Steady-Periodic Three-Dimensional Foundation Heat Transfer From Refrigerated Structures

2000 ◽  
Vol 122 (2) ◽  
pp. 69-83 ◽  
Author(s):  
Pirawas Chuangchid ◽  
Moncef Krarti
Keyword(s):  
Heat Transfer ◽  
Parametric Analysis ◽  
Three Dimensional ◽  
Thermal Characteristics ◽  
Mean Amplitude ◽  
Phase Lag ◽  
Heat Gain ◽  
U Value ◽  
The Mean ◽  
Rectangular Slab

Analytical solutions for steady-periodic ground-coupled heat conduction problems for cylindrical and three-dimensional rectangular slab-on-grade floors beneath refrigerated structures with uniform and partial insulation are presented in this paper. The solutions provide the soil temperature field, and the total slab heat gain. A parametric analysis is conducted to determine the effect of thermal insulation U-value and insulation width on the mean, amplitude, and phase lag of total slab heat gain. In particular, it was found that the mean and the amplitude of the total slab heat gain are effectively independent of its shape but are strongly affected by the slab size and thermal characteristics. [S0199-6231(00)00502-5]

Steady-State Component of Three-Dimensional Slab-on-Grade Foundation Heat Transfer

2000 ◽  
Vol 123 (1) ◽  
pp. 18-29 ◽  
Author(s):  
Pirawas Chuangchid ◽  
Moncef Krarti
Keyword(s):  
Steady State ◽  
Heat Loss ◽  
Parametric Analysis ◽  
Three Dimensional ◽  
Thermal Characteristics ◽  
U Value ◽  
Rectangular Slab ◽  
Steady State Heat ◽  
Profile Estimation ◽  
State Component

General semi-analytical solutions for the steady-state heat conduction problems for circular and three-dimensional rectangular slab-on-grade floors with uniform insulation are presented. The soil temperature field, and the total slab heat loss are presented and analyzed using the Interzone Temperature Profile Estimation (ITPE) technique. A parametric analysis is conducted to determine the effect of thermal insulation U-value, slab size, and water table depth on the total slab heat loss. In particular, it was found that the total slab heat loss is independent of its shape but is strongly affected by the slab size and thermal characteristics.

A Numerical Study of Three-Dimensional Natural Convective Heat Transfer From a Plate With a “Wavy” Surface

2001 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Matt Garrett
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Surface Waves ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Wavy Surface ◽  
Surface Waviness ◽  
Dimensionless Amplitude ◽  
The Mean

Abstract Natural convective heat transfer from a wide isothermal plate which has a “wavy” surface, i.e., has a surface which periodically rises and falls, has been numerically studied. The surface waves run parallel to the direction of flow over the surface and have a relatively small amplitude. Two types of wavy surface have been considered here — saw-tooth and sinusoidal. Surfaces of the type considered are approximate models of situations that occur in certain window covering applications, for example, and are also sometimes used to try to enhance the heat transfer rate from the surface. The flow has been assumed to be laminar. Because the surface waves are parallel to the direction of flow, the flow over the surface will be three-dimensional. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces, this being treated by means of the Boussinesq type approximation. The governing equations have been written in dimensionless form, the height of the surface being used as the characteristic length scale and the temperature difference between the surface temperature and the temperature of the fluid far from the plate being used as the characteristic temperature. The dimensionless equations have been solved using a finite-element method. Although the flow is three-dimensional because the surface waves are all assumed to have the same shape, the flow over each surface thus being the same, and it was only necessary to solve for the flow over one of the surface waves. The solution has the following parameters: the Grashof number based on the height, the Prandtl number, the dimensionless amplitude of the surface waviness, the dimensionless pitch of the surface waviness, and the form of the surface waviness (saw-tooth or sinusoidal). Results have been obtained for a Prandtl number of 0.7 for Grashof numbers up to 106. The effects of Grashof number, dimensionless amplitude and dimensionless pitch on the mean heat transfer rate have been studied. It is convenient to introduce two mean heat transfer rates, one based on the total surface area and the other based on the projected frontal area of the surface. A comparison of the values of these quantities gives a measure of the effectiveness of the surface waviness in increasing the mean heat transfer rate. The results show that while surface waviness increases the heat transfer rate based on the frontal area, the modifications of the flow produced by the surface waves are such that the increase in heat transfer rate is less than the increase in surface area.

