Mean Heat Transfer Coefficient Research Articles

Heat transfer characteristics of horizontal flow boiling with uniform and non-uniform circumferential heat flux

This study assesses effects of the non-uniform circumferential heat flux on horizontal flow boiling of R141b in a stainless-steel tube at ambient system pressure with an inner diameter of 10.92 mm. The main motivation for this are application in Concentrated Solar Power using the Direct Steam Generation process inside horizontal absorber tubes. Experiments were conducted for two mass velocities (50 and 150 kg m−2s−1) and two mean heat fluxes (3.4 and 11.0 kW m−2), with three different heating conditions (uniform, top-concentrated, and bottom-concentrated). The differences in the Onset of Nucleate Boiling between uniform and bottom-concentrated heating are assessed, and the transient behavior of the wall temperatures is investigated. It is found that the heating condition significantly affects the mean heat transfer coefficient in the case of non-annular flow regimes but practically not in annular flow. The circumferential wall temperature gradient is with uniform heating highest for non-annular flow regimes. But with non-uniform heating the circumferential wall temperature gradient is highest for annular flow. The use of empirical correlations for the heat transfer coefficients are evaluated.

Analysis of the effect of the number of injector nozzles on the pressure and heat transfer coefficient in a hydrogen-diesel mixture diesel engine

In reciprocating internal combustion engines, the calculation of the heat transfer coefficient (HTC) is essential to estimate the heat transfer during combustion in the combustion chamber. The HTC calculation takes into account fluid flow and combustion processes and varies as a function of crank angle and location within the chamber. The mean HTC value is commonly used to calculate the thermo-mechanical analysis of various combustion chamber components. In this study, dynamic grids for the intake port, exhaust port and chamber are created in the chamber modelling section of the AVL-Fire software. The intake and combustion processes are then simulated and the calculated pressure data are compared with experimental data at 2800 rpm with 1, 3 and 6 hole injectors. Finally, the distribution of HTC over the chamber walls was evaluated using a time step method. The research also included verification of the HTC results with theoretical data obtained by Woschni and Hohenberg. In addition, with the decreasing availability of fossil fuels and the need for lower exhaust emissions from diesel engines, the use of blends of diesel and hydrogen fuel has become widespread. In this engine, a mixture of 10 % hydrogen and 90 % diesel fuel is used. The final results show that the heat transfer coefficient increases by approximately 1.72 % when hydrogen is added to diesel fuel due to the number of collisions between hydrogen and other fuel components.

Experimental Heat Transfer Coefficients for Zeotropic Mixture Condensation of Hexamethyldisiloxane/Octamethyltrisiloxane and Ethanol/Hexamethyldisiloxane

AbstractLegal requirements for refrigerants necessitate a continuous development of these fluids, also focusing on mixtures. This article contributes three aspects to the ongoing research: (1) Experimental mean heat transfer coefficients were determined for the condensation of two novel zeotropic mixtures, hexamethyldisiloxane (MM)/octamethyltrisiloxane and ethanol/MM, gathered for filmwise condensation on a vertical tube. (2) Both mixtures were investigated with several compositions to provide a comprehensive understanding of the mixture effects. (3) The results were taken to develop a novel superposition approach to predict mixture condensation.

Study of the flow characteristics and augmentation of heat performance in a horizontal tube with and without spring inserts

In this project, heat transfer and thermal performance factor characteristics in a tube fitted with coil wire and twisted tape inserts, using air as working fluid are investigated experimentally. Enhancement forced convection heat transfer characteristics is studying for air Reynolds number range from 10.328×103 to 11.769×103 and 10.927×103 to 12.029×103 in the tube without and with coil wire inserts. Effects of various hydrostatics parameters on the heat transfer are considered in this work with heat flux are constant conditions of 600 W/m² and 800 W/m² with using the coil wire and twisted tapes with three ratios (y/w = 3, 4 and 5). The test section is a horizontal annular passage with outer diameter 10 cm. The results indicated that the enhancement of heat transfer coefficient factors in tube with coil wire inserts provide local heat transfer coefficient percentages of (5.1% to 7.8%) for heat fluxes (600) W/m² and (800) W/m² respectively. While tube with swirl inserts provide local heat transfer coefficient percentages of (3.6% to 6.1%) for heat fluxes (600) W/m² and (800) W/m² respectively. The obtained results show that mean Nusselt number and heat transfer coefficient in the tube with twisted tape and coil wire increase with decreasing twisted ratio (y/w). It is also observed that the percentage of heat transfer coefficient for the coil wire when compared with that of swirl inserts tube were ranged between (10.6%) to (16.5%) and (11.5%) to (17.3%) for the heat flux (600) W/m².

