Helical Heat Research Articles

Experimental investigation on thermo-hydraulic performance of a helical plate heat exchanger

ABSTRACT The current research presents an experimental study on heat transfer and fluid flow characteristics of a helical plate heat exchanger (HP-HEx). Helical plate with different pitches and cross sectional area of the flow channel was investigated for various fluid mass flow rates and inlet temperatures. The results show that the proposed heat exchanger performed an overall heat transfer coefficient (U) and exergy efficiency (ηex ) about 279.77 W/m2.K and 60.87% respectively. Also, the HP-HEx showed effectiveness (ε) and number of transfer unit (NTU) reach about 0.694 and 1.79 respectively with pressure loss reached 202 kPa, for hot and cold fluids flow rate 0.083 kg/s and 0.07 kg/s at inlet hot and cold fluid temperature 45°C and 28°C respectively, and pitch = 56 mm. The pitch and cross sectional area of the flow channel variation can augment heat transfer rate and decrease the pressure loss. For pitch decreasing from 76 mm to 46 mm, the U, ε, NTU, ηex , and pressure loss increase by 50.60%, 22.39%, 50.60%, 10.35%, and 20.87% respectively. Empirical general correlations were obtained from the experimental data of the present study with maximum deviations about ±16.81%, ±13.33%, ±17.73%, ±16.60% and ±15.60% for U, ε, NTU, ηex , and pressure loss, respectively.

Design development and comparative performance evaluation of variable pitch helical fluropolymer heat exchanger

Design development and comparative performance evaluation of variable pitch helical fluropolymer heat exchanger

Nuclear Hydrogen Production: Modeling and Preliminary Optimization of a Helical Tube Heat Exchanger

Hydrogen production is a topical issue in an energy scenario where decarbonization is a priority, especially with reference to the transport sector that has a great weight on global emissions. Starting from this consideration, GIF (Generation-IV International Forum) investigated the possibility to produce hydrogen by nuclear energy. The “classic” strategy is based on the use of nuclear as energy source for the electrolysis; but on the medium-long term, a more sustainable and smart approach could be founded on the use of thermochemical processes (e.g., I-S) that require a direct coupling of a chemical plant to a nuclear reactor. In order to develop this strategy, it is mandatory to design and optimize all the key components involved in this complex plant. In this study, we developed the 3D-CAD and CFD models of the intermediate heat exchanger (IHX) installed in the Japanese HTTR nuclear power plant. This component is extremely important for both the safety of the two plants and the stability of the whole hydrogen production plant. Initially, our model (developed by AutoCAD 3D and implemented in Star CCM+) was validated on the basis of experimental data available in literature; then, an initial optimization of the IHX testing innovative materials, such as Alloy 617 and ODS–MA754, and a different primary coolant (supercritical CO2) was performed.

Experimental analysis of heat transfer coefficient in counter flow shell and helical coil tube heat exchanger with hybrid nanofluids to enhance heat transfer rate using in food processing industries

The impact of overall heat transfer coefficient and the pressure drop on performance of a counter flow helical tube heat exchanger with Cu-Ni-water hybrid nanofluid are computed. To evaluate heat transfer rate for a mix of base fluid with copper and nickel nanoparticles of volume concentrations 0.02,0.04 and 0.06 are added. To control the sedimentation of nanoparticles in the base fluid Ultrasonication followed by magnetic stirrer method is used. In this work experiments are conducted with to enhance heat transfer rate rather than stability of nanoparticles. Experiments are conducted for different concentrations and coil turns under laminar flow regime. The results are shown that 0.04 % vol of Cu-Ni/H2O with 12 turns is more predominate foe food processing applications due to its consistency in maintaining a constant temperature.

