency of impeller and characteristic frequency due to the aerodynamic forces. Experiment was carried out to see the natural frequency and numerical analysis based on the Vortex Element Method is performed to get the characteristic frequency. Comparing the natural frequencies that are calculated as described, we believe that resonance occurs.

Radiant frost tolerance in pulse crops—a review

Radiant frost is a major abiotic stress, and one of the principal limiting factors for agricultural production worldwide, including Australia. Legumes, including field pea, faba bean, lentil and chickpea, are very sensitive to chilling and freezing temperatures, particularly at the flowering, early pod formation and seed filling stages. Radiant frost events occur when plants and soil absorb the sunlight during the day time and radiate heat during the night when the sky is clear and the air is still. Dense chilled air settles into the lowest areas of the canopy, where the most serious frost damage occurs. The cold air causes nucleation of the intracellular fluid in plant tissues and the subsequent rupturing of the plasma membrane. Among the cool season grain legume crops, chickpea, lentil and faba bean and field pea are the most susceptible to radiant frost injury during the reproductive stages. The more sensitive stages are flowering and podding. Frost at the reproductive stage results in flower abortion, poor pod set and impaired pod filling, leading to a drastic reduction in yield and quality. In contrast, in the UK and European countries, frost stress is related to the vegetative stages and, in particular, the effects of frost have been studied on cotyledon, uni/tri-foliolate leaf and seedling stages during the first few weeks of growth. Few winter genotypes have been identified as frost tolerant at vegetative stages. Vegetative frost tolerance is not related to reproductive frost tolerance, and hybrids from the vegetative frost-tolerant genotypes may not necessarily be tolerant at the reproductive stage. Tolerance to radiant frost has an inverse relationship with plant age. In the field, frost tolerance decreases from the vegetative stage to reproductive stage. Unlike wheat and barley, it is difficult to analyse and score frost damage in grain legume crops due to the presence of various phenophases on one plant at the reproductive stage. The extent of frost damage depends on the specific phenophases on a particular plant. However, current studies on genetic transformation of cold tolerant gene(s), membrane modifications, anti-freeze substances and ice nucleating or inhibiting agents provide useful information to improve our current understanding on frost damage and related mechanisms. The effects of frost damage on yield and grain quality illustrate the significance of this area of research. This review discusses the problem of radiant frost damage to cool season legumes in Australia and the associated research that has been carried out to combat this problem locally and worldwide. The available literature varies between species, specific climatic conditions and origin.

Sustainable design for audio, video, and broadcast facilities.

Meeting sustainable design goals in facilities that include technical production spaces for audio, video, or broadcast presents special challenges to the design and construction team. Materials selections and sources affect not only the acoustical finishes, but may also influence larger building systems. Daylighting goals must be balanced with appropriate acoustical isolation. The integration of alternative chilled air delivery systems and lighting sources must be weighed against critical technical function. As a result, the acoustician’s role should expand to include an understanding of the sustainability goals, the impact of acoustical design recommendations, changes to the specification process, and the necessary coordination efforts with the rest of the participants. Examples from radio and television broadcast facilities, music recording studios, and performance spaces are given.

Impact of cooling method and incoming sheet quality on final part surface quality in thick sheet paint film thermoformed parts

AbstractThick sheet, “dry paint” film parts were thermoformed using different cooling methods and sheet temperatures to determine whether these two parameters had a direct effect on the surface quality of the final part. Although some thermoformers have claimed that applying chilled air after forming “dry paint” film parts improves the gloss of the parts, the data from this study showed that application of chilled air did not have an effect on either the parts' initial gloss or their gloss after time‐dependent hazing. The critical factor in maintaining surface quality in these parts was the maximum temperature reached by the “dry paint” film during heating. In addition, analysis of the data taken on the sheet prior to forming versus that taken on the part after forming demonstrated the importance of validating the surface quality of the as‐received sheet prior to conducting process versus appearance experiments. On the basis of these findings, a recommendation is made for incoming sheet surface quality levels for both process development studies and production applications. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

Heat Transfer Prediction of Recycle Effect for Improved Device Performance in Cool-Thermal Discharge Systems

