Reynolds Number Values Research Articles

Conjugate heat transfer enhancement over heated blocks using airfoil deflectors

This study focuses on laminar air cooling of multiple blocks mounted in a channel, with airfoils placed above the blocks and used as vortex generators. The unsteady governing equations are solved by the finite volume method using the commercial CFD code Fluent®. The flow and temperature structures are analyzed in the whole channel in both solid and fluid phases for Reynolds numbers ranging from 500 to 1800. The vortex shedding flow generated by the successive airfoils penetrates in the inert-block cavity in addition to the flow directed toward the block face, resulting in significant heat transfer. The increase in Reynolds number leads to the amplification of the heat transfer rate. It is found that the rate of heat transfer improvement achieved exceeds 200% for all Reynolds number values studied.

Hydrogen dispersion phenomenon in nominally closed spaces

The hydrogen dispersion phenomenon in an enclosure depends on the ratio of the gas buoyancy-induced momentum and diffusive motions. Random diffusive motions of individual gas particles become dominative when the release momentum is low, and a uniform hydrogen concentration appears in the enclosure instead of the gas cumulation below the ceiling. The expected hydrogen behavior could be projected by the Froude number, which value ~1 predicts a decline of buoyancy. This paper justifies this hypothesis by demonstrating full-scale experimental results of hydrogen dispersion within a confined space under six different release variations. During the experiments, hydrogen was released into the test room of 60 m3 volume in two methods: through a nozzle and through 21 points evenly distributed on the emission box cover (multi-point release). Each release method was tested with three volume flow rates (3.2 × 10−3 m3/s, 1.6 × 10−3 m3/s, 3.3 × 10−4 m3/s). The tests confirm the decrease of hydrogen buoyancy and its stratification tendencies when the Mach, Reynolds, and Froud number values decrease. Because the hydrogen dispersion phenomenon would impact fire and explosive hazards, the presented experimental results could help fire protection systems be in an enclosure designed, allowing their effectiveness optimization.

Building a MATLAB applicaton for preliminary design and optimization of shell and tube heat exchangers

Designing shell and tube heat exchangers is a complex and time-consuming procedure. Since they are one of the most common process units in process industry, great effort should be made to improve their design and to facilitate the design procedure. Therefore, in this study, an easy-to-use MATLAB application for shell and tube heat exchanger preliminary design and optimization was developed. The application enables users to select operating parameters manually and test their effect on heat transfer area and pressure drop. Moreover, the application helps users to optimize the preliminary design, in terms of finding the minimal heat transfer area required to meet the process requirements. The validity of the application was tested on the example from the literature, where the heat transfer area was 61.91 m2. During the proposed optimization procedure, different parameter values were tested and an optimal combination of parameters was found within 5 seconds (for all combinations), resulting in the heat transfer area of 53.27 m2. The application has a great feature of displaying the impact of baffle cut value and baffle spacing on most important design parameters: heat transfer area, tube-side pressure drops and shell-side pressure drops. Also, new correlations were developed for the calculation of the Colburn heat transfer factor and friction factor as a function of Reynolds number and baffle cut value. Overall, the application has proven to be useful for the preliminary design of shell and tube heat exchangers, and can represent the foundation for the development of advanced heat exchanger design applications.

Experimental implementation of thermal enhancement performance of air heat exchanger’s pipes utilizing unconventional turbulator

Heat exchangers are widely used in industry, however, raising their performance are important for the variety of applications. Consequently, efficiency improvement associated with low production cost is considered in this experimental work. The current study aims to enhance the rate of heat transfer in pipe-type heat exchangers experimentally by using a novel nozzle as a turbulator. The cross-sectional shape of the nozzle is hexagonal, and the diameter ratio DR is equal to 0.5. Constant heat flux was maintained in the vicinity of the section of the test tube, while the working fluid was pumped into the open system at six discrete Reynolds number values ranging from 6000 to 19500. To investigate the effect of distance among the pieces, three turbulators with different numbers were assigned and named as (N=4, 5 and 6). The results indicated an increase of 172 %, 194 % and 216 % of the heat transfer rate for cases 4, 5 and 6 respectively comparing to the benchmark tube. On the other hand, the friction factor values increased remarkably due to the inserting of turbulators by about of 722.9 % for N=4, 823.9 % for N=5 and 886.7 % for N=6 compared to a plain tube case. Moreover, it has been established that with the insertion of 6 pieces two enhancements was observed; heat transfer rate and thermal performance, where, thermal performance of all cases exceeds unity (maximum thermal performance of 1.62 has been obtained by inserting 6 pieces of hexagonal nozzles turbulators). A comparison with another types of vortex generators shows the gap between the turbulator and heated surface offers a solution for problems occurred in the pipes of heat exchanger. The study therefore suggests a wider practical implementation of the turbulators