Heat transfer enhancement of supercritical carbon dioxide in eccentrical helical tubes

A type of eccentrical helical tube (EHT) was proposed for more efficient and compact supercritical carbon dioxide (SCO2) heat exchangers in refrigeration systems. The forced convective heat transfer of SCO2 flowing in three designed eccentrical helical tubes with pitches of 25, 50 mm and eccentricities of 0.9, 1.5 mm was simulated by using the three-dimensional steady Reynolds-averaged Navier-Stokes equations, shear stress transport turbulence model and energy equation in ANSYS CFX 2019 R2 at mass fluxes of 200, 400 kg/m2s, inlet pressures of 8, 9 MPa, outwards wall heat fluxes of 12, 24 kW/m2. The flow and heat transfer models were validated in the plain tube with experimental mean heat transfer coefficient and empirical Darcy friction factor. Influences of pitch, eccentricity and operational conditions on heat transfer enhancement were identified. Flow pattern, heat transfer mechanism and vortex kinematics were clarified. Heat transfer enhancement of SCO2 in the EHT was compared with water and air in the EHT, twisted elliptical tube and conical tube, respectively. A pitch of 25 mm and eccentricity of 1.5 mm at 6 mm tube diameter can achieve a better thermal-hydraulic performance. A higher SCO2 mass flux raises Nusselt number and reduces friction factor, a higher inlet pressure and a larger wall heat flux reduces Nusselt number but increases friction factor. The ratio f/f0 is ranged in 2.52–1.68 and drops off with increasing inlet pressure and nominal Reynolds number, the ratios Nu/Nu0, ψ and η curves show a concave shape near the pseudocritical point ranged in 1.68–1.06 and 1.06–1.55, 1.23–0.83 and 0.83–1.30, 0.67–0.50 and 0.50–0.92 at the pitch of 25 mm and eccentricity of 1.5 mm, inlet pressure of 8 MPa, mass flux of 400 kg/m2s, and wall heat flux of 12 kW/m2. A helical flow pattern with a core flow occurs in the EHT, the local heat transfer coefficient can be correlated to absolute helicity. The high-wall shear stress on the ridge of the EHT is responsible for the heat transfer enhancement. The f/f0 value of the EHT is in between the twisted elliptical tube and the conical tube, but the Nu/Nu0 and ψ values are comparable.

Experimental Investigation of Local Heat Transfer Coefficient in a Plate Heat Exchanger Using a Thin Heat Transfer Surface

Abstract This paper presents an experimental investigation of local heat transfer characteristics of single-phase flow in a plate heat exchanger (PHE). The local heat transfer coefficient is evaluated using a test section with PHE geometry for measuring wall temperature distribution. The test section of 1.5 mm thickness is employed to consider the heat conduction effect of the heat transfer plate. The results indicated that the local heat transfer coefficient is influenced by the development of the thermal boundary layer along the flow direction and the maldistribution of water flows along both the direction perpendicular to the flow and the stacking direction. The harmonic mean heat transfer coefficient calculated by the measured local heat transfer coefficient agrees with the average heat transfer coefficient evaluated by the modified Wilson plot method within ±25% and within ±16% for the hot side and the cold side, respectively.

