A Tiny Detector Made of a Self-Heated Thermistor for Determining Thermal Conductivity of Biomaterials in Temperature Range 233~313K

2002 ◽  
Author(s):  
H. F. Zhang ◽  
S. X. Cheng ◽  
L. Q. He ◽  
A. L. Zhang ◽  
Y. Zheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Carotid Artery ◽  
Temperature Rise ◽  
Measurement Errors ◽  
Homogeneous Medium ◽  
Standard Samples ◽  
Temperature Range ◽  
A New Technique ◽  
Maximum Measurement

In this paper, a new technique, using a tiny thermistor with 0.3~0.5mm in diameter to determine thermal conductivity of biomaterials in wide temperature range, has been developed. Based on steady spherical heat transfer in an infinite homogeneous medium, thermal conductivity of the measured medium can be determined by power applied and temperature rise of the thermistor. Compared with recommended values, maximum measurement errors of standard samples, aqueous glycol and CaCl2 solutions, water and ice, are 5.1% in temperature range 233~313K. The thermal conductivities of rabbit’s liver, kidney, heart and carotid artery in temperature range 233~293K are determined. Error caused by measurement parameters, effects of the finite scale of the measured medium and the decoupler between the thermistor and the medium are analyzed.

scholarly journals An experimental study of soil thermal conductivity using a guarded hot plate apparatus

2021 ◽  
Author(s):  
Ivan Nikolaev
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Moisture Content ◽  
Measurement Errors ◽  
Specimen Preparation ◽  
Preparation Technique ◽  
Soil Thermal Conductivity ◽  
Hot Plate ◽  
Guarded Hot Plate ◽  
Plate Apparatus

A guarded hot plate apparatus was used to generate comprehensive sets of thermal conductivity for two types of soils, namely Ottawa sand and Richmon Hill clay-loam, for temperature variation from 2 to 92°C and moisture content variation from complete dryness to full saturation with measurement errors of less than 3%. Numerical simulation of heat transfer within the apparatus with sample inside was performed to validate the experimental design and setup. To prepare the samples, a consistent specimen preparation technique was developed for the cases of dry, barely-to-moderately moist, and highly-to-fully saturated moist soils. On the basis of gathered datasets, empirical correlations for soil thermal conductivity were developed as a function of both temperature and moisture content. The proposed correlations produced excellent fit to majority of the experimental data, and could be easily integrated into numerical analysis of underground heat transfer. As an application example, one of the correlations was employed to evaluate soil thermal conductivity in a numerical study of underground heat loss from a basement wall and floor, in order to illustrate the importance of considering the dependence of soil thermal conductivity on soil texture, temperature and degree of saturation.

scholarly journals Механизмы переноса тепла и температурная зависимость теплового сопротивления кристаллов CaLa-=SUB=-2-=/SUB=-S-=SUB=-4-=/SUB=-

2020 ◽  
Vol 62 (1) ◽  
pp. 186
Author(s):  
С.М. Лугуев ◽  
Н.В. Лугуева ◽  
Т.С. Лугуев
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Temperature Dependence ◽  
Debye Temperature ◽  
Temperature Range

The results of the study of the temperature dependence of the thermal resistance of CaLa2S4 crystals in the temperature range of 80–450 K according to the measurement of their thermal conductivity are presented. The mechanisms of heat transfer in samples with different technological background are established. The causes that determine the magnitude and characteristics of the temperature dependence of the thermal resistance of CaLa2S4 crystals in the region and above the Debye temperature are revealed.

Inverse Heat Transfer Study of a Nonlinear Straight Porous Fin Using Hybrid Optimization

2014 ◽  
Author(s):  
Ranjan Das ◽  
Rohit Kumar Singla
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Temperature Distribution ◽  
Gas Turbine ◽  
Measurement Errors ◽  
Turbine Blades ◽  
Gas Turbine Blades ◽  
Porous Fin ◽  
Inverse Heat Transfer ◽  
Transfer Study

Gas turbine blades are subjected to excessive heating load and for safe operation they must be properly cooled for protecting the blade material from damage. This involves external film cooling and internal pin-fin cooling. Cooling using fins are used for gas turbine blades by passing cold air over small extended surfaces. However, it is found that compared to conventional solid fins, for same weight, the usage of porous fins gives better thermal performance. In order to satisfy a given temperature distribution, the fin designer needs to determine various important properties and parameters, which requires solution of inverse problems. These parameters are generally thermo-physical properties for selecting suitable material and dimensions. In this work, an inverse heat transfer study of a porous rectangular fin using a hybrid Differential Evolution (DE)-nonlinear programming (NLP) algorithm has been carried out. The energy exchange in the porous fin is governed by conductive, convective and radiative heat transfer alongwith mass diffusion through the porous media, which makes the problem nonlinear. The fluid medium is assumed to be air. Using DE-NLP algorithm, four important parameters such as porosity, thermal conductivity of solid, length and thickness of the porous fin have been estimated for satisfying a given temperature distribution. Initially, the prescribed temperature distribution is calculated by solving a forward problem based on an implicit Runge-Kutta method working on Lobatto technique. Effects of random measurement errors, comparison of number of iterations and reconstruction distributions for the hybrid DE-NLP and individual NLP, DE schemes are performed. It is observed that the hybrid DE-NLP method converges faster than other two methods working separately. For all measurement errors, a very good reconstruction of the temperature distribution is observed using DE-NLP algorithm. In addition to this, it is found that many feasible combinations of the parameters can satisfy a given temperature distribution, which offers flexibility in selecting various parameters by adjusting the fin size, solid thermal conductivity and porosity.

