Cooling Heat Transfer Coefficient Research Articles

Regenerative cooling in hybrid rocket engines based on Self-Pressurized liquid nitrous oxide

An experimental investigation of the reliability and feasibility of a regenerative cooling system in hybrid rocket engines based on saturated nitrous oxide is presented. The novelty of the work consists in the use of a cooling system based on saturated liquid nitrous oxide, wrapping the external surface of a COTS graphite nozzle. The detrimental heat fluxes developed at the throat are handled with a slight increase in assembly complexity. Ten firing tests are performed with an incremental logic of the mass flow rate from 9 to 45 g/s, which is controlled by cavitating the fluid through orifices with different diameters upstream of the cooling system. The tests have been performed at different ambient temperatures in different seasons. The multiphase state of the coolant is evaluated by measuring pressure and temperature upstream and downstream of the cavitation orifice and cooling channels. The test with the smallest mass flow rate developed the highest vapour fraction downstream of the orifice and cooling channels at 0.458 and 0.481, respectively. The cooling performance is indirectly evaluated by measuring the nozzle temperature at 3, 5, and 8.5 mm from the throat internal surface. The results show that steady temperatures are achieved inside the nozzle, with throat temperatures included between 700 and 1200 K in a chamber pressure range between 5 and 30 bar. Nozzle erosion never occurs in the entire experimental campaign, and the nozzles are totally reusable for more ignitions. The coolant heat transfer coefficient increased from 3912 to 21181 W/(m2∙K) by increasing the flow rate per channel from around 3 to 15 g/s. Compared to cryogenic oxygen, liquid nitrous oxide displays higher cooling performance. Finally, the cavitation orifice is moved downstream of the cooling system, showing worse performance of the overall propulsion system.

Thermal Modeling With Surrogate Model-Based Optimization of Direct Oil Cooling Heat Transfer Coefficient for HEV Motor

Thermal Modeling With Surrogate Model-Based Optimization of Direct Oil Cooling Heat Transfer Coefficient for HEV Motor

Statement of Retraction: The effect of laminar cooling heat transfer coefficient on the temperature field of steel plate

Statement of Retraction: The effect of laminar cooling heat transfer coefficient on the temperature field of steel plate

Effect of the acoustic manipulation on single phase immersion cooling performance of discretely heated vertical plate

In the cooling of high heat capacity systems, immersion cooling systems are increasing importance due to the insufficient heat dissipation rates of conventional cooling systems. In this study, the effects of ultrasonic sound waves on cooling performance in single-phase immersion cooling systems were investigated. Experimental study was carried out with ultrasonic sound waves for 9.6 kHz, 14.4 kHz, 19.2 kHz, 24 kHz and silent conditions. In addition, the effects of discrete heat sources on thermal performance were investigated by changing the surface (embedded, 2 mm protruding, 4 mm protruding) and location configurations. According to the results obtained, the highest heat transfer coefficient was calculated as 1703.36 W/m2 °C for the embedded heat source closest to the tank bottom for at 24 kHz frequency. The lowest heat transfer coefficient was calculated as 373.28 W/m2 °C for the maximum protrusion amont heat source closest to the tank upper and when ultrasound manipulation was not applied. In addition, the immersion cooling heat transfer coefficient was increased by 107.49% with ultrasonic sound wave. The heat transfer coefficient increased with increasing ultrasound frequency and decreased with increasing protrusion thickness.

Beyond traditional boundaries: Exergo-economic and thermo-mechanical optimization of segmented thermoelectric generators with varied cross-sections

In this work, we present a comprehensive optimization study of a concentrating solar segmented thermoelectric generator (CSSTEG) with variable area leg geometry. We consider not just geometrical parameters but also concentrated solar heat flux and convective cooling film coefficients, pushing the boundaries of traditional studies. Performance is evaluated on multiple fronts: power output, exergy efficiency, entropy generation, CO2 savings, dollar per watt, and thermal stress. Uniquely, we establish that an optimal skutterudite content of 6.17% provides maximum power output (47.47 W) and exergy efficiency (10.95%) at a solar heat flux of 50 kWm−2. This optimized configuration also delivers maximal annual CO2 savings (22.5 kgyr−1). Additionally, we pinpoint that a semiconductor height of 0.2 mm minimizes the dollar per watt (0.0048 $W−1) at 100 kWm−2 solar irradiances and reduces thermal stress (0.25 GPa) at a cooling heat transfer coefficient of 4 kWm−2 K−1. Our research is pioneering in its holistic approach to CSSTEG optimization, providing valuable insights for creating efficient, sustainable energy systems.

