Circulation Heat Research Articles

Inlet/outlet flow through various size of needle in the presence of magnetic field

Influence of Magnetohydrodynamics (MHD) on the fluid in channel flow in the presence of thin needle across the fluid movement is observed in this study. A two-dimensional computational analysis has been performed to see the effects of inlet/outlet conditions with inserted curvilinear shaped body in the channel. In this case, temperature on all boundaries is colder than that of inlet air and flat part of the inserted body. The governing equations are solved by using finite element method and magnetic field is also taken into account. With suitable dimensionless variables, PDEs are transformed into dimensionless PDEs, then raised parameter is simulated against the streamlines, isotherms and temperature distribution at mean position. Effect of Reynolds number, Richardson number, Magnetic hydrodynamic, size and state of needle is observed on local Nusselt number at the mean position. On isotherm profile, Reynolds number has a noticeable impact. With an increase in Re, heat circulation close to the needle increases, and for higher Ri, velocity on the outlet port increases. The inlet and outlet portions of the channel generate streamlines that have a significant impact on the diameter of the needle. Increased needle diameter causes heated lines to be pushed away from the centre. It is also found that the temperature gradient in the flow fields and heat transfer over the heated wall of the cavity are significant, altered by the placement of needle size during various computations.

Dynamic Simulations on Enhanced Heat Recovery Using Heat Exchange PCM Fluid for Solar Collector

Facing the goal of carbon neutrality, energy supply chains should be more low-carbon and flexible. A solar chemical heat pump (SCHP) is a potential system for achieving this goal. Our previous studies developed a silicone-oil-based phase-change material (PCM) mixture as a PCM fluid for enhancing heat recovery above 373 K in the solar collector (SC) of the SCHP. The PCM fluid was previously tested to confirm its dispersity and flow properties. The present study proposed a 3D computational fluid dynamics model to simulate the closed circulation loop between the SC and reactor using the PCM fluid. The recovered heat in the SC was studied using several flow rates, as well as the PCM weight fraction of the PCM fluid. Furthermore, the net transportable energy is considered to evaluate the ratio of recovered heat and relative circulation power. As a result, it was verified that the recovered heat of the SC in the experiment and simulation is consistent. The total recovered heat is improved using the PCM fluid. A lower flow rate can enhance the PCM melting mass and the recovered heat although sensible heat amount increases with the flow rate. The best flow rate was 1 L/min when the SC area is 1 m2. Furthermore, the higher PCM content has higher latent heat. On the other hand, the lower content PCM can increase the temperature difference between the SC inlet and outlet because of the lower PCM heat capacity. For the 1 L/min flow rate, 2 wt% PCM fluid has shorter heat-storing time and larger net transportable energy than 0 wt% PCM fluid (426 kJ←403 kJ) for the SCHP unit.

Calculation of temperature data from an automatic solar heat supply system

<p><span lang="EN-US">This paper calculates the temperature in an automated solar heat supply system. The study used an automatic controller to monitor the temperature data of the entire system. The developed solar heat supply system has a flat solar collector, heat-insulating translucent glass, and double glazing with reduced pressure. The coolant is made of thin-walled corrugated stainless pipe. The heat from the solar flow heats the liquid removed from the collector, and cold water from the siphon enters its place. There is a constant circulation of heat, which increases heat transfer efficiency by eliminating additional partitions between the panel and thermal insulation. The controller has sensors that register using field-programmable gate array (FPGA) STM32, designed to monitor the entire solar system, and the actuators include power relays. During the experiment, it was found that temperature sensors save energy by 2% due to the use of power relays, which has a significant impact on the service life of the equipment.</span></p>

Projected Changes in the Seasonal Cycle of Madden‐Julian Oscillation Precipitation and Wind Amplitude

AbstractAlthough recent studies have examined the responses of annual‐ and seasonal‐mean Madden‐Julian oscillation (MJO) activity to global warming, little is known about the seasonal cycle changes that determine the timing of the peak MJO influence on local weather and climate. By analyzing the Community Earth System Model version 2 large ensemble at the end of the 21st century, we report changes in both the phase and amplitude of the seasonal cycle of MJO precipitation over the tropical Indian Ocean and southwestern Pacific. While the seasonal delay in phase of the MJO is related to the seasonal delay of total precipitation, with contributions from surface latent heat flux and circulation changes, the amplification in seasonal amplitude is consistent with the increase in MJO amplitude due to mean temperature increases. The shifts in phase of the seasonal cycle of the MJO under global warming may influence the predictability of extreme events.

