Cold Plate Temperature Research Articles

Performance-Dryout Limits of Oscillating Heat Pipes: A Comprehensive Theoretical and Experimental Determination

The performance limits of oscillating heat pipes (OHPs) have been the subject of research in recent years in order to understand their limitations and allow their broad application in the aerospace field. The present work describes the experimental determination of the performance dryout limits for an additively manufactured OHP geometry filled with R-134a and R-123, as well as the performance limits theoretical predictions using a recently developed analytical approach. Thermal experiments were carried out using a constant-temperature cold-plate approach at three cold plate temperatures, allowing the OHP device to reach steady state for each power step. Results show good agreement for the performance limits predictions with experimental data for both working fluids R-134a and R-123, opening the way for the analytical framework to be used in the design and development of OHPs.

Field study on the temperature uniformity of containerized batteries using a two-phase liquid cooling system under mismatched conditions

The conventional liquid cooling system carries the risk of dew condensation and air cooling has poor thermal management performance for battery energy storage systems. To address these issues, a novel two-phase liquid cooling system was developed for containerized battery energy storage systems and tested in the field under mismatched conditions. The thermal management performance and safety during the charging and discharging processes were analyzed by investigating the main influencing factors, including battery temperature and cooling system characteristics (battery temperature variation, temperature uniformity, supply liquid temperature, cold plate temperature distribution, and compressor status). The results showed that the novel system can maintain a maximum cell temperature difference of less than 3°C at the rack level and less than 2°C at the pack level, resulting in a 60% reduction compared to the traditional air cooling system. Relative to a supply liquid temperature of 15∼25°C, a relatively high supply temperature of 20∼30°C for two-phase liquid cooling can not only reduce the running time of the compressor but also enhance its start-stop consistency. Compared to other studies, this novel system is reliable and safe for containerized energy storage batteries, even in capacity mismatch and direct return pipeline conditions.

A study on a battery pack in a hybrid battery thermal management system integrating with thermoelectric cooling

An inherent limitation of lithium-ion batteries is their restricted use within a specific thermal working range. To address this problem, efficient battery thermal management systems (BTMS) are required to dissipate the heat created by the cells in the battery pack. In order to control the maximum temperature and minimise the temperature difference through the battery pack during a 5C discharging process, this study investigates a phase change material (PCM)-porous battery thermal management system, cooled by thermoelectric coolers (TEC) on its walls. To calculate the heat generation of Li-ion batteries, the equivalent circuit model (ECM) is employed. In this model, a battery is made up of a set of electric elements, including R–C pairs. Different PCM and porous materials are studied to determine the most suitable material for controlling the thermal behaviour of the battery pack. The study reveals that the solidus temperature and latent heat of PCM are the two most crucial factors in PCM selection. A thermoelectric cooler is an instrument that uses electrical energy to transfer heat from one side of the device to the other, depending on the current direction. The study examines the use of a TEC (thermoelectric cooler) under various ambient temperatures and applied voltage differences. The results demonstrate that adjusting the voltage difference between the two TEC heads from 900 to 1500 mV, while the ambient temperature ranges from 303 K to 323 K, allows for achieving a cold plate temperature between 288 K and 308 K. The designed BTMS is tested in various TEC positions, and it is shown that when TECs are used on side walls, the maximum temperature of the battery back can decrease up to 1 K, and better temperature uniformity is observed.

DOE optimization of a liquid cold plate used in a thermal management system for power converters in the railway sector through 3D CFD analysis

The thermal management system for power electronics is becoming a key factor in order to guarantee optimal working conditions, efficiency and safety of those components. In the field of liquid-cooled power electronics, the design of an optimal liquid cold plate (LCP) is fundamental to increase the heat transfer, minimizing the maximum temperature and the pressure drop. This work presents an optimization procedure of a finned extruded profile of an LCP for insulated gate bipolar transistor (IGBT) power module, for railway propulsion. The optimization has been performed through DOE, by considering different values of several control factors (shape of the fin, length of the fin, pitch between the channels created by the fins), in order to minimize the LCP maximum temperature and the pressure drop between inlet and outlet. The combination of different values of control factors results in 18 prototypes, which have been compared using three-dimensional CFD simulations, performed in Ansys Fluent environment. The influence of parameters variation on the objective functions (i.e. maximum temperature of the liquid cold plate and pressure drop) has been verified.

