Decrease In Temperature Difference Research Articles

Temperature field characteristics of railway steel-concrete composite girger with different pavement layers

The temperature distribution in steel-concrete composite girders is complex, existing specifications and studies for temperature gradients in such girders are inadequate as they fail to fully account for the influence of track slabs and ballast. Therefore, this study takes into consideration the effects of laying track slabs and ballast and conducts temperature field experiments on steel-concrete composite girders. A finite element thermal analysis model was established and validated by the experimental data, and the effects of track slabs, ballast thickness, and wind velocities on the temperature field is analyzed. Results show that ballast and track slabs with a thickness of 40 mm exert similar effects on temperature field of girder. Compared to an uncovered composite girder, they change the temperature distribution of the concrete slab from a reverse "C" curve to a top-to-bottom decreasing trend under cooling and from a top-to-bottom decreasing trend to uniform distribution during heating, increasing vertical temperature difference in concrete slab by 4 °C when cooling 15 °C. Interestingly, the steel-concrete interface exhibits temperature differences during all test conditions. The temperature gradient curve observed in the steel-concrete composite girders with railway pavement layers in this study reveals substantial deviations from the temperature gradient curve stipulated by existing bridge design codes. Parameter analysis reveals that, as wind velocities increase, the maximum vertical temperature difference decreases, and the thickness variation of the railway pavement layer within the range of 30–50 mm was found to have no discernible effect on the temperature gradient of composite girder. This study provides reference for research on temperature gradients in railway steel-concrete composite girders.

Bidirectional interlayer cooling of 3D chip stack for temperature uniformity enhancement and hotspot mitigation

In this work, bidirectional interlayer cooling with both enhanced temperature uniformity and low flow resistance is proposed for effective 3D chip stack thermal management. Staggered uniform micropin fins and curved entrance and exit regions are elaborately designed. Experimental and numerical studies are carried out to investigate the cooling characteristics under different Reynolds numbers and heat fluxes. In comparison with common interlayer cooling solutions, counter-flow arrangement is achieved between the layers and vertical heat transfer within the chip stack is utilized. Heat fluxes of 300 W/cm2 and 100 W/cm2 are dissipated in the hotspot and background zones respectively. Total thermal resistance of 0.18 K/W is obtained. The maximum decrease in temperature difference is up to 66.2%. Both thermal resistance and coefficient of performance (COP) are considered and compared with the results from previous studies for comprehensive performance evaluation. The maximum COP of 11,523 is reached. The thermal and hydraulic performance advantages of the present design can be verified. The bidirectional interlayer cooling offers new potential for thermal management of 3D chip stack.

Toroidal tube latent heat exchanger: An experimental study

Concentric shell and tube latent heat exchangers integrated with phase change material (PCM) are widely used in many heat storage/transfer applications specially for building energy management due to their high energy storage density and fair simplicity in design. However, inadequate phase change in such systems reduces the thermal performance. The innovative geometric design is key in addressing this issue and accelerating the phase change process. The present work reports an experimental effort to investigate the progression of the melting process of PCM inside a novel design of toroidal tube embedded in the system as a shell and tube latent heat exchanger. The experimental setup consists of a toroidal enclosure filled with a bio-based PCM (i.e., coconut oil) and a constant temperature bath as a heat exchange environment. Digital images of melting progression and melting front at three different boundary temperatures (high, middle, and low temperature differences) are captured. Moreover, the time dependent temperature at a selected prob. point is also measured during the phase change process. As expected, decreasing temperature difference, decrease the melting rate, as the experiments show that the completed melting times are 20, 32, and 75 min for the high, middle, and low temperature differences. The melting front is sharper and more distinct to track for higher temperature differences as well. To observe the melting pattern and melting front inside the system (cross-sectional area of the tube) better, the melting progression in different selected times in a half-toroidal tube is also investigated. Furthermore, an extensive uncertainty analysis associated with measuring devices is reported.

