Transient behavior of a plate-fin-and-tube heat exchanger taking into account different heat transfer coefficients on the individual tube rows

Experimental studies of multi-row plate-fin heat exchangers show that the highest average heat transfer coefficient on the air side occurs in the first row of tubes when the air velocity in front ofthe exchanger is less thanapproximately 3.5 m/s. In the subsequent rows of tubes up to about the fourth row the heat transfer coefficient decreases. In the fifth and further rows, it can be assumed that the heat transfer coefficient is equal in each tube row. It is necessary to find the relationships fortheair–side Nusselt number on each tube row to design a plate–fin and tube heat exchanger(PFTHE) with the appropriate number of tube rows. The air–side Nusselt number correlations canbe determined experimentally or by CFD modeling (Computational and Fluid Dynamics). The paper presents a newmathematical model of the transient operation of PFTHE, considering that the Nusselt numbers on the air side of individual tube rows are different. The heat transfer coefficient on an analyzed tube row was determined from the equality condition of mass– average air temperature differences on agiven tube row determined using the analytical formula and CFD modeling. The results of numerical modelingwere compared with the results of the experiments.

Transient behavior of a plate-fin-and-tube heat exchanger taking into account different heat transfer coefficients on the individual tube rows

Plate-fin and tube heat exchangers (PFTHE) are made of round, elliptical, oval or flat tubes to which continuous fins ( lamellas) are attached. Liquid flows inside the tubes and gas flows outside the tubes perpendicularly to their axes and parallel to the surface of continuous fins. Experimental studies of multi-row plate-fin and tube heat exchangers show that the highest average heat transfer coefficient on the air side occurs in the first row of tubes when the air velocity in front of the exchanger is less than approximately 3.5 m/s when a Reynolds number based on an equivalent hydraulic diameter equal to the distance between tube rows in the direction of air flow is less than 10,000. In the subsequent rows of tubes up to about the fourth row the heat transfer coefficient decreases. In the fifth and further rows, it can, that the heat transfer coefficient is equal in each tube row. It is necessary to find the relationships for the air-side Nusselt number on each tube row to design a PFTHE with the appropriate number of tube rows. The air-side Nusselt number correlations can be determined experimentally or by CFD modeling (Computational and Fluid Dynamics). The paper presents a new mathematical model of the transient operation of PFTHE, considering that the Nusselt numbers on the air side of individual tube rows are different. The heat transfer coefficient on an analyzed tube row was determined from the equality condition of mass- average air temperature differences on a given tube row determined using the analytical formula and CFD modeling. The results of numerical modeling were compared with the results of the experiments.

KINERJA PRODUKSI PENDEDERAN JUVENIL LOBSTER PASIR Panulirus Homarus MENGGUNAKAN SELTER INDIVIDU

Kanibalisme yang tinggi adalah salah satu permasalahan utama dalam budidaya lobster. Penggunaan selter individu pada budidaya pendederan lobster dimaksudkan untuk meniadakan kontak langsung antar lobster dalam media budidaya. Tujuan penelitian ini adalah untuk menganalisis kualitas air dan pengaruh penggunaan selter individu terhadap kinerja produksi pendederan lobster pasir Panulirus homarus dengan sistem resirkulasi. Lobster berukuran 51,29 ± 7,26 g/ekor dipelihara selama 60 hari dengan pemberian pakan 3%-4% sebanyak satu kali per hari. Penelitian dilakukan dengan empat perlakuan dan dua ulangan. Jenis perlakuan yang digunakan, yaitu selter pipa PVC sebagai kontrol (K), selter individu persegi (SI n), selter individu segitiga (SI ), dan selter individu tabung (SI l). Hasil penelitian menunjukkan bahwa kualitas air budidaya menggunakan sistem resirkulasi masih memenuhi syarat untuk budidaya lobster. Penggunaan selter individu berpengaruh positif terhadap respons sintasan, tetapi berpengaruh negatif terhadap pertumbuhan lobster.High cannibalism was an important issue in lobster rearing. The use of individual shelter in lobster rearing was intended to eliminate a direct contact between lobsters in a rearing media. The purpose of this study was to analyze water quality and the effect of individual shelter on the growth response of spiny lobster (Panulirus homarus) juvenile reared in an aquaculture media equipped with a recirculation system. Lobsters with an average size of 51.29 ± 7.26 g were reared for 60 days and fed with trash fish of 3%-4% of the biomass daily. This study used four treatments with two replications. The treatments consisted of a PVC pipe shelter as control (K), individual square shelter (SI n), individual triangle shelter(SI ), and individual tube shelter (SI l).The results of the study showed that the water quality in the aquaculture media was still within the suitable range for lobster rearing. The use of individual shelter had positive effects on the survival rate but had negative effects on the growth of spiny lobster juvenile.

