Heat Transfer Load Research Articles

Research on flow structure and heat transfer mechanism of windward bend lattice frame

The lightweight lattice sandwich structure is considered a promising heat transfer technology with broad application prospects for improving the heat dissipation capacity of thermal management systems. The heat transfer performance needs to be further researched urgently. In this study, the flow resistance and heat transfer characteristics of windward bend lattice frames with heat transfer and mechanical load capacity were investigated by experimental and numerical methods. The flow mechanism and enhanced heat transfer mechanism of windward bend lattice frame was revealed from the point of view of unit structure. The results show that the bending shape alters the flow state of the fluid in the passage within the windward bend lattice frame truss to enhance the mixing effect of high-temperature and low-temperature fluids in the passage. Additionally, as the angle of inclination increases, there is a significant improvement in local flow resistance characteristics and enhanced heat transfer performance due to deflection in movement direction and rotation direction of inverse spiral vortex at rear truss rod. Furthermore, it is observed that at constant pumping power, the changes in Angle of inclination significantly affect heat transfer on different surfaces: lower surface (increasing by 101%), upper surface (increasing by 57%), followed by end wall (increasing by 16%). This work has valuable engineering applications for structures with similar bending characteristics.

Steady Heat Transfer Analysis of the Refrigerator Seal Considering Rigid and Flexible Contact

The rigid and flexible contact of the refrigerator seal has a significant impact on its heat transfer characteristics, but existing research has ignored this important factor. In this paper, the assembly physical model at the seal region is established by static structural analysis. Then a three-dimensional heat transfer numerical simulation is carried out. The assembly distance affects the contact state of the seal by changing the contact position between the seal and the door or the cabinet. The calculation results show that the calculated temperature at the seal region considering the actual assembly deformation is closer to the measured temperatures. In the case study, the heat leakage load decreases by 18.57% and 19.99% at the compressed state, while it increases by 4.45% under the stretching state. The proportion of heat transfer load in the path of rubber strip-cold air and rubber strip-outer shell of the cabinet is the largest, reaching over 30.0%. The heat transfer load of the cold bridge also accounts for over 20.0%. When optimizing the seal structure, reducing the contact interface length of rubber strip-cold air, reducing thermal conductivity, and increasing the contact thermal resistance of cold bridge should be focused on.

Effect of structural improvement of gaskets on the heat leakage load and energy consumption of the refrigerator

Gaskets play a significant role in the thermal insulation of refrigerators. Previous studies mainly focused on how to obtain the heat and moisture transfer load of a given gasket, but lacked appropriate structural improvement measures and their effect on the heat leakage load and energy consumption of refrigerators. In this paper, the heat transfer analysis of an original gasket was conducted via numerical simulation. It was found that the main thermal insulation weaknesses of the original gasket are gasket-cold air, gasket-outer shell of the cabinet, gasket-inner lining of door and gasket-hot air. Thus, adding an auxiliary-airbag to the original gasket and a comprehensive new-design gasket were proposed to improve the thermal insulation. Compared with the original gasket, the numerical simulation results showed the heat leakage loads of the auxiliary-airbag and new-design gasket were reduced by 18.44 % and 27.49 %. The total heat leakage loads of refrigerators equipped with improved gaskets were reduced by 4.46 % and 6.64 %. The effect of two structurally improved gaskets on the refrigerator energy consumption was experimentally studied. The repetitively measured results showed the energy consumption of refrigerators with the auxiliary-airbag and the new-designed gasket were reduced by 0.93 % and 3.19 %. The reason why the reduction in refrigerator energy consumption is lower than the reduction in heat leakage load is due to the difficulty in achieving the designed assembly state of the gasket during actual installation. Based on the holdings of refrigerators around the world, it is estimated that the refrigerators energy consumption can be reduced by 106.776 billion kWh per year and carbon emissions can be reduced by 12.74 million tons per year when using the new-design gasket proposed in this study.

