Heat Absorption Rate Research Articles

Heat Transfer Augmentation of Concentrated Solar Absorber Using Modified Surface Contour

This work aims to compare the cavity surface contour’s thermal performance to that of the solar absorber’s plain surface contour for Scheffler type parabolic dish collectors. The absorber is tested for the temperature range up to 600°C without working fluid and 180°C with the working fluid. The modified absorber surface's thermal performance is compared with the flat surface absorber with and without heat transfer fluid. The peak temperature reached by the surface modified absorber (534°C) is about 8.6% more than that of the unmodified absorber (492°C) during an outdoor test without fluid. The energy efficiency of cavity surface absorber and plain surface absorber are 67.65% and 61.84%, respectively. The contoured cavity surface produces a more uniform temperature distribution and a higher heat absorption rate than the plain surface. The results are beneficial to the design of high-temperature solar absorbers for concentrated solar collectors.

Floquet prethermalization in dipolar spin chains

Periodically driven Floquet quantum systems provide a promising platform to investigate novel physics out of equilibrium. Unfortunately, the drive generically heats up the system to a featureless infinite temperature state. For large driving frequency, the heat absorption rate is predicted to be exponentially small, giving rise to a long-lived prethermal regime which exhibits all the intriguing properties of Floquet systems. Here we experimentally observe Floquet prethermalization using nuclear magnetic resonance techniques. We first show the relaxation of a far-from-equilibrium initial state to a long-lived prethermal state, well described by the time-independent ''prethermal'' Hamiltonian. By measuring the autocorrelation of this prethermal Hamiltonian we can further experimentally confirm the predicted exponentially slow heating rate. More strikingly, we find that in the timescale when the effective Hamiltonian picture breaks down, the Floquet system still possesses other quasi-conservation laws. Our results demonstrate that it is possible to realize robust Floquet engineering, thus enabling the experimental observation of non-trivial Floquet phases of matter.

Multi-objective performance optimization of ammonia decomposition thermal storage reactor

Heat storage technology plays an essential role in the stable operation of solar thermal power generation. In this paper, a one-dimensional model of a tubular filled bed heat absorption reactor for ammonia decomposition is established by applying finite time thermodynamics. Taking the inlet temperature, the outside diameter and the length of the reactor as optimization variables, the multi-objective particle swarm optimization is used to perform multi-objective optimization considering the maximum heat absorption rate and the minimum total entropy generation rate, and the Pareto Fronts are determined under different reactor outer wall temperatures. Finally, three optimized reactors’ design parameters and performance indicators are obtained by LINMAP, TOPSIS and Shannon Entropy decision methods, and the cross-sectional comparisonof the optimal reactors at different outer wall temperatures. Compared to the reference reactor, the three optimized reactors improve heat absorption rate by 58%-143%, while the total entropy generate rate is reduced by 26.4%-38.8%. The obtained results have some guidance for optimal designs of ammonia decomposition reactor in real engineering.

Non-Equilibrium Solidification Behavior With Solute Trapping Associated With Powder Characteristics During Electron Beam Additive Manufacturing

For components built by powder bed fusion with electron beam (PBF-EB), the resulting microstructure arising from non-equilibrium solidification–microsegregation and the formation of interdendritic phases significantly affects the mechanical properties and hot cracking resistance. Notably, the powder characteristics influence heat absorption and conduction, thereby altering the molten pool behavior and solidification parameters. However, the effect of powder feedstock on non-equilibrium solidification during PBF has not been widely investigated. In this study, a CoCrMo alloy was built using powders prepared by gas-atomization (GA) and plasma rotating electrode process (PREP). Under the given operating conditions, the samples built with the two powders were experimentally characterized and their compression properties were compared. By performing multi-scale numerical simulations, powder melting and solidification were visualized and analyzed to elucidate the mechanism through which the powder characteristics influence the non-equilibrium solidification behavior during PBF-EB. The study revealed that upon appropriated size control, compared to the GA powder, the PREP powder had a smaller specific surface area and higher sphericity; thus, the generated powder layer exhibited higher heat absorption and dissipation rates. Therefore, a high solidification rate is facilitated, thereby suppressing microsegregation. The findings contribute to PBF knowledge related to feedstock, thus proving to be an essential reference for selecting and optimizing metallic powders applicable to additive manufacturing.