Enhancement of cooling performance in MEMS by modifying 3D packaging structure: A design, integration, analysis and test study

The heat dissipation of three-dimensional (3D) integrated Micro-Electro-Mechanical Systems (MEMS) has garnered considerable attention in scientific research and electronic applications in recent years. As power demands increase, device sizes decrease, and energy consumption is limited, the use of liquid and forced air cooling techniques is diminishing. In light of the growing emphasis on achieving carbon neutrality, there is renewed interest in passive cooling methods, which present a new imperative for environmentally-friendly thermal management of chips in the field of green energy. While the concept of designing thermal paths to mitigate heat in chips is not novel, it has become increasingly important due to the rapid accumulation of heat, reduction in chip volume, and the need to minimize energy consumption and carbon emissions. Consequently, the implementation of appropriate cooling structures within the available space of the chips has emerged as an appealing approach to enhance passive cooling. In order to tackle this challenge, four cooling structures, namely embedding network structure, overlaying extension platform, overlaying micro-pillar array, and overlaying surface microstructures, have been employed in the packaging process to augment the passive cooling capabilities of the chips. In this study, a 3D packaging model is developed to analyze the thermal characteristics of MEMS under the influence of power, TSV voltage, and heat source area using the finite element method. Additionally, the cooling structures are optimized based on the cooling performance analysis, taking into account the self-remaining space within the system and the heat source area factor. The application of four different cooling structures in 3D MEMS leads to enhanced cooling performance. In the event that liquid cooling and forced air cooling are not utilized, the system experiences a decrease in maximum temperature by 3.66 K, resulting in a corresponding decrease in temperature difference by 43.79 %. These reductions significantly contribute to the mitigation of thermal deformation and stress in MEMS, thereby enhancing the thermal reliability of the system. To verify the accuracy of the thermal simulation, a thermal test is conducted on the embedded network structure under simulated conditions. The thermal simulation, which has been validated through thermal testing, indicates that the implementation of four cooling structures within the self-contained area of MEMS has a notable effect on reducing temperature. This finding holds promise for its potential application in 3D MEMS.

Effect of thermal management system parameters on the temperature characteristics of the battery module

In the present inquiry, a novel electric-thermal coupled model is devised to delve into the battery module's temperature distribution characteristics at different ambient temperatures and discharge rates. The accuracy of temperature prediction accuracy is contingent upon the experimental determination of the entropy heat coefficient and convective heat transfer coefficient. In the absence of a thermal management system for the battery module, an escalation in the discharge rate correlates with an increase in the average temperature, average temperature rise, and maximum temperature difference, while a decline in the initial ambient temperature relates to a decrease in these values. Under typical vehicle driving cycle conditions, the average temperature curves show peaks before the end of the cycle. The wider speed range, longer testing time, and reduced regularity of the driving cycles cause both the average temperature and maximum temperature difference to increase. Further research is done into the effects of coolant flow rate and temperature, and contact thermal resistance on the efficiency of thermal management systems. Gradual decrease in the average temperature transpires as the coolant flow rate increases, but excessively high flow rates engender a larger maximum temperature difference. As the coolant temperature decreases, both the average and maximum temperature difference decrease, but temperature uniformity is worsened. The average and maximum temperature difference generally rise when the thermal contact resistance increases, and a low thermal contact resistance leads to a more uniform low-temperature distribution.

A flexible optimization study on air-cooled battery thermal management system by considering of system volume and cooling performance

When the battery temperature exceeds the normal range, the battery efficiency performance, and life will be significantly reduced, and the battery may even explode. Therefore, an optimal battery thermal management system is required to dissipate heat efficiently. The existing research focuses on the structural design to reduce the maximum temperature of the system. However, the volume of the cooling system is also important for electric vehicle design, which has received little attention. In this study, a new flexible optimization strategy for a battery thermal management system is proposed, which is a hybrid of system volume and cooling performance and can determine the appropriate optimized structure according to the engineering applications. The proposed method belongs to four steps: optimization system design, establishment of shortcut computation codes, multi-objective optimization and comprehensive fuzzy decision making. The numerical simulation based on computational fluid dynamics (CFD) is used to verify the cooling performance of the optimized system. Compared with the three existing designs of battery thermal management system from previous literatures, the volume is reduced by a maximum of 13.01 %. In the process of stable heat generation, the maximum temperature difference decreased by 65.79 %, 40.65 %, and 63.69 %, and the temperature uniformity increased by 65.87 %, 34.93 %, and 60.80 %, respectively. In the unsteady heat generation of the battery pack, at the discharge rate of 5C, the maximum temperature difference decreases by 2.28 K, and the maximum temperature difference and temperature uniformity decrease by 57.11 % and 49.15 %, respectively.

