Maximum Critical Heat Flux Research Articles

Low Mass Flux Laminar Jet Cooling with Different Additives: An Enhancement-cum-Comparative Study

The low flow rate laminar water jet is the most economical and efficient cooling methodology; however, the low heat removal capacity makes this process inappropriate for fast cooling operations. In the current work, the heat transfer rate has been increased by enlarging the stagnation zone length. This was attained by reducing the viscosity, surface tension and altering other thermo-physical properties of the coolants. The thermal analysis reveals that the maximum critical heat flux is achieved in case of 240 ppm Cetyltrimethylammonium bromide + water i.e., 1.7 MW/m2, which is 1.39 times higher than pure water. This is attributed to the significant reduction in the surface tension and viscosity. Use of additives like sodium carbonate and surfactant enhance the stagnation zone length. Furthermore, due to foaming nature of the coolant (500 ppm Ethanol + water), the heat transfer rate declines and a critical heat flux of 1.37 MW/m2 is observed. The visual observations are consistent with the results obtained for each coolant. Based on the high heat removal capacity, the low mass flux laminar jet cooling methodology with additives provide better cooling than that of the high-pressure laminar jet and high mass flux spray cooling.

High pressure saturated flow boiling of CO2 at the micro scale

Saturated flow boiling heat transfer of carbon dioxide (CO2) at the microscale was studied with pressures ranging from 2.4 MPa to 6 MPa (i.e., reduced pressure ranging from 0.3 to 0.81, respectively), mass fluxes ranging from 1199 kg/m2s to 2428 kg/m2s, mass qualities up to 0.94, heat fluxes up to 270 W/cm2, and ΔTsat up to 150 K. A maximum heat transfer coefficient (HTC) of about 150 kW/m2K, and a maximum critical heat flux (CHF) of about 200 W/cm2 was recorded. Comparison to established correlations were made and discussed based on a flow map of saturated flow boiling of carbon dioxide by Cheng et al. The map classified the flow into different patterns (i.e., bubbly, annular, dry-out, and mist flows), and provided insight about the observed HTC trends based on the mass quality. The Shah and the Cheng et al. correlations predicted the HTC reasonably well for mass qualities of up to 0.45 with mean average errors of about 23%, but for a mass quality of 0.94, the Kandlikar, the Shah, and the Cheng et al. correlations underpredicted experiments with mean average errors of 80%, 24%, and 98%, respectively. The critical heat flux condition was predicted well with different models, and the Katto et al. correlation provided the lowest mean average error of 23.0%.

Enhancement of pool boiling heat transfer using 3D-printed groove structure

Groove structures were fabricated by selective laser melting (SLM) technique to enhance saturated boiling heat transfer at atmospheric pressure. Prepared groove structures have different groove lengths and heights, and the printing material used is AlSi10Mg. Pool boiling experiments were explored with deionized water as the working fluid, and the heat transfer performance of different groove structures was compared based on smooth surface. It was found that the groove structure can significantly increase the boiling heat transfer coefficient (HTC) and critical heat flux (CHF) compared with the smooth surface. With the increase of groove length, the CHF of the groove structure gradually increases until it reaches the maximum at the groove length of 2.2 mm, which corresponded to the bubble departure diameter. Maximum CHF and HTC improvements were 3.1 times and 2 times, respectively. The HTC and CHF of groove structure decrease with the increase of groove height, which is due to the increase of liquid and vapor flow resistance in the groove. Difference of HTC of samples with the same structure size and different height declines with the increase of groove length. Groove structure facilitates gas-liquid flow and separation, thereby enhancing boiling heat transfer. The semi-melted powder bonding on the surface of the 3D-printed skeleton and the groove structure work together to improve the boiling heat transfer performance.

