Horizontal Tube Heat Exchanger Research Articles

Investigation of Thermal Conductivity and Convective Heat Transfer Coefficient of Water-based ZnO Nanofluids

Nanofluids are stable suspensions of nanoparticles in a conventional fluid. They have shown superior potential in heat transfer enhancement. In this research, ZnO/water nanofluids were prepared at various concentrations from 0.2 to 1.5vol%, and their thermal conductivity was measured. The results showed that the thermal conductivity of ZnO/water nanofluids depends on particle concentration and increases non-linearly with the volume fraction of nanoparticles. The effects of particles size and temperature on the thermal conductivity were also investigated at 1.5vol%. The results indicated that thermal conductivity enhanced with decreasing particles size and increasing with temperature. For nanofluids containing 10-15 nm and 45-50 nm particle sizes, the enhancements were 26.3 and 22.8% at 40oC, respectively. In this research, the convective heat transfer coefficient of ZnO/water nanofluids with the above particle sizes was also measured under laminar flow in a horizontal tube heat exchanger. It was observed that both nanofluids showed higher heat transfer coefficients compared to the base fluid at a constant concentration (1.5 vol%). For nanofluids with 10-15 nm and 45-50 nm particle sizes, the average heat transfer coefficient enhancement was 18.1 and 14.9% at Re=1115, respectively.

Fabrication and Experimental Analysis of Absorber Based LiBr – Water Absorption Refrigeration System

The goal of this research work is to design, construct and analyse the performance of a single stage vapour absorption unit of 1kW rated cooling capacity. The correlations required for the design and analysis are mentioned in the section III. The solution heat exchanger of spiral tube and shell type was designed and installed in the unit. A forced horizontal tube heat exchanger type condenser was designed and used in the construction of the unit. A pool boiling generator has been installed in the unit. The determined hypothetical results including the overall heat transfer coefficient are compared with the test results inferred for a developed unit with a nominal output of 1kW. At last the performance parameters are examined in connection to the concentration of the absorber and mass flow rates. The actual COP of the system increased by 15% with the decrease in solution concentration at absorber inlet. Critical analysis is carried-out at each level to calculate the each accessory heat load and other parameters.

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%.

Numerical investigation on prevention of fouling in the horizontal tube heat exchanger: Particle distribution and pressure drop

To improve the performance of fouling prevention in liquid–solid fluidized bed heat exchanger with the horizontal tube bundle, parametric study of particle distribution and pressure drop in the heat exchanger was numerically conducted. Eulerian multiphase fluid model was used to calculate the flow of liquid–solid two phase in heat exchanger by means of the commercial software Fluent. In the simulation result, it was demonstrated that more particles occurred in the lower tubes of the horizontal tube bundle in low velocity due to the lack of full fluidization. Relative to that in low velocity, uniformity distribution of particle was obtained in high velocity which was accompanied with greater dynamic pressure drop. The particle with the greater density and diameter was inclined to sediment in the lower tubes due to larger sediment velocity and difficulty in the realization of full fluidization. Meanwhile an increase in size and density of particle would bring about greater pressure drop originating from more particle kinetic energy consumed. Effect of volume fraction of solid phase on particle distribution and pressure was discussed. It showed that an increase in volume fraction of solid phase led to significant rise of pressure drop. It was because consumed kinetic energy and collision energy of particles were greatly amplified with the increasing volume fraction of solid phase. Therefore greater volume fraction of solid phase, especially for the particle with the greater diameter and density, would not be recommended in the performance of fouling prevention in the horizontal tube bundle heat exchanger.

The mechanisms of heat transfer during convective boiling under the influence of AC electric fields

In this investigation the local heat transfer coefficients along the top and bottom of a horizontal tube heat exchanger within which convective boiling of HFE7000 is occurring are measured. Of particular focus is the influence of Electrohydrodynamics (EHD) on the flow regimes and associated heat transfer. To achieve this, thermocouples are embedded into the walls of a transparent sapphire tube coated with a transparent yet electrically conductive layer of Indium Tin Oxide (ITO). The ITO layer allows visual access to the two phase flow while at the same time acts as an electrical heater element for the heat transfer and electrical ground for establishing the electric field. Tests have been performed for a fixed mass flux of G=100kg/m2s, inlet quality of x=3% and applied heat flux of q″=12.4kW/m2. An AC 60Hz high voltage was applied across the fluid up to 8kV in increments of 1kV. The results show that, for the conditions tested, the application of EHD substantially increases the heat transfer coefficient at all measurement locations on the heat exchanger. Near the entrance, the top surface heat transfer enhancement reached over 7.2-fold and this decreased monotonically to 2.4-fold at the exit region. The bottom enhancement was more uniform along the heat exchanger ranging between approximately 3 and 4-fold at the highest applied voltage tested. The mechanisms responsible for the observed enhancement levels are discussed in the context of the flow regimes observed using high speed videography.

Heat transfer properties of nanoparticle-in-fluid dispersions (nanofluids) in laminar flow

The convective heat transfer coefficients of several nanoparticle-in-liquid dispersions (nanofluids) have been measured under laminar flow in a horizontal tube heat exchanger. The nanoparticles used in this research were graphitic in nature, with aspect ratios significantly different from one ( l/ d ≈ 0.02). The graphite nanoparticles increased the static thermal conductivities of the fluid significantly at low weight fraction loadings. However, the experimental heat transfer coefficients showed lower increases than predicted by either the conventional heat transfer correlations for homogeneous fluids, or the correlations developed from the particle suspensions with aspect ratios close to one. New correlations on heat transfer need to be developed for nanofluid systems.

Natural Convection from a Horizontal Tube Heat Exchanger Immersed in a Tilted Enclosure

Heat transfer rates of a single horizontal tube immersed in a water-filled enclosure tilted at 30 deg are measured. The results serve as a baseline case for a solar water heating system with a heat exchanger immersed in an integral collector storage. Experiments are conducted for isothermal and stratified enclosures with both adiabatic and uniform heat flux boundary conditions. Natural convection flow in the enclosure is interpreted from measured water temperature distributions. Formation of an appropriate temperature difference that drives natural convection is determined. Correlations for the overall heat transfer coefficient in terms of the Nusselt and Rayleigh numbers are reduced to the form NuD=0.675RaD0.25 for 9×105⩽RaD⩽4×107.

Experimental investigation of heat transfer in a horizontal tube falling film absorber with aqueous solutions of LiBr with and without surfactants

To learn about the physical background of the absorption process, the accompanying heat transfer was studied experimentally. A horizontal tube heat exchanger, similar to commercial absorbers, was built. Two different types of tubes were tested, one with a plain, the other with a knurled surface. The solution volume flow, the temperatures of the cooling water and of the solution, and the concentration of the solution were varied to search for correlations of the heat-transfer coefficient with the physical properties of the solution. The heat-transfer coefficients decrease with increasing viscosity and augmenting surface tension. They also depend on the fluid regime of the solution film, i.e. they increase with growing solution volume flow. The influence of two surfactants — 1-octanol and 2-ethyl-1-hexanol in various concentrations — on the absorption process was examined quantitatively. An increase of 60–140% was measured for the heat-transfer coe coefficients.