Thermal Conductivity Of Polyurethane Foam Research Articles

EFFECT OF BENTONITE AND DOLOMITE ADDITIVES ON RIGID POLYURETHANE

In this study, clay minerals such as bentonite and dolomite were included to increase the compressive tensile strength and decrease the thermal conductivity of rigid polyurethane foam. The effect of different combinations and amounts of clay minerals on the test parameters of the foam was investigated. The surface morphology of the doped foams was investigated by scanning electron microscopy (SEM). Polyurethane foams were subjected to compressive-tensile strength and thermal conductivity tests. Improvement was observed in the thermal conductivity of polyurethane foams containing 1% bentonite and in the compressive and tensile strengths of polyurethane foams containing 2% dolomite. When clay minerals were added to polyurethane foam in combination, both thermal conductivity and compressive and tensile strengths were improved.

Effect of the shape and the distribution of cells on the effective thermal conductivity of polyurethane foam

AbstractTo design foams with specific properties, it is important to be able to predict their effective properties. The objective of this study is to compare and quantify the effect of the geometrical parameters on the thermal properties. Then the study uses both analytical and numerical homogenization methods to connect micro‐scale parameters to the macro‐scale thermal behavior. Several statistical studies of the morphology have been used to model the different categories of PU foams. The foam is modeled by a periodic structure of open, closed, or mixed cells. For each type of cell, different idealized shapes of a single cell are used, while keeping a constant porosity for each category. In the case of mixed cells, the effect of the relative positioning of cells is investigated. The results show that the effective thermal conductivity is considerably impacted by the cell shape. Moreover, the geometrical modeling of the struts, in the heuristic modeling, has also an important effect. Furthermore, the relative position of gas cavities, in the spherical representation, influences the effective thermal conductivity. However, the distribution of open and closed cells, in the case of mixed cell foam, has a limited effect.

Experimental Studies of the Effective Thermal Conductivity of Polyurethane Foams with Different Morphologies

Polyurethane foam (PUF) is actively used for thermal insulation. The main characteristic of thermal insulation is effective thermal conductivity. We studied the effective thermal conductivity of six samples of PUF with different types and sizes of cells. In the course of the research, heat was supplied to the foam using an induction heater in three different positions: above, below, or from the side of the foam. The studies were carried out in the temperature range from 30 to 100 °C. The research results showed that for all positions of the heater, the parameter that makes the greatest contribution to the change in thermal conductivity is the cell size. Two open-cell foam samples of different sizes (d = 3.1 mm and d = 0.725 mm) have thermal conductivity values of 0.0452 and 0.0287 W/m⸱K, respectively, at 50 °C. In the case of similar cell sizes for any position of the heater, the determining factor is the type of cells. Mixed-cell foam (d = 3.28 mm) at 50 °C has a thermal conductivity value of 0.0377 W/m⸱K, and open-cell foam (d = 3.1 mm) at the same temperature has a thermal conductivity value of 0.0452 W/m⸱K. The same foam sample shows different values of effective thermal conductivity when changing the position of the heater. When the heater is located from below the foam, for example, mixed-cell foam (d = 3.4 mm) has higher values of thermal conductivity (0.0446 W/m⸱K), than if the heater is located from above (0.0390 W/m⸱K). There are different values of the effective thermal conductivity in the upper and lower parts of the samples when the heater is located from the side of the foam. At 80 °C the difference is 40% for the open-cell foam (d = 3.1 mm).

Cryogenic thermal insulating and mechanical properties of rigid polyurethane foams blown with hydrofluoroolefin: Effect of perfluoroalkane