The Effect of Vibrating Inner Cylinder on Natural Convective Heat Transfer in Concentric and Eccentric Horizontal Cylindrical Annuli

In this study, natural heat convection caused by centric and vertically eccentric long horizontal cylinders under the influence of vibration is experimentally investigated. The internal wall of the annulus is heated and kept at a constant heat flux, while the outside wall is cooled and maintained at a constant temperature. The vibration frequency impacts the annular convection heat transfer process and the effects of the Rayleigh number, heat flow, and eccentricity. This work employed a moderate, laminar-ranging Rayleigh number from (5×104 to 6.48×106), while the eccentricity range is varied from (-0.667, 0, and+0.667). The investigation is carried out at five different frequencies (0, 2, 5, 10, 15, and 20 Hz); therefore, it was decided to compare the case under the same circumstances in both the absence and presence of vibration. The present results' verification worked exceptionally well in concordance with previous studies. When heat fluxes are considered, the study demonstrates that the temperature difference along the gap (radial difference) between the two cylinders significantly decreases for negative as opposed to positive eccentricities for each Rayleigh number. For different eccentricities, it was discovered that the temperature difference decreased as the Rayleigh number increased. Along with these reductions, the temperature difference was promoted as the vibration frequency increased, which is significant at (20 Hz) within the range considered for controlling parameters. It was also observed that the decrease in temperature difference is higher for the negative eccentric position than for the centric and positive positions. At vertical positive eccentricity at a low Rayleigh number, the gain in vibrational average Nusselt number caused by applying vibration had a minimum value of 22.50601475%, While at the higher value of the Rayleigh number, the maximum increase in negative vertical eccentricity was 86.66933125%. However, the gain in the average Nusselt number depends on the position of the heated inner cylinder, the Rayleigh number, and the vibrational frequency.

Impact of buoyant jet entrainment on the thermocline behavior in a single-medium thermal energy storage tank

This paper presents the characterization and management of dynamic thermocline behaviors in a single-medium thermocline (SMT) thermal energy storage tank with the aim of its performance improvement. In particular, the flow mixing induced by the entering thermal jet, its impact on the temperature stratification and its mitigation measure are systematically explored by both numerical and experimental methods. Results of CFD simulation and Particle Image Velocimetry (PIV) visualization clearly demonstrate the jet entrainment phenomenon and the typical flow patterns featured by the rising buoyant plumes. For the storage tank with simple inlet port, this thermal jet would cause the thermal overturning, the strong fluid mixing and convection heat transfer, resulting in the degradation of temperature stratification and the thermocline decay (Rigradient<0.25 at certain positions of the tank). It has also been shown by PIV measurement that the impact of thermal jet, characterized by the jet penetration length, becomes stronger with the increasing injecting flow rate and with the decreasing temperature difference between the injecting and existing fluids.Orifice baffle-type distributor has then been proposed and optimized, showing clearly its effectiveness for mitigating the impact of thermal jet on the temperature stratification. Both the initial uniform orifice baffle and the optimized orifice baffle distributors are then fabricated and installed into a lab-scale cuboid SMT storage tank. Charging operations are performed under different inlet flow rates (Qin: 0.3 to 1.5 L·min−1) and temperature differences between hot and cold fluids (∆T: 30 to 50 K). Experimental results obtained show that the optimized distributor could always lead to the better thermal performance (capacity ratio up to 0.94 and charging efficiency up to 0.8) than the initial uniform baffle distributor, providing more flexible operating conditions of the SMT storage systems in different industrial sectors.

Electrical–thermal–fluidic coupling Li-ion battery pack consistency study

The thermal effect of lithium (Li)-ion batteries affects its performance and service life and threatens its safety. Therefore, a new tree-shaped channel heat sink was developed for cooling Li-ion battery packs and compared with fractal and serpentine channel heat sinks. Moreover, the electrical–thermal–fluidic multi-physics simulation was implemented based on the equivalent circuit model. The temperature distribution effect on the battery pack's consistency was investigated. Different circuits were established through various series–parallel topologies, and the battery pack's discharging and temperature characteristics were examined when the cells' initial parameters were different. The results demonstrated that the new tree-shaped channel heat sink offered effective heat dissipation and small flow resistance. The decreasing temperature difference enhanced the current consistency, while the decreasing temperature rise reduced the voltage consistency. The series or parallel connection between the battery modules slightly affected the battery pack's discharging and temperature characteristics. Within the module, a reduction in the number of batteries in series or augmentation in the parallel branches reduced the battery consistency and increased the battery pack's average temperature rise and temperature difference. The battery consistency in the parallel-first topology module was better than that in the series-first topology module under the same number of parallel branches. These results are helpful for the battery pack consistency studies.