Critical heat flux enhancement using composite porous structure produced by selective laser melting

• Uniform porous structures (with single pore size) and Composite porous structures（with two different pore sizes) are fabricated by selective laser melting. • Composite porous structure has the best heat transfer performance. • Critical heat flux enhancement of up to 3.2 times is achieved. • Gas-liquid flow characteristics of the composite porous structure is analyzed. Cross scale composite porous structures have been proved to have a better effect on enhanced boiling heat transfer. Accurate control of composite pore size and porous structure thickness is important for the study of enhanced boiling heat transfer. In this study, composite porous structures were manufactured with selective laser melting (SLM) technique from aluminum alloy (AlSi10Mg) powder. The heat transfer characteristics of a composite porous structure with composite pores (0.6 mm small pores and 2 mm large pores) for pool boiling under atmospheric pressure were investigated. A comparative analysis was performed with the uniform porous structure (0.6 mm pores) and the composite porous structure. The results shown that the composite porous structure can significantly increase the critical heat flux (CHF) compared to the plain copper surface. The CHF of the composite porous structure was higher than that of the uniform porous structure with the same height. As the height increases, the nucleate boiling heat transfer performance with composite porous structures will decrease, due to the larger gas–liquid resistance as a result of the height increment. In the range of 1.5–4.5 mm studied in this research, the 1.5 mm high composite porous structure achieves the maximum increase in CHF. The maximum CHF was 346.6 W/cm 2 , which was 3.2 times that of the plain surface. The large pores in the composite porous structure can play a role of shunting to reduce the escape resistance of the bubbles, which can further enhance CHF.

Effect of Nanofluids on the Enhancement of Boiling Heat Transfer: A Review

Boiling heat transfer can play a vital role in the two-phase flow applications. The analysis of the boiling hat transfer enhancement is of importance in such applications and the enhancement can be mostly conducted by using various active and passive techniques. One type of passive techniques is the enhancement of heat transfer by nanofluids. This article presents an extensive review on the effect of different nanofluids on the enhancement of heat transfer coefficient (HTC) and critical heat flux (CHF) for both pool as well as flow boiling. Nanoparticles addition to a working fluid is done arbitrarily to improve the thermophysical properties which in turn improves heat transfer rate. Numerous works have been done in the studies on nanofluid boiling. Among various nanoparticles, the most frequently used nanoparticles are Al2O3 and TiO2. In the case of binary nanoparticles, the most commonly used combination is Al2O3 and TiO2. After reviewing the relevant literatures, it is found that for pool boiling, the maximum HTC is increased to 138% for TiO2 nanoparticles and the maximum CHF is increased to 274.2% for MWCNTs. Conversely, in flow boiling the maximum HTC is increased to 126% for ZnO nanoparticles and the maximum CHF increased to as 100% for GO nanoparticles. In addition, when two or more nanoparticles in succession or binary nanofluids are used the CHF in pool boiling increased up to 100% for Al2O3 and TiO2 as well as the CHF in flow boiling increased up to 100% for Al2O3, ZnO, and Diamond. Though the information of the coefficient of heat transfer and the critical heat flux varied for different nanofluids and vary from experiment to experiment for each of the nanofluids. This variation happens because the coefficient of heat transfer and the critical heat flux in boiling is dependent upon several factors.

CHF enhancement of downward-facing saturated pool boiling on the SCGS-modified surfaces with multi-scale conical pin fin structures

Enhancing the critical heat flux (CHF) of external reactor vessel cooling (ERVC) to achieve the strategy of in-vessel retention (IVR) has been deemed as an essential requirement for the security of modern commercial PWR nuclear power plants. A new type of multi-scale conical pin fin structures had been designed to meet this need. These conical structures of four different axial heights (1.0, 1.5, 2.0 & 2.5mm) and similar radial geometric parameters were fabricated on four heating surfaces of copper substrates by supersonic cold gas spray technique (SCGS), and the conical pin fin structures were combined with a thin layer of micro porous structures. Transient-state (quenching) and steady-state (heating) pool boiling experiments had been respectively conducted on 6 different downward-facing surfaces under different inclination angles including 5°, 30°, 45°, 60°, 75° & 90° (in vertical), which included above-mentioned four pin fin surfaces, a plain surface and a coated surface covered with a 1mm-thick layer of uniform porous coating fabricated by SCGS with copper particles. The experimental results showed that the CHF increased with the inclination angles. The CHF of all the SCGS-modified surfaces were significantly enhanced compared with those of the plain surface. The maximum CHF value and the maximum CHF enhancement belonged to the 2.0mm-height pin fin surface whose CHF values were more than 1.7 times of those of the plain surface, and up to 2.1 times in 90°. The 1.0mm pin fin surface had the greatest performance in boiling heat transfer coefficient (HTC) and its CHF-enhancing performance also greatly exceeded that of 1.0mm uniform porous coating surface. Remarkable performances of multi-scale conical pin fin structures had been experimentally confirmed, hence the safety margin of IVR-ERVC will be greatly enhanced after adopting them. In addition, the CHF enhancement mechanism of the multi-scale conical pin fin structures was analyzed.

