Effect Of Coolant Flow Rate Research Articles

Thermal cooling system with Ag/Fe3O4 nanofluids mixture as coolant for electronic devices cooling

The thermal dissipation resistance has encountered a problem in the thermal analysis of the electronic components. Due to the limitation of the coolant heat removal capacity, the nanofluid and flow feature of the coolant flowing through the thermal cooling system have proposed. The mixture of Ag and Fe3O4 nanoparticles and flow direction guide vane of coolant for cooling electronic devices have been investigated. The effects of coolant flow rate, coolant type, and heat sink configuration on the thermal dissipation efficiency are considered. Ag and Fe3O4 nanoparticles suspending in the base fluid test and compared with the de-ionized water. The obtained results found that the proposed water blocks have a significant effect on the flow feature of coolant flowing through the thermal cooling system, which results in 11.94% increase in thermal dissipation efficiency. Besides, the thermal dissipation efficiency from Ag/Fe3O4 nanofluid mixture as the coolant is higher than Ag nanofluids and higher than that de-ionized water as the coolant, respectively.

Research on Control Strategy for a Battery Thermal Management System for Electric Vehicles Based on Secondary Loop Cooling

A secondary loop cooling battery thermal management system is designed, and then, a phased control strategy for adjusting the compressor speed according to the battery temperature interval is proposed. On this basis, the compressor speed as the decision variable, and the energy consumption of the compressor and the aging losses of the battery are as the optimization goals, which constitute a multi-objective optimization model, and a genetic algorithm is adopted to solve it. Under different weight coefficients, the Pareto Frontier of the energy consumption of the compressor and the aging losses of the battery are established. The simulation analysis is conducted on high speed dynamic conditions at an ambient temperature of 30 °C. The effects of coolant flow rate and compressor speed on battery pack temperature rise and temperature uniformity are analyzed. The simulation results show that the energy consumption of the phased control strategy is reduced by 10.7% compared with the traditional constant compressor speed control strategy under the same conditions. Under different weight coefficients, different simulation results and control strategies can be obtained, and results show that the maximum temperature and temperature uniformity can meet the requirements. There is a contradiction between the energy consumption of compressor and the aging losses of battery, but both them are highly sensitive. According to the Pareto Frontier curve, when the weight coefficient is 0.17, a balanced control strategy can be obtained, which can reduce the battery aging losses of 61.8% by only sacrificing 9.22% of the vehicle driving mileage.

Hydrothermal performance of different alumina hybrid nanofluid types in plate heat exchanger

To enhance the energetic and exergetic performances of the counter-flow plate heat exchanger with corrugations, several experiments were conducted using different Al2O3 hybrid nanofluids as a coolant. The combinations studied were Al2O3–SiC, Al2O3–AlN, Al2O3–MgO, Al2O3–CuO and Al2O3–MWCNT in 4:1 nanoparticle volume ratio and 100% Al2O3 with 0.1 vol% concentration suspended in DI water. Parameters which were varied are the coolant flow rate ranging from 2.0 to 4.0 lpm and coolant inlet temperature from 10 to 25 °C. Effect of coolant flow rates and inlet temperatures on different parameters like heat transfer coefficient ratio, heat transfer coefficient to pressure drop ratio, pump work, performance index and irreversibility has been investigated. A maximum enhancement of around 31.2% has been observed in the heat transfer coefficient for Al2O3–MWCNT (4:1) hybrid nanofluid with the negligible enhancement of 0.08% in the pump work and 12.46% enhancement in the performance index. The maximum enhancement in the irreversibility is around 1.6% for Al2O3–CuO (4:1) hybrid nanofluid. Among the studied nanoparticle combinations, Al2O3–MWCNT (4:1) gives better performance. This study suggests that Al2O3–MWCNT hybrid nanofluid can be a good alternative to enhance thermal performance.