A Study of Three-Dimensional Mixed Convective Heat Transfer From Short Vertical Cylinders in a Horizontal Forced Flow

2000 ◽  
Author(s):  
David A. Scott ◽  
P. H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Three Dimensional ◽  
Forced Flow ◽  
Low Velocity ◽  
Buoyancy Forces ◽  
The Mean ◽  
Mixed Convective Flow ◽  
Comparison Of The Results

Abstract Heat transfer from relatively short vertical isothermal cylinders in a horizontal forced fluid flow has been considered. The flow conditions are such that the buoyancy forces resulting from the temperature differences in the flow are in general significant despite of the presence of a horizontal forced flow of air, that is, mixed convective flow exists. Because the cylinders are short and the buoyancy forces act normal to the forced flow, three-dimensional flow exists. The experiments were performed in a low velocity, open jet wind tunnel. The study involved the experimental determination of the mean heat transfer coefficient and a comparison of the results with a previous numerical analysis. Mean heat transfer rates were determined using the ‘lumped capacity’ method. The mean Nusselt number has the Reynolds number, Grashof number and the height to diameter ratio of the cylinders as parameters. The results have been used to determine the conditions under which the flow departs from purely forced convection and enters the mixed convection regime, i.e., determining the conditions for which the buoyancy effects should be included in convective heat transfer calculations for short cylinders.

Oscillating heat flow from rabbit's pinna

1988 ◽  
Vol 255 (3) ◽  
pp. R464-R469 ◽  
Author(s):  
F. S. Mohler ◽  
J. E. Heath
Keyword(s):  
Surface Temperature ◽  
Oryctolagus Cuniculus ◽  
Infrared Imaging ◽  
Imaging System ◽  
Thermal Characteristics ◽  
Mean Amplitude ◽  
Mean Frequency ◽  
Infrared Imaging System ◽  
New Zealand White Rabbits ◽  
The Mean

Thermal characteristics of the pinnae of the ears of New Zealand White rabbits (Oryctolagus cuniculus) were measured with an infrared imaging system, and vasomotor oscillations were observed to occur spontaneously in the pinnae of all rabbits at an ambient temperature of 20 degrees C. Measured fluctuations in surface temperature were used to characterize the observed vasomotor oscillations, whereas heat loss from the pinnae was calculated using the mean pinna temperatures. The pulsing related to thermoregulation had a mean frequency of approximately 0.025 Hz with a mean amplitude of approximately 0.35 degrees C. When surface temperature was measured simultaneously from both pinnae of individual rabbits, the thermal pulsing was synchronous in the two pinnae. Many of the characteristics of the vasomotor rhythm measured in the pinnae of rabbits were consistent with an active and controlled oscillation, and a possible thermoregulatory role for a controlled vasomotor oscillation is discussed.

scholarly journals TWO-PHASE MODELLING OF THERMAL DISSIPATION IN A NATURAL BASIN

2004 ◽  
Vol 12 (3) ◽  
pp. 103-107 ◽  
Author(s):  
Pranas Baltrenas ◽  
Petras Vaitiekūnas ◽  
Vladislovas Katinas ◽  
Antanas Markevičius
Keyword(s):  
Heat Transfer ◽  
Wind Velocity ◽  
Three Dimensional ◽  
Viscosity Coefficient ◽  
Thermal Dissipation ◽  
Stream Velocity ◽  
Mixing Rate ◽  
Two Phase ◽  
Transfer Processes ◽  
The Mean

The state of two‐phase flow ‘liquid‐gas’ has been modeled numerically by the three‐dimensional method of complex research of heat and mass transfer. This allows examining the interaction of some transfer processes in a natural cooling basin (the Drūkšiai lake): the wind power and direction, variable water density, the coefficient of heat conduction and heat transfer of the water‐air interface. Combined effect of these natural actions determines the heat amount that the basin is able to dissipate to the surrounding atmospheric media in thermal equilibrium (without changes in the mean water temperature). This paper presents a number of the most widely used expressions for the coefficients of vertical and horizontal heat transfer. On the basis of stream velocity and mean temperature profiles measured in the cooling pond as well as on that of their time variations suggestions are made that the mixing rate at the water surface is caused by natural space ‐ time variation of the wind, and can be described by the value of eddy viscosity coefficient ‐ 1 m2/s (numerical modeling with 0,9–1,3 m2/s). The wind influences the surface of the lake according to the experimental data, i e 1–3 % of the mean wind velocity. The model applies to the weakly wind, approximately 1–5 m/s of the mean wind velocity. Comparison of experimental and numerical results showed a qualitative agreement. For a better quantitative approximation, it is necessary to have more boundary conditions variable with time and to solve unsteady set equations for transfer processes.

