Single-phase Flow Heat Transfer Research Articles

Study of Single Phase Flow Heat Transfer and Friction Pressure Drop in a Spiral Internally Ribbed Tube

AbstractThe experimental results of single‐phase flow heat transfer and pressure drop experiments in the turbulent flow regime in a spirally ribbed tube and a smooth tube are presented in this paper. The ribbed tube has an outside diameter of 22 mm and an inside diameter of 11 mm (an equivalent inside diameter of 11.6 mm) and the smooth tube has an outside diameter of 19 mm and an inside diameter of 15 mm. Both tubes were uniformly heated by passing an electrical current along the tubes with a heated length of 2500 mm. The working fluids are water and kerosene, respectively. The experimental Reynolds number is in the range of 104–5 · 104 for water and is in the range of 104–2.2 · 104 for kerosene. The experimental results of the ribbed tube are compared with those of the smooth tube. The heat transfer coefficients of the ribbed tube are 1.2–1.6 fold greater than those in the smooth tube and the pressure drop in the ribbed tube is also increased by a factor of 1.4–1.7 as compared with those in the smooth tube for water. The corresponding values for kerosene are 2–2.7 and 1.5–2, respectively. The heat‐transfer enhancement characteristics of the ribbed tube are assessed. This tube is especially suitable for augmenting single‐phase flow heat transfer of kerosene. Correlations for the heat transfer and the pressure drop for the spirally ribbed tube are proposed, according to the experimental data.

Performance Evaluation of Liquid Flow With PCM Particles in Microchannels

A two-phase, non thermal equilibrium-based model is applied to the numerical simulation of laminar flow and heat transfer characteristics of suspension with microsize phase-change material (PCM) particles in a microchannel. The model solves the conservation of mass, momentum, and thermal energy equations for liquid and particle phases separately. The study focuses on the parametric study of optimal conditions where heat transfer is enhanced with an increase in fluid power necessary for pumping the two-phase flow. The main contribution of PCM particles to the enhancement of heat transfer in a microsize tube is to increase the effective thermal capacity and utilize the latent heat effect under the laminar flow condition. An effectiveness factor εeff is defined to evaluate the heat transfer enhancement compared to the single-phase flow heat transfer and is calculated under different wall heat fluxes and different Reynolds numbers. The comparison is also made to evaluate the performance index, i.e., the ratio of total heat transfer rate to fluid flow power (pressure drop multiplied by volume flow rate) between PCM suspension flow and pure water single-phase flow. The results show that for a given Reynolds number, there exists an optimal heat flux under which the εeff value is the greatest. In general, the PCM suspension flow with phase change has a significantly higher performance index than the pure-fluid flow. The comparison of the model simulation with the limited experimental results for a MCPCM suspension flow in a 3mmdia tube reveals the sensitivity of wall temperature distribution to the PCM supply temperature and the importance of characterizing the phase change region for a given tube length.

Heat transfer augmentation in 3D internally finned and microfinned helical tube

Experiments are performed to investigate the single-phase flow and flow-boiling heat transfer augmentation in 3D internally finned and micro-finned helical tubes. The tests for single-phase flow heat transfer augmentation are carried out in helical tubes with a curvature of 0.0663 and a length of 1.15 m, and the examined range of the Reynolds number varies from 1000 to 8500. Within the applied range of Reynolds number, compared with the smooth helical tube, the average heat transfer augmentation ratio for the two finned tubes is 71% and 103%, but associated with a flow resistance increase of 90% and 140%, respectively. A higher fin height gives a higher heat transfer rate and a larger friction flow resistance. The tests for flow-boiling heat transfer are carried out in 3D internally micro-finned helical tube with a curvature of 0.0605 and a length of 0.668 m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D internally micro-finned helical tube is increased by 40–120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance is increased by 18–119%, respectively.