Validation and Application of a Finned Tube Heat Exchanger Model for Rack-Level Cooling

Abstract A thermosyphon-based modular cooling approach offers an energy efficient cooling solution with an increased potential for waste heat recovery. Central to the cooling system is an air-refrigerant finned tube heat exchanger (HX), where air is cooled by evaporating refrigerant. This work builds on a previously published two-dimensional (2D) model for the finned-tube HX by updating and validating the model using in-house experimental data collected from the proposed system using R1233zd(E) as the working fluid. The results show that key system variables such as refrigerant outlet quality, air and refrigerant outlet temperatures, and exchanger duty agree within 20% of their experimental counterparts. The validated model is then used to predict the mean heat transfer coefficient on the refrigerant side for each tube in the direction of airflow, indicating a maximum heat transfer coefficient of nearly 1200 W/(m2 K) for a HX duty of 5.3 kW among the tested cases. The validated model therefore enables accurate predictions of HX performance and provides insights into improving the heat exchange efficiency and the corresponding system performance.

Thermal performance investigation of metal foam heat exchanger for micro-gas turbine

This study presents the experimental monitoring of heat transfer performance of metal foams in transient state. Micro gas turbines require a compact recuperator with high effectiveness to achieve higher thermal efficiency. Porous media such as metal and ceramic foams are characterised by high surface-to-volume ratio. They are known to increase heat transfer and potentially can be incorporated in recuperators. Their structure is ideal for thermal management of compact and lightweight applications. The idea is to combine excellent thermal properties of metal foams with turbine gases heat fluxes exploitation, in order to elevate the temperature of a different working fluid such as water or compressed air before it enters the combustor. A novel facility was designed and developed for monitoring heat transfer mechanisms that occur in metal foams. A copper cylinder is filled with metal foam which is heated in transient state by a sudden switch from cold to hot water flow whereas a cold stream cools the device in a crossflow configuration. The study demonstrates a method based on computerisation of true-colour analysis of digital images for surface temperature visualisation using thermochromic liquid crystals (TLC). Results of temperature as well as local and mean heat transfer coefficient were obtained showing that the hot flow inside the foam was more dominant in heat transfer than the cold flow in the empty channel. The method is promising for the evaluation of transient phenomena in a tube that is filled with porous media.

Heat transfer investigation on under-expanded supersonic impinging jets

In this study, wall-resolved large-eddy simulations are performed to investigate the underpinning physics of impingement heat transfer in under-expanded supersonic impinging jets. The jet is generated with an infinite-lipped nozzle of diameter D, has a nozzle-to-wall distance of 5D, a nozzle pressure ratio (NPR) of 3.4 and a Reynolds number of 6×104 based on the ideally-expanded jet velocity. Two thermal boundary conditions of a heated isothermal wall and an adiabatic wall for the impingement plate are considered.Both impinging jets in the current study feature a strong stand-off shock, which oscillates periodically in front of the impingement plate at two dominant frequencies. These oscillations result in two local peaks of the mean heat transfer coefficients with the first peak located in the stagnation region but shifted away from the stagnation point (i.e. jet axis), whilst the second peak is located in the wall jet region. The instantaneous fields of pressure, vorticity and Nusselt number are first discussed to study qualitatively the connection between these two peaks of the mean heat transfer coefficient and the near-wall flow structures. The characteristics of these two peaks are then analysed using the near-wall statistics and spectra of the pressure, axial velocity and Nusselt number distribution.It is found that the first peak of the Nusselt number forms as a consequence of the jet impingement of the non-periodic turbulent structures, whilst the second peak is linked to the reattachment of the recirculation bubble in the wall jet. It is shown that the unsteady separation and reattachment processes are strongly related to the oscillatory motion of the stand-off shock at the dominant frequencies. Last but not the least, the first local minimum close to the stagnation point is also found to be associated with the strong oscillatory behaviour of the stand-off shock.

