Influence Of Heat Transfer Coefficient Research Articles

Optimization for the temperature range of radiator for preventing draught risk of cold window

High surface temperature of radiator can provide thermal plume with enough momentum intensity and thus counteracts the downdraft caused by window. Meanwhile, it is necessary to avoid causing indoor temperature to exceed upper limit of thermal comfort zone. In this paper, influence of heat transfer coefficients of window and exterior wall, outdoor temperature, and average surface temperature of radiator on operative temperature (Top) and temperature difference between indoor air and window (Td) was investigated. Based on response surface method, single factor and interaction effects for the four influencing factors on Top and Td were analyzed. A framework optimizing average surface temperature of radiator for preventing draught risk of window was established. When the heat transfer coefficient of window was around 1.4 W/m2·°C and satisfied related energy-conservation standard, cold draught could be eliminated without causing indoor environment overheating. Based on the optimized temperature range, the supply water temperature was controlled, and seasonal performance using the variable temperature strategy was investigated based on TRNSYS simulation. With the variable water temperature control strategy, the output hourly indoor air temperature was within the comfortable range. In the whole heating season, hours that did not meet cold draught requirement occupied 77.22 %, as the heat transfer coefficients of window dis-satisfied the energy-saving design standard. As meeting the design standard, the proportion decreased to 12.97 %. Utilizing the optimized temperature interval can prevent discomfort caused by cold draught to the greatest extent. This study is conducive to improving thermal environment with the convective–heating system and may lead to the reduction of energy consumption for heating.

Optimal battery preheating in critical subzero ambient condition using different preheating arrangement and advance pyro linear thermal insulation

Low temperatures have a substantial impact on the overall performance of traction batteries (0°C and below) as a result, it is essential in developing an effective battery preheating that can efficiently heat up batteries and aid in the start-up of electric cars or energy storage in cold climates. This study explores three different heating methods to find the optimal placement of heating films. Furthermore, based on optimal placement of heating films, we introduced wall-enhanced pyro lining thermal insulation to store potential generated heating temperature inside the battery pack for a longer duration even though power supply from heater is cut-off. The achieved results suggest's, heating model 1 (front face heater) provides uniform heating as compared to heating mode 2 (side face films) and heating mode 3 (bottom face films). In addition to the heating modes, the battery thickness, heat transfer coefficient (HTC) and heating power are explored in the article. The conclusive results show, with heating method 1 time required to achieved 25℃ from initiating battery temperature low as −20℃ required 624s along with ΔT of 3.51℃, heating method 2 required 395s with ΔT of 33.19℃, and heating method 3 required 290s along with ΔT of 59.04℃. Similarly from the parametric and statistical investigation over the influence of HTC on required heater energy, we conclude that by increasing the amount of HTC, energy required by heater also increases qualitatively as suggested with HTC of 5 W/m2K, 624s of time is required along with 1020 J of energy; for HTC of 10W/m2K, 700s is required with 1150 J of energy; and for HTC of 15 W/m2K, 765s is required with 1280 J of energy. Similarly for the objective of storing maximum generated heat inside the volumetric domain of battery pack when heater power is cut-off at 25°C, the internal temperature of generic model drops by 20°C by the end of 1000s, on other hand improved model drops only 4°C of temperature by the end of 1000s.

The Influence of Heat Transfer Coefficient α of Insulating Liquids on Power Transformer Cooling Systems

The power transformer plays an important role in electric power systems. One of the conditions for the proper operation of the transformer is to ensure a sufficiently low temperature. This condition can be met if the heat exchange is effective. Heat transfer depends, among other things, on the electrically insulating liquid. The thermal property describing the ability of a liquid to transfer heat is the heat transfer coefficient α. At the design stage of the transformers, it is most often assumed that the value of the α coefficient is constant and equal to 100 W·m−2·K−1. Such simplifications can lead to the improper design of the transformer since this factor depends on many factors. The article presents the results of research on the dependence of the heat transfer coefficient α on the type of electrical insulation liquid, the thermal load of the cooled surface, and the length of the heating element. Four types of electrical insulating liquids were considered: mineral oil, synthetic ester, natural ester, and natural ester with reduced viscosity. The obtained results prove that the type of electrical insulating liquid and the thermal surface load value affect the α coefficient. The length of the heating element did not affect the α factor.