Heat transfer in a high temperature region of spray cooling interacting with liquid film flow

We present experimental results on heat transfer distribution in the high temperature region of spray cooling interacting with subcooled liquid film flow. The results show that the flow field can be divided into the interacting and film flow regions by the heat transfer distribution. In the interacting region, the heat transfer coefficient can be correlated to the liquid-film-flow heat transfer by using a heat-transfer enhancement coefficient defined as the ratio of the droplet flow rate to liquid film velocity. In the wall region, it can be predicted from the equation obtained from a previous study, which is very similar to that of turbulent heat transfer of single-phase flow. © 1998 Scripta Technica. Heat Trans Jpn Res, 26(4): 236–248, 1997

Heat Transfer in High Tempetature Region of Spray Cooling Interacting with Liquid Film Flow.

We present experimental results on heat transfer distribution in the high temperature region of spray cooling interacting with subcooled liquid film flow. The results show that the flow field can be divided into the interacting and film flow regions by heat transfer distribution. In the interacting region, the heat transfer coefficient can be correlated to the liquid-film-flow heat transfer by using a heat-transfer enhancement coefficient defined as the ratio of the droplet flow rate to liquid film velocity. In the wall region, it can be predicted from the equation obtained from the previous study, which is very similar to that of turbulent heat transfer of single-phase flow.

HEAT TRANSFER OF LAMINAR MIST FLOW IN CONCENTRIC ANNULI

Heat transfer of single-phase flow or mist flow in confined spaces has important application in industrial heat exchangers and nuclear reactors. Extensive research has been conducted for single-phase flow in concentric tubes and eccentric annuli, and an excellent review can be found. However, very few analyses have been devoted to the heat transfer of mist flow in confined spaces due to the complexities of the geometries and phenomena. Numerical results are presented for convective heat transfer of a laminar mist flow in the thermal entrance region of a concentric annulus with a heated core and an insulated outer wall. Both constant temperature and constant heat flux on the inner wall are considered. The saturated droplets in the mist flow are considered as equivalent heat sinks distributed in the superheat vapor velocity, droplet number density, and the local Nusselt number in the streamwise direction until the single-phase fully developed condition is reached. The effects of different governing parameters on heat transfer characteristics are studied.

Fluid Flow and Heat Transfer in Corrugated Wall Channels : 2nd Report, Experiments in the Case Where Channels Are Bent Perpendicularly Two Times

In the present experiment augmentation of forced convection heat transfer in single-phase flows was investigated using a channel whose parallel walls are bent perpendicularly at two locations. Heat transfer characteristics in both laminar and turbulent flow situations were observed by varying the pitch. Visualization of the flows revealed the formation of separation bubbles in the corners of the bends and the reattachment of the flows in downstream regions. It is accordingly concluded that augmentation of heat transfer occurs as a result of the reattachment and acceleration of the flows.

Heat Transfer of Laminar Mist Flow in Tubes

Connective heat transfer of laminar mist flow is analyzed for constant wall temperature and constant heat flux conditions, respectively. The diminishing of droplet size, the increasing of vapor velocity, and the dilution of droplet density along the tube are considered in the present study. Calculations are performed from the inlet of thermal entrance region to the final fully developed single phase flow of vapor at the far downstream. Non-dimensional parameters influencing mist flow heat transfer are revealed and discussed. Fundamental heat transfer behavior of mist flow is studied and the results appear as an extension of our present understanding of single phase flow heat transfer.

An Analysis of Heat Transfer to Axial Dispersed Flow between Rod Bundles under Reactor Emergency Cooling Conditions

Analysis is carried out for dispersed flow heat transfer under reactor emergency cooling conditions. The present formulation explicitly reveals an extra dependence of the heat transfer coefficient and Nusselt number on the mean vapor temperature for droplet dispersed flow which is not found in single phase flow heat transfer. The heat transfer results obtained from three different geometries—an infinite square array of cylindrical rods, an annulus and a circular pipe—are compared; all have the same hydraulic diameter. It is found that, within the framework of the present analysis, results for the annulus and the rod bundles agree well when the pitch-to-diameter ratio is 1.5 or greater. The circular pipe is in general a poor approximation for rod bundle geometries except at a pitch-to-diameter ratio of about 1.3 which is typical of present day light water reactor fuel assemblies.