Chung Min Liao

Characterizing the performance of alternative evaporative cooling pad media in thermal environmental control applications

Abstract This paper outlines the test procedure and describes how the alternative pad performance is affected by pad thickness and pad materials in the thermal environmental control applications. Many experimental pads were tested including one made of nonwoven fabric perforated pad and one made of coir fiber material. A wind tunnel experiment was performed to obtain equations for heat and mass transfer coefficients for the evaporative process through various thickness of alternative pad media. Heat and mass transfer coefficients are nondimensionalized and curve fitted to yield the working equations: (1) coir fiber pad: hH / hM =, 0.32paCPaLe,2/3 (Les /Le,)1/4, and (2) nonwoven fabric pad: hH / hM , = 1.899paCPaLe,2/3 (Les / Le,)1/4; where hH , is heat transfer coefficient, hM , is mass transfer coefficient, pa , is air density, Cpa , is specific heat of air, Le, is Lewis number, and Les ,, is Lewis number at water temperature. A determination for cooling efficiency in a wind tunnel system is also develop...

Quantitative prediction of traffic pollutant transmission into buildings.

Abstract An integrated air quality model that combines a CFD model and multi-room pollutant transport model has been developed to study the effect of traffic pollution on indoor air quality of a multi-room building located in close proximity to busy roads. The CFD model conducts the large eddy simulation of the three-dimensional turbulent flows and pollutant transport processes in outdoor, whereas the multi-room pollutant transport model performs zonal airflow and pollutant transport in indoor. The integrated model is verified with available field measurement of traffic-induced CO concentrations. Twelve scenarios of numerical experiments for various configurations of window openness are carried out to study the effects of the air change rate and the outdoor pollutant dispersion on indoor air quality. It is concluded that the windward side opening is a significant factor contributing to indoor air quality. Using air inlets on the sideward and leeward envelopes simultaneously can effectively lower the daily mean and peak indoor levels of traffic pollutants and maintain a desirable air change rate.

Modeling dust-borne odor dynamics in swine housing based on age and size distributions of airborne dust

Abstract In this paper, we derive a mathematical model characterizing the adsorption of odor on the surface of airborne dust in swine housing based on the concept of homogeneous surface diffusion of a complete mixing airflow system. The philosophy of the paper is to incorporate the age and size distributions of airborne dust into the diffusion model for evaluating the dust-borne odor dynamics in a ventilated airspace. A closed-form solution is presented here to allow a series of numerical experiments for investigating the effects of adsorption characteristics, the mean age of airborne dust, surface effective diffusivity, and dust particle size on the adsorption of odor to the existing aerosol. Results obtained show that the most favorable performance of a ventilation system in reducing odor concentrations is when the system model is operated under r p / D s τ in which rp is the radius of an airborne dust, Ds the effective diffusivity of bulk odor in air, and τ is the mean residence time of airborne dusts in ventilated airspace. The model enables engineers to evaluate the performance of the ventilation systems in reducing the odor emitted from stored manure in swine housing.

Exposure assessment model for odor causing VOCs volatilization from stored pig slurry

A mathematical model taking into account source depletion with time and the actual thickness of manure layer was derived to evaluate indoor inhalation exposure dynamics to three selected odor causing volatile organic compounds (VOC-odors) of p-cresol, toluene, and xylene volatilization from stored pig slurry. The model assumes that pig slurry is undisturbed and the VOC-odors released in a contaminated layer and transported through a clean layer as well as a manure-air interface boundary. The model simulates time-dependent volatilization, the depletion of source contaminant via both volatilization and degradation, and could be used with a contaminated zone of finite thickness. For a given VOC-odor, the predicted total exposure and resulting manure cleanup criteria can be a large variability depending on the model whether a finite or infinite manure layer thickness was considered. Results obtained from model comparisons suggest that the model incorporating depth-varying of manure layer and contaminant source depletion is more suitable to evaluate the VOC-odor exposure dynamics in swine housing bioclimate.

Combining bioaccumulation and coping mechanism to enhance long-term site-specific risk assessment for zinc susceptibility of bivalves

The purpose of this study is to conduct a long-term site-specific risk assessment for zinc (Zn) susceptibility of bivalves, green mussel Perna viridis and hard clam Ruditapes philippinarum, based on published experimental data by linking the biologically-based damage assessment model with the subcellular partitioning concept. A comprehensive risk modeling framework was developed to predict susceptibility probability of two bivalve species exposed to waterborne Zn. The results indicated that P. viridis accumulates more Zn toxicity, whereas both toxic potency and the recovery rate of Zn are higher for R. philippinarum. We found that negative linear correlations exist in elimination-recovery and elimination-detoxification relationships, whereas a positive linear correlation was observed in recovery-detoxification relationships for bivalves exposed to waterborne Zn. Simulation results showed that the spatial differences of susceptibility primarily resulted from the variation of waterborne Zn concentration under field conditions. We found that R. philippinarum is more susceptible of Zn than P. viridis under the same exposure condition. Results also suggested that Zn posed no significant susceptibility risk to two bivalve species in Taiwan. We suggested that these two species can be used to biomonitor the water quality on Taiwan coastal areas.