Influence of coolant flow rates on the heat exchanger parameter at variable operation modes

Introduction. Being used in various industries, heat exchangers most often work under conditions of variable coolant flows and temperatures. At the same time, the existing theories of calculating the heat exchanger operation modes are based on the use of constant unitless parameters at any operation mode. Taking into account the effect of coolant rates on the heat transfer coefficient of the heat exchangers, the given relations are bound to specific types of heat exchangers and can only be used at constant coolant temperatures. The purpose of this study is to obtain expressions for determining the effect of coolant flow rates on the variable heat exchanger parameter.
 Materials and methods. The main variable operation modes for water-to-water heat exchangers used in heat supply systems are determined. Using simulation in the PTC Mathcad software, dependencies describing the change in the heat exchanger parameter for all the considered variable operation modes are defined. This made it possible to obtain a general formula for the change in the heat exchanger parameter for varying coolant flow rates. Coefficients in this formula take into consideration the effect of coolant temperatures, which cannot be known when calculating variable conditions, especially when the interconnected heat exchangers are operating.
 Results. To test applicability of the existing relations describing the change in the heat exchanger parameter and of obtained formula, a large number of heat exchangers is calculated at variable operation modes. Comparison with the simulation results shows that the correlations of heat exchanger theories work well at the mode with constant coolant temperatures only, while their use at other operation modes can lead to large calculation errors.
 Conclusions. The obtained formula allows finding the effect of coolant flow rates on the variable heat exchanger parameter. The formula can be used to predict the operation modes of large systems including a large number of various-type heat exchangers.

Investigations on the Sealing Effectiveness and Unsteady Flow Field of 1.5-Stage Turbine Rim Seal

This paper presents a numerical investigation on the sealing effectiveness and unsteady flow field of a 1.5-stage turbine with the front and aft wheel-space cavities. The sealing effectiveness and flow structure are studied by solving three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations and shear stress transfer (SST) turbulence model. The numerical pressure and swirl ratio distributions in cavities with two computational models are compared with experimental data to determine the position of stationary/rotating domain interface. The time-averaged mainstream pressure distribution and sealing effectiveness of the rim seal at the front and aft cavities are studied by the steady and unsteady calculations. The unsteady results agree well with experimental data by comparison of the steady calculations. The effects of coolant flow rates on the sealing effectiveness and the flow field of the rim seal at the front and aft cavities are investigated. The obtained results show that the sealing effectiveness of the rim seal at the aft cavity is much larger than that of the rim seal at the front cavity at the same coolant flow rate. The less mainstream pressure fluctuation near the aft rim seal clearance and the clockwise vortex due to the pumping effect in the aft rim seal leads to this result. The mainstream pressure fluctuation downstream of the blade and the sealing effectiveness of the rim seal at the aft cavity under five operating conditions are computed. It shows that the square root of the mainstream pressure fluctuation amplitude downstream of the blade is proportional to the mainstream flow rate. The increase of the mainstream flow results in gradual decrease of the sealing effectiveness of the rim seal at the aft cavity.

A comparison of temperature distribution in PEMFC with single-phase water cooling and two-phase HFE-7100 cooling methods by numerical study

Thermal management has been considered as one of the critical issues in proton exchange membrane fuel cell (PEMFC). Key roles of thermal management system are maintaining optimal operating temperature of PEMFC and diminishing temperature difference over a single fuel cell and stack. Severe temperature difference causes degradation of performance and deterioration of durability, so understanding temperature distribution inside a single fuel cell and stack is crucial. In this paper, two-phase HFE-7100 cooling method is suggested for PEMFC thermal management and investigated regarding temperature change inside a fuel cell. Also, the results are compared to single-phase water cooling method. Numerical study of temperature distribution inside a single PEMFC is conducted under various conditions for the two different cooling methods. Fuel cell model considering mass transfer, electrochemical reaction and heat transfer is developed.The result indicates that two-phase HFE-7100 cooling method has an advantage in temperature maintenance and temperature uniformity than single-phase water cooling method, especially in high current density region. It is also revealed that the cell temperature is less dependent on system load change with two-phase cooling method. It indicates that the fuel cell system with two-phase cooling method has high thermal stability. In addition, the effect of coolant flow rate and coolant inlet pressure in two-phase HFE-7100 cooling method are discussed. As a result, two-phase cooling method showed reliable cooling performance even with low coolant flow rate and the system temperature increased as coolant pressure rose.

