Thermal Performance Of Heat Exchanger Research Articles

Extensive numerical analysis of the thermal performance of a corrugated tube with coiled wire

Utilizing passive methods is an efficient way in order to improve the thermal performance of heat exchangers. The novelty of the present paper is that two kinds of passive techniques for heat transfer enhancement, including a corrugated tube equipped with a coiled wire as turbulator, are combined in the present study. Heat transfer and pressure drop in a corrugated tube with a wire coil are analyzed numerically by a commercial CFD software. The range of the considered Reynolds number is 5000–20,000, which guarantees that the flow regime is fully turbulent. The effects of two different geometrical parameters and of two flow operating parameters, namely the Reynolds and Prandtl numbers, are numerically investigated. The conservative equations for momentum are closed using the k-e realizable model. Results indicate that the geometrical and fluid flow parameters have significant effects on the thermal performance of the system. When one increases the pitch ratio of the wire coil (P/d), the heat transfer enhancement ratio NuER decreases. The maximum decrease is obtained for P/d = 5 with − 7.78% at Re = 20,000 in comparison with the baseline case P/d = 2. The maximum increase in the performance evaluation criterion (PEC) is observed at Re = 5000: + 11.16% and + 17.4% for P/d = 3 and P/d = 5, respectively. The configuration with a roughness height equal to e = 3 mm exhibits the best thermal performance with a maximum enhancement in terms of NuER of + 3.3% at Re = 10,000 in comparison with the baseline case e = 0.5 mm. By considering the PEC number, increasing the parameter e has a negative effect on the thermal performance of the proposed system.

Thermal performance of shallow spiral-tube ground heat exchanger for ground-source cooling system

This study present an investigation of thermal performance of spiral-tube ground heat exchanger (GHE) buried in shallow depth of borehole. The spiral-tube GHE consisting of spiral pipe installed in the borehole provides a better performance in application of ground-source cooling system. Experimental study was carried-out by circulating water through the spiral-tube GHE which is buried in the ground of 3 m depth. Temperatures of inlet and outlet water in the GHE were measured and recorded periodically. The thermal performance of the GHE was calculated with different inlet water temperatures. Heat exchange rate for different inlet water temperature of the spiral-tube GHEs are 44 W/m (35 °C), 126 W/m (40 °C) and 110 W/m (45 °C). The results show that the utilization of shallow borehole of spiral-tube GHE is appropriated for application in ground-source cooling system especially for the hot climate like Indonesia.

Effect of Wet Soil on Thermal Performance of Air-Fluid Ground Heat Exchanger for Heating

The energy crises that emerged after the economic problems in the world increased the interest in alternative energy resources. The effects of global warming, which has a serious threat, will be reduced by the more efficient use of these energy resources. In this study, the thermal effects of wet soil were investigated experimentally using a ground source heat exchanger (GHE), which is an alternative energy resource, in an area on the Esentepe campus of Sakarya University. Researches on this subject are mostly directed to dry soil applications. In this research, the performance of soil in an artificial pool was examined in terms of heat transfer. By means of the artificial pool formed under the ground, it is aimed to increase in heat transfer between the soil and the process fluid. In the experiments which are conducted, air is used as the process fluid. The system has a significant advantage in certain temperature ranges due to the passive heating method, in other words, the process fluid can be circulated under the soil without using a compressor. The purpose of this method is to reduce the cost of heating in the winter season. The temperature difference at GHE inlet and outlet is approximately 9.07 °C in the experiments. The heat transfer rate has been increased by 46.28% compared to dry soil application for the same air velocity speed.

