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This paper presents experimental results on rapid freezing of water droplets injected into a low temperature environment. A heat balance method was applied to determine the ratio of the water droplets frozen at the collection after the airborne time. The experimental results show that rapid freezing of water droplets could be achieved within three seconds of airborne time. Droplet size distribution of the frozen water droplets after collection was estimated. Heat transfer during the airborne time was calculated with consideration of the droplet size distribution. At attempt was taken to compare the heat transfer obtained with some previous studies on heat transfer of spherical objects in air. The research results show that droplet size distribution is important for the prediction of heat transfer of water droplets traveling in air. The results presented in this study contribute to the understanding of heat transfer of water droplets injected into a low temperature air.

This study uses a novel concept of capacity coupling of chiller-cooling tower system to investigate the system energy performance. System performance factor (SPF) of the chiller-cooling tower system is used in the analysis. A regression function is obtained for hourly reset of condensing water temperature so to achieve maximum SPF. The regression function includes parameters such as ambient wet bulb temperature, chiller load ratio, tower capacity ratio, and a dimensionless relative efficiency of chiller and cooling tower. The regression function has an R2 close to 1 compared to the computed results. It is found that for capacity coupling ratio of 1.1 ∼ 1.6, SPF would increase by about 3 ∼ 6% compared with a typical base control. The effect of wet air return is presented as an equivalent wet bulb temperature. It has been found that SPF would decrease significantly when higher equivalent wet bulb temperature occurs at the tower inlet.

Multi-cone diffusers have good air distribution characteristics in cooling applications. However, surface condensation has been a problem impeding the use of multi-cone diffusers in cold air applications. An experimental study and a computer analysis are presented to show the causes of surface condensation on a multi-cone diffuser when distributing cold air. This study also attempts to alter the flow field characteristics near the diffuser cone surfaces by using an open inner cone with an insert that has a porous structure. Computer analysis has shown that the resultant airflow from the inner cone will repel the entrained room air away from the diffuser, thus preventing contact of the more humid air with the cold cone surfaces. The analysis has also shown that the altered flow field will cause the air dew point temperature in the vicinity of the diffuser to be lower than the temperature of the cone surfaces. Inserts with different porosities that were effective in preventing surface condensation were tested and the results are presented. These results indicate that the proposed airflow control method is effective in preventing surface condensation.

The performance of fan coil heat exchangers with smooth continuous aluminum fins on three rows of copper tubes was studied for heat and mass transfer, and for dehumidifier performance. Such fan coil units are common in industrial situations. Experiments were conducted to measure the heat and mass transfer performance for various air velocities and water flow rates. The results are presented below. Published correlations were used for an analysis of heat and mass transfer. Discrepancies between the calculated and the experimental results resulted because the calculated results were made from published correlations most commonly with more than six rows. The experimental results also showed an inadequacy of analysis in predicting the dehumidification capacity of finned tube heat exchangers. A revised correlation equation for heat exchangers of this type is proposed.

Interleukin-27 (IL-27) has a pleiotropic role either as a pro-inflammatory or anti-inflammatory cytokine in inflammatory related diseases. The role and involvement of IL-27 during malaria was investigated and the effects of modulating its release on the production of major inflammatory cytokines and the histopathological consequences in major affected organs during the infection were evaluated. Results showed that IL-27 concentration was significantly elevated throughout the infection but no positive correlation with the parasitaemia development observed. Augmentation of IL-27 significantly elevated the release of anti-inflammatory cytokine, IL-10 whereas antagonising and neutralising IL-27 produced the opposite. A significant elevation of pro-inflammatory cytokines (IFN-γ and IL-6) was also observed, both during augmentation and inhibition of IL-27. Thus, it is suggested that IL-27 exerts an anti-inflammatory activity in the Th1 type response by signalling the production of IL-10 during malaria. Histopathological examination showed sequestration of PRBC in the microvasculature of major organs in malarial mice. Other significant histopathological changes include hyperplasia and hypertrophy of the Kupffer cells in the liver, hyaline membrane formation in lung tissue, enlargement of the white and red pulp followed by the disappearance of germinal centre of the spleen, and tubular vacuolation of the kidney tissues. In conclusion, it is suggested that IL-27 may possibly acts as an anti-inflammatory cytokine during the infection. Modulation of its release produced a positive impact on inflammatory cytokine production during the infection, suggesting its potential in malaria immunotherapy, in which the host may benefit from its inhibition.