Pool boiling enhancement and a method of bubble diameter determination on surfaces with deep minichannels

Pool boiling heat transfer experiments were conducted with ethanol, Novec-649 and FC-72 at atmospheric pressure on surfaces with deep minichannels. The minichannels 5.5, 6.0 and 10 mm deep and 0.5–1.2 mm wide were uniformly spaced with a pitch of 2.0 mm on the base surfaces. Heat transfer coefficients obtained with ethanol were similar for all surfaces tested. Novec-649 and FC-72 produced the highest coefficients at heat fluxes above 100 kW/m2 in 1 mm wide minichannels. All the working fluids provided a significant increase in the maximum (critical) heat flux. The images were recorded using high speed imaging techniques across the entire surface of the samples. Boiling visualization aimed to study vapor bubble diameter changes during the growth period and measure the bubble departure diameter.The bubble diameter at departure was also determined analytically according to force balance static and dynamic variants. The dynamic variant provided a high consistency between the theoretical and experimental data for bubble departure diameter with FC-72 and Novec-649.

Pool Boiling of Water on Surfaces with Open Microchannels

Boiling, as the most efficient type of convective heat transfer, is an area of interest in many fields of industry and science. Many works have focused on improving the heat transfer efficiency of boiling by altering the physical and chemical properties of surfaces by using different technological processes in their fabrication. This paper presents experimental investigations into pool boiling on enhanced surfaces with open microchannels. The material of the fabricated surface was copper. Parallel microchannels made by machining were about 0.2, 0.3, and 0.4 mm wide, 0.2 to 0.5 mm deep, and spaced with a pitch equal to twice the width of the microchannel. The experiments were carried out in water at atmospheric pressure. The experimental results obtained showed an increase in the heat flux and the heat transfer coefficient for surfaces with microchannels. The maximum (critical) heat flux was 2188 kW/m2, and the heat transfer coefficient was 392 kW/m2K. An improvement in the maximum heat flux of more than 245% and 2.5–4.9 times higher heat transfer coefficient was obtained for the heat flux range of 992–2188 kW/m2 compared to the smooth surface. Bubble formation and growth cycle in the microchannel were presented. Two static computational models were proposed to determine the bubble departure diameter.

Phase-change heat transfer of bare surface evaporator with phase-separating wick in downward facing orientation