Numerical investigation of hydrogen absorption in a stackable metal hydride reactor utilizing compartmentalization

In this paper, a three-dimensional model for hydrogen absorption in a metal alloy has been developed, validated against the experimental data in the literature, and then applied to a novel design for a hydrogen storage unit. The proposed design is similar to the fuel cell stack, but here the Membrane Electrode Assembly (MEA) has been replaced by a metal hydride (MH) reactor placed between the flow-field plates. These are stacked together to achieve the required amount of hydrogen storage. The flow-field plates have channels engraved on one side for hydrogen supply and on the other, for coolant/heating medium. It is known that the effectiveness of a hydrogen storage unit is directly related to its heat transfer area, and therefore, the choice of its geometry is very important. The larger the size, the more the resistance to heat transfer. Although, the internal tubular heat exchangers have proven to be effective in heat transfer, they pose severe challenges such as cooling/heating medium leakage due to tube erosion, stresses generated, etc. and they displace the active metal hydride from the tank. The present stacked MH reactor configuration helps to overcome these challenges by stacking small MH reactors together and there is no chance of the cooling/heating medium leaking into the metal hydride. Numerical simulations were performed to investigate the effect of coolant flow rate and percentage of flow-field plate rib area exposed to the MH reactor on temperature evolution and the amount of hydrogen stored. Further, a detailed study was carried out to understand the effect of compartmentalization of the MH reactor on temperature distribution. The results revealed that compartmentalization substantially helps to uniformly distribute the temperature in the metal bed, which is very important to maintain uniform utilization of the metal powder. Consequently, the uniform metal powder density for repeated absorption-desorption cycles without significant loss of its hydrogen storage capabilities.

Effects of coolant flow rate under ultrasonic vibrations transmitted to surface roughness in grinding SKD11 steel

The ultrasonic assisted machining method is now widely applied and supported in machining processes such as drilling, turning, milling and especially grinding. This paper presents the effect of coolant flow rate q (3.5, 4.5 and 5 l.min-1 respectively) under ultrasonic vibrations transmitted in grinding SKD11 steel. The surface roughness Ra was used to evaluate the impact. The results show that, when no ultrasonic vibrations were transmitted, the surface roughness values are approximately equivalent when changing the coolant flow rate. However, when transmitting the ultrasonic oscillator to the coolant, the coolant flow rate increases, the effect of ultrasound is clear. The results show that the surface roughness of the workpiece decreases as the coolant flow increases. In other words, the coolant was transmitted by ultrasonic vibrations that clean the grinding wheel surface, removing the grinding chips that stick to the space between the abrasives grains, ensuring the grindability of grinding wheels.

Investigation on the thermal performance of a battery thermal management system using heat pipe under different ambient temperatures

The thermal performance of a battery thermal management system (BTMS) can be enhanced by cooling strategies, which are seldom taken into account in the study of heat pipe-based BTMS (HP-BTMS). The effects of coolant flow rate, ambient temperature, coolant temperature and start-up time on the thermal performance of HP-BTMS are crucial for the development of cooling strategies and are experimentally investigated in the present study. Results show that the thermal performance of HP-BTMS increases slightly with the decrease of ambient temperature as it is under 25 °C. When the ambient temperature is under 35 °C, the thermal performance of HP-BTMS can be kept nearly unchanged by reducing coolant temperature. The enhancement is little when ambient temperature is under 25 °C. Additionally, a drastic rise in the non-uniformity of battery temperature is observed at the moment of HP-BTMS initiation if HP-BTMS starts operating after battery temperature exceeds equilibrium value. Finally, intermittent cooling and constant cooling can achieve similar battery cooling performance, which indicates that the power consumption can be reduced by decreasing running time of HP-BTMS.