Investigations on Hot Air Anti-Icing Characteristics with Internal Jet-Induced Swirling Flow

The tangential jet-induced swirling flow is a highly efficient technology for enhancing heat transfer. This paper explores the application of swirling flow of an airfoil/aero-engine in a hot air anti-icing chamber, aiming to improve the anti-icing performance and achieve a more uniform temperature on the surface. A series of numerical computations adopting the SST k − ω turbulent model was carried out to obtain the internal flow and heat transfer characteristics, as well as the surface temperature distributions, considering water evaporation and solid heat conduction. Three jet arrangements, including impingement jets, offset jets, and swirl jets, were studied and compared, which evidently showed that the swirling effect was helpful to elevate the internal heat transfer. Compared to the impingement jets at the Reynolds number of 40,000, the Nusselt number with the offset jets is increased by 19.5%, while the corresponding Nusselt number of the swirl jets is augmented by 44.3%. The swirling flow significantly elevates the swirl number within the internal chamber, intensifying the vortex strength near the wall and increasing the circumferential velocity, which also results in an augmentation of internal pressure loss. By adopting the swirling internal flow, the temperature distribution on the anti-icing surface is more uniform and is increased by up to about 4.1 K in the leading edge when the internal-to-external temperature difference is 80 K. Simultaneously, the heat absorption of water evaporation and the matches between the internal heat transfer and external icing load are of particular importance to determine the anti-icing performance, and this has been discussed in this paper.

Experimental study of the noise suppression of supersonic impinging jets with chevrons

Supersonic impinging jets may cause many adverse ground effects, including surface erosion, nonuniform surface heat transfer, lift loss, and acoustic loading. In this study, chevron nozzles are used to suppress the noise generation of supersonic impinging jets originated from a circular convergent nozzle with the jet Mach number of 1.2. An array of microphones is used to measure the far-field acoustic fields, and a schlieren system is employed to measure the near-field flow structures. Three impinging distances are considered to examine the differences between the impinging jets and the free jet, and to assess the effect of impinging distance on the noise characteristics. Two chevron nozzles with different penetration angles are designed to investigate the potentials of chevron nozzles in controlling the supersonic-impinging-jet noise. Results show that the chevron nozzles do not alter the directivity of overall sound pressure levels, but significantly reduce the amplitude at all emission angles. The discrete tones in the impinging jets are dramatically mitigated or eliminated, and the levels of broadband noise are also significantly reduced over a wide range of frequency band, regardless of the impingement distance. The influences of chevrons on the near-field flow structures are checked with the root-mean-square values and proper orthogonal decomposition of schlieren images, which provide more evidence on the noise suppression mechanism with chevrons.

Cooling Design Analysis of The Use of Land Engine On Ship

Based on the survey, the majority of fishermen in Indonesia choose to use land engines as propulsion for the main engine and auxiliary engine on ships because in terms of the price of land engines, they are much cheaper than ship engines produced by marine engine factories. Therefore, not a few workshops that often serve land engine modifications for further use as ship propulsion. Regulations regarding the use of land engines as ship’s main engines in Indonesia are currently not widely regulated in the Classification Agency regulations. Heat exchanger that supports the cooling system for optimal use of land engines on ships. Furthermore, the heat exchanger design process with a heat transfer load of 17,416 Watt was carried out using the LMTD method and obtained a heat transfer area value of 1,204 m2 with a staggered arrangement configuration. From the results of the CFD simulation, the temperature value at the hot water outlet is 51.39 C.