Horizontal carbon nanotube interconnects for advanced integrated circuits.

ABSTRACTHorizontal carbon nanotube (CNT) interconnects are fabricated using a novel integration scheme yielding record wall densities >1013 shell/cm2, i.e. close to the density required for implementation in advanced integrated circuits. The CNTs are grown vertically from individual via structure and subsequently flipped onto the horizontal wafer surface. Various electrode designs are then used to produce different geometries of metal-to-tube contact such as side contact or end contact. CNT lines - 50 to 100 nm wide and up to 20 µm long - are realized and electrically characterized. The sum of the contact resistances from both ends of the lines is close to 500 Ω for 100 nm diameter lines which leads to a specific contact resistance of 1.6 10-8 Ω.cm2 per tube. With the developed technology, post-annealing of the contact does not improve the resistance values. Both chromium and palladium are used as contact metal. While contact resistance is equivalent with the two metals, the resistance per unit length of the lines does change and is better with palladium. This dependence is explained using a tunnelling model which shows that statistics of individual tube-metal contact is required to properly model the electrical results. Direct experimental evidences showing that only a part of the CNTs in the bundle is electrically connected are also given. Our best line resistivity achieved is 1.6mΩ.cm which is among the best results published for horizontally aligned CNTs and the only one with a realistic geometry for future VLSI interconnects.

Circumferences Lead to Enhancements of Nonresonant Third-Order Susceptibilities for Carbon Nanotube Bundles

Nonresonant enhancements of third-order susceptibility χ(3)(-ω; ω, ω, -ω) have been investigated for zigzag carbon nanotube (n,0) bundles (n = 5, 7, 11, 13, 8, 10, 14, 16) based on the energy band theory combined with the classic anharmonic oscillator model. The obtained results show that the (3) values increase as circumference of tube varies in the order of 5<7<11<13 and 8<10<14<16 for (n,0) tube bundles, respectively. The origination of the large third-order susceptibility is ascribed to the circumference effect of individual tube. The nonresonant third-order susceptibility is estimated to be about 10-6 esu in the axial direction of (16,0) tube bundles, and it is possible for a good candidate to make optical phase conjugate device.

Waterwall Quench Crack Inspection Without Cleaning or Scaffolding

The Mutual Inductance Bridge (MIB) system scans waterwalls for multiple defect types. Already used successfully to detect fireside corrosion and erosion, the capability has been expanded to quench cracking. The MIB electromagnetic approach uses in-phase and quadrature information to detect defects well before potential breakouts might cause plant outages. Fireside corrosion, scale and clinker deposits as large as 0.5” do not interfere with measurement accuracy or speed. Although quench crack defects alone do not change the mass of ferromagnetic material, the magnetic field perturbations caused by their presence provide a unique signature. The robotic MIB deployment containing a position measuring laser, video cameras and proprietary electronics scans 400 ft2 per hour; the handheld unit scans 125 ft2/hr. Scan results include color-coded maps that describe the condition of scanned areas, and individual tube profiles. Results of several applications are presented.

On the Inability of Multiple Exhausters to Eliminate Condenser Excess Back Pressure at High Air In-Leakage

A comprehensive theoretical development, confirmed by inplant measurements, will be summarized showing the dependence of condenser air in-leakage and exhauster capacity on build up of excess back pressure caused by the establishment of a zone of stagnation near the condenser’s air removal section. It has been generally believed that there will not be a zone of stagnation and an associated excess back pressure, above the design pressure, provided the exhauster capacity for air removal remains higher than the air in-leakage regardless of the leakage size. This paper will show, however, that excess back pressure can occur at high air in-leakage, even though exhauster capacity is adequate. A gradual increase in the concentration of non-condensables as steam scavenges these gases toward the air removal section is presented. This results in a reduction of individual tube heat transfer coefficient in the high air concentration region which is accompanied by an increase in condenser pressure. It will be shown that this may be the condition of heat transfer reduction that many authors have used throughout the 20th century to describe the effect of air on all tubes in the condenser. An associated condition will also be discussed related to subcooling of the gas and vapor space between tubes within the region of reduced heat transfer. With high air in-leakage and high exhauster capacity, it will be shown that near the air removal section the large amount of air flow will scavenge steam through the subcooled region, directed toward the vent line, causing generation of a condensate mist that becomes suspended in the moving air. The reported theoretical explanation is derived using a condenser model developed earlier by the author. The results are confirmed from measurement data taken on an operating plant using a RheoVac® condenser performance and diagnostic instrument, the description of which may be found in the open literature.