The effect of perfluoroalkane (PFA) on the morphology, thermal conductivity, mechanical properties and thermal stability of rigid polyurethane (PU) foams was investigated under ambient and cryogenic conditions. The PU foams were blown with hydrofluorolefin. Morphological results showed that the minimum cell size (153 μm) was observed when the PFA content was 1.0 part per hundred polyols by weight (php). This was due to the lower surface tension of the mixed polyol solution when the PFA content was 1.0 php. The thermal conductivity of PU foams measured under ambient (0.0215 W/mK) and cryogenic (0.0179 W/mK at −100°C) conditions reached a minimum when the PFA content was 1.0 php. The low value of thermal conductivity was a result of the small cell size of the foams. The above results suggest that PFA acted as a nucleating agent to enhanced the thermal insulation properties of PU foams. The compressive and shear strengths of the PU foams did not appreciably change with PFA content at either −170°C or 20°C. However, it shows that the mechanical strengths at −170°C and 20°C for the PU foams meet the specification. Coefficient of thermal expansion, and thermal shock tests of the PU foams showed enough thermal stability for the LNG carrier’s operation temperature. Therefore, it is suggested that the PU foams blown by HFO with the PFA addition can be used as a thermal insulation material for a conventional LNG carrier.

Computational Effective Thermal Conductivity of Polyurethane Mixed Cell Foams

The objective of this paper was to calculate effective thermal conductivity of polyurethane foam used in thermal insulation of buildings with a new modeling approach. The proposed approach was more realistic as it simulated the real fraction of closed cells and open cells in the foam and it modeled the real physical phenomena that happen when both types of cells are present. This study was investigated for polyurethane foam with 70 % of closed cells and 30 % of open cells, by using finite element method and numerical homogenization. The result showed that there was a systematic change in thermal conductivity when the type of cell (closed, open and mixed cell) varied at fixed volume fraction. Also the effective thermal conductivity of mixed cell of this PU foam was about λm= 0.07 W.m-1.K-1. Simulation proved the interest of this approach. Indeed, it brought new factor that influence the effective parameters which was fraction of closed cells and open cells. They suggested new method for computing thermal conductivity as a function of thermal conductivity of closed and open cell foam.

구조 복합재료 기반 이종재료 첨가시의 유리섬유의 열적 성능 평가에 대한 실험적 연구

Glass wool is an eco-friendly materials that is manufactured through a continuous process by processing waste glass. This materials is low cost compared with another materials and has excellent thermal conductivity. For this reason, glass wool is installed as insulation system for LNG carriers and as insulation of building wall as well as various industries. The mechanism of insulation of glass wool is the conduction of the wool itself and convection by space between fibers. Therefore, in order to develop the enhanced thermal conductivity of glass wool is necessary to reduce its own conduction or to insert additional material after manufacturing as well as prevent convection. In this respect, many researchers have been actively studying to decrease thermal conductivity of polyurethane foam using by inserted glass wool or change the chemical component of glass wool. However, many research are aiming reduction of glass wool itself. This study focus on post-processing and inserted different materials; silica-aerogel, kevlar fiber 1mm, 6mm and glass bubble. Experimental results show that the thermal conductivity almost decreases with the addiction of glass bubble and silica aerogel.

Modeling of Flexible Polyurethane Foam Shrinkage for Bra Cup Moulding Process Control.

Nowadays, moulding technology has become a remarkable manufacturing process in the intimate apparel industry. Polyurethane (PU) foam sheets are used to mould three-dimensional (3D) seamless bra cups of various softness and shapes, which eliminate bulky seams and reduce production costs. However, it has been challenging to accurately and effectively control the moulding process and bra cup thickness. In this study, the theoretical mechanism of heat transfer and the thermal conductivity of PU foams are first examined. Experimental studies are carried out to investigate the changes in foam materials at various moulding conditions (viz., temperatures, and lengths of dwell time) in terms of surface morphology and thickness by using electron and optical microscopy. Based on the theoretical and experimental investigations of the thermal conductivity of the foam materials, empirical equations of shrinkage ratio and thermal conduction of foam materials were established. A regression model to predict flexible PU foam shrinkage during the bra cup moulding process was formulated by using the Levenberg-Marquardt method of nonlinear least squares algorithm and verified for accuracy. This study therefore provides an effective approach that optimizes control of the bra cup moulding process and assures the ultimate quality and thickness of moulded foam cups.

Thermal and Mechanical Characterization of Polymeric Foams with Controlled Porosity Using Hollow Thermoplastic Spheres.