Experimental Study on the Thermal Performance of Flat Loop Heat Pipe Applied in Data Center Cooling

The cooling system is the auxiliary equipment that consumes the most energy in a data center, accounting for about 30 to 50% of the total energy consumption. In order to effectively reduce the energy consumption of a data center, it is very important to improve the heat exchange efficiency at the chip level. Compared with air cooling, single-phase cold plate liquid cooling, and immersion liquid cooling, the flat loop heat pipe (FLHP) is considered to be a better chip-level cooling solution for data centers. It has extremely high heat transfer efficiency and heat flux variability, and it can avoid the operation risk caused by liquid entering the server. In this paper, a FLHP with an evaporator designed with a “Tesla valve” flow channel configuration is developed. Experiments on the FLHP are carried out, focusing on the installation angles and cooling condition factors. The results show that an inclination angle of 20° is the critical point of the influence of gravity on the performance of the FLHP; to ensure good operation of the FLHP, the installation angle should be greater than 20°. The equivalent heat transfer coefficients of the FLHP condenser under different cooling conditions are calculated. It is found that water cooling can provide higher cooling heat transfer coefficients with lower energy consumption and operating noise. Additionally, the heat transfer limit, operating temperature uniformity, and start-up stability of the FLHP are significantly improved under water cooling conditions. The maximum heat load of the FLHP is up to 230 W, and the temperature difference of the evaporator surface can be controlled within 0.5 °C, under 20 °C water cooling. Finally, using the FLHP for thermal management of the chip, its heat transfer efficiency is 166 and 41% higher than that of air cooling and water cooling, respectively.

The Effect of Microencapsulated PCM Slurry Coolant on the Efficiency of a Shell and Tube Heat Exchanger

This paper describes the results of experimental studies on heat transfer in a shell and tube heat exchanger during the phase changes of the HFE 7000 refrigerant. The studies were performed using a mixture of water and a microencapsulated phase change material as a coolant. HFE 7000 refrigerant condenses on the external surface of the copper tube, while a mixture of water and phase change materials flows through the channels as coolant. Currently, there is a lack of research describing cooling using phase change materials in heat exchangers. There are a number of publications describing the heat exchange in heat exchangers during phase changes under air or water cooling. Therefore, the research hypothesis was adopted that the use of mixed water and microencapsulated material as a heat transfer fluid would increase the heat capacity and contribute to the enhancement of the heat exchange in the heat exchanger. This will enable an increase in the total heat transfer coefficient and the heat efficiency of the exchanger. Experimental studies describe the process of heat transfer intensification in the above conditions by using the phase transformation of the cooling medium melting. The test results were compared with the results of an experiment in which pure water was used as the reference liquid. The research was carried out in a wide range of refrigerant and coolant parameters: ṁr = 0.0014–0.0015 kg·s−1, ṁc = 0.014–0.016 kg·s−1, refrigerant saturation temperature Ts = 55–60 °C, coolant temperature at the inlet Tcin = 20–32 °C, and heat flux density q = 7000–7450 W·m−1. The obtained results confirmed the research hypothesis. There was an average of a 13% increase in the coolant heat transfer coefficient, and the peak increase in αc was over 24%. The average value of the heat transfer coefficient k increased by 5%, and the highest increases in the value of k were noted at Tin = 27 °C and amounted to 9% in relation to the reference liquid.

Determination of Film Cooling Effectiveness and Heat Transfer Coefficient Simultaneously on a Flat Plate

In this paper, flat plate film cooling with two rows of compound angle cylindrical film cooling holes was investigated. A data processing method was evaluated which could determine the film cooling effectiveness and heat transfer coefficient simultaneously from the transient wall temperature data. The method was based on solving an inverse problem of the one-dimensional transient heat conduction equation. To evaluate the performance of the method, wall temperature data were obtained using the known film cooling effectiveness and heat transfer coefficient data as the convection boundary condition. Then, the method was applied to calculate the film cooling effectiveness and heat transfer coefficient based on the wall temperature data. Different blowing ratios, heat transfer coefficients, mainstream temperatures, and material thermal conductivities were investigated. In general, the data and calculation were in good agreement. It was found that the error decreased when the heat transfer coefficient increased and the material thermal conductivity decreased. The percentage error of the span-wise averaged film cooling effectiveness was mainly between 0% and 10%, and the percentage error of the span-wise averaged heat transfer coefficient was mainly between 0% and 4%.