Comprehensive Fall Velocity Study on Continuous Flow Plungers

Summary The objective of this study is the experimental and theoretical investigation of the fall mechanics of continuous flow plungers. Fall velocity of the two-piece plungers with different sleeve and ball combinations and bypass plungers are examined in both static and dynamic conditions to develop a drag coefficient relationship. The dimensionless analysis conducted included the wall effect, inclination, and the liquid holdup correction of the fall stage. A fall model is developed to estimate fall velocities of the ball, sleeve, and bypass plungers. Sensitivity analysis is performed to reveal influential parameters to the fall velocity of continuous flow plungers. In a static facility, four sleeves with different height, weight, and outer diameter (OD); three balls made with different materials; and a bypass plunger are tested in four different mediums. The wall effect on the settling velocity is defined, and it is used to validate the ball drag coefficient results obtained from the experimental setup. Two-phase flow experiments were conducted by injecting gas into the static liquid column, and the liquid holdup effect on the drag coefficient is observed. Experiments in a dynamic facility are used for liquid holdup and deviation corrections. The fall model is developed to estimate fall velocities of the continuous flow plungers against the flow. Dimensionless parameters obtained in the experiments are combined with multiphase flow simulation to estimate the fall velocity of plungers in the field scale. Reference drag coefficient values of plungers are obtained for respective Reynolds number values. Experimental wall effect, liquid holdup, and inclination corrections are provided. The fall model results for separation time, fall velocity, total fall duration, and maximum flow rate to fall against are estimated for different cases. Sensitivity analysis showed that the drag coefficient, the weight of plungers, pressure, and gas flow rate are the most influential parameters for the fall velocity of the plungers. Furthermore, the fall model revealed that plungers fall slowest at the wellhead conditions for the range of gas flow rates experienced in field conditions. Lower pressure at the wellhead had two opposing effects; namely, reduced gas density, thereby reducing the drag and gas expansion that increased the gas velocity, which in turn increased the drag. Estimating fall velocity of continuous flow plungers is crucial to optimize ball and sleeve separation time, plunger selection, and the gas injection rate for plunger-assisted gas lift (PAGL). The fall model provides maximum flow rate to fall against, which is defined as the upper operational boundary for continuous flow plungers. This study presents a new methodology to predict fall velocity using the drag coefficient vs. Reynolds number relationship, wall effect, liquid holdup, deviation corrections, and incorporating multiphase flow simulation.

Comparative study of mixing behaviors using non-Newtonian fluid flows in passive micromixers

High-performances micromixers are widely used in various industrial applications. Mixing in the laminar regime and at low Reynolds numbers is of major importance in some processes. Implementing the physical phenomenon of chaotic advection to improve the mixing efficiency is a well-established technique, therefore, the secondary flows resulting from this technique are very intense and act at the microscopic level on homogenization. This study aims to compare different configurations of passive micromixers. The four examined micromixers are: Two-Layer Crossing Channels Micromixer (TLCCM), Semicircular Serpentine Micromixer (SCSM-90), Curved micromixer with Grooves (CG), and C-Shape micromixer. All micromixer geometries have the same hydraulic diameter and the equivalent unfolded length. The numerical simulations have been carried out at low Reynolds numbers using the CFD Fluent code to solve the 3D momentum equations, the continuity equation, and the species transport equation. The employed non-Newtonian shear-thinning fluids are the CMC solutions which are modeled by the power-law model with power-law index range from 0.73 to 1 and the generalized Reynolds number varies between 0.1 and 50. The mixing efficiency has been evaluated by calculating the mixing index (MI) based on the standard deviation of the mass fraction in different cross-sections. To examine the obtained results, the mass fraction distributions, the velocity profiles, and the mixing energy cost (MEC) have been presented. The results show that the TLCCM micromixer has a high mixing index which exceeds 0.96 for all the generalized Reynolds number values and the considered power-law index, it also has a lower mixing energy cost compared to other studied micromixers.

