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Abstract There are instances in remote areas where heat is being wasted, e.g., in internal combustion, engines, etc. Some of this heat can be recovered to produce distilled water in solar stills. The solar still replaces the cooling tower, ponds, or radiators normally used to control the engine temperature. The diesel cooling water in such a system remains separate from the saline water in the solar still. The advantages of using such a system compared with a conventional solar still are: 1. (a) water costs are very much reduced 2. (b) the area occupied is much less, i.e., about 1 5 th 3. (c) production has much less seasonal variation 4. (d) the efficiency of the solar still is improved due to the higher operating temperatures. From experiments conducted at Highett using a Mk VI solar still fitted with a simple heat exchanger and a separate electrically-heated source of hot water to simulate the waste heat, design data are not available for application to working systems. The information required to match a solar still to a diesel's cooling requirement is: 1. (a) engine efficiency 2. (b) hourly fuel consumption 3. (c) hourly solar radiation 4. (d) hourly ambient temperatures. A by-product of this work has been the production of a “solar water heater” which costs less than that of the cheapest conventional system. This “solar” hot water system uses a heat exchanger similar to what is used to transfer the waste heat to the saline water. It is envisaged to have hot water productions approximately the same as the distilled water productions. The influence of hot water production on the output of the waste heat solar still is discussed.

Abstract There are instances in remote areas where heat is being wasted, e.g., in internal combustion, engines, etc. Some of this heat can be recovered to produce distilled water in solar stills. The solar still replaces the cooling tower, ponds, or radiators normally used to control the engine temperature. The diesel cooling water in such a system remains separate from the saline water in the solar still. The advantages of using such a system compared with a conventional solar still are: 1. (a) water costs are very much reduced 2. (b) the area occupied is much less, i.e., about 1 5 th 3. (c) production has much less seasonal variation 4. (d) the efficiency of the solar still is improved due to the higher operating temperatures. From experiments conducted at Highett using a Mk VI solar still fitted with a simple heat exchanger and a separate electrically-heated source of hot water to simulate the waste heat, design data are not available for application to working systems. The information required to match a solar still to a diesel's cooling requirement is: 1. (a) engine efficiency 2. (b) hourly fuel consumption 3. (c) hourly solar radiation 4. (d) hourly ambient temperatures. A by-product of this work has been the production of a “solar water heater” which costs less than that of the cheapest conventional system. This “solar” hot water system uses a heat exchanger similar to what is used to transfer the waste heat to the saline water. It is envisaged to have hot water productions approximately the same as the distilled water productions. The influence of hot water production on the output of the waste heat solar still is discussed.

Theoretical analysis of a solar desalination system utilizing an innovative new concept, which uses low-grade solar heat, is presented. The system utilizes natural means of gravity and atmospheric pressure to create a vacuum, under which liquid can be evaporated at much lower temperatures and with less energy than conventional techniques. The uniqueness of the system is in the way natural forces are used to create vacuum conditions and its incorporation in a single system design where evaporation and condensation take place at appropriate locations without any energy input other than low grade heat. The system consists of solar heating system, an evaporator, a condenser, and injection, withdrawal, and discharge pipes. The effect of various operating conditions, namely, withdrawal rate, depth of water body, temperature of the heat source, and condenser temperature were studied. Numerical simulations show that the proposed system may have distillation efficiencies as high as 90% or more. Vacuum equivalent to 3.7 kPa (abs) or less can be created depending on the ambient temperature at which condensation will take place.

Theoretical analysis of a solar desalination system utilizing an innovative new concept, which uses low-grade solar heat, is presented. The system utilizes natural means of gravity and atmospheric pressure to create a vacuum, under which liquid can be evaporated at much lower temperatures and with less energy than conventional techniques. The uniqueness of the system is in the way natural forces are used to create vacuum conditions and its incorporation in a single system design where evaporation and condensation take place at appropriate locations without any energy input other than low grade heat. The system consists of solar heating system, an evaporator, a condenser, and injection, withdrawal, and discharge pipes. The effect of various operating conditions, namely, withdrawal rate, depth of water body, temperature of the heat source, and condenser temperature were studied. Numerical simulations show that the proposed system may have distillation efficiencies as high as 90% or more. Vacuum equivalent to 3.7 kPa (abs) or less can be created depending on the ambient temperature at which condensation will take place.

Abstract A linear relation between the efficiency of solar ponds and factor θ d H which is the temperature difference between the pond bottom and the ambient divided by the average insolation is presented. This relation, which has been developed based on a steady state analysis provides valuable information on the relative importance of the parameters involved in the operation of solar ponds. It is found that the existence and the thickness of the top convective zone has a profound negative effect on the yield of solar ponds. The optimum thickness of the density gradient layer under various conditions is also presented. The effect of ground losses is discussed, and it is shown that for the case of wet soil, especially if the level of the underground water is high, the pond should be thermally insulated. It is also shown that the steady state analysis can predict with good accuracy the yearly average response of solar ponds under transient conditions.