Augmentation of thermal performance of heat exchanger using elliptical and circular insert with vertical twisted tape

ABSTRACT Present work deals with the experimental and computational investigation of thermal properties and fluid flow characteristics on circular tube with elliptical inserts. The major axis is taken equal to hydraulic diameter i.e. 6.81cm. A new parameter, height ratio (γ = b/D) has been defined with three values – 0.45, 0.66, and 0.74. The test section is 1.5 m long which is provided with a constant heat flux of 1000 W/m2 along with air as working fluid at Reynolds number ranging from 3,000 to 21,000. The results show that the augmentation in heat transfer was six times for case γ = 0.74 and the maximum thermal performance factor (TPF) obtained is 2.43 for insert with γ = 0.45 at Re = 3000 over the smooth tube. Computational fluid dynamics (CFD) investigation is also carried out for elliptical inserts, and the results are in good agreement with the experimental results where the maximum deviations in Nusselt number, friction factor, and TPF are ±9.39, ±8.68, and ±8.58%, respectively. CFD investigation for tube having circular inserts with vertical twisted tapes (CVTT) and elliptical inserts with vertical twisted tapes (EVTT) is also presented where the augmentation in heat transfer ranges 3–8 times for CVTT placed in full length and TPF is ranging 1.19–2.63 times for CVTT placed in TL length over to smooth tube.

Experimental and numerical studies on the thermal performance of ground heat exchangers in a layered subsurface with groundwater

Thermal performance of the ground source heat pump (GSHP) system can be significantly affected by the complex geological substructures (such as ground stratification and groundwater advection). This study installed a seepage box inside the two-layered laboratory device to investigate the heat transfer processes of the unsaturated, saturated and infiltrated ground. Various operational and geological conditions were designed to study the temperature distributions at various locations and time experimentally and numerically. The groundwater effect on ground heat exchanger (GHE) thermal performance depends on the thermal properties, flow advection and the relationship between temperatures of the groundwater and ground. If the ground was partially saturated during the heat injection period, the cooling seepage will efficiently remove the heat of GHEs in upper-stream rather than those located in the bottom-stream. Meanwhile, the heat transfer can be enhanced if two legs of the U-tube vertical to the direction of groundwater seepage. The groundwater flow can redistribute the heat within the ground and showed a better recovery performance which advance an even temperature distribution by 3 h. The temperature and carried heat load of the cooler groundwater will increase during the heat injection experiment, and further contributed to various temperature distributions of ground at different locations and time.

Effects of Double V Cuts in Perforated Twisted Tape Insert: An Experimental Study

The thermal performance of heat exchanger is considerably enhanced by the use of inserts. Twisted tape inserts are known for producing large heat transfer enhancements at the expense of fairly large friction penalty. With the objective to explore the effect of twisted tape with perforations and V cuts, the present study investigates the thermo-hydraulic performance of solid twisted tape, perforated twisted tape, and perforated twisted tape with double V cuts for the Reynolds number range of 2000–25000. During the experiments, the twist ratio of tapes is varied in the range of 2–6, while the depth ratio and width ratio of V cuts for perforated twisted tape with double V cuts are varied in the range of 0.2–0.27. The maximum enhancements in Nusselt number and friction factor were found to be 3.5 and 9.63, respectively, corresponding to the perforated twisted tape with double V cuts having V cut depth ratio and width ratio of 0.27 and twist ratio of 2.

Improving the thermal performance of ground air heat exchanger system using sand-bentonite (in dry and wet condition) as backfilling material

Thermal performance of ground-air heat exchanger (GAHE) depends on the rate of heat transfer between air and soil, which is governed by thermal properties of soil surrounding the GAHE pipe. Soil thermal properties around GAHE pipe can be improved either by increasing its moisture contents or by using some thermally enhanced backfilling materials. In the present study experimentally investigates the thermal performance of ground-air heat exchanger system using a sand-bentonite mixture (dry as well as wet) and compare their performance with the ground air heat exchanger system having native soil (dry as well as wet) as backfilling material. The study acknowledges the highest cooling capacity (125 W) for GAHE with wet sand-bentonite as backfilling material, and after 6 h of continuous operation, it is 38.4%, 18.4% and 11.1% higher than that obtained with dry native soil, dry sand-bentonite and wet native soil, respectively. The study also revealed that thermal performance deterioration factor (TPDF) increases with the duration of the operation. At airflow velocity of 5 m/s, after 6 h of continuous operation highest TPDF is noticed for ground-air heat exchanger with dry soil (0.22); whereas, lowest TPDF is observed for ground-air heat exchanger system with wet sand-bentonite (0.07).