Development and heat transfer analysis of thermoelectric self‐powered fuel‐fired residential boiler

AbstractSolid‐state thermoelectric (TE) devices offer many interesting features compared with other methods of generation, such as no moving parts, high reliability, low maintenance, and straightforward integration with other heating equipment. In this study, a thermoelectric assembly was integrated into a residential heating boiler to convert a portion of combustion heat to electricity while meeting space and/or water heating needs. A prototype was developed, in which recently developed thermoelectric modules were incorporated into a gas‐fired boiler. The electricity generated by the thermoelectric assembly would be sufficient to power the electrical auxiliary components of the heating system. In this way, the heating system could operate entirely on fuel combustion and provide the consumer with heating system reliability and a reduction in power consumption. A model for the thermoelectric conversion system was established and the thermal resistance analysis was carried out to show the influence of heat transfer coefficients and other parameters on power output and efficiency, and thus improve the system design. In this study, the single‐module integrated assembly can produce a 22.5 W power output. However, each module of the four‐/eight‐module integrated assembly can only generate a power output of 7.85/9.175 W on average. The performance of a single module in a multimodule assembly is worse than that of a single module assembly. The number of modules placed on the furnace wall is not as many as possible but has an optimal value. In this experimental environment, the assembly of eight modules is the optimal choice. Furthermore, it is found that enhancing combustion‐side heat transfer capacity is an effective way to promote system performance. The power output of the assembly composed of four modules will increase by 70% from 7.85 to 13.5 W due to the installation of the fin on the hot end.

Optimization method for prefabricated restroom envelope energy saving characteristics in hot summer and cold winter zone

In order to reduce the restroom envelope energy consumption, one optimization method on basis of analyzing the influence of heat transfer coefficient on the performance of a prefabricated restroom envelope in a hot summer and cold winter zone was proposed. An energy-consuming model of prefabricated restroom in Nanjing is initially built based on Designer's Simulation Toolkit software. Subsequently, the effect of external walls, rooftops, external windows with various thermal characteristics on the building envelope is analyzed respectively. Simultaneously, a method that only changes the heat transfer coefficient of the prefabricated restroom envelope while keeping other parameters unchanged is adopted. Results show that, for a prefabricated restroom, the optimal range of heat transfer coefficient of the external wall, rooftop, and external window in hot summer and cold winter zone is 0.199∼0.22, 0.16∼0.19, and 3.0∼3.1 W/(m2·K), respectively. When the window-to-wall ratio is less than 0.2, the priority of the wall heat transfer coefficient on building energy consumption is higher than that of the rooftop heat transfer coefficient, simultaneously, the rooftop heat transfer coefficient has priority higher than window heat transfer coefficient. Thus, it is of great significance to optimize the design of the prefabricated restroom envelope in a hot summer and cold winter zone, which provides relative reference for thermal performance improvement of prefabricated restrooms.

Effects of process conditions on the heat transfer coefficient at the polymer-mold interface and tensile strength of thin-wall injection molding parts

Abstract Generally, the strength at the weld line of the injection molded part is very weak. The heat transfer coefficient (HTC) between the polymer melt and the mold cavity surface was analyzed to solve this problem. The surface roughness of the mold cavity and the material of the mold insert were changed to adjust the interface environment between the polymer melt and the mold cavity surface. HTC was obtained by combing the experimental measurement with the theoretical calculation. In the current study, the influence of HTC on the tensile strength of the weld line of the molded specimen was investigated. The results show that the weld line strength of the molded specimen increases with the decrease in HTC between the polymer and the mold cavity surface. Meanwhile, the decrease in the surface roughness of the mold cavity or replacing the mold material with lower thermal conductivity can reduce the value of the HTC between the polymer and the mold effectively and can delay the cooling rate of the hot polymer melt. This provides a new idea to solve thin-wall injection molding weld line defects.

