LAMINAR FLOW HEAT TRANSFER WITH INLINE MIXERS INSERTS

Heat transfer coefficients were measured for heat transfer to a Newtonian fluid flowing in laminar flow through a tube with inline mixer inserts. Kenics “Static” mixer and Ross LPD mixer inserts were studied as heat transfer augmentation devices. The mixer inserts were in the inner tube of a concentric tube heat exchanger. Steam was condensed in the annulus of the exchanger. Significant heat transfer enhancement was obtained with both inserts at the expense of even greater pressure drop increases. The use of the Ross mixer insert gave greater augmentation than did the use of the kenics insert. An analysis using the analogy between momentum and heat transfer allowed the prediction of heat transfer coefficients from pressure drop measurements. The predicted coefficients were in good agreement with experimentally measured heat transfer coefficients for laminar flow.     

HEAT TRANSFER WITH PULSATING FLOW

This report concerns the frequency dependence of the heat transfer coefficient for water flowing in a tube. The investigation of this phenomenon was conducted in a double pipe heat exchanger in which the center stream was pulsed. The frequencies used ranged from 10 to 160 cycles per minute, and the average flow rates corresponded to a Reynolds number range of 3700 to 21,400.

The data obtained indicate that pulsing can increase the individual heat transfer coefficient by as much as a factor of 5 or more, with the greatest increase occurring when the average Reynolds number is in the range typically considered as corresponding to the transition from laminar to turbulent regimes in steady flow. The percentage increase in the heat transfer coefficient also appears to be a function only of a dimensionless group which represents the frequency divided by the flow reversal frequency     

HEAT TRANSFER WITH PULSATING FLOW

This report concerns the frequency dependence of the heat transfer coefficient for water flowing in a tube. The investigation of this phenomenon was conducted in a double pipe heat exchanger in which the center stream was pulsed. The frequencies used ranged from 10 to 160 cycles per minute, and the average flow rates corresponded to a Reynolds number range of 3700 to 21,400.

The data obtained indicate that pulsing can increase the individual heat transfer coefficient by as much as a factor of 5 or more, with the greatest increase occurring when the average Reynolds number is in the range typically considered as corresponding to the transition from laminar to turbulent regimes in steady flow. The percentage increase in the heat transfer coefficient also appears to be a function only of a dimensionless group which represents the frequency divided by the flow reversal frequency     

HEAT TRANSFER IN A LAMINAR CYLINDRICAL WALL JET WITH UNIFORM SURFACE HEAT FLUX

The steady state flow and heat transfer characteristics of a laminar cylindrical wall jet are obtained for uniform surface heat flux conditions. Local nonsimilarity solutions as well as series solutions are presented for the velocity and thermal fields. Numerical results are given for the wall shear stress, surface temperature variation and temperature field for a Prandtl number of 0.73.     

STEADY LAMINAR FLOW THROUGH TWISTED PIPES: FLUID FLOW AND HEAT TRANSFER IN RECTANGULAR TUBES

Fluid flow and heat transfer characteristics in a twisted rectangular tube having an aspect ratio of two were studied using a numerical solution to the momentum and energy equations. Fluid flow solutions are presented for a fully developed laminar flow of a Newtonian fluid. Heat transfer results are presented for the case of axially uniform wall temperature. For the case of peripherally uniform wall temperature, the overall Nusselt number in a twisted rectangular tube was found to be higher than a straight tube by up to 30 percent over certain ranges of twist lengths. However, for the case of non-uniform wall temperature, the overall absolute Nusselt number increased very rapidly with decrease in the twist length     

HEAT TRANSFER IN TUBES FITTED WITH TRAPEZOIDAL-CUT AND PLAIN TWISTED TAPE INSERTS

Experimental investigation of heat transfer and friction factor characteristics of a circular tube fitted with plain twisted tapes (PTT) and trapezoidal-cut twisted tapes (TTT) with twist ratios y = 2.0, 4.4, and 6.0 was carried out. The experimental data obtained from plain tube and PTT were verified with the standard correlation to ensure the validation of experimental results. The experimental results revealed that heat transfer rate, friction factor, and thermal enhancement factor in the tube equipped with TTT were significantly higher than in the tube fitted with PTT and the plain tube. The additional disturbance and secondary flow in the vicinity of the tube wall generated by the TTT compared to that induced by the PTT was determined as the reason for enhancement. Subsequently, an empirical correlation was also formulated to match with experimental results with ±6% and ±5% variation respectively for Nusselt number and the friction factor.     