Experimental Study of the Effects of Inclusion of Rectangular-Cut Twisted Tapes on Heat Transfer and Pressure Drop in a Round Tube

Twisted tape inserts were used as swirl generators in the flow through a tube for enhancing heat transfer. Twisted tapes have commonly been applied in many thermal applications used in industry. Several modified twisted tapes have been investigated for improving the thermal performance of heat exchangers. The effects in tubes with modified rectangular-cut twisted tape (RC-TT) inserts with various free-spacing ratios (s/w = 2.0, 2.5, 3.0, 3.5 and 4.0) and edge–width ratios (t/W = 0.1, 0.15, 0.2 and 0.25) on heat transfer and pressure losses are reported. The RC-TT used in this work had a fixed thickness of 1.2 mm, width of 60 mm, length of 2000 mm and twist ratio (y/W) of 3.0. Experiments were performed over a range of Reynolds numbers, 10,000 ≤ Re ≤ 20,000, using air as a test fluid. A tube with a classical/typical twisted tape was also tested for comparison. In all cases, the Nusselt number tended to increase with the Reynolds number, while the friction factor and thermal performance showed the opposite trend. For the rectangular-cut twisted tape inserts, the friction factor and Nusselt number decreased, while thermal performance increased with increasing free-spacing ratios (s/w) and edge–width ratios (t/W). Furthermore, the maximum thermal performance was achieved at the lowest free-spacing ratio (s/w), edge–width ratio (t/W) and Reynolds number (Re).

Evaluation the effects of geometrical parameters on the performance of pillow plate heat exchanger

The growing demand for energy-saving in industries has led to numerous researches to improve the heat exchangers thermal performance in a variety of methods. The pillow plate heat exchanger (PPHE) is one of the new types of plate heat exchangers that have specific functional properties compared to conventional plate heat exchangers. The objective of the present investigation is providing comprehensive information about effective geometrical parameters of PPHEs for optimal design. In the present study, the performance of PPHEs is studied by numerical simulation. The obtained results have shown that the geometrical parameters of the PPHEs have a significant effect on thermal performance. The considered geometrical parameters include the height of pillow plate channels, and the longitudinal and transversal distance of welding spots. The heat exchanger thermal performance increases by expanding the height of the pillow channel mostly at low Reynolds number. After increasing longitudinal and transversal distance of welding spots the heat transfer and friction factor decreases in both cases. However, the effect of friction factor decrement on heat exchanger performance is more than decreasing in heat transfer. Thereby the PPHE with longer longitudinal or transversal distance of welding spot is efficient.

Performance evaluation of a double-pipe heat exchanger fitted with self-rotating twisted tapes

This study presents heat transfer and frication factor characteristics of heat exchanger tube with self-rotating twisted tapes (SRTTs). A comparison of SRTTs and stationary twisted tapes (STTs) as well as an examination of the effects of SRTTs with different twist ratios (Y = 2.2, 3, 4, and 6) on the thermal characteristics were experimentally investigated under turbulence flows (12000 < Re < 45000). The experimental results showed that SRTTs under rotating conditions could enhance the thermal performance of heat exchanger as compared with STTs. The twist ratios were found to have less effect on the initial stages of the rotating behavior, and the SRTTs with lower twisted ratios rotated faster under the same operating conditions. In addition, it was observed that the Nusselt number, pressure drop, and thermal performance factor increased with decreasing twist ratios. The maximum thermal performance factors of 1.03, 0.9444, 0.924, and 0.898 could be achieved at the start of rotating behavior for Y = 2.2, 3, 4, and 6, respectively. Finally, some correlations of the Nusselt number and frication factor were established within ±10% deviation of the experimental data.

