Heat transfer and pressure drop in plate heat exchangers

The thermal-hydraulic performance of plate heat exchangers (PHEs) with chevron plates is investigated experimentally. PHEs are employed in many chemical industry process heating and cooling applications, as they provide significant heat transfer enhancement and operational flexibility. Their efficient use in such applications, however, requires precise calculations of heat transfer and pressure drop characteristics. The existing correlations have large disagreements and lack general applicability. Also, very limited results are available for PHEs in laminar flows; a typical operating condition in several process applications involving heating and cooling of highly viscous liquids.; Experimental steady-state heat transfer data for cooling of hot viscous liquid flows, and isothermal and diabatic pressure drop data are acquired. Three different chevron plate arrangements are used in the test PHE; two symmetric and one mixed plate arrangement.; The variation of Nusselt number and Fanning friction data with Re and {dollar}beta{dollar} are presented for the three different chevron plate arrangements. The results indicate a strong influence of the chevron inclination angle {dollar}beta{dollar} and surface enlargement factor {dollar}phi.{dollar} Based on the experimental results, power-law type equations are obtained by a regression analysis of the Nu and f data. However, in an attempt to devise more generalized correlations, the present data along with selected previously reported results are analyzed to identify the effects of plate surface geometry.; Finally, the heat transfer enhancement in the chevron plate PHE is quantified for several different operating constraints. This is accomplished by using energy conservation principles and entropy generation minimization methods. The heat transfer enhancement in chveron plates is up to 2.9 times relative to an equivalent flat-plate pack for fixed geometry and constant pumping power applications. For the constraint of fixed heat duty and pressure drop, chevron plates can provide 8% to 48% reduction in heat transfer surface area depending upon {dollar}beta{dollar} and Re. Furthermore, depending upon Re, {dollar}beta,{dollar} and {dollar}rmvarphisb{lcub}o{rcub}{dollar} (critical irreversibility ratio), the entropy generation is also reduced. However, for {dollar}rmvarphisb{lcub}o{rcub}approx0.01,{dollar} while there is a reduction in entropy generation with increasing {dollar}beta{dollar} in laminar flows, the reverse trend is observed in turbulent flows (Re {dollar}geq{dollar} 1000). The performance evaluation results based on these three different figures of merit indicates that chevron plate PHEs are especially suitable in the low to medium flow rates range (20 {dollar}leq{dollar} Re {dollar}leq{dollar} 2000), and that there is no significant advantage of using a mixed-plate arrangement over a symmetric-plate arrangement. (Abstract shortened by UMI.)...