Indoor air quality and energy-saving potential improvement of a range-hood-integrated air cleaner

Local exhaust systems based on range hoods are widely used to reduce cooking oil fumes (COF) of kitchen spaces. This work proposes a range-hood-integrated air cleaner to improve air distribution in residential kitchens and reduce individual inhalation exposure to COF. Effects of hood exhaust rates, cooking–heating intensities, and airflow parameters of the air cleaner on the volume-averaged concentration (VAC) of kitchen space and the intake fraction (IF) are discussed through orthogonal experimental design, and significant factors are the hood exhaust rate, the air supply velocity, and angle of the air cleaner by evaluating significance levels. Optimal airflow parameters of the air cleaner are obtained through single-factor analysis, and VAC is reduced by approximately 90% compared with the single range-hood exhaust system. The energy-saving potential of the air cleaner is identified and evaluated using the concept of the equivalent exhaust rate. The air cleaner is more conducive to creating a comfortable kitchen environment and reducing heat transfer load. This work provides a new solution for optimizing air distribution in highly polluted kitchen environments.

Rheological properties and volumetric isothermal expansivity of bamboo kraft black liquor with high solids content and low lignin content

In this study, a certain percentage of lignin in original bamboo kraft black liquor (BKBL) was separated, and the residual BKBL with low lignin content was expected to be fed into the alkali recovery boiler to reduce the heat transfer load of the alkali recovery boiler. With the decrease in lignin content, the rheological properties/volumetric isothermal expansivity (VIE) of BKBL change. When the lignin content was 70% remaining in the original BKBL, the viscosity of BKBL with low lignin content is close to that of the passivated BKBL at the same solids content, the dynamic viscoelasticity is superior, and the VIE decreases by 57.2%. When the amount of desilication agent is 1.5%, the viscosity of BKBL with low lignin content did not change much, and the VIE increased sharply and was 62.7% higher than that of the passivated BKBL. Therefore, the combination of partial lignin separation process and sodium aluminate desilication process can effectively improve the ability of alkali recovery boiler to deal with BKBL and reduce the influence of “silicon interference”.

Selective Cerebrospinal Fluid Hypothermia: Bioengineering Development and In Vivo Study of an Intraventricular Cooling Device (V-COOL)

Hypothermia is a promising therapeutic strategy for severe vasospasm and other types of non-thrombotic cerebral ischemia, but its clinical application is limited by significant systemic side effects. We aimed to develop an intraventricular device for the controlled cooling of the cerebrospinal fluid, to produce a targeted hypothermia in the affected cerebral hemisphere with a minimal effect on systemic temperature. An intraventricular cooling device (acronym: V-COOL) was developed by in silico modelling, in vitro testing, and in vivo proof-of-concept application in healthy Wistar rats (n = 42). Cerebral cortical temperature, rectal temperature, and intracranial pressure were monitored at increasing flow rate (0.2 to 0.8 mL/min) and duration of application (10 to 60 min). Survival, neurological outcome, and MRI volumetric analysis of the ventricular system were assessed during the first 24 h. The V-COOL prototyping was designed to minimize extra-cranial heat transfer and intra-cranial pressure load. In vivo application of the V-COOL device produced a flow rate-dependent decrease in cerebral cortical temperature, without affecting systemic temperature. The target degree of cerebral cooling (− 3.0 °C) was obtained in 4.48 min at the flow rate of 0.4 mL/min, without significant changes in intracranial pressure. Survival and neurological outcome at 24 h showed no significant difference compared to sham-treated rats. MRI study showed a transient dilation of the ventricular system (+ 38%) in a subset of animals. The V-COOL technology provides an effective, rapid, selective, and safe cerebral cooling to a clinically relevant degree of − 3.0 °C.

Design and Characteristic Analysis of an Inductive Link for Wireless Current Charging of a HTS Magnet

