Abstract: The plate and concentric tube heat exchangers are tested by using the water-water and nanofluid-water streams. The ZnO/water (0.5 v/v%) nanofluid has been used as the hot stream. The heat transfer rate omitted of hot stream and overall heat transfer coefficients in both heat exchangers are measured as a function of hot and cold streams mass flow rates. The experimental results show that the heat transfer rate and heat transfer coefficients of the nanofluid in both of the heat exchangers is higher than that of the base liquid (i. e. water) and the efficiency of plate heat exchange is higher than concentric tube heat exchanger. In the plate heat exchanger the heat transfer coefficient of nanofluid at

Abstract: A numerical study has been conducted to examine the heat transfer from a metal foam-wrapped solid cylinder in cross-flow. Effects of the key parameters including the free stream velocity and characteristics of metal foam such as porosity, permeability, and form drag coefficient on heat and fluid flow are examined. Being a determining factor in pressure drop and heat transfer increment, the porous layer thickness is changed systematically to observe that there is an optimum layer thickness beyond which the heat transfer does not improve while the pressure drop continues to increase. This has been verified by the application of Bejan’s Intersection of Asymptotes method. Results have been compared to those of a finned-tube heat exchanger to observe much higher heat transfer rate with reasonable excess pressure drop leading to a higher area goodness factor for metal foam-wrapped cylinder.

Abstract: The present study investigated the comparisons of the heat transfer and pressure drop of the microchannel and minichannel heat exchangers, both numerically and experimentally. The results obtained from this study indicated that the heat transfer rate obtained from microchannel heat exchanger was higher than those obtained from the minichannel heat exchangers; however, the pressure drops obtained from the microchannel heat exchanger were also higher than those obtained from the minichannel heat exchangers. As a result, the microchannel heat exchanger should be selected for the systems where high heat transfer rates are needed. In addition, at the same average velocity of water in the channels used in this study, the effectiveness obtained from the microchannel heat exchanger was 1.2–1.53 times of that obtained from the minichannel heat exchanger. Furthermore, the results obtained from the experiments were in good agreement with those obtained from the design theory and the numerical analyses.

Abstract: This experimental study investigates the heat transfer characteristics of a liquid flow with micro-encapsulated phase change material (MEPCM). The MEPCM mass concentration is varied between 0 and 20 percent with average particle diameter of 10 μm. Tube wall temperature profile, fluid inlet and outlet temperatures are measured and the corresponding heat transfer coefficient is determined for various operating conditions. A wide range of the controlling parameters, MEPCM concentration, heat flux, inlet temperature, and flow rate are covered. The results showed significant enhancements in heat transfer coefficient (higher than 50%) and reduction in tube wall temperature (higher than 40%). The results also showed that the heat transfer enhancement curve showed resemblance to the MEPCM specific heat curve.

Abstract: An air-cooled motorcycle engine releases heat to the atmosphere through the mode of forced convection. To facilitate this, fins are provided on the outer surface of the cylinder. The heat transfer rate depends upon the velocity of the vehicle, fin geometry and the ambient temperature. Many experimental methods are available in literature to analyze the effect of these factors on the heat transfer rate. However, an attempt is made to simulate the heat transfer using CFD analysis. The heat transfer surface of the engine is modeled in GAMBIT and simulated in FLUENT software. An expression of average fin surface heat transfer coefficient in terms of wind velocity is obtained. It is observed that when the ambient temperature reduces to a very low value, it results in overcooling and poor efficiency of the engine.

Abstract: a novel method of locating the pinch is presented for the design of heat exchanger networks. The method is based on the pinch design method for heat exchanger networks which was first introduced by Linnhoff. The method first consider the heat capacity flowrate of a stream with variation in temperature. This is because heat capacity flowrate of a stream with variation in temperature not only affect minimum utility requirement for heat exchanger network but also affect the pinch location, choice ofΔTmin.

