Synergistic experimental and numerical characterization of a dry-heat, fluid-warming device.

Fluids that are infused into the human body must be at a temperature that is compatible with the internal thermal state of the body. Since infusants are typically stored at temperatures that are too low for compatibility, a heating means is required to achieve the appropriate infusion temperature. This paper sets forth a synergistic investigation involving coupled experimentation and numerical simulation of the characteristics of one of the main categories of body-fluid heating means. The methodology developed here serves equally well as a design optimization tool. The paper encompasses two stages: (a) an experimental and numerical evaluation of a generic warming device in common use and (b) a redesign utilizing the same tools to elevate the performance of devices of this category. The numerical simulation dealt with steady and unsteady three-dimensional fluid flow and heat transfer which are endemic to devices of this kind. The two-pronged approach developed here was shown to be capable of coping with an operating feature called stopflow wherein an officiating physician orders an immediate cessation of fluid flow. The thermal events following stopflow are well described by the numerical simulations.

Use of multi-lumen catheters to preserve injected stem cell viability and injectant dispersion.

Infusion catheters, when used with balloons, are susceptible to compression of the catheter lumen. A consequence is that shear stress is increased in the fluid that passes through the lumen. When the injected fluid contains viable cells, hemolysis of the cells can result. This study investigates the effect of a new injection catheter design which is intended to resist the deleterious effect of balloon compression on cell viability for various flowrates, balloon pressures, and fluid viscosity values. Two types of catheters were employed for the study; a standard single-lumen device and a newly designed multi-lumen alternate. Experimental and numerical simulations show that for a single-lumen injection catheter, balloon pressures in excess of 7-8atm have the potential for causing hemolysis for flows of approximately 1-4ml/min. The critical balloon pressure is dependent on the viscosity of the cell-carrying fluid and the injectant flowrate. Higher injection rates and viscosities lead to lower threshold balloon pressures. The results show a sharp rise in cell death when pressures rose above approximately 7atm. On the other hand, the multi-lumen design was shown to resist hemolysis for all tested and simulated balloon pressures and flowrates up to 10ml/min. Experimental results confirmed the numerical findings that hemolysis-causing shear stress was not found with the multi-lumen, up to 12atm. This study indicates that a pressure-resistant multi-lumen catheter better preserves cell viability compared to the standard.

Comprehensive method to predict and quantify scald burns from beverage spills.

A comprehensive study was performed to quantify the risk of burns from hot beverage spills. The study was comprised of three parts. First, experiments were carried out to measure the cooling rates of beverages in a room-temperature environment by natural convection and thermal radiation. The experiments accounted for different beverage volumes, initial temperatures, cooling period between the time of service and the spill, the material which comprised the cup, the presence or absence of a cap and the presence or absence of an insulating corrugated paper sleeve. Among this list, the parameters which most influenced the temperature variation was the presence or absence of a cover or cap, the volume of the beverage and the duration of the cooling period. The second step was a series of experiments that provided temperatures at the surface of skin or skin surrogate after a spill. The experiments incorporated a single layer of cotton clothing and the exposure duration was 30 s. The outcomes of the experiments were used as input to a numerical model which calculated the temperature distribution and burn depth within tissue. Last was the implementation of the numerical model and a catalogue of burn predictions for various beverage volumes, beverage service temperatures, and durations between beverage service and spill. It is hoped that this catalogue can be used by both beverage industries and consumers to reduce the threat of burn injuries. It can also be used by treating medical professionals who can quickly estimate burn depths following a spill incident.

Rationalization of thermal injury quantification methods: application to skin burns.

Classification of thermal injury is typically accomplished either through the use of an equivalent dosimetry method (equivalent minutes at 43 °C, CEM43 °C) or through a thermal-injury-damage metric (the Arrhenius method). For lower-temperature levels, the equivalent dosimetry approach is typically employed while higher-temperature applications are most often categorized by injury-damage calculations. The two methods derive from common thermodynamic/physical chemistry origins. To facilitate the development of the interrelationships between the two metrics, application is made to the case of skin burns. This thermal insult has been quantified by numerical simulation, and the extracted time-temperature results served for the evaluation of the respective characterizations. The simulations were performed for skin-surface exposure temperatures ranging from 60 to 90 °C, where each surface temperature was held constant for durations extending from 10 to 110 s. It was demonstrated that values of CEM43 at the basal layer of the skin were highly correlated with the depth of injury calculated from a thermal injury integral. Local values of CEM43 were connected to the local cell survival rate, and a correlating equation was developed relating CEM43 with the decrease in cell survival from 90% to 10%. Finally, it was shown that the cell survival/CEM43 relationship for the cases investigated here most closely aligns with isothermal exposure of tissue to temperatures of ~50 °C.