This study investigates experimentally the performance of radiant floor cooling modules. Different radiant cooling modular units with embedded chilled water piping were tested for cooling performance. The effects of pipe pitch and also the effects of extended fins were tested. The results of the experiments show that the modular design of radiant floor used has low heat resistance between the chilled water and the radiant cooling surface. Mean radiant temperature was analyzed to measure the cooling comfort performance. An increase of radiant cooling surface area was found to be important for effective radiant heat exchange. Moreover, the larger the temperature difference between the radiant surface and the walls, higher rate of radiant cooling can be achieved. The cooling intensity in terms of per unit area was tested to be as high as 60 W/m2. In conclusion the radiant floor cooling modular units are effective to remove sensible heat and provide comfort cooling. In practice it can be supplemented with lower humidity outdoor air supply for the removal of latent heat.

Desiccant dehumidifiers have been used in industrial and commercial processes to provide air of lower relative humidity than can be achieved readily with vapor compression equipment. Parallel passage rotary wheel regenerators with silica gel on the passage walls are used as dehumidifiers for air-conditioning applications. This study presents an investigation of transient mass transfer in a parallel passage dehumidifier with a thin layer of silica gel on the passage walls. A two-film resistance model was used to approximate the overall transfer resistance between the process air and the solid desiccant. Isothermal transient mass transfer experiments using parallel passages with silica gel coated walls were conducted and analyzed. It was found that the two-film model agrees with the experimental results within the experimental accuracy. Although only silica gel was used in this study, the results may be extended to other solid desiccants.

Experimental measurements are reported which indicate the relationship between particle loading and dryout heat flux for pool boiling from a horizontal surface covered with a mixture of water and light particles. This study specifically examines the dryout conditions for particles which have low settling velocities and are easily suspended by the bubble-generated turbulence in the liquid pool above the surface. Dryout data are presented for pool boiling of mixtures of saturated water and glass beads with diameters ranging from 0.105 mm to 0.475 mm. Data are also presented for methanol and glass beads. At high particle loadings, a portion of the load is suspended, while the remainder forms a layer on the surface. The dryout mechanism apparently is similar to the Helmholtz instability mechanism previously identified as the cause of dryout in shallow beds of heavy particles. However, the suspension of particles in the liquid pool produces very unusual trends in the dryout data. In particular, conditions have been observed in which a decrease in the heat flux can cause dryout to occur. An approximate theoretical model of the particle suspension mechanism is proposed and used to predict the dryout conditions for very light particles. This model explains the trends in the data and predicts dryout conditions which compare favorably with the experimental results for very light particles.

Experimental data are presented which indicate the effects of a thin layer of unconfined particles on saturated pool boiling heat transfer from a horizontal surface. Results are presented for two different types of particles: (1) 0.275 and 0.475-mm-dia glass spheres which have low density and thermal conductivity, and (2) 0.100 and 0.200-mm-dia copper spheres which have high density and thermal conductivity. These two particle types are the extremes of particles found as corrosion products or contaminants in boiling systems. To ensure that the surface nucleation characteristics were well defined, polished chrome surfaces with a finite number of artificial nucleation sites were used. Experimental results are reported for heat fluxes between 20 kW/m{sup 2} and 100 kW/m{sup 2} using water at 1 atm as a coolant. For both particle types, vapor was observed to move upward through chimneys in the particle layer, tending to fluidize the layer. Compared with ordinary pool boiling at the same surface heat flux level, the experiments indicate that addition of light, low-conductivity particles significantly increases the wall superheat, whereas addition of heavier, high-conductivity particles decreases wall superheat. Heat transfer coefficients measured in the experiments with a layer of copper particles were found to be as muchmore » as a factor of two larger than those measured for ordinary pool boiling at the same heat flux level. The results further indicate that at least for thin layers, the boiling curve is insensitive to layer thickness. These results are shown to be consistent with the expected effects of the particles on nucleation, fluid motion, and effective conductivity in the pool at or near the surface. The effect of surface nucleation site density on heat transfer with a particle layer present is also discussed.« less