Liquid-vapor, phase-change heat transfer using wicks can provide reliable and high heat flux cooling capability, especially in microgravity applications. However, the maximum heat removal capacity, also known as Critical Heat Flux (CHF), is related to the capillary-driven liquid supply limit and/or vapor removal limit. A key is to develop a novel wick structure, offering efficient liquid supply as well as vapor removal pathways. In this study, the Bare Surface Evaporator with Phase-Separating Wick (BEPSW) is examined to understand the liquid supply and vapor removal limits in a downward facing orientation for microgravity environment. The BEPSW consists of a bare surface evaporator for the efficient evaporation, and the distributed, sintered-particle post wicks with the phase-separating wick for enhanced liquid supply and vapor removal. The bare surface is fabricated from a copper disk 19.1 mm in diameter, while the post and phase-separating wicks are manufactured using 10 and 3 layers of sintered copper particles, respectively. The heat flux is measured as a function of the surface superheat for different post-post pitch distances (Lp = 2.5, 3.5, 4.5, and 7 mm) and average particle sizes (<dp> = 350 and 550 μm), using distilled water as a working fluid. The results show that the CHF increases as the pitch distance decreases from Lp = 7 to 3.5 mm in both particle sizes due to the increased liquid supply through the post wicks, while it decreases below Lp = 2.5 mm in both particle sizes due to the liquid entrainment limit, i.e., the maximum CHF is observed at Lp = 2.5 to 3.5 mm. The measured maximum CHF and Heat Transfer Coefficient (HTC) with 350 μm particle size is 184 W/cm2 (24.9°C superheat) and 7.7 W/cm2-K (144 W/cm2 heat flux), respectively, and 207 W/cm2 (44.3°C superheat) and 5.4 W/cm2-K (118 W/cm2 heat flux) for the 550 μm particle size, both at Lp = 3.5 mm. The CHF models, both the capillary-viscous and entrainment limits, predict the optimal particle size, showing that it increases with increasing pitch distance of the post wicks at given post wick geometries. This is related to the type of limitation that controls the CHF, i.e., either capillary-viscous limit or the entrainment limit. Also, the results show that the CHF using the 550 μm wick exceeds that of 350 μm at given pitch distance, due to the large liquid permeability.

Effect of material arrangement pattern on different-mode-interacting boiling in narrow gaps with two liquid supply systems

• Effect of different-mode-interacting boiling in narrow gaps on CHF is investigated. • Different material patterns inside plate with material pitch and gap size are investigated. • Performances are compared for cross and parallel arrangements and conventional form. • Effect of open forms of narrow gaps of 4 sides and 2 sides is also investigated. • Cross arrangement pattern shows significant augmentation of CHF in 4-sides-open. Different-mode-interacting boiling has been proven to improve the critical heat flux (CHF) inside narrow gaps in a water pool in previous studies. This method expands the area of the wetted region and delays the occurrence of CHF with the irregular movement of the vapor and liquid near the boundary between two thermally different materials with interaction of different boiling modes on the non-uniform conductance plate. In the present study, while retaining the characteristics of this method, further improvement of heat transfer characteristics was investigated. To increase the density of different material boundaries, a new arrangement of low-conductance material with cross-type geometry was adopted. The performance on a horizontally arranged 20 mm square copper surface was compared with those of parallel arrangement and the conventional form. Furthermore, performance under the open forms of narrow gaps to surrounding liquid of 2 sides and 4 sides were examined with gap size and material pitch as parameters. Significant enhancements in CHF are achieved in cross-type arrangements. The maximum CHF of 1140 kW/m 2 and 946 kW/m 2 with large increases of 83% and 75% were achieved for 4-sides-open and 2-sides-open systems, respectively.

Model-based experimental analysis of enhanced boiling heat transfer by micro-nano porous surfaces

Small bubbles are desirable to be frequently generated and detach from the heated surface in pool boiling. Bubble nucleation and bubble departure can be influenced by the size of micro-nano structure. In this work, four honeycomb micro-nano porous copper surfaces with successively increasing pore sizes are prepared by controlling the electrodeposition current densities. Both experiments on saturated pool boiling of water and numerical simulations are conducted. The heat transfer performance of prepared surfaces is improved significantly and then decreased slightly when the pore size ranges from 48 μm to 128 μm, with maximum critical heat flux and heat transfer coefficient reaching 187.3 W/cm2 and 23.7 W/cm2/K, respectively. Numerical simulations considering three-dimensional (3D) complex geometries of the four samples reconstructed by a computed tomography scanning technique are conducted. Numerical results show that the percentage of heat flowing out of the three-phase contact lines by phase change at high heat-flux supply can increase to 90%, which is consistent with previous literature results. Subject to a parametric 3D transient heat-conduction forward model developed in this work, a multi-layer end-to-end convolutional neural network is for the first time constructed and trained to solve the corresponding ill-posed inverse problems of 3D transient heat conduction efficiently. It provides a promising alternative way to develop a highly efficient temperature-to-heat-flux soft sensor technique for both boiling applications and many other similar engineering problems.

