Average Cell Temperature Research Articles

Cold-Air Bypass Characterization for Thermal Management of Fuel Cell Gas Turbine Hybrids

The effect of cathode airflow variation on the dynamics of a fuel cell gas turbine hybrid system was evaluated using a cyber-physical emulator. The coupling between cathode airflow and other parameters, such as turbine speed or pressure, was analyzed comparing the results at fixed and variable speed. In particular, attention was focused on fuel cell temperatures and gradients: cathode airflow, which is generally employed for thermal management of the stack, was varied by manipulating a cold-air bypass. A significant difference was observed in the two cases in terms of turbine inlet, exhaust gas, cathode inlet, and average cell temperatures. When the turbine speed was held constant, a change in cathode airflow resulted in a strong variation in cathode inlet temperature, while average cell temperature was not significantly affected. The opposite behavior was observed at variable speed. The system dynamics were analyzed in detail in order to explain this difference. Open-loop response was analyzed in this work for its essential role in system identification. However, a significant difference was observed between fixed and variable speed cases, because of the high coupling between turbine speed and cathode airflow. These results can give a helpful insight of system dynamics and control requirements. Cold-air valve bypass position also showed a strong effect on surge margin and pressure dynamics in both cases.

Cooling design and evaluation for photovoltaic cells within constrained space in a CPV/CSP hybrid solar system

A hybrid solar energy system has been designed by combining the advantages of concentrated solar power (CSP) technology and high performance concentrated photovoltaic (CPV) cells which outperforms either single technology. Thermal management is crucial to CPV cells in this hybrid solar system, as concentrated solar radiation onto the PV cells leads to higher heat flux. If the heat is not dissipated effectively, it can cause obvious temperature rise and efficiency reduction in the cell. In addition, the constrained space available for PV cell cooling in such hybrid solar systems presents more challenges. In this study both passive cooling and active cooling techniques were systematically investigated in both numerical and experimental ways. For the passive cooling method, two different designs from off-the-shelf heat pipes with radial fins or annular fins were proposed and studied under various heat rejection requirements. Results shows that heat pipes with radial fins exhibited narrow capability of dumping the heat, while heat pipes with annular fins presented better performances under the same conditions. Numerical optimal designs of annular fin numbers and fin gaps were then carried out and experimentally validated, indicating a capability of dumping moderate waste heat (∼45W). For active cooling technique, a comprehensive study of designing plate fin heatsinks were conducted corresponding to high Ingress Protection (IP) rated off-the-shelf fans. Results show that with a less than 2W fan power consumption, this active cooling method can control the average PV cell temperature below our target temperature of 75°C even under 45°C ambient. To evaluate the overall performance in a year round life cycle, the enhancement in the annual electricity output of the PV cells was estimated according to the cooling effects subjected to the climate of Tucson, Arizona. Finally, taking into consideration of both the temperature control results and net gain/loss analysis, an active cooling design was chosen for our system to dissipate a maximum waste heat of 84W (21.8W/cm2) due to its lower cost, lower CPV temperature, and higher net energy efficiency gain. It is also demonstrated that passive cooling will become more attractive when the heat dissipation requirement is less than 50W (13.0W/cm2).

Solar potential assessment and performance indices analysis of photovoltaic generator for isolated Lakshadweep island of India

Lakshadweep island is located in the Arabian Sea (8° and 12°13′ North Latitude, 71° and 74° East Longitude) of India where the island inhabitant depends upon the power generation from diesel generator because of inaccessibility to the grid power due to its location hinder. As an alternative viable option for this island, inhabitant is to use photovoltaic power generation. This paper presents the normalized performance results obtained from photovoltaic (PV) system and the solar potential assessment for four islands of Lakshadweep, mainly, Andrott, Kavaratti, Kiltan and Minicoy. The monthly average and annual average normalized performance parameters such as array yield, reference yield, array capture losses, system losses and performance ratio of 10kWp photovoltaic system is calculated. Besides, the monthly average and annual average capacity factor and cell temperature are also obtained. It is found that the obtained results for annual average performance ratio and capacity factor vary in the range of 64.22–65.83% and 15.51–16.09%, respectively. The annual average array yield, reference yield, final yield, array capture losses and system losses for the considered islands are found to be 4.13–4.29h/d (symbolized as h/d), 5.78–5.88h/d, 3.72–3.86h/d, 1.58–1.66h/d and 0.41–0.43h/d, respectively.