Study on the Influence of Air Inlet and Outlet on the Heat Dissipation Performance of Lithium Battery

The heat dissipation characteristics of the lithium-ion battery pack will have an effect on the overall performance of electric vehicles. To investigate the effects of the structural cooling system parameters on the heat dissipation properties, the electrochemical thermal coupling model of the lithium-ion power battery has been established, and the discharge experiment of the single battery has been designed. The voltage and temperature curves with time are similar to those obtained from the numerical model at various discharge rates, and the experimental results are relatively accurate. Based on this model, the height, angle, and number of different air inlets and outlets are designed, and the heat dissipation characteristics of different structural parameters are analyzed. The results show that the maximum temperature decreases by 3.9 K when the angle increases from 0° to 6°, the average temperature decreases by 2 K and the maximum temperature difference decreases by 2.9 K when the height increases from 12 mm to 16 mm, and the more the number of air inlets and outlets there are, the better the heat dissipation effect is. Therefore, the air vent of the battery cooling system has an important impact on the heat dissipation characteristics of the battery, which should be fully considered in the design.

STUDI KASUS KONDISI RADIATOR PADA PERFORMA MESIN SISTEM PENDINGIN MELALUI KOMPUTASI DINAMIK FLUIDA DI PLTD BATAKAN

Computational fluid dynamics (KDF) is a commonly used method to solve physics cases that have the advantage of reducing operating costs, especially in the study of cooling systems in engines. In this study, the engine cooling system observed was located at the Diesel Power Plant (PLTD), Batakan. The cooling system on the engine has several important components that affect performance, one of which is the radiator. The condition of the radiator is observed with different fin designs, namely ideal conditions with fins (100%), 75%, and 50%. KDF helps to provide a detailed analysis of the performance of the engine cooling system. Under ideal conditions, the value of the temperature difference between the inlet and outlet in high temperature (HT) and low temperature (LT) pipes is 220C. From this study gave results, the condition of the radiator fins that were not ideal resulted in a decrease in temperature difference between the inlet and outlet in the HT and LT pipes.

Cost-Optimal Renovation Solutions for Detached Rural Houses in Severe Cold Regions of China

High heating expenses are observed in numerous Chinese rural houses located in severe cold regions due to the high heating demand, inferior envelope performance and low-efficiency heating equipment. The local traditional heating methods include Chinese Kangs and coal boilers with water-based radiators. The intermittent operation and manual regulation of these systems result in significant temperature differences and inadequate thermal comfort. This study presents the cost-optimal envelope renovation solutions with the minimized lifecycle cost (LCC) during a 20-year discount period and CO2 emissions of annual delivered energy consumptions. A single-family detached rural house in Harbin was used as a case building, illustrating the typical state of comparable houses in this climate context. Simulation-based multi-optimization analysis was conducted in this study using the building simulation tool IDA ICE and its integrated optimization tool AutoMOO. The results indicate that the cost-optimal renovation solutions with intermittent and continuous heating can cut CO2 emissions by 30% and 40%, respectively. The LCC with intermittent heating is still 7% greater than its pre-renovation case, which may require external financial support to encourage the renovation conduction, while the LCC with continuous heating decreased by 8% after renovation. According to the comparison results, cost-optimal solutions have significant advantages in both reductions of LCC and CO2 emissions over standard-based solutions. Moreover, utilizing intermittent heating is more effective than continuous heating in demonstrating the positive impacts of envelope renovation on increasing average temperature, decreasing temperature differences and lowering occupied time at low thermal comfort levels.

Numerical investigations on heat transfer enhancement and energy flow distribution for interlayer battery thermal management system using Tesla-valve mini-channel cooling

Targeted at addressing cooling concerns of high power Cell-Pack, a novel interlayer battery thermal management system applying Tesla-valve mini-channel is proposed. The effect of cold plate position and Tesla-valve channel parameters is investigated to obtain optimal thermal performance through coupled battery cold-plate simulations with a 2C-discharge rate and wide Re range. Compared to main face cooling, side face cooling demonstrates more favorable thermal performance with decreasing maximum temperature and maximum temperature difference by 5.6 °C and 8.5 °C respectively. With application of forward Tesla-valve mini-channel, the maximum temperature decreases by 3.8 °C compared to straight mini channel at a moderate Re of 500. This prior thermal performance is corresponded to the even distributed heat transfer enhancement zones with flow fluctuations. Furtherly, the thermal–hydraulic performance is optimized by channel number, Tesla valve number and contraflow design with doubled Nusselt number and normalized thermal performance factor, maintaining the maximum temperature below 38 °C at a higher discharge current of 210 A. Consequently, the optimal forward Tesla-valve mini-channel owns considerable cooling efficiency factor of 369 and the highest energy flow percentage of 59.2% compared to the straight mini-channel, demonstrating the improved thermal–hydraulic performance and cooling efficiency.