Analysis of Deformation of Float Glass with Heat Treatment in Vehicle Windshield Applications

The purpose of this study was to determine the shape change characteristics of float sheet glass using heat treatment experiments on its surface. This involved the use of a float glass type with a thickness of 5 mm, a width of 840 mm, and length of 1350 mm as the test specimen and the heat transfer experiments and treatment were conducted through conduction with the heat distribution recorded to be between 34 °C and 600 °C at every 5 minutes within 60 minutes in a heating furnace. The analysis focused on the characteristics of the glass surface exposed to fire with emphasis placed on the temperature during the deflection changes in the entire glass surface, the dimensional changes at the edges of the glass which follow the glass printing pattern, and the changes in temperature on the upper and lower surfaces of the curved glass mold. The results showed the existence of a very clear change in each temperature or conduction heat when the shape of the glass is changed to curve with the ideal shape observed to have changed at a temperature of 482.50 °C. Moreover, dimensional changes were 1.0427 m2 and the variations in the temperature were 107.55 °C and the continuous increase in the heat was to have led to a faster change in the glass shape by 11.2°. This, therefore, means a higher temperature or room temperature affects the firing rate of glass bending and also increases the rate of heat absorption.

Experimental studies on vapour compression refrigeration system using Al2O3/mineral oil nano-lubricant

ABSTRACT Nowadays, in many developing countries like India they are facing the shortage of energy. The Refrigeration system has become the major consumer of energy for many industrial as well as household applications. So, it is the need to enhance the energy efficiency of the refrigeration systems. Performance of the refrigeration system can be improved either by increasing the rate of heat absorption in evaporator or by reducing the compressor power. Use of efficient lubricant oil can help to remove the heat generated in the compression process which leads to less power consumption. Development in Nanotechnology makes it possible to develop a new class of lubricant called nanolubricant, in which nanoparticles are added in base lubricant oil to enhance the thermal properties. The two step technique with ultrasonic agitation force is used to synthesise stable nanolubricant.The present study investigates the performance of a R-134a refrigerant vapour compression refrigeration system using nanolubricant with different volume concentrations (0.05%, 0.075%, 0.1% and 0.2%) of Al2O3 to mineral oil (MO) experimentally. The result shows maximum enhancement in COP approximately as 85% for 0.075 % volume fraction Nano lubricant as compared to base fluid. Use of nanolubricant saves approximately 27% compressor power.

Experimental investigation of temperature and heat distribution across 220 MWe Indian PHWR channel under boil-off condition

Under very low probability postulated accident like LOCA with unavailability of ECCS, the moderator heat sink maintains the channel integrity by providing adequate cooling. As the cooling is external to channel, the circumferential as well axial temperature gradient exists within the channel internals. An experimental set-up was fabricated to simulate the boil-off condition during a postulated accident in NPP. The experiments were conducted at average fuel bundle temperature 600 °C, 800 °C and 1100 °C with superheated mixture of steam and argon. The minimum and maximum temperature in CT, PT and fuel bundle were diametrically opposite to each other; the circumferential as well axial temperature gradient increased with an increase in bundle temperature. The rate of moderator heat absorption increases with increase in bundle temperature. The moderator was successfully able to prevent a breach in the channel; it proved to be the ultimate heat sink during a postulated LOCA with unavailability of ECCS.

The effect of heat transfer from formation to wellbore on the key parameters of supercritical CO2 in toe-point injection horizontal wells

