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An experimental investigation was conducted to examine critical heat flux (CHF), boiling pressure drop, and local heat transfer coefficient in a horizontal channel with transverse grooves for flow boiling with R-123. Measurement of the wall temperature of the channel was done using a thermal camera. Five test sections were used for the study. A combination of groove pitch (<i>p</i>) of 18.6 and 11 mm and groove height (<i>e</i>) of 1 mm and 0.55 mm were used for the study. The groove pitch-to-height (<i>p/e</i>) ratios used were 11, 20, 18.6, and 33.8. Experiments were carried out for different heat fluxes in the range from 180 to 1259 kW/m², six different mass fluxes from 180 to 1259 kg/m²s, and Reynolds numbers from 5834 to 51770. In the grooved channel compared with the smooth tube, an improvement in heat transfer and CHF with the higher pressure drop was found. The boiling heat transfer coefficient increases with a decrease in (<i>p/e</i>) ratio. The enhancement of heat transfer coefficient and CHF improves with a decrease in (<i>p/e</i>) ratio. The maximum enhancement of CHF for (<i>p/e</i>) ratios of 11, 18.6, 20, and 33.8 is found to be 134&#37;, 87&#37;, 57&#37;, and 53&#37;, respectively. An abrupt increase in test channel wall temperature is an indication of CHF occurring. CHF was observed at the top portion of the grooved channel and was found to be of departure from nucleate boiling type.

Heat exchanger is essential devices in process industries, power plant and refineries for the exchange of heat from one fluid to another fluid. It finds wide industrial, commercial and domestic applications. Keeping in mind today's energy crisis lots of researchers are working on active and passive methods for the enhancement of heat transfer rate. Use of twisted tape insert is one of the passive methods of enhancing heat transfer rate in conventional conduits with pressure drop penalty. An exhaustive review has been presented in this paper so it will be ready reference for those who want implement twisted tape insert in the heat exchanger. The experimental investigation of plain twisted tape and modified twisted tape of various configurations with its main findings are presented in compact form. The main focused of the present study is heat transfer enhancement, friction factor and enhancement ratio for the compactness, savings in pumping power for the operation of heat exchanger.

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