Thermal Performance Of Heat Exchanger Research Articles

CFD simulation of a heat pipe using the homogeneous model

Heat pipes are important in many industrial applications improving the thermal performance of heat exchangers and increasing energy savings. Computational Fluid Dynamics (CFD) were used to simulate the steam/water two-phase flow and heat transfer processes of a heat-pipe. The novelty of the study is that the evaporation, condensation and phase change processes were modelled using a homogeneous multiphase model and implemented source terms inspired by the Lee phase change model. The 3D CFD simulations could reproduce the heat and mass transfer processes in comparison with experiments from the literature. Reasonable good agreement was not only observed between CFD temperature profiles in relation with experimental data but also in comparing the thermal performance of the heat-pipe. It was found that the heating power should not increase above 1000 W for the analyzed type of heat pipe design using copper material. In future, the use of the improved advanced numerical models is planned.

Thermal and flow characteristics in a vertical spiral-type ground heat exchanger based on linear non-equilibrium thermodynamic principle

The thermal and flow performances in a single spiral-type ground heat exchanger in one-week operation were numerically simulated by considering the coupled thermal and moisture migration model for backfill and soil fields. The main factors involved Reynolds number (3000–10000), inlet temperature (30–40 °C), initial volumetric moisture content (6.95–20.8%), backfill materials (native sand, and sand/kaolin blend with 5% adding ratio of kaolin), spiral diameters (0.4–0.8 m), spiral pitches (0.1–0.8 m) and operation modes. The thermal performance of the heat exchanger without considering the coupled thermal and moisture migration model in unsaturated soil could be overestimated in long-term operation. The average temperatures in the blend enhanced by about 2% compared with the sand field, but the change degrees for the moisture content in the blend field were about 33% lower than that in the sand field, which imply that the kaolin additive could simultaneously enhance the thermal migration and water-holding capacity of the sand. The heat transfer rate of the heat exchanger in the blend enhanced by 24–36% with widening the spiral diameter from 0.4 to 0.8 m or narrowing the spiral pitch from 0.8 to 0.1 m, while the pressure drop rose by 50–92% and 4–5 times, respectively. 3-h-on/3-h-off mode among three intermittent operation modes (12-h-on/12-h-off, 6-h-on/6-h-off and 3-h-on/3-h-off) for the blend was more effective one to urge the soil temperature restoration. The intermittent operation mode should be also a feasible technique for prompting the thermal performance of the ground heat exchanger.

Numerical investigation of grooves effects on the thermal performance of helically grooved shell and coil tube heat exchanger

Heat exchangers are integral parts of important industrial units such as petrochemicals, medicine and power plants. Due to the importance of systems energy consumption, different modifications have been applied on heat exchangers in terms of size and structure. In this study, a novel heat exchanger with helically grooved annulus shell and helically coiled tube was investigated by numerical simulation. Helically grooves with the same pitch of the helical coil tube and different depth are created on the inner and outer wall of annulus shell to improve the thermal performance of heat exchanger. In the first section, thermal performance of the shell and coil heat exchanger with the helical grooves on its outer shell wall was compared with same but without helical grooves. At the second section, helically grooves created on both outer and inner wall of the annulus shell with different groove depths. The results showed that the heat exchanger with grooves on both inner and outer shell wall has better thermal performance up to 20% compared to the heat exchanger with grooves on only outer shell wall. The highest thermal performance achieves at lower flow rates and higher groove depths whereas the pressure drop did not increase significantly.

Experimental and numerical study of thermal-hydraulic performance in a heat exchanger tube with circular ring’s angular cutting inserts

ABSTRACT This paper experimentally and numerically studied the effects of inserting circular rings with four angular indexes and three diameter ratios at Re = 5000–24000 using air as the working fluid in a pipe. Researchers have proposed obstacles with various geometries to improve thermal performance in heat exchangers. However, research has not fully addressed the application of circular ring obstacles with different angle indexes and obstacle structure optimization. The results indicated, the Nusselt number increased by inserting a circular ring with an angular index of (360, 270, 180, and 90) by 3.9, 3.15, 2.92, and 2.74 times compared to a smooth tube, respectively. Likewise, the thermal performance coefficient for ring obstacles improves by 1.32, 1.39, 1.55, 1.8 times, respectively. Also, by increasing the ring diameter ratio, the Nusselt number increases, the friction coefficient decreases, and the thermal performance coefficient increases. Thus, it is be concluded that the better thermal performance of a circular ring’s cut sections as a passive component makes it a good choice for heat transfer and industrial applications. Besides, the results indicate that thermal efficiency in the case of using a ring with less angular index is higher, making it an appropriate choice economically.