Declining winter heat loss threatens continuing ocean convection at a Mediterranean dense water formation site

A major change in winter sea surface heat loss between two key Mediterranean dense water formation sites, the North–West Mediterranean (NWMed) and the Aegean Sea, since 1950 is revealed using atmospheric reanalyses. The NWMed heat loss has weakened considerably (from −154 Wm−2 in 1951–1985 to −137 Wm−2 in 1986–2020) primarily because of reduced latent heat flux. This long-term weakening threatens continued dense water formation, and we show by evaluation of historical observations that winter-time ocean convection in the NWMed has declined by 40% from 1969 to 2018. Extension of the heat flux analysis reveals changes at other key dense water formation sites that favour an eastward shift in the locus of Mediterranean convection towards the Aegean Sea (where heat loss has remained unchanged at −172 Wm−2). The contrasting behaviour is due to differing time evolution of sea-air humidity and temperature gradients. These gradients have weakened in the NWMed due to more rapid warming of the air than the sea surface but remain near-constant in the Aegean. The different time evolution reflects the combined effects of global heating and atmospheric circulation changes which tend to offset heating in the Aegean but not the NWMed. The shift in heat loss has potentially significant consequences for dense water formation at these two sites and outflow to the Atlantic. Our observation of differential changes in heat loss has implications for temporal variations in the balance of convection elsewhere e.g. the Labrador-Irminger-Nordic Seas nexus of high latitude Atlantic dense water formation sites.

Effects of Soil Thermal Conductivity on Rainy Season Precipitation in Northern China

Abstract Parameterization schemes such as soil thermal conductivity (STC) have an important impact on precipitation simulation. The precipitation in the rainy season (April–September) is the main factor affecting aridification in northern China. However, it is unclear how STC affects precipitation simulation during the rainy season. In this study, comparative experiments were conducted using the regional climate model RegCM4.6 coupled with the third-generation land surface model NCAR CLM4.5 to assess the effect of the Johansen and Lu–Ren STC schemes on precipitation. The results show that the STC had a significant effect on the simulation of rainy season precipitation and its variation in northern China. The precipitation variation characteristics simulated by the Lu–Ren scheme were closer than that of the Johansen scheme to the observation. The difference in land surface temperatures (LSTs) simulated by the two STC schemes could be a major cause of the sensitivity in the simulated precipitation. When the local LST increases by 1 K, precipitation decreases by 5–30 mm in most areas of northern China. The numerical experiments revealed that the rise of LST increases the longwave radiation, reduces the surface net radiation, and causes the redistribution of sensible and latent heat flux, forming local water vapor and thermal conditions that are not conducive to precipitation. Moreover, the difference of LST significantly changes the 500-hPa large-scale circulation field, the 700-hPa vapor transportation, and its divergence. The combined action of local heat, water vapor, and large-scale circulation factors reduces the precipitation in the rainy season. On the other side, the variation of the East Asia summer monsoon (EASM) affects the soil water content. In addition, a new STC scheme was added to NCAR CLM4.5, promoting the development of this land surface model.

Improving the Efficiency of Environmental Temperature Control in Homes and Buildings

This research developed an effective environmental temperature control system for homes and buildings. The study used a photovoltaic panel (PV) and developed a solar installation with thermosiphon circulation, which has a flat solar collector and heat-insulating translucent glass with double glazing with reduced pressure. The coolant is made of thin-walled corrugated stainless pipe. The heat from the solar flux heats the liquid removed from the collector, and cold water from the siphon enters its place. There is a constant circulation of heat, which increases heat transfer efficiency by eliminating additional partitions between the panel and thermal insulation. We have also developed a solar system control controller, which includes an electronic unit with six sensors. The six sensors are controlled by the STM32 programmable Logistics Integrated circuit (FPGA), designed to monitor the entire solar system, and the drives include power relays. The performance of the photovoltaic panel and the room’s temperature change are calculated during both the simulation and testing of the controller. The standard error was 20% compared to other controllers. During the experiment, the consumption savings amounted to about 1% due to the control signal in the controller, which has a significant impact on the service life of the equipment.