The influence of cooling rate on the microstructure and phase fraction of gas atomized NiAl3 alloy powders during rapid solidification

NiAl3 alloy powders were produced by nitrogen gas atomization in this paper. The microstructure and phase compositions of different particle size powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The atomized powders are composed of Ni2Al3, NiAl3 and Al-eutectic phases, and three main types of solidification microstructures were identified: dendrites, refined dendrites, and compounds. Phase fraction of three representative particles with diameter of 60, 140 and 220 μm were measured. Moreover, the Newtonian heat transfer formulation coupled with the classical heterogeneous nucleation was used for analyzing the influence of heat transfer coefficient and cooling rate on the thermal history of droplets. Therefore, this work highlights the experimental results matched well with the theoretical calculation and guides the further production of high NiAl3 phase Raney nickel catalytic powders.

EVALUATION OF VARIABLE INTENSITY OF HEAT REMOVAL FROM THE SURFACE OF FALLING AND CRYSTALLIZING MELT DROPLETS IN THE PROCESS OF THEIR PRILLING

The method of calculation of the intensity of heat removal from the surface of the crystallizing melt droplets is presented. A comparison with the experimental fixed values representing the intensity of the heat transfer between the surface of the resulting pellet and cooling agent is carried out. The influence of heat transfer coefficient on the surface of the pellet changes on complete crystallization time, and therefore on the size of the granulation tower, is analyzed. Conditions defining the heat transfer between the granule surface and surrounding coolant, while full crystallization in conjunction with the dependence of the rate of nucleation and growth of the granules determine mechanical properties of ammonia fertilizer granules.

An experimental investigation on flow boiling heat transfer of R-600a in a horizontal small tube

The local heat transfer coefficient and flow pattern were studied experimentally during flow boiling of R-600a inside a horizontal small tube (inner diameter ID = 1.0 mm). The effects of heat flux, mass velocity and vapor quality have been investigated. The tests were conducted at heat fluxes from 5 to 60 kW m−2, mass velocity from 240 to 480 kg m−2 s−1 at 25 °C saturation temperature. Results show that flow patterns are related to the heat transfer coefficient. Convective boiling was found to be predominant during the tests. Nucleate boiling was predominant only in low vapor quality region. The resultant database was compared against predicting correlation available in literature for heat transfer coefficient. It was found that mass velocity have significant influence of heat transfer coefficients.

Study on the Evaporator Area Effects in the Gravity Feed Liquid Refrigeration System

In order to the small gravity feed liquid system cold storage optimization, it is analyzed that the evaporator area in gravity feed liquid system is how to influence the efficiency of the system. The visual basic software is used to simulation. The influence of heat transfer coefficient, heat transfer temperature difference and refrigerating capacity is simulated with the change of the evaporator area of the refrigeration system. Through the experiment, the feasibility of the application software is determined. Also it is found that the reduction of 25% evaporator area can make the system work best under the condition of - 18 °C cold storage temperature.

Study of far-field pressure wavelet of air-gun bubble based on potential flow theory

The study of far-field pressure wavelet of air-gun bubble is the basic research of air-gun sources. In this paper, a boundary element bubble model is established to simulate the dynamics of bubble, and an energy equivalent method is put forward to solve the bottleneck of bubble jet. In our simplified model, the bubble model takes into consideration the thermodynamic factors such as heat transfer and gas release, and the numerical results agree with the data of Nucleus software well. Based on the established model, the influence of heat transfer coefficient, air-gun firing time, and specific heat at constant volume on the pressure wavelet are studied. Finally, the three-dimensional bubble merging numerical method is put forward, which is an expansion of the axisymmetric model. Thus, the preliminary study of coherent air-gun is conducted, especially the influence of the space between two bubbles on the wavelet. This paper provides a reference for the research of air-gun.

Experiment Study of Heat Transfer in Aeroengine Bearing Chambers

In this paper, a method of heat transfer test research in aeroengine bearing chamber has been introduced. The method attains the law of heat transfer in bearing chamber and the influence of heat transfer coefficient on bearing dn value, oil flow, supply oil temperature, sealing air flow by simulating the oil work condition in turboshaft engine typical high temperature bearing chamber.