Heat Transfer Normal to Paired Arterioles and Venules Embedded in Perfused Tissue During Hyperthermia

1988 ◽  
Vol 110 (4) ◽  
pp. 277-282 ◽  
Author(s):  
C. K. Charny ◽  
R. L. Levin
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Three Dimensional ◽  
Numerical Data ◽  
Tissue Temperature ◽  
Three Dimensional Model ◽  
Sources And Sinks ◽  
The Mean ◽  
Krogh Cylinder ◽  
Subsequent Incorporation

A numerical model of the heat transer normal to an arteriole-venule pair embedded in muscle tissue has been constructed. Anatomical data describing the blood vessel size, spacing, and density have been incorporated into the model. This model computes temperatures along the vessel walls as well as the temperature throughout the tissue which comprises an infinitely long Krogh cylinder around the vessel pair. Tissue temperatures were computed in the steady-state under resting conditions, while transient calculations were made under hyperthermic conditions. Results show that for both large- (1st generation) and medium-sized (5th generation) vessel pairs, the mean tissue temperature within the tissue cylinder is not equal to the mean of the arteriole and venule blood temperatures under both steady-state and transient conditions. The numerical data were reduced so that a comparison could be made with the predictions of a simple two-dimensional superposition of line sources and sinks presented by Baish et al. [1]. This comparison reveals that the superposition model accurately describes the heat transfer effects during hyperthermia, permitting subsequent incorporation of this theory into a realistic three-dimensional model of heat transfer in a whole limb during hyperthermia.

Performance Evaluation of Thermal Attributes in Impinging Jet Heat Sink using Airfoil Pillars with and without Nano Fluid

2021 ◽  
Vol 7 (5) ◽  
pp. 2808-2820
Author(s):  
Deepak Kumar ◽  
Mohammad Zunaid ◽  
Samsher Gautam
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Three Dimensional ◽  
Thermal Characteristics ◽  
Exchange Coefficient ◽  
Dimensional Model ◽  
Heat Exchange Coefficient ◽  
Three Dimensional Model ◽  
Nano Fluid ◽  
Nano Fluids

Objectives: In the current research three techniques have been operated to enhance the rate of heat transfer in a heat sink. The amalgamation of Impingement of jet, airfoil pillars and Nano fluids are used. Nano fluids has a lot of potential to enhance the heat transportation in contrast to the water. The investigation has been executed with the help of three dimensional numerical model using Computational fluid Dynamics. At the onset the model has been validated with the inspection carried out already in experimental form. The observations in the form of thermal attributes are investigated. From the results the conclusion is made that the use of airfoil pillars and Nano fluids has increased the thermal characteristics of the three dimensional model in the form of heat exchange coefficient by almost 28.2%. The Nano fluid has been utilized for the 0.5% concentration.

Fluid Flow and Heat Transfer in a Lid-Driven Cavity Due to an Oscillating Thin Fin: Transient Behavior

2004 ◽  
Vol 126 (6) ◽  
pp. 924-930 ◽  
Author(s):  
Xundan Shi ◽  
J. M. Khodadadi
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Computational Study ◽  
Transient Behavior ◽  
Phase Lag ◽  
Dimensionless Time ◽  
Number Range ◽  
Flow And Heat Transfer ◽  
Periodic State ◽  
The Mean

A finite-volume-based computational study of transient laminar flow and heat transfer (neglecting natural convection) within a lid-driven square cavity due to an oscillating thin fin is presented. The lid moves from left to right and a thin fin positioned perpendicular to the right stationary wall oscillates in the horizontal direction. The length of the fin varies sinusoidally with its mean length and amplitude equal to 10 and 5 percent of the side of the cavity, respectively. Two Reynolds numbers of 100 and 1000 for a Pr=1 fluid were considered. For a given convection time scale tconv, fin’s oscillation periods (τ) were selected in order to cover both slow τ/tconv>1 and fast τ/tconv<1 oscillation regimes. This corresponded to a Strouhal number range of 0.005 to 0.5. The number of the cycles needed to reach the periodic state for the flow and thermal fields increases as τ/tconv decreases for both Re numbers with the thermal field attaining the periodic state later than the velocity field. The key feature of the transient evolution of the fluid flow for the case with Re=1000 with slow oscillation is the creation, lateral motion and subsequent wall impingement of a CCW rotating vortex within the lower half of the cavity. This CCW rotating vortex that has a lifetime of about 1.5τ brings about marked changes to the temperature field within a cycle. The dimensionless time for the mean Nusselt numbers to reach their maximum or minimum is independent of the frequency of the fin’s oscillation and is dependent on the distance between the oscillating fin and the respective wall, and the direction of the primary CW rotating vortex. The phase lag angle between the oscillation of the fin and the mean Nusselt number on the four walls increases as the distance between the fin and the respective wall increases.