A modeling study on freezing characteristics of sessile and pendant water droplets on cold plate surfaces

The freezing phenomena of sessile and pendant water droplets on horizontal and inverted surfaces are widespread in industrial fields, which always causes great structural destruction and energy waste. Considering the gravity effect on the droplet profile, a theoretical model is developed to calculate the freezing characteristics of sessile and pendant droplets and experimentally verified. The average deviation of the model in the droplet freezing time is 10.53 % and the determination coefficient in the droplet profile is above 98 %. Based on the model, the freezing characteristics of sessile and pendant droplets under different water droplet volumes (characterized by the Bond number, Bo), contact angles and cold plate temperatures are investigated. When Bo ≤ 1, there is almost no difference in the freezing characteristics of sessile and pendant droplets. When Bo > 1, obvious differences are observed with a pendant droplet having a higher height and a longer freezing time. For both sessile and pendant droplets, the freezing height is approximately proportional to the initial height with the sessile droplet yielding a smaller proportion coefficient. Their freezing times can be written as a function of the Bond number, contact angle and cold plate temperature. Under the same condition, the ratio of freezing time by the pendant droplet to that by the sessile one is scaled as Bo1/4 when Bo > 1. The findings in this study help better understand the freezing characteristics of the sessile and pendant droplets and thus optimize anti-icing and anti-frosting technologies.

An experimental study on edge-affected frosting characteristics on a vertical cold plate at different surface temperatures

Frosting has received significant attention in various fields due to its potential threat. To accurately predict and control the frosting process on vertical cold plate surface considering the edge effect, the frosting characteristics with surface temperature between −15.0 °C and −5.0 °C are experimentally studied under forced convection. The results show that as the cold plate temperature decreases, the durations of droplet solidification stage in the edge-affected region decreases slowly. Meanwhile, the area-average equivalent contact diameter and the coverage area ratio of edge-affected droplets both increases. The density difference of droplet distribution between the edge-affected and unaffected regions increases from 1.02 × 107 to 3.58 × 108 per m2. The average frost layer thickness reaches 7.41 × 10−4 m for −7.5 °C at 2,400 s, and it increases by 21.20%, 38.40%, and 82.08% when the temperature decreases to −10.0 °C, −12.5 °C, and −15.0 °C, respectively. Results of this study are expected to be meaningful for the optimization of frost detection and defrosting technologies.

Designing an Accurate Temperature Control System for Infrared Earth Simulators Using Semiconductor and Air Cooling Integration.

In a laboratory environment, in order to test the attitude recognition capability and accuracy of the satellite attitude sensor-the infrared Earth sensor-the infrared Earth simulator is fixed on a five-axis turntable to enable multi-angle testing. In the past, the temperature control system of the Earth simulator was water cooled, which not only affected the working accuracy of the Earth simulator but also affected its size and portability and made it more difficult to use on the turntable. Therefore, we designed a cooling method for the cold plate based on semiconductor cooling technology combined with air cooling, and we designed a fuzzy PID control algorithm to accurately control the temperature according to this cooling method. In this article, we use SOLIWORKS to build the system model for the system and use the ANAYS Workbench to perform temperature analysis of the Earth simulator. The results show that the cold plate temperature can be maintained at 20.089 °C when the hot plate temperature is 85 °C. The overall temperature uniformity of the hot plate is better than ±0.3 °C, which meets the index requirements of the Earth simulator. We found that this cooling method can replace water cooling, giving the simulator the advantage of being miniaturized, and it can be adaptable to the turntable, which can be widely used in various sizes of Earth simulators and in various complex environments and operating conditions.

Experimental and numerical study on two-phase minichannel cold plate for high-power device

In this study, the flow and heat transfer performance of the two-phase minichannel cold plates with 10 kW level heat load is designed and studied. The numerical simulation can guide the optimization of the structure on both channel level and whole level, which roughly matches the experimental results. An abnormal phenomenon that the temperature increase with flow rate is observed and explained by boiling point change. The influence of channel structure, fluid characteristics, flow uniformity, and pressure resistance on cold plate temperature and pressure drop are investigated. The fusiform channel performs better than the rectangular channel and refrigerant R1234ze(E) beats R1233zd(E) in the cold plate. Flow uniformity and pressure drop improvement methods are explained and tested. The cold plate can keep its surface temperature below 80 °C and pressure drop below 0.6 bar when the heating power is 20 kW, utilizing R1234ze(E) with a temperature of 60 °C and a flow rate of 9 L/min. A high-power two-phase cold plate can be designed with reference to this study.