Experimental Investigation of Thermal and Hydraulic Performance of a Plate Heat Exchanger Using Nanofluids

Gasketed plate heat exchangers (PHEs) occupy a crucial position in the energy sector due to their efficient and compact design. A number of studies have focused on making the plate heat exchangers more efficient and compact, since energy usage increases day by day. Therefore, the idea of utilizing nanofluids, whose thermophysical properties are better than those of industrial fluids, have drawn the attention of researchers. An experimental setup was designed and constructed at the TOBB ETU Heat Exchangers Laboratory to investigate the effect of utilizing nanofluids in a plate heat exchanger. The experiments were performed with three different working fluids, namely, tap water and 1 and 0.5 wt.% Al2O3/water nanofluids in a hot cycle. For all cases, the flow rates were 100–450 L/h, and the experiments were repeated three times for accuracy. As a result of this study, new correlations for the Nusselt number and heat transfer enhancement rates were obtained. Moreover, the friction factor correlations were found for all cases, and the effect of nanofluids on the pressure drop has been revealed.

Thermal performance of a micro heat exchanger (MHE) working with zirconia-based nanofluids for industrial cooling

An experimental investigation was performed with the view to assess the heat transfer characteristics of a water-based nanofluid in a micro heat exchanger employed to quench a high heat flux heater for industrial and microelectronic cooling applications. The experiments were conducted at heat fluxes 10–70 kW/m2 and for nanofluids at various mass concentrations of 0.1–0.3% and passing flow rates of 0.1–5 l/min. Thermo-physical properties of the nanofluid including thermal conductivity, heat capacity, density and viscosity of nanofluid were experimentally measured at 40 °C close to the temperature of the experiments. Results showed that the heat transfer coefficient and pressure drop were augmented by 40.1% and 67% at wt% = 0.3 compared to the base fluid, respectively. The enhancement in the heat transfer coefficient was associated with the improvement in the thermal conductivity of the base fluid together with the intensification of Brownian motion and thermo-phoresis effect. The increase in the pressure drop was also attributed to the increase in the viscosity of the working fluid which induces layer–layer frictional forces in the bulk of the coolant in micro heat exchanger.

Quantifying Implications of Deposit Aging from Crude Refinery Preheat Train Data

Heat exchanger fouling has been studied for some time in the petroleum industry. As understanding of fouling dynamics and mitigation methods improves, refinery fouling mitigation strategies are changing. The implications of deposit aging in refinery units have not been addressed in detail: aging refers to where the deposit undergoes physical and chemical conversion over time. In the 2009 Heat Exchanger Fouling and Cleaning conference, Wilson et al. [Ageing: Looking back and looking forward] presented a simple framework illustrating how deposit aging impacts heat exchanger thermal and hydraulic performance. This paper presents insights into deposit aging gained from analysis of refinery monitoring data. Two case studies are presented: (i) one from the Preem refinery in Sweden where stream temperature, flow and gauge pressure measurements indicated a higher deposit thermal conductivity in exchangers located in the hotter section of the preheat train. (ii) US refinery stream temperature, flow and plant cleaning log data, showing an increased resistance to cleaning when deposits are exposed to high temperature for a prolonged period. The use of deposit aging analysis to improve exchanger operation is discussed.

Thermal Performance of a Low-Temperature Heat Exchanger Using a Micro Heat Pipe Array