Analysis of the Chimney Effect During the Reflooding Phase of a Large Break LOCA Transient With the 3D Module of the CATHARE2 Code

2008 ◽  
Author(s):  
Isabelle Tamburini ◽  
Valia Guillard ◽  
Nathalie Seiler
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Three Dimensional ◽  
Test Configuration ◽  
The Core ◽  
The Mean ◽  
The One ◽  
The Heat Transfer Coefficient ◽  
Dimensional Module ◽  
Chimney Effect

This study deals with the ability of the three-dimensional module of the CATHARE2 code to simulate the thermalhydraulic behavior of a 900MWe Pressurized Water Reactor (PWR) in Large Break Loss of Coolant Accident (LOCA) conditions. The CATHARE2 code is a “Best-Estimate” system code, developed by the CEA, in collaboration with EDF, AREVA NP and IRSN, used in France in the frame of realistic methodology to evaluate safety margins. Particularly, the realistic simulation of the so-called “chimney effect”, which occurs during the reflooding phase of a Large Break LOCA is of primary importance. Observed during experiments, this effect is indeed characteristic of the hydraulic behavior of a nuclear core presenting a non-uniform radial power profile. Several separate effect tests such as PERICLES 2D reflood and CCTF/SCTF experiments have demonstrated the existence of cross-flows between the hot assembly and the mean assemblies of the core during this reflooding phase. Liquid goes from the mean assemblies toward the hot one beneath the quench front leading to an increase in the heat transfer coefficient in the hot assembly compared to the one in the mean assemblies, and hence to a better cooling of the hot rod. After a literary survey on the “chimney effect”, quantitative information has been found in several publications concerning SCTF and CCTF tests. More precisely, a correlation has been established from the results of these tests providing the increase rate of the heat transfer coefficient in the hot assembly compared to the one in the mean assemblies depending on the power features of the core. The assumptions related to the establishment of this correlation are first validated in case of the PERICLES 2D Reflood test configuration. Then the simulation of the “chimney effect” by the three-dimensional module of the CATHARE2 code is analyzed by comparing simulation and experimental results in the PERICLES 2D Reflood test configuration. Finally, the same kind of study is performed with the simulation of a 900MWe PWR core in reflooding conditions typical of a Large Break LOCA transient. In both cases, the difference between the heat transfer coefficients of the hot assembly and the mean ones obtained during the CATHARE2 simulations is compared to the correlation derived from the SCTF and CCTF experimental results. While the simulation of a Large Break LOCA in a 900MWe PWR has quite well reproduced SCTF/CCTF experimental evidences, the study performed with PERICLES configuration has not given such satisfying results, probably due to the lack of representativeness of the device (only three aligned assemblies).

Fluid Flow and Heat Transfer in a Lid-Driven Cavity Due to an Oscillatory Thin Fin: Transient Behavior

2004 ◽  
Author(s):  
Xundan Shi ◽  
J. M. Khodadadi
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Computational Study ◽  
Transient Behavior ◽  
Phase Lag ◽  
Dimensionless Time ◽  
Number Range ◽  
Flow And Heat Transfer ◽  
Periodic State ◽  
The Mean

A finite-volume-based computational study of transient laminar flow and heat transfer (neglecting natural convection) within a lid-driven square cavity due to an oscillating thin fin is presented. The lid moves from left to right and a thin fin positioned perpendicular to the right stationary wall oscillates in the horizontal direction. The length of the fin varies sinusoidally with its mean length and amplitude equal to 10 and 5 percent of the side of the cavity, respectively. Two Reynolds numbers of 100 and 1000 with a Pr = 1 fluid were considered. For a given convection time scale (tconv), fin’s oscillation periods (τ) were selected in order to cover both slow (τ/tconv&gt;1) and fast (τ/tconv&lt;1) oscillation regimes. This corresponded to a Strouhal number range of 0.005 to 0.5. The number of the cycles needed to reach the periodic state for the flow and thermal fields increases as τ/tconv decreases for both Re numbers with the thermal field attaining the periodic state later than the velocity field. The key feature of the transient evolution of the fluid flow for the case with Re = 1000 with slow oscillation is the creation, lateral motion and subsequent wall impingement of a CCW rotating vortex within the lower half of the cavity. This CCW rotating vortex that has a lifetime of about 1.5τ brings about marked changes to the temperature field within a cycle. The dimensionless time for the mean Nusselt numbers to reach their maximum or minimum is independent of the frequency of the fin’s oscillation and dependent on the distance between the oscillating fin and the respective wall, and the direction of the primary CW rotating vortex. The phase lag angle between the oscillation of the fin and the mean Nusselt number on the four walls increases as the distance between the fin and the respective wall increases.

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