Experimental investigation on incipient boiling in narrow closed gaps with water

This research deals with characterization of the Onset of Nucleate Boiling (ONB) in an enclosed narrow gap system containing a stationary liquid. In the experimental system, subcooled water at atmospheric pressure is confined between two parallel vertical rectangular copper plates. One of the plates is heated electrically and the opposite one is cooled with an external water-cooling system, maintaining its constant temperature.The experimental gaps explored in this research are: 5 mm, 3 mm, 0.9 mm and 0.5 mm. In each gap, several experiments are performed with a different controlled cold plate temperature. Various heat transfer mechanisms are observed (convection, transition and conduction), depending on the gap size. In the convection regime, the results are in good agreement with a correlation from the literature. In the gap 0.5 mm wide, the heat transfer occurs by conduction through the water, whereas for the gap 0.9 mm wide, single-phase experiments show a “transition” heat transfer regime. The onset of nucleate boiling (ONB) is detected as the point at which the heat transfer coefficient behavior changes dramatically, and is revealed also by visualization of the experimental channel. The wall superheat and the heat flux are evaluated at ONB.An analytical model is developed, based on the [1] correlation and on the experimental values of the heat transfer coefficient. A good agreement for the ONB heat flux prediction is achieved with the model, whereas the ONB superheat is over-estimated, except for the really narrow, 0.5 mm, gap.

Experimental Study of Frost Crystals Dendrite Growth on Two Neighboring Separate Frozen Water Drops on a Cryogenic Cold Surface under Natural Convection Conditions

The effects of cold surface temperature, wet air state (temperature and humidity) and original drop size on frost dendrites growth of two neighboring separate frozen water drops of same size under natural convection conditions were investigated by quantitative measurement. It was determined that for different cold plate surface temperature conditions, i.e., the ordinary-low temperature and the cryogenic temperature range, the frost formation mechanism is different. Under the conditions that the air temperature is not too high and absolute humidity is not too excessive, the influence of frozen water drop size on the longest dendrite of frost crystals becomes more and more obvious with the decrease in cold plate temperature. The changes in air temperature and relative humidity both change air absolute humidity, so they have similar effects on the growth of dendrites. However, the effect of wet air state on the growth of frost dendrites is not monotonous, which needs to be considered comprehensively in combination with heat and mass transfer and the existence of heavy phase layer. The thickness of ‘the initial continuous frost layer’ was measured and it was disclosed that the initial frost layer thickness is 1.7–3.0 times that of the height of the frozen water drop diameter. This value may be possibly used as initial frost layer thickness in heat and mass transfer-based frost layer growth prediction models, at least for ordinary-low temperature conditions.

An experimental study on the frost formation over a flat plate: Effect of frosting on heat transfer

Frost accumulation on cooled surfaces generates thermal barrier between the surface and air. Apart from the frost layer thickness, the thermal properties of the frost also affect its heat transfer characteristics. In this experimental study, the effect of the frosting on heat transfer is investigated at different cold surface temperatures and at different air velocities in a closed loop wind tunnel. A large number of experiments is performed by altering the parameters of free stream air velocity, relative humidity, and cold plate temperature. Frost layer impact on heat transfer rate is measured through a high precision thin film heat flux sensor for 60 min. Accordingly, heat flow was significantly obstructed due to frosting. The rate of diminishment in the heat flux was not found to be constant over time but shows a decreasing trend. Furthermore, an enhancement on the heat transfer was reported during the early stage of frost formation under certain environmental conditions, majorly due to the increase in effective heat transfer area induced by ice crystals and corresponding increase in latent heat generation. The densification of the frost layer and its effect on the total thermal resistance was discussed. Based on the convective heat and mass transfer balance over the frost layer, frost surface temperature was predicted. Lastly, a correlation for estimating the heat transfer decrease during frosting is proposed via non dimensional numbers.

On thermal management of pouch type lithium-ion batteries by novel designs of wavy minichannel cold plates: Comparison of co-flow with counter-flow

The liquid cooling technique is the most preferred technique among the common methods of battery thermal management (BTM) due to its greater compactness and better efficiency. The temperature uniformity within batteries, mainly when they operate under extreme conditions (thermal runaways) is of utmost importance because a uniform temperature distribution can noticeably affect the performance, safety, and lifetime of batteries. Concerning this issue, novel wavy minichannel cold plates are proposed to establish better thermal management and temperature uniformity in pouch type lithium-ion batteries. The considered cases have variable wave amplitudes, which are varied in each wavelength of the wavy minichannels. These cases are investigated for the co-flow and the counter-flow patterns to improve conventional wavy cold plate temperature gradient problems in the laminar flow regime. The results indicate that replacing the conventional wavy cold plate with novel designs can improve temperature uniformity and decline the corresponding factor by 38.7%. It is found that a cold plate with the counter-flow pattern has a better temperature uniformity than the case with the co-flow pattern. Moreover, it is worth mentioning that the temperature distribution and uniformity of the conventional model are considerably influenced by the flow pattern compared to the novel cases. Using a counter-flow pattern in the conventional case leads to 73.1% decline in the maximum temperature difference compared to the co-flow pattern.