Domestic heat exchangers, even though widely used in industry, are not adequate for studies on low-temperature flue-gas use technologies. Despite spite their limitations, very few theoretical models have been investigated based on practical applications. Moreover, most of the existing studies on heat exchangers have focused particularly on one-dimensional and two-dimensional heat transfer models, while limited studies focus on three-dimensional ones. Therefore, this study aims at investigating the thermal performance of a low-temperature flue-gas heat recovery unit in the cold regions. Specifically, this study was conducted in the context of Changchun of Jilin Province, China, a city with the mean ambient temperature of −14 °C and mean diurnal temperature of −10 °C during winter. Experimental results showed that the thermal efficiency of the heat exchanger was higher than 60%. Through assessing the heat exchange coefficient and heat exchange efficiency of the heat exchanger, it is found that the thermal efficiency had been improved up to 0.77–0.83. Furthermore, the ICEPAK software and the standard k-ε RNG turbulence model were used to carry out simulations. The velocity and outlet temperature of fresh airflow and polluted airflow were simulated through setting different inlet temperatures of fresh air and polluted air inlet. Numerical results further indicated that the flow state was laminar flow. The micro heat pipe array side had small eddies and the heat transfer was significantly improved due to the flow of air along the surface of the micro heat pipe.

Analysis on Thermal Performance of Ground Heat Exchanger According to Design Type Based on Thermal Response Test

A ground source heat pump (GSHP) system has higher performance than air source heat pump system due to the use of more efficient ground heat source. However, the GSHP system performance depends on ground thermal properties and groundwater conditions. There are many studies on the improvement of GSHP system by developing ground heat exchanger (GHX) and heat exchange method. Several studies have suggested methods to improve heat exchange rate for the development of GHX. However, few real-scale experimental studies have quantitatively analyzed their performance using the same ground conditions. Therefore, the objective of this study was to evaluate the thermal performance of various pipe types of GHX by the thermal response test (TRT) under the same field and test conditions. Four kinds of GHX (HDPE type, HDPE-nano type, spiral fin type, and coaxial type) were constructed in the same site. Inlet and outlet temperatures of GHXs and effective thermal conductivity were measured through the TRT. In addition, the borehole thermal resistance was calculated to comparatively analyze the correlation of the heat exchange performance with each GHX. Result of the TRT revealed that averages effective thermal conductivities of HDPE type, HDPE-nano, spiral fin type, and coaxial type GHX were 2.25 W/m·K, 2.34 W/m·K, 2.55 W/m·K, and 2.16 W/m·K, respectively. In the result, it was found that the average borehole thermal resistance can be an important factor in TRT, but the effect of increased thermal conductivity of pipe material itself was not significant.

Study on Thermal and Hydrodynamic Performance of a Triple Fluid Heat Exchanger with Different Passes and Rows

Hybrid cooling system has become a promising thermal management system for data center considering its capability of removing heat from various electronic components systematically. Water cooling and air cooling can be used for cooling the active component and passive component respectively. A novel triple fluid heat exchanger (TFHEX) is designed to dissipate the heat from these fluids into the coolant. This paper discusses thermal and hydrodynamic performance of TFHEX that specially designed for hybrid cooling of data. In present work, the THFEX is designed to dissipate heat from 32kW rack in which the server that dissipates 90% of heat from the active component and 10% of from passive component. Since the water side has much higher load, heat transfer from tube to tube in TFHEX has to be carefully maintained without significant increase in pressure drop. It was found that TFHEX can dissipate heat from different heat source at various load without significant increase in the pressure drop if designed carefully and therefore this heat exchanger can be a feasible solution for hybrid cooling data center. The results critically evaluated the trade-off between the heat transfer capacity of TFHEX and its pressure drop i.e. the pumping power requirement. This can be a reference for data center engineers to select the appropriate configuration for TFHEX for hybrid cooling.

A hybrid numerical-experimental analysis of heat transfer by forced convection in plate-finned heat exchangers

A hybrid numerical-experimental approach to obtain the thermal performance of heat exchangers is presented. The proposed methodology combines numerical simulation with wind tunnel experimental data to predict the average convective heat transfer coefficient and overall finned surface efficiency. The technique is applied to a plate-finned tube heat exchanger with in-line arrangement. Validation of the present methodology is performed by comparing the results against empirical correlations for the Nusselt number available in the literature. A parametric study is performed aiming to evaluate the influences of the airflow velocity (Reynolds number) and fin materials (aluminium, carbon steel and copper) upon the heat transfer characteristics. The main results indicate an increase of the average convective heat transfer coefficient with air velocity; whereas the overall fin surface efficiency presents an opposite behaviour. Furthermore, the Nusselt number based on the overall heat transfer coefficient is larger for higher conductive fin materials. In addition, aluminium and steel fins are found to be the most weight and cost-effective fin materials, respectively.