Abstract: This paper describes an experimental setup for the investigation of two-phase heat transfer inside microchannels and reports local heat transfer coefficients measured during flow boiling of HFC-245fa in a 0.96-mm-diameter single circular channel. The test runs have been performed during vaporization at around 1.85 bar, corresponding to 31°C saturation temperature. As a peculiar characteristic of the present technique, the heat transfer coefficient is not measured by imposing the heat flux; instead, the boiling process is governed by controlling the inlet temperature of the heating secondary fluid. In the data, mass velocity ranges between 200 and 400 kg m−2 s−1, with heat flux varying from 5 to 85 kW m−2 and vapor quality from 0.05 up to 0.8. Since these data are not measured at uniform heat flux conditions, a proper analysis is performed to enlighten the influence of the different parameters and to compare the present data to those obtained when the heat flux is imposed. Besides, the test runs have been ...

Abstract: Numerical studies under supercritical pressure are carried out to study the heat transfer characteristics in a single-root coolant channel of the active regenerative cooling system of the scramjet engine, using actual physical properties of pentane. The relationships between wall temperature and inlet temperature, mass flow rate, wall heat flux, inlet pressure, as well as center stream temperature are obtained. The results suggest that the heat transfer deterioration occurs when the fuel temperature approaches the pseudo-critical temperature, and the wall temperature increases rapidly and heat transfer coefficient decreases sharply. The decrease of wall heat flux, as well as the increase of mass flow rate and inlet pressure makes the starting point of the heat transfer deterioration and the peak point of the wall temperature move backward. The wall temperature increment induced by heat transfer deterioration decreases, which could reduce the severity of the heat transfer deterioration. The relational expression of the heat transfer deterioration critical heat flux derives from the relationship of the mass flow rate and the inlet pressure.

Abstract: Modeling a fin-and-tube heat exchanger as porous media based on volume averaging theory (VAT), specific geometry can be accounted for in such a way that the details of the original structure can be replaced by their averaged counterparts, and the VAT based governing equations can be solved for a wide range of heat exchanger designs. To complete the VAT based model, proper closure is needed, which is related to a local friction factor and a heat transfer coefficient of a representative elementary volume. The present paper describes an effort to model a fin-and-tube heat exchanger based on VAT and obtain closure for the model. Experiment data and correlations for the air side characteristics of fin-and-tube heat exchangers from the published literature were collected and rescaled using the “porous media” length scale suggested by VAT. The results were surprisingly good, collapsing all the data onto a single curve for friction factor and Nusselt number, respectively. It was shown that using the porous media length scale is very beneficial in collapsing complex data yielding simple heat transfer and friction factor correlations and that by proper scaling, closure is a function of the porous media, which further generalizes macroscale porous media equations. The current work is a step closer to our final goal, which is to develop a universal fast running computational tool for multipleparameter optimization of heat exchangers. [DOI: 10.1115/1.4004393]

Abstract: Implementing tube-inserts, namely tube-side enhancement, is an efficient way to increase the heat transfer coefficients of shell and tube heat exchangers, which can achieve substantial energy saving in heat exchanger network (HEN) if suitable retrofit strategies are used (Pan et al., 2011). In this paper, a new optimization method is proposed to consider more details of tube-side enhancement for HEN retrofitting, such as multiple tube passes, logarithmic mean temperature difference (LMTD), LMTD correction factor (FT). Even though LMTD and FT will lead to complex nonlinear terms in mathematical programming, the proposed approach can deal with the relevant computational difficulties efficiently. The validity of new optimization approach is illustrated with solving a literature example (Li and Chang, 2010). Copyright ? 2011, AIDIC Servizi S.r.l.

Abstract: A heat pump system (1), the operation of which is controlled using a temperature difference between a water inlet and a water outlet of a heat exchanger (20), exchanging heat between a refrigerant and water, and a control method thereof. The heat pump system includes temperature sensors (23a,23b) installed on a water circulation pipe unit at water inlet and outlet sides of a heat exchanger, and heats a load to a set temperature by controlling a compressor (14) or an expander (16) according to a difference between temperatures sensed by the temperature sensors. Here, a temperature of water transmitted to the load is set to be greater than a target load temperature by a reference value, and if the temperature difference is smaller than a designated value, the operation of the heat pump system is stopped.