A comprehensive parametric investigation of hemispherical cavities on thermal performance and flow-dynamics in the triangular-duct solar-assisted air-heater

The thermal energy available in the form of solar radiation is collected and converted into heat with the help of a solar air heater. The flow and thermal characteristics change significantly with the cross-sectional shape of the flow passage. The effect of hemispherical dimple-cavities that were employed over the heat-collector plate has been analyzed based on the flow and heat characteristics of a triangular solar air heater. A comprehensive investigation of roughness and flow parameters is carried out experimentally, while the flow dynamics over the heat-collector plate are predicted using commercial software (ANSYS). The remarkable results are observed in terms of Nusselt number and friction factor with the use of dimples over the heat-collector plate in the solar air heater. The higher heat transfer is noticed at the training edge in comparison to the leading edge of the dimple. The best augmentation in Nusselt number obtained is of the order of 5.33 that is observed for transverse-pitch ratio, longitudinal-pitch ratio and relative dimple depth values of 11, 11 and 0.039 respectively, at Reynolds number value of 2160. A close fit curve was obtained between the values obtained from the developed correlation and experimental values with a maximum error of 6.61% and 7.03%, respectively.

An Experimental Study on Hydraulic Model of Water Intake Canal at Steam and Gas Power Plants

The performance of the canal water intake used in the Gas and Steam Power Plant (PLTGU) cooling system is carried out by testing the physical model of the water intake canal with a 1:15 scale model. In which, the canal water intake prototype has dimensions of length, L = 33.30 m, width, B = 13.40 m and height, T = 11.67 m, scaling the prototype dimensions to the model dimensions is done by complying with Froude’s law. The purpose of this paper is to determine the flow patterns that occur in the physical model and the minimum elevation allowed based on applicable guidelines [1]. The variables measured in this study were the flow velocity in the canal and also the visual documentation of the flow pattern in the canal including the formation of vortices. Tests were carried out on three variations of tidal elevation, namely HWL, MSL and LWL. The experimental results show that the flow pattern in the channel varies with depth with an average Reynolds Number value = 3.5 × 104. Vortex formation occurs at all elevations where the vortex is formed in the area near the pump. The observations show that the critical elevation of the canal is at H = 0.29 m for the model and H = 4.35 m for the prototype.

Application of fully convolutional neural networks for feature extraction in fluid flow

Accurate extraction of features in fluid flows is of importance due to the presence in many natural and technological systems. Recently, methods based on machine learning have emerged as an alternative to traditional Eulerian-based methods to extract features in fluid flows. One broad category in ML is the convolution operation-based methods. The precision of feature extraction in convolution operation-based methods increases by constraining the measurement box, such as dividing the input data into small patches and using them as input boxes in convolutional neural networks. In this work, we propose a method that transforms each cell of the computational domain into a detection pixel (measurement box) to perform the task of feature extraction at the smallest possible computational level. To demonstrate the performance, we extract the vortical structures in a benchmark two-dimensional lid-driven cavity flow employing a symmetric, fully convolutional network. The number of convolution and deconvolution blocks in the network’s structure is studied to obtain the highest accuracy and yet to avoid the degradation problem. Different parameters, such as the Reynolds number and velocity boundary values, are considered in the complete and clipped cavity cases to create the training and test datasets. The semantic segmentation metrics, including Jaccard and Dice, yield values close to 1 for the test set on complete and clipped cavity cases with varying the Reynolds number or the velocity boundary values.

The Generalized Lévêque Equation and its application to flat tubes without and with passive inserts

Searching for an analogy concept between heat transfer and pressure drop is anything but new, nevertheless it is still the subject of researches as it enables the prediction of heat transfer from pressure drop data, which helps reducing experimental effort for heat transfer measurements. The Generalized Lévêque Equation (GLE) is a widely-used analogy concept, which allows the prediction of heat transfer from pressure drop data, if hydrodynamic boundary layer is developed or still developing. This analogy concept has been successfully applied to flow situations with practical relevance like chevron-type plate heat exchangers, packed beds and in tube bundles, where the boundary layers are forced to reform continuously. In this contribution, the GLE is applied to flat tube flow without and with passive inserts, investigating the impact of passive inserts, which force the boundary layers to reform continuously, on the application of the GLE.This paper presents results of an experimental investigation on pressure drop and heat transfer in flat tubes without and with passive inserts, covering a wide range of Prandtl number (8 < Pr < 60) and Reynolds number values (40 < Re < 3500). These parameter ranges and the passive inserts represent the typical conditions and design used for the liquid side of single-phase flat tube heat exchangers used in the automotive industry. 238 experimental data points for heat transfer coefficients are compared to heat transfer coefficients calculated from pressure drop data with the GLE.The results show that the GLE is not applicable to flat tubes without passive inserts, yet becomes applicable with passive inserts, which are forcing a re-formation of boundary layers in the whole range of investigated Reynolds and Prandtl numbers.