Thermal-exergetic behavior of a vertical double-tube heat exchanger with bubble injection

ABSTRACTThe use of air bubbles as a heat transfer improvement technique for heat exchangers has been proposed by some researchers. The vertical motion of tiny bubbles because of density difference with liquid provides extra vibration, eddies, turbulences, and consequently further heat transfer rate. The variety of affected parameters, such as injection method, air mass flow rate, bubbles size, number of perforations that forms bubbles, etc., has added to the complexity of this phenomena so that any change in the said parameters significantly influences the thermal-exergetic behavior of the heat exchanger. The quality and quantity of the impact of bubbles on the thermal performance of heat exchangers are different for any type of them. Moreover, each type of heat exchanger requires a specific injection method depending on the heat exchanger structure. In the present research, an injection way is proposed for vertical double-tube heat exchangers, and the effect of bubbles on thermal-exergetic characteristics is experimentally studied and discussed, which have not been performed before. Nondimensional exergy destruction, number of heat transfer units, and effectiveness are the main evaluated parameters in the present paper. Results showed a significant thermal improvement of the heat exchanger under the bubble injection.

Inclination Angle Optimization for “Inclined Projected Winglet Pair” Vortex Generator

Abstract Vortex generators (VG) are widely used in multifunctional heat exchangers/reactors for augmenting the heat transfer from fin plates to the working fluid. In this study, numerical simulations for longitudinal VGs are performed for both laminar and turbulent flow regimes. The shear-stress transport (SST) κ–ω model is used for modeling turbulence. Inclination angle for a new streamlined VG configuration called inclined projected winglet pair (IPWP) was varied to study the effect of this angle on the heat transfer enhancement and pressure drop. Response surface methodology (RSM) was used to deduce the inclination angle effects on heat transfer, pressure drop, and vorticity from both local and global points of view. Such study highlights the optimization for this VG configuration for better heat transfer intensification, based on thermal enhancement factor (TEF). Finally, it is found that the VG with inclination angle ranging from 30 deg to 35 deg exhibits the best global performance compared to other inclination angles. This type of studies is important for the enhancement of the thermal performance of heat exchangers and static mixers in various engineering applications.

Bir gövde borulu ısı değiştiricisinde farklı levha türlerinin ısıl performansa etkisinin sayısal olarak incelenmesi

In this study, the thermal performance of a small scale shell and tube heat exchanger was performed according to the baffle type by using three dimensional Computational Fluid Dynamics (CFD) method. In numerical calculations, segmental and continuous helical baffle types were selected to get the comparative results. For helical baffle type, we used two different models that the numbers of helical rotations and baffle spacing length were different. Thus, we determined five different numerical models and the thermal performance of each models were evaluated under different inlet temperature values selected as 50, 60 and 70°C for the tube side. The inlet temperature value and the mass flow rate of shell side were kept constant during all the numerical calculations. The heat transfer calculations were achieved by using Logarithmic Mean Temperature Difference (LMTD) method. We also employed the Bell-Delaware method which can be used accurately for shell and tube heat exchangers. The highest thermal performance was determined in Case-IV which had equal baffle spacing and the maximum number of rotations for continuous helical baffle. The predicted total pressure drop results obtained from the numerical calculations were in good agreement with the calculated total pressure drop from Bell-Delaware method. The lowest pressure drop and the highest thermal performance were achieved for continuous helical baffle type compared to the segmental equal spacing baffle type. The numerical simulations based on CFD analysis can provide more information about heat exchangers and this tool can be used to improve both design and the thermal performance of heat exchangers.