Finite Element Simulation of Nickel-Based Alloy Cutting Process Based on DEFORM- 3D

To analysis cutting mechanism and heat transfer coefficient of Ni-based superalloy IN718, this paper introduced a three-dimensional finite element model for cutting process based on DEFORM-3D V6.1, and cutting force Fy and cutting temperature T under different feed rate f , cutting speed v and back engagement ap were obtained. The temperature variation during cutting process under different cooling method was analyzed. The simulation results indicate that the influence of back engagement ap on the cutting force Fy is the greatest, while that of cutting speed v is minor; and for cutting temperature T, influence of cutting speed v is the greatest, while that of back engagement ap is minor. Influence of heat transfer coefficient on highest temperature and average cutting force Fy is minor, but its influence on average temperature is quite obvious. Greater heat transfer coefficient is less average temperature.

Development of a thermoelectric self-powered residential heating system

Self-powered heating equipment has the potential for high overall energy efficiency and can provide an effective means of providing on site power and energy security in residential homes. It is also attractive for remote communities where connection to the grid is not cost effective. Self-powered residential heating systems operate entirely on fuel combustion and do not need externally generated electricity. Excess power can be provided for other electrical loads. To realize this concept, one must develop a reliable and low maintenance means of generating electricity and integrate it into fuel-fired heating equipment. In the present work, a self-powered residential heating system was developed using thermoelectric power generation technology. A thermoelectric module with a power generation capacity of 550 W was integrated into a fuel-fired furnace. The thermoelectric module has a radial configuration that fits well with the heating equipment. The electricity generated is adequate to power all electrical components for a residential central heating system. The performance of the thermoelectric module was examined under various operating conditions. The effects of heat transfer conditions were studied in order to maximize electric power output. A mathematical model was established and used to look into the influence of heat transfer coefficients and other parameters on electric power output and efficiency.

The influence of heat transfer coefficient on cooling time in injection molding

The cooling time of the polymer melt in injection molding is a major part of the total time of the processing cycle. Estimation of cooling time is therefore important. The effect of heat transfer coefficient, thermal conductivity and diffusivity on the cooling time is studied theoretically, showing high effects of variations in heat conductivity on cooling time.

Entropy Production due to Time Exponentially Varying Laser Pulse: Convective Boundary Condition Case

Laser pulse heating with convective boundary at the surface finds applications in laser gas-assisted processing. Thermodynamic irreversibility associated with the thermal system can be quantified through entropy production. Consequently, in the present study, analytical formulation of entropy production is carried out for exponentially varying time laser pulse heating with convective boundary condition at the surface. Entropy ratio (ratio of entropy produced to its counterpart corresponding to the no-convection-boundary situation at the surface) is introduced. It is found that entropy production is low in the early heating period. The influence of heat transfer coefficient on entropy production is significant in the surface region, which becomes more pronounced as the heating period progresses.

Prediction and measurement of residual stresses in quenched stainless-steel spheres

A finite element (FE) technique has been used to predict the residual and thermal stresses which occur during water quenching of solid stainless-steel (SS) spherical balls. The variations of residual stresses at different positions and cross-sections, e.g. the radial, axial and tangential directions, have been examined. Also, the influence of heat transfer coefficient, the initial temperature and the hardening assumption on residual stress results has been investigated. The results show that high compressive residual stresses occur along the cooling surface. Moving away from the surface, these residual stresses begin to decrease and reverse their sign, and near the centre are tensile. Preliminary quenching experiments have been carried out using spheres of type 316L stainless steel. The temperature during quenching was recorded and compared with finite element simulations. The surface residual stresses were determined using the incremental centre-hole measurement technique. Neutron diffraction (ND) was used to determine the residual stresses in the centre of the sphere. The paper compares these measurements with the finite element results as well as comparing the measured cooling temperature history with simulation. Overall there is good agreement between the predicted and measured stresses.