Laboratory electromagnets are a type of scientific instrumentation widely used to study physical characteristics such as magneto-optical, magnetic hysteresis, and susceptibility properties. In laboratory electromagnets, it is important to generate a high field stably while also reducing the weight. This can generally be achieved by improving the magnetic properties of the ferromagnetic material used for the iron yoke or by increasing the operating current density of the excitation coil. High-temperature superconducting (HTS) coils can generate higher magnetic fields with smaller volumes compared to the copper coils used in conventional laboratory electromagnets due to their high current-carrying capacities. However, when excitation current in conventional HTS coils is generally charged using a power-driven mode, a high heat transfer load from the busbar occurs. The heat transfer load to the HTS coil deteriorates the operational efficiency and stability of the electromagnet system. To mitigate this problem, this paper proposes an inductive link for wireless current charging for laboratory HTS magnets. A magnetic coupler for the inductive link is also designed in consideration of the coupling coefficient, and a resonance circuit and rectifier circuit are designed using elements whose operational characteristics were verified in a cryogenic environment. Evaluating the feasibility of the proposed method is carried out via a finite element analysis combined with an electrical circuit analysis.

Optimal ferrofluids for magnetic cooling devices

Superior passive cooling technologies are urgently required to tackle device overheating, consequent performance degradation, and service life reduction. Magnetic cooling, governed by the thermomagnetic convection of a ferrofluid, is a promising emerging passive heat transfer technology to meet these challenges. Hence, we studied the performance metrics, non-dimensional parameters, and thermomagnetic cooling performance of various ferrite and metal-based ferrofluids. The magnetic pressure, friction factor, power transfer, and exergy loss were determined to predict the performance of such cooling devices. We also investigated the significance of the magnetic properties of the nanoparticles used in the ferrofluid on cooling performance. γ-Fe2O3, Fe3O4, and CoFe2O4 nanoparticles exhibited superior cooling performance among ferrite-based ferrofluids. FeCo nanoparticles had the best cooling performance for the case of metallic ferrofluids. The saturation magnetization of the magnetic nanoparticles is found to be a significant parameter to enhance heat transfer and heat load cooling. These results can be used to select the optimum magnetic nanoparticle-based ferrofluid for a specific magnetic cooling device application.

An optimization of microtube heat exchangers for supercritical CO2 cooling based on numerical and theoretical analysis

This paper presents a new simulation method with lower computation consumption for microtube heat exchangers (MSTEs) used for supercritical CO2 cooling, which maintains high precision. The heat transfer characteristics in the shell pass and tube pass and the relationship between them are both analyzed. Baffles lead to various regions with different follow patterns and heat transfer features in the shell pass. Furthermore, higher heat transfer performance in the shell pass leads to heat transfer enhancement in the tube pass due to the CO2 near-pseudocritical characteristics. The optimization method based on the eigenfunction of ΔPi = F(Ai) which characterizes the influence of baffles on the comprehensive performance of MSTEs focuses on the difference among local heat exchange and pressure loss in multiple segments and guides to reduce the pressure loss while the heat transfer load and area remain unchanged. The optimized baffles arrangement is found according to the numerical results and the optimization method. The comparison between the simulation results of the original and optimized MSTEs shows that the optimization method is effective for heat exchangers with variable local heat exchange features and pressure loss performances.

Scuffing load capacity calculation of worm gears

Worm gears with wheels of harder materials, such as cast iron or steel, are often prone to the damage type scuffing, which can cause a sudden and rapid failure of the gear box. Contact temperature is a suitable criterion to determine the scuffing safety for other types of gears. However, for worm gears, a scuffing load capacity calculation is not available at the moment. This paper presents a numerical temperature simulation for worm gears that considers transient multidimensional heat transfer and local frictional loading due to the contact. Based on the results of this simulation, this paper derives a simplified calculation of worm gear contact temperatures. The calculation only contains input parameters that are already part of current standards. Its result, the contact temperature of worm gears, can be used to rate the scuffing load capacity.

A study on heat transfer load in large space buildings with stratified air-conditioning systems based on building energy modeling: Model validation and load analysis.