Heat transfer deterioration in vertical sCO2 cooling in 3 mm tube

In this publication, the cooling heat transfer coefficient (htc) is investigated in a 3 mm diameter tube with vertical flow orientation. Commonly used calculation methods of the heat transfer coefficient are presented. Although developed for heating of sCO2, the mixed convection criterion is used to evaluate the heat transfer deterioration. The effects of the CO2 mass flux of 141−354kg/m²s and bulk fluid temperatures of 20−50°C with a constant pressure of 80bar on the heat transfer were examined. The upwards flow shows a steady decrease in the htc with the reduction of the mass flux. However, the downwards flow shows significant effects of buoyancy. At low mass flux the distinct peak in the htc at the pseudocritical temperature (Tpc) disappears. The deteriorated heat transfer in the downwards flow showed significant lower wall temperatures compared to the upwards flow. The separate evaluation of the liquid-like and gas-like region indicates that the deterioration may vary based on the fluid properties. The results were regressed within +-15% in the forced convection region and +-40% in the mixed convection region. The comparison with the literature data of vertical cooling in 6 mm showed different behaviour which indicates an influence of the tube diameter.

Structural optimization of thermoelectric modules in a concentration photovoltaic–thermoelectric hybrid system

Concentration photovoltaic (CPV) cells can only partially convert solar energy into electricity. The remaining energy is converted into thermal energy. This not only causes the temperature of the photovoltaic cell to rise, but also reduces the generation efficiency of the cell. The excess CPV heat can be recovered using a thermoelectric generator (TEG). The design of the structure of the TEG is important for a CPV-TEG hybrid system because it affects the heat dissipation of the CPV and thus its efficiency. In this study, a mathematical model of a hybrid system was established. The focus was to examine the effect of the structural parameters of the TEG on the system efficiency. The results showed that an optimal structural parameter (the ratio of the cross-sectional ratio to the height) with the value of 0.36 mm−1 existed for the TEG, enabling the system efficiency to reach a maximum of 41.73% under simulated conditions. In addition, the relationship between the optimal structural parameter, CPV temperature coefficient, concentration ratio, and cooling heat transfer coefficient was analyzed. The results can provide guidance for the efficient design of a hybrid system.

Numerical simulation of flow and cooling heat transfer of supercritical pressure refrigerants in chevron-type plate heat exchanger

In industrial fields, heat sources exceeding 130°C are necessitated; hence, the development of industrial high-temperature heat pump systems is anticipated. For the heat release process in such heat pump systems, the use of a plate heat exchanger (PHE), in which high-pressure working refrigerant flows, is examined. In this study, to predict the cooling heat transfer coefficient and pressure drop of supercritical pressure refrigerants flowing in a chevron-type PHE, a computational fluid dynamics model is developed. HFC134a and HFO1234ze(E) are selected as the working refrigerants. Calculations are performed by changing the inlet fluid enthalpy under three reduced pressure conditions from 1.01 to 1.21 and two mass flow rate conditions. The heat transfer coefficient and pressure drop obtained from the simulation reproduced the experimental results well, including the effects of pressure and mass velocity. Therefore, the present model can be applied to existing and new refrigerants if their physical properties are available. Furthermore, it can be used to optimize the plate shape of chevron-type PHEs. Finally, based on the simulation results, the characteristics of the flow behavior and heat transfer of refrigerants in the PHE are discussed.

RETRACTED ARTICLE: The effect of laminar cooling heat transfer coefficient on the temperature field of steel plate

We, the Editors and Publisher of the journal Ironmaking & Steelmaking, have retracted the following article: Xiao-li Tian, Jie Zhang, Hong-bo Li & Jie Guo (2021) The effect of laminar cooling heat transfer coefficient on the temperature field of steel plate, Ironmaking & Steelmaking, 48:9, 1076-1082, DOI: 10.1080/03019233.2021.1915646 Since publication, concerns about the integrity of the data in the article have been raised. As we cannot verify the validity of the published work, we are therefore retracting the article. Xiao-li Tian, Jie Zhang and Hong-Bo Li have informed us that they did not participate in the research work and were not aware of this submission. All authors listed in this publication have been informed and agree with the retraction of this article. We have been informed in our decision-making by our editorial policies and the COPE guidelines. The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as ‘Retracted’.