An experimental investigation on heat transfer performance of electrostatic spraying used in machining

Electrostatic spraying is a new generation of green and efficient cooling/lubrication technique in machining. Critical heat flux reflects the heat transfer potential of electrostatic spraying. In this paper, an evaluation device for cooling capacity of electrostatic spraying is developed to study the effects of voltage, target distance, flow rate of nanofluids, and volume fraction of nanoparticles on critical heat flux by transient heat transfer tests. The electrostatic field between the nozzle and the heat transfer surface is simulated to analyze the heat transfer mechanism. The results show that the critical heat flux is greatly affected by the thermophysical properties of nanofluids, the electric field strength, and the deposition of nanoparticles on the heat transfer surface. Under the cone-jet mode, increasing voltage, flow rate of nanofluids, and volume fraction of nanoparticles and reducing target distance can considerably increase critical heat flux. The maximum critical heat flux can be obtained when the voltage, target distance, flow rate of nanofluids, and volume fraction of nanoparticles are taken as − 8.4 kV, 15 mm, 0.63 ml/min, and 0.15%, respectively.

Heat transfer performance and influences of spray cooling under quenching

In this study, a closed-loop spray cooling system using R134a as the working fluid was established. The heat transfer characteristics and influencing mechanism of transient spray cooling were studied. The transient spray cooling curve under quenching was built accurately. The results show that the vapor film suppressed time, tsup, is the main period that the spray cooling must pass through. The flow rate and the sub-cooling of R134a have little effect on the cooling rate but the critical heat flux, which are mainly affected by chamber pressure. The transient Jacob number decreases with the increases of chamber pressure. As Jacob number decreases, the growth of vapor film is inhibited, then the tsup reduces in consequence. The surface temperature drop point and critical heat flux increases with the rise of chamber pressure. The maximum critical heat flux is 70.08 W/cm2 in this experiment.

An experimental investigation on the pool boiling of multi-orientated hierarchical structured surfaces

With the increasing power consumption in the worldwide energy-intensive sectors, a more efficient thermal heat transfer during the boiling process is pressingly needed. The fundamental understanding of the boiling mechanism is essential for the enhanced heat transfer and subsequently the improvement of heat utilization. The present study decouples the contributions of the intrinsic surface wettability from the hierarchical (dual-layer) structure on the boiling enhancement by growing nanograss as the substructure and the micro flowers with different cover density as the superstructure. The structured surfaces show maximum critical heat flux (CHF) enhancement by 68%. While for the multi-orientated (from 0° to 180°) substrates, the surface orientation will influence the boiling performance through different physical mechanisms. It discloses that the departure time and the thickness of the fully developed vapor film of the inclined surfaces increase with increasing surface orientation, resulting in impeded boiling performance of the downward-facing surface. Moreover, enhanced critical heat flux and heat transfer coefficient can be observed for the nanograss surface with the downward-facing orientations. In addition, new correlations regarding the downward-facing CHF prediction based on the horizontal CHF are proposed for the future multi-oriented surface design in advanced heat-transfer applications.

Assessment of nanofluids pool boiling critical heat flux

Despite contradiction in nucleate pool boiling heat transfer coefficient of nanofluids, the enhancement in critical heat flux (CHF) has been widely approved. This study is dedicated to the assessment of pool boiling CHF of the nanofluids. The assessment is based on a new consolidated CHF database consisting of 431 data points amassed from 62 sources, and includes 14 nanoparticle materials and 4 base fluids, pressures from 3 to 1100 kPa, orientation angles from 0 to 150°, and covering a variety of particle concentrations. It is shown that the maximum CHF ratio of nanofluid to base fluid can achieve 4 and 4.6 for upward-facing heater and inclined heater, respectively. The heater type (wire or block) has an important effect on CHF, as the direct electric-heating wire heater causes electrophoresis, accelerating nanoparticle deposition. The CHF ratio is reduced with increasing pressure in the present range, but nanoparticle size has a minor effect on it, which is more determined by the dispersion level of particles in base fluid. Two major mechanisms, including improved wettability and enhanced capillary wicking caused by nanoparticle deposition, are responsible for the enhancement of CHF, latter of which warrants more theoretical studies in the future.

