Phase Change Around Insulated Buried Pipes: Quasi-Steady Method

1981 ◽  
Vol 103 (3) ◽  
pp. 201-207 ◽  
Author(s):  
V. J. Lunardini
Keyword(s):  
Heat Transfer ◽  
Thermal Properties ◽  
Phase Change ◽  
Transfer Problem ◽  
Approximate Solutions ◽  
Burial Depth ◽  
Field Phase ◽  
Buried Pipes ◽  
Pipe Surface ◽  
Insulation Thickness

The heat transfer problem for cylinders embedded in a medium with variable thermal properties cannot be solved exactly if phase change occurs. Approximate solutions have been found using the quasi-steady method. The temperature field, phase change location, and pipe surface heat transfer can be estimated using graphs presented for parametric ranges of temperature, thermal properties, burial depth, and insulation thickness. The accuracy of the graphs increases as the Stefan number decreases and they should be of particular value for insulated hot pipes or refrigerated gas lines.

Approximate Phase Change Solutions for Insulated Buried Cylinders

1983 ◽  
Vol 105 (1) ◽  
pp. 25-32 ◽  
Author(s):  
V. J. Lunardini
Keyword(s):  
Thermal Properties ◽  
Phase Change ◽  
Numerical Solutions ◽  
Single Point ◽  
Approximate Solutions ◽  
Burial Depth ◽  
Pipe Surface ◽  
Insulation Thickness ◽  
Theoretical Results ◽  
Good Agreement

The conduction problem for cylinders embedded in a medium with variable thermal properties cannot be solved exactly if phase change occurs. New, approximate solutions have been found using the quasi-steady method. These solutions consider heat flow from the entire pipe surface, rather than from a single point, as has been assumed in the past. The temperature field, phase change location, and pipe surface heat transfer can be evaluated using graphs presented for parametric ranges of temperature, thermal properties, burial depth, and insulation thickness. The theoretical results show good agreement with complete numerical solutions. The accuracy of the method increases as the Stefan number decreases and the results are of particular value for insulated hot pipes or refrigerated gas lines.

Effectiveness of heat protection of fabrics loaded with phase change materials

e-Polymers ◽  
2009 ◽  
Vol 9 (1) ◽  
Author(s):  
Elham Fallahi ◽  
Mohammad Barmar ◽  
Mohammad Haghighat Kish
Keyword(s):  
Heat Transfer ◽  
Fourier Transform ◽  
Thermal Properties ◽  
Phase Change ◽  
Phase Change Materials ◽  
Chemical Nature ◽  
Woven Fabrics ◽  
Temperature Changes ◽  
Heat Protection ◽  
Exponential Relation

AbstractAmong different natural and non-corrosive products paraffin wax and camel fat are selected as phase change materials (PCM). These PCMs are applied to glass, polyester/viscose and wool/polyester woven fabrics. To examine their efficacy, their thermal behavior in a condition similar to the actual end uses is measured. Chemical nature and thermal properties of the PCMs are measured by Fourier transform infrared spectroscope and differential scanning calorimeter. A relation based on the principle of heat transfer is used to determine the temperature of a thermometer covered by fabrics loaded with PCMs. A simple exponential relation explains the experimental results. For glass and polyester/viscose fabrics use of these PCMs leads to substantial delays in the temperature changes. The important parameters for the evaluation of the products are discussed.

scholarly journals Effect of Inclined Magnetic Field on the Entropy Generation in an Annulus Filled with NEPCM Suspension

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Seyyed Masoud Seyyedi ◽  
M. Hashemi-Tilehnoee ◽  
M. Sharifpur
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Phase Change ◽  
Entropy Generation ◽  
Phase Change Materials ◽  
Transfer Problem ◽  
Mass Conservation ◽  
Melting Process ◽  
Industrial Applications ◽  
Inclined Magnetic Field

The encapsulation technique of phase change materials in the nanodimension is an innovative approach to improve the heat transfer capability and solve the issues of corrosion during the melting process. This new type of nanoparticle is suspended in base fluids call NEPCMs, nanoencapsulated phase change materials. The goal of this work is to analyze the impacts of pertinent parameters on the free convection and entropy generation in an elliptical-shaped enclosure filled with NEPCMs by considering the effect of an inclined magnetic field. To reach the goal, the governing equations (energy, momentum, and mass conservation) are solved numerically by CVFEM. Currently, to overcome the low heat transfer problem of phase change material, the NEPCM suspension is used for industrial applications. Validation of results shows that they are acceptable. The results reveal that the values of N u ave descend with ascending Ha while N gen has a maximum at Ha = 16 . Also, the value of N T , MF increases with ascending Ha . The values of N u ave and N gen depend on nondimensional fusion temperature where good performance is seen in the range of 0.35 < θ f < 0.6 . Also, Nu ave increases 19.9% and ECOP increases 28.8% whereas N gen descends 6.9% when ϕ ascends from 0 to 0.06 at θ f = 0.5 . Nu ave decreases 4.95% while N gen increases by 8.65% when Ste increases from 0.2 to 0.7 at θ f = 0.35 .