Efficacy of the number of plates, fluid flow rate and volume fractions of aluminum oxide nanoparticles on thermal performance of gasket plate heat exchanger

The analytical model using the Second Law of Thermodynamics is applied to determine the thermal performance of a gasket plate heat exchanger. The gasket plate heat exchanger under analysis was initially projected for milk pasteurization, with water as a refrigerant, a mass flow rate equal to 0.42 kg/s, and a few plates equal to 20. The present work aims to determine the thermal performance of the heat exchanger, varying the number of plates, the flow rate of the refrigerant fluid, and using nanofluid with variations of volume fractions of aluminum oxide. Thermal efficiency, thermal effectiveness, generation entropy rate, heat transfer rate, and refrigerant and milk outlet temperatures were determined for comparison. In addition, the physical configuration of the plate heat exchanger, concerning the size and heat exchange area of the plates, was maintained.

Numerical analysis of thermal performance of heat exchanger: Different plate structures and fluids

Due to compact size, high power density, low cost and short construction time, the small modular reactors are considered as one of the candidate reactors, in which the power generation system is important with a compact heat exchanger for modular construction. Therefore, the effect of plate structure and nature of the working fluid on the thermal performance of plate heat exchanger are analyzed for the design of compact and efficient heat exchanger. The heat transfer rate, temperature counters, velocity vectors, and pressure drop have been optimized and investigated using FLUENT. The Nusselt number has been calculated for the corrugated and flat plate heat exchanger to validate the convective heat transfer. The numerical results are agreed well with correlation within deviation of ~5-7%. The performance of heat exchanger can be improved by controlling the mass-flow rate, and temperature of working fluid. The corrugation plate heat ex-changer increases the heat transfer rate 20% and effectiveness 23%, respectively, as compare to flat plate heat exchanger when the working fluid is water. In the case of air, heat transfer rate, and effectiveness are about 10% and 9%, respectively. The results show that the corrugated plate heat exchanger is more effective than the flat plate heat exchanger because corrugation pattern enhances the turbulence of fluids, which further increase heat transfer rate and coefficient. The selection of the working fluid and structure of the plate must be considered carefully for efficient and compact design of heat exchanger.

Thermal performance of ground heat exchanger under winter conditions

The use of buried pipe ground source heat pump technology can provide a green and environmentally friendly solution for the winter bridge snow melting project. However, the factors affecting the heat transfer efficiency of buried pipes in winter conditions are still unclear. For the single U-bend buried pipe heat exchanger, numerical calculations were preformed to study the effects of different inlet temperatures, backfill material ratio, hole depth, and spacing on the heat extraction capacity and the surrounding soil temperature distribution. Combined with an actual bridge heating project, three single heat exchanger models with different buried depths and three heat exchanger group models with different spacing were established. The results show that when the system runs for 48 hours, the heat transfer power at 2 ℃ will increase by about 82% compared with that at 8 ℃. Reducing the content of bentonite in the backfill is beneficial to heat transfer. As the heat exchanger depth increases, the heat extraction capacity per linear meter decreases. The expansion of the heat exchanger spacing can reduce the thermal interference effect between each other. When running 8 hours, the heat transfer power at an interval of 4 m is increased by 5.4% compared with that at the interval of 3 m, and the heat transfer power at an interval of 5 m is increased by 1.9% compared with that at the interval of 4 m.

