Bio-heat transfer

The most common representation of the spatial and temporal distribution of temperature in living systems is the so-called bio-heat transfer equation (BHTE). It was first suggested by Pennes (1948) in the following form ... 

The bio-heat transfer equation with both of these assumptions has been solved for various tissue geometries and initial and boundary conditions (Shitzer and Eberhart, 1985). Because of scalar treatment of the convective heat transport by blood, the use of the bio-heat transfer equation has been questioned repeatedly (Charny, 1992). Considering tissue as porous media, Wulff (1974, 1980) introduced the blood velocity vector ub, in the bio-heat transfer equation. Unfortunately, the complex nature of the system defies any attempt to specify the circulation vector at the microscopic level. As non-invasive technologies (e.g., MRI) provide improved spatial resolution, it may be possible to incorporate such data numerically (Dutton et al., 1992). 

A second criticism of the bio-heat transfer equation originates from the fact that it does not account for the countercurrent heat exchange in the capillary bed. Assuming that the velocity vector is one-dimensional, Mitchell and Myers (1968), and later, Keller and Seiler (1971), analyzed... 

While these various improvements in the bio-heat transfer equation provide new insight into the heat transfer process in the microvascular bed, mathematical complexity in describing the microcirculation and vascular topology makes their application to normal and neoplastic tissues... 

Once all the model parameter values are specified, the geometry of the model system must be defined. Depending upon the information desired, either a particular organ (or tissue region) or the whole mammalian body may be considered as the region in which the bio-heat transfer equation must be solved. Both of these approaches have been discussed in depth elsewhere (Shitzer and Eberhart, 1985) for application in the normal tissues therefore, we will focus our attention on tumors. 

While the bio-heat transfer equation, as it stands, appears to give adequate results in several applications, a precise description of heat transfer in tissues remains a tedious but challenging problem. 

In Chitrphiromsri and Kuznetsov s model [47] heat and moisture transport in fire fighters protective clothing dining a flash fire exposure are investigated. The garment consists of three fabric layers (outer shell, moisture barrier and thermal barrier). The skin also has three layers epidermis, dermis and subcutaneous. The bio-heat transfer equation for the skin, based on the Pennes model [54], is written as ... 

In the fast pyrolysis processes, the temperature control and residence time are important variables due to the formation of secondary reactions. High heating rates and good heat transfer at the interface between the particles and gases/vapors are necessary for the reaction to occur. The thermal conductivity of the materials is very low, which requires very fine solid particles of about 4 mm. Besides, it is necessary to remove quickly the carbon to avoid and/or minimize cracking, and cooling the vapor to facilitate the formation of bio-oil. 

Molten salts are not only useful as solvents in chemical synthesis, electrolysis, soldering, enameling, de-enameling, metal recycling and preparation, coal gasification, and desulfuration, but they are also reactants, catalysts, and ambients for heat storage and heat transfer, as well as electrolytes in fuel cells (molten carbonates). The solvent can participate in the reaction that is carried out in fluxes. BaTiOa is made in molten TiO, as a solvent and Bio(AlClJ, can only be made in a very acidic cryolite (NaAlClJ. 

In a vacuum reactor, heat transfer becomes more difficult because of the absence of a medium for convection, however. As a consequence, this type of reactor is characterized by slower heating rates. Still, it is possible for the vacuum pump to remove organic volatiles rapidly. Typically, bio-oU yields in vacuum reactors stay in the range 60-65 wt.%. Despite its use on the lab scale, the vacuum pump requirements make the vacuum reactors very difficult to scale up. 

Utilization of nanoparticle systems for enhancing a phenomenon or process, such as chemical reactions, nano-elcctronics, nano-ionics, magnetic processes, optical processes, heat transfer, bioseparation, bio and chemical reactivity. 

Heat efficacy is defined as the difference between the amount of heat produced and the amount of heat lost. Therefore, effective ablation can be achieved by optimizing heat production and minimizing heat loss within the area to be ablated. The relationship between these factors has been characterized as the bio-heat equation. The bio-heat equation governing RF-induced heat transfer through tissue has been previously described by Pennes (1948), with this equation simplified to a first approximation by Goldberg et al. (2000b) as follows ... 

Quaternary ammonium compounds (quats) are prepared - by moderate heating of the amine and the alkyl halide in a suitable solvent - as the chlorides or the bromides. Subsequently conversion to the hydroxides may be carried out. Major applications of the quat chlorides are as fabric softeners and as starch cationizing agent. Several bio-active compounds (agrochemicals, pharmaceuticals) possess the quat-structure. Important applications of quat bromides are in phase transfer catalysis and in zeolite synthesis. 

Dichlorodibenzo- -dioxin. 2-Bromo-4-chlorophenol (31 grams, 0.15 mole) and solid potassium hydroxide (8.4 grams, 0.13 mole) were dissolved in methanol and evaporated to dryness under reduced pressure. The residue was mixed with 50 ml of bEEE, 0.5 ml of ethylene diacetate, and 200 mg of copper catalyst. The turbid mixture was stirred and heated at 200°C for 15 hours. Cooling produced a thick slurry which was transferred into the 500-ml reservoir of a liquid chromatographic column (1.5 X 25 cm) packed with acetate ion exchange resin (Bio-Rad, AG1-X2, 200-400 mesh). The product was eluted from the column with 3 liters of chloroform. After evaporation, the residue was heated at 170°C/2 mm for 14 hours in a 300-cc Nestor-Faust sublimer. The identity of the sublimed product (14 grams, 74% yield) was confirmed by mass spectrometry and x-ray diffraction. Product purity was estimated at 99- -% by GLC (electron capture detector). 

With fixed-bed updraft gasifiers, the air or oxygen passes upward through a hot reactive zone near the bottom of the gasifier in a direction counter-crrrrent to the flow of solid material. Exothermic reactions between air/oxygen and the charcoal in the bed drive the gasification process. Heat in the raw gas is transferred to the bio-... 

These ordered array materials find interest not only in catalysis, but in several other applications, from optical materials, sensors, low-k materials, ionic conductors, photonic crystals, and bio-mimetic materials.Flowever, with respect to these applications, catalysis requires additional specific characteristics, such as the presence of a thermally stable nanostructure, the minimization of grain boundaries where side reactions may occur, and the presence of a porous structure which guarantees a high surface area coupled to low heat and mass transfer limitations. An ordered assembly of ID nanostructures for oxide materials could, in principle, meet these different requirements. 

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