Horizontal Double-pipe Heat Exchanger Research Articles

Experimental Investigation of the Horizontal Double Pipe Heat Exchanger Utilized Phase Change Material

The melting of a phase change material (PCM) inside a horizontal concentric two-pipe heat exchanger is experimentally investigated. The PCM RT-42 (Rubitherm) is contained in the annular space between the inner tube of diameter 25 mm and outer insulated shell of diameter 75mm. The hot water as a heat transfer fluid (HTF) flows inside the inner tube at different temperatures, 60, 70 and 80 °C. The experimental setup involves twelve thermocouples to record the transient temperatures of PCM at different locations. Also, the progress of the solid-liquid front during the melting process is tracked photographically by a digital camera. The experimental findings revealed that the heat conduction, accompanied by the same melting rate around the inner tube of the heat storage unit, is predominant at the beginning of the melting process. As time progresses, the natural convection role is strengthened and causes a higher melting at the top part than is shown at the lower part, which is still dominated by conduction. Also, the melting rate is directly affected by the temperature of the HTF. The melting time is reduced by about 27% and 46% when the HTF temperature varies from 60 to 70°C and 80°C, respectively. The variation of the Nusselt number during the melting process is evaluated. There is a positive influence of the HTF temperature on the energy stored by the PCM.

Annulus eccentricity optimisation of a phase-change material (PCM) horizontal double-pipe thermal energy store

Abstract The application of phase-change materials (PCMs) has received significant interest for use in thermal energy storage (TES) systems that can adjust the mismatch between the energy availability and demand. In the building sector, for example, PCMs can be used to reduce air-conditioning energy consumption by increasing the thermal capacity of the walls. However, as promising this technology may be, the poor thermal conductivity of PCMs has acted as a barrier to its commercialization, with many heat-transfer enhancement solutions proposed in the literature, such as microencapsulation or metal foam inserts, being either too costly and/or complex. The present study focuses on a low-cost and highly practical solution, in which natural-convective heat transfer is enhanced by placing the PCM in an eccentric annulus within a horizontal double-pipe TES heat exchanger. This paper presents an annulus-eccentricity optimisation study, whereby the optimal radial and tangential eccentricities are determined to minimize the charging time of a PCM thermal energy store. The storage performance of several geometrical configurations is predicted using a computational fluid dynamics (CFD) model based on the enthalpy-porosity formulation. The optimal geometrical configuration is then determined with response surface methods. The horizontal double-pipe heat exchanger studied considered here is an annulus filled with N-eicosane as the PCM for initial studies. In presence of N-eicosane, for the concentric configuration (which is the baseline case), the charging is completed at Fo = 0.64, while the charging of optimum eccentric geometries with the quickest and slowest charging is completed at Fo = 0.09 and Fo = 2.31, respectively. In addition, an investigation on the discharging performance of the studied configurations with N-eicosane shows the quickest discharge occurs with the concentric annulus case at Fo = 0.99, while the discharge time of the proposed optimum annuli is about three times this value. In other words, the proposed optimum geometry with the quickest charging time charges ~7.1 times faster but also discharges ~3 times slower, which is ideal for a TES, especially when used as passive thermal storage systems in nearly zero-emission buildings. Complementary studies demonstrate that the proposed optimum configuration improves the TES performance also when employing other PCM types as well as various shell-to-tube diameter ratios.

Experimental study of R600a/oil/MWCNT nano-refrigerant condensing flow inside micro-fin tubes