FLOW BOILING HEAT TRANSFER WITH FLUIDIZED SOLID PARTICLES

In order to solve the fouling problems in boiling processes,a boiling system was designedby adding solid particles to the boiling liquid In this paper.both theoretical analyses andexperimental studies on the boiling heat transfer in such a three-phase flow boiling were carried out.Based on the analysis of heat transfer characters of this three-phase flow boiling,a mathematical mod-el for the heat transfer coefficient of flow boiling was developed.The experiments show that,in thepresence of particles the boiling heat transfer is enhanced and is about 2 times that of the vaporliquid two phase one with better flow stability.The fluidized particles rub the heat transfer wall toprevent and to clean the fouling.     

FINITE ELEMENT ANALYSIS FOR LAMINAR FLOW AND HEAT TRANSFER IN FINITE ROD BUNDLES

This investigation deals with the application of finite element method to solve the thermohydraulic problem of laminar fully developed flow in the interior and wall sub-channels of finite fuel rod bundles. A variational principle has been used for the solution of the momentum and energy equations. Wall shear stress and temperature distributions, ?Re and Nusselt numbers are obtained for the sub-channels of different configurations. The results are compared with solutions generated by collocation and finite difference methods.     

ANALYTICAL STUDY OF HEAT TRANSFER TO LAMINAR FLOW OF NON-NEWTONIAN FLUIDS IN ANNULUS

An analytical study is made of the problem of laminar flow heat transfer to pseudoplastic fluids in a concentric circular tube annulus. The solution is obtained for simultaneously developing velocity and temperature profiles and constant wall heat flux. Constant property results are presented for different values of flow behavior index, n, and several inner to outer tube radius ratios and Prandtl numbers. Variable property solutions, with strongly temperature-dependent consistency index are obtained. The effect of viscous dissipation on the results of heat transfer is also presented.     

FINITE ELEMENT ANALYSIS FOR LAMINAR FLOW AND HEAT TRANSFER IN FINITE ROD BUNDLES

This investigation deals with the application of finite element method to solve the thermohydraulic problem of laminar fully developed flow in the interior and wall sub-channels of finite fuel rod bundles. A variational principle has been used for the solution of the momentum and energy equations. Wall shear stress and temperature distributions, ƒRe and Nusselt numbers are obtained for the sub-channels of different configurations. The results are compared with solutions generated by collocation and finite difference methods.     

SIMULTANEOUSLY DEVELOPING LAMINAR FLOW AND HEAT TRANSFER IN THE ENTRANCE REGION OF A CIRCULAR TUBE WITH CONSTANT WALL TEMPERATURE

The developing flow and heat transfer in the entry region of a heated circular tube is analyzed for the case of constant wall temperature. An integral or boundary-layer solution is presented which has a number of advantages over earlier Karman-Pohlhausen integral analyses. Thus, in the present analysis, the velocity and temperature distributions, the local and mean drag coefficients, and the local and mean Nusselt numbers approach their fully-developed values asymptotically. The new analysis is based on the hydrodynamic inlet-filled region concept originally proposed by Ishizawa (1966) and later adopted by Mohanty and Asthana (1978) to flow through a circular tube. This concept is extended to the combined entry-length problem by introducing a thermal transition region, herein called the thermally-filled region, between the thermal inlet boundary-layer region and the thermally fully-developed region. A thermal shape factor is also introduced which ensures smooth transition of all pertinent thermal quantities from the entrance region to the fully-developed region. Results for the variation of the local and mean Nusselt numbers with axial distance along the tube for Pr = 0.1,0.5,0.7,1,5, and 10 are presented. These results agree well with the numerical solutions of Hombeck (1965), Manohar (1969), and Hwang and Sheu (1974) and also with the correlations of Churchill and Ozoe (1973).     

MASS TRANSFER INTO LAMINAR GAS STREAMS IN WETTED-WALL COLUMNS WITH COUNTERCURRENT GAS-LIQUID FLOW

The effect of the gas and liquid flow rates on the mass transfer rate in laminar gas streams in wetted-wall columns with countercurrent gas-liquid flow was studied. An approximate analytical solution was obtained for the average gas-phase Sherwood number as a function of the gas-phase Graetz number and the dimensionless interfacial gas velocity. Experiments were carried out on the absorption of ammonia into aqueous sulfuric acid solution and of methanol vapor into water, using two columns of different lengths. The agreement between the experimental and the predicted effects of both gas and liquid flow rates on the gas-phase mass transfer rate was found to be fairly good.     

HEAT TRANSFER IN PACKED BED REACTORS WITH ONE PHASE FLOW

An extensive array of literature data on the heat transfer from a reactor wall to a fluid flowing through a packed bed and those obtained from some experimental runs were interpreted with a model containing two parameters: k_e, (effective radial thermal conductivity within the bed) and h_w (heat transfer coefficient at the wall).