Pool Boiling of NOVEC-649 on Microparticle-Coated and Nanoparticle-Coated Surfaces

In this study, microparticle coatings and nanoparticle coatings were fabricated on copper surfaces by an electrochemical deposition method and an electrophoretic deposition method, respectively. Pool boiling of NOVEC-649 was experimentally studied on the coated surfaces, concerning heat transfer, bubble dynamics, and critical heat fluxes. Compared with a smooth surface, heat transfer coefficients and critical heat flux (CHF) were improved, achieving a maximum heat transfer enhancement of 460% on the nanoparticle-coated surface and a maximum CHF enhancement of 60% on the microparticle-coated surface. Based on high speed visualizations, bubble departure diameters were measured and compared with several correlations, and then the heat transfer was analyzed by a mechanistic model, considering natural convection, transient heat conduction and microlayer evaporation. The mechanistic model demonstrated a good ability to predict the present results. In addition, wickability, representing a liquid supplement ability, was measured, indicating that the wickability enhancement was probably responsible for the CHF improvement.

Ultra-low pressure drop membrane-based heat sink with 1000 W/cm2 cooling capacity and 100% exit vapor quality

This paper presents the most recent progress on advancing the membrane-based heat sink (MHS) science. A model developed to predict the MHS performance suggested that the membrane permeability limited the critical heat flux (CHF). The new generation MHS discussed here benefits from a newly developed membrane with 7 times higher permeability compared to the membrane used in the previous generation MHS. Experimental studies were conducted on a heat sink with a heater surface area of 0.7 × 0.7 cm2. The results confirmed that a higher membrane permeability substantially increases the CHF of surface structures with enhanced wickability and surface area ratio (Ar) at low pressure drops. A maximum CHF of about 1000 W/cm2 was achieved on a surface with Ar = 3.45 at a supplied liquid pressure of only 4 kPa, 2.5 times higher than the CHF reached with the low permeability membrane used in the first generation MHS. The new membrane enhanced the heat transfer coefficient at low supplied liquid pressures but substantially less than the 1.8 MW/m2 K reached at the highest pressure (i.e. 20 kPa). This low pressure drop along with a heat sink exit vapor quality of 100% resulted in an extremely low pumping power. The ratio of CHF versus the theoretical pumping power is 1–2 orders of magnitude higher than that of the other two-phase heat sinks reported in the literature.

Experimental investigation of closed loop spray cooling with micro- and hybrid micro-/nano-engineered surfaces

With the urgent demands of ultra-high heat flux cooling technology, enhancement of spray cooling by surface structure as an effective thermal management method has drawn increasing attention. Combining micro- and nano-structures is a promising way to improve spray cooling but only a few attempts have been made, especially in an application oriented closed loop system. Here, spray cooling heat transfer of flat, rough, micro-structured and hybrid micro-/nano-structured surfaces are experimentally investigated in a closed loop spray cooling system based on R134a refrigeration cycle. The results show that compared with the flat surface, the rough heating surface, micro-structured surfaces and hybrid micro-/nano- engineered structures can increase the critical heat flux (CHF) by 15%, 42% and 59%, and heat transfer coefficient (HTC) of spray cooling system by 14%, 28% and 42%, respectively. The optimum characteristic size of micro structure is 200 μm, which corresponds to the mean droplet diameter. By combining this micro structure with irregular ZnO nanowires, the maximum CHF, HTC and system efficiency are obtained as 180 W/cm2, 30 kW/m2K and 29.4%. The system combines the advantages of high cooling performance of spray cooling and the stable operation of refrigeration cycle. With closed loop experiments, the heat transfer enhancement by micro- and hybrid micro-/nano-structures is validated, and parametric influences as well as corresponding mechanisms are analyzed, which provide insights to guide industrial applications, and facilitate interdisciplinary study between advanced engineering materials and heat transfer to help expanding the frontier of spray cooling.

