Cold Blowing Research Articles

Improving magnetic cooling efficiency and pulldown by varying flow profiles

Magnetic refrigeration systems are promising cooling solutions that employ the active magnetic regenerator refrigeration cycle to achieve practical temperature spans and environmental benefits. The hydraulic system that ensures a continuous flow of the heat transfer fluid through the system with a reciprocating flow in each regenerator bed is critical to the performance of the refrigeration cycle. Hence, we investigate the characteristics of the parallel flow circuit of a rotary active magnetic regenerator system, which consists of thirteen trapezoid-shaped regenerators, each filled with 295 g of gadolinium spheres. Fluid flow is controlled via electrically actuated solenoid valves (both piloted and direct-acting) connected to the regenerator hot side. By varying the percentage of opening of the control valves, different blow fractions (or fluid flow waveforms) could be investigated. The objective of the study is twofold: (i) assess whether flow imbalances of the heat transfer fluid exist in the cold-to-hot blow (cold blow) and hot-to-cold blow (hot blow) directions, and (ii) determine whether there is an optimal value of the blow fraction both to maximize the cooling performance and realize a rapid temperature pulldown. Flow resistance measurements demonstrate a symmetric flow circuit design and resistances that are similar in the cold and hot blow directions. Moreover, for the studied temperature spans of 6 K and 16 K, the best blow fraction was found to be about 41.6 %. For instance, at a 16 K span, a utilization of 0.32, and at 1.4 Hz, increasing the fluid blow fraction from 25.0 to 41.6 % enhanced the cooling capacity and second-law efficiency from 70 to 330 W and from 2.6 to 17.4 %, respectively. In turn, lower blow fractions favored a more rapid temperature pulldown. The magnetocaloric system was about 30 % faster in establishing approximately 14 K temperature span when the blow fraction was reduced from 41.6 to 30.6 %. Hence, magnetic refrigeration systems can benefit greatly from solenoid valves, which allow the system to operate either in a time-saving mode or an energy-saving mode.

Influence of timing between magnetic field and fluid flow in a rotary magnetic refrigerator

An active magnetic regenerator with magnetic Brayton cycle is adopted in a rotary-magnet type refrigerator. For the performance of the magnetic refrigerator, timing between the magnetic field and fluid flow profiles is important. This paper experimentally studied the influence of timing between magnetic field profile and fluid flow profile on the performance of a rotary magnetic refrigerator. A timing ratio is defined to indicate the relative time lengths of four processes (magnetization, hot blow, demagnetization, cold blow). Under four different timing ratios, the cooling capacity, temperature span, pressure drop and power consumption are experimentally investigated. A no-load temperature span of 19.8 K is achieved at the timing ratio of 1:4:1:4, which is 2.6 K higher than that at the ratio of 1:1:1:1. The results reveal that, at the same utilization factor and frequency, the longer the flow time, the larger the temperature span. The influence of utilization factor and operating frequency are also studied. Though limited by the motor power, a cooling power of 20 W at temperature span of 12.3 K is achieved with the timing ratio of 1:2:1:2 at 0.75 Hz, and the corresponding specific cooling power is approximately 94 W/kg.

Numerical simulation and experimental study of high-power thermal equilibrium inductively coupled plasma