Trade-offs between elimination and detoxification in rainbow trout and common bivalve molluscs exposed to metal stressors

The purpose of this paper was to examine trade-offs between elimination and detoxification in rainbow trout and three common bivalve molluscs (clam, oyster, and scallop) exposed to cadmium (Cd), copper (Cu), and zinc (Zn) based on recent reported experimental data. We incorporated metal influx threshold with subcellular partitioning to estimate rate constants of detoxification (k(d)) and elimination (k₂). We found that the relationships between k₂ and k(d) were negative for rainbow trout and positive for bivalve molluscs. However, the relationships between k(d) and % metal in metabolically detoxified pool were found positive for rainbow trout and negative for bivalve molluscs. Our results also indicated that rainbow trout had higher accumulation (~60-90%) in metabolically active pool when exposed to essential metals of Cu and Zn and had only 10-50% accumulation in response to non-essential metal of Cd. Based on a cluster analysis, this study indicated that similarity of physiological regulations among study species was found between Cd and Zn. Our study suggested that detoxification can be predicted by an elimination-detoxification scheme with the known elimination rate constant. We concluded that quantification of trade-offs between subcellular partitioning and detoxification provides valuable insights into the ecotoxicology of aquatic organisms and enhances our understanding of the subcellular biology of trace metals.

Swine manure cleanup criteria calculation for odor causing volatile organic compounds based on manure‐to‐ventilation air exposure pathway

A mathematical model was derived to calculate swine manure cleanup criteria for odor causing volatile organic compounds (VOCs) so that acceptable total dose would not exceeded through the inhalation of ventilation air in swine housing for workers and pigs. A hypothetical scenario was used which assumed that subsurface contaminant in swine manure diffuses through a layer of manure-air interface then is swept into the ventilated airspace via advection, where long-term inhalation of contaminant was assumed to occur. The philosophy of the transport model is to incorporate the age distribution of contaminated air and a first-order decay of contaminant sources into the diffusion model for simulation of air concentrations of VOCs and total exposure dose. A closed-form solution is presented to allow a series of numerical experiments for investigating the effects of adsorption characteristics between manure gas and manure, the mean age of contaminated air, effective diffusivity, and degradation coefficient on total dose. Swine manure cleanup criteria based on non-exceedence of the total hazardous dose corresponding to an acceptable risk from indoor inhalation of four selected VOCs of p-cresol, hexane, toluene, and xylene were calculated in a typical pig unit. The model can be used in the future to compute the relative effectiveness of VOCs filtration systems and/or altered ventilation rates on the VOC exposure problem in animal housing.

Toxicokinetics/toxicodynamics with damage feedback improves risk assessment for tilapia and freshwater clam exposed to arsenic

It has been proposed that irreversible responses of organisms exposed to contaminants are due to a systems-level feedback. Here we tested this hypothesis by reanalyzing the published data on toxicokinetics and survival probability based on a systems-level threshold damage model (TDM) incorporating with a positive damage feedback to explore the steady-state response and dynamic behavior of damage for tilapia and freshwater clam exposed to waterborne arsenic (As). We found that ultrasensitivity appeared in As–tilapia and freshwater clam systems with Hill coefficient nxa0≥xa04, indicating that the positive damage feedback mechanism has been triggered. We confirmed that damage can trigger a positive feedback loop that together with As stressor increases irreversibility. This study also showed that TDM with positive feedback gave a much better predictability than that of TDM at As concentrations ranging from 100 to 500xa0mgxa0l−1 for freshwater clam, whereas for tilapia, two models had nearly same performance on predictability. We suggested that mortality–time profile derived Hill coefficient could be used as a new risk indicator to assess the survival probability for species exposed to waterborne metals. We anticipated that the proposed toxicokinetics/toxicodynamics with a positive damage feedback may facilitate our understanding and manipulation of complex mechanisms of metal susceptibility among species and improve current risk assessment strategies.

Characterizing odor adsorption on dust surface based on age and size distributions of airborne dust in a ventilated airspace

Abstract A mathematical model characterizing the adsorption of odor on the surface of airborne dust in a ventilated airsapce is derived based on the concept of homogeneous surface diffusion of a complete mixing airflow system. The main scheme of the paper is to incorporate the age and size distributions of airborne dust into the diffusion model for evaluating the odor adsorption on the ambient aerosol. A closed‐form solution is presented here to allow a series of numerical experiments for investigating the effects of adsorption characteristics, the mean age of airborne dust, surface effective diffusivity, and dust particle size on the adsorption of odor to the existing aerosol. Results obtained show that the most favorable performance of a ventilation system in reducing odor concentrations is when the system model is operated under rp / √Dsτ, < 1, in which rp , is the radius of an airborne dust, D,, is the effective diffusivity of bulk odor in air, and τ is the mean residence time of airborne dusts in ven...

Design of an airborne dust control system in ventilated animal housing

Abstract The dynamics of a lumped-parameter model for describing the behavior of airborne dust in animal housing are used in the development of controllers for an airborne dust control system. Proportional ( P ) and Proportional-integral ( PI ) feedback controllers designed from the viewpoint of modern state-variable control theory are used as an airborne dust control system in ventilated animal housing. Linear quadratic regulators ( LQRs ) with output feedback control of a linear-invariant system are chosen for this study. The plant is represented by a linear dynamic equation that describes the dynamic behavior of airborne dusts undergoing turbulent diffusive deposition and gravitational settling in a ventilated airspace. To illustrate this procedure, the design was applied to control the dust concentration in typical animal housing.