Thermal-hydraulic performance of TiO2-water nanofluids in an offset strip fin heat exchanger

The flow and heat transfer characteristics of the TiO2-water nanofluid assuming as a single-phase in the rectangular offset strip fin structure for different Reynolds number (500-1000) and TiO2 nanoparticle volume concentration values (0-4%) were investigated numerically under 3-D, steady-state, and laminar flow conditions. Simulations were also performed for 1% and 4% nanoparticle volume concentrations of Al2O3-water nanofluid, and the results were compared with those of TiO2-water nanofluid. Results show that when the TiO2-water nanofluid is used, the heat transfer rate, heat transfer coefficient, and Nusselt number increase with increasing both Reynolds number and nanoparticle volume concentration, and parallel to these, both pressure loss, and pumping power increase. Considering the values of the performance evaluation criteria number, it is clear that the use of TiO2-water nanofluid in offset strip fin structure at all Reynolds numbers examined between 1-4% volume concentration values is quite advantageous. It is observed that TiO2-water nanofluid is much superior to Al2O3-water considering the performance evaluation criteria number. When the Reynolds number is 1000 and the volume concentration value of the TiO2 nanoparticle is 4%, the performance evaluation criteria number value is found to be 1.19, that is, there is a 19% increase compared to water. It is considered that the results of this study can be used as important data on the design of automobile radiators, air-conditioning, and defense.

Determination of longitudinal dispersion coefficients of a channel having rigid vegetation

The impact of the rigid flora on longitudinal dispersion was examined in the laboratory channel located at Thapar University Patiala. The total of nine rigid plant density used with a varying diameter of 12, 16, and 20 mm. The total 27 velocities taken and the discharge is calculated using calibrated v-notch. Rhodamine dye is used as a tracer and injected in upstream of flow and collection of a sample every 1 m distance in downstream of the canal. The dispersion coefficient stands influenced by the diameter of the rigid flora. As the diameter of rigid vegetation is increased the dispersion coefficient increases and declines with increases in the density of the flora. In vegetation, the longitudinal scatter is reduced as the vegetation density increases, with a decrease of about 30% to 50% when the density is doubled. In the pollution aspect, the speed of cloud and dispersion play a vital role and as the Reynolds number value is large the speed of cloud is slow and vice-versa. The results of the experiences gained in this study are compared with the empirical relationship of different researchers. Also, the equation is developed for calculating the dispersion coefficient with rigid vegetation in the flow of the channel of varying density and diameter.

Numerical optimization of pulse frequency and heat transfer for a subsonic impinging jet array

Jet impingement technique with pulsed jet arrays has proved to be one of the most efficient heat transfer technologies for cooling applications. Detailed investigations are required to optimize the different parameters to achieve maximum heat transfer. Present study is an effort in this direction by analyzing the heat transfer from a flat heating film of dimension 60 × 60 × 0.1 mm. The chip generates a heat of 30 W which is to be carried away by means of air jets. The nozzle plate at the top generating the air jet has a set of 9 nozzles arranged in a 3x3 inline configuration. Two sides of the flow arrangement are confined and flow is only along one direction. The nozzle diameter is 5 mm and pitch length from center to center X/D and Y/D are 3. The nozzle plate, heating plate gap Z/D is 4. The Reynolds number values are in the range 3500 to 14000. The cross-flow approaches in a direction perpendicular to the jets and mixes with the jet flow. The results obtained predict a dominance of pulsed jets over steady jets, if heat transfer is considered. Among pulsed jets, those with higher amplitudes and lower frequencies showcase better heat transfer and more uniform distribution throughout the heated plate.

Effect of rib arrangements on the flow pattern and heat transfer in internally ribbed rectangular divergent channels

In this article, a numerical investigation is conducted to analyze three-dimensional incompressible Navier-strokes flows through the rectangular divergent square ribbed channels with different Reynolds number value 20,000, 40,000 and 60,000 having five different configurations of square ribs (p/e = 2.5, 3.33, 5, 10, and 20) has been used as roughness element. The commercial finite-volume based CFD code ANSYS FLUENT is used to simulate turbulent airflow through the channels. The RNG k-ε turbulence model is used to solve the transport equations for turbulent flow energy and dissipation rate. Detailed results about average heat transfer and fluid friction in a rectangular divergent square channel are presented and discussed.