Abstract A linear relation between the efficiency of solar ponds and factor θ d H which is the temperature difference between the pond bottom and the ambient divided by the average insolation is presented. This relation, which has been developed based on a steady state analysis provides valuable information on the relative importance of the parameters involved in the operation of solar ponds. It is found that the existence and the thickness of the top convective zone has a profound negative effect on the yield of solar ponds. The optimum thickness of the density gradient layer under various conditions is also presented. The effect of ground losses is discussed, and it is shown that for the case of wet soil, especially if the level of the underground water is high, the pond should be thermally insulated. It is also shown that the steady state analysis can predict with good accuracy the yearly average response of solar ponds under transient conditions.

INTRODUCTION Thermosiphon (natural circulation) solar domestic hot water systems were investigated, both experimentally and numerically, by Close[l], Gupta and Garg[2], Ong[3], and Young and Bergquam[4]. Close used a 1.6m 2 (17.3ft 2) collector and a 113.6L (30gal) storage tank, while Ong utilized a 1.4m 2 (15ft 2) collector and a 106L (28gal) storage tank. These systems do not represent practical size systems although they do maintain the ratio between the storage tank volume and collector area, in English units, at about 2 which is a design rule of thumb[5]. Larger systems can have higher mass flow rates which can lead to transition or turbulent flow throughout the system. These higher mass flow rates increase the mixing in the storage tank and can complicate numerical modeling efforts. In the investigation of Young and Bergquam, a practical size thermosiphon system was tested, e.g. a 3.47 m 2 (37.4 ft 2) collector and 250L (66gal) storage tank§ Numerical models were presented in [4] for the collector, storage tank, and the thermosiphon mass flow rate. The relatively low velocities typical of natural circulation systems make the measurement of collector mass flow rates difficult. Consequently, only a few investigators have attempted to measure the flow rate in these systems. Even a small flow restriction placed in the flow to measure the flow rate can drastically reduce the flow and change the hydrodynamic behavior of the system. Ong[3] measured the mass flow rate by timing the passage of a single dye streak. A laser doppler anemometer was used by Morrison and Ranatunga[6] to measure mass flow rates of a scaled down laboratory system (an electric heater for the collector and a 66.7L (17.6gal) storage tank were used). The velocity profile was measured across a transparent test section and the resulting velocity profile integrated to obtain the mass flow rate. In all cases the flow was laminar. Accuracies of 2 per cent were reported in [6]. Although a laser doppler anemometer does not introduce any restrictions in the flow field its expense and complexity limit its use. An energy balance on the storage tank was used in [4] to calculate collector mass flow rates. The technique was verified by comparison to measurements taken on a pumped system using a turbine flow meter.

INTRODUCTION Thermosiphon (natural circulation) solar domestic hot water systems were investigated, both experimentally and numerically, by Close[l], Gupta and Garg[2], Ong[3], and Young and Bergquam[4]. Close used a 1.6m 2 (17.3ft 2) collector and a 113.6L (30gal) storage tank, while Ong utilized a 1.4m 2 (15ft 2) collector and a 106L (28gal) storage tank. These systems do not represent practical size systems although they do maintain the ratio between the storage tank volume and collector area, in English units, at about 2 which is a design rule of thumb[5]. Larger systems can have higher mass flow rates which can lead to transition or turbulent flow throughout the system. These higher mass flow rates increase the mixing in the storage tank and can complicate numerical modeling efforts. In the investigation of Young and Bergquam, a practical size thermosiphon system was tested, e.g. a 3.47 m 2 (37.4 ft 2) collector and 250L (66gal) storage tank§ Numerical models were presented in [4] for the collector, storage tank, and the thermosiphon mass flow rate. The relatively low velocities typical of natural circulation systems make the measurement of collector mass flow rates difficult. Consequently, only a few investigators have attempted to measure the flow rate in these systems. Even a small flow restriction placed in the flow to measure the flow rate can drastically reduce the flow and change the hydrodynamic behavior of the system. Ong[3] measured the mass flow rate by timing the passage of a single dye streak. A laser doppler anemometer was used by Morrison and Ranatunga[6] to measure mass flow rates of a scaled down laboratory system (an electric heater for the collector and a 66.7L (17.6gal) storage tank were used). The velocity profile was measured across a transparent test section and the resulting velocity profile integrated to obtain the mass flow rate. In all cases the flow was laminar. Accuracies of 2 per cent were reported in [6]. Although a laser doppler anemometer does not introduce any restrictions in the flow field its expense and complexity limit its use. An energy balance on the storage tank was used in [4] to calculate collector mass flow rates. The technique was verified by comparison to measurements taken on a pumped system using a turbine flow meter.

The salt gradient solar pond is a long-term heat storage system with a considerable warm-up time. A pond is efficient when it reaches the desired temperature quickly and maximum heat is subsequently retrieved at steady state. This requires optimum sizing of the non-convective zone. In the present work, the optimum size of the non-convective zone for fast warm-up is determined. This is found to differ considerably from the optimum size of the steady state criterion. The possibility of achieving both performance parameters, i.e. fast warm-up and maximum heat collection later on, is analyzed. It is suggested that when commissioning a pond, the size of the non-convective zone should at first be the optimum value from the warm-up rate criterion, but may later be changed to the optimum size from the steady state criterion.