A finite element approach to investigate the thermomechanical behavior of solid and annular type nuclear fuel rods

Reliable prediction of nuclear fuel rod behavior is of prime concern for assessing proper design parameters as well as operating conditions and sustainability aspects in a nuclear reactor. In this study, a numerical analysis has been conducted to investigate the thermomechanical behavior of solid and annular fuel rods individually, considering a pressurized water reactor (PWR). The transient heat conduction equation has been employed for the heat-generating uranium dioxide pellet along with the surrounding zircaloy cladding and solved numerically using the finite element method. Loss of coolant conditions has been simulated by reducing the coolant heat transfer coefficient and compared with the normal operating conditions. In all the cases considered, the annular fuel has shown superior properties in terms of minimized fuel surface heat flux, lower but relatively uniform radial temperature, and thermal strain distribution.

Estimation of Oil Spray Cooling Heat Transfer Coefficients on Hairpin Windings With Reduced-Parameter Models

Hairpin windings and spray cooling are becoming an increasingly popular combination in the field of high-performance electrical machine design. Machines adopting hairpin windings can achieve higher torque and power densities while enabling them to be manufactured automatically on a large scale to meet the rapid market growth of electric transport. Spray cooling is an effective way for high heat flux removal, which has shown great potentials in electrical machine applications. Although spray cooling has been studied for decades in different engineering applications, the focus had been on investigating its performance on regular surfaces using low-viscosity liquids, such as water. In addition, many existing models for spray cooling heat transfer were built on spray parameters that are difficult to obtain without specialist equipment. Thus, most results from previous studies are difficult to be interpreted and directly applied to electrical machine applications. Practical and economical approaches for estimating the heat transfer coefficients (HTCs) of spray cooling on hairpin windings are needed. This article proposes and validates an experimental approach based on reduced-parameter models that can be applied to predict the HTC of spray cooling setups on hairpin windings.

Thermal-hydraulic analysis of Al2O3 nanofluid as a coolant in Canadian supercritical water reactor by porous media approach

In this study, thermal-hydraulic analysis of Canadian Supercritical Water Reactor (Canadian SCWR) with nanofluid coolant has been done by porous media approach. In the applied analysis the derived conservation equations of mass, momentum and energy for coolant and conduction heat transfer equation for fuel and clad were discretised by finite volume method and solved numerically using C# program. Nanofluid coolant with various concentration of Al2O3 (Alumina) nanoparticle (up to 40% mass fraction) was selected for this study. Since in Canadian SCWR coolant and moderator are separated, higher mass fraction of nanofluid can be applied in this concept. The achieved results show that by increasing Al2O3 mass fraction, coolant heat transfer coefficient and average coolant temperature grow up in the middle of the core and pressure drop will be raised. Average clad and fuel temperature in the core was calculated. The results show that by using Alumina nanofluid with 40% nanoparticle mass fraction, maximum clad wall and fuel temperatures decrease about 20 °C and 30 °C respectively.

Heat transport in nanofluid coolant car radiator with louvered fins

Heat transport capacity of conventional coolants for car radiators can be enhanced by adding nano size metal oxide particles. This paper presents a three-dimensional thermo-fluid analysis of real size car radiator with louvered fins and nanofluid based coolants. The base coolant consisting of 60% Ethylene glycol and 40% Water is dispersed with Aluminum oxide, Copper oxide and Zinc oxide nanoparticles. Effects of nanoparticle concentration and flow velocity on heat transfer have been reported. Dependence of thermophysical properties on nanoparticle concentration has also been evaluated. The heat transfer coefficient for coolant was increased by 42.5%, 47.4% and 51.1% on addition of 2% of Aluminum oxide, Zinc oxide and Copper oxide respectively. A Significant linear increase in heat transfer coefficient and Nusselt number was observed with rise in flow Reynolds number. Copper oxide nanoparticles based coolants are found to be more effective. A set of simplified correlations for the Nusselt number is presented.