NUMERICAL INVESTIGATION OF DEVELOPING LAMINAR FLUID FLOW THROUGH RECTANGULAR ANNULUS DUCT

The laminar fluid flow of water through the annulus duct was investigated numerically by ANSYS fluent version 15.0 with height (2.5, 5, 7.5) cm and constant length (L=60cm). With constant heat flux applied to the outer duct. The heat flux at the range (500,1000,1500,2000) w/m2 and Reynolds number values were ≤ 2300. The problem was 2-D investigated. Results revealed that Nusselt number decrease and the wall temperature increase with the increase of heat flux. Also, the average Nusselt number increase as Re increases. And as the height of the annulus increase, the values of the temperature and the local and average Nusselt number increase.

Numerical Investigation of Heat Transfer Rate in Helically Coiled Pipe Using Al2O3/Water Nanofluid

Nanofluid materials play an important role in the industry nowadays, which has drawn the attention of researchers to enhance the characteristics of the heat transfer of the fluids in the coiled shape heat exchangers. The effect of using Al2O3/water Nano fluid on the characteristic of the heat transfer rate inside the helically coiled pipe was numerically studied at different Reynolds numbers. Moreover, fluid flow analyses were investigated numerically in terms of pressure and velocity profile. The heat transfer enhancement using this Nano fluid has been studied and then compared to pure water at Reynolds number values of 200, 600, and 1500 respectively. The results showed that a reduction in the temperature of the outer wall pipe when Al2O3/water Nano fluid was applied particularly at a low Reynolds number compared to pure water. Generally speaking, it has been seen that the reduction in the temperature profile is much better than the high Reynolds number.

Analysis of boundary layer flow over a broad rotating cone in still fluid with non-stationary modes

This study focuses on analyzing the effects of traveling modes on the boundary layer flow over a rotating cone in a still fluid system. Non-stationary modes are known to manifest in the boundary layer of rotating cones with highly polished, very smooth surfaces. In this paper, only the broad rotating cone (defined as a cone with the half angle ψ ≥ 40°) system is considered. An asymptotic analytical method is used to solve the governing equations and output the waveangle and wavenumber of the system. This is then compared to a numerical formulation that uses a Chebyshev spectral method. The resulting solutions show that increasing the wave frequency destabilizes the system with a much stronger destabilization for the viscous wall type II modes than the inviscid cross-flow type I modes, where the type I mode is the dominant mode seen in experiments. This result suggests that a slower frequency wave should be selected in order to increase the stability of the system. It was also observed that the negative frequency values have a minimum of the critical Reynolds number values for each cone half angle. It also shows that there is a comparison limit for high frequency positive values. After this, an energy balance analysis is conducted to see the effect on the total mechanical energy transferred between the basic flow and the perturbation quantities. This showed that as the frequency of the traveling modes increases, the energy transferred decreases.

Non intrusive method for parametric model order reduction using a bi-calibrated interpolation on the Grassmann manifold

Approximating solutions of non-linear parametrized physical problems by interpolation presents a major challenge in terms of accuracy. In fact, pointwise interpolation of such solutions is rarely efficient and generally leads to incorrect predictions. To overcome this issue, instead of interpolating solutions directly by a straightforward approach, reduced order models (ROMs) can be efficiently used. To this end, the ITSGM (Interpolation On a Tangent Space of the Grassmann Manifold) is an efficient technique used to interpolate parameterized POD (Proper Orthogonal Decomposition) bases. The temporal dynamics is afterwards determined by the Galerkin projection of the predicted basis onto the high fidelity model. However, such interpolated ROMs based on ITSGM/Galerkin are intrusive, given the fact that their construction requires access to the equations of the underlying high fidelity model. In the present paper a non-intrusive approach (Galerkin free) for the construction of reduced order models is proposed. This method, referred to as Bi-CITSGM (Bi-Calibrated ITSGM) consists of two major steps. First, the untrained spatial and temporal bases are predicted by the ITSGM method and the POD eigenvalues by spline cubic. Then, two orthogonal matrices, determined as analytical solutions of two optimization problems, are introduced in order to calibrate the interpolated bases with their corresponding eigenvalues. Results on the flow problem past a circular cylinder where the parameter of interpolation is the Reynolds number, show that for new untrained Reynolds number values, the developed approach produces sufficiently accurate solutions in a real-computational time.

