Search

In this work, the authors wanted to demonstrate the possibility to increase the heat transfer efficiency by using simple wire coil inserts to create turbulent flow in the boundary layer as well as ...

In this paper, the possibility of heat transfer enhancement in the U-bend exchanger was presented. Experimental research has been carried out for four individual heat exchanger constructions i.e. plain tube in tube, turbulized tube in tube, plain U-bend and U-bend with turbulator. Also, heat transfer experiments for various boundary conditions were performed to obtain reference values. In case of U-bend exchanger with and without turbulator, tests were conducted based on the water-water system. The study covered a wide measuring range, i.e. Re = 800–9000 - on the jacket side, Pel = 500–1400 W (for reference) cold water temperature of 9°C and hot water of 50°C. The exchangers were made from a copper pipe with an external diameter of 10 mm and 18 mm and wall thickness of 1 mm. The helicoidal vortex generator was made from brass wire with a diameter of 2.4 mm, coil diameter 13 mm and pitch 11 mm. For these geometries, the values of pressure drop and rate of heat transfer were determined. The comparison of heat transfer efficiency was performed based on NTU-e method. For the same thermal-flow parameters, wire inserts provide up to 280% heat transfer enhancement and 85% higher heat transfer rate.

The latent heat thermal energy storage units are very popular because of their high energy density and almost close to constant temperature during the charging/discharging. In the present study has been proposed new shell-and-coil geometry with a shifted coil position to enhance the performance of phase change thermal magazine. The experimental investigations have been performed both for the melting and solidification process of coconut oil for constant wall temperature conditions. The experiments have been carried out for cylindrical as well as coil shape geometry of the TES unit. In the case of annular TES, the copper tube with outer diameter d = 10 mm and total length equal to 165 mm were used (4). In the case of shell-and-coil TES the coil has been also made of a copper tube but with an outer diameter d = 6 mm. The total length of the tube was 460 mm. However, the length of the tube element that has been used in the process of bending the coil had a total length equal to 360 mm. The rest of the tube was straight. The coil pitch was 15 mm and the outer coil diameter was 26 mm. The experiments have been conducted for the coil position at the top and the bottom of the tank. The results showed the influence of heat transfer geometry for phase change efficiency. The article presents the thermal characteristic of melting and solidification phenomena as well as their visual analysis. A significant impact of heat transfer geometry at the shape of the melting and solidification profile. The optimal performance has been achieved for shell-and-coil TES with a coil arranged at the top of the tank.

This article presents the experimental investigations of the coconut oil-based TES module for HVAC applications in the ambient and-sub ambient temperature range. To properly study this problem modular experimental module and test loop were developed. Special attention has been paid to study the physical mechanism of the melting/solidification process for natural substance (coconut oil) which has perspectives to be used in thermal energy storage systems. It has been a highlight that the melting/solidification process is much more complex for non-eutectic mixtures and there are limited analytical models witch could be used to design TES working with such substances. Due to the limit of literature data for thermophysical properties of coconut oil own experimental data has been conducted. The article presents both visual and thermal characteristics of the melting and solidification process. It has been confirmed the strong influence of natural convection phenomena at the melting process. What is more, it has been observed that in the case of coconut oil it is better to talk about appearance melting temperature than melting temperature. The experimental analysis confirmed that appearance melting temperature is a function of radial distance from the heat source. In the case of solidification, the influence of natural convection is reduced quickly due to the increasing domination of the conduction heat transfer mechanism. For the solidification temperature profiles are characteristic of the occurrence of subcooling temperature. The level of temperature drop in sub cooling is a function of radial distance from the heat source. It has been also confirmed that in case of melting as well as solidification process the shape of the phase-change profile seems to form a truncated cone (in case of melting inverted). To validate the engineering approach to vast discrepancies in the literature data own experiment has been evaluated with a simple mathematical model to verify the applicability of the literature data in system behavior prediction. Based on the best-fit approach the parameters thermal resistance of the module R = 1.3 W/K was found. Additionally the latent heat of the coconut oil of 178 kJ/kg with Gaussian distribution ( σ = 1.1 ) for melting in temperature of 25 °C and solidification at 21 °C. The proposed correlation can be easily used to optimize latent thermal energy storage cooperated with the HVAC system.

In contrast to the very rich literature on modeling and the determination of the thermal conductivity of nanofluids the forced convection data are limited. This work presents preliminary results of the experimental investigation of the forced convection heat transfer of water-Al2O3 nanofluids inside stainless steel tube with 8 mm internal diameter and 2000 mm length. Nanoparticles were tested at the concentrations of 0.01%, 0.1%, 1% and 5% by weight and the Reynolds number range encompasses laminar as well as turbulent flows.

In this paper, forced convection of water/EG-Al2O3 nanofluids inside horizontal stainless steel tube is studied experimentally. As base fluid served water/EG mixture of two ratios (60:50 and 50:50). Nanoparticle mass concentrations was 0.1% or and 1%. Transition and turbulent flow regimes were tested. Average heat transfer coefficient and pressure drop values were determined for nanofluids and compared to base fluids. Deterioration of heat transfer for all tested nanofluids has been recorded compared to base fluid. Negligible increase of pressure drop for nanofluids compared to base fluids has been observed.

W artykule zostaly przedstawione klasyczne metody usuwania śniegu i lodu z nawierzchni uzytkowych. Dokonano analizy skutkow wykorzystywania środkow chemicznych. Opisano szacunkowe koszty wynikające z konieczności utrzymania nawierzchni uzytkowych „niszczonych” w skutek zmian temperaturowych i wykorzystywanych środkow chemicznych. Przedstawiono nowoczesne metody odmrazania oparte o zastosowanie systemow podgrzewania elektrycznego jak i ukladow wykorzystujących odnawialne źrodla energii. W artykule polozono nacisk na rozszerzenie informacji w zakresie stosowalności i technologii pasywnych ukladow odladzania opartych o wykorzystywanie rurek ciepla i ukladow termosyfonowych. Zaprezentowano budowe stanowiska pomiarowego i zaawansowanie prac badawczych w kierunku opracowania wysokoefektywnego ukladu odladzania/odśniezania powierzchni wykorzystującego rurke ciepla (termosyfon).