Experimental study of falling film evaporation heat transfer coefficient on horizontal tube

Self Cite

An experimental study on heat transfer characteristics of falling film evaporation outside horizontal tube was carried out at low evaporation temperature. The Al-brass tubes with 19 mm outer diameter and 1,600 mm effective length were adopted and arranged vertically in the evaporator. The electric heater was fixed tightly in the test tube for generating uniform heat flux. And thermocouples were installed in the surface of the test tube to measure surface temperatures. The experimental fluids are water and seawater with salinity of 1.5, 3, and 4.5%. The variations of heat transfer coefficient h were studied in detail with saturation temperament ranging from 50 to 70˚C, the spray density Γ ranging between 0.017 and 0.087 kg m −1 s −1 , and the heat flux q varying from 7.75 to 12.30 kW m −2 . The results show that the average heat transfer coefficients of both water and seawater increase with the spray density until about 0.052 kg m −1 s −1 . The heat transfer coefficient of fresh water increases with evaporation temperature whereas that of the seawater decreases slightly with the evaporation temperature. The average heat transfer coefficient decreases with salinity. In addition, the circumferential distribution of local heat transfer coefficients and the effect of defoamer on heat transfer are studied.

Section: The Effect Of Evaporation Temperaturesupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Heat transfer characteristics of horizontal tube falling film evaporation for desalination

Shen

Chen

et al. 2014

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“…Results of Computational Fluid Dynamic (CFD) studies on sea water with a bundle of five inline and staggered tubes also shown for comparison. A recent study by Mu et al [14] on 25.4 mm Al-brass tubes under vacuum conditions reported that heat transfer coefficient gradually increases from 4,000 to 7000 W/m 2 K for a feed rate of 0.02-0.07 kg/ms(Re = 150-520) and a declining trend beyond. Feed water temperature was varied from 45 to 70˚C.…”

Section: Effect Of Film Reynolds Number On Heat Transfermentioning

confidence: 96%

Experimental studies on thermal spray-coated horizontal tubes for falling film evaporation in multi-effect desalination system

Abraham¹,

Mani²

2014

A B S T R A C TMulti-effect distillation is an important principle in desalination technology, in which the thin film evaporation of sea water takes place at the outer surface of bundle of tubes, normally arranged in horizontal. Heat of condensation inside the tube is transferred to the falling water film by conduction, thereafter convective evaporation of film takes place. Heat transfer on the outside is unpredictable due to the uncertainty in nature of film, film thickness, film dryout, etc. and film coefficient is considerably less compared to inside. Thermal spray coating on metallic surface with molten metal particles create porous surface which enhances heat transfer due to higher turbulence and nucleation sites, if sufficient temperature difference available. This paper discusses the experimental studies carried out on a 3 × 5 bundle of 25.4 mm ∅ Al horizontal tubes with thermal spray coating of aluminum. Influences on temperature profile, heat transfer coefficient, mass evaporation, etc. are studied. A comparison of sea water and fresh water is carried out for the performance of the system. The experimental setup is established at IIT Madras, Chennai, India.

“…An interesting phenomenon shown in the figures is that the HTC becomes low during the increase of T sat . It is different from the experimental fluid of fresh water [11], because the heat conduction λ of seawater decreases with T sat (Table 2) [12]. Meanwhile, we can see from Fig.…”

Section: Effect Of the Tube Arrangementmentioning

confidence: 96%

Experimental investigation on heat transfer in horizontal-tube falling-film evaporator

Shen

Yang

et al. 2014

Self Cite

A B S T R A C TAn experimental platform for horizontal-tube falling-film evaporation was set up to measure heat transfer characteristics. Experiments were carried out to show how the heat transfer coefficient (HTC) was affected by different parameters including spray Reynolds number (Re), saturation temperature, salinity, and tube arrangement. The results revealed that the HTC increased first and then decreased with growth of Re, and the HTC of seawater decreased with increasing saturation temperature. The results also showed that the HTC of rotated square pitch was higher than triangular pitch, rotated triangular pitch, and square pitch, but the heat transfer capacity per unit volume of triangular pitch was the highest. Meanwhile, the HTC decreased during the increase of salinity.