Propagation, deposition, and suspension characteristics of constant-volume particle-driven gravity currents

In this laboratory study, propagation behaviour, particle deposition patterns, and suspension characteristics of non-cohesive particle-driven gravity currents formed under constant-volume release conditions were investigated. The experimental gravity currents were created in a two-dimensional lock exchange type tank using two different particles (silicon carbide and glass beads) with four different median diameters. Video imaging and image processing techniques were utilized to monitor the current propagation, laser diffraction size analysis and dry weighing techniques were utilized to examine the size and mass characteristics of the deposits and suspensions, and acoustic Doppler velocimetry was utilized for flow velocity measurements for turbulence analysis. Our observations showed that the experimental gravity currents experienced two different propagation phases based upon the particle settling regimes. The first propagation phase was named as the propagation with the turbulence-dominated settling (TDS) and the later propagation phase was named as the propagation with gravity-dominated settling (GDS). It is found that a critical turbulent Reynolds number value (estimated to be O(1)) delineates the settling regimes, hence determines the transition between the propagation phases. With increasing particle settling velocity, the observed propagation phases in our experimental currents showed increasing deviations from the slumping, inertia-buoyancy, and viscous–buoyancy propagation phases that have been reported for homogeneous constant-volume gravity currents with no or negligible settling in the literature. Propagation observations showed that the initial median particle diameters of the currents have negligible effect on the current propagation characteristics during the TDS phase, but become important during the GDS phase. The currents with smaller initial median particle diameters propagated faster and a longer distance in the GDS phase than their counterparts with larger median particle diameters. The deposited particle characteristics indicated that particles of different sizes settle at similar speeds during the TDS phase due to turbulent mixing and the settling speed becomes dependent on the particle size during the GDS phase. As a result, size sorting of the deposited particles became more pronounced during the GDS phase. At the earlier stages of propagation, the vertical profiles of suspended particle concentrations in the current head showed some extent of vertical uniformity due to turbulent mixing around the half height of the current head. On the other hand, at the later stages of propagation, suspended particle concentration profiles exhibited an exponential profile. Deposited and suspended particle characteristics showed that horizontal particle sorting, that is size grading of particles in the flow direction, was more pronounced than the vertical particle sorting, that is size grading of particles at different elevations within the current head.

Single-phase natural circulation in a rectangular loop with a finite capacity heat sink positioned below the heater section

One of the passive safety systems employed in nuclear reactors is a large water pool positioned at an elevation, which acts as a heat sink to remove decay heat from the reactor core in the event of an accident using the natural circulation phenomena. A large mass of water at an elevated position has concerns regarding the safety of support structure, and therefore an alternative methodology where the heat sink is positioned just below the heater section is investigated in this study. Results of an experimental and numerical investigation for the thermal-hydraulic behavior of single-phase natural circulation in a rectangular loop of height 4300 mm and width 1900 mm with the heat sink located at an elevation just below the heater section is reported here. The heat sink was a finite one, a constant volume insulated tank filled with water, whereas the heat source was a constant heat flux type. The loop was constructed with circular pipe elements with a nominal inner diameter equal to 40 mm. The heater section was 1m in height and three input power values equal to 1.15 kW, 1.55 kW, and 2 kW were used in the study. The flow behavior in a single and twin parallel heater system with a single riser was studied. The loop fluid is initially in a single-phase and becomes two-phase as the heat sink temperature rises, but only the results for the loop fluid in the single-phase regime are presented in the current study. The measured mass flow rate, after an initial transient, settles down to values which slowly decreases with time. The average temperature of the heat sink is shown to rise continuously with increasing time, demonstrating the effectiveness of the heat sink in removing the energy input to the working fluid in the heater section. However, the heat sink removes only 60–70% of the input heat while the rest is either lost to the ambient or utilized to raise the enthalpy of the working fluid.The Nusselt numbers in the heater section are also presented which steadily rise after an initial transient. In addition, the values are much higher than those for the corresponding Reynolds number values in forced convection due to the influence of buoyancy-induced convection. The Nusselt number is well correlated by the expression Nu‾=1.35(Ra*‾)0.3 for 2×105≤Ra*‾≤6.5×105and 600≤Re≤1000. Numerical predictions for loop flow rate, temperature variation, and sink temperature using the RELAP5/MOD3.2 code for the experimental configuration of the current study are presented which compare well with the measurements the maximum deviation being less than 10%. Numerical results for pressurizing the working fluid and permitting boiling in the heat sink to drive the system towards steady-state operation are also presented.