This research studies the heat transfer characteristic of an unsteady close-contact melting on a flat plate in the cool-thermal discharge systems with external recycle, develops the mathematical model theoretically to simulate the conduction-convection heat-transfer phenomena, and calculates the theoretical prediction of the outlet chilled air temperature by solving the energy balance associated with integral boundary-layer analysis. It is found that the recycle effect can enhance the average Nusselt numbers and heat-transfer efficiency improvement effectively. Three numerical examples of inlet ambient air temperature are illustrated to compute the chilled air temperature, average Nusselt numbers and heat-transfer efficiency with three specified volumetric flow rate and three traversed length of the ambient inlet air as parameters.

Workpiece surface integrity of Ti-6-4 heat-resistant alloy when employing different polishing methods

The use of heat-resistant titanium alloys for the manufacture of gas turbine engines components for aerospace/energy applications has become a routine exercise. However, components with complex designs specifications might pose manufacturing challenges especially when finishing processes are needed to enable their compliance with tight industrial standards for workpiece surface integrity. Information on polishing processes for such sensitive industrial applications is scarce. The paper reports on the influence of polishing methods/strategies on the quality and integrity of workpiece surfaces obtained after different polishing methods on Ti-6-4 heat-resistant alloy. The research focuses on identifying an “optimised” polishing strategy that will enable finishing a family of targeted safety critical aero-engine (TSCA-E) components, on which the simultaneous fulfillment of the following technological/quality criteria is required: (i) tool life to enable polishing of minimum of workpiece surface areas that are related with specific features of TSCA-E components; (ii) removal of pre-machining (i.e. milling) marks while obtaining required surface finish; (iii) generation of damage-free polished surfaces, i.e. high workpiece surface integrity. Two (belt; bob) polishing methods with various media/grades (Al 2O 3, SiC, polycrystalline diamond) of the abrasive materials in conjunction with three cutting media (dry; chilled air; minimum quantity of lubricant) have been tested to address the overall finishing of TSCA-E components. Although significant differences in tool life performance exist between belt and bob polishing methods, both are capable to meet the requirements of minimum workpiece surface coverage if “optimised” operating parameters are employed. When considering surface roughness criteria, Al 2O 3 belts and SiC bob tools were found appropriate. Furthermore, surfaces obtained with these tools when employing cooling media (chilled air for belt polishing and minimum quantity of lubricant (MQL) for bob polishing) showed compliance with the tight requirements of industrial standards for workpiece surface integrity (metallurgical damage and residual stresses). This proved that belt and bob polishing methods can be employed in conjunction as “hybrid” technique to enable automated overall finishing of complex geometrical components.

Evaluation of a Recirculation Scheme for Ice Storage Melting with Air as the Working Fluid

A new device has been developed for producing chilled air in the heat discharge flux for a cool-thermal discharge system with melt removal and external recycling, resulting in substantial improvement in the heat transfer rate. A mathematical formulation is developed using the integral boundary-layer analysis associated with the moving boundary condition. The theoretical predictions are presented graphically and compared to that in the device without external recycling and with the same working dimensions under a specified volumetric air flow rate. Considerable improvement in heat transfer is obtainable by employing the recycling operation instead of using the device without external recycling. The effects of the volumetric air flow rate and recycling ratio on the heat transfer efficiency enhancement and power consumption increment are also discussed. This study provides an improved heat-transfer efficiency design for a cool-thermal discharge system. The mathematical treatment presented in this study can be applied to any heat convection-conduction problems with moving boundaries.