The present experimental study aims to investigate condensation heat transfer characteristics of R600a/oil/multi-walled carbon nanotube (MWCNT) nano-refrigerant flow inside a horizontal micro-fin tube. The test condenser is a horizontal double-pipe heat exchanger consists of a copper micro-fin tube with 14.18 mm inner diameter which is installed in a polyethylene shell with a diameter of 6 cm. The experiments cover a wide range of parameters, including mass velocity of 54 to 90 kg/m2 s, vapor quality of 0.03 to 0.76, and condensation pressure of 550 to 700 kPa. The investigations are conducted in three parts, including the characteristics of pure R600a condensing flow inside micro-fin tubes, the effect of adding lubricating oil with concentration of 1%, and the impact of adding nano-oil with nanoparticles compactness of 0.1, 0.2, and 0.3%. Comparison of the experimental data for the pure refrigerant flow with three well-known correlations shows the maximum deviation of ±20% which validates the test procedure. Based on the results, R600a/oil heat transfer coefficient is higher than pure R600a in low and medium vapor qualities, while at high qualities the pure R600a shows higher coefficient due to the impact of lubricating oil on the condensate liquid film thermal resistance. In addition, adding nanoparticles is more effective at low and medium vapor qualities and high mass velocity. The results showed that using MWCNT nanoparticles with the compactness of 0.3% increases the heat transfer coefficient up to 74.8% in comparison to the pure refrigerant.

Second law analysis of turbulent convection flow of boehmite alumina nanofluid inside a double-pipe heat exchanger considering various shapes for nanoparticle

The main objective of this research is to study the effects of nanoparticle shape on the entropy generation characteristics of boehmite alumina nanofluid flow in a horizontal double-pipe heat exchanger. The examined boehmite alumina nanofluids include dispersed cylindrical, brick, blade, platelet and spherical nanoparticles in a mixture of water/ethylene glycol. The nanofluid and water flow through the tube side and annulus side of the heat exchanger, respectively. Two-phase mixture model is applied to precisely simulate the behavior of nanofluid. The effects of the various Reynolds numbers, nanoparticle concentrations and nanoparticle shapes on the frictional, thermal and total entropy generation rates as well as the Bejan number are numerically investigated. The results indicated that the highest and lowest frictional entropy generation rate belongs to the nanofluids with platelet shape and spherical shape nanoparticles, respectively, while the nanofluid containing spherical shape and platelet shape nanoparticles represented the maximum and minimum thermal and total entropy generation rates. Furthermore, it was inferred that the frictional entropy generation rate is enhanced with an increase in nanoparticle concentration, whereas except for nanofluid with spherical shape nanoparticles, the opposite is true for thermal and total entropy generation rates and Bejan number.

Experimental investigation on the hydrothermal performance of a double-pipe heat exchanger using helical tape insert

This study experimentally examines the hydrothermal performance of horizontal Double Pipe Heat Exchangers (DPHEs) with and without continuous Helical Tape Insert (HTI) conducted on the outer surface of the internal pipe. Ten DPHEs of counter-flow configurations were constructed; nine of them were with HTI fabricated with different ratios of HTI height to the clearance between the two pipes (δ), and different ratios of HTI pitch to HTI diameter (λ). The experiments were performed with pure water in both sides with 2050≤Rean≤15925, and Ret≈26700. Compared with plain annulus-case, the results showed that using the HTI increases both annulus average Nusselt number (Nu¯an) and Fanning friction factor (fan), with average increases of 69.4–164.4% and 48.6–113.1%, respectively, when δ increases from 0.275 to 1, and with average increases of 78.1–183.2% and 67.6–99.2%, respectively, when λ decreases from 1 to 0.333. The hydrothermal performance index (HTPI) was determined to compare the performance of DPHEs with HTI to that of plain annulus case. The results demonstrated that HTI of δ = 0.667 provides the highest HTPI, while HTPI increases with decreasing λ. Finally, correlations for Nu¯an, fan, and HTPI for DPHEs with HTI in the annulus as a function of the investigated parameters were proposed.