Cold Plate Temperature Effect on Droplet and Frost Crystal Behaviors at the Early Condensation Frosting Stage Considering Plate Edge Effect

Cold Plate Temperature Effect on Droplet and Frost Crystal Behaviors at the Early Condensation Frosting Stage Considering Plate Edge Effect

Modeling study on sessile water droplet during freezing with the consideration of gravity, supercooling, and volume expansion effects

Droplet freezing phenomenon widely exists in many fields, including aerospace, power production, and cryopreservation, etc. Considering the effects of supercooling, gravity and volume expansion, a theoretical model of droplet freezing is developed. A good agreement is found between the predicted results of freezing front radius and height and experiments for both hydrophilic and hydrophobic surfaces. The developed model also shows good performance in predicting freezing times. The average prediction deviation is 7.63%, and more than 93% simulation results show the deviation within ±15%. Gravity has a more obvious influence on final freezing times with the increase of cold plate temperature, contact angle, and droplet volume. For the droplet freezing process under various contact angles and cold plate temperatures, the fastest average temperature change rates inside water droplet are -2.48 °C/s and -1.72 °C/s, respectively. This study is beneficial for the better understanding of the droplet solidification as well as the optimization of refrigeration and defrosting technologies.

System and Component Level Risk Assessment for SiC MOSFET Based Inverter for Traction Application at High Coolant Temperatures and Off-Road Mission Profile

Abstract Monitoring and predicting temperatures at critical locations of a power electronic system is important for safety, reliability, and efficiency. As the market share of vehicles with electric powertrains continues to increase, there is also an important economic cost of failing electronic components. For inverters present in such a drive system, exceeding the temperature limit for certain critical components, such as DC-link capacitors and Silicon carbide MOSFETs, can lead to failure of the system. In such an application, extracting the temperatures using sensors from locations such as dies and capacitors require expensive modifications and poses technical challenges. It is therefore necessary to create a thermal model for the inverter system to estimate the temperature at various components in order to ensure operation within temperature limits. The model approach is also suitable for predicting the effect on the component temperature and reliability of boundary conditions such as coolant, ambient temperature, and mission profile. This study assesses the reliability of a 250 kW liquid cooled inverter system designed for traction application. The critical failure areas are the DC-link capacitors, and the SiC MOSFET dies, which are rated at 175 °C. The system is modeled as a compact system by reasonably considering each component as a lumped capacitance and estimating the thermal resistance using physical dimensions. Results from the model are then compared against experimental data from constant power testing, and good agreement is observed for the cold plate and gate driver temperatures. With the model fidelity established, the model is then used to implement drive cycles from the Environmental Protection Agency for nonroad applications. The resulting temperature profile for each component is a series of temperature peaks and troughs that contribute to damage and failure. Rainflow counting algorithm is then used to quantify the damage per mini-cycles and used to estimate the predicted life for each component based on their manufacturer provided reliability qualification, and the mission profile is executed on the test bench for validation. The results are then used to generate a system risk matrix that relates the failure risk associated with a certain mission profile and the cooling scheme. It therefore demonstrates that an automotive inverter with SiC switching devices can be credibly assessed for failure risk using a compact model that is independent of boundary conditions, in combination with established reliability correlations and techniques.

Viability of Cryogenic Cooling to Reduce Processor Power Consumption

Abstract Through the application of cryogenic cooling via liquid nitrogen (LN2), the power consumption of a CPU was substantially reduced. Using a digitally controlled solenoid valve and an additively manufactured cold plate, the manual process of LN2 cooling was automated for precise control of cold plate temperature. The power consumption and frequency relationship of the processor were established across three different thermal solutions to demonstrate the effect of temperature on this relationship. It was found that power consumption of the processor decreased at lower temperatures due to a reduction in current leakage and the core voltage necessary for stable operation. This culminated in a reduction of up to 10.7% in processor power consumption for the automated solution and 21.5% for the manual LN2 solution when compared to the air-cooled baseline. Due to the binary nature of the solenoid valve used, flow rate was tuned via an in-line needle valve to increase thermal stability. It was found that for lower flow rates, approximately 5.0 g/s, temperatures oscillated within a range of ±11.5 °C while for higher flow rates of 10–12 g/s, generated amplitudes are as small as ±3.5 °C. Additionally, several tests measured the rate of LN2 consumption and found that the automated solution used 230%–280% more coolant than the manual thermal solution, implying there is room for improvement in the cold plate geometry, LN2 vapor exhaust design, and coolant delivery optimization.