全空気雪冷房システムの温度の制御に関する基礎研究（全空気方式温度β制御の場合）

Energy, food, the environment are basics of the life. The snow can contribute to these many problems to have greatly even if not decisive. The snow/ice as the cold heat source has a remarkable substitute effect for fossil energy as energy. And there is not the discharge of the warm temperature from a system depending for a mechanical refrigerating cycle, and there is an effect for environmental safeguard without using refrigerants such as Freon with this snow air conditioner. In this study, the authors have suggested many systems of the air-conditioner in which the snow is used for cold heat source, and the authors call them all-air type snow air-conditioner and have been analyzing the performance of them. This snow air-conditioner is made by simple construction of a snow storage room, a blower and a dumper for regulation of air flow. The temperature/humidity of the conditioning area is controlled by the mixing hot return air and chilled air from the snow storage room. In this report, the authors discussed on the simplest system among many all air type snow air-conditioning ones. In this system, only the temperature in the air-conditioning area is controlled and this temperature is adjusted by mixing with the circulation hot air through a dumper and the cold air cooled by the snow, and the authors call this system all-air type temperature control β system. In this paper, the system is classified into different three models for the analysis, and characteristics of them are investigated analytically and discussed.

The influence of secondary refrigerant air chiller U-bends on fluid temperature profile and downstream heat transfer for laminar flow conditions

This paper describes numerical investigations, using computational fluid dynamics, conducted to examine the heat transfer mechanisms by which air-chiller U-bends cause enhanced downstream internal convection, where single phase secondary refrigerants under laminar conditions are employed as the heat exchanger fluid. The numerical model, created using FLUENT, consists of a single heat exchanger tube pass incorporating an inlet pipe, a U-bend and an outlet pipe. The model was validated using experimental data from the literature. Numerical investigations indicate that within the U-bend, secondary flows partially invert temperature profiles resulting in a significant localised decrease in average fluid temperature at the pipe surface. As a result, downstream heat transfer enhancement is observed, the magnitude of which can exceed that typical of a pipe combined entry condition in some circumstances by greater than 20% for up to 20 pipe diameters downstream. Heat transfer enhancement was found to increase with increasing U-bend radius, but to decrease with increasing heat exchanger pipe radius and internal Reynolds number. A simple technique based on quantification of the degree of temperature inversion at the U-bend is proposed which provides a mechanism by which heat transfer enhancement can be estimated.

An Inverse Estimation Method for Surface Film Conductance During Cooling of Fish Packages

A temperature history detected by measuring sensor, along with other relevant system’s parameters have been used to predict the surface film conductance through transient temperature measurements in fish flesh samples during their cooling in a chilled air duct at a constant temperature of 1°C. The Inverse Heat Conduction Problem (IHCP) solution was performed by using the sequential function specification method to estimate heat flux, which was then utilized to solve the direct problem for the temperature distribution at any position including at the sensor position on the fish sample using Crank-Nicolson implicit finite difference scheme. The predicted and measured temperature distribution profiles were compared numerically, yielding good agreement indicating the accuracy of the present approach in calculating surface film conductance.

Transient heat conduction in cool-thermal discharge systems with producing chilled air under constant discharge fluxes and external recycle

The mathematical model of the heat transfer phenomena in the cool-thermal discharge systems with external recycle and constant discharge flux has been derived theoretically in this study. The chilled air was produced by the ambient air flowing through the ice layer surface and water layer surface after the ice melting. The conduction–convection heat-transfer problem with a moving boundary was solved using the energy balance associated with integral boundary-layer analysis. The effects of recycle operation on the outlet chilled air temperature, air mass velocity and average Nusselt numbers for three numerical cases with three different discharge fluxes were discussed. The results show that a considerable device performance improvement was obtained by employing external recycle in a cool-thermal discharge system.

Effects of Actively Cooled Coolant for Grinding Ductile Materials

An active cooling approach for coolant during ductile material grinding is proposed and examined. The aim is to enhance surface quality and to enhance productivity. The problem associated with the cryogenic cooling approach and the one with the chilled air approach are addressed. An active cooling prototype was developed utilizing a compact heat pump design, which is easy to use, movable, and can be easily fitted into different type of machine designs with relatively low costs. The system is based on the use of forced convection of the heat generated during the machining process. Experimental and computational studies of the effects of actively cooled coolant for grinding ductile materials are carried out. The experimental results show that the use of actively cooled coolant is able to improve surface quality by up to 29.95% on average in terms of surface roughness Ra. Computational testing results show that the heat can be taken away more effectively by using the proposed approach. The results of optical and SEM examinations also confirmed that the proposed approach is advantageous.