Prediction of frictional pressure drop of R134a during condensation inside smooth and corrugated tubes

In the present paper, in order to understand the accuracy of 38 different correlations derived by various researchers in this field, the correlations were executed for condensation frictional pressure drop. To accomplish this goal, experimental data provided from authors' previous publications encompassing 412 points for two smooth tubes, and 334 points for five corrugated tubes, have been utilized so as to compare the determined results. The experimental setup is composed of a 2.5m double tube for horizontal configuration and smooth and corrugated tubes at the inner diameters of 0.0081m, while the applied mass flux range spans between 709 and 1974kgm−2s−1. The average quality of vapor and saturation pressure ranges lie within 0.09 to 0.97, and 10 to 13bar, respectively. Determining the frictional pressure drop in two-phase flows does not involve corrugated tube geometry in the calculation of friction factor, to make this available, a slight alteration that requires the replacement of a correlation with another one in the literature was suggested with regard to friction factor approach. As a result of this, it was noticed that performances of some correlations were optimized to predict the frictional pressure drop in corrugated tubes. Additionally, the most effective correlations have been selected for the horizontal double pipe heat exchanger having smooth and corrugated tubes. Finally, alteration of the condensation pressure drop with Reynolds number are presented using both experimental data and best predictive correlations.

Inner pipe downward movement effect on melting of PCM in a double pipe heat exchanger

This study is aimed to investigate the melting of phase change material (PCM) in a horizontal double pipe heat exchanger. The area between the pipes is filled with RT50 as PCM and water is used as a heat transfer fluid (HTF) which flows through inner pipe. The downward movement of inner pipe, inlet temperature and mass flow rate of HTF are considered and compared with the base system. The results show that inner pipe downward movement increases the convection-dominant zone which reduces melting time considerably (up to 64%). Results also indicate that by increasing the HTF inlet temperature thermal potential of the system increases which accelerates the melting process. However increasing the mass flow rate of HTF does not have significant role in melting rate.

Experimental investigation on the thermal performance of a double pipe heat exchanger with segmental perforated baffles

This work experimentally investigates the characteristics of convective heat transfer and pressure drop of water flow in the annulus-side of horizontal double pipe heat exchangers. Twelve heat exchangers of counter-flow configurations are constructed with/without Single Segmental Perforated Baffles (SSPBs), which are fabricated with different holes spacing, void, cut, pitch ratios and inclination angle. The experiments are performed for annulus-side Reynolds number from 1380 to 5700, and for Prandtl number from 5.82 to 7.86. The results revealed that increasing SSPBs holes spacing and void ratios and inclination angle and decreasing SSPBs cut and pitch ratios increase the annulus average Nusselt number (Nu¯an) as well as friction factor (fan). The thermal performance index (TPI) is calculated to compare the thermal performance of perforated baffled double pipe heat exchangers with un-baffled one. It is observed that increasing SSPBs holes spacing ratio and inclination angle, and decreasing SSPBs void ratio, cut ratio and pitch ratio enhances the thermal performance index. Finally, correlations for Nu¯an in addition to fan for concentric tube heat exchangers with SSPBs as a function of the investigated parameters are obtained.

Modeling of the melting characteristics of commercial paraffin wax in an inverted equilateral triangular enclosure: Effect of convective heat transfer boundary conditions

ABSTRACTA horizontal double-pipe heat exchanger with an inverted outer equilateral triangular tube is modeled to numerically investigate the low-temperature thermal energy storage capability of an impure phase change material (PCM). The energy source fluid (hot water) flows through the inner tube and transfers heat to the PCM (heat sink) residing in the annular gap. The results show that the inlet temperature of the heat transfer fluid (HTF) has a significant effect on the melting process compared with the mass flow rate (MFR). The configuration, as well the concentricity/eccentricity of the inner tube has a great influence on the energy storage.

Numerical analysis of magnetic field effects on hydro-thermal behavior of a magnetic nanofluid in a double pipe heat exchanger

This study attempts to numerically investigate the hydro-thermal characteristics of a ferrofluid (water and 4vol% Fe3O4) in a counter-current horizontal double pipe heat exchanger, which is exposed to a non-uniform transverse magnetic field with different intensities. The magnetic field is generated by an electric current going through a wire located parallel to the inner tube and between two pipes. The single phase model and the control volume technique have been used to study the flow. The effects of magnetic field have been added to momentum equation by applying C++ codes in Ansys Fluent 14. The results show that applying this kind of magnetic field causes kelvin force to be produced perpendicular to the ferrofluid flow, changing axial velocity profile and creating a pair of vortices which leads to an increase in Nusselt number, friction factor and pressure drop. Comparing the enhancement percentage of Nusselt number, friction factor and pressure drop demonstrates that the optimum value of magnetic number for Reff=50 is between Mn=1.33×106 and Mn=2.37×106. So applying non-uniform transverse magnetic field can control the flow of ferrofluid and improve heat transfer process of double pipe heat exchanger.