Effect of surface structure on flow and heat transfer using lattice Boltzmann method in a microchannel exchanger

The D2Q9 multiple relaxation time (MRT) model and D2Q5 MRT model of lattice Boltzmann method are proposed for the fluid flow and heat transfer in a microchannel exchanger. The appropriate flow and thermal boundary conditions are adopted by non-equilibrium extrapolation method. The performance of heat convection between cold fluid and hot wall in rectangular microchannel is simulated and the results are verified through experiments by Liu et al. and previous numerical results by Ebrahimi et al. Effects of structured surface with rectangular, hemispherical and triangular micro-bulges on the flow behavior and heat transfer of fluid are analyzed. Simulated results indicate that the structured heat transfer surface can effectively enhance the heat transfer, the surface with rectangular micro-bulges for the best performance. Subsequently, the optimal ratio of the micro-bulge height to the micro-channel height of 0.25 is obtained based on the relative Nusselt number of rectangular structured surface, and the Reynolds number decreases with the increase of the micro-bulge height, and the relative logarithmic temperature difference is the opposite. The relative Nusselt number and relative logarithmic temperature difference decrease first and then increase with the increase of micro-bulge distance, while the Reynolds number changes on the contrary. The effect of micro-bulges interval on the heat transfer efficiency is less than that of micro-bulge height, and the thermal efficiency is increased by 15% with an optimal height and distance of the rectangular micro-bumps in the microchannel.

Pinch point determination and Multi-Objective optimization for working parameters of an ORC by using numerical analyses optimization method

In parallel with Kyoto, Paris and the green production agreements, the nowadays crucial subject is minimising energy consumption, increasing renewable energy usage and recovering waste heat. When it comes to waste heat, the organic Rankine cycle (ORC) technology comes fore. However, although the presence of many studies on the ORC in the literature, there is still an intense gap related to information on ORC working conditions, pinch point detection and numerical design and analysis methods. In this respect, the present paper suggests a multi-objective optimization model for an ORC by considering many parameters that affect the performance of the ORC like fluid type, thermodynamic properties of the organic fluids, pinch point temperature etc. For the analyses, experimentally recorded exhaust gas parameters for a reheat furnace located in the iron and steel plant were used. By considering all these, all performance-affecting parameters were included through the development of the multi-objective model. For the analyses, two wet types (ethanol, methanol), two isentropic (acetone, butene), and two dry types (cyclohexane, benzene) working fluids were selected to develop the multi-objective design and optimising method. After comprehensive analyses, it was seen that the developed mathematical model was valid for the designing and analysing of the ORC. In addition, it was observed that the system performance increases as the pinch point temperature difference decreases. In addition, it was seen that isentropic fluids have low efficiency in medium-temperature heat sources. Considering the system performance, initial investment cost and payback periods, it was seen that a waste heat recovery plant using Benzene, Methanol and Ethanol as working fluids is more feasible.

Design and construction of a solar powered grill using a wooden box

A solar powered grill using wooden box cooker was successfully constructed with cheap and locally available material with efficiency from the various experiments that were carried out, the highest temperature gotten both on the ground floor and at the top of the roof was 72ºC both on the days with air temperature of 38ºC and 35ºC respectively. Efficiency was found to increase with decreasing temperature difference between collector temperature and ambient temperature. Increase in temperature does not necessarily lead to increase in efficiency. Efficiency decreased with decreasing solar radiation. Now a day non-renewable energy available less percentage, that’s why we have to use renewable energy i.e. solar energy, wind energy etc. Nothing is cheaper than free of cost .But solar energy is available in abundant amount in nature at free of cost so that we can use solar energy as option for non-renewable energy source. Hence to replace traditional cooking method by solar energy can be considered. Solar cooker is one of the best appliances to utilize solar energy for cooking. Solar cooking is a form of outdoor cooking and is often used in situation where minimum fuel consumption is important or the danger of accidental fire is high and the health and environmental consequences of alternative are severe.

