Mohammad S. Khan

Review of Heat Transfer and Pressure Drop Correlations for Evaporation of Fluid Flow in Plate Heat Exchangers (RP-1352)

Plate heat exchangers have been widely used in dairy, food processing, paper/pulp, heating, ventilating, and other related industry. While single-phase flow in plate heat exchangers has been studied extensively, the industry lacks basic information on fluid flow evaporating in plate heat exchangers. This paper provides a review of heat transfer and pressure drop correlations for fluid flow evaporating in plate heat exchangers. Emphasis is placed on the application of a plate heat exchanger as an ammonia evaporator in a refrigeration system. It is shown via thorough research of related thermal–hydraulic phenomena that heat transfer and pressure drop correlations are needed for liquid ammonia flow evaporating in plate heat exchangers. The effects of plate geometry, plate material, oil/lubricant concentration, and several operating parameters on heat transfer coefficient and pressure drop for plate heat exchangers also need to be quantified.

Design of a Cross Flow Turbine for a Micro-Hydro Power Application

The total installed capacity of the hydropower stations in Pakistan is about 7,000 MW which is about 20% of the total available hydro power potential. For possible micro-hydro stations, a potential of about 1300 MW exists at a number of low head and high flow rate sites. Work has been reported by Chattha et al. [1, 2] related to installation of a micro-hydro power station at one of the typical sites. An axial flow pump-as-turbine (PaT) was installed to generate electrical power at the micro-hydro station. The site selected for this work is quite typical and efforts are now being made to utilize the maximum potential of the site conditions. The PaT only utilizes about half of the available flow of water and a spillway was constructed at this site to divert the excess amount of water. The diverted water flows back to the main stream after bypassing the PaT. Work is now being carried out to explore the installation of a turbine in the spillway to harness the energy potential of the diverted water stream. This work includes selection, design, fabrication and installation of a turbine in order to generate electrical power utilizing the energy of water diverted to the spillway. A 100 ft3 /sec flow rate with about 11 ft head is available at the spillway side. Considering these site conditions and indigenous fabrication expertise, cross flow type turbine has been selected for installation. Cross flow turbines are being manufactured in Pakistan and are usually quite successful for micro-hydro systems. Based on the available site conditions, a cross flow turbine has been designed. The diameter and length of the turbine runner have been calculated. Furthermore, the number of blades and radius of curvature have been determined along with other design parameters. The designed turbine is expected to produce about 50 kW of power. The complete design of the turbine, based on the available site conditions is presented in this paper.© 2010 ASME

Micro-Hydro Power Systems: Current Status and Future Research in Pakistan

The total installed electric power capacity of Pakistan is about 20,000 MW. Pakistan is currently facing a power deficit of about 4,000 MW. This deficit is creating huge difficulties for the consumers as electrical power load shedding has become a norm in all over the country. Currently only about 33% of the total power is being produced by hydro sources and major electric power is still produced by burning oil and gas. The hydro potential of Pakistan is estimated to be about 41 GW, out of which 1,290 MW can be generated by micro-hydro systems. These potential off grid micro-hydro systems are very essential for the consumers living in the remote areas of Pakistan and may be installed on canals and water falls which are abundant in the remote areas. This paper discusses the potential and the status of installed of hydro power systems in Pakistan. Cross flow turbines are being manufactured in Pakistan and are usually quite successful for micro-hydro systems. However, cross flow turbines are not suitable for majority of the prospective site conditions. Furthermore, custom made conventional turbines are not mass produced and for the micro-hydro systems, standard centrifugal pumps may be used as turbines. These centrifugal pumps are easily available in the market at comparatively much lower cost and shorter delivery periods. A pump was installed at a suitable site for generation of electricity, while running in turbine mode. It was initially estimated that the Pump as Turbine, PaT would be able to generate about 70 kW of power based on the available flow rate and head parameters at the site. Currently only half of that power is being generated by the PaT, under study. Efforts are underway to rectify the problems being faced and improve the power generation capacity of the installed unit. This paper discusses the problems associated with the use of PaT and measures being undertaken to make it feasible for the use of micro-hydro systems. Two major issues; draft tube design and presence of trash in the canal water, responsible for performance deterioration have been discussed in this paper.Copyright

Experimental Investigation of Single-Phase Heat Transfer in a Plate Heat Exchanger

The present experimental study is carried out to verify previously published heat transfer results attained using a simpler yet nascent data reduction technique for the same plate heat exchanger. A gasketed, commercially available plate heat exchanger with mixed (30/60) plate configuration was used in this study to obtain experimental heat transfer coefficient using modified Wilson plot method for data reduction. The comparison between current data and previously published results has shown excellent agreement between the two techniques hence verifying the results of the simpler method used earlier.

Experimental Study to Test an Axial Flow Pump as a Turbine and Development of Performance Characteristics for Micro-Hydro Power Plant

Standard centrifugal pumps are manufactured in a large number of sizes in order to cover a wide range of heads and flow rates. Conventional turbines, however, are not mass produced since they are custom designed and manufactured. Therefore, pumps are available in the market at comparatively lower cost and shorter delivery periods. In this paper an experimental study is presented in which the use of pumps as turbine (PAT) is explored for micro-hydro power generation. The objective of the study is to explore cheap alternate sources of energy production in remote locations of Pakistan. Extensive research has been carried out by Williams [1] in the field of using pumps as turbines. Only centrifugal pumps were studied to explore their use as turbines in that work. Since then quite a bit of advancement in this sector of technology has taken place. However, to the best of our knowledge, axial flow pumps have never been tested as turbines. The site conditions for micro-hydro power station usually find axial flow pumps to be more appropriate compared cross flow and pelton turbines. A commercially available axial flow pump was selected and test rig was designed and constructed in order to determine the performance characteristics of using the pump as a turbine. The test bed has a provision of simulating various head and flow rate conditions and dynamometer to measure the power output in order to determine the performance of the turbine. The simulated head and flow rates were varied for various typical conditions. Some minor modifications in the basic pump unit were made to accomplish these tests. The experimental study resulted in generating data for which head was varied from 4 to 12 m and flow rate from 700 to 900 m3 /hr. For these conditions power developed ranged from 5–20 kW with a maximum efficiency of 70% corresponding to a head of 6.8 m and a flow rate of 800 m3 /hr. Pump affinity laws and the data collected in this experimental study were then used to select a Kaplan turbine. This information was then used to choose a commercially available pump for typical low head and high flow rate conditions in Pakistan to generate about 100 kW of electric power, when running in turbine mode. This paper discusses the design and construction of the test rig to carry out experiments for testing pumps as turbines. Details of experimental procedure and results to determine performance characteristics are also presented. Finally selection procedure of a pump for a specific head and flow condition are also discussed in this paper.Copyright