In this paper, a novel model is proposed to characterize CO2 pressure and temperature distribution in horizontal wells with toe-point injection technique. Firstly, the mathematical model of CO2 flow in both tubing and annulus is established based on the mass, momentum, and energy conservation equations, and it is solved by employing finite difference method. The mass and heat transfer are coupled with formation CO2 absorption and heat exchange between tubing and annulus by iterative technique. Then, the proposed model is validated by field data. Finally, the integrated analyses of heat transfer mechanism, advantage of toe-point injection over heel-point injection, and effect of injection parameters on CO2 temperature, pressure, and mass flow rate in annulus and heat absorption rate from formation are conducted. Results indicate that (1) the model is applicable within wide ranges of CO2 pressure, temperature and mass flow rate. The predicted results are in good agreement with field data. (2) The CO2 temperature in annulus is first dominated by heat absorbed from formation and increases with the distance to toe point, then it is dominated by heat released to tubing and turns to decrease near heel point. (3) With a narrower temperature variation range, the performance of CO2 with toe-point injection technique is more stable and homogeneous. (4) The CO2 temperature and pressure in both tubing and annulus decrease with the increasing of injection rate. (5) The influence of injection temperature on CO2 pressure can be negligible, while the increase of injection pressure will contribute to the increase of CO2 temperature. The theoretical studies in this paper can be taken as a reference for engineers in optimization of injection parameters and provide following researchers with the very basic theory for the application of toe-point injection technique.

The promotional effect of sodium chloride on thermophysical properties of nitrate

Nitrate are the excellent phase change materials (PCMs) for thermal energy storage. Nitrate has no phase separation during phase transition and has good chemical stability. The present study concentrates on improving the latent heat of phase change and of heat absorption rate by adding various proportions NaCl into the nitrate/mixed nitrate. Sodium nitrate and sodium chloride were selected to prepare binary mixture by static melting method. The melting point and latent heat of phase change were measured by differential scanning calorimetry (DSC). Compared with pure sodium nitrate, the melting point and solidification point of binary molten salt containing 5% NaCl are reduced by 9°Cand 16°C, respectively. On the other hand, the latent heat of melting and solidification increased by 12J/g and 10J/g, respectively.

Experimental Investigation of Castor Oil and Methanol Powered DI-CI Engine with Thermal Barrier Coated Piston

Biodiesel has gained the attention of many researchers all over the world. Although several biodiesel are utilized as fuel for diesel engine, the thermal efficiency of the engine while running with biodiesel does not meet the standards of neat diesel. In this research work an attempt was made to run the direct injection compression Ignition (DI-CI) diesel engine with thermal barrier coated piston with castor oil and methanol fuel blends. Thermal barrier coating (TBC) increases the heat absorption rate thereby reduces the amount of heat rejected to the exhaust system. TBC also overcomes the problem of using biodiesel in CI engines that it compensates the efficiency loss due to lower calorific value of biodiesel. On the other hand, methanol blended with castor oil has the ability to reduce the oxides of nitrogen and smoke emissions simultaneously. The experimental results show that an increase of 3.07% in brake thermal efficiency is achieved when the thermal barrier coated CI engine is fuelled with methanol and castor oil blend when compared with neat diesel. Also, the NOx emissions and smoke intensity are reduced by 44% and 28.5% respectively with the same blend.

Development of a 100-K pneumatically driven split-type cryogenic Stirling cryocooler based on experimental and numerical study

This study is aimed at the development of a 100-K class pneumatically driven split-type cryogenic Stirling cryocooler. The pneumatically driven displacer is floating in the expander and is supported dynamically by the gas enclosed in a bounce space. An efficient theoretical model combining the dynamic and thermodynamic analysis is developed to simulate the transient behavior of the cooler in the starting period by improving the weakness of the existing models. In parallel, a prototype cooler is built to validate the theoretical model. Experimental measurements of cold head temperature, cooling load and coefficient of performance are conducted. A close agreement between the numerical and the experimental data is found. Results show that as the charged pressure is 5 bar and the rotation speed is 2000 rpm, the zero-load temperature of the cold head of the developed cryocooler can reach 103 K in 15 min. Effects of rotation speed on the phase angle, heat absorption rate, displacer stroke and power input are predicted, and the optimal operating ranges of the rotation speed at different charged pressures are presented.

