Current Projects

Phase change heat transfer in the microchannel is fundamentally essential for various thermal management and energy conversion processes. Especially for thermal management of high power density electronic devices where heat dissipation requirement has reached more than 1000 W/cm². Flow boiling in microchannels is one of the best possible solutions for dissipating a large amount of heat from a small space. However, heat dissipation through flow boiling in the microchannel is afflicted by boiling instabilities due to explosive vapour growth in the channel, hindering the implementation of microchannels as a heat sink for electronic devices. Flow boiling instabilities reduce the heat transfer rate and critical heat flux limit of microchannel heat sinks. Although modification of channel geometry has appeared as one of the prominent technique for mitigating flow boiling instabilities, it cannot reduce the instabilities due to upstream compressible volume formed in the microchannel. Upstream compressible volume forms due to periodic dryout and rewetting of the channels at very high heat flux which significantly contributes for boiling instabilities deteriorating the heat transfer performance in the microchannel heat sinks. In this proposal, a nanoporous membrane based vapour venting technique would be introduced to curb the formation of upstream compressible volume for mitigating flow boiling instabilities and enhance the heat transfer rate in a geometrically modified microchannel heat sink. A hydrophobic nanoporous membranes would be introduced in the channel to repel the water and attract the vapour phase. The separated vapour phase would be withdrawn through different passage from the channel which would completely eliminate the compressible volume formation and reduce the boiling instabilities. Further the nanoporous membrane would enable the formation of small bubbles with high releasing frequency which would effectively address the boiling crisis at high heat flux, thus by increasing the critical heat flux. The effects of different parameters of the porous membrane i.e. hydrophobicity, pore size, permeability, physical dimensions and thermo-mechanical properties on the vapour venting process and their consequence on the heat transfer performance of the microchannels would be investigated in the proposal. A detailed understanding on the influence of the capillary pressure on reducing the accelerated two-phase pressure drop at very high heat flux would be explored. An effort would be also made to correlate the spatially varying temperature and pressure fluctuations with capillary effects on nanoporous membrane. The proposal would provide a new nanostructuring approach combined with geometric modification for mitigating flow boiling instabilities and enhancing heat transfer coefficient and critical heat flux limit of the microchannel heat sinks.

Project Title:

Effect of burnup on ballooning and burst behavior of Zircaloy-4 cladding tubes under simulated LOCA

Principal Investigator:

Dr Mohd Kaleem Khan (PI) / Dr Manabendra Pathak (co-PI)

Sponsoring Agency:

Board of Research in Nuclear Sciences, DAE, Govt. of India

Project Amount:

Rs. 32.991 lakhs

Project Summary:

In the previous DAE projects undertaken at IIT Patna, the burst investigations were carried out on as-received and pre-hydrided zircaloy-4 cladding tubes. In the ongoing project, it is proposed to carry out the burst experiments on the pre-oxidized cladding tubes in the steam environment, which is more realistic. Zircaloy-4 cladding tube will be first subjected to oxidation on its outer as well as inner surfaces to simulate the extended burnup condition of Indian PHWR fuel. Then it will be used for carrying out burst tests in steam environment. During normal reactor operation, the outer surface of cladding tube gets oxidized as it is exposed to coolant (water), inner surface oxidation due to oxide fuel. With the onset of LOCA sequence, the loss of coolant leads to steam generation with temperature and pressure inside cladding tube starts rising. The clad tube balloons and finally bursts. The proposed work will plug the gap in previous study where bursting of as-received and hydrided Zircaloy-4 cladding tubes were performed in inert environment. Studies show that the effect of radiation induced defects gets annealed out at 600 ºC and ductility is restored back. So burnup effect on the ballooning and burst behaviour of the PHWR fuel cladding boils down to the effect of oxide layer and the hydrogen picked up during service only.