The Experimental Research and Numerical Simulation on Thermal Properties of Molten Salt at Melting Point

2009 ◽  
Author(s):  
Yannan Liang ◽  
Jiemin Zhou ◽  
Ying Yang ◽  
Ye Wu ◽  
Yanyan He
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Phase Change ◽  
Molten Salts ◽  
Phase Change Materials ◽  
Heat Storage ◽  
Phase Interface ◽  
Measuring System ◽  
Solid Liquid

The use of phase-change materials for latent heat storage is a new type of environmentally-friendly energy-saving technologies. Molten salts, one kind of phase-change materials, which have high latent heats, and whose phase transition temperatures match the high temperatures of heat engines, are the most widely used high-temperature phase-change heat storage materials. However, the heat transfer at solid/liquid phase interface belongs to Micro/Nanoscale Heat transfer, lots of the thermal properties of molten salt at melting point is difficult to test. In this investigation, based on the theory that the thermal conductivity can be determined by measuring the speed of the propagation of the solid/liquid phase interface during phase change, a set of system is developed to investigate the thermal conductivity of molten salts at liquid/solid phase transformation point. Meanwhile, mathematical calculation is applied to intuitively simulate the melting and solidifying process in the phase change chamber, by which the error could be analyzed and partly corrected and the result precision could also be increased. And a series of verification experiments have been performed to estimate the precision and the applicability of the measuring system to evaluate the feasibility of the method and measuring system. This research will pave the way to the follow-on research on heat storage at high temperature in industry.

On the Problem of Heat Transfer in a Phase-Change Slab Initially Not at the Critical Temperature

1987 ◽  
Vol 109 (1) ◽  
pp. 5-9 ◽  
Author(s):  
L. N. Gutman
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Transfer Problem ◽  
Maximum Error ◽  
Additional Time ◽  
Total Phase ◽  
Slab Temperature ◽  
Indirect Evaluation ◽  
Time Required ◽  
Perturbation Problems

A one-dimensional heat transfer problem in the phase-change slab, one side of which is isothermal while the other is insulated, is considered. Both cases—fusion and solidification—are treated. Slab temperature at the intitial moment is assumed constant and not critical. The main goal of this paper is to find the additional time required for a total phase change, compared with the case of the critical initial temperature. By analogy with perturbation problems in hydrodynamics, an appropriate solution is constructed consisting of an inner and an outer solution. The evaluation of the maximum error of the integral heat balance equation of the slab is treated as an indirect evaluation of the accuracy of the solution obtained. This evaluation shows that the solution can provide sufficient accuracy only in cases in which at least one of the three nondimensional parameters of the problem is small.

The Boiling Interface in a Misaligned Two-Phase Mechanical Seal

1997 ◽  
Vol 119 (2) ◽  
pp. 265-271 ◽  
Author(s):  
I. Etsion ◽  
M. D. Pascovici ◽  
L. Burstein
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Approximate Solutions ◽  
Operating Conditions ◽  
Mechanical Seal ◽  
Two Phase ◽  
Iterative Solutions

The boiling interface in a misaligned two-phase mechanical seal is analyzed using a complete thermohydrodynamic approach that requires complex simultaneous iterative solutions of the nonaxisymmetric heat transfer and phase-change problems. It is shown that under certain operating conditions, characterized by a modified Sommerfeld number, several approximate solutions with various levels of simplification can be utilized to calculate the boiling radius.

The Speedup of the Calculation of Heat Transfer Parameters in Thermal Insulation Coating Experiments

2019 ◽  
Vol 391 ◽  
pp. 11-17
Author(s):  
Michal Kopčok ◽  
Milan Jurči ◽  
Gabriela Pavlendová ◽  
Peter Šín
Keyword(s):  
Heat Transfer ◽  
Thermal Properties ◽  
Transfer Problem ◽  
Calculation Procedure ◽  
Concrete Material ◽  
Fourier Decomposition ◽  
Determination Process ◽  
Insulation Coating ◽  
Order Of Magnitude ◽  
Computational Aspects

This paper presents a quick calculation procedure to solve the heat transfer problem in some specific experimental arrangements. A brief overview of our previous efforts related to this topic is found in [1][2]. The goal of our effort is to quantify the thermal properties of insulation coatings applied to concrete material. We mostly deal with the computational aspects of thermal properties’ determination process. The proposed calculation approach is based on restricting the calculation to the first four members of the Fourier decomposition of the heat transfer partial differential equation’s solution. The reason for such a level of restrictions is given. The approach to the problem of deciding on the sufficient number of Fourier series’ members is indicated [3]. The effecting speedup is of three order of magnitude. Simplified formulas allowing the quick calculation of estimated values of material parameters are derived. The outline of an even quicker calculation procedure is described in a simplified manner.

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