Pair Of Heaters Research Articles

Furnace for Inelastic X‐Ray Scattering from Liquids up to 1600 °C

The design and implementation of a furnace for inelastic X‐ray scattering from liquids with sample temperatures up to ≈1600 °C is described. Carbon composite heaters operating in vacuum provide robust heating elements: one pair of heaters has been used for >18 days of operational time above 1500 °C, including eight cycles to room temperature. High‐quality data are obtained to scattering angles as low as 7 mrad in 2θ (Q < 1 nm−1 at 25.7 keV) from a sample at 1560 °C.

Flow Boiling in an In-Line Set of Short Narrow Gap Channels

Heat transfer coefficients in a set of three symmetrically heated narrow gap channels arranged in line are reported at power densities of 1 kW/cm3 and wall heat flux of 3–40 W/cm2. This configuration emulates an electronics system wherein power dissipation can vary across an array of processors, memory chips, or other components. Three pairs of parallel ceramic resistance heaters in a nearly adiabatic housing form the flow passage, and length-to-gap ratios for each pair of heaters are 34 at a gap of 0.36 mm. Novec™ 7200 and 7300 are used as the heat transfer fluids. Nonuniform longitudinal power distributions are designed with the center heater pair at 1.5X and 2X the level of the first and third heater pairs. At all levels of inlet subcooling, single-phase heat transfer dominates over the first two heater pairs, while the third pair exhibits significant increases because of the presence of flow boiling. Reynolds numbers range from 250 to 1200, Weber numbers from 2 to 14, and boiling numbers from O(10−4) to O(10−3). Exit quality can reach 30% in some cases. Overall heat transfer coefficients of 40 kW/m2K are obtained. Pressure drops for both Novec™ heat transfer fluids are approximately equal at a given mass flux, and a high ratio of heat transfer to pumping power (coefficient of performance (COP)) is obtained. With a mass flux of 250 kg/m2s, heater temperatures can exceed 95 °C, which is the acceptable limit of steady operation for contemporary high performance electronics. Thus, an optimal operating point involving power density, power distribution, mass flux, and inlet subcooling is suggested by the data set for this benchmark multiheater configuration.

Eulerian–Lagrangian modeling of solid particle behavior in a square cavity with several pairs of heaters and coolers inside

In this study, the deposition of solid particles in natural convection flow in a square cavity (heat exchanger) filled with air is investigated numerically using an Eulerian–Lagrangian hybrid method. Walls of the enclosure are insulated and several pairs of heater and cooler (HACs) with isothermal walls of Th and Tc (Th>Tc) are placed inside the cavity. An Eulerian (finite volume) approach is used to solve the flow mass, momentum and energy conservation (in a two-dimensional domain) for the ambient continuum. A Lagrangian method is then used to track about 6000 discrete particles, randomly distributed within the domain (i.e., the enclosure). Effects of the drag, lift, gravity, buoyancy, pressure gradient, shear stress terms, thermophoresis and Brownian forces on particles movements are addressed. Furthermore, effects of various design parameters on the heat transfer rate and deposition of particles such as Rayleigh number (104≤Ra≤107), number of the cooler and segmentation of the heater and cooler (HAC) are investigated. The simulations show that the thermophoretic force can significantly affect the distribution of nanoparticles at lower Rayleigh numbers. It is also found that at lower Rayleigh numbers the particle distribution is strongly non-uniform. Moreover, the results of this study showed by increasing the number of coolers and splitting HAC into smaller segments, the deposition rate of the solid particles and heat transfer rate changes significantly.

Two-phase mixture modeling of mixed convection of nanofluids in a square cavity with internal and external heating

Steady state mixed convection heat transfer of nanofluid in a two-sided lid driven cavity with several pairs of heaters and coolers (HACs) inside is investigated numerically using two-phase mixture model. The governing equations have been discretized using the finite volume method while the SIMPLE algorithm has been introduced to couple the velocity–pressure. The influences of volume fraction, diameter and type of the nanoparticles, Richardson number, number of the Heaters and Coolers (HACs), external and internal heating and moving direction of the cavity walls on flow structure, the heat transfer rate and distribution of nanoparticles are investigated. The results of this investigation illustrate that, at low Richardson number by increasing number of the HACs, the heat transfer rate increases. On the other hand, at high Ri, a saturated number of HACs exists which beyond that the value of mean Nusselt number does not changes significantly. In addition, the results reveal that by reducing the diameter of the nanoparticles and Ri, the heat transfer rate increases. It is also observed that at high Richardson numbers, distribution of nanoparticles with dp≥145nm is fairly non-uniform while at low Richardson numbers particle distribution remains almost uniform. Moreover, it is found that by changing direction of the moving walls the heat transfer rate changes significantly.