Completed Projects

The project mainly focuses on the development of a self-adaptive cooling system based on a closed-loop two-phase thermosyphon (CLTPT) with enhanced heat transfer in the evaporator and the condenser. The first part of the report explains heat transfer enhancement with structured surfaces, and the second part presents the temperature-controlled self-adaptive thermosyphon loop. A closed-loop two-phase thermosyphon (CLTPT) is a gravity-assisted heat dissipation device that works on the principle of evaporation and condensation to facilitate large amounts of heat transfer without any pumping device. An efficient heat transfer mechanism should act in the evaporator and the condenser to produce a sufficient buoyancy effect in the loop. In the first part of the work, an effort is being made to enhance the heat transfer in the evaporator section with a structured heating surface. A novel structured heating surface i.e. segmented finned microchannels has been used to enhance the heat transfer rate and its performance has been compared with that of plain heating surface. Compared to the plain heating surface, the segmented finned structured heating surface produces an enhancement of 157% in heat transfer coefficient whereas it produces 145% enhancement in the critical heat flux (CHF). The present structured surface also produces better heat transfer performance compared to similar works reported in the literature.

For heat transfer enhancement in the condenser a feedback control mechanism is introduced to produce an adaptive cooling in the condenser according to the temperature rise in the evaporator. Compared to the ordinary CLTPT system, the CLTPT with feedback control mechanism produces a 68% enhancement in the heat transfer rate whereas it produces 12.5% enhancement in the critical heat flux (CHF) value. Enhanced cooling in the condenser and higher pressure difference across the loop helps in better heat transfer performance in the modified loop compared to the ordinary loop. Further better bubble dynamics, crossflow effects of coolant liquid, and better rewetting of the heating surface in the evaporator improve the heat transfer coefficient and CHF value in the modified CLTPT system. Thus, in the present work an efficient closed-loop two-phase thermosyphon system has been developed that can provide adaptive cooling based on the temperature of the substrate.

Zirconium alloys are widely used in nuclear power reactors as structural materials. Zircaloy, an alloy of zirconium–tin, is extensively used as the nuclear fuel cladding material in water-cooled nuclear power reactors due to its low thermal neutron absorption cross section, resistance to corrosion in high temperature and pressure conditions, and high mechanical strength. Zircaloy-4 is used as the nuclear fuel cladding material in the Indian Pressurised Heavy Water Reactors (IPHWRs). Although Zircaloy-4 nuclear fuel cladding has shown satisfactory behaviour in service, its degradation due to waterside corrosion can limit the in-reactor design life. The critical phenomenon is the precipitation of brittle hydride phase due to pickup of a fraction of hydrogen produced during waterside corrosion. The degradation of mechanical properties due to the presence of hydrides alters the creep performance, crack behaviour, and fracture procedure— each phenomenon being crucial during the lifespan of the cladding. The present research work is carried out to determine the effects of hydrogen/hydride in Zircaloy-4 fuel cladding tubes on (a) creep during normal operation, (b) burst behaviour during the first phase of LOCA transient, and (c) crack instability during spent fuel storage using both experimental and numerical techniques.

S. Suman, M.K. Khan, M. Pathak and R.N. Singh, 2018, Effects of hydrogen on thermal creep behaviour of Zircaloy fuel cladding, Journal of Nuclear Materials, vol.498, pp.20-32. Click Here

S. Suman, M.K. Khan, M. Pathak and R.N. Singh, 2018, Effects of delta-hydride precipitated at a crack tip on crack instability in Zircaloy-4, International Journal of Energy Research, vol.42, pp. 284-292. Click Here

S. Suman, M.K. Khan, M. Pathak and R.N. Singh, 2017, Investigation of elevated-temperature mechanical properties of delta-hydride precipitate in zircaloy-4 fuel cladding tubes using nanoindentation, Journal of Alloys and Compounds, vol.726, pp. 107-113. Click Here

S. Suman, M.K. Khan, M. Pathak and R.N. Singh, 2017, 3D simulation of hydride-assisted crack propagation in zircaloy-4 using XFEM, International Journal of Hydrogen Energy, vol. 42, pp.18668-18673. Click Here

S. Suman, M.K. Khan, M. Pathak and R.N. Singh, 2017, Effects of hydride on crack propagation in zircaloy-4, Procedia Engineering, vol. 173, pp. 1185-1190. Click Here

S. Suman, M.K. Khan, M. Pathak and R.N. Singh, 2016, Rupture behaviour of nuclear fuel cladding during loss-of-coolant accident, Nuclear Engineering and Design, vol. 307, pp. 319-327. Click Here

S.Suman, M.K. Khan, M.Pathak and R.N. Singh, J.K. Chakravartty, 2015, Hydrogen in Zircaloy: Mechanism and its Impacts, International Journal of Hydrogen Energy, Vol.40(17), pp.5976-5994. Click Here