Thermal Performance of Helical Ground Air Heat Exchanger Under Saharan Climate Conditions: An Experimental Study

Thermal Performance of Helical Ground Air Heat Exchanger Under Saharan Climate Conditions: An Experimental Study

나선형 튜브 열교환 방식의 포화 상태 액체질소의 비등열전달 특성에 대한 실험적 연구

나선형 튜브 열교환 방식의 포화 상태 액체질소의 비등열전달 특성에 대한 실험적 연구

Experimental assessment of heat exchangers with nested helical coils for an absorption heat transformer

ABSTRACT The studies of nested helical coil heat exchangers for an absorption heat transformer are very limited, although this arrangement has a greater heat transfer area in a smaller volume. The heat exchangers are vertically placed to develop the desorption, condensation, evaporation and absorption processes by falling film mode. The usage of energy from point of qualitative view in these times is mandatory, due to the fossil fuels reduction and pollution. This experimental study analyses the behavior the nested helical coils heat exchangers through the first and second law of thermodynamics. The physical and chemical exergy for the main components and whole system is calculated by using the conventional method. All the experimental tests are carried out by varying the source temperature from 343.15 to 358.15 K with heating mass flow rate in the generator between 0.07 and 0.13 kg/s. For this study, the condensation and absorption processes reach the highest exergy destruction at high temperatures, while the solution heat exchanger presents the lowest irreversibility. The exergy coefficient of performance always improves when the supplied heat in the generator increases owing to the heating mass flow rate and temperature, however there is an increment considerably of total irreversibility at 349.15 K.

Experimental and numerical investigation on bare tube cross flow heat exchanger-using COMSOL

ABSTRACTIn this study, COMSOL multi-physics modelling software was used to make a computational model of a bare helical tube cross flow heat exchanger in order to simulate the temperature changes in the heat exchanger. The computational results of heat transfer are validated by using the analytical models. A conjugate convection/conduction heat transfer model was developed, which exhibited good agreement to the experiments. A different velocity of air taken into the consideration to find out the temperature distribution through the pipe and air temperature inside the duct. The temperature profile, and the overall heat transfer rate from the wall of the tube were calculated and plotted for theoretical, experimental and Numerical method using the k- conjugate heat transfer model. The model is validated through comparison with theoretical relations for single-pass cross-flow arrangements and with experimental results also. Simulation results showed good agreement with experimental values with respect to different mass flow rates.

Evaluation of Existing Heat Transfer Correlations in Designing Helical Coil Evaporators for Low-Temperature Organic Rankine Cycles via Inverse Design Approach

ABSTRACTFor evaluating the heat transfer correlations from literature in designing helical coil evaporators for low-temperature organic Rankine cycles (ORC), an inverse evaporator design methodology is used. This is done by taking four already performed measurements with different working fluid mass flow rates (0.21–0.23 kg/s) and saturation pressures (1.93–3.05 MPa, reduced pressures of 0.51–0.82) at the helical coil evaporator (66 m long) in an already operational experimental solar/thermal ORC system as real-case references for the evaporator inverse design's boundary conditions. R-404A is considered as the working fluid. The heating water inlet temperature is changed between 353 K and 373 K. The total length is inversely calculated via 15 helical coil two-phase heat transfer correlations for each case. Their end designs are compared with the actual length. Results show that the correlations can be used interchangeably for designing helical coil evaporators for low-temperature ORCs since the heat transfer resistance is dominant on the shell-side. For evaluating the sensitivity of these results, a secondary analysis was made by means of changing the shell-side correlation's accuracy from its initial value of 10% to more accurate 7%. Predictions with several correlations design shorter heat exchangers at reduced pressures less than 0.7.

A Study on Heat Flow Characteristics of Forced Convection in a Helical Tube Heat Exchanger using CFD

A Study on Heat Flow Characteristics of Forced Convection in a Helical Tube Heat Exchanger using CFD

English

English

Numerical research of stream analysis on helical baffles heat exchangers

In this paper, the numerical simulations for a helical baffles heat exchanger and a segmental baffles heat exchanger with component clearance are performed to reveal the features of leakage streams and their effect on heat exchanger performance. Helical baffles heat exchanger models with four different angles and segmental baffles heat exchanger model were established and calculated via Gambit and Fluent software. The results reveal that the heat exchanger with a 40° helix angle shows the best comprehensive heat transfer performance in turbulent state, and the heat exchanger with a 50° helix angle shows better comprehensive heat transfer performance in laminar flow state. The leakage streams proportion of the helical baffles heat exchanger varies from 5.5% to 6.1%, compared with the leakage streams proportion changes from 16.6% to 21.0% in the segmental baffles heat exchanger. In both turbulent flow state and laminar flow state, with the rise of shell-side Reynolds number, the main spiral stream B proportion decreases and the leakage streams proportion increases in the segmental baffles heat exchanger, while the stream B proportion increases and the leakage streams proportion decreases in helical baffles heat exchanger. The proportion of stream B increases with the increase of the helix angle β and the proportions of leakage streams decrease with the increase of β. The proportion of the tube-baffle leakage stream A increases in radial direction. Both the proportion of stream A and that of the baffle-shell leakage stream E fluctuate in the intermediate zone in axial direction; the stream A proportion decreases at the inlet and outlet zone, while the stream E proportion increases at the inlet and decreases at the outlet zone. The results of this paper could be of great significance in the optimal design and manufacture of the helical baffles heat exchanger.