Entropy Generation and Thermal Performance of Tubular Heat Exchanger Fitted with Louvered Corner-Curved Baffles

Entropy Generation and Thermal Performance of Tubular Heat Exchanger Fitted with Louvered Corner-Curved Baffles

Effect of Tube-in-Tube Configuration on Thermal Performance of Coaxial-Type Ground Heat Exchanger

Effect of Tube-in-Tube Configuration on Thermal Performance of Coaxial-Type Ground Heat Exchanger

Analysis of Thermal Performance of Coaxial Borehole Heat Exchanger Using Liquid Ammonia

Analysis of Thermal Performance of Coaxial Borehole Heat Exchanger Using Liquid Ammonia

Effect of Nanofluids on the Thermal Performance of Double Pipe Heat Exchanger

Effect of Nanofluids on the Thermal Performance of Double Pipe Heat Exchanger

Thermal and acoustic performance of silencing heat exchanger for engine waste heat recovery

The integrated design of gas heat exchanger and after-treatment unit can reduce the size and weight of the engine waste heat recovery system, releasing the back pressure of exhaust gas and enhancing net benefit of the waste heat recovery system. In this study, we propose a silencing heat exchanger that integrates an exhaust heat exchanger with an impedance composite muffler in the post-treatment system, using metal foam material instead of the sound absorbing material in the impedance composite muffler. By adapting ANSYS Fluent and LMS Virtual.Lab, thermal simulation and acoustic simulation of the silencing heat exchanger were realized, and comparative analysis of the modified structure and the basic structure was carried out. The modified silencing heat exchanger was then designed and fabricated, and the thermal and acoustic performance were tested. The results show that the modified silencing heat exchanger can achieve improved heat transfer and flow performance, and more uniform temperature distribution at the hot side, simultaneously resulting in an 8.4% reduction in exhaust pressure drop. Even more, the improvement of silence effect in the middle and high frequency band is fairly obvious, and the overall transmission loss is 44.4% higher than that of the basic structure.

IMPROVING THE THERMAL PERFORMANCE OF CONCENTRIC-TUBE HEAT EXCHANGERS USING MAGNETIC NANOFLUIDS

IMPROVING THE THERMAL PERFORMANCE OF CONCENTRIC-TUBE HEAT EXCHANGERS USING MAGNETIC NANOFLUIDS

W-Cut Twisted Tape's Effect on the Thermal Performance of a Double Pipe Heat Exchanger: A Numerical Study

W-Cut Twisted Tape's Effect on the Thermal Performance of a Double Pipe Heat Exchanger: A Numerical Study

Numerical Study on Non-Uniform Temperature Distribution and Thermal Performance of Plate Heat Exchanger

In this study, computational fluid dynamics (CFD) analysis was performed to investigate the cause of the thermal stratification in the channel and the temperature non-uniformity of the plate heat exchanger. The flow velocity maldistribution of the channel and the merging parts caused temperature non-uniformity in the channel width direction. The non-uniformity of flow velocity and temperature in the channel is shown in Section 1 > Section 3 > Section 2 from the heat exchanger. The non-uniform temperature distribution in the channel caused channel stratification and non-uniform outlet temperature. Stratification occurred at the channel near the merging due to the flow rate non-uniformity in the channel. In particular, as the mass flow rate increased from 0.03 to 0.12 kg/s and the effectiveness increased from 0.436 to 0.615, the cold-side stratified volume decreased from 4.06 to 3.7 cm3, and the temperature difference between the stratified area and the outlet decreased from 1.21 K to 0.61 K. The increase in mass flow and the decrease in temperature difference between the cold and hot sides alleviated the non-uniformity of the outlet temperature due to the increase in effectiveness. Besides, as the inlet temperature difference between the cold and the hot side increases, the temperature non-uniformity at the outlet port is poor due to the increase in the stratified region at the channel, and the distance to obtain a uniform temperature in the outlet pipe increases as the temperature at the hot side increases.