Optimization and Kinetics Evaluation of Bachmann Process for RDX Synthesis

Abstract 1,3,5-Trinitro-1,3,5-triazacyclohexane (RDX) is one of the high explosives extensively used for various military and civil applications. RDX is predominantly used in warheads, the most advanced solid propellants for guns and rockets and in plastic bonded explosives for improving performance characteristics. Thus the increasing demand of RDX necessitates study on reaction engineering and reactor stability in view of enhancement of safety as well as productivity. In present study, Bachmann process has been studied in detail for understanding role of reagents, time and temperature on reaction yield. Reaction rates of RDX and side products have been evaluated at various temperatures using continuous flow technique. Second order reaction was found sensitive towards temperature and concentrations of nitric acid and acetic anhydride. Higher magnitude of activation energy was evaluated for side products (25.2 kcal/mol) than RDX (18.71 kcal/mol). Optimum temperature of reaction has been obtained on profiling its progression at various reaction rates and temperature. Further, reactor stability analysis has been carried out to identify the safe operation conditions for this highly exothermic reaction. Effect of coolant flow rate and temperature as well as feed temperature has been analyzed on heat removal rate to obtain the safe regime of reaction. The information related to maximization of RDX formation and safe design of continuous process has been presented in manuscript.

Experimental Investigation of Heat Transfer Characteristics of Automobile Radiator using TiO2-Nanofluid Coolant

The use of nanoparticle dispersed coolants in automobile radiators improves the heat transfer rate and facilitates overall reduction in size of the radiators. In this study, the heat transfer characteristics of water/propylene glycol based TiO2 nanofluid was analyzed experimentally and compared with pure water and water/propylene glycol mixture. Two different concentrations of nanofluids were prepared by adding 0.1 vol. % and 0.3 vol. % of TiO2 nanoparticles into water/propylene glycol mixture (70:30). The experiments were conducted by varying the coolant flow rate between 3 to 6 lit/min for various coolant temperatures (50°C, 60°C, 70°C, and 80°C) to understand the effect of coolant flow rate on heat transfer. The results showed that the Nusselt number of the nanofluid coolant increases with increase in flow rate. At low inlet coolant temperature the water/propylene glycol mixture showed higher heat transfer rate when compared with nanofluid coolant. However at higher operating temperature and higher coolant flow rate, 0.3 vol. % of TiO2 nanofluid enhances the heat transfer rate by 8.5% when compared to base fluids.

Effect of coolant flow rate on the dynamics of delayed recycle continuous stirred tank reactor

Abstract Numerical bifurcation analysis of delayed recycle stream in a continuous stirred tank reactor was studied using DDE-BIFTOOL. A first-order irreversible exothermic reaction s 1 → k 2 , 1 s 2 was considered for analyzing effect of delay on the stability of the delayed recycle system. The non-isothermal CSTR was operated at both infinite and finite coolant inlet flowrates. A constant delay was considered in the recycle stream of CSTR for concentration of reactant, and temperature. DDE-BIFTOOL solver was used for finding dependency of delays on the bifurcation parameters, and its stability characteristics. The bifurcation parameters considered were: (i) fresh feed flowrate, (ii) coolant temperature, and (iii) coolant inlet flowrate. In the absence of delay, the system exhibits the region of dynamic instability for both infinite and finite coolant inlet flowrates. For infinite coolant flowrate, the region of dynamic instability on the reactor temperature was modified as a result of delay by varying either fresh feed flowrate or coolant temperature. The steady-state multiplicity was observed on the coolant temperature by varying fresh feed flowrate at finite coolant inlet flowrate. In the absence of delay, the fold and Hopf bifurcations were observed on the multiple steady-states of coolant temperature. The concentration and temperature delays do not alter substantially the dynamic characteristics of coolant temperature at Tc,in = 298 K. However, delays can alter the region of dynamic instability for coolant temperature when coolant inlet temperature is higher than 298 K. These are the main result of present work.