Effect of substrate layers on thermo-electric performance under transient heat loads

Due to thermal resistance, the temperature difference between the hot and cold sides of thermoelectric elements and power generation in thermoelectric generators are affected by the module’s substrate. Moreover, there are various types of applications where thermoelectric generators operate under transient heat load, and other material properties of the substrates, such as heat capacity, have impact on temperature profile of the thermoelectric generator. This paper, therefore, aims to evaluate transient behavior of thermoelectric generator, affected by its geometry, under periodic and oscillated thermal loads in order to provide a link between the power output and power management of thermoelectric generators. A three dimensional COMSOL Multiphysics model of the thermoelectric generator is developed to evaluate performance of the module under transient heat loads, different substrate materials and thicknesses, and various coolant heat transfer coefficients. Results of the simulations, which are in a good agreement with experimental data, show that the rectangular heat load provides highest power generation between the investigated heat loads, and the thermoelectric generator with Kapton substrates produces maximum voltage oscillation amongst the studied substrate layers. The numerical results of this study conclude that, the material properties and thickness of the substrate have significant effect on the thermo-electric behavior under transient heat loads.

Evaluation of the Effect of Cooling Conditions and Heat Transfer Coefficients on Solidification of Al-Cu Binary Alloy in Static Casting Process

Source-based method for modelling solidification problems have been modified and presented in the current work. It coupled the effect of thermal radiation to macro-transport codes and was solved using finite volume method. The problem was formulated based on the classic continuum energy conservation equation for transient conduction controlled solidification system. Radiation heat transfer and latent heat evolution were added as source terms and solved with appropriate numerical treatments to obtain a system of linearized source terms. This circumvented the need for the application of any analytical solution to the intricate heat transfer regimes included in the model. The effect of cooling was carried out under various cooling conditions imposed on different surfaces of the mould for the solidifying metal. The resultant influence of cooling on the solid fraction evolution during static casting was then evaluated. The simulated cooling curves show that thermal radiation have no influence on the rate of heat extraction and the results show that the predicted cooling curves and solid fraction updates are similar to the results of previous models. The predicted curves at the top section of the open mould however show a little deviation due to effect of surface tension gradient forces. It was further revealed that heat transfer coefficients has more effect cooling curves and temperature contours at the lateral mould surfaces than the interior of the casting which is in agreement with theory of Newtonian cooling.

Film cooling performance measurement over a flat plate for a single row of holes embedded in an inclined trench

Film cooling heat transfer coefficient and effectiveness measurements downstream of a single row of holes embedded in an inclined trench injecting secondary fluid into the mainstream over a flat surface are reported here. The well-studied trench geometry is one where the walls of the trench are perpendicular and film injection holes are at an angle to the mainstream flow direction. In the current investigation, the trench is inclined at an angle to the mainstream and the injection holes are normal to the flow direction. Coolant injection in the form of a uniform stream at an angle to the mainstream is likely with this configuration. The trench inclination is kept constant at 35° and three hole pitch to diameter ratios equal to 3, 4.5 and 6 are studied for the blowing ratio varying between 0.3 and 2.5. The injection hole length to diameter ratios equal to 1.8 and 5.5 were studied and the influence on the net heat flux reduction ratio was found to be very small. The local effectiveness and the heat transfer coefficient values are presented and the variations in the cross-stream direction are observed to be very small. The effectiveness values for the current angular trench are higher whereas the heat transfer coefficients are smaller compared to the normal trench at higher blowing ratios. This results in increased Net Heat Flux Reduction ratio (NHFR) values for the current configuration which are observed to remain high at large downstream locations also.

Lithium divertor of KTM tokamak

At present time the project of Kazakh material science tokamak KTM is under implementation. In addition to solving problems in the study of materials for fusion technologies on tokamak is working out innovative design elements of the divertor. The design of the lithium divertor module based on lithium capillary-porous systems has been developed and successfully tested under real tokamak conditions. In this design, the solution to the problem of removal of heat flows of high density was implemented through the use of a liquid metal coolant based on the eutectic alloy Na-K. Requirements to improve the safety and compatibility of the design of the divertor with other in-vessel elements of the tokamak, cooled by water, and limiting the temperature of the lithium receiving surface at <600°C at heat flows of 10-20 MW/m2 led to the creation of a new design solution for the experimental module of the divertor and the use of a new coolant – gas dispersed water flow (gas-water spray). The article describes and justifies the design solutions of the new version of the module, the parameters of the coolant and the cooling system scheme. Experimental results on determination of heat transfer coefficient for coolant based on gas-water spray are considered