Extinguishing Characteristics of a Pool Fire with a Rubber Balloon Filled with Inert Gases

In this study, an extinguishing method using a rubber balloon filled with inert gas is proposed against fires in confined space such as spacecraft and space station. The proposed method has a possibility to increase extinguishing effectiveness of inert gas and decrease its volume amount needed for firefighting. In order to clarify the extinguishing characteristics, the blowoff experiments have been performed under normal gravity condition. CO2, N2, Ar and Ar + N2 mixture gases were used as an extinguishing gas and ethanol, 1-butanol and n-heptane were used to form a pool fire. The fuel pan diameters were varied from 47 mm to 94 mm. From the experimental results, it is found that there exists the extinguishment limit, which indicates the minimum inert gas volume needed for achieving flame extinguishment with the rubber balloon. By using the magnitude of the extinguishment limit value, the extinguishing ability of inert gas in the rubber balloon extinguishment can be evaluated. As a result, the effectiveness ranking of the inert gas in rubber balloon extinguishment agrees well with that of cup-burner tests. Moreover, it is found that when the size of the pool fire (fuel pan diameter) is same, the value of the lower heating value of fuel divided by the inert gas heat capacity at the extinguishment limit shows a certain constant value independent of inert gas and fuel species. As a result, the extinguishment limit of the rubber balloon extinguishing method is considered to be determined due to the balance between the heat release rate of the pool fire and the heat absorption rate of inert gas released from the bursting balloon. Thus, a rubber balloon can be used as an extinguishing capsule, by which a high concentration inert gas is easily delivered to the flame. In addition, it is much easier to grasp heat capacity effect of inert gas on flame extinguishment than the conventional methods, such as the cup-burner test.

Comparative study of different storage bed designs of a solid-state hydrogen tank

Abstract This work discusses the influence of different metal hydride storage bed configurations. The objective was to design and optimize a solid-state hydrogen storage for a nonpolluting mobility. A study of the absorption and desorption dynamics of a loose powder bed was performed first, followed by three different storage bed configurations: compacted Ti-Mn alloy powder, alternated Ti-Mn alloy compacts with stainless steel fins and compacted [Ti-Mn alloy/Stainless steel] powder mixture. A numerical model was developed to simulate the heat transfer and the hydrogen absorption and desorption rates. The alternation and compact mixture configurations gave better heat transfer efficiencies, absorption and desorption rates and increased hydrogen storage densities. Indeed, an efficient heat transfer (between the tank and its surrounding fluid), a tailored porosity of the metal hydride storage bed and the addition of high thermal conductivity materials allowed the overall storage performance to be improved. Thus, the required time for loading/unloading hydrogen was reduced drastically. The alternation configuration would offer the additional advantage of a simple, inexpensive and efficient recycling procedure.

Numerical study of unsteady natural convection of variable-order fractional Jeffrey nanofluid over an oscillating plate in a porous medium involved with magnetic, chemical and heat absorption effects using Chebyshev cardinal functions

The unsteady natural convection of an incompressible, magnetohydrodynamic (MHD), Jeffrey nanofluid in the vicinity of a vertical oscillating plate in a porous medium is examined. Several involving parameters such as thermal radiation, chemical reaction, Soret effect, thermal diffusion, magnetic field and heat absorption are taken into account. To gain an insight into the behavior of a memory-dependent fluid, the variable-order fractional calculus for heat, mass and concentration equations is implemented, which, to the best of the author's knowledge, has not been tackled by the researchers for the present comprehensive problem. The set of governing equations are reformed to the dimensionless form via invoking appropriate variables. A computational matrix method based on the Chebyshev cardinal functions (CCFs) is given to examine the behavior of the relevant problem. In fact, regarding to the established method, the unknown solutions are expanded by the CCFs. Then, the operational matrix of the variable-order fractional derivative is utilized to transfer the problem into solving an algebraic system of equations. The applicability and accuracy of the suggested method are investigated by solving some test problems. The numerical results confirm the high accuracy of the presented approach. The effect of several parameters such as Grashof, Hartmann, Prandtl, Soret and Schmidt numbers, in addition to oscillation frequency, retardation time, radiation, heat absorption and reaction rate are determined and presented graphically. According to the results, increasing the value of fractional order improves the natural convection mechanism as well as the peak value of the velocity profile.

