Journal Press India^®

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This paper mainly deals with the problem of reverse flow and explicit expressions have been presented which shows that the placement of hot water storage tank above the collector helps to eliminates reverse flow and it was observed that if tank is kept very high above the collector then there is always some flow of liquid through the collector especially if the outlet of the collector is connected near the middle of the storage tank. This is due to considerable heat losses resulting poor thermal efficiency of the system. The new design based on single and multi pass systems for domestic hot water systems which completely eliminate reverse flow problems have been forwarded and studies in details. The single pass systems besides avoiding reverse flow has two distinct features: (i) Allows the place the main water storage tank at any desirable place (even below the collector) (ii) Water is obtained at pre-determined temperature irrespective of insolation levels. The numerical calculations for single pass natural convection pressurized solar hot water systems meander tube fluid flow channel absorber, serpentine tube collectors and for non pressurized thermosyphonic solar hot water systems using parallel tube absorber were performed. The experimental measurements on such modified systems were performed manually by noting thermosyphonic flow rate and temperatures at every half hours time interval. The theoretical results matches well with experimental results. It was found that the non pressurized solar hot water systems using parallel tube absorber have average thermal efficiency of 41 % in the single pass and 27. 3 % in the multi-pass modes. The system efficiency of pressurized solar hot water systems using meander tube absorber are 30 % in single pass mode and 20 % in the multi pass mode due to higher temperature of absorber and higher heat losses from absorber in pressurized solar hot water systems.

Keywords

Natural Convection; Hot water Systems; Pressurized and Non Pressurized Solar Systems; Meander and Serpentine Collectors.

1. R. S. Mishra, Thermal Performance of Meander Tube Collector for Solar Hot Water Systems, National Conference of Mechanical Engineers, I.I.T. Kanpur, 1993


2. R.S. Mishra, Thermal Analysis of Novel Natural Convection Modified Solar Hot Water Systems, National Conference of Agricultural Engineers, Junagarh, 1994.