The Potential Value of Combining Assimilation of Water Vapor Radiances and Cloud Liquid/Ice Water Path From ABI on Analyses and Forecasts for Hurricane Irma (2017)

AbstractAll‐sky assimilation of infrared (IR), near‐IR, and visible band measurements are beneficial for forecasting cloud‐covered tropical cyclones, but numerous challenges remain. This study uses the combined assimilation of clear‐sky water vapor radiances and the cloud liquid/ice water path (CWP) retrieved from the Advanced Baseline Imager on the new generation geostationary environmental satellites. The two measurements are spatial complementary to one another. Microphysics schemes, cumulus parameterizations, and dynamic CWP observation errors are optimized using sensitivity tests. The cycling assimilations and subsequent forecasts of Hurricane Irma (2017) are investigated to assess the added value of the combined assimilation and its impacts on hurricane forecasts. Comparisons with ERA5 and dropsonde observations from the National Hurricane Operations Plan show that the combined assimilation can improve the prognostic variables of Hurricane Irma (2017) for both the large‐scale circumstances and the inner‐core area, resulting in a clear improvement in hurricane track and intensity predictions. The detailed diagnostics show that the improved track predictions can be attributed to the more precise steering flow produced by the combined assimilation. Moreover, the additional CWP assimilation allows for a more accurate initialization of water vapor in the hurricane's inner‐core area when the model produces dry simulated water vapor bias. Then the subsequent phase changes of water vapor improve the hurricane intensity forecasting by enhancing the feedback between heating and vortex circulation. The combined assimilation shows the potential value of better utilization of all‐sky satellite measurements to improve hurricane initialization and forecast.

A Drying system for Rhizoma et Radix Baphicacanthis Cusiae Based on multi-source coupling and efficient energy storag

The traditional Chinese Herbal Medicine Rhizoma et Radix Baphicacanthis Cusiae mostly grows in Southwest China. However, due to the lack of technology, the key drying process in the production of Rhizoma et Radix Baphicacanthis Cusiae has the problems of low efficiency, long time and uneven quality. The paper designed a drying system of Rhizoma et Radix Baphicacanthis Cusiae based on multi-source coupling and efficient energy storage by investigating the production of Rhizoma et Radix Baphicacanthis Cusiae in southwest China and studying the natural effects of geographical advantages and light conditions in the region. The main body of the system is composed of a two-position water tank heat circulation system, a hemispherical Fresnel lens array, an air source heat pump, a dehumidification and waste heat recovery device, a temperature and humidity sensor, and a heat exchange tube group. The drying system can better meet the drying needs of Chinese herbal medicine Rhizoma et Radix Baphicacanthis Cusiae. It has the advantages of high efficiency, energy conservation and environmental protection, stable operation, and can independently adjust according to the drying temperature. It has strong practicability. While saving energy, it saves high drying cost for farmers, and meets the special requirements of building intelligent agriculture and enriching rural economic business forms.

Hydrogeochemical Characteristics and Genesis of the Chazi Geothermal Field Area in Tibet

The Chazi geothermal field area is located in the large region of Shigatse in southern Tibet. The geothermal resources in this area are abundant, but their exploitation and utilization are low. By studying the water chemistry and isotope characteristics of geochemical fluids in the study area, information on water chemistry, heat storage temperature, recharge source, recharge elevation, and circulation depth was obtained. These results provide a scientific theoretical basis for improving the genetic mechanism of high-temperature geothermal systems in the study area. The type of geothermal fluid hydrochemicals in this area is mainly HCO3–Na. The isotopic geochemical method was used to determine that the recharge source of geothermal fluids was atmospheric precipitation, and the recharge elevation was 5200–6000 m. The geochemical thermometer, Na–K–Mg equilibrium diagram, and silica-enthalpy mixed model indicated the shallow and deep thermal storage temperatures of approximately 150 and 200°C, respectively, and the average circulation depth of 1163.38 m in the study area. Combined with the fracture structure and magmatic activity characteristics of the southwest Qinghai-Tibet Plateau, the source, storage, cover, and general situation of the area were preliminarily summarised, and the conceptual model of geothermal origin was established. The results can provide a scientific theoretical basis for the mechanism of high-temperature geothermal systems and subsequent drilling and resource development.