Experimental Study of Heat Transfer Enhancement in a Heated Tube Caused by Wire-Coil and Rings

This study investigates heat transfer characteristics and the pressure drop of a horizontal double pipe heat exchanger with wire coil inserts. The amplification of convection heat transfer coefficient in the heat exchanger reduces the weight, size and cost of heat exchanger. One way of augmenting the heat transfer is to disturb the boundary layer. When an object is placed in a boundary layer, it affects the flow structure and alters the velocity and thermal profiles. The change is affected by the formation of jets and wakes in the boundary layer as it alters modifies transfer and friction coefficients on the wall. This paper studies the characteristics of the heat transfer and the pressure drop of a double pipe horizontal tube heat exchanger with an inserted wire coil and rings. Wire coil acts as a swirl flow, which increases turbulence and roughness whereas rings increase heat transfer as a promoter of turbulence and roughness. The experimental data sets were extracted from wire coils and rings tested within a geometrical range with a pitch of (P/D=1, 2, 4) and wire diameter of (d/D=0.05, 0.07, 0.11). For wire coil with d/D=0.11, P/D =1 and Reynolds number of 10000, the overall enhancement efficiency amounted to 128%.

Experiments on New Arrangements of Convex and Concave Corrugated Tubes through a Double-pipe Heat Exchanger

The main scope of this article paper is to experimentally clarify the effects of outer-tube and inner-tube corrugations on thermal and frictional characteristics in a horizontal double-pipe heat exchanger. Nusselt number, friction factor, and thermal performance factor are evaluated for new various arrangements of convex and concave corrugated tubes. Smooth tubes were corrugated by means of a special machine. Findings indicate that the arrangement type of corrugated tubes has a significant effect on the mentioned parameters. The best performance was obtained for a heat exchanger made of a concave corrugated outer tube and a convex corrugated inner tube.

Experimental study of Al2O3/water nanofluid turbulent heat transfer enhancement in the horizontal double pipes fitted with modified twisted tapes

In this study, fluid flow of the Al2O3 nanofluid in a horizontal double pipe heat exchanger fitted with modified twisted tapes were experimentally studied under turbulent flow conditions. The experiments with different geometrical progression ratio (GPR) of twists as the new modified twisted tapes and different nanofluid concentration were performed under similar operation condition. Pitch length of the proposed twisted tapes and consequently the twist ratios changed along the twists with respect to the geometrical progression ratio (GPR) whether reducer (RGPR 1). Regarding the experimental data, utilization of RGPR twists together with nanofluids tends to increase heat transfer and friction factor by 12% to 52% and 5% to 28% as compared with the tube with typical twisted tapes (GPR = 1) and nanofluid. Contrarily, performances were weakened by using for IGPR twists 0.6 to 0.92 and 0.75 to 0.95. The thermal performances of the heat exchanger with nanofluid and modified twisted tapes were evaluated for the assessment of overall improvement in thermal behavior. Generalized correlations were developed for the estimation of Nusselt number, friction factor and thermal performance factor under turbulent flow conditions. Satisfactory agreement between the present correlations and obtained experimental data validate the proposed correlations.