Experimental performance evaluation and modeling of jet impingement cooling for thermal management of photovoltaics

Thermal management of PV systems is one of the most important factors that affect the overall performance especially in hot climate regions. In this paper, the viability of jet impingement cooling for PV panels subjected to the climatic conditions of Dhahran region of Middle East has been discussed. Experimental and numerical performance evaluation was carried out for two configurations, an uncooled PV system and an impingement cooled PV system. The complete cooling model incorporates optical, radiation, thermal, geometric and electrical model for the overall performance analysis of the PV system. Jet impingement geometric model for PV was developed to carry out the heat transfer analysis for single nozzle for analyzing the cell temperature, power output and conversion efficiency of PV strings. For precise prediction of the performance of the PV cell, seven parameters electrical model is employed, whereas for absorbed radiation calculation isotropic sky model is adopted. Temperature measurements revealed cell temperature as high as 69.7°C and 47.6°C for an uncooled system for June and December, respectively. By applying jet cooling, average cell temperature was reduced to 36.6°C for June and 31.1°C for December. Power output and conversion efficiency was enhanced by 51.6% and 66.6% by employing jet cooling for June, respectively. Similarly, December results revealed performance improvement by 49.6% in power output and 82.6% in conversion efficiency. Simulation carried out reveals that jet cooling with optimum parameters has not only significantly increased the electrical power output and cell efficiency but has reduced the cell temperature while keeping it uniform for each cell.

In-plane nonuniform temperature effects on the performance of a large-format lithium-ion pouch cell

Due to the temperature sensitive behavior of lithium-ion batteries a thermal management system (TMS) is typically integrated into the battery pack design. This system plays a crucial role in the total battery pack performance. During operation the TMS will induce nonuniform temperature distributions within the cells of the pack, due to relatively low cell thermal conductivity. However, limited research has been published regarding the effects of thermal nonuniformity throughout a cell, module, or pack. Understanding these effects will be beneficial to heat exchanger design and TMS control strategy optimization. Here, an experimental investigation is performed where fixed one-dimensional temperature distributions, emulating the effects of edge-based heat transfer, are applied across the face of a 10Ah NiCoMn Li-ion pouch cell. Average cell temperature conditions of 15, 25, and 35°C with edge-to-edge temperature differences (ΔT) of 0, 5, 10, and 20°C are applied. At each thermal treatment the effects on: (1) the pulse resistance at 50% state of charge, (2) the bulk resistance on a Charge-Depleting US06 power profile, and (3) the overpotential during Constant-Current charge are investigated. Pulse resistance is decreased with increased ΔT. However, the discharge resistance on the Charge-Depleting cycle was increased with increased ΔT. The Constant-Current charging overpotential (and therefore resistance) was also increased with increased ΔT. All effects are largest at 15°C, and negligible at 35°C.

Experimental and numerical performance analysis of a converging channel heat exchanger for PV cooling

An experimental and numerical investigation of a cooling technique called as converging channel cooling intended to achieve low and uniform temperature on the surface of PV panel is presented in this paper. Experimental evaluation for an uncooled PV system and a converging channel cooled PV system was carried out subjected to the hot climate of Saudi Arabia for the month of June and December. Detailed modeling was performed using numerical analysis to investigate the effect of changing the converging angle on the thermal characteristics of the PV system. Based on the developed model, two degrees angle showed the best performance in terms of temperature distribution and average cell temperature with a standard deviation of 0.91°C. A comprehensive system model was developed to assess the performance of PV systems numerically by coupling the optical, radiation, thermal, computational fluid dynamics, and electrical model. Thermal measurements for an uncooled PV showed cell temperature as high as 71.2°C and 48.3°C for the month of June and December, respectively. By employing converging cooling, cell temperature was reduced significantly to 45.1°C for June and to 36.4°C for December. Maximum percentage improvement in power output was 35.5% whereas maximum percentage increase in the conversion efficiency was 36.1% when compared to the performance of an uncooled PV system. For cost feasibility of an uncooled and cooled PV system, levelized cost of energy (LCE) analysis was performed using the annual energy yield simulation for both systems. LCE was found to be 1.95(€/kWh) for an uncooled PV system which was reduced to 1.57(€/kWh) for converging cooled PV system with a relative percentage decrease of 19.5%, hence making it economically viable.