MESIN PENGERING GABAH MODEL BAK MENGGUNAKAN BAHAN BAKAR LPG

Conventional drying relies on sunlight has a number of drawbacks. In terms of productivity, drying takes a long time, for example: two until three days for sunny day or four to five days for cloudy weather. Design of a combined gas-fueled rice drying machine (Liquefied Petroleum Gas) as an alternative in drying rice does not depend on weather conditions, in both rainy and dry season. This drying machine uses a hot air distribute in pipe that have functions to remove water evaporation from the dried materials. The circulation of hot air in the room is very important to produce drainage in the drying chamber. Heat circulation in the drying chamber can take place naturally or forcibly using a fan into the extruder tube. Centrifugal blower has functions to suck or dispose hot air in a room. Heater drum of dry air functions as a drying device where hot steam is placed into the drum. The furnace has functions as a device for heating. From this study it can be concluded that the humidity in the drying chamber is 0.1875 kg water/kg air, the mass of drying air is 26.4915 kg, the requirement of fuel during the drying process is 3 kg of fuel, the time required for drying is 5.1623 - 11.6023 hours, the drying temperature of rice is 40oC, 45oC, and 50oC. The thickness of rice pile are 100 mm and 200 mm, mass of dried rice 50 kg and 100 kg, and efficiency of rice drying is 52.67% - 58.41%.

Effects of tank heating on hydrogen release from metal hydride system in VoltaFCEV Fuel Cell Electric Vehicle

Metal hydride (MH) storage is known as a safe storage method because it does not require complex processes like high pressure or very low temperature. However, it is necessary to use a heat exchanger due to the endothermic and exothermic reactions occurring during the charging and discharging processes of the MH tanks. The performance of the MH is adversely affected by the lack of a heat exchanger or a suitable temperature range and it causes non-stable hydrogen supply to the fuel cell systems. In this study, effect of the tank surface temperature on hydrogen flow and hydrogen consumption performance were investigated for the MH hydrogen storage system of a hydrogen Fuel Cell Electric Vehicle (FCEV). Different temperature values were arranged using an external heat circulator device and a heat exchanger inside the MH tank. The fuel cell (FC) was operated at three different power levels (200 W, 400 W, and 600 W) and its performance was determined depending on the temperature and discharge flow rate of the MH tank. When the heat exchanger temperature (HET) was set to 40 °C, the discharge performance of the MH tank increased compared to lower temperatures. For example, when the FC power was set to 200 W and the HET of the system was at 40 °C, 1600 L hydrogen was supplied to the FC and 2000 Wh electrical energy was obtained. The results show that the amount of hydrogen supplied from the MH tank decreases significantly by increasing the flow rate in the system and rapid temperature changes occur in the MH tank.

Green hydrogen production based on the co-combustion of wood biomass and porous media

The production of green hydrogen by utilizing wood pellets is an effective way to solve the problem of energy shortage and environmental pollution. In order to improve the hydrogen production efficiency of biomass, a co-combustion system of inert porous media and wood pellets was built, and the combustion characteristic of wood pellets was studied with different porous media structures. The results demonstrated that the increasing of air velocity was beneficial to increase the combustion temperature, and hydrogen production reached the maximum value at v = 4 cm/s. Meanwhile, the hydrogen production increased with the increasing of inert bed length due to the intensification of heat circulation. When the length ratio of the hybrid to inert bed was 6: 3, the lower heating value of syngas was 3.69 MJ/Nm3 and the molar fraction of hydrogen increased by 69 % compared to the single wood pellets combustion. Moreover, the decreasing of pellets diameter was conducive to increase syngas production. The co-combustion of inert porous media and wood pellets realized the efficient utilization of biomass, and maximum growth rate of hydrogen reached 142 %.