A numerical study on frosting and its early stage under forced convection conditions with surface and environmental factors considered

To accurately control the frosting process, analyzing the influence of different factors on frosting is meaningful and challengeable, especially in the early frosting stage. According to the sensitivity analysis, the influence of different surface wettability and environmental factors on the growth of frost layer were quantitatively analyzed. Based on the experimental data on cold plate surface under forced convection conditions, new models with emphasis on the initial conditions of the frosting process are developed. Results show that supersaturation degree, supercooling degree and cold plate temperature are the key factors on the growth of frost layer, but their specific influence varies in the early frosting stage. And proportions of these three factors reach 39.42%, 35.58% and 21.15%, respectively. The coincidence rates of the new models with an error of 15% reach>90% for the whole frosting process, and 83% for the early frosting stage. Compared with previous models, the coincidence rates of the new models for the whole frosting process and the early frosting stage are increased by at least 8.86% and 15.28%, respectively. Contributions of this study are expected to predict the growth of frost layer in the early frosting stage and provide a reference for the optimal defrosting control of air source heat pumps.

The process of preparation of tellurium epitaxial films and layers with high structural perfection during vapor-deposition process in the pure hydrogen environment

The work is devoted to studying a new methodology for epitaxial films preparation on the mi-ca (muscovite) plates and based on carrying out the tellurium vapor-deposition process in the pure hydrogen environment. The formation of Н2Te molecules during reaction of H2 with sol-id Te in the hot zone, diffusion of Н2Te towards the cold surface with efficient thermalization due to high thermal conductivity of H2, Н2Te dissociative adsorption on the growth surface followed by H2 desorption and atomic Te accumulation are considered as key steps of crystal-line epitaxial films formation. Atomic Te assists the appearance and growth of directional liquid nucleuses at cold plate temperatures near Te melting point (about 450C). During coa-lescence of these liquid nucleuses the gradual formation of a liquid film is observed with a mosaic of voids of various size. After continuous liquid sheet formation, auto-epitaxial film growth begins also taking place according to vapor-liquid-crystal process described. The structural perfection of films formed is closed to three-dimensional monocrystalline samples. As a result, Te films with such characteristics may be put to use in various branches of micro-, opto-, acoustoelectronics.

Experimental study on water transfer of remolded loess under freezing

The change of the internal moisture field of the loess is an important factor for the study of the cause of the loess engineering disease, and the freezing effect has a certain effect on the change of the internal moisture field of the loess. In order to analyze the law and mechanism of water distribution in the loess under four different factors, the indoor experiments of water transfer were carried out under different temperature gradients and different temperature levels. The results show that:Under the action of freezing, the greater the temperature gradient applied on both ends of the soil sample, the farther away from the top of the steady-state freezing front, the lower the water content increment in the early stage, and the higher the water content increment in the later stage, and the more obvious the change of water content near the steady-state freezing front, the greater the total amount of water migration; For the soil samples with higher dry density, the closer the frozen front is to the top, the increase of water content in the early stage is decreasing, and that in the later stage is increasing; With the increase of the initial moisture content, the water transfer of the soil sample increases, and the position of the steady-state freezing front of the soil sample with different initial moisture content is basically the same; At different temperature levels, the lower the cold plate temperature is, the farther the frozen front is from the top. When the cold plate temperature is in a certain range, the water transfer phenomenon is significant.

Modeling Simulation and Temperature Control on Thermal Characteristics of Airborne Liquid Cooling System

Aiming at the temperature control of the liquid cooling system of aircraft electronic equipment, the thermal characteristics of the system under different temperature conditions are analyzed through model simulation, and a calculation method is given for the thermal design of the liquid cooling system. This paper simplifies the system and establishes a numerical calculation model for the heat transfer of the main components (such as liquid storage tanks, gear pumps, radiators, etc.). The temperature changes in the main components of the system within the operating temperature range of the system (-40 °C-50 °C) were calculated, and the thermal characteristics of the cold plate were obtained by using the AMESim software. Further, temperature control schemes of several liquid cooling systems are compared for their working efficiency under low temperature and over-temperature conditions based on the original model. The results show that the temperature index of the airborne liquid cooling system basically meets the technical requirements of the cold plate inlet temperature (5 °C-30 °C) under typical operating conditions. Under low-temperature conditions, the rapid heating of the cold plate can be achieved through the electric heater control scheme. Under high-temperature circumstances, opening the ram air port scheme has a better cooling effect than increasing the fan speed scheme, but the former needs to consider the flight conditions to avoid the cold plate temperature exceeding the target range.