This work deals with the experimental investigation on Nusselt number, friction factor and thermal performance factor in a circular tube equipped with perforated twisted tape inserts with four ...different porosities of Rp=1.6, 4.5, 8.9 and 14.7%. The experiments were conducted in a turbulent flow regime with Reynolds number ranging from 7200 to 49,800 using air as the working fluid under uniform wall heat flux boundary condition. The experimental results revealed that both heat transfer rate and friction factor of the tube fitted with perforated twisted tapes were significantly higher than those of the plain tube. Over the range investigated, Nusselt number, friction factor and thermal performance factor in the tube with perforated twisted tape inserts was found to be 110 –340, 110 –360 and 28–59% higher than those of the plain tube values, respectively. In addition, the empirical correlations of Nusselt number, friction factor and thermal performance factor were formulated from the experimental results of tape inserts.
In the present study, the influences of triple twisted tapes on heat transfer rate, friction factor and thermal enhancement efficiency were experimentally investigated. The triple twisted tapes were ...used as swirl flow generators in the test section. The investigations were conducted using the mild steel triple twisted tapes with four different twist ratios (y=1.92, 2.88, 4.81 and 6.79) for Reynolds number ranging from 7200 to 50,200 under uniform heat flux condition. The experimental results demonstrated that the Nusselt number, friction factor and thermal enhancement efficiency increased with decreasing twist ratio. The results indicated that the presence of triple twisted tapes led to a higher increase in the heat transfer rate over the plain tube. The Nusselt number and friction factor of using the triple twisted tape inserts were found to be increased up to 3.85 and 4.2 times when compared with the plain tube, respectively. The heat transfer performance was evaluated based on the constant blower power and the performance was achieved to be 1.44 by the use of triple twisted tape inserts. Finally, correlations were developed based on the data gathered during this work for predicting the heat transfer, friction factor and thermal enhancement efficiency through a circular tube fitted with triple twisted tape inserts in terms of twist ratio (y), Reynolds number (Re) and Prandtl number (Pr).
Influence of triple helical tapes inserted for turbulent flow through a tube on heat transfer enhancement was studied experimentally. The triple helical tapes made of mild steel with different helix ...angles,
α
=
9°, 13°, 17°, and 21° were examined for Reynolds number ranging from 22,000 to 51,000. The experiment showed that the Nusselt number, effectiveness and friction factor for the inserts were found to be up to 4.5, 3.45 and 3.0 times, respectively, over the plain tube. The highest enhancement efficiency achieved was 3.7 for the inserts based on constant blower power. Finally, new correlations for predicting heat transfer and friction factor for turbulent flow through a circular tube fitted with the inserts were proposed.
The present study explored the effects of the double counter twisted tapes on heat transfer and fluid friction characteristics in a heat exchanger tube. The double counter twisted tapes were used as ...counter-swirl flow generators in the test section. The experiments were performed with double counter twisted tapes of four different twist ratios (y=1.95, 3.85, 5.92 and 7.75) using air as the testing fluid in a circular tube turbulent flow regime where the Reynolds number was varied from 6950 to 50,050. The experimental results demonstrated that the Nusselt number, friction factor and thermal enhancement efficiency were increased with decreasing twist ratio. The results also revealed that the heat transfer rate in the tube fitted with double counter twisted tape was significantly increased with corresponding increase in pressure drop. In the range of the present work, heat transfer rate and friction factor were obtained to be around 60 to 240% and 91 to 286% higher than those of the plain tube values, respectively. The maximum thermal enhancement efficiency of 1.34 was achieved by the use of double counter twisted tapes at constant blower power. In addition, the empirical correlations for the Nusselt number, friction factor and thermal enhancement efficiency were also developed, based on the experimental data.
In the present study, the heat transfer performance and friction factor characteristics in a circular tube fitted with twisted wire brush inserts were investigated experimentally. The twisted wire ...brush inserts were fabricated with four different twisted wire densities of 100, 150, 200, and 250 wires per centimeter by winding a 1mm diameter of the copper wire over a 5mm diameter of two twisted iron core-rods. Heat transfer and friction factor data in tubes were examined for Reynolds number ranging from 7,200 to 50,200. The results indicated that the presence of twisted wire brush inserts led to a large effect on the enhancement of heat transfer with corresponding increase in friction factor over the plain tube. The Nusselt number and friction factor of using the twisted wire brush inserts were found to be increased up to 2.15 and 2.0 times, respectively, than those over the plain tube values. Furthermore, the heat transfer performance was evaluated to assess the real benefits of using those type of inserts and the performance was achieved 1.85 times higher compared to the plain tube based on the constant blower power. Finally, correlations were developed based on the data generated from this work to predict the heat transfer, friction factor, and thermal performance factor for turbulent flow through a circular tube fitted with the twisted wire brush inserts in terms of wire density (y), Reynolds number (Re), and Prandtl number (Pr).