Inductively coupled plasma generator is one of the core components of the near-space high-speed target plasma electromagnetic scientific experimental research device, which is often used to simulate high enthalpy and high speed plasma sheath environment. In order to study the discharge characteristics of inductively coupled plasma generator under high power, radio frequency and medium pressure, the numerical simulation and experiment are combined to study its internal heat transfer and flow characteristics in this paper. Based on the local thermodynamic equilibrium conditions, the numerical simulation of large-scale radio frequency and medium pressure inductively coupled plasma with a power of 100–400 kW is carried out through the multi-field coupling of flow, electromagnetic and temperature field, and verified by light intensity and spectrum experiment. The results show that the electromagnetic field distribution in the high-power thermal balance inductively coupled plasma generator is similar to that of the small- and medium-sized power plasma generator. The discharge energy dissipation occurs mainly in the area where the induction coil is located. The temperature of the inner wall of the quartz tube is higher at the coil location than in other areas, and the plasma has a ring-shaped high-temperature structure. The outer wall of the quartz tube is set to be the boundary condition of heat flux for simulating the temperature change of the quartz tube under cold blowing. This setting is in coincidence with factual situations. The wall temperature of the quartz tube at the entrance and at the induction coil section are found to be relatively high. When the large-size inductively coupled plasma generator works, an obvious return vortex is generated at the entrance due to the temperature difference and the electromagnetic pumping effect, and the exit velocity increases slightly with the increase of power. At the same time, the discharge experiment under the corresponding conditions shows that there is found a ring structure with bright edges and dark centers in the axial image of the argon discharge. Moreover, the emission spectrum of argon plasma is measured through the spectrum diagnosis system and the spatial distribution of the generator electron temperature is obtained. The light intensity of the discharge image and the electron temperature measured by the spectrum are found to be in comparative coincidence with the COMSOL simulation temperature result, demonstrating the validity of the numerical simulation results under thermodynamic equilibrium conditions. The numerical simulation results in this paper are also applicable to the optimization design and temperature resistance evaluation of the inductively coupled plasma generator.

Dependence of energy characteristics of ascending swirling air flow on velocity of vertical blowing

In the model of a compressible continuous medium, for the complete Navier-Stokes system of equations, an initial boundary problem is proposed that corresponds to the conducted and planned experiments and describes complex three-dimensional flows of a viscous compressible heat-conducting gas in ascending swirling flows that are initiated by a vertical cold blowing. Using parallelization methods, three-dimensional nonstationary flows of a polytropic viscous compressible heat-conducting gas are constructed numerically in different scaled ascending swirling flows under the condition when gravity and Coriolis forces act. With the help of explicit difference schemes and the proposed initial boundary conditions, approximate solutions of the complete system of Navier-Stokes equations are constructed as well as the velocity and energy characteristics of three-dimensional nonstationary gas flows in ascending swirling flows are determined.

Analysis of gas dynamics in a single-phase two-channel plasma torch at cold blowing and considering the interaction with the electric arc

This article is devoted to the simulation of cold gas purge and flow taking into account the plasma arc in the channels of a single-phase two-channel high-voltage plasma torch with cylindrical electrodes. The results obtained in the process of modeling made it possible to simplify the model for further modeling, which will result in the distribution of velocities, temperatures and voltage drop on the arc depending on the time.

ACCOUNTING INFLUENCE OF CENTRIFUGAL FORCE IN THE NUMERICAL MODELING OF RISING SWIRLED GAS FLOW

In work the consistent inclusion of centrifugal force in the numerical calculations of three-dimensional gas-dynamic characteristics of the unsteady flow of compressible viscous heat-conducting gas in an upward swirling flow caused by the vertical cold blowing. Provides detailed conversion of the complete system of Navier-Stokes equations associated with consistent view of the centrifugal force. Results of thermodynamic calculations and comparisons, speed and power characteristics of emerging upward swirling flows. There was a slight influence of the centrifugal force on the basic parameters of the gas-dynamic study of complex flows of gas.

Experimental Investigation of the Dispersion of Liquids by Ejection Atomizers

This paper presents the results of an experimental investigation of the dispersivity of liquid droplets in the spray cone of ejection atomizers. The calculational droplet size distribution function was measured by the method of low angles of the probe laser radiation scattering indicatrix on a pneumohydraulic bench under cold blow conditions. The efficiency of the proposed circuit designs of atomizers has been analyzed.