Modeling for Shell-Side Heat Transfer Coefficient and Pressure Drop of Helical Baffle Heat Exchangers

This study has suitably modified the existing heat transfer and pressure drop correction factors of the modified Bell–Delaware method used for heat exchangers with segmental baffles, taking into consideration the helical baffle geometry. These correction factors are presented in parametric formulas based on the Taborek presented procedure for segmental baffles. These formulas are functions of the geometrical and physical parameters of discontinuous helical baffles. In addition, the parametric formulas are presented graphically based on the Stehlik method. The correction design method proposed by Stehlik for the helical baffle is presented in detail and a theoretical model for shell-side heat transfer and pressure drop is developed. In general, the results show that the present model matches more closely with the graphically proposed correction factors of Stehlik. In order to calculate the shell-side heat transfer coefficient and pressure drop using the present method, a computational code has been developed by the authors. In addition, in order to examine the validity, the results of the code for a case study are compared with the results obtained from EXPRESS software and experimental formulas presented by Zhang. The results of comparison show that the proposed method is accurate and can be used by designers confidently.

Theory and Design of Counter Flow Shell-and-Coil Heat Exchanger for CO2Based Solar Water Heater

A shell type helical tube countercurrent flow heat exchanger was designed, fabricated and tested using CO2 refrigerant material. Helical copper tube was immersed in bulk water tank. Hot CO2 was piped to upper coil baffle and cold CO2 was circulated into collector loop through lower baffle. Cold water was made to enter through lower tap and hot water was taken out from upper tap. Both in/out pipes were inserted from the top and coil tubes from upper and lower sides of water tank. Supercritical thermosyphon operation was achieved by evacuated glass tube solar heat collector using CO2 refrigerant. U shaped copper pipes enveloped in aluminum foil were inserted in evacuated glass tubes to transfer heat under thermosiphon principle to upper header connected to inlet baffle of shell type helical coil heat exchanger. Lower header was connected to heat exchanger helical coil outlet baffle. Solar collector heat raised CO2 refrigerant temperature from 35 to 78C giving temperature difference of 43C. Temperature of CO2 refrigerant at exit from heat exchanger was found to be 40C at surrounding ambient temperature of 36C. Heat exchanger raised the inlet water temperature from 26 to 55C under off water tap condition in about 3 hours. Inlet and outlet temperature difference of heat exchanger was measured to be 27C. We believe system efficiency can further increase if we use the system in mild sunshine cold weather regions duplicating geothermal loop.

Experimental investigation of the reverse heat transfer of R134a flow through non-adiabatic coiled capillary tubes

This research represents an experimental investigation of the metastable flow and re-condensation phenomenon through non-adiabatic lateral helical capillary tubes and suction tube heat exchanger. The results show that mass flux ratio has a vital role: It affects metastable flow and also reverse heat transfer phenomenon through non-adiabatic helical capillary tube. Therefore, by increasing of the mass flux ratio, the rate of heat transfer between them decreases. In contrast to the strong rate condition of heat transfer between them, reverse heat transfer or re-condensation maybe happen. Moreover, experimental results show that for R134 flow with mass flux ratio more than 57.84, metastable flow exists in non-adiabatic capillary tube with 0.9144 mm inner diameter, 30 mm coil diameter, 6.18 m length, 4 mm inner diameter of compressor suction tube.