Polyurethane (PU) foams with controlled porosity and pore structure are prepared via judicious study on expanding process parameters for thermoplastic expandable microspheres which are compatible with PU synthetic process. Thermal and mechanical properties of PU foams are found to be generally governed by amount of the porosity. Thermal conductivity of PU foams with controlled porosity is measured at 30 °C with transient hot bridge method. The measured thermal conductivity of PU foams is estimated using theoretical models, proving the formation of spherical pore structures of expandable microspheres in PU matrix and serving as an internal porous material.

Numerical predictions of the effective thermal conductivity of the rigid polyurethane foam

A reconstruction method is proposed for the polyurethane foam and then a complete numerical method is developed to predict the effective thermal conductivity of the polyurethane foam. The finite volume method is applied to solve the 2D heterogeneous pure conduction. The lattice Boltzmann method is adopted to solve the 1D homogenous radiative transfer equation rather than Rosseland approximation equation. The lattice Boltzmann method is then adopted to solve 1D homogeneous conduction-radiation energy transport equation considering the combined effect of conduction and radiation. To validate the accuracy of the present method, the hot disk method is adopted to measure the effective thermal conductivity of the polyurethane foams at different temperature. The numerical results agree well with the experimental data. Then, the influences of temperature, porosity and cell size on the effective thermal conductivity of the polyurethane foam are investigated. The results show that the effective thermal conductivity of the polyurethane foams increases with temperature; and the effective thermal conductivity of the polyurethane foams decreases with increasing porosity while increases with the cell size.

Statistical evaluation of the effect of formulation on the properties of crude glycerol polyurethane foams

In our pursuit of developing ecofriendly materials, the effect of the main components of the formulation used for the preparation of polyurethane foams (PUFs) derived from unrefined crude glycerol (CG) has been systematically studied. A series of PUFs has been prepared using formulations with judicious variations of the percentage of each component. The physical properties of the resulting PUFs were measured and the data collected were statically treated using a four-way functional ANOVA method. From the ANOVA results, the paramount importance that the blowing agent and the surfactant have on the regulation of density and thermal conductivity of PUFs was recognized. Regarding the mechanical properties, the isocyanate content presented a dominant influence on the increase of Young's modulus, toughness and compressive stress of PUFs.

Can We Make Better Polyurethane Composite Foams with Oil Sands Mature Fine Tailing?

This study explains how to make rigid polyurethane/mature fine tailings (PU/MFT) foam composites with good mechanical and thermal properties by in situ polymerization. Compared to PU/Cloisite Na+ and PU/Cloisite 30B composites, the novel PU/MFT composites have similar tensile properties, but better thermal properties. Adding 2 parts per hundred parts (pphp of polyol by weight) of MFT particles decreases the thermal conductivity of polyurethane foam by 10%, while adding Cloisite Na+ or Cloisite 30B decreases it by only 6% and 5%, respectively, resulting in considerable energy savings in large-scale insulation applications. PU/MFT foams also sustain about the same compressive strength and modulus even when loaded up to 20 pphp MFT. These results are important for oil sands industries trying to decrease the environmental footprint of their operations and for polyurethane-producing companies attempting to improve properties of their products and contribute to environmental cleanup.

THE USE OF INTEGRAL FOAMS TO IMPROVE THE EFFICIENCY OF INSULATION OF PIPELINES

Foamed plastics are an effective material for pipe insulation. Among the advantages of this material include the ability to form heat-insulating coating with a given density distribution through the thickness, to obtain a so-called integral foams. This allows to increase the density and hence the strength of external insulation layers most exposed to external mechanical influences. This decreases the moisture permeability of the coating, which is important for underground laying underground pipeline. Insulation effect of the inner layers, and consequently the coating is enhanced through reduction of their density, since there is a direct correlation between the density of the insulation and its thermal conductivity. Achieved such a redistribution of density by influencing the technology of production of foam during the polymerization. In the presented work are given the solution of the heat conduction equation for a stationary case at the steady state temperatures at the inner and the outer surfaces of the insulation. The thermal conductivity of the insulation was considered as a variable depending on the density of the insulation, which is distributed in a certain way through the thickness of the coating. The formula allowing to calculate the equivalent thermal conductivity of the coating at any possible density distribution along its thickness. Taking into account the linear character of the dependence of the thermal conductivity of polyurethane foam is its density, obtained a modification of this formula for the case when the heat-insulating coating consists of two layers: the inner, fixed minimum allowable density, and external, where the density increases to the maximum value on the surface of the coating. A recommendation to determine the thickness of each layer at a known specific weight of foam per unit of pipe length. On the example of thermal insulation of polyurethane foam with an integral structure for medium diameter tubing shown the ability to reduce heat loss by nearly 14% compared with homogeneous insulation of the same specific gravity.