The characteristics of heat transfer load from the non-air-conditioned (NAC) area can help to understand the complex airflow movement and thermal physical mechanisms inside large space buildings. Based on building energy modeling, the indoor thermal environment and building energy consumption of a plant for computerized numerical control (CNC) machine tools are studied. Considering the form of the stratified air-conditioning system and the phenomenon of heat retention near the roof in the plant, the double zone and triple zone models are established. The vertical air temperature, the parameters of the terminal of the air-conditioning system and the heat/cool source system of the plant in summer and winter were measured on site, which verifies the accuracy of the established model. Based on the validated model, the proportion of heat transfer load from the NAC area is calculated, at the range of about 60%-85%. The positive influence of the roof heat transfer coefficient on the sensible heat load in the NAC area is revealed. The recommended value of the non-dimensional zone-mixing flow rate between the air-conditioned (AC) and NAC areas is given, with 30% (in summer). The results of this work can help understand the composition of the stratified air-conditioning load in large spaces and optimize the design of air distribution.

Thermal performance augmentation of a semi-circular cylinder in crossflow using longitudinal fins

In the present work, the thermal/hydraulic characteristics of a semi-circular cylinder in crossflow of air have been numerically investigated at Reynolds number range between 103 and 104. Various attack angles between −90 and 90° were considered. The effect of finning was investigated at zero attack angle using three fin configurations (front fin, rear fin, and double fin) with different values of fin length and thickness. Flow patterns, local heat transfer coefficient, overall-averaged Nusselt number, and drag coefficient were reported and discussed. Correlations for Nusselt number and relative heat transfer rate were presented for plain and finned semi-circular cylinders, respectively. The irreversibility minimization approach was used to assess the performance of the semi-circular cylinder with/without fins compared to a plain circular cylinder with the same surface area, surface temperature, and heat transfer load. The semi-circular cylinder delivers the highest performance around an attack angle of 15 ° , while the worst performance occurs when the flat surface faces the flow. Additionally, finning significantly improves the performance by reducing the irreversibility. The front-fin and rear-fin configurations delivered relatively similar performances, while the best performance was attained using the double-fin configuration.

DESIGN AND ANALYSIS OF THERMAL SHOWCASE MINI AS A BEVERAGE COOLER USING A THERMOELECTRIC MODULE

In Indonesia, which has a tropical climate, a beverage cooler is needed. Almost every home, office, company, supermarket, and mall has installed beverage coolers. This has become a major necessity for people living in tropical countries. Especially those who live in eastern Indonesia, such as Ambon, NTT, and Papua, which have very hot temperatures. There are various types of use of the thermoelectric or peltier module, including food coolers, medicinal coolers, drinking water coolers in dispensers, and computer processor coolers. Besides being easy to apply, this tool is expected to be able to open up ideas in the use of thermoelectric modules that are more environmentally friendly than refrigerants. This research was conducted to obtain the size of the showcase mini design, the assembly process of the showcase mini tool, and to obtain the thermal analysis results contained in the showcase mini tool as a cooling medium. Showcase is a refrigerator that is used to display food or drinks that you want to display using glass media as a standout for the product being displayed. Thermoelectric technology is a technology that works by converting heat energy into electrical energy directly or vice versa, from electrical energy to produce cold energy. Thermoelectric is made of solid state material (solid material) which can convert energy from temperature difference to potential difference or vice versa. In this study, 2 variations of cooling load were used, namely without cooling load and with cooling load. Thermal analysis was carried out and got the results. The highest result from the calculation of conduction heat transfer load without cooling load is 0.013 Watt. The highest result from the calculation of the conduction heat transfer load with the cooling load is 0.010 Watt. The highest result from calculating the product heat load is 1.555 Watts. The highest result from the calculation of COP (Coefficient Of Performance) is 4,823. The expenses incurred each month are 16,000 rupiah.