Performance analysis and drying kinetics of beetroot slices dried in an innovative solar dryer without and with thermal storage unit

ABSTRACT An active indirect solar dryer (AISD) has been used to conduct drying experiments of beetroot slices without a thermal storage unit (TSU) (mode-I) and with TSU (mode-II) using paraffin wax as a phase change material. The performance analysis and drying curves of beetroot slices were assessed in both modes and compared. The average drying efficiency and drying rate were enhanced by 48.63% and 41.72% in mode-II compared to mode-I. Two-term exponential and modified Page models were the best models for beetroot slices in mode-I and mode-II, respectively. The specific energy consumption was estimated to be 1.706 and 0.96 kWh/kg, the average moisture diffusivity was 7.11 × 10−9 and 7.22 × 10−9 m2/s, and the mean mass transfer coefficients were 3.56 × 10−3 and 3.64 × 10−3 m/s, respectively. The specific moisture extraction rate was 0.586 and 1.041 kg/kWh and the mean heat transfer coefficient was 4.103 and 4.2 W/m2K, in mode-I and mode-II, respectively. The collector outlet temperature is increased by 2.5 to 10.7°C when the heat is discharged from TSU. In comparison to mode-I, the performance of AISD is superior in mode-II, exhibiting better drying performance due to TSU in the drying section in mode-II.

Numerical study on conjugate heat transfer in a liquid-metal-cooled pipe based on a four-equation turbulent heat transfer model

Conjugate heat transfer between liquid metal and solid is a common phenomenon in a liquid-metal-cooled fast reactor's fuel assembly and heat exchanger, dramatically affecting the reactor’s safety and economy. Therefore, comprehensively studying the sophisticated conjugate heat transfer in a liquid-metal-cooled fast reactor is profound. However, it has been evidenced that the traditional Simple Gradient Diffusion Hypothesis (SGDH), assuming a constant turbulent Prandtl number (Prt, usually 0.85 - 1.0), is inappropriate in the Computational Fluid Dynamics (CFD) simulations of liquid metal. In recent decades, numerous studies have been performed on the four-equation model, which is expected to improve the precision of liquid metal’s CFD simulations but has not been introduced into the conjugate heat transfer calculation between liquid metal and solid. Consequently, a four-equation model, consisting of the Abe k−ε turbulence model and the Manservisi kθ−εθ heat transfer model, is applied to study the conjugate heat transfer concerning liquid metal in the present work. To verify the numerical validity of the four-equation model used in the conjugate heat transfer simulations, we reproduce Johnson’s experiments of the liquid lead-bismuth-cooled turbulent pipe flow using the four-equation model and the traditional SGDH model. The simulation results obtained with different models are compared with the available experimental data, revealing that the relative errors of the local Nusselt number and mean heat transfer coefficient obtained with the four-equation model are considerably reduced compared with the SGDH model. Then, the thermal-hydraulic characteristics of liquid metal turbulent pipe flow obtained with the four-equation model are analyzed. Moreover, the impact of the turbulence model used in the four-equation model on overall simulation performance is investigated. At last, the effectiveness of the four-equation model in the CFD simulations of liquid sodium conjugate heat transfer is assessed. This paper mainly proves that it is feasible to use the four-equation model in the study of liquid metal conjugate heat transfer and provides a reference for the research of conjugate heat transfer in a liquid-metal-cooled fast reactor.

An experimental study integrated with prediction using deep learning method for active/passive cooling of a modified heat sink