Heat transfer enhancement in a PV cell using Boehmite nanofluid

Experiments were conducted to investigate the cooling performance of channels by water-based nanofluids containing small concentrations of Boehmite (AlOOH⋅xH2O) for the PV cell. The channels were fabricated in two different configurations as straight and helical. The straight channel consists of 23 parallel rectangular channels with a hydraulic diameter of 4.1mm, a length of 24.5cm, a width of 5mm and a depth of 3.5mm. For the helical configuration the plate was divided into four symmetrical sections which, each part contains a helical channel with a width of 5mm, a depth of 3.5mm and a hydraulic diameter of 4.1mm. The nanofluid cooling performance was assessed from the results obtained for the average temperature and electrical output of the PV cell. Results showed that the nanofluid perform better than water and caused higher decrease in the average PV cell temperature. They were about 39.70% and 53.76% for 0.1wt.% (the best case) at flow rate of 80ml/min for the helical and straight channel, respectively. Moreover, the highest decrease of average temperature relative to the reference temperature was observed for 0.1wt.% nanofluid concentration in both channels. This led to the highest electrical efficiency about 20.57% and 37.67% for the straight and helical channel, respectively. Furthermore, power-hydraulics performance was defined to compare the performance of the studied channels. The results showed that the helical channel works in more efficient way compared with the straight one.

Comparison and validation of methods for estimating heat generation rate of large-format lithium-ion batteries

The heat generation rate of a large-format 25 Ah lithium-ion battery is studied through estimating each term of the Bernardi model. The term for the reversible heat is estimated from the entropy coefficient and compared with the result from the calorimetric method. The term for the irreversible heat is estimated from the intermittent current method, the V–I characteristics method and a newly developed energy method. Using the obtained heat generation rates, the average cell temperature rise under 1C charge/discharge is calculated and validated against the results measured in an accelerating rate calorimeter (ARC). It is found that the intermittent current method with an appropriate interval and the V–I characteristics method using a pouch cell yield close agreement, while the energy method is less accurate. A number of techniques are found to be effective in circumventing the difficulties encountered in estimating the heat generation rate for large-format lithium-ion batteries. A pouch cell, using the same electrode as the 25 Ah cell but with much reduced capacity (288 mAh), is employed to avoid the significant temperature rise in the V–I characteristics method. The first-order inertial system is utilized to correct the delay in the surface temperature rise relative to the internal heat generation. Twelve thermocouples are used to account for the temperature distribution.

The 2014 Joseph W. Richards Summer Research Fellowship -- Summary Report: Thermogalvanic Waste Heat Recovery in Transportation Energy Systems

Waste heat recovery remains an inviting subject for research. Solid state thermoelectric devices have been widely investigated for this purpose, but their practical application remains challenging due to high cost and the inability to fabricate them in geometries that are easily compatible with heat sources. An alternative to solid-state thermoelectric devices are thermogalvanic cells.1-7 The temperature difference between the hot and the cold electrodes creates a difference in electrochemical potential of the redox couples at the electrodes. Once connected to a load, electrical current and power is delivered, converting thermal energy into electrical energy. The aim of this summer project is to extend ongoing research to study the feasibility of incorporating thermogalvanic systems into automobiles. A climate-controlled wind tunnel (Fig. 1) was built to provide equivalent conditions to the ambient air stream under the car. Temperature was controlled using a window air conditioner, while an air mover drove the flow up to 6 m s−1. A heat gun provided the equivalent of a low-temperature exhaust gas stream (~110 oC). The annular cell was bound by concentric copper pipes (electrodes) and CPVC bulkheads; all sealed with silicone. K-type thermocouples were attached with epoxy onto electrode surfaces to measure the electrode temperature, which were monitored and recorded by a Campbell Scientific CR23X Micrologger. The cell potential (E) was probed using a Fluke 8846A Digital Multimeter. An Elenco RS-500 resistor box (Rext) was connected in parallel to measure power output, P = E/Rext. A 0.7 M CuSO4 aqueous electrolyte was used, with 0.1 M H2SO4 as the supporting electrolyte. The Tcold was varied based on the quad-monthly average ambient air temperature (Tambient) in Phoenix, AZ of 31.6, 22.5, and 14.1 oC. Because thermal resistance from the hot air stream to the inner copper pipe is large relative to the thermal resistance of the cell, the Thot was measured to be less than the hot air stream’s temperature. Reducing this resistance would greatly improve the system performance. The experimental values of Thot and Tcold are shown next to their resultant plots in Fig. 2. These results showed that higher Tambient yielded a higher P, because of the higher average cell temperature, Tavg = (Thot+ Tcold)/2. This trend agreed with our previous study.8 Since the resistor could only be Fig 1. 3D CAD drawings of the wind tunnel and the cross-sectional diagram of the annular Cu/Cu2+ thermogalvanic cell.