Eulerian–Lagrangian analysis of solid particle distribution in an internally heated and cooled air-filled cavity

A parametric study has been conducted to investigate particle deposition on solid surfaces during free convection flow in an internally heated and cooled square cavity filled with air. The cavity walls are insulated while several pairs of heaters and coolers (HACs) inside the cavity lead to free convection flow. The HACs are assumed to be isothermal heat source and sinks with temperatures Th and Tc (Th>Tc). The problem is numerically investigated using the Eulerian–Lagrangian method. Two-dimensional Navier–Stokes and energy equations are solved using finite volume discretization method. Applying the Lagrangian approach, 5000 particles, distributed randomly in the enclosure, were tracked for 150s. Effects of drag, lift, gravity, buoyancy, pressure gradient, shear stress terms, thermophoresis and Brownian forces on particles movements are considered. Furthermore, effects of various design parameters on the heat transfer rate and deposition of particles such as Rayleigh number (104⩽Ra⩽107) as well as orientation and number of the HACs are investigated. Our simulations indicate that thermophoretic force can significantly affect the distribution of particles of dp=1μm diameter. It is also found that at low Rayleigh numbers the particle distribution is strongly non-uniform. Moreover, it was observed that by increasing number of the HACs and changing orientation of the HACs from vertical to horizontal, deposition rate of the solid particles increases significantly.

Numerical simulation of natural convection of nanofluids in a square cavity with several pairs of heaters and coolers (HACs) inside

In this study, natural convection inside a square cavity filled with nanofluids with several pairs of heaters and coolers (HACs) inside is investigated numerically in the range of Rayleigh numbers between 104 and 107. Walls of the cavity are insulated and heaters and coolers walls are isothermal with temperatures of Th and Tc (Th>Tc). Two-dimensional Navier–Stokes and energy equations are solved using finite volume discretization method. Effects of various design parameters on the heat transfer rate are investigated. Design parameters considered in this study are: position, surface area, shape and orientation of HACs, volume fraction and types of nanoparticles. The results show that the highest and the lowest impacts of design parameters, on the enhancement of heat transfer rate are caused by changing the HAC position and types of nanoparticles, respectively. Moreover, it is found that for a constant surface area of the HAC at the entire range of Rayleigh number, rate of the heat transfer increases with changing orientation of the HAC from horizontal to vertical. Our simulations indicate that the heat transfer rate at all Rayleigh numbers can be enhanced more efficiently by increasing number of HACs than increasing the HAC size. The optimum value of volume fraction of nanoparticles which result in the highest rate of heat transfer in most cases found to be equal to 1%, and beyond that the heat transfer rate decreases.

A High Performance MEMS Flow Sensor Based on a New Sensing Method

This paper presents a new type of bidirectional thermal flow sensor which has a wide dynamic range and excellent temperature characteristics. This sensor has a pair of heaters and a temperature sensor on a diaphragm. The heaters are located on opposite sides to each other. A single bridge circuit provides an adequate heating current to the upper stream heater so as to keep the voltages supplied to each heater balanced. The heating current, which represents the required sensor output, increases as the flow rate increases. A reverse flow can be also detected since the current decreases when the flow is reversed. A wide dynamic range of 500 and excellent temperature characteristics of less than ±3% of the reading value of flow rate (from 0 to 50°C) were obtained. This sensor responded to a step change of flow rate from 40 to 137 L/min within 0.5 sec.

Differential output type microflow sensor

AbstractTo realize a flow sensor sensitive to a flow rate lower than 0.1 cc/min, a differential output‐type mass‐flow sensor with a pair of heaters was fabricated using the micromachining technique. In a conventional sensor with a single heater, sensitivity degradation occurs because of the natural convection around the heater. On the other hand, in the sensor in this study, the influence of the convection was eliminated by utilizing the differential outputs between the pair of heaters which were located closely together. As a result, the nonlinearity of the sensor was less than 2 percent even when the flow was lower than 0.1 cc/min.