In this paper, the effects of various cooling methods for electronic chipsets integrated with a deep learning algorithm are studied. For this purpose, the separated and simultaneous impacts of active/passive cooling methods on the thermal management of a modified heat sink are experimentally investigated. As active methods, two modules of circulating liquid flow and fan are employed. For the circulating liquid flow, distilled water and multiwalled carbon nanotubes (MWCNT) nanofluid, with flow rates in the range of 50–150 ml/min, pass through the heat sink which is attached to a printed circuit board (PCB) where heat fluxes in the range of 20000–40000 W/m2 are generated. For the fan, two modes of 4.5 and 9 W are applied in order to generate air forced convection. Regarding the passive methods, a phase change material (PCM) and nano-phase change material (NPCM) are integrated with the heat sink; paraffin is used as a PCM while MWCNT is added into paraffin to prepare NPCMs with mass fractions of 0.5 % and 1 %. The results show that employing a combination of MWCNT nanofluid flow, air forced convection, and NPCM with 0.5 % mass fraction leads to the best thermal performance where the PCB maximum temperatures of 29.9, 34.4, and 39.4 °C are measured under heat fluxes of 20000, 30000, and 40000 W/m2, respectively. Applying a hybrid configuration where all active and passive cooling methods are utilized, may enhance the mean heat transfer coefficient by a substantial amount (e.g., 42.7 % for 20000 W/m2) compared to the case where only circulating water flow is used. This observation demonstrates the high potential of hybrid methods for the purpose of cooling electronic chipsets. Next, to predict the temperature of the PCB during the operation under different working conditions, various deep learning algorithms are considered. These algorithms include reinforcement learning-group method of data handling (RL-GMDH), multi-layer perceptron (MLP), radial basis function (RBF), support vector regression with the linear kernel (SVRL), and Gaussian kernel (SVRG). The RL-GMDH algorithm is found to result in the best prediction for the PCB temperature (up to 30 s during the operation) which agree well with those of the experiments for various intermittent/continuous operation loads. The predictions of this learning algorithm can open a new approach for the controlling systems to prevent overheating of the electronic chipsets.

Investigations of Performance of Mini-Channel Condensers and Evaporators for Propane

This paper provides the results of experimental investigations of the exemplary mini-channel heat exchanger in its application as a condenser and an evaporator in a compressor refrigeration system with propane as a working fluid. The aim of the investigations was to identify the mean heat transfer coefficient of the refrigerant side for the entire operating range of the tested heat exchanger. The experiments covered a mass velocity range from 50 to 160 kg/(m2 × s). The experiments covered a range of liquid subcooling in the condenser from 3 to 15 K and a range of vapour superheating at the outlet of the evaporator from 3 up to 15 K. The experiments on the condenser were conducted at the saturation temperature of 34 °C, and in the case of the evaporator, at the saturation temperature of 8 °C. The average heat transfer coefficients as well as pressure drops in the case of the operation of the tested heat exchanger as an evaporator and condenser were calculated. The heat transfer coefficient was calculated by means of the separated thermal resistance method with the application of the Wilson plot technique. The experiments confirmed the increase in the heat transfer coefficient with the increase in the refrigerant mass flow rate for the tested mini-channel heat exchanger. A dimensionless correlation was proposed for the pressure drop based on the modified Müller-Steinhagen correlation in the case of the operation of the mini-channel heat exchanger as a condenser and as an evaporator.

Heat transfer enhancement of water-cooled triply periodic minimal surface heat exchangers

Whether triply periodic minimal surface (TPMS) heat exchangers are applicable to cooling or cold storage systems as a cooler for supercritical carbon dioxide (SCO2) is undocumented. Here the conjugated heat transfer of SCO2 in TPMS Schoen-G heat exchanger and printed circuit heat exchanger (PCHE) was predicted based on three-dimensional steady turbulent Reynolds-averaged Navier-Stokes equations, energy equation and shear stress transport model using computational fluid dynamics software ANSYS CFX when SCO2 inlet temperature and pressure vary in 65–30 ℃ and (8–9)MPa. SCO2 in two heat exchangers is cooled under counter-flow conditions by a stream of cold water with given inlet temperature and mass flow rate. It was shown that the mean heat transfer coefficient of SCO2 in TPMS Schoen-G heat exchanger is larger than PCHE. As the inlet pressure rises, the friction factor increases and Nusselt number decreases in the heat exchangers due to decreased Reynolds number and Prandtl number, respectively. The friction factor ratio, Nusselt number ratio and performance evaluation criterion vary in the range of 0.38–0.50, 1.07–1.49, and 1.45–2.04 with Reynolds number and inlet temperature when the PCHE serves as a reference heat exchanger. The streamlines in TPMS Schoen-G heat exchanger are quite smooth even though the areas with a higher velocity appear. The streamlines in PCHE exhibit a spiral flow pattern to result in extra hydraulic loss. The heat transfer enhancement of TPMS Schoen-G heat exchanger is much better TPMS Schwarz-D heat exchanger at a Reynolds number higher than 16,000. The enhancement is attributed to a larger heat transfer surface area and more topological tortuosity without flow separation than PCHE.

