A Comparative Analysis of Thermal Blood Perfusion Measurement Techniques

1987 ◽  
Vol 109 (3) ◽  
pp. 218-225 ◽  
Author(s):  
R. Kress ◽  
R. Roemer
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Time Window ◽  
Measurement Techniques ◽  
Temperature Response ◽  
Blood Perfusion ◽  
Analytical Models ◽  
Transient Temperature ◽  
Two Dimensional ◽  
Transient Heating

The object of this study was to devise a unified method for comparing different thermal techniques for the estimation of blood perfusion rates and to perform a comparison for several common techniques. The approach used was to develop analytical models for the temperature response for all combinations of five power deposition geometries (spherical, one- and two-dimensional cylindrical, and one- and two-dimensional Gaussian) and three transient heating techniques (temperature pulse-decay, temperature step function, and constant-power heat-up) plus one steady-state heating technique. The transient models were used to determine the range of times (the time window) when a significant portion of the transient temperature response was due to blood perfusion. This time window was defined to begin when the difference between the conduction-only and the conduction-plus-blood flow transient temperature (or power) responses exceeded a specified value, and to end when the conduction-plus-blood flow transient temperature (or power) reached a specified fraction of its steady-state value. The results are summarized in dimensionless plots showing the size of the time windows for each of the transient perfusion estimation techniques. Several conclusions were drawn, in particular: (a) low perfusions are difficult to estimate because of the dominance of conduction, (b) large heated regions are better suited for estimation of low perfusions, (c) noninvasive heating techniques are superior because they have the potential to minimize conduction effects, and (d) none of the transient techniques appears to be clearly superior to the others.

Experimental and Theoretical Analysis of Transient Response of Plate Heat Exchangers in Presence of Nonuniform Flow Distribution

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
N. Srihari ◽  
Sarit K. Das
Keyword(s):  
Steady State ◽  
Heat Exchangers ◽  
Sudden Change ◽  
Temperature Response ◽  
Flow Distribution ◽  
Transient Temperature ◽  
Nonuniform Flow ◽  
Flow Rates ◽  
Plate Heat ◽  
Flow Maldistribution

Transient analysis helps us to predict the behavior of heat exchangers subjected to various operational disturbances due to sudden change in temperature or flow rates of the working fluids. The present experimental analysis deals with the effect of flow distribution on the transient temperature response for U-type and Z-type plate heat exchangers. The experiments have been carried out with uniform and nonuniform flow distributions for various flow rates. The temperature responses are analyzed for various transient characteristics, such as initial delay and time constant. It is also possible to observe the steady state characteristics after the responses reach asymptotic values. The experimental observations indicate that the Z-type flow configuration is more strongly affected by flow maldistribution compared to the U-type in both transient and steady state regimes. The comparison of the experimental results with numerical solution indicates that it is necessary to treat the flow maldistribution separately from axial thermal dispersion during modeling of plate heat exchanger dynamics.

Transient Behavior of Crossflow Heat Exchangers With Longitudinal Conduction and Axial Dispersion

2004 ◽  
Vol 126 (3) ◽  
pp. 425-433 ◽  
Author(s):  
Manish Mishra ◽  
P. K. Das ◽  
Sunil Sarangi
Keyword(s):  
Heat Transport ◽  
Heat Exchangers ◽  
Temperature Response ◽  
Transient Behavior ◽  
Axial Dispersion ◽  
Transient Temperature ◽  
Inlet Temperature ◽  
Conductive Heat ◽  
Two Dimensional ◽  
Transient Temperature Response

Transient temperature response of the crossflow heat exchangers with finite wall capacitance and both fluids unmixed is investigated numerically for step, ramp and exponential perturbations provided in hot fluid inlet temperature. Effect of two-dimensional longitudinal conduction in separating sheet and axial dispersion in fluids on the transient response has been investigated. Conductive heat transport due to presence of axial dispersion in fluids have been analyzed in detail and shown that presence of axial dispersion in both of the fluid streams neutralizes the total conductive heat transport during the energy balance. It has also been shown that the presence of axial dispersion of high order reduces the effect of longitudinal conduction.