The present study explored the effects of perforated double counter twisted tapes on heat transfer and fluid friction characteristics in a heat exchanger tube. The twisted tapes with four different ...porosities of Rp=1.2, 4.6, 10.4 and 18.6% were used as counter-swirl flow generators in the test section. The experiments were conducted in a circular tube in turbulent flow regime with Reynolds number ranging from 7200 to 50,000 using air as the working fluid under uniform wall heat flux boundary condition. The experimental results demonstrated that the Nusselt number, friction factor and thermal enhancement efficiency were increased with decreasing porosity except porosity of 1.2%. The results also revealed that the heat transfer rate of the tube fitted with tapes were significantly increased with corresponding increase in friction factor. In the range of the present investigation, heat transfer rate and friction factor were obtained to be around 80 to 290% and 111 to 335% higher than those of the plain tube values, respectively. Based on constant blower power, the highest thermal enhancement efficiency of 1.44 was achieved. In addition, the empirical correlations of Nusselt number, friction factor and thermal enhancement efficiency were developed based on the experimental data.
Yield, dry matter production, nitrogen (N) uptake and nitrogen use efficiency (NUE) of Bangladesh Rice Research Institute (BRRI) dhan29 were investigated during two consecutive dry (Boro) seasons of ...2009-10 and 2010-11. The experiments were set up in a randomized complete block design with three replication having six nitrogen (N) levels of 0, 40, 80 120, 160 and 200 kg ha
−1
. Nitrogen fertilization increased yield characters, dry matter production and N uptake. The economic optimum rate of N was 166 and 155 kg ha
-1
in first and second year, respectively, with corresponding yield of 7.1 and 6.5 t ha
−1
. NUEs were higher in the first year, decreased with increasing N rates in most cases. Gross return over fertilizer reached the highest Tk 692 in 2009-10 and Tk 489 in 2010-11 with 160 kg N ha
-1
. The results suggest that BRRI dhan29 should receive an average of 160 kg N ha
−1
for economic optimum yield.
Given the increasing dairy and poultry industries, cowdung (CD) and poultry manure (PM) might become alternative sources of nitrogen (N) for rice production in South Asia. A field experiment was ...conducted during dry season (Nov-April) in Chhiata clay loam soil. The experiment aimed to evaluate the effect of N from organic and inorganic sources on dry matter and N uptake pattern of rice. We compared (i) N-control, ii) Optimum dose of nitrogen (164 kg N/ha) from urea, iii) 50% N from urea and 50% N from CD, iv) 50% N from urea and 50% N from PM, v) 100% N from CD and vi) 100% N from PM. Two mega varieties BRRI dhan28 and BRRI dhan29, were used as test crops. Application of N from urea, urea + PM and absolute PM increased dry matter significantly both in BRRI dhan28 and BRRI dhan29. The combination of urea and PM, absolute urea and absolute PM gave greater N uptake compared to other treatments in different growth stages of rice. The urea + PM treatment gave similar yield to that of urea in both the varieties, however, BRRI dhan29 gave about 1.17 t /ha higher yield than BRRI dhan28. The PM treatment gave similar yield to that with urea + PM in BRRI dhan28, but BRRI dhan29 gave significantly lower yield in PM than the urea + PM. Sole cowdung or poultry manure application produced significantly lower grain yield than urea + PM treatment and sole urea application. Because of insufficient mineralization of N from CD and PM, sole organic sources of N were not as good as combined use of organic and inorganic fertilizer amendments.
The augmentation of heat transfer for turbulent fluid flow through a tube by using double helical tape inserts was investigated experimentally in the present work. The effects of insertion of the ...helical tape turbulators with different helix angles (9°, 15°, 21° and 28°) on heat transfer and pressure drop in the tube for Reynolds number ranging from 22,000 to 51,000 were examined. Experimental results showed that the heat transfer and thermal performance of the inserted tube were significantly increased compared to those of the plain tube. The study showed the Nussselt number, friction factor as well as thermal enhancement efficiency were increased with decreasing helix angles under the same operating conditions. The results indicated that the Nusselt number and friction factor were increased up to 305% and 170%, respectively, than those over the plain tube while the maximum thermal performance was found to be 215% for using the double helical tape insert with helix angle 9° at high Reynolds number. Furthermore, correlations of the Nusselt number and friction factor were developed in terms of the helix angle (α), Reynolds number (Re) and Prandtl number (Pr) based on the experimental data.
An experimental investigation was accomplished to evaluate the performance of heat transfer for turbulent flow through a tube with helical tape inserts. The mild steel helical tape inserts with ...different twist ratios of 1.88, 3.13, 4.69, 6.41 and 7.81 were used in the flow field. Heat transfer and pressure drop data were prompted for a wide range of Reynolds number from 7200 to 50,000. The experimental results indicated that the Nusselt number, friction factor and thermal performance factor were increased with decreasing twist ratio. The results also showed that helical tape inserts of different geometries in a circular tube enhanced the heat transfer rate significantly with corresponding increase in friction factor. Nusselt number and friction factor for the tube with inserts were found to be increased up to 260 and 285 %, respectively, than those over the plain tube values at the comparable Reynolds number. The heat transfer performance was evaluated and found to be 44 % higher compared to the plain tube based on the constant blower power. Finally, new correlations were proposed for the twist ratios ranging from 1.88 to 7.81 for predicting the heat transfer, friction factor and thermal performance factor for turbulent flow through a circular tube fitted with helical tape inserts.
PDF