General circulation and global heat transport in a quadrupling CO2 pulse experiment

To investigate the response of the general circulation and global transport of heat through both atmosphere and ocean to two-types of carbon dioxide removal scenario, we performed an earth system model experiment in which we imposed a pulse-type quadrupling of CO2 forcing for 50 years and a gradual peak-and-decline of four-time CO2 forcing. We found that the results from two experiments are qualitatively similar to each other. During the forcing-on period, a dominant warming in the upper troposphere over the tropics and on the surface at high latitudes led to a slowdown in the Hadley circulation, but the poleward atmospheric energy transport was enhanced due to an increase in specific humidity. This counteracted the reduction in poleward oceanic energy transport owing to the suppression of the meridional overturning circulation in both Hemispheres. After returning the original CO2 level, the hemispheric thermal contrast was reversed, causing a southward shift of the intertropical convergence zone. To reduce the hemispheric thermal contrast, the northward energy transports in the atmosphere and ocean surface were enhanced while further weakening of the global-scale Atlantic meridional overturning circulation led to southward energy transport in the deep ocean.

DEVELOPMENT OF NONLINEAR MODEL OF NPP STEAM GENERATOR FOR INFORMATION TECHNOLOGY OF CONTROL OPTIMIZATION

Steam generators of modern power units of nuclear power plants are critical elements of power units and are subject to modernization. Identification of the steam generator model for optimizing the control of the steam generator is an urgent task. The purpose of this article is to develop a nonlinear mathematical model of a steam generator in relative variables for its use in information technology for optimizing control. Mathematical models of heat transfer and steam formation processes in a steam generator are presented in the form of systems of differential equations in relative variables. These models are intended for simulation modeling of thermal processes in a steam generator. Thermal processes are associated with the supply of feed water to the steam generator from the water treatment system and coolant from the nuclear reactor, as well as with the removal of steam from the steam generator to the main steam collector. According to the law of conservation of the momentum of the working medium in the circulation circuit of the steam generator under the evaporation mirror, a nonlinear differential equation for the process of circulation of the steam-water mixture is obtained. A nonlinear differential equation has been developed to calculate the derivative of the steam flow through the evaporation mirror in relative variables. The equations for the auxiliary equipment – the main steam header, the steam turbine valve actuator and the control feed valve actuator – are reduced to relative variables. Using the equations of heat transfer, steam formation, circulation and auxiliary equipment, a nonlinear model of the steam generator in the state space as a control object in relative variables is constructed. Formulas are given for calculating the values of the constant parameters of the steam generator model from the values of its design and technological parameters. A program for a nonlinear mathematical model of the PGV-1000 steam generator has been developed, which is included in the information technology steam generator model module. This will make it possible to solve the problems of identifying and optimizing the information control system of the water level in the steam generator PGV-1000 of the power unit with a nuclear reactor VVER-1000.

Flow and heat transfer due to partially heated moving lid in a trapezoidal cavity with different constraints at inner circular obstacle

The main emphasis of the current work is to deal with the forced convection of magnetohydrodynamics (MHD) flow and its heat transfer due to force convection generated by a moving lid in a trapezoidal enclosure. Various cases of temperature at the surface of the circular obstacle inside the cavity are determined. The trapezoidal cavity has a moveable and partially heated top lid while the bottom wall is kept at a low temperature. The linearly inclined walls on the left and right sides of the cavity are both adiabatic. The finite element method is applied for computations validated with existing work. Numerical simulations are conducted to analyze this trapezoidal cavity model for various thermal conditions of the inner circular obstacle, various heated lengths (0 ≤ LH ≤ 1), various Reynolds number (100 ≤ Re ≤ 700), Richardson number (0.001 ≤ Ri ≤ 10) and Hartmann number (0 ≤ Ha ≤ 100). The entire analysis describes that high Reynolds numbers improve the thermal performance of liquid. However, moving lid generates fluid molecules specifically directed according to wall movement. The force convection phenomenon becomes more dominant as the Reynolds number and heated length increase. A cold circular obstacle resists the circulation of heat in the cavity whereas the local Nusselt number drops when the simultaneous effects of the moving lid force and heated sources move away from the surface.