雪山横穴空洞式熱交換システムの開発に関する研究（イチゴ育苗ハウスへの雪冷房システムの利用）

In the cold climate and deep snow regions in the winter season of Japan, it has been advanced to utilize the snow as the cold energy source for air conditioning in summer. In this study, a system to extract the chilled air directly from the snow mound of several thousand ton through a horizontal borehole in it is proposed. Some troubles caused by mud in the snow melting water can be avoided by means of transferring heat from the melting water to the supply air. The thermal design for the heat exchange of this system is carried out by theoretical means and verified by the practical experiment. According to results of the experiment, it is proved sufficiently that the theoretical thermal design method predicts appropriate values of the system. The snow cooling system has been applied to a strawberry seedling greenhouse with 270m2 as a practical experiment. And predicted values and experimental results are 9.90 kW as the cooling power gained from the snow mound using two blowers needed 0.8 kW totally.

Recycle Effect on Cool-Thermal Discharge Systems from Ice Melting with Chilled Air Produced Under Complete Melt Removal and Specified Heat Fluxes on the Boundary

This article discusses of the recycle effect on the heat transfer for producing chilled air in cool-thermal discharge systems by ice melting under constant heat flux and melt removal. The outlet chilled air temperature is investigated, and the heat transfer behavior coupled with moving boundary by direct contact of the ambient air at the ice surface under melt removal is analyzed. The required air mass velocity is estimated and indicates that the application of recycle effect on cool-thermal discharge systems enhances the heat transfer rate and thus the lower outlet chilled air temperature during on-peak daytime hours. Installing cool-thermal discharge systems with external recycle, at larger convective heat transfer rate than for a device without recycle, can often increase the discharge capacity of the existing system.

Simplified Thermal Model of Spaces Cooled with Combined Positive Displacement Ventilation and Chilled Ceiling System

An improved plume-multilayer model was developed and validated to represent thermal transport in enclosures conditioned by radiant cooling and displacement ventilation systems. A novel approach was developed to estimate wall plumes for non-isothermal surfaces using the similarity solution derived for power law representation of temperature difference between the room air and the wall. The nonuniform wall plume flow rates predicted by the model agreed well with flow rates in an enclosure produced by computational fluid dynamics (CFD) simulations. Wall plumes associated with a nonuniformly heated wall with varying temperature difference between the wall and the air were found to be substantially higher than the plume predicted by isothermal wall correlation. The wall plume model is integrated with a multilayer space thermal model to predict the stratification height in the space, the vertical distribution of wall and air temperatures as a function of the chilled ceiling temperature and space air supply conditions. The plume-multilayer model results were compared with results of three-dimensional CFD simulations using commercially available software. Three test cases were considered for the simulations at cooling loads of 40 W/m2 (12.7 Btu/h·ft2), 67 W/m2 (21.2 Btu/h·ft2), and 100 W/m2 (31.7 Btu/h·ft2) and supply airflow rates per unit area of 22.5 (1.2 ft3/min·ft2), 30 (1.6 ft3/min·ft2), and 37.5 m3/h·m2 (2.1 ft3/min·ft2), respectively. The vertical wall and average air temperatures for each layer agreed well with the results of the plume-multilayer model, showing maximum errors in values of average air temperature of 0.13°C (0.23°F), 0.37°C (0.66°F), and 0.3°C (0.54°F) for the low, medium, and high load cases, respectively. The simplified model accurately predicted the stratification height at a maximum error of ±0.05 m (0.16 ft) in the three test cases. The stratification height is overestimated by 35% if wall plumes are neglected in the plume-multilayer model.

The recycle-effect on cool–thermal discharge systems under melt removal and flow rate variations

A mathematical model to simulate the production of chilled air during on-peak power consumption hours in cool–thermal discharge systems with external recycle under melt removal and varied flow rate of flowing air has been developed theoretically. Equations have been derived for estimating the controlling air flow rate when the outlet chilled air temperature is specified. Three cases of inlet ambient temperatures of flowing air were illustrated to study the influence of recycle ratio on the performance improvement of cool–thermal discharge systems, the volumetric flow rate variations and Nusselt number increment due to a larger convective heat transfer rate were also delineated.