Effect of Variable Thermo-Physical Properties of LiBr-H2O Solution on the Performance Parameters of Horizontal Tube Absorber

Absorber is the most important component in LiBr-H2O absorption systems as its operating performance directly influences the performance of the whole system. In simulating absorption heat and mass transfer in horizontal tube absorber, many authors, for simplicity, make some assumptions. One of these assumptions is that the thermo-physical properties of the solution are constant across the absorber. In this paper, LiBr-H2O horizontal tube absorber was simulated with constant and variable thermo-physical properties and a comparison between the performance parameters (solution concentration, solution temperature, absorber heat duty and rate of vapor absorption) was made. Two solution flow rates are used in this simulation ([Formula: see text][Formula: see text][Formula: see text][Formula: see text] and [Formula: see text][Formula: see text][Formula: see text][Formula: see text]) and a computer program was developed to simulate the two cases (constant and variable thermo-physical properties). The comparison results show that, in case of variable thermo-physical properties, the heat duty and vapor absorption rate are less than those in case of constant thermo-physical properties whereas solution concentration and temperature are slightly greater. Also, it is found that increasing solution volume flow rate [Formula: see text] increases the difference in heat duty and absorption rate and slightly decreases the difference in solution concentration and temperature.

Chebyshev polynomials for generalized Couette flow of fractional Jeffrey nanofluid subjected to several thermochemical effects

The generalized Couette flow of Jeffrey nanofluid through porous medium, subjected to the oscillating pressure gradient and mixed convection, is numerically simulated using variable-order fractional calculus. The effect of several involving parameters such as chemical reactions, heat generation, thermophoresis, radiation, channel inclination, and Soret effect is also considered. To the best of the authors’ knowledge, the described general form of the Couette flow problem is not tackled by the researchers yet. The non-dimensional form of heat, mass, and momentum equations is solved as a coupled set. The effect of several parameters such as Grashof, Hartmann, Prandtl, Soret, and Schmidt numbers in addition to oscillation frequency, retardation time, radiation, heat absorption, and reaction rate are determined and presented graphically. An operational matrix method based on the second kind shifted Chebyshev polynomials is proposed to investigate the behavior of the interested problem. In fact, regarding the established method, the unknown solutions are expanded by the mentioned basis polynomials. Then, the operational matrix of the variable-order fractional derivative is utilized to transfer the problem into solving an algebraic system of equations. According to the obtained results, the growth of fractional order from 0 to 1 changes the skin friction coefficient, Nu and flow rate by $$-18.1$$ , 35.5, and $$10\%$$ , respectively.

Interaction relationship analysis between heat transfer and hydrate decomposition for optimization exploitation

Heat transfer influences hydrate decomposition. Hydrate dissociation produces water. Then, water remained in the hydrate sediment shows impact on heat transfer. Six runs of experiment with different exploitation methods and well arrangements were conducted to study the interaction relationship between heat transfer and hydrate decomposition. For water production, results show that by combination method, the wellbore heating can greatly improve the water produced outside the reactor in production stage (WPII) until the hydrate decomposition ceases. While in depressurization regime, the WPII is more easily influenced by hydrate distribution and the water produced outside the reactor in the free and mix gas stage (WPI). For heat transfer, the overall heat transfer trend is not affected by less WPII. So the decomposition was hardly impacted. On the other hand, the heat transfer promotes heat absorption by hydrates, which improves hydrate decomposition. Subsequently, the hydrate decomposition consumes heat, but it cannot prevent the rise of temperature even in depressurization. So the heat from the surrounding environment is enough for hydrate decomposition. Then, the heat absorption by hydrate decomposition (Qd) and the heat absorption rate (Rd) are quantitatively studied. Specially, the heat absorption ratio (λ) is firstly defined to show the ratio of Qd to the wellbore heating consumption (Ec). It provides a fresh attitude for optimizing exploitation according to the heat transfer. In order to save more heat and improve λ, we need to utilize the heat transfer from the ambient environment and make progress in reducing wellbore heating consumption.