Solar power plant performance evaluation: simulation and experimental validation

In this work the performance of solar power plant is evaluated based on a developed model comprise photovoltaic array, battery storage, controller and converters. The model is implemented using MATLAB/SIMULINK software package. Perturb and observe (P&O) algorithm is used for maximizing the generated power based on maximum power point tracker (MPPT) implementation. The outcome of the developed model are validated and supported by a case study carried out using operational 28.8kW grid-connected solar power plant located in central Manchester. Measurements were taken over 21 month's period; using hourly average irradiance and cell temperature. It was found that system degradation could be clearly monitored by determining the residual (the difference) between the output power predicted by the model and the actual measured power parameters. It was found that the residual exceeded the healthy threshold, 1.7kW, due to heavy snow in Manchester last winter. More important, the developed performance evaluation technique could be adopted to detect any other reasons that may degrade the performance of the P V panels such as shading and dirt. Repeatability and reliability of the developed system performance were validated during this period. Good agreement was achieved between the theoretical simulation and the real time measurement taken the online grid connected solar power plant.

A method for using CPV modules as temperature sensors and its application to rating procedures

A method is presented herein that allows the determination of the average temperature of solar cells in a concentrator photovoltaic (CPV) module. The module is measured systematically in a sun simulator while the average module temperature and the irradiation are varied. Two different approaches are discussed to heat a CPV module in a sun simulator. From the measurements, a function is derived that allows the derivation of the average solar cell temperature when the I– V curve of the CPV module is measured. Consequently, the module itself can be used as a temperature sensor. Outdoor I– V measurements of different CPV modules are then presented. Their temperatures are calculated by applying the newly developed method. A multi-linear regression is conducted on the data measured outdoors. In particular, the modules’ maximum powers are correlated to direct normal irradiation, the solar spectrum and the average solar cell temperature. The impact of temperature on the module’s maximum power is shown to be significantly smaller than the impact of the solar spectrum. Finally, the maximum power values for the modules are re-calculated for two different rating conditions.

Quantification of Temperature Driven Flow in a Polymer Electrolyte Fuel Cell Using High-Resolution Neutron Radiography

In this study, the effect of a controlled temperature gradient on water transport across a single fuel cell was quantitatively investigated using high-resolution neutron imaging. The direction of liquid water transport under isothermal and non-isothermal conditions was observed in both hydrophilic and hydrophobic diffusion media (DM). The change in distribution of liquid saturation with time revealed two different mechanisms of water transport; capillary driven flow and phase-change induced (PCI) flow, in which a water vapor concentration gradient is created by condensation at a colder location. This concentration gradient drives diffusion flow toward the colder location. A maximum liquid saturation plateau of ca. 30% was shown for all conditions tested, indicating a critical transition between pendular and funicular modes of liquid water storage was captured. Based on this, it is suggested that PCI-flow may be the main mode of liquid transport below this critical transition threshold, above which, capillary flow dominates. As expected, both average cell temperature and the magnitude of temperature gradient were shown to significantly affect the rate of condensation within the DM. Experimental results were compared with water saturation distribution model predictions from literature and show reasonable qualitative agreement. Finally, it was concluded that current available models significantly over predict vapor phase diffusive transport in saturated fuel cell media using a Bruggeman type model.