Comparison between hot-gas bypass defrosting and reverse-cycle defrosting methods on an air-to-water heat pump

Frost build-up blocks the gap between fins and decreases the airflow rate, and the heating capacity and COP of air-source heat pump become lower. The reverse-cycle defrosting (RCD) and hot-gas bypass defrosting HGBD are the two common methods of frost removal. The comparison between the RCD and HGBD methods on one heat pump were not found by authors up to now. This paper compared the dynamic characteristics during the RCD and HGBD periods on one medium air-to-water heat pump of 55 kW. The feasibility of the HGBD method without heat provided to evaporate the liquid refrigerant after melting frost, which was supposed in the danger of the compressor liquid slugging, was especially discussed. The results showed the liquid refrigerant leaving the air cooled coils for the HGBD method was trapped in the suction accumulator and flashed into the saturated gas by the compressor pumping action, and no compressor liquid slugging happened in our tests. The HGBD time was much longer than the RCD time. The amenity for the HGBD method was better than that for the RCD method, due to lower refrigerant noise, smaller indoor temperature fluctuation, and no cold blowing. The suction superheat and discharge superheat for the HGBD method were lower than those for the RCD method. The HGBD could overcome the main disadvantages of the RCD method and deserved the further investigation.

Transient response in magnetocaloric regeneration

We report on the first experimental demonstration of the details of the transient response in the four sequential processes of active magnetic regenerative refrigeration: magnetization, warm blow, demagnetization, and cold blow. The experimental results display the details of the gradual temperature divergence due to regeneration. The temperature change of the stationary solid bed is due to the magnetocaloric effect in a periodic field. The theory for the active magnetic regenerative refrigeration is applied to the transient processes in magnetocaloric regeneration. A time and spatial dependent model of temperature profile of the magnetization and demagnetization with thermal wave regenerative processes is developed.

高温集塵用セラミックフィルタの熱衝撃時の温度・熱応力解析

A thermal cyclic fatigue testing method for a hot gas tubular filter proposed by Matsushima, et al. simulates the stress state in the filter during reverse pulse cleaning by blowing air. The filter is composed of two layers, one is a thick inner layer made of silicon carbide with coarse pores and the other is a thin outer layer made of mullite with fine pores. In this paper, we presented a new technique for analyzing temperature distributions in a filter in cold blowing air on the assumption that a Biot number could express a heat loss inside the filter caused by blowing air. Temperature and stress distributions in the filter were analyzed numerically on condition that the filter was exposed to high temperature flue gas and received thermal shock by cyclic blowing air. Residual stresses after sintering were also analyzed. The results revealed that the stresses were greatly affected by the thickness of the mullite layer, there were considerable tensile residual stresses in the mullite layer, and the thicker layer of silicon carbide had higher thermal shock stresses on the inner surface of the filter.

Practical concepts to minimize the emission of halogenated organic compounds from municipal solid waste incinerators

The authors present their research findings at four different municipal waste incinerators (MWIs) concerning generation and release of dioxins and furans. The analytical results of the following design and operation conditions are described: “cold blowing”, flue gas cooling and “soot blowing”. In addition, input variation test results are presented. Consequences for reducing the emission of halogenated dioxins and furans are discussed.

Used Automotive Engines in a Solar Assist, Biomass Fuelled Power System

A new concept for an air-charged open-cycle engine is presented. The engine is based on a modified automotive engine because these are cheap and readily available when derived from scrap cars. Such engines can often be readily modifed and lightly renovated to provide long life, low cost, light load systems. The proposed heating system includes locally manufactured linear parabolic solar collectors with low cost tubular biomass furnaces for heating in the dark hours. Use of either or both types of heater is optional depending on local circumstances. Pressurised air from the engine is circulated through the furnace/collector heating system and back to the engine. The same air is the working medium in the engine. In a typical case two cylinders operate as expansion engines, two as compression cylinders with two regenerators added, one experiencing the hot blow, one experiencing the cold blow. Switching valves are operated by the crankshaft.

Kraft Pulp Manufacturing by the Kamyr Continuous Digester with Hi-heat Diffusion

This report described the comparison of the kraft pulp manufacturing by the 4hr. hi-heat diffusion washing digester followed by one drum washer with the manufacturing of the same pulp made by the cold blow digester followed by three drum washers. The composition of the raw wood species and the cooking conditions were kept almost same in the two digesters. The hi-heat diffusion digester gave the same or a little better washing efficiency and better color and physical strengths of the pulp. The operation of the hi-heat diffusion digester is more difficult and some troubles occurred.However these difficulties can be overcome by the good quality control of the chips and the good maintenance of the equipments.