Numerical study of free-falling particle receivers with curtain and particle interchange for high receiver efficiency and low temperature difference

Shunt-wound and series-wound free-falling particle receivers (FFPRs) are developed for receiving incident energy with two opposite directions. In order to increase receiver efficiency and decrease temperature difference between the highest and lowest temperature particles at the outlet of receiver, inclined plates and novel structures with particle flow channels are respectively installed in series-wound FFPRs for curtain and particle interchange. The effect of the incident energy ratio between two opposite directions on the performance of shunt-wound FFPRs, series-wound FFPRs with curtain interchange and series-wound FFPRs with particle interchange has been numerically investigated. The receiver efficiency, temperature difference and temperature distribution have been calculated and analyzed at different incident energy ratios. The results indicate curtain interchange is more beneficial to improve receiver efficiency, and particle interchange contributes more on the decrease of temperature difference. The highest receiver efficiency of 84.3 % and the lowest temperature difference of 109.5 °C are both found in series-wound FFPRs with particle interchange.

Surrogate model of liquid cooling system for lithium-ion battery using extreme gradient boosting

Battery thermal management system (BTMS) has been widely regarded as an effective means to mitigate the sensitivities of lithium ion batteries (LIBs) to temperature, as to uphold the safe and high-performance operation of LIBs. On the premise that the volume and cost are limited, optimizing the structure of BTMS becomes relevant. Owing to the complex flow and heat transfer processes, the objective functions of BTMS structural optimization cannot be expressed analytically, but has to be evaluated using finite element method (FEM), which is time-consuming and therefore not scalable. The well-known solution to speed up the evaluation of objective functions is to engage a surrogate model, which offers a fast but slightly inaccurate mapping from the input variable space to the response. In this article, two innovations on surrogate modeling for BTMS structural optimization are proposed. One of them is in terms of input variables of surrogate model, which takes into consideration not only the structural parameters, but also the operating conditions. The other is on the surrogate model itself, in that, extreme gradient boosting (XGBoost) is used to replace the conventional kriging and response-surface methods, which is able to reduce the maximum absolute error of the model by 50%. The errors of maximum temperature and temperature difference decrease 0.179°C and 0.255°C, respectively. Moreover, the computational time of the XGBoost-based model is just 2 ms. The method proposed in this article can be applied on a wide range of structural optimization tasks in real driving cycle of electric vehicles.

Simulation on thermal characteristics of high-speed motorized spindle

High-speed motorized spindle is a key component of precision machining machine. Thermal deformation caused by internal heat accumulation is one of the main factors affecting machining accuracy. Therefore, there is important theoretical and practical significance to accurately simulate and analyze thermal characteristics inside the spindle. In this paper, a three-dimensional finite element analysis model is established and the heat transfer mechanisms of the boundary conditions in the model. The temperature field and thermal displacement field of the spindle under thermal load are simulated. According to the simulation results, it is found that the overall temperature is radially distributed from the middle of the spindle core to surroundings after the temperature reaches dynamic equilibrium, and the axial (z-direction) thermal displacement is the largest, which is the main cause affecting the machining accuracy. Applying Peltier material to the spindle shell to decrease temperature difference and using carbon fiber material with negative coefficient of temperature expansion to restrain thermal deformation are proposed innovatively in this paper. The combination of those two methods shows that the optimized spindle temperature distribution is more uniform, and the thermal deformation reduces from 31.4 μm to 24.1 μm, which decrease by 23.2%.

Heat Transfer and Pressure Drop in Single-Phase Flows in Tapered Microchannels

Abstract This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created with a plain 10 mm × 10 mm heated copper surface and a polysulfone cover that was either uniform or tapered with an angle of 3.4 deg, and average gap heights of 400 and 800 μm. Experiments were conducted with single-phase water flow with an inlet temperature of 30 °C for flow rates varying from 57 to 498 mL/min and heat flux from 27 to 153 W/cm2 depending on the flowrate and microgap configuration. The uniform configuration resulted in the lowest pressure drop due to the less constricted flow. A slight decrease of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates and shorter average gap. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in the converging gaps, which compensates for the decrease in temperature difference between the fluid and the surface along the flow length. Overall, the converging microgaps have better performance than uniform or diverging ones for single-phase flows, and this effect is more pronounced at lower flow rates, where the fluid experiences higher temperature changes.