Friction and Heat Transfer in Membrane Distillation Channels: An Experimental Study on Conventional and Novel Spacers.

The results of an experimental investigation on pressure drop and heat transfer in spacer-filled plane channels, which are representative of Membrane Distillation units, are presented and discussed. Local and mean heat transfer coefficients were obtained by using Thermochromic Liquid Crystals and Digital Image Processing. The performances of a novel spacer geometry, consisting of spheres that are connected by cylindrical rods, and are hereafter named spheres spacers, were compared with those of more conventional woven and overlapped spacers at equal values of the Reynolds number Re (in the range ~150 to ~2500), the pitch-to-channel height ratio, the flow attack angle and the thermal boundary conditions (two-side heat transfer). For any flow rate, the novel spacer geometry provided the least friction coefficient and a mean Nusselt number intermediate between those of the overlapped and the woven spacers. For any pressure drop and for any pumping power, the novel spacer provided the highest mean Nusselt number over the whole Reynolds number range that was investigated. The influence of buoyancy was also assessed for the case of the horizontal channels. Under the experimental conditions (channel height H ≈ 1 cm, ΔT ≈ 10 °C), it was found to be large in empty (spacer-less) channels that were up to Re ≈ 1200 (corresponding to a Richardson number Ri of ~0.1), but it was much smaller and limited to the range Re < ~500 (Ri < ~0.5) in the spacer-filled channels.

Numerical investigation of forced convection heat transfer from a sphere at low Prandtl numbers

Direct numerical simulations of the flow and forced convective heat transfer around a sphere at Reynolds numbers between Re=500 and Re=1000 are performed. We investigate the effects of the Prandtl number (Pr) on the forced convective heat transfer from a sphere for various fluids having Pr=0.01,0.1,0.7. At the larger Prandtl number, the convective transport due to the vortex shedding process dominates over the diffusive transport. As the Prandtl number decreases, diffusive effects become important. Moreover, the thermal boundary layer increases with decrements of the Prandtl number, which results in a reduction in the local and mean non-dimensional heat transfer coefficient. It is seen that at Re=500 and Re=750, the vortex shedding process is asymmetric, which results not only in a non-zero lift coefficient, but in an asymmetric temperature field in the wake of the sphere at Pr≥0.1. The dual asymmetry in the flow and the convective heat transfer is smooth out when the Prandtl number reaches Pr=0.01 as the heat diffusion dominates and asymmetries in the vortex formation zone are no longer relevant in the heat transport. The descend in Prandtl number also produces an attenuation of the temperature fluctuations and thereby, in the turbulent heat transfer. As a direct consequence, two factors emerge at Pr=0.01: (1) a lower decay ratio of the temperature in the wake centreline, and (2) a larger wake spread compared to higher Prandtl numbers.

Experimental investigation of two-side heat transfer in spacer-filled channels representative of membrane distillation

Heat transfer in spacer-filled plane channels was investigated by using thermochromic liquid crystals and digital image processing. A novel test section allowed the establishment of two-side cooling, closely representative of the conditions existing in real plane or spiral-wound membrane distillation (MD) modules. Several spacer configurations were investigated, differing in design (overlapped or woven filaments), pitch-to-height ratio and orientation with respect to the main flow direction. The Reynolds number Re ranged from 160 to 2500, as is typical in MD. At all flow rates investigated, symmetric two-side cooling provided significantly higher (25–35%) local and mean heat transfer coefficients hh than one-side cooling. The mean heat transfer coefficient increased when the pitch-to-height ratio increased from 2 to 4, and was much higher for woven than for overlapped spacers. Overlapped spacers with a flow attack angle ϕ of 0°-90° with respect to the two layers of spacer filaments exhibited significantly different distributions and mean values of hh on the two sides, the larger values occurring where the flow was orthogonal to the filaments. In all cases, the dependence of hh on Re could not be described by a simple power law.