Performance analysis of a tubular solid oxide fuel cell with an indirect internal reformer

A 2-D steady-state mathematical model of a tubular solid oxide fuel cell with indirect internal reforming (IIR-SOFC) has been developed to examine the chemical and electrochemical processes and the effect of different operating parameters on the cell performance. The conservation equations for energy, mass, momentum as well as the electrochemical equations are solved simultaneously employing numerical techniques. A co-flow configuration is considered for gas streams in the air and fuel channels. The heat radiation between the preheater and reformer surface is incorporated into the model and local heat transfer coefficients are determined throughout the channels. The model predictions have been compared with the data available in the literature. The model was used to study the effect of various operating conditions on the cell performance. Numerical results indicate that as the cell operating pressure increases, the reforming reaction extends to a larger portion of the cell and the maximum temperature move away from the cell inlet. As a result, a more uniform temperature prevails in the solid structure which reduces thermal stresses. Also, at higher excess air, the rate of heat transfer to the air stream is augmented and the average cell temperature is decreased. Copyright © 2010 John Wiley & Sons, Ltd.

Measured performance of a 1.72 kW rooftop grid connected photovoltaic system in Ireland

This paper presents results obtained from monitoring a 1.72 kW p photovoltaic system installed on a flat roof of a 12 m high building in Dublin, Ireland (latitude 53.4°N and longitude 6.3°E). The system was monitored between November 2008 and October 2009 and all the electricity generated was fed into the low voltage supply to the building. Monthly average daily and annual performance parameters of the PV system evaluated include: final yield, reference yield, array yield, system losses, array capture losses, cell temperature losses, PV module efficiency, system efficiency, inverter efficiency, performance ratio and capacity factor. The maximum solar radiation, ambient temperature and PV module temperature recorded were 1241 W/m 2 in March, 29.5 °C and 46.9 °C in June respectively. The annual total energy generated was 885.1 kW h/kW p while the annual average daily final yield, reference yield and array yield were 2.41 kW h/kW p/day, 2.85 kW h/kW p/day and 2.62 kW h/kW p/day respectively. The annual average daily PV module efficiency, system efficiency and inverter efficiency were 14.9%, 12.6% and 89.2% respectively while the annual average daily performance ratio and capacity factor were 81.5% and 10.1% respectively. The annual average daily system losses, capture losses and cell temperature losses were 0.23 h/day, 0.22 h/day and 0.00 h/day respectively. Comparison of this system with other systems in different locations showed that the system had the highest annual average daily PV module efficiency, system efficiency and performance ratio of 14.9%, 12.6% and 81.5% respectively. The PV system’s annual average daily final yield of 2.4 kW h/kW p/day is higher than those reported in Germany, Poland and Northern Ireland. It is comparable to results from some parts of Spain but it is lower than the reported yields in most parts of Italy and Spain. Despite low insolation levels, high average wind speeds and low ambient temperature improve Ireland’s suitability.

Modeling of electrochemistry and steam–methane reforming performance for simulating pressurized solid oxide fuel cell stacks

This paper examines the electrochemical and direct internal steam–methane reforming performance of the solid oxide fuel cell when subjected to pressurization. Pressurized operation boosts the Nernst potential and decreases the activation polarization, both of which serve to increase cell voltage and power while lowering the heat load and operating temperature. A model considering the activation polarization in both the fuel and the air electrodes was adopted to address this effect on the electrochemical performance. The pressurized methane conversion kinetics and the increase in equilibrium methane concentration are considered in a new rate expression. The models were then applied in simulations to predict how the distributions of direct internal reforming rate, temperature, and current density are effected within stacks operating at elevated pressure. A generic 10 cm counter-flow stack model was created and used for the simulations of pressurized operation. The predictions showed improved thermal and electrical performance with increased operating pressure. The average and maximum cell temperatures decreased by 3% (20 °C) while the cell voltage increased by 9% as the operating pressure was increased from 1 to 10 atm.

Transport phenomena in a semi-passive direct methanol fuel cell

A two-dimensional, steady state, non-isothermal, multi-fluid, two-phase flow model is presented for a semi-passive direct methanol fuel cell at which air flows through a channel at the cathode side while liquid methanol solution is fed passively at the anode. The evaporation/condensation rates are formulated in a manner to capture the non-equilibrium effects between the liquid and gas phases. The model also accounts for the methanol and water crossover through the membrane. The behavior of a semi-passive system, including the temperature, oxygen and water vapor mass fractions, and the liquid saturation at different air flow rates is well described. Capturing the thermal effect in a semi-passive system is vital, since transport variables are highly dependent on temperature. While a higher flow rate of air at the cathode channel decreases the average cell temperature, it enhances the liquid removal from the porous media at the cathode side. The results also show that a higher flow rate results in a more uniform distribution of transport variables along the channel. For a cell that does not suffer from the flooding effect, a lower air flow rate through the channel results in a higher performance of the cell due to the temperature increase.