Thermal performance of building-integrated horizontal earth-air heat exchanger in a subtropical hot humid climate

The current energy crisis across the globe is a major obstacle to human growth and development. The majority of energy use is accounted for by buildings, which must be controlled and reduced using energy-efficient technologies. Several passive technologies have been shown to be effective in reducing building energy consumption. The earth-air heat exchanger (EAHE) is one such technology capable of saving energy in buildings without relying on habitual mechanical equipment. Though different types of EAHE models have been developed over the last few decades, building-integrated EAHE model development using real-time data is rarely seen for a subtropical climate. This paper thus evaluates the cooling performance of a building-integrated horizontal EAHE system in a warm and humid subtropical climate in Rockhampton, Australia. To measure the cooling performance, a building-integrated horizontal EAHE model is developed in Ansys Fluent. Impacts of relative humidity, air velocity, soil temperature, and air temperature on the building cooling performance have also been investigated. The building-integrated horizontal EAHE system reduced the temperature in a single room building by a maximum of 2.18 °C, saving 415.92 kWh energy (on average 59.91 kWh) during a 3-months summer. This equates to an energy cost savings of AU$190.31, with an average savings of AU$105.10. The energy saved by the present system will make a substantial contribution to building energy management.

Thermal performance of a single U-tube ground heat exchanger: A parametric study

Thermal performance of a single U-tube ground heat exchanger: A parametric study

Improvement of Thermal Performance of Coiled Tube Heat Exchanger Utilizing Air Bubble Injection Technique

The heat transfer enhancement in terms of temperature of a vertical helically coiled tube heat exchanger is carried out experimentally. The experiments were achieved in a heat exchanger with a 50 cm height and 15 cm internal diameter under four different cold and three hot water mass flow rates and four different airflow rates. At the same time, the temperature difference was taken invariant (ΔT=20°C). To avoid some uncertainties, the hot side temperature of the heat exchanger was measured via k-type thermocouples. The results showed that the increase of air injection flow rate improved heat transfer from the hot stream flowing in the coil to the shell’s cold stream. An intimate thermal mixing when air injected is clearly observed, which could be responsible for the heat exchanger’s thermal enhancement. Finally, the injected air pressure was noticed to be having only a minor effect on thermal performance improvement.

Frost layer growth behavior on ultra-low temperature surface with a superhydrophobic coating

Experimental research was conducted to study the frost formation on superhydrophobic surfaces at ultra-low temperatures, which might broaden the insight into frost growth behavior on the heat exchangers. The frost properties were examined over time, and the frost retardation according to the frosting factor was identified using the frost reduction ratios. The ablimation-dominant (desublimation) mechanism was observed at ultra-low temperatures in which almost no water droplets were generated. Consequently, the influence of the superhydrophobic surface on frost retardation was insignificant within −5% owing to the frosting mechanism. It is difficult to expect an increase in thermal performance of heat exchangers by applying superhydrophobic surfaces; using superhydrophobic surfaces for the purpose of frost retardation at ultra-low temperatures is not recommended.

Thermal performance optimization of heat exchanger with mixed cross-corrugated sinusoidal plate channels

• The flow and heat transfer in cross - corrugated plate unit channels are investigated. • Effect of phase shift angles on heat transfer performance of wavy channels are analyzed. • The heat transfer performance of mixed wavy channel is optimal at a phase shift angle of 324°. • For each wavy channel, the heat transfer performance of the lower wall is always greater than that of the upper wall. The thermal performance of heat exchanger with mixed cross-corrugated plate plays a fundamental role in the efficiency of the heat exchanger. Based on RNG k-ε model, the heat transfer characteristics of unit channels of three different mixed cross-corrugated plate heat exchangers (30°-50°, 30°-60°, 30°-70°) under different Reynolds numbers ( Re ) are investigated. The distributions of the average Nusselt number ( Nu ¯ ), friction factor ( f ) and Performance Evaluation Criterion ( PEC) of the three mixed unit wavy channels under different phase shift angles (0°≤θ ≤ 360°) are researched. The results indicate that a vortex area is appeared at the bottom wall. As the Reynolds number increases, the vortex area increases, and the vortex shape of the 30°-70° mixed wavy channel is close to circular. In addition, the heat transfer performance of the lower wall is always greater than that of the upper wall for each channel. Moreover, the optimal heat transfer performance for three mixed wavy channels is obtained at phase shift angle of 324°.