scholarly journals A Study on Thermal Performance of Palladium as Material for Passive Heat Transfer Enhancement Devices in Thermal and Electronics Systems

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Gbeminiyi Musibau Sobamowo ◽  
S. A. Ibrahim ◽  
M. O. Salami
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Efficiency ◽  
Internal Heat ◽  
Transfer Model ◽  
Temperature Range ◽  
Extended Surface ◽  
External Conditions ◽  
Materials Used ◽  
Proper Material

In this work, the thermal behavior of fin made of palladium material under the influences of internal transfer mechanisms such as thermal radiation and temperature-dependent internal heat generation is investigated. The thermal model for the extended surface made of palladium as the fin material is first developed and solved numerically using finite difference method. The effects of various parameters on the heat transfer model of the extended surface are investigated. The results show that the rate of heat transfer through the fin and the thermal efficiency of the fin increase as the thermal conductivity of the fin material increases. This shows that fin is more efficient and effective for a larger value of thermal conductivity.  However, the thermal conductivity of the fin with palladium material is low and constant at the value of approximately 75 W/mK in a wider temperature range of -100oC and 227oC. Also, it is shown that the thermal efficiencies of potential materials (except for stainless steel and brass) for fins decrease as the fin temperatures increase. This is because the thermal conductivities of most of the materials used for fins decreases as temperature increases. However, keeping other fin properties and the external conditions constant, the thermal efficiency of the palladium is constant as the temperature of the fin increases within the temperature range of -100oC and 227oC. The study will assist in the selection of proper material for the fin and in the design of passive heat enhancement devices under different applications and conditions.

scholarly journals Measuring thermal conductivity of frozen soil using fiber optic sensors

2021 ◽  
Vol 135 (2) ◽  
pp. 82-93
Author(s):  
Bing Wu ◽  
◽  
Hong-Hu Zhu ◽  
Dingfeng Cao ◽  
◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Measurement Errors ◽  
Measurement Accuracy ◽  
Fiber Optic ◽  
Frozen Soil ◽  
In Situ Monitoring ◽  
Geotechnical Parameters ◽  
Lower Limits

The thermal conductivity is crucial for determining heat transfer in frozen soil. However, it is a challenge to obtain accurate measurement values due to the instability of soil properties. Recently, the fiber optic sensing technologies has enabled accurate and distributed in-situ monitoring of a variety of geotechnical parameters. This paper aims to explore the feasibility of actively heated fiber Bragg grating (AH-FBG) method in measuring thermal conductivity of frozen soil. A series of laboratory experiments were performed on frozen soil samples at different initial temperatures from −16 to 5 ℃. The theoretical upper and lower limits of thermal conductivity were used to evaluate the AHFBG measurements. The thermal conductivity recorded by a heat transfer analyzer was used to identify the measurement accuracy. The experimental results that the AH-FBG method can accurately measure the thermal conductivity of frozen soil when the initial temperature is below −6 ℃, and the measurement error is within acceptable range of 0.8%. When the soil temperature is between −6 and 0 ℃, significant measurement errors were observed due to the disturbance of heating to the frozen soil.

A High-Performance Heat Exchanger Using Modified Polyvinylidene Fluoride-Based Hollow Fibers

2012 ◽  
Vol 479-481 ◽  
pp. 115-119 ◽  
Author(s):  
Baoan Li ◽  
Han Han Fan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Hollow Fiber ◽  
Polyvinylidene Fluoride ◽  
Small Diameter ◽  
Water System ◽  
Hollow Fibers ◽  
Thin Wall ◽  
Temperature Range

Plastic heat exchangers has the shortcomings of bulky, thick pipe wall with large thermal resistance, poor heat transfer, aging of plastic and a narrow temperature range. The key to increase the heat transfer performance of heat exchanger is improving thermal performance of heat conduction.To enhance heat transfer effects and expand the temperature range of using plastic heat exchanger, PVDF with good temperature resistance is used as matrix and modification with graphite fillers to prepare composite hollow fiber which has the advantage of small diameter, thin wall and good thermal conductivity. Also, composite materials hollow fibers are used to prepare shell and tube hollow fiber heat exchanger.The testing of "water - water" system for our heat exchanger module has been done, and the results indicate that adding graphite is helpful to improve thermal conductivity of PVDF-based heat conductive hollow fiber heat exchanger to a certain extent.hen the content of graphite is 3%, the heat transfer effect is the best.