Probabilistic-Based Design Methodology for Solid Oxide Fuel Cell Stacks

A probabilistic-based component design methodology is developed for a solid oxide fuel cell (SOFC) stack. This method takes into account the randomness in SOFC material properties as well as the stresses arising from different manufacturing and operating conditions. The purpose of this work is to provide the SOFC designers a design methodology so that the desired level of component reliability can be achieved with deterministic design functions using an equivalent safety factor to account for the uncertainties in material properties and structural stresses. Multiphysics-based finite element analyses were used to predict the electrochemical and thermal mechanical responses of SOFC stacks with different geometric variations and under different operating conditions. Failures in the anode and the seal were used as design examples. The predicted maximum principal stresses in the anode and the seal were compared with the experimentally determined strength characteristics for the anode and the seal, respectively. Component failure probabilities for the current design were then calculated under different operating conditions. It was found that anode failure probability is very low under all conditions examined. The seal failure probability is relatively high, particularly for high fuel utilization rate under low average cell temperature. Next, the procedures for calculating the equivalent safety factors for the anode and seal were demonstrated so that a uniform failure probability of the anode and seal can be achieved. Analysis procedures were also included for non-normal distributed random variables so that more realistic distributions of strength and stress can be analyzed using the proposed design methodology.

Effect of inlet flow maldistribution in the stacking direction on the performance of a solid oxide fuel cell stack

This study examines the performance of a ten-cell solid oxide fuel cell (SOFC) stack with a non-uniform flow rate in the stacking direction. The author develops a two-dimensional numerical method to solve the electrochemical, mass and energy equations one stack at a time. The energy equations couple the heat exchange between the interconnector and both the cell and the flowing gas of adjacent cells. Moreover, this paper considers two boundary conditions, adiabatic and constant temperature, on the top and bottom faces of the SOFC. The results show that the non-uniform inlet flow rate of the fuel dominates the current density distribution; it causes the cell voltage to vary by over 13% for both boundary conditions. In addition, the constant temperature condition in this study can produce 3% more power than with the adiabatic condition. On the other hand, the air dominates the temperature field of a SOFC, and the non-uniform inlet flow rate of the air produces a variation of 3% in the average cell temperature of the cells when the boundary condition is adiabatic. This non-uniform effect on the electrical performance of each stack is apparently larger than in the transverse direction, which has been examined in our previous research.

Non-concentrating and asymmetric compound parabolic concentrating building façade integrated photovoltaics: An experimental comparison

Concentration of solar energy increases the illuminated flux on the photovoltaic (PV) surface thus less PV material is required. A novel asymmetric compound parabolic photovoltaic concentrator has been characterised experimentally with a similar non-concentrating system. Different numbers of PV strings connected within the system have been analysed and a power ratio of 1.62 measured compared to a similar non-concentrating PV panel with the same cell area. The solar to electrical conversion efficiency of 8.6% and 6.8% was achieved for the non-concentrating panel the concentrating system, respectively. The measured average solar cell temperature of the PV in the concentrator system was only 12 °C higher than that of the similar non-concentrating system with same cell area.

Three-dimensional thermo-fluid electrochemical modeling of planar SOFC stacks

A simulation tool for modeling planar solid oxide fuel cells is demonstrated. The tool combines the versatility of a commercial computational fluid dynamics simulation code with a validated electrochemistry calculation method. Its function is to predict the flow and distribution of anode and cathode gases, temperature and current distributions, and fuel utilization. A three-dimensional model geometry, including internal manifolds, was created to simulate a generic, cross-flow stack design. Similar three-dimensional geometries were created for simulation of co-flow, and counterflow stack designs. Cyclic boundary conditions were imposed at the top and bottom of the model domains, while the lateral walls were assumed adiabatic. The three cases show that, for a given average cell temperature, similar fuel utilizations can result irrespective of the flow configuration. Temperature distributions however, which largely determine thermal stresses during operation, are dependent on the chosen design geometry/flow configuration. The co-flow case had the most uniform temperature distribution and the smallest thermal gradients, thus offers thermo-structural advantages over the other flow cases.