Experimental Study of Deicing Process in an Airfoil Application

2013 ◽  
Author(s):  
Pablo Perez Pereira ◽  
Luis D. Vilar-Carrasquillo ◽  
Gerardo Carbajal
Keyword(s):  
Steady State ◽  
Flow Characteristics ◽  
Temperature Response ◽  
Leading Edge ◽  
Transient Temperature ◽  
Experimental Setup ◽  
Trailing Edge ◽  
Steady State Temperature ◽  
Fluid Flow Characteristics ◽  
Transient Temperature Response

A customized airfoil for deicing process was designed, built and tested in order to investigate the effect of icing on the airfoil and the process of removing it by heating processed. A numerical simulation was performed to provide more details of the fluid flow characteristics of the presence of the ice and the temperature distribution on the airfoil when it reached the steady state conditions. An experimental setup was developed to measure and record the transient temperature response on the trailing and leading edge respectively. The experimental results suggest that from a minimum temperature of −10°C on the trailing edge, and 0°C in the leading edge with ice on the surface, the time to reach the steady state temperature of 46°C in the leading edge and 38°C in the trailing edge was close to 8 minutes approximately.

scholarly journals On the heating of a two-dimensional slab in a microwave cavity: aperture effects

2001 ◽  
Vol 43 (1) ◽  
pp. 137-148 ◽  
Author(s):  
T. R. Marchant ◽  
B. Liu
Keyword(s):  
Steady State ◽  
Power Level ◽  
Temperature Response ◽  
Input Power ◽  
Microwave Cavity ◽  
Two Dimensional ◽  
Fixed Temperature ◽  
Aperture Width ◽  
The Galerkin Method ◽  
Thermal Absorptivity

AbstractThe steady-state heating of a two-dimensional slab by the TE10 mode in a microwave cavity is considered. The cavity contains an iris with a variable aperture and is closed by a short. Resonance can occur in the cavity, which is dependent on the short position, the aperture width and the temperature of the heated slab.The governing equations for the slab are steady-state versions of the forced heat equation and Maxwell's equations while fixed-temperature boundary conditions are used. An Arrhenius temperature dependency is assumed for both the electrical conductivity and the thermal absorptivity. Semi-analytical solutions, valid for small thermal absorptivity, are found for the steady-state temperature and the electric-field amplitude in the slab using the Galerkin method.With no-iris (a semi-infinite waveguide) the usual S-shaped power versus temperature curve occurs. As the aperture width is varied however, the critical power level at which thermal runaway occurs and the temperature response on the upper branch of the S-shaped curve are both changed. This is due to the interaction between the radiation, the cavity and the heated slab. An example is presented to illustrate these aperture effects. Also, it is shown that an optimal aperture setting and short position exists which minimises the input power needed to obtain a given temperature.

Dynamic Behavior of Three-Fluid Crossflow Heat Exchangers

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Manish Mishra ◽  
P. K. Das ◽  
Sunil Sarangi
Keyword(s):  
Dynamic Behavior ◽  
Transient Response ◽  
Heat Exchangers ◽  
Temperature Response ◽  
Axial Dispersion ◽  
Transient Temperature ◽  
Inlet Temperature ◽  
Two Dimensional ◽  
Large Capacitance ◽  
Transient Temperature Response

A transient temperature response of three-fluid heat exchangers with finite and large capacitance of the separating sheets is investigated numerically for step, ramp, exponential, and sinusoidal perturbations provided in the central (hot) fluid inlet temperature. The effect of two-dimensional longitudinal conduction in the separating sheet and of axial dispersion in the fluids on the transient response has been investigated. A comparison of the dynamic behavior of four possible arrangements of three-fluid crossflow heat exchangers has also been presented.

scholarly journals A THREE LAYER MODEL FOR THE THERMAL IMPEDANCE OF THE HUMAN SKIN: MODELING AND EXPERIMENTAL MEASUREMENTS

2015 ◽  
Vol 15 (04) ◽  
pp. 1550044 ◽  
Author(s):  
MARIA STRA̧KOWSKA ◽  
GILBERT DE MEY ◽  
BOGUSŁAW WIȨCEK ◽  
MICHAŁ STRZELECKI
Keyword(s):  
Human Skin ◽  
Blood Perfusion ◽  
Experimental Results ◽  
Time Dependent ◽  
Transient Temperature ◽  
Thermal Impedance ◽  
Layer Model ◽  
Transient Heating ◽  
Laplace Domain ◽  
Thermographic Camera

In this paper a dynamic three layer model for the heat transfer in the human skin is presented. The model is solved in the Laplace domain using the phasor notation. In order to compare the theoretical model with experimental results, a transient heating was carried out and the time dependent skin temperature was recorded with a thermographic camera. The transient temperature could be fitted very well to an analytical function, which could easily be transformed into the Laplace domain allowing an easy comparison between the model and the experimental results. The aim of the research is to evaluate the skin thermal parameters for all layers including the blood perfusion.