Performance Study of Continuous Helical Baffle Shell and Tube Heat Exchanger With Central Low-Pressure Regions

Shell and tube heat exchanger (STHX) is a class of indirect contact heat exchangers which has wide applications in various industries. In this paper, the shell-side performance characteristics of a small STHX with differently notched continuous helical baffle (CHB) geometries are numerically studied and compared with same CHB without notched regions. The indentations are uniquely produced by placing the notch near the core of the heat exchanger, thereby conferring the flow with low-pressure drop regions. Two set of models of inner notched continuous helical baffle (ICHB), i.e., ICHB1 and ICHB2, are studied with notch width of about 5% and 10% of the inner shell diameter of the same heat exchanger. In comparison with the CHBSTHX, it is seen that the STHXs incorporated with ICHBs, the heat transfer rate dropped slightly, but a significant decrease in pressure drop is observed. It is found that the heat transfer coefficient to pressure drop ratio for ICBH1 and ICHB2 shows significant increase in comprehensive performance of about 3.5% and 32.42%, respectively, when compared with same CHB without notched regions.

Numerical investigation of two-phase laminar pulsating nanofluid flow in a helical microchannel

ABSTRACTNumerical investigations on the thermal and hydraulic characteristics of pulsating laminar flow in a three-dimensional helical microchannel heat sink (HMCHS) model are performed using Al2O3-water-based nanofluid. The simulation is performed in the laminar regime for Reynolds number ranging from 6 to 25. The two-phase mixture model with modified effective thermal conductivity and viscosity equations is employed to solve the problem numerically. The detailed results for thermal and flow fields are reported for the effects of amplitude (1–3), frequency (5–20 rad/s), and nanoparticle concentration (1%–3%). The results indicate that the heat transfer performance improves significantly for sinusoidal velocity inlet conditions compared with steady flow conditions.

Numerical simulation on the performance of trisection helical baffle heat exchangers with small baffle incline angles

ABSTRACTNumerical simulation was conducted on oil–water heat transfer in five circumferential overlap trisection helical baffle shell–and–tube heat exchangers (cothSTHXs) with 16 tubes and incline angles of 12°, 16°, 20°, 24°, and 28° and a segmental baffle heat exchanger of the identical tube layout for comparison under laminar flow calculation conditions. The local images represent shell-side flow patterns, and heat transfer properties are presented showing the detailed “secondary vortex flow” and “shortcut leakage flow” patterns to explain the different characteristics of the six schemes. The simulation curves of the heat transfer coefficient and pressure drop are compared with those of the experimental ones, with satisfactory agreement. The average values of the shell-side heat transfer coefficient and the comprehensive index ho/Δpo of the 12° helical scheme are respectively 47% and 51% higher than those of the segmental baffle scheme with about the same pressure drop.

Two-Phase Analysis of A Helical Microchannel Heat Sink Using Nanofluids

A three-dimensional helical microchannel heat sink (HMCHS) model is developed to investigate the heat transfer characteristics using Al2O3–water-based nanofluid. The two-phase mixture model with modified effective thermal conductivity and viscosity equations is employed for solving the problem numerically. The model developed is validated by comparing the results of Nusselt number with available experimental and numerical data for a wide range of Reynolds number. The detailed results of the thermal field are reported for the effects of helix radius (0.15–0.30 mm), pitch (0.5–2.0 mm), number of turns (7–10), and aspect ratio (1.5–3.0). The analysis presents a unique fundamental insight into the complex secondary flow pattern in the channel due to curvature effects.

Performance Study of a Circumferential Overlap Trisection Helical Baffle Heat Exchanger at the Shell Side

Using the three-dimensional (3D) modeling software Gambit, a mathematical model of a circumferential overlap trisection helical baffle shell-and-tube heat exchanger (cothSTHX) was developed with 34 tubes and three pulling rods with an equilateral triangle tube layout and a baffle incline angle of 20°. The numerical simulation of flow and thermal performances was performed with the analysis software Fluent. The temperature, pressure, and velocity nephograms are shown for different slices, including spiral, concentric hexagon longitudinal, meridian, eccentric longitudinal, and transverse slices. The nephograms of temperature, pressure, and velocity with superimposed velocity vectors vividly display the important parameters of the cothSTHX. The “Dean vortex secondary flow” is a key mechanism to enhance the heat transfer in heat exchangers, which is clearly depicted to show that the spiral fluid flows outward under the centrifugal force, then flows back to the axis under the radial differential pressure, forming a single vortex in each helix cycle. The structure of circumferential overlap baffles restricts the shortcut leakage flow, and the flow pattern in the cothSTHX is very close to “plug flow” on the unfolded hexagon slices.