Condensation heat transfer and pressure drop characteristics of R-290, R-600a, R-134a and R-22 in horizontal tubes

This paper presents the experimental results of condensation heat transfer coefficients of hydrocarbon (HC) refrigerants R-290 and R-600a, hydrochlorofluorocarbon (HCFC) refrigerant R-22, and hydrofluorocarbon (HFC) refrigerant R-134a in a horizontal double-pipe heat exchanger having pipe inner diameters of 10.07, 7.73, 6.54, and 5.80 mm. The condensation process experiments were conducted at mass flux of 35.5–210.4 kg/m2 s and condensation temperature of 40°C. The main results were summarized as follows: The average condensation heat transfer coefficients of R-290 and R-600a were higher than those of R-22 and R-134a. The pressure drops of the four refrigerants were in the order of R-600a > R-290 > R-134a > R-22. The pressure drops of R-600a, R-290, R-134a, and R-22 were approximately 6–15, 9.8–12.5, 4.3–6.7, and 2.1–4.6% higher, respectively, in the 10.7 mm diameter tubes compared to the 5.80 mm diameter tubes. Comparing the condensation heat transfer coefficients of our experimental results with those of other correlations, our experimental data in all the test tubes coincided best with that of Haraguchi et al.

12.7mm 내면핀관을 이용한 R-1270의 열전달 특성

This paper deals with the heat transfer characteristics of R-290 (Propane), R-600a (Iso-butane) and R-1270 (Propylene) as an environment friendly refrigerant and R-22 as a HCFC's refrigerant for evaporating. The experimental apparatus has been set-up as conventional vapor compression type refrigeration and air-conditioning system. The test section is a horizontal double pipe heat exchanger. Evaporating heat transfer measurements were performed for smooth tube with the outer diameters of 12.70, 9.52 and 6.35 ㎜ and micro-fin tube 12.70 ㎜, respectively.<BR> For the smooth and micro-fin tubes measured in this study, the evaporating heat transfer coefficient was enhanced according to the increase of the mass flux and decrease of the tube diameter. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to those of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficients in hydrocarbon refrigerants showed 20 to 28% higher values than those of R-22. Also, the evaporating heat transfer coefficients of R-22 in the tube diameter of the 12.70 ㎜ smooth and micro-fin tube were compared. Generally, the local heat transfer coefficients for both types of tubes increased with an increase of the mass flux. The heat transfer enhancement factor (EF) between smooth and micro-fin tube varied from 1.9 to 2.7 in all experimental conditions.

수평관내 R-290과 R-600a의 증발 열전달 특성

본 논문은 수평 이중관식 열교환기 내 프레온계 냉매의 대체냉매인 탄화수소계 냉매(R-290과 R-600a)의 증발 열전달 계수에 대한 실험적 결과를 나타내었다. 증발기의 내관 내경은 각각 10.07 mm와 6.54 mm의 2가지를 사용하였다. 증발실험은 질량유속 <TEX>$35.5{\sim}210.4\;kg/m^2s$</TEX>이고, 냉각용량 <TEX>$0.95{\sim}10.1\;kW$</TEX>인 조건에서 수행하였다. 실험결과를 요약하면, 탄화수소계 냉매 R-290과 R-600a의 증발 열전달 계수가 프레온계 냉매 R-22보다 높았다. 즉, R-22의 증발 열전달 계수에 비해, R-290와 R600a는 각각 <TEX>$56.7{\sim}70.1%$</TEX>와 <TEX>$46.9{\sim}59.7%$</TEX> 정도 높았다. 실험데이터와 종래의 상관식을 비교한 결과, 모든 냉매와 관경에 대해서 Kandlikar상관식이 가장 좋은 일치를 보였다. This paper presents the experimental results of evaporation heat transfer coefficients of HC(e.g. R290 and R600a), R-22 as a HCFCs refrigerant in horizontal double pipe heat exchangers, having four different inner diameters of 10.07 mm and 6.54 mm respectively. The experiments of the evaporation process were conducted at mass flux of <TEX>$35.5{\sim}210.4\;kg/m^2s$</TEX> and cooling capacity of <TEX>$0.95{\sim}10.1\;kW$</TEX>. The main results were summarized as follows : The average evaporation heat transfer coefficient of R-290 and R-600a was higher value than that of R-22. In comparison with R-22, the evaporation heat transfer coefficient of R-290 and 600a is approximately <TEX>$56.7{\sim}70.1$</TEX> and <TEX>$46.6{\sim}59.7%$</TEX> higher, respectively. In comparison with experimental data and some correlations, the evaporation heat transfer coefficients are well matched with the Kandlikar's correlation regardless of a type of refrigerants and tube diameters.