Bio-Heat Transfer Model of Human Eye Subjected to Retinal Laser Irradiation

2010 ◽  
Author(s):  
Arunn Narasimhan ◽  
Kaushal Kumar Jha
Keyword(s):  
Heat Transfer ◽  
Laser Radiation ◽  
Numerical Model ◽  
Laser Irradiation ◽  
Laser Power ◽  
Blood Perfusion ◽  
Transient Temperature ◽  
Transfer Model ◽  
Two Dimensional ◽  
Human Eye

Retinopathy is a surgical process in which maladies of the human eye are treated by laser irradiation. A two-dimensional numerical model of the human eye geometry has been developed to investigate steady and transient thermal effects due to laser radiation. In particular, the influence of choroidal pigmentations and choroidal blood convection — parameterized as a function of choroidal blood perfusion are investigated in detail. The Pennes bio-heat transfer equation is invoked as the governing equation and a finite volume formulation is employed in the numerical method. The numerical model is validated with available experimental and two-dimensional numerical results. For a 500 μm diameter spot size, laser power of 0.2 W, with 100% absorption of laser radiation in the Retinal Pigmented Epithelium (RPE) region, the peak RPE temperature is observed to be 175 °C at steady state, with no blood perfusion in choroid. It reduces to 168.5 °C when the choroidal blood perfusion rate is increased to 23.3 kgm−3s−1. However, under transient simulations, the peak RPE temperature is observed to remain constant at 104 °C after 100 ms of the laser surgery period. A truncated three-dimensional model incorporating multiple laser irradiation spots is also developed to observe the spatial effect of choroidal blood perfusion. For a circular array of seven uniformly distributed spots of identical diameter and laser power of 0.2 W, steady and transient temperature evolution are presented with analysis.

Transient Temperature Profiles in Tissues With Nonuniform Blood Flow Distributions

1982 ◽  
Vol 104 (3) ◽  
pp. 202-208 ◽  
Author(s):  
A. B. Elkowitz ◽  
A. Shitzer ◽  
R. C. Eberhart
Keyword(s):  
Heat Transfer ◽  
Blood Flow ◽  
Steady State ◽  
Flow Distribution ◽  
Tissue Blood Flow ◽  
Transient Temperature ◽  
Temperature Profiles ◽  
Heat Transfer Equation ◽  
Blood Flow Distribution ◽  
Steady State Temperature

Numerical methods and the bio-heat transfer equation are employed to calculate temperature profiles in tissues subjected to nonuniform blood flow distributions, for initial and boundary conditions which simulate experimental physiological situations. Results indicate that one can infer, from sudden changes in temperature distribution, the occurrence of sudden changes in tissue blood flow. However, prediction of blood flow distribution from near equilibrium or steady-state temperature profiles is of poor resolution, and does not appear useful as a practical technique. The methods and results are useful for predictions of temperature profiles in the absence of significant endogenous or exogenous heating; they can be extended to such applications by straightforward methods.

Effects of Transient Heating on Two-Phase Flow Response in Microchannel Heat Exchangers

2009 ◽  
Author(s):  
Josef L. Miler ◽  
Roger Flynn ◽  
Gamal Refai-Ahmed ◽  
Maxat Touzelbaev ◽  
Milnes David ◽  
...  
Keyword(s):  
Steady State ◽  
Cooling System ◽  
Temperature Response ◽  
High Heat ◽  
Bubble Nucleation ◽  
Heat Sinks ◽  
High Heat Flux ◽  
Transient Heating ◽  
Two Phase ◽  
Pulsed Heating

Two-phase microfluidic heat sinks promise high heat flux cooling at reduced pumping power compared to pumped liquid microchannel heat sinks. However, flow instabilities caused by bubble nucleation and expansion severely reduce heat transfer performance of two-phase microfluidic heat sinks. This study probes the governing physics of bubble nucleation and expansion by comparing the effects of pulsed heating to steady-state heating in a single microchannel. Pulsed heating at 8 Hz causes an increase in the average hotspot temperature of as much as 8°C compared to steady-state heating. Upstream and downstream temperature response does not vary significantly between heating conditions. The results correspond well with thin-film evaporation models for bubble growth. This study provides insight for designing two-phase microfluidic cooling system subjected to transient hotspots.

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