Co-Axial Laminar Multiphase Jet: A Novel Methodology for the Attainment Enhancement in Transition Boiling Regime

Abstract In the current investigation, by using a very low mass flux co-axial laminar multiphase fluid jet, enhancement in heat transfer rate, uniformity in heat flux distribution, and reduction in coolant consumption rate characteristics are simultaneously tried to achieve in case of cooling from a very high initial temperature (900 °C). The information on quenching technology depicting all the above-mentioned advantages has not been reported in the literature. In the present work, kerosene–water, nanofluid (Al2O3 = 0.15%)–kerosene, and nanofluid (Al2O3 = 0.15%)–polyethylene glycol combinations were used for co-axial cooling experimentation. From the heat transfer analysis, it is observed that nanofluid (Al2O3 = 0.15%) and kerosene combination produces maximum critical heat flux due to the alteration of thermophysical and interfacial properties, which enhance the driving force and flow behavior defining momentum and thermal diffusivities in the favorable direction of heat transfer, respectively. In addition to the above, the comparative study ensures a significant reduction in coolant consumption and augmentation in uniformity in heat flux distribution.

Review of pool boiling critical heat flux (CHF) and heater rod design for CHF experiments in TREAT

Preventing the occurrence of a departure from nucleate boiling (DNB) event is an important aspect of nuclear safety in pressurized water reactors (PWRs). This phenomenon is partially governed by the cladding-to-coolant heat transfer under transient irradiation conditions, such as during a reactivity-initiated accident (RIA). Currently, there are large uncertainties about cladding-to-coolant heat transfer under these rapid transient conditions. This effort aims to elucidate the mechanisms of CHF under in-pile fast transient irradiation conditions using the Transient Reactor Test (TREAT) facility. These experiments will be carried out under pool boiling conditions, within experimental capsules that will be inserted into the TREAT reactor. A heater rodlet made from stainless steel 304 with tailored natural boron content will be usedin these experiment capsules to induce CHF when submitted to a TREAT power pulse. We will investigate the impacts of the presence of an oxide layer, radiation-induced surface activation (RISA), heat transfer time constant, and rapid surface heating effects on the CHF phenomenon.We review the parameters with significant effects governing the predictions of pool boiling CHF. Only CHF influencing parameters that are highly important, among them coolant subcooling and pressure, as well as oxide layer thickness, RISA, and rapid heating effects were included in this literature assessment.Preliminary neutronics and thermal hydraulic results from the design of the experimental apparatus are also presented in this paper. To aid in the modeling approach, the energy deposition and occurrence of CHF were identified as the most crucial key Figures of Merit (FoMs).In the heater rod design, boron concentrations between 0.1 and 2.09 wt% were considered. Further, a self-shielding study was performed to determine whether an instrumented borated tube could be used in place of a solid borated rod. This study determined that the inner region of the rod can be excluded or instrumented without heat generation penalties. Lastly, a thermal-hydraulics sensitivity study determined the lowest limiting boron concentration needed to induce CHF in water with different degrees of subcooling. Additionally, the value of CHF is known to increase during a rapid transient. Therefore, a CHF multiplier sensitivity study determined what multipliers would inhibit CHF for varying degrees of subcooling of two chosen power coupling factors (PCFs). The current borated tube rodlet geometry configuration achieved a maximum CHF multiplier value of 7.8 using a 1400 MJ power pulse in TREAT. Although this was the power pulse with the greatest energy deposition considered for this study, the TREAT facility is capable of pulses up to ~2500 MJ. This provides a significant margin in energy capacity that was not included within the scope of the calculations carried out to date.The application of the heater rod design was successfully demonstrated in initial experiments in December 2019. The results of these experiments will be explored in future publications.