Boiling heat transfer characteristics of binary magnetic fluid flow in a vertical circular pipe with a partly heated region

Abstract

An investigation was conducted for heat transfer characteristics of binary magnetic uid ow in a partly heated circular pipe experimentally. The boiling heat transfer characteristics on the effects of the relative position of the magnetic eld to the heated region were particularly considered in the present study. F rom the experimental veri cation, the N usselt number, representing boiling heat transfer characteristics, was obtained for various ow and magnetic conditions which were represented by the non-dimensional parameters of the R eynolds number and the magnetic pressure number. Additionally, the rate of change of the N usselt number found by applying the magnetic eld was also estimated and the optimal position of the eld to the partly heated region was discussed. The results indicated that the effect of the magnetic eld to the heat transfer rate from the heated wall was mainly subjected to the effect of the vortices induced in the magnetic eld region and the possibility of controlling the heat transfer rate by applying an outer magnetic eld to utilize the effect. Keywords: magnetic uid, heat transfer, boiling two-phase ow NOTATION C p0 speci c heat of the uid at the representative temperature D inner diameter of the ow pipe and the test sectionˆ0.01 m D 0 outer diameter of the test sectionˆ0.05 m G mass owrate (kg/s) h heat transfer coef cient H r radial component of the magnetic eld H z axial component of the magnetic eld L length of the heated wallˆ0.1 m M max magnetization of the uid at the eld H max M r radial component of magnetization M s saturation magnetization of the uid at the representative temperature M z axial component of magnetization N u average N usselt number N u…z ‡ † local N usselt number for z ‡ p pressure of the uid (Pa) Pr Prandtl number Q total heat transfer from the heated wall to the uid R e R eynolds number R p the magnetic pressure number T in temperature of the uid at the inlet of the test sectionˆ327 K (representative temperature) T w temperature of the heated wallˆ377 K T w, in mean temperature of the inner wall of the test section T w, out mean temperature of the outer wall of the test section u speci c internal energy (J/kg) U in mean velocity of the uid at the inlet of the test section z ‡ non-dimensional length from the inlet of the test sectionˆ…z=D †=…Re=Pr † Dc distance from the centre of the heated region to the distribution centre of magnetic eld DN u m rate of change of the average N usselt number after applying the magnetic eld l 0 heat conductivity of the uid at the representative temperature l B heat conductivity of brassˆ118 W/m K

Development of magnetically-driven cooling device with concentric pipe structure

“…Magnetic pressure Δ p acting on TSMF per unit volume is given as the following equation with the assumption of H // M 1,12 where H is the magnetic field and M is the magnetization, and index 1 and 2 denote specific places of magnetic field. For the binary TSMF, the magnetic pressure Δ p can be written with the following formula, due to the dependence of magnetization on temperature and the void in the bulk body of magnetic fluid, 8,9 we have where μ 0 is the vacuum magnetic permeability, χ is the magnetic susceptibility, α is the void fraction of the gas in the binary TSMF, and T is the temperature with T c and T 0 denoting the Curie and reference temperature. In order to illustrate the basic structure of the present cooling device, Figure 1 shows the schematic diagram of the operating principle with concentric pipe structure, where the magnetic field can be imposed by solenoid coil externally.…”

“…Since a pioneering research of energy conversion using TSMF was originally conducted by Resler and Rosensweig, 2 much efforts have been devoted to the investigation of flow characteristics of TSMF for achieving perfect energy conversion devices. 3–11 As an advantage of the heat transport medium utilizing the TSMF, the structure of the heat exchanger can be drastically simplified and the heat transport apparatus can be modified and downsized in view of actual application for developing a new conventional energy transporting devices. However, previous studies so far reported have revealed that the driving force of TSMF and the heat transporting capacity are too small to meet industrial requirement, when the heat transport device utilizes the only temperature-sensitive magnetization characteristic.…”

“…Based on the past research attempts, Yamaguchi et al. 7–11 have proposed the utilization of a boiling two-phase flow using a binary mixture of magnetic fluid, which is a mixture of a low boiling point solution to the bulk of magnetic fluid. By the appearance of boiling bubble of low boiling point solution in the binary mixture of magnetic fluid, not only the improvement of driving force due to the spatial average magnetization reduction and the magnetic ejection effect, which is a reverse force acting on bubble against magnetic body force, 1,4 but also much enhancement of heat transfer by boiling latent heat can be expected without any requirement of external power consumption.…”

“…By the appearance of boiling bubble of low boiling point solution in the binary mixture of magnetic fluid, not only the improvement of driving force due to the spatial average magnetization reduction and the magnetic ejection effect, which is a reverse force acting on bubble against magnetic body force, 1,4 but also much enhancement of heat transfer by boiling latent heat can be expected without any requirement of external power consumption. In the series of studies, 7–11 self-driven heat transport is in fact realized by heating a magnetic fluid from the outside of a simple circular pipe configuration. However, considering practical engineering applications such as heat recovery from low- to high-temperature wasted gas, there is structural difficulty to recover heat from the outside of a simple circular pipe configuration.…”

Review of two-phase flow and flow boiling of mixtures in small and mini channels

“…These studies generally include experimental work on flow boiling heat transfer, two-phase flow pressure drop, subcooled flow boiling in tubes and in heat exchangers. In addition, the study of flow boiling of other mixtures such as water/ammonia, ammonia/lithium nitrate, water/lithium bromide, mixtures of ethylene glycol and water, and binary mixed magnetic mixtures were also performed by some researchers (Rivera and Best, 1999;Ruvera et al, 2003;Kandlikar and Bulut, 2003;Shuchi et al, 2002;Shuchi et al, 2004). As the present paper aims to review the study of two-phase flow and flow boiling of mixtures in small and mini channels, here just to list a few papers in this section to show the generalized research status of flow boiling with mixtures in normal size channels.…”