scholarly journals An experimental study of soil thermal conductivity using a guarded hot plate apparatus

2021 ◽  
Author(s):  
Ivan Nikolaev
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Moisture Content ◽  
Measurement Errors ◽  
Specimen Preparation ◽  
Preparation Technique ◽  
Soil Thermal Conductivity ◽  
Hot Plate ◽  
Guarded Hot Plate ◽  
Plate Apparatus

A guarded hot plate apparatus was used to generate comprehensive sets of thermal conductivity for two types of soils, namely Ottawa sand and Richmon Hill clay-loam, for temperature variation from 2 to 92°C and moisture content variation from complete dryness to full saturation with measurement errors of less than 3%. Numerical simulation of heat transfer within the apparatus with sample inside was performed to validate the experimental design and setup. To prepare the samples, a consistent specimen preparation technique was developed for the cases of dry, barely-to-moderately moist, and highly-to-fully saturated moist soils. On the basis of gathered datasets, empirical correlations for soil thermal conductivity were developed as a function of both temperature and moisture content. The proposed correlations produced excellent fit to majority of the experimental data, and could be easily integrated into numerical analysis of underground heat transfer. As an application example, one of the correlations was employed to evaluate soil thermal conductivity in a numerical study of underground heat loss from a basement wall and floor, in order to illustrate the importance of considering the dependence of soil thermal conductivity on soil texture, temperature and degree of saturation.

Experimental Investigation of Natural Convection Heat Transfer of an Ionic Liquid in a Rectangular Enclosure Heated From Below

2011 ◽  
Author(s):  
Titan C. Paul ◽  
A. K. M. M. Morshed ◽  
Elise B. Fox ◽  
Ann Visser ◽  
Nicholas Bridges ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Ionic Liquid ◽  
Nusselt Number ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Temperature Range

This paper presents an experimental study of natural convection heat transfer for an Ionic Liquid. The experiments were performed for 1-butyl-2, 3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, ([C4mmim][NTf2]) at a Rayleigh number range of 1.13×107 to 7.7×107. In addition to determining the convective heat transfer coefficients, this study also included experimental determination of thermophysical properties of [C4mmim][NTf2] such as, density, viscosity, heat capacity, and thermal conductivity. The results show that the density of [C4mmim][NTf2] varies from 1.437–1.396 g/cm3 within the temperature range of 10–50°C, the thermal conductivity varies from 0.125–0.12 W/m.K between a temperature of 10 to 70°C, the heat capacity varies from 1.015 J/g.K–1.760 J/g.K within temperature range of 25–340°C and the viscosity varies from 243cP–18cP within temperature range 10–75°C. The results for density, thermal conductivity, heat capacity, and viscosity were in close agreement with the values in the literature. Measured dimensionless Nusselt number was observed to be higher for the ionic liquid than that of DI water. This is expected as Nusselt number is the ratio of heat transfer by convection to conduction and the ionic liquid has lower thermal conductivity (approximately 20% of DI water) than DI water.

Conjugate Heat Transfer With Buoyancy Effects From Micro-Chip Sized Repeated Heaters

1997 ◽  
Vol 119 (4) ◽  
pp. 275-280 ◽  
Author(s):  
D. Yu ◽  
T. A. Ameel ◽  
R. O. Warrington ◽  
R. F. Barron
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mixed Convection ◽  
Forced Convection ◽  
Temperature Rise ◽  
Internal Heat ◽  
Maximum Temperature ◽  
Transient Heating ◽  
Maximum Temperature Rise ◽  
Laminar Mixed Convection

Laminar mixed convection heat transfer across five in-line microchipsized heaters, surface mounted on printed circuit board (PCB), was investigated by the weighted residual finite element method. The effects of axial heat conduction within the PCB for both mixed convection and pure forced convection are reported. The flow regime considered was 200 ≤ Re ≤ 800 and 0 ≤ Gr ≤ 58,000. Internal heat generation was included in the microchip-sized blocks in order to accurately model the thermal response to predict the maximum temperature rise. On the outer PCB walls, convective heat transfer conditions were given. Thermophysical and transport properties based on materials used in the electronics industry, including orthotropic thermal conductivity in PCB, were used. The flow and solid domains were solved simultaneously. A sensitivity study of PCB heat transfer coefficients, isotropic thermal conductivity, thermal conductivity variations, and spacing effects was performed. The mixed convection transient heating process was compared with the steady-state formulation to estimate the influence of flow oscillation in heat transfer. It was found that the maximum temperature rise in the microchips predicted by pure forced convection was, at most, 10 percent higher than that predicted by mixed convection. The difference in maximum temperature between the trailing and leading chips in the array was 30 percent.

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