Flow distribution and cooling performance of needle-to-ring ionic wind blowers with multiple electrodes

Electronics have an increased thermal flow density due to the development of miniaturization and high integration. Effective heat management is a pressing technological issue that must be addressed. Ionic wind cooling technology is gaining popularity as a means of improving local heat dissipation. Ionic wind blowers with two non-uniform ‘needles-to-ring' subunits in series were proposed in the present work. The dynamic evolution process and flow distribution characteristics of the ionic wind for different combined structures were investigated. The operation and maintenance characteristics were optimized to increase ionic wind strength. Experiments are performed to explore the variability of system temperature and mean heat transfer coefficient when the combined ionic wind blowers are employed to improve cooling performance. The results reveal that by employing an additional collecting electrode, charged particles may be accelerated twice, increasing the ionic wind intensity. The dual-stage ionic wind blower with D1=32 mm and D2=22 mm has a greater mean velocity and a wider flow dispersion than the others. There will be apparent backflow near the ring electrode during the early stages of ionic wind production, but the backflow steadily lessens until it evaporates. The operating performance of a dual-stage blower is better when cooling a high-power heat source.

New Approach to Obtain the Mean Heat Transfer Coefficients for Single-Phase Fluid Flow Inside Tubes by Simulating Evolution of Nusselt Equation (I)

New Approach to Obtain the Mean Heat Transfer Coefficients for Single-Phase Fluid Flow Inside Tubes by Simulating Evolution of Nusselt Equation (I)

A Guide for Water Bolus Temperature Selection for Semi-Deep Head and Neck Hyperthermia Treatments Using the HYPERcollar3D Applicator.

Simple SummaryHyperthermia cancer treatment is used as an adjuvant treatment modality to standard radiotherapy and/or chemotherapy treatments. The HYPERcollar3D allows focused microwave heating to 40–44 °C in the head and neck region. A flexible bolus is placed between patient and applicator, and deionized water is circulated, to improve power transfer efficiency and allow for surface cooling. The temperature at which this water is controlled influences the temperature distribution in this target region but its influence was unknown. To understand the impact of the water bolus temperature we performed a simulation study. We experimentally established the mean heat transfer coefficient for the water bolus as 292 W m−2K−1 (range 59–520). Then, we studied the influence of the water bolus temperature on temperatures in the target region using 20 patient specific 3D models. We found that for targets located up to 20 mm from the surface (median depth), the water bolus HYPERcollar3D temperature 30 °C can be increased to 35 °C, which will increase the temperature in the target region and thus translates to overall improvements in the hyperthermia treatment quality.During hyperthermia cancer treatments, especially in semi-deep hyperthermia in the head and neck (H&N) region, the induced temperature pattern is the result of a complex interplay between energy delivery and tissue cooling. The purpose of this study was to establish a water bolus temperature guide for the HYPERcollar3D H&N applicator. First, we measured the HYPERcollar3D water bolus heat-transfer coefficient. Then, for 20 H&N patients and phase/amplitude settings of 93 treatments we predict the T50 for nine heat-transfer coefficients and ten water bolus temperatures ranging from 20–42.5 °C. Total power was always tuned to obtain a maximum of 44 °C in healthy tissue in all simulations. As a sensitivity study we used constant and temperature-dependent tissue cooling properties. We measured a mean heat-transfer coefficient of h = 292 W m−2K−1 for the HYPERcollar3D water bolus. The predicted T50 shows that temperature coverage is more sensitive to the water bolus temperature than to the heat-transfer coefficient. We propose changing the water bolus temperature from 30 °C to 35 °C which leads to a predicted T50 increase of +0.17/+0.55 °C (constant/temperature-dependent) for targets with a median depth < 20 mm from the skin surface. For deeper targets, maintaining a water bolus temperature at 30 °C is proposed.