Evaporation Heat Transfer Characteristics of Hydrocarbon Refrigerants R-290 and R-600a in the Horizontal Tubes

This paper presents the experimental results of evaporation heat transfer coefficients of HC refrigerants (e.g. R290 and R600a), R-22 as a HCFCs refrigerant and R-134a as a HFCs refrigerant in horizontal double pipe heat exchangers, having four different inner diameters of 10.07, 7.73, 6.54 and 5.80 ㎜ respectively. The experiments of the evaporation process were conducted at mass flux of 35.5~210.4 ㎏/㎡s and cooling capacity of 0.95~10.1 ㎾. The main results were summarized as follows : The average evaporation heat transfer coefficient of hydrocarbon refrigerants(R-290 and R-600a) was higher than the refrigerants, R-22 and R-134a. In comparison with R-22, the evaporation heat transfer coefficient of R-134a is approximately -11~8.1 % higher, R-290 is 56.7~70.1 % higher and R-600a is 46.9~59.7 % higher, respectively. In comparison with experimental data and some correlations, the evaporation heat transfer coefficients are well predicted with the Kandlikar's correlation regardless of a type of refrigerants and tube diameters.

Condensing heat transfer and pressure drop characteristics of hydrocarbon refrigerants

This paper presents the experimental results of condensing heat transfer coefficients and pressure gradients of HC refrigerants (e.g. R-1270, R-290 and R-600a) and R-22 in horizontal double pipe heat exchangers, having two different internal diameters of 12.70 mm and 9.52 mm (OD), respectively. Both the local condensing heat transfer coefficients and pressure drops (inside the tube) of hydrocarbon refrigerants were higher than R-22. The average condensing heat transfer coefficient increased with the mass flux. The experimental heat transfer coefficients agreed with the correlations of Shah, Travis and Cavallini–Zecchin’s to within ±20%. These results can be useful in the design of new heat exchangers involving hydrocarbon refrigerants for future air-conditioning systems.

Characteristics of condensing and evaporating heat transfer using hydrocarbon refrigerants

This paper discusses the heat transfer characteristics of R-290 (propane), R-600a (iso-butane) and R-1270 (propylene) as an environment-friendly refrigerant and R-22 as a HCFCs refrigerant for condensing and evaporating. An experiment was performed for a conventional vapor compression type heat pump system. The test section was a horizontal double-pipe heat exchanger. A tube diameter of 12.70mm with 1.315mm wall thickness was used for this experiment. The experimental results show that the local condensing heat transfer coefficients of hydrocarbon refrigerants were higher than those of R-22. The average condensing heat transfer coefficient for R-1270 was a maximum value and for R-22 was a minimum value among the refrigerant tested. The experimental results of comparing the condensing heat transfer coefficients agreed satisfactorily to the referenced simulation data such as the Cavallini–Zecchin’s correlation for all refrigerants. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were higher to those of R-22. The average evaporating heat transfer coefficient increased with the increase of mass velocity. The results show that the evaporating heat transfer coefficients in hydrocarbon refrigerants were higher than that of R-22. The experimental results for all the refrigerants in general agreed with Kandlikar’s correlation for the evaporating heat transfer.

Condensing heat transfer characteristics of hydrocarbon refrigerants in 9.52 and 12.7 mm smooth tube

Experimental results for heat transfer characteristic and pressure gradients of hydrocarbon (HC) refrigerants and R-22 during condensing inside horizontal double pipe heat exchangers are presented. The test sections which have one tube diameter of 12.70 mm with 0.86 mm wall thickness, another tube diameter of 9.52 mm with 0.76 mm wall thickness are used for this investigation. The local condensing heat transfer coefficients of HC refrigerants were higher than that of R-22. The average condensing heat transfer coefficient increased with the increase of the mass flux. It showed the higher values in HC refrigerants than R-22. Comparing the heat transfer coefficient of experimental results with that of other correlations, the presented results had a good agreement with most of the Cavallini’s correlations.