Both parameters were considered in terms of a stagnant contribution (due to the heat conduction through the solid particles and the fluid in the void space) and a radial mixing contribution (due to the heat convection by turbulent mechanism.

The stagnant contribution was interpreted with a model similar to that proposed by Kunii and Smith (1966) for heat transfer in a packed bed with motionless fluid.

General correlating equations for calculating the stagnant and the turbulent contributions of both k_e, and h_w are proposed.     

LAMINAR BOUNDARY LAYER HEAT TRANSFER TO POWER-LAW FLUIDS

The heat transfer for the steady two-dimensional incompressible laminar boundary layer of power-law non-Newtonian fluids past a semi-infinite static or moving flat plate is studied by local similarity method. Four cases are considered: static plate with prescribed wall temperature and heat flux; and moving plate with prescribed wall temperature and heat flux. The effescts of the flow index, streamwise distance and modified Prandtl number on the temperature distribution and heat transfer rate are discussed in detail.     

MASS TRANSFER INTO LAMINAR GAS STREAMS IN WETTED-WALL COLUMNS WITH COUNTERCURRENT GAS-LIQUID FLOW

The effect of the gas and liquid flow rates on the mass transfer rate in laminar gas streams in wetted-wall columns with countercurrent gas-liquid flow was studied. An approximate analytical solution was obtained for the average gas-phase Sherwood number as a function of the gas-phase Graetz number and the dimensionless interfacial gas velocity. Experiments were carried out on the absorption of ammonia into aqueous sulfuric acid solution and of methanol vapor into water, using two columns of different lengths. The agreement between the experimental and the predicted effects of both gas and liquid flow rates on the gas-phase mass transfer rate was found to be fairly good.     

CONJUGATE HEAT TRANSFER IN FALLING LAMINAR LIQUID FILMS

An analysis is presented for the heat transfer characteristics of a falling liquid film flow over a fin by the conjugate convection-conduction theory. Numerical results are presented for the dimensionless heat transfer coefficients, local and overall heat fluxes and temperature distribution of the fin by a simultaneous solution of the convective boundary layer equations of the fluid and the energy equation of the fin.     

LAMINAR BOUNDARY LAYER HEAT TRANSFER TO POWER-LAW FLUIDS

The heat transfer for the steady two-dimensional incompressible laminar boundary layer of power-law non-Newtonian fluids past a semi-infinite static or moving flat plate is studied by local similarity method. Four cases are considered: static plate with prescribed wall temperature and heat flux; and moving plate with prescribed wall temperature and heat flux. The effescts of the flow index, streamwise distance and modified Prandtl number on the temperature distribution and heat transfer rate are discussed in detail.     

CONJUGATE HEAT TRANSFER WITH TURBULENT FLOW IN A CIRCULAR TUBE

A steady heat transfer problem has been analyzed as a conjugate problem with turbulent flow in a circular tube. The three kinds of thermal boundary conditions considered here are specified as constant temperature, constant heat flux and constant heat transfer coefficient at the outer surface of the wall.

From the results of numerical calculation for Prandtl numbers in the range 0.01 ≤ Pr ≤ 10 and for Reynolds numbers in the range 10⁴ ≤ Re ≤ 10⁵, it was confirmed that the dimensionless parameter R_c could have significant effects on the heat transfer and the temperature field in the fluid adjacent to the wall.     

螺旋槽管管壳式换热器的传热与流阻研究

以螺旋槽管为强化传热管,以空气为传热介质,研究了管壳式换热器壳程以气体纵向冲刷为特点的传热与流阻性能,并在相同的实验条件下,与弓形隔板管壳式换热器的传热性能加以比较,结果表明,螺旋槽管管壳式换热器可比普通弓形隔板管壳式换热器提高总传热系数48％,节省传热面积32.4％。     

EXPERIMENTAL STUDIES ON HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS OF TURBULENT FLOW THROUGH A CIRCULAR TUBE FITTED WITH RIGHT AND LEFT HELICAL SCREW-TAPE INSERTS

Experimental investigation on heat transfer and friction factor characteristics of a circular tube fitted with right-left helical screw inserts of equal and unequal length of different twist ratios is presented. The experimental data obtained were compared with those obtained from plain tube published data. The heat transfer enhancement for right-left helical screw inserts is higher than that for straight helical twist for a given twist ratio. The effect of right-left twist length on heat transfer augmentation is presented. The empirical relations for Nusselt number, friction factor relating Reynolds number, twist ratio, and right-left twist distance were formed and found to fit the experimental data within 10% and 20% for Nusselt number and friction factor respectively. Performance evaluation analysis was made, and the performance ratio of more than one was obtained, indicating that the proposed twist inserts can be used effectively for heat transfer augmentation without any loss in pumping power.