Thermal-fluid-structure analysis of fast pressure relief valve under severe nuclear accident

Fast pressure relief valve (FPRV) equipped at the pressurizer of nuclear power system is used to release steam with high pressure and high temperature rapidly from the primary circuit loop and to prevent high temperature core melting in case of severe accident condition. When releasing the steam, the time-varying temperature, mass flow and interior pressure of the inlet will affect the reliability of FPRV. In this study, the thermal analysis and the static structural analysis of FPRV under severe transient thermal shock are conducted by a 3D thermal-fluid-structure coupling numerical simulation considering the transient coupled flow, heat transfer and mechanical load. In the analysis, one-way coupling simulation is conducted. Firstly, the fluid flow and heat transfer in the valve and valve body are simulated with time. Then the instantaneous temperature fields of FPRV structure obtained from the CFD analysis at different critical moments, at which the valve is bearing high temperature, high mass flow or high interior pressure, are imported into static structural analysis as thermal load for stress analysis. Through comparative analysis of stress under mechanical load, thermal load and their combined effect, it is found that the thermal stress is the primary component of the coupled stress of FPRV and the thermal loads rather than the pressure loads are responsible for accidents related to stress overload in nuclear power plants. Therefore, the coupled stress including thermal stress should be less than the allowable stress intensity for the safety evaluation of the FPRV in a nuclear power plant.

Heat transfer characterization and improvement in an external catalyst cooler fluidized bed

Gas–solid fluidized beds have been widely used in heat transfer processes, and so there have been many studies focused on increasing heat transfer in such units. In the present work, a pilot scale cold mode experimental rig was constructed to assess the effects of hydrodynamics on bed-to-wall heat transfer and to investigate various means of enhancing heat transfer in a dense gas–solid fluidized bed with external solid circulation. The experimental results show that heat transfer in the dense region played a dominant role in total bed-to-wall heat transfer, accounting for more than 88% of the total heat transfer load. Heat transfer could be lowered as a result of solids bypass that occurred because of external solids circulation, but this effect was weakened by the radial mixing of particles. The heat transfer characteristics identified in this study indicate that a specially designed baffle can be used to enhance bed-to-wall heat transfer. After installing such baffles in the fluidized bed test structure, a 70% increase in the total heat transfer coefficient was obtained.

Study on the calculation of unsteady radiant heat transfer load with stratified air distribution based on harmonic reaction method

The stratified air conditioning systems are widely used in large space buildings. Stratified air conditioning load (SACL) is the basis for determining the cooling capacity of air conditioning system, and it is also the key to assess its energy savings of stratified cooling. Calculation of the radiant heat transfer load (RHTL) is the difficult point to determine the SACL. In recent years, there have been many researches on the calculation of SACL. Most of them are steady-state calculation processes, and there are few studies on dynamic calculation processes. Therefore, the RHTL is taken as the research object, a novel calculation method is proposed according to the harmonic reaction method (HRM) and verified by the experiments. Experimental radiant heat transfer load can be received through convection and radiation separating method. The experimental and theoretical values of RHTL were compared and it was found that the theoretical values were in good agreement with experimental values. Therefore, the proposed method can be used to predict the unsteady RHTL accurately. Based on the verified calculation method, the effects of outdoor climatic conditions, building types and stratified heights on RHTL of an actual large space building are analyzed, which will contribute to the design and optimization of stratified air conditioning system for large space buildings.

Heat transfer performance of a deep ground heat exchanger for building heating in long-term service

Based on an experimental project of a deeply buried coaxial double-pipe with a burial depth of 2539 m in Xi’an, Shaanxi Province, China, this study gave due consideration to the symmetry of a buried pipe structure, built a full-scale axisymmetric model for heat transfer inside and outside the coupled pipe, and verified the reliability of the model. The vertical initial temperature distribution, lithology, and thermophysical parameters of the surrounding ground of the buried pipe in the model came from the optical fiber temperature measurement of the vertical borehole wall, the interpretation of drilling data, and the experimental detection of drilling cores, respectively. This study discusses the variations in ground temperature and thermal effective radius with time in the 50-year service process of the buried pipe based upon the model, explored the heat transfer performance of the buried pipe under different constant heat transfer loads and inlet water temperatures, and analyzed the attenuation rules of its water temperature or heat transfer capacity in long-term service.