Determination of effective thermal conductivity for polyurethane foam by use of fractal method

The microstructure of polyurethane foam is disordered, which influences the foam heat conduction process significantly. In this paper foam structure is described by using the local area fractal dimension in a certain small range of length scales. An equivalent element cell is constructed based on the local fractal dimensions along the directions parallel and transverse to the heat flux. By use of fractal void fraction a simplified heat conduction model is proposed to calculate the effective thermal conductivity of polyurethane foam. The predicted effective thermal conductivity agrees well with the experimental data.

Reaction injection molding of polyurethane foam for improved thermal insulation

AbstractA study on the apparent thermal conductivity of polyurethane foam was carried out. A HCFC (hydrochlorofluorocarbon) gas and carbon dioxide were used as the physical blowing agent and ultrasonic excitation was applied to increase the rate of bubble nucleation. The thermal conductivity of the binary gas mixture was predicted theoretically to estimate the apparent thermal conductivity of the polymer foam. Effects of conduction and radiation on the apparent thermal conductivity of the cellular polyurethane were considered with respect to the cell size and the effect of convection was neglected because of the small cell size. A laboratory RIM machine was designed and built for foaming experiments. The foaming experiments were performed at various processing conditions, and density, apparent thermal conductivity, number of cells, and cell sizes were measured. Best results such as low thermal conductivity and small bubbles were obtained when the polyol was mixed with the HCFC gas and saturated with carbon dioxide at 0.3 MPa, and foamed with ultrasonic nucleation.

Thermal conductivity of polyurethane foams

The thermal conductivity of polyurethane (PU) foams at gas pressure between 760 torr and 0.014 torr is investigated theoretically and experimentally. Six different cell sizes ranging from 150 to 350 μm of PU foam insulation are used as the samples. Experimental results are also obtained for the spectral extinction coefficient using a Fourier transform infrared spectrometer. The thermal conductivity of PU foams for different cell sizes at 760 torr varies from 33.3 to 34.5 mW/m K, and reduces to 6.82–9.15 mW/m K at a gas pressure of 0.014 torr; the effective thermal conductivity decreases when the cell size becomes smaller. At gas pressure 0.014 torr, radiative heat transfer accounts for approximately 20% of the total heat transfer through PU foams, while solid conduction accounts for the other 80%.

Thermal conductivity of polyurethane foams from room temperature to 20 K

The thermal conductivity of the polyurethane (PU) foam in the temperature range between 300 and 20 K is investigated theoretically and experimentally for the development of liquid hydrogen storage tanks. An experimental set-up based on the JIS standard A1412 is built to measure the thermal conductivity of the foams under various temperature and pressure conditions. An analytical model, including the contributions from radiative heat transfer, is used to predict the thermal conductivity of the PU foams. The model is found to be able to accurately predict the thermal conductivity of the PU foams under normal and reduced pressures. The thermal conductivity of the PU foam can be reduced by as much as 70% by evacuating the gases in the foam cells. Radiative heat transfer is found to account for about 10–20% at room temperature. The thermal conductivity data below 90 K are available for the first time.

Thermal transport in polystyrene and polyurethane foam insulations

The thermal transport in polystyrene (PS) and polyurethane (PU) foam insulations is described, with special emphasis on the radiative transfer. Calorimetric measurements of the total conductivity are performed in a guarded hot-plate device. The radiative properties of the foams are derived from infraredoptical investigations with an FTIR spectrometer. In the case of the PS foam, radiative properties are also extracted from calculations using the Mie scattering theory for infinite cylinders and platelets, representing the struts and walls of the foam cells, respectively. The total thermal conductivity of PU foams, including condensation effects of the blowing agent R 11, is modelled.