Effect of Coolant Flow Rate on the Performance of Gas-Turbine Units

Results are presented from a study of the effect of the flow rate of cooling air on the efficiency of gas-turbine units with open air cooling over wide ranges of temperature variation after the combustion chamber, degrees of pressure increase in the compressor, and efficiencies of internal heat-transfer in the blade system. The feasibility of increasing the efficiency of power generating gas-turbine units to 40 – 41% is demonstrated.

Simulation of convective heat removal in a stratified tank of the integrated collector storage solar water heater with builtin heat exchanger

Free convective heat removal in a stratified inclined storage tank with builtin heat exchanger is numerically simulated. The effects of coolant flow rate and tank installation angle on heat transfer are investigated. The possibility of the integration of several of tanks into the battery is analyzed. If there are not many tanks, their serial connection in the battery is more preferable than parallel because of the significant output gain.

Effects of coolant flow rate, groundwater table fluctuations and infiltration of rainwater on the efficiency of heat recovery from near surface soil layers

This paper aims to investigate experimentally the effects of circulating coolant flow rate, groundwater table fluctuations, infiltration of rainwater, on the amount of thermal energy that can be recovered from the near surface soil layers. A comprehensive experimental investigation was carried out on a fully equipped tank filled with sand. A heat collector panel was embedded horizontally at the mid-height of the tank. Measurements of the temperature at various points on the heat collector panel, adjacent soil, inlet and outlet were continuously monitored and recorded. After reaching a steady state, it was observed that increasing water saturation in the adjacent soil leads to a substantial increase on the amount of heat recovered. A model was proposed for the estimation of temperature along the heat collector panel based on steady state conditions. It accounted for thermal resistance between pipes and the variability of water saturation in the adjacent soils. This model showed good agreement with the data. Whilst increasing the flow rate of the circulating fluid within the panel did not cause noticeable improvement on the amount of heat energy that can be harnessed within the laminar flow regime commonly found in ground source heat panels. Infiltration of rainwater would cause a temporary enhancement on the amount of extracted heat. Measurement of the sand thermal conductivity during a cycle of drying and wetting indicates that the thermal conductivity is primarily dependent upon the degree of water saturation and secondary on the flow path.

Simulative method for determining the optimal operating conditions for a cooling plate for lithium-ion battery cell modules

Extended battery system lifetime and reduced costs are essential to the success of electric vehicles. An effective thermal management strategy is one method of enhancing system lifetime increasing vehicle range. Vehicle-typical space restrictions favor the minimization of battery thermal management system (BTMS) size and weight, making their production and subsequent vehicle integration extremely difficult and complex. Due to these space requirements, a cooling plate as part of a water–glycerol cooling circuit is commonly implemented.This paper presents a computational fluid dynamics (CFD) model and multi-objective analysis technique for determining the thermal effect of coolant flow rate and inlet temperature in a cooling plate—at a range of vehicle operating conditions—on a battery system, thereby providing a dynamic input for one-dimensional models. Traditionally, one-dimensional vehicular thermal management system models assume a static heat input from components such as a battery system: as a result, the components are designed for a set coolant input (flow rate and inlet temperature). Such a design method is insufficient for dynamic thermal management models and control strategies, thereby compromising system efficiency. The presented approach allows for optimal BMTS design and integration in the vehicular coolant circuit.

Effects of coolant flow rates on cooling performance of the intermediate pressure stages for an ultra-supercritical steam turbine

The effects of the coolant flow rates on the thermal and flow fields of the first two intermediate pressure (IP) stages of an ultra-supercritical steam turbine was numerically investigated using the Conjugate Heat Transfer (CHT) method, and the un-cooled case was also simulated for comparison. The three-dimensional Reynolds-Averaged Navier–Stokes (RANS) solution was utilized to analyze the flow field and temperature distributions of the first two IP stages. The numerical results show that the steam cooling system has proved its ability to cool down the high temperature components, even in the case with the low coolant flow rate. The cooling performance can be improved with increased coolant flow rate, however, great flow losses would be induced and make the stage efficiency reduce by 1.23%. The different coolant flow rates also lead to great differences in the flow field in the front cavity of the first stage: ingress dominated flow condition with the low coolant flow rate and egress dominated flow condition with the high coolant flow rate. The negative influence of the ingested hot main steam on the cooling effect was also described.

