Vibration effects on heat transfer during solidification of paraffin

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Previous work looked at the solidification process of PCM (phase change material) paraffin wax. Experimental results were compared with numerical work done in CFD package FLUENT. In the current study, the effects of vibration on heat transfer during the solidification process of PCM in a sphere shell are investigated. Enhancement of heat transfer results in quicker solidification times and desirable mechanical properties of the solid. The amount of PCM used was kept constant during each experiment by using a digital scale to check the weight, and thermocouple to check consistent temperature. A small amount of air was present in the sphere so that the sphere was not filled completely. Commercially available paraffin wax, RT35, was used in the experiments. Experimentations were done on a sphere of 40 mm diameter, wall temperature 20°C below mean solidification temperature, and consistent initial temperature. A vibration frequency was varied from 10-300 Hz was applied to the set-up and results compared with that of no vibration. Samples were taken at different times during the solidification process and compared with respect to solid material presentdc201

Experimental study of vibration effects on heat transfer during solidification of paraffin in a spherical shell

Two effects that have been observed when metals and metal alloys are vibrated during solidification are a decrease in dendritic spacing, which directly affects density, and faster cooling rates and associated solidification times. Because these two effects happen simultaneously during solidification, it is challenging to determine the one effect independently from the other. Most previous studies were on metals and metal alloys. In these studies, the one effect, i.e., the decrease in dendritic spacing, might influence the other, i.e., the faster cooling rates, and vice versa. The direct link between vibration and heat transfer has not yet been studied independently. The purpose of this study was to experimentally investigate the effect of vibration only on heat transfer and thus solidification rate. Experiments were conducted on paraffin wax, because it had a clearly defined macroscopic crystal structure consisting of mostly large straight-chain hydrocarbons. The advantage of the large straight-chain hydrocarbons was that the dendritic spacing was not affected by the cooling rate. Experiments were done with paraffin wax inside hollow plastic spheres of 40mm diameter with 1mm wall thickness. The paraffin wax was initially in a liquid state at a uniform temperature of 608C and then submerged into a thermal bath at a uniform constant temperature of 158C, which was approximately 208C below the mean solidification temperature of the wax. Experiments were conducted in approximately 300 samples, with and without vibration at frequencies varying from 10–300 Hz. The first set of experiments was conducted to determine the solidification times. In the second set of experiments, the mass of wax solidified was determined at discrete time steps, with and without vibration. The results showed that paraffin wax had vibration independent of solid density contrary to other materials, e.g., metals and metal alloys. Enhancement of heat transfer resulted in quicker solidification times and possible control over the heat transfer rate. The increase in heat transfer leading to faster solidifcation times was observed to first occur as frequency increased and then to decrease.The University of Pretoria and Prof. J. P. Meyer.http://www.tandfonline.com/loi/ueht202017-05-31hb2016Mechanical and Aeronautical Engineerin

Cleaning secondary effluents with organoclays and activated carbon

Abstract BACKGROUND: Flocculation, adsorption and ultrafiltration, alone and in combination, were tested for tertiary treatment of Beer Sheva (southern Israel) municipal wastewater. The focus was on the adsorption of soluble organics with powdered activated carbon (PAC) and with organoclays

Modelling Of High-Speed Jet Cooling On Microscale

In the present work, experimental and numerical studies were performed in order to investigate the cooling performance of a single-phase flow in micro-channel/slot-jet system. A three-dimensional numerical model of jet cooling was developed and implemented using commercial software ANSYS Fluent. The 3D conjugate conduction/convection heat transfer in the micro-channel simulations were used to complement experiments and to obtain detailed flow patterns of the jet, temperature, and heat flux distribution on the heater area, and fluid temperature distribution. The model has been verified in a preliminary study where its time-step and grid independency was established and validated vs. experiments

Local Heat Transfer Coefficients Measurement Under Micro Jet Impinging Using Nitrogen Gas (N2)

Experimental and simulation studies were performed to reveal local heat transfer coefficients under jet impinging in micro domain with Nitrogen gas. The experimental device was made of a 500 μm thick Pyrex and 400 μm thick silicon wafers. On the Pyrex wafer, four 100 nm thick resistance temperature detector (RTD) thermistors and a heater were fabricated from titanium. Jet orifices were etched by deep reactive ion etching (DRIE) on a silicon wafer, which was attached to the Pyrex wafer through a vinyl sticker (250 μm thick). A 1.9 mm × 14.8 mm × 250 μm micro channel was formed by laser drilling into the sticker. Varying flow rates of Nitrogen gas and heat fluxes of the heater, temperatures of the four thermistors were collected and local heat transfer coefficients were inferred enabling to divulge the jet impinging cooling characteristics. Initial simulations were used to complement experiments and to obtain detailed flow patterns of the jet, temperature distribution on the heater area, and fluid temperature distribution

Experimental And Numerical Investigation Of Heat Removal By Microjets

In an ongoing collaborative work, experimental and numerical studies are performed to investigate the cooling ability of single-phase microjets of various configurations. Experimental studies include manufacturing and testing of microdevices. Three-dimensional numerical models of jet cooling are developed and implemented using commercial software ANSYS ® Fluent. The simulations are used to reproduce the experimental conditions and to obtain detailed flow fields of the jet, heat flux, and temperature distribution on the impingement area, temperature distribution in the fluid, and heat transfer coefficients at the heated surface