The Influence of Tilt Angle on Heat Loss and Solar Gain in Triple Vacuum Glazing

Hundreds of thousands and perhaps millions of riyals are spent each year for heating and cooling homes and workplaces. Globally, buildings are responsible for approximately 40-45 percent of the total world annual energy consumption. Most of this energy is used for the provision of lighting, heating, cooling and air conditioning. The severity of the climatic conditions in the period considered and the rapid development and increased affluence of recent last decades are among the contributing factors. In particular, much research is focused on thermal energy storage due to heat transfer between the building envelope and the surrounding environment, in order to predict the rate of heat transfer and to develop minimisation strategies. However, the design and construction of modern residential buildings, which are heavily reliant on electrical systems for control of the internal built environment, are causing greater concern. Also, most of the environmental pollution caused by fossil energy are used that feeling the need to make use of alternative energy and efforts to minimize the energy dissipation. As a result, local attention is focused on improving energy efficiency for residential buildings. Among the various components of the building envelope, windows require a careful design because much of the heat dissipation occurs there. Windows are responsible for a disproportionate amount of unwanted heat gain and heat loss between buildings and the environment. Solar heat gain plays a major role in determining the thermal performance of a building and increasing or decreasing solar gains can be of crucial importance in design problems. Energy efficient windows should minimize thermal losses as well as air leaks; this is achieved in practice by a combination of different technical solutions, such as multi-layer glazing, low thermal conductivity gas fills, painted glass surfaces, low-emission coatings, edge spacers, and frame materials. An optimal window design with a suitable glazing compound can considerably reduce the energy consumption of air conditioning systems in the residential buildings. In commercial, industrial and public buildings, an optimum window design has the potential to reduce the cost of illumination as well as that of heating, ventilation and air-conditioning (HVAC). Computer simulations are commonly used to provide an expanded scope of systematic study and enable consideration of wide ranges and combinations of parameters. In this study, by computer modeling of the thermal dissipation of impact of tilt angle on the triple vacuum glazing with a thickness of 42 mm, in which a layer of Argon gas used to compare the three main technical factors that have been examined. These three main factors are heat transfer coefficient, relative rate of heat absorption and solar heat gain coefficient. The model of triple vacuum glazing is based on a commercial product that is available on the consumer market in Tehran. The results show that using triple vacuum glazing reduction more than 70 percent in energy dissipation And 60 degree glass on average in the southern facade of the building to optimize solar gain of solar energy with no apparent increase in thermal dissipation in energy of building.

A comparative study and analysis of natural convection flow of MHD non-Newtonian fluid in the presence of heat source and first-order chemical reaction

Heat and mass transfer of fractional Jeffrey’s flow over infinite vertical plate moving exponentially with variable temperature and mass diffusion has been detailed. Additionally, first-order chemical reaction, magnetohydrodynamics and rate of heat absorption are also considered. The classical Jeffrey’s fluid model is generalized to a fractional model of non-integer-order ‘α.’ The present problem is solved by two approaches, namely, Caputo and Caputo–Fabrizio. The exact solutions for temperatures, concentrations and velocities have been obtained via Laplace transform method. The corresponding rates of heat, mass and skin friction are also computed. We have drawn a comparison approach between the solutions of two fractional models of Jeffrey’s fluid modeled with Caputo and Caputo–Fabrizio fractional derivatives by means of graphical illustration using MathCad software. Physical impact of fractional parameter ‘α’ on the Sherwood number, Nusselt number and skin friction was presented in a table and found that they are increased by increasing the value of ‘α.’ In comparison, the rates of heat and mass transfer and skin friction of Caputo fractional derivative have greater values than Caputo-Fabrizio.

A numerical model for wet steam circulating in horizontal wellbores during starting stage of the steam-assisted-gravity-drainage process

Steam-assisted-gravity-drainage (SAGD) has been proved effective in heavy oil recovery. Preheating of the wellbore-surrounding reservoir is to circulate steam in the injector and producer so that heat can be conducted into surrounding oil layer. At this stage, the amount of steam injected into the reservoir is neglected. As a result, creating a large temperature difference between wellbore and annuli is key during the preheating process. A model is established for estimating steam properties in the wellbores so that the highest steam temperature in wellbores can be achieved. The model is comprised of mass, energy and momentum balance equations and the model is solved with numerical method. It is found that: (a) rich heat energy reflected in high steam quality does little effect on heat absorption rate of oil layer. The only effective method for temperature increase in oil layer is to increase the steam temperature in wellbores; (b) in order to increase the heat conduction rate to oil layer, a lower steam quality, a higher steam pressure and a lower mass flow rate is recommended.