Modeling of an Exhaust Gas Cooler in a High-Altitude Test Facility of Large-Area Ratio Rocket Engines

AbstractIn this numerical study, the cooling of exhaust gas issued from a rocket engine in a ground test facility has been investigated by solving the three-dimensional governing equations. Simulations have been performed by employing discrete phase model with plain-orifice atomizer to cool the exhaust flow effectively by injecting the coolant (water) in the form of a fine spray. The effects of coolant flow rate, inlet gas temperature, injection pressure, injector diameter, gas cooler length, and distribution of water droplets on the cooling characteristics, such as the temperature at the gas cooler exit, droplet diameter, and percentage of unevaporated water have been discussed in detail. Simulations highlight that optimum particle diameter needs to be identified for effective cooling, and also uniform cooling of the exhaust gas is attained by employing staggered injector distribution (more injectors at the periphery compared to the core region). Predicted values of static temperature and pressure agree ...

An Advanced Multiconfiguration Stator Well Cooling Test Facility

Optimization of cooling systems within gas turbine engines is of great interest to engine manufacturers seeking gains in performance, efficiency, and component life. The effectiveness of coolant delivery is governed by complex flows within the stator wells and the interaction of main annulus and cooling air in the vicinity of the rim seals. This paper reports on the development of a test facility which allows the interaction of cooling air and main gas paths to be measured at conditions representative of those found in modern gas turbine engines. The test facility features a two stage turbine with an overall pressure ratio of approximately 2.6:1. Hot air is supplied to the main annulus using a Rolls-Royce PLC Dart compressor driven by an aero-derivative engine plant. Cooling air can be delivered to the stator wells at multiple locations and at a range of flow rates which cover bulk ingestion through to bulk egress. The facility has been designed with adaptable geometry to enable rapid changes of cooling air path configuration. The coolant delivery system allows swift and accurate changes to the flow settings such that thermal transients may be performed. Particular attention has been focused on obtaining high accuracy data, using a radio telemetry system, as well as thorough through-calibration practices. Temperature measurements can now be made on both rotating and stationary disks with a long term uncertainty in the region of 0.3 K. A gas concentration measurement system has also been developed to obtain direct measurement of re-ingestion and rim seal exchange flows. High resolution displacement sensors have been installed in order to measure hot running geometry. This paper documents the commissioning of a test facility which is unique in terms of rapid configuration changes, nondimensional engine matching, and the instrumentation density and resolution. Example data for each of the measurement systems are presented. This includes the effect of coolant flow rate on the metal temperatures within the upstream cavity of the turbine stator well, the axial displacement of the rotor assembly during a commissioning test, and the effect of coolant flow rate on mixing in the downstream cavity of the stator well.

A New Scheme for Controlling Part Cooling in Injection Molding

Abstract Part cooling parameters such as coolant flow rate and coolant temperature has been shown to have an important influence on the part quality in plastic injection molding. Molders commonly manipulate the coolant flow rate in an unclear manner to adjust part quality and reduce the overall cycle time. Manipulating such parameters effectively can indirectly control part quality when deviations in the injection processing variables occur if it is done in a controlled manner. In this investigation, coolant flow rate is selected to be the manipulated variable that affects an average temperature of the part surface as it cools within the mold cavity. The average part temperature is the controlled variable and its control represents the indirect control of part quality. Experiments were conducted to quantify the effects of coolant flow rate on the part surface temperature demonstrating that it is highly nonlinear and its control would require an advanced control scheme. An adaptive online modeling algorithm that uses information from temperature and flow rate sensors was developed to continuously retune a predictive controller for controlling the part surface temperature. Good control performance was obtained from the adaptive strategy for tracking setpoint changes in the part temperature and when the cooling cycle was reduced from 16 to 14 s.