Thermal and optical investigations of self-loop system based on liquid quantum dots for laser lighting

This study proposes a self-loop converter (SLC) based on liquid quantum dots (QDs) that is designed for laser lighting. QDs exhibit unique illumination and display advantages because of their high light conversion efficiency and color purity. However, the unavoidable heat generated during light conversion leads to thermal quenching and limits their application in high-power laser lighting. The proposed SLC reduces the temperature and temperature fluctuations in the excited heating and gas circulation areas. After excited by laser for 240 min, the radiation power only decreases from 529.65 mW to 464.13 mW, a decrease of 12.37%. But the radiation power of hermitic converter (HC) decreased from 520.52 mW to 361.35 mW, decreasing by 30.5% after excited by laser for the same time. The experimental results demonstrate that the proposed SLC is promising for laser headlights, aerospace, coal mining, and other fields.

Numerical investigations on thermal performance and flame stability of hydrogen-fueled micro tube combustor with injector for thermophotovoltaic applications

In order to design a micro tube combustor with good thermal performance and flame stability for thermophotovoltaic applications, in this work, thermal performance and flame stability of hydrogen-fueled micro tube combustors with backward facing step and with injector are compared. It is found that the decrease of diameter ratio d2/d1 leading to expansion of the symmetrical recirculation zone, which is helpful for fluid and heat circulation, and higher flame locations, which is not helpful for flame stabilization. Furthermore, effects of diameter ratio d2/d1 on thermal performance and flame stability are analyzed and discussed. Results suggest that when the diameter ratio d2/d1 is decreased from 0.9 to 0.8, positive effects of injector on thermal performance are enhanced and flame stability is improved under lower hydrogen/air equivalence ratio. Finally, the applications conditions of the micro tube combustor with injector are achieved. This work will provides us significant reference for designing micro tube combustor with injector.

Effects of inclination angle and heat power on heat transfer behavior of flat heat pipe with bionic grading microchannels

Bionic structure has become a popular tool to design heat pipes for its ability of heat transfer enhancement and liquid transport. Inspired by the powerful water collection and transfer capability of pitcher plant surface, this paper presents a new flat heat pipe design with bionic grading microchannels (BGFHP) based on special high-low structured surface. Firstly, the performance advantages of BGFHP are revealed by comparing the heat transfer performance and visible internal flow characteristics of BGFHP and conventional FHP. Secondly, the performance variation and influence trend of BGFHP are investigated experimentally with inclination angle and thermal power as variables. Finally, thermal management effects of natural cooling, FHP and BGFHP in fuel cells are compared to demonstrate the practical application of BGFHP. Results show that the high-low channel structure of BGFHP has the advantages of micro-channel hydraulic transport, and the small channel increases the heat transfer area, circulation efficiency and gas phase flow area, resulting in better start-up time and heat transfer capacity than the traditional FHP. The thermal resistance of BGFHP is reduced by 22%, while the thermal conductivity is increased by more than 40%. In the load range of 10–26 W and inclination angle range of 0–90°, the overall thermal resistance and temperature uniformity of BGFHP decreases and then increases as the inclination angle increases. With the increase of heat power, the thermal resistance of BGFHP gradually decreases, whereas the temperature uniformity first decreases and then increases. The optimal working condition of BGFHP is 45° and 24 W, with a minimum thermal resistance of 0.21 K/W. In the fuel cell temperature control test, the BGFHP was able to maintain the temperature below 52 °C, which is 5 °C lower compared to the FHP. This result shows the advantage of the BGFHP in terms of temperature control.

Thermocapillary convection in liquid-in-liquid capillary bridges due to a heating/cooling ring

A liquid bridge connecting two solid disks is surrounded by a heating/cooling ring in the presence of another immiscible liquid. The thermocapillary convection and the interface deformation thus generated in a gravitational environment are studied for a range of bridge aspect ratios and ring temperatures using 2D axisymmetric simulations. A stark difference between the heater and cooler cases is observed in their flow and heat transfer patterns. Interfacial velocity and bridge deformation are seen to be more stable when a cooling ring surrounds the liquid bridge. Fluid trajectories inside the bridge show longer paths as the temperature difference between the cooler/heater and the surroundings is raised. Moreover, a cooler lessens the deformation, whereas a heater enhances the deformation of the phase interface. Anomalous results for a heat transfer rate, interface deformation, and circulation patterns are obtained in the heater configuration for larger height to radius ratios.