Review on phase change materials (PCMs) for cold thermal energy storage applications

Thermal energy storage for low and medium temperature applications using phase change materials – a review

Properties of aqueous solutions of lithium and calcium chlorides: formulations for use in air conditioning equipment design

Introduction T reattachment of a turbulent shear layer is an important process in a large number of practical engineering configurations, including diffusers, airfoils with separation bubbles, buildings, and combustors. In order to predict these complicated flows, we must understand and be able to predict the behavior of reattaching shear layers. However, our current understanding of the reattachment process is poor, a fact demonstrated by our inability to predict simple reattaching flows over a wide range of parameters. In fact, a complete list of the parameters that affect reattachment has yet to be formulated. Among two-dimensional flows, the backward-facing step is the simplest reattaching flow. The separation line is straight and fixed at the edge of the step, and there is only one separated zone instead of two, as seen in the flow over a fence or obstacle. In addition, the streamlines are nearly parallel to the wall at the separation point, so significant upstream influence occurs only downstream of separation. Although they are not always stated explicitly, these are the reasons why most of the research on reattachment has been done in backward-facing step flows. The backward-facing step is also used as a building block flow for workers developing turbulence models. Therefore, it is important to supply data which can be used to test codes and information that may aid the development of future codes. Bradshaw and Wong reviewed the experimental data for reattaching flows in 1972. Since that time there has been a proliferation of new research in the area, particularly since the advent of the laser anemometer and the pulsed-wire anemometer. This research has been conducted by a number of independent groups, and therefore the net result is somewhat disorganized. Very little systematic study has been done on the effect of the governing parameters on reattachment. In addition, most of the experiments, when viewed separately, have failed to cast any new light on the underlying physics of the reattachment process. The purpose of this paper is twofold. The primary purpose is to review the available data for turbulent flows over backward-facing steps, including some new data of our own and other previously unpublished data. Second, we suggest several areas of research that we feel could lead to improvements in our ability to predict flows with separation bubbles. Several physical mechanisms will be proposed to explain some of the phenomena that have been observed. It is our hope that these suggestions will provoke further thought, comment, and research. The review covers subsonic flows over backward-facing steps in which the Reynolds number is high enough to insure that the separated shear layer is fully turbulent. Important work on laminar and transitional reattaching shear layers has been performed by Goldstein et al. and Armaly et al. but will not be referred to here. Primary emphasis is on planar flows, but some data from axisymmetric flows will be utilized. Double-sided, sudden expansion flows in which the flow is asymmetric are not considered here, because these flows are even more complicated than flows with a single separation bubble. A companion paper examines the uncertainty of the available data in more detail. It also assesses the usefulness of the various data sets as test cases for computational procedures.

A Review of Research on Subsonic Turbulent Flow Reattachment

Twenty-seven studies on the thermal conductivity of snow (k eff ) have been published since 1886. Combined, they comprise 354 values of k eff , and have been used to derive over 13 regression equations predicting k eff vs density. Due to large (and largely undocumented) differences in measurement methods and accuracy, sample temperature and snow type, it is not possible to know what part of the variability in this data set is the result of snow microstructure. We present a new data set containing 488 measurements for which the temperature, type and measurement accuracy are known. A quadratic equation, k eff = 0.138 - 1.01ρ + 3.233ρ 2 {0.156 ≤ ρ ≤ 0.6} k eff = 0.023 + 0.234ρ {ρ < 0.156}, where ρ is in g cm -3 and k eff is in W m -1 K -1 , can be fit to the new data (R 2 =0.79). A logarithmic expression, k eff = 10 (2.650ρ-1.652) {ρ ≤ 0.6}, can also be used. The first regression is better when estimating values beyond the limits of the data; the second when estimating values for low-density snow. Within the data set, snow types resulting from kinetic growth show density-independent behavior. Rounded-grain and wind-blown snow show strong density dependence. The new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set. This shift is attributed to differences in snow types and sample temperatures in the sets. Using both data sets, we show that there are well-defined limits to the geometric configurations that natural seasonal snow can take.

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The thermal conductivity of seasonal snow

The paper reviews and discusses data and information on the thermophysical properties of ice, snow, and sea ice. These properties include thermal conductivity, specific heat, density, thermal diffusivity, latent heat of fusion, thermal expansion, and absorption coefficient. The available data are shown graphically for convenience in conjunction with the recommended correlation equations.

Thermophysical properties of ice, snow, and sea ice

Experimental visualization of natural convective flow was carried out by using several kinds of fluid contained in a narrow vertical rectangular cavity with one vertical wall heated, the opposing vertical wall cooled and the upper and lower walls insulated. The effects of the Prandtl number Pr of the working fluid and the width of the cavity W on the flow pattern are discussed qualitatively in the present paper. The occurrence of flow patterns consisting of unicellular flow, steady secondary flow, tertiary flow and transition (from laminar to turbulent) flow is categorically demonstrated by the photographs taken. Moreover, experimental measurements of the net heat transfer through the vertical fluid layer are given for aspect ratios of 6-30 and Prandtl numbers of 4-12 500.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112078000427

Visual observation of natural convective flow in a narrow vertical cavity

Heat transfer in a confined rectangular cavity packed with porous media

Experiments to measure the heat transfer characteristics for various cavities situated at a duct-wall were performed. Flow visualization, measurements of pressure and temperature distributions on the heated bottom surface of cavity were carried out. It was observed that the effects of main flow stream, reattachment of separated flow, and vortex flow in the cavity on heat transfer unexpectedly large. It was found that heat transfer did not always decrease monotonously with an increase of aspect (depth-width) ratio D/W, in the flow range of laminar to turbulent. Correlations between Num and Rew were made in laminar and turbulent heat transfer ranges.

Shoichiro Fukusako

Papers

Thermophysical properties of ice, snow, and sea ice

Visual observation of natural convective flow in a narrow vertical cavity

Heat transfer in a confined rectangular cavity packed with porous media

Forced Convection Heat Transfer on Heated